MUSEUM OF COMPARATIVE ZOOLOGY. 201 



surface, there is apparently a greater development of dusky on the ven- 

 tral ; this type forming the Vulpes " melanogastcr" of the south of Europe. 

 According to Professor Baird, the black varieties in some of the American 

 squirrels reach their greatest numerical development in the northern por- 

 tions of their habitat; :f where also melanic specimens of the marmot and 

 racoon are most frequent. On the Atlantic slope there is a noticeable 

 tendencv to a predominance of gray rather than rufous tints, while in 

 the interior, particularly in the Mississippi Valley, ami on the Plains, the 

 reverse is the case, in at least a number of species. I have in another place f 

 called attention to the faded appearance of the plumage of many species 

 of birds on the Plains, in those that range across the continent; in others 

 there is a tendency to an increase of fulvous and rufous, as is noticeable in 

 some mammals. In the Sonoran region there is a marked inclination to 

 pied varieties, such occurring in the weasels (P. frenatus and P. xantho- 

 genijs), skunks (Mephitis bicolor and also in M. mephitica), the bears and 

 squirrels. The changing to white in winter of many species at the 

 north which at the south constantly retain their summer colors, as the 

 weasels, the Arctic fox.J the wolf, and some of the hares,J it seems to me 

 is also to be' properly classed in the category of climatic and geographi- 

 cal peculiarities of coloration. The prevalence of neutral mouse-gray 

 tints in so large a proportion of the mammals of Australia, and of 

 plumbeous and black in those of Africa, in contrast with the brighter 

 and more varied colors of those »of the other continents, is but a grander 

 exhibition of the same kind. The hibernation of certain species in 

 the cold regions that in the warmer are constantly active, as in the 

 Ursidcc and Vespertilionidae, for example, is in some respects a similar 

 phenomenon. 



There are differences in size between specimens of the same species 

 from different localities that are not apparently explainable on the ground 

 of difference in the latitude and altitudes of their respective places of 

 birth. On the Mississippi prairies, for example, some species of Muridce, 



* North Amer. Mam., p. 241. 



t Mem. Bost. Sou. Nat. Hist., Vol. I, p. 513. 



X Concerning this point Mr. Alfred Newton observes : "I have never seen it re- 

 marked, but it is unquestionably the case, that nearly all the Icelandic examples of 

 Canis lagopus are 'blue' foxes ; that is to say, their winter coat is nearly the same 

 color as their summer coat. This fact, I think, must be taken in connection with the 

 comparatively mild climate which Iceland enjoys in winter ; and if so, is analogous to 

 the circumstance that of the Alpine Hare (Lepas timidus Linn., non auct.) always be- 

 coming white in Scandinavia, generally so in Scotland, but seldom in Ireland." (Proc. 

 Zool. Society of London, Dec. 1SG4, p. 497.) Dr. Richardson also states that the Arctic 

 fox is of a purer white on the shores of Hudson's Hay than at Bhering's Straits, where, 

 as is well known, the climate is considerably milder. (Faun. Bor. Amer., I, p. S7.) 



