American Fisheries Society 239 



grounds, for example, did not call forth adaptive responses. 

 In other words, the pigments corresponded, in all cases, to 

 components of the habitual background of the species, 

 although it is true that shades were assumed which the 

 fishes had probably never encountered in nature. 



(3) Upon a homogeneous ground the visible pigment of 

 the skin was commonly much more uniformly distributed 

 than upon a background having a pronounced pattern. 



(4) Upon a mixed background, such as was afforded 

 by the ordinary sand or gravel of its customary habitat, 

 the fish took on a definite pattern, which varied with the 

 texture of the material. 



(5) Experiments with painted squares and circles of 

 black and white showed that the resulting skin patterns 

 depended not only upon the relative amounts of black and 

 white in the background, but upon the degree of subdivision 

 of the areas of the latter. P^or example, when the back- 

 ground was divided into areas 2 mm. square, a finer 

 grained appearance was produced in the fish than when 

 1 cm. squares were used. 



(6) Artificial patterns of pure black and white gave far 

 more contrast in the skin patterns than did the less con- 

 trasted tones of ordinary sand and gravel. Areas of almost 

 pure black and white were in many cases displayed by 

 the fishes. 



(7) The various markings constituting these patterns 

 were, however, found to be permanent in the sense they 

 always reappeared in the same positions ; and even when the 

 animal adapted itself to a homogeneous background, and 

 appeared to lose the pattern altogether, the outlines of most 

 of these spots were still distinguishable. The arrangement 

 of these blotches was, in its essentials, constant for all 

 members of the species. 



(8) The patterns assumed were consequently limited, in 

 great degree, by fixed morphological conditions. Thus, 

 squares, crossbands, circles, etc., were never copied, in any 

 true sense, by the fishes. 



