134 Facts Compelling Us to Reject Pre formation 



this himself, as we have seen in the case of those with 

 double symmetry, are opposed on one side to simple 

 epigenesis because they show that between the two 

 organisms, even though they have so great a part of 

 the body in common there do not exist any general 

 reciprocal actions tending to make a single whole of the 

 two bodies, they are on the other side, also opposed to 

 pre formation, in that they demonstrate in the same man- 

 ner as do the experiments upon isolation of blastomeres, 

 the equipotency or qualitative identity of the two first 

 segmentation nuclei. 



And this equipotency is not limited only to the two 

 first but exists also in all the first blastomeric nuclei as is 

 demonstrated by the inverse phenomenon obtained by 

 Morgan of the formation of a single embryo from two 

 blastulas of Sphaerechinus which had grown together of 

 themselves. 106 



Finally preformation as we have said, is quite irrecon- 

 cilable with all the manifold processes of regeneration 

 without exception. 



Above all, Weismann interprets in fundamentally the 

 same sense as we, the experiments and observations of 

 Roux upon the peculiar regeneration constituted by the 

 postgeneration or completion of the half embryos which 

 we have so often mentioned. For they signify as he 

 himself admits, "that this completion took place by a kind 

 of cell infection, of such a nature that mere contiguity, for 

 example with ectoderm cells, caused the as yet undifTeren- 

 tiated cells of the side operated upon to become developed 

 into ectodermal cells, while similar contiguity with me- 



10<5 E. H. Morgan: The Formation of one Embryo from two 

 Blastulae. Arch. f. Entwicklungsmech. d. Org., 1895. Bd. II. Heft 

 I. P. 6571. 



