• 50 CORA D. REEVES 



Therefore the red filter was removed and in its place 

 was put the photographic negative already referred to. 

 By means of this negative there was obtained a dull patch 

 of mixed (gray) light which was then matched to the blue 

 with the aid of a flicker photometer by varying the width 

 of the slit. The two patches were thus made alike in bright- 

 ness for the human eye dark-adapted. The dace H and 

 Md and three sunfish were presented, each separately, 

 with the matched patches, and were fed before the blue 

 plate. The behavior of the fish was so significant that 

 this discussion might be placed in the division of this paper 

 on Unlearned Responses but is placed here to preserve the 

 chronological order so that the previous experience of the 

 fish may be clearly in mind.« 



The results are shown in Table II. Large Sunfish, Small 

 Sunfish, and 552 chose the blue plate seventeen times and 

 the gray plate but three times. The record for dace H 

 shows 76 per cent of blue choices, not a high percentage. 

 Of the 43 choices made by the five fish used 72 per cent 

 were to be blue. These records are similar to those in which 

 matched blue and red were used. As in that series the 

 percentage of blue choices increased when the red was 

 held at matched intensity, so here a longer series might 

 have shown increase of percentage of blue choices. How- 

 ever, the number of tests made was relatively few. Fur- 

 ther work will doubtless show what significance the per- 

 centage of choices may have as evidence that blue and 

 gray are different for fish. That red was different from 

 gray was evident from the behavior of the fish, for both 

 delayed response and peculiar behavior occurred. 



a. Delayed Response. — On the first trial each sunfish 

 swam rather quickly up to the blue, but for the succeeding 

 trials the time of response was either greatly increased or 

 there was no response, and the fish remained lurking in 



* Chronological Summary for //, Md, and Large Sunfish. 1914. Oct. 13 Intro- 

 duced into Experiment Aquarium. 1. Blue-red Experiment. Oct. 13-Jan. 1, Red 

 Maximum (A few early tests with decreased red). 1915. Jan. 1-March 20, Red De- 

 creasing. 2. Check tests. Mar. 20-Apr. 2, With solutions. Ap.-il 3-5. Blue-Gray 

 Experiment. April 8-10, Equated Energy. 



The data of introduction of Yi, YP, also Sma". Sunfish and S.S- was the last of 

 November 1914. Their dates differ in that the Blue-red series is shorter but in the 

 following experiments the dates are the same. 



