ADJUSTMENT OF FLATFISHES 469 



9. Thus, while the adaptation was most complete upon such 

 backgrounds as formed a part of the natural habitat of the 

 species, it was plainly not restricted to these cases, and the pigment 

 was at times disposed in ways which, it seems likely, were quite 

 foreign to the previous experience either of the individual or the 

 race. For example, the extremely pale, and perhaps also the very 

 darkest conditions; likewise the vividly contrasted black-and- 

 white condition, without intermediate shades, which was assumed 

 by certain specimens upon some of the artificial backgrounds. 

 Accordingly, the notion that the fish is limited to a few stereo- 

 typed responses, representing the most familiar types of habitat, 

 must be rejected at once. 



10. Fishes of the same species differed greatly in their indi- 

 vidual powers of adaptation, and some seemingly normal specimens 

 possessed this power in a very limited degree. Again the same 

 fish acquired with practice (if this word may be allowed) the 

 power of changing much more rapidly than before. The time 

 required for a radical change of shade or of pattern ranged from a 

 fraction of a minute to several days. 



11. In the case of Rhomboidichthys, the underlying surface 

 (more strictly, that part of the bottom immediately surrounding 

 the fish) appeared to be the one chiefly effective in calling forth 

 these changes. The influence of the vertical walls of the vessel 

 commonly seemed to be a subordinate one, even in cases where 

 the fish was so large that it covered a considerable fraction of the 

 bottom, and was obliged to lie constantly with its eyes close to one 

 or another side of the jar. Fairly conclusive evidence was offered, 

 however, of the influence of the vertical walls of the latter, even 

 upon this species. What the fish saw directly overhead seemed, 

 on the contrary, to exert a negligible influence upon the color 

 pattern. 



12. With the sand-dab, much clearer evidence was obtained 

 of the influence of the vertical walls of the receptacle. These, at 

 times, appeared to have an effect as great as, if not, indeed, greater 

 than, that exerted by the bottom. It must be noted here that this 

 difference between the two species is perhaps to be attributed 

 to the differing positions of their eyes. Those of Rhomboidich- 



