Chromosomes in Living Organisms . 315 
but the cytoplasm divides but once, and each half receives 
only one functional nucleus, whilst the remaining two nuclei, 
being superfluous, become disorganized.’ O. Hertwig thus 
compares the processes occurring in these zygotes with the 
reducing divisions in the mother-cells of the ova and sperma- 
tozoa of animals which he defines as follows 1 : 6 The essential 
feature of these divisions is that two closely related divisions 
follow each other in immediate succession, such that the 
second succeeds the first without an intervening resting-stage 
of the nucleus. Consequently the groups of nuclear segments 
resulting from the first division are immediately divided, 
without previous longitudinal splitting, into two daughter- 
groups. At the close of the second division the ripe ovum 
or spermatozoon receives only half so many nuclear segments, 
and, consequently, only half so much nuclein, as do the 
nuclei formed in an ordinary division in the same animal/ 
O. Hertwig thinks 2 that accurate counting of the nuclear 
segments in the various stages of division, would confirm his 
view that a reducing division takes place in the zygotes of 
the Desmids. If, however, my interpretation of the process is 
correct, then the reduction in the number of the chromosomes 
must take place at the commencement of the prophase of the 
nucleus of the zygote, and, as in so many other cases, its 
rapid division into four would be the consequence of changes 
undergone during the process of reduction. 
When the morphological value of the polar bodies of the 
ova of animals is correctly estimated, and when the com- 
parisons between the generative processes of animals and those 
of plants are accurately drawn, it becomes at once apparent 
how little justification there was for the attempt to find, in 
connexion with the ova of plants, structures which should 
correspond to the polar bodies of animals ; and how erroneous 
it was to regard the ventral canal-cells of Vascular Cryptogams 
and Gymnosperms as structures of this nature. This con- 
1 Loc. cit., p. 189 : see also Vergleich der Ei- und Samenbildung bei 
Nematoden, p. 65 of the separate copy. 
2 Loc. cit., p. 225. 
