336 ANIMAL BIOLOGY 



as the highest. A little patch of meadow soil two feet square has 

 revealed, within about an inch from the surface, over a thousand 

 animals and three thousand plants. There is a struggle for existence. 

 Take a single example. A common food Fish, the Squeteague, 

 captures the Butter-fish or the Squid, which in turn have fed on 

 young Fish, which in their turn have fed on small Crustacea, which 

 themselves have utilized microscopic Algae and Protozoa as food. 

 Thus the food of the Squeteague is actually a complex of all these 

 factors, and such a nutritional chain is no stronger than its single 

 links. Circumstances which modify or suppress the food and 

 thereby reduce the abundance of the Algae and Protozoa of the 

 sea are reflected in correlative changes in the abundance of eco- 

 nomically important food Fishes. And this same principle is 

 true throughout living nature, though only occasionally is it pos- 

 sible to trace it. 'Nature is a vast assemblage of linkages." 

 (Figs. 220, 266.) 



1. Communal Associations 



Perhaps the simplest associations of organisms are represented 

 by gregarious animals, such as Wolves which hunt in packs, and 

 Buffaloes and Horses which herd for protection. Here the associa- 

 tion is more or less temporary and there is no division of labor 

 between the members, other than leadership by one animal. 



Communal animals, however, exhibit highly complex associa- 

 tions in which the members merge, as it were, their individuality 

 in that of the community. This is well exhibited, for example, 

 among the Ants, in which all of the various species, about 5,000 in 

 number, are communal, and the Wasps and Bees in which all 

 gradations exist from solitary to hive-dwelling species. In the 

 case of the Bees, and still more in the Ants, the division of labor 

 has developed to the extent that structural differentiations have 

 given rise to classes of individuals specially adapted for the per- 

 formance of certain functions in the economy of the hive. 



But the differentiations of various members of a colony of Ants 

 or Bees are limited to their bodies and are practically fixed and 

 irreversible, while in human society, differentiations are no longer 

 confined to the bodies of individuals. Man's ingenuity has de- 

 vised what are to all intents and purposes artificial, accessory 

 organs — tools and machines. Accordingly it is in Man that we 

 find the highest expression of communal cooperation, because in- 



