9,8 THE SOCIAL LIFE OF ANIMALS 



in a none-too-large crystallizing dish. The consump- 

 tion of food per animal by the grouped fish fell off, 

 and as was shown by appropriate tests, this was due to 

 the action of a so-called confusion effect. When fewer 

 Daphnia were present, a fish might be observed to 

 swim after an isolated crustacean and eat it, whereas 

 a dozen Daphnia or so in the immediate field of 

 vision seemed to offer conflicting stimuli that blocked 

 the feeding response. Working on this suggestion, 

 one group of four was given the usual quota of some 

 six hundred Daphnia all at once; another group was 

 given only one hundred at a time, and when these 

 were approximately all eaten then another hundred 

 would fjc introduced, and so on until the end of the 

 regular feeding period. This prevented the Daphnia 

 from being too dense at the beginning of the hour's 

 feeding time. The isolated fish were fed as usual. 

 Under these conditions the grouped goldfish which 

 were fed one hundred Daphnia at a time ate defi- 

 nitely more than those given the whole confusing 

 mass at once. 



Here we come upon two, not one, mass effects. In 

 the first place we see that the fish in groups of four 

 were stimulated to eat more food than if isolated, 

 and this depended on their state of aggregation. But, 

 incidental to this demonstration, we hnd that in the 

 presence of too many animated food particles a con- 



