Functional and Ontogenetic Stimuli 303 
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.” 71° 
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, 
2°Roux: Der Kampf der Tcile im Organismus. P. 180—181. 
