246 
A lien. — Nuclear Division in the 
which are comparable to those produced by a somatic division, the two 
mitoses must follow each other without an intervening stage of growth. 
This is the reason why the condition of distribution of the chromatin — 
the ‘ resting ’ stage — is commonly omitted between the heterotypic and 
homoeotypic divisions. In cases in which some time elapses between 
these two divisions (e. g. in the embryo-sac of Liliurn) the material of 
the chromosomes shows a tendency to pass into the usual distributed 
condition ; but that no growth occurs at this time is shown by the size 
of the chromosomes when they appear upon the homoeotypic spindle. 
It seems, then, that all of the characteristic peculiarities of the hetero- 
typic and homoeotypic mitoses result from the fact that the fusion of the 
hereditary substances contained in the parental germ nuclei, instead of 
being effected by the fusion of the germ-cells, is postponed until the close 
of the generation which results from the fusion of these cells. The fusion 
of the hereditary substances necessitates a further set of processes (the 
heterotypic mitosis) which shall reduce the mass of the chromatin in each 
segment of the fusion thread to that characteristic of the prophases of 
an ordinary mitosis. The period of growth which precedes synapsis, there- 
fore, may be thought of as belonging strictly to the prophases of the 
homoeotypic division, which have been interrupted by the occurrence 
of the fusion and the further processes necessitated by it. 
It must be remembered that we have no direct evidence that all 
the segments of one of the two daughter spirems produced by longitudinal 
fission pass finally into the same daughter nucleus. It is possible that it is 
entirely a matter of chance whether one or the other daughter segment of 
any particular chromosome shall pass into a particular daughter nucleus. 
The possibility of such variations, as already mentioned, has been con- 
sidered by Sutton (’03), and has served as a basis for an attempt to 
harmonize his conception of chromosome reduction with Mendelian results 
in hybridization. On the other hand, the regularity of the processes leading 
to the separation of the chromosomes in this and in other divisions, and 
the elaborateness of the mechanism devised apparently for the securing of a 
very definite result, make it seem unlikely that the element of chance should 
play so large a part in this or in any other mitosis. It seems to me much 
more probable that each daughter thread resulting from the longitudinal 
splitting contains the chromatic substance destined for one of the daughter 
nuclei, and that the phenomena of chromosome reduction in the lily offer 
an explanation of the experimental facts without involving the hypothesis 
of a chance distribution of the chromosomes between the daughter nuclei. 
The Distribution of Parental Characters to the Germ-cells. 
In respect to the nature of the germ-cells produced by the heterotypic 
and homoeotypic divisions, there is an important difference between the 
