287 
Chromosomes in Living Organisms. 
sac-mother-cell is therefore constructed of twenty-four chromo- 
somes: yet in the next prophase it nevertheless uniformly 
gives rise to only twelve chromosomes. In connexion with 
this reduction the nucleus does not undergo any diminution 
either in size or in mass : on the contrary, those nuclei in 
which the reduction in the number of the chromosomes takes 
place are remarkable for their size and for the abundance 
of chromatin which they contain. I contrasted, also in 
Liliiim , the cell which gives rise to the embryo-sac with 
the mother-cells of the pollen ; but it must be borne in 
mind that in L ilium , as in Tulip a and Fritillaria , this cell 
develops directly into the embryo-sac without undergoing 
that division which, in other cases, distinguishes the cell as 
a mother-cell. Hence these observations left open the 
possibility that the reduction in the number of the nuclear 
chromosomes might take place in the young embryo-sac and 
not in the mother-cell of the embryo-sac. I have, however, 
succeeded 1 in determining that the reduction of the chromo- 
somes to eight or twelve in the embryo-sac-mother-cells of 
the ovules of Allium and Helleborus respectively, takes place 
before they have undergone their characteristic divisions. 
Hence the cell of L ilium , in which the reduction in the 
number of the chromosomes takes place, must undoubtedly 
be regarded as an embryo-sac-mother-cell, the course of 
development being abbreviated. The successive divisions 
of this cell, in those cases in which they actually take 
place, give rise, in addition to the embryo-sac, only to re- 
duced cells which are immediately compressed and absorbed. 
The idea suggested by Biitschli 2 that the polar bodies of 
animals may be reduced ova was definitively established by 
O. Hertwig’s 3 comparative investigation of the development 
of the ova and spermatozoa of the Nematodes. The mother- 
cell of the egg in animals gives rise, by two successive divi- 
1 Ueb. Kern- und Zell-Theilung, p. 243. 
2 Gedanken iib. die Morphol. Bedeutung der sogenannten Richtungskorper, 
Biol. Centralbl., IV, p. 5, 1884. 
3 Archiv filr mikr. Anat, Bd. 36, 1890. 
