462 FRANCIS B. SUMNER '* 



found to show no appreciable differences of color or shade from 

 specimens which were kept in a well lighted box, having a white 

 interior. 



The two sets of fishes, which had now been in their respective 

 boxes for six to nine days, were next transposed, i.e., those from 

 the gray box were transferred to the covered white one, and vice- 

 versa. At the end of 5 days, the relations in respect to pigmenta- 

 tion were found to be reversed, those which had formerly been 

 darker now being paler and vice-versa. One of those which had 

 previously been very pale was now (when on gray) recorded as 

 "one of the best cases of resemblance in respect to general color 

 tone which T have had."''^ 



Reference should be made here to one exceptional specimen 

 which, when dark, was placed in the shaded white box for three 

 days with little or no effect. , Upon being removed, to an un- 

 shaded white box, on the contrary, some change was noticeable 

 during the same day, while on the next day the fish was very pale. 

 In the case of this specimen, therefore, it would seem that the 

 scant illumination of the interior of the former box had exerted 

 an inhibitory influence. ^"^ On the other hand, this result may have 

 been due merely to my having dealt with a rather refractory 

 specimen, which was on the point of changing at the time of re- 

 moval from the shaded box, and would have done so if left there. 



How is the fish able to adjust itself to a bottom of given shade, 

 independently of the degree of illumination? 



As was pointed out earlier, (p. 441) it is plain that, in order 

 that the change of shade on the part of fish should be adaptive, 

 the latter would have to behave exactly as described. When, 

 however, we begin to inquire as to the visual stimuli responsible 



^^ Indeed, a number of specimens, aside from those employed in the present 

 experiment, harmonized quite strikingly with this and other gray bottoms which 

 were used. This harmony was enhanced by the transparency of the fins and mar- 

 ginal portions of the body, but was also due, in no small measure, to a disappear- 

 ance of the yellow and brown tones and the assumption of a nearly pure gray. 



■"> It may well be that the degree of illumination at times affects the rate of ad- 

 justment (Cf. Mayerhofer, op. cit., p. 554), but not its character. 



