256 



A YEAR IN SCIENCE 



There are about 3500 different kinds of mammals. 

 The highest of these is man. Very similar to man are 

 the monkeys, apes, gorillas, and chimpanzees. Differing 

 more in general appearance, but still having the charac- 

 teristics of mammals are : the rat, the squirrel, the 

 beaver, the whale, the horse, the cow, the pig, the sheep, 

 the dog, the cat, the lion, the tiger, and the bat. Most 

 of these forms live on the land, but a few, such as 



Fig. 112. Skeleton of squirrel. 



In gnawing mammals the canine teeth are absent. The front, 

 incisor, teeth grow continuously and are kept sharp by the gnawing 

 on hard substances. 



whales, porpoises, and sea-lions, inhabit the ocean. They 

 are all air breathing. They vary greatly in size from 

 the w^hale and the elephant to very small mice and 

 moles. Many adaptations to habitat and methods of 

 life occur in this group. Whales, sea-lions, and por- 

 poises have the limbs modified into flippers for swim- 



