ADJUSTMENT OF FLATFISHES 429 



as regards color. It became of a homogeneous tone, however, 

 having previously shown a pattern with considerable contrast. ^^ 



It was with various painted patterns, in black and white, that 

 perhaps the most striking of all my results were obtained. The 

 following backgrounds of this sort were employed: — 



13. Squares of black and white, alternating as in a checker- 

 board. These were of four sizes, viz. 2 mm., 1 cm., 2 cm. and 

 4:h cm. square, respectively. One of the most interesting of my 

 results is the difference in the appearance assumed by the same 

 fish upon the 2 mm. squares and the 1 cm. squares. (Compare 

 fig. l/i and li; also figs. 4a and 45). In each case, the skin pre- 

 sents a much more fine-grained appearance when the animal is 

 upon the smaller squares. The effect is much as if a draughts- 

 man had taken fig. Ih, or fig. 46 and 'stippled' the pale areas with 

 dark ink, thus breaking them up into smaller subdivisions ; at 

 the same time doing exactly the reverse with the dark areas, by 

 filling them in with pale dots. Thus the degree of subdivision of 

 the background — independently of the relative amounts of black 

 and white — is shown to be an important factor in the stimulus. 



The 2 cm. squares, which were painted rather crudely upon 

 the bottom of a glass vessel, called forth a somewhat interesting 

 appearance in specimen no. 1, the only one which was used for 

 the purpose (fig. 1/). The same large dark blotches will be seen 

 to have come into view, as were manifested by this fish upon 

 the coarse gravel. But the pale spots, in the present instance, 

 are likewise conspicuous, so that there is now^ more contrast be- 

 tween the lightest and darkest portions of the surface. 



The effect of the 4^ cm. squares was tested with specimens 1 and 

 4. The former fish was kept upon this pattern for a period of 

 seven days. During most of this time the animal seemed ill at 

 ease, swimming around the jar at frequent intervals, and seldom 

 lying upon the bottom in the attitude of complete rest. This 



^1 These experiments are confessedly too few, and their duration too brief, to 

 permit of our forming any final opinions, even as regards this species. Other ob- 

 servers have recorded radical changes of color in fishes, as witness the effects of 

 monochromatic light upon Nemachilus, as reported by Secerov (Archiv fur Ent- 

 wicklungsmechanik, 1909). 



