1200 BULLETIN OF THE 



extends to other species I have not at present the moans of determining, 

 though it is hardly to be expected that it will to all, since some of them are 

 to a considerable degree migratory, going southward in winter, as the 

 lynxes, martens, and some others. Hence extremes of climate, whether 

 of heat or cold, seem to unfavorably influence the development of animal 

 life generally, a mean or temperate region being as necessary for the 

 highest development of the lower orders of mammalia as for that of man. 



Besides the marked climatic modifications in size and in other features 

 in the species cited above, certain other variations in them may be here 

 appropriately referred to. These, though slight, so commonly appear in 

 a number of species inhabiting the same region as to lead one at once to 

 suspect a common cause for such differences. Dr. Richardson* long since 

 pointed out slight differences in the color and texture of the fur, and in 

 the breadth of the foot, in species which he considered identical in North 

 America and Europe, between their representatives from Northern North 

 America and Central Europe; the former having a finer and thicker 

 coat, and broader feet, to better adapt them to a colder climate and a 

 more snow-covered country, as well as brighter and livelier colors. These 

 modifications appear also, he says, in the native domestic dogs.* 



Naturalists have repeatedly remarked the narrower form of the head 

 in the moose, bear, fox, and wolf in Eastern North American specimens 

 as compared with others from "Western Europe. In the former, the abso- 

 lute breadth of the skull is generally less, while there is at the same 

 time, a greater development of the facial portion. In these animals a 

 difference in size has also been claimed to distinguish their representatives 

 from the two continents ; but, owing to the variation in size on either con- 

 tinent with the latitude and elevation of the locality at which they were 

 collected, observations on this point are somewhat contradictory. The 

 general indication, however, seems to be that the American somewhat 

 exceed the European when both are from near the same isotherm. 



I have already called attention to the fact of the same species varying in 

 color in different portions of its habitat, as in the case of the Cants luj)tis. 

 On both continents, this species gradually changes from nearly white 

 (yellowish or grayish white) in the Arctic regions to very dark or "black " 

 in the southern. Individuals of the black and cross varieties of the fox 

 (I'll') i ) are mosi numerous on both continents towards the 



north ;t at the south, while the general fulvous color prevails on the dorsal 



* I li-Americana, Vol. I, p. 91. 



t Mr. II. R. Ross gives the proportion of the different colors in the foxes killed in the 

 nsred f ^ths,cross j^ths, silvei- ,'v 11 : or sixty per cent of the 

 dark variety t'> forty of the red ; while as tar south as the United States the dark vari- 

 eties probably scarcely exceed one percent. — Nat. Jlist. Rev., 1862, p. 272. 



