CHAPTER 5 



THE INTEGUMENTARY SYSTEM 



The outer surface of an animal is the portion which is in immediate 

 contact with the environment. This surface, of necessity, must perform 

 a number of very important functions inchiding protection and the re- 

 ceiving of various sensations. Among the vertebrates, the skin and 

 its derivatives make up the integumentary system which performs these 

 varied tasks. 



The integument covers all portions of the body including the eye- 

 balls, and is continuous with the moist mucous membranes which line 

 the inner portions of body openings. 



THE FUNCTIONS OF THE INTEGUMENT 



Some of the many important functions of the integumentary system 

 are as follows. 



1. Protection. The outer surface of the skin consists of tough 

 horny cells which form an effective line of defense against the pene- 

 tration of bacteria or against mechanical and chemical injury. Infec- 

 tions seldom occur on the intact skin, but easily happen when the surface 

 is broken to reveal the underlying tissues. 



In addition to the skin itself, many animals are equipped with special 

 protective structures. Additional protection is afforded by the scales 

 of the snake, the shell of the turtle, or even the cushioning effect of 

 the hair of many mammals. Feathers and cushions of fat are like- 

 wise effective in preventing mechanical injury to the body. 



Among some human beings, the skin gives great protection against 

 excessive burning by its ability to darken when exposed to sunlight. 

 Persons without pigment in their skin (albinos) cannot survive any 

 excessive exposure to sunlight. 



Structures such as scales, hair, and feathers perform another nn- 

 portant service to the animal possessing them : they prevent the ex- 



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