A GENERAL EEVIEW OF THE ANIMAL KINGDOM 



145 



the preceding, partly because the animals composing it differ 

 more among themselves than in the other classes. It includes 

 animals as widely different as snakes, lizards, turtles, and croco- 



FlG. 66. 



PORIFERA 

 SBOO 



COELEKTERATA 



4son 



FxG. 66. Diagram showing the general relations of the chief divisions of the animal kingdom. 

 The number of species belonging to each is roughly approximate, only. 



diles. The reptiles have some features which indicate that 

 they may be distantly related to both birds and mammals, as 

 well as to the next class. This is an additional reason why the 

 group of reptiles is a difficult one to define. In general they 

 may be recognized by the fact that their bodies are covered by 



