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Show 1903.] IIAIR-SLOPE IN MAMMALS. 81 The Ox presents no pectoral whorl as do the Dog and Ilorse, 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 constantly- (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. (viii) Cervical whorls, featherings, and crests in several situations. (ix) Gluteal whorl, feathering, and crest. (x) Tuft on lateral aspect of the abdomen. In passing from the simple type 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 aetiology. 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 possible resistance to movements in the water and in burrows. 2. In the case of the Domestic Dog the departures from a primitive 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. P r o c . Z o o l . S o c .- 1903, V o l . I. No. YI. 6 |
