CHAP. XVI Backboned Animals 257 



The class includes four orders, of which the Labyrinthodonts 

 are wholly extinct, the other three being represented by tail-less 

 frogs and toads (Anura), by newts and salamanders (Urodela) with 

 distinct tails, and by a few of worm-like form and burrowing 

 habit, e.g. Cacilia. Some, the last for example, are terrestrial, but 

 usually live in damp places ; most pass their youth at least in fresh 

 water ; none can endure saltness, and they are therefore absent from 

 almost all oceanic islands. The common British newis {Triton and 

 Lissotriton), and the often brightly-coloured salamanders (Sala- 

 mandra) have in adult life no trace of gills; the rice-eel {Amphiumd) 

 and the genus Menopoina lose their gills, but persistent clefts indi- 

 cate their position ; the blanched blind Proteus from caves and the 

 genus Menobranchus keep their gills throughout life. The remark- 

 able Axolotl from North American lakes occurs in two forms, both 

 of which may bear young ; the one form (Axolott) has persistent 

 gills, the other form (Amblystomd) loses them, and the change 

 from the Axolotl to the Amblystoma is in part associated with the 

 passage from the water to the swampy shore. A large fossil dis- 

 covered by Scheuchzer in the beginning of the eighteenth century 

 was quaintly regarded as a fossil man and as a testimony of the 

 deluge. But Cuvier showed that Scheuchzer's Hotno diluvii testis 

 was but a large newt. 



The common frogs {Rana), the Surinam toad {Pipa), the 

 common toads {Bufo), and the tree-frogs {Hyla) illustrate the tail- 

 less order Anura. In none of them is there in adult life any trace 

 of gills. 



The worm-like, limbless, burrowing Amphibians (Gymnophiona) 

 must not be confused with the blind- or slow-worms, which are 

 lizards. There are only very few genera, Siphotiops, Rhinatrema, 

 Epicriuni, Cacilia. The newly-born Cacilia has external gills, 

 but these are soon lost. The eyes are covered with skin, but are 

 well developed. 



The race of Amphibians began in the Carboniferous ages. 

 Most of the Labyrinthodonts which flourished then and in the two 

 succeeding periods were newt-like in form, but some were serpen- 

 tine. They seem to have been armoured, and were sometimes 

 large. 



Amphibians are naturally sluggish. For long periods they can 

 fast and lie dormant ; they can survive being frozen quite stiff, 

 and though tales of toads within stones are mostly due to mistakes 

 or fancies, there are some authentic cases of prolonged imprison- 

 ment. 



Few are found far from water, and the gilled condition of 

 the young is skipped over only in a few cases. In the black 

 salamander {Salamandra atra) of the Alps, which lives where 



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