Continuous Formative Influence 23 
by differentiated cells upon other less differentiated cells 
which are immediately adjacent to them.” 
“In the latter process very different degrees of action 
are possible. There can, for example, emanate from the 
differentiated cells an influence which simply sets free 
the process of differentiation allowing the entire series 
of necessary changes after this preliminary impulse to 
proceed of itself. Or, each of these changes may not 
merely receive from the differentiated cell a simple 
initial impulse, but may on the contrary be determined 
by that throughout. Between these two extremes one 
can imagine a whole series of intermediate stages. On 
account of the at first atypical disposition of the material 
which at last becomes typically differentiated I am 
inclined to think that the action of the differentiated cells 
upon the nondifferentiated cells is not a mere liberating 
one or a mere stimulating one.” ® 
These facts of postgeneration indicate then above all 
that the action of the half embryo already formed upon 
the other half in process of formation is exercised in a 
continuous manner throughout the whole development 
of this latter. 
One would be led also to this conclusion, that there 
is a continuous action exercised throughout the whole of 
development, by the fact that the postgeneration of the 
undeveloped half goes on with greater rapidity, so that 
it soon overtakes the other half and proceeds with it to 
the same stage of development. 
Wilhelm Roux: Uber die kiinstliche Hervorbringung ,,halber“ 
Embryonen durch Zerstorung einer der beiden ersten Furchungszellen, 
sowie iiber die Nachentwicklung, Postgeneration der fehlenden 
Kérperhalfte. Virchows Archiv, Bd. 114. October 1888, P. 279—28z. 
Gesamm. Abhandl., Zw. Band. P. 507—509. 
