THE EARTHWORM AND THE METHOD OF TRIAL 



L. H. BITTNER, G. R. JOHNSON, AND H. B. TORREY 



Reed College, Portland, Oregon 



About ten years ago Jennings attempted to clarify existing 

 conceptions of the behavior of the lower organisms by sub- 

 stituting for what he believed to be an inadequate theory of 

 tropisms a conception that rested on what has come to be 

 known as the " method of trial." 



Tropism hypotheses have existed at various times that have 

 differed in various respects. There is no doubt that in one 

 respect or another, some of these hypotheses have been open 

 to just criticism. That the method of trial affords an escape 

 from such criticism, however, is becoming less and less apparent 

 with the passage of time. 



Notwithstanding their differences, all tropism hypotheses 

 agree in excluding the conception of orientation by trial reac- 

 tions. Fundamental to them all is the conception of orienta- 

 tion by means of movements that, with reference to a given 

 source of stimulation, are predictable as to direction. However 

 cogent, then, the criticism of a particular variety of tropism 

 hypothesis in other respects, it can hardly affect the funda- 

 mental characteristic which they all possess in common. 



Some months ago, an analysis of the behavior of Porcellio 

 scaber showed that the method of trial was incompetent to inter- 

 pret the orientation of this organism under photic stimulation. 1 

 In the present paper we shall consider the orientation, under 

 similar stimulation, of the earthworm (Allolobophora sp.), an 

 organism of some complexity -of structure, whose behavior has 

 seemed to some observers to lend support to the method of 

 trial. These critics have based their conclusions in part on 

 observations, 2 in part on the identification of "random" with 



1 Torrey and Hays. The Role of Random Movements in the Orientation of 

 Porcellio scaber to Light. Jour. Animal Behav., 1914, 4, p. 110. 



2 See especially Holmes. The Selection of Random Movements as a Factor in 

 Phototaxis. Jour. Comp. Neur. Psych., 1905, 15, p. 98. 



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