Gnawing Animals. 



109 



are known by their long cylindrical scaly tails, and 

 usually rooted teeth (except in the voles). The 

 common grey rat, introduced from the banks of the 



FIG. 53. 



The spalax, or blind rat. 



Volga in 1727 into Western Europe, has now nearly 

 exterminated the black rat. Spalax (fig. 53), the rat- 

 mole of SE. Europe and NW. Asia, has rudimental 

 eyes covered by the skin, and Dipus, the jerboa of the 

 East, has long, kangaroo-like hind legs and very 

 small fore legs. The porcupines have a covering of 

 quill-like hairs, and have an enormous hole in the front 

 of the skull wall, directly under the eye (fig. 52), which 

 is partly occupied by a muscle of mastication. The 

 chinchillas, coypu, &c. which are sought for their fur, 

 are also examples of this order. 



Hybernation. Many rodents, like some mam- 

 mals of other orders, bears, bats, &c., spend their 

 winter in a condition of sleep : this process is called 

 hybernation. Previous to retiring to this rest, these 

 animals store up fat in different regions of the body, 



