CLASSIFICATION OF ANIMAL AGGREGATIONS 15 



deegener's classification of aggregations 



Part I. Accidental unions or associations are groups of animals 

 without mutual benefit for individual members. "Accidental" is, to 

 Deegener's mind, a better term for these aggregations than "in- 

 different," because to him it plainly indicates the method of their 

 formation, and also because the members of accidental aggregations 

 are not always indifferent to each other. Accidental aggregations 

 will be seen to be of various kinds, formed in various ways. They 

 may consist of one or of a number of species. One cannot always be 

 sure concerning the proper classification of a given association, which 

 may as yet be merely a matter of opinion. Deegener recognizes that 

 even the major distinctions are not always clean cut and that one of 

 a pair of apparently closely similar groupings may be assigned to the 

 accidental associations while the other is called an "essential so- 

 ciety." In the minor categories the methods of formation determine 

 the classification to a considerable degree. 



A. Eomotypical associations consist of members of the same spe- 

 cies which have arisen either sexually or asexually, which may have 

 remained together because they are the oft'spring of the same parent, 

 or which may have become accidentally associated together although 

 of different parentage. The former are called "primary," and the 

 latter "secondary," associations. 



Alpha. Kormogene associations^ are confined to invertebrates and 

 do not occur in arthropods, echinoderms, and mollusks. They are 

 those colonial forms in which the different individuals remain mor- 

 phologically attached to each other. The advantages of the colony 

 are not always clear. In Protozoa, relationships of individuals in the 

 colony are not such as to guarantee nourishment for the entire 

 colony; thus there is no advantage in this respect with this phylum. 

 In the hydroid colonies, nourishment is better assured for the in- 

 dividual by the colonial form. The colony does not appear to be 

 formed necessarily because it is a more favorable adaptation to living 

 conditions but because of the failure of the different elements to 

 separate at fission. The tendency toward colony-building increases 



' Budded colonial forms, as among the hydroids, cannot be regarded as "accidental" 

 in the usual usage of that word. 



