Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/813

Rh AMPHIBIA 760 regions ; and, indeed, in Triton and Sircd&n, the teeth precede the corresponding bones, which arise by the ossification of the mucous membrane about the bases of the teeth ; and there are no labial cartilages, and no horny labial papillse, or beak-like armature of the jaw. The abdomen is slender, in accordance with the brevity of the intestine, and the little animal is altogether carnivorous. In the Anura, on the other hand, teeth are not developed until a later stage. A pair of cartilages appear in the roof of the mouth in front of the ends of the trabecuke (&quot;rostraux supe ricurs, Duges ; &quot;upper labials,&quot; Parker), and another pair opposite them (&quot;rostraux inferieurs,&quot; Duges ; &quot;lower labials,&quot; Parker) ; and the epithelium of the mucous membrane covering them becomes con verted into an upper and a lower brown horny toothed plate, having seme resemblance to the beaks of a Chelonian. The curtain-like lips, which surround the oral aperture, are also beset with horny papillae, which call to mind the corneous teeth of the Marsipo- branchii. The abdomen is swollen and almost globular, and lodges a long and spirally-coiled intestine. The animal is herbivorous, though it does not despise animal food, even in the shape of the weaker members of its own family. The space allotted to this article does not allow the details of the development of the Amphibia to be even sketched ; but attention may be directed to one or two of the more important points. The skull presents some singular differences in the course of its development in the Urodela (Triton, Siredon) and the Anura (Rana, Ah/tcs) respectively. In the former, the mandibular and trabecular arches become connected only at their dorsal ends, by the pedicle of the mandibular arch ; the pterygoid arch is developed late ; and the mandibular arch appears to give rise to no orbital process. In the latter, the mandibular and trabecular arches not only unite at their dorsal ends by the pedicle, but, at a very early period, the mandi bular arch is united with the antorbital process of the trabecula ; and the pterygoid grows pan passu with the subsequent divergence of the mandibular and the trabecular arches. A large orbital pro cess is developed from the mandibular arch. In the Urodela, the hyoidean and branchial apparatus consists, at first, of elongated cartilaginous hyoidean cornua, united with a median chondrification, which represents the basihyal and basi- branchial pieces, to which last two cerato-branchials are attached. The first cerato - branchial is continued dorsally into the first epibranchial, while the second cerato-branchial supports the other three epibranchials. As the development of the Triton proceeds, the hyoidean arch becomes connected with the suspcnsorium, and with the stapes, by ligament. The second basi-branchial ossifies, detaches itself from the first, and lies as a forked bone in front of the larynx ; and only the two cerato-branchials, with the first epi branchial, remain the rest of the branchial apparatus disappearing. In the Anura, the hyoidean arches are, at an early period, very thick, and relatively short, and are articulated with the suspensoria. A relatively broad and short cartilage represents the basihyal and basibranchial, and at the sides of this are two very broad cartilages, which correspond with the two cerato-branchials, inasmuch as their dorsal edges bear the four epibranchial cartilages. As the tadpole grows older, the hyo-branchial apparatus becomes more like that of the Urodele larva, the hyoid arch elongating into a slender rod, and the two cerato-branchials becoming distinct. The basibranchial region of the median cartilage, which unites the cerato-branchials ventrally, becomes forked, and the processes which form the fork ossify and become the thyro-hyals, which therefore would seem to correspond with the os ypsil&ides of the Urodela. Finally, the extreme dorsal end of the hyoidean arch detaches itself from the suspensorium, and enters into close union with the periotic capsule, from the outer wall of which the columella auris is developed. 1 The Distribution of the Amphibia. Darwin has pointed out (Origin of Species, p. 350) that Amphibia are met with on no islands but New Zealand, New Caledonia, the Andaman Islands, and perhaps the Solomon Islands and the Seychelles. This general absence of frogs, toads, and newts in so many true oceanic islands cannot be accounted for by their physical conditions ; indeed, it seems that these are peculiarly fitted for those animals, for frogs have been introduced into Madeira, the Azores, and Mauritius, and have multiplied so as to become a nuisance. But as these animals and their spawn are immediately killed (with the exception, so far as is known, of one Indian species) by sea-water, there would be great difficulty in their transportal across the sea, and therefore we can see why they do not exist in strictly oceanic islands.&quot; Leaving the oceanic islands aside, the distribution of the Am- 1 See the Memoirs of Duges and Parker, already cited, for the details of -these metamorphoses. The account given by Mr Parker of the modifications of the dorsal extremity of the hyoidean arch, how ever, does not accord with the results of the present writer s later investigations. No coalescence of the hyoidean with the mandibular urch takes place ; and the &quot; supra-hyo-mandibular &quot; has nothing to &amp;lt;io with the columella auris. phibia is world-wide, but the different groups are very remarkably localised. The Urodela, for example, are limited not only to the arctogocal province, but to the temperate parts of that province ; and, in curi ous correspondence with the Ganoid fishes, their headquarters are in North America. Siren, Menobranchus, Amphiuma, Menopoma, Dicamptodon, Hcrcdia, Anaides, Desmognathus, Bairachoscps, Hemi- dadylus, and Plethodon are exclusively North American ; and the majority of species of Amblystoma and Spelerpcs appertain to that region, Amblystoma being represented in North Asia, and Spelerpcs in the circum-Mediterranean area. Triton alone is spread over the whole temperate arctogceal area. Salamandra, Pleurodeles, Bradybatcs, Chioglossa, and Salamandrina are confined to Europe and North Africa. The singular Salamandra atra is limited to the Swiss and Austrian Alps, Proteus to Carniola and Carinthia. Four genera Ellipsoglossa, Isodactylium, Onychodactylus, and Ranodon are confined to North Asia ; and Cryptobranchus, if it be a distinct genus, is limited to Japan. If the distribution of the Urodela calls to mind that of the Ganoid fishes, that of the Peromcla is rather comparable to the distribution of the Tapirs. Of the four genera, Siphonops and Rhinatrema are exclusively inhabitants of the hotter part of the Austro-Columbian province as are the great number of the species of CceciKa; but the remaining species of that genus are East Indian, and Epicrium is confined to Java and Ceylon. In strong contrast with the foregoing, the Anura* are of world wide distribution, being abundantly represented in all the great provinces. A great preponderance of the genera and species, how ever, are Austro-Columbian, the Anura having their headquarters in South America, as markedly as the Urodela have theirs in the northern division of that continent. North America, in fact, is poor in Anura, having only three peculiar genera, viz., Scaphiopus, Acris, and Pseudavris; while the rest of northern Arctogaea has five, viz., Pelodytcs, Discoglossus, Alytes, Pelobates, and Bombinator. The genus JRana itself, however, is characteristically arctogaeal, having only a single species in the Mexican border-land of Austro- Columbia, and none in Australia. Rana esculenta extends from France to China and Japan, and from North Europe to Tunis. Rana temporaria covers even a larger area, as it occurs in the British Islands and in North America, as well as in North Asia and Japan. The Austro-Columbian region not only presents the greatest number of species, but among them are some of the most singular forms, such as Pseudis, Ceratophrys, Brachycephalus, Rhinoderma, Engystoma, Otilophus, Nototrema, Opisthodelphys, Rhinophrynus, and Pipa; in which respect the South American Anura run parallel with the birds of the same region. And, as is seen in other cases, the nearest allies of many of these singular forms are to be found in Ultra-Saharal (^Ethiopia) Africa, e.g., Hemisus (Brachycephalus), Breviceps (Engystoma}, Dactylethra (Pipa). It is remarkable that Pseudophryne, which is closely allied with the ^Ethiopic Hemisus and the Austro-Columbian Brachycephalus; and Chelydobatrachus, which is similarly related to the Ethiopia Breviceps and the Austro- Columbian Engystoma, are Australian. The Australian region is remarkable for the absence of the genera Rana and Bufo, which occur everywhere else ; and for the occurrence of Cystignathus, which is an Austro-Columbian, North American, and ^Ethiopian form, but does not occur in India. If it were not for its tree-frogs, Australia would be poorer in Anura than Europe is. These AnUra, modified for arboreal life, or &quot; tree-frogs,&quot; are repre sented in all the distributional provinces the genus Hyla having its chief seat in Austro-Columbia, and extending thence over North America, Europe, North Africa, Western and Eastern Asia, and Australia, but not into India or Ultra-Saharal Africa, in which other forms of the same group are met with. The British Islands possess the following species of Amphibia: Rana temporaria, Bufo vulgaris, B. calamita, Triton cristatus, T. Bibronii, Lissotriton punctatus, L. palmipes. Geological Distribution. No fossil Peromela are known. Anura occur in the Miocene deposits of France and Germany. The best preserved forms belong to the genera Palaobatrachus and Latonia, and occur in the schists of (Eningen along with their tadpoles. They possess maxillary teeth, and present no important differences from existing Anura, except that, in Palceobatrachus, the sacral vertebra has coalesced with the two preceding vertebrae, while, in existing forms, only one of the pros-sacral vertebrae is known to become confluent with the sacral. Urodela also occur in the same Miocene deposits. Of these the famous Andrias Scheuchzcri is very closely allied to Menopoma and Cryptobranchus, while other forms appear to be generically identical with Triton and Salamandra. The singular genus Orthophysis presents a good deal of resemblance to Proteus, but appears to have possessed no limbs. The older Cainozoic and the upper and middle Mesozoic forma tions have yielded no Amphibia. A doubtful form, Rhinosaurus, 2 See Dr Giiuther ? valuable Catalogue of the Batrachia salientia. I. - 97