COUES ON INSECTIVOROUS MAMMALS. 635 



eiitially or in practice, by most authors. The only question is, bow much 

 to allow. It is also certain that the recognized species must be largely 

 reduced in number, specific characters having been too often drawn from 

 features which can be proven to not hold good. 



The study of these diminutive quadrupeds would be difficult under 

 the most favorable circumstances; and the kind of material that reaches 

 us increases the difficulty. The skins are for the most part indifferently 

 or very poorly prepared, and unaccompanied by cleaned skulls; while 

 neither these nor the smaller number of alcoholic specimens are, as a 

 rule, accompanied by the data requisite for their satisfactory utilization. 

 They are generally unmarked for sex (difficult or impossible to determine 

 from dried preparations at least) or date of capture. Measurements of 

 dried skins are never more than approximately correct, frequently give 

 very fallacious results, and must always be taken with allowance for 

 probable error. This, in the case of such small objects, gives rise to 

 much uncertainty. The date of capture is a very important item ; for 

 the seasonal changes of the pelage are evidently as decided as they are 

 in the cases of animals better known in this respect, though terms 

 expressive of length, fullness, softness, etc., of the fur continually 

 recur in descriptive writing, without a hint as to what seasonal condi- 

 tion may be in point. To render such terms available in diagnosis, the 

 date of capture must be known. 



Similar remarks apply to the coloration. Color is unquestionably a 

 good specific character in many or most cases, perfectly reliable within 

 certain limits, or rather within limits still uncertain. Color-vadation 

 in this family is presented under three conditions (aside from purely 

 individual variation in this respect), namely, with age or sex, with 

 season, and with geographical distribution — none of which have hitherto 

 received sufficient attention on the part of American writers. I am not 

 aware that the first-mentioned variations have entered to any appre- 

 ciable extent into the establishment and description of species; and I 

 must confess my own very slight knowledge of the subject. Seasonal 

 color- variation I know to be much greater than has ever been practically 

 recognized by our writers, most of whom seem to have never even sus- 

 pected its extent. In the Arctic material before me are some very 

 striking illustrations of this variability in color. Under certain condi- 

 tions of the change of pelage, specimens normally coucolor or imper- 

 fectly bicolor show a narrow dark stripe along the back, sharply de- 

 fined against I'ich-colored sides, the resulting pattern of 'Coloration 

 being comparable as to sharpness of efifeot with the pelage of a Weasel 

 during the change from the summer to winter coat. I hope to enlarge 

 hereafter upon this subject, which is one that no author, so far as I 

 know, has adequately presented. The geographical variation in color 

 is a third point which demands carefal consideration. My studies up to 

 the present go to show a very interesting parallelism with the state of 

 the case I have determined for other snudl Mammals, notably the Mice 



