THE MAMMALS 233 



of the body have the form of stiff, barbed spines (Fig. 132), 

 readily dislodged so that the animal requires no other wea_ 

 pon of defense. The rabbits and hares are of smaller size, 

 and the cottontails especially are widely distributed. West 

 of the Mississippi the jack-rabbits are familiar, and are 



Fro. 132. Porcupine (Hystrix cristatd). One-tenth natural size. After BREITM. 



famous for their great speed. Like the porcupines, they 

 feed on leaves and grass, and are often very destructive. 

 The mice, especially the field and white-footed mice, are 

 abundant in woodland and meadow throughout the United 

 States. The house-mouse (Mus musculus) is a native of 

 Europe, as is the common rat (M. decumanus), which was 

 imported over a century ago. The wood-rat (Neotoma)^ 

 however, is native, and may be found in many localities 

 from east to west. The muskrat (Fiber zibetliicus), beaver 

 (Castor canadensis), and woodchuck (Arctomys monax) were 

 also more or less plentiful formerly, but in many localities 

 are well-nigh exterminated. The squirrels, on the other 

 hand, continue to exist in large numbers. The prairie- 



