142 Facts Compelling Us To Refect Pre formation 



"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 



116 Weismann : Das Keimplasma. P. 145 146, 147. 



