586 
C. F. U. MEEK. 
and throughout its construction Rhunibler has kept before 
liini the phenomena that he seeks to explain. But Hartog 
lias pointed oat that the actions of osmosis and currents in 
the cell have been shown to be the same at both poles, and 
that, because the two centrosomes must accordingly have the 
same sign, spindle formation between them is impossible. 
We must therefore ask if Rhumbler assumes the spindle to 
be a figure formed entirely by the action of forces at its poles ; 
for, if he does not assume this, Hartog’s objection need not 
be considered. Now, it is obvious that he does not regard 
the spindle as being formed in this manner, because, in order 
to overcome the difficulty presented by an assumed spindle 
formation between like poles, he invokes other forces, which 
are said to convert the anti-spindle into the spindle by causing 
coalescence of rays. This explanation is identical in principle 
with that put forward by Glallardo, and accords with the 
conclusion at which we arrived in our criticism of Hartog’s 
theory. 
We must now ask if Rhumbler’s theory of mitosis depends 
for its proof upon the conformation of the spindle. It does 
depend upon it, because division is directly attributed to 
tractive forces exei’cised by the reticular rays. But, if the 
conformation of the achromatic figure can no longer be 
regarded as an index of the actions at the poles — and in the 
circumstances it cannot be regarded as an index — we have no 
reason for believing that the rays represent a migration of 
fluid from the region of the centrosomes. And, if proof of this 
migration is not established, we cannot infer that the rays 
conti'act as a result of loss of fluid. The theory therefoi’e 
remains for the present a suggestion. 
Let us now turn to the recent work of Lawson. This is 
not offered as an explanation of mitosis, but merely consti- 
tutes an interpretation of the achromatic figure in vascular 
plants. His researches have led him to affirm that in the 
prophase the karyolymph difi^uses thi’ough the nuclear mem- 
brane into the cytoplasm, thus causing diminution of the 
nuclear vacuole ; that the contracting membrane draws the 
