HIGH SCHOOL ZOOLOGY. 



145 



stitute the fur, and tliose which form the whiskers {vih^issce); 

 the hitter from the richness of their nerve-supply are especially 

 tactile in function. In many of the Carnivoi-a and other 

 ordei'S a soft under-fur is overlaid by stronger bristle-like haii-a, 





Fif,'. inO— Section throujrh skin of horse — enlarged. «, epid- 

 ermis ; b, its Malphigian layer, c, pai)illary layer of coriuni, rf; 

 c, Subcutaneous tissue ; /, hair in its follicle, p, with papilla h ; 

 i, old hair being replaced by k ; I, sebaceous glands ; tii, sweat 

 glands ; n, sweat duct. 



which form the external coat. The hairs ai'e lubricated ))y the 

 secretion of the sebaceous glands, which open into the necks of 

 the hair-follicles. The skin of the Mammal is therefore aicher 

 in glands than is that of the Reptiles or Birds. In addition 

 to these, however, there are also sweat glands, which select 

 from the blood certain materials which have to be excreted 

 from it, and so the skin of the Mammal comes to be an im- 

 portant excretory organ. Aquatic Mammals alone are desti- 

 tute of these glands. Of the two kinds of glands referred to, 

 it is the sebaceous kind which the milk-glands resemble most 

 as to structure. 



