LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 



35 



for them to " get used " to the red. H was of distinctly 

 different temperament from Md; he gave more evidence 

 of fright reactions and was more " cautious." Doubtless 

 his failure to approach the red until after 40 trials was 

 due to these peculiarities. The curves of Yl and YP are 

 then more typical than those of // and Md in so far as they 

 show a rapid adaptation to the red stimulus patch. Dur- 

 ing the ' red decreasing ' part of the curves, temporary 

 failure to discriminate is shown for Md at slit width 0.9 

 mm. In Yl it occurs at width 5.0 mm. In the case of 

 YP, as the graph shows, no trials were made between 

 slit widths 2.0 mm. and 0.6 mm. Had trials been made 

 at this width, i. e., between trials 120 and 121 of this fish, 

 a drop in the curve would probably have taken place. 

 Although trials were made with H at slit width 1.0 mm. and 

 0.9 mm., no considerable drop occurs at this point or else- 

 where in his curve. The curve shows merely a lower region 

 between slit widths 2.0 mm. and 0.9 mm. Somewhere in 

 this region the stimulus patches probably matched in 

 brightness for this fish. The fact that this fish discrimin- 

 ated more accurately than any of the others when the red 

 was' greatly reduced in intensity (trials 221-260) is con- 

 sistent with his better discrimination at matched bright- 

 ness. The greater caution of this fish has been referred to. 



JO ^O /O S-2 /OSI OS'n^o/'^e 



SO 



eo 



FIG. 14 



Graph made by plotting the percentage of correct choices found by averaging 

 all the records from the four dace for each successive width of slit. The individual 

 graphs of these dace are shown in figure 13. Abscissae indicate successive slit widths 

 in millimeters, ordinates percentage of correct choices at the given widths. 



