The Somatic Mitoses in Hyacinthus orientalis var. albnlus. 
371 
From the heavy reticulum there emerges a kind of pro-spireme in 
wliich the- chromatin forms a ribbon-like thread round the nucleus, with 
jagged or spiny processes along its edges. Two stages of this are shown 
in Figs. 4, 5; in the former the cross-connections wliich formed the reti- 
culum have broken down, but the thread still shows diamond-shaped 
areas, corresponding to the meshes of the net. In Fig. 5 the coalescence 
has proceeded further, leaving a jagged ribbon. There is now no indica- 
tion of the split which appears soon after, and it would seem that the 
chromatin shrinks, in the breaking of the reticulum, and that the two 
edges collapse and adliere together for a time, before they become stretched 
again in the lengthening of the spireme. After this the ragged edges 
are gradually drawn in, and the spireme has the appearance of a ribbon, 
in which may be seen the beginning of the longitudinal split. At first 
the fission is only indicated by a thinner portion in the centre of the 
ribbon, but soon it becomes definite, and the two threads lie separate 
from each other (Figs. 6, 7). Meanwhile the nucleus has enlarged, and 
the spireme is coiled loosely about the nuclear area. This condition 
holds until the Segmentation of the spireme, and in some cases the split 
is still clearly visible at the time when the chromosomes are formed 
(Fig. 8). 
At about the time of Segmentation the nuclear membrane disappears 
and the spindle begins to form; it arises in the cytoplasm outside the 
nuclear area, and is often clearly recognizable before the Segmentation 
is complete (Fig. 9). In the best preparations the spindle fibres are ex- 
ceedingly delicate, and sliow rather as indications of some stress in the 
cytoplasm than as definite cell organs. 
After Segmentation the longitudinal split temporarily disappears 
(Fig. 10) and the appearance of the nucleus gives one the impression 
that whenever the chromatin is release'd from any strain, e. g. in the 
formation of the spireme from the reticulum, when the cross Connections 
break, or again when the spireme breaks up into chromosomes, it tends 
to shrink together and become for the moment more homogeneous. This 
supposition accords with the view that the chromatin is a viscous but 
soinewhat elastic substance, and there is no doubt that in Hyacinthus 
the whole appearance of the chromatin in all stages of mitosis gives 
Support to such a theory (Figs. 5, 9, 10, 121. 
The sixteen chromosomes are now drawn on to the spindle and ar- 
range themselves about the equator (Figs. 11, 12) and the split reappears. 
The nucleolus seems to fragment and disappear with extraordinary rapi- 
cüty, for at this stage it suddenly ceases to be visible, and leaves no trace 
