240 Fortieth Annual Meeting 



(9) Within the hmits thus imposed, however, the capa- 

 city of the fish to adapt itself in respect to the general 

 proportions and distribution of pigment was often re- 

 markable. 



(10) This power of adaptation was best shown upon 

 such backgrounds as formed a part of the natural habitat 

 of the species. It was not, however, restricted to such cases, 

 but the pigment was at times disposed in ways which, it is 

 safe to say, were quite foreign to the previous experience of 

 the race. For example, the nearly white, and perhaps also 

 the nearly black conditions ; likewise the vividly contrasted 

 black-and-white condition, without intermediate shades, 

 which was assumed by certain specimens upon some of the 

 artificial backgrounds. Thus the notion that the fish is 

 limited to a few stereotyped responses, representing the 

 most familiar types of habitat, must be rejected at once. 



(11) Fishes differed greatly in their individual powers 

 of adaptation, and some seemingly normal specimens 

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

 same fish acquired with practice (if we may use the ex- 

 pression) the power of changing more rapidly than before. 

 The time necessary for a radical change of shade or of 

 pattern ranged from a few seconds to several days. 



Some further experiments were tried, and are now being 

 continued (though I am forced to employ a much less 

 favorable object) with a view to determining the mode of 

 operation of the stimulus which is effective in bringing about 

 these chromatic changes. Some of the more important of 

 these results we may sum up as follows : 



(1) The animal depends upon sight for the perform- 

 ance of these adaptive responses. This, in fact, had 

 already been proved and needed no corroboration. Indeed, 

 it is impossible to see how adaptive changes of color pattern 

 could be brought about by any other sense. If blinded when 

 in the dark condition, the fishes remained dark, though they 

 did not ordinarily retain the maximum degree of pigmenta- 

 tion; if blinded when pale, they remained pale for some 



