470 FRANCIS B. SUMNER 



thys are situated at the ends of movable stalks, so that this fish 

 must be able to obtain a much nearer view of the bottom than is 

 possible for Lophopsetta. 



13. Within very wide limits, the degree of illumination of the 

 background was found to have little or no effect upon the shade 

 assumed by the fish. As a special example of this principle, fishes 

 in a white receptacle, even when the latter was heavily shaded, 

 became paler than fishes in a gray receptacle, even when this was 

 exposed to bright light. In such cases, the dimly lighted white 

 bottom of the one tank was actually darker than the brightly 

 lighted gray bottom of the other, in the sense that the former 

 reflected an absolutely smaller amount of light to the observer — 

 whether human or piscine — than the latter. A rather curious 

 problem was raised by a consideration of these facts, which was 

 dealt with at some length and was made the object of special tests. 



14. A specimen of Rhomboidichthys which was transferred 

 while extremely pale to black sand, acquired a very dark shade, 

 even though the fish remained persistently buried in this material, 

 with only its eyes protruding. Again, specimens of Lophopsetta 

 having their skin deeply stained, or wearing masks of cloth, were 

 found, in some cases, to undergo pronounced adaptive changes, 

 despite the fact that their body surface was disguised in this way. 

 It is thus rendered highly improbable that any direct visual com- 

 parison on the part of the fish between its own body surface and 

 the surrounding background is an essential factor in the pro- 

 duction of these changes. 



15. Fishes (Rhomboidichthys), when given the choice of two 

 backgrounds, displayed no preference for the one which conformed 

 more nearly to their own shade at the time. Likewise, specimens 

 which were glaringly out of harmony with a given shade of sand 

 appeared no more likely to conceal themselves beneath its sur- 

 face than when their skin color was adjusted very closely to this. 



16. When examined at night, after several hours of complete 

 darkness, the fishes (Lophopsetta) were found to be in the same 

 condition of pigmentation as when previously observed by day- 

 light. Pale specimens, which were kept 5 to 7 days in a black- 

 painted, light-proof box, became considerably darker during this 



