REPTILIA 2^^ 



the alligators are found In North America and in China. The true 

 Crocodiles of Africa and Asia have an American relative. The 

 Snakes are widely distributed, the common grass snake {Tropi- 

 donotus natrix) ranging from Sweden to Algeria. 



Fig. 182. The sidewinder or horned rattler {Crotalus cerastes). (Courtesy of Chas. 



Bogert.) 



Anatomy and Locomotion. — The Reptiles vary from the limbless 

 Snake to the Lizards and Crocodiles which have well-developed 

 limbs and a powerful tail. 



The oddest appearing forms are of course the Turtles. In the 

 Chelonia both dorsal and ventral surfaces are covered by large 

 horny plates. The scales are confined to the head, neck, limbs and 

 tail. The Lizards and Snakes have horny plates covering their 

 entire surface. In the skin of the geckos there are minute hard 

 bodies intermediate between cartilage and bone. In the Crocodilia 

 the whole surface is covered with horny plates underlaid with a pad 

 of dermal connective tissue. In all Reptiles, except the Crocodilia, 

 a periodical moult or ecdysis occurs. This casting of the old skin 

 is done completely in Snakes and some Lizards, while in other 

 Reptiles it is by degrees. 



Lizards move by means of their limbs and tail. Snakes have an 

 undulatory movement on land and are able to swim very well. 

 The aquatic Chelonia utilize their legs very effectively in swimming. 

 Crocodilia depend upon limbs and tail and are able to swim with 

 rapidity. On land their activity is much reduced but they are 

 surprisingly quick in seizing prey and in the use of their powerful 

 tail. 



Digestive System. — For the most part Lizards are non-poison- 

 ous. The Mexican beaded Lizards have grooved teeth and are 

 supplied with poison glands. Snakes rarely have premaxillary 

 teeth. The vipers have a single large curved hollow poison fang 



