ADJUSTMENT OF FLATFISHES 437 



outside. Add to this the view overhead, which, as we have seen, 

 was not wholly ignored, and it is truly a matter for surprise that 

 the bottom was the surface chiefly concerned in evoking these pig- 

 ment changes. To what degree, if any, surfaces lying in other 

 planes might influence the fish was tested by special experiments. 



A fish (no. 8) which had first been photographed on a gravel 

 bottom (fig. 8a) was used in a series of such tests. This specimen, 

 whose length was 12.4 cm., w^as placed in a glass jar having a bot- 

 tom diameter of 20 cm. The bottom of the jar was painted blacli, 

 but the walls were left transparent. Thus when this vessel was 

 set into a larger jar and surrounded by gravel,^'' the latter could 

 be clearly seen by the fish. In this contrivance, the animal became 

 much darker in the course of the next few days, the annuli being 

 reduced to rings of white dots. These last remained conspicuously 

 pale, however, so that the fish was far from being concealed on this 

 bottom. (Fig. 86 represents the condition at the close of seven 

 days.) 



The same specimen was now transferred to a contrivance exactly 

 the reverse of the last, i.e., one having the walls painted black, 

 and the gravel visible through the bottom. A partial return to the 

 gravel appearance was noted in the course of one day, and this 

 increased during the next day or two, although the original 

 appearance was not resumed in full, even after the lapse of ten 

 days^i (fig. 8c). 



The fish was next transferred to a jar having a white bottom, 

 20 cm. in diameter, and black walls. Within two days it was notice- 

 ably lighter, and after three days ''very much lighter and more 

 homogeneous." It is doubtful whether any further change oc- 



^° Under water, of course, so that total reflection from the walls of the jar was 

 avoided. 



*i The fish, after seven days, had been changed to a smaller jar, having s diameter 

 of only 16 cm., but no certain change was noted. Gravel was now (after ten days,) 

 placed in the bottom of the dish, so that the fish lay upon this directly, rather than 

 upon a glass bottom. It is probable that some further change took place in the 

 direction of adaptation to the gravel, for my notes state later that the fish now 

 harmonized quite well. I do not believe, however, that this higher degree of adap- 

 tation had any relation to the tactile stimuli derived from direct contact with the 

 gravel, but rather to an alteration of the visual stimuli. 



