144 MR A. ANSTRUTHER LAWSON ON 
We have here, from figs. 3 to 7, a series of stages which, as far as I know, has never 
before been described. That it represents early phases in the development of the 
spindle is, I think, quite obvious. It also demonstrates that with the gradual decrease 
in the nuclear volume there is a corresponding increase in the cytoplasmic volume. It — 
should be remembered that throughout these stages, as well as those immediately pre- 
ceding, the cell is surrounded by a firm cell-wall of considerable thickness, to which the 
peripheral cytoplasm is closely associated, and that a perceptible diminution in the 
volume of the celd-cavity is inconceivable. It should also be remembered that the 
nuclear membrane is part of the cytoplasm. With these facts in mind it is quite clear 
that in the stage represented by fig. 7 the cytoplasm fills a cubical space which is more 
than double that shown in fig. 1, but there is no change in the dimensions of the cell 
as a whole. That varying osmotic relations constitute a causal factor in these trans- 
formations seems to me a safe and rational assumption. LHverything necessary to 
promote osmotic diffusion is present. There is a permeable membrane and substances 
of different chemical composition and presumably of different density on either side of 
it. It is therefore not difficult to understand the gradual diminution of the karyo- 
lymph, as shown in these figures, on the basis of osmotic diffusion. The karyolymph 
has passed out into the cytoplasm by exosmosis. 
All of these circumstances bring about a condition where a limited amount of 
cytoplasm of reticulate structure is obliged to oceupy a cubical space which is gradually 
increased by reason of the diminution of the large nuclear space. This necessarily sets 
up a state of tension in the cytoplasm—a tension sufficient to cause a readjustment and 
changed configuration in the reticulate form of the cytoplasm; a change to the form 
of threads or fibrils which are drawn out from the reticulum by the receding nuclear 
membrane. With the closing in of the nuclear membrane about the chromosomes the 
cytoplasm must follow the membrane, and the changed configuration of the cytoplasm 
would first make itself evident in the region of the membrane. On examination of the 
serial stages represented in figs. 1 to 7, the conclusion is irresistible that this is really 
what has happened. ‘The kinoplasmic fibrils are drawn-out threads of cytoplasm— 
drawn out by reason of the inward movement of the membrane. 
But now, what follows the stage represented in fig. 7? In fig. 8 we have a later 
condition, where the karyolymph and membrane are no longer visible. This invisi- 
bility, however, does not prove that these elements of the nucleus no longer exist. They 
are both present—the one very much reduced and saturating the chromosomes, and the 
other completely enveloping each chromosome. So that we now have, not a single ~ 
osmotic system as formerly, but as many osmotic systems as there are bivalent 
chromosomes; and in this case there are five. 
This closing in of the membrane about each bivalent chromosome is doubly 
interesting. It not only establishes a number of osmotic systems which are more or 
less independent of one another, but it clears up a doubtful matter, mentioned above, 
as to the manner in which the kinoplasmic threads become attached to the chromosomes. 
