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.” °* 
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 
51Qscar Hertwig: Die Zelle und die Gewebe. Zw. Buch. P. 69. 
