CLASS 3. REPTILES (Reptilia)* 



The reptiles are cold-blooded vertebrates whose bodies are covered 

 with horny scales or plates, and which have claws on their digits. The 

 legs are well developed, when present, and are often adapted for rapid 

 running, but they do not usually support the body above the ground 

 except during locomotion. Respiration is always pulmonary. The 

 skeleton, including the skull, is well developed and ossified, the skull 

 articulating by a single condyle. The eggs are large and are usually laid 

 on or in the ground, even when the animals are aquatic, although many 

 species are ovoviviparous, and the embryo is meroblastic and provided 

 with an amnion and allantois; the young animals resemble the parents, 

 when born, there being no postnatal metamorphosis. 



History. — The cold-blooded, egg-laying quadrupeds were named 

 Amphibia by Linnaeus, and subdivided into two orders, the Serpentia 

 and Reptilia, the latter order including turtles, frogs and lizards. Opin- 

 ion fluctuated as to the exact relation existing between amphibians 

 and reptiles for almost a century, although Blainville as early as 181 6 

 correctly defined them, until near the middle of the last century the 

 anatomical and embryological studies of Johannes Miiller, Gegenbaur 

 and others definitely established the two groups as distinct and equiva- 

 lent classes. 



The foundation of our knowledge of American reptiles was laid 

 principally by John Edward Holbrook, Spencer F. Baird and Edward 

 D. Cope, the work of Cope on The Crocodilians, Lizards and Snakes 

 of Xorth America being the most important single one on the subject; 

 in more recent times the works of Leonhard Stejneger have been very 

 important. 



Number of Species and Distribution. — About 5,500 species of 

 reptiles are known at the present time, most of which live in the warmer 

 regions of the world. There are no reptiles in Arctic regions, and but 

 few in the colder portions of the Temperate zone. About 300 species 

 are known in the United States, which are grouped in 4 orders. 



Key to the Orders of Reptiles 

 ai Jaws with teeth. 



bi Teeth set in alveoli; anus a longitudinal slit i. Crocodilia (p. 178). 



" Revised by Dr. E. R. Dunn. 



177 



