THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 



151 



region is further divisible into northern and southern belts, 

 called the Hudsonian and Canadian faunas, the limit between 

 them approximately following the isothermal line of 57° F. 

 The mammals of this subregion are largely of Old World 

 origin, many of them coming in with the great immigrations 

 of the PHocene and Pleistocene epochs ; but there are also 

 native American elements and even one genus of South American 

 origin, the Short-tailed or Canada Porcupine {Erethizon). 



In considering the mammals of this subregion, it should be 

 remembered that they are not uniformly distributed through- 

 out even one subdivision, but in a scattering way and in ac- 

 cordance with their habits and stations, and also in accordance 

 with a gradual change to 

 the south, following the 

 changing temperature. The 

 Muskrat will not be found 

 far from water or the Por- 

 cupine from woods. Espe- 

 cially characteristic of the 

 Canadian subregion are the 

 Old World types of deer, 

 none of which range farther 

 south than the Transition 

 zone. The Wapiti, errone- 

 ously called the Elk (Cervus 

 canadensis), is very closely 

 allied to the European Stag 

 (C elaphus) and still more 

 closely to the Stag of the 

 Thian Shan in Central Asia 

 (C eustephanus) . So great 

 is the resemblance, that some naturalists would refer all three 

 forms to a single species. The Moose {Alee amerieanus), which 

 should be called the Elk, is so near to the Scandinavian Elk 

 {A. maehlis) that it is hardly distinguishable as a separate 



Fig. 58. 

 tus).- 

 Soc. 



-Canada Porcupine {Erethizon dorsa- 

 By permission of the N.Y. Zoolog. 



