NUCLEAR OSMOSIS AS A FACTOR IN MITOSIS. Lop 
until the nuclear membrane completely envelops each individual chromosome (figs. 46 
and 47), thus providing each of these bodies with a series of fibrils. On account of 
the great length of the chromosomes, the greater number of fibrils—and consequently 
the dominating lines of tension—would be drawn to the broad sides of the chromosomes, 
and in this fashion the equatorial plate would be established, and the mature spindle 
presents the appearance shown in fig. 48. 
An examination of fig. 48 will convince one that the poles of the spindle are not 
very remotely situated from the equator. It will also be seen without any doubt in 
figs. 49 and 50 that the daughter chromosomes move in opposite directions beyond the 
positions of the actual poles of the spindle. From this fact alone it would seem that 
the attached fibrils are not actively concerned in this movement. As I have stated 
elsewhere, they may possibly act as ouide lines. 
The organisation of the daughter nuclei, as illustrated in figs. 50, 51, 52, and 58, is 
important and interesting, because it shows how the tension originally set up in the 
eytoplasm during the prophase and expressed in the spindle fibrils eventually becomes 
relaxed. In fig. 50, for instance, we see the daughter chromosomes arranged in two 
groups at opposite sides of the cell: The state of tension in the cytoplasm is still 
evident by the drawn-out threads of cytoplasm stretching between the two groups. 
This same condition is still shown in fig. 51, where the chromosomes in each group are 
closely massed together. In fig. 52 we have a stage where each chromosome has 
become more or less vacuolated, clearly indicating that a considerable amount of 
karyolymph has been taken in by endosmosis. This would necessarily release the 
tension in the cytoplasm to a considerable extent. When, finally, as shown in fig. 53, 
the combined volumes of the two daughter nuclei approximates the original mother 
nucleus, all tension is relaxed and all fibrils disappear. 
The interpretations which I have given above for these new stages in spindle 
formation in the various types mentioned are quite in harmony with certain well-known 
facts concerning important changes which take place in the nucleus both before and 
after mitosis. In the first place, it is an established fact that in the re-organisation of 
the daughter nuclei there is an accumulation of karyolymph within the chromosomes. 
This nuclear sap first appears in the form of minute lacunze which increase in size and 
flow together, giving the chromosomes a vacuolated appearance. With the accumula- 
tion of the karyolymph the chromosomes become very finely divided, and the chromatin 
eventually appears as a fine reticulum suspended in a large vacuole of nuclear sap. 
It is also well known that out of this finely divided condition there is developed 
a stage commonly called the spireme, where the chromatin assumes the form of long, 
fairly thick threads, and not so finely divided as in the reticulum. And, finally, the 
spireme threads give rise to the more compact chromosomes. Now, the point of 
interest is that during this transition period between the finely divided condition of the 
reticulum and the more compact condition of the chromosomes there always occurs 
