58 Indications of a Central Zone of Development 
To one or other of these conclusions, either to the 
presence of an undetected micronucleus or to the pos- 
thumous action of the nucleus, one is necessarily driven, 
as we said, by the fact that only the nucleated fragments 
of an infusorian already completely developed, are capable 
of regeneration. For this capacity of reorganization, 
as one may call it, of the protoplasmic substance, 
which gives to it again the form of the complete 
individual but of correspondingly smaller size, cannot 
possibly arise either from the properties of this sub- 
stance itself or from its specific “physiological units” for 
which the adult form of the individual would constitute 
the only state of equilibrium. This is quite impossible 
because a mass of protoplasm as large as the nucleated 
part, but which contains no nucleus, does not manifest the 
slightest tendency to regenerate, although it is capable of 
surviving its ablation for several days. The impulse 
tending to produce the specific form of the ordinary 
equilibrium is present only when the nucleus is not 
lacking. 
Nevertheless the material which disposes itself in this 
definite specific form of equilibrium is not the nuclear ma- 
terial but the protoplasmic. The nuclear substance with- 
out participating itself in the process of reorganization, 
merely provokes it in the protoplasmic substance, which in 
this respect remains totally indifferent. This is dem- 
onstrated among other things by the observation of 
Gruber that the four nucleated fragments into which one 
individual was cut by a transverse and a longitudinal in- 
cision required in all cases the same time to regain their 
complete specific form including the adoral ciliated zone. 
The anterior end which already contained a portion of it 
and which one would suppose to be better adapted in its 
