128 Facts Compelling Us to Reject Pre formation 



external or internal to the individual exert upon these 

 determinants a certain formative action. But if one 

 assumes that a certain formative action becomes thus 

 exerted upon each of the determinants by abnormal cir- 

 cumstances in their development, one must then assume 

 that a similar formative action is exerted upon each of 

 these same -determinants by the other parts of the organ- 

 ism when the development of these parts proceeds quite 

 normally. But what remains then of the preformistic 

 action of these determinants which should fashion the 

 organism like a piece of mosaic-work? 



The experiments of Born also, which, as we have 

 seen above, are absolutely opposed to simple epigenesis 

 are just as little reconcilable with preformation, because 

 they denote in general the epigenetic nature of the process 

 of growth. We need recall here only the union of 

 portions of different tadpoles ; for example, of the anterior 

 portion of one tadpole with the posterior portion of 

 another. 



In this latter case, if the anterior portion were limited 

 by a section passing through the medulla oblongata, while 

 the posterior portion had been obtained by a section 

 passing through the medulla spinalis, it would follow 

 that the two surfaces of amputation of the medulla 

 which ought to match exactly would present on the con- 

 trary unlike forms and surfaces. In spite of this a 

 short time after the two ends of the medulla were united, 

 the two half tadpoles having meanwhile continued their 

 development, they showed a union in which no angle 

 or sharp fault persisted but gentle curves of transition 

 were present instead. The two medullary canals went 

 over into one another also gradually and without inter- 

 ruption, so that one could no longer recognize the exact 



