22 ANIMAL AGGREGATIONS 



lo. Synaporia are collections due to unfavorable conditions, as 

 when beetles are collected by the wind and deposited in beetle drifts 

 in the same way that snow is drifted. 



Krizenecky (1923) recognizes two different types of synaporia, 

 the passive and the active. The first are formed when the animals 

 are passively carried together, as by wind or wave action. The latter 

 are formed when animals faced with unusual disturbing con- 

 ditions collect together. Such aggregations may be noted in the 

 worm Enchytraeis humicolor, which ordinarily hves singly in the 

 soil but which aggregates into symphagia about decaying food ma- 

 terial. If the worms are placed in a dish of water, they aggregate 

 into larger or smaller masses with the worms closely intertwined. 

 Such clumped masses do not remain together; but after the group 

 is closely formed, there comes a disintegrating movement which re- 

 sults in the animals finally coming to rest scattered singly over the 

 bottom of the dish. The animals remain thus scattered as long as the 

 water is undisturbed. When subjected to renewed stimulation by 

 adding chemicals or by mechanically disturbing the water, another 

 aggregation cycle is set up. 



B. Heterotypical associations consist of collections of unlike species 

 which may occur for the reasons given above, and which may be 

 designated by adding the prefix hetero- to the proper term for the 

 homotypical aggregation, as: heterosymphagopaedium, heterosyncho- 

 rium, heterosyncheimadium, etc. Deegener recognizes also co-incuha- 

 tia, which are breeding aggregations of different species of birds, for 

 example, selecting a common, restricted nesting site. Finally he adds 

 symphoria, which are formed when one or more species of animals 

 settle upon another of different species, forming a heterotypical 

 aggregation without obvious mutualism or parasitism, and are weU 

 illustrated by the barnacles, hydroids, snails, bryozoans, and others 

 growing on the shell of an old horse-shoe crab {Limuliis poly pJiemiis) . 



chemicals, touch, gravity, and the like. Rather, it seems preferable to replace this cate- 

 gory by some such term as syntropia, meaning those collections which are brought about 

 by tropistic reactions to some environmental factor. Such collections occur, due to a 

 combination of elements, including that of a limited space into which tropistic reactions 

 lead animals to assemble and the incidental presence of numerous individuals in the 

 region at one and the same time. In all these collections there is this time factor 

 working; otherwise we could not recognize them as aggregations. 



