CHAPTER LXVII 



PROTECTIVE PIGMENTS AND APPEARANCES 



400. Pigments and light. Animals that live at great depths 

 of the sea, and those that live in caves, — situations in which 

 there is little or no exposure to light, — do not generally show 

 much pigment in the skin. 

 This fact may be interpreted 

 in two ways : 



1. Where there is no dan- 

 ger of being injured by light, 

 the species will be able to main- 

 tain itself without acquiring 

 the pigment-forming habit. 



2. Where there is no light 

 stimulation, pigment will not 

 be formed. 



In the human race the dark 

 pigment of the skin is un- 

 doubtedly a protection against 

 the light, as shown by the 

 relative sensitiveness of light- 



Katydids 



Microcentrum retineii'is (above) ; Cyriopliyl- 

 liis coiicavics (below). These insects match 

 the color of the foliage upon which they 

 feed ; in some species the resemblance to a 

 green leaf is even more striking than in the 

 two shown here 



skinned races and dark- 

 skinned races to the influence of the tropical sun. It is also 

 shown by the behavior of the skin of a person who has been 

 tanned and the behavior of the skin of the same person before 

 the tan has formed. A person who does not get tanned is likely 

 to be sunburned with every exposure to strong sunlight. On the 

 other hand, in a person who is dark-skinned, or who has be- 

 come tanned, the pigment acts as a screen, cutting off the rays 

 that are injurious to the protoplasm. 



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