20 THE BIOLOGICAL PROBLEM OF TO-DA Y 



nervous system, and so forth, until there are sepa- 

 rated the germs for all the separate organs, and for 

 the production of the minutest histological differ- 

 entiation.' 



Weismann calls the diverging nuclearplasms into 

 which the primitive germplasm is gradually trans- 

 formed histogenous, because they determine the 

 specific characters of the tissues. He assumes that 

 the primitive, original germplasm has a most com- 

 plicated molecular structure, while the histogenous 

 nuclearplasms for tissue-cells, like muscle-cells, 

 nerve-cells, sense-cells, gland-cells, and so forth, 

 have relatively simpler structures. As, during the 

 growth of the embryo, the germplasm becomes 

 transformed into the histogenous plasms, its mole- 

 cular structure becomes simpler in proportion to 

 the fewer different possibilities of development each 

 separated portion of it comes to contain. 



Following out this chain of ideas, Weismann 

 attributes only to those cells which contain un- 

 altered germplasm the power of giving rise to 

 complete new individuals, while cells with histo- 

 genous nuclearplasm, whether these be embryonal 

 cells or cells of the ectoderm or of the endoderm, 

 he regards as having lost this capacity, because 

 nuclearplasm of a simpler molecular structure 

 cannot retransform itself into that with the more 

 complicated structure. The further conclusion is 

 necessary that a part of the nuclearplasm of the 

 original nucleus of the fertilised egg- cell must 

 remain unaltered throughout the various nuclear 

 divisions, although it may be mingled with the 



