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." 43 

 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- 



43 Wilhelm Roux: Uber Mosaikarbeit und neuere Entwicklungs- 

 hypothesen. Anat. Hefte, Edited by Mcrkel and Bonnet, Febru- 

 arheft 1893. P. 320. Gesamm. Abhandl. Zw. Bd. P. 859. 



44 Wilhelm Roux: Uber Mosaikarbeit etc. Anat. Hefte, P. 320. 

 Gesamm. Abhandl. Zw. Bd. P. 859860. 



