FOUNDATION OF A THEORY OF HEREDITY. 209 



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 transforma- 

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

 why the displacement occurs 1^ 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 hypo- 

 thesis 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 sub- 

 stance 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 maintained. 

 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 

 transformations of nuclear substance are effected by purely internal 

 causes, viz. that they follow from the constitution of the nucleo- 



P 



