1903. ] HAIR-SLOPE IN MAMMALS, 81 
The Ox presents no pectoral whorl as do the Dog and Horse, the 
dewlap in this region being covered with perfectly smooth and 
uniformly arranged hair. 
These are the only four constant peculiarities of hair-slope, but 
occasionally the flank and post-humeral regions, and extensor 
surface of the thigh, show small whorls and featherings connected 
apparently with the action of the panniculus carnosus muscle. 
(4) The Horse is more specialized in the matter of hair-slope 
than any other animal except man. 
It shows ¢ 
(i) Frontal whorl, feathering, and crest. 
(ii) Tuft between the external ears. 
(iii) Longitudinal crest or mane. 
(iv) Strong efficient tail with bushy hair, reaching to the 
fetlock. 
(v) Inguinal whorl, feathering, and crest. 
(vi) Pectoral whorl, feathering, and crest. 
Frequently but not constantly :— 
(vii) Post-humeral whorl, feathering, and crest. 
(vill) Cervical whorls, feather ings, and crests in several 
situations, 
(ix) Gluteal whorl, feathering, and crest. 
(x) Tuft on lateral aspect of the abdomen. 
In passing from the simple ty pe found on the Otter to that of 
the Horse, a very significant series of changes is thus displayed. 
Such facts as are here referred to have little or no intrinsic 
interest or importance, but the phenomena of Nature, small and 
great, demand explanation in accordance with the methods of 
science, and it is impossible to ignore the peculiarities of hair- 
slope which have been taken here as typical of a vastly greater 
number in other animal forms. Any other interest they may 
have is subordinate to their relation to the problems of heredity. 
The four groups of facts suggest apparently two explanations as 
to their zetiology. The first and most obvious is that some of them 
are adaptive modifications of value to the animal; the second, 
that others are produced by its habits; and it is not difficult to 
distinguish these two classes in the four typical forms chosen for 
consideration. 
1. In the Otter the uniform trend of hair requires no other 
explanation than that this arrangement of hair offers the least 
ossible resistance to movements in the water and in burrows. 
2. In the case of the Domestic Dog the departures from a primi- 
tive type can hardly be ascribed to anything else than to use or 
habit: they are adapted by the habits of the animal, not for its 
needs. 
Proc. Zoot, Soc.—19038, Vou. I. No. VI. 6 
