120 INTRODUCTION TO ZOOLOGY. 



purpose. In the pigeon the consolidated vertebrae 

 furnish a more solid support for the wings, while in 

 the turtle the consolidation of the vertebrae into the 

 shell furnishes a protection for the animal. 



The corpuscles of the blood are nucleated, and the 

 turtle is cold blooded. 



Tlie eggs of the turtle are large, like those of 

 birds, and contain much white surrounding the large 

 yolk. In some species of turtles, the egg has a calca- 

 reous shell, as in birds, while in others the shell is not 

 calcareous. 



There are four orders of living reptiles : — 

 Ghelonia — turtles. 

 Ophidia — snakes. 

 Lacertilia — lizards. 

 Crocodilia — alligators and crocodiles. 

 There are six orders of reptiles that are extinct. 

 The snakes and crocodiles represent the extreme 

 forms of the orders. 



