120 ZOOLOGY 



in the case of the branching corals) where the single polyps would 

 be practically helpless. The arrangement of the polyps on the 

 common skeleton and the rate of growth of the different polyps 

 are beautifully adapted to the best use of the currents of water 

 by which the food and oxygen are conveyed. 



154. Library and Museum Exercise. What phyla of the animal kingdom 

 supply instances of colonies? Trace different degrees of polymorphism. In 

 what different ways do the individuals occur on the common stock? Show how 

 the relative rate of growth of the differently placed individuals determines the 

 ultimate form of the colony as a whole. 



155. Social and Communal Life. Animals of the same 

 species often become associated even when there is no organic 

 connection between the individuals. The association may be 

 temporary or permanent. The bond in these cases is not phys- 

 ical, but instinctive and psychical. In its simplest form this is 

 merely a matter of gregariousness such as is seen in the schools of 

 fishes or flocks of birds, which are apparently brought together 

 at certain periods by a common instinct or by common needs. 

 A step more intimate is the banding together of predaceous 

 animals as wolves or vultures, or pelicans, for mutual help in 

 finding or capturing the prey. Corresponding to this, on the 

 part of their victims, we find the herding of the bison, of deer, 

 and their allies for protection, whether by fighting together or 

 by the stationing of sentinels to give notice to the feeding herd 

 of the approach of danger. In still other forms, notably among 

 such insects as the bees and ants, there is a very intimate and 

 permanent union in social life. This is usually associated with 

 the instinct of home building, and thus a high degree of division 

 of labor with its great advantages becomes possible. This is 

 carried to such an extent that often polymorphic individuals 

 result, much as in the organic colonies. In such cases it is clear 

 that the individual life comes to be bound up in the success of 

 the community. Such forms usually exert great care for their 

 young and develop a relatively high order of "intelligence." 

 The principal social forms are the ants, of which there are more 

 than two thousand species; some of the bees and wasps; the 

 termites, or so-called white-ants; beavers; some monkeys and 

 man. 



