Conclusions 309 
the functional stimulus acquires anew the power which 
it once had possessed in the ancestors of the existing 
species :—another proof that the functional and onto- 
genetic stimuli can act at the same time, that their 
actions can be added together, and that they must con- 
sequently be of the same nature. 
We can then draw the following conclusions: 
1. The essential similarity of the two stimuli, onto- 
genetic and functional, the reality of which the facts 
which we have just cited and a thousand others like 
them permit us to deduce, combined with the fact that 
external influences, upon which alone the functional 
stimulus depends, are generally lacking during the 
embryonal period, is sufficient even by itself to justify 
us in concluding that ontogenetic stimuli are nothing else 
than the reactivation and restitution of the functional. 
It constitutes thus at the same time a new argument in 
favor of the inheritance of acquired characters. 
2. This conception of development based upon the 
essential identity of the functional stimulus and the onto- 
genetic stimulus, and up till now at least only this con- 
ception, makes it possible to explain the ontogenetic facts 
without presupposing in any of the stages of development 
any phenomenon which is not a normal physiological 
phenomenon, of the very same nature as those mani- 
fested by the organism in the adult state. And it thus 
indicates that the whole of life, at every moment of it, 
preserves an absolute unity in its nature. 
3. Ontogeny finally appears to us in this way 
simply as @ continual functional adaptation, by the 
embryo, to the successive active modes of being of the 
central gone of development. 
Having thus set forth and explained the way in which 
