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Show 1900.] HAIR-SLOPE IN CERTAIN MAMMALS. 685 All the characters of hair-slope here referred to may be taken as congenital. Being then inherited they may have arisen in certain ancestors in one of tbe three w a y s :- 1. They may have been due to selection (Natural, i.e. Personal, Sexual or Germinal). 2. They may have arisen from the action of habits or environments- Lamarckian factors ; or, 3. They may be vestigial. Considering that, so far as it is possible to understand animal life, the survival-value of these differences of hair-slope is nil, natural selection and germinal selection may be put aside as accounting for them. Though the slope on the extensor surface of the fore-arm is claimed to be vestigial, these peculiarities are not so claimed, and cannot be, in the face of the very tangled relationships which are presented. The possibility of accounting for them by sexual selection must be considered; but as some of these divergences of slope are difficult for a human eye to discover at close quarters, and as usually no markings or coloration are attached to them', this theory cannot be seriously entertained. If it m a y be fairly held that these exceptional forms of slope of hair found on the head, dorsal region, fore-arm, and gluteal region, indicate the working of certain Lamarckian factors, there is a much greater body of evidence pointing in a similar direction, viz., all those hairy mammals which conform to the ordinary type. Indeed the general trend of hair from the cephalic to the caudal extremity of every animal, and from the proximal to the distal extremity of each limb, may even be open to similar interpretations. As there is no evidence forthcoming as to the prototype of hair-covered mammals, no speculation as to the habits and environments thereof can be profitable. Whether it were Ornithodelphous, Marsupial, or Insectivorous in its type, there must have been a time when the development of hair was feeble, and capable of being affected by habits and environments. It is surely as reasonable to attribute to these the slope of hair which w e find existing, and compatible with them, as to attribute it to any survival-value, under selection -if not considerably more so. I would suggest that one habit which is common to such animals as here in question, that of cleaning their external coverings by friction, either against other objects, with their fore-paws, or with their tongues, must have a very potent influence in determining the general trend of hair referred to as found on all hairy animals. It is obvious that such forces must in the main act in the direction indicated. 1 The " star " or " blaze" on Horses is one of the comparatively few instances of markings in this region ; but Eqnus caballus is not an animal in a state of nature, and has been so much modified by artificial selection as to prevent this combination of markings and exceptional hair-slope from being brought under Sexual Selection. PROC. ZOOL. Soc-1900, No. XLV. 45 |