IV. VERTEBRATA: AMPHIBIA. 



587 



Order II. Gymnophiona (Caecilise, Apoda). 



These are the nearest of living forms to the Stegocephali, 

 but fossils are entirely unknown. The 

 group is exclusively tropical, occurring 

 in Ceylon, African islands, and America, 

 a discontinuous distribution indicative 

 of great age. They are burrowing ani- 

 mals and feed on small invertebrates. 

 As a result of this subterranean life the 

 eyes are small and concealed under the 

 skin, the legs are entirely lost, so that 

 the animals are snake-like in appearance. 

 In the skin there are usually small bony 

 scales; the drum of the ear is lacking; 

 the vertebrae are amphicrelous. Inside 

 the egg many species have three pairs 

 of beautifully feathered gills (fig. 618), a 



nrrknf nf fVimr r^H- inpnoA fn fVm Am 



tneir pertmenc< to tne Am- 

 phibia. Later, for a time, there is an 

 external gill opening which finally closes. 

 ffypoffeophis, Seychelles; C'acilia, America. 



FIG. 618. Larva of Ichthyophis 



u i u tinfafu*. (From Boas, after 

 Sarasins.) 



Ichihyophis, Ceylon; 



Order III. Urodela (Gradientia). 



Of recent forms of Amphibia the urodeles are the most fish- 

 like. The vertebral column consists of numerous vertebrae, and 

 of these a large part are behind the sacrum and consequently 

 belong to the tail. Ribs are present, but so short that they do not 

 reach the sternum, which is weakly developed or is entirely absent. 

 Tympanum, and Eustachian tube are entirely lacking, as are the 

 vocal chords and the production of sound. 



Sub Order I. PERENNIBRANCHIATA. Two or three gill slits, three 

 bushy gills, and a swimming tail persist throughout life. Necturus,* mud 

 puppy, with legs and two gill slits. Siren,* three gill slits, hind legs lack- 

 ing. Proteus, of Austrian caves, much like Necturus, but nearly blind. 



Sub Order II. DEROTREMA. External gills lost, but an opening in 

 the neck leading to the gill slits. Meiwpoma* (Cryptobranchus), hell- 

 bender, legs strong ; Amphiuma* legs rudimentary. 



Sub Order III. SALAMANDRINA (Hyetodera). After the loss of gills 

 the gill slits close. Amblystoma,* remarkable for the length of time the 

 larvae retain their gills, A. tigrinum (fig. 5) and the Mexican axolotl even 

 breeding in the larval stage. The adult of the true axolotl is unknown. 

 Pletliodon* Spelerpes.* The European Salamandra atra and 8. macu- 



