STRUCTURE OF CERTAIN CHROMOSOMES 17 
chromosomal trabeculae, but show no other lateral processes nor 
sheath, though they may show in considerable abundance 
minute nodes or varicosities. And the appearances suggest 
that these are nothing but nodes of contraction and torsion 
which may well be the first visible stage of the formation of 
periaxial spirals and processes. In more advanced stages of the 
spireme, such as that of fig. 26, lateral processes and a sheath 
can often be made out with certainty, though with extreme 
difficulty. At this time (when the loops of the chromosomes are 
still so closely crowded together that almost all the sheaths are 
in contact with their neighbours) the lateral processes are 
sometimes so abundant that when fairly well visible they 
give the image of a dense network spread over the whole of 
the ground of the nucleus, as shown in fig. 26. Periaxial spirals 
cannot be made out on the axes at this time ; but since we have 
found that lateral processes are signs of the existence of the 
spirals—being in fact only lateral expansions of these outwards— 
we must admit that by this time the spirals are in course of 
formation, if not completely formed, even when we cannot so 
much as glimpse them. 
As the chromosomes contract, they become more widely 
spaced, and by the time they have contracted imto the state 
known as the “segmented” spireme the lateral processes and 
sheath have come into evidence as clearly as in the anaphase, 
figs. 27 and 28. In fig. 27 the periaxial spirals cannot be made 
out, the moieties of the chromosomes being here especially thin 
(as I invariably find to be the case in endothelium nuclei). 
In fig. 28 they can just be glimpsed in some places. But not 
till we come to the chromosomes of the equatorial plate, 
figs. 19 to 28, do we find the axis clearly differentiated into a 
shaft with regular spirals on its surface. In equatorial plates 
whose chromosomes have not entirely assumed the form which 
they show when definitively arranged on the spindle, the 
aspect of the axes is still rather that of a structureless though 
twisted thread than that of a shaft with spirals on it (fig. 19). 
In the entirely completed and regularized plate the spirals 
certainly exist throughout, see figs. 20 to 23. If they do not 
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