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 which 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 
