THE EXCRETORY SYSTEM 19! 



manner in which the kidneys relieve it of urea, salts, and 

 water, it now remains for us to consider the part played 

 by the skin in eliminating water and a certain amount of 

 carbon dioxid and salts. 



The skin, unlike the kidneys, is not set apart for the 

 performance of one special function. It is not only an 

 important excretory organ, but also an absorbing organ; 

 it is likewise the principal seat of the sense of touch, and 



FIG. 97- Vertical section of skin : sbg, Sebaceous glands ; ep, epidermis ; 

 h t hair; d, derma (Fox). 



also serves as a protective covering for the underlying 

 tissues. The skin, like the mucous membrane, consists 

 of two distinct layers an epithelial covering and a 

 connective-tissue basis. The epithelium is stratified, 

 and is called the epidermis or scarf-skin; the con- 

 nective-tissue layer is called the derma (true skin) or 

 corium. 



The epidermis is composed of layers of cells, the 



