PHYLUM CHORDATA 



433 



salamanders, lose both gills and gill- 

 slits completely in the adult : while in 

 others (such as Proteus, Nccturus, and 

 Siren), either gills are retained through- 

 out life, or, as in the American Meno- 

 poma, or hell-bender, gill-slits remain 

 as a permanent record of their pres- 

 ence in the larva. In some of the 

 tailed Amphibians the limbs are well- 

 developed ; in others they are very 

 small. 



Widely different in many respects 

 from both the Anura and Urodela are 

 a group of Amphibia — the Gymno- 

 phiona — which are quite snake-like 

 in appearance, owing to the elongated 

 and narrow form of the body and the 

 entire absence of limbs. The group is 

 represented by the blind snake (C«- 

 cilia) of Central and South America. 



■ | 



CLASS IV. KEPTILIA 



The class Reptilia comprises the 

 lizards and snakes, the tuataras, the 

 turtles and tortoises, and the alligators 

 and crocodiles. On a superficial com- 

 parison of these with the Amphibia, it 

 might be inferred that there is a close 

 alliance between the two groups; but 

 this impression becomes weakened 

 when a closer examination is made of 

 the structure and development, and it 



2 F 



Fig 260. — Siren lacer- 

 tina. (From Mivart.) 



