314 



THE VERTEBRATE ANIMALS 



Skull of a porcupine, a rodent. Notice the large 

 overlapping incisor teeth. Compare them with the 

 teeth of a dog (see page 313). 



edge because the back part of the teeth is softer and wears away 

 more rapidly. The canine or dog teeth are lacking. We are 

 all familiar with the destructive gnawing qualities of one of the 



commonest of all ro- 

 dents, the rat. The 

 common brown rat is an 

 example of a mammal, 

 harmful to civilized 

 man, which has fol- 

 lowed in his footsteps 

 all over the world. 

 Starting from China, it 

 spread to eastern 

 Europe, thence to west- 

 ern Europe, and in 1775 

 it had obtained a lodg- 

 ment in this country. 

 In seventy-five years it 

 reached the Pacific coast, and is now fairly common all over the 

 United States, being one of the most prolific of all mammals. A 

 determined effort is now being made to exterminate this pest be- 

 cause of its connection with bubonic plague. 



Although most rodents may be 

 considered as pests (as the rat and 

 mouse), others are of use to man. 

 Some of this order furnish food to 

 man, as the rabbit, hares, and squir- 

 rels. Rabbits, although rapid 

 breeders, are kept in check in most 

 parts of this country by their nat- 

 ural enemies, birds of prey, and 

 flesh-eating mammals. But in 

 Australia, where they were intro- Beaver ^ Castor **M)- North 



, , ' , America. Copyright, 1900, by A. 



duced by man, they have become Radc i iffe Dugmore. 

 so numerous as to require govern- 

 ment action in the form of a bounty for their destruction. Thou- 

 sands of sheep are starved to death each year because rabbits eat 

 up their pasturage. The fur of the beaver, one of the largest of 



