236 THE DEER OF AMERICA. 



overlap the upper part of the black so as to hide a portion of it. 

 This condition usually occurs in the fall of the year and on 

 young animals not more than three or four years old. The 

 former condition is, to some extent at least, artificial. It results 

 from those white hairs near the lower part of the tail becoming 

 worn off so that they are shorter. This is rendered possible 

 from the white hairs being open, spongy, non-elastic, and brittle, 

 so that they are readily broken off by coming in contact with 

 objects when the tail is moved by the animal. Those hairs near 

 the upper end of the tail are less exposed to abrasion than those 

 lower down and near the end. The black hairs composing the 

 switch are different. They are quite solid, firm, and elastic, 

 like those on the tail of the horse, and so can bear a great 

 amount of friction without being broken off. They endure the 

 violence, while the white hairs just above them become worn 

 down short. The two extremes and an intermediate form are 

 shown in the illustrations. Figs. 2, 3, 4, p. 234. 



Independent of this abrasion there is in most specimens a cer- 

 tain degree of taper resulting from the fact that on them the 

 white hairs are shorter on the lower than on the upper part of 

 the tail. On aged specimens these white hairs are more brittle 

 than on younger animals, hence they are worn shorter on them 

 and so present a much more tapering form. 



Take a specimen about the first of August, when the old white 

 hairs are nearly shed and the new ones are still short, and above 

 the black tuft the tail is verj^ small all the way up, while the 

 black hairs which are constant, like those on the tail of the horse, 

 remain conspicuous throughout the year. These black hairs are 

 genei'ally shorter and stand in a more radical position on the old 

 sj)ecimens than on the young. On the young, that which is 

 worn off of the black hairs is replaced by new growth which is 

 more vigorous on the young than the old ; on the latter the growth 

 is tardy and does not fully repair the loss, so that on the young 

 the black tuft appears longer and of less diameter than on the old. 



I have said that the under side of the tail of the Mule Deer 

 is naked down to near the end, like tlie horse's tail. This is 

 not absolutely so, for even the on young specimens a careful in- 

 spection will reveal to the naked eyes a number of scattering 

 very short fine hairs, more abundant towai'ds the lower end of 

 the naked space ; these grow somewhat larger as the animal 

 grows older, but are always kept worn short, so that on old 

 specimens the lower part of the naked portion exhibits a good 



