American Fisheries Society 243 



seems to be concealment and nothing else. No appeal to 

 thermal regulation, to the possible "photo-receptive" power 

 of the skin, nor to any other purely physiological explanation 

 of the phenomenon seems adequate. A complete explana- 

 tion must regard ecological factors as well. Whether the 

 utility of these changes to the fish consists in their conceal- 

 ing the latter from its prey or from its enemies cannot, 

 however, be stated without a greater familiarity with the 

 bionomics of the animal than we possess. 



I do not myself know what are the chief enemies of the 

 flounders. Perhaps some of you may be able to tell me. 

 I learn from Prof. Irving Field that he has taken flounders 

 from the stomach of the goose-fish, but the latter had been 

 caught in a fish trap and consequently had opportunities 

 to gorge itself with other fishes which it would not have had 

 in its ordinary life.* As to the prey of the flat-fishes, I can 

 only state that the sand-dabs which I have used this summer 

 were found to have eaten the sand-launce (Ammodytes) in 

 large numbers. It may be, therefore, that their power of 

 concealment is of advantage in enabling them to hide from 

 smaller fishes until the latter come within dangerous prox- 

 imity to them. 



In regard to the lantern slides it must be stated that they 

 do not represent occasional or exceptional instances. They 

 represent appearances which were frequently observed, 

 though not equally well in all fishes. Slides such as these 

 fail to give an idea of the completeness of the adjustments, 

 inasmuch as the colors are not reproduced, and the color 

 resemblance between fish and background is often striking. 

 The extremely pale condition resulting from a prolonged 

 stay upon a white background cannot be reproduced by 

 ordinary photographic processes, since the skin of the fish 

 always retains a certain amount of yellow, and, as you well 

 know, this looks disproportionately dark in a photograpli. 



*Mr. Nichols, of the American Museum of Natural History, informs 

 me that flounders are frequently taken from the stomach of the 

 dusky shark. 



