98 THE SOCIAL LIFE OF ANIMALS 



vice such that if in nature one or a few fish in a 

 group find plenty of food, apparently without will- 

 ing to do so they regurgitate some food particles 

 which are taken by others, a sort of automatic shar- 

 ing. Again, in water that changes rapidly, such stag- 

 nant-water fishes as goldfish, if present in numbers, 

 are able to condition their environment, perhaps by 

 the secretion of mucus, so that it becomes a more 

 favorable place in which to live and grow. 



Perhaps I have lingered too long over this one 

 case; I am so close to the facts and to the tactics used 

 in collecting them that they may seem rnore interest- 

 ing to me than they will ten years hence. We have 

 run the same experiment with positive results with 

 a few other species of fishes; and we have also found 

 by experimentation that certain fish will regenerate 

 tails that have been cut off if several are present in 

 the same water more rapidly than if each is isolated. 

 (112) The same is true for the young tadpoles of sala- 

 manders, with which we have had experience. The 

 explanation of the more rapid regeneration of such 

 cut tails is probably relatively simple. The several 

 animals together more readily bring the surrounding 

 fresh water to approximately the salt content of the 

 cut and regenerating tissues than can be done by a 

 single animal placed in the same amount of water. 



