CLASSIFICATION OF ANIMAL AGGREGATIONS 21 



isolation of four days. Marked sympaedia, some of which differed 

 from each other in size of individuals, fused to a single sysympae- 

 dium. When this divided late, the resultant groupings usually con- 

 tained members derived from different original sympaedia. 



3. Sympolyandria are accidental polyandric associations formed 

 on a sjTichoric basis, as that of Alcippe, a barnacle which dwells on 

 the deserted snail shells occupied by hermit crabs, forming an ac- 

 cidental hetero typical association; but the barnacles, considered 

 alone, form a sympolyandria. Polyandria form a type of essential 

 mating society to be discussed later in this outline. 



4. Synchoria are locality aggregations formed primarily because of 

 a limited expanse of particularly favorable locations for living. Bar- 

 nacles gathered together on available rocks are a good example. 



5. Syncheimadia are hibernating aggregations, such as those of 

 snakes or salamanders. 



6. Synhesia are swarming aggregations under the influence of the 

 breeding season, as illustrated by palolo worms. Factors concerned 

 here include the simultaneous ripening of the sex cells, a limited 

 favorable area, and the correct external conditions,' which are fre- 

 quently associated with lunar rhythms. Similarly, the swarms of 

 May flies are due at least in part to simultaneous pupation rather 

 than to sex attraction. 



7. Symphagia are aggregations about a favorable food supply, as 

 flies collect about carrion or sugar. Here there is no obvious benefit 

 from the association. 



8. Symporia are migration aggregations joined either because they 

 originated in the same place or because they are going in the same 

 direction, and may be illustrated by the migrating masses of fiddler 

 crabs, of butterflies, or of salmon. 



9. Symphotia^ occur when the aggregations collect about a source 

 of fight. Such a reaction is given by a great many insects, as well as 

 by other animals (Mast, 191 1). 



' Considerations given later, particularly in chapters xvi and xvii, indicate that such 

 swarms have a rather obvious survival value and hence should not be placed among the 

 "accidental" groupings. 



^ If this type of category be included, it is necessary to include similar headings for 

 tropistic collections due to the reaction to other environmental factors, such as heat, 



