472 FRANCIS B. SUMNER 



We have seen that the skin of some of these fishes commonly 

 assumes a nearly homogeneous tone upon a bottom of uniform 

 color and shade, while presenting a more or less pronounced 

 pattern upon a bottom of diversified appearance. Abbot Thayer^^ 

 has pointed out that the breaking up of a uniform color tone by 

 markings of any sort makes for concealment, and this is particu- 

 larly true against a diversified background. This principle, 

 without question, accounts for much of the effectiveness of the 

 various patterns assumed by Rhomboidichthys and other floun- 

 ders, and we must not be in too great haste to point out specific 

 resemblances to particular backgrounds, merely because the fish 

 ceases to be conspicuous upon these. I think, however, that a 

 careful consideration of the experiments as a whole, and partic- 

 ularly of the facts referred to in paragraph 8 of the summary, 

 forces us to the belief that there may be very specific relations 

 between the distribution of light and shade in the background and 

 the pigment pattern assumed by the fish. 



Had we to do here merely with a general paling or darkening of 

 the entire body surface, affecting spots and ground color to an 

 equal extent, or even were there at the disposal of the fish one of 

 two of these pigment patterns, corresponding to certain of the 

 most frequent types of bottom, we might ascribe this power to a 

 few comparatively simple reflexes. But we have seen that the 

 responses are far from being as stereotyped as this. Certain areas 

 become paler and others become darker, each more or less inde- 

 pendently, and in varying degrees, depending upon the circum- 

 stances. At one time we have a large dark blotch covering a 

 given portion of the surface; at another time, the pigment of this 

 blotch has practically disappeared from view; at another yet this 

 area has become broken up and diversified by the appearance of 

 paler specks within it. Most of this change, too, is brought about 

 by variations in the conspicuousness of groups of pigment cells 



'* Popular Science Monthly, December, 1909; also book by Gerald Thayer 

 entitled "Concealing Coloration in the Animal Kingdom. A Summary of Abbot 

 H. Thayer's Discoveries," N. Y., 1909. It is likely that few biologists can follow 

 Mr. Thayer in the unbridled zeal with which he strives to universalize this and the 

 other important principles of animal coloration which he has discovered. 



