44 THE SOCIAL LIFE OF ANIMALS 



active toleration for the close proximity of others. 



Similarly close aggregations occur as a result of 

 the less spectacular trial and error reactions, in 

 which the animals wander here and there, more or 

 less vaguely stimulated by internal physiological 

 states or external conditions, and so come to collect 

 in favorable locations. Collections of animals about 

 limited sources of food give a good illustration. 

 These, too, may show only the social qualities of 

 inertia and toleration. 



A decided advance is made when animals react 

 positively to each other and so actively collect to- 

 gether, not primarily because the location is favor- 

 able or through environmental compulsion, but as 

 the result of the beginnings of a social appetite. In 

 early stages of such reactions, the movement together 

 may come primarily because the collection of isopods 

 or earthworms or starfishes are substitutes for miss- 

 ing elements in the environment. 



Take, for example, the snake or brittle starfishes 

 of the New England coast. These are rare now along 

 Cape Cod, but before the wasting disease swept away 

 the eel grass they were abundant in favorable locali- 

 ties, but were rarely found close together. I have 

 spent hours peering down through a glass-bottomed 

 bucket here and there and round about in one of 

 these localities, and have not seen more than one 



