COLOR CHANGES AND ADAPTATION IN FISHES. 2O3 



the background, so that one eye was on the black and the other on the white bottom. 

 The entire surface soon became gray of a shade about halfway between maximum 

 white and maximum black. No further change occurred, although it was held in this 

 position until 11.55 a. m. At this time it was photographed (fig. 45) and then set free 

 in the dish. 



The following morning at 6 a. m. it was found, with only the head to a point a trifle 

 over a centimeter back of the eyes, on the white. The specimen appeared nearly if 

 not quite maximum white. It was kept in this position until 9.20 a. m. and then 

 photographed (fig. 46), after which it was rotated until the anterior end was on the 

 black bottom. In this position it was held until 12 m. and then again photographed 

 (fig. 47). This photograph shows several light lines crossing each other in the central 

 part of the surface of the fish. These lines are not normal; they are due to abrasions 

 in the skin and do not show in the other photograph because of the light shade. 



The animal was now moved backward until the dividing line in the background 

 was below a point about i cm. back of the eyes. The entire surface became distinctly 

 whiter. The fish was then moved forward again, and the entire surface soon became 

 distinctly darker. This was repeated several times with the same results. 



The fish was then put entirely on the white with the head directed from the black, 

 and left until it became maximum white. It was then turned through an angle of 

 180 degrees and moved forward so that the anterior end faced the black and was 2 

 cm. from the dividing line. In the course of a few minutes the entire surface became 

 distinctly darker. This entire experiment was repeated several times with the same 

 results. 



Similar results were also obtained with color. On August 22, I was much sur- 

 prised to find a specimen of P. albiguttus on a black and white checkered background 

 distinctly yellowish. This specimen had been used in experimental work on black 

 and white backgrounds almost continuously since July 22, and at no time before was 

 there any evidence of yellow or any other color in the skin. When this specimen was 

 discovered in the yellow state it was in a crystallizing dish in close contact with the 

 edge. The dish was on an artificial black and white background, which at this point 

 extended 2.5 cm. beyond the edge. Beyond this a brownish-yellow water-soaked 

 cypress board, on which it rested, was exposed. This board, which was somewhat 

 over 2.5 cm. from the eyes of the fish, evidently caused the flounder to become yellowish. 



At 3.10 p. m. the dish was moved farther from the exposed part of the board. 

 Fifteen minutes later there was only a trace of yellow left in the skin of the fish, and 

 the following morning there was nothing more to be seen of it. At 9.30 a. m. the fish 

 was so placed that the exposed part of the cj'press board was 6 cm. from the anterior 

 end of the fish and directly in front of it. In this position it was held until 10.45 a. m. 

 There was no apparent effect of the yellow color. The fish was then moved forward 

 until it was 5 cm. from the exposed part of the board and held until 12 m. Still there 

 was no visible effect. It was then moved forward 2 cm., i. e., 3 cm. from the board, and 

 held. An hour later, at i p. m., the skin of the fish was distinctly yellowish. 



These results, without further analysis, show very clearly that under normal ■ 

 conditions the shade and the color in the skin of Paralichthys are regulated by the 

 effect of light received by the eyes. There is no evidence whatever indicating that 



