184 FOOT-NOTES TO EVOLUTION. 
that no reducing division in Weismann's sense takes 
place, though the actual number, of the chromosomes is 
also reduced. 
Boveri has shown for the egg and Brauer for the 
sperm that the tetrads arise by a double, longitudinal 
splitting of the chromatin filament which later breaks 
into two segments. Thus adcd would again represent 
the unsegmented filament, a-d-c-d the individual chromo- 
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dinary division. In the maturation of the egg and in 
spermatogenesis, however, the thread segments into ad, 
cd, and splits twice longitudinally into a. = 2s the 
two tetrads of Bin Fig. 11. The reduction of chromatin 
here is only a reduction in mass and not a qualitative 
one, in Weismann’s sense, as in the Crustacea and in- 
sects. In Ascaris the actual reduction in number of 
chromosomes takes place in the nucleus previous to the 
maturation divisions of the ovocyte and spermatocyte 
respectively. In Cyclops the formation of the tetrads is 
merely a pseudo-reduction, the actual reduction taking 
place in the second division which gives rise to the ma- 
ture egg on the one hand, or to the spermatids, which 
develop into the spermatozoa, on the other. 
One fundamental fact is clear in these divergent 
accounts. The number of the chromosomes is reduced 
in both sorts of the germinal cells as a preliminary to 
their union. Whether there is likewise a guaditative dis- 
tribution of the chromatin elements remains for future 
investigation to decide. 
From the facts of ordinary cell division we have seen 
the probability of the hypothesis that the chromatin of 
the nucleus is to be regarded as the bearer of hereditary 
qualities in the cell. The phenomena of fertilization 
somes, and & their splitting longitudinally in or- 
