128 Facts Compelling Us to Reject Preformation 
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 
