106 ANIMAL LIFE AND SOCIAL GROWTH 



each other, they move their sensitive barbels 

 (which are tentacle-like processes that grow out 

 from around the mouth) over each other and 

 appear to get a definite chemical stimulus to 

 which they react. If they have moved towards a 

 black paraffin model of a catfish minnow, on touch- 

 ing it with the barbels, they move away appar- 

 ently recognizing that the model is not the real 

 thing. Their touch-chemical sense is not very 

 sensitive for they apparently cannot distinguish 

 other species from their own. They attempt to 

 to push against a second fish whether of their 

 own or of another species; if both are catfishes a 

 mutual pushing results which, if many are present, 

 leads to a dense group formation. If the second 

 fish belongs to some other species, it moves away 

 and leaves the catfish again alone. There is some 

 evidence too, that even blinded catfishes can rec- 

 ognize the passing of another fish by the vibra- 

 tions which it sets up and that they will turn and 

 follow such vibrations. 



With these catfishes, the groups at the outset 

 are family affairs, but this condition soon changes, 

 first usually, by the withdrawal of the female, 

 then by the withdrawal of the male; with the 

 young catfish groups, the daily separation and 

 reforming of the aggregations brings in represen- 

 tatives of other family groups in the vicinity. 



