CELL SIZE AND NUCLEAR SIZE $1 
on cell division, and if Kernplasma-Spannung is a cause of cell- 
division it must be a minor factor in this case. It seems to me 
probable from my observations and experiments on segmenting 
eggs, that the Kernplasma-Relation in these blastomeres is a re- 
sult rather than a cause of the rhythm of cell division, and that 
the factors which bring on cell division are to be found in some 
intrinsic condition in the nucleus or centrosome, rather than in the 
maintenance of a constant ratio of nuclear volume to cell volume. 
Support is lent to this view by the phenomena of odgenesis, for 
we have in the germinal vesicle the largest nucleus in the entire 
life cycle, following upon the longest resting period, while the 
second maturation division follows immediately upon the first, 
usually before a resting nucleus is formed. The long delay in 
the appearance of the first maturation division, as well as the 
short period intervening between the first and second maturation 
divisions, must both be attributed, as it seems to me, to intrinsic 
conditions in the cell, other than ‘ Kernplasma-Spannung.’ 
In the cleavage of the egg the rate of division seems to depend, 
in part, on the quantity of protoplasm present. As long as a con- 
siderable quantity of plasma is present in the blastomeres the rate 
of division is rhythmical, but when the macromeres have given off 
almost all the plasma in the formation of the three quartets of ecto- 
meres, a long resting period follows. The first of these macro- 
meres to divide, giving rise to the fourth quartet, is the one with 
the largest amount of plasma, viz., 3D, while the cells 3A-3C 
normally divide much later. However if, by centrifuging at the 
right stage, 3C is caused to contain more plasma than usual it 
may divide at the same time as 3D, as shown in fig. 37. The cells 
4A-4D, in which the resting period is particularly long, contain 
very little plasma, and this appears to be absorbed by the nucleus 
almost as fast as it is formed. The micromere /d is slightly 
smaller than its fellows, /a-/c, and it divides later than the latter. 
The ‘turret’ cells, /a?-/d?, are the smallest cells in the egg, when 
they are formed, and they have the longest resting period. 
In spite of this evidence that the quantity of protoplasm has 
to do with the rate of division, there is other conflicting evidence 
which is hard to harmonise with it; thus, these same ‘turret’ cells, 
