ADJUSTMENT OF FLATFISHES 467 



no experimental results of interest to offer. The essential require- 

 ment for such a test would seem to be that the background to 

 which the fish is to cause its own shade to conform shall be illumi- 

 nated from a source of light independent of that which falls upon 

 the animal's eyes from overhead. Thus this background might be 

 made to appear dark or the contrary, relatively to the light which 

 seerned to illuminate it. A human observer, under similar cir- 

 cumstances, would be deceived, and would misjudge the shade 

 of the surface in question. Would not a fish do the same.'"* 



After considerable experimenting, I believe that I have devised 

 an apparatus calculated to fulfil these conditions. This apparatus 

 I will not describe here, since I am not prepared to report upon 

 any results from its use. Owing to a lack of flounders of the right 

 species, the experiments must be deferred until the coming sum- 

 mer, when, I hope, it will be possible to settle the question at issue 

 by a few decisive tests. 



SUMMARY AND CONCLUSIONS 



Flounders of several species were found to undergo marked 

 changes in their color pattern or their general shade, when trans- 

 ferred from one type of bottom to another. The range and char- 

 acter of these pigment changes, and the nature of the stimuli 

 which provoked them, were subjected to considerable experimental 

 inquiry. The following are some of the principal facts which were 

 revealed through these investigations: 



1. Fishes became very pale (in one species extremely so) 

 upon a white background; dark brown or nearly black upon a 

 black one, and of various intermediate shades upon bottoms of 

 gray, brown, etc. 



2. The animals appeared to be limited in their capacity for 

 adjustment almost wholly to black, white, brown and gray tones. 

 Bright red or yellow backgrounds, for example, failed to call 

 forth adaptive responses, at least during periods quite sufficient 



^* Again the spectre of 'anthropomorphism' may seem to rear its head. But 

 no. An optical illusion does not presuppose intelligent judgment (or misjudg- 

 ment), any more than does an ordinary normal perception. 



