THE

CAMBRIDGE NATURAL HISTORY

EDITED BY

S. F. HARMER, Sc.D., F.R.S., Fellow of King's College, Cambridge; Superintendent of the University Museum of Zoology

AND

A. E. SHIPLEY, M.A., Fellow of Christ's College, Cambridge; University Lecturer on the Morphology of Invertebrates

VOLUME VIII

MACMILLAN AND CO., Limited
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AMPHIBIA AND REPTILES

By Hans Gadow, M.A. (Cantab.), Ph.D. (Jena), F.R.S., Strickland Curator and Lecturer on Advanced Morphology of Vertebrata in the University of Cambridge.

MACMILLAN AND CO., LIMITED
ST. MARTIN'S STREET, LONDON
1909

First Edition 1901
Reprinted 1909

PREFACE

Linnaeus had but a poor opinion of the Amphibia and their describers, or he would not have called the former "pessima tetraque animalia," nor would he have dismissed the latter with the terse remark: "Amphibiologi omnium paucissimi sunt nullique veri." That was, however, nearly 150 years ago; and at the present time there are fewer difficulties in writing a book on Amphibia and Reptiles. Those who care for the study of Amphibia and Reptiles–the Herpetologists, to give them their scientific title–have never been numerous; but most of them have been serious students. One reason for the fact that this branch of Natural History is not very popular, is a prejudice against creatures some of which are clammy and cold to the touch, and some of which may be poisonous. People who delight in keeping Newts or Frogs, Tortoises or Snakes, are, as a rule, considered eccentric. But in reality these cold-blooded creatures are of fascinating interest provided they are studied properly. The structure of animals is intimately connected with their life-habits; and this correlation is perhaps more apparent in Amphibia and Reptiles than in any other class. The anatomist who studies internal and external structure is as much struck with the almost endless variety in details as he who takes the trouble to observe the living animal in its native haunts, or at least under conditions not too unnatural. He will agree with V. von Scheffel's Toad "that those above seem to have no notion of the beauties of the swamp"–brilliantly coloured Newts engaged in amorous play, concert-giving Frogs, and metamorphosing Tadpoles. The motto assigned to the Reptiles seems singularly appropriate when we consider that poisonous snakes have been developed from harmless forms, and that many kinds of reptiles have lost limbs, teeth, and eyesight in the process of evolution.

The present work is intended to appeal to two kinds of readers–to the field-naturalist, who, while interested in life-histories, habits, and geographical distribution, beauty or strangeness of forms, is indifferent to the homologies of the metasternum or similar questions;–and to the morphologist, who in his turn is liable to forget that his specimens were once alive.

A great portion of the book is anatomical and systematic. It was necessary to treat anatomy, especially that of the skeleton, somewhat fully, since it has long been recognised that it is impossible to base a scientific classification upon external characters. The reader familiar with Vertebrate anatomy has a right to expect that questions of special morphological interest will be dwelt upon at length. Those who have no anatomical foundation must be referred to one of the now numerous introductory manuals on the subject.

The account of the Amphibia is more complete than that of the Reptilia. It was possible to diagnose practically all the recent genera; and this has been especially done in the Anura, in order to show how in an otherwise very homogeneous group almost any part of the body, internal or external, can be modified in kaleidoscopic variety. The same could not be done with the Reptilia. Their principal groups,–called sub-classes in the present work, in order to emphasise their taxonomic importance in comparison with the main groups of Birds and Mammals,–differ so much from each other that it was decided to refrain from attempting a general account of them. Moreover, the number of species of recent lizards and snakes is so bewildering, the genera of many families being but tedious variations of the same theme, that only those forms have been described which are the most important, the most striking, or which the traveller is most likely to come across. The student who wishes to go farther into systematic details must consult the seven volumes of the Catalogue of Reptiles in the British Museum (London, 1889-1896). Mr. G. A. Boulenger, the author of this magnificent series, has rendered the systematic treatment of recent Amphibia and Reptiles an easy task. During many years of the most friendly intercourse I have profited on countless occasions by his ever-ready advice. Although he has kindly read the proofs of the part dealing with the Amphibia it would be unfair to associate him with any of its shortcomings or with contestable opinions, for which I alone am responsible.

Cope's large work on the Crocodilians, Lizards, and Snakes of North America (Rep. U.S. Nat. Mus. for 1898 (1900)) has unfortunately appeared too late to be used in the present work.

The drawings on wood were, with few exceptions, made by Miss M. E. Durham, mostly from living specimens–a procedure which has to a great extent determined the selection of the illustrations.

Since both the metric and the English systems of measurements have been employed, it may be well to state for the convenience of the reader that the length of a line of the text is four inches or approximately ten centimeters.

I have frequently and freely quoted accounts of previous authors instead of paraphrasing them. Especial thanks are due to Messrs. Longmans, Green, and Co., and to Messrs. Murray, for their courteous permission to make several long quotations from Sir J. E. Tennent's Ceylon, and from H. W. Bates' Naturalist on the River Amazons.

Lastly, a remark about my Editors. Instead of being a source of annoyance they have rendered me the greatest help.

H. GADOW.

Cambridge, December 19, 1900.

CONTENTS

SCHEME OF THE CLASSIFICATION ADOPTED IN THIS BOOK

CLASS AMPHIBIA.
Sub-Class.		Order.		Sub-Order.		Family.		Sub-Family.
STEGOCEPHALI (p. [78])		Stegocephali Lepospondyli (p. [80])		Branchiosauri (p. [80]). Aistopodes (p. [81]).
		Stegocephali Temnospondyli (p. [81]) Stegocephali Stereospondyli (p. [83])
LISSAMPHIBIA (p. [84])		Apoda (p. [84])				Coeciliidae (p.89).
		Urodela (p. [94])				Amphiumidae (p. [97]).
						Salamandridae (p. [102])		Desmognathinae (p. [102]). Plethodontinae (p. [103]). Amblystomatinae (p. [109]). Salamandrinae (p. [115]).
						Proteidae (p. [132]). Sirenidae (p. [136]).
		Anura (p. [138])		Aglossa (p. [143]).
				Phaneroglossa (p. [152])		Discoglossidae (p. [152]). Pelobatidae (p. [160]). Bufonidae (p. [166]).
						Hylidae (p. [185])		Amphignathodontinae (p. [188]). Hylinae (p. [189]).
						Cystignathidae (p. [209])		Hemiphractinae (p. [210]). Cystignathinae (p. [211]). Dendrophryniscinae (p. [224]).
						Engystomatidae (p. [225])		Engystomatinae (p. [225]). Dyscophinae (p. [235]). Genyophryninae (p. [236]).
						Ranidae (p. [237])		Ceratobatrachinae (p. [237]). Raninae (p. [238]). Dendrobatinae (p. [272]).
CLASS REPTILIA (p. [277]).
PROREPTILIA (p. [285]). Eryops (p. [286]). Cricotus (p. [287]).
Sub-Class.		Order.		Sub-Order.		Family.		Sub-Family.
PROSAURIA (p. [288])		Microsauri (p. [288]).
		Prosauri (p. [290]).		Protorosauri (p. [290]). Rhynchocephali (p. [292]).
THEROMORPHA (p. [300])		Pareiasauri (p. [304]). Theriodontia (p. [306]). Anomodontia (p. [309]). Placodontia (p. [311]).
CHELONIA (p. [312])		Atheca (p. [333])				Sphargidae (p. [333]).
		Thecophora (p. [338])		Cryptodira (p. [338])		Chelydridae (p. [338]). Dermatemydidae (p. [341]). Cinosternidae (p. [342]). Platysternidae (p. [345]). Testudinidae (p. [345]). Chelonidae (p. [378]).
				Pleurodira (p. [388])		Pelomedusidae (p. [390]). Chelydidae (p. [399]). Carettochelydidae (p. [404]).
				Trionychoidea (p. [404])		Trionychidae (p. [404]).
DINOSAURIA (p. [412])		Sauropoda (p. [418]). Theropoda (p. [420]).
		Orthopoda (p. [424])		Stegosauri (p. [425]). Ornithopoda (p. [426])
		Ceratopsia (p. [430]).
CROCODILIA (p. [431])		Pseudosuchia (p. [432]). Parasuchia (p. [433]).
		Eusuchia (p. [434])				Teleosauridae (p. [450]). Metriorhynchidae (p. [451]). Macrorhynchidae (p. [451]). Gavialidae (p. [451]). Atoposauridae (p. [453]). Goniopholidae (p. [453]). Crocodilidae (p. [454]).
PLESIOSAURIA (p. [473])		Nothosauri (p. [476])				Mesosauridae (p. [476]). Nothosauridae (p. [477]).
		Plesiosauri (p. [477])				Pliosauridae (p. [477]). Plesiosauridae (p. [478]). Elasmosauridae (p. [478]).
ICHTHYOSAURIA (p. [478])		Ichthyosauri (p. [483]).
PTEROSAURIA (p. [484])		Pterosauri (p. [486])		Pterodactyli (p. [486]). Pteranodontes (p. [487]).
PYTHONOMORPHA (p. [487])		Dolichosauri (p. [489]). Mosasauri (p. [489]).
SAURIA (p. [491])		Lacertilia (p. [491])		Geckones (p. [502])		Geckonidae (p. [507])		Geckoninae (p. [507]). Eublepharinae (p. [512]). Uroplatinae (p. [512]).
				Lacertae (p. [513])		Agamidae (p. [515]). Iguanidae (p. [528]). Xenosauridae (p. [536]). Zonuridae (p. [536]). Anguidae (p. [537]). Helodermatidae (p. [540]). Lanthanotidae (p. [541]). Varanidae (p. [542]). Xantusiidae (p. [547]). Tejidae (p. [547]). Lacertidae (p. [549]). Gerrhosauridae (p. [559]). Scincidae (p. [559]). Anelytropidae (p. [564]). Dibamidae (p. [564]). Aniellidae (p. [564]). Amphisbaenidae (p. [565]). Pygopodidae (p. [567]).
				Chamaeleontes (p. [567])		Chamaeleontidae (p. [573]).
		Ophidia (p. [581])				Typhlopidae (p. [593]). Glauconiidae (p. [594]). Ilysiidae (p. [594]). Uropeltidae (p. [595]).
						Boidae (p. [596])		Pythoninae (p. [598]). Boinae (p. [601]).
						Xenopeltidae (p. [605]).
						Colubridae (p. [606]) Aglypha (p. [606])		Acrochordinae (p. [606]). Colubrinae (p. [607]). Rhachiodontinae (p. [622]).
						Colubridae Opisthoglypha (p. [623])		Dipsadomorphinae (p. [623]). Elachistodontinae (p. [625]). Homalopsinae (p. [625]).
						Colubridae Proteroglypha (p. [625])		Elapinae (p. [626]). Hydrophinae (p. [635]).
						Amblycephalidae (p. [637]).
						Viperidae (p. [637])		Viperinae (p. [638]). Crotalinae (p. [644]).

PART I

AMPHIBIA

"'s scheint, dass die hier oben keine

Ahnung haben von dem Sumpf und

Seiner Pracht."

The "plattgedrückte Kröte,"

Scheffel's Trompeter von Säkkingen.

CHAPTER I

AMPHIBIA

CHARACTERS AND DEFINITION–POSITION OF THE CLASS AMPHIBIA IN THE PHYLUM VERTEBRATA–HISTORICAL ACCOUNT OF THE CLASSIFICATION OF AMPHIBIA

A bird is known by its feathers, a Beast by its hairs, a Fish by its fins, but there is no such obvious feature which characterises the Amphibia and the Reptiles. In fact, they are neither fish, flesh, nor fowl. This ill-defined position is indicated by the want of vernacular names for these two classes, a deficiency which applies not only to the English language. All the creatures in question are backboned, creeping animals. Those which are covered with horny scales, and which from their birth breathe by lungs only, as Crocodiles, Tortoises, Lizards, and Snakes, are the Reptiles. The rest, for instance, Newts or Efts, Frogs and Toads, are the Amphibia. Their skin is mostly smooth and clammy and devoid of scales; the young are different from the adult in so far as they breathe by gills and live in the water, before they are transformed into entirely lung-breathing, terrestrial creatures. But there are many exceptions. Proteus and Siren the mud-eel, always retain their gills; while not a few frogs undergo their metamorphosis within the egg, and never breathe by gills. If we add the tropical limbless, burrowing Coecilians, and last, not least, the Labyrinthodonts and other fossil forms, the proper definition of the class Amphibia,–in other words, the reasons for grouping them together into one class, separated from the other backboned animals,–requires the examination of many other characters.

So far as numbers of living species are concerned, the Amphibia are the least numerous of the Vertebrata. There are about 40 limbless, burrowing Apoda; 100 Urodela or tailed two- or four-footed newts, and about 900 Anura, or tailless, four-footed frogs and toads; in all some 1000 different species. Few, indeed, in comparison with the 2700 Mammals, 3500 Reptiles, nearly 8000 Fishes, and almost 10,000 Birds. But we shall see that the Amphibia have not only "had their day," having flourished in bygone ages when they divided the world, so far as Vertebrata were concerned, between themselves and the Fishes, but that they never attained a dominant position. Intermediate between the aquatic Fishes and the gradually rising terrestrial Reptiles they had to fight, so to speak, with a double front during the struggle of evolution, until by now most of them have become extinct. The rest persist literally in nooks and corners of the teeming world, and only the Frogs and Toads, the more recent branch of the Amphibian tree, have spread over the whole globe, exhibiting almost endless variations of the same narrow, much specialised plan. The greatest charm of the Anura lies in their marvellous adaptation to prevailing circumstances; and the nursing habits of some kinds read almost like fairy-tales.

Characters of the Amphibia.[^[1]]

1. The vertebrae are (a) acentrous, (b) pseudocentrous, or (c) notocentrous.

2. The skull articulates with the atlas by two condyles which are formed by the lateral occipitals. For exceptions see p. [78].

3. There is an auditory columellar apparatus, fitting into the fenestra ovalis.

4. The limbs are of the tetrapodous, pentadactyle type.

5. The red blood-corpuscles are nucleated, biconvex, and oval.

6. The heart is (a) divided into two atria and one ventricle, and (b) it has a conus provided with valves.

7. The aortic arches are strictly symmetrical.

8. Gills are present at least during some early stages of development.

9. The kidneys are provided with persistent nephrostomes.

10. Lateral sense-organs are present at least during the larval stage.

11. The vagus is the last cranial nerve.

12. The median fins, where present, are not supported by spinal skeletal rays.

13. Sternal ribs and a costal or true sternum are absent.

14. There is no paired or unpaired medio-ventral, copulatory apparatus.

15. Development takes place without amnion and allantois.

None of these characters is absolutely diagnostic, except 1 (c), and this applies only to the Anura and most of the Stegocephali.

Numbers 1 (b), 1 (c), 2, 3, 4 and 12 separate the Amphibia from the Fishes.

Numbers 1, 6 (b), 7, 8, 9, 11, 13, 15 separate them from the Reptiles, Birds, and Mammals.

Number 2 separates them from the Fishes, Reptiles, and Birds.

Number 5 separates them from the Mammals.

Number 6 (a) separates them from the Fishes (excl. Dipnoi), Birds and Mammals.

We can, therefore, very easily define all the Amphibia, both recent and extinct, by a combination of the characters enumerated above. For instance, by the combination of numbers 2, 3 or 4 with either 7, 8, 9, 11, 13 or 15.

Amphicondylous Anamnia would be an absolutely correct and all-sufficient diagnosis, but it would be of little use in the determination of adult specimens; and the tetrapodous character is of no avail for Apoda. Amphicondylous animals without an intracranial hypoglossal nerve is a more practical diagnosis.

In the case of living Urodela and Anura the absence of any scales in the skin affords a more popular character; it is unfortunately not applicable to the Apoda, many of which possess dermal scales, although these are hidden in the imbricating transverse rings of the epidermis; and the frequent occurrence of typical scales of both ecto- and meso-dermal composition in many of the Stegocephali forces us to discard the scales, or rather their absence, as a diagnostic character of the class Amphibia. The same applies to the mostly soft, moist, or clammy, and very glandular nature of the skin.

The position of the class Amphibia in the Phylum Vertebrata.–There is no doubt that the Amphibia have sprung from fish-like ancestors, and that they in turn have given rise to the Reptilia. The Amphibia consequently hold a very important intermediate position. It was perhaps not a fortunate innovation when Huxley brigaded them with the Fishes as Ichthyopsida, thereby separating them more from the Sauropsida (= Reptilia and Aves), than is justifiable,–perhaps more than he himself intended. The connecting-link, in any case, is formed by the Stegocephali; all the recent Orders, the Apoda, Urodela, and Anura, are far too specialised to have any claims to the direct ancestral connections. The line leading from Stegocephali to fossil Reptiles, notably to such Proreptilia as Eryops and Cricotus, and even to the Lepospondylous Prosauria, is extremely gradual, and the steps are almost imperceptible. Naturally, assuming evolution to be true, there must have lived countless creatures which were a "rudis indigestaque moles," neither Amphibia nor Reptilia, in the present intensified sense of the systematist. The same consideration applies equally to the line which leads downwards to the Fishes. But the great gulf within the Vertebrata lies between Fishes and Amphibia, between absolutely aquatic creatures with internal gills and "fins," and terrestrial, tetrapodous creatures, with lungs and fingers and toes. On the side of the fishes only the Dipnoi and the Crossopterygii come into consideration.

The piscine descent of the Amphibia is still proclaimed by the following features.–(1) The possession by the heart of a long conus arteriosus, provided with, in many cases, numerous valves, or at least (Anura) one series at the base, another at the beginning of the truncus where the arterial arches branch off; (2) the strictly symmetrical arrangement of these arches; (3) the trilocular heart is still like that of the Lung-fishes or Dipnoi; (4) the occurrence of as many as four or even five branchial skeletal arches in the larval stage; (5) the glottis is supported by cartilages which themselves are derivatives of posterior visceral arches; (6) the development of the vertebrae (Stegocephali and Urodela) from four pairs of arcualia, and the formation of the intervertebral joints by a split across the intervertebral ring of cartilage: this feature is unknown in Reptilia, but it occurs also in Lepidosteus, most probably also in Polypterus; (7) the hypoglossal still retains the character of a post-cranial or cervical spinal nerve; (8) the presence of lateral sense-organs; (9) the possession of external gills is of somewhat doubtful phylogenetic value, although such gills occur amongst fishes only in Dipnoi and Crossopterygii. It is not unlikely that in the Amphibia these organs owe their origin to entirely larval requirements, while the suctorial mouth of the larvae of the Anura and many fishes has certainly no ancestral meaning, but is a case of convergent development.

The usual diagnoses of the Amphibia contain the statement that they, or most of them, undergo a metamorphosis, or pass through a larval stage. The same applies to various fishes; while, on the other hand, the larval (not ancestral) stage has become permanent in the Proteidae and Sirenidae; and lastly, we cannot well speak of larvae in the viviparous Salamandra atra.

The evolution of an adequate classification of the Amphibia has been a long process. Even their recognition as a class, separate from, and of equal rank with that of, the Reptilia, was by no means generally accepted until comparatively recent times. A historical sketch of the laborious, often painful, striving for light, in France and Germany, then in England, and lastly in America, is not without interest.

The term Amphibia was invented by Linnaeus for the third class of animals in his famous "Systema Naturae." It comprises a very queer assembly, which, even in the 13th edition (1767), stands as follows:–

1. Reptiles pedati, with the four "genera" Testudo, Draco, Lacerta, and Rana. Lacerta includes Crocodiles, Lizards, and Newts!

2. Serpentes apodes.

3. Nantes pinnati. Elasmobranchs, Sturgeons, Lampreys, and various other fishes.

Laurenti, 1768, in a dissertation entitled "Specimen medicum, exhibens Synopsin Reptilium ...," uses Brisson's term, Reptiles, and divides them into:–

Reptilia salientia, these are the Anura.

Gradientia, namely the Urodela and Lizards.

Serpentia, the Snakes and the Apoda.

Brongniart, 1800, "Essay d'une classification naturelle des Reptiles,"[^[2]] distinguishes:–

Chelonii, Saurii, Ophidii, Batrachii; the last for the Frogs, Toads, and Newts.

Latreille, 1804, "Nouveau Dict. Hist. Nat." xxiv.,[^[3]] accepts the four Orders of Brongniart's "Reptiles," but clearly separates the fourth Order, "Batrachii," from the rest by the following, now time-honoured, diagnosis: Doigts des pattes n'ayant pas d'ongles; des branchies, du moins pendant un temps; des métamorphoses. But there is not one word about "Amphibia" in opposition to "Reptilia."

Duméril, 1806, "Zoologie analytique" (p. 90), and "Élémens de l'histoire naturelle," 1807, divides the "Reptiles batraciens," or "Batracii," into Ecaudati and Caudati; he also introduces the terms "Anoures" and "Urodèles" as their equivalents; but since these terms appear in the French form purists do not admit their having any claim to recognition!

Oppel, 1811, "Die Ordnungen, Familien und Gattungen der Reptilien," establishes the term Apoda for the Coeciliae, and recognises their affinity to the Ecaudata and Caudata by removing them from the Snakes.

De Blainville, 1816, "Prodrome d'une nouvelle distribution du règne animal"[^[4]]–

Amphibiens squamifères. [The Reptilia.]

Amphi"iens nudipellifères s. Ichthyoides. [The Amphibia.]

Merrem, 1820, "Tentamen systematis Amphibiorum."

Pholidota. [The Reptilia.]

Batrachia: APODA.
Batrachia: SALIENTIA.
Batrachia: GRADIENTIA { Mutabilia [with metamorphosis, e.g.
Batrachia: GRADIENTIA { Newts.]
Batrachia: GRADIENTIA { Amphipneusta [Perennibranchiate Urodeles.]

F. S. Leuckart, 1821, "Einiges ueber die fischartigen Amphibien."[^[5]]

Monopnoa. [The Reptilia.]

Dipnoa. [The Amphibia] { with temporary gills: Ecaudata + Caudata pt.
Dipnoa. [The Amphibia] { with permanent gills: "Proteidae," Menopoma
Dipnoa. [The Amphibia] { and Amphiuma.

Latreille, 1825, "Familles naturelles du règne animal." The Vertebrata are divided into Haematherma and Haemacryma. These terms for warm and cold-blooded creatures were later on amended by Owen to Haematotherma and Haematocrya. The latter are divided by Latreille as follows:–

Reptilia. Still including the Coeciliae amongst the Snakes.

Amphibia { Caducibranchiata.
Amphibia { Perennibranchiata.

Pisces.

Wagler, 1830, "Systema Amphibiorum."

Testudines, Crocodili, Lacertae, Serpentes, Angues, Coeciliae, Ranae, Ichthyodi.

Ranae I. AGLOSSA.

Ra"ae II. PHANEROGLOSSA: 1. Cauda nulla. [The Anura.]

Ra"ae II. PHANER" GLOSSA: 2. Cauda distincta. [The Salamandridae.]

Ichthyodi I. ABRANCHIALES. Menopoma [Cryptobranchus] and Amphiuma.

Icht"yodi II. BRANCHIALES. [The Perennibranchiate Urodela.]

J. Müller, 1831, "Beiträge zur Anatomie ... der Amphibien."[^[6]]

Gymnophiona, Derotremata, Proteidae, Salamandrina, Batrachia.

J. Bell, 1836, Todd's "Cyclopaedia of Anatomy and Physiology," Art. "Amphibia."

Amphipneusta, the Perennibranchiate Urodeles; Anoura, Urodela;

Abranchia, Menopoma and Amphiuma; Apoda.

Stannius, 1856, "Handbuch der Zootomie: Anatomie der Wirbelthiere." (2nd ed.)

Amphibia Monopnoa. The Reptilia.

Amphibia Dipnoa. 1. Urodela. PERENNIBRANCHIATA.
Amphibia Dipnoa. 1. Urodela. DEROTREMATA: Amphiuma and Menopoma.
Amphibia Dipnoa. 1. Urodela. MYCTODERA.[^[7]]
Amphibia Dipni. 2. Batrachia. AGLOSSA.
Amphibia Dipnoa. 1. Urodela. PHANEROGLOSSA: Systomata =
Engystomatidae.
Amphibia Dipnoa. 1. Urodela. Bufoninae. Without manubrium sterni.
Amphibia Dipnoa. 1. Urodela. Raninae. With manubrium.
Amphibia Dipnoa. 1. Urodela. Hyloidea. With adhesive finger-discs.
Amphibia Dipnoa. 1. Urodela. GYMNOPHIONA.

Gegenbaur, 1859, "Grundzüge der vergleichenden Anatomie."

Amphibia as a separate class, equivalent to that of the Reptilia, are divided into the four Orders: PERENNIBRANCHIATA, SALAMANDRINA, BATRACHIA, and GYMNOPHIONA. In the second edition of the "Grundzüge" (1870) they are divided into URODELA, ANURA, and GYMNOPHIONA.

Huxley, 1864, "The Elements of Comparative Anatomy."

Mammals.
Sauroids, subsequently changed into Sauropsida = Reptilia + Aves.
Ichthyoids, bseque"tly chan"ed into Ichthyopsida = Amphibia + Pisces.

Haeckel, 1866, "Generelle Morphologie."

Amphibia. A. Phractamphibia s. Ganocephala = Labyrinthodonta + Peromela [Apoda].
Amphibia. B. Lissamphibia s. Sozobranchia = Sozura [Urodela] + Anura.

Cope, 1869.[^[8]]

Stegocephali, Gymnophidia, Urodela, Proteidea, Trachystomata, Anura.

Huxley, 1871, "A Manual of the Anatomy of Vertebrated Animals."

Amphibia I. Saurobatrachia [v.d. Hoeven's term] s. Urodela
Amphibia 1. Proteidea.
Amphibia 2. Salamandridae.
II. Labyrinthodonta.
III. Gymnophiona.
IV. Batrachia s. Anura.

Boulenger, 1882, "Catalogue of the Batrachia Gradientia s. Caudata and Batrachia Apoda," divides the Caudata simply into: SALAMANDRIDAE, AMPHIUMIDAE, PROTEIDAE, and SIRENIDAE.

1882, "Cat. Batrachia Salientia s. Ecaudata," see p. [140].

Cope, 1890, "Synopsis of the Families of Vertebrata."[^[9]]

Class Batrachia.
IISub-Class I. Stegocephali.
Order 1. Ganocephali: Trimerorhachis, Archegosaurus.
Order 2. Rhachitomi: Eryops.
Order 3. Embolomeri: Cricotus.
Order 4. Microsauri: Branchiosaurus, Hylonomus, etc.
ISub-Class II. Urodela.
Order 1. Proteidae: Proteus.
Order 2. Pseudosauria. [All the rest of the Urodela + Coeciliidae.]
Order 3. Trachystomata: Sirenidae.
Sub-Class III. Salientia.

P. and F. Sarasin, 1890, "Zur Entwicklungsgeschichte der Ceylonesischen Blindwühle, Ichthyophis glutinosa."[^[10]]

Sub-Class I. Archaeobatrachi s. Stegocephali.
Sub-ClassII. Neobatrachi.
Order 1. URODELA.
Order 1. a. Salamandroidea. [The Urodela.]
Order 1. b. Coeciloidea = Amphiumidae + Coeciliidae.
Order 2. ANURA.

The classification adopted in this volume is as follows:–

Class Amphibia.
Sub-Class I. Phractamphibia.
Order III. Stegocephali Lepospondyli.
Sub-order 1. Branchiosauri.
Sub-order 2. Aistopodes.
Order III. Stegocephali Temnospondyli.
Order III. Stegocephali Stereospondyli.
Sub-Class II. Lissamphibia.
Order III. Apoda.
Order III. Urodela.
Order III. Anura.
Sub-order 1. Aglossa.
Sub-order 2. Phaneroglossa.

CHAPTER II

SKELETON OF URODELA AND ANURA–SKIN–COLOUR-CHANGING MECHANISM–POISON-GLANDS–SPINAL NERVES–RESPIRATORY ORGANS–SUPPRESSION OF LUNGS–URINO-GENITAL ORGANS–FECUNDATION–NURSING HABITS–DEVELOPMENT AND METAMORPHOSIS

Skeleton of the Urodela

The vertebral column.–The number of vertebrae is smallest in the terrestrial, greatest in the entirely aquatic forms, and is exceptionally large in the eel-shaped Amphiuma. In the following table the sacral vertebra is included in those of the trunk.

The vertebrae of the Urodela and those of the Apoda differ from those of all the other Tetrapoda[^[11]] by possessing no special centra or bodies. That part which should correspond with the centrum is formed either by the meeting and subsequent complete co-ossification of the two chief dorsal and ventral pairs of arcualia (tail-vertebrae), or entirely by the pair of chief dorsal arcualia. There is consequently no neuro-central suture. Moreover, the central region of each vertebra is strongly pinched in laterally, widening towards the ends. Another feature of the vertebral column of the Urodela is the possession of a considerable amount of intervertebral cartilage, by which the successive vertebrae are held together. This cartilage does not ossify, and it either remains continuous, serving in its entirety and owing to its flexibility as a joint, or it becomes more or less imperfectly separated into a cup and ball portion, the cup belonging to the posterior end of the vertebra. Such joints are called opisthocoelous, and occur in the Desmognathinae and Salamandrinae. In the adult the cup and ball frequently calcify, and the chorda dorsalis or notochord is completely destroyed. Those vertebrae between which the intervertebral cartilage remains unbroken, are called amphicoelous, since in them, most obviously in macerated or dried skeletons, the vertebrae appear hollowed out at either end. In such amphicoelous vertebrae a considerable amount of the chorda always remains, running in an unbroken string through the whole length of the vertebral column. Towards adult life the chorda becomes constricted, and is ultimately squeezed out or destroyed, in the middle of the vertebra, by the invasion of cartilage from the chief arcualia. This intravertebrally situated cartilage has been described erroneously as chordal cartilage.

The development of the vertebrae proceeds as follows. First appear a pair of basidorsalia and a pair of basiventralia (Fig. 1, 1, B.D, B.V), blocks of cartilage, imbedded in and resting upon the thin sheath of the chorda dorsalis. Next appears a pair of interdorsal blocks, immediately behind the basidorsals; and somewhat later appears a pair of interventral blocks. These four pairs of cartilages or "arcualia" each meet, above or below the chorda, and form semi-rings, which again by extending upwards or downwards fuse into complete rings, in such a way that the interdorsal and interventral elements form the intervertebral mass spoken of above. The basidorsals fuse with the basiventrals, and form the body of the vertebra, the fusion being effected chiefly by the calcification and ossification of the lateral connecting portion of the skeletogenous layer. The basidorsalia form the neural arches with their unpaired short spinous or neural, and the paired anterior and posterior zygapophysial processes. Concerning the basiventralia we have to distinguish between the trunk and the tail. In the latter they produce a pair of ventral outgrowths or haemapophyses, which ultimately enclose the caudal blood-vessels. In the trunk the basiventral blocks of cartilage are suppressed; they appear in the early larvae, but disappear during or even before metamorphosis.

Fig. 1.–1-5, Five successive stages of the development of a caudal vertebra of a newt; 6-7, the second and the first cervical vertebra of Cryptobranchus; 8-9, side view of the constituent cartilaginous blocks of a caudal vertebra (8) and a trunk-vertebra (9) of Archegosaurus as typical examples of Temnospondylous quadripartite and tripartite vertebrae. The cross-hatched parts indicate the articular facets for the ribs. The anterior end of all the vertebrae looks towards the right side. af, In 7, articulating facet for the occipital condyle; B.D, basidorsal piece or neural arch; B.V, basiventral piece or ventral arch; Ch, chorda dorsalis, or notochord; I.D, interdorsal piece; I.V, interventral piece; I.V.L, intervertebral ligament; N, spinal nerve–these are numbered I, II, III in 6 and 7; R, rib; T, in 7, rib-like tubercle on the first vertebra.

Towards the end of the tail the vertebrae diminish in size, and their constituent cartilages assume a more and more indifferent shape, until they become confluent into a continuous rod of cartilage, resembling in this respect the Dipnoi and Holocephali. A periodical revival of this rod, at least of its connective tissue, appears in the tail-filament of the male Triton palmatus during the breeding-season.

The first vertebra, called the atlas, because it carries the head, is remarkable for the possession of an odontoid process. The latter is formed by a pair of cartilages and represents part of a vertebra, the dorsal portion of which seems to have been added to the occipital part of the cranium.

All the trunk-vertebrae, with the exception of the atlas, carry ribs, at least vestiges thereof. Owing to the early disappearance of the basiventral cartilages the capitular portions of the ribs are much reduced, and are mostly represented by strands of connective tissue only. The ribs develop therefore occasionally at some distance from the vertebral column, and that portion of the rib which in the metamorphosed young newt looks like the capitulum is to a great extent really its tuberculum. Witness the position of the vertebral artery, which still indicates the true foramen transversarium. The homologies of these parts are still more obscured by the fact that a new process grows out from the rib, by which the latter gains a new support upon a knob of the neural arch. Thus an additional foramen is formed, sometimes confounded with the true transverse canal. The meaning which underlies all these modifications is the broadening of the body, the ribs shifting their originally more ventral support towards the dorsal side. The whole process is intensified in the Anura; it is an initial stage of the notocentrous type of vertebrae. The transverse ossified processes of the adult are often much longer than the vestiges of the ribs themselves, and are somewhat complicated structures. They are composed first of the rib-bearing cartilaginous outgrowths of the neural arches; secondly, of a broad string of connective tissue which extends from the ventro-lateral corner of the perichordal skeletogenous layer to the ribs.

Fig. 2.–Transverse section through a trunk-vertebra of a larva of Salamandra maculosa, enlarged. The right side shows the actually existing state, while on the left side the rib and its attachments are restored to their probable original condition. A, Vertebral artery within the true transverse canal; B.V, remnant of the basi-ventral cartilage; Ch, chorda dorsalis; Sp.c, spinal canal; *, the false transverse canal.

The shoulder-girdle is extremely simple. It remains almost entirely cartilaginous, and the three constituent elements are not separated by sutures. Ossification is restricted to the base of the shaft of the scapula, and may extend thence over the glenoid cavity. The coracoids are broad, loosely overlap each other, and are "tenon and mortised" into the triangular or lozenge-shaped cartilaginous sternum, which latter has no connection with the ribs. The precoracoid is a large, flat process, directed forwards, not meeting its fellow; it is absent in Siren.

The humerus articulates with both radius and ulna, and these two bones of the forearm remain separate. The elements which compose the wrist and hand exhibit an almost ideally simple arrangement, slightly varied by the frequent fusion of two or more neighbouring carpalia into one, and by the reduction of the number of fingers. Most frequently the intermedium and the ulnar carpal element fuse together, and there is more often one centrale instead of two. The wrist and hand of the Urodela represent, however, no longer the entirely primitive pentadactyle type, owing to the loss of one finger together with its metacarpal and carpal element. Comparison with the Anura makes it probable that the Urodela have lost the pollex, their four fingers being consequently the 2nd, 3rd, 4th, and 5th. Siren has four or three fingers; Proteus has only three fingers and three large compound carpal cartilages. In Amphiuma, with either three or two fingers, the ulnare, intermedium, and carpale are fused together, the radiale with the neighbouring carpale. The number of phalanges in the four-fingered species is generally 2, 3, 3, 2 respectively.

The pelvic girdle.–The ilium stands vertically to the vertebral axis, slanting slightly forwards and downwards. It is attached by means of a rib to only one vertebra, and this ilio-sacral connection is acetabular in its position, i.e. it lies in the same transverse plane with the acetabulum, in other words vertically above it. The ventral portion of the pelvis is formed by one large continuous mass, the united pubo-ischia, the anterior or pubic portion of which extends forwards in the shape of a broad triangle (Necturus) or as a slender, stalked, Y-shaped cartilage, the epipubis, which is often movably jointed at its base. The lateral portion of the pubic cartilage is always perforated by the nervus obturatorius. Ossification is restricted to the ischium and to the middle of the shaft of the ilium. The acetabular fossa for the femur is closed. The tibia and fibula remain separate. The foot is still more primitive than the anterior extremity, as the majority of Urodela possess the full complement of five toes, with 2, 2, 3, 3, 2 phalanges respectively. Concrescence of the tarsalia applies most frequently to the fourth and fifth distal and to the two centralia; exceptional, for instance, in Cryptobranchus japonicus, are as many as three centralia, but this is an individual, even a one-sided variation, as shown for instance by a specimen in the Cambridge Museum. Loss of the fifth toe occurs sporadically in genera of different groups, namely, in Salamandrella, Batrachyperus, Salamandrina, Necturus, Manculus, Batrachoseps. In Amphiuma the number is reduced to three or two; in Proteus to two; and in Siren the hind limbs, with their girdle, are altogether absent. Lastly, in some species of Spelerpes and Batrachoseps both fore and hind limbs have become so small as to be practically without function, parallel cases being found among various Scincidae and other Lizards.

The hyoid apparatus is still very primitive in many, especially in larval, Urodela. Besides the hyoid there are as many as four pairs of branchial arches, which, however, decrease in size and completeness, so that the last two have lost their connection with the median copular piece, and become attached in various ways to the second branchial arch. This is the arrangement apparently in all larvae, but four pairs of branchials persist in the adult Siren, Amphiuma, and Cryptobranchus alleghaniensis. The whole branchial apparatus is reduced to three pairs of arches in Necturus and Proteus, to two in the adult Cryptobranchus japonicus and in the Salamandridae. Of considerable interest is the vestige of a fifth pair of arches in the larvae of Triton and Salamandra, in the shape of a pair of tiny cartilages, which lie in front and on each side of the opening of the trachea, and give rise to the formation of the laryngeal cartilages, better developed in the higher Vertebrata.

The following are noteworthy characters of the skull of Urodela. The articulation of the skull with the vertebral column is not always effected entirely by the two condyles of the lateral occipital bones, but the median basal cartilage often possesses a pair of facets for the odontoid-like process of the first vertebra; such additional facets are perhaps best developed in Cryptobranchus and in the Salamandrinae.

The middle portion of the primitive cranium, from the exit of the optic nerve to the ethmoid cartilage, is formed by a pair of separate bones, the orbito-sphenoids. The parietal and frontal bones remain separate. One or more periotic bones exist, besides the prootic, in the aquatic families.

A pair of prefrontal bones is present in most Salamandridae, e.g. Salamandra, Triton, Amblystoma, especially in the larva, and in Cryptobranchus; these bones are absent in Amphiuma, Necturus, Proteus, and Siren.

Fig. 3.–Skulls of various Urodela. 1, Salamandra maculosa, ventral view, and 2, dorsal view; 3, Axolotl stage of Amblystoma; 4, adult stage of Amblystoma; 5, Salamandrina perspicillata (after Wiedersheim); 6, Salamandra maculosa, dorsal view of the lower jaw. A, Articulare; C₁, C₂, outer and inner occipital condyles; Ch, choana or posterior nasal opening; d, dentary; E, ethmoid; F, frontal; LO, lateral occipital; M, maxillary; N, nasal; No, nostril; OS, orbito-sphenoid; P, parietal; Pf, prefrontal; Pl, palatine; Pm, premaxillary; Po, prootic; PS, parasphenoid; Pt, pterygoid; Q, quadrate; S, angulo-splenial; Sq, squamosal; St, stapes; Vo, vomer; II, VII, X, exits of the optic, facial, and glosso-vagus nerves.

The lacrymalia are still separate in some Amblystomatinae, e.g. Ranidens and Hynobius. A pair of nasalia are generally present, but are absent in Necturus, Proteus, and Siren. The parasphenoid is furnished with teeth in the Plethodontinae and Desmognathinae.

Separate palatine bones exist in Necturus and Proteus, and in the larva of Amblystoma, but in the adult form they fuse with the vomers, producing the vomero-palatines characteristic of the majority of Urodela.

The pterygoid bones are most fully developed, so as to reach the vomero-palatines, in the Amblystomatinae, in Necturus, and in Proteus; they are reduced, so as to leave a gap, in Cryptobranchus, and still more in the Salamandrinae; they are absent in Amphiuma and in Siren.

The quadrates are directed forwards in Necturus, Proteus, and Siren, while in the other Urodela they extend transversely and almost horizontally. The hyomandibular remnant, the so-called operculum, is small, and forms a plate which fits into the fenestra ovalis, extending as a ligamentous process upon the quadrate.

The quadrato-jugal elements are reduced to ligaments. In many Salamandrinae the large orbito-temporal space is divided into an orbital and a temporal fossa by an arch which is formed by the meeting of two corresponding processes from the squamosal and frontal bones respectively. This bridge is rarely bony (Salamandrina, Triton), mostly ligamentous;–apparently a reminiscence of the Stegocephalous condition. The two premaxillary bones are liable to fuse into one, for instance in Cryptobranchus, generally in adult Tritons. They are most reduced, and are toothless, in Siren.

The two maxillary bones are absent only in Necturus, Proteus, Typhlomolge, and Siren. Their posterior end is frequently free, loosely connected by ligaments with the pterygoid in Cryptobranchus; or with the distal portion of the quadrate, and in this case either just touching it (Tylototriton), or forming a broad junction (Pachytriton).

Each half of the lower jaw consists of a dentary, articular and angulo-splenial. The splenial remains as a separate element in Siren; in others only during the larval period. There are no mento-Meckelian elements.

Skeleton of the Anura

The vertebral column.–The distinctive peculiarities of the vertebrae of the Anura are that they are notocentrous, and that about a dozen of them are modified and fused into an os coccygeum. The whole column is the most specialised found in the Vertebrata; and various stages are rapidly hurried through and obscured caenogenetically during the embryonic development. Paired cartilages appear on the dorsal side of the thin chordal sheath, and whilst tending to enclose the spinal cord in a canal, their bases grow head- and tail-wards into what will ultimately become the intervertebral region. This extension of cartilage leads to a fusion with that of the next following pair of arches, so that the axial column at this early stage consists of a right and left longitudinal ridge of cartilage which sends off dorsal processes, neural arches, in metameric succession. Next, the intervertebral cartilage increases in such a way as to constrict the chorda either laterally (Rana) or obliquely from above downwards and inwards (Bufo, Hyla). We recognise in this cartilage the interdorsalia. Ventral arcualia are late and much obscured. There is scarcely any cartilage which could represent the interventralia, the intervertebral cartilage being almost entirely made up of the interdorsalia. These fuse together and form a disc or nodule, which later fuses either with the vertebra in front, and in this case fits into a cup carried by the vertebra next behind (procoelous vertebrae), or the knob is added to the front end of the vertebra, fitting into a cup formed by the tail end of the vertebra next in front (opisthocoelous vertebrae). Much later than the two longitudinal dorsal bands there appears on the ventral side an unpaired band in which appear metamerically repeated swellings of cartilage, likewise unpaired. These swellings become confluent, in a way similar to that which produced the dorsal bands, and form the unpaired ventral band of cartilage, the hypochordal cartilage of some authors. The swellings in this band, equivalent to the basiventralia, become semilunar in a transverse view, their horns tending upwards towards the basidorsal cartilages, but there is no actual meeting. Both dorsal and ventral elements are, however, joined together and form the chief portion of the vertebrae, owing to the rapidly proceeding calcification and later ossification of the all-surrounding "membrana reuniens" or skeletogenous layer so far as that is not cartilaginous.

Procoelous vertebrae exist in the overwhelming majority of Anura; opisthocoelous are those of the Aglossa, the Discoglossidae, and of some Pelobatidae. The systematic value of this pro- or opistho-coelous character has been much exaggerated. We have seen that the centra of the vertebrae of the Anura are formed entirely by the interdorsal elements, hence the term "notocentrous," and these centra sometimes remain in adult specimens of Pelobates as separately ossified and calcified pieces, not fused with the rest of the vertebrae. This important discovery has been made by Boulenger, but Stannius had previously mentioned a specimen of Pelobates in which the second and fourth vertebrae are biconvex, the third, sixth, and eighth biconcave. Moreover, since the sacral vertebra, generally the ninth, in all the Anura is invariably biconvex, the eighth being biconcave in the procoelous families, opisthocoelous like the remaining seven vertebrae in the other families, it is not difficult to imagine that in the Anura the production of pro- or opistho-coelous vertebrae depends simply upon the centra or articulating knobs happening to fuse either with the hind or the front end of the vertebrae. This must of course ultimately be determined by a mechanical problem of motion.

A second type of the vertebrae amongst the Anura is the epichordal type, an exaggeration in degree of the notocentrous tendencies of the more usual perichordal arrangement. It shows, namely, the almost complete suppression of all the ventral cartilaginous elements, so that the chorda remains for a long time on the ventral surface of the axial column in the shape of a flattened longitudinal band. These two types are not unconnected. The suppression of the ventral elements applies most typically to the trunk region, while hypochordal cartilage exists in the anterior cervical vertebrae, and above all in the coccyx. Typically epichordal are the vertebrae of Pipa, Xenopus, Bombinator, Pelobates, Discoglossus and Alytes. It is significant that the epichordal often coincide with opisthocoelous vertebrae, and still more suggestive is the fact that Bombinator is eminently aquatic, Pipa and Xenopus entirely so, having lost the tympanum, at least externally. The epichordal feature is not necessarily indicative of relationship. It has probably been developed independently in various groups, in correlation with a resumption of aquatic life. Various genera of Pelobatidae and most likely some Cystignathidae, e.g. Pseudis, will not improbably connect the two types and their several correlated features, for instance, the frequent reduction of the tympanic cavity.

The os coccygeum has retained rather primitive features in so far as much dorsal and ventral cartilage is developed; but this has almost entirely lost its metameric arrangement, and the posterior half of the coccyx is formed chiefly by the ventral mass of cartilage, while the dorsal elements are more or less reduced. Only two vertebrae, generally the tenth and eleventh of the whole column, are clearly visible, each being composed of a pair of dorsal and a pair of ventral cartilaginous blocks. The sacral vertebra articulates with the coccyx by one or two convexities, but in the Aglossa, in some Pelobatidae, and a few others, the coccyx is fused with the sacral vertebra. Beyond the first and second component vertebrae of the embryonic coccyx, the cartilage is continued in the shape of two dorsal, and one ventral, bands, which soon fuse with each other. Dorsally this cartilage surrounds the spinal cord; the latter degenerates towards the end of the tadpole-stage, leaving, however, the empty spinal canal. The chorda, completely surrounded by cartilage, persists into the post-larval stage, but is destroyed long before the creature attains maturity. Ultimately the whole coccyx ossifies.

The tail proper, namely that portion which is absorbed during the metamorphosis, remains throughout its existence in an apparently primitive condition. The chorda dorsalis and the spinal cord extend through its whole length, surrounded by continuous connective tissue without any cartilage; in fact it represents a piece of typical vertebral column before the appearance of cartilage. The reduction of this swimming organ begins at the hind end.

The vertebral column of the adult.–The first vertebra (we will call it the atlas since it carries the skull) is not, as in the Urodela, provided with an odontoid process. It articulates by two cups with the condyles of the occiput. In some Anura it co-ossifies, rather incompletely, with the second vertebra, regularly in the fossil Palaeobatrachus, often in Ceratophrys, Breviceps, and occasionally in Pelobates, Bufo, Rana, and Xenopus. This is, however, no justification for looking upon the first vertebra as a complex of two vertebrae, although the atlas is frequently very thick and broad, and even carries, in the Aglossa, considerable lateral wings or diapophyses. Those of the trunk-vertebrae are often very long, acting thereby as substitutes for ribs which are absent, except on the second, third, and fourth vertebrae of the Discoglossidae, and on the second and third of the Aglossa. In the adult Aglossa these ribs fuse with the processes which carry them.

The diapophyses of the sacral vertebra carry no ribs, the ilia being attached to them directly. They are either cylindrical as in the Ranidae and Cystignathidae, or they are more or less dilated as in all the other families, most strongly in the Pelobatidae and the Aglossa. In some members of the large sub-family of the Cystignathidae the otherwise cylindrical diapophyses are slightly dilated.

Fig. 4.–Dorsal view of the sacral or ninth vertebra (9), with the attachment of the ilium, of (1) Rana temporaria, (2) Bufo vulgaris, showing the whole coccyx and pelvis, (3) Pelobates fuscus, as examples of cylindrical and of dilated sacral diapophyses. (About nat. size.) a, Acetabulum; c, coccyx; i, ilium; z, anterior zygapophyses.

The sacrum is formed by the ninth vertebra, but there are a few interesting exceptions. Pelobates, Pipa, and Hymenochirus possess two sacral vertebrae; and, neglecting individual abnormalities, these three genera form the only exception amongst recent Amphibia. In the three genera the coccyx is fused with the second sacral vertebra, and such a fusion occurs elsewhere normally only in Bombinator with its single sacral vertebra. The morphologically oldest condition is normally represented by Pelobates, the sacral vertebrae being the tenth and ninth. One case has been recorded by Boulenger of Bombinator pachypus "with eleven segments," the last carrying the ilium. Individual lop-sided abnormalities have been described in Bombinator and Alytes, where the right ilium articulated with the tenth, the left ilium with the ninth vertebra. This shifting forwards of the ilium to the extent of one metamere has been continued further in Pipa, in which the sacrum is formed by the ninth and eighth vertebrae, their diapophyses fusing on either side into extra broad wing-like expansions. In old specimens of Palaeobatrachus fritschi the seventh vertebra is in a transitional condition, the ilium being carried by the ninth and eighth, and slightly also by the diapophyses of the seventh vertebra; and in P. diluvianus the diapophyses of all these vertebrae are united into one broad plate to which the ilia are attached. Lastly, in Hymenochirus the first sacral is the sixth vertebra, and this creature has thereby reduced the pre-sacral vertebrae to the smallest number known.

This shifting forwards of the iliac attachment implies the conversion of original trunk into sacral vertebrae, and the original sacral vertebra itself becomes ultimately added to the urostyle. The second sacral, the tenth of Pelobates, the ninth of Pipa, and the tenth on the right side of the abnormal Bombinator, are still in a transitional stage of conversion. In Discoglossidae the tenth is already a typical post-sacral vertebra, and is added to the coccyx, but it still retains distinct, though short, diapophyses. In the majority of the Anura the tenth vertebra has lost these processes, and its once separate nature is visible in young specimens only. In Bombinator even the eleventh vertebra is free during the larval stage. In fact the whole coccyx is the result of the fusion of about twelve or more vertebrae, which from behind forwards have lost their individuality. We conclude that originally, in the early Anura, there was no coccyx, and that the ilium was attached much farther back; and this condition, and the gradual shifting forwards, supply an intelligible cause of the formation of an os coccygeum. The fact that the sacral vertebrae of the Anura possess no traces of ribs as carriers of the ilia, is also very suggestive. The ilia have shifted into a region, the vertebrae of which had already lost their ribs. By reconstructing the vertebral column of the Anura, by dissolving the coccyx into about a dozen vertebrae, so that originally, say the twenty-first vertebra carried the ilia, we bridge over the enormous gap which exists between the Anura and Urodela. That whole portion of the axial continuation behind the coccyx, more or less coinciding with the position of the vent, is the transitional tail.

The disappearance of both notochord and spinal cord, and the conversion of the cartilaginous elements into a continuous rod in the case of the os coccygeum, find an analogy in the hinder portion of the tail of Dipnoi and Crossopterygii, and in the tail-end of most Urodela, portions which are not homologous with the os coccygeum. The term urostyle should be restricted to such and similar modifications of the tail-end, and this latter happens to be lost by the Anura during metamorphosis.

Strictly speaking, or rather in anatomical parlance, the Vertebrate tail begins with the first post-sacral vertebra. In the Anura that portion of the whole tail has retained most cartilage, and has become the coccygeum, which is required as a "backbone" for the often enormous belly. This requirement is an outcome of the great shortening of the trunk proper (if the trunk be defined as ending with the pelvic region), and this shortening of the trunk is again intimately connected with the jumping mechanism, enlargement of the hind-limbs, elongation of the ilia, and throwing the fulcral attachment forwards as much as possible. The pre-acetabular ilio-sacral connection is carried to the extreme in the Anura.

The shoulder-girdle and "sternum" are more complete than in the Urodela, there being also a pair of clavicles, fused with the precoracoidal bars. The whole apparatus presents two types. In the arciferous type the coracoids and precoracoids retain a great amount of cartilage in their distal portions, and these cartilages (the epicoracoids of some authors) overlap each other movably on one another, the right usually lying ventrally upon the left. The epicoracoidal cartilage of each side, by connecting the distal end of the coracoid with the precoracoid of the same side, forms an arc, hence "arciferous." In the firmisternal type the epicoracoidal cartilages are much reduced, and, instead of overlapping, meet in the middle line and often fuse with each other, forming thereby a firm median bar, which connects the ventral ends of the precoracoids with those of the coracoids. This type is morphologically the higher and more recent, and passes in the larval stage through the arciferous condition. It is restricted to the Ranidae, Engystomatinae, and Aglossa. Although these two types afford an excellent distinctive character for the main divisions of the Anura, they are to a certain extent connected by intermediate forms in such a way, that, for instance, in Bufo and among Cystignathidae in Ceratophrys, the two opposite epicoracoidal cartilages begin to unite at the anterior end.

In many Engystomatinae the precoracoids together with the clavicles are much reduced, sometimes to thin ligaments, being in this case mostly curved back and lying closely against the coracoids; or they may be lost completely. Very rarely the precoracoidal bars are actually much stronger than the coracoids, and the median symphysial bar of cartilage is lost; this is the case in Hemisus.

The scapula is always large and curved into transverse, dorsally broadening blades, the dorsal greater portion of which, the so-called supra-scapula, does not ossify but calcifies.

Fig. 5.–Ventral views of the shoulder-girdles of various Anura. (Slightly enlarged.) 1, Bombinator igneus, and 2, Bufo vulgaris, as examples of the arciferous type; 3, adult, 4, metamorphosing Rana temporaria showing change from the arciferous into the firmisternal type; 5, Hemisus guttatum; 6, Breviceps gibbosus; 7, Cacopus systoma. (5, 6, 7, after Boulenger.) Cartilaginous parts are dotted; ossified parts are left white. Cl, Clavicle; Co, coracoid; E, epicoracoidal cartilage; H, humerus; M, metasternum; O, omosternum; P, precoracoid; Sc, scapula; S.S, supra-scapula.

It is very doubtful if the Anura possess a true sternum, if by sternum we understand a medio-ventral apparatus which owes its origin to the ventral portions of ribs. The so-called sternal apparatus of the Anura consists of two pieces. One, anterior, variously named episternum, presternum, or omosternum, rests upon the united precoracoids and extends headwards, being either styliform or broadened out. Sometimes it is partly ossified, with a distinct suture at its base; this is the case especially in the Firmisternia; in many Arcifera the omosternum remains cartilaginous and is continuous, without a sutural break, with the cartilage of the precoracoids, indicating thereby its genetic relation to the shoulder-girdle. Hence omosternum is the preferable name. It is frequently much reduced, even absent, for instance in most Bufonidae and in the Engystomatinae. The posterior so-called sternal part may be termed metasternum. It forms the posterior counterpart of the omosternum. It is attached behind to the epicoracoidal cartilages, or fusing with them forms their posterior continuation. It appears mostly in the shape of a style, which is frequently ossified, and broadens out behind into a cartilaginous, partly calcified blade. In the Discoglossidae only it diverges backwards into two horns, assuming a striking resemblance to the typical xiphisternum of the Amniota. In young Anura the metasternal cartilage is intimately connected with the pericardium, an indication of its being derived not from ribs but from the shoulder-girdle.

The glenoid cavity is always formed by the coracoids and by the scapula, but the precoracoid often takes part in its formation, for instance in Bufonidae, Hylidae, and Discoglossidae.

In the fore-limb the humerus has a crest, stronger in the males than in the females; it assumes extraordinary strength in some Cystignathidae, notably in the male Leptodactylus. Radius and ulna are fused into one bone. The carpalia are originally nine in number: radiale, ulnare, two centralia, and five carpalia distalia, the fifth of which is reduced to a tiny nodule or to a ligamentous vestige. The primitive condition still prevails in the Discoglossidae. In most of the other Anura the fourth and third distal carpalia, in any case very small, fuse with the enlarged ulnar centrale; the radial centrale comes, in the Bufonidae and Pelobatidae, into contact with the radius, so that the forearm articulates with three elements as in the Urodela, but with this difference, that the intermedium of the Urodela has been lost by the Anura. There are five metacarpalia and five fingers, but the elements of the first or thumb are nearly vestigial, so that the pollux is reduced to one or two nodules, scarcely visible externally. The normal number of the phalanges of the second to fifth fingers is 2, 2, 3, 3. The distal phalanges are generally straight, either pointed or expanded or with Y or T-shaped ends; but in the Hylidae, in Hylambates amongst the Ranidae, and in Ceratohyla, one of the Hemiphractinae, the terminal phalanges are produced into curved claws which support the adhesive finger-discs. There are, however, many genera of different families, which possess finger-discs and have no claw-shaped phalanges. The Hylidae, and many of the climbing members of the Ranidae with adhesive discs, possess an extra skeletal piece intercalated between the last and last but one phalanges of the fingers and toes. This piece, a mere interarticular cartilage in Hyla, is in the following Raninae developed into an additional phalanx, so that their numbers are 3, 3, 4, 4 in the hand and 3, 3, 4, 5, 4 in the foot: Cassina, Hylambates, Rappia, Megalixalus, Rhacophorus, Chiromantis, Ixalus, and Nyctixalus. All the other Ranidae are without this additional phalanx, irrespective of the presence or absence or size of digital expansions.[^[12]]

The pelvic girdle looks like a pair of tongs (see Fig. 4, p. [22]). The ilium is enormously elongated and is movably attached to the sacral diapophyses. This connection is always pre-acetabular in position. The ilium and ischium co-ossify completely, and make up nearly the whole of the pelvis; the pubis is very small, and remains cartilaginous unless it calcifies. It rarely possesses a centre of ossification, for instance in Pelobates, where the osseous nodule is excluded from the acetabulum, recalling certain Labyrinthodonta, whose ossa pubis likewise do not reach that cavity. The latter is open or perforated in young Anura and remains so in the Discoglossidae, but in the others it becomes closed up as in the Urodela. The ventral halves of the pelvis, besides forming a symphysis, closely approach each other, just leaving room for the passage of the rectum and the urino-genital ducts.

The hind-limbs are in all cases longer than the fore-limbs. The femur is slender, the tibia and fibula are fused into one bone. The tarsus is much modified by the great elongation of the two proximal tarsalia (there being no intermedium) into an astragalus and a calcaneum, both of which fuse together distally and proximally, or completely as in Pelodytes; in the latter case the limb assumes a unique appearance, since it consists of three successive and apparently single bars of nearly equal length. The other tarsal elements, especially the more lateral ones, are practically reduced to pads. The Anura have thereby acquired two well-marked joints, one cruro-tarsal, the other tarso-metatarsal; this shows a high stage of specialisation in comparison with the Urodelous and Stegocephalous type of still undefined joints.

The Anura possesses five well-developed toes with normally 2, 2, 3, 4, and 3 phalanges, and the rudiments of a sixth digit, the so-called prehallux, which consists of from two to four pieces, including the one which represents its metatarsal. This prehallux, as a vestige of a once better developed digit, is exactly like the elements on the radial side of the wrist, which, we are certain, are the remnants of a once complete finger, namely the pollex. The only weighty difficulty against its interpretation as a prehallux lies in the fact that hitherto no six-toed Stegocephali have been found; but the fact that there are no Stegocephali known with more than four fingers could be used as an argument against there being a pollex-vestige in recent Anura with just as little reason.

The skull of the Anura differs from that of the other recent Amphibia in the following features:–

The orbital region of the primitive cranium remains cartilaginous, but further forward the cranial cavity is closed by the unpaired sphenethmoid, which forms a ring round the anterior portion of the brain-cavity, hence called "os en ceinture" by some anatomists. The frontals and parietals fuse into one pair of fronto-parietal bones, and these again can fuse together in the middle line; as in Aglossa and Pelobates. The palatal portion of the palato-quadrate cartilage is complete, reaching forwards to the sides of the ethmoid region. The curved arch, formed by this cartilage, is covered by the following bones: (1) the quadrato-jugal, reduced to a thin splint which connects the quadrate and squamosal with the posterior end of the maxilla; (2) the pterygoid, always strong, extending from the distal inner corner of the quadrate to the maxilla, sometimes also to the palatine, and with a broad, median process to the parasphenoid, this process covering ventrally most of the otic region; (3) the palatines, which vary considerably in shape and size; they are placed transversely and meet in the middle line; in Bombinator and Pelodytes they are absent.

The quadrates are directed transversely and backwards, in conformity with the wide gape of the mouth. The squamosal is always well developed, covering the whole of the quadrate on its outer side; it has a forwardly directed process which ends freely in Rana, meets a corresponding process of the maxilla and forms a bony arch with it in Discoglossus, Pelobates, and others, or is scarcely developed at all, for instance in Bufo. In Pelobates cultripes the squamosal is very wide and forms a junction with the fronto-parietals, thus producing a broad bridge across the temporal fossa.

The nasal bones are large and meet in the middle line. Frequently they leave a space between them and the diverging anterior portion of the fronto-parietals, through which gap appears part of the dorsal surface of the ethmoid cartilage. A fontanelle between the frontals occurs in most Hylidae, many Cystignathidae, some few Bufonidae, in Pelodytes amongst the Pelobatidae, and in the Discoglossidae.

The tympanic cavity is bordered in front, above, and below by the squamosal and quadrate, behind by the musculus depressor mandibulae, internally by the otic capsule, and by the cartilage of the cranium between this and the lateral occipital bone. The cavity communicates, however, by the wide and short Eustachian tube with the mouth, the passage being bordered anteriorly by the pterygoid, posteriorly by soft parts. Partly imbedded in these soft tissues is the styloid process or stylohyal, which is attached to the cranium, mostly behind the otic region, and is continued downwards into the anterior horn of the hyoid. The whole partly cartilaginous, ligamentous, and osseous string is, in fact, the entire ventral half of the hyoid arch, while the dorsal half or hyomandibular portion of this, the second visceral arch, is modified into the columellar or auditory chain. The inner end of this chain, the stapes, is inserted into and around the fenestra ovalis of the otic capsule, while the outer end is somewhat T-shaped, and is loosely attached to or near the upper rim of the tympanic ring and to the middle of the tympanic disc. In many Anura this terminal bar can be seen from the outside. The middle portion of the columellar chain is ossified, the rest remains cartilaginous. But the whole chain exhibits various modifications in different genera, especially in the number and the extent of the processes sent out by the outer cartilaginous portion; these are attached in various ways to the tympanum and its rims. The tympanic disc is carried by a cartilaginous ring, which rests against a special process sent out by the quadrate, and is probably itself a differentiation of this element.

In some very aquatic genera, but also in Pelobates, the tympanic cavity is much reduced, for instance in Bombinator, Liopelma. In Batrachophrynus not only the cavity, but also the Eustachian tubes are suppressed. In the Aglossa only the two tubes are united into one short but wide median canal, opening at the level of the pterygoids on the roof of the mouth.

The lower jaw is remarkable for the possession of mento-Meckelian cartilages, absent only in the Aglossa and Discoglossidae. At first they are much longer than the rest of the jaw; during the larval life they indeed form the functional jaw, and they are now covered with horny sheaths instead of teeth. Owing to the absence of teeth on them, these mento-Meckelian cartilages are later not invested by bone, although in many Anura they ultimately ossify, either retaining their separate nature or fusing partly with the dentary bones. The bulk of the lower jaw, the Meckelian cartilage, becomes invested by the dentary, a small articulare, and an inner angulare, while a splenial element is absent. The dentary itself is mostly reduced to a small dentigerous splint, while the angulare forms by far the greater part of the bony jaw.

Teeth are more restricted in their occurrence than in the Urodela. On the jaws they always stand in one row. With the exception of the Hemiphractinae, Amphignathodontinae, Ceratobatrachinae, and Genyophryninae, no recent Anura carry teeth on the lower jaw, and even in these genera they are mostly much reduced in size and firmness, having all the appearance of vanishing structures. The premaxillae and maxillae are frequently furnished with teeth, except in the Dendrobatinae, Genyophryninae, Engystomatinae, Dendrophryniscinae, Bufonidae, Pipa, and Hymenochirus. The vomers mostly carry a series of teeth on their posterior border; when these teeth are absent, as in many species of Bufo, a kind of substitute sometimes occurs on the palatines in the shape of a row of tuberosities. The palatines carry teeth in Hemiphractinae. The parasphenoids are rarely toothed, e.g. Triprion, Diaglena, Amphodus, and occasionally in Pelobates.

A few Anura possess peculiar substitutes for teeth in the anterior portion of the lower jaw, namely, a pair of conical bony processes, sometimes rather long, but always covered by the dense gums, or investment of the jaws; e.g. Lepidobatrachus, several Rana, e.g. R. adspersa, R. khasiana, R. kuhli, and Cryptotis brevis.

Cranial dermal ossifications are developed in some species of Bufo, still more in the Hemiphractinae, and above all in Pelobates cultripes and in the Cystignathoid genus Calyptocephalus.

The hyoid apparatus of the Anura is complicated. It is originally composed of the hyoidean and four branchial arches, with one median, copular piece. The branchial arches form in the early life of the tadpole the elaborate framework of the filtering apparatus mentioned on p. [44]. During metamorphosis the whole filter disappears, owing to resorption of the greater part of the branchial arches; only their median portions remain, and fuse with the enlarged copular piece and the hyoidean arches into a broad shield-shaped cartilage (corpus linguae), whence several lateral processes sprout out, the posterior pair of which are generally called thyrohyals or thyroid horns. The true hyoid horns give up their larval lean-to articulation with the quadrate, become greatly elongated, and gain a new attachment on the otic region of the cranium. The transformation of the whole apparatus has been studied minutely by Ridewood, in Pelodytes punctatus.[^[13]]

Skin

The epidermis of the young larvae of Amphibia is furnished with cilia, which later on are suppressed by the development of a thin hyaline layer or cuticula, but clusters of such cilia remain, at least during the larval life and during the periodical aquatic life of the adult, in the epidermal sense-organs. In the frog, currents are set up by the ciliary action at an earlier stage, and are maintained to a later stage than in the newt. In the latter the tail loses its ciliation, whereas in the frog it remains active almost up to the time of the metamorphosis. In tadpoles of 3-10 mm. nearly the whole surface is ciliated (Assheton).[^[14]] The cilia work from head to tail, causing the little animal, when perfectly quiet, to move forwards slowly in the water. Beneath the cuticula, in the Perennibranchiata and the larvae of the other Urodela, lies a somewhat thicker layer of vertically striated cells, the so-called pseudo-cuticula, which disappears with the transformation of the upper layers of the Malpighian cells into the stratum corneum. The latter is very thin, consists of one or two layers of flattened cells, and is shed periodically by all Amphibia in one piece. In the Urodela it generally breaks loose around the mouth, and the animal slips out of the delicate, transparent, colourless "shirt," which during this process of ecdysis or moulting becomes inverted. In the Anura it mostly breaks along the middle line of the back, the creature struggles out of it, pokes it into its mouth, and swallows it. Urodela also eat this skin. As a rule the first ecdysis takes place towards the end of the metamorphosis, preparatory to terrestrial life. So long as the animal grows rapidly, the skin has to be shed frequently, since this corneous layer is practically dead and unyielding. Adult terrestrial Urodela do not seem to moult often, mostly only when they take to the water in the breeding season. Anura, on the other hand, moult often on land, at least every few months. The surface of the new skin is then quite moist and slimy, but it soon dries and hardens.

The Malpighian stratum consists of several layers, thickest in the Perennibranchiata; in them it contains mucous cells throughout life, in others such slime-cells are restricted to larval life. Later, regular slime-glands are developed, which open on the surface. They are very numerous, and more evenly distributed, over most parts of the body, than the specific or poison-glands, which are restricted to certain parts, often forming large clusters, especially on the sides of the body. They reach their greatest development in the "parotoid glands" of the Anura. Both kinds of glands are furnished with smooth muscle-fibres, which are said to arise from the basal membrane underlying and forming part of the Malpighian layer; these muscle-cells extend later downwards into the corium. For the action of the poison, see p. [37].

The stratum corneum is mostly thin, but on many parts of the body, especially in Anura, the epidermal cells proliferate and form hard spikes or other rugosities, generally stained dark brown. With these may be grouped the nuptial excrescences so frequent in the Anura, especially on the rudiment of the thumb, and on the under surface of the joints of the fingers and toes. In many Anura, less frequently in the Urodela, the tips of the fingers and toes are encased in thicker horny sheaths, producing claws or nails. They are best developed among newts in Onychodactylus, among the Anura in Xenopus and Hymenochirus. The horny covering of the metatarsal tubercles reaches its greatest size in the digging spur or spade of Pelobates. In most of these cases the cutis is elevated into more or less wart-like papillae, covered, of course, by the proliferated and cornified epidermis. In the female of Rana temporaria nearly the whole surface of the body becomes covered with rosy papillae during the breeding season. Similar nuptial excrescences are common, and are most noteworthy in the male of the Indian Rana liebigi.

The epidermis also contains sense-organs. They attain their highest development in the larvae; later on they undergo a retrogressive change. Each of these sense-organs is a little cup-shaped papilla, visible to the naked eye. It is composed of elongated cells which form a mantle around some central cells, each of which ends in a stiff cilium perforating a thin, hyaline membrane which lines the bottom of the cup, and is perhaps the representation of the cuticula. These ciliated cells are connected with sensory fibres, the nerve entering at the bottom of the whole organ. The cilia are in direct contact with the water, but the outer rim of the whole apparatus is protected by a short tube of hyaline cuticula-like secretion. These sense-organs are, in the larvae, scattered over the head, especially near the mouth and around the eyes, whence they extend backwards on to the tail, mostly in three pairs of longitudinal rows, one near the vertebral column, the others lateral. They are supplied by the lateral branch of the vagus nerve. They disappear during the metamorphosis, at least in the Anura, with the exception of Xenopus, in which they form conspicuous white objects. The white colour is caused by the tubes becoming choked with the débris of cells or coagulating mucous matter, so that it is doubtful if these organs, which moreover have sunk deeper into the skin, are still functional. In the terrestrial Urodela these organs undergo a periodical process of retrogression and rejuvenescence. During the life on land they shrink and withdraw from the surface, and their nerves likewise diminish, but in the breeding season, when the newts take again to aquatic life, they revive, are rebuilt and become prominent on the surface. They are an inheritance from the fishes, in which such lateral line organs are universally present.

The cutis of most Amphibia is very rich in lymph-spaces, which, especially in the Anura, assume enormous proportions, since the so-called subcutaneous connective tissue forms comparatively few vertical septa by which the upper and denser layers, the corium proper, are connected with the underlying muscles. The spaces are filled with lymph, and into some of them the abnormally expanded vocal sacs extend, notably in Paludicola, Leptodactylus, and other Cystignathidae, and in Rhinoderma.

The cutis frequently forms papillae and prominent folds, sometimes regular longitudinal keels on the sides of the back; but dermal, more or less calcified or ossified scales are restricted to the Stegocephali and to the Apoda, q.v., pp. [79], [87]. We conclude that the Urodela and Anura have entirely lost these organs. Dermal ossifications, besides those which now form an integral part of the skeleton, like many of the cranial membrane-bones, are rare, and are restricted to the Anura. They are least infrequent on the head, where the skin is more or less involved in the ossification of the underlying membrane-bones, for instance in Triprion, Calyptocephalus, Hemiphractus and Pelobates. The thick ossifications in the skin of the back of several species of Ceratophrys are very exceptional. In Brachycephalus ephippium these dermal bones enter into connection with the vertebrae; small plates fuse with the dorsal processes of the first to third vertebrae, while one large and thick plate fuses with the rest of the dorsal vertebrae. Simple calcareous deposits in the cutis are less uncommon, for instance, in old specimens of Bufo vulgaris. We are scarcely justified in looking upon these various calcifications and even ossifications as reminiscences of Stegocephalous conditions.

The skin contains pigment. This is either diffuse or granular. Diffuse pigment, mostly dark brown or yellow, occurs frequently in the epidermis, even in the stratum corneum. The granular pigment is stored up in cells, the chromatophores, which send out amœboid processes, and are restricted to the cutis, mostly to its upper stratum, where they make their first appearance. Contraction of the chromatophores withdraws the pigment from the surface, expansion distributes it more or less equally. The usual colours of the pigment are black, brown, yellow, and red. Green and blue are merely subjective colours, due to interference. A peculiar kind of colouring matter is the white pigment, which probably consists of guanine, and is likewise deposited within cells; cf. the description of the white spots in the skin of Hyla coerulea.

Most Amphibia are capable of changing colour, the Urodela, however, far less than the Anura, some of which exhibit an extraordinary range and adaptability in their changes.

The mechanism by which the change of colour is produced in frogs has been recently studied by Biedermann.[^[15]] If we examine the green skin of the common Tree-frog, Hyla arborea, under a low power and direct light, we see a mosaic of green, polygonal areas, separated by dark lines and interrupted by the openings of the skin-glands. Seen from below the skin appears black. Under a stronger power the black layer is seen to be composed of anastomosing and ramified black pigment-cells. Where the light shines through, the skin appears yellow. The epidermis itself is quite colourless. The mosaic layer is composed of polygonal interference-cells, each of which consists of a basal half which is granular and colourless, while the upper half is made up of yellow drops. Sometimes the tree-frog appears blackish, and if then the black pigment-cells are induced to contract, for instance, by warming the frog, it appears silver-grey; in this case the pigment in the yellow drops is no longer diffuse, but is concentrated into a round lump lodged between the interstices of the granular portions; the black pigment-cells are likewise balled together. These black chromatophores send out numerous fine branches, which occasionally stretch between and round the polygonal cells. When each of these is quite surrounded and covered by the black processes, the frog appears black. On the other hand, when the black pigment-cells withdraw their processes, shrink up, and, so to speak, retire, then the light which passes through the yellow drops is, by interference, broken into green.

Stoppage of the circulation of the blood in the skin causes the black chromatophores to contract. Carbon dioxide paralyses them and causes them to dilate. This is direct influence without the action of nerves. But stimulation of the central nerve-centres makes the skin turn pale. Low temperature causes expansion, high temperature contraction, of the chromatophores. Hence hibernating frogs are much darker than they are in the summer. Frogs kept in dry moss, or such as have escaped into the room and dry up, turn pale, regardless of light or darkness, probably owing to a central, reflex, nerve-stimulus.

Tree-frogs turn green as the result of the contact with leaves. Dark frogs will turn green when put into an absolutely dark vessel in which there are leaves. This is reflex action, and blinded specimens do the same. The principal centres of the nerves which control the chromatophores, lie in the corpora bigemina and in the optic thalami of the brain. When these centres are destroyed, the frog no longer changes colour when put upon leaves, but if a nerve, for instance the sciatic, be stimulated, the corresponding portion of the body, in this case the leg, turns green. Rough surfaces cause a sensation which makes the frog turn dark. Rana seems to depend chiefly upon temperature and the amount of moisture in the air, so far as its changes of colour are concerned. Biedermann concludes that the "chromatic function of frogs in general depends chiefly upon the sensory impressions received by the skin, while that of fishes depends upon the eye."

All this sounds very well, but the observations and experiments are such as are usual in physiological laboratories, and the frogs, when observed in their native haunts, or even when kept under proper conditions, do not always behave as the physiologist thinks they should. There is no doubt that in many cases the changes of colour are not voluntary, but reflex actions. It is quite conceivable that the sensation of sitting on a rough surface starts a whole train of processes: roughness means bark, bark is brown, change into brown; but one and the same tree-frog does not always assume the colour of the bark when it rests, or even sleeps upon, such a piece. He will, if it suits him, remain grass-green upon a yellow stone, or on a white window-frame. I purposely describe such conditions, changes, coincidences, and discrepancies in various species, notably in Hyla arborea, H. coerulea, Rana temporaria, Bufo viridis, to show that in many cases the creature knows what it is about, and that the eye plays a very important part in the decision of what colour is to be produced. The sensory impression received through the skin of the belly is the same, no matter if the board be painted white, black, or green, and how does it then come to pass that the frog adjusts its colour to a nicety to the general hue or tone of its surroundings?

Boulenger[^[16]] has given us a summary of the action of the poison of Amphibia:

It is well known to all who have handled freshly-caught newts, and certain toads, especially Bombinator, that their secretion acts as a sternutatory, and causes irritation of the nose and eyes, the effects produced on us by Bombinator being comparable to the early stages of a cold in the head. Many collectors of Batrachians have learned, to their discomfiture, how the introduction of examples of certain species into the bag containing the sport of their excursion may cause the death of the other prisoners; for although the poison has no effect on the skin of individuals of the same species, different species, however closely allied, may poison each other by mere contact. But when inoculated the poison acts even on the same individual.

Miss Ormerod, to personally test the effect, pressed part of the back and tail of a live Crested Newt between the teeth. "The first effect was a bitter astringent feeling in the mouth, with irritation of the upper part of the throat, numbing of the teeth more immediately holding the animal, and in about a minute from the first touch of the newt a strong flow of saliva. This was accompanied by much foam and violent spasmodic action, approaching convulsions, but entirely confined to the mouth itself. The experiment was immediately followed by headache lasting for some hours, general discomfort of the system, and half an hour after by slight shivering fits."

Numerous experiments have shown that the poison of toads, salamanders, and newts is capable, when injected, of killing mammals, birds, reptiles, and even fishes, provided, of course, that the dose be proportionate to the size of the animal. Small birds and lizards succumb as a rule in a few minutes; guinea-pigs, rabbits, and dogs in less than an hour.

This poison of Amphibia is not septic, but acts upon the heart and the central nervous system. That of the common toad has been compared, in its effects, to that of Digitalis and Erythrophlaeum. Some authorities hold that the poison is an acid, others regard it as an alkaloid.

Phisalix[^[17]] has come to the conclusion that toads and salamanders are possessed of two kinds of glands, different both anatomically and physiologically. These are, first the mucous glands, spread over the greater part of the body, with an alkaloid secretion, which acts as a narcotic; secondly, specific glands, as the parotoids and larger dorsal glands, the secretion of which is acid, and acts as a convulsive.

The Indians of Colombia are said to employ the secretion of Dendrobates tinctorius for poisoning their arrows. The poison is obtained by exposing the frog to a fire, and after being scraped off the back is sufficient for poisoning fifty arrows. It acts on the central nervous system, and is used especially for shooting monkeys. Concerning the use of this poison for "dyeing" parrots, see p. [272].

The milky secretion of toads protects them against many enemies, although not always against the grass-snake. A dog which has once been induced to bite a toad, suffers so severely that it will not easily repeat the experiment. The handling of tree-frogs also irritates both nose and eyes. The hind limbs of the Water-frog, Rana esculenta, have a very bitter, acrid taste. In short, most, if not all, Amphibia are more or less poisonous, and it is significant that many of the most poisonous, e.g. Salamandra maculosa, Bombinator, Dendrobates, exhibit that very conspicuous combination of yellow or orange upon a dark ground, which is so widespread a sign of poison. Other instances of such warning colours, protective in a defensive sense, are the Wasps and Heloderma, the only poisonous lizard.

Nerves

Spinal nerves.–Each spinal nerve issues originally immediately behind the neural arch of the vertebral segment to which it belongs. This intra-vertebral position is ultimately modified into a more inter-vertebral one, owing to the predominant share of the neural arches, basidorsalia, in the composition of the whole vertebra. Consequently the nerves issue behind their corresponding vertebra.

The first spinal nerve, or N. suboccipitalis, is exceptional in several respects. It develops a dorsal and a ventral root like a typical spinal nerve, but the dorsal root soon degenerates in all Amphibia, while in the Phaneroglossal Anura the whole nerve disappears. The first spinal nerve reduced to its ventral half persists therefore only in the Apoda, Urodela, and the Aglossal Anura. It issues originally between the occiput and the atlas, but in the adult it is partly imbedded in the anterior portion of the atlas. Its own vertebra is lost, having probably been added to the cranium.

In the Urodela the first spinal nerve either remains separate, or it joins the second spinal, forming with it and with a branch from the third nerve the cervical plexus, which supplies the muscles of the cervical region. The third, fourth, and fifth nerves, and sometimes also the sixth, form the brachial plexus.

In the Aglossal Anura N. spinalis I. mostly sends a fine thread to the second spinal nerve, the rest supplies chiefly the M. levator scapulae, in Pipa the abdominal muscles also. In all the other Anura this N. spinalis I. is lost; occasional vestiges have been reported in Bufo vulgaris and Rana catesbiana, and remnants of it may possibly be found in Pelobatidae and Discoglossidae. The first actually persisting nerve of the Phaneroglossa is consequently N. spinalis II.

The brachial plexus is composed as follows:–Pipa, N. spinalis II. and III.; Xenopus and Phaneroglossa, N. spinalis III. and IV., with a small branch from the second; the next following three nerves, numbers V., VI., and VII., behave like ordinary trunk nerves.

The pelvic plexus of the Phaneroglossa is formed in Rana by the VIII. + IX. + X. + XIth nerves, the tenth issuing between the sacral vertebra and the coccyx. In Bufo and Hyla the plexus is composed of five nerves, the seventh spinal sending a branch to it. Occasionally the twelfth nerve contributes a small branch to the posterior portion of the plexus. This and the eleventh nerve leave the coccyx by separate holes, thereby indicating its composition. The rest of the spinal cord gives off no more recognisable nerves, owing to its reduction during the later stages of metamorphosis; its terminal filament passes out of the posterior end of the coccygeal canal.

Concerning the cranial nerves it is necessary to draw attention to one point only. The last nerve which leaves the cranium of the Amphibia is the vagus or tenth cranial nerve. There is consequently no eleventh, and no twelfth or hypoglossal, pair of cranial nerves. Their homologues would be the first and second spinal nerves, but the whole tongue of the Amphibia, with its muscles, is supplied by the glossopharyngeal, or ninth cranial pair, and is morphologically not homologous with the tongue of the Amniota.

Respiratory Organs

A very important and characteristic feature of the Amphibia is the development of two sets of respiratory organs: Gills and Lungs. It is as well to give definitions of these organs. Lungs are hollow evaginations from the ventral wall of the pharynx, and their thin, vascularised walls enable the blood to exchange, by osmosis, carbon dioxide for oxygen from the air which enters the lungs by the mouth or the nostrils, and the windpipe. The latter is unpaired, the lungs themselves are paired. Gills are highly vascularised, more or less ramified excrescences, covered by a thin epithelium of ecto- or endo-dermal origin, which permits of the exchange of carbon dioxide for oxygen from the air which is suspended in the surrounding water. It is obvious that this definition applies to all sorts of well-vascularised organs whose thin surface comes into contact with the water. Various recesses of the pharyngeal cavity, the dorsal and ventral folds of the tail-fin, nay, even any part of the skin of the body can, and does occasionally, assume additional respiratory functions. The proper definition of gills, in Vertebrates, requires, therefore, the restriction that they must be developed upon and carried by visceral arches.

The general statement that the Amphibia breathe by lungs, and, at least during some stage of their life, also by gills, requires various restrictions. As a rule the majority of Amphibia first develop gills, later on also lungs, whereupon, during the metamorphosis, the gills are gradually suppressed, so that the perfect animal breathes by lungs only (see p. [61]). But a number of Urodela retain their gills throughout life, although the lungs are also functional. These are the Perennibranchiata, not a natural group, but a heterogenous assembly, Proteidae and Sirenidae. Some species of Amblystoma remain individually Perennibranchiate (cf. Axolotl, p. [112]). On the other hand, in some Anura the gills are almost or entirely suppressed, or restricted to the embryonic period only. Lastly, a considerable number of Salamandridae have lost their lungs; they breathe by gills until their metamorphosis, but have in the adult state to resort to respiration by the skin (cf. p. [46]).

The general plan of the development of the branchial respiratory apparatus is as follows:–The six visceral arches, namely, the mandibular, the hyoidean, and the four branchial arches, correspond, long before they are cartilaginous, with four main arterial arches of the truncus arteriosus. The first, the arteria hyo-mandibularis, belongs to the hyoidean and mandibular segments, the second to the first branchial, the third to the second branchial, while the fourth soon splits in two for the third and fourth or last branchial arch. On the dorsal side these branchial arterial arches combine to form the radix of the dorsal aorta. These arches, especially the three branchials, appear in newts, less clearly in frogs, as transverse ridges on the sides of the future neck. Between the arches the pharynx gradually bulges out in the shape of five lateral gill-pouches; the first between the mandibular and the hyoidean arch, the second between the hyoidean and the first branchial arch, etc. These pouches soon break through to the outside and become gill-clefts, except the first pouch in Urodela. Before the breaking through of the clefts there appears upon the outside of the middle of the rim of each arch a little knob, which soon ramifies and forms an external gill. The knob owes its origin to the development of a blood-vessel which buds from the arterial arch, ramifies and breaks up into capillaries, and returns a little further dorsalwards into the arch. A secondary loop to the outside of the primary arterial arch is thus formed; and whilst this outer loop sprouts out further, driving before it the likewise proliferating skin, and thus producing the gill, the middle portion of the primary arch remains in the Urodela as a short cut, but in the Anura it partly obliterates, and henceforth acts as the internal efferent vessel of the gill. When, during metamorphosis, the gills disappear, their intrinsic afferent and efferent vessels vanish likewise, and the short cut completes the circuit. In order to do this they have, in the Anura, to form new connections with the trunks of the afferent vessels.

The arterial arches themselves are modified as follows:–The first pair become the carotids, the second form the right and left aortic arches, while the third and fourth unite and are transformed into the pulmonary arteries and "ductus Botalli," the last arterial arch having previously sent a branch into the developing lungs. In the Anura the third arch obliterates.

The gills and clefts present various modifications. The Urodela possess three pairs of gills, one each upon the dorsal half of the three branchial arches, just near the upper corners of the clefts; and the skin of the body is continued upon the stem of each gill, pigmented like the rest of the surface of the body. Such a gill is more or less like a blade, standing vertically, and is composed of a stem of connective tissue, thick at the base, and, as a rule, carrying two series of fine lamellae, which, however, do not form two opposite series, but hang downwards, being, so to speak, folded down, so that the upper surface of the stem is bare, and carries the lamellae on its under side. In the Axolotl some of these lamellae are further subdivided. In Necturus they are enormously increased in numbers, but are rather short, and they stand no longer in two rows, but are crowded into one. Those of Proteus form two rows of dendritic filaments; those of Siren are likewise much ramified.

The larvae of the Urodela have four clefts. In the adult Siren these are reduced to three, the first, namely, that between the hyoid and the first branchial arch, being closed up. In Necturus, Proteus, and Typhlomolge the clefts are further reduced to two, owing to the closing up of the first and last, only those between the first, second, and third arches remaining. Amphiuma, and usually Cryptobranchus alleghaniensis, possess only one pair of clefts, while in C. japonicus and in the Salamandridae all the clefts are abolished.

The gills of the Urodela are always uncovered, although a short operculum is formed from the posterior margin of the hyoidean arch; the halves of this fold meet below the throat, and persist in various terrestrial and aquatic species as the "gular fold." It reaches its greatest size just before metamorphosis, but scarcely ever produces a proper outer gill-chamber, and it does not cover the gills owing to their rather pronounced dorsal position. It is perhaps best developed in Typhlomolge, and even there its dorsal portion is continued upon the first of the three broad vertical and short-fringed blades which form the gills.

A description of the gills of the Apoda will be found in the systematic part.

In the Anura the gills are complicated, owing to the development of the so-called internal gills. First appear, exactly in the same way as in the Urodela, the external gills, one upon each of the first three branchial arches. In the larva of Rana esculenta, 5 mm. in length, a little protuberance appears upon the first, and then upon the second arch. In the 6 mm. larva the first gill shows four knobs, the second two, the third one knob. They are always delicate and thin, although sometimes pigmented, long, and much-ramified structures. The first pair is always the largest; well developed and persisting a long time in Rana temporaria; smaller in R. esculenta and Bufo vulgaris; very short, scarcely forked, in B. viridis and Hyla arborea. They are relatively largest in Alytes, while still in the egg. Numerous descriptions of these gills will be found in the systematic part.

Great changes take place about the time when the fourth or last branchial arch and the pulmonary arteries are developed. This occurs in R. esculenta when the larva is about 9 mm. long. The sprouting of the gills extends gradually downwards along the arches upon their ventral halves, and these new gill-filaments or loops transform themselves into numerous dendritic bundles, resting in several thickset rows upon the hinder margin of the first to the third arch, one row only on the fourth arch, which carries no external gill. These "internal gills" look like red bolsters or thick and short-tasselled bunches. Whilst they are developing the dorsal, older gills become arrested in their growth and disappear, and at the same time a right and left opercular fold grows out from the head and covers these new gills, shutting them up in an outer branchial chamber, just like that of Teleostei and other Tectobranch fishes. This is the reason why these new gills have been called internal, and the mistaken notion has sprung up that they are comparable with the true internal gills of fishes. In reality Amphibia have only external gills. They are always covered by ectoderm, are restricted to the outside of the branchial arches, and are developed before the formation of the clefts. These gills are in many cases directly continuous with the more dorsally and more superficially placed earlier external gills; but although nearly every one who has studied their development has observed this agreement, the old error still prevails. They are morphologically as little internal as the true internal gills of Elasmobranch embryos are external gills, because these have become so elongated that they protrude out of the gill-clefts.

The fact that the Amphibia possess only external gills throws important light upon their phylogeny. Not only do the Apoda, Urodela, and Anura agree much more with each other than would be the case if the Anura possessed both internal and external gills, but the Amphibia reveal themselves also in this point as connected with the Crossopterygii and the Dipnoi, some of which fishes also possess external gills. It is of course quite possible that the Amphibia have developed these organs independently, but we understand now that the latter are accessory, and not the primitive respiratory organs; they are developed in adaptation to embryonic conditions and to prolonged larval, occasionally perennibranchiate, aquatic life (cf. the chapter on Neoteny, p. [63]).

There is no valid reason for supposing that the Stegocephali had true internal gills. We know their branchial skeleton, and we can discern even gill-rakers on the arches. Such gill-rakers occur also, although but feebly developed, in Urodela. The whole branchial framework of the Urodela and Apoda undergoes simple reductions during metamorphosis (see p. [86]), but in the Anura these arches are in early tadpole life transformed into a most complicated basket-work which acts as a straining apparatus or filter, to prevent any particle of food or other foreign matter from finding its way into the delicate gills, the current of water passing from the mouth through the filter, past the gills and out of the clefts. During metamorphosis this whole elaborate apparatus is again transformed, almost beyond recognition, into the hyoidean apparatus for the support of the generally very movable and much-specialised tongue. The fact that the hyoid apparatus of the Aglossa, especially that of Xenopus, is constructed upon the same lines, is a strong indication that these creatures have arrived at their tongueless condition through the loss of this organ, and this is intelligible in correlation with their absolutely aquatic life.

The opercular folds assume great dimensions in all tadpoles. They cover the whole gill-region, thereby producing on either side an outer gill-chamber. The posterior margins of the folds gradually become continuous with the rest of the surface of the body. Each gill-chamber opens at first by one lateral canal, usually called the spiracle. This condition prevails in the tadpoles of the Aglossa. In the Discoglossidae the two canals gradually converge and combine into one median opening on the middle of the belly. In all the other Anura the right opening becomes closed, or rather its canal passes over to and joins that of the left side, both opening by one short tube laterally on the left side, at a variable distance between the eye and the vent. Hence the elegant terms of Amphi-, Medio-, and Laevo-gyrinidae (γυρῖνος being the Greek for tadpole).

The external gills lead to a further consideration. Protopterus possesses a vestigial external gill on the shoulder-girdle. Lepidosiren has them on the gill-arches, resembling piscine internal gills, and Polypterus has a large biserially fringed external gill (in some cases not disappearing until the fish is adult), which starts from the mandibular arch, at the level of the spiracle or first visceral cleft, and overlaps the operculum externally. The axis of this peculiar organ is possibly based upon the homologues of the spiracular cartilages, which themselves are the branchiostegal rays of the dorsal half of the quadrato-mandibular arch. The branchiostegal rays of the hyoidean arch, at least their material, have given rise to the elaborate opercular apparatus; and, in conformity herewith, the hyomandibular itself is not known to carry a gill. Quite possibly the large external gill of Polypterus is not serially homologous with other external gills–it may not be a true gill at all, it has perhaps quite a different function–but it seems to throw light upon a mysterious pair of organs which are common in larval and young Urodela, in the larval Aglossa and in the Apoda. These are the "balancers."

In Triton taeniatus, before hatching, there appears a little protuberance behind and below the eye; it rests upon the angle of the mandibular arch, and is separated from the first transverse, externally visible ridge of the first branchial arch by the beginnings of the hyoidean arch. A few days later the arteria hyomandibularis sends a vessel into this knob, forms a vascular coil, and leaves it as a vein which, instead of returning into the arterial arch, passes into the veins of the body. Its epithelium is not covered with flat, but with cubical cells; and sensory cells have not been found in it. These organs attain some size, and are shaped like rods, with thickened ends; they are movable, and are used by the larvae as "balancers," keeping the head from sinking into the slime at the bottom. But they may have other functions besides, and it is not unlikely that they develop into sensory organs like feelers. They occur in many Salamandridae, and are not reduced until, or even after, the metamorphosis, and during this time they shift their place with relation to the eye and the mouth.

The same kind of organs occur in Amblystoma.[^[18]] They appear, previous to the breaking open of the gill-clefts, as protrusions of epiblast, long before any of the external gills on the branchial arches. When the clefts have broken open, the quadrate sends out laterally a tiny crescent-shaped process a little above the jaw-joint, and this process extends to the base of the balancer, but not into it, and a bundle of muscle-cells grows into the balancer. It is easy to recognise the same organ in the extremely long thread-like structures of the larva of Xenopus. In the Apoda they are likewise present, but are retained permanently as highly specialised, probably tentacular organs (cf. p. [86], Apoda).

One of the most unexpected features is the suppression of the lungs in various kinds of Salamandridae. The lungs are either reduced to useless vestiges or they are quite absent. This occurs in aquatic and terrestrial, American and European forms, and it is noteworthy that the reduction of the lungs does not apply to all the species of the various genera, nor is it restricted to one sub-family.

The following list is due to the researches of H. H. Wilder,[^[19]] L. Camerano,[^[20]] E. Lönnberg,[^[21]] and G. S. Hopkins[^[22]]:–All the Desmognathinae and Plethodontinae; Amblystomatinae, Amblystoma opacum; Salamandrinae, Salamandrina perspicillata. In Triton and other Salamandrinae the length of the lungs varies; in some they extend more, in others less, than half way down the distance between head and pelvis. Hopkins remarks: "Two questions are naturally suggested by this apparently aberrant condition of the respiratory organs. First, what structures or organs have taken on the function of the lungs and branchiae; and secondly, is there any modification in the form or structure of the heart which in any way may be correlated with the above-mentioned peculiarities of the lungless forms?" Wilder concluded that respiration was probably carried on by the skin, and perhaps, to some extent, by the mucosa of the intestine. Camerano thinks that, at least in the European forms, respiration is effected by the bucco-pharyngeal cavity, and that the skin affords no efficient aid. The left auricle in the lungless forms is much smaller in comparison than the right, and there is no pulmonary vein. The auricular septum has a large aperture, the communication between the auricles being larger than even in Necturus (which breathes essentially by gills). The sinus venosus, instead of opening into the right auricle only, opens more freely into the left than into the right, and the latter communicates more directly with the ventricle than the left, instead of about equally. In short, the heart of these creatures appears almost bilocular, instead of being trilocular, at least functionally.

The lungs of the Urodela are always simple, extremely thin-walled bags. They are highly developed in the Anura, the walls being modified into numerous air-cells, whereby the respiratory surface is considerably increased. The lungs are filled with air by the pumping motion of the throat while the mouth is closed, the nostrils being provided with muscular valves. A muscular apparatus assists the filling of the lungs in the Anura.[^[23]]

Fig. 6.–Internal view of the mouth of A, Rana esculenta, B, Bufo calamita (cf. Fig. 52, p. [269]). Ch, Choana, or inner nasal opening; E, opening of the Eustachian tube; S, slit leading into the vocal sac; T, tongue; Vo, patches of teeth on the vomers.

Most, if not all, Anura and some Urodela have a voice produced by the larynx, which, especially in the Anura, is provided with a complicated cartilaginous and muscular apparatus and with vocal cords. The voice of the Urodela is at the best a feeble squeak. The females of the Anura are either mute or they produce a mere grunt, but that of many males is very loud, and, moreover, in many species it is intensified by vocal sacs which act as resonators. These sacs are diverticula of the lining of the mouth-cavity, and bulge out the outer skin and the muscles, chiefly the mylo-hyoid, of the throat. The nostrils and the mouth are firmly closed during the croaking. "The sacs are called internal when they are covered by the unmodified gular integument, however much this may be distended; external when their membrane projects through slits at the sides of the throat, as in Rana esculenta (Fig. 52, p. [269]), or when the skin is thinned and converted into a bladder-like pouch, as in Hyla arborea."[^[24]] These sacs exhibit many modifications. They may be unpaired and median, and open by two slits into the mouth, on either side below the tongue; in Bufo one of the slits or openings, either the right or the left, is obliterated. They may be paired and symmetrical, and open one on each side of the head, below and near the posterior angle of the jaws. These modifications differ in closely allied species. They reach their greatest complication in Rhinoderma and in some of the Cystignathidae by extending far back beneath the skin into the wide lymphatic spaces. In Rhinoderma they are put to the unique use of nurseries for the young (see p. [228]). Leptodactylus typhonius has a very distinct pair of outer vocal sacs and a well-marked unpaired sac which extends into the belly and communicates with each outer sac. Several species of Paludicola, e.g. P. fuscomaculata and P. signifera, have a similar arrangement, in addition to an unpaired gular sac which can be inflated independently of the rest (see Fig. 45, p. [220]).

Urino-Genital Organs

The kidneys and the male generative glands are still intimately connected with each other. The general plan is as follows:–

The kidneys consist of a large number of glomeruli, produced by the coiled segmental tubes, each of which is composed of a nephrostome or funnel opening into the body-cavity, a Malpighian body and an efferent canal. The latter combine to form the segmental duct which opens into the cloaca. The testes, composed of a large number of sperm-producing glands, are drained by transverse canals which combine into a longitudinal canal, and this again sends off numerous efferent canals which open into the efferent canals of the kidney, so that the segmental duct (Leydig's duct of many authors) conveys both sperma and urine.

Fig. 7.–Diagrammatic representation of modifications of the urino-genital ducts. 1, 2, Male and female Newt; 3, a tubule of the kidney; 4, male Rana; 5, male Bufo; 6, male Bombinator; 7, male Discoglossus; 8, male Alytes. a, Artery entering, and producing a coil in, the Malpighian body, M; B, Bidder's organ; ef.s.c, efferent segmental canal; F.B, fat-body; gl, glomerulus; K, kidney; l.c.c, longitudinal collecting canal; M, Malpighian body; Md, Müllerian duct; N, nephrostome; O, ovary; Ov, oviduct; s.d, segmental duct; T, testis; Ur, ureter; V.d, vas deferens; V.s, vesicula seminalis.

In the female the network of transverse and longitudinal canals, which originally connect the generative glands with the kidney's efferent canals, is deduced in so far as the connection is interrupted and the vestiges of the transverse canals are no longer functional. The eggs fall into the body-cavity and are caught up by the ostium or inner abdominal opening of a special duct, the oviduct (Müllerian duct of many authors). Vestiges, more or less complete, of these oviducts persist in the males of most Amphibia.

This general scheme presents some modifications in the various groups of Amphibia.

The Apoda retain the most primitive conditions. The kidneys are still long and narrow, and the glomeruli are, at least in the anterior part of the organ, still strictly segmental, agreeing in number and position, each with a vertebral segment; later, the number of the glomeruli is greatly increased, and the former agreement becomes quite disturbed. The generative glands still retain their segmental arrangement, but they are restricted to a much shorter region than the kidneys. In the male Apoda a considerable portion of the cloaca can be everted by special muscles, and acts as an intromittent organ. Both sexes possess a ventral urinary bladder.

In the Urodela both kidneys and testes are much concentrated, the testes especially have lost all outward appearance of segmentation, and their efferent canals, connecting them with the longitudinal collecting canal, are much reduced in numbers. The greater portion of the kidneys, at least their anterior half, has all the appearance of a degenerating organ and is on the way to losing its urinary function, although it still possesses Malpighian bodies and complete ducts; the main function of the latter is now the conveyance of the sperma. In the Perennibranchiata, and in some others, e.g. Spelerpes variegatus, the longitudinal collecting canal, between testis and kidney, is sometimes suppressed, a very simple, but pseudo-primitive arrangement. A urinary bladder is present. The cloaca is not eversible.

In most Anura, e.g. Rana and Bufo (Fig. 7; 4, 5), the same scheme is adhered to. The efferent canals of the testis form a network, with a longitudinal canal, and open into the efferent canals of the kidney, in the substance of which they are more or less deeply imbedded. The ducts which lead out of the kidney to compose Leydig's duct, are frequently dilated, or the latter duct is much elongated, convoluted or varicated, and this whole portion is enclosed in a sheath of connective tissue, giving an appearance as if the single duct itself were dilated in the greater part of its length; hence the occasional name of vesicula seminalis. Such means of storing the sperma enable the latter to be ejected suddenly in great quantities.

In Bombinator (6) some of the most anterior seminal canals do not perforate the kidney, but run over it superficially and open directly into a branch of Leydig's duct. This branch, no doubt equivalent to a number of segmental canals which have lost their uriniferous function, is curved round the upper end of the permanent kidney, while its forward continuation, ending blindly, is the remnant of its former headward extension. This arrangement of Bombinator is carried further in Discoglossus (7). The testis conveys its sperma through a wide duct directly into Leydig's canal, without interfering with the kidney, and all the testicular efferent network is lost. The anterior end of Leydig's duct still extends headwards; its middle portion acts solely as a vas deferens, while the lower portion still behaves like a typical segmental duct, conveying both sperma and urine. Lastly, in Alytes (8) the functional division of the old segmental duct has been carried to an extreme. The kidney is drained by one canal only, now a true ureter, and this is of course produced by a consolidation of the multiple exclusively uriniferous canals of the lower half of the kidney. The whole of the segmental duct is now in the service of the testis, and near its junction with the ureter it forms a large diverticulum or true vesicula seminalis.

Remnants of oviducts, or Müllerian ducts, are common in the male Anura; they are best developed in Bufo, much reduced, and individually absent, in Rana. In Bombinator each duct is restricted to its upper or abdominal portion, and is attached to the vestigial headward extension of Leydig's duct. Lastly in Discoglossus and in Alytes all traces of oviducts seem to have vanished, at least in the adult males.

It is interesting to note that in the arrangement of the urino-genital ducts the Discoglossidae are the most advanced of all Amphibia, instead of showing the most primitive conditions. This is rather unexpected, but is paralleled by the epichordal type of the vertebral column.

The oviducts of the Apoda and Urodela remain more or less straight; in the viviparous species they form uterus-like dilatations. In the Anura they become greatly elongated during the breeding season and form many convolutions. As a rule each oviduct opens separately into the cloaca, but in Hyla they have one unpaired opening, while in Bufo and Alytes the lower parts of both oviducts are themselves confluent.

All Amphibia possess Fat-bodies. They consist of richly vascularised lymphatic tissue, the meshes of which are filled with lymph-cells, globules of fat and oil. In the Apoda these bodies lie laterally to the generative glands, and along the posterior half of the kidneys. In the Urodela they accompany the anterior half of the kidney. In the Anura they are lobate, and are placed upon the anterior end of the testes or ovaries. Their exact function is still doubtful, but it is intimately connected with that of the generative glands. The old notion, that they are simply stores of fat for the nourishment of the animal during hibernation, is quite untenable. The fat-bodies do not decrease during this period, on the contrary they attain their fullest size in the spring at the time of the rapidly awaking activity of the reproductive organs, and they enable considerable quantities of sperma and of eggs to be produced and ripened without detriment to, or utter exhaustion of, the animals, which often spawn before they have had time or opportunity to feed. After the spawning season the fat-bodies have dwindled down to inconspicuous dimensions.

Lastly, there is in some Anura, hitherto observed in Bufo only, a mysterious organ, intercalated between the fat-body and the testis or ovary. This is "Bidder's organ" and it seems to be a rudimentary ovary, or rather that upper, anterior portion of the whole organ which undergoes retrogressive metamorphosis. It disappears in old female toads, but in the males it sometimes assumes a size equal to, or surpassing that of the testes. The males are in this respect hermaphrodite, and cases are known in which parts of the generative glands have developed testes and egg-bearing ovaries.

The spermatozoa of the Apoda and Urodela have an undulating membrane along the tail, while the head-end is either pointed or truncated. Those of Spelerpes fuscus and of Ichthyophis glutinosa measure about 0.7 mm. in total length, those of the other Urodela being much smaller. A peculiarity of the Urodela is that their spermatozoa are massed together in or upon spermatophores, an arrangement which undoubtedly facilitates the internal fecundation of the female without actual copulation. The female takes up such a deposited spermatophore with the cloacal lips, squeezes the sperma out of the capsule which remains behind, and either conveys the former into a special receptaculum seminis, e.g. in Salamandra atra and in Triton, or the spermatozoa wriggle their way, thanks to the undulating tail, directly up the oviducts to the ova.

The spermatophores are composed of a colourless, soft, gelatinous mass, which is probably produced by the cloacal gland. The shell of jelly is in fact a cast of the cloacal cavity, reproducing all its ridges, furrows and folds, while a toad-stool-shaped papilla of the cloaca makes the inside lumen of the cast, e.g. in Triton. Those of Salamandra maculosa are much simpler, consisting, in conformity with the absence of a cloacal papilla, merely of a cone with a globular mass of sperma on the top. Those of Amblystoma are similar.

The spermatozoa of the Anura show considerable differences in the various genera, of which, however, only the European forms have been properly examined. The "head" is wound like a corkscrew in Discoglossus, Pelobates, and Pelodytes; spindle-shaped, more or less curved, in Rana temporaria and R. agilis, Hyla, Bufo and Bombinator, in the latter with an irregular membrane on one side; cylindrical in Rana esculenta and R. arvalis. The tail is mostly long and filiform, but in Bufo vulgaris and Discoglossus it is provided with an undulating membrane. Their size is generally very small, only about 0.1 mm., excepting those of Discoglossus which reach the astonishing length of 3 mm. These differences in shape, especially that of the head, explain why species of the same genus, e.g. Rana temporaria and R. arvalis, cannot fertilise each other.

Fig. 8.–A bell-shaped spermatophore of Triton alpestris. × 3. (After Zeller.)[^[25]]

The eggs differ much in size, colour, and numbers. They are holoblastic, with unequal cleavage, but those species which possess an unusual amount of food-yolk, for instance Rhacophorus schlegeli and the Apoda, approach the meroblastic type of segmentation. As a rule, the greater the amount of yolk, the smaller is the number of eggs produced. But the number which is laid during one season is not only difficult to calculate, but it varies individually, old females laying more than young specimens. Moreover, some kinds, e.g. the Discoglossidae, spawn several times in one year. Alytes, Rhinoderma, Hylodes, Rhacophorus, Pipa, in fact those kinds which are remarkable for special nursing habits, lay only a few dozen eggs at a time. Hyla arborea produces up to 1000, Rana temporaria about 3000, Bufo vulgaris averages 5000, Bufo viridis and Rana esculenta up to 10,000 and more. T. H. Morgan[^[26]] has observed a Bufo lentiginosus which laid 28,000 eggs within ten hours! The number of eggs produced by the Apoda and Urodela is comparatively moderate, in the average a few dozen, Amblystoma alone laying about 1000.

The eggs possess a gelatinous mantle of variable thickness and consistency. In Amphiuma they are strung together like the beads of a rosary, and the envelope hardens into a kind of shell. Many Newts and some Anura fasten their eggs singly on to plants and other objects in the water, with or without threads of stiffening mucus. In many Anura, e.g. Bufonidae, they pass out as closely-set strings of beads, one string out of each oviduct; in others, e.g. Ranidae, they are disconnected, and form large, lumpy masses, especially when the gelatinous mantle swells up in the water. The use of this mantle seems to be chiefly the protection of the growing embryo, which in many species, when hatched out of the egg proper, drops into and remains for some time in the softened jelly. Possibly the latter affords some nutriment to the early larva.

Concerning the mode of fecundation it is to be remarked that copulation proper takes place only in the Apoda. For the Urodela Boulenger[^[27]] has given the following summary. In no case does actual copulation take place. The male deposits the spermatophores which it is the office of the female to secure:–

II. No amplexus, but a lengthy courtship in the water; the male is more brilliantly coloured than the female, and ornamented with dorsal and caudal crests, or other appendages: Triton, cf. also systematic part.

II. Amplexus takes place; there are no marked sexual differences in colour and no ornamental dermal appendages.

A. Amplexus of short duration, partly on land, but deposition of the sperma in the water. No accessory sexual characters: Terrestrial Salamanders, namely Salamandra, Chioglossa, Salamandrina. Spelerpes breeds in damp caves without water.

B. Amplexus of lengthy duration and in the water.

a. The male, distinguished by a greater development of the fore-limbs, which are armed with temporary excrescences, clasps the female in the axillary region with the fore-limbs: Triton waltli.

b. The male, distinguished by a greater development of the hind-limbs and a prehensile tail, clasps the female in the lumbar and caudal regions: The Euproctus-group of newts: Triton asper, T. rusconii, and T. montanus.

The act of fecundation of most of the other kinds of Urodela, notably Cryptobranchus, Amphiuma, Proteus, has not yet been observed.

Embracing of the two sexes is the universal rule with the Anura, the male creeping on to the back of the female and clasping her firmly with the arms and hands either in the inguinal region, higher up, or under the armpits. See the numerous statements in the systematic part. This often extremely forcible, pressing embrace seems to be necessary, although the females can deposit the eggs without the help of the male, but in such cases the expulsion takes place at irregular intervals instead of at one time. When the eggs appear at last, and this happens in many species many hours, or even some days, after the beginning of the embrace, the male voids the contents of its seminal vesicles over them. Fertilisation is consequently external, with the possible exception of Pipa, q.v. p. [152].

Deposition of the eggs and nursing habits.–The majority of the Amphibia are oviparous, but some Apoda and Urodela are viviparous. It is unnecessary to call the latter condition ovo-viviparous, since this is really a distinction without a difference.

Viviparous forms:–amongst Urodela; Salamandra maculosa, the young burst the egg-membrane in the act of being born, and are provided with long gills; S. atra, the young undergo their whole development and metamorphosis within the uterus (see p. [119]); Spelerpes fuscus, the young are likewise born in the perfect condition: amongst Apoda; Typhlonectes compressicauda and Dermophis thomensis.

The oviparous Apoda, at least Ichthyophis and Hypogeophis, and a few of the Urodela, as Desmognathus and Amphiuma, take care of their eggs by coiling themselves around them in a hole underground.

Nursing habits are very common amongst the Anura. Boulenger[^[28]] has summarised the various conditions concerning the deposition and care that is taken of the eggs, in the following list, in which more recent discoveries have been interpolated.

I. The ovum is small, and the larva leaves it in a comparatively early embryonic condition.

A. The eggs are laid in the water:–

a. Without further care or preparations: probably the majority of Anura; all European forms, except Alytes.

b. The eggs are laid in a specially walled-in part of the pond: Hyla faber.

B. The eggs are deposited out of the water:–

a. In holes, or under grass, near the banks of pools. The larvae are liberated and washed into the water by the next heavy rain: Leptodactylus ocellatus, L. mystacinus, Paludicola gracilis, Pseudophryne australis and P. bibroni.

b. On leaves above the water, the larvae dropping down when leaving the egg: Chiromantis rufescens, Phyllomedusa iheringi, Ph. hypochondrialis.

II. The yolk is very large and the young undergoes the whole or part of the metamorphosis within the egg; at any rate the larva does not assume an independent existence until after the loss of the gills.

A. The eggs are deposited in damp situations, or on leaves. The young escape as:–

a. Tadpoles: Arthroleptis seychellensis, Rhacophorus schlegeli, Rh. maculatus.

b. Perfect, air-breathing frogs: Rana opisthodon, Hylodes martinicensis, Hyla nebulosa.

B. The eggs are carried by a parent.

a. By the male:–

α. Round the legs; the young leaves the egg in the tadpole stage: Alytes.

β. In the enlarged vocal sacs; the young leave in the perfect state: Rhinoderma.

b. By the female:–

α. Attached to the belly: Rhacophorus reticulatus.

β. Attached to the back; the young complete their metamorphosis within the egg: Pipa.

γ. In a dorsal pouch which the young leave as tadpoles: Nototrema marsupiatum;–or in the perfect state: Nototrema testudineum, N. cornutum, N. oviferum, N. fissipes, and Hyla goeldii.

The development and metamorphosis of many species have been described in the systematic part. The following is a short general account of some of the more important features. Metamorphosis in the Apoda and Urodela is restricted chiefly to the reduction of the gills, the closing of the clefts, and the loss of the gill-chamber and the finny margins of the tail; but the change from the tadpole to the final Anurous animal implies an almost entire reorganisation.

Fig. 9.–Four stages of the development of the adhesive apparatus (A) of Bufo vulgaris; M, Mouth; Sp.T. spiracular tube. In 3 the gills are almost completely hidden by the united right and left opercular folds. The small outlined figures indicate the shape and natural size of the tadpoles. (After Thiele.)

In the earliest condition the embryo consists of a large head and body, while the tail is still absent. Behind the beginnings of the future mouth appears a transverse crescentic fold, with the convexity looking backwards, which develops into the paired or unpaired adhesive apparatus. This consists of large complex glands, developed in the Malpighian layer, originally covered by the cuticula, which soon disappears, whereupon the sticky secretion enables the larva to attach itself to the gelatinous mantle of the egg, later on to weeds or other objects in the water. The name of suckers, often applied to this apparatus, conveys a wrong idea, there being neither muscles nor any suctorial function. The shape of this organ undergoes many changes during the early life of the individual, and differs much in the various genera, affording thereby diagnostic characters.[^[29]] At first a crescent, it divides into a right and a left oval or disc, which either remain asunder and behind the mouth (Rana, Bufo), or they move forwards to the corners of the mouth (Hyla) or further back, and unite again more or less completely, as in Discoglossus and Bombinator. It is mostly of short duration, and disappears by the time that the larva, by the proper development of the gills and the tail and the functional mouth, changes into the tadpole. But in a few species these discs transform themselves into an elaborate ventral disc. Such an organ persists throughout the greater part of the tadpole-stage in certain Oriental species of Rana, all of which, when adult, possess fully webbed toes and strongly dilated discs on the fingers and toes, e.g. Rana whiteheadi, R. natatrix, and R. cavitympanum of Borneo, R. jerboa of Java (this larva was originally described and figured as that of Rhacophorus reinwardti), and R. afghana of the Himalayan system. These tadpoles, at least those of R. jerboa, are further remarkable for having the "spiracular" opening very far back on the left side, nearer to the base of the tail than to the snout, so as to be well out of the way when the creature has attached itself by the adhesive disc.

Fig. 10.–1, Front view of the mouth of a tadpole of Rana temporaria, showing the transverse rows of tiny horny teeth; 2, three successive horny teeth, much magnified. (After Gutzeit.)

The mouth of the tadpoles of Anura is furnished with horny armaments, substitutes for teeth. Their development and that of the mouth in general has been well described by Gutzeit.[^[30]] In the young larvae of Rana temporaria, one or two days after hatching, a shallow groove appears above the conspicuous pair of adhesive organs. The groove becomes rhombic in outline, and when the mouth has been formed in its centre, the jaws appear in the median corners of the rhombus. The epidermis then rises like a circular wall around the jaws, and divides into an upper and lower lip; furrows appear on them, and between these various papillae and comb-like transverse plates of teeth. The papillae are possibly tactile organs, but although nerves enter them, nerve-endings of a sensory nature have not yet been discovered. On the fourth day the jaws become black, by the tenth day horny teeth have appeared upon all the plates of the mouth-armature, and on the seventeenth day the mouth-apparatus has reached the configuration typical of the tadpole, which is now about 14 mm. long. The number of horny teeth in R. temporaria amounts to about 640. These teeth are not cuticular products, but cornified cells; they are very small, and consist each of one horny cell, which is shaped like a nightcap, the apex of which is curved back and serrated. The little teeth are shed continuously, the renewal taking place by successive cells growing into the bases of the older series. The shape and size differ much in the various genera and species. The comb-like plates, composed of those teeth which surround the lips, seem to be used chiefly for the fixing or hooking of the food, while those which compose the horny beak proper, the armature of the jaws, are used like the radulae of snails. These beaks are likewise composed of a great number of individual teeth, closely packed together in several rows, but the teeth themselves are simple and not serrated.

In Hyla arborea there are in all about 560 teeth. The development of the mouth does not begin before the eleventh day; the horny teeth break through, and the jaws get black edges, on the eighteenth. In Pelobates fuscus the number of horny teeth is increased to about 1100. In Borborocoetes taeniatus the horny teeth form series of five bells, which fit into each other like the joints of a rattlesnake's tail.

One of the most extraordinary kinds of tadpoles is that of Megalophrys montana.[^[31]] Mr. Annandale (Skeat Expedition) found it at Bukit Besar, Malay Peninsula, from 2000 to 3000 feet above the level of the sea. The tadpoles (Fig. 11) were found in the beginning of the month of May 1899 in sandy streams and in pools of rain-water; they floated in a vertical position, the peculiar membranous funnel-shaped expansion of the lips acting as surface-floats. The inside of the funnel is beset with radiating series of little horny teeth, and the whole apparatus is possibly used for scraping the under-surface of the leaves of water-plants in search of food. Total length of the tadpoles 1 inch.[^[32]]

The gills, the formation of the operculum, and the modifications of the branchial arterial arches have been described fully on p. [43]; those of the hyo-branchial skeleton on p. [31]. Fusion of the opercular fold with the skin of the neck, across the branchial region, causes the head to become confluent with the trunk (cf. Fig. 9, 3, p. [57]). The body becomes oval, more or less globular, and the alimentary canal is greatly elongated and stowed away in the shape of a neat, very regular spiral, shining through the ventral wall of the body; the anus opens at the end of a somewhat protruding tube, either in the median line, just in front of the ventral fin (Discoglossidae, Pelobates, Bufo), or it assumes an asymmetrical position by turning to the right side (Hyla, Rana).

Fig. 11.–Tadpoles of Megalophrys montana from Bukit Besar, Malay Peninsula. × 3.

Although both pairs of limbs begin to bud simultaneously, or the fore-limbs even earlier, the hind-limbs are hurried on, and appear first, long before the fore-limbs. The latter lie ready beneath the skin of the gill-chamber, and the right always breaks through the skin, while the left does the same in the Mediogyrinidae, while in the Laevogyrinidae it is generally pushed through the left-sided spiracular opening, immediately behind the outer gills. According to Barfurth the right limb appears, in about 80 per cent. of Rana esculenta, from two to eight hours before the left.

Meanwhile the lungs are being developed, and the tadpole occasionally rises to the surface to breathe air. The gills, which, as has been explained elsewhere, are less ancestral than they are larval organs, degenerate, and all the organs are modified for the coming terrestrial life. The fins of the tail are absorbed, the horny armature of the mouth and lips is shed in pieces and makes room for the true teeth, the eyes receive lids, and the whole cranium, especially the apparatus of the jaws, undergoes the final modifications–widening and lengthening of the mouth, arresting of the mento-Meckelian cartilages, elongation of the Meckelian cartilages or lower jaw proper, shifting backwards of the suspensorium, and lengthening of its orbital process to form the pterygo-palatine bridge.

The tadpole ceases to feed, the whole intestinal canal is voided of its contents, and by "histolysis" is thoroughly rebuilt, becoming wider and shrinking to about one-sixth of its original length,–undoing thereby the spiral–preparatory for the coarser food, which consists of insects, worms, and other strictly animal, living matter. Hitherto the tadpoles have lived on "mud," confervae, Diatoms, rotting vegetable and animal matter. The anal tube collapses, becomes ultimately absorbed, and a new vent is formed at and below the root of the tail.

Barfurth[^[33]] has made interesting observations and experiments with regard to the absorption of the tail and other organs which disappear during the metamorphosis. This is retarded by low temperature; it is accelerated by rest and freedom from mechanical disturbances, as, for instance, concussion of the water. Hunger shortens or hurries on the last stages of metamorphosis, the absorption of the tail taking place in four instead of five days. Amputation of the tail has no retarding influence; it is followed at once by regeneration, although the tadpole may be on the verge of reducing the tail. Whilst hungering the whole organism draws upon its available store of material, naturally first upon those parts which sooner or later are to become superfluous. This applies eminently to the tail, which represents a considerable amount of "edible" matter, and also to that portion of the skin which still covers the fore-limbs. The elements of the cutis are resorbed, thereby thinning the skin; and consequently the limbs break through earlier in fasting than in well-fed specimens. Nature herself seems to apply hunger as an accelerator. Mlle. von Chauvin found that the larvae of Urodela normally fast during the transformation, and according to Barfurth the larvae of Rana temporaria eat less after their hind-limbs are fully developed. This is, however, also preparatory for the reorganisation of the gut, which has to be more or less empty during the shortening process.

The loss of the tail is not due to a sudden dropping off of this organ–a crude but by no means uncommon belief–but is brought about by a very gradual process of resorbtion. When the fore-limbs begin to break through the skin, the tip of the tail shrinks and becomes black, owing to an increase, or rather concentration, of the pigment cells. The reduction proceeds from the tip forwards until on about the fifth day there remains only a short, conical, black stump. From the beginning of this process of reduction the tail is scarcely used for locomotion, the tadpole rowing with its legs, or it crawls and hops about, although the tail may still be 20 mm. long. The cells of the epidermis atrophy, shrink, and peel off, while those of the cutis, blood-vessels, nerves, muscles, and chorda dorsalis become disintegrated, often undergoing fatty degeneration. The leucocytes eat up the débris and other dissolved tissue, and carry it away through the lymphatic vessels, to be used as new building material in the rest of the animal.

Barfurth asks very properly, Why do these tissues degenerate and die? Because the vasomotor nerve-fibres cease to regulate the circulation. And why does this trophic influence of the central nervous system stop? Because the function of the tail becomes superfluous through the appearance of the fore-limbs. The tail is doomed, and degenerates like any other organ without a function. The whole process is, of course, a recapitulation of ancestral, phylogenetic evolution.

CHAPTER III

NEOTENY–REGENERATION–TEMPERATURE–GEOGRAPHICAL DISTRIBUTION

Neoteny.–It has long been known that the larvae of the Spotted Salamander occasionally attain the size of 80 mm. or about 3 inches, whilst the majority undergo metamorphosis when they are only 40 mm. long. Again, larvae of Triton have been found, in the months of April and May, 80 to 90 mm. long, still with functional gills, but with the sexual organs fully developed. De Filippi[^[34]] found in one locality in Lombardy, besides a few normal fully metamorphosed specimens of only 30 mm. in length, more than forty specimens, which, although they had attained full size, about 55 mm., and were sexually mature, still retained their gills. According to him such gill-breathing, otherwise mature specimens, occur constantly in a small lake in the Val Formazzo, on the Italian slope of the Alps, in the province of Ossola. Later Duméril[^[35]] astonished the world by his account of the metamorphosis of the Mexican gill-breathing Axolotl into an entirely lung-breathing and terrestrial creature, hitherto called Amblystoma, and supposed to be not only a different species, but to belong to a different family from the Axolotl, which was known as Siredon axolotl s. pisciforme, and naturally classed with the Perennibranchiata.

This discovery led to a series of observations and experiments, chiefly conducted by Marie von Chauvin, instigated thereto by Koelliker and by Camerano.[^[36]] It was then found that many, if not most of the European Amphibia, both Urodela and Anura, occasionally postpone their metamorphosis, and also that such Urodela sometimes become adult for all practical purposes, but retain their gills.

This retardation, the retention of larval characters beyond the normal period, was called Neotenie by Kollmann[^[37]] (νέος, young; τείνω, extend, stretch). He distinguished further between:–I. Partial Neoteny, namely, simple retardation of the metamorphosis beyond the normal period, for instance, the wintering of tadpoles of Pelobates fuscus, Bombinator pachypus, Pelodytes punctatus, Alytes obstetricans, Hyla arborea, Rana esculenta, R. temporaria, Bufo vulgaris, and B. viridis: II. Total Neoteny, where the animal retains its gills, but becomes sexually mature; hitherto observed in Urodela only, e.g. Triton vulgaris, T. alpestris, T. cristatus, T. boscai, T. waltli and Amblystoma. Intermediate stages between these two categories are not uncommon.

A satisfactory explanation of the meaning of neoteny is beset with difficulties. Some authorities look upon the phenomenon simply as the result of adaptation to the surroundings, which make it advantageous for the creature to retain its larval features. Others think that the surroundings somehow or other retard or prevent the assumption of the adult characters. Undoubtedly there are many cases in which larvae have been reared in water-holes with steep walls, so that they could not change from aquatic to terrestrial life, and it stands to reason that abnormally forced and prolonged use of the gills and of the tail may stimulate these organs into further growth at the expense of the limbs and other organs which are intended for terrestrial life. But not unfrequently typical neotenic and overgrown specimens occur side by side with others which have completed their metamorphosis, and the same is true of larvae of newts which were reared, for experimental purposes, under exactly the same conditions–for instance, in a high-walled glass vessel.

Weismann tried to explain neoteny as cases of reversion to atavistic ancestral conditions, but this idea is based upon an assumption which is probably wrong. His idea necessitates the supposition that all the Amphibia were originally gill-breathing, aquatic, and limbless animals, and that every feature seen in a larva must necessarily indicate an ancestral phylogenetic stage. It is, on the contrary, much more probable that the external gills of the Urodela have been developed in adaptation to their embryonic and larval, essentially aquatic, life. Consequently the possession of such gills would be a secondary, and not, strictly speaking, an atavistic feature. Normal loss of these gills, exclusively pulmonary respiration, and preponderating terrestrial life characterise the final adult Amphibian. These cases of neoteny are therefore instances of more or less complete retardation, or of the retention, of partially larval conditions.

The whole problem is, however, by no means simple. Salamandra atra has become viviparous, and the whole metamorphosis takes place within the uterus; in fact, the young have an embryonic, but no larval period, if by the latter we understand the free swimming and still imperfect stage. Similarly, various Anura–for instance, Hylodes martinicensis–pass rapidly through their metamorphosis, and have suppressed the stage of free swimming tadpoles. On the other hand, in many newts, the duration of the larval period is much prolonged, and moreover is very subject to individual variation. In the Axolotl this larval period is continued until and after sexual maturity is reached. The extreme condition would then be represented by the Perennibranchiate genera. It may seem reasonable to look upon these as the youngest members of the Urodela, and the loss of the maxillae in the Sirenidae and Proteidae supports this idea. But it so happens that the majority of the most neotenic genera are more primitive in the composition of the skull and the vertebral column than the typically terrestrial and rapidly metamorphosing genera. Witness the amphicoelous vertebrae, the completeness of the pterygoids, the separate nature of the palatine bones, and the separate splenials, as mentioned in detail in the description of their skull.

We have therefore to conclude, first, that the various Perennibranchiate genera do not form a natural group, but are a heterogeneous assembly; secondly, that they have become Perennibranchiate at a phylogenetically old stage–in fact, that they are the oldest, and not the newest, members of the present Urodela. At the same time, it would be erroneous to suppose that the first Urodela were aquatic creatures, provided with a finny tail, with small, ill-developed lungs, and with epidermal sense organs. All these features are, on the contrary, directly correlated with aquatic life, and are larval acquisitions, not ancestral reminiscences. It would be equally wrong to allude to the absence of lungs in many newts as a piscine and therefore ancestral feature. The development of the typical pentadactyloid limb, the connexion of the pelvic girdle with the vertebral column, the development of the lungs, and absolute suppression of internal gills point without doubt to terrestrial creatures. What then, may we ask, were the first Amphibia like? and how about the external gills? They were undoubtedly akin to the less specialised Lepospondylous Stegocephali, in particular the gill-less Microsauri, and the various stages may perhaps be reconstructed as follows:–

(1) Terrestrial, with two pairs of pentadactyloid limbs; breathing by lungs only; with a fully developed apparatus of five pairs of gill-arches, which during the embryonic life perhaps still carried internal gills; with or without several pairs of gill-clefts. Reduction of the dermal armour and of the cutaneous scutes had taken place.

(2) Additional respiratory organs were developed by the embryo, in the shape of external gills; these were at first restricted to embryonic life (as in the existing Apoda), but were gradually used also during the aquatic life of the larva. These external gills, together with the lungs, have superseded the internal gills, of which there are now no traces either in Urodela or in Anura.

(3a) Some Urodeles, retaking to aquatic life, retained and further enlarged the external gills into more or less permanent organs (cf. also Siren, p. [136]).

(3b) The majority of Urodela hurried through the larval, aquatic stage, and some–e.g. Salamandra atra–became absolutely terrestrial. The possession of unusually long external gills by this species and by the Apoda indicate that these organs are essentially embryonic, not larval, features.

Regeneration.–Most Amphibia possess the faculty of regenerating mutilated or lost limbs. This takes place the more certainly and quickly the younger the animal. The amputation necessary to study these phenomena need not be experimental. Axolotls and other Urodelous larvae frequently maim each other fearfully, by biting off the gills or one or more limbs. The gills do not even require amputation. If the larvae are kept in stagnant water the gills often shrivel up or slough off and grow again. The same applies to the larvae of viviparous species, e.g. Salamandra atra, which, when cut out of the uterus and put into water, soon cast off their long, tender gills and produce a stronger set. In an Axolotl,[^[38]] two years old, a hand was cut off. After four weeks there was a conical stump; after the sixth week this stump had two points; in the eleventh week three or four fingers were discernible, and a week later the complete hand. Frequently these creatures reproduce five instead of the normal four fingers. But the more proximal the cut, the more liable is the new limb to reproduce supernumerary fingers, or even extra hands and feet. Complete regeneration of the limb, cut off in the middle of the humerus, took place within five months.

Triton taeniatus, adult, reproduces cut fingers within five or six weeks, and if the hand be cut above the carpus, new finger-stumps appear in about one month. Götte has observed that an adult Proteus did not completely reproduce its whole leg until after eighteen months; and, according to Spallanzani, more than one year elapses before the limb, bones, and cartilages of Triton regain their normal strength.

The Anura are likewise capable of regenerating their limbs, the more readily the younger the specimens. For instance, in a tadpole of Rana temporaria, in which the fore-limbs were still hidden, the hind-limb, cut at the middle of the thigh, reproduced nineteen days later a knee, followed by a short two-toed stump. Ultimately the whole limb became completed. The tail of tadpoles regenerates very quickly and completely, even if it be cut off shortly before the final metamorphosis, when the tail would in any case be reduced. Metamorphosed Anura have almost entirely lost this faculty, but not absolutely. I myself have kept two specimens of Rana temporaria, which, when already adult, had each lost a hand at the wrist. First there was only the clean-cut stump with a scar, but within a year this changed into a four-cornered stump, and two of the protuberances developed a little further, reaching a length of about 4 mm. These specimens lived for four years without further changes.

Temperature.–Amphibia, like Fishes and Reptiles, are, as a rule, classed as cold-blooded animals, in opposition to the warm-blooded Birds and Mammals. This distinction is one of degree only. The terms poikilothermous and homothermous (ποίκιλος, variable; ὅμος, equable) are based upon a sounder principle, but are likewise liable to exceptions. Those creatures which, like Birds and Mammals, possess a specific temperature of their own under normal conditions, that of hibernation being excepted, are homothermous. Cold-blooded creatures have no specific temperature; they more or less assume that of their surroundings. Frogs and newts, for instance, when living in the water, naturally assume its temperature, which is, of course, many degrees lower in a cold spring than in a shallow pond warmed by the sun on a hot summer's day. The same applies to the changes from day to night. Dark-coloured tortoises basking in the sun are sometimes so hot that they are disagreeable to touch, since they possess but little mechanism for regulating their heat. The same individual cools down during a chilly night by perhaps 40° C. Anura are, however, very susceptible to heat; most of them die when their temperature rises to about 40° C. Under such conditions they die quickly when in the water, but in the air their moist skin counteracts the heat, lowering it by evaporation; otherwise it would be impossible for a tree-frog to sit in the glaring sun in a temperature of 120° F. Toads and others with drier skins seek the shade, hide under stones, or bury themselves in the coolest spots available, and many Amphibia and Reptiles aestivate in a torpid condition during the dry and hot season. Many of them can endure a surprising amount of cold, and during hibernation their temperature may sink to freezing-point. This power of endurance does not apply to all alike; tropical species can stand less than those which live in temperate and cold regions. In spite of many assertions to the contrary, it may safely be stated that none of our European frogs, toads, and newts survive being frozen hard. They may be cooled down to nearly -1° C., and they may be partially frozen into the ice. Circulation of the blood is suspended in such cooled-down frogs; their limbs may become so hard that they break like a piece of wood, but the citadel of life, the heart, must not sink much below freezing-point, and must itself not be frozen, if the animal is to have a chance of recovering. The protoplasm resists a long time, and so long as some of it is left unfrozen the rest will recover. Hibernating frogs are lost if they are reached by prolonged frost during exceptionally severe winters. Every frog will be killed in an artificial pond with a clean concrete bottom, but if there is sufficient mud, with decaying vegetable matter, the creatures survive, simply because they are not absolutely frozen. A severe winter not infrequently kills off all the younger creatures, while the older and more experienced hide themselves more carefully and live to propagate the race.

Geographical Distribution.

There is a very ably written chapter on the geographical distribution of the Amphibia by Boulenger in the Catalogue of Batrachia Gradientia, pp. 104-118. He came to the important conclusion that the geographical distribution of the Amphibia agrees in general with that of the freshwater fishes. Günther's division into a Northern, Equatorial, and Southern zone is modified only in so far as the last two are combined into one, "Tasmania and Patagonia not differing in any point regarding their Frog Fauna from Australia and South America respectively."

Boulenger recognises–

II. The Northern zone–(1) Palaearctic, (2) North American, region.

II. The Equatorial Southern zone.

A. Firmisternia division = Cyprinoid division of Günther.

1. Indian region.

2. African region.

B. Arcifera division = Acyprinoid division of Günther.

1. Tropical American region.

2. Australian region.

In the chapter on geographical distribution in Bronn's Thierreich, Vögel, Systematischer Theil, p. 296 (1893), and in my Classification of Vertebrata (1898), due attention had been paid to the Amphibia as well as to the other classes of Vertebrata. It will be seen in the following pages that my arrangement is well applicable to the Amphibia so far as fundamental principles are concerned.

It cannot be sufficiently emphasised that any attempt to form the various faunas of the different classes of animals into one scheme must necessarily be a petitio principii. The time-honoured six zoo-geographical regions established by Sclater and Wallace represent fairly well the main continental divisions: North America, South America, Africa, Australia, and the large northern continental mass of the Old World, with India as a tropical appendix. There is no correlation and no subordination in this scheme. Huxley's division (1868) into Notogaea and Arctogaea (see p. [74]) is of fundamental importance. The next improvement was the combination of the Palaearctic and Nearctic "regions" into one, an advance originally due to Professor Newton, carried out by Heilprin (1887) as the Holarctic region. I have, in 1893, substituted for it the more appropriate term Periarctic, meaning the whole mass of land which lies around the indifferent Arctic zone. The want of further co-ordination and subordination required the combination of the African and Oriental or Indian countries into a Palaeotropical region (1893); the Ethiopian or African and the Indian or Oriental regions of Sclater and Wallace thereby assuming their proper subordinate rank of subregions.

The two primary divisions Notogaea and Arctogaea are fundamental. The four secondary divisions, namely the Australian and Neotropical, Periarctic and Palaeotropical regions, also stand the test of application to the various classes and main groups of Vertebrata; but naturally, under the present configuration of the world, the Palaeotropical region is nothing but the Southern continuation of the Eastern half of the Periarctic mass of land. This is especially obvious so far as India is concerned. There is, however, that broad belt of desert, sand, and salt-steppes, which extends from North-West Africa to Manchuria, and this belt is one of the most important physical features of the Old World. It is complicated by the system of mountain-chains which, broadly speaking, centre at the Pamirs, and radiate westwards through the Caucasus and Alps into Spain, eastwards through the Himalayas into China, and north-eastwards to Kamtschatka; interrupted by Bering's Sea, it is continued as the backbone of both Americas to Patagonia.

The tertiary divisions, the subregions, have no real existence. They depend upon the class, or even order, of animals, which we happen to study. The faunistic distribution of the Urodela is not that of the Anura, and both follow separate lines of dispersal, different from those of the various orders of Reptiles, Birds, and Mammals. This must be so. There is no doubt that the distribution of land and water was totally different in the Coal Age from what it is now. The face of the globe at the Jurassic Age can scarcely be compared with the aspect which the world has assumed in the Miocene period.

This leads to another consideration, often neglected. We know that the various classes, orders, families, etc., of animals have appeared successively upon the stage. A group which arose in the Coal Age followed lines of dispersal different from one which was not evolved until Jurassic times, and post-cretaceous creatures could not avail themselves of what assisted their ancestors, and vice versâ. The Amphibia are bound absolutely to the land and to fresh water; transportation across salt water is not excluded, but must be accidental, and is not a case of regular "spreading." Speaking generally, the older a group, the more likely is it to be widely distributed. If it appears scattered, this may be due to extinction in intermediate countries or to submergence of former land-connexions.

There is great danger of arguing in a circle. It is one of the most difficult tasks to decide in cases of great resemblance of groups of animals between their being due to direct affinity or to heterogeneous convergence, or parallel development. It is the morphologist who is ultimately responsible for the establishment of faunistic regions, not the systematist, least of all he who accepts an elaborate classification, and then mechanically, mathematically, by lists of genera and species, maps out the world. Let us take an example. The Neotropical region and Madagascar, but not Africa, are supposed to be faunistically related to each other. In both namely occur Boa and Corallus amongst snakes, Dendrobatinae amongst Ranidae, and of the Insectivora Solenodon in Cuba, Centetes in Madagascar. More cases can no doubt be found which would strengthen this resemblance, perhaps in support of the startling view that Madagascar and South America have received part of their fauna from the famous Antarctica. But the value of the Insectivores has been disposed of by their recognition as an extremely ancient group, or as a case of convergence, and the two genera are no longer put into the same family as Centetidae. The Dendrobatinae (Mantella in Madagascar, the others in South America) are decidedly not a natural group, but an instance of very recent convergence (cf. p. [272]). About the members of the ancient Boidae we do not feel quite so sure.

It is therefore advisable to eliminate for zoogeographical purposes groups about which there can be any reasonable doubt, otherwise we may argue that certain genera must constitute a very old family, because they are now restricted to widely separated countries, or on the strength of their distribution we may conclude that the genera in question cannot be related to each other, and do not belong to the same sub-family or family as the case may be. Such groups are the Engystomatinae and the genus Spelerpes; amongst reptiles the Eublepharidae, Helodermatidae, Anelytropidae, Ilysiidae, Amblycephalidae.

It is customary to represent the various regions and sub-regions as if they had boundaries as fixed as political frontiers. Such limitations are quite arbitrary, and what is of more importance, they differ in reality according to the class or order of animals with which we happen to deal. Moreover, there has been, and is probably still going on, an exchange or overlapping of faunas. Such debatable grounds are Central America and the highlands of North-western South America. The famous Wallace's line, between Borneo and Celebes, Java and Lombok, is absolutely inapplicable to the Anura. From their point of view the Austro-Malayan countries, Papuasia and Polynesia do not form a sub-region of the Australian, but rather of the Palaeotropical region. Concerning the Urodela, the division into Palae- and Ne-arctic sub-regions is unjustifiable since Eastern Asia has emphatically American affinities (cf. also p. [96]). The Sahara and the rest of Northern Africa are intimately connected with Arabia, Persia, Afghanistan, and Northern India, just as equatorial Africa and Madagascar possess strong faunistic relationship with Southern India and the Malay islands.

Limiting factors of distribution.–Common salt is poison to the Amphibia; even a solution of 1 per cent prevents the development of their larvae. Consequently seas, salt lakes, and plains encrusted with saline deposits act as most efficient boundaries to normal "spreading." But undoubtedly many individuals have made long and successful voyages across the seas on floating trees. Solutions of lime are likewise detrimental to many species, and it is a general fact that limestone-terrain is poor in Amphibian life, unless, of course, sufficient accumulation of humus counteracts or prevents the calcareous impregnation of the springs and pools in meadows. Salamandra maculosa is, for instance, absent in Central Germany on the Muschelkalk, but it occurs in abundance in neighbouring districts of red sandstone or granite; nor can the larvae be reared successfully in very "hard" water. On the other hand, Proteus lives in the subterranean waters of Carniola, where the whole country is nothing but limestone.

Cold is another powerful limiting factor. The absolute northern limit of Amphibian life coincides rather closely with the somewhat erratic line of 0° Centigrade of annual mean temperature, a little to the north of which line the ground remains permanently frozen below the surface. The surface-crust, which thaws during the summer, engenders an abundance of insects as food-supply, but its freezing down to the icy bottom makes hibernation impossible. There are, of course, some exceptions, for instance the occurrence of Urodela in the Schilka river and in the district of Lake Baikal.

Ranges of mountains are far less effective barriers than is generally supposed. In many cases the fauna is the same on either slope, and they act rather as equalising or dispersing factors, especially when they extend from north to south. Witness the Andes, owing to which Ecuador and Peru bear a great resemblance to the Central American fauna, and differ from the tropical parts of South America. The existence of an Amblystoma in Siam is another instance.

The more specialised a family the more intimately is it connected with the physical features of the country. Typically arboreal frogs are dependent on the presence of trees. Some have undoubtedly spread into treeless countries and have changed into prairie-frogs, e.g. Acris. They come out, so to speak, as something different at the other end, and it is unlikely that these modified descendants redevelop exactly the same features as their ancestors before the migration. Baldwin Spencer[^[39]] met with only six species of frogs in Central Australia, Limnodynastes, Chiroleptes, Heleioporus, and Hyla. They are in the main identical with certain forms found in the dry inland parts of New South Wales and Queensland. They are to be regarded as immigrants from the latter regions, which have been able in the majority of cases to adapt themselves to unfavourable climatic conditions by means of a marked development of the burrowing habit, to which in certain cases has been added a capacity for absorbing and holding water.

Faunistic divisions of the Amphibia.

NOTOGÆA.–South World.

* indicates Amphibia which are peculiar to the respective regions or sub-regions.

Characterised by the Cystignathidae* and by the predominance of Arcifera, which form nearly 90 per cent of the Anurous population.

I. Australian region.–Absence of Apoda and Urodela. All the Anura are arciferous, with the exception of one species of Rana in the Cape York peninsula. The fauna of the Australian continent and of Tasmania consists chiefly of Cystignathidae and Hylidae (Hyla and Hylella) and several small genera of Bufonidae (Pseudophryne,* Notaden,* and Myobatrachus*).

It is customary, and from the study of other Vertebrata quite justifiable, to divide the Australian region into several sub-regions, but the Amphibia lend no support to this. The only Amphibian in the Sandwich Islands is a Bufo, closely related to North American species. The only Amphibian in New Zealand is Liopelma,* one of the Discoglossidae which are otherwise confined to Europe, North-east Asia, and North-west America, and, to judge from their low organisation, had formerly a much wider distribution. New Caledonia possesses no Amphibia. The Fiji Islands are inhabited by one or two species of Cornufer, a genus of Ranidae. The same genus is typical of the Austro-Malayan and Papuasian islands, the fauna of which consists of Rana and Cornufer, Ceratobatrachus, several genera of Engystomatinae, Hylidae, and Pelobatidae.

II. Neotropical region.–Characterised by Apoda, Aglossa (Pipa), abundance of Cystignathidae (Hemiphractinae,* Cystignathinae, and Dendrophryniscinae*), Hylidae (Hylinae and Amphignathodontinae*), numerous Bufonidae and Engystomatinae; Dendrobatinae*; the Raninae are represented by a few peculiar genera, mostly restricted to the Andesian province; the genus Rana occurs there in a few species only.

Absence of Discoglossidae, Pelobatidae and Dyscophinae.

Several species of Urodela, of the genus Spelerpes, extend from Central America into the Andesian province, one occurs in Hayti, and Plethodon platense in Argentina.

This region is by far the richest in the number of families, genera and species; the total number of the latter being, according to Boulenger, about four-ninths of the known species. The region comprises South America, Central America, and the West Indian islands. Central America is naturally debatable ground; one species of Hylodes and one Engystoma, besides about twenty Hylidae, extend into North America proper, while possibly the Raninae have entered the Neotropical region from the north. Bufo is too cosmopolitan to assist our conclusions. The occurrence of four species of Hylella in South America, one in Australia, and one in New Guinea indicate that this is not a natural genus.

From the point of the Amphibia the whole region can be divided into two sub-regions only: (1) The West Indian islands with Central America and the north-western Andesian province; (2) the rest of South America.

ARCTOGAEA.–North World.

Characterised by the absence of Cystignathidae.

I. Periarctic Region.–Characterised by the Urodela, these being almost peculiar to the region (cf. p. [96]). Absence of Apoda. Presence of Discoglossidae, Pelobatidae, Bufonidae, Raninae. Few Hylinae occur.

The whole region can be subdivided into three sub-regions.

1. Western Palaearctic.–Prevalence of Salamandrinae (Salamandra,* Chioglossa,* Salamandrina,* Triton); Proteidae (Proteus anguinus*); Spelerpes fuscus.*–Discoglossus, Bombinator, Alytes,* Bufo, Hyla arborea, Pelobates,* Pelodytes,* Rana.

2. Eastern Palaearctic.–Amphiumidae (Cryptobranchus); Salamandrinae (Triton, Pachytriton,* Tylototriton*); Amblystomatinae.–Bombinator, Bufo, Hyla arborea, Rana, Rhacophorus.

3. Nearctic.–Amphiumidae (Cryptobranchus, Amphiuma*); Proteidae (Typhlomolge,* Necturus*); Sirenidae*; Amblystomatinae; most Plethodontinae; Desmognathinae.*–Discoglossidae, Pelobatidae (Scaphiopus*); Bufo; Hylidae (Hyla, Acris, Chorophilus); Rana.

II. Palaeotropical region.–Characterised by the presence of Apoda and by the great prevalence of Firmisternal Anura, which amount to nearly 90 per cent of the total population. Absence of Urodela (except Amblystoma persimile*), of Cystignathidae, and practically of the Hylidae, only two of which occur in the Himalayan district. But this great chain of mountains should not be included within the region, while the outlying spurs in Upper Burma (with Amblystoma) are debatable ground. The subdivision of this widely extended region is beset with difficulties, chiefly on account of Madagascar and Papuasia. The fauna of Madagascar is very remarkable. All its Amphibia are Firmisternal, a mixture of African and Indian forms. The island agrees with Africa, in opposition to the Oriental countries, in no special point; all the Raninae, except Megalixalus, Rappia, and two rather common species of Rana, belong to different genera. Madagascar differs from Africa by the absence of Apoda, of Aglossa, and Bufonidae. On the other hand, it agrees with India or with the Malay islands, in opposition to Africa, by the possession of Dyscophinae, of the Ranine genus Rhacophorus, and the Engystomatine genus Calophrynus.

Africa and India agree with each other, and differ from Madagascar by the possession of Apoda, the genera Bufo and Nectophryne, and by the close resemblance of several genera of Raninae.

India, the Malay islands, and Papuasia with Melanesia possess Pelobatidae (Leptobrachium,* Batrachopsis,* Asterophrys*), and thereby differ considerably from Africa and Madagascar. Batrachylodes* of the Solomon Islands has unmistakable affinities with Phrynoderma* of Karen, between Burma and Siam; Oreobatrachus* of Borneo much resembles Phrynobatrachus* of West Africa; and Cornufer, typical of the Malay and Melanesian islands, occurs also in West Africa. All these Raninae indicate that the Austro-Malayan and Melanesian islands belong to the Palaeotropical region. Ceratobatrachus,* type of a sub-family, is peculiar to Melanesia.

There are consequently several possible modes of subdivision, all with a different result, according to the group of Amphibia, which we may select as of leading importance, e.g. Apoda or Pelobatidae, or Dyscophinae and Rhacophorus. The Engystomatinae and Raninae are to be eliminated, since they occur in all the countries in question. We have either to leave the whole region undivided–and it is a significant fact that the Indian countries possess not one sub-family of their own–or we must break it up into four provinces, not sub-regions:–

1. Ethiopian, or continental African, with Aglossa and Apoda, no Pelobatidae, no Dyscophinae, few Bufonidae, and many Raninae.

2. Indian and Malayan, with Apoda, no Aglossa, but with Pelobatidae, Dyscophinae, many Bufonidae and Raninae, amongst which Rhacophorus.

3. Malagasy, without either Apoda or Aglossa; with Firmisternal Anura only, chiefly Dyscophinae, and Rhacophorus and other Raninae.

4. Papuasian, without Apoda, Aglossa, Dyscophinae, and Bufonidae, but with Pelobatidae and Ranidae.

DISTRIBUTION OF FAMILIES AND SUB-FAMILIES OF THE AMPHIBIA.

CHAPTER IV

STEGOCEPHALI OR LABYRINTHODONTS–LISSAMPHIBIA–APODA

Sub-Class I. STEGOCEPHALI OR PHRACTAMPHIBIA

With a considerable amount of dermal armour, especially on the head.

The earliest known terrestrial four-footed creatures occur in the Carboniferous strata of Europe and North America. They and their immediate allies, which extend through the Permian into the Upper Trias, are now comprised under the name of Stegocephali, so called because the whole of the dorsal side of the cranium is covered, or roofed over, by dermal bones (στέγος, roof; κεφαλή, head). That these creatures, of which naturally only the skeletal parts are known, were not fishes, is shown by the typically pentadactyloid limbs; but to recognise them as Amphibia, and as distinct from Reptiles, is difficult, especially if the incipient Reptilia, which have sprung from some members of this Stegocephalous stock, are taken into account. However, they possess either two occipital condyles, or none, and their vertebrae are either pseudocentrous or notocentrous, but not gastrocentrous. Moreover, the whole skeletal organisation is still so ideally generalised, that it is easy to derive directly from it the arrangement prevailing in the Apoda and Urodela.

The vertebral column always comprises a well-developed, sometimes a very long tail. The vertebrae exhibit three types, two of which are fundamentally distinct, while the third is a further development of the second.

1. Lepospondylous and pseudocentrous.–The vertebra consists of a thin shell of bone surrounding the chorda dorsalis, and is composed of two pairs of arcualia, which meet each other, forming a suture, along the lateral side of the vertebra, both partaking in the formation of a transverse process which carries the rib.

2a. Temnospondylous.–The vertebra is composed of three pairs of units, which remain in a separate, unfused state. Two of them are dorsal arcualia, one of which tends to form the centrum of the vertebra, which then carries the neural arch.

2b. Stereospondylous.–The three component units fuse by co-ossification into a solid, amphicoelous vertebra.

The ribs are one- or two-headed, rather strong, but short, rarely reaching half-way round the body. They occur on all the vertebrae of the trunk and on most of those of the tail. One pair of ribs connects one vertebra, the sacral, with the pelvis, of which the ilium and ischium are generally ossified, rarely also a portion of the pubic region.

The shoulder-girdle is very primitive, greatly resembling that of the Crossopterygian fishes. It consists of the following bones:–a median, rhombic, or T-shaped interclavicle, a pair of clavicles, of cleithra, of coracoids, and of scapulae. The limbs show the typical pentadactyle plan, but even in these earliest Tetrapoda the hand possesses only four fingers, with 2, 2, 3, 2 phalanges respectively. The foot has five toes, with 2, 3, 4, 4, 3, or 2, 2, 3, 4, 3 phalanges.

Many Stegocephali were possessed of a dermal armour, covering either the whole body or only the under parts. Hence the term Phractamphibia (φρακτός, armoured). The armour consists of a great number of small cutaneous scales, partly calcified, or perhaps ossified, and arranged in many more or less transverse rows. We can only surmise that these scales were covered by corresponding epidermal sheaths. The skull is ideally complete in the number of separate bones which appear on its surface. Besides the outer nares and the orbits there is always an unpaired, small, interparietal foramen. The whole temporal region is completely roofed over. The following bones are present:–nasals, frontals, parietals, supra- and latero-occipitals; lacrymals (unless fused with the jugals?), prefrontals, postfrontals, postorbitals, squamosals, and epi-(or opisth-)otics; premaxillaries, maxillaries, jugals, quadrato-jugals, and supra-temporals; quadrates, pterygoids, palatines, vomers, and an unpaired parasphenoid.–The lower jaw is composed of a pair of dentaries, articulars, angulars, and splenials. The dentaries and apparently sometimes the splenials, the palatines, maxillae, and vomers carry teeth. The eyes possess a ring of sclerotic bones.

Order I. STEGOCEPHALI LEPOSPONDYLI.

Vertebrae pseudocentrous.

Sub-Order 1. Branchiosauri.–The young had several pairs of gill-arches, which, to judge from their size and from the fact that they are beset with numerous nodules, denticles, or irregular little processes like gill-rakers–seem to have been exposed to the surface and to have carried gills. In the adult the arches and gills seem to be absent.

Fig. 12.–A, Dorsal and B, ventral views of the cranium of Branchiosaurus salamandroides, × about 4. (After Fritsch.) C, Posterior view of the cranium of Trematosaurus, × about ½. (After Fraas.) Br, Branchial arches; C, condyle; Ep, epiotic; F, frontal; J, jugal; L.O, lateral occipital; M, maxillary; N, nasal; No, nostril; Pa, parietal; Pl, palatine; Pm, premaxillary; P.o, postorbital; Pr.f, prefrontal; Ps, parasphenoid; Pt, pterygoid; Ptf, postfrontal; Q, quadrate; Qj, quadrato-jugal; S.o, supraoccipital; Sq, squamosal; St, supratemporal; V, vomer.

One of the commonest genera is Branchiosaurus, including Protriton. B. salamandroides of the Lower Red Sandstone of Europe is known in every stage, from larvae of 16 mm. to the full grown animal of 64 mm. in length. The whole body was covered with little cutaneous scales. Pelosaurus and perhaps Melanerpeton are allied genera.

The following genera are small newt-like creatures of the Carboniferous age of Europe and North America. In Keraterpeton of Bohemia, Ireland, and Ohio, the dermal scales were restricted to the under parts; and the ribs were rather long, reaching half way round the body. Gills have not been observed. K. crassum, a European species, reached more than one foot in length, two-thirds of which fall to the tail. The ventral side is covered with a most elaborate armour, which consists of about eighty chevron-shaped rows of little scale-shaped nodules. The epiotic bones end in strange processes, carrying a pair of spikes, giving the skull a "horned" appearance, hence the generic name. Urocordylus is an allied genus.

Sub-Order 2. Aistopodes.–Body snake-like and without any limbs, hence the name ἄιστος, unseen; ribs long, and reaching half way round the body; from Carboniferous strata in Ireland and Bohemia, with allied, or perhaps identical forms in Ohio. Dolichosoma longissimum possessed more than 150 vertebrae, and was about a yard long. The epiotics end in obtuse projections, recalling those of Keraterpeton. These marvellous creatures had strange appendages, extending from behind the sides of the head, which were possibly the supports of external gills; since the upper end of one of the visceral arches, probably the hyoidean arch, is attached to the labyrinthic region, and from this arch starts a bony rod which carries long skeletal filaments. The body seems to have been naked.

Ophiderpeton had a compound ventral shield, while the skin of the back contained granular scutes. Although the Aistopodes have, not without reason, been looked upon as greatly resembling the Coeciliae or Apoda in organisation, especially in that of the vertebral column, the total absence of any other fossils which might bridge over the enormous gulf between the Coal Age and recent times, makes the attempt to derive the Apoda from these creatures very hazardous.

Order II. STEGOCEPHALI TEMNOSPONDYLI.

Mostly with rather long ribs and with chiefly ventral armour.

Chelydosaurus from the Lower Red Sandstone of Bohemia was 3 feet long, and possessed a beautiful, complicated, ventral armour, consisting of about sixty chevron-shaped rows, about three times as numerous as the vertebrae in the corresponding region. Sphenosaurus from the same strata and localities must have been 2 yards long. The trunk-vertebrae of both these genera were composed of four pairs of arcualia. Trimerorhachis from the Permian of Texas is very imperfectly known, but its trunk-vertebrae, as the name implies, consist of three pairs of separate arcualia, one of which, the interdorsal pair, tends to form a kind of centrum.

Dissorophus multicinctus, also from the Permian of Texas, has been described by Cope[^[40]] as a "Batrachian Armadillo," and considered allied to Trimerorhachis. Ten vertebrae are known, of an aggregate length of 93 mm.; the length of the creature was perhaps one yard. The neural spines are elevated, and the apex of each extends in an arch on each side to the ribs. These spinous branches touch each other, forming a carapace. Above, and corresponding to each of them, is a similar dermal and osseous element, which extends from side to side without interruption in the median line, forming a dermal layer of transverse bands which correspond to the skeletal carapace beneath it. This creature remotely approaches the genus Zatachys, Cope, where a dermosteous scute is co-ossified with the apex of the neural spine. The systematic position of this genus is at least doubtful.

Archegosaurus decheni from the Lower Red of Germany, known by many well-preserved specimens, reached a length of 4 or 5 feet. The trunk vertebrae are tri-partite, those of the tail quadri-partite, like those of the trunk of Chelydosaurus. Young specimens show traces of gill-arches. The thoroughly terrestrial walking limbs have four fingers and four toes; the arrangement of the tarsalia, most of which are ossified, lend support to the view that the morphological axis went through femur, fibula, intermedium, the centralia, the second distal tarsale, and the second toe. The dentine and enamel of the teeth are much folded, and this feature, which applies to most members of this Order, to a lesser degree also to others, has caused them to be comprised under the name of Labyrinthodonta. The upper surface of the head shows very characteristically arranged grooves, which probably contained slime-canals and possibly sensory organs.

Actinodon and Euchirosaurus are closely allied forms, chiefly from the Lower Red Sandstone of France; Gondwanosaurus occurs in the Permian of India.

Order III. STEGOCEPHALI STEREOSPONDYLI.

These are the most highly developed members of the typical Labyrinthodonta, characterised by their much-folded teeth, and by their solid, bi-concave vertebrae. Loxomma occurs in the Upper Carboniferous of England and in the Lower Red of Bohemia: Trematosaurus, Capitosaurus, and Metopias from the New Red or Lower Trias to the Keuper of Germany. Mastodonsaurus from the Trias of England and Germany is the most gigantic Amphibian known, with a skull of nearly 1 yard in length.

Labyrinthodon from the Keuper of Warwickshire is one of the latest members of the group. Labyrinthodont creatures have also been described from the Trias of South Africa, e.g. Rhytidosteus; those from North America are insufficiently preserved.

Many of these and allied genera have left their footprints in slabs of Sandstone, both Lower and New Red, in Europe, Africa, and America. But although their spoors are common enough, only a few can with certainty be referred to Stegocephali, e.g. Saurichnites salamandroides of the Lower Red of Germany. The spoors of Chirotherium, common in the New Red of Germany and England, for instance in Cheshire, belong to unknown owners; both the large hind feet (which measure nearly half a foot in length) and the much smaller fore feet, had five digits, the first of which stood off like a thumb. Five-fingered Stegocephali are unknown.

There is an almost complete absence of fossil Amphibia from the Upper Trias to the Oligocene. The Stegocephali as such seem to have died out with the Trias. The recent Amphibia, of course, must have had ancestors in the Mesozoic age. There is one little skeleton, from the Wealden of Belgium, which belonged to a newt-like creature, called Hylaeobatrachus croyi. Scarce fragments, described as Megalotriton, are known from the Oligocene of France, and Triton itself seems to be indicated by remnants in the Lower Miocene of France and Germany. But fairly complete specimens of large creatures, much resembling Cryptobranchus, have been found in the Upper Miocene of Oeningen, Canton Solothurn, Switzerland. The first known specimen, now at Haarlem, indicating a total length of 3 feet or more, was described and figured in the year 1726 by Scheuchzer, in a learned dissertation entitled "Homo diluvii testis."

Betrübtes Beingerüst von einem alten Sünder

Erweiche Herz und Sinn der neuen Bosheitskinder.

Which may be rendered as follows:–

Oh, sad remains of bone, frame of poor Man of sin

Soften the heart and mind of sinful recent kin.

This was the motto attached to the illustration, and it remained a warning to mankind until Cuvier declared the skeleton to be that of some large newt. Tschudi named it Andrias scheuchzeri, but it is scarcely generically distinct from Cryptobranchus, being almost intermediate between C. alleghaniensis and C. japonicus, see p. [97].

Sub-Class II. LISSAMPHIBIA.

Amphibia without dermal armour.

Order I. APODA or LIMBLESS AMPHIBIA.

The Amphibia Apoda, Coeciliae or Gymnophiona, are a small group of worm-shaped, burrowing creatures, restricted to the Neotropical and Palaeotropical regions, excluding Madagascar. They have no limbs and no girdles. The tail is extremely short; the vertebrae are pseudo-centrous, and most of them carry rather long ribs, none of which, however, meet to form a sternum. The whole snake-like body is covered with a smooth and slimy skin which forms numerous transverse folds or rings.

The most remarkable feature of the skull is its solid compactness, which stands in direct correlation with the burrowing habits of these creatures. The whole dorsal surface of the cranium is practically roofed in by bone, so that, in this respect, it greatly resembles that of the Stegocephali; but this resemblance is produced chiefly by a broadening of those bones which exist also in the other Lissamphibia, while supratemporals and supra-occipitals are absent.

Fig. 13.–Skull of Ichthyophis glutinosa. × 3. (After Sarasin.) A, Lateral, B, ventral, C, dorsal view. A, Posterior process of the os articulare; Ca, carotid foramen; Ch, choana or posterior nasal opening; F, frontal; J, jugal; Lo, lateral occipital; Mx, maxillary; N, nasal; No, nostril; O, orbit; P, parietal; Pa, palatine; Pm, premaxillary; Pof, postfrontal; Prf, prefrontal; Pt, pterygoid; Q, quadrate; S, squamosal; St, stapes; T, tentacular groove; Vo, vomer; X, exit of vagus nerve.

There is, however, a pair of bones which represent either the postorbitals or the postfrontals, perhaps both, of the Stegocephali. The quadrato-jugal arch is enormously developed, and by reaching the parietal, frontal, and postorbito-frontal bones (which latter occur only in Ichthyophis and Uraeotyphlus) and the maxilla, extends over the whole of the orbito-temporal fossa. The squamosal is completely fused with the quadrato-jugal. The stapes has the typical stirrup-shape, is even perforated by an artery, and articulates distally with the shaft of the quadrate (as in the snakes). The maxilla is very large and broad. Owing to its broad junction with the quadrato-jugal arch, the prefrontal and frontal, the orbital fossa is reduced to a very small hole, or the maxilla completely covers the eye. Somewhere between the latter and the nares the maxilla is perforated by the tentacular groove. The periotic bones are represented by the prootics and epiotics; they fuse with the lateral occipitals and with the parasphenoid. The whole orbito-ethmoidal region of the primordial skull is also turned into one mass of bone.

The angular element of the lower jaw forms a thick and large process which projects upwards and backwards from the mandibular joint. The former possession of a splenial bone is indicated by the occurrence of a second series of teeth in the mandibles of Ichthyophis and Uraeotyphlus. Other genera have vestiges of this second row, or it may be completely lost.

The hyoid and branchial apparatus is more primitive than in any other recent Amphibia. In the larva the hyoid and the first and second branchial arches are connected with each other by a median copular piece. The third branchial arches are free from the rest, but are fused in the middle line, the fourth are loosely attached to the previous pair. In the adult both fuse into one transverse, curved bar, and the second pair of branchials lose their connexion with the basal longitudinal piece and likewise form a transverse bar.

The vertebrae are built upon the pseudocentrous type, are amphicoelous, and the chorda is intravertebrally destroyed by cartilage, as in the majority of the Urodela. The number of vertebrae is great, amounting in some species to between 200 and 300, of which a few belong to the tail. The first vertebra is devoid of an odontoid process. The ribs are proximally bifurcated as in the Urodela.

The eyes are practically useless, being either more or less concealed under the skin, or they are covered by the maxillary bones. All Coecilians possess a peculiar tentacular sensory apparatus, which consists of a conical flap-shaped or globular soft tentacle, which is lodged in a special groove or canal of the maxilla, between the eye and the nose, whence it is frequently protruded while the animal is crawling about. These tentacles in the young Siphonops lie, according to the Sarasins, quite close to the eyes, but are later transferred nearer to the nose. The organ consists of a peculiarly rolled up and pointed fold which arises from the bottom of the sac or pit, where it receives a nerve. It is protruded by becoming turgid with blood, and is retracted by a strong muscle. Into the lumen of the sac are poured secretions from the large orbital (Harderian) gland, to keep the apparatus clean. Hence arose the mistaken notion of its being a poison-organ. The whole structure is possibly an offshoot of the naso-lacrymal duct.

The skin is most remarkable. In the ripe embryo the epidermis passes smoothly over the surface. Beneath follow two layers of soft cutaneous connective tissue, bound together by transverse or vertical lamellae, so that ring-shaped compartments are formed, and in these are embedded slime-glands. In the adult each compartment is modified into an anterior glandular belt and a posterior space, from the bottom of which grow several scales. The number of cutaneous rings agrees originally with that of the vertebrae; but later, and especially in the hinder portion of the trunk, each ring breaks up into two or more secondary segments, and these no longer agree with those of the skeleton. Each scale is beset with numerous smaller scales which consist of hardened cell-secretions infiltrated with calcareous matter. The whole scale is consequently an entirely mesodermal product of the deeper layers of the cutis. The usual statement that the skin forms imbricating lamellae, on the inner side of which appear the scales, is wrong. The "lamellae" can be lifted up only after the general epidermal sheath has been broken artificially in the constrictions between the rings. No scales exist in the Indian genus Gegenophis and in the American Siphonops, Typhlonectes, and Chthonerpeton, a secondary loss which does not indicate relationship. The scales develop late in embryonic life, and they are reasonably looked upon as inheritances from the Stegocephali. The glands either produce slime, whose function seems to be the keeping clean of the surface of the body, or they are squirt-glands. The latter kind are also numerous and are filled with a fluid which is squeezed out by muscular contraction, and seems to be poisonous, as it causes sneezing to those who handle or dissect fresh specimens.

The Coecilians live in moist ground and lead a burrowing life. Their developmental history has only recently been studied, and in but a few species, see Ichthyophis, p. [91], and Hypogeophis, p. [92]. The female is fertilised internally, copulation taking place by means of eversion of the cloacal walls in the shape of a tube. The spermatozoa possess an undulating membrane; the eggs undergo meroblastic division and the embryos have three pairs of long external gills. Some are viviparous.

The snake-like, limbless shape of the body (Fig. 15) is, as in snakes, correlated with an asymmetrical development of the lungs; the left is reduced, while the right is drawn out into a long cylindrical sac. The liver is likewise very long, and partly constricted into a great number of lobes. Owing to the great reduction of the ribs progression is effected in an almost earthworm-like fashion by the peristaltic motion of the skin, assisted by its numerous ring-shaped constrictions.

The systematic position of the Coeciliae has been, and is still, a controversial matter. The Sarasins took up Cope's suggestion, that their nearest allies are the Urodela, especially Amphiuma, and they went so far as to look upon Amphiuma as a neotenic form of the "Coecilioidea," which they divided into Amphiumidae and Coeciliidae; the Coecilioidea and Salamandroidea forming the two sub-orders of the Urodela. They based this startling conclusion chiefly upon remarkable resemblances between Amphiuma and Ichthyophis, namely, (1) the mode of laying the eggs on land and coiling themselves around them; (2) the existence of remnants of a tentacular apparatus in Amphiuma; (3) Cope's statement that Amphiuma alone among the Urodela possesses an ethmoid like the Coeciliae. This latter point is, however, erroneous; it has since been shown by Davison[^[41]] that Amphiuma possesses no ethmoid bone, but that, instead of it, descending plates of the frontals join below the premaxilla and function as a nasal septum, with a canal for the olfactory nerves.

We look upon the Apoda with more reason as creatures which of all the Lissamphibia have retained most Stegocephalous characters and at the same time form a highly specialised group equivalent to the Urodela and the Anura. The following are Stegocephalous inheritances peculiar to the Apoda in opposition to the other recent Amphibia: retention of cutaneous scales with calcareous incrustations, greatly resembling the scales of the Carboniferous Microsauri; occasional retention of post-frontal and lateral nasal or lacrymal bones, and of a second row of teeth in the mandible. To these may be added the presence of epiotic bones, and the primitive character of the branchial arches. The loss of all these characters would turn the present Apoda into limbless Urodela, but this assumption does not justify their inclusion in this Order. The possible homology of the tentacular apparatus has been discussed elsewhere, p. [45].

Fossil Apoda are not known; their subterranean life does not favour preservation.

Fig. 14.–Map showing the distribution of the Coeciliae or Amphibia Apoda.

Only family, Coeciliidae. About forty species are known. These have been placed in seventeen genera, mostly on comparatively slight grounds, and several of these genera are probably unnatural, the distinctive characters having undoubtedly been developed independently in various countries. We have to remember that the recent species are the remainder of a formerly much more numerous group; it is also likely that more will be discovered in the tropical forests of South America and Sumatra.

Boulenger[^[42]] has distinguished them as follows:–

I. Cycloid scales embedded in the skin.

A. Eyes distinct, or concealed under the skin.

a. Two series of teeth in the lower jaw.

α. Quadrato-jugal (squamosal) and parietal bones in contact.

Tentacle between eye and nostril.

Ichthyophis, 2 species, India and Malay islands, p. [90].

Tent"cle below and behind nostril.

Hypogeophis, 3 species, East Africa and Seychelles, p. [92].

Tent"cle below and in front of eye.

Dermophis, 5 species, America and Africa, p. [93].

Tent"cle below the nostril.

Coecilia, 6 species, America.

β. Quadrato-jugal separated from parietal.

Tentacle close to the eye.

Rhinatrema, 2 species, America.

Tent"cle below and behind nostril.

Geotrypetes, 1 species, West Africa.

Tent"cle below nostril.

Uraeotyphlus, 3 species, West Africa and India.

b. One series of teeth in the lower jaw.

Tentacle in front of the eye.

Cryptopsophis, 1 species, Seychelles.

B. Eyes below the cranial bones. Quadrato-jugal in contact with parietal.

Tentacle near the nostril.

Gymnophis, 4 species, South America.

Herpele, 2 species, Panama and Gaboon.

II. Without scales.

A. Eyes distinct, or concealed under the skin.

a. Two series of teeth in the lower jaw.

α. Quadrato-jugal in contact with parietal.

Tentacle behind nostril; end of body laterally compressed.

Typhlonectes, 3 species, America, p. [93].

β. Quadrato-jugal separated from parietal.

Tentacle between eye and nostril.

Chthonerpeton, 2 species, America.

b. One series of teeth.

α. Quadrato-jugal and parietal in contact; tentacle in front of the eye.

Siphonops, 4 species, America.

β. Quadrato-jugal separated from parietal.

Bdellophis, 1 species, East Africa.

B. Eyes below the cranial bones.

a. Two series of teeth. Quadrato-jugal and parietal in contact; tentacle behind and below nostril.

Gegenophis, 1 species, India.

b. One series of teeth. Quadrato-jugal separated from parietal.

Scolecomorphus, 1 species, East Africa.

Boulengerula, 1 species, East Africa.

Ichthyophis glutinosa extends from the slopes of the Himalayas to Ceylon, the Malay islands, and into Siam. A second species, I. monochrous, occurs in Malabar, Malacca, Borneo, and Java. I. glutinosa reaches about one foot in length, with a greatest thickness of a little more than half an inch. The general colour is dark brown or bluish black, with a yellow band along each side of the body.

This species has been studied extensively by the Sarasins.[^[43]] It breeds in Ceylon after the spring monsoon. The ovarian egg is oval, measuring 9 by 6 mm. The yolk is yellow; the blastoderm lies towards one of the poles. The strong vitelline membrane becomes surrounded in the oviduct by a dense albuminous membrane, which forms twisted chalazae, just like those of birds' eggs, and by these two cords the eggs are strung together. Around all this lies another mantle of albumen. The female digs a hole close to the surface in moist ground near running water, and there lays about two dozen eggs. The egg-strings become glued together, entangled into a bunch, and the female coils herself round the bunch and remains in that position, probably to protect the eggs against other burrowing creatures, as blind snakes (Typhlops and Rhinophis) and certain limbless lizards, with which the ground literally swarms. During this kind of incubation the eggs assume a round shape, and grow to twice their original size, and the mature embryo weighs four times as much as the newly laid egg.

Fig. 15.–Ichthyophis glutinosa × 1. (After P. and F. Sarasin.) 1, A nearly ripe embryo, with gills, tail-fin, and still with a considerable amount of yolk; 2, female guarding her eggs, coiled up in a hole underground; 3, a bunch of newly laid eggs; 4, a single egg, enlarged, schematised to show the twisted albuminous strings or chalazae within the outer membrane, which surrounds the white of the egg.

The external gills are delicately fringed and red, and they move up and down in the fluid of the egg. The body of the embryo is at first white, but becomes pigmented with dark grey. A strong line of lateral sense-organs is formed, and a ring of them lies around the eye and others on other parts of the head. The short tail develops a fin. Of the three pairs of gills the third is the shortest, and is generally turned dorsalwards. In embryos of 4 cm. in length the longest gill measures as much as 2 cm. Yolk is still present in embryos which have reached the surprising length of 7 cm. Then the gills begin to shrink a little, and at this time one pair of gill-clefts breaks through at the base of the third external gill.

When the larvae are hatched the gills are lost. The young larva takes to the water in a gill-less state, and moves about like an eel. At the bottom of the gill-hole on each side two arches are visible, and there are at this stage neither inner nor outer gills. The larvae frequently come up to the surface to breathe. The eyes are large and clearly visible, but the tentacles are still undeveloped. The epidermal sense-organs are numerous, and appear as white spots in the grey skin; about fifty extend from the gill-opening to the tip of the tail.

Ichthyophis seems to live a long time in the larval state. At last the gill-clefts close, the tail-fin disappears, and the tentacles come to the surface. The whole skin assumes a totally new structure, and the fish-like larva turns into a burrowing, subterranean creature so terrestrial that it gets drowned when made to remain in the water.

Hypogeophis.–According to A. Brauer[^[44]] three species of Coecilians are found in the Seychelles: Cryptopsophis multiplicatus, which is rare, Hypogeophis rostratus and H. alternans. They live in moist ground, near the coast in swamps, higher up in humus, under rotten trees and rocks, down to the depth of one foot. In the island of Silhouette, Brauer found them in brooks, at least during the dry season, from May to September. The natives call them "vers de terre." They seem to propagate during the greater part of the year, provided there is sufficient moisture. The female coils round the eggs, which vary from half a dozen to thirty in number, those of H. rostratus measuring 7-8 mm., those of H. alternans only 4-5 mm.

The embryos undergo their whole development in the egg. Four pairs of gill-clefts break through, the first between the hyoid and the first branchial arch, the fourth between the third and fourth branchial arches. There appears also a spiracular cleft between the quadrate and the hyoid arch; this cleft is, however, only developed dorsally, and persists for a shorter time. The external gills appear at the same time as the clefts, upon the first three branchial arches; the third gill is the latest, and remains in a vestigial condition covered up by the two others. The gills, of which the second is the longest, are not (as stated by the Sarasins) direct prolongations of the gill-arches, but they begin as button-like growths upon the arches. They begin to disappear with the absorption of the yolk, getting actually smaller. In embryos of 6 cm. they are 6 mm. long, while in embryos of 6.5 cm. they are reduced to 4.5 mm. in length. The first to disappear is the third gill, of course by being resorbed; and the clefts are closed before the creature leaves the egg. Hypogeophis not leading an aquatic larval life possesses no tail-fin in the embryonic state, the gill-holes are closed, and the epidermal sensory organs disappear long before the time of hatching.

Vestiges of gills appear also on the hyoid and on the mandibular arch, but on the latter they are of very short duration. Those of the hyoid gradually fuse with the first of the branchial gills, and these also concentrate with their bases so that they ultimately seem to spring from one common stem. Brauer remarks that the distinction between internal and external gills seems to be one of degree only; the hyoidean and mandibular gills namely start from the hinder margin of the arches, just like the internal gills of Torpedo according to Ziegler, while the other gills start from the sides of the branchial arches. He also found a pair of little swellings behind the last gill-cleft, and an unpaired swelling (corresponding with a double one in Ichthyophis) in front of the vent. Not unreasonably he sees in these swellings the last, very transitional vestiges of the paired limbs.

Typhlonectes compressicauda of Guiana and Venezuela is one of the largest Coecilians, reaching a length of 18 inches, with a body-diameter of ¾ inch. The general colour, as in most of these creatures, is olive brown to black. A sort of adhesive disc surrounding the vent occurs in this genus. Peters, who described this species, found in one female six embryos of comparatively enormous size, one of them being 157 mm. (more than 6 inches) long, and 12 mm. thick, and devoid of a tail-fin. Instead of lateral gill-openings there is a "bag" on each side 55 mm. long, upon which is distributed a blood-vessel. The Sarasins have examined the same specimen: The gills are not a bag, but consist of two flat, unbroken membranes which are closely connected with each other. In fact the outer gills of all Amphibia may be said to begin in the shape of small bags, whence sprout secondarily the gill-fringes; but in Typhlonectes they form these flaps instead of growing into the usual three gills. The embryos have no epidermal sense-organs, but plenty of skin-glands. Probably when born they take at once to terrestrial life, the flaps are possibly shed at birth, and there remains a little cicatrix.

Dermophis thomensis of West Africa (its other relations live in East Africa, South and Central America) is also viviparous.

CHAPTER V

LISSAMPHIBIA (CONTINUED)–URODELA

Order II. URODELA or TAILED AMPHIBIA.

The recent tailed Amphibia, Salamanders and Newts in the wider sense, have been grouped into four families which can be conveniently diagnosed by the following characters:–

Both the upper and lower jaws are furnished with teeth. Fore- and hind-limbs are always present.

Maxillary bones present.

Eyes free and devoid of lids .......... Amphiumidae, p. [97].

Eyes with movable lids[^[45]] .......... Salamandridae, p. [102].

Maxillary bones absent.

Eyes without lids. Perennibranchiate .......... Proteidae, p. [132].

Both jaws are toothless. The hind-limbs, the maxillary bones and eyelids are absent. Perennibranchiate .......... Sirenidae, p. [136].

These four families are closely allied to each other, especially the Amphiumidae and the Salamandridae.

The geographical distribution of the Urodela is essentially Periarctic, except that about one dozen species each of Amblystoma and of Spelerpes extend southwards into Central America, and in the case of the latter genus even into the Andesian parts of South America. Plethodon platense inhabits Argentina.

The Urodela afford good reasons for dividing the Periarctic region into three co-ordinate sub-regions, namely, Nearctic, Eastern and Western Palaearctic. The difference between the European and the Eastern Asiatic fauna is well marked; the two are–at least with our present knowledge–separated by a wide stretch of country very poor in Urodele forms; while, lastly there are not a few resemblances between this Eastern Asiatic and the American fauna. The Urodela thus lend no support to the usual division of the Periarctic into a Palaearctic and a Nearctic sub-region. Nor is it possible to divide the Palaearctic into a Eurasian and a Mediterranean province. We have in this case to distinguish between an American, an Asiatic, and a European fauna. The Asiatic or Eastern Palaearctic sub-region assumes the central position, at least from a merely geographical point of view. It would be unjustifiable to assume a spreading from this centre into Europe, and, on the other hand, into America. The centre existed more probably in the Arctic circle, now devoid of Urodela.

Fig. 16.–Map showing the distribution of the Urodela. "Ichthyodea" = Amphiumidae + Proteidae + Sirenidae.

So far as mere numbers of species are concerned the huge Asiatic or Eastern Palaearctic region is the poorest, but it is also the least explored, and China will probably yield a good many new forms. We know at present only 15 species, nearly all from the eastern half. These 15 species represent no less than 11 genera, 8 of which (= 73 per cent) are peculiar to the sub-region. Next comes the Western Palaearctic or European sub-region with about 21 recent species of 5 genera, 4 of which are peculiar. America is by far the richest, with no less than 66 species (36 eastern, about 16 western, and the rest Central American, etc.), belonging to 19 genera, 17 of which (= 90 per cent) are peculiar to the New World. But this richness in species is due mainly to the abundance of the two genera Amblystoma and Spelerpes, just as Europe is characterised by its many Tritons.

One of the most striking features of the Asiatic sub-region is its difference from the European. They have very little in common. Pachytriton, Tylototriton, and two species of Triton (T. pyrrhogaster and T. sinensis) are the only Salamandrinae, while all the rest are Lechriodont (see p. [102]), like the American Urodela, excepting the two American Tritons, T. torosus and T. viridescens.

Geographical Distribution of the Urodela

				Western Palaearctic.	Eastern Palaearctic.	American.
Sirenidae				... ...		1 Siren 1 Pseudobranchus
Proteidae				1 Proteus		1 Necturus
Amphiumidae				... (1 Andrias, Miocene)	... 1 Cryptobranchus	1 Amphiuma 1 Cryptobranchus
Salamandridae		Desmognathinae		... ... ... ...		1 Thorius 1 Haptoglossa 3 Desmognathus 1 Typhlotriton
		Pleithodontinae		... ... ... ... ... ...		21 Spelerpes 2 Manculus 7 Plethodon 3 Batrachoseps 1 Typhlomolge 2 Autodax
		Amblystomatinae			1 Amblystoma ... 1 Batrachyperus 1 Ranidens 1 Geomolge 1 Onychodactylus 2 Salamandrella 3 Hynobius	16 Amblystoma 1 Dicamptodon
		Salamandrinae		... ... 14 Triton 1 Salamandrina 1 Chioglossa 3 Salamandra	1 Pachytriton 1 Tylototriton 2 Triton	2 Triton
				21 species, 6 genera	15 species, 11 genera	66 species, 18 genera

The occurrence of an Amblystoma, A. persimile, in the mountains of Siam and Burmah, is most suggestive, and others will in all probability be found. It must also be borne in mind that the differences between the genera of Amblystomatinae are in reality very slight; and the same applies to the sub-families themselves. The presence or absence of teeth on the parasphenoid, the possession of amphi- or opistho-coelous vertebrae, do not mean much, and certainly do not forbid the notion that all the recent Urodela are the offspring of one common generalised stock which inhabited the northern portion of the globe. Nothing is gained by hiding the solitary European species of the essentially American genus Spelerpes under the name of Geotriton. It is a Spelerpes in all characteristic points. Speaking broadly, each of the three principal sub-families of Salamandridae is characteristic of a sub-region; the Salamandrinae of the Western Palaearctic, the Plethodontinae of the American, while the Amblystomatinae are chiefly Asiatic, at least so far as diversity of genera is concerned.

Fam. 1. Amphiumidae.–Without gills in the perfect state. The gill-clefts are in a vanishing stage, being either reduced to one pair of small holes or being altogether absent. The maxillary bones are present. Teeth occur in both jaws; those of the vomers form transverse rows. The vertebrae are amphicoelous. The fore-limbs and hind-limbs are present, but small. The small eyes are devoid of lids.

This family is now represented by two genera, with only three species, found in the United States and in Eastern Asia.

Cryptobranchus.–The limbs are functional, with four fingers and five toes. The outer digits and the sides of the limbs are bordered with folds of skin. The head and body are stout and depressed; the tail is short, laterally compressed, and provided with a fin. The skin is very glandular and slimy, and forms a thick, irregularly-shaped fold along the side of the body.

C. (Menopoma) alleghaniensis.–The gill-clefts are normally reduced to one pair, individually to the left cleft, the right closing up. There are, however, four branchial arches and vessels. The general colour is brown or grey above, sometimes with darker patches, lighter below. The "Hellbender" reaches a length of nearly 18 inches (about 46 cm.), is entirely aquatic, and is apparently restricted to the rivers and streams of the mountainous districts of the Eastern United States. It is very voracious, living on worms and on fish, being much disliked by the fishermen, as it takes the angler's bait, and destroys great quantities of the valuable food-fish Coregonus albus. Although rather common and easily kept, its larvae still remain unknown.

Fig. 17.–Cryptobranchus japonicus. Japanese Giant Salamander. × ⅙.

C. japonicus s. maximus.–The Giant Salamander of Japan differs from its American relation in one essential point only, namely, by the absence of gill-openings and of the modifications of the branchial apparatus connected therewith. It has but three branchial vessels, and the skeletal arches are reduced to two. It lives in Japan and in China, from 600 to 4500 feet above the level of the sea, in small streams of mountain-meadows. It feeds upon fishes, Amphibia, worms, and insects. It is easily fished with the hook and is eaten by the Japanese.

The first living specimen was brought to Europe in 1829 by Th. von Siebold, its discoverer. It grew within a few years from 1 foot to 3 feet in length, and died in 1881, at least fifty-two years old. Another specimen lived in the Hamburg aquarium for fourteen years, during which time it is said to have grown 36 cm. (more than 14 inches), having attained a length of nearly 4½ feet, or 134 cm. The largest specimen known measures 159 cm = 5 feet 3 inches.

The life-history of this species is still imperfectly known. Japanese picture-books contain drawings of the adult and of larvae, the latter showing three pairs of fringed external gills. Young specimens of 16 cm. length have already lost the gills, but still retain a cleft on either side of the neck, in the shape of a horizontal slit, and this is soon after closed up by the skin.

The best account has recently been given by Sasaki.[^[46]] According to him the Giant Salamander leads a solitary life, concealed in dark places, under rocks in swift-flowing, thickly shaded small brooks of clear and cold water.

The animal may be easily captured with a fish-hook, baited with a fish, frog, or several earth-worms, and tied to a string a few feet in length. This is thrust by the aid of a small bamboo-stick into the salamander's retreat. The string is not tied to the stick, but the point of the loaded hook is forced into one end of it, far enough to keep it in place while this end of the rod is pushed under the rock. When the bait has been thus brought near the salamander, any bite will be instantly felt through the rod. The latter is then withdrawn as quietly as possible, the hook and bait being left. As soon as a jerk of the string is noticed, a pull is made, which generally ends in the capture of the unfortunate animal. If the first pull should fail, the bait is replaced as before, and a second opportunity is offered, which the unwary creature accepts as readily as the first. The fisherman, having obtained one bite, is sure of ultimate success, as the salamander does not learn by experience to refuse the proffered morsel. When captured, it emits a peculiar slimy secretion, having an odour much like that of the leaves of the Japan pepper (Xanthoxylon peperitum). This secretion hardens into a gelatinous mass after a short exposure to the air.

Temminck and Schlegel state that the act of inspiration is ordinarily performed once every 6-10 minutes. This is true for specimens kept in tubs; but Sasaki is inclined to think that they perform this act less frequently in their native brooks. The eyes are so small that they are obviously of little importance; the salamanders capture their prey not by pursuing, but by waiting for its near approach, whereupon they seize it with their teeth by a swift lateral movement of the head. The eggs are said to be laid in August and September, and they form a string resembling a rosary. Each egg floats in a clear fluid, inclosed in a bead-shaped gelatinous envelope, and this is connected with the next by means of a comparatively small string. The egg measures about 6 mm. by 4 mm., and is yellow everywhere except at the upper pole, where it is whitish. All attempts to make Cryptobranchus breed in captivity have failed hitherto, owing no doubt to the difficulty of obtaining the cool temperature of its mountain streams. Sasaki's smallest specimens measured 19 to 20 cm. These had three pairs of very short branchial processes, from 3 to 5 mm. in length, attached just inside the branchial orifice. Each process was somewhat flattened and tapering, most of them still with branchlets. In another specimen, 20.5 cm. in length, the gills had almost wholly disappeared, but the branchial slits were still visible. One of 24.5 cm. length showed no trace of gills, and the branchial orifice was completely closed, but still marked by a light streak.

Fig. 18.–Amphiuma means. × ⅕.

Amphiuma means s. tridactyla.–The limbs are very much reduced, and end in two or three little fingers or toes. Just in front of the fore-limbs lies the pair of small gill-clefts, each guarded by two flaps of the skin. There are four branchial arches. The general colour of this eel-shaped creature is black, lighter below. The head is covered with numerous pores, arranged in several rows, which unite in the region of the neck, so that only two rows extend along the sides of the body. It reaches a length of three feet, and lives in swamps or muddy waters, for instance in the ditches of rice-fields, burrowing occasionally in the mud, feeding on crayfishes, molluscs, small fishes, etc. It is confined to the south-eastern States of North America, from Carolina to Mississippi. According to Davison,[^[47]] copulation takes place in May. The rather hard-shelled eggs are deposited in the following August or September, and are connected by a twisted cord. The female lies about them in a coil. The embryos, which are hatched in the month of November or December, have well-developed external gills. By the following February they have reached a length of from 68 to 90 mm. (about 3 inches), living in damp localities under rocks or rooted stumps, and have already lost their gills. The legs are said to be relatively longer than they are in the adult.

Fam. 2. Salamandridae (Salamanders and Newts).–Without gills in the perfect state. Maxillaries are present. Both jaws are furnished with teeth. The eyes are protected by movable lids, except in Typhlotriton. Fore- and hind-limbs present, although sometimes very much reduced.

To this family belong by far the greater number of tailed Amphibia. They have been, for the sake of convenience, grouped into four sub-families, the determining characters of which are all internal and of comparatively slight importance. Little better is the division into Mecodonta, with the teeth of the palate in two longitudinal rows diverging behind and inserted upon the inner margins of the two palatine processes, which are much prolonged posteriorly, and Lechriodonta, in which the series of palatal teeth are restricted to the posterior portion of the vomers and form either transverse or posteriorly converging rows.

III. Series of palatal teeth transverse, restricted to the posterior portion of the vomers. Parasphenoid beset with dentigerous plates.

Vertebrae opisthocoelous: Desmognathinae, p. [102].

Verte"rae amphicoelous: Plethodontinae, p. [103].

III. Series of palatal teeth transverse or posteriorly converging, restricted to the posterior portion of the vomers. Parasphenoid toothless. Vertebrae amphicoelous: Amblystomatinae, p. [109].

III. Series of palatal teeth in two longitudinal series, diverging behind, inserted on the inner margin of the long palatine processes. Parasphenoid toothless. Vertebrae amphicoelous: Salamandrinae, p. [115].

Sub-Fam. 1. Desmognathinae.–Comprising only three genera, with five species, in North America. Five toes.

Desmognathus.–The tongue is attached along the median line, free behind, oval in shape. Three species in the eastern half of the United States. D. fuscus is one of the lungless Urodela, for which condition see p. [46]. The skin is nearly smooth; parotoids prominent, gular fold strongly marked. General colour above, brown suffused with pink and grey, sometimes with a dark lateral band; under parts mottled brown. The vomerine teeth are frequently absent. Total length, about 4 to 5 inches. They live, carefully concealed in the daytime, under stones in or on the edge of the banks of little mountain streams. The eggs are laid in two long strings, and are wrapped round the body of the female like a rosary, the female having resorted to a hollow in the mud, below a stone or other suitable place. The outer envelope of each egg tapers out into a short stalk, and the several stalks all converge, or are glued together into one common knot, "much like a bunch of toy balloons held in the hand of a street vendor." The egg is said to be meroblastic. The larvae seem to remain in the egg until they are nearly adult, and they emerge at midsummer, with the gills already much reduced. The complete metamorphosis takes place in the autumn of the same year. These little newts can, according to Wilder,[^[48]] be collected all the year round, in Massachusetts from March to December, except during the time of deep snow. They are nocturnal and are easily kept.

Fig. 19.–Desmognathus fuscus; female with eggs in a hole underground. × 1. (After Wilder.)

Thorius pennatulus, from Orizaba, Mexico, the only species, is noteworthy for its extremely large nostrils, and for the tongue, which is supported by a central pedicle, free all round, and ending in a thick knob, which can probably be protruded. The limbs are weak, and the digits are also much reduced. Total length, under 2 inches, or 50 mm.

Typhlotriton spelaeus, of the Rock House Cave in Missouri, is blind, the eyes becoming concealed by the skin during metamorphosis, when the gills are lost.

Sub-Fam. 2. Plethodontinae.–The five genera of this almost entirely American sub-family (only one species of which, Spelerpes fuscus, occurs in Europe) can be distinguished as follows:–

I. The tongue is attached by its central pedicle only, is free all round, ends in a soft knob and can be shot out to a considerable distance.

With 5 toes: Spelerpes, p. [104].

With 4 toes: Manculus, p. [106].

II. The tongue is attached along the middle line and cannot be protruded out of the mouth.

Jaws with numerous small teeth.

With 5 toes: Plethodon, p. [106].

With 4 toes: Batrachoseps.

Maxillary and mandibular teeth few in number but very large.

With 5 toes: Autodax, p. [107].

Spelerpes.–Except in a few species the limbs are well developed and possess 4 fingers and 5 toes, which are either free or webbed. But in the Colombian S. parvipes, still more in S. lineolus of Orizaba and S. uniformis of Costa Rica the limbs and digits are reduced to mere vestiges, and are practically without function, the body, with the extremely long tail, having assumed a wormlike shape. The young of many, if not all, species have a pair of short balancers below each nostril; in the adult these organs are reduced to little swellings or lost completely. Several species are lungless, see p. [46].

The geographical distribution of this genus, of which some twenty species are known, is very remarkable. The majority live in Mexico and in the United States, a few are found in Colombia and Northern Peru (S. altamazonicus and Plethodon platense being the only Urodeles hitherto recorded from south of the equator), one in Hayti (S. infuscatus), two (S. subpalmatus and S. uniformis) in Costa Rica, and S. fuscus in Europe.

S. bilineatus is a little newt under 4 inches in length–60-95 mm.–found in the Atlantic States. It is brownish-yellow above, with a black lateral line extending from the eye to nearly the end of the tail. The under parts are bright yellow. It lives on land, in damp places, concealed during the daytime under stones or old trees, whence it emerges after a rain or in the dusk of evening.

According to H. H. Wilder,[^[49]] "the eggs are deposited in May and June in a single layer upon the lower side of submerged stones, each batch containing 30 to 50 eggs. The stones which are suitable for this purpose must be in the form of an arch, allowing the water to flow beneath. They are generally in the more rapidly flowing portions of the brook, but the depth of water must be such that the eggs are at all times entirely submerged. They are attached to the stone by gelatinous threads, proceeding from the outer envelope, and although they are generally contiguous, they are each attached separately." The eggs are holoblastic. The larvae hatch early and continue for a long time in the larval state, probably two or three years.

S. porphyriticus s. salmoneus.–Yellowish-brown or purplish-grey above with tiny darker dots and markings. The sides of the body are salmon-coloured, with a tinge of yellow. The under parts are whitish, turning into salmon-pink on the tail. This beautiful newt reaches about 6 inches in length and has a very moist, slimy skin, which, combined with the lively motions of the creature, make it as slippery as an eel. It is found in the Alleghany range, from New York to Alabama.

Specimens which I am keeping prefer the wettest part of the cage, where they lie concealed in the moss and mud, leaving their hiding-places at night in search of insects. One of them escaped into the greenhouse and was discovered after nine months, having established its permanent home in a cleft between mossy stones: when the sweepings of a butterfly-net are emptied near its hiding-place it peeps out and with a flash of its long, forked, white-coloured tongue it secures its prey. Occasionally it goes into a tank, when it swims with rapid, undulating motions, the limbs being laid back and remaining inactive; it sometimes rises to the surface to emit and to take in air, but, although mostly resting half in the water, upon a rotten stump, it often lies for hours at the bottom without stirring. When kept in dry surroundings, the skin soon dries and wrinkles, and the animals show every sign of suffocation and general discomfort. The respiration of this lungless species by means of rapid movements of the throat is very limited, most of the necessary oxidisation of the blood being effected through the skin.

S. fuscus.–This, the only European species, is thoroughly terrestrial. It is found in the mountains bordering the Gulf of Genoa, and in Sardinia. Its total length remains under four inches. The smooth, very delicate and easily broken skin is brown above, light below, and speckled with lighter and darker markings. Below each nostril is a slight swelling, the remnant of the cirri or balancers common to the young of many species. It lives in shady surroundings, under stones, in old trees and in limestone-caves, glued to the walls with spread-out toes, belly and tail, quietly waiting for insects and spiders which it catches by flashing out the long tongue.

According to J. Berg,[^[50]] it keeps well in cool, moist and well-ventilated places. It lives on flies, small beetles, and maggots; ants are also taken at once, probably owing to their lively movements, but a few minutes later the newts roll about in spasms and soon die. Towards the end of March one of Berg's specimens gave birth to four young, which were 36 mm., or nearly 1½ inches long, and differed from the adult only by their exceptionally large nostrils, thereby resembling the Mexican Thorius. The little ones shot out their tongues about 10 mm., feeding on Aphides.

Fig. 20.–Spelerpes fuscus, showing the position and shape of the partly and fully protruded tongue. The figure on the right side shows the tongue and the skeleton of the hyoid apparatus. B, the threadlike, elongated, first branchial arch; H, hyoid, in reality attached by its outer end to the vicinity of the quadrate; T, tongue. About × 2. (After Berg and Wiedersheim.)

Manculus.–The two species of this genus live in Carolina and Florida. M. quadridigitatus is a very slender, graceful little animal, about 3 inches in length, the long and thin tail being considerably larger than the rest of the body. Yellowish, minutely speckled with brown above and on the sides, greyish-white below. Life entirely terrestrial.

Plethodon.–About seven species in North America. This genus has given its name to that of the subfamily, which might with more reason be called Spelerpinae.

P. glutinosus is slaty or bluish-black, with small whitish specks, especially on the sides of the trunk, where they are large and often confluent. The skin is smooth and shiny. Total length about 5 inches, half of which belong to the tail. Holbrook considered this as one of the commonest of the North American newts, and mostly widely distributed, from Ohio to the Gulf of Mexico. It usually lives concealed under stones, but prefers fallen trees, probably on account of the insects upon which it preys. When taken in the hand it gives off a great quantity of slime.

P. erythronotus extends into Canada and is much smaller. Brown or grey above, mostly with a broad, reddish-brown band over the head, back, and tail. The under parts are white, with grey and brown specks.

Autodax s. Anaides.–The large tongue is attached along the median line. The jaws are furnished with few, but surprisingly large, knife-shaped teeth, about ten in the upper and fewer in the lower jaw. The small teeth of the vomers form a chevron-shaped series behind the choanae, those of the parasphenoid stand in one elongated patch. The tail is round; number of toes, five. Three species in Western North America, from California to Oregon.

A. lugubris.–The eyes are very large and prominent. The upper jaw shows a peculiar recess on either side for the reception of the large lower teeth. The skin is smooth, devoid of parotoid glands, but has a strong gular fold. The upper parts are dark brown or lead-coloured, with whitish dots on the sides; under parts white. Total length some 6 inches, about half of which belongs to the tail. The fingers and toes are very rich in subcutaneous venous sinuses.

The habits of these creatures are in many respects peculiar. Van Denburgh[^[51]] says of A. iecanus "that it usually moves quite slowly, moving one foot at a time, but is capable of motion surprisingly rapid for a salamander. When moving rapidly, it aids the action of its legs by a sinuous movement of its whole body and tail. The latter is prehensile. Several individuals, when held with their heads down, coiled their tails around my finger, and, when the original hold was released, sustained themselves for some time by this means alone. One even raised itself high enough to secure a foothold. This animal's tail is also of use in another way. When caught, it will often remain motionless, but if touched, will either run a short distance with great speed, or quickly raising its tail and striking it forcibly against the surface on which it rests, and accompanying this with a quick motion of its hind-limbs, will jump from four to six inches, rising as high as two or three."

Ritter and Miller[^[52]] have made extensive observations on the life-history of A. lugubris. When wishing to pass from the hand to the table, the creature will frequently execute a well co-ordinated spring and alight on its feet some distance away, instead of falling over the edge in the typical salamander-fashion. This species is nocturnal and entirely terrestrial, and seems to be indifferent even to proximity to water. Rotten stumps and logs are the habitations preferred, and wherever these occur in the region about San Francisco Bay, even though at the places remotest from water, specimens are sure to be found.

The eggs are laid in a hollow under ground, and the female seems to remain curled around them until they are hatched, which takes place in two or three weeks. The specimen observed by Ritter and Miller laid 19 eggs. Each was contained in a gelatinous capsule 6 mm. in diameter, and was firmly anchored to a clump of earth by a narrow peduncle about 8 mm. long. The embryos developed very large gills, each being composed of three broad membranous lobes, the latter being thin and delicate, much expanded, highly vascular and widely confluent at their bases, so that the gills of each side really form one three-lobed mass. Their dorsal surfaces are applied to the inner surface of the egg-capsule. The amount of food-yolk is considerable. The whole larval life is passed through within the egg. Before the young is hatched the gills wither and cease to be functional, and the gill-slits close up. The tail is round, and shows no indication of a fin at any time during the larval period. Newly hatched individuals appeared much distressed when put into water, and were quite unable to swim. They immediately sank to the bottom and remained there until they were removed. The integumentary sense-organs, so well developed in the aquatic larvae of Urodeles, are entirely wanting. When hatched the young creature is about 32 mm. long; its general colour is blackish-grey, finely sprinkled with bluish-silver. During the second year this garb is changed to the dusky brown of the adult, and the fine silver speckling is replaced by much larger and less numerous yellow spots.

Although one of the most terrestrial of Urodeles, this species is lungless, but the skin remains delicately smooth and moist throughout life. According to the observers quoted, the pharynx plays an important part in respiration. From 120 to 180 or even more vibrations are made by the throat in a minute, and in some cases these movements are grouped into series of about 20 to 25 extremely rapid vibrations, with periods between each two series.

Subfam. 3. Amblystomatinae.–Composed of seven closely allied genera, the distinguishing characters of which are the grouping of the palatal teeth and the number of the toes, which varies between 4 and 5. The geographical range of the subfamily extends over the whole of North America and Mexico and over the whole of Northern Asia, from Kamtchatka and Japan westwards to the Ural, and southwards into China. The occurrence of one species, Amblystoma persimile, in the mountains of Siam, makes it highly probable that other species and genera exist in the hitherto unexplored intervening countries.

Boulenger gives the following synopsis:–

III. The series of palatal teeth converge backwards, forming a V-shaped figure.

With 5 toes: Hynobius, 3 species in Japan.

With 4 toes: Salamandrella, 2 species Lake Baikal, Ussuri and Schilka rivers, and Kamtchatka, p. [109].

III. The series of palatal teeth form an uninterrupted, doubly arched V-shaped figure.

The 4 fingers and 5 toes are furnished with black, horny claws: Onychodactylus japonicus.

III. The series of palatal teeth form two arches, convex forwards, separated by a wide interspace.

The two series are short, confined to the space between the choanae.

With 5 toes: Ranidens sibiricus, Eastern Siberia and N.E. China.

With 4 toes: Batrachyperus sinensis, Moupin in China.

The series are long and converge backwards, 5 toes: Dicamptodon ensatus, California.

IV. The palatal teeth are arranged in a nearly straight, transverse line, or they form an angle which points slightly forwards; they are not separated by a wide median space. With 5 toes: Amblystoma. Some 16 species in North and Central America, one in Siam, p. [110].

Salamandrella keyserlingi.–The mode of propagation of this newt-like species has been observed by Shitkow near Jekaterinburg in the Ural mountains. The eggs were laid at the end of April and were deposited in bags, which were attached to a plant, with one end about an inch below the surface of the water. The bag measured 15 cm. in length and 2 cm. in width and contained 50 to 60 eggs. The larvae were hatched in 14 days in a sunny aquarium; in another with a northern aspect the hatching took 23 days. The larvae were 10 mm. long, and remarkable for the length (1 mm.) of their balancers.

Amblystoma opacum.–The general shape is very much like that of the European Spotted Salamander. The head is short and broad, the snout is rounded. The eyes are very prominent, with a black pupil and a dark-grey iris. The neck has a well-marked gular fold. The tail is thick and almost round. The hind-limbs are considerably larger than the fore-limbs. The general colour of the shiny, moist skin is a purplish-black with light grey, transverse, partly confluent bars, giving the creature a pretty appearance; the under parts are paler, bluish-grey. Total length between 3 and 4 inches, or 9 cm.

This beautiful species inhabits many of the United States east of the Rocky Mountains, from New Jersey to Florida and Texas. In the perfect state it is thoroughly terrestrial and easily kept. My specimens prefer the holes of rotten and moist, moss-covered stumps, or holes beneath stones, which they leave, at night only, in search of earthworms and insects.

A. talpoideum is closely allied, somewhat stouter and almost uniform brownish-back. According to Holbrook, "it chooses light soil in which it will bury itself in a few seconds like a mole, and there continue its course concealed from view; but its track can often be followed by the elevation produced on the surface of the soil, similar to that seen in fields infested by moles."

Fig. 21.–Egg-sac of Salamandrella schrenki. × ½. (After Shitkow.)

A. punctatum is bluish-black, with a row of roundish yellow spots on each side of the body and tail and upon the limbs.

E. A. Andrews[^[53]] has made observations upon the breeding of this species. Near Baltimore the eggs are very abundant in March and even in February, in small pools in the woods, but the adults are then rarely seen. Even when small pools, but 4 feet wide and 9 inches deep, were thoroughly raked out before and after the eggs appeared, no adults were found, so that it is to be inferred that the laying takes place in the night and that the adults leave the water every day to conceal themselves under stones. One female was found moving away from a bunch of eggs early in the morning. This specimen was kept isolated, and laid many eggs, and as these developed into normal larvae, the existence of internal fertilisation was proved. Previously to the laying of the eggs white spermatophores were found in the small pools, on the dead twigs and leaves covering the bottom.

A. jeffersonianum.–This very slender and slippery species, reaching a length of 6 inches, is remarkable for its long fingers and toes, and its rather compressed tail. The general colour is brown above, dirty whitish below, generally with numerous, small, light blue and pale brown spots on the sides of the neck, body, limbs, and tail. There are several colour-varieties, one of them with white specks. It is a very active and surprisingly good climber, easily escaping out of high-walled bell-glasses, hiding in the daytime in dark and moist localities. Its range extends from Indiana and Virginia to Quebec.

A. persimile.–This species is remarkable on account of its geographical distribution. It is the only non-American species, inhabiting the higher mountains of Siam and Upper Burmah. There is no doubt about its belonging to the genus Amblystoma, although it had originally been described as a Plethodon. It closely resembles A. jeffersonianum in most of its characters, notably in the arrangement of the palatal teeth, general proportions, slender toes, and even in the presence of whitish spots, which are scattered over the sides of its blackish, smooth skin.

A. tigrinum.–This, the commonest species, is conspicuous for its large, depressed head, which is as broad as it is long, its width being enhanced by the unusually large parotoid glands. The mouth is very wide. The large, prominent eyes are golden, and reticulated with brown. The gular fold is strong. The limbs are stout, the fingers and toes short. The trunk is strongly constricted by twelve intercostal grooves. The tail, which is as long as the rest of the body, is somewhat compressed laterally, but bears no trace of a fin. The general colour is more or less dark brown or bluish black, marked with numerous yellow spots and large blotches; the under surface inclines to grey. The length of the adult male is about half a foot; the females, as usual being larger, sometimes reach the length of 9 inches. The range is from New York to California and to Central Mexico.

The larva of this species is the famous Axolotl. It is provided with three pairs of delicate and much-branched external gills, a flat, long tail with a broad ventral and dorsal fin, the latter extending along the back almost to the neck. The limbs, although comparatively slender, are fully developed, and the head is much more pointed than it is in the perfect form. The larvae usually reach 8 or 9 inches in length; exceptional specimens have been recorded of one foot in length, and have been described as Triton ingens.

Fig. 22.–Axolotls or larvae of Amblystoma tigrinum. × ½.

These larvae were found by the Spanish conquerors to occur in great numbers in the lakes near Mexico City, and were called Axolotl by the natives, a word signifying "play in the water." They were, and are still, eaten, either roasted or boiled, with vinegar or cayenne pepper.

For many years these creatures were looked upon as a species of the Perennibranchiata, under the generic name of Siredon (S. axolotl, s. pisciformis, s. mexicanus, etc.), although Cuvier suspected that they were but the larvae of an otherwise unknown terrestrial Urodele. The mystery was not cleared up until the year 1865, when some Axolotls which had been kept for a year in the Jardin des Plantes at Paris, suddenly began to pair, and laid eggs which within six months developed into full-sized Axolotls. This certainly looked as if these creatures were not larvae, but a true Perennibranchiate species. But to the general surprise several of these young Axolotls gradually lost their gills, the clefts closed up, the fins of the back and tail disappeared, the head became broader, the creatures left the water permanently, and in fact turned into the already well-known terrestrial Amblystoma tigrinum. The other brothers and sisters of the same brood remained aquatic Axolotls, which thereby revealed themselves after all as the larval and not as the perfect stage of this remarkable species.

At the suggestion of Kölliker and Weismann, Frl. Marie von Chauvin[^[54]] undertook, at the University of Freiburg, long and carefully conducted experiments, showing (1) that little Axolotls can comparatively easily be caused to develop further into the perfect Amblystoma if they are induced to breathe air more frequently than usual; shallow vessels, perhaps also insufficiently aerated water, will produce the desired result; (2) that the commencing metamorphosis can again be checked, the shrinking gills then undergoing fresh development; (3) that they can be forced to remain Axolotls; (4) that the cutting off of the gills has no influence upon their possible metamorphosis, the gills being easily and quickly renewed. The same lady found also that Amblystoma, the perfect form, lives in the water during the pairing time and behaves in the same way as the Axolotls.

The latest observations have been made by Metzdorff.[^[55]] Axolotls, at least those which are kept in captivity in Europe, are ready for propagation several times in the year, either in the spring, from April to June, or in December. The male deposits spermatophores, which in the following night are taken up by the female into the cloaca. On the following day, preferably in the afternoon, she grasps a suitable leaf, for instance that of Vallisneria, with the hind-limbs, and presses it against the vent. The eggs are expelled by strong wriggling movements of the body, and are formed into three or four packets of six to ten eggs each, so that about thirty eggs are laid at one sitting. Then she takes a rest before proceeding again; the whole process, in which the male takes no further interest, lasting about two days. The most suitable temperature is one of 18-20° C., or about 68° F. The water must be well aerated. Sterile eggs turn white on the second day. The little larvae are hatched in about a fortnight. Eggs which are kept in a higher temperature, from 22-24° C., develop more quickly, but the resulting young are smaller; they show already on the fifth day head, tail, and the beginning of the gills. According to Bedriaga, they live at first upon Infusoria and Daphnia; when they are 20-25 mm. long they eat Tubifex rivulorum; later on they take scraped meat and are liable, when hungry, to nibble off each other's gills, but these are easily reproduced. When 20-25 cm. long, at the age of about six months, they are able to breed. The chief point of interest is the fact that this species of Amblystoma frequently remains throughout life in the larval state, except that it develops generative organs. The natural causes of this retention are not completely known. According to Shufeldt, who observed them under natural conditions near Fort Wingate in New Mexico, plenty of food, the drying up of the swamps, and the increasing temperature of the diminishing water, hurries on the metamorphosis, while deeper water retards it. Weismann[^[56]] suggested that the specimens in the Mexican lakes which remained Axolotls were prevented from becoming perfect Amblystomas on account of these lakes, after the disappearance of the surrounding forests, having receded from their former boundaries, which are now covered with a saline, uninhabitable crust. This may be an explanation, although Axolotls do not live in brackish water. But Weismann went farther, and with his well-known dialectic powers has succeeded in spreading the belief not only that the Axolotl is a case of reversion to an ancestral stage, but that the present Amblystoma, instead of being the progressive, perfect form, is likewise a case of reversion. A reversion from a reversion! The whole line of evolution would then be as follows: Amblystoma; its young, owing to adverse circumstances, revert to the stage of the Perennibranchiate ancestors of all Urodela; if some of these Axolotls lose their gills and fins, they revert thereby into the original Amblystoma. Surely a roundabout way of explaining a curious but after all rather simple process of Neoteny; cf. p. [63].

Observations on the metamorphosis of Siredon lichenoides into Amblystoma mavortium have been made by Marsh, who also gives figures of the larval and adult forms.[^[57]]

Sub-Fam. 4. Salamandrinae.–The six genera of this subfamily fall into two natural groups: I, True Salamanders, with the palatal teeth arranged in a pair of S-shaped figures, and without a fronto-squamosal arch. II, Tritons, with the palatal teeth in the shape of a Λ, i.e. the right and left series meet at an angle; the fronto-squamosal arch is present, either bony, or at least ligamentous. Triton cristatus is, however, exceptional, in that the two palatal series often do not meet and that the arch is absent. The number of fingers is universally four, that of the toes is five except in Salamandrina, which has only four.

The geographical distribution of the sub-family, entirely Periarctic, may be said to be the reverse of that of the Amblystomatinae. Of the twenty-five species namely, only two are American, four are Eastern Asiatic, and of the remaining nineteen, two are Algerian, while the rest live in Europe or in Asia Minor. It is in fact an essentially Palaearctic group.

The six genera can be distinguished as follows:–

II. The palatal teeth are arranged in two S-shaped curves. True Salamanders.

Tongue short and thick. Salamandra, p. [115].

Tongue long and projectile. Chioglossa, p. [121].

II. The palatal teeth are arranged in a Λ shape. True Tritons.

With only four toes. Salamandrina, p. [122].

With five toes.

Pterygoids separated from the maxillary and quadrate bones: Triton, p. [122].

Pterygoids touching the maxillae and quadrates. Himalo-Chinese: Tylototriton, p. [132].

Pterygoids united broadly with the maxillae. Chinese: Pachytriton, p. [132].

Salamandra.–Without fronto-squamosal arch. Five toes. Tail round. Three species in Europe and Western Asia.

S. maculosa.–The Spotted or Fire Salamander. General habit stout. Usual length about 5 to 6 inches; the females are mostly larger than the males; specimens of more than 8 inches in length are giants. Head as broad as it is long, snout rounded. Limbs and digits stout and short. The skin is smooth, shiny and full of pores, with a strong gular fold. The parotoid glands are large and covered with large pores. A series of distinct swellings, or cutaneous glands, each with a distinct opening, extends along either side of the back, and a shorter series along the flanks. The general colour of the Spotted or Fire-salamander is black, with irregular, large yellow patches on the back and limbs. These markings vary extremely, so much so that scarcely two specimens, collected at random, are alike. In some the yellow patches form two more or less regular bands, in others they are partly confluent; again the yellow may be preponderant on the back or much restricted. Occasionally the chrome-yellow is replaced by orange. The under surface is as a rule bluish grey-black. This combination of shiny yellow and black is a good instance of warning colours. The creature is poisonous, cf. p. [38]. When left in peace, or handled gently, it is perfectly harmless, but when treated with violence, or submitted to severe pain, a milky white fluid exudes from the glands and is, under violent contractions of the muscular skin and body, sometimes squirted out in fine jets to the distance of a foot. Burning pain and subsequent inflammation result if this poison gets into the eye. The same applies to the mucous lining of the mouth and throat. A few drops of this poison introduced into the blood or into the stomach of a small animal are sufficient to cause its death. Cold-blooded animals are as susceptible as warm-blooded creatures.

I once put two American bull-frogs into the same outdoor enclosure with a large number of salamanders. Next morning the huge frogs were found dead, each having swallowed a salamander, which they were not acquainted with and had taken without suspicion.

The Fire-salamander has a wide range, namely the whole of Central, Southern, and Western Europe with the exception of the British Isles. It extends southwards into Corsica and Algeria, eastwards through Asia Minor into Syria. Where it does occur it is rather common, provided the terrain is mountainous or hilly and covered with vegetation. There it lives under moss or rotten leaves, in the roots of old trees, in the cracks and clefts of the ground, of rocks or of ruins of buildings; in default of anything better under heaps of stones, or in the holes dug by mice or moles. One chief necessity for its happiness is moisture.

The salamander does not occur everywhere, but is rather local. On certain kinds of limestone it is rare or absent; granitic terrain and red sandstone seem to suit it best, for instance the Hartz Mountains, Thuringia, and Heidelberg are favourite localities. But even there we may spend days and weeks and never come across a single specimen. We may turn stones, rake up the moss and leaves, pry into cracks, and we unearth perhaps a few sorry-looking, listless, dull and dry, half-emaciated creatures. The same place after a thunderstorm will be literally swarming with sleek, lively salamanders, in search of earthworms and all kinds of insects, especially at dusk or during the night. They disappear in the autumn, in October, to hibernate in the ground, out of the reach of frost, and they reappear again in April. Later on they congregate at little springs, always at running water, to reach which they have often to make long migrations. This is the only time when these thoroughly terrestrial creatures approach water, in which they easily get drowned.

Although this species is so common its mode of reproduction has been satisfactorily discovered only quite recently. There are some puzzling facts which it took a long time to observe correctly and to interpret. The larvae are born in April, May, or June, while there are no eggs in the oviducts, but in July these are full of fertilised eggs before copulation takes place. This seems contradictory. The explanation is as follows. In July there is an amplexus of the sexes, short, and often on land–a sort of preliminary exciting performance. Both sexes then descend into the water, but generally remain on land with the fore part of the body. The male deposits a spermatophore and the female takes part of this into its cloaca. In the case of a virgin female the eggs are fertilised in the oviduct and ripen until the autumn, but the larvae nearly ready for birth remain within the uterus until the following May, i.e. about ten months. The mother then crawls half into the water, mostly at night, and gives birth to from a few to fifty young, fifteen being perhaps the average. The young are surrounded by the egg-membrane, which either bursts before or shortly after expulsion. This species is consequently viviparous in the proper sense. If she produces a few young only, say from two to five, these are much larger and stronger than those of a large litter. Occasionally a few addled or only partly developed eggs are also expelled.

In the case of old females which have produced offspring before, the whole process is more complicated. The sperma, taken up in July, remains in the receptaculum of the cloaca until the May or June following, i.e. until the previous larvae have passed out of the uterus and are born. Then the spermatozoa ascend to the upper ends of the oviducts, where they meet and fertilise the new eggs. After these have descended into and filled the uterus, and are already developing into embryos, copulation takes place again in July, preparatory for next year's eggs.

The new-born salamanders have three pairs of long external gills, a long tail furnished with a broad dorsal and ventral fin, and four limbs, although these are small. The total length is about 25 mm. or 1 inch. The general colour is blackish with a pretty metallic golden and greenish lustre. The little creatures are very active, and at once eat living or dead animal matter. In captivity they are liable to nibble each other's gills and tails. During the first six or eight weeks they assume a row of dark spots on the sides; these spots enlarge, and the whole skin becomes darker. Yellow spots appear next, first above the eyes and on the thighs, later upon the back; the ground-colour at the same time becomes black, until at the beginning of the fourth month they look like the parents.

The metamorphosis is very gradual. The tail-fin diminishes first, but the gills grow until shortly before the little creatures leave the water. Darkness, cold, and insufficient food retard the metamorphosis, sometimes until October. It is easy to rear them artificially provided they are well fed, kept in a light place, and in clean, well aerated water. If prevented from leaving the latter, for instance when kept in a glass vessel with vertical walls, or if hindered by a piece of gauze from rising to the surface and taking in air, they can be kept as larvae well into the winter.

Very young, perfect little salamanders, of from 1 to 2 inches in length, are excessively rare; even specimens of 3 inches are far from common. They probably spend the first two or three years of their life in careful seclusion.

A few adults can be easily kept for many years in shady places provided with moss, rotten stumps and stones, to afford them suitable moist and cool hiding-places, and they readily take earthworms, larvae of beetles, snails, woodlice, etc. But any attempt to keep them in large numbers ends in failure. They congregate together in clumps, all making for the same cavity or recess, as if that were the only one in existence (very likely they are right in so far as that place is probably the best), and they get rapidly enlarging sores, chiefly on the elbows and knees. These are soon infested with fungoid growths, and this disease spreads like an epidemic and soon carries them off.

S. atra.–The Alpine Salamander differs from the Spotted Salamander by its uniform black colour and smaller size, which averages between 7 and 5 inches. It is restricted to the Alps of Europe, from Savoy to Carinthia, at from 2000 to as much as 9000 feet elevation, living with predilection near waterfalls, the spray of which keeps the neighbourhood moist, or in mossy walls, in the shade of forests near brooks, or under flat stones on northern slopes. The most interesting feature of this species is that it produces only two young at a time. These are nourished at the expense of the partially developed eggs in the uterus, and they undergo their whole metamorphosis before they are born. By far the best and most complete account of this mode of propagation has been given by G. Schwalbe.[^[58]] The length of the ripe embryos is about 45 mm.; they lie mostly bent up, with their heads and tails turned towards the head of the mother. The gills are beautiful, delicate red organs, the first pair being generally directed forwards and ventralwards, the second upwards, the third backwards; they are longest when the creature is about 32 mm. long, while there is still much yolk present. At this stage the gills are so long as to envelop nearly the whole embryo. There is rarely a second embryo in the same uterus, and an extra foetus is generally smaller, frequently a monstrosity not fit to live; it is probable that it is not used as food, but that it is expelled at parturition. The embryo passes through three stages, (1) still enclosed within its follicle and living on its own yolk, (2) free within the vitelline mass which is the product of the other eggs, (3) there is no more vitelline mass, but the embryo is possessed of gills 10-12 mm. in length, and is still growing. During the second stage the yolk is directly swallowed by the mouth. The walls of the maternal uterus are rather red. The exchange of nutritive fluid takes place through the long external gills, which thereby function in the same way as the chorionic villi of the Mammalian egg. Each gill contains a ventral artery and a dorsal vein, each of which looks like the midrib of a pinnate leaf; there is also a fine nerve and a weak bundle of striped muscular fibres. Each gill-filament receives a capillary artery which extends to the epithelium of the tip, where it turns into a capillary vein. The epithelium of these filaments, which are full of blood, is ciliated, the resulting current being directed from the base towards the tip. In older larvae this ciliation becomes restricted to the tips. The body of the gills is furnished with flat epithelium, these non-ciliated portions alone are closely appressed to the uterine wall, and it is here that the exchange of gas takes place between mother and larva. The nutrition takes place through the gills, as they are bathed by the yolk-mass.

Schwalbe also explains the whole question of the reduction of the number of embryos. He says rightly that in S. maculosa, which gives birth to many young, there are in the oviduct many eggs which have only partly developed into embryos, and these, perhaps from want of room and nourishment, degenerate into the irregularly shaped whitish-yellow bodies which are occasionally found packed in between the developing embryos. Consequently all those eggs had been fertilised near the ovaries. S. atra exhibits a further stage in so far as most of the eggs, fertilised above in the oviduct, degenerate, and only two or three become fully developed. These few embryos live on the degenerating eggs, which together produce the vitelline material spoken of above. The two full-grown and metamorphosed embryos, each measuring about 50 mm. in length, are equivalent to the numerous new-born larvae of S. maculosa, especially if the smaller size of the adult Alpine Salamander is taken into consideration.

Mlle. von Chauvin[^[59]] has experimented with the unborn larvae of this Salamander. She cut out 23 larvae and put them into water. One of them, already 43 mm. long, took earthworms on the next day, and the beautiful long, red gills became pale and shrunk, and on the third day were cast off close to the body. New gills sprouted out on the same day, first in the shape of three tiny knobs on either side. After three weeks they had become round globes, which gradually sprouted out into several branches, far shorter and more clumsy than the original gills. During the whole time the larva was lying quietly at the bottom, in the darkest corner, but showed a good appetite. The fin of the tail disappeared and was supplanted by a stronger one. In the sixth week the skin was shed in flakes, and this process took fifteen days. This larva lived in the water for fourteen weeks and grew to 6 cm. in length! When the new gills gradually shrank, the compressed and finny tail assumed a round shape, the skin became darker and shinier, and after the larva had again shed its skin, there appeared the dark rugose skin of the typical S. atra. The gills were reduced to useless appendages–not cast off–and the creature crawled out of the water. A fortnight later the gill-clefts were closed. A second larva behaved similarly, first casting off the feathery gills, substituting a new and stronger set, which, however, fourteen days after excision from the uterus, shrank again, and on the nineteenth day the gill-clefts were closed. The lady also observed that nearly ripe larvae, when cut out, rushed about in the water and ate, just like the new-born larvae of the Spotted Salamander.

A third species, S. caucasica, is found in the Caucasus. It rather resembles the Spotted Salamander in coloration, but has a larger tail and lacks the lateral warts. The male is remarkable for the possession of a soft permanent knob or hook at the top of the root of the tail. This pommel possibly prevents the slipping off during the amorous amplexus, provided the sexes then entwine like certain Tritons.

Chioglossa lusitanica.–The only species of this genus is restricted to the north-western third of the Iberian peninsula. This graceful, slenderly-proportioned and beautiful Salamander is apparently very rare and local, having hitherto been found at a few places, namely, near Coimbra, Oporto and Coruña. It lives under moss, and runs and climbs with an agility surprising in a Urodele. The tongue is long, ending in a fork, and is supported by a median pedicle so that the tip can be quickly protruded to the distance of more than an inch. The whole length of the animal is about 5 to 6 inches, two-thirds of which belong to the long tail, which is compressed at the end. The skin is smooth and shiny, with a gular fold and large parotoids. The general colour is a rich dark brown, with a pair of broad reddish-golden bands along the back and tail, the bands being separated by an almost black vertebral line.

The few specimens which I have been lucky enough to observe made little holes or passages in the moist moss of their cage, peeping out with their heads in wait for little insects, which they caught with flash-like quickness. They seem to be crepuscular.

Salamandrina perspicillata.–This genus, represented by one species, a native of Liguria and Northern Italy, possibly extending into Dalmatia, is the only Salamander which has but four toes. The skin is not shiny and smooth, but is finely granular and dry, forms no gular fold, and is devoid of parotoid glands. The tail is more than half the length of the animal, which measures from 3 to 4 inches. The general colour is black-brown with a broad V-shaped orange-yellow mark extending from eye to eye over the occiput. A faint irregular yellowish line extends along the middle of the back and tail. The throat is black, with a diffused white patch in the middle; the belly is white, with black dots; the anal region, the inner sides of the legs and the under side of the tail are carmine-red.

This slender and pretty Salamander is diurnal, and feigns death when discovered. Only the female goes into the water, in March, to glue the eggs on to submerged rocks or water-plants. The young finish their metamorphosis by the month of June, and reach full size during the winter, the climate of their home being sufficiently genial to make hibernation scarcely necessary.

Triton s. Molge.–The tail is strongly compressed and frequently has a permanent fin. The fronto-squamosal arch is variable, it being either bony as in the South European, Eastern and American species, or reduced to a ligament, or lastly absent as in T. cristatus. The males of all the English Newts, of T. vittatus and of T. marmoratus, develop a high cutaneous crest on the back and tail during the breeding season, and this crest acts not only as a swimming organ and ornament, but also as a sensory organ.

The whole genus comprises some eighteen species, twelve of which are European, although some of these extend into Western Asia; T. pyrrhogaster and T. sinensis are found in N.E. China, the former also in Japan; T. poireti and T. hagenmuelleri live in Algeria, and only two, T. torosus and T. viridescens, are North American. Some of the species have a limited range; thus T. montanus is confined to Corsica, T. rusconii to Sardinia, T. boscai to the north-west of the Iberian peninsula and T. asper to the Pyrenees.

Newts all prefer moisture without heat. During the pairing season they take to the water, mostly to stagnant pools, which sometimes implies long migrations. During this period, which is in some cases rather prolonged, they become thoroughly aquatic and undergo some important changes. The tail-fins are much enlarged; in the males of some species a high cutaneous fold grows out on the back, devoid of muscles, but rich in sense-organs. The whole skin, instead of being dry, possesses numerous mucous glands and, what is of more importance, specialised sensory apparatuses which are arranged chiefly along the lateral lines of the body and part of the tail.

After the breeding season Newts become terrestrial, hiding in cracks, trees, or in the sandy soil. Some species aestivate during the hot and dry season. They hibernate either in the ground, or occasionally in ponds. T. vulgaris is difficult to keep in the water beyond the pairing season, while this is easily done with T. alpestris and T. cristatus; T. waltli can live in the water for years. The food consists of all kinds of insects, centipedes, worms, snails, etc., which are searched for chiefly at night. It is astonishing to see a little Triton getting hold of and gradually swallowing a wriggling earthworm almost as thick and as long as itself. When two newts seize the same worm, as these voracious and jealous creatures often do, each gets hold of one end, and swallowing as much as it can, twists and rolls round in a direction opposite to that of its rival, until the worm breaks, or until the jaws of the two newts meet and the stronger of the two draws it out of the weaker one and swallows the whole worm. They do not drink, but soak themselves in the water.

The skin is shed periodically, and rather often by the rapidly growing young; by the adult, during the life in the water, rarely during the sojourn on dry land. The skin breaks round the mouth; assisted by the fingers and by contortions of the body, it is then slipped backwards over the trunk and tail, whereupon the newt seizes the skin with the mouth, draws the shirt off entirely, and–swallows it. Such freshly shed skins are very delicate and pretty objects when suspended in water or some preserving fluid. The shed skin, consisting only of the outermost layer of the epidermis, is entire, but turned inside out, with fingers and toes complete, the only holes being those for the mouth, eyes, and vent.

None of the Tritons are viviparous. The eggs, which are glued singly or in small numbers on to stones or water-plants, are hatched in about a fortnight, sooner or later according to the species and the prevailing temperature. The larvae are always provided with three pairs of branched external gills; the fore-limbs appear much earlier than the hind-limbs. Most, perhaps all, larvae develop two pairs of thread-like protuberances on the sides of the upper jaw, by means of which they attach or anchor themselves on to water-plants shortly after they are hatched. Thus moored they remain motionless in a slanting position, now and then wriggling their tails and shifting their place, or sinking to the bottom. The metamorphosis is finished during the first summer, and the little newts, often partially transparent, leave the water to hide under stones. Not unfrequently the metamorphosis is retarded and not finished by the autumn. The larvae of T. cristatus, especially when reared in ponds with abrupt or overhanging banks, so that they cannot leave the water, retain considerable remnants of the gills, still more frequently the clefts, although breathing chiefly by the lungs. Such individuals reach a length of 3 inches, and are larvae so far as the finny tail and the gills are concerned. They hibernate in this condition, and in exceptional cases reach sexual maturity;–at least the females, which develop ripe eggs; the males are not known to produce spermatozoa.

Much has been written on the amorous games of newts, but it is only recently that the mode of fecundation has been actually observed. Gasco[^[60]] placed the newts in glass vessels suspended from the ceiling of his laboratory. The antics of the enamoured male around the female, rubbing the latter with its head, or lashing it gently with the tail, and playing around it in its often beautiful nuptial dress, are meant to excite the female. The male then at intervals emits spermatophores, which sink to the bottom, and the female takes them up into its cloaca. For further information see p. [54].

Triton cristatus.–The Crested Newt has a slightly tubercular skin with distinct pores on the head, on the parotoid region and on a line along the side of the trunk. There is a strong gular fold. The general colour above is dark or black-brown with an olive tinge, interspersed with darker spots; the sides of the body bear irregular white spots. The under parts are yellow, almost always with large black spots. The iris is golden yellow.–The nuptial dress of the male is very striking. A high, serrated crest occurs on the head and body; the upper surface of the head is marbled with black and white; the under parts are orange-yellow with black spots, and the sides of the tail are adorned with a bluish-white band.–The female, always devoid of a crest, generally exhibits a yellow line along the middle of the back.–The average length of fully adult specimens is about 5-6 inches or 13-15 cm.; the females are as usual larger than the males; 144 and 162 mm. for an English male and female respectively are exceptional records.

Fig. 23.–Triton cristatus. 1, Female; 2, male in nuptial dress. × ⅔.

Propagation takes place in April. The newly hatched larvae are yellowish-green, with two black dorsal bands, and with a whitish edge to the tail-fin. By the middle of July they are about 5 cm. long, and the white-margined tail now ends in a thread 1 cm. in length. The general colour above is light olive-brown, dotted with black; the flanks and belly have a golden shimmer.

The Crested Newt has a wide distribution, extending from England and Scotland through Central Europe into Transcaucasia; the northern limits are Scotland and Southern Sweden. Although found in Greece and Lombardy, it does not occur in the Iberian peninsula nor in the South of France, where it is represented by the next following species.

Triton marmoratus.–The Marbled Newt is of the same size as the Crested Newt. Its ground colour is grass-green above, brown below, with numerous large and small irregularly shaped marbling patches, spots and dots of black. The crest of the neck and trunk is entire, not serrated, adorned with dark vertical bands, and separated from the high dorsal fin of the tail by a deep indenture or gap. The female has an orange line, slightly sunk in, instead of the crest. This newt is confined to France and the Iberian peninsula. In the North of Portugal and in Galicia it is frequently seen in little streams and ponds during the months of March and April. The rest of the year it spends on land. In France occur hybrids of this species and T. cristatus. They have been described as T. blasii.

T. alpestris.–The Alpine Newt is easily distinguished by the rich orange colour of its under parts, which are unspotted, excepting a few dark specks across the throat, below the gular fold. Specimens with many ventro-lateral black spots are exceedingly rare. All the upper parts are dark, but vary individually. The prettiest specimens are dark purplish grey, with black marblings; others incline more towards brown ground-tones, the blackish markings then appearing more prominent. The sides are often stippled with tiny whitish dots. The iris is golden yellow.–The nuptial male has a low, not serrated crest, which extends uninterruptedly from the nape into the dorsal fin of the tail. The crest is pale yellow, with black vertical bands and spots. The ground-colour of the upper parts inclines to blue, especially on the sides. The lower fin of the tail assumes an irregular band of bluish-white confluent patches.

This newt is rather small, females rarely exceeding 100 mm. or 4 inches in length. Its home is chiefly the hilly and mountainous parts of Central Europe, from Holland to Lombardy, Austria-Hungary, and Greece. Although it ascends the Alps to between 6000 and 7000 feet, it is also found in the Netherlands, but not in the North German plain.

T. vulgaris (s. taeniatus, s. punctatus).–The Common or Spotted Newt usually reaches 3 inches (7-8 cm.) in length. Boulenger's record-specimen measured 104 mm. It is characterised by the yellow, partly orange under surface, which is always spotted with black. The upper parts are olive-green or brown, inclining to white on the flanks; the black spots of the back, sides, and especially of the tail, are arranged in more or less distinct lines, giving a somewhat banded appearance to some females.–The breeding dress of the male shows a non-serrated, but "festooned" high and very wavy crest, which extends from the neck without interruption into the likewise wavy tail-fin. The tail is adorned with a lateral, glittering blue stripe, interrupted by vertical dark spots. The larvae are marked by a series of yellow dots, which extend over the lateral line and the tail, which latter temporarily possesses a terminal filament like that of the larvae of T. cristatus.

The distribution of the Spotted Newt is the same as that of T. cristatus, namely Europe with the exception of the Iberian Peninsula, and Western Asia.

T. palmatus s. helveticus.–This is the smallest of all the European newts, rarely reaching more than 3 inches in length. It is distinguished by several specific characters. The tail ends in a thread which is in some males 10 mm. in length, but is only just indicated in the female. The breeding male develops a cutaneous fold along each side of the back, and a low, entire, vertebral crest; the toes are fully webbed. The under parts are pale yellow, inclining to orange towards the middle of the belly, and with a few blackish dots. The lower caudal crest has its edge blue in the male, orange in the female. The general colour of the smooth skin is olive-brown above, with numerous dark spots, which are arranged in more longitudinal streaks on the head.

The Webbed Newt is a native of Western middle Europe, ranging from Great Britain and Northern Spain to Switzerland and Western Germany.

Closely allied to the last species are T. boscai of Spain and Portugal, T. italicus, T. montadoni of Moldavia, and the beautiful T. vittatus of Asia Minor. From China and Japan are known T. pyrrhogaster and T. sinensis.

The North American species are T. torosus and T. viridescens. The former, of Western North America, is one of the largest newts, reaching a length of more than six inches. The head is much depressed and broad, and has very prominent parotoid and other glands. The limbs are strong, especially in the male. The skin of the upper parts is very granular, uniform dark brown, without a crest. The tail, which is larger than the head and body, is strongly compressed, with a low dorsal and ventral fin. The under parts and the lower edge of the tail are uniform yellow or orange red. The iris is green. A specimen in my keeping spends most of its time in the cracks of rotten stumps or on the top of moss in the darkest shade. It lives on earthworms but despises insects. Like most of the other newts it becomes lively at dusk.

Fig. 24.–Triton viridescens. 1, Egg just after deposition, with the outer membrane opened, × 6; 2, a spermatophore just discharged showing its gelatinous base with a projecting spike which bears a tuft of spermatozoa, × 2. (After Jordan.)

T. viridescens is common throughout the Northern and Eastern parts of the United States. Large females are about 11 cm. long, the males 1 cm. less. The general colour above is brown, with a tinge of green; on each side of the trunk, with a row of bright vermilion spots; the under parts are orange, studded with small black dots. Half-grown specimens are brownish red, with the same lateral red spots as the adult. According to Jordan,[^[61]] this voracious species lives chiefly on the larvae of insects, on small molluscs such as Cyclas and Planorbis, on earthworms and on small Crustacea. It is eminently aquatic in the adult stage. The eggs are laid from April to June, the period lasting for one individual four to six weeks, or even longer. One female laid 108 eggs in all from 20th April to 30th May. After having selected a suitable plant, for instance an Anacharis or a bunch of Fontinalis leaflets, she bestrides the plant and gathers in the surrounding shoots with her hind-limbs, pressing the leaves closely around the cloaca. She next turns on her side, or occasionally on her back; with fore-limbs outstretched and rigid, with hind-limbs and leaves completely hiding the cloaca, she remains perfectly motionless for six to eight minutes. Then she slowly leaves the "nest," which now holds an egg well protected by a tangle of shoots glued together by the gelatinous secretion poured out of the cloaca. Jordan concludes, from the fact that he never found spermatozoa in the oviducts, that the eggs are fertilised just before they are expelled, when passing the receptaculum seminis.

The metamorphosed young pass their life on land under stones and logs as the so-called red variety, which is merely a stage in the life-history of the species. It seems to take them several years to reach maturity, and to become again typically aquatic. Young, red individuals which I have myself kept, have behaved for more than a year like the young of other newts, spending their time under moss and bark without going into the water.

The change from the red-spotted stage has been exhaustively studied by Gage.[^[62]] He remarks that this species is very common near Ithaca, in an upland forest and along the head-waters of the Susquehannah. The transformation takes place either in the autumn or in the spring, either while the newt is still on land, or after entering the water.

Of two which were kept in a jar with moist wood, one was especially brilliant, but within two weeks it assumed, in the middle of September, the characteristic coloration of the viridescent form. The two specimens were in the jar until the following July, when they were placed where they could enter the water. This they did with great readiness, and they remained submerged for a considerable time at first. The time under water increased in length, until within two or three days the pharyngeal respiration under water was fully established. On the other hand, viridescent specimens never reassume the red garb when kept out of the water.

Red specimens entering the water in the spring, changed into the greenish form within a few weeks, and established the pharyngeal respiration, losing the ciliated oral epithelium. Branchiate larvae and the adult aquatic forms have non-ciliated epithelium, and the cilia are re-established when a green specimen is forced again to live on land. Ciliation always exists in the red stage, and in the green stage before the newt has taken to the water. The cilia sweep towards the stomach.

The three following South European species belong to the Euproctus group, so called on account of the mostly conical, backward directed, and vividly coloured vent.

T. asper s. pyrenaeus.–The Pyrenean newt has hitherto been found only in the Pyrenees, for instance in Lac Bleu and Lac d'Oncet, which latter lies about 7000 feet above the level of the sea. According to Bedriaga,[^[63]] it prefers lakes which are supplied during the whole summer with water from glaciers. It is very sluggish, only moving to breathe and when in search of food, which consists of worms and insects. The general colour is greenish brown, dark above; the under side of the head and body are bright orange red in the female, yellow in the male; dark spots separate this bright colour from the flanks. The tail has a narrow ventral stripe of bright red and yellow. The cloaca of the female is bright red, that of the male dull grey. The total length amounts to about 4 inches or 10 cm.

The pairing time is the end of June, or later in cold seasons. The male gets hold of the female by forming a noose with its tail round her; it lies underneath, the cloacae being pressed together so that the spermatozoa can be taken in directly. The larvae have large yellow-green spots on the back and sides, and a bright red ventral tail-fin; when metamorphosed the greenish spots become more confluent on the back, producing a broad spinal band. Larvae which live in deep water are dark, while those in sunny places are light-coloured and spotted with yellow.

T. montanus in Corsica and T. rusconii in Sardinia are allied forms, but the males are distinguished by a spur-like process or dilatation at the end of the fibula.

T. waltli, the Iberian Newt, is olive-brown above, yellowish with blackish markings below. The tail has a yellow or orange ventral line. There is no crest. A remarkable peculiarity of this species (which it shares only with Tylototriton andersoni of the Loo-Choo Islands) is its ribs, which are very long, sharply pointed, and frequently perforate the skin. Before perforation the point of the rib lies in a lymphatic space. This surprising feature has by many authorities been considered as abnormal or pathological. Certainly young, and even many adult, individuals are found in which the skin is not perforated, but when these are handled the wriggling motions of this strong newt force the points of the ribs through the skin, and they remain sticking out to the extent of several millimetres. The wounds heal up, the skin forming a neatly finished-off hole through which the spike projects, not as a formidable, but as a sufficiently awkward, protective weapon.

Fig. 25.–Triton waltli. Spanish Newt, adult and larvae. × ⅔.

Large females reach a length of 10 inches. The larvae metamorphose, as a rule, when they are between 2 and 3 inches long, but those which have been bred in tanks often reach double this length. These newts are frequent inhabitants of the rain-water cisterns common in the South of Portugal and Spain, into which they tumble without ever being able to get out again. This species spends most of its time in the water, preferring ponds, among the vegetation of which they can be watched lying motionless, with their limbs hanging down and with the head close to the surface; but they are lively during the night. When their ponds dry up they leave them, crawling into the most unexpected places, to aestivate under rocks, or even in the walls of old buildings, where they are found by accident only. The range extends from Central Spain and Portugal into Morocco.

Tylototriton verrucosus lives in the Eastern Himalayas and in the mountains of Yunnan. The skin is tubercular, with large parotoids; above uniform black-brown, pale below; the tail has a ventral yellow or orange line. Total length about 6 inches. T. andersoni of the Loo-Choo Islands is remarkable for the pointed ribs which perforate the skin.

Pachytriton brevipes, discovered in Kiansi, Southern China, has a smooth skin, olive-brown above, with many black dots; the under parts are yellowish, dotted with black. Total length about 7 inches.

Fam. 3. Proteidae.–The three pairs of fringed external gills persist throughout life. Both fore- and hind-limbs are present. The eyes are devoid of lids. The maxillaries are absent. Teeth are present on the premaxillaries, on the vomers, and on the mandible. The vertebrae are amphicoelous.

This family consists of only three genera, with one species in each.

Necturus maculatus s. Menobranchus lateralis.–The eyes are functional, being covered by the thin transparent skin. The limbs, although short, are well developed, and have four fingers and four toes. The whole animal, which reaches the length of one foot, is quite smooth and slimy, brown with irregular dark, blackish spots and patches, which frequently form a dark lateral band extending from the mouth to the tail. The latter, which measures about one-third of the whole length, is strongly compressed, carries a thick dorsal and ventral fin, and is rounded off at the end. The skin of the throat forms a strongly-marked transverse fold. The thick stalks of the gills are brown, while the numerous and delicate fringes are dark red in life; beneath and behind them are two gill-clefts. N. maculatus is found in the eastern half of the United States, chiefly the eastern part of the basin of the Mississippi and the Canadian lakes.

These creatures are rather dull; they remain mostly at the bottom of the water, more or less concealed in the weeds or between rocks during the daytime. Mine, which are kept in a roomy, light-coloured tank, lie motionless, with their gills spread out transversely. Every now and then the gills contract suddenly and become pale, whereupon they are filled again with blood. Very rarely they rise to the surface, but tiny air-bubbles are let out more frequently, especially when the animals are disturbed. Then the gills collapse, are laid flat against the neck, and the creature darts about with quick, eel-like motions. At night they leave their hiding-places, swim about or creep along the ground with slow, undulating movements, the limbs being scarcely used, in search of food, which in their wild state consists of rather large Crustacea, small fishes, worms, insects and frogs. They are most voracious, and absolutely indifferent to cold. The spawning takes place in the months of April and May.

Proteus anguinus.–The fore- and hind-limbs are fully developed, but possess only three fingers and two toes. The eyes are completely hidden beneath the opaque skin. This peculiar creature is restricted to the subterranean waters of Carniola, Carinthia, and Dalmatia. The vast caves of Adelsberg not far from Trieste are especially celebrated for the occurrence of the "Olm," the German name of this animal. The river Poik, a moderate mountain-stream, but a large, fierce torrent during the rainy season, disappears into the limestone-hills, and rushes through enormous stalactite-grottoes, most of which have been only partially explored, until several miles farther on it reappears on the surface. There, deep down below the surface, in absolute darkness, in an almost constant temperature of about 50° F. is the home of Proteus.

Their total length is scarcely one foot. The whole body is white, occasionally suffused with a slight fleshy, rosy tinge, while the three pairs of gill-bunches are carmine-red. They are easily kept in captivity, and live for many years, provided three conditions are strictly adhered to, viz. fresh and clean water, an equable low temperature of about 50° F. = 10° C. and darkness. The question of food is not so very important, since specimens are known to have existed for years, although they refused to take any nourishment. How far darkness is an absolute necessity is not known. Anyhow, the white skin is almost as susceptible to light as is a photographic plate. If light is not absolutely excluded the white skin becomes in time cloudy, with grey patches, and if kept exposed to stronger light, the whole animal turns ultimately jet-black. Mr. Bles has succeeded in producing several totally black specimens, having kept them for several months in a white basin under ordinary conditions of light. No experiments have yet been made to find out if the black pigment deposited is lost again in darkness. Those which are kept in a tank in an absolutely dark cellar of the Cambridge Museum, with permanent water-supply, are doing very well. When approached with a candle they become restless or remain partly hidden in all sorts of seemingly most uncomfortable attitudes, squeezed in between the sharp-edged tiles and drain-pipes with which their lodgings are furnished. But the introduction of a wriggling worm, a little crustacean or other live bait draws them from their hiding-places, and, guided by the motions of the prey in the water, possibly also by the sense of smell, they snap it up and devour it.

Fig. 26.–Proteus anguinus. × ⅔. Front view of the mouth in the left upper corner.

If the water is not sufficiently well aerated, they rise to the surface, emit a bubble of air, and take a new supply into their lungs. As a rule they remain motionless under water, but the gills contract spasmodically and become paler, whereupon they fill again with blood and darken; the contrast between the pure white body and the carmine-red feathery gills is very beautiful.

Until recently the mode of propagation was quite unknown. Several Proteus, kept by E. Zeller, laid, in the middle of April, a number of eggs which were then fastened singly on to the under side of projecting stones in the water. The pale yellow yolk measured 4 mm. in diameter and was surrounded by a cover of 1 mm. in thickness, besides an outer gelatinous mantle, so that the whole egg measured about 11 mm. The larvae were hatched after 90 days; they were 22 mm. long, and already much like the adult, except that the fin was not restricted to the tail, but extended over the last quarter of the trunk, and that their eyes were still visible. The fore-limbs were already typical in shape, but the hind-limbs were still toe-less little stumps.[^[64]]

Typhlomolge rathbuni.–It is of the greatest interest that a subterranean Perennibranchiate newt, in many respects closely resembling Proteus, has recently been discovered in Texas. There can be no doubt that similar conditions of life have produced these two forms from Necturus- and Spelerpes-like ancestors,[^[65]] one in Europe, the other in North America, absolutely independently of each other. The limbs of Typhlomolge are long and very slender, the four fingers and five toes are thin, free and pointed. The head is large, the mouth square. The eyes are completely hidden and the whole animal is colourless and white. The tail is furnished with a dorsal and a ventral fin. The very deep gular fold is nothing but the pair of united but large opercular flaps. The three pairs of gills are remarkable for their blade-like stalks, while the gill-lamellae proper are short and restricted to the tapering ends. Total length about 75 mm., of which the head measures 15, the tail 32 mm.

This peculiar creature inhabits subterranean caves in Texas, to judge from the fact that all the specimens hitherto known have come up with the water of an artesian well 188 feet deep, near San Marcos. According to Blackford,[^[66]] "the legs are used for locomotion and the animals creep along the bottom of the aquarium with a peculiar movement, swinging the legs in irregular circles at each step. They climb easily over the rocks piled in the aquarium, and hide in the crevices between them. All efforts to induce them to eat have been futile, as has also been the case with blind cave-fish in captivity, and they are either capable of long fasts or live on infusoria in the water." It seems more reasonable to suppose that these newts live upon Crustacea, four kinds of which, all new to science, also came up with the water.

Fam. 4. Sirenidae.–The three pairs of fringed external gills persist throughout life. The body is eel-like. Hind-limbs are altogether absent, while the fore-limbs are short and have three or four fingers. The maxillary bones are absent. With the exception of small teeth on the vomer the mouth is toothless, but the jaws are furnished with horny sheaths. The eyes are devoid of lids, but shine through the skin.

Fig. 27.–Siren lacertina. × ½.

The Sirenidae are the most degraded members of the Urodela and are represented by two closely-allied genera, each with one species, in the south-eastern parts of the United States. Their most interesting feature, which bears upon the question of neoteny, is their retrograde metamorphosis as described by Cope.[^[67]] The gills atrophy in the young and are subsequently redeveloped. Cope therefrom concludes rightly that the ultimate or persistent gills of Siren are signs of maturity and not a larval character. In young specimens of Siren of 5 to 6 inches in length the gills are functionless; in one of 3 inches they were found to be entirely vestigial and "subepidermal," i.e. covered by a common dermal investment. Unfortunately really young larvae are still unknown. Old Sirens can live without gills, as has been shown by aquarium-specimens. In the adult Pseudobranchus all the gills are normally covered up by an investment of the skin so as to be quite without function and movability.

Siren lacertina, the "mud-eel," is distinguished by the possession of three pairs of gill-clefts and by its four fingers. It reaches a length of 70 cm., or about 2½ feet, of which about one-third is taken up by the tail, which is strongly compressed and finned. The skin is smooth, mostly blackish, lighter below, sometimes with whitish specks all over the body. This creature is frequently found in ditches and ponds, where it burrows in the mud. When swimming the limbs are folded back. They are said sometimes to leave the water and to crawl about on the moist ground.

Pseudobranchus striatus has only one pair of gill-clefts and only three fingers. The slightly granular skin is dusky brown above, with a broad yellow band on either side and with a paler, narrower stripe below. Total length about 7 inches.

CHAPTER VI

LISSAMPHIBIA (CONTINUED)–ANURA

Order III. ANURA or TAILLESS AMPHIBIA.

The recent tailless Amphibia, or Frogs and Toads in the widest sense, contain such a great number of species (about 900), with such a diversity of characters, that it is necessary, if only for the sake of mere convenience, to group them into a considerable number of families and sub-families. The characters available for this purpose are few.

1. The possession of a tongue characterises the Phaneroglossa, the absence of a tongue the Aglossa.

2. The character of the shoulder-girdle.–Overlapping of the two halves of the shoulder-girdle on the ventral side characterises the Arcifera, while in the Firmisternia the two ventral halves meet in the middle line and form a firm, median bar. See, for details, p. [24].

3. The shape of the transverse processes or diapophyses of the sacral vertebra which carries the iliac or hip-bones. These processes are either dilated or cylindrical.

4. The presence or absence of teeth in the upper and lower jaws. This is indicated by a formula in which 0 means absence of teeth; max. means presence of teeth in the upper jaw; mand. means presence of teeth in the lower jaw.

5. The terminal joints or phalanges of the fingers and toes are sometimes claw-shaped. See p. [26].

6. The shape of the centra of the vertebrae.–Opisthocoelous, if the posterior end is cup-shaped or concave, procoelous if the anterior end is concave and the posterior is convex. See p. [19].

By means of these characters we can arrange the Anura in the following key:–

II. Aglossa. Sacral diapophyses dilated.		AGLOSSA, p. [143].
Vertebrae opisthocoelous, with ribs.
II. Phaneroglossa.
A. Arcifera.
a. Sacral diapophyses dilated.
α. Terminal phalanges not claw-shaped.
Opisthocoelous, with ribs, max./0		DISCOGLOSSIDAE, p. [152].
Procoelous, without ribs, 0/0		BUFONIDAE, p. [166].
Precocious, or opisthocoelous, without ribs, max./0		PELOBATIDAE, p. [160].
β. Terminal phalanges claw-shaped–		max./mand. Amphignathodontinae, p. [188].
HYLIDAE		max./0 Hylinae, p. [189].
b. Sacral diapophyses cylindrical–		max./mand. Hemiphractinae, p. [210]. max./0 Cystignathinae, p. [211]. 0/0 Dendrophryniscinae, p. [227].
CYSTIGNATHIDAE
B. Firmisternia.
a. Sacral diapophyses dilated–		max./0 Dyscophinae, p. [235]. 0/mand. Genyophryninae, p. [236]. 0/0 Engystomatinae, p. [225].
ENGYSTOMATIDAE
b. Sacral diapophyses cylindrical–		max./mand. Ceratobatrachinae, p. [237]. max./0 Raninae, p. [238]. 0/0 Dendrobatinae, p. [272].
RANIDAE

Concerning the evolution of the classification of the Anura, it is interesting to follow the changes of the value attached to the various anatomical characters by systematists. At first the presence or absence of teeth and of adhesive discs on the fingers and toes were considered to be of prime importance for the division of the Phaneroglossa.

Duméril et Bibron, 1841. "Erpétologie générale."

II. Phrynaglosses = Aglossa of Wagler: Pipa and Xenopus.

II. Phanéroglosses. 1. With teeth. a. Without discs: Raniformes.

II. Phanéroglosses. 1. With teeth. b. With discs:out Hylaeformes.

II. Phanéroglosses. 2. Toothless. Bufoniformes.

Stannius, 1856 (see p. [8]), separated the Engystomatidae as "Systomata," and used the presence or absence of the "manubrium sterni" (omosternum) as a character of distinction between his Bufoninae and Raninae.

Günther, 1858, "Catalogue of the Batrachia Salientia." No progress was made by his scheme, which relied upon the tongue and digits.

Aglossa with Myobatrachus.

Opisthoglossa. a. Oxydactyla. b. Platydactyla.

Proteroglossa: Rhinophrynidae.

Cope, 1864. "On the limits and relations of the Raniformes."[^[68]] He introduces the shoulder-girdle and the sacral diapophyses, and drops the discs as too adaptive and misleading. He distinguishes between Raniformes and Arciferi.

Cope, 1865. "Sketch of the primary groups of the Batrachia Salientia."[^[69]]

Aglossa.

Bufoniformia (Bufonidae).

Arcifera (Discoglossidae, Scaphiopodidae, and Hylidae).

Raniformia.

In 1867 Cope separates the genus Hemisus as Gastrechmia on account of its peculiar pectoral arch.[^[70]]

In 1875, "Check-list of North American Batrachia and Reptilia," Cope elaborates his system:

Class Batrachia. Order Anura.

1. Raniformia.

2. Firmisternia. [Dendrobatinae and Engystomatidae.]

3. Gastrechmia: Hemisus.

4. Bufoniformia. [Bufonidae.]

5. Aglossa. Pipa.

6. Odontaglossa. Xenopus.

7. Arcifera. [Cystignathidae, Hylidae, Pelobatidae and Discoglossidae.]

Cope consequently considered the characters of the pectoral arch as equivalent to those of the dentition.

Boulenger, 1882, "Catalogue of the Batrachia Gradientia s. Ecaudata," recognises that the pectoral arch is of greater systematic value than the dentition. The latter is used, together with the shape of the sacral diapophyses, for the separation into families.

I. Phaneroglossa.	A. Firmisternia.		1. Ranidae.
			2. Dendrobatidae.
			3. Engystomatidae.
			4. Dyscophidae.
	B. Arcifera.		5. Cystignathidae.
			6. Dendrophryniscidae.
			7. Bufonidae.
			8. Hylidae.
			9. Pelobatidae.
			10. Discoglossidae.
			11. Hemiphractidae.
			12. Amphignathodontidae.
II. Aglossa.			13. Dactylethridae.
			14. Pipidae.

This emendation of the Arcifera and Firmisternia was accepted by Cope in his synopsis of the families of Vertebrata (Amer. Natural. xxiii., 1890), except that he still retained his suborder Gastrechmia.

Since the publication of Boulenger's great work a number of forms have been discovered which, from the characters of their dentition, have necessitated the establishment of certain new families, namely, Ceratobatrachidae and Genyophrynidae; and Boulenger was the first to recognise that the taxonomic value of the mere presence or absence of teeth in the jaws had been overestimated. I therefore propose using it as a character distinctive of the sub-families only, thereby reducing the number of families, relying first (leaving the Aglossa aside) upon the firmisternal or arciferous condition of the pectoral arch, secondly upon the dilated or cylindrical shape of the sacral diapophyses, thirdly upon the dentition. Blindly consistent application of these principles would reduce the Phaneroglossa to four families only, namely Ranidae, Engystomatidae, Cystignathidae and a fourth family comprising all the Arcifera with dilated sacral diapophyses. This would obviously be wrong. We have therefore to resort to other additional characters or rather peculiarities. The opisthocoelous character of the vertebrae and the possession of distinct ribs, together with the disc-shaped tongue, separate the Discoglossidae and justify their retention as a family. The Hylidae are marked off by the claw-shaped terminal phalanges, but the remaining forms, comprising the Bufonidae and Pelobatidae, cannot be separated except by their dentition, and I plead guilty of inconsistency in retaining them as separate families.

After all, our classification may not represent the natural system, and it may be nothing but a convenient key.

When we have eliminated the characters of the vertebrae, the dentition, the claw-shaped phalanges and the adhesive discs, it may well be asked what characters remain. The firmisternal is a further, higher modification of the older, more primitive arciferous condition. The difference between the dilated and cylindrical shape of the sacral diapophyses is in not a few cases very slight, and there are various, most suggestive exceptions. The presence or absence, size and shape of the omosternum and metasternum are of very limited taxonomic value, not always applicable to all the members of the same family. The fact is, that the Anura are a very recent and a most adaptive, plastic group. The earliest known fossils are scarcely older than the Middle Eocene.

Almost every one of the greater families has produced terrestrial, arboreal, aquatic, and burrowing forms. Their habits have modified, and are still shaping their various organs, first of course those by which the animals come first and most directly into contact with their surroundings (e.g. adhesive discs, dentition, general shape of the body, length of limbs, wartiness of the skin, tympanic disc). These are the so-called adaptive characters, sometimes decried as merely physiological; as if habits, use, and requirements did not likewise influence and ultimately model every other organ (e.g. tympanic cavity, Eustachian tubes, vertebrae, ribs, coccyx, pectoral arch, etc.). There are true Toads, Bufonidae, which are as smooth, wartless, slender-bodied and long-legged as the most typical of "Frogs"; true Ranidae, like Rhacophorus, which by their green colour, large adhesive discs and arboreal habits may well put many of the Hylidæ to shame. Ceratohyla has developed the claw-shaped terminal phalanges which are otherwise typical of, and peculiar to, the Hylidae, but this genus reveals itself by various details as a close relation of the other Hemiphractinae; and these fall in with the Cystignathidae on the strength of their cylindrical, not dilated, sacral diapophyses.

In sketching the phylogenetic tree of the families of the Anura we have to proceed with great caution.

There is not much doubt about the Aglossa. They have retained some of the most primitive characters, but have by now been so much modified and specialised that they are to be looked upon as an early side-branch.

Among the Phaneroglossa the Discoglossidae are with certainty the oldest, but are now scarce in genera and species, and much specialised. The Pelobatidae connect them with the Bufonidae. The Cystignathidae form a rather ill-defined assembly which points downwards to the Pelobatidae, upwards to the Hylidae. There is no divergence of opinion about the Ranidae being the highest of all the Anura, and amongst them the Raninae the most typical, the Dendrobatinae the most specialised. If we assume that moderately dilated sacral diapophyses represent a more primitive stage than cylindrical processes, we shall naturally look to the Engystomatidae as the connecting link between the Ranidae and the Arcifera, through Bufonoid creatures still with teeth in both jaws. If, on the other hand, we take the dilatation to be a further development from more or less cylindrical processes, then the Ranidae can be considered as having sprung from Cystignathoid creatures, which have consolidated their pectoral arch into the firmisternal condition; and in this case the Firmisternia would not be a natural group, the Engystomatidae pointing, to the Bufonoid stock. This would, to a great extent, mean a reversion to Cope's idea.

Sub-Order 1. Aglossa.–The two diagnostic peculiarities of the few members of this group are: first, the absence of a tongue; secondly, the union of the Eustachian tubes into one median pharyngeal opening in the posterior portion of the palate.

Fig. 28.–Map showing distribution of Aglossa. Hymenochirus to be added in Equatorial Africa.

The pharyngeal opening and the tubes themselves are wide, the tympanic cavities are present, but the tympanic discs are not distinct from the rest of the skin. The fronto-parietal bones are fused into one mass, a rare feature in the Anura. The nasals are large. Pipa and Hymenochirus have no teeth, Xenopus has teeth on the upper jaw. The vertebrae are opisthocoelous and typically epichordal in their development; the second, third, and fourth carry long ribs, which in old specimens fuse with the supporting diapophyses. The sacral diapophyses are enormously dilated, and the sacrum is fused with the os coccygeum. The serial number of the sacral vertebrae exhibits a most interesting gradation. In Xenopus the ilium is carried by the diapophyses of the 9th, in Pipa the 9th and 8th, in Hymenochirus the 7th and 6th. In these cases the two diapophyses of each side are fused together into a single broad blade, and their original duplicity is indicated only by the holes for the spinal nerves. Hymenochirus has consequently only 5 presacral vertebrae, the vertebral column being shortened to the greatest extent known amongst Vertebrata. For further information see p. [22]. The ilia are much broadened vertically, and are firmly attached to the sacrum. The shoulder-girdle is sometimes described as of the arciferous type, but this is quite unjustifiable. The epicoracoid cartilages do not overlap each other, but meet, and partly fuse in the middle line. The three genera exhibit some differences. In Pipa and Hymenochirus the bony portions of the coracoids are much expanded dorsally, and there is a considerable amount of epicoracoid cartilage, that of the precoracoid bars extending backwards as a broad-based and blunt omosternum. Xenopus is devoid of an omosternum, and the configuration of the whole apparatus is more slender. The metasternum of Xenopus and Hymenochirus broadens out laterally. Hymenochirus greatly resembles Breviceps, a genus of Engystomatinae, in the relative position and size of the various parts of the shoulder-girdle and sternum.

The tibio-fibula of Hymenochirus has a wing-like expansion of thin bone on each side, forming a deep groove on the outer aspect. The astragalus and calcaneum are united by a similar bony expansion with wing-like projections.

The lungs are remarkable for the prominent development of trabecular projections and niches, so that their free lumen is much restricted; they have thereby reached a much higher stage than in any other Amphibia or even many Autosauri. The persistence of an arteria sacralis s. caudalis, a vessel absolutely absent in the adult Rana, is a primitive feature, and the same applies to the presence of a true first spinal or suboccipital nerve.

The skin of the back and belly is supplied by two great branches from the arteria anonyma, one arising proximally, the other distally from the subclavian; herewith is correlated the almost complete absence of the arteria cutanea magna, which as a branch of the ductus pulmo-cutaneus plays such a prominent rôle in the other Anura. Only in Pipa, but not in Xenopus, is the great cutaneous vein represented by a very small branch. Both these genera possess a much more complicated "diaphragm" than the other Anura, chiefly owing to a special muscle which arises from the anterior end of the ilia and spreads out fan-like to the oesophagus and to the bases of the lungs.[^[71]] This diaphragmatic arrangement is correlated with the great development of the lungs, and is not a primitive but an advanced feature. It is reasonable to suppose that this has caused the reduction of the usual arteria pulmo-cutanea, and that the other two cutaneous arteries have been developed secondarily. The Aglossa are generally considered as the lowest Anura, and only Cope looked upon Pipa and Xenopus as two convergent terminal branches. Beddard came to the conclusion that both are closely related to each other, chiefly on account of their peculiar diaphragmatic arrangement. The whole question has entered upon a new stage since the recent discovery of Hymenochirus, which is in many ways intermediate between the two other genera. Moreover, the mid-Tertiary Palaeobatrachus of Europe is undoubtedly related to them, and we conclude now that all these four genera belong to one group with a distribution formerly much wider than Africa and part of South America. But this does not necessarily mean that the Aglossa are in all respects the most primitive group of living Anura. On the contrary, they possess few decidedly primitive characters, namely, the long typical ribs, the presence of the first spinal nerve, the unimportant persistence of the arteria sacralis, and lastly, the possession in the tadpoles of a right and left opercular "spiracle." The absence of the tongue cannot possibly be an archaic feature, considering its universal presence in all the other Amphibia, including the Apoda, and the suggestive circumstance that this organ is least developed in the entirely aquatic members of the Urodela. In fact, thoroughly aquatic creatures, which seize and swallow their prey under water, require no elaborate tongue; and since we know that the Anura must owe their typical formation to terrestrial life, it follows that those which have again taken to the water and are tongueless, have lost this organ. As I have shown elsewhere,[^[72]] the epichordal development of the vertebrae is likewise a secondary feature, far from primitive; and the tendency of the shortening of the vertebral column, which has reached its extreme in Hymenochirus, points to the same conclusion. The apparatus of the shoulder-girdle and sternum is in the last transitional stage from the former arciferous to the typically consolidated firmisternal type. In fact there is little left which is primitive, but much that is very specialised and highly developed in the Aglossa, mostly in adaptation to their absolutely aquatic life, to which they must however have taken very early. They are in a position somewhat analogous to the Ratitae among Birds, which are likewise an old group, although many of their most striking features have been acquired secondarily.

Xenopus s. Dactylethra. The upper jaw is furnished with teeth. The ilia are attached to the ninth vertebra. The pupil is round. The terminal phalanges are pointed. The fingers are free, the toes broadly webbed, and the first three are covered with sharply pointed, horny, black-brown nails, a feature which is alluded to by the alternative generic names. A cutaneous tentacle projects from below the eye and naturally invites comparison with the tentacle of the Apoda and of Urodela. The skin is smooth, rich in mucous glands, besides certain tube-like apparatuses, possibly sensory, which are scattered over the body, especially on the head, and form a conspicuous series of white dots along the dorso-lateral line, from the eye to the vent. The general colour of the upper parts is olive brown, mottled darker, while the under parts are whitish. The female has three cutaneous flaps closing the vent. The male develops black nuptial brushes along the inner side of the fingers. There are several species, all African (Ethiopian).

X. laevis, ranging from the Cape to Abyssinia, is distinguished by the absence of a metatarsal spur. The tentacle is very short. Size about 3 inches. X. muelleri of Zanzibar and Benguella, is smaller. The tentacle is conspicuous, as long as the diameter of the eye. The inner metatarsal tubercle carries a sharp claw. X. calcaratus of tropical West Africa is only 2 inches long, and has strong metatarsal claws, short tentacles and very minute eyes.

The habits and oviposition of the "Clawed Toad" have been described by Leslie.[^[73]] The Boers call it "Plathander," i.e. flat hand. Entirely aquatic, it rests floating in the water, with the nostrils exposed, and leaves the water only if it has to change the locality on account of drought or scarcity of food. The pairing takes place, at least at Port Elizabeth, in the early spring, i.e. in the month of August. The only sound which is emitted is heard during this time, a very slight and dull tick-tick, audible at only a few feet distance. The male grasps the female by the loins; the eggs are extruded singly, measuring only 1.5 mm. in diameter, but swell to double that size. They are attached singly to stones or water-plants.

Fig. 29.–Xenopus laevis. Clawed Toad, adult and larvae, × ⅔.

Latterly these creatures have frequently been brought over to England. They stand confinement very well, even in a little aquarium with sufficient water-weeds to keep the water fresh; and they do not require special heat. They greedily snap up worms, strips of liver, or meat, and poke the food in with their hands. A few kept by Boulenger in a glass jar have lived for the last eleven years in the ordinary temperature of a room in London. Curiously enough they are often in amorous embrace, regardless of the season, but they have never shown any signs of spawning.

Some of those in the Zoological Gardens in London laid eggs on Saturday the 27th of May, and on the morning of the following Monday the larvae were already hatched. They have been described by Beddard.[^[74]] The larvae are provided with an unpaired circular, ventral sucker. The tentacles begin to sprout out on the sixth day after hatching, at first not in connexion with the cranial cartilage, but soon a cartilaginous rod runs into the tentacle from the ethmoid "just above the joint with the under jaw.". Boulenger has most reasonably compared these organs with the "balancers" of Triton and Amitystoma (cf. p. [46] for the possible homologies of the balancers). The tentacles soon reach a great length and give the tadpole a curious appearance. In tadpoles of X. calcaratus, 65 mm. long, the tentacles are 30 mm. long, and are inserted just at the angle of the mouth. By the time that these tadpoles show their fore-limbs, the feelers are reduced to 4 mm. in length, and their relative position has been shifted to a little above the angle of the gape, and whilst the latter gradually extends further and further back, the feelers come to lie, or rather remain, below and a little in front of the eyes.

The tadpoles have no traces of horny teeth. External gills project as low conical or lamellar processes from the first three branchial arches, but so-called internal gills are not developed.

Amongst a number of Clawed Toads imported in the spring one female became swollen with eggs, but as they did not show signs of wanting to breed, a pair was put into the tropical tank in the Cambridge Botanic Gardens, a transfer which had the desired effect. Eggs were laid, and more during the following nights; they hatched out within thirty hours. The whole brood was lost, before any of them were older than a few days, since they were attacked, beyond the possibility of a cure, by a Saprolegnia or some similar pest.

Hymenochirus, represented by one species, H. boettgeri, has been discovered in the Ituri, German East Africa, and in the French Congo, and has no doubt a much wider distribution. It is scarcely 1½ inch long, and is easily recognised by the toothless mouth, the half-webbed fingers (hence the generic name), the incompletely webbed toes, the third of which is longer than the fourth, and the absence of sensory muciferous canals in the skin. The three inner toes are, as in Xenopus, furnished with small black claws. The skin is rough, beset with small granular tubercles. The general colour above and below is olive-brown. The vent is, as in Xenopus, produced into a spout or semi-canal, but is devoid of dorsal flaps of skin.

Pipa.–This Neotropical member of the Aglossa is quite toothless, but the jaws of the adult have horny substitutes. The only species is P. americana, the famous Surinam Toad, chiefly known from the Guianas, but undoubtedly extending much further, having recently been reported from the neighbourhood of Pará.

The general shape of this creature is very peculiar. The head is much depressed and triangular; the eyes are very small; the skin forms several short, irregularly-shaped flaps and tentacles on the upper lips and in front of the eye, and at the angle of the mouth. The tympanum is invisible. The pupil is round. The fingers are very slender and free, ending in star-shaped tips; the toes are broadly webbed. The whole skin is covered with small tubercles and is dark brown above, while the under parts of the very flat and depressed body are whitish, sometimes with a dark brown stripe along the middle line. In the female the skin of the back forms growths for the reception of the eggs, and in these the young undergo their whole metamorphosis.

Fig. 30.–Pipa americana. Surinam Toad. × ⅔.

The most characteristic feature of the skin,[^[75]] which has exactly the same structure in both sexes, is the papillae, which are spread over the whole surface, except on the webs of the toes, on the cornea and on the star-shaped points of the fingers. Each papilla carries a little horny spike, and a poison-gland frequently opens near its base. Larger poison-glands exist on the dorsal and ventral side in four rows, and smaller glands open upon the sides of the body, but there are no parotoid complexes. Slime-glands occur all over the surface. The epidermis consists of the usual layers, namely the Malpighian, the stratum corneum, and the part which is shed periodically. The latter is completely horny, appearing to be structureless like a cuticle, but it is in reality composed of polygonal cells with flattened nuclei; each little spike is one modified horny cell. The whole outermost layer contains black-brown pigment. The upper portion of the cutis is devoid of pigment, then follows a layer of clusters of ramified dark pigment-cells, and lastly the rest of the cutis.

Each of the four fingers ends in a four-armed star, the tips of which again carry four or five sensory papillae. The cartilage of the terminal phalanges is correspondingly star-shaped.

According to Klinckowstroem these toads, which are entirely aquatic, are easily collected at the end of the long dry period, when they are all confined to the half-dried-up pools. But they do not spawn there. This happens after the rains have inundated the forest, and then it is very difficult to get the females with eggs on their backs. Each of the eggs, when once they have been glued on to the back, sinks into an invagination of the skin. The initial stages are probably the same as those caused by the eggs on the belly of Rhacophorus reticulatus (see p. [248]). Later, each egg is quite concealed in a cavity with a lid. These cavities are simply pouches of the skin, and are not formed by enlarged glands as has been suggested by some anatomists. Each cavity consists of the epidermal pouch and the lid. How the latter is produced is not known. According to the authors quoted above, the lid looks like a shiny or sticky layer which has hardened into horn-like consistency. It lies exactly like a lid upon the rim of the pouch itself, and is certainly not in structural or organic continuity with the epidermis. Most probably it is produced by the remnant of the egg-shell itself, which, after the larva is hatched, is cast up to and remains on the top of the cup.

Bartlett[^[76]] has described the spawning of specimens in the Zoological Gardens in London.

"About the 28th of April 1896 the males became very lively, and were constantly heard uttering their most remarkable metallic, ticking call-notes. On examination we then observed two of the males clasping tightly round the lower part of the bodies of the females, the hind parts of the males extending beyond those of the females. On the following morning the keeper arrived in time to witness the mode in which the eggs were deposited. The oviduct of the female protruded from her body more than an inch in length, and the bladder-like protrusion being retroverted, passed under the belly of the male on to her own back. The male appeared to press tightly upon this protruded bag and to squeeze it from side to side, apparently pressing the eggs forward one by one on to the back of the female. By this movement the eggs were spread with nearly uniform smoothness over the whole surface of the back of the female to which they became firmly adherent. On the operation being completed, the males left their places on the females, and the enlarged and projected oviduct gradually disappeared from one of the females. In the other specimen, the oviduct appears not to have discharged the whole of the eggs."

Boulenger, who examined this second specimen, which died, confirmed this egg-bound condition. He remarks further: "The ovipositor formed by the cloaca (not by the prolapsed uterus), was still protruding and much inflamed. It may be deduced from the observation made by the keeper, that fecundation must take place before the extrusion of the eggs, and it is probable that the ovipositor serves in the first instance to collect the spermatozoa which would penetrate into the oviducts, the eggs being laid in the impregnated condition, as in tailed Batrachians."

Sub-Order 2. Phaneroglossa–Fam. 1. Discoglossidae.–The tongue has the shape of a round disc, adherent by nearly the whole of its base, and it cannot be protruded. The vertebrae are opisthocoelous, and in the aquatic genera are of the most exaggerated epichordal type; the diapophyses of the second to the fourth vertebrae carry short, free ribs, and those of the sacral vertebra are dilated. The metasternum behind is forked. The upper jaw and the vomers are provided with teeth. The males have no vocal sac. The tadpoles are distinguished by having the opercular spiracle placed in the middle of the thoracic region (see general anatomical part, p. [44]).

The few members of this family have a peculiar distribution. Liopelma is confined to New Zealand, where it is the solitary representative of the Amphibia. Ascaphus is found in North America. The other genera, Discoglossus, Bombinator, and Alytes, are typical of the Palaearctic sub-region, and are, with the exception of Bombinator, confined to the Western Provinces (cf. Map, Fig. 32, on p. [161]).

Discoglossus.–The tympanum is frequently more or less concealed by the skin. The pupil is round or triangular. The omosternum is small. The vertebrae are of the epichordal type.

D. pictus, the only species, has a smooth and shiny skin, provided with numerous small mucous glands. The palms of the hands are provided with three tubercles, of which the innermost is the largest, and is carried by the vestige of the thumb. The coloration of this species is very variable. The ground-colour of the upper parts is a rich olive brown with darker, light-edged patches, which are either separate or confluent in various ways, forming broad, longitudinal bands, or a few larger asymmetrical patches, separated in some individuals by a broad and conspicuous light brown or yellowish vertebral stripe. An irregular reddish band frequently extends from the eyes backwards along the sides. The under parts are mostly yellowish white. This variability is purely individual, the most differently marked and variously coloured specimens being found in the same locality and even amongst the members of one and the same brood. The male develops various nuptial excrescences, consisting of minute, dark, horny spines, notably on the inner palmar pad, on the inner side of the first and second finger, on the chin and throat, and smaller and more scattered spicules on the belly and legs.

This pretty and extremely active little creature, which measures between 2 and 3 inches in length, is confined to the south-western corner of the Palaearctic sub-region, being found in Algiers and Morocco, Sicily, Sardinia, Corsica, and the southern and western parts of the Iberian Peninsula. Curiously enough it is absent in the Balearic Isles. Rather aquatic in its habits, frequenting pools and streams, it is also often found on land.

The male has a feeble voice, which sounds like "ha-a, ha-a-a," or "wa-wa-wa," uttered in rapid succession. The pairing season lasts a long time, in Algeria from January to October, but a much shorter time in the north of Portugal, where it extends over the spring and summer months. Boulenger has made extensive observations on many specimens kept in captivity. The embrace, which never lasts long, is lumbar. The eggs are small, 1 to 1.5 mm. in diameter, dark brown above and greyish below, each surrounded by a gelatinous capsule of 3-7 mm. in diameter. The eggs are laid singly, and a set amounts to from 300 to 1000, the whole mass sinking to the bottom of the pool. Each female lays several times during the season. The eggs are developed very rapidly, the larvae escaping sometimes after thirty-six hours, but usually from the second to the fourth day. The external gills are lost on the seventh day, when the tadpoles are 11 mm. long; the hind-limbs appear on the tenth, and after four weeks the tadpoles reach their greatest length, namely from 25-30 mm. The fore-limbs appear on the thirtieth day, and a few days later the most precocious specimens leave the water and hop about. Others, however, of the same brood took from two to three months in metamorphosing.

This species lives on insects and worms, and can swallow its prey under water.

Bombinator.–The tympanum is absent and the Eustachian tubes are very minute. The pupil is triangular. The omosternum is absent. The vertebrae are absolutely epichordal. The fingers are free, the toes are webbed. The upper parts are uniformly dark, and are covered with small porous warts. The general shape of the head and body is depressed or flattened downwards. The habits are eminently aquatic. This genus consists of three species, two of which are European, the third Chinese.

B. igneus.–The under parts are conspicuously coloured bluish black with large irregular red or orange-red patches; the upper parts are more or less dark grey or olive black. The iris is golden, speckled with brown. The male has a pair of internal vocal sacs by which the throat can be inflated; nuptial excrescences are developed on the inner side of the fore-arm and the first two fingers. Total length from 1½ to 2 inches, the males being generally smaller than the females. This "Fire-bellied toad," the "Unke" of the Germans, is essentially a native of lakes, ponds, and other standing waters of the plains.

It ranges through the whole of North Germany, Bohemia, and Hungary into Russia, eastwards as far as the Volga. The latter river, the Danube, and the Weser form, roughly speaking, its boundaries; northwards it extends into Denmark and the southern extremity of Sweden.

Fig. 31.–Bombinator igneus. × 1. Fire-bellied Toad. Two of them in "warning" attitude.

B. pachypus.–The under parts are yellow instead of red. The male is devoid of vocal sacs, but has nuptial excrescences on the under surface of most of the toes, in addition to those on the fore-arm and fingers. The "Yellow-bellied Toad" is the representative of the red-bellied species in Southern and Western Europe, preferring, although not exclusively, the hilly and mountainous districts. It ranges from France and Belgium through South-Western Germany, continental Italy, and the whole of Austria and Turkey in Europe. Where both species meet, for instance in the hilly districts between the Weser and the Rhine, in Thuringia and in Austria, the predilection of the yellow-bellied species for the hills, and that of the other for the plains, is well marked.

While B. igneus prefers standing waters with plenty of vegetation, B. pachypus is often found in the smallest occasional puddles produced by recent rain, for instance in the ruts of roads. Both species have otherwise much in common. They are essentially aquatic. They hang in the water, with their legs extended, nose and eyes just above the surface, and bask or lie in wait for passing insects, the fire-bellied kind preferring to conceal itself in the vegetation of the margins of ponds. During the pairing season, in Germany in the month of May, they are very lively and perform peculiar concerts, one male beginning with a slowly repeated note like "hoonk, hoonk," or "ooh, ooh," in which all the other males soon join, so that, when there are many, an almost continuous music is produced. This sound is not at all loud, a little mournful and very deceptive. It appears to be a long way off, certainly at the other end of the pond, until by careful watching you see the little creature almost at your very feet. But on the slightest disturbance the performance ceases, they dive below and hide at the bottom. The yellow-bellied kind, when surprised in a shallow puddle, skims over the mud, disturbs it, and allows it to settle upon its flat body, so that nothing but the little glittering eyes will betray its concealment. When these toads are surprised on land, or roughly touched, they assume a most peculiar attitude, as shown in Fig. 31. The head is partly thrown back, the limbs are turned upwards with their under surfaces outwards, and the whole body is curved up so that as much as possible of the bright yellow or red markings of the under parts is exposed to view. The creature remains in this strained position until all danger seems passed. In reality this is an exhibition of warning colours, to show the enemy what a dangerous animal he would have to deal with. The secretion of the skin is very poisonous, and the fire-toads are thereby well protected. I know of no creature which will eat or even harm them. I have kept numbers in a large vivarium, together with various snakes, water-tortoises, and crocodiles, but for years the little fire-bellies remained unmolested, although they shared a pond in which no other frog or newt could live without being eaten. Hungry water-tortoises stalk them under water, touch the intended prey with the nose in order to get the right scent, and then they withdraw from the Bombinator, which has remained motionless, well knowing that quick movements, or a show of escape, would most likely induce the tortoise to a hasty snap, with consequences to be regretted by both.

After they have been handled frequently, they do not readily perform, but simply lie still, or hop away. Miss Durham experienced considerable difficulty in inducing her tame specimens to assume and to keep up the correct warning attitude. The statement that they "turn over on the back" is a fable, graphically fixed in various illustrated works.

It has been said that these two species are diurnal and thoroughly aquatic. They are certainly active in the daytime, sing in full sunshine, and spend most of their time in the water, but they display much more liveliness towards the evening and during the night, especially when there is a moon. My fire-toads live by no means always in the water, but conceal themselves in the daytime under stones, while they are regularly all astir at night in search of worms and all kinds of small insects.

The spawning takes place several times during the spring and summer. The amplexus is lumbar, and the eggs are extruded singly. They sink to the bottom, or are attached to water-plants. The oviposition takes a long time, perhaps the whole night, and several dozen eggs, not hundreds as in the allied genera, make a set. The egg, with its swollen gelatinous capsule, is large for so small a creature, namely 7-8 mm. in diameter. The embryos escape after a week, and the tadpoles reach two inches in total length. Those of B. igneus have a triangular mouth, but in B. pachypus this is elliptical, as in Alytes and Discoglossus. Metamorphosis is completed in the same autumn; the little toad is then about 15 mm. long, and differs from the adult by the absence of the conspicuous coloration of the under parts. In reasonable conformity herewith it does not take up the warning attitude. The colour appears gradually during the second year, but full growth is generally not reached until the third year. They do not hibernate in the water, but hide on land out of the reach of frost.

Alytes.–The tympanum is distinct, the pupil vertical, the omosternum is absent. The only two species live in South-Western Europe. The male attaches the eggs to its hind limbs, and nurses them until they are hatched.

A. obstetricans, the "Midwife-toad," has the general appearance of a smooth toad. The upper parts are rather smooth, sometimes almost shiny, in spite of the numerous more or less prominent warts, of which those of the lateral lines, and those above the ear, are generally most marked. The colour of the upper parts varies a great deal according to the prevalence of greenish and reddish spots upon the grey or brown ground-colour. The red is sometimes, especially in the breeding males, rather conspicuous on the parotoid region and on the upper sides of the body. The under parts are whitish grey. The iris is pale golden, with black veins. The male has no vocal sac, and is as a rule smaller than the female, the latter reaching a length of two inches.

This species occurs in the whole of the Iberian Peninsula and in France, extending into Switzerland and beyond the Rhine valley into Thuringia. Altitude above the sea does not seem to have any influence upon its range, which reaches from sea-level to the tops of subalpine mountains. I have found great quantities of its tadpoles in Portugal on the Serra d'Estrella, nearly 6000 feet high, and they are recorded from 6500 feet in the Pyrenees. They seem to be ubiquitous in Spain and Portugal, not that they are often found or seen, but they are heard everywhere; besides, tadpoles are sure to be in the clear cold lakes on the tops of the mountain-ranges, in the dirty puddles caused by the village fountains, and in the sun-heated swampy ditches on the roadside with scarcely enough water to hold the wriggling mass. Wherever there is water within easy reach, on the lonely mountains, in fertile valleys, in the gardens of the busy towns, you hear during the whole night, from March to August, the double call-note of the male, sounding like a little bell; but to see the performer is quite a different matter. He sits in front of his hole, dug out by himself or appropriated from a mouse, in a crack of the bottom of a wall, under stones, or in a similar place into which he withdraws for the day.

The pairing and the peculiar mode of taking care of the eggs by the male, which habit has given it the specific name obstetricans, the midwife, have been most carefully observed by A. de l'Isle du Dréneuf, near Nantes. A condensed account has been given by Boulenger. Several males collect around a female on land, not in the water, and the successful one grasps her round the waist. For nearly half an hour the male lubricates the cloacal region of the female by more than one thousand strokes of his toes, whereupon the female extends the hind-limbs, forming with the bent hind-limbs of the male a receptacle for the eggs, which are then expelled with a sudden noise. The eggs are yellow and large, up to 5 mm. in diameter, and are fastened together in two rosary-like strings, several dozen making one set. During the expulsion of the eggs the male shifts its body forwards, clasps his fore-limbs round the female's head, and fecundates the eggs. After a rest he pushes first one hind-limb and then the other through the convoluted mass of eggs, which then have the appearance of being wound round the hind-limbs in a figure of 8. Then the sexes separate and the male withdraws with its precious load into its hole, which it, however, leaves during the following nights, in search of food, taking this opportunity to moisten the eggs in the dew, occasionally even immersing them in the water. After at least three weeks, when the larvae are nearly ready, he betakes himself to the nearest water, and the larvae burst the thereby softened gelatinous cover of the eggs. Not infrequently the same male ventures upon a second pairing, and adds another load to the one which already hampers its movements. The eggs being large, owing to the great amount of yellow food-yolk, the embryos are enabled to be hatched in a more advanced stage than in most other Anura. The larva develops only one pair of external gills within the egg. These appear first in the shape of oval bags upon the third branchial arch, which sprout out secondary branches, soon in their turn to be resorbed and replaced by the so-called internal gills before hatching.

Fischer-Sigwart[^[77]] gives the following account of the growth of this species. The male took to the water, with its load of twenty to thirty eggs, on the 6th of June. The larvae escaped out at once, 16-17 mm. long, the body measuring 5 mm. On the 14th they had reached 32 mm. in length, whereupon they grew very slowly, although they were well fed, in a temperature of about 50° F. This same brood did not metamorphose until May of the next year. The growth took place as follows:–The hind-limbs appeared on the 8th of September, when the tadpoles were 50 mm. long; by the middle of the next May they had reached their greatest length, 76 mm., the hind-limbs being 18 mm. long, whilst the fore-legs were just indicated. On the 21st of May the hind-limbs were 27 mm. long, and the whole creature was practically metamorphosed, except for the tail. The latter was resorbed on the 13th of July, and the little toads, 25 mm. in length, were actually smaller, certainly far less bulky and heavy, than the tadpoles, which had required one year and a quarter for their metamorphosis.

The early broods probably finish their development by the autumn of the same year, but those which are born later, in July and August, certainly hibernate in the water. I have found very small tadpoles, scarcely 15 mm. long, on the Cantabrian mountains as late as the end of September, and rather large ones in the spring at the time of first pairing; the fact that this takes place during the whole summer explains the occurrence of tadpoles in all stages of development almost the whole year round.

A. cisternasi has only two palmar tubercles, the middle or third one of A. obstetricans being absent; the outer finger is short and thick. Instead of a very long and wide fronto-parietal fontanelle, the fronto-parietal bones diverge only in front so that there are two fontanelles, a small one in the parietal and a large triangular one in the frontal region. The limbs are relatively shorter and stouter in conformity with the habits of this species, which prefers to burrow in sandy localities. Otherwise it leads the same kind of life as A. obstetricans, and the male carries the eggs. It has hitherto been found in Central Spain and in the middle provinces of Portugal.

Liopelma is intermediate between Alytes and Bombinator, agreeing with the latter, in conformity with its essentially aquatic life, in the absence of a tympanum, while the Eustachian tubes are entirely suppressed. The tongue is disc-shaped, but is slightly free behind. The pupil is triangular. The male is devoid of a vocal sac. L. hochstetteri is the sole representative of the Amphibia in New Zealand, where it is apparently rare. The upper parts are covered with smooth tubercles, and are dark brown with blackish spots; the under parts are whitish. Total length only 1½ inch.

Fam. 2. Pelobatidae.–The upper jaw and, as a rule, the vomers are provided with teeth. The tongue is oval, slightly nicked, and free behind, so that it can be thrown out, except in Asterophrys turpicola of New Guinea, which has a large but entirely adherent tongue. The vertebrae are procoelous, except in Asterophrys and the Malay genus Megalophrys, where they are opisthocoelous. The sacral diapophyses are strongly dilated. The omosternum is small and cartilaginous. The metasternum has a bony style, and ends in a cartilaginous, rounded or heart-shaped disc, but in Scaphiopus it forms an entirely cartilaginous plate. The tympanic disc is mostly hidden or indistinct, and is quite absent in Pelobates. The Eustachian tubes are very small in Pelobates, and exceedingly minute in Scaphiopus stagnalis of New Mexico. The pupil is vertical. This family contains seven genera with about twenty species, with a rather scattered distribution.

Fig. 32.–Map showing distribution of Cystignathidae, Discoglossidae, and Pelobatidae.

A. Toes extensively webbed, sacrum and coccyx confluent.

a. Metasternum a cartilaginous plate. America .......... Scaphiopus, p. [164].

b. Metasternum with a bony style. Europe .......... Pelobates, p. [162].

B. Toes nearly free. Metasternum with a bony style.

a. Vertebrae procoelous.

α. Sacral vertebra articulating by one condyle with the coccyx.

Europe .......... Pelodytes, p. [165].

New Guinea .......... Batrachopsis.

β. Sacral vertebra with two condyles.

India and Malaya .......... Leptobrachium, p. [166].

b. Vertebrae opisthocoelous.

Ceylon and Malayan Islands .......... Megalophrys, p. [60] (Fig. 11).

New Guinea .......... Asterophrys.

Pelobates ("Spade-foot").–The tympanum is absent; the toes are webbed. The inner tarsal tubercle is large, and is transformed into a shovel which is covered with a hard, sharp-edged, horny sheath. The skin of the upper surface of the head is partly co-ossified with the underlying cranial bones, giving them a pitted appearance. The general shape is toad-like.

P. fuscus.–The smooth skin is brown above, with darker marblings, while the under parts are whitish, but the coloration varies greatly, from pale to dark brown or olive-grey with more or less prominent irregular dark, sometimes confluent, patches. Some specimens are adorned with numerous red spots. The tarsal spur is yellow or light brown. The iris is metallic red or golden. The male has a long oval gland on the upper surface of the upper arm, and although possessed of a voice, has no vocal sacs. The total length of full-grown females is nearly 3 inches, that of males half an inch less.

The "Spade-footed Toad," which occurs throughout the whole of Central Europe, extends from Belgium and the middle of France to North-Western Persia, and from the southern end of Sweden to Northern Italy. It prefers sandy localities, in order to dig its deep hole, in which it sits concealed during the daytime. Owing to the looseness of the sand, the hole is filled up so that no trace of its inhabitant is left. The digging is done by means of the spades, and in suitable localities the animal soon vanishes, sinking backwards out of sight. Except in the breeding season, or at night, it is therefore found only accidentally. The sand-loving habits do not, however, prevent it from enjoying moist localities. Several which I have kept for years dig themselves into the wettest moss in preference to the drier parts of their habitation. Being thoroughly nocturnal, they hunt after nightfall, the food consisting of all sorts of insects and of worms. When captured they utter a startling shrill cry, and their skin becomes covered with a dermal secretion which smells like garlic, a peculiarity which has given them in Germany the name of "Knoblauchskröte," "garlic-toad." Although they become very tame, so that they no longer smell when handled, they can be made ill-tempered by being pinched or otherwise teased, whereupon they take up a defiant attitude, and with open mouth continue to cry for several minutes. Some such scenes occur now and then, without my interference, with the specimens which share their abode with several species of Amblystoma and Spelerpes; there are heard now and then sudden loud yells, like the squeak of a cat or the yapping of a little dog.

In the spring the Spade-footed Toads take to the water for about a week, and the male's call-note is an ever-repeated clucking sound, which can also be produced under water, with the mouth shut, the air being shifted backwards and forwards through the larynx. The male grasps his mate below the waist; the eggs are combined into one thick string, which is about 18 inches long, and is wound round and between the leaves and stalks of water-plants. The eggs measure 2-2.5 mm., and are very numerous, a large string containing several thousands. The larvae are hatched on the fifth or sixth day in a very unripe condition. They are only 4 mm. long, quite black, and still devoid of gills and tail. They attach themselves to the empty gelatinous egg-membranes, which they possibly live upon. On the following day the tail begins to grow; two days later fringed external gills sprout out and serve for about ten days, when they in turn give way to new, inner gills. The little tadpoles then leave their moorings and become independent. The hind-limbs appear in the ninth week, the fore-limbs in the twelfth. At the age of three months they begin to leave the water. The most remarkable feature is the enormous size of the full-grown tadpole, the body of which is as large as a pigeon's egg; the usual total length, including the tail, amounts to about 4 inches or 100 mm., but occasionally regular monsters are found. This was the case some thirty years ago, when the Berlin Museum received a number of tadpoles, the largest of which measured nearly 7 inches. They were found in the month of December near Berlin, in a deep clay-pit with high, steep walls, so that the tadpoles were prevented from leaving the water. Similarly hemmed-in broods probably hibernate in the water under the ice, and such instances have been recorded. Normally they metamorphose into the much smaller toad within the same year.

P. cultripes.–This is the Spade-foot of the whole of Spain and Portugal and of the southern and western parts of France. It is similar in habits to P. fuscus, from which it differs but slightly. The tarsal spur is black, and there is a parieto-squamosal bridge which completely roofs over the temporal fossa and closes the orbit behind.–Boulenger has discovered the rare, individual occurrence of minute teeth on the parasphenoid and on the pterygoids of this species. These teeth are unquestionably the last reminiscences of a condition almost entirely superseded in the recent Anura.

P. syriacus from Asia Minor and Syria agrees with P. cultripes in the cranial configuration, but has the yellow or brown spur of P. fuscus.

Fig. 33.–Pelobates cultripes, Spade-foot Toad, × 1, and under surface of left foot.

Scaphiopus.–The Spade-foot of North America and Mexico differs slightly from those of Europe, chiefly by the presence of a more or less hidden tympanum and of a subgular vocal sac, and by the sternum, which forms an entirely cartilaginous plate without a special style. The close relationship of these two genera is further indicated by the occurrence of peculiar large glandular complexes in some of the species, pectoral in S. solitarius, tibial in S. multiplicatus of Mexico. At the same time this genus approaches Pelodytes.–About eight species are known, two of which inhabit the United States, the others Mexico.

S. solitarius is the commonest species of the Southern States. It is brown above, with darker patches; its total length is about 2 inches. According to Holbrook it excavates small holes half a foot deep, in which it resides, seizing upon such unwary insects as may enter its dwelling. It never leaves the hole except in the evening or after long-continued rains. It appears early in March, and soon pairs; as an instance of hardiness Holbrook mentions that he has met it whilst there was still snow on the ground. When teased they assume a humble attitude, bending the head downwards with their eyes shut, as illustrated by Boulenger.[^[78]]

Pelodytes is, like the rest of the genera, devoid of the tarsal digging spur. The tympanic disc is rather indistinct; the male has a subgular sac. The general appearance of the slender body with long hind-limbs and toes is frog-like. Two species only are known, one in South-Western Europe, the other in the Caucasus.

P. punctatus.–The "Mud-diver" has the upper parts covered with small warts, and is about 1½ inch in length. Its coloration is variable, and changes much. One day it may appear greenish brown, the next day pale grey; in the daytime perhaps with many bright green spots, and in the evening spotless and unicoloured. The under parts are mostly white, sometimes with a fleshy tinge. The male has a voice like "kerr-kerr" or "creck-creck," uttered during the breeding season, which lasts from the end of February until May, according to the temperature and the more Southern or Northern locality. Occasionally they breed a second time in the summer or autumn. The male develops nuptial excrescences, chiefly three rough patches on the inner side of the fore-limbs or on the inner side of the first two fingers, while the belly and thighs are covered with small granules. In the mode of copulation, the laying of the small and numerous eggs, the hatching of the larvae in a tail- and gill-less condition, this genus closely resembles Pelobates; but the tadpoles never reach a colossal size, the usual length being 2 inches, and even this is comparatively large for so small a species. It inhabits the greater part of France, most of Portugal, and the southern half of Spain, avoiding, however, the central plateaux and the mountain-ranges. Its habits are essentially nocturnal, living in the immediate vicinity of the water, into which it hops with a long jump in order to hide in the mud. Easily kept, it breeds regularly in captivity, according to circumstances at almost any time of the year.

P. caucasicus has been discovered in the Caucasus at an altitude of 7000 feet. The remaining genera of this family contain only a few species each, and are restricted to South-Western Asia, the Malay and Papuan Islands. The commonest is Leptobrachium, which ranges from the Himalayas to Borneo and Java. Pupil vertical. Vomerine teeth sometimes absent. Tongue roundish, very slightly nicked behind. Tympanum indistinct. Omosternum small, cartilaginous. Male with internal vocal sacs. Tarsus with a roundish tubercle. Some of the species, e.g. L. carinense from the Karen Hills, attain to a large size, namely, 6 inches; they seem to live on rats and mice, and one specimen contained a young squirrel.

Fam. 3. Bufonidae (Toads).–The formula:–no teeth in the upper and lower jaws, vertebrae procoelous and without ribs, sacral diapophyses dilated,–is sufficiently diagnostic of this cosmopolitan family. The generally entertained notion that toads have a rather thick-set, short-limbed, warty appearance, does not apply to all the members of the family. The majority are quite terrestrial, many are burrowing, the Javanese Nectes is aquatic, the Afro-Indian Nectophryne is arboreal, while the Australian Myobatrachus and the Mexican Rhinophrynus eat termites and are correspondingly modified; lastly, Bufo jerboa is a slender, long-legged creature.

Teeth are almost entirely absent, except in Notaden, which has teeth on the vomers. The omosternum is mostly absent, except in Engystomops and in some species of Bufo, while in Notaden it is merely vestigial. The metasternum shows more variety. The tympanum is usually distinct, but varies even within the same genus, being hidden beneath the skin or being entirely absent. The terminal phalanges are modified according to the habits of the species, but they are never claw-shaped.

The Bufonidae are connected in various directions. The Neotropical Engystomops greatly resembles the likewise Neotropical Cystignathoid Paludicola, and the Australian Pseudophryne closely approaches the Australian Cystignathoid Crinia. It is therefore all the more remarkable that a similar approach, in another direction, namely, towards the Firmisternal family of the Engystomatidae, is indicated by the Mexican Rhinophrys and the Australian Myobatrachus. However, since there are no true Engystomatidae in Australia, although several genera occur in Papuasia, these cases may be instances of convergence without necessarily implying relationship. An unmistakable line of connexion leads, according to Boulenger, to the Pelobatidae, the link being the Himalayan Cophophryne, with very strongly dilated sacral diapophyses, with a single condylar articulation of the coccyx with the sacral vertebra (as in some Indo-Malayan Pelobatidae), while this articulation is bicondylar in all the other Bufonidae.

Fig. 34.–Map showing distribution of Bufonidae. The vertical lines indicate the occurrence of Bufonidae, but not of Bufo.

The whole family is divided into nine genera with more than a hundred species, of which only about fifteen do not belong to the genus Bufo. The distribution of the family is well-nigh cosmopolitan, with the remarkable exception of Madagascar, Papuasia, and the small islands of the Pacific; Bufo has been wrongly said to inhabit the Sandwich Islands. The greatest number of species, chiefly Bufo, occur in the Neotropical region, the greatest number of genera in Central America, where Bufo is rare, and in Australia, where it is absent.

A. Pupils contracted to a horizontal slit. Typically arciferous.

a. Australian. Tympanum invisible. Fingers and toes not dilated.

1. With vomerine teeth. Both the omo- and meta-sternum are rudimentary. East Australia: .......... Notaden bennetti.

2. Without vomerine teeth. Omosternum absent. Metasternum cartilaginous: .......... Pseudophryne, p. [168].

b. Not Australian.

1. Omosternum narrow and cartilaginous. Metasternum with a bony style ending in a cartilaginous disc. Fingers and toes slightly swollen. Neotropical: .......... Engystomops, p. [168].

2. Omosternum absent. Metasternum cartilaginous.

α. Fingers and toes webbed; terminal phalanges T-shaped and with adhesive broadened tips. Africa and India: .......... Nectophryne, p. [169].

β. Fingers free, toes webbed; terminal phalanges simple, not dilated. Tympanum distinct. Java: .......... Nectes, p. [169].

3. Metasternum cartilaginous, sometimes ossified along the middle. Fingers free; toes more or less webbed; tips simple or dilated into very small discs: .......... Bufo, p. [169].

B. Pupil a vertical slit. The epicoracoid cartilages are narrow and scarcely overlap. Omosternum absent except in Cophophryne. Vomerine teeth absent. Sacral diapophyses strongly dilated. The terminal phalanges are simple and the tips are pointed.

a. Australian. Tympanum distinct. The metasternum is calcified along the middle: .......... Myobatrachus, p. [184].

b. Mexican. Tympanum absent. Metasternum rudimentary: .......... Rhinophrynus, p. [185].

c. Himalayan. Tympanum absent. Metasternum with a slender bony style: .......... Cophophryne sikkimensis.

Engystomops is interesting because it closely resembles the Cystignathoid genus Paludicola, and thereby seems to connect these two families. It differs from Paludicola chiefly by the absence of teeth, by the moderately dilated sacral diapophyses and by the slightly swollen tips of the fingers and toes, the end-phalanges of which are, in one species, E. petersi, T- or anchor-shaped The tympanic disc is either distinct or hidden. The males have a large subgular vocal sac. The generic name refers to the small head with a prominent snout. Three species are known from Central America and Ecuador.

Pseudophryne appears to be another link with the Cystignathidae by its resemblance to the Australian genus Crinia, from which it differs by the absence of teeth and by the absence of an omosternum. The sacral diapophyses are but moderately dilated. The males have a flat oval gland on the hinder side of the thighs, and they are provided with a subgular vocal sac. The 3 or 4 species of this genus which live in Australia, both East and West, are not unlike Bombinator in their general shape, short limbs and coloration. The skin of P. australis and P. bibroni is covered with small smooth warts and is blackish brown, while the under parts are blackish with large yellow patches. Total length little more than one inch. Concerning the breeding habits, see p. [223].

Nectophryne.–The sacral diapophyses are strongly dilated. N. afra, without a tympanum, but with fully-webbed digits and several broad, cushion-like or lamellar pads on the fingers and toes, inhabits the Cameroons, N. tuberculosa of Malabar, and N. guentheri and N. hosei of Borneo, have a visible tympanum and the fingers are webbed at the base only. These slender and long-legged species are most probably arboreal, as indicated by the broadened, but truncated, tips of their fingers and toes. N. hosei is about 4 inches long, N. misera is a little creature of only ¾ inch in length. Nectes, hitherto known by one species, N. subasper of Java, is a swimmer and exceeds 6 inches in length. The tympanum is very distinct; the small nostrils look upwards. The toes are long and webbed to the tips; the hind-limbs are very long. The sacral diapophyses are strongly dilated. The skin of the upper parts is very rugose, covered with round warts, and dark brown; the under parts are granular and uniformly light brown.

Bufo.–The great number of species, more than 100, renders a strict definition of this genus difficult. The tongue is pear-shaped, thicker in front, entire, not cut out, but free behind, so that it can be projected. The fingers are free, the toes more or less webbed although never completely so. The terminal phalanges are obtuse and sometimes carry tiny discs. The omosternum is absent or merely vestigial. The metasternum is a rather large cartilaginous plate with a waist, which is sometimes incompletely calcified. The sacral diapophyses are moderately dilated. The tympanum is distinct or hidden. The skin of the upper parts is always rich in specific poison-glands, a concentration of which forms in many species very conspicuous, thickened parotoid glands. The surface of the skin may be smooth, moist and slimy, or rough and warty, sometimes covered with tiny, sharp, horny spikes and quite dry.

The genus is cosmopolitan, with the exception of the whole Australian region and Madagascar, from which we may perhaps conclude that its original centre was not in Notogaea, in spite of the diversity of species in the Neotropical region, which now contains about half of all the species known. Next to Central America the Indian region is richest in species of Bufo.

B. vulgaris.–The Common Toad of the Palaearctic region. The skin of the upper parts is much wrinkled and beset with numerous round warts or poison-glands, the openings of which can be seen with the naked eye, especially on the large parotoid complexes. The outermost layer of the epiderm, in fact all that portion which is periodically shed, is elevated into numerous little cornified spines. The extent of their development varies much; southern specimens, especially those from Portugal, being perhaps the roughest. Others appear quite smooth to the touch, and this is the case with many English specimens. The skin of the under parts is more granular and devoid of specific glands. The general colour of the upper parts is olive grey to dark brown, more or less mottled; the under parts are whitish, often with a brown, yellow or reddish tinge.

The coloration of this species varies considerably and is moreover very changeable. These changes depend chiefly upon the surroundings and the locality, in which certain styles of coloration seem to be the fashion, not necessarily to the absolute exclusion of others. Some specimens are of a rich brown colour, with or without dark brown spots and patches, and these are sometimes confluent, forming irregular, longitudinal bands. The ground-colour of other individuals is olive grey, with or without darker patches, and these paler tones prevail in toads which live on light-coloured soil, for instance on chalk. I recently found one between two dark-coloured slates, and this creature was so black that it gave the impression of having soiled itself with coal-dust. One and the same specimen will appear paler or darker according to its mood and the leading tones of its immediate surroundings, but it cannot change its dominant ground-colour. A third colour-variety occurs more frequently in the mountainous districts of Southern Europe. I have obtained the most handsome specimens in the Serra Gerez, in North Portugal. Their ground-colour is pale brownish-yellow, with many large and small, rich brown patches, or if the latter colour predominates, these patches and spots are separated from each other by creamy seams, with the occasional effect of dark brown, yellow-ringed eyes. Eastern Asiatic specimens often have a fine yellow vertebral line and the under parts are inclined to be marked with dark spots.

The iris is red or coppery, mottled with black. The male has no vocal sacs, and, besides being smaller than the female, is distinguished by slight nuptial excrescences in the shape of little horny brushes on the inside of the inner palmar tubercle and the three inner fingers. The full size of this toad varies extremely. Taking the standard of everyday experience in England and Central Europe, one would call any female beyond 3½ inches in length, and any male of more than 2½ inches, unusually large. But occasionally they grow to a much larger size, especially in the mountains of Southern Europe, provided there is a rich vegetation of meadows and deciduous trees so as to insure a variety of plentiful food. Although Fatio[^[79]] mentions a toad 153 mm. = 6 inches long, and Boulenger succeeded in getting a toad from Paris which measured 132 mm., i.e. almost 5¼ inches, one of my specimens from the Serra Gerez seems to hold the record with a total length from snout to vent of 135 mm. or more than 5¼ inches. Jersey is also famous for its large toads, possibly on account of the many large greenhouses. These large specimens do not constitute a special race. The monsters among them are without exception females, often but not always sterile, as I have often found large masses of eggs in them. Food is the chief cause. At least I have observed that the more voracious of some Spanish and Portuguese specimens, which were already 3½ inches long, and therefore entitled to respect, continued to grow rather rapidly, adding about half an inch within a year. Again, if the growth of a promising toad is arrested for a season–not necessarily by starvation, but by uncongenial surroundings, sameness, and unvaried nature of food–they consolidate so to say, or settle down, and no amount of future good feeding will turn them into exceptionally big specimens. There are no data to tell how old such monsters really are. At least ten years are required by the Southerners to reach four inches. The usual length of life attained by a toad is likewise unknown. Boulenger kept one in a box provided with a sod, a pan of water and plenty of varied food, but twelve years of close captivity did not make any appreciable difference in its appearance.

Fig. 35.–Bufo vulgaris. Portuguese specimen. × ⅔.

A number of large Spanish and Portuguese specimens in my greenhouse were at first very shy, and tried every possible means of escape or sullen hiding, but gradually they condescended to take food when lifted on to the slate-covered stage upon which their food was spread. After a few weeks they had learned this so thoroughly that, towards the usual hour of feeding, they climbed most laboriously on to the slates, lying in wait between the flower-pots, and coming forward when we entered the house. The rest of the day and night they spent on the ground, under stones or plants, each in its individual lair. The biggest of all, and several others, became so tame that they took food whilst sitting on the hand, and then they looked up for more. The food must be alive and show movement. Mealworms, snails, beetles and other small creatures are first carefully inspected with bent-down head, and are sometimes followed for a few inches; then comes an audible snap, a flash of the rosy tongue and the prey has disappeared. Large earthworms are nipped up with the jaws and laboriously poked in with the hands, the fingers being so placed as to clean the worm of adherent soil and other impurities. Very large worms are shaken, twisted, pressed against the ground and gulped down with convulsive movements, but not unfrequently the tip-end remains for some minutes sticking out of the tightly shut mouth. Several are taken at one sitting, until the toad is gorged. One of the biggest took full-grown mice, which were not "fascinated by the fiery eyes" but were stalked into a corner and then pounced upon immediately when they moved. The shells of snails can for half a day be felt through the body; they then dissolve or are disgorged. The dung, which is passed in large, long masses, is often full of fine earthy matter, the contents of the earthworm's intestines, and sometimes it contains the chitinous remains of certain beetles which are supposed to be excessively rare. I know of no instance of slugs being eaten.

The regular hunting-time begins with the evening and is continued throughout bright nights, the toads crawling and hopping about. They are expert climbers of rocks, and succeed in reaching apparently inaccessible places by shoving themselves up between vertical walls, and taking advantage of any roughnesses for foothold. Every few weeks they shed their skins. Without any preliminary symptoms or loss of appetite or liveliness, the body makes a few twisting motions, the back is now and then curved, and the skin splits down the middle line. Owing to the more forcible contortions of the body it slides down to the right and left of the back, whereupon the toad gets hold of the peeling-off skin with fingers and toes, scraping the head and sides, and conveys the thin, transparent, slightly tinged skin into the mouth, slips out of it backwards and swallows it. The new surface is then quite wet and shiny, but it soon dries and hardens.

Many toads, for instance the Common Toad and the Pantherine Toad, assume a peculiar attitude when surprised. Instead of blowing themselves up by filling their lungs with air, they raise themselves upon their four limbs as high as possible, but turning the back towards the enemy in a slanting position, either to the right or to the left side, apparently in order to present as much surface as possible, in other words to look their biggest.

Some of my specimens hibernated regularly for a few months, burying themselves completely in loose, dry soil, under leaves, or,–a favourite place,–in a heap of cocoa-nut fibre. Others, and this applies also to English specimens transferred from the garden into the greenhouse, are lively all the year round, but even they withdraw for an occasional sleep of a few weeks at any time of the year.

The whole family of large toads came to a sad end after four years, when they were put into new temporary quarters, a slate-bottomed terrarium. Being kept during my absence in wringing wet moss, which became fouled by their own excretions, they contracted a mysterious disease from which they never recovered. They are rather averse to wet surroundings, and except during the short pairing season they live in cool, shady places, preferably with just a little dampness. Occasionally they take a soaking bath. One specimen, living in the garden, repaired during the hot and dry summer nights to a standpipe in the garden, enjoying the occasional drips of water.

Considering the amount of snails and other noxious creatures destroyed by them during their regular nocturnal hunts, toads are eminently useful creatures. Nevertheless, they suffer much through the stupid superstition of people who ought to know better. It is difficult to find a gentle, absolutely harmless and useful creature that is more maligned than the European toad. It brings ill-luck to the house, the "slimy toad" spits venom, sucks the cows' udders and after that destroys their power of giving milk; it poisons the milk in the cellar, and a certain builder's horse, which was grazing in the grounds of the Cambridge Museums, and died there from a large concrement obstructing its bowels, was solemnly declared to have swallowed one of my toads. Silly superstitions, owing to faulty, or rather entire want of, observation! The toad is not slimy, but dry; it is often found in buildings, where it keeps down the woodlice; it cannot suck, nor does it drink at all; it does not spit venom, but becomes covered with milky white and very strong poison when in acute agony, for instance when trodden upon; and unless the big skin-glands be forcibly squeezed, there will be no squirting. Therefore, leave it alone, or put down food on its evening beat, and it will soon come to know and to recognise its friends.

The Common Toad can exist without food for a long time, provided the locality is cool and damp, but it wastes away almost to skin and bones. In order to disprove the persistently cropping up fable and sensational newspaper-accounts of toads having been discovered immured in buildings, where they were supposed to have lived for many years, Frank Buckland put a dozen specimens into separate holes bored in a block of porous limestone, covered them up tightly with a glass plate and buried the block a yard deep in the soil. A second dozen were treated similarly, but were put into a block of dense sandstone. After a year and two weeks all the toads enclosed in the latter block were of course found dead and decomposed, but most of those in the porous block were still alive, with their eyes open, and did not succumb to starvation until eighteen months of confinement. These poor creatures could of course not move about, and were practically undergoing enforced continuous hibernation. Otherwise they would soon have wasted away and have died within six months. Those which tumble into deep and dry wells remain rather small, but generally manage to keep alive for years on the spiders, woodlice, earwigs and other insects which likewise tumble in.

Toads hibernate far from the water in dry holes or clefts, retiring in the middle of October in Central Europe, and they do not reappear before March. Soon after, and this depends naturally upon the season, they congregate in ponds or pools, and the males, which far outnumber the females, for whom they fight, make a peculiar little noise, something like the whining bleat of a lamb, uttering this sound day and night. The male having, after much wrestling with competitors, secured a female, which is often several times bigger than himself, clasps her tightly, by pressing his fists into the armpits, and the pair swim or crawl about in this position sometimes for a week before the spawning takes place. The number of eggs laid at one sitting is enormous, varying from 2000 to 7000. They are very small, only 1.5-2.0 mm. in diameter, and are expelled in two double rows or strings, one coming out of each oviduct. These strings consist of a soft gelatinous mass, in which the double rows of entirely black eggs are imbedded, and they measure in the swollen condition about 6 mm. or ¼ inch in diameter, and from 10 to 15 feet in length. The strings are wound round and between water-plants by the parents, which move about during the laying and fertilising process. According to the coldness or warmth of the season the larvae are hatched in about a fortnight, and for the next few days they hang on to the dissolving gelatinous mass of the egg-strings. They then leave the slime and fasten themselves by means of their suckers to the under side of grasses and water-plants or sticks, with their tails hanging downwards, still in a rudimentary condition, but henceforth progressing rapidly.

Fischer-Sigwart[^[80]] found the time of development as follows:–The eggs were laid on the 6th of March; the larvae left the jelly on the 16th, being 4 mm. long. On the 2nd of April they measured 13 mm.; on the 25th, 20 mm. On the 7th of May the hind-limbs appeared. On the 18th of May the tadpoles had reached their greatest length, namely 24 mm., and this is a rather small size for so large a species. The fore-limbs broke through on the 28th, and the metamorphosis was completed eighty-five days after the eggs were laid, the creatures leaving the water on the 30th of May. The tadpoles showed a preference for rotten pieces of Agaricus, which were floating in the water. The little baby-toads are surprisingly small, scarcely 15 mm. long, and live in the grass, under stones, in cracks of the ground, and hop about in much better style than their heavier and more clumsy-looking parents. Where many broods have been hatched they can be met with in myriads, the ground literally swarming with them, and as they are naturally stirred up by a sudden warm rain, perhaps after a drought, people will occasionally state it as an observed and well-ascertained fact that "it has rained toads."

What becomes of all these hopeful little creatures? Although it takes them fully five years to reach maturity, one would expect that the whole country would be swarming with toads; but since this is not the case, there being not more toads now than there were before, it follows that their enormous fecundity is only just sufficient to keep the race going. Adult toads seem to have scarcely any enemies except the Grass Snake, which takes them in default of anything better. But how about the reduction where there are no snakes? We know nothing about epidemics which might carry them off, but elderly toads are liable to a horrible disease produced by various kinds of flies, notably by Lucilia bufonivora and Calliphora silvatica, the maggots of which somehow or other eat their way from the nostrils into the brain and into the eyes. Those which reach the brain at first produce effects similar to those of Coenurus cerebralis, the hydatid or bladder-worm of sheep. The toad inclines its head towards one side, and cannot crawl straight, but walks in a circle. By eating away the brain they gradually destroy the host's life. But if none enter the brain, and a few only find their way into the eye, they only impair or destroy its sight. Such toads show signs of pain, poking at or stroking the affected eye, which becomes inflamed, and ultimately remains enlarged, with the iris partially or entirely destroyed by the maggot, which does not develop further, but dies in the eye-chamber, this being really an unsuitable place for it. The eyesight is of course affected, and is mostly, but not in all cases, lost. Such half-blind individuals–the disease affecting sometimes one eye only–recover their health, and except for a little awkwardness, behave like normal specimens. This applies to Bufo vulgaris as well as to B. calamita. Australian Anura are cursed with a fly of their own, called Batrachomyia.[^[81]]

B. vulgaris inhabits almost the whole of the Palaearctic region;–the whole of Europe, with the exception of Ireland, the Balearic Islands, Sardinia and Corsica. Northwards it extends to Trondhjem, and thence along a line drawn across Russia and Siberia to the Amoor. Its southern limit in Asia is indicated by a line drawn from the Caucasus through the Himalayas into China. In Asia Minor and in Persia it is absent. South of the Mediterranean it occurs only in Morocco and Algeria.

B. melanostictus is the common toad of the whole Indian region and of the Malay Archipelago. The epidermis of the fingers and toes is thicker and more cornified than usual, and is stained black brown, hence its specific name. The male has a subgular vocal sac. In other respects the Indian species much resembles the more spinous or rough-skinned and brown varieties of the European species. According to S. S. Flower this toad is very common in the Straits Settlements, hiding by day under stones or logs, or in holes, coming out shortly before sunset, and remaining abroad till dawn; it may be met with on the roads and in the grass, hopping or crawling about in search of ants, bees, and similar food. It utters a rather feeble, plaintive cry when handled for the first time. It can change its colour from light yellowish to dark brown. The spawn, which resembles that of B. vulgaris, may be seen in March and April in ponds, in long strings twined about the water-weeds. The tadpoles are very like those of the common English toad in form, size, colour, and structure of mouth. The largest adult found in Penang measured 115 mm. (about 4 inches) from snout to vent.

B. lentiginosus s. americanus is the common toad of North America, from Mexico to the Great Bear Lake. It is worth noting that this species resembles in its coloration the Eastern races of B. vulgaris, in so far as they generally have a light vertebral line, and frequently dark spots on the under surface. The upper parts are brown and olive, with darker spots, two of which form a chevron behind the eyes. But the tympanum is large, and the male has a subgular vocal sac; the inner metatarsal tubercle is very large, and is used as a kind of digging spur. During the pairing time they take to the pools in great numbers, uttering their music, which consists of a prolonged trill, continued by different individuals, both day and night. Holbrook knew an individual which was kept for a long time, and became perfectly tame. During the summer months it retired to a corner of the room into a habitation which it had prepared for itself in a small quantity of earth placed there for its convenience. Towards the evening it wandered about in search of food. Some water having been squeezed from a sponge upon its head one hot day in July, it returned the next day to the spot, and seemed well pleased with the repetition, nor did it fail during the extreme heat of the summer to repair to it frequently in search of its shower-bath.

Several varieties of this widely distributed species, whose average length is 2½ inches, have been described. The prettiest was called B. quercinus by Holbrook–according to whom it is mostly found in sandy places covered with a small species of oak–which springs up abundantly where pine-forests have been destroyed. It is called the "oak-frog," as it spends most of its time in concealment under fallen oak-leaves, or partially buried in the sand.

B. marinus s. agua is the giant among toads, and is one of the commonest species of the Neotropical region, ranging from the Antilles and Mexico to Argentina. It frequently reaches a length of 6 inches, with a width of 4 inches when squatting down in its favourite attitude. The upper parts are rough, owing to the prominent warty glands, of which the parotoid complex is enormous. The general colour above is dark brown, with sooty dark patches; below whitish, often with blackish patches. This creature appears at dusk, often in large numbers, especially during the rainy season, hopping about, not crawling, with surprising activity. The voice of the male, strengthened by a subgular sac, is said to be a kind of loud snoring bark. The pairing time begins, according to Hensel,[^[82]] with the winter rainy season, especially June, and lasts several months, until October, but it is interrupted by the cold, which in the hills of South-Eastern Brazil covers the ponds with ice. Then the tremulous bass voice of the males is heard no longer; they have all withdrawn beneath stones and trees in the neighbourhood of the water. The eggs are laid in strings. The larvae are at first quite black and very small, and the young baby-toads are only 1 cm. in length. They differ considerably from the adult until they are more than 1 inch long; the upper parts are yellowish brown, with darker ocellated patches, each with a light seam, most conspicuous along the sides of the head and back. The under parts are grey, finely stippled with yellow.

Budgett[^[83]] remarks that B. marinus feeds on all kinds of insects. "One half-grown specimen sitting by a man's foot picked off fifty-two mosquitoes in the space of one minute, picking them up with the tongue as they settled. The call of this very common toad consists of three bell-like notes; the middle one being the highest. The enormous parotoid glands are discharged like squirts when the creature is roughly handled. When wet weather comes on it hops out from its hiding-place to sit in a puddle, with its head out."

In many species of Bufo the crown of the head forms more or less prominent ridges, especially strong in the region between the eyes; for instance, in B. melanostictus and B. lentiginosus. The skin overlying these ridges is liable to be involved in the cranial ossification, and this reaches its greatest extent in the two Cuban species B. empusus and B. peltocephalus. It is a curious coincidence, to say the least, that such dermal ossifications should be best developed in Neotropical species, in those very countries which amongst the Cystignathidae have produced the abnormal genera Triprion, Calyptocephalus, and Pternohyla. The most peculiar and odd-looking species is Bufo ceratophrys, a native of Ecuador, which has the upper eyelid produced into a horn-like appendage, the two sharply-pointed cones standing out transversely, reminding us of several species of the Cystignathoid genus Ceratophrys; there is also a series of four small pointed appendages on each side of the body. Protective concealment is possibly the reason of these queer outgrowths.

B. viridis s. variabilis, the Green or Variable Toad, reaches a length of about 3 inches, and is the prettiest toad of Europe. The skin is distinctly smooth, the numerous porous, large and small warts being flattened. Parotoid glands are well developed, and a similar pair of glands sometimes occurs on the inner side of the calf, especially in Central Asiatic and in Algerian specimens. The coloration is very variable and changeable. The ground-colour of the upper parts is creamy, with large and small, partly confluent and irregularly shaped spots and patches of green, here and there interspersed with vermilion-red specks, especially along the sides of the back. The under parts are whitish, sometimes spotted with black. The iris is brass-coloured, greenish-yellow, with fine dark dots. The male does not differ from the female in size, but has an internal subgular vocal sac, a conspicuous callosity on the inner side of the first finger, and nuptial brushes on the first three fingers and on the inner palmar tubercle.

The changing of colour affects mainly the intensity of the green; the same individual which now looks almost uniformly dull, almost grey, with dusky olive patches, will, if put into grass and sprinkled with water, within a few minutes appear in a tastefully combined garb of grass-green on a creamy ground. Some Southern and Eastern specimens have a creamy stripe along the vertebral line, thereby closely resembling B. calamita, from which, however, they can always be distinguished by the little pads below the joints of the toes; these pads being single in B. viridis, and double in B. calamita and in B. vulgaris.

The Green Toad spends most of the day in holes, although it is not averse to daylight, and it roams about chiefly in the evening. It can jump well, much better and oftener than the Brown Toad. The food consists strictly of insects of all kinds, and most individuals prefer slow starvation to eating an earthworm. Although continuing to live four or five years in captivity, they do not readily become tame; they are indeed no longer wild, and when handled they no longer emit their peculiar insipid smell, but on being approached they still crouch deeply into the grass, or withdraw into their holes, just as they did when recently caught. The voice is heard during the pairing season, and sounds like the slow creaking of a door, or a combination of a spinning top and rattle. In Germany, during the months of April and May, they take to the ponds, or, improvident like the common frog, to a roadside ditch. The male sits upon the female and grasps her below the arms, his hands on her breast, and in this position they remain for days. The eggs are laid in two strings, twisted around water-plants, and are very numerous. Héron-Royer has calculated them at 10,000 or more in one set. The embryos are hatched, like those of the Common Toad, before the appearance of the external gills and of the tail. In this imperfect condition they remain in the jelly of the egg-strings for a few days, while their external gills sprout out like unbranched little stumps, only to disappear again. In about eight weeks the tadpoles, which reach a length little more than 1½ inch or 40 mm., have metamorphosed and leave the water as baby-toads scarcely half an inch in length.

This species has a very wide range, namely, the whole of Middle Europe excepting the British Isles, France and the Iberian Peninsula; the region between the Elbe and Rhine being its western limit; southwards it extends over all the Mediterranean islands and the north coast of Africa, eastwards through the whole of Russia, Western and Central Asia, not entering India, but spreading along the Himalayas into China. Stoliczka mentions its having been found in the Himalayas at an altitude of 15,000 feet, the highest record of any Amphibian, at least in such latitudes.

B. calamita.–The Natterjack is practically the representative of the Green Toad in Western Europe, but both species occur together in Denmark, Southern Sweden, and nearly the whole of Germany. Its southern limit is Gibraltar. In the British Isles it occurs in South-Western Ireland, in Co. Kerry, and in England and Wales, being however local, and preferring sandy localities, where it is found in considerable numbers. This predilection is shown by its frequency on the sandy dunes of most of the islands off the German and Dutch coast, where it may be seen running about in glaring sunshine.

Besides in the coloration, it differs from B. viridis in the following points. The little subarticular pads of the toe-joints are paired, not single, and the hind-limbs are decidedly shorter, so much so that this species cannot hop. But it runs well, like a mouse, generally in jerks, stopping every few seconds, and owing to this habit it is called the "running toad" by the field-labourers of Cambridgeshire. The skin is smooth, but less so than in B. viridis, owing to the slightly more prominent warts; the parotoids are small; a similar pair of glands lies on the upper surface of the fore-arm and another on the calf. The tympanum is rather indistinct. The ground-colour of the upper parts is light brownish yellow, with a green tinge and scattered green spots; most specimens have a narrow yellow stripe along the vertebral line and over the head. The under parts are white, more or less speckled with black. The iris is greenish yellow and speckled. The male, which is of the same size as the female,–very large specimens reaching 3 inches in length,–has a large subgular vocal sac, and develops nuptial brushes on the first three fingers, but the first lacks the thickened pad of B. viridis.

The yellow vertebral line is sometimes absent in specimens from the south of France and the Iberian Peninsula; and since these southerners are as a rule more handsomely marked, the green being more pronounced and arranged in larger patches, interspersed with red spots, they much resemble B. viridis. Boulenger, who has paid especial attention to this vertebral streak, which is a not uncommon design in various species of different families, has made the interesting observation that the streak has never been found in Danish and German specimens of B. viridis, where B. calamita occurs also, while it is not uncommon in B. viridis of Italy, South-Eastern Europe, Asia, and North Africa, where B. calamita is not found. Lastly, he remarks that in Eastern Asia, where neither B. viridis nor B. calamita with such a line occurs, the same character is assumed by some specimens of B. vulgaris. The only conclusion we can draw from these facts is, that for some unknown reason the streak is a desirable, but not necessary, possession, but that it is not kept by two species in the same country, B. viridis dropping it entirely where the typically streaked species, B. calamita, also occurs. The breeding season does not begin in England and Middle Europe until the end of April, in cold springs not before May, but it lasts for several months. The males, congregating in pools in great numbers, make a loud noise, each individual uttering a rattling note which lasts a few seconds, the repetition distending its bluish throat into the shape of a globe as large as its head. As the note is taken up by all the other males, a continuous chorus is established, which on warm and still nights can be heard nearly a mile off. Single croaks are uttered at any time of the day. The embrace, the male digging its fists into the armpits of the female, often takes place on land, near the edge of the water, to which they resort in the night for spawning. The egg-strings are slung around water-plants, unless the water is a mere puddle, and are much shorter than those of B. viridis, measuring only 5 to 6 feet, and containing altogether 3000 to 4000 eggs. The larvae, when hatched, are very small, imperfect, and blackish; the external gills last a very short time. The young tadpoles live on mud, subsisting on diatoms and low Algae; they are the smallest tadpoles of all the European kinds, scarcely reaching more than one inch in length, and they metamorphose quickly, the baby-toads leaving the water and running about in less than six weeks, when they are only 10 mm., scarcely three-eighths of an inch, in length. By the end of their second summer they are still only three-quarters of an inch long, and they do not reach maturity until the fourth or fifth year, with a size of 1½ to 2 inches; still smaller young males become mature several years before they are full grown.

Natterjacks stand captivity well and become very tame. When discovered, they first do their best to run away, instead of hiding or squatting down, and when caught they become covered with a slightly foamy lather, the exudation of their glands, which has a peculiar smell, reminding some people of gunpowder, others of india-rubber. They are not very particular as to food, all sorts of insects and earthworms being taken. Natterjacks are great climbers and diggers. Many of mine have established themselves in the peat with which the walls of the greenhouse are covered, where they have dug out, or enlarged, holes in which they pass the daytime, just peeping out with their bright eyes; others sit high up, always in dry places, and bask. In the evening they descend, hunting about on the ground, and occasionally they go into the water, whereupon they become quite flaccid and soft. When taken up and held between two fingers, being slightly pressed under the armpits, both sexes utter little jerky notes, as–by the way–most toads and frogs do under similar conditions.

In Cambridgeshire they frequent certain clay-pits surrounded by high and steep walls of sand, the breeding places of large colonies of sand-martins. During the months of May and June they are found in the shallow water, running about on the mud, sometimes swimming, in which they are not very proficient, and rarely diving. But they spend most of the time on land. Early in October they climb up and enter the holes of the sand-martins, or they dig large, deep burrows for hibernation, and the old males are the first to disappear.

B. mauritanica s. pantherina.–The "Pantherine Toad" is one of the few African species, and is one of the prettiest of all toads. The skin is almost smooth, although provided with porous glands. The parotoids are large, but flat; large glandular complexes on the legs or arms are absent. The tympanum is very distinct. The upper parts are adorned with a delicate pattern of dark-edged, rich brown or olive patches upon a light, buff-coloured ground; the under parts are uniform white; the male has a subgular vocal sac. The total length is 3 to 4 inches. This beautiful species is one of the gentlest, and it becomes tame enough to lap up food whilst sitting on one's hand. It lives entirely upon insects, prefers shade and dusky light, and utters a sound like "kooh-rr." It is a native of North-Western Africa, Algiers, and Morocco. In the rest of Africa, from Egypt to the Cape, Senegambia to Abyssinia, it is represented by B. regularis. This species has often little spiny tubercles upon the warts, and occasionally a light vertebral line; the colour of the upper parts either closely resembles that of the previous species, or it is uniform light brown, while the under parts are whitish, or variegated with brownish patches. West African specimens are the smallest, only 2 inches long; those of the Cape are the largest, reaching 5 to 6 inches.

The next two genera approach the Engystomatinae, and thereby lead from the arciferous towards the firmisternal type. The epicoracoid cartilages are narrow, and they scarcely overlap, so that by a further step in this direction they could easily fuse into the firmisternal condition. Another bond between these two genera and the Engystomatinae is their habits, they being ant-eaters of an extremely stout appearance, with exclusively short limbs and very small heads.

Myobatrachus gouldi, living in Australia, has a smooth skin, brown above, lighter beneath, and is about 2 inches long.

Rhinophrynus dorsalis of Mexico is remarkable for its tongue, which is elongated, subtriangular and free in front, so that it can be protruded directly–not by reversion as in other toads–and can be used for licking up the termites which seem to be its principal food. The body of this ugly creature is almost egg-shaped, and the head is merged into this mass, only the narrow truncated snout protruding. The limbs are very short and stout. The toes are more than half webbed, and there is a large oval, shovel-like metatarsal tubercle, covered with horn and used for digging. The general colour is brown, with a yellow stripe along the spine and with irregular spots and patches on the flanks and limbs. Total length 2 to 2½ inches.

Fig. 36.–Map showing distribution of Hylidae. The vertically shaded countries are inhabited by Hyla and by other genera of Hylidae; the horizontally shaded countries only by Hyla.

Fam. 4. Hylidae (Tree-frogs).–The upper jaw–in Amphignathodon the lower jaw also–and the vomers carry teeth; Triprion and Diaglena alone have teeth on the parasphenoid also, and the latter genus is further distinguished by possessing palatine teeth. The vertebrae are procoelous and have no ribs; the sacral diapophyses are dilated. The omo- and meta-sternum are cartilaginous, the latter forming a plate with scarcely any basal or style-shaped constriction. The terminal phalanges are invariably claw-shaped and swollen at the base, and carry a flattened, roundish, adhesive cushion. The tympanic disc is variable in appearance, being either free, or more or less hidden by the skin. The tongue is also variable in its shape and in the extent to which it can be protruded.

Most, if not all, Hylidae are climbers, and many lead an arboreal life, but it does not follow that all the "Tree-frogs" are green.

Their distribution is very remarkable. To say that this family is cosmopolitan with the exception of the African region, is literally true, but very misleading. There are in all about 150 species, and of these 100 are Notogaean; one-half of the whole number, or 75, being Neotropical; 23 are Central American, 7 Antillean, and about 18 are found in North America. One species, Hyla arborea, extends over nearly the whole Palaearctic sub-region, and two closely allied forms occur in Northern India and Southern China. Consequently, with this exception of three closely allied species, the Hylidae are either American or Australian. We conclude that their original home was Notogaea, and that they have spread northwards through Central and into North America. The enormous moist and steamy forests of South America naturally suggest themselves as a paradise for tree-frogs, and it is in this country, especially in the Andesian and the adjoining Central American sub-regions, that the greatest diversity of generic and specific forms has been produced. It is all the more remarkable that similar forest-regions, like those of Borneo and other Malay islands, are absolutely devoid of Hylidae (while there are about a dozen species in Papuasia), whose place has however been taken for all practical purposes by correspondingly modified Ranidae, notably the genus Rhacophorus. Lastly, the fact that tropical evergreen forests of Africa and Madagascar possess no Hylidae, but are inhabited by several kinds of tree-climbing Rhacophorus, points with certainty to the conclusion that the origin of this large and flourishing family of Hylidae was not in Arctogaea.

The versatility and the wide distribution of the Hylidae has naturally produced cases of convergent analogy, and the various species of one "genus" may be in reality a heterogeneous assembly. Such an instance is probably the genus Hylella, of which four species live in the Andesian and Central American provinces, while the two others occur in New Guinea and Australia.

The two North American genera Chorophilus and Acris, and the Brazilian Thoropa, connect the Hylidae with the Cystignathidae, in so far as their finger-discs are very small, or even absent, and their sacral diapophyses are only slightly dilated. On the other hand, it has to be emphasised that the possession of adhesive discs on the fingers and toes does not necessarily constitute a member of the Hylidae. That requires the further combination of an arciferous sternum, with dilated sacral diapophyses and teeth in the upper jaw. Finger-discs are easily developed, and still more easily lost. Those of the typical Hylidae are constructed as follows. The terminal phalanx is elongated, claw-shaped, swollen at its base. Between it and the penultimate phalanx lies an interphalangeal cartilaginous disc which projects ventrally below the end-phalanx, thus assisting the formation of the ventral pad, and the turning upwards of the whole disc-like phalanx like the claw of a cat. This peculiar motion can be well observed in Tree-frogs which are at rest upon a horizontal leaf, or, better still, upon a rough stone, when the creatures take good care to adjust their discs into a safe and easy position. The pad or disc itself is furnished with unstriped, smooth muscular fibres, the contraction of which produces one or more longitudinal furrows on the under side. When the disc is in action or adhering, being flattened to a smooth surface, the end-phalanx sinks into the cushion; when not in action, the cushion swells and the phalanx appears as a slight dorsal ridge. The disc is rich in lymph-spaces, and its surface contains mucilaginous glands.

Various suggestions have been made to explain the function of these discs. Suction, adhesion, and glueing-on have been resorted to. Suction, through production of a vacuum, is quite imaginary and does not exist. The question has been thoroughly studied by Schuberg.[^[84]] Adhesion is due to the molecular attraction of two closely appressed bodies. The less air remains between them the stronger it is. Consequently it can be increased by the interference of a thin layer of fluid, which as everyday observation shows, possesses both adhesion and cohesion. The more sticky the fluid, the more effective it is, as shown experimentally by Schuberg, who moistened the under surface of a glass plate, and pressed it against a little disc of glass from which was suspended a weight. A disc of 16 square millimetres, approximately equal to the aggregate surface of the 18 discs of a European tree-frog of 4 grammes in weight, carried with water-adhesion no less than 14 grammes, with glycerine-solution 20 grammes,–more than sufficient to suspend the frog. The sticky secretion of its glands greatly enhances the adhesive power. Tree-frogs, when hopping on to a vertical plane of clean glass, slide down a little, probably until the secretion stiffens, or dries into greater consistency. After a few days I find the glass-walls of their recently cleaned cage quite dirty, covered everywhere with their finger-marks. On the other hand, wet leaves or moist glass-walls afford no hold. The adhesion of these frogs is assisted in most cases by their soft and moist bellies, just as a dead frog will stick to a pane of glass.

All Hylidae have a voice, often very loud, and enhanced by vocal sacs, which are either internal, swelling out the throat, or external, paired or unpaired.

The various Hylidae resort to all kinds of modes of rearing their broods. Most of them lay many eggs, up to one thousand, in the water, not coherent in strings but in clumps; others lay only a few, attach them to various parts of the body, or, as in the genus Nototrema, the female receives them in a dorsal pouch. These modifications will be described in connexion with the different species.

Sub-Fam. 1. Amphignathodontinae.–Both upper and lower jaw with teeth.

Amphignathodon, of which only one species is known, A. guentheri of Ecuador, agrees with Nototrema in all important characters except that it possesses teeth in the lower jaw in addition to those in the upper. There are further differences, but they are of degree only. The sacral diapophyses are more strongly dilated and the omosternum is absent. The tympanum is distinct. The pupil is horizontal; the roundish tongue is slightly free behind. The terminal phalanges are claw-shaped and carry large discs. The female has a dorsal pouch opening backwards. The skin of the head is involved in the ossification of the cranial bones. The skin of the back is smooth, slightly tubercular, non-granular below. The middle of the upper eyelid carries a small, pointed, cutaneous appendage, and even this little character occurs also in some species of Nototrema, e.g. in N. longipes and in N. cornutum. The heel carries a triangular little flap. The upper parts are olive in spirit-specimens, probably green in life; the borders of the dorsal pouch are black. The sides of the body are adorned with a black, white-edged streak, the limbs are whitish, with black cross-bars. The total length of the female type-specimen is 3 inches.

Sub-Fam. 2. Hylinae.–Lower jaw toothless.

The Hylinae are divided by Boulenger into 13 genera, which can be recognised by the following key, without reference to their natural affinities:–

A. The contracted pupil forms a horizontal slit.

a. Tips of the fingers and toes with large discs,

α. With vomerine teeth.

Female without a dorsal pouch .......... Hyla, p. [189].

Female with a dorsal pouch .......... Nototrema, p. [202].

β. Without vomerine teeth .......... Hylella, p. [203].

γ. With parasphenoid teeth and peculiar helmet-shaped head.

Yucatan .......... Triprion, p. [207].

Ecuador and Mexico .......... Diaglena, p. [207].

b. Tips with very small discs. Tongue free behind.

Tympanum distinct. North America and Peru .......... Chorophilus, p. [208].

Tympanum indistinct. North America .......... Acris gryllus, p. [207].

c. Tips simply swollen, not dilated into discs. Brazil .......... Thoropa miliaris, p. [209].

B. The contracted pupil forms a vertical slit. Tropical America.

a. Tips with large discs.

α. Tongue extensively free behind.

Inner finger and toe opposable .......... Phyllomedusa, p. [203].

Inner finger and toe not opposable .......... Agalychnis, p. [206].

β. Tongue scarcely free behind. Ecuador .......... Nyctimantis rugiceps, p. [206].

b. Tips without discs. Without parasphenoid teeth, but head peculiar in shape. Mexico .......... Pternohyla fodiens, p. [207].

C. Pupil rhomboid. Without parasphenoid teeth. Large discs. Head helmet-shaped. Brazil .......... Corythomantis greeningi, p. [207].

Hyla.–The pupil is horizontal. The tympanum is distinct or hidden. The tongue is entire or slightly nicked in its hinder margin, which is more or less free behind. The fingers and toes are provided with typical adhesive discs.

This is the largest genus of all Amphibia, containing about 150 species, and its distribution coincides with that of the whole family. Many of the species are very closely allied to each other, differing only in small points, for instance in the extent of the webs to the fingers and toes, the configuration of the vomerine teeth, the size and appearance of the tympanic disc, and the relative length of the hind-limbs. In some of the West Indian, and in one Brazilian species, H. nigromaculata, the upper surface of the head is rough, owing to the cutis being involved in the cranial ossification. Bony or perhaps only calcareous deposits in other parts of the skin are rare, but are notably developed in H. dasynotus of Brazil, in which they extend from the head to the sacrum, rendering the skin immovable.

Many are capable of changing colour to a great extent, and it is a popular error to suppose that all tree-frogs are green, although this colour is perhaps the most common in the arboreal kinds.

Fig. 37.–Hyla arborea, var. meridionalis. South European Tree-frog, × 1.

H. arborea.–The tongue is rather round, slightly nicked behind, and can be protruded but little. The tympanum is distinct, but small. The upper parts are grass-green, quite smooth and shiny owing to the skin being covered with a film of moisture; the under parts are yellowish-white and granular, flesh-coloured or rosy on the thighs. Total length of large females 2 inches. This, the Tree-frog of Europe, has an enormous range, namely, from Morocco, France, and the south of Sweden, across the whole of Europe and Asia Minor to Japan and Southern China.

Several varieties have been described: the typical or European form is ornamented with a narrow black stripe, which, beginning at the nose, extends backwards along the side of the body to the groin, where it generally forms a hook turned upwards. This black colour forms the ventral boundary of the green, and is itself narrowly seamed with white on its upper border.

In the south of France, the Iberian Peninsula, Morocco, and the Canary Islands the black lateral stripe is often absent; this is the var. meridionalis. In Spain and Portugal both forms are found in the same localities.

In the Asiatic, chiefly in the eastern specimens, the lateral stripes tend to break up into irregular spots, vanishing altogether towards the groins; this var. savignyi s. japonica occurs also on most of the Mediterranean islands.

H. arborea can change colour to a great extent, mostly in adaptation to its immediate surroundings, but ill health and moulting may also influence it. The change is slow. The usual colour is green, brightest on bright, sunny hot days, dull when the sky is overcast, or when it is windy and showery. Day and night have no influence upon the colour-changes. The hue of the green agrees mostly with that of the foliage on which the frog happens to take its rest, for instance a field of Indian corn, birch-trees, or oak-trees. I once received a consignment from Saxony. When the box with moss was unpacked, they were of the dullest greenish-grey; they were put into a wired-off corner of the yard and were given the freshly cut branches of a lime-tree to sit upon. On the following morning I at first looked for most of the frogs in vain. The leaves had withered and all those frogs which sat upon the dark brown branches had put on a light brown garb, mottled with darker patches.

Another specimen, one of several which were at liberty in a greenhouse, took to resting on the frame of the window-pane, in a corner where putty, glass, and discoloured white paint met; in the morning it was always of a mottled leaden colour, but during the nocturnal hunting it was green. In the winter, the window-corner being of course cold, the frog remained stationary for several months, but kept the leaden grey colour, until one day in the early spring it was mottled with green, and soon after it joined its green mates.

Liebe observed a half grown tree-frog which he kept in Gera during the winter in a glass with water-cress. While the temperature was near freezing the frog sat in the water, very lethargic, breathing perhaps once every quarter of an hour. Its colour was light green. When the water-cress was cut and removed, the frog darkened and became at last quite a discoloured grey. When the water-cress was put back, the creature reassumed the light yellowish-green colour, remaining in its lethargic condition until it became lively in the spring sunshine.

The European tree-frog spends most of its time in the summer, after the pairing is over, in trees, often in the very crowns; but the neighbourhood of even a small patch of Indian corn has still greater attractions. There are all sorts of green insects to be caught, there are fair chances of coming across the common Cabbage White, a butterfly which the tree-frog loves, and last not least the large luscious leaves afford a firm foothold, and the axillae between stalk and broad-based leaves are just the places for the frog to slip into, where nobody can find it. During the day they mostly sit still, on the keen look-out for passing insects, which, when they settle within reach, are jumped at; otherwise they have first to be stalked. The jump is quite fearless, regardless of the height above ground; there is the leaf upon which the prey sits, and even if this leaf be missed, there are others, and one of them is sure to be struck by some of the discs of either fingers or toes. If the fall is broken by the toes, and the new leaf or branch is very elastic and bends down, then there are some frantic antics to be gone through until the frog has settled itself again. Then the large blue-bottle, or the butterfly, is devoured at leisure, wings and all being poked in with the assistance of the little hands. But the real hunting-time is the night.

During a shower the frog shifts its position to the under side of the leaf, or into a less slippery position, and during continuous wet it descends into the grass, or it takes to the water. Its greatest enemy is the Grass Snake, which prefers it to anything else, not minding the poisonous secretion of the skin, which is sharp enough to produce sneezing or even temporary blindness when incautiously brought into the human eye.

The male has an internal vocal sac, which, when inflated, bulges out the whole throat into a globe, much larger than the head. The voice is a sharp and rapidly-repeated note, something like "epp-epp-epp," or "creck, creck, creck," with more or less of an a sound. It is uttered at any time of the day, more frequently at dusk, and of course chiefly during the pairing season. This tree-frog suffers from the reputation of being a good weather-prophet, and it is for this reason often kept in confinement, the orthodox abode being a muslin-covered glass jar, with a hole to put flies through, water and plants at the bottom, and a little ladder to sit upon. The prophesying is of the usual popular unreliable nature, although the little creature, provided it is a male, often sounds its voice on the approach of a shower, or when there is a thunderstorm in the air. During continuous fine weather it sits on the top of the ladder, or is glued on near the rim of the glass, while on wet and dull days it is less active, and may keep nearer the ground or in the water. There is a German rhyme which well expresses the prophet's reliability by its ambiguity:–

Wenn die Laubfrösche knarren,

Magst du auf Regen harren.

When the tree-frogs croak, you may wait for rain. Sometimes it does come true.

Tree-frogs are not very intelligent, although they have a keen sense of locality; but they are nice pets, being easily kept, and have a pretty appearance. There is a record of one which lived for twenty-two years in confinement.

The pairing begins soon after the frogs reappear from their hibernation in the ground; in Germany in the month of May. The congregating males make a great noise and take to the water before the females, which join them when ready to spawn. The male grasps his mate near the shoulders, and the pair swim about together, sometimes for days, until the eggs are expelled. These are laid in small clumps of 800 to 1000, which soon swell up and remain at the bottom of the pond. The larvae are hatched in ten days; two days later the adhesive sucker below the throat appears, and after another two days a pair of thread-like external gills are developed. The tadpoles, which reach a length of 2 inches, owing to the long tail, which is nearly three times as long as the body, metamorphose in about twelve weeks, and the baby tree-frogs, scarcely half an inch in length, hide in the grass for the next two years, until they are about half grown, not reaching maturity until the fourth year.

Since many pairs congregate in the same pool, and each produces up to one thousand eggs, most of which are hatched, the neighbouring meadows sometimes literally swarm with tiny tree-frogs. Nevertheless the adults are comparatively rare and are very local.

H. carolinensis s. lateralis of the South-Eastern States of North America greatly resembles H. arborea in general appearance, size, and habits. But the head is more pointed, and the vivid green of the upper parts is separated from the yellowish white under surface by a conspicuous, pure white line, giving the little creature a very smart and neat appearance. According to Holbrook, it ascends trees, but most commonly lies upon broad-leaved water-plants, like Nymphaea, and in fields of Indian corn. Motionless during the daytime, they emerge in the morning and evening from their hiding-places, and become very brisk and noisy, often repeating their single note, which is not unlike that of a small bell. When one begins, hundreds take it up from all parts of the corn-field.

Among other tree-frogs of the South-Eastern States may be mentioned H. squirella, 1½ inch in length, which is very changeable in colour, generally olive above with darker spots and bars on the limbs, and with a white upper lip. It lives in trees, sheltering in the bark. H. femoralis of the same size, without the white lip, lives high up in the trees of the dense forests of Georgia and Carolina.

H. versicolor is one of the most delicately coloured species of Eastern North America, extending northwards into Canada. It is about 2 inches long. Its colour passes within a short time from dark brown or olive grey to pale delicate grey, almost white, occasionally retaining a few large darker patches on the back, and delicate cross-bars on the limbs. A small portion of the sides and the posterior part of the belly are bright yellow. The skin is granular, owing to the presence of small warts which produce an acrid secretion. It is said to be found in trees, or about old stone fences overgrown with lichens, the colour of which it resembles to perfection. It becomes very noisy towards the evening, in cloudy weather or before rain, the voice consisting of a liquid note, terminating abruptly, like "l-l-l-l-luk." My own captives fully bear out this statement of Holbrook's. Settled motionless during the day upon a piece of bark in a shady corner, but occasionally uttering the quaint and rather faint note, they become very lively in the evening, catching insects by long jumps, or investigating the hollows of decaying mossy stumps. Their general colour is then spotless, almost silvery grey. In the day-time they are sometimes suffused with delicate green.

The propagation has been studied by Miss M. H. Hinckley.[^[85]] They pair in shallow pools, in Massachusetts, in May. On the 10th of that month eggs were attached singly, and in groups, on the grasses resting upon the surface of the water; first drab-coloured, they became lighter in a few hours. Some larvae escaped from the gelatinous envelopes on the following day, the others on the third day; they clung to the grasses by means of their prominent suckers. The head and body were cream-coloured, with olive dots, and averaged ¼ inch in length. Gills appeared on the fourth day, to disappear again during the four following days, first those of the right, then those of the left, side; the suckers became less conspicuous, and the general colour turned into deep olive-green, with fine golden dots on the upper and lower surfaces. The eyes were of a brilliant flame-colour. On the eleventh day the suckers or "holders" had disappeared, and the hind-limbs were indicated by small white buds. By June 5th, i.e. the twenty-seventh day, the toes developed the terminal discs; the mottling of gold had given way to a uniform olive or pea-green. Movements of the future arms beneath the skin appeared on the 28th of June, at the age of seven weeks. The arms, mostly the right one first, were thrust out on the 2nd of July; the fins of the tail were absorbed rapidly, and towards the end of the seventh week the nearly transformed creatures began to leave the water. The young frogs changed colour rapidly, in adaptation to their surroundings, but the four specimens which survived were never all found to be of the same colour during the next three months. They first lived upon Aphides, later upon flies, and they were alert nocturnally. About the beginning of October they left the fronds of their fernery and nestled away in the damp earth, which they left only when the temperature rose above 60° F.

H. vasta of Hayti is the giant of the tree-frogs, reaching a length of 5 inches. In order to support its great weight the adhesive discs of the fingers and toes are of a surprising size, about as large as a threepenny piece. The skin is covered with small warts, and forms a peculiar fold on the hinder surface of the fore-arm and on the tarsus, and small flaps near the vent. The colour is grey above, blackish on the head, with a brown band between the eyes; the under parts are flesh-coloured, the throat with black spots.

H. maxima, of the forests of British Guiana, is scarcely less gigantic, and is distinguished by a projecting rudiment of the pollex, while the adhesive discs are smaller than the tympanum. The skin forms folds on the arms and tarsus, like those of H. vasta, in addition to a triangular flap at the heel. The general colour is reddish-brown above, sometimes with a dark vertebral line, the under parts are whitish and covered with large granules; the throat of the male, which has an inner vocal sac, is brown.

H. faber of Brazil is closely allied to the last species, but the skin of its upper parts is quite smooth. There is a small tarsal fold, and one extending from the upper eyelid to the shoulder. It is light brown above, with darker marks which form a conspicuous vertebral line, transverse bars on the hind-limbs, and a few irregular, scattered, vermicular or linear marks on the head and body. The adult, when put into a strong light, will rapidly turn pale; at night the longitudinal stripe on the back and the bars on the hind-limbs become very distinct; the under parts are white, and exhibit a beautiful orange tinge. This is the famous "Ferreiro" or "smith." As will be seen from the following graphic account by Dr. Goeldi[^[86]] of Para, this species doubly deserves its name of faber, not only in virtue of its voice, but also because of the marvellous nest-building habits recently discovered.

"The Ferreiro is common in the Province Rio de Janeiro, more frequently still in the mountain regions of the Serra dos Orgãos than in the hot lowland. Its voice is one of the most characteristic sounds to be heard in tropical South America. Fancy the noise of a mallet, slowly and regularly beaten upon a copper plate, and you will have a pretty good idea of the concert, given generally by several individuals at the same time and with slight variations in tone and intensity. When you approach the spot where the Tree-frog sits, the sound ceases. But keep quiet, and it will be resumed after a few moments. You will discover the frog on a grass-stem, on a leaf of a low branch, or in the mud. Seize it quickly, for it is a most wonderful jumper, and it will utter a loud and shrill, most startling cry, somewhat similar to that of a wounded cat."

The "Smith" makes very regular pools, in the shallow water of ponds, or nurseries for the tadpoles surrounded by a circular wall of mud. Dr. Goeldi has watched the building process during a moonlit night: "We soon saw a mass of mud rising to the surface carried by a Tree-frog, of which no more than the two hands emerged. Diving again, after a moment's time, the frog brought up a second mass of mud, near the first. This was repeated many times, the result being the gradual erection of a circular wall. From time to time the builder's head and front part of body appeared suddenly with a load of mud on some opposite point. But what astonished us in the highest degree was the manner in which it used its hands for smoothing the inside of the mud wall, as would a mason with his trowel. When the height of the wall reached about 4 inches, the frog was obliged to get out of the water. The parapet of the wall receives the same careful smoothing, but the outside is neglected. The levelling of the bottom is obtained by the action of the lower surface (belly and throat principally) together with that of the hands."

The male takes no active share in the construction of the nest, but will suddenly climb up the wall of his home, and then upon the back of his busy mate. The building operation may take one or two nights, and is performed in the most absolute silence; the croakers around are all males clamouring for a mate.

The eggs are laid during one of the following nights, and are hatched some four or five days later, the parents keeping hidden in the neighbourhood of the nursery. Heavy rains may destroy the walls, and thus prematurely release the tadpoles.

It is only owing to such keen observers and lovers of nature's fascinating ways that the breeding habits of some Brazilian Hylidae have become known.

H. nebulosa s. luteola also living in Brazil, is yellow above, with brown dots; the sides of the belly and thighs have transverse bluish bars, the under parts are whitish. Its size is under 2 inches. Goeldi has often found it in the sheaths of decaying banana-leaves. It glues the lumps of eggs on to the edges and to the inside of the withered leaves, where even during the hot hours of the day sufficient coolness and moisture are preserved. These lumps are enveloped in a frothy substance, in which the nearly metamorphosed tadpoles can be watched wriggling. If these are put into water, all will die in a few hours.

H. polytaenia deposits its eggs in free lumpy masses on water-plants. It is a small creature, little more than 1 inch in length, light olive above, with numerous brown parallel longitudinal bands on the body and limbs. A dark, white-edged band extends from the nose along the side of the body. The heel has a short flap of skin. The male has an internal vocal sac.

H. goeldii is a most interesting form, leading to the allied genus Nototrema. Boulenger[^[87]] has described a female which was captured by Goeldi in January on the Serra dos Orgãos. It is about 1½ inch long. The whole surface of the back is occupied by a layer of twenty-six pale yellow eggs which are 4 mm. in diameter. The skin of the back is expanded into a feebly reverted fold, which borders and supports the mass of eggs on the sides, thus suggesting an incipient stage of a dorsal brood-pouch. Owing to the great amount of yolk, the young are probably able to remain upon the mother until they are nearly metamorphosed.

Fig. 38.–Hyla goeldii. × 1. Female with eggs in the incipient dorsal brood-pouch.

H. coerulea s. cyanea is one of the largest Australian green tree-frogs, ranging from the South to the very North of Australia. The discs are as large as the fully-exposed tympanum. There is no projecting rudiment of the pollex, but a slight cutaneous fold borders the inner side of the tarsus. The skin is smooth and shiny, always a little moist, and studded with numerous rather large pores on the nape and shoulders; this somewhat thickened region forms a prominent fold which begins behind the eyes. The belly and the under parts of the thighs are granular as in most Hylidae. The male has an internal vocal sac; and during the breeding season, which seems to occur during our autumn and winter, develops brown rugosities on the inner side of the first finger. The tongue is round, slightly notched behind and free enough to be protruded a little.

Fig. 39.–Hyla coerulea. Australian Tree-frog (from photographs). Length of the large specimen 4.2 inches. The upper right specimen with vocal sac inflated.

The alternative specific names are most unfortunately chosen, as they apply only to spirit-specimens. During life this tree-frog exhibits a considerable amount of colour-changes. The normal colour is bright green above, white below. A conspicuous feature of this species is the frequent occurrence of white specks or spots, which are probably due to the deposition of guanine, a peculiar white colouring matter. The spots appear in any part of the green skin, and are quite irregular in their distribution. Sometimes they remain for weeks in the same place, or they disappear after a few days and others appear. They are in no way connected with the shedding of the skin, nor do they indicate ill-health. H. coerulea lives well in confinement, and becomes tame enough to take food from one's fingers, even when sitting upon the hand. Some of mine took to living during the daytime in a small box, preferring a crowded condition in companionship with Natterjacks. Others squeeze themselves into the most uncomfortable cracks, while others again prefer the broad leaves of Philodendron. A favourite place for two or three at a time is the funnel-shaped spaces formed by Bromelia-plants. Those specimens which are hidden in the box or in the hollows of rotten stumps are, almost without exception, dull, very dark brownish olive, while those on the Bromelias assume exactly the sombre dull green of its leaves. Lastly, those which sit in the light, exposed places, no matter if upon a leaf, on a white stone, or upon a board, are emerald-green, especially beautiful on hot, sunny days;–and they are not always averse to the full glare of the sun. When squatting upon a flat surface, such as a broad leaf, they tuck the fore-paws under the head like a cat, and with half open eyelids, the pupil contracted to a tiny slit, so that the golden iris is exposed, they remain motionless during the day. They take food when offered, but at night they roam about, either hopping on the ground, or making enormous leaps from leaf to leaf, sometimes deliberately stalking some choice insect, and patiently climbing up a stem, hand over hand. At night their whole aspect is changed. The colour is saturated green, the eyes are transformed into round, projecting shiny black beads, and the head is erect. The ludicrously dreamy, complacent look has given way to wide-awake alertness. They take all kinds of living food. When they find an earthworm, they first look at it, bending the head sharply down, lift themselves upon the fore-limbs and then pounce upon it, nipping the prey with the jaws, and then poking it down deliberately with the hands. Cockroaches are simply lapped up, and disappear in the twinkle of an eye. Mealworms, wood-lice, butterflies and moths, flies and spiders are taken. The stomach of a specimen in the Dresden Museum, from the Aru Islands, contained some four or five young freshwater Crustaceans of the genus Sesarma. They fortunately do not molest smaller frogs of their own kind and of other species. Like many Amphibia they like a change of diet, and ultimately refuse their food if it is unvaried. To my surprise my largest specimen, which measures a little more than 4 inches, takes snails, Helix virgata, half-a-dozen at a time, and on the following day, not during the night, vomits the sucked-out shells in a lump, like the pellets of birds of prey. During this rather painful-looking procedure the whole tongue and about half an inch of the everted gullet are protruded out of the mouth, and are then slowly withdrawn. After having roamed about all night, they return to their respective resting-places, where each individual is sure to be found in exactly the same spot, day after day. They do not mind being looked at, but if taken up and put back they avoid that place for perhaps a week, taking shelter somewhere else.

Both sexes have a voice, but that of the female is only a grunting noise, while the male inflates its gular sac and sends forth a sharp cracking sound, which can turn into a regular bellowing like the gruff barking of an angry dog. They bellow at any time of the year, frequently on the approach of a shower or during a thunderstorm. Certain noises will also induce them to bark. The rattling produced by the syringing of the greenhouse, sawing of wood, hammering, the raking of the gravel, or even the scraping of boots on the gravel-path is liable to start one of the males, and the others are sure to chime in.

According to Fletcher, H. coerulea and H. aurea lay their eggs in round white frothy patches, which float in the water, chiefly during the months of August and September; but when the spring months are very dry, the pairing is delayed until the following January. Several other Australian species of Hyla, e.g. H. ewingi, spawn at any time of the year if the conditions are favourable. They attach their eggs to submerged blades of grass or to twigs.

H. aurea is one of the commonest and most beautiful species, occurring throughout Australia and Tasmania, excepting of course in the large deserts. It has the appearance and restlessness of a water-frog, is not unlike Rana esculenta, and grows to about three inches in length. The tympanum is very distinct, but rather small. The fingers are without a pollex-rudiment, the tarsus has a fold along its inner edge. The adhesive discs are decidedly small. The male has two internal vocal sacs, which bulge out sideways. The skin is smooth and shiny. The under parts are white; the upper parts are, speaking generally, a mixture of blue and olive, with blue or brown spots, but spirit-specimens give no idea of the beauty which this changeable species can assume. Sometimes the same individual is saturated blue and green, with several longitudinal stripes of burnished copper along the back; a few minutes later the stripes glitter like gold, and in other moods the whole upper surface is mottled blue, green, and brown. My specimens often went into the water and did not climb. The food is said to consist chiefly of other small frogs in preference to insects.

Nototrema differs from Hyla in so far as the female has a pouch on the back for the reception of the eggs. This bag is formed by an infolding of the skin; it opens backwards in front of the vent, it has a sphincter and is permanent, although it distends to larger dimensions when in use. An initial stage of such a pouch is possessed by Hyla goeldii (Fig. 38). The pupil is horizontal, the tongue can be protruded but little; the tympanum is free, and the adhesive discs of the fingers and toes are well developed. These "marsupial frogs," of which about half-a-dozen species are known, live chiefly in the tropical forest-region of South America, notably from Peru to Venezuela.

N. marsupiatum is green with darker blue-green spots, or with longitudinal patches which are each surrounded by a whitish or yellow seam of little dots. The limbs have cross-bars. Total length about 2½ to 3 inches. The eggs of this species are comparatively small and numerous. The very small tadpoles have no external gills, and escape from the pouch to finish their metamorphosis in the water.

N. testudineum, about 3 inches in length, is of a uniform lead-colour, but is lighter beneath. The skin of the back is studded with stellate calcareous deposits, a peculiarity which is alluded to in the specific name.

N. oviferum is brown above, with darker patches on the sides of the body and with cross-bars on the limbs. The last two species and N. fissipes of Brazil, near Pernambuco, carry their young in the pouch until the metamorphosis is completed. This long nursing-period necessitates a great amount of food-yolk in the eggs, and this enlargement in turn implies a considerable reduction in their number. The female's load consists of about fifteen eggs only, but these are of a great size, namely one-eighth of the length of the mother's body.

N. pygmaeum, in Venezuela, is a tiny creature. The female, just one inch in length, carries only from four to seven eggs. It looks then "as if it carried a sac filled with a few gigantic balls." This species is further worthy of note on account of the opening of the brood-pouch, which is a longitudinal slit, whence a kind of thin and slightly elevated ridge or fold of the skin extends on to the neck. The suggestion, that this seam is burst open, in order to set the full-grown young free, instead of their passing through the existing opening, is scarcely credible.

These Neotropical tree-frogs seem to be rare, and females with embryos are of course still more uncommon, so that the best account of their structure is still that given by Weinland[^[88]] of N. oviferum. How the eggs get into the pouch has not yet been observed, but it is most likely with the help of the male, immediately after fertilisation. The pouch forms two blind sacs which extend forwards over the sides of the back. The eggs are large, 1 cm. in diameter, and the enclosed embryos, or rather tadpoles, had a length of 15 mm., with a large amount of yolk still contained in the spirally wound intestine. The first two gill-arches carried each a double thread, which expanded into a funnel-shaped membrane, not unlike the flower of a Convolvulus, and furnished with a capillary network; the stalk contained muscular fibres. These most peculiar structures are of course the much modified external gills. Those of N. testudineum and N. cornutum are likewise bell-shaped.

Hylella differs from Hyla chiefly by the absence of vomerine teeth, and consists of about half-a-dozen small species, about one inch in length. The fact that two species live in Queensland and New Guinea, while the others are natives of tropical America, suggests that this genus is not a natural but an artificial assembly, an instance of convergent evolution.

Phyllomedusa, composed of about one dozen species of tree-frogs, is characterised by the vertically contracted pupil, large adhesive discs, and the opposable nature of the inner finger and of the hallux, the last joints of which are like thumbs. The sacral diapophyses are strongly dilated. The range of the genus extends from tropical Central America to Buenos Aires. Most of the species are about 2 inches in length, blue-green to violet above, with white purple-edged patches on the sides of the body; the under parts uniform white, or with purple or brown patches. The male has a subgular vocal sac. Some have more or less distinct parotoid glands. Ph. dacnicolor of Mexico is uniform green above, whitish below, and attains a size of more than 3 inches. In Ph. bicolor of Brazil, the skin of the upper parts is studded with calcareous deposits, and the parotoids are large. It is blue-green above, purplish white below, the sides of the body and limbs with white purple-edged spots.

Ph. hypochondrialis has been found breeding freely in the Paraguayan Chaco by Budgett,[^[89]] from whose account the following notes have been extracted. This brilliantly coloured frog is green above, which colour may become brown-grey or bluish at will; below, white and granular. The flanks are scarlet, with black transverse bars, and the plantar surfaces are deep purplish black. Total length about 1½ inch.

The "Wollunnkukk," as it is called by the Indians, from the call of both male and female at pairing time, is extremely slow in its movements, and is active only at night. At this time, if it is seen by the aid of a lantern as it slowly climbs over the low bushes and grass, it is very conspicuous. In the daytime, however, nothing is seen but the upper surface of the body as it lies on the green leaf of a plant. It has a remarkable power of changing its colour to harmonise with its surroundings, and can effect a change from the brightest green to light chocolate in a few minutes. The skin is also directly sensitive to light; for if the frog is exposed to the sun while in a tuft of grass in such a way that shadows of blades of grass fall across it, on removal it will be found that dark shadows of the grasses remain on the skin, while the general colour has been raised to a lighter shade. Its food consists largely of young locusts. The ovaries on each side are divided into five distinct clusters. The rectum has a large saccular diverticulum, which is very heavily pigmented.

In the breeding season–December to February–this beautiful frog collects in considerable numbers in the neighbourhood of pools. During the night-time they call incessantly to one another, and produce a sound as of a dozen men breaking stones, well imitated by the native name.

The eggs are enclosed in batches in leaves near the margin of the water. Budgett has been able to watch the whole process of oviposition and fertilisation. He found, at 11 P.M., a female carrying a male upon her back, wandering about in search of a suitable leaf. At last the female, climbing up the stem of a plant near the water's edge, reached out and caught hold of the tip of an overhanging leaf, and climbed into it. Both male and female held the edges of the leaf together, near the tip, with their hind-legs, while the female poured her eggs into the funnel thus formed, the male fertilising them as they passed. The jelly in which the eggs were laid was of sufficient firmness to hold the edges of the leaf together. Then moving up a little further, more eggs were laid in the same manner, the edges of the leaf being fastened together by the hind-legs, and so on up the leaf until it was full. As a rule, two briar-leaves were filled in this way, each containing about 100 eggs. The time occupied in filling one leaf was three-quarters of an hour.

Development proceeds rapidly. Within six days the embryo increases from the 2 mm. of the egg-diameter to 9 or 10 mm. When it leaves the leaf it is a transparent glass-like tadpole, whose only conspicuous parts are the eyes. These are very large and of a bright metallic green colour, so that when swimming in the water all that is seen is a pair of jewel-like eyes. The newly-hatched tadpole has also a bright metallic spot between the nostrils somewhat in front of the pineal spot. This is the point which touches the surface of the water when the tadpole is in its favourite position. Whether it is a protective coloration, or some mechanical arrangement for holding the surface, Budgett could not make out.

The egg contains a great amount of yolk; the rest of the jelly-like contents of the egg becomes fluid, so that towards the end of embryonic life the larva comes to lie quite freely within a membranous capsule. The external gills appear on the third day, and reach their greatest size on the fifth, when these bright red filamentous organs extend beyond the vent. By the time the tadpoles are ready to be hatched these gills have quite disappeared, there is a median spiracle, and the lungs are shining through the transparent body-wall. Five weeks later, i.e. six weeks after the eggs were laid, the tadpole is 8 cm. long, glossy green above, rosy and silvery below, and the hind-limbs protrude. The young frog at the close of its metamorphosis is two-thirds the length of the adult, and at this time acquires the red flanks barred with black.

The first account of the breeding of Phyllomedusa was given by v. Ihering[^[90]] concerning Ph. iheringi of Southern Brazil.

"Phyllomedusa does not lay its eggs in the water, although the larva develops in that element, but in the open air in masses 50 millim. long by 15-20 broad, between leaves hanging over the water. Willows are frequently used for that purpose. The egg-mass contains rather large white ova, wrapped up between two or three leaves in such a way as to be completely enveloped save an inferior opening. My attempts at rearing the eggs failed owing to the leaves drying up; but I am assured that the tailed larvae may be seen wriggling in the gelatinous mass. As at a later period the latter is found empty, we must infer that the larvae drop into the water below. The eggs are found only on plants hanging over stagnant water."

Fig. 40.–A branch with eggs of Phyllomedusa iheringi, × 1, enveloped in the leaves. (After v. Ihering.)

"The adult animal is a stupid creature, and will let itself be taken without attempting to escape. Their moderately loud voice resembles somewhat the sound produced by running the finger nail over the teeth of a comb. Only during the breeding season, in the month of January in Rio Grande do Sul, do these frogs make their appearance; at other times not one is to be seen, probably because they establish themselves high up in the trees."

Agalychnis, with two species in Central America, is practically like Hyla; but the pupil is vertical, and the tongue is extensively free behind.

Nyctimantis differs from either by its round tongue, which is not nicked behind, and is almost completely adherent, much resembling that of the Discoglossidae. The sacral diapophyses are but slightly dilated. The only species, N. rugiceps, lives in Ecuador, and grows to nearly three inches in length. The head is large and rough owing to the skin being involved in the cranial ossification. It is further peculiar in its coloration, the under parts being chestnut-brown instead of whitish. The upper parts are olive-grey or brown.