THE GERM-PLASM THEORY 379 



cell multiplies into a large number of primitive germ-cells, or in the 

 multiplication of the blood-cells, or of the epithelial cells of a particular 

 region ; in short, whenever mother and daughter-cells have the same 

 developmental import, that is, when they are to become nothing more 

 than they already are. In all such cases a similar group of deter- 

 minants, or a similar single determinant, must in the nuclear division 

 penetrate into each of the two daughter- cells. 



It is in this way, it seems to me, that the determinants gain 

 entrance into the cells they are to control, by a regulated splitting 

 up of the ids into ever smaller groups of determinants, by a gradual 

 analysis or segregation of the germ-plasm into the idioplasms of the 

 different ontogenetic- stages. When I first developed this idea 

 I assumed that the splitting process would in all cases set in at the 

 same time, namely, at the first division of the ovum. But since then, 

 in the controversies excited by the theory, many facts have been 

 brought to light which prove that the ova of the different animal 

 groups behave differently, and that the splitting up of the aggregate 

 of primary constituents may sometimes begin later — but I shall return 

 to this later on. 



If we accept the segregation hypothesis, which is similar in 

 purport to that advanced by Roux as the ' niosaic theory,' it must strike 

 us as remarkable that the chromatin mass of the nucleus does not 

 become notably smaller in the course of ontogeny, and even ultimately 

 sink to invisibility. Determinants lie far below the limits of visibility, 

 and if there were really only a single determinant to control each cell 

 there would be no chromatin visible in such a case. This objection has 

 in point of fact been urged against me, although I expressly empha- 

 sized in advance the assumption that the determinants are continually 

 multiplying throughout the whole ontogeny, so that in proportion 

 as the number of the kinds of determinants lying within a cell 

 diminishes the number of resting determinants of each kind increases. 

 When, finally, only one kind of determinant is present there is a whole 

 army of determinants of that kind. 



It follows from this conception of the gradual segregation of the 

 components of the id in the course of development that we must 

 attribute to the determinants two different states, at least in regard 

 to their effect upon the cell in which they lie: an active state, 

 in which they control the cell, and a passive state, in which they 

 exert no influence upon the cell, although they multiply. From the 

 egg onwards, therefore, a mass of determinants is handed on by the 

 cell-divisions of embryogenesis, which will only later become active. 



My conception of the manner in which the determinants become 



