1902,] HAIR-SLOPE IN MAMMALS. 151 



the " law of parsimony " to look for any other cause of this whorl 

 than the pressure of the weight of the animal's body on the hair 

 over this pi'ominent region. 



In almost all the Carnivores and Ungulates, the hair on the 

 gluteal region curves over this rounded surface, taking a coui'se in 

 the long axis of the limb itself, as in a horse, or veiy often in the 

 long axis of the trunk, as may be seen in a short-haired dog. 

 The sweep of this gluteal stream towards the peiineum is inter- 

 rupted by the whorl mentioned, in a few animals which sit, such 

 as short-haired dogs and many of the Simiadse, though in most of 

 the latter it is rather a bare area or callosity than a whorl — but 

 equally significant as to causation. In all such Ungulates as 

 Bovidae, Equidae, Oervidae, Ovidae, Ga-pra, Tapiridae, and in Felidae, 

 Ursidae, and most wild Oanidae — animals in which the sitting- 

 posture is either impossible, inconvenient, or little adopted — it is 

 conspicuous by its absence. 



(5) The posterior or extensor aspect of the Femoral region in 

 many animals shows on its inner half the marks of pressure 

 against the ground, in a reversed slope of hair which passes 

 upwards and outwards to meet the downward and inward slope of 

 the stream coming from the outer half of this limb-segment. 



B. Active Habits. — The eflects on the ari'angement of hair of 

 animals pi'oduced by active habits are shown mainly in the 

 formation of whorls at certain critical points, with their associated 

 featherings terminating in crests or ridges. The greater or less 

 activity of locomotion is the most important fact about an animal 

 in this respect ; but three regions of the body present whorls which 

 are not directly connected with locomotion, and these may be 

 considered fii'st. They are the Nasal, Frontal, and Spinal regions. 



On the Nasal region the slope of hair varies in a remarkable 

 degree in different animals, and has been considered elsewhere \ 

 It is therefore only necessary to remark here that a nasal whorl 

 and commencement of feathering is found very constantly close to 

 the muzzles of those animals with long, pointed snouts, such as 

 Ganidae and Cervidae, and that in such as Felida?, with broader 

 snouts, it is found at the level of the orbits. Thus the slope of 

 hair on the nasal region in the former is from snout to orbit, and 

 on the latter from oi-bit to snout. This is obviously not a mere 

 unaccountable correlation of facts, but a mechanical result of the 

 shape and jjose of the head, which thus confers on the narrow 

 snout a backward, and the broad snout a forward and downward 

 trend of hair, owing to constant friction in their respective 

 directions. That this difiering direction of hair is an adaptive 

 modification produced for the benefit of the animal, cannot be 

 seriously maintained. 



In Tapii-s the bilateral nasal whorl is situated in a very 

 suggestive position, just where the large projecting snout begins 

 to curve downwards. 



1 Proc. Zool. Soc. 1900, pp. 677-680. 



