BRANCH CHORDATA: CLASS REPTILIA 309 



have the same habitat and general habits as the adult, 

 there is no such metamorphosis in their life-history as is 

 shown by the batrachians. The reptiles are widespread 

 geographically, occurring, however, in greatest abund- 

 ance in tropical regions, and being wholly absent from the 

 Arctic zone. They are not capable of such migrations 

 as are accomplished by the birds and many mammals, 

 but withstand severely hot or cold seasons by passing into 

 a state of suspended animation or seasonal sleep or torpor. 



FIG. 123. A lizard in the grass. (Photograph from life by Cherry Kear- 

 ton; permission of Cassell & Co.) 



Body form and organization. The chief variations in 

 body form among the reptiles are manifest when a turtle, 

 lizard, and snake are compared. In the turtles, the body 

 is short, flattened, and heavy, and provided always with 

 four limbs, each terminating in a five-toed foot; in the 

 lizards the body is more elongate and with usually four 

 legs, but sometimes with two only, or even none at all; 

 while in the snakes the long, slender, cylindrical body is 

 legless or at most has mere rudiments of the hinder limbs. 

 With the reptiles locomotion is as often effected by the 

 bending or serpentine movements of the trunk as by the 

 use of legs. Among lizards and snakes the body is 

 covered with horny epidermal scales or plates, while 



