lO CARPAL SENSE ORGAN chap. 



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

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

 ])omestic 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 (^uite similar hairs occurs on the hand of 

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

 case of Bdssarifyon, are connected with a strong l)ranch from the 

 arm-nerve. These tufts also occur in Lemurs, in the Cat, various 

 Eodents and Marsupials, and are proliably quite general in 

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

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

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

 perhaps significant of the importance of these sensory l»ristles. 

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

 although traces uf them are sometimes found in the emljryo. 

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

 Ungulates. Whether the presence of ])lul:)ber in the former case 

 and the existence of a very thick skin in the latter animals are 

 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 ^'aries consideralily. The 

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

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

 hair is examined in its entirety. The sul)stance of the hair is 

 made u]) of a central medulla or pith with a ])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 l)e reduced to a series of liands 

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

 contained tlie ])igment to which the colour of mammals is 

 chielly due. Tracts of brightly-coloured skin may exist, as in 

 the Ai)es of certain genera ; but such structures are not general. 

 Tlie ])igment of tlie hair seems to consist of those pigmentary 

 substances known as melanins. It is remarkal>le to find such an 

 uniform cause of coLiration, when we consider the great variety 

 of feather-pigments found in birds. 'JMie variations of colour 

 of the hair of manimals are due to tlie unequal distriluition of 

 these brown pigments. There are very few mammals which can 



