622 



TEXTBOOK OF ZOOLOGY 



rats, mice, ^-ound squirrels, squirrels, chipmunks, prairie dogs, kan- 

 garoo rats, cotton rats, wood rats, muskrats, woodchucks, porcupines, 

 guinea pigs and beavers are representative. They all have long 

 chisellike incisors but no canine teeth. 



The prairie dogs {Cynomys ludovicianus) are heavy -bodied, bur- 

 rowing, rodents that live on the plains west of the Mississippi River. 



Fig. 334. — Identical armadillo quadruplet embryos attached to the placenta. 



These animals are gregarious, living in "towns" or colonies. The 

 burrows are provided with a mound around the entrance, and they 

 are usually quite deep and fifteen to thirty feet apart. Forty or 

 fifty acres of land may be covered by one town. 



The ground hog or woodchuck, Marmota monax, is a larger solitary, 

 burrowing animal which hibernates during the winter. It bears 

 about six young in the burrow early in the spring. The ground 

 squirrels are also burrowing animals somewhat similar to the ground 

 hog, but much smaller. They are found from the Mississippi basin 



