CONCLUSION. 253 



and it still remains to test the theory in all its 

 applications. It opens up a new method of explor- 

 ation. Its bearing on psychological problems seems 

 especially important, as having to do with the 

 development of mind, and there seems to be a 

 new field opened in the direction of comparative 

 psychology. I have not attempted to include this 

 investigation in the present work, and what little 

 I have indicated in this line is not meant to be 

 applied in a materialistic sense to explain or sug- 

 gest the nature of mind. 



It may be objected that by using psychic pro- 

 cesses and properties of living matter as means of 

 explanation of heredity, I have departed from the 

 modern purpose of natural science, which is to give 

 a mechanical explanation of the universe. But I 

 have in this only anticipated the conclusion which 

 all biological facts render most probable, that psychic 

 processes have always their physical counterpart. 

 When physiological psychology can discover and 

 express the exact inter-relation of the physical and 

 the psychical, then general biology can make use of 

 the expression ; but meantime it were foolish to neg- 

 lect the facts of psychology. Even though arrived at 

 indirectly, we can accept no other conclusion than 

 that all evolution, psychic and organic, is a definite 

 causal series. The theory here given seems to em- 



