328 



MAMMALS 



which arc the spines, or quills, which constitute a notably 

 efficient means of defense. W'hen on the defensive, a por- 

 cupine arches its back and rolls up into a ball. The tail, 



which is thickly 

 covered with spines, 

 is the main organ of 

 defense. The un- 

 wary dog or person 

 worrying the pjorcu- 

 pine is often caught 

 within striking dis- 

 tance. The spines 

 are rough and 

 jagged at the ends, 

 but shar]), and when 

 they once enter the 

 flesh, tend to work 

 farther in. 



Prairie marmots. 

 — These little ani- 

 mals, better known 

 as " prairie dogs," 

 are closely related to 

 the woodchuck of 

 New England and the middle states. The best-known 

 species is found on the prairies west of the Mississippi 

 River. They live in colonies anil dig deep burrows in the 

 ground. The great cjuantities of earth brought up in dig- 

 ging these holes are jjiled in a mound near the mouth of the 

 buri'ow. 



Beavers. — The Ijcavcr is one of the largest and heaviest 

 rodents, often weighing thirty to hfty pounds. The body 



Fig. 21.?. — Porcupine in tree top. Redrawn 

 from an illustration b}' Diigmorc in McClurc's 

 Mmiazinr, 1900. 



