Centroepigencsis vs. Preformation and Epigenesis 17 
germinal substance, and one suspects at once that it may 
be just this substance which constitutes the central zone. 
If so it would follow that the central zone must be at 
the same time the germinative zone, that is to say, the 
place whence the sexual cells get the germinal substance 
which makes them capable of reproduction. Let us 
hasten to add now that the central zone must coincide 
with the effective germinal zone, but may possibly be quite 
separate and distinct from the apparent germinal zone. 
The latter would be then only the place of formation of 
the sexual cells, inasmuch as these constitute in a certain 
sense the mere envelope in which later the germinal sub- 
stance is assembled, which alone is able to give them 
reproductive capacity. 
The hypothesis of centroepigenesis includes then that 
of a continuous action exercised by the germinal sub- 
stance upon the soma throughout the whole duration of 
its development. We shall endeavor in the second chapter 
to learn what is the nature of this action and we shall 
reserve for consideration in the third chapter the central 
zone itself, as well as other facts and arguments which 
make its existence seem probable and which serve to make 
the hypothesis clearer. 
We shall limit ourselves here to putting in special light 
the fundamental characteristics which differentiate this 
hypothesis as well from the preformistic as from the 
epigenetic theories. 
While Weismann and the preformists in general con- 
sider that the germ plasm separates itself before the com- 
mencement of development from the portion set apart to 
form the new organism, and remains passively aside in a 
detached part of the soma until it later steps in to form 
the future sexual cells; consequently it would not control 
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