440 FRANCIS B. SUMNER 



beneath them, assuming a much blotched appearance resembUng 

 that which was commonly shown upon a bottom of fine gravel. 

 Upon the removal of the plate from beneath them, they had re- 

 turned to a nearly unspotted condition. The spotted plate, now 

 mounted on corks, as above described, was next inserted above the 

 fishes (under the surface of the water, of course). The plate, in 

 its present position, was brightly lighted by the mirror below. 

 That the fishes could see this spotted surface cannot be doubted. 

 Nevertheless, not one* of the specimens showed any appreciable 

 influence, even after several days.*^ Return of the spotted plate 

 to the bottom of the tank, beneath the fishes, resulted in each case 

 in a resumption of the blotched condition within a few hours at 

 the most. 



With two specimens an attempt was made to force the animal 

 to look directly upward. The eyes, or rather the eye-stalks, were 

 tied together by means of threads stitched through the skin. This 

 drastic treatment resulted in the blindness of the fishes, and no 

 significant results were obtained. 



Relation between the degree of illumination and the character of the 



response 



The foregoing experiments were conducted in a laboratory room 

 of medium size, lighted from one side only. Different jars were 

 exposed to very different amounts of light, and the degree of illu- 

 mination for all of them varied greatly, of course, with the weather 

 and with the time of day. Nevertheless, no undoubted relation 

 was discovered between the intensity of the light and the rapidity 

 or extent of the adaptive changes. In a few instances, it is true, 

 certain of the pigment patterns were found to be much less con- 

 spicuous on dark, cloudy days. It has been pointed out, however, 

 that the completeness of these adaptations varied at different 

 times in the same individual, even when no external cause was dis- 

 coverable. And even if some specimens were actually affected at 

 times by the intensity of the illumination, this was certainly not 



" The fishes were observed through the walls of the tank, by raising the dark 

 curtains; also by removing the spotted plate. 



