92 



increased by a number of bands, which pass from the centre of the cir- 

 cumference, and are of a denser" character than the rest of the hair, and 

 contain a larger amount of pigment. These evidently have a similar 

 intention to those we have already seen in the peccari and the porcupine. 

 This outer coating is usually marked by a number of dark brown spots, 

 which vary in size, from points almost too small to be measured, to the 

 thousandth of an inch in diameter. 



In this respect, the fibrous structure of bristles is very similar to that 

 of horns, hoofs, claws, and other appendages of the skin. 



This similarity is most marked in the large hairs of the elephant, a 

 transverse section of which does not materially differ from a section of 

 the horn of the rhinoceros, or the hoof of a horse. 



The most important distinction is, that on the application of the polari- 

 scope to the hair, scarcely any change is effected, while the horn shows 

 a number of crosses dividing each circle, precisely as we see in a trans- 

 verse section of the haversian canals of bone. 



It is not uninteresting to enquire into the probable reasons of the vast 

 difference that exists between objects of so similar a nature as hairs and 

 bristles. We shall find, as a general rule, that all the pachydermatous, 

 or thick skinned animals, have strong and bristly hair, — that those who 

 stand next to them, in the same scale, are those whose hair is not much 

 required for warmth, or defence against the inclemency of the weather. 



Those animals, on the contrary, whose hide is comparatively thin, such 

 as the graminivora, and who are, from their habits, constantly exposed to 

 the winter's cold, have soft and cellular hairs. 



It has long been known that furs, when wrapped round a heated 

 body, prevent it parting rapidly with its caloric : consequently they are 

 familiarly spoken of as warm coverings. 



This property arises from the power they have of retaining a large 

 amount of air (which is a very bad conductor of heat) in their interior. 



The air may be retained in two ways, namely, by being confined in the 

 interstices of a long staple, as in the long wool of the alpaca, sheep, and 

 goat, or by being retained in small cells in each individual hair, as in 

 the deer, hare, and other animals. 



In the first, the solidity of the structure is made up for by its length, — 

 in the latter, the shortness of the fur is made up for by its cellular nature. 



It is obvious, that by this contrivance, the means of preserving warmth 

 is not accompanied by any material increase of weight. The design is 

 beautiful. The hare and deer, for example, (they being graminivora,) have 

 less power of resisting cold than carnaria, they have to shun their enemies 

 more carefully in the winter than the summer. The presence of snow. 



