ADJUSTMENT OF FLATFISHES 451 



consideration the dark blotches were vaguely visible much of the 

 time, even when the fish was on a homogeneous ground. The pres- 

 ence of dark spots in its neighborhood merely served to accentuate 

 these. 



Direction of the stimulus 



A point which was tested much more thoroughly than at Naples 

 was the relative influence of the bottom and of the vertical walls 

 of the receptacle in determining the changes of shade on the part 

 of the fish. The bottoms employed were, as just stated, 70 centi- 

 meters long and 30 centimeters wide. The length of the fishes 

 varied from 24 to 35 centimeters, and their area probably ranged 

 from 200 to 400 square centimeters, or from 10 to 20 percent of the 

 area of the bottom. The fishes lay, much of the time, near one or 

 another wall of the box, and the larger specimens naturally could 

 not at any time reach a position very far removed from the latter. 



Boxes were employed having 1, walls and bottomipainted black; 

 2, walls and bottom white; 3, walls black, bottom white ; 4, walls 

 white, bottom black. In addition to this, false walls of galvanized 

 iron were made, which were painted white or black or both. These 

 could be inserted into any of the boxes without disturbing the 

 fishes. 



1. In boxes of the first type, the fish became (or remained) as 

 dark as it was capable of being. The shade varied, of course, 

 with the specimen, but was usually a very dark brown, and fairly 

 homogeneous, though certain small white spots sometimes 

 showed distinctly. Usually the fishes were very inconspicuous 

 in the black boxes. 



2. In the white boxes, the fishes commonly attained a consider- 

 able degree of pallor, assuming a shade which may perhaps best 

 be characterized as buff, i.e., a pale yellowish or brownish gray. 

 In this condition, while of course far less conspicuous than previ- 

 ously, they could not be regarded as very well concealed, at least 

 from a nearby observer. The harmony with the pale bottom was 

 furthered by the fact that, with the withdrawal from view of 

 the dark pigment, not only the marginal fins (already partially 

 transparent), but the adjacent portions of the body proper, be- 



