172 TROPISMS 



will be willing to admit that it is a forced movement or 

 an instinctive reaction. After the C0 2 has evaporated 

 the animals become indifferent to light, and while formerly 

 they had only one degree of freedom of motion they now 

 can move in any direction. In this case the motions appear 

 to be spontaneous or free, since we are not in a position to 

 state why Daphnia a moves to the right and Daphnia b 

 to the left, etc. As a matter of fact, the motion of each 

 individual is again determined by something but we do 

 not know what it is. The persistent courtship of a human 

 male for a definite individual female may appear as an 

 example of persistent will, yet it is a complicated tropism 

 in which sex hormones and definite memory images are 

 the determining factors. Removal of the sex glands abol- 

 ishes the courtship and replacing the sex glands of an 

 individual by those of the opposite sex may lead to a 

 complete reversal of the sex instincts. What appears as 

 persistent will action is, therefore, essentially a tropistic 

 reaction. The production of heliotropism by C0 2 in 

 Daphnia and the production of the definite courtship of 

 the male A for the female B are similar phenomena differ- 

 ing only by the nature of the hormones and the additional 

 tropistic effects of certain memory images in the case of 

 courtship. Our conception of the existence of "free will" 

 in human beings rests on the fact that our knowledge is 

 often not sufficiently complete to account for the orienting 

 forces, especially when we carry out a "premeditated" 

 act, or when we carry out an act which gives us pain or 

 may lead to our destruction, and our incomplete knowl- 

 edge is due to the sheer endless number of possible com- 

 binations and mutual inhibitions of the orienting effect 

 of individual memory images. 



