American Fisheries Society 237 



find another one. Now all of you who have visited the 

 aquarium at Naples doubtless recall the tank devoted to 

 flounders and other bottom-dwelling fishes. No one can 

 fail to be impressed by the harmony of appearance between 

 these fishes and their background, a harmony which relates 

 not only to general color-tone, but to texture and pattern 

 as well. (I will add that one need not go as far as Naples 

 to see beautiful instances of this phenomenon. Our own 

 aquarium in New York is provided with some good ex- 

 amples.) In viewing specimens of one of the common 

 European turbots (Rhombus ina.vimus) I was particularly 

 struck by the detailed resemblance which obtained between 

 the markings of the skin and the appearance of the sur- 

 rounding gravel. Now, while the pattern of the fish was 

 such as to harmonize wonderfully with this gravel, it would 

 not, on the other hand, have harmonized particularly well 

 with the fine sand, even if similarly colored, and would 

 have been no better adapted to a bottom of large stones. 

 The query at once suggested itself : is it a mere coincidence, 

 this detailed agreement of the fish with its present back- 

 ground, or does the fish have the power of controlling the 

 color-pattern as well as the general color-tone of the body 

 as a whole? 



Here, then, was a problem worth looking into. But, 

 strange as it may seem, I found practically no references 

 in the literature to adaptive changes in the color pattern of 

 fishes. And, stranger yet, the possession of such a faculty 

 — which soon become evident when I began my observa- 

 tions — was a source of surprise to others at the station, in- 

 cluding one investigator who had carried on some impor- 

 tant studies upon the color changes of Crustacea and fishes. 

 That this power exists I think will be plain to you from the 

 lantern slides which I shall soon show you. 



The fish from which I had the most favorable results was 

 a small species of flounder (Rhoinboidichthys podas) 

 belonging to the Psettinae or turbot group. Unfortunately 

 this species is not at all as common as one would desire for 



