Cell Division Hereditarily Equal 81 



successive blastomeric divisions the nuclei always remain 

 like the first, that of the egg from which they sprung. 



The contrary cases of the formation of half embryos, 

 or of incomplete embryos, after the separation or killing 

 of one of the two first, or of several of the first blasto- 

 meres, are found always and only in embryos rich in 

 deutoplasm, so that, as we have already seen, they cannot 

 afford any ground for the conclusion that the nucleus or 

 nuclei from which these incomplete embryos develop must 

 be different from the first nucleus, that of the egg. 



We shall examine in the following chapter the very 

 complex and untenable subsidiary hypotheses, to which 

 the partisans of unequal division have been driven, in 

 order to bring their principal hypothesis into accord with 

 experiments upon the isolation and displacement of 

 blastomeres, and also with other equally irreconcilable 

 processes, such as post-generation and regeneration. Here 

 we shall only quote and adopt the conclusion which Oscar 

 Hertwig has drawn from these experiments, namely : "It 

 is self-evident that such an interchange of blastomeres 

 without injury to the product of development, is possible 

 only if one nucleus has the same characters as the others, 

 that is, only if all the nuclei are produced from the seg- 

 mentation nucleus by hereditarily equal division." 51 



In order that this hereditarily equal division may be 

 materially possible in a germinal nucleus constituted by 

 innumerable, different, infinitely small particles, that is 

 in order to permit the division of each of these particles 

 or substances between the two daughter nuclei, it would 

 be sufficient that they become disposed during mitosis in 

 little transverse layers one over another in the various 



"Oscar Hertwig : Die Zelle und die Gewebe. Zw. Buch. P. 69. 



