THE LIFE OF MAMMALS 
weasels of both continents wherever the climate is so cold 
that snow lies continuously on the ground from autumn until 
spring. The British stoat and our own weasels remain brown 
in winter (though paler) south of the line of persistent snow, 
and turn white north of it, and also on lofty (and consequently 
cold) mountain tops. On the Cascade Mountains along Pu- 
get Sound you may collect in winter brown weasels in 
the coast valleys, drab ones halfway up the range, and pure 
white ones on the summit. The change in color appears to 
be wholly beyond the will of the animal, and to be due to the 
shedding of the old hairs and their replacement by hairs which 
come in wholly white, but it appears that the process may be 
hastened by the early arrival of cold and snow, or retarded by 
a late season. The same molt takes place in warm regions, 
but there the new hair comes in brown instead of white. Nev- 
ertheless it is impossible to dismiss wholly the old belief that 
the change is brought about in some cases at least by the grad- 
ual blanching of the hairs; for we cannot dispose of such facts 
as Dr. Coues’s statement that he had seen many autumnal 
skins in which the hairs were white at the roots and dark 
at the tips. A very full discussion of this subject may be found 
in Poulton’s ‘* and Beddard’s*’® books on animal coloration, 
and in Lydekker’s ‘Mostly Mammals.” 
As to the purpose of the change, it seems evident, at least, that it is bene- 
ficial in two ways. First, in screening the weasel from the eyes of both its 
enemies and its prey, by making it unnoticeable amid the snow; and second, 
in helping it to retain its bodily heat, which would be radiated more rapidly 
by a dark dress than by a light one. How far the former advantage is 
neutralized by the fact that its principal victims in winter, the hares, lem- 
mings, and ptarmigan, are equally “‘invisibly” white, the reader may deter- 
mine for himself. 
The mink is the last, and one of the most important and 
interesting, of this tribe, —a musteline with toes somewhat 
webbed, and of stouter build than a weasel, about twenty-eight 
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