206 ANIMAL BIOLOGY 



Short ears ? Why ? Which are aquatic ? Which dig or bur 

 row ? Which are largely nocturnal in habits ? Which are 

 arboreal? Which are protected by coloration ? Which 

 escape by running ? By seeking holes ? 



Economic Importance. Rabbits and squirrels destroy the 

 eggs and young of birds. Are rabbits useful ? Do they 

 destroy useful food ? The use of beaver and muskrat skins 

 as furs will probably soon lead to their extinction. Millions 

 of rabbits' skins are used annually, the hair being made into 



FIG. 375. FLYING SQUIRREL (Pteromysvolucella). x y 4 . 



felt hats. There are also millions of squirrel skins used 

 in the fur trade. The hairs of the tail are made into fine 

 paint brushes. The skins of common rats are used for the 



thumbs of kid gloves. Order . Why? 



Elephants. Elephants, strange to say, have several 

 noteworthy resemblances to rodents. Like them, elephants 

 have no canine teeth ; their molar teeth are few, and marked 

 by transverse ridges and the incisors present are promi- 

 nently developed (Figs. 376, 377). Instead of four incisors, 

 however, they have only two, the enormous tusks, for there 

 are no incisors in the lower jaw. Elephants and rodents 



