ADJUSTMENT OF FLATFISHES 433 



paired. I can offer no explanation for such an utter failure to 

 respond to a new background, on the part of a fish so well endowed 

 with this power. Certain other specimens, as already stated, 

 reacted adaptively to this material, one to its texture onlj^, the 

 other apparently to its color as w^ell. 



- Another instance of the same phenomenon was offered by speci- 

 men no. 6, which, after undergoing adaptive changes on a number 

 of bottoms (including the just mentioned red sand), finally refused 

 to adapt itself further, and remained for thirteen days conspic- 

 uously out of harmony upon two of the artificial backgrounds. 



No. 8,^^ likewise, after having adapted itself strikingly to gravel 

 (fig. So), and later responding unmistakably to black and to white 

 bottoms, remained for nineteen days in the pale condition which 

 was induced by the last, almost regardless of successive changes 

 to a black-bottomed jar, colored gravel, and even the familiar 

 dark sand. Whether or not the later condition of this fish was a 

 pathological one I cannot state, since an accident brought its 

 life to an end. At all events, the animal could see, as was shown 

 by its following moving objects with the eye. 



Again, it frequentlj^ happened that the degree of adaptation, 

 even after the maximum effect had been reached, varied from 

 time to time, and sometimes became reduced to nil, even while the 

 fish remained undisturbed. This was noticed, for example, with 

 specimen no. 1, upon such large patterns or stones as called forth 

 the coarsely blotched appearance. These blotches were at times 

 scarcely distinguishable. It was thought at the time that some of 

 these changes in the extent of the adaptedness bore a direct rela- 

 tion to the degree of illumination, since it was on dark cloudy 

 days that certain of these cases of disappearing pattern were re- 

 corded. I was not, however, able to verify this conjecture.^* 



Lastly, in a few cases, after the maximum effect had been 

 reached, the resemblance to the background seemed actually to 

 undergo a permanent decline. This appears to have been the 



5* Cf. p. 438. 



'^ Pouchet (op. cit., p. 130 et seq.) had already observed such fluctuations in 

 the degree of adaptedness, and these he was inclined to attribute to differences in 

 the brightness of the day. 



THE JOURNAL Or EXPERIMENTAL ZOOLOGY, VOL. 10, NO. 4 



