ADAPTATION OF MAMMALS 221 



What a contrast these animals present to the mammals 

 adapted by nature to life in the air as the bats ! Physically, 

 they are alike, that is, in structure. They provide their 

 young with milk, are mammals, yet nature has intended 

 them to feed on insects, to capture which the fore arms are 

 wonderfully developed into long, attenuated fingers which 

 serve to brace and spread a weblike wing very similar to 

 that of a bird, their flight being quite as perfect and rapid ; 

 indeed, few birds are so skillful, as a bat can avoid the most 

 delicate obstacles in a dark room. 



Then we have other mammals, as the flying squirrels, 

 which are adapted for limited flight. They have devel- 

 oped parachutes, a loose skin, which, when they spread 

 their limbs, fill out to a remarkable extent, presenting a sur- 

 face so broad that it bears up the animal and enables it 

 to make extraordinary leaps, in no sense flying, but yet 

 enabling them to dart from tree to tree and cover long dis= 

 tances in the seeming aerial flight. 



The antelope is an excellent illustration of a mammal 

 adapted for life in the open. Nature provides its defense 

 in flight, has given it limbs by which it can outrun all but 

 few other animals. How sharp the contrast between this 

 graceful creature and the hippopotamus, a veritable whale 

 out of water in its clumsiness. Yet nature has not over- 

 looked this uncanny beast and has adapted it for life in 

 pools and rivers in the tropics, where it is singularly active 

 and perfectly at home. It is very difficult to drive a hare, 

 the jack rabbit, into a hole in the ground ; it depends 

 upon its long, machinelike legs and its marvelous speed 

 to escape its enemies, even building its nest on the 

 surface and scorning any retreat ; but with a short- 



