THE GER>r-PLASM 69 



The construction of the whole body, as well as its differentia- 

 tion into parts, its segmentation, and the formation of its organs. 

 and even the size of these organs, — determined by the number 

 of cells composing them. — depends on this complicated disi 

 tegration of the determinants in the id of germ-plasm. The 

 transmission of characters of the ?nost general kind — that is to 

 say, those -which determine the structure of an animal as well as 

 those characterising the class, order, family, and genus to which 

 it belongs — are due exclusively to this process. The slight 

 differences only, namely those which distinguish species from 

 species, and individual from individual, depend partly on the 

 characters of the individual cells. De Vries has overlooked 

 this in his attempt to explain all the facts of heredity by the 

 theory of • /;//r<7-cellular " pangenesis. As was mentioned in 

 the • Historical Introduction" to this book, it must be borne in 

 mind that most of the ' characters ' of any of the higher forms 

 of life result not from the characters of the individual cells, 

 but from the way in which they are combined. On the other 

 hand, the construction of a living organism is not conceivable 

 unless we presuppose the determination of the characters of each 

 cell. 



We have therefore to give an explanation of this concluding 

 part of the process of ontogeny ; this has already been done to 

 a great extent above, in the section treating of the control of the 

 cell by the idioplasm. I there assumed, as de Vries has also 

 done, that this determination depends on the migration of minute 

 vital particles from the nucleus into the cell-body. We have 

 now seen by what means the biophors characteristic of any 

 particular cell reach that cell in the requisite proportion. This 

 results from the fact that the biophors are held together in a 

 determinant which previously existed as such in the germ-plasm, 

 and which was passed on mechanically, owing to its ontogenetic 

 disintegration, to the right part of the body. In order that the 

 determinant may really control the cell, it is necessary that it 

 should break up into its constituent biophors. This is an inevi- 

 table consequence of the assumed mode of determination of the 

 cell. We must suppose that the determinants gradually break 

 up into biophors when they have reached their destination. 

 THTs assumption allows, at the same time, an explanation of the 

 otherwise enigmatical circumstance, that the rest of the de- 

 terminants, which are contained in every id except in the last 



