CLASS 11. REPTILIA. 



Members of the Class Eeptilia pass their lives under extremely various- 

 conditions and circumstances. Many, as the larger number of the turtles^ 

 some snakes and the crocodiles, are given to haunting the waters of the sea, 

 or of the rivers, lakes and ponds. Others, such as most snakes, and many 

 tortoises, and the lizards, spend their lives on the land, and some of them 

 in the hottest and most arid situations. Their eggs, even those of the 

 most aquatic species, are always laid on the land ; and the young, though 

 they may, immediately after they are hatched, betake themselves to the 

 water, never have gills, and depend wholly on their lungs for the oxygen 

 that enters their blood. Their form is from the first like that of the 

 adults. 



In nearly all cases the epidermal layer of the skin of reptiles is disposed 

 in the form of scales or plates. These may, on the one hand, be so small 

 as to form mere granules, or, on the other hand, they may consist of a few 

 large plates, like those of most tortoises. The soft-shell turtles, however, 

 furnish us with an exception to the rule given. The epidermis of these 

 is soft and moist, and is not broken up into definite areas. When limbs 

 are present they are made up of the same elements as those of Batrachians, 

 Birds and Mammals. But many reptiles, such as the snakes and many 

 lizards, are entirely devoid of limbs. The blood of reptiles is cold, the 

 heart has only three chambers (except in the crocodiles), and the arterial 

 blood, as it is distributed to the body, becomes more or less mixed with 

 the venous blood. As to their reproduction, most lay eggs ; others bring 

 forth their young alive, the eggs being retained in the body until the 

 young have reached a considerable size. 



Key to the Orders of Existing Reptiles. 



A. Body covered with small, usually overlapping epidermal scales ; 



these supported or not by bony plates of similar form and size, 



which also do not articulate with one another. 



a. Body usually extremely elongated ; bones of upper jaws loosely 



connected with the rest of the skull; rami of lower jaw 



loosely connected at symphasis by elastic tissue. Serpents. 



Ophidia, p. 75^ 



