334 Biology in America 



many beetles and birds. Metallic colors and iridescence are 

 generally super-imposed on pigment color producing a com- 

 pound effect, white being the only purely physical color that 

 we know in animals. 



The functions of animal colors are doubtless manifold, but 

 concerning them our knowledge is unfortunately very frag- 

 mentary. Omitting those internal pigments such as haemo- 

 globin, bile pigments and the like, which are intimately re- 

 lated to the physiology of the animal, and pigments derived 

 from the animal's food, such as the green or yellow color of 

 some caterpillars fed on green leaves or yellow flowers re- 



ONE OF THE FLATFISHES 



Animals having remarkable powers of adjusting their appearance to 

 the bottom on which they lie. The same fish photographed on different 

 backgrounds. 



Courtesy of Dr. F. B. Sumncr. 



spectively; and considering surface color only, we are struck 

 with the apparent lack of any physiological use of such color. 

 One might expect arctic animals to be black so as to absorb 

 the maximum of heat energy from the sun, and tropical ani- 

 mals to be white, thereby reflecting the sun's rays and avoid- 

 ing absorption of heat; but the reverse is true of the for- 

 mer, while the latter are widely variable in color. 



How then may the multitude of colors and markings in ani- 

 mals be explained? The follower of Darwin bases his an- 

 swer on the efficacy of selection in preserving those forms 



