Royal Physical Society. 367 



human and other hairs of a similar appearance. Like them, 

 and most other hairs of that texture also, these fine hairs are 

 imbricated, as may be faintly seen in the woodcut. 



It is held by physiologists that both these kinds of hair are 

 modelled on the same plan, viz., that of a cellular interior, sur- 

 rounded by a horny cortical exterior, and that the difference in 

 texture arises from the difference in the extent of development of 

 the internal cellular pith or of the external cortical covering. In 

 the one extreme forming the soft hair of the deer ; in the other, 

 the hard bristle of the sow. This view recommends itself by its 

 simplicity and the unity of the modus operandi; but although 

 it may be correct, so far as it goes, it does not explain the whole 

 of the phenomena. For example, it does not explain why the 

 hairs, where the horny covering predominates, are imbricated, 

 while those which are cellular are not ; and it is to be observed, 

 that there is a want of transition between the two characters of 

 hair which certainly is opposed to a common mode of develop- 

 ment. If it were the same, we ought to find hairs exhibit- 

 ing all the gradations of passage between the two extremes, 

 which we do not. Furthermore, they appeared to be designed 

 for different purposes. Speaking in a general way, the horny 

 or bristly hair is characteristic either of carnivorous animals, 

 who have a greater supply of caloric than vegetable feeders, 

 or of graminivorous animals inhabiting warm climates ; while 

 the cellular hairs in question are confined to the deer tribe, 

 most of whom inhabit cold climates. It has usually been said, 

 that the fine hair found at the roots of the coarser hair in these 

 animals is an additional provision of nature for the warmth of 

 the animal. It rather appears to me that in the deer at least it is 

 the larger cellular hairs which have been added for this purpose 

 (no one can look at them, I think, without seeing how admirably 

 they are adapted for this), and that the horny hairs, whose 

 office may possibly be as much that of a regulator of tempera- 

 ture as of a heating apparatus, are the normal hairs of the 

 animal reduced to the smallest dimensions. If these two kinds 

 of hair have distinct functions, their mode of development 

 may also possess distinctive characters. We see that their 

 roots extend to very different depths in the skin, and although 

 we know that the hair is a mere appendage of the skin, pro • 



