Lloyd Williams . — Shi dies in the Dictyotaceae . 143 
a tendency to draw away from the nuclear membrane (Fig. 1). It is true 
that this effect is probably due to the fixing reagent, but the readiness 
with which the effect is produced both in this and the corresponding 
stage of the next mitosis shows that the relation of the network to the 
membrane — probably to the cytoplasm — is much less intimate than it 
is during the spirem stage. 
The spirem is very coarse, the chromatin granules being unequal in 
size and the staining not 'deep. It frequently seems polarized, but at this 
stage no signs of splitting can be seen. The nucleolus now becomes vacuo- 
late. Frequently, but not as regularly as in the next division, there is 
a large central vacuole with deeply stained inclusions. Immediately before 
the segmentation of the thread (Fig. 2) the nucleolus becomes swollen, 
irregular in form, and distinctly fibrillar in texture, — an appearance which 
is also seen at this stage in most of the other mitoses. Soon the nucleolar 
membrane disappears and the free, fluffy ends of the fibrillae project from 
the general mass of nucleolar substance. This is identical with what 
occurs in the prophase of the next division (Fig. 19). At this time the 
nuclear cavity has no reticulum within it. 
The chromosomes now begin to appear and are often disposed in the 
neighbourhood of the nucleolus. The latter loses its coherence and 
becomes an irregular mass of granules and curved fibrils, some of them 
looking not unlike minute chromosomes, and, unless very carefully counter- 
stained, very similar in their staining reactions. Besides these, the 
nucleolar globule, which always accompanies the spindle, is already differ- 
entiated. This is much less deeply stained, and, except for a small vacuole 
which sometimes appears in it, is quite homogeneous. Two sheaves of 
fibres now project into the nuclear cavity, their extremities reaching about 
one-third of the way to the opposite pole, leaving the equatorial region 
free. Here are aggregated the fragmenting nucleolus and the chromosomes. 
The latter are considerably bigger than during the succeeding mature 
spindle stage; they are curved and distinctly split. Fig. 3 represents one 
of three oblique sections through such a nucleus. After making allowance 
for chromosomes that have been cut and consequently appear partly in 
this and partly in other sections of this nucleus, the number of chromo- 
somes is from thirty to thirty-four. 
The spindle when fully formed is intranuclear, the membrane per- 
sisting close up to the poles. The spindle proper is truncated at the poles, 
and in some cases (Fig. 4) is not greatly dilated at the equator. The 
space between the spindle and the membrane is occupied by a few mantle 
fibres and a large number of curved fibrils almost certainly derived from 
the disintegrating nucleolus. The nucleolar globule is also seen somewhere 
in the vicinity of the spindle — it now stains just like the cytoplasm. The 
chromosomes are uniformly distributed through the nuclear plate in a dense 
