LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 



21 



duller plate, and each time the fish fed from the bar on 

 that side. It seemed that, since the fish had fed from the 

 bar at once and on the side of the duller plate, only a few- 

 trials would be required to fix the response. But more 

 than 150 trials were not enough to show any increase in 

 accuracy of response, and at no time was a more persistent 

 " position habit " formed than developed here. The lack 

 of learning is expressed in the curve, figure 9, which was 

 made by plotting the average percentages of correct choice 

 of each twenty consecutive trials. 



Because there are individual differences and abnormal- 

 ities among fish, Bu was taken from the experiment aquar- 

 ium, and two other dace of the same reserve stock were 

 placed in the aquarium and tested one at a time, under 



RRIGHTNtSS 



N umber Of trlnlJ io 40 



DISCRIMINATION 



60 60 100 120 140 



Fig. 9 



Graph showing the percentage of correct choices in each 20 consecutive trials in 

 a series of 140 trials of horned dace Bu. The choice was between two white plates 

 of relative brightness 1 :4. The fish was fed at the duller plate. 



the same conditions as described for Bu. Of the first ten 

 trials given, seven for each fish were to the duller, or posi- 

 tive plate. Again it seemed that it would be easy to train 

 the fish to go to that plate for food, but sixty-five trials 



