MUSEUM OF COMPARATIVE ZOOLOGY. 149 



clothing of the feet, species with the soles thickly furred in winter often 

 having them sparsely so in summer, northern individuals differing in 

 like manner from southern. The variation in this respect increases 

 with the distance in latitude between the localities whence the speci- 

 mens compared are taken. 



Besides these geographical or climatic variations, we have found by 

 a careful comparison of scores of specimens of the same species, collected 

 at the same locality, that there is a much greater range of variation 

 between individuals of the same species — the variation extending to 

 every part — than is commonly conceded ; and also that differences de- 

 pending upon season,* as in the color, thickness, length, and general tex- 

 ture of the pelage, and others depending upon age * and sex, instead of 

 being always recognized by authors as such, have not unfrequently been 

 taken to indicate a constant specific diversity. From this cause there 

 has arisen, in numerous instances, an undue increase of so-called species. 

 Specimens have too often been described instead of species. It is not 

 surprising that these mistakes should have happened in the earlier days 

 of our science, when the material for study was scanty and diagnoses 

 were commonly drawn up from stuffed .-kins, the authors being in total 

 ignorance of the appearance of the animal in life ; when the extent of 

 individual variation had not been especially investigated, and it was un- 

 known that in animals possessing a wide distribution there were marked 

 variations accompanying wide differences in locality. But even now 



* In spring, as is generally well known, mammals shed the long, thick coat worn in 

 winter; this is replaced by a much shorter, thinner, less soft, and generally differently 

 colored pelage. In this there is a gradual change throughout the summer, and late in 

 fall it becomes either entirely replaced or effectually concealed by the growth of the 

 long winter coat. The winter differs from the summer pelage not only in being longer 

 and thicker, but generally in the different character of the hair composing it, and in the 

 fulness of the soft under fur, as well as more or less in color. The shortness of the sum- 

 mer coat renders the ears of such animals as have these members very short, as the 

 different species of Arvicola, Sorex, Sciums, &c, much more conspicuous at that season 

 than in winter, when in some of them they are nearly concealed. In young animals, 

 too, the first pelage differs much from the succeeding, being shorter, darker, and gen- 

 erally more or less crisp. The general health of the animal, as no one need be told who 

 has attentively observed domestic animals, has a marked effect upon the character of 

 the coat, and on the time it is changed, as does also scantiness or abundance of food. 



As previously stated in the text, species with the soles of the feet furred have them 

 less densely so in summer than in winter. It is perhaps needless to advert to the fact of 

 the existence of a temporary set of teeth in young animals, which gradually give place 

 to a permanent one differing from the first in number and character. 



