EFFECTS OF AMPHIMIXIS ON ONTOGENY 263 



give up the whole idea of the controlHng influence of the nuclear 

 substance were we to suppose that this apparatus actually directs 

 the process of division. The entire process of development of 

 the animal from the ovum depends so essentially on the rate of 

 division of the cells, that the nuclear substance could no longer 

 be considered to correspond to the hereditary substance if it 

 merely caused the visible ditTerentiation of the cell. But in 

 the Introduction I have already stated the reasons which 

 prove beyond a doubt that the nuclear matter actually contains 

 the primary hereditary constituents, and it follows from this fact 

 that there can be no question of a self-determination of the 

 apparatus for division. We must, in fact, suppose that the ulti- 

 mate structure of the cell-body, which is invisible to our eyes, 

 controls its entire growth as well as its method and rate of 

 division, this structure itself being controlled by the nuclear sub- 

 stance or idioplasm. Ultimately, therefore, everything depends 

 on the determinant of the cell ; and in the case of sexual 

 reproduction, the co-operation of the paternal and maternal de- 

 terminants determines the character of the cell, whether this char- 

 acter is visible or invisible. As every cell in the entire ontogeny 

 is, according to our view, controlled by one kind of determinant 

 only, irrespective of the fact whether it also contains other 

 determinants in a latent condition or not, the co-operation of 

 maternal and paternal determinants always determines the 

 character of the cell, and controls the development of the 

 individual as far as the influence of this cell extends. In spite 

 of its greater histological differentiation, a slighter influence is 

 therefore obviously exerted by one of the final cells in ontogeny, 

 — that is, one of the tissue-cells, — than by one of the first 

 four segmentation-cells, or by the primary cell of the entire 

 germinal layer, or, again, by any cell from which many and 

 various kinds of cells may subsequently arise. On the other 

 hand, w^e must not forget that each embryonic cell only 

 determines its oivii method of division, and not necessarily 

 that of its daughter-cells, and that consequently in these a new 

 counter-balance or co-operation of the paternal and maternal 

 determinants again takes place. 



The determinants which control the daughter-cells are, how- 

 ever, derived from the latent ids of the mother-cell, and it there- 

 fore essentially depends on the methods of division and on the 

 architecture of these ids as to which determinants are to control 



