1 900.] HAIR-SLOPE IN CERTAIN MAMMALS. 685 



All the characters o£ hair-slope here referred to may be taken 

 as congenital. Being then inherited they may have arisen in 

 certain ancestors in one of the three ways : — 



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 environ- 

 ments — 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 may 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 we 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 Equus cabalhis 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 



