ASSOCIATION AND COLOR DISCRIMINATION 489 



A circle of black paper 4.5 cm. in diameter pasted on a white 

 card was not distinguished from a black square 4 cm. across, 

 when they were presented under the same conditions as those 

 used in the tests described above, by mudminnow no. 39 during 

 thirty-seven days. 



In order as nearly as possible to duplicate the conditions of 

 the experiments with colored lights, two pieces of glass were cut 

 the size of the gelatin filters. Upon the center of one was placed 

 a square of black paper 2.7 cm. across and upon the other four 

 black circles 1 cm. in diameter. These plates of glass were in- 

 serted in the tin box and the light flashed through them upon 

 the fishes. The appearence of the square was accompanied by 

 food and the black dots were to suggest paper. At the end of 

 thirty-eight days (February 27 to April 5) mudminnow no. 27 

 showed no signs of discrimination (fig. 9). 



Two sticklebacks, no. 63 and no. 64, were subjected to the 

 following experiment. Glass plates fitting into the tin box were 

 used. On one was a square 2 cm. in size and on the other a 

 black circle 2.5 cm. in diameter. Neither fish showed that it 

 perceived the difference between them, though the experiment 

 continued sixty days. 



While these experiments do not absolutely prove that differ- 

 ences in pattern are not perceived by mudminnows and stickle- 

 backs, they suggest that the discrimination of patterns and 

 differences in backgrounds does not have a very important 

 function in their search for food. No associations appeared to 

 be formed with the patterns used. These results are in sharp 

 contrast with those of the tests with colors. 



ASSOCIATIONS FORMED IN FISHES 



Types of associations 



The analysis of the psychology of a fish, like that of any other 

 animal, can only be made by interpreting its immediate reactions 

 to stimuli of various sorts. The nature of the sense organs and 

 the reacting organism must determine the types of associations 

 formed, whether they are merely associations of particular 



