208 MOSTLY MAMMALS 
summer. Again, many mammals vary to a great extent 
in coloration according to locality, so that there may be 
dark-coloured and light-coloured races inhabiting different 
localities. The most striking instance of this is, perhaps, 
the big-horn wild sheep of North America, which in the 
Rocky Mountains is a khaki-coloured animal with a white 
rump, but in Alaska is nearly pure white all over through- 
out the year. It is true, indeed, that American naturalists 
prefer to regard the big-horns of the Rocky Mountains and 
Alaska as distinct species rather than local races of a 
single variable animal, but for our present purpose such 
slight differences of opinion do not really affect the case 
one way or the other. 
That white fox and blue fox skins are not (as was once 
supposed to be the case by some naturalists) the summer 
and winter coats of the same individual animals will be 
apparent by a comparison of furs of the two descriptions 
worn by our lady friends. Both descriptions have the 
same long thick hair, with a woolly under-fur at the base, 
and are evidently the winter coats of the animals to which 
they respectively belong. Indeed, with all long-haired 
animals of the northern parts of the Old World, with the 
possible exception of the Polar bear, it is the winter coat 
that is alone valued by the furrier. 
That blue and white foxes are not local races of the 
same species (or distinct species) is evident from the fact 
that in certain districts both occur together, although in 
other localities (as in Iceland, where all the foxes are 
blue) only one form may be met with. It is, indeed, 
possible that in some cases blue and white cubs may appear 
in the same litter. For instance, Prof. A. S. Packard, in 
his work entitled “The Labrador Coast,” states he was 
informed by a native “that the white and blue fox littered 
