THE SKIN 27 



the Angora or Persian cat is remarkable for the length and 

 delicacy of its soft fur. The hair, like the nails, is an extreme 

 modification of the epidermis. Each hair grows from a papilla 

 at the bottom of a small sac, the follicle, which is a depression 

 in the corium. The central part of the hair is the pith, and 

 the external portion, formed of thin overlapping scales, the 

 cuticle. The coloring-matter lies in the cortex, and may be 

 disposed in such an irregular manner that one-half of a hair is 

 white, and the other half yellow. 



The large hairs on either side of the nose are known as 

 vihrisscB. Their roots are provided with delicate nerve-endings 

 of touch, so that the animal may find its way with ease through 

 dark narrow passages. There are a few long hairs above the 

 eyes, forming the eyebrows, but no eyelashes are present. 



Most of the hairs are inserted obliquely into the skin, but 

 when angered the cat can erect them by the contraction of a 

 small muscle passing from the skin to the hair-bulb. 



On some mammals the hairy covering is partial and limited 

 to particular regions; in others, as the hippopotamus and the 

 Sirenia, it is very scanty, but scattered over the whole sur- 

 face; while in the Cetacea it is reduced to a few small bristles 

 about the mouth. 



Some kinds of hair, as those of the mane and tail of the 

 horse, are shed and renewed annually. Most mammals have 

 a long hairy coat in winter which gives place in spring to a 

 short coat. The Arctic fox, hare, ermine, and numerous other 

 animals of the colder regions undergo a complete change of 

 color in the two seasons, being white in winter and brown or 

 gray in summer. By this protective coloration they escape 

 many of their enemies. 



