TO MAMMALS. r 



hoofed or ending in two blunt horny toes, as in Ruminants, and 

 some Pachyderms, or blunt and almost entirely enclosed, as in the 

 Elephant and Camel. 



The temperature of Mammals being lower than that of Birds, 

 less effectual means are required of preserving the internal heat, 

 and, accordingly, we find them provided with a covering more or 

 less dense of hair, or fur. In Monkeys and Bats there is only one 

 kind of hair, in most other animals there are both hair and wool, 

 and these vary in amount in different animals. Wool differs from 

 hair in having a serrated edge as seen under the microscope, and on 

 this depends the quality of felting. It is generally more abundant 

 in animals living in cold countries, and is highly developed in all 

 the Himalayan Mammals. Hairs are of two kinds as regards their 

 growth. One kind grows continually and is never shed, as the 

 mane of the Horse. The second kind, of which is the fur of most 

 animals, grows to its full extent, and is shed and renewed periodi- 

 cally. This causes a very considerable change in the general hue 

 of many animals, as well as in the amount of fur, so that the win- 

 ter and summer vestures are exceedingly dissimilar. 



A few animals have some of the hairs thick and strong (bristles), 

 and others have them flat a,nd somewhat rigid, as in certain Kats. 

 Spiaes are found on Hedgehogs and Porcupines ; and a very few 

 Mammals are clad with scales or horny plates, as the Scaly Ant- 

 eaters and Armadillos. These spines and scales are all made up of 

 agglutinated hairs. Many Ruminants are adorned with horny 

 appendages on their heads, some of which are of the nature of 

 a horny sheath covering an internal bony cone; others have no 

 internal nucleus and are renewed yearly. The former kind of horn 

 is, like the spines mentioned above, formed of agglutinated hairs. 

 The latter kind of horns partakes more of the nature of bone. 



In many animals the hairs are not uniformly colored, but are 

 colored differently at the base and the tip, and in some tribes 

 are ringed with different colors. The wearing down of these hairs 

 causes a difference in the external hue of such animals. 



In the Cetacea, which have no hair, the warmth of the body is 

 retained by a thick coating of fat or blubber. 



