CHAPTER 28 



PM 



Class Reptilia. 



Turtles, Lizards, 



Snakes, Crocodiles, 



and Others 



HE reptiles constitute one of the most in- 

 teresting, and, in general, one of the least- 

 known classes of the vertebrates. They are 

 cold-blooded; usually covered with scales, 

 and, frequently, with bony plates; and they 

 always breathe by lungs. The popular no- 

 tion that reptiles are slimy is erroneous. 

 Contrary also to general belief, very few- 

 reptiles, at least those in the United States, 

 are dangerous to man; the majority are harm- 

 less, and many are even beneficial. The rep- 

 tiles living today are but a fraction of the 

 vast hordes that inhabited the earth's sur- 

 face in prehistoric times. In fact, of the 

 approximately 16 orders of reptiles now 

 recognized by herpetologists, only 4 possess 

 living representatives, and one of these in- 

 cludes a nearly exterminated species con- 

 fined to New Zealand. The 4 orders of living 

 reptiles are as follows: 



Order 1. Chelonia ( Testudinata ) . Turtles 

 and tortoises. 



Order 2. Rhynchocephalia. Sphenodon, a liz- 

 ardlike reptile confined to New Zealand. 



Order 3. Squamata. Lizards, and snakes. 



Order 4. Crocodilia. Crocodiles, alligators, 

 gavials, and caimans. 



The reptiles are better adapted for living 

 on land than amphibians. Some of the ad- 

 vances shown by reptiles over amphibians 

 are: ( 1 ) a dry scaly skin which is an adapta- 

 tion for a complete existence on land, (2) 

 limbs better suited for rapid locomotion, (3) 

 partial or complete separation of the ven- 

 tricle resulting in further separation of the 

 oxygenated and nonoxygenated blood in the 

 heart, (4) well-ossified skeleton, (5) some 

 form of copulatory organ which is necessary 

 for internal fertilization, (6) eggs with shells 

 suited for development on land and protec- 

 tive embryonic membranes to prevent dry- 

 ing, another adaption for life on land. 



Reptiles are most abundant in the warmer 

 regions of the world; very few live in the 

 colder parts of the temperate zone, and none 

 in the Arctic or Antarctic regions. Neverthe- 

 less, the United States is well supplied with 



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