288 Str as burger . — The Periodic Reduction of 
sions, to four cells, and so does the sperm-mother-cell 1 . But 
whilst the products of division are, in the latter case, all 
similar, each developing into a spermatozoon, in the former 
only one develops into a fertile ovum, the other three are 
polar bodies, that is, they are merely reduced ova. Whilst in 
plants a reduction in the number of the chromosomes takes 
place in an unmistakable manner in the nuclei of the mother- 
cells of the pollen and of the embryo-sacs, it appears, on the 
contrary, as if in the Nematodes a doubling of the number of 
chromosomes took place, in the first instance, in the mother- 
cells of the ova and spermatozoa. But this increase in the 
number of the chromosomes is only apparent, for it is de- 
pendent upon the fact that, in this case, the chromosomes for 
the two following divisions are provided by longitudinal split- 
ting before they have begun. The phenomenon is merely 
one of abbreviation : it is nothing more than the compression 
into one of the longitudinal splittings of the chromosomes 
attending two successive divisions. The reduction of the 
number of the chromosomes to one-half thus only becomes 
apparent in the spermatozoa, the ovum, and the polar bodies, 
although, as a matter of fact, it takes place in the mother- 
cells. 
But what is the significance of this reduction in number of 
the chromosomes in the sexual cells, and of the equality of 
their number in the male and female cells? The physio- 
logical utility of the arrangement readily suggests itself : for 
were it not so, the number of chromosomes in the nuclei of 
each generation would be twice as great as in the preceding ; 
and again, by this means each parent is represented in the 
offspring by an equal number of chromosomes, and thus 
equally transmits its hereditary characters. The morpho- 
logical cause of the reduction in number of the chromosomes 
and of their equality in number in the sexual cells is, in my 
opinion, phylogenetic. I look upon these facts as indicating 
1 The literature relating to this subject is cited in my work ‘ Schwarmsporen, 
Gameten, pflanzliche Spermatozoiden, das Wesen der Befruchtung,’ p. 151. 
