150 Lloyd Williams . — Studies in the Dictyotaceae . 
This shows clearly that the loop- figures have not been caused by cutting 
off the ends of elongated rings. The failure to find evidences of a second 
split of the chromatin thread, and a careful study of the development of 
the chromosomes, inclines me strongly to Farmer and Moore’s view of the 
origin of these bodies, as recently advanced before the Royal Society 1 . 
According to this the space inside a ring-chromosome, or that between the 
two limbs of a loop-figure, does not represent the first split, but rather 
the space between the two constituents of a bivalent chromosome bent 
over on itself so that the two ends meet, or the two limbs cross, or some 
modification of these forms is brought about. The split itself (the only 
split according to this theory), though partly obliterated by the condensa- 
tion of the chromosomes, is still evident in the free ends of several of 
the chromosomes in Figs. 17 and 18. During this stage the nuclear 
reticulum is somewhat dense and the nucleolus minutely vesicular. 
By the time the spindle cones begin to develop the chromosomes have 
still further condensed until they are small and deep-staining, but the 
ring form is very prevalent (Fig. 19). Thus, although a long time has 
elapsed since the spirem stage, and in the meantime all traces of it have 
been lost in the apparently formless reticulum, yet the chromosomes make 
their appearance already segmented and longitudinally split. The length 
of the spirem period and the comparative shortness of the prophase 
irresistibly suggest that the arrangements for mitosis are completed, or 
nearly so, in the former ; that the grouping of the various constituents 
is there determined, and however disguised in the reticulum of the post- 
spirem stage that it still exists. This is equivalent to saying that the 
spirem maintains its identity throughout, and that when the stimulus is 
given which produces the prophase there is a rapid condensation of the 
previously extended, unrecognizable spirem into compact, deeply stainable, 
split, bivalent chromosomes. This does not exclude the possibility of 
substance passing into the chromosomes from the nucleolus. From actual 
observation, however, we can determine that this must be small in amount, 
for the bulk of the nucleolar substance is otherwise accounted for. In 
Fig. 19 the nucleolar membrane has disappeared, and the contained 
fibrillae, as deeply staining as the chromosomes, lie together in an irregular 
mass, some of them with their free ends projecting. Other sections show, 
as in the case of the stalk-cell division, that the spherical globule sub- 
sequently seen near the spindle is also formed out of the disintegrating 
nucleolus. 
The Spindle Stage. Of this a great many examples have been 
studied, and they all agree in their main features. The spindle is intra- 
nuclear, very narrow, and nearly iso-diametric. The nuclear membrane 
is intact excepting at the poles, where there are evident gaps nearly as 
1 Proc. Roy. Soc., vol. lxxii, p. 104, 1903. 
