Nuclear Osmosis and Meiosis. 
25 
appears to me to be specially difficult to reconcile with the 
hypothesis that nuclear osmosis constitutes a fact of serious 
importance in mitosis. It is well known that the whole spindle, in 
certain cells, may be intra-nuclear, and this from the time of its first 
appearance ; and yet the structures themselves so precisely resemble 
the extra-nuclear spindles in every other respect, that .it is 
impossible to regard them as fundamentally distinct in character. 
Intra-nuclear spindles have been recognised in a number of animal 
cells, and the example of Fucus, already quoted, is only a little less 
striking. In the latter plant the spindle is partly extra-nuclear, i.e., 
cytoplasmic, and partly intra-nuclear, and indeed the nuclear wall 
persists as a barrel-like body enclosing the spindle and chromosomes 
even during the metaphase. There is no need to regard the spindle 
fibres as “ pushing into ” the nucleus. They appear to originate by 
differentiation from the nuclear contents, just as the fibrils in the 
cytoplasm arise, by differentiation, from the cytoplasmic substance. 
And in both positions they seem to map out lines of force or of 
strain. 
Amongst the numerous points which will have to be worked 
out in detail in connection with any theory which aspires to explain 
the mechanics of mitosis will be:—(i) the shape of the spindle, its 
straight and its convex appearance in profile; (ii) the lack of 
adherence to the cytoplasmic boundary, so frequently observed, 
i.e., its differentiation and blind ending in the cytoplasm ; (iii) the 
details of the convergence of multipolar to bipolar arrangements, 
and the analysis of the causes of these rearrangements; (iv) the 
definite arrangement of the equatorial plate, and the polarised 
character of the spindle in the connection therewith ; (v) the 
frequent suppression of the peripherally directed fibres, present in 
so many cells, during this period of metaphase ; (vi) the detailed 
analysis of the processes leading to the formation of the interzonal 
spindle—a study of those forms of belated cell-wall formation, e.g., 
those encountered in some endosperms, might well help to elu¬ 
cidate this ; (vii) the intra-nuclear spindle. 
Although these suggestions are by no means exhaustive, they 
may, I think, be taken as representing a fair sample of the problems 
that have to be faced. It is by no means likely that their entire 
solution will be achieved in the immediate future, nor indeed until we 
obtain to a far deeper and more accurate knowledge of the micro¬ 
physics of the cell, and of the modifications of structure and con¬ 
sistency depending on chemical and physical change, than we possess 
just now. For the present, then, we must continue to work with 
hypotheses. But we may reasonably ask that, while embracing the 
observed facts, these hypotheses should not conflict with the 
principles of elementary physical science. 
We may now leave these matters and turn to the main results 
of Professor Lawson’s most recent communication. Here we reach 
ground where, happily, a closer agreement is possible. The plant 
principally selected for the investigation of the meiotic phase was a 
species of Stnilacina, and it has evidently turned out to be a most 
fortunate choice. Some of the stages which have proved trouble¬ 
some in forms otherwise satisfactory, seem to exhibit a clearness 
that leaves nothing to be desired. The chief results are, briefly, a 
follows :—The chromatic substance, as it differentiates from the 
resting nucleus at the prophase of the first meiotic division is seen 
