CLASS IV. : AMPHIBIANS (AMPHIBIA). 



VERTEBRATE animals of varying body temperature (cold-blooded), with 

 naked skin, breathing by gills in the earlier stages of their life, later by 

 lungs as well as gills, or lungs only ; mostly oviparous ; limbs in form of 

 legs (in a few amphibians not noticed here the posterior pair or both 

 pairs of limbs are absent) . 



1. Form of Body and Limbs. In regard to the shape of their body, 

 the amphibia may be divided into two distinct groups, in one of which, 

 the frog-like amphibians (Batrachia or Anoura), the body is broad, flat, 

 and tailless, and the limbs well developed, and adapted for leaping, 

 walking, and climbing; in the other group, tailed amphibians (Sauro- 

 batrachia or Urodela), the limbs are small and feeble, and the body 

 accordingly much elongated, lizard-like, or almost vermiform, and 

 provided with a long tail. Among the terrestrial species of the latter 

 group (e.g., spotted salamander), the tail is rounded (supporting tail); in 

 those which are principally or exclusively confined to an aquatic life, it 

 is laterally compressed (swimming-tail). 



2. The Skeleton corresponds to these two chief types of body shape. 

 In the Batrachia, the vertebral column consists of only a small number 

 of vertebrae. Its terminal segment (see Fig., p. 255) as well as the pelvic 

 girdle form a strong and firm support for the hind-limbs, which are 

 specially concerned in locomotion. In the Urodela, on the other hand, 

 there is a large number of vertebrae freely movable on one another, and 

 the pelvic girdle is weak. The limbs, and the pectoral and pelvic girdles, 

 consist of bony elements corresponding to those of the higher Vertebrata 

 (see Part I., p. 2). 



3. Integument. (a) Amphibians, like reptiles, are animals of 

 varying body temperature (see p. 229), and are therefore without any 

 special provisions for the preservation of heat. Hence, in the temperate 

 zone, these animals only lead an active life during the warm season ; with 

 the approach of the colder period of the year, their vital activities (respira- 

 tion, circulation) grow slacker and slacker, until finally the animals 

 relapse into the sleep of hibernation. On this account, too, many species 



