142 Facts Compelling Us To Reject Preformation 
“In caenogenetic regeneration, (and a fortiori when 
the regenerated part remains of abnormal conformation), 
one cannot but admit that certain double or multiplied 
determinants must be present beside one another in the 
germ plasm, some of them being destined to embryonic 
development, others to regeneration. These latter must 
have their interior forces and particularly their growing 
force so arranged in advance as to split off, either alone 
or together with neighboring determinants of regenera- 
tion, as reserve idioplasm, at the proper moment of 
development.” 116 
Epigenetic theories contain in themselves an imme- 
diate explanation of the well known fact that when a 
worm is cut in two, the anterior part regenerates the 
posterior while the posterior regenerates the anterior. 
Weismann on the contrary is forced to have recourse 
to the following artificial hypothesis: “As the two halves 
become always complete again, no matter at what place 
the worm is cut, it therefore follows that the cells situated 
in any particular transverse planes of the body are not 
merely provided with reserve determinants for generating 
in some planes the head, in others the tail, but every cell 
must be able to act in either way, according to whether it 
happens to lie anteriorly or posteriorly to this plane. In 
order therefore to explain the twofold reaction of these 
cells, and stick to our fundamental view,—which regards 
the cells concerned in regeneration, as arranged and con- 
trolled by forces lying within themselves, and not by any 
external directing power,—it seems to me that we must 
assume that each of them contains two different reserve 
determinants, one for reconstruction of the head, the 
*°Weismann: Das Keimplasma. P. 145—146, 147. 
