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. 859860. 



