IV.] FOUNDATION OF A THEORY OF HEREDITY. 



213 



of my theory, the presence of germ-plasm is indispensable for 

 this purpose. I do not see how we can escape the conclusion 

 that there is continuity of the germ-plasm ; for if it were 

 supposed that somatic idioplasm undergoes transformation 

 into germ-plasm, such an assumption would not explain why 

 the displacement occurs by small stages, and with extreme 

 and constant care for the preservation of a connexion with 

 cells of the ancestral area. This fact can only be explained 

 by the hypothesis that cell-generations other than those which 

 end in the production of the cells of the ancestral area, are 

 totally incapable of transformation into germ-cells. 



Strasburger has objected that the transmission of germ- 

 plasm along certain lines, viz. through a certain succession of 

 somatic cells, is impossible, because the idioplasm is situated 

 in the nucleus and not in the cell-body, and because a nucleus 

 can only divide into two exactly equal halves by the indirect 

 method of division, which takes place, as we must believe, in 

 these cases. ' It might indeed be supposed,' says Strasburger, 

 ' that during nuclear division certain molecular groups remain 

 unchanged in the nuclear substance which is in other respects 

 transformed, and that these groups are uniformly distributed 

 through the whole organism ; but we cannot imagine that their 

 transmission could only be effected along certain lines.' 



I do not think that Strasburger's objections can be main- 

 tained. I base this opinion on my previous criticism upon the 

 assumed equality of the two daughter-nuclei formed by indirect 

 division. I do not see any reason why the two halves must 

 always possess the same structure, although they may be of 

 equal size and weight. I am surprised that Strasburger should 

 admit the possibility that the germ-plasm, which, as I think, is 

 mixed with the idioplasm of the somatic cells, may remain 

 unchanged in its passage through the body ; for if this writer 

 be correct in maintaining that the changes of nuclear substance 

 in ontogeny are effected by the nutritive influence of the cell- 

 body (cytoplasm), it follows that the whole nuclear substance 

 of a cell must be changed at every division, and that no 

 unchanged part can remain. We can only imagine that one 

 part of a nucleus may undergo change while the other part 

 remains unchanged, if we hold that the necessary transforma- 

 tions of nuclear substance are effected by purely internal 



