man is not determined by examining the tails of 

 the subsequently conceived mice. 



7. The idea that the power of an organism 

 is a function of its structure is the same fallacy 

 that resides in the mind of a man who tries to 

 make a perpetual motion machine. That man 

 thinks that if he can get the proper structure he 

 can get unlimited power for nothing. 



A race is made up of individuals, and improve- 

 ment of the race consists in improving the in- 

 dividuals which compose it. The improvement of 

 an individual consists in developing (increasing) 

 some one or more of his powers. An individual 

 can come into possession of such an improvement 

 only by exercise or by inheritance. But an in- 

 dividual cannot inherit from parents something 

 which those parents did not have, and those par- 

 ents could come into possession of the improve- 

 ment only by exercise or by inheritance. Unless 

 we are to accept spontaneous generation, or spe- 

 cial creation, for the form of improvements here 

 under consideration, we have to accept the idea 

 that powers developed by exercise in one genera- 

 tion are inherited by the next. 



xi 



