THE MOUSE AND ITS ALLIES 321 



mouth; (4) the jumping mice, with greatly elongated 

 hind legs; (5) the muskrat and the various wood and 

 field mice, closely related to the genus Mus ; (6) the por- 

 cupines, with bristles replacing hairs ; (7) the hares, with 

 long ears and short tails. All of these familiar rodents 

 are, on the whole, destructive to agriculture. As there 

 are, however, other interests in life than agriculture, it is to 

 be hoped that the warfare against our native rodents will 

 not be too relentlessly pursued. At least one interest- 

 ing species has been rendered well-nigh extinct by the 





FIG. 296. Ornithorkyncnus anatmus, the duckbill. After Vogt and Specht. 



avarice of fur hunters this is the American beaver, an 

 animal which has developed extraordinary instincts for the 

 construction of dams and subaquatic passages. 



Other Mammals. The Monotremata 1 are the lowest 

 mammals, and in many ways seem to connect the class 

 with reptiles or amphibians. The milk glands are in a 



s, single, r/o^a, hole or opening ; so called because urinary, geni- 

 tal, and alimentary canals have a common external opening. 



Y 



