116 DEVELOPMENT AND HEREDITY. 



number of times it has reacted to the series of 

 stimuli which make up an individual life, the con- 

 clusion follows, that in the latest generation the 

 associations will be strongest and the co-ordinations 

 most complex. This latest generation, owing to 

 its more complex constitution thus acquired, will be 

 affected by the same unchanged forces in a manner 

 slightly different from the manner in which each of 

 its predecessors was affected. The repetition neces- 

 sitates that there will be a new element — i.e. the 

 change in the internal resistance — added to the 

 stimuli affecting each successive generation. The 

 same unchanged forces of environment tend thus to 

 produce new effects and increase the complexity of 

 constitution in each generation. 



As the difference between two successive genera- 

 tions depends on the fact that the later generation 

 has performed the series of reactions constituting 

 development one time more than the preceding 

 generation, it is evident that the difference between 

 the two will be most pronounced when the later 

 generation has almost finished its round of develop- 

 mental reactions. Therefore at this period in the 

 life of the second generation, — when the organ- 

 ism is approaching maturity, — the element in the 

 stimuli which is caused by the change in the rela- 

 tion between the unchanged external forces and the 



