64 ANIMAL AGGREGATIONS 



than toward other forms." The aggregation arises from the tend- 

 ency of the other catfish to respond by appropriate positive reac- 

 tions, instead of making-off as fishes of other species do when ap- 

 proached. 



With these fairly well-integrated aggregations of young bullheads 

 analysis shows that the social appetite is diffuse rather than specific, 

 and that in the normal fishes, aggregation involves a sight reflex, a 

 touch reflex, and possibly a low-frequency vibration reflex, all of 

 which may be given to other moving objects, non-living as well as 

 living; a chemical reflex, the sign of which is reversed with non- 

 living models; and, finally, reciprocal behavior on the part of the 

 different individual members of the aggregation. The matter of re- 

 ciprocal responses contributes the distinctly social element in this 

 behavior. The extent to which the combination of these reflexes into 

 a functioning whole depends upon the presence of an inherited social 

 appetite, or upon early conditioned behavior, remains to be investi- 

 gated. 



