CHAPTER THREE 



PHENOMENA WHICH POINT TO THE EXISTENCE OF A 



CENTRAL ZONE OF DEVELOPMENT HYPOTHESIS OF 



THE STRUCTURE OF THE GERMINAL SUBSTANCE. 



i. Phenomena Which Point to the Existence of a 

 Central Zone of Development 



The only group of organisms in which one can say 

 that the existence of a central zone of development is di- 

 rectly demonstrated is that of the unicellular organisms, 

 in which this zone is constituted by the nucleus. In 

 pluricellular organisms it is only indirectly that we are 

 able to arrive at the conclusion that the central zone 

 exists. 



Experiment has shown that the necessary and suffi- 

 cient condition for the ontogenetic development of the 

 Infusoria is the presence of a nucleus. This latter con- 

 stitutes therefore for them an effective central zone of 

 development and consequently ontogenesis consists in 

 them in a true and proper centroepigenesis. 



If one divides an amoeba or a rhizopod or an infuso- 

 rian already completely developed, into many pieces, that 

 one of these fragments which remains provided with its 

 nucleus though it be the smallest of all, is yet capable of 

 reproducing by new formation all the missing organs and 

 of developing again into a normal individual ; whereas the 



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