158 THE SOCIAL LIFE OF ANIMALS 



usually shown by paired and by isolated birds, prov- 

 ing that the type of reaction given was a result of 

 the numbers present rather than of the working of 

 other factors. With these love birds then, contrary 

 to the original assumption, all indications were that 

 being paired in the maze slowed down the rate of 

 learning and increased the erratic character of their 

 behavior. 



Our experience with the general problem did not 

 end here. I teach at the University of Chicago a 

 favorite course called Animal Behavior. In this class 

 the beginning research students attempt some small 

 problem and frequently make good progress toward 

 its superficial solution. One of these student projects 

 has been the training of the common mud-minnow 

 to react to traffic lights. The fish were trained to 

 jump out of water and obtain a bit of earthworm 

 when red was flashed. Under the green light they 

 were conditioned to retire to one of the bottom cor- 

 ners. If they did jump under green light they were 

 fed filter paper soaked in turpentine. Within two 

 months a lot of fishes, isolated one in each small 

 aquarium, could be trained so that they would have 

 been given an A for the project if they had been 

 properly enrolled students. 



When, however, several fishes were placed together 

 in the same aquarium and an attempt was made to 



