68 Indications of a Central Zone of Development 
latter is not at all bound up by reciprocal actions with the 
absent parts, and also that it is not accomplished by the 
reciprocal action of parts of the whole organism.” #% 
These conditions are just those existing in a centro- 
epigenesis with ramifying and independent networks of 
correlation. 
The formation of double monsters with double 
symmetry in the disposition of their organs is particularly 
in accord with centroepigenesis. Concerning this Roux 
expresses himself in this way: “In these double forma- 
tions the fragment which is lacking in a symmetrically 
similar manner from each of the two individuals, can be 
any selected piece limited by a plane surface; and in them 
the organs are nearly all present and normal in form up 
to the plane of union, as if from two embryos, fully 
developed and ready to be born, one had cut off two 
symmetrical pieces so as to leave plane surfaces, and the 
twins had then been reunited by the cut surfaces.” “The 
simultaneous development of two formations so exten- 
sively united, into two distinct bodies, of which each is 
centered in itself, indicates directly that there are not any 
general reciprocal actions operating to combine them into 
a single whole.” 44 
According to the centroepigenetic hypothesis, the 
formation of these monsters would be due to the fact that 
the two blastomeres concerned, which are quite identical 
with each other since they arise from the segmentation of 
one and the same egg, have become, on account of ab- 
‘“Wilhelm Roux: Uber Mosaikarbeit und neuere Entwicklungs- 
hypothesen. Anat. Hefte, Edited by Merkel and Bonnet, Febru- 
arheft 1893. P. 320. Gesamm. Abhandl. Zw. Bd. P. 859. 
44Wilhelm Roux: Uber Mosaikarbeit etc. Anat. Hefte, P. 320. 
Gesamm. Abhandl. Zw. Bd. P. 859—860. 
