60 CORA D. REEVES 



without being fed. There were 28 approaches to the 

 patches, 14 of them to the blue. The two patches were 

 approached by all the fish in the same way and with equal 

 frequency; the time of approach varied from three seconds 

 to three and one-half minutes. When identical matched 

 patches were presented immediately afterward except 

 that one was now red, the other blue, the behavior changed. 

 Two of the fish, after patching for a time at the doorway, 

 slipped out of the discrimination compartment, went an 

 inch or two into the stimulus compartment, and then 

 returned by backing out of the stimulus compartments. 

 They repeated this manoeuver. One did not leave the 

 discrimination compartment for seven minutes; another 

 still lurked in the discrimination compartment after fifteen 

 minutes. 



Semotilus. — A horned dace, an untrained fish from the 

 same stock as the Pimephales, was placed in the experiment 

 aquarium one noon. The ceiling light was turned on. At 

 3:15 that afternoon the sliding door was raised and matched 

 blue and red plates were exposed. For a time the fish was 

 quiet, then it went slowly a short distance into the stimulus 

 compartment, then lay in the doorway across the shadow 

 of partition .4. It then swam back into the discrimination 

 compartment and circled around the back of the compart- 

 ment facing the lights. After 295 seconds the fish went 

 up to the blue plate. It was closed back into the discrim- 

 ination compartment by use of partition ^4, and after fifteen 

 minutes the sliding door was again raised to expose the 

 matched blue-red patches. Five times the fish upon com- 

 ing to the door-way turned with its head away from the 

 stimulus patches so that the posterior half of the body 

 projected out of the door into the stimulus compartment, 

 then swung its head across the doorway and moved back 

 into the discrimination compartment. It then circled across 

 the end of the aquarium and after 340 seconds swam to 

 the blue plate. 



This dace was tested with matched blue and gray patches, 

 two hours later. Twenty seconds after the slide door was 

 raised the fish was at the gray plate, and 30 seconds was 

 the time for its second trial. Three hours later the blue 



