Connected Partial Embryos of Roux 115 
individuals may actually be any given piece whatever 
that is limited by a plane surface; and that in them the 
organs are nearly all present in their normal form up 
to the plane of reunion, just as if two symmetrical pieces 
had been cut away so as to leave two plane surfaces, 
from two twins, after they were fully developed and 
ready for birth, and the foetuses had then been united 
by the cut surfaces. This normal formation of defective 
organs up to any given plane of separation as, for 
example, the 8-shaped double cornea or double lens of 
the third eye common to both organisms, speaks likewise 
strongly in favor of a capacity of self-differentiation 
possessed even by parts of these organs, as the simul- 
taneous development of two structures united so exten- 
sively, to form bodies of which each is self centered, 
indicates directly the absence of the action of general 
reciprocal influences, connecting them into one whole.” 78 
We remark nevertheless in our turn that the evolu- 
tionistic theory does not in any way explain as Roux 
asserts, how the two organisms are limited by a plane 
surface which is perfectly symmetrical, rather than by 
any kind of irregular surface whatever. This theory 
merely shows that it is possible that the development of 
organs which differentiate themselves automatically, may 
be arrested at any given surface, without thereby dis- 
turbing the normal form of any of the remaining portions, 
not even in the neighborhood of the surface where 
development is arrested. But it does not explain why 
the surface of division must be a plane surface, and 
perfectly symmetrical in the two individuals. One 
should rather expect here a manifold reciprocal inter- 
Wilhelm Roux: Uber Mosaikarbeit etc. Anat. Hefte, P. 320. 
Gesamm., Abhandl. II. P. 859—860. 
