700 



ZOOLOGICAL SOCIETY BULLETIN. 



a black bottom and a very pale shade upon a 

 white bottom, but exhibited one color pattern 

 upon sand (Fig. 1), another upon fine gravel 

 (Fig. 2), and jet another upon a bottom of small 

 stones. A number of entireh' artificial bottoms, 

 such as variously painted strips of glass, were 

 also employed in these experiments, sometimes 

 with rather surprising results. For example, 

 the skin patterns were found to vary both with 

 the relative amounts of black and white in the 

 background, and with tiie degree of subdivision 

 of the areas of the latter. Comi^arison of Fig- 

 ures 3 and i will illustrate this point. 



Now this capacity of the fish to adapt itself 

 to different backgrounds, although at times very 

 striking, was restricted within certain definite 

 limits. In general, brilliantly colored back- 

 grounds seemed to be beyond the fish's power of 

 imitation. The animal ap- 

 peared to be limited almost 

 wholly to the black, white, 

 gray and brown of its cus- 

 tomary habitat. Then, too. 

 the creature was found to 

 possess permanent spots and 

 markings, due to the special 

 grouping of the p 

 cells in its .skin.* 



]5roved to be fixed mor])ho- 

 logical structures, however 

 much they might vary at 

 different times in their rela- 

 tive intensity. Even when 

 the fish was ada])ted to a 

 ]3erfectly uniform b a c k - 

 ground, the outlines of these 

 spots were for the most part 

 dimly visible, and when they 

 rea])peared they always had 

 the same form and occupied 

 the same position. Under 

 such circumstances, we could 

 not reasonably expect that 

 squares, cross-bands, circles, 

 etc., should be copied in any 

 true sense by the fishes, and 

 as a matter of fact they were 

 not. 

 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 pig- 

 ment was at times disposed in ways which, it is 

 safe to say, were quite foreign to the previous 

 experience of the race. F^or example, the near- 

 ly white and perhaps also the darkest condition 

 attained by the fish, likewise the vividly con- 

 trasted black-and-white condition, without in- 

 termediate sjiades (Figures 3 and ,5) 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. 



The individuals used differed greatly in their 

 powers of adaptation, and some seemingly nor- 



*The color changes of fi: 

 are due to the movement of 

 pigment granules within 

 chroniatophores, or color cell 

 under the influence of stimu 

 transmitted through nerves, 

 chromatophores themselv 

 probably do not change either 

 in shape or position. 



SAME FISH AS IN FIG 3, ON A DIFFERENT BOTTOM. 



