FORMATION OF ANIMAL AGGREGATIONS 47 



symplasm, cell fusion, parasitism, and symbiosis. Obviously these 

 are real phenomena; but, as detailed information concerning the proc- 

 ess by which the cells or organisms come together is lacking, the fact of 

 their being together is no more evidence for the existence of a posi- 

 tive prototaxis than the separateness of other cells or organisms is 

 proof of the existence of a negative prototaxis. 



If we waive this objection to accepting the principle of prototaxis 

 as an all-inclusive explanation of all aggregations whether of cells or 

 of organisms, and proceed to examine the nature of prototaxis, we 

 find that, instead of a simple tropism which may be best understood 

 as a reflex action of an entire organism, prototaxis is a compound or 

 complex tropism which Wallin says cannot be analyzed. Certainly 

 we can recognize different elements, such as chemotropism, thigmo- 

 tropism, stereotropism, as well as reactions due to surface tension, 

 temperature, light, moisture, and electrical potential. In fact, such 

 an analysis indicates that WalUn's conception of prototaxis is merely 

 another name for the type of reactions referred to by many writers 

 as being instinctive, except that no one would ordinarily regard the 

 reaction of tissue cells as belonging in this category. Logically there 

 is no real reason why they should not be so regarded, but the usage 

 has been otherwise. 



Wallin's conception of the formation of aggregates, whether of 

 cells or of organisms, as being due to the expression of a fundamental 

 biological tendency or principle, has two merits. In the first place 

 it recognizes rightly that there is no logical line to be drawn between 

 the behavior of tissue cells forming an animal body and that of plants 

 or animals forming a close aggregation like those seen in symbiotic or 

 parasitic relations. This is in line with the conclusions of Espinas 

 and of Deegener, which I believe to be essentially correct, that 

 there is no hard and fast line that can be drawn between the 

 social and the infrasocial. Further, Wallin specifically recognizes 

 that the ideas that have developed about symbiosis and parasitism 

 have usually been based on the utility of the relationships and have 

 also involved the idea of purpose. When such phenomena are con- 

 sidered from the point of view of prototaxis, then parasitism and 

 symbiosis and presumably all their related phenomena are merely 



