2l8 THE HISTORY OF CEEATIOX. 



however, they differ externally by the absence of the coat 

 of scales. Most gilled Batrachia live in North America : 

 among others of the class is the Axolotl, or Siredon, already 

 mentioned. (Compare above, vol. i. p. 241.) In Europe the 

 order is only represented by one form, the celebrated " 01m" 

 (Proteus anguinus), which inhabits the grotto of Adelsberg 

 and other caves in Carinthia, and which, from living in the 

 dark, has acquired rudimentary eyes which can no longer see 

 (vol. i. p. 13). The order of Tailed Batrachia (Sozura) have 

 developed out of the gilled Batrachia by the loss of external 

 gills ; the order includes our black and yellow spotted land 

 Salamander (Salamandra maculata), and our nimble aquatic 

 Salamanders (Tritons). Many of them — for instance, the 

 celebrated giant Salamanders in Japan (Cryptobranchus 

 Japonicus) — still retain the gill-slits, although the gills 

 themselves have disappeared. All of them, however, retain 

 the tail throughout life. Tritons occasionally — when 

 forced to remain in water always — retain their gills, and 

 thus remain at the same stage of development as gilled 

 Batrachia. (Compare above, vol. i. p. 241.) The third order, 

 the tailless or frog-like Batrachia (Anura), during their 

 metamorphosis, not only lose their gills, with which in 

 early life (as so-called tadpoles) they breathe in water, but 

 also the tail with which they swim about. During their 

 ontogeny, therefore, they pass through the course of 

 development of the whole sub-class, they being at first 

 Gilled Batrachia, then Tailed Batrachia, and finally Frog- 

 Uke Batrachia. The inference from this is evidently, that 

 Frog-like Batrachia developed at a later period out of 

 Tailed Batrachia, as the latter had developed out of Gilled 

 Batrachia which originally existed alone. 



