148 A Homogeneous Germ Substance Inadmissible 



those parts of the body which are independently and 

 hereditarily variable, we have thus an exact measure for 

 determining the number of the little vital particles which 

 must compose the germ plasm : they cannot be fewer." 



"We are then logically forced to assume that a special 

 element exists in the germ plasm for each of these pecul- 

 iarities, not because the inheritance of even the smallest 

 details is possible, but because each of these parts of the 

 body can have its variations inherited individually, each 

 by itself. If all men possessed a certain depression in 

 front of the ear, one could not conclude that because it 

 was hereditary, it must be represented in the germ plasm 

 by a special element * * * the fact which forces us 

 to accept this hypothesis is that all men do not possess this 

 depression, that we can imagine two people who resemble 

 each other in all other respects but of whom one pos- 

 sesses this depression and the other does not." 



This is then the great and only argument of all the 

 theories of preformistic germs. 



One cannot fail to see that it really possesses a very 

 great value against such theories as that of Spencer, \vho 

 supposes the germ plasm to be constituted by a homogene- 

 ous substance. In the almost complete darkness in which 

 we still find ourselves in respect to the nature and causes 

 of ontogenetic phenomena, there are very few things 

 which we can venture to call impossible. Nevertheless 

 the supposition which is implied in the epigenetic theories 

 of the Spencer type, namely, that a homogeneous germ 

 substance a little different chemically from an other, is 

 able to give rise to an individual quite identical with that 

 which the other substance produces, except for one little 



122 Weismann : Das Keimplasma, P. 72 74. 



