RATS. 225 



branches of trees and mud, but aside from this instinct 

 showing little intelligence. It is found occasionally in 

 France and Germany, and was formerly very abundant 

 in North America, where it lived in large colonies, and 

 constructed lodges that excited the admiration of travel- 

 lers. Under the hair of the beaver, which is usually of 



FIG. 154. 



PRAIRIE-DOGS (Cynomys ludovicianus). 



a reddish color, is a fine gray down that makes the fur 

 much esteemed. 



The rats include a number of species, much alike in 

 appearance and in habits. Properly, the rats may be clas- 

 sified as black rats and brown rats. The black rats in- 

 vaded Europe at the time of the Crusades, and during 

 several centuries ravaged the country and the cities. 

 About a hundred years ago a few individuals of the 

 brown species were brought from Persia ; they multi- 

 plied rapidly, and waged such a terrible war on the 

 black rats that the latter were driven from the cities. 



The field-rat is smaller than the house-rat and larger 

 P 



