lO CARPAL SENSE ORGAN 



and for the horns of the Bldnoceros. It is a matter of common 

 knowledge that upon the head of various animals, e.g. the 

 Domestic Cat, long and sensitive hairs are developed, which are 

 connected with the terminations of nerves, and perform a sensory, 

 probably tactile function. These occur on the snout, above the 

 eyes, and in the neighbourhood of the ears. It is an interesting 

 fact that a tuft of quite similar hairs occurs on the hand of 

 many mammals close to the wrist, which, at least in the 

 case of Bdssaricyon, iiiv. connected with a strong branch from tlie 

 arm-nerve. These tufts also occur in Lenmrs, in the Cat, ^-arious 

 Eodents and ilarsupials, and are probably quite general in 

 mammals who " feel " with their fore-limbs ; — in which, in fact, 

 the fore-limbs are not exclusively running organs. That the last 

 remaining hairs of the Cetaeea are found upon the muzzle, is 

 perhaps significant of the importance of these sensory bristles. 

 The ejitire absence of hairs is quite common in this order, 

 although traces of them are sometimes found in the embryo. 

 The Sirenia, too, are comparatively hairless, as are also many 

 Ungulates. Whether the presence of blubber in the former case 

 and the existence of a very thick skin in the latter animals ai'e 

 facts which have had anything to do with the disappearance of 

 hair or not, is a matter for further inquiry. 



The intimate structure of the hair varies considerably. The 

 variations concern the form of the hair, which may be round in 

 transverse section, or so oval as to ap"|)ear quite flat when the 

 hair is examined in its entirety. The substance of the hair is 

 made up of a central medulla or pith with a j.)eripheral cortex ; 

 the latter is scaled, and the scales are often imbricated and 

 with prominent edges. The amount of the two constituents also 

 differs, and the cortex may be reduced to a series of bands 

 surrounding only tracts of the enclosed pith. In the hair is 

 contained the pigment to which the colour of mammals is 

 chiefly due. Tracts of brightly-coloured skin may exist, as iu 

 the A]ics of certain genera; but such structures are not general. 

 The pigment of the hair seems to consist of those pigmentarv 

 substances known as melanins. It is remarkal_)le to find such an 

 uniform cause of coloration, when we coTisider the great variety 

 of feather-pigments found in birds. The variations of colour 

 of the Iiair of mammals are due to the unequal distribution of 

 these brown pigments. There are veiy few mammals wliich can 



