XXI. SNAKES, TURTLES, LIZARDS, CROCODILES 



Chordata (continued) 



Glass IV. — Reptilia (creeping animals) 



The reptiles are cold-blooded animals that differ markedly 

 from the amphibians in many important respects. The 

 life history of a reptile is comparatively simple, for no rep- 

 tile passes through the remarkable changes that are char- 

 acteristic of most of the amphibians. The majority of 

 reptiles possess an outside covering of scales, or horny 

 plates, or, in the case of turtles, of a bony box, while am- 

 phibians, for the most part, are smooth skinned. Super- 

 ficially, some reptiles resemble certain amphibians and vice 

 versa, some amphibians are often mistaken for reptiles. 



An Example of the Class — the Six-lined Lizard 



External features. ■ — The body is long, slender, and more 

 or less cylindrical. It presents four divisions — head, neck, 

 trunk, and tail, all of which are clothed with scales. This 

 contrasts quite strongly with the smooth, short, broad, and 

 tailless body of the frog. Like the frog, the hzard has four 

 legs, but they are more nearly equal in size and none of them 

 are fitted for leaping. Each leg terminates in five digits 

 furnished with claws. 



The eyes. — The eyes are conspicuous, but they do not 

 protrude. Each has an opaque upper and under lid and a 

 nictitating membrane. The latter may be drawn completely 



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