ASSOCIATION AND COLOR DISCRIMINATION 491 



hour, even if the fishes had been fed, for they were more Ukely 

 to become excited. Goldsmith ('12) reports place association 

 in gobies and plaice. This has not been confirmed by tests on 

 the mudminnow and the stickleback in any respect other than 

 their swimming to the surface for food. An effort was made to 

 induce them to seek habitually a certain end of the tank where 

 food was dropped in through a tube, but there was no indication 

 that such a habit had been formed. 



Delicacy of associations 



It was presumed that associations formed in the nervous or- 

 ganism of fishes would not be such as to admit of fine discrimi- 

 nations; this was borne out by the experiments. Filters of 

 different shades of red and green could be interchanged without 

 affecting the reactions. The pattern experiments brought no 

 positive results. 



A stickleback, no. 57, was offered minced liver and gray paper 

 alternately thirty-nine times in thirty-five days. The fish 

 learned very quickly to refuse the paper and to leap out after the 

 liver, but small pieces of angleworm could be substituted for the 

 liver without the fish obviously perceiving the difference. The 

 successes were 84.62 per cent and the errors 15.38 per cent; 

 during the last ten da^^s of the experiment not a single error 

 was recorded. A similar record was shown when the experiment 

 was repeated with the same stickleback, when in thirty days the 

 successes were 83.03 per cent and the mistakes were 17.07 per 

 cent; all the reactions during the last nine days were perfect 

 (fig. 10; table 3). 



Complexity of associations. 



Fishes are evidently capable of forming only very simple as- 

 sociations directly related to their struggle for existence. This 

 is to be expected, since, so far as is indicated, they possess only 

 the kind of attention which leads directly to activity. Thorn- 

 dike ('11) reports being able to induce Fundulus to seek exit from 



