Functional and Ontogenetic Stimuli 363 



stimuli, but they do determine them. External influences 

 and functional stimuli are two special forms of energy, 

 the first of which can transform itself into the second, 

 but they are fundamentally different from each other. 

 The one is inorganic, the other biologic and vital in 

 nature. And the designation "functional stimulus" 

 properly applies to the external action, in so far as, and 

 at the moment when, it transforms itself into vital 

 energy. The possibility of a substantial identity between 

 the functional stimulus and the ontogenetic stimulus can 

 obviously exist only in case the former is understood in 

 this way. 



That being disposed of, it becomes worth while to 

 recollect that Roux distinguishes embryonic life and adult 

 life as two things of totally different nature: "In the 

 life of all parts (of the organism) two periods must be 

 distinguished : an embryonic period in the widest sense 

 in which the parts develop, differentiate, and grow of 

 themselves, and an adult period in which growth, and in 

 many parts indeed, the complete replacement of material 

 used up, goes on only with the co-operation of stimuli. 

 These stimuli might thus give origin to something new 

 which, if it were produced in this manner throughout 

 several generations, would become hereditary, that is, be 

 formed without these stimuli in the descendant, and be- 

 come thus in our sense embryonal/' 219 



These two periods characterized respectively by 

 embryonic differentiations and by functional changes are 

 regarded by Roux, as we have said, as essentially differ- 

 ent : "Since the changes going on in adult men, are pro- 

 duced only by means of external transforming influences, 



219 Roux: Der Kampf der Teile im Organismus. P. 180 181. 



