COLOR CHANGES AND ADAPTATION IN FISHES. 205 



same effect when both eyes are functional as it has when but one is functional. In other 

 words, the pattern and the shade assumed are the result of a sort of superimposition of 

 the effects of the stimuli received by each of the two eyes. 



RELATION BETWEEN THE INTENSITY OF LIGHT AND THE REACTION OF CHROMATOPHORES. 



Keeble and Gamble (1904, p. 353) maintain that the response of the chromato- 

 phores in higher Crustacea, under normal conditions, is independent of the intensity of 

 the light. They found that specimens in a white porcelain jar covered with black 

 paper "pierced with several pinholes" became just as pale as others of the same species 

 in the same kind of jar uncovered. 



Sumner ( 1 9 11 , p. 460) obtained similar results in experiments on the flatfishes, Rhom- 

 boidichthys and Lophopsetta. In these experiments he used two boxes, one painted gray, 

 the other white. To the latter so little light was admitted that the white surface appeared 

 distinctly darker than the gray surface in the other box, and by means of a photographic 

 method it was proved that less light was reflected from the white than from the gray 

 surface. He found, however, that specimens became maximum white on the former 

 and gray on the latter. 



I was able to confirm these results in experiments on Paralichthys. In addition to 

 tests similar to those described above, numerous obsen.^ations were made at night, 

 usually about 10 p. m., on animals in various stages of adaptation to backgrounds differ- 

 ing in shade, color, and pattern. In making these observations a strong electric light 

 was momentarily turned on. In all cases in which adaptation was complete the shade, 

 color, and pattern of the skin appeared to be the same as it had been during the preced- 

 ing evening. If there was any change it consisted in slight contractions of the chromato- 

 phores. These statements apply especially to Paralichthys. 



In those specimens in which adaptation was not complete there were usually marked 

 changes of such a nature as to show that the adaptive process continues in very weak 

 light. This was repeatedly observed in specimens changed from dark to light back- 

 grounds or vice versa late in the evening. Thus, to cite one instance, August 21, a 

 Paralichthys very dark in shade was put upon a white background at 7 p. m. At this 

 time it was already so dark that the fish could be seen only against the white background, 

 and later it became still darker. At 10 p. m., however, when the fish was examined in 

 strong electric light, it appeared maximum white. 



There is some evidence indicating that the pattern assumed in weak light is not as 

 conspicuous as is that assumed in strong light. This was most evident in specimens on 

 backgrounds containing small black dots, of such a number as to produce relatively few 

 black spots in the skin. For example, Paralichthys, individual (B), on a white back- 

 ground containing black dots 2 mm. in diameter and 10 mm. apart, regularly had in the 

 skin a number of distinct black spots (fig. 54), but when examined in artificial light, at 

 10 p. m. on two different occasions, not a trace of these spots was found. 



Ancylopsetta becomes much darker at night. This was repeatedly seen in various 

 specimens in the colored boxes. Verrill (1897) observed similar phenomena in other 

 forms. I was unable, however, to see any change in Paralichthys in the same boxes with 

 Ancylopsetta. Moreover, both in Paralichthys and in Ancylopsetta, the shade assumed 

 on any given background is the same in direct as it is in diffused sunlight. It, there- 

 fore, seems well established, at least for Paralichthys, that the shade assumed by the 

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