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EVOLUTION OF ANIMALS 



Part V 



RoHlesnoke 



Fig. 35.1. Types of North American reptiles. Fence Lizard (Sceloporus). 

 Length, 5 to 6 inches. Gray brown to green. A dozen and a half species ranging 

 throughout south-central United States and in the west north to Oregon. A com- 

 mon pet. Horned Lizard or Toad (Phrynosoma). Length 5 inches. Several species 

 in western United States only. Unlike most lizards they give birth to living young. 

 Six-lined Lizard. Race runner (Cnemidophorus). Length to 10 inches of which 

 7 inches is tail. Easily identified by the prominent yellow Hnes in a brown back- 

 ground. Allied species common in south to south-central regions across the 

 continent. Gila Monster (Heloderma). Length to 24 inches. Beautifully colored 

 gray with rose patches and beading. The only poisonous lizard in the United 

 States. It lives in desert places in the southwest, especially Arizona. Common 

 Garter Snakes (Entema sirtalis) live in every part of America where snakes 

 exist, the first to come out of hibernation in spring, the last to go into it in 

 autumn. With several related species it ranges the north and north-central United 

 States. Rattlesnakes. There are 15 species of rattlesnakes in the United States 

 and with one or another of them their range extends over all but the northern- 

 most part of the country. They are all dangerously poisonous. Snapping Turtle 

 (Chelydra). Less protected by shell than most turtles, snappers are demons for 

 fighting and will snap even as they are hatching. Found in ponds. Common 

 snapper grows to 50 pounds or more. (Courtesy, Palmer: Field book of Natural 

 History. New York, McGraw-Hill Book Co., 1949.) 



Respiration, Reptiles cannot breathe through their skins and they have 

 no gills. They do have lungs, however, with greater capacity than the most 

 elaborate amphibian ones. In most reptiles, the heart is incompletely four- 

 chambered; in crocodilians, it is completely so insuring a supply of better 

 oxygenated blood. 



Locomotion. Reptiles long ago developed legs and speed such as never 



