. Biology in America. Biology. 334 Biulogy in America many boetlos and birds. Metallic colors and iridescence are generally super-imposed on pigment color producing a com- pound eil'ect, 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 i)igments such as haemo- globin, bile pigments and the like, which are intimately re- lated to the physiology of the animal, and pigments derived from tlie animal's food, such as the green or yel
. Biology in America. Biology. 334 Biulogy in America many boetlos and birds. Metallic colors and iridescence are generally super-imposed on pigment color producing a com- pound eil'ect, 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 i)igments such as haemo- globin, bile pigments and the like, which are intimately re- lated to the physiology of the animal, and pigments derived from tlie 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 jjhotographed on different backgrounds. Courtesy of Dr. F. B. Sumner. 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 bo 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, Avhile the latter are widely variable in color. How then may the multitude of colors and markings in ani- mals be explained? The follower of Danvin bases his an- swer on the efficacy of selection in preserving those forms. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Young, R. T. (Robert Thompson), b. 1874. Boston, R. G. Badger
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