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THE A ME UK AX X A TUB ALT ST [Vol. xliii 



such a way that it leaves the region where these changes occur. 

 It was here that I pointed out especially that for each step "an 

 adequate objective cause exists." These relations, which Bohn 

 neglects, are fundamental both for an understanding of the con- 

 cept under discussion, and for any real understanding of be- 



2. The same causes that prevent Bohn from understanding 

 what I meant by "trial and error" equally prevent him from 

 understanding my criticism of the tropism theory. He says: 



Jennings, from lack of having made the distinction between tropism 

 ;ui<l sc!]>il)ility to differences, has been led to criticize, in an unjust 

 manner, the tropisms of Loeb (p. 173). The notion of sensibility to 

 differences has escaped Jennings; this investigator made the mistake 

 of confounding it with that of tropisms, etc., etc. (p. 179). 



Xow. my reason for criticizing the application of the theory 

 of tropisms was precisely because I did make the distinction 

 Bohn speaks of. I dealt with a question of fact. The reac- 

 tions of the organisms I studied had been commonly designated 

 tropism (or taxis) and I used the same term until I had shown 

 clearly what the nature of the reaction was. Then, being in- 

 terested in the facts of behavior, I made an analysis showing that 

 as a matter of fact the behavior did not consist of tropisms. that 

 "the theory of tropisms is not of great service in helping us to 

 understand the behavior of these lower organisms."- 4 I can 

 readily understand how it might be held that the theory is of 

 service for certain reactions, but it is hardly worth while to 

 attack my presentation on such mistaken ground as that I did 

 not distinguish tropisms from reactions to variations in the 

 environment. I have set forth in full my position on the 

 tropisms in a recent paper, 23 so I may pass over it here. There 

 is little in Bohn's impassioned defense of the tropisms that I 

 could not assent to in principle; though I might object to the 

 application to particular cases, and especially to the views which 

 he attributes to me on the matter. 



Points with which I could warmly agree are the following: 

 He warns against "the deplorable results into which authors 

 have been led by adopting the view according to which there 

 would be tropisms everywhere" (p. 241). He says that "the 

 activity of lower animals is composed of complex elements; 



u " The Theory of Tropisms," Pub. Cam. Inst., 16, 1904, p. 105. 



23 " The Interpretation of the Behavior of the Lower Organisms," 



