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 a continual functional adaptation, by the 

 embryo, to the successive active modes of being of the 

 central zone of development. 



Having thus set forth and explained the way in which 



