MAMMALS 



205 



reducing the food still finer after it has been gnawed off 

 (Fig. 345). The lower jaw fits into grooves in place of 

 sockets. This allows the jaw to work back and forth in- 

 stead of sidewise. The rabbits and some squirrels have a 

 hare lip ; i.e. the upper lip is split. What advantage is 

 this in eating ? In England the species that burrow are 

 called rabbits ; those that do not are called hares. 



Name six enemies of rabbits. Why does a rabbit usually 

 sit motionless unless approached very close ? Do you 

 usually see one before it dashes off ? A rabbit has from 

 three to five litters of from three to six young each year. 

 Squirrels have fewer and smaller 

 litters. Why must the rabbit 

 multiply more rapidly than the 

 squirrel in order to survive ? 

 English rabbits have increased 

 in Australia until they are a 

 plague. Sheep raising is inter- 

 fered with by the loss of grass. 

 The Australians now ship them to England in cold storage 

 for food. Rabbits and most rodents lead a watchful, 

 timid, and alert life. An exception is the porcupine, 

 which, because of the defense of its barbed quills, is dull 

 and sluggish. 



The common rodents are : 



FIG. 374. POSITION OF LIMBS 

 IN RABBIT. 



porcupines 



pouched gopher ground hog 

 prairie dog field mouse 



prairie squirrel 

 guinea pig chipmunk 



Which of the above rodents are commercially important ? 

 Which are injurious to an important degree ? Which have 

 long tails? Why? Short tails? Why? Long ears ? Why? 



squirrels beavers 

 rabbits muskrats 

 rats 

 mice 



