198 BULLETIN OF THE BUREAU OF FISHERIES. 



long enough to become fully adjusted to the new color. The autochrome shows that 

 the fish was still bluish and does not indicate that there was any marked adaptation to 

 the green. The autochrome is valuable, however, in that it demonstrates fairly con- 

 clusively that the color represented in the various autochromes is due to the structure 

 of the skin and not to light reflected from the sides of the boxes or transmitted through 

 the fish from the bottom, as many who have seen them intimated. 



Yellow. — July 27, A. quadrocellata, 16 cm. long, taken from the white aquarium and 

 put into the chrome-yellow box (slightly darker than Bradley's orange yellow) . It became 

 distinctly yellowish within a few hours, as did also a specimen of P. albiguttus put in at 

 the same time. Adaptation on yellow occurs much more rapidly than it does on blue, 

 green, or red, and there is no indication of adaptation in shade before adaptation in color 

 occurs, as appears to be true for some of the other colors. August 7, the color of the 

 skin is very much like that in the background except in the two large light areas and in 

 the four ocelli, but as a whole Ancylopsetta is much more conspicuous than Paralichthys, 

 the color of which is remarkably similar to that of the background and very uniformly 

 distributed, making the animal very inconspicuous. AfKylopsetia autochromed and 

 photographed. The colors are quite faithfully reproduced. (Fig. 63, 76.) 



On a background consisting of alternate black and yellow squares the skin of 

 Paralichthys assumes a conspicuous pattern consisting of black and yellow patches 

 similar in size, form, and arrangement to the black and white patches assumed on a 

 background consisting of alternate black and white squares of the same size. 



Conclusions. — The evidence which we have presented leaves no reasonable doubt 

 that in both Paralichthys and Ancylopsetta the skin simulates the background in color 

 as well as in shade and pattern, and that the colors which are simulated range at least 

 from dark blue to dark red. It shows that adaptation in shade ordinarily occurs more 

 rapidly than adaptation in color and that adaptation to yellow is ordinarily attained 

 in a much shorter time than adaptation to most of the other colors tested. In the case 

 pf yellow it may occur in a few minutes, while in the case of the other color it takes days 

 and even weeks. 



Thus it is evident that both the quality and the quantity of the light, the length of 

 the waves, and the energy are functional in adaptive processes that occur in the skin. 

 Concerning the question as to how these charapteristics of light function and the ques- 

 tion as to the process and mechanism involved, we shall have something to say later. 



RATE OF ADAPTATION TO BACKGROUND. 



The difference in the time required for different individuals of a given species to 

 simulate the background is very great. This has been noted by practically all who 

 have investigated the subject. This great difference is largely due, not to innate indi- 

 vidual variation, but to variation in the experience of the individual; to training, if 

 you please. Van Rynberk (1906), Sumner (191 1), and others maintain that the reac- 

 tion time of the chromatophores is much reduced by repetition. Sumner, referring to 

 flatfishes, says (p. 469): "The same fish acquired with practice (if this word may be 

 allowed) the power of changing much more rapidly than before. The time required 

 for a radical change of shade or of pattern ranged from a fraction of a minute to several 

 days." 



