THE GERM-PLASM THEORY 411 



but in descendants which arise from it by budding. This last case 

 occurs especially in the colonial hydroid polyps, which multiply by 

 budding. Here the primordial germ-cell is separated from the ovum 

 by a long series of cell-generations, and the sole possibility of 

 explaining the presence of germ-plasm in this primordial cell is to be 

 found in the assumption that in the divisions of the ovum the whole 

 of the germ-plasm originally contained in it was not broken up into 

 determinant groups, but that a part, perhaps the greater part, was 

 handed on in a latent state from cell to cell, till sooner or later 

 it reached a cell which it stamped as the primordial germ-cell. 

 Theoretically it makes no difference whether these 'germ-tracks,' 

 that is, the cell-generations which lead from the ovum to the primordial 

 germ-cell, are short or very long, whether they consist of three or six 

 or sixteen cells, or of hundreds and thousands of cells. That all the 

 cells of the germ-track do not take on the character of germ-cells 

 must, in accordance with our conception of the ' maturing ' of deter- 

 minants, be referred to the internal conditions of the cells and of the 

 germ-plasm, perhaps in part also to an associated quantum of somatic 

 idioplasm which is only overpowered in the course of the cell- 

 divisions. 



This splitting up of the substance of the ovum into a somatic 

 half, which directs the development of the individual, and a propaga- 

 tive half, which reaches the germ-cells and there remains inactive, 

 and later gives rise to the succeeding generation, constitutes the theory 

 of the continuity of the germ-plasm, which I first stated in a work 

 which appeared in the year 1885. Its fundamental idea had already 

 been expressed much earlier by Francis Galton (1872), without how- 

 ever being fully appreciated at the time or having any influence on 

 the course of science, and the same is true with the later theoretical 

 views of Jager, Rauber, and Nussbaum, all of whom reached the 

 same idea quite independently of each other, and sought to elaborate 

 it more or less fully. 



The hypothesis does not depend for support merely on a recogni- 

 tion of its theoretical necessity; on the contrary, there is a whole 

 series of facts which may be adduced as strongly in its favour. 



Thus, even the familiar fact that the excision of the reproductive 

 organs in all animals produces sterility proves that no other cells of 

 the body are able to give rise to germ-cells ; germ-plasm cannot be 

 produced de novo. An unmistakable corroboration of this, it seems 

 to me, is to be found in the conditions of germ-cell formation in the 

 medusoids and hydroid polyps, for here it is apparent that the birth- 

 place of the germs, that is, the place at which the germ-cells of the 



