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the skin dressed with the hair on forms a clothing so 
impervious to cold that a person dressed in a suit of this 
material and wrapped in a mantle of the same, may safely 
pass the night in the snow during the intensity of an arctic 
winter, throws light on the importance of this cellular hair 
to animals fitted for living in cold climates and at the same 
time having a constitution which requires them to be 
provided with a very warm external covering. The whole 
interior of these cellular hairs is occupied by air, which, as 
is well known, forms the best possible non-conductor of 
heat, and, in considering their efficiency for this purpose, 
the manner in which they are implanted in the skin should 
be noticed. In the Musk-deer there appears to be 
absolutely no fine wool or under-fur on the back and sides 
(which were the only parts examined), and the thick cellular 
hairs are so closely set in the skin that they necessarily 
stand out from it like the spines of a hedgehog, the conse- 
quence being that the thickness of the warm covering is not 
much less than the entire length of the hairs ; and it should 
be further noticed that their effect is increased by the 
uniform thickness which they preserve for so great a pro- 
portion of their length, and also by the wavy form already 
described, which allows them to fit, as it were, to one 
another. 
In the Roebuck there are a few slender hairs having the 
ordinary appearance of under-fur scattered among the large, 
rigid, cellular hairs which are seen standing out like quills ; 
these latter are of the same length as in the Musk, though 
not quite so thick, but they are still so closely set in the 
skin that they form a warm covering on the same principle. 
In the true Deer which have been found to possess these 
wavy cellular hairs the perfect development, as seen in the 
Musk, is further departed from, and they become longer in 
proportion to their thickness, wiry, and more scattered, and 
at the same time mixed with a greater quantity of under-fur. 
