Note.–Xenobatrachus ophiodon, New Guinea. Palatine bones, each with two large curved teeth. Otherwise imperfectly known.
Rhinoderma.–Omosternum and precoracoids present. Palate without teeth. Tympanum indistinct. Terminal phalanges simple, and not dilated. Tongue heart-shaped, and free behind. Pupil horizontal. Habitat, Chili.
Rh. darwini, the only species, was discovered by Darwin, during the voyage of the Beagle. Its total length is only 3 cm., or little more than one inch. The shape is grotesque, as the skin is prolonged, beyond the very small triangular mouth, into a false nose, i.e. a nose-shaped projection, while the nostrils remain at their original place. The skin is smooth above, granular on the under parts, and forms a triangular flap or spur-shaped appendage on the heel. A glandular fold extends along the sides of the body. The general colour is brown above, black below, with large white patches, the latter colour being sometimes predominant on the throat and chest. The male has a pair of internal vocal sacs, and the use of these as nurseries for the young has made this species famous.
Espada[[99]] has given an elaborate account of this species, which lives on the ground in shady woods. Its voice sounds like a little bell, and before taking its short jumps, it erects itself vertically upon the hind-limbs. The gular sac of the male opens by two slits, one on each side of the tongue. Generally this sac does not extend beyond the middle of the chest, but during the breeding time the eggs are put into it, whereupon it becomes greatly distended, so much so indeed that it reaches back as far as the groins; dorsalwards around the flanks, almost to the vertebral diapophyses; ventrally and forwards it reaches the chin. The walls of the sac are of the same structure as the buccal lining, of which they are in fact continuations. They adhere, at intervals, to the cutis and to the pectoral and abdominal muscles.
The effect of the distension of the sac upon neighbouring organs is twofold. First, the viscera are pressed back within the abdomen; this disturbance is temporary and does not apply to all specimens; the feeding in no way impeded. Secondly, a permanent change is produced in the direction of the precoracoid bars, in such a way that each bar is curved tailwards and rests with its ventral half upon the coracoid; owing to this forcible bending the clavicles do not meet each other. There is, of course, not so much space gained by this slight rearrangement of the shoulder-girdle as Espada implies, but we have here, perhaps, an illustration of direct correlation between two originally independent organs, namely, shoulder-girdle and vocal sacs. Repeated distension of the throat-bag during every breeding season, while the whole organisation of the male is in a highly excitable condition, has pressed the clavicular bars back, or rather has staved them in, and this at first pathological and abnormal condition has at last become a fixed feature. It is to be regretted that we know next to nothing about the habits, especially the mode of breeding, of the other genera which likewise have reflected or very feeble precoracoids and clavicles. Their weakness or even complete absence must have a reason, or rather must have had a cause.
The pairing and oviposition, and the manner in which the eggs are conveyed into the gular sac, have not yet been observed. Espada examined five males with young, the number of which varied from five to fifteen. In one male with eleven embryos the most developed tadpoles measured 13.5 mm. from the snout to the end of the tail, and they were lying within the chest of the father, the less advanced in the farther recesses of the bag. Three of the tadpoles had already completely-formed fore- and hind-limbs, while the arms were still hidden. The least developed were still globular, a proof that the eggs are conveyed into the bag. Another male with fifteen embryos looked as if it had gorged itself with the almost fully-formed tadpoles, which measured 14 mm. They were quite irregularly distributed, and nowhere attached to the walls of the bag. None of them had horny jaw-armaments, and not even the smallest specimens showed any traces of gills, resembling in this latter character those in the female brood-pouch of Nototrema. The intestine of the tadpoles is short and thick, coiled up spirally and filled with yolk, certainly not with vegetable or other foreign matter. Consequently the entire development from the egg to the complete stump-tailed little creature is undergone within the pouch; and this, after the young have escaped, probably shrinks back to its original size and acts as a gular vocal sac.
Phryniscus.–About ten species of this tropical American genus are known; they extend from Costa Rica to Buenos Aires. They differ not inconsiderably in various details. The tongue is elliptical, entire, and free behind. The palate is smooth. The tympanic disc is absent. Fingers and toes more or less webbed, sometimes with swollen tips, without, however, forming adhesive discs. In a few species the first toe is quite indistinct. The male has a subgular vocal sac. The mouth is small, and there is a short snout. The general appearance varies much. Ph. nigricans of Uruguay, etc., is stout and has very short hind-limbs; the skin of the upper parts is black, spotted with white, and covered with warts. Most of the other species are slender, with larger hind-limbs and a perfectly smooth skin, the coloration of which ranges from dull uniform brown, or black with crimson markings, to bright green with purple spots. The under parts are, as a rule, conspicuously coloured, a rare feature in Anura, the favourite colours being orange, yellow, or even crimson, with or without black patches.
Phryniscus nigricans has been observed in Paraguay by Budgett,[[100]] who gives the following account. This is a brilliantly coloured frog of toad-like appearance, and about 33 mm. in length. The ground-colour is black, with yellow spots or patches on the upper parts, the under parts are black, with scarlet blotches, the palms of the hands and soles of the feet are scarlet. At the breeding season both sexes utter a call-note which consists of two clear musical "rings," followed by a long descending "trill," like that of our British Greenfinch. This frog, which at ordinary times is the slowest and boldest of frogs, is now active and excessively shy. Swimming rapidly between the blades of grass, it climbs a tuft, and dilating its throat, repeats its call; but if in the least disturbed, it is suddenly gone. The eggs are laid in quite temporary pools in grassy ground, and form separate globules of jelly, which float on the surface of the water, and are heavily pigmented. The development is excessively rapid. The segmentation beginning at 10 A.M., they were hatched and wriggling about by 7 A.M. the following day. They are probably washed down into deeper pools by the retreating waters, and for this purpose the manner in which the eggs are laid, namely, in separate globules of jelly, seems especially suited.
Brachycephalus ephippium in Brazil, the only species, is remarkable for the development of a broad dorsal shield of bone, which is fused with the processes of the second to seventh vertebrae, an ossification which strongly resembles that of several species of the likewise Brazilian Ceratophrys, a genus of the Cystignathinae.
Stereocyclops is remarkable for the peculiar formation and protection of the eyeballs. The anterior portion of the sclerotic is ossified into a ring, which surrounds the transparent cornea. Another peculiarity lies in the metasternum, which is so much broadened out that its cartilage is in wide contact with the posterior edge of the coracoids. The epidermis is everywhere "thickened by a chitin-like deposit." The only species, S. incrassatus, found near Rio Janeiro, is an altogether aberrant creature. Its general appearance recalls that of Pipa. The gape is large, with a slightly projecting muzzle; the limbs are so short that the upper arms and the thighs scarcely stand out from the broadened and flattened body, which is leathery brown, with a narrow white median line extending dorsally from the nose to the vent.