Tailed Batrachians,
Sometimes called Urodeles, from ουρα, "tail," δηλος, "manifest." The constant external character which distinguishes these Amphibians in a general manner is the presence of a tail during the whole stage of their existence. Nevertheless they are subject to the metamorphoses to which all the Amphibians submit. "The division, therefore, of reptiles," says Professor Rymer Jones, "into such as undergo metamorphoses and such as do not, is by no means philosophical although convenient to the zoologist, for all reptiles undergo a metamorphosis although not to the same extent. In the one the change from the aquatic to the air-breathing animal is never fully accomplished; in the tailed Amphibian the change is accomplished after the embryo has escaped from the ovum."
Salamanders have had the honour of appearing prominently in fabulous narrative. The Greeks believed that they could live in fire, and this error obtained credence so long, that even now it has not been entirely dissipated. Many people are simple enough to believe from the Greek tradition that these innocent animals are incombustible. The love of the marvellous, fostered and excited by ignorant appeals to superstition, has gone even further than this; it has been asserted that the most violent fire becomes extinguished when a Salamander is thrown into it. In the middle ages this notion was held by most people, and it would have been dangerous to gainsay it. Salamanders were necessary animals in the conjurations of sorcerers and witches; accordingly painters among their symbolical emblems represented Salamanders as capable of resisting the most violent action of live coal. It was found necessary, however, that physicians and philosophers should take the trouble to prove by experiment the absurdity of these tales.
The skull of the Land or Spotted Salamander, Salamandra maculosa, is well described by Cuvier as being nearly cylindrical, wider in front so as to form the semi-circular face, and also behind for the crucial branches, containing the internal ears. The cranium of the aquatic Salamander differs from the terrestrial in having the entire head more oblong, and they differ also among themselves.
Fig. 9.—Land Salamander.
In the Land Salamander the body is black and warty with large irregular yellow spots distributed over the head, back, sides, feet, and tail. They affect obscure and moist places, and only issue from their retreat in the night or morning, walking slowly, and dragging themselves with difficulty along the surface of the ground. They live upon flies, beetles, snails, and earth worms. They remain in the water to deposit their eggs; the young are born alive, and furnished with fully-developed gills. Moreover Salamanders are gifted with a power which causes them to be much dreaded by other animals: it has the power of discharging an acrid and milky humour, with a very strong odour, from the surface of its body, which serves as a defence against many animals which would otherwise attack it. It has been proved by experiment that this liquid, when introduced into the circulatory system by a small wound is a very active poison, and causes certain death to the smaller animals. This species is found in most parts of Europe, but not in the British Islands.
The Black Salamander, Triton alpestris, has no spots; it is found on the highest European mountains, in the regions of snow, and principally on the highest Alps.
Fig. 10.—Newts, or Aquatic Salamanders.
Newts, or Aquatic Salamanders, have not a round conical tail like the terrestrial species, but have that appendage compressed or flattened laterally. The males (during the breeding season only) are recognised chiefly by the membranous serrated ridge or crest which extends along the whole length of the back, from the head to the extremity of the tail, as represented in [Fig. 10]. Newts are highly aquatic; they are found in ditches, marshes, and ponds, which after the breeding season they leave for moist places on land, often then finding their way into drains and cellars. They are carnivorous, feeding upon different insects and on the spawn of Frogs, not even sparing individuals of their own species. The females deposit their eggs singly, fixing them on the under surface of the leaves of aquatic plants. "Some Newts," says Professor Owen, "deposit their eggs upon aquatic plants, such as Polygonum persicaria, folding the leaf by means of the hind feet in such a way that its under surface is turned inwards and the fold made to stick by the adhesive coating of the egg, which she inserts in the fold." The young are hatched fifteen days after. These animals give utterance to a very peculiar noise, and when touched emit an odour quite characteristic.
It has been ascertained that Newts can live for a long time, not only in very cold water, but even in the midst of ice, being sometimes taken in blocks of ice which are formed in the ditches and ponds which they inhabit. When the ice-flakes melt they seem to awaken from their torpor, and betake themselves to their accustomed movements with their recovered liberty. Lacépède states that he found Aquatic Salamanders even during summer in pieces of ice obtained from the ice-dealers, where they had remained without movement or nourishment from the time when the ice had been gathered from the marshes.
Newts present another remarkable feature in the facility with which they repair any mutilations they may have undergone. Not only do their tails grow again when broken off, but even their feet are reproduced in the same manner, and the process may be many times repeated.
The Crested Newt, Triton cristatus, is frequently found in the neighbourhood of Paris; the skin of its back is rough and warty, of a brownish colour, with large black spots and white projecting points; the belly has black spots upon an orange ground.
The Dutch traveller, Sieboldt, has introduced a species of Aquatic Salamander, which inhabits the mountain lakes and marshes of Japan. This species is remarkable for its gigantic growth. Instead of being the size of a finger, as is the case with those indigenous to Europe, this Batrachian is four feet and a half in length, and weighs fifty pounds.
Magnificent specimens of this gigantic Salamander, the Sieboldtia maxima, may be seen by the visitors to the London Zoological Gardens. The largest of them measured and weighed as above (March 3rd, 1869). An analogous large fossil species was described as the Homo diluvii testis!
The transformation of the tailed Batrachians, from the tadpole condition to the air-breathing and four-footed state, is one of the most interesting exhibitions of Nature, and one which everyone may verify for himself. We cannot in our brief description have a more trustworthy guide than Professor Rymer Jones, who selects the Water Newt, Triton cristatus, as an example:—
"Immediately before leaving the egg," he says, "this tadpole presents both the outward form and internal structure of a fish. The flattened and vertical tail, fringed with a broad dorsal and oval fin; the shape of the body and gills, appended to the side of the neck, are all apparent; so that were the creature to preserve this form throughout its life the naturalist would scarcely hesitate in classing it with fishes, properly so called.
"When first hatched it presents the same fish-like body, and rows itself through the water by the lateral movement of the caudal fin. The only appearance of legs as yet visible consists in two minute tubercles, which seem to be sprouting out from the skin immediately behind the branchial tufts, and which are, in fact, the first buddings of anterior extremities. Nevertheless, to compensate to a certain extent for the total want of prehensile limbs, which afterwards become developed, two supernumerary organs are provisionally furnished in the shape of two minute claspers on each side of the mouth; by means of these the little creature holds on to the leaves which are under water.
"Twelve days after issuing from the egg, the two fore-legs, which at first resembled two little nipples, have become much elongated, and are divided at their extremity into two or three rudiments of fingers. The eyes, which were before scarcely visible, being covered by a membrane, distinctly appear. The branchiæ, at first simple, are divided into fringes, wherein red blood now circulates; the mouth has grown very large, and the whole body is so transparent as to reveal the position of the viscera within. Its activity is likewise much increased; it swims with rapidity, and darts upon minute aquatic insects, which it seizes and devours.
"About the twenty-second day the tadpole for the first time begins to emit air from the mouth, showing that the lungs have begun to be developed. The branchiæ are still large. The fingers upon the fore-legs are completely formed. The hind-legs begin to sprout beneath the skin, and the creature presents, in a transitory condition, the same external form as that which the Siren lacertina permanently exhibits.
"By the thirty-sixth day the young Salamander has arrived at the development of the Proteus anguinus; its hind-legs are nearly completed; its lungs have become half as long as the trunk of the body, and its branchiæ more complicated in structure.
"At about the forty-second day the tadpole begins to assume the form of an adult Newt. The body becomes shorter, the fringes of the branchiæ are rapidly obliterated, so that in five days they are reduced to simple prominences covered by the skin of the head; and the gills opening at the sides of the neck, which allowed the water to escape from the mouth as in fishes, and were, like them, covered with an operculum formed by a fold of the integument, are gradually closed; the membranous fin of the tail contracts, the skin becomes thicker and more deeply coloured, and the creature ultimately assumes the form and habits of the perfect Newt, no longer possessing branchiæ, but breathing air, and in every particular the Reptile."
But however curious the phenomena attending the development of the tadpoles of the Amphibian Reptiles may be to the observer who merely watches the changes perceptible from day to day in their external form, they acquire tenfold interest to the physiologist who traces the progressive evolution of their internal viscera; more especially when he finds that in these creatures he has an opportunity afforded him of contemplating, displayed before his eyes, as it were, upon an enlarged scale, those phases of development through which the embryo of every air-breathing vertebrate animal must pass while concealed within the egg, or yet unborn.[11]
CHAPTER II.
OPHIDIAN REPTILES, OR TRUE SNAKES.
Reptiles are, as has been said in the preceding chapter, Vertebrated Animals, breathing by lungs, having red and cold blood; that is to say, not producing sufficient heat to render their temperature superior to that of the atmosphere. Destitute of hairs, of feathers, of mammary glands, and having bodies covered with scales.
Snakes, properly so called, have the tympanic bone, or pedicle of the lower jaw, movable, and nearly always suspended to another bone, analogous to the mastoid bone, which is attached to the cranium by muscles and ligaments, a conformation which gives to these animals the vast power of distension they possess. Their trachea is long, their hearts placed far back, and the greater number have one very long lung and vestiges of a second. They are divided into non-venemous and venemous; and the latter are subdivided into venemous with maxillary teeth, and venemous with isolated fangs.
The Snakes prey almost exclusively on animals of their own killing; the more typical species attacking such as are frequently larger than themselves: and the maxillary apparatus is, as we have seen, modified so as to permit of the requisite distension. According to Professor Owen's clear and intelligible description, the two superior maxillary bones have their anterior extremities joined by an elastic and yielding fibrous tissue with the small and single intermaxillary bone; the lower maxillary rami are similarly connected. The opposite extremity of each ramus is articulated to a long and movable vertical pedicle formed by the tympanic bone, which is itself attached to the extremity of a horizontal pedicle formed by the mastoid bone, so connected as to allow of a certain yielding movement upon the cranium. The other bones have similar loose movable articulations, which concur in yielding to the pressure of large bodies with which the teeth have grappled.
The class of Reptiles is divided into three orders:—the Ophidians, comprehending the Snakes; the Saurians, the Lizards and Crocodiles; and the Chelonians, the Turtles and Tortoises.