98 Hypothesis of Structure of Germ Substance 



itself felt. This process corresponds essentially to that 

 described in the above mentioned researches on the trans- 

 position of the blastomeres, in which the latter were com- 

 pressed for example between two plates and so all com- 

 pelled to lie in the same plane. But when the pressure 

 ceased they resumed at once their normal disposition. 

 Each of these two processes constitutes another proof 

 of the self -regulating capacity or elasticity of devel- 

 opment which finds in centroepigenesis its most simple 

 explanation. 



Centroepigenesis implies further, as we have seen, that 

 the distribution of nervous energy in each stage of de- 

 velopment forms in itself a system in complete dynamic 

 equilibrium, which becomes disturbed and replaced by an- 

 other system in equilibrium, only through the activation 

 by the central zone of a new specific potential element. 

 This is the conception from w r hich as a starting point we 

 have built up our hypothesis. 



It follows that if the activation of the specific potential 

 elements successive to any given stage is prevented 

 through certain abnormal circumstances, development will 

 stop without thereby causing the organism thus remain- 

 ing behind in an earlier ontogenetic stage, to cease to 

 form a dynamic system in complete equilibrium. 



Such transitory or permanent arrests of development 

 are extremely numerous, much more numerous than com- 

 monly believed. All the phenomena called atavistic rever- 

 sion belong in this category. Metamorphoses also, with 

 the exception of certain characteristic and remarkable 

 phenomena which have been added later, are only similar 

 arrests of development, which proceeds at once on its 

 course as soon as external conditions, and with them also 



