Significance of Tropisms for Psychology 61 



indicate that the role ascribed to symmetry has no importance 

 for the theory of tropisms. I am, however, inclined to draw 

 another conclusion, namely, that in the fiddler crabs in the 

 first place there is an entirely different connection between the 

 retina and the locomotor muscles from that in other crustaceans, 

 and that, secondly, there is a special peculiarity in regard to 

 the function of the two retinae whereby they do not act like 

 symmetrical surface elements. I believe that a new discovery 

 may be made here.^ 



XI 



These data may suffice to explain my point of view. To me 

 it is a question of making the facts of psychology accessible 

 to analysis by means of physical chemistry. In this way it is 

 already possible to reduce a set of reactions, namely, the tro- 

 pisms to simple rationalistic relations. Many animals, because 

 their body structure is not only morphologically, but also 

 chemically, symmetrical, are obliged to orient their bodies in 

 a certain way in relation to certain centers of force, as, for in- 

 stance, the course of light, an electric current, the center of 

 gravity of the earth, or chemical substances. This orientation 

 is automatically regulated according to the law of mass action. 

 The application of the law of mass action to this set of reactions 

 is thus made possible. I consider it unnecessary to give up 

 the term *' comparative psychology," but I am of the opinion 

 that the contents of comparative psychology will under the 

 influence of the above-mentioned endeavors be different from 

 the contents of speculative psychology. But I believe also 

 that the further development of this subject will fall more to 

 the lot of biologists trained in phj^sical chemistry than to the 

 specialists in psychology or zoology, for it is in general hardly 



1 From which. I expect, furthermore, that they will only confirm still more 

 the laws of heliotropism. This expectation is based upon analogous relations in 

 the pleiironectids, which I cannot, however, discuss further here. However, 

 probably no one will maintain that the existence of the pleiironectids invalidates 

 all laws in regard to the symmetrical body structure. 



