LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 41 



the blue-food association, /. c. the learning to discriminate, 

 indicated by the rise in the curve to the (i^S per cent level, 

 The curve of 552 shows the same divisions (trials 1-60), but 

 since this fish was given no trials with the red at maximum 

 value the whole of its curve falls within the red decreasing 

 part of its series of trials. In the case of Small Sunfish 

 there is no initial avoidance of red. Its curve rises imme- 

 diately from the 45 per cent (trials 1-20) level and ascends 

 to 85 per cent (trials 21-40) as the food association is 

 established. 



In the red decreasing part of the series of trials the 

 graphs again show a general likeness to those of the dace. 

 In each of these curves there is a drop, shown most typ- 

 ically in the curve of Small Sunfish. Here it corresponds 

 to slit width 0.9 mm., at which point the curve falls to the 

 55 per cent level (trials 121-140). This is in the region of 

 matched brightness for the human dark-adapted eye and 

 shows an initial failure to discriminate at this value of the 

 red. As the slit-width is held at this value, discrimination 

 is re-established in vSmall Sunfish (trials 140-180), and its 

 curve rises above the 90 per cent level. A similar but less 

 pronounced drop in the curve occurs in 552 (trials 61-80) 

 and is followed by recovery. In Large Sunfish the drop 

 occurs at 1.80 mm. slit (trials 181-200) and is followed by 

 recovery. In general the sunfish graphs show the same 

 characteristics as those of dace. In the composite sunfish 

 graph (fig. 16) there is, however, a shorter region of inac- 

 curate response with decreasing red brightness than in 

 that of the dace. This might be expected from the greater 

 ability of the sunfish to discriminate intensities of white 

 lights. Their brightness discrimination has been shown 

 to be more accurate. The peculiarities of the individual 

 sunfish graphs may now be considered. 



b. Large Sunfish.— The long graph of this fish differs 

 from those of the other sunfish in showing a lack of dis- 

 crimination at slit- widths 1.8-1.5 mm. rather than at 

 0.9 mm. None of the other experiments with red and blue- 

 indicates that in this region the brightness of the red 

 matches the blue for sunfish. Small Sunfish and 55o gave 

 from the first high percentages of blue choice at these 



