THE DOOILE MAMMALS. 243 



by the slow, ugly porcupine, vhich either lives in trees or 

 burrows in the earth ; it eats the bark and leaves of pine, 

 larch, spruce, and other trees, and the buds of the willow. 

 The quills fall out at the slightest touch, and, lodged in 

 the skin of a dog or wolf, are said in some cases to make 

 their way into the body until they cause death. The more 

 intelligent, active forms are the beaver, musk-rat, the rats 

 and mice, squirrels, and, lastly, the marmots. The two 

 domestic rats, namely, the brown or Norway rat {Mus decu- 

 manus), and the black rat {Miis rattus), and the common 

 house mouse {Mus miisculus), are cosmopolitan animals. 

 The musk-rat or musquash {Fiber zibethicus) has the hind 

 feet partly webbed, so that it swims and dives well. It 

 ranges from Florida to Arctic America. Northward it has 

 three litters in the course of the summer, and from three 

 to seven at a litter. It feeds on the roots and tender shoots 

 of rushes and of the sweet flag, as well as mussels. In the 

 autumn, before the shallow lakes and swamps freeze over, 

 it builds its low conical house of mud, the base high enough 

 to raise the interior above the level of the water; the en- 

 trance being under water. When the ice forms the musk- 

 rat makes breathing-holes through it, and protects them 

 from the frost by a covering of mud. In the summer it 

 makes long burrows in the banks of streams, with a dry 

 nest at the end. 



Of the squirrels, the chipmunk ( Tamias Asiaticus) inhab- 

 its Northwestern America; it is striped with five black and 

 four white stripes on the back. It is an active and indus- 

 trious little creature, with its cheek-pouches full of seeds. 

 During the winter it lives in a burrow, with several open- 

 ings made at the base of a tree. The chickaree or common 

 red squirrel {Sciurus Hudsonius) may be seen in the dead 

 of winter in pleasant weather; it burrows under trees; 

 it feeds chiefly on nuts and seeds, and in the fur countries 

 subsists chiefly on the seeds and young buds of the spruce. 

 In New England it eats the seeds in pine cones, letting the 

 scales fall to the ground und^r it? §e»t on » lofty pine 



