3 1 2 Slrasburgcr — The Periodic Reduction of 
double division which takes place in the mother-cells of the 
spermatozoa, and of the ova in connexion with the develop” 
ment of the sexual cells in animals, may not be interpreted as 
indicating the existence of a distinct generation. The remark- 
able uniformity presented by the double divisions in the 
development of the sexual cells of animals is unfavourable to 
the assumption that the product of the double division 
represents what remains of a once independent sexual gener- 
ation. Were this the case, it is certain that the reduction 
would be manifested in different degrees in the various 
sub-divisions of the animal kingdom. It may, with greater 
probability, be assumed that, in all those sub-divisions of 
the animal kingdom, sexual differentiation occurred at the 
very beginning of phylogenetic development, and that the 
product phylogenetically developed from the sexual act is 
the direct continuation of the ontogeny of the individual. 
The process of reduction which takes place in the mother- 
cells of ova and spermatozoa of animals is associated, as in 
plants, with far-reaching changes 1 ; and the abundance of 
chromatin in these altered nuclei may, as also in plants, 
induce a rapid division into four of the nuclei. In plants 
this division into four takes place in the spore-mother-cells, 
without any direct relation to the sexual cells. That the 
constitution of the mother-nuclei induces the two divisions 
which rapidly follow each other, is shown by the fact that the 
mother-cells of the ova in animals give rise, on division, to 
products of unequal size : hence the subsequent division into 
four cannot be attributed to the form of the mother-cell. 
The division into four of the so-called paranuclei of the 
Infusoria doubtless takes place in relation with a correspond- 
ing reducing process 2 , although under conditions which differ 
from those obtaining in the conjugating Infusoria. The 
uniformity in the phenomena of reduction and in the processes 
1 Compare O. Hertwig, Lehrbuch der Entwicklungsgeschichte, 4. Aufh, 1893, 
p. 32. 
2 Compare O. Hertwig, Die Zelle und das Gewebe, 1893, p. 216, where the 
literature is cited. 
