CLASSIFICATION OF ANIMAL AGGREGATIONS 23 



Some of the overlapping inherent in this type of subject-matter 

 classification appears when one considers a heterosynaporium. a col- 

 lection of different species due to the action of unfavorable condi- 

 tions, which Deegener illustrates by the growing concentration of 

 water animals in a drying pond. Obviously, such a collection would 

 be at the same time a heterosymphagium and a heterosynchorium. 

 Apparently, Deegener would classify the animal community of 

 modern ecology as a heterosynchorium, since it is composed of sev- 

 eral species occupying the same place, although the individuals of the 

 group are not of obvious advantage to each other. He does not ac- 

 tually say that an ecological community should be so classified; he 

 does use the term hiococnosis in connection with his discussion of a 

 coral reef heterosynchorium. 



Part II. Essential aggregations or societies are communities of spe- 

 cies of similar or dissimilar animals which have a real value for the 

 individuals composing them, thereby differing from the "associa- 

 tions" treated in the previous sections. 



A. Homotypical societies are composed of the same species. 



Alpha. Kormogene societies have the different individuals compos- 

 ing them organically connected with each other. 



I. Primary colonies have arisen from the same mother. 



I. Reciprocal colonies are those in which all the individuals repre- 

 sented stand in reciprocal relationship to each other. 



a) Homomorphic colonies have all the individuals morphologically 

 similar and may be found among sponges and at certain times among 

 hydroids and bryozoans. 



(i) Colonies formed by division may be illustrated by the colonies 

 of Volvox so long as they remain free from specialized reproductive 

 cells. 



(2) Colonies formed by budding occur commonly among the Hy- 

 drozoa, the Bryozoa, and in many colonial chordates. 



b) Heteromorpliic and polymorphic colonies are formed when there 

 is a differentiation between the different members of the colony, as 

 occurs in the hydroid Hydractinia, in which feeding, reproductive, 

 and protective zooids may be recognized. Polymorphism is carried 

 much farther in the Portuguese man-of-war, Physalia, and its aUies. 

 Here again we may recognize (i) colonies formed by division, as in 



