134 Facts Compelling Us to Reject Preformation 
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 
preformation, 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.1°¢ 
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 undifferen- 
tiated cells of the side operated upon to become developed 
into ectodermal cells, while similar contiguity with me- 
106K H. Morgan: The Formation of one Embryo from two 
Blastulae. Arch. f. Entwicklungsmech. d. Org., 1895. Bd. II. Heft 
1. P. 65—71. 
