COLOR CHANGES AND ADAPTATION IN FISHES. 



223 



INDIVIDUAL METHOD. 



A number of specimens of Paralichthys and Ancylopseila were kept for several 

 weeks in a shallow wooden aquariinn 2.6 meters long and 1.3 meters wide. One half 

 of this aquarium, sides as well as bottom, was painted black and the other half white, 

 with the dividing line extending crosswise. 



It was repeatedly noted that most of the specimens in the aquarium persistently 

 remained on the white, but a few tended to remain on the black. When those on 

 the white background were forced over onto the black they almost invariably returned 

 at once, and the same was found to be true for those on the black background, indi- 

 cating a selection of background in harmony with the shade of their skin. 



More detailed results regarding this, however, were obtained as follows: Individuals 

 fully adapted to either white or black were placed on the dividing line in the aquarium 

 in such a position that one eye was over black and the other over white. In this posi- 

 tion they were held with the hands until they became quiet, which usually occurred 

 in a very few moments, and then released. In some instances they remained quiet 

 after being released. Whenever this occurred the tip of the tail was touched repeat- 

 edly until they started off. The direction in which they turned was then noted and 

 recorded, after which the whole process was repeated. In returning the animal, in 

 about half of the individual tests it was moved across the line to the opposite end of 

 the aquarium and then brought back onto the line so as to counteract any possible 

 influence of the direction of movement before the test, on the direction of turning 

 during the test. The results of nearly all of these tests are summarized in table vi. 



Table VI.— The Relation Between the Shade of the Skin and that of the Background 



Selected. 



These results, without further analysis, show clearly that there is a tendency, both 

 in Paralichthys and Ancylopseita, to turn toward that shade to whicli they are adapted. 



