442 HEREDITY AND DEVELOPMENT 



cell and a purely nutritive cell, and so on, it seems legitimate 

 to suppose that corresponding differential divisions on a finer 

 scale go on in the course of development. The embryonic 

 cells go on dividing into daughter-cells having dissimilar deve- 

 lopmental import or prospective value, and " such differential 

 divisions will continue to occur until the determinant archi- 

 tecture of the ids is completely analysed or segregated out into 

 its different kinds of determinants, so that each cell ultimately 

 contains only one kind of determinant, the one by which its 

 own particular character is determined. This character, of 

 course, consists not merely in its morphological structure and 

 chemical content, but also in its collective physiological capacity, 

 including its power of division and duration of life " (1904, 

 vol. i. p. 378). 



It goes without saying that development also includes many 

 integral divisions. Cells are continually producing their like, 

 especially when there are numerous similar organs or parts in 

 the organism. It must also be noted that the segregation- 

 process cannot be pictured unless we suppose that the deter- 

 minants being alive can multiply among themselves, so that 

 a cell dominated by one kind of determinant may contain a 

 whole army of determinants of that kind. We must also suppose 

 that determinants may remain for a long period in an inactive 

 state, and that it is only when they find themselves in an ap- 

 propriate environment, largely determined by the cellular 

 neighbourhood, that liberating stimuli awaken them to their 

 controlling power. 



The Breaking -up of the Determinants. The segregation 

 or distribution of the determinants goes on, and each unit-area 

 or cell of the developing organism becomes the seat of a particular 

 kind of determinant or of a contingent of these. What then 

 happens ? Weismann supposes that the determinant, having 

 attained mature strength and its appropriate environment, 

 breaks up into the biophors which compose it, and that these 



