266 THE DEER OF AMERICA. 
That the odor emitted by these glands is left upon the track 
of the deer may be presumed, but as the trail of other animals 
not provided with these organs seems to be as readily followed 
by the hounds, we may safely conclude that they are not the 
only sources of the scent left in the track. The capacity of an 
animal to leave ascent which may be followed by an enemy, 
would seem to be detrimental to its safety or well being, es- 
pecially in a wild state, but it is common to most if not all ter- 
restrial animals. There are compensating advantages, no doubt, 
at least to some extent, for it enables them to find companions 
which they might otherwise seek in vain. 
Whatever may be the uses of these glands, certain it is that 
they are very active, constantly secreting matter; and this, in 
every case where I have examined the live or recently killed 
animal, emits a pungent odor. 
I prefer rather to give the facts, than to advance or maintain 
doubtful theories. 
The longer and the more minutely I have examined this gland- 
ular system on the hind legs of the different species of this genus, 
the more I have become impressed with its importance in the 
division into or identification of species. As Dr. Gray justly 
remarked, they are not transient, or exceptional, like the antlers, 
but are present on both sexes and at all ages, and had he studied 
them with care he would have added that they are as near alike 
as possible on each individual of each species, and that those on 
the outside of the legs, when present, are entirely unlike on the 
different species; so that upon an examination of the part of the 
skin containing this gland, no one familiar with the subject could 
hesitate to declare with certainty from which species it came. 
Hardly any other single mark pervading so many species is so re- 
liable as this, and certainly none of so small dimensions. The tail 
of the mule deer, no doubt, will always declare itself, and so will 
the foot of the caribou ; but still they vary in size even propor- 
tionately, while this gland is so exact that from it alone one may 
closely approximate the size of the animal. Should I be presented 
with a piece of skin, containing a gland similar to the one which 
I have above described, yet differing from it, I should conclude 
that it came from some distant country, and that other distine- 
tions would probably be found establishing a species differing 
from any of ours. As, for instance, should I find one resembling 
that on our Virginia deer, but without the white band, or es- 
pecially with a black band around it, or one otherwise corre- 
