MAMMALIA 



625 



dams for its home. The dams are built of trees which are cut with 

 its teeth, floated into position, and chinked with mud. 



The muskrat. Fiber zibethicus, belongs in a large family with lem- 

 mings, rats, meadow mice, and white-footed mice. It lives in slow 

 streams, ponds, and swamps, and feeds on roots of water plants, 

 fresh-water mussels, dock, corn, and other grain when it is available. 

 It builds houses of stalks, leaves, cattail leaves and mud out in the 

 water of swamps. In ponds it uses a burrow in the bank. The home 

 is lined with cattail down or grass ; here it rears the young and spends 

 the winter. 



The porcupine, Erethizon dorsatus, is principally a northern ani- 

 mal but is found in the mountains as far south as Virginia and also 



Fig. 338. — Muskrat, Fiber zibethicus, an important fur bearer. (From Metcalf, 

 Textbook of Economic Zoology, published by Lea and Febiger.) 



in the mountains of the Southwest in Texas and Arizona. These ani- 

 mals have the hairs of the back modified into spines which normally 

 lie flat, but which can be elevated by muscles when the animal is 

 frightened or angered. The black rat, Battus rattus, the Norway 

 rat, Rattus norvegicus, and the common mouse, Miis musculus, have 

 all been introduced into this country from Europe. The chinchillas, 

 viscachas, and the cavies (guinea pigs) have all been introduced from 

 South America. 



Order Lagomorpha. — The rabbits and hares constitute a very inter- 

 esting and important group. The jack rabbit is the most common 

 hare of the western plains, mountain region, and Southwest. It is 



