CLASSIFICATION OF ANIMAL AGGREGATIONS 17 



from a loose to a firm integration. The primary cause of their being 

 together hes in their common origin, but the cause of their remaining 

 together is not of a genetic nature but may depend on the favorable 

 character of the place or on the presence of food. In other cases one 

 must assume the operation of a social instinct which holds the ani- 

 mals together. 



1. Syngenia are primary associations which arise by means of 

 asexual reproduction. This may be illustrated by Stcnior coeruleus, 

 which Hves on decayed water plants and occurs frequently in such 

 abundance as to give a blue color to the surface of the water. The 

 aggregation is located in space by favorable food conditions. So long 

 as there are only offspring from a single mother present, the aggre- 

 gation would be called a monosyngenium; but when second and third 

 generations appear from the same stem-mother, the group becomes a 

 polysyngenium. Other unrelated individuals may wander into this 

 favorable niche, forming a secondary association. Similar relations 

 hold with Vorticella, but with both these aggregations there may be 

 some social value accruing to the different individuals, since the 

 combined vortex action of the cilia brings more food to each animal. 

 This does not occur in hydroids, such as the common fresh-water 

 Hydra, which reproduces asexually and remains in a purely acciden- 

 tal aggregation in which there is no reciprocal relationship before 

 sexual reproduction begins. Similar relations hold with various other 

 simple coelenterates whose slight powers of locomotion tend to con- 

 fine them close to the place in which they are budded free, providing 

 it is a generally favorable location. 



2. Primary associations arising from sexual reproduction may form 

 close unions which may rise to the widely extending reciprocity of 

 the highest types of society found among animals. In the inverte- 

 brates these are represented by the conditions obtaining in ant and 

 termite colonies; in the vertebrates, by human societies. This part 

 of Deegener's outHne undertakes to consider only the more primi- 

 tive, purely accidental forms of this family union, in which the par- 

 ents need not necessarily be concerned. Various combinations of sim- 

 ple families where the young all originate from the stem-mother may 

 be distinguished and divided as follows: 



