“ Nuclear Osmosis .” 
based on the diameters actually figured. Thus as nearly as could 
be measured, the diameters of the mass taken as a sphere, shewn 
Figs. I, 7 and 13, are respectively 24, 22 and 20 mm. The volume 
of the respective spheres occupied by the chromatin works out at 
7238, 5575 and 4190 cub. millimetres. That is to say a shrinkage 
occurs of about 43% as between the presynaptic stage of Fig. 1 
and the synapsis stage stage of Fig. 13. 
Naturally it is difficult to obtain very accurate measurements, 
but the results just given are not discordant with the views more 
generally held on the existence of contraction as might have been 
anticipated on mere linear measurements. 
The increase in the size of the nucleus has, of course, been 
noted by other observers, and the author is probably correct in 
attributing it to an increase of nuclear sap resulting from higher 
osmotic tension. It is less easy to follow him in his view as to the 
direction to which this pressure is assumed to act, for surely it must 
act equally in all directions, although differences of surface tension 
may and will determine the actual form assumed by the nucleus. 
The hypothesis as to the supposed relation between the directive 
extension of the nuclear vacuole and the rounding off of the 
the individual spore mother-cell, appears to need further explanation 
than is accorded to it. 
It is not improbable that many investigators who are familiar 
with the facts of mitosis, in so far at least as they can be ascertained 
by observation, may find themselves unable to share Dr. Lawson’s 
conviction that “ Nuclear osmosis ” is to be regarded as a satis¬ 
factory explanation of the complex mechanism commonly known as 
the achromatic spindle. Dr. Lawson, after his friendly criticism 
of a paper of which the present writer is a joint author, will not 
misunderstand the situation if the points in which his own hypo¬ 
thesis appears to be defective are rather frankly examined. For it 
is only by fair discussion that the meaning of the facts is likely to 
be elucidated. It is not the writer’s intention to defend here and 
at length the thesis that electrical conditions, resulting from 
chemical changes occurring in the peculiar physical substances of 
which the cell is composed, are responsible for the structures in 
question. But it must be pointed out that Dr. Lawson seems to 
under-rate the circumstance that electrical disturbance is a very 
common and a very easily ascertained fact in many phases of 
cellular activity, that the forces concerned are or may be of con¬ 
siderable magnitude having regard to the limited space in which 
