352 



ELEMENTARY ZOOLOGY. 



and widely distributed. (See Fig. 150.) They do not 

 have canine teeth, but the incisors continue to develop 

 in such a way as to maintain a sharp edge of enamel 

 in spite of wear. They feed on vegetable diet chiefly, 

 as nuts, acorns, grains, growing shoots, and are often 

 attracted to stores that man has made. The rats and 



FIG. 150. The jumping rat (Perodipus richardsonf) , adult male. Photo by Shufeldt. 



Questions on the Figure. What order of mammals is illustrated 

 by this form? What explanations have been offered as to the cause 

 of the light-colored belly and the darker back of animals? Of 

 what conceivable advantage is the difference? How does the tail 

 of this species compare with that of our common rat ? 



mice follow civilization and find harbors and food in 

 the homes of men. Many of them burrow extensively, 

 as the gophers, ground squirrels, prairie-dogs, ground- 

 hog, beaver, etc. Most of them are more active at 

 twilight or in the night. For this reason the smaller 

 species furnish a large part of the food of owls. 



