304 Explanation of Inheritance 
whereas embryonal differentiations, on the other hand, 
take place without or almost without such differentiating 
stimuli, there is reason to believe that these results are 
produced in another way which, while undoubtedly con- 
trolled by natural laws, is nevertheless for the time 
incomprehensible by us. Consequently the essence of 
embryonic differentiation and its immediate physico- 
chemical causes are for the moment quite inaccessible to 
us.” 220 
Centroepigenesis, on the contrary, teaches us, as we 
have seen, that embryonic and functional differentiation 
are essentially the same. And in support of this view we 
may recall among others the following principal orders 
of facts: 
“All the organs which fulfill their specific function 
already in the embryo have there a life dependent upon 
stimulus (Reizleben) in proportion to this function.” 2?! 
This indicates that an organism in process of develop- 
ment may be at one and the same moment in the 
embryonic period in respect to some of its parts and in 
the functional period in respect to other parts, without 
ceasing for that reason to behave in all its manifestations 
as a whole of a thoroughly individual nature. 
A number of characters begin to develop embryon- 
ically which later require the help of the functional 
stimulus to complete their development: “In embryonic 
development some parts are ontogenetically formed and 
developed to a certain grade of functional capacity, which 
have been formed phylogenetically entirely by functional 
adaptation. Functional stimuli seem to be necessary only 
for that remainder of development which belongs from its 
"Roux: Ibid. P. 166. 
*=Roux: Der Kampf der Teile im Organismus. P. 182. 
