72 DEVELOPMENT AND HEREDITY. 



stimulus has been removed the reaction still con- 

 tinues. Such cases are particularly interesting, as 

 they show that a very simple organism without 

 any visible nervous structures, when accustomed 

 to performing certain actions as a result of external 

 forces, will still continue to perform those actions 

 frofn force of habit, after the external forces have 

 been withdrawn. This is illustrated in the experi- 

 ments described in the following passages from 

 Professor Detmer's paper. (I begin the quotation 

 with his introductory remarks, because they seem 

 to me so very significant, and are so harmonious 

 with my own views.) "For many years I have 

 entertained the conviction — which forced itself upon 

 me first in 1876 on the occasion of my investigations 

 of the periodicity of the root-pressure upon the sap 

 — that the phenomena of after-effects or subsequent 

 reactions {Nachwirkiitigsphdnomene) differ only in 

 degree and not in their essential nature from the 

 phenomena of inheritance, — a view which may 

 become the starting-point for investigations of 

 heredity. Of course the after-effects play their 

 part only in the individual life of an organism, 

 whereas heredity stretches out its grasp over the 

 individual life and onward to the next generation ; 

 but nevertheless the essential similarity of the two 

 classes of phenomena cannot escape the attentive 

 observer. 



