FIELD BOOK OF MAMMALS 



ence. To get Beaver fur the trappers and fur companies, like 

 the Hudson Bay Company, pushed across the continent and 

 laid the foundation for a later occupation in force by settlers. 

 Other fur-bearers contributed to this motive, but the Beaver 

 made up the bulk of the traffic. For years the hat makers 

 would use only Beaver fur for felting material of fine hats. 



In literature, the Beaver has been held up as the mirror of 

 sagacity, engineering skill, and general all-around industry. 

 Whole volumes have been devoted to him alone. As is to be 

 expected, not all that has been written of the Beaver is so. 

 Several of the best works are cited in the bibliography in the 

 back of this field book, and the reader is referred to them for 

 the many interesting details of the Beaver's home life. Plate 

 XXVIII. 



The Beaver is not peculiar to the New World but has an 

 extensive distribution throughout most of the Northern 

 Hemisphere. It has become extinct, however, over much of 

 its Old World range. The large size, flat, scaly tail, and 

 aquatic habit serve as unmistakable characters of 

 identification. 



The number of young at a birth varies from two to six, or 

 rarely eight. The average number seems to be four, and the 

 young are born in April to May, occasionally late in March. 

 The young stay with the parents for a year and the known 

 facts indicate that Beavers are monogamous and remain 

 mated for life. 



Beaver may be active any hour of the twenty-four, but are 

 most active from sunset to sunrise, especially in a region where 

 they are apt to be molested by enemies. 



Family Cricetidae. Native Rats and Mice 



Form typically rat or mouse-like; molar teeth never more 

 than three on a side; molar crown pattern composed of tuber- 

 cles arranged in two primary longitudinal rows, or made up 

 of angular figures. 



Subfamily Cricetinae 



Molars rooted and with tubercles arranged in two primary 

 longitudinal rows. 



332 



