346 Canadian Record of Science 



of the country was based upon a beaver standard, a full- 

 grown beaver-skin being regarded as the unit of cur- 

 rency; and those of us who may have read the. late Mr. 

 Horace T. Martin's book on the "History and Traditions 

 of the Canadian Beaver" (Montreal, 1892), will under- 

 stand that it has formed the theme of a good deal of 

 poetry and literature besides. 



In some of its habits and instincts the beaver exhibits 

 a certain degree of analogy with the musk-rat or mus- 

 quash, and there is a striking agreement in the contour 

 of the body ; but the resemblances are superficial. These 

 rodents have acquired their water-loving propensities 

 independently, and the necessities of adaptation to the 

 rigours of a northern climate have led to somewhat 

 similar modifications. Both of them include the succu- 

 lent roots or rhizomes of Nuphar advena, the large 

 yellow pond-lily, in their diet; they build winter lodges 

 which rise above the water-level, the beaver using mud 

 and chipped branches from which the bark has been 

 stripped for food, the musk-rat mud and rushes; their 

 eyes and ears are small and the toes of their hind-feet 

 are united by a web. The fur, with its outer covering of 

 coarse guard-hairs and the soft wool or under-fur below, 

 is very much the same in both. But whereas the scaly 

 tail of the beaver is flattened from above downwards, the 

 scal} r tail of the musk-rat is flattened from side to side. 

 Moreover, the lodge of the musk-rat only lasts for a sea- 

 son, while that of the beaver is repaired and added to 

 from year to year. The construction of the winter lodge 

 of the musk-rat has been described by 0. L. Herrick 

 (Mammals of Minnesota, Minneapolis, 1892). 



The musk-rat is in fact related to the true rats and 

 mice; as shown by the structure of its teeth and other 

 characters of the skull, it is a typical member of the 

 subfamily (Arvicolina?) of the mouse family (Muridae) 

 to which the common Water-Vole of Europe and North- 

 ern Asia belongs, only it has gone farther than the latter 

 in its adaptation to an aquatic life. The toes of the 

 amphibious vole are not webbed and the tail is not 



