Nuclear Division in the Hepaticae . 485 
plate of the nucleus. Nothing has hitherto been said as to 
the origin of the spindle, which must now be considered. 
At an early period in the process of mitosis, a centrosphere 
appears at four points on the periphery of the nucleus, and 
these points correspond with the four lobes of the spore- 
mother-cell, just as in Fossombronia. The centrosphere con- 
tains a minute centrosome, and from it, though starting at 
a very short distance from it, are seen radiations which extend 
into the lobe in front of which it is situated. The small clear 
space around the granule may perhaps be caused by the fusion 
of the radiating filaments. Each centrosphere apparently 
exercises a pull on the nucleus, which becomes drawn out at 
each of the four spots, and forms a small protuberance into 
each lobe. Later on the radiations diminish, and the nuclear 
protuberances are less easily seen ; in some cases they seem 
to fuse pairwise, probably by the mutual fusion of the centro- 
spheres, but in other instances there is no doubt but that this 
quadripolar spindle persists through the first mitosis (Fig. 23). 
It must be clearly emphasized that the nuclear wall is quite 
visible to a late period, and that the quadripolar figure is 
entirely, in its earlier stages at least, of nuclear origin ; only 
the centrosphere is cytoplasmic. But the nuclear wall can no 
longer be distinguished when the chromosomes reach the 
equator, and the achromatic spindle-fibres are completely 
formed. The achromatic spindle is often very short, but it 
varies a great deal in this respect. The difference seems to 
depend on the length of the arms of the quadripolar body. 
If they have extended far into each lobe of the spore-mother- 
cell, then the spindle is elongated, and it often is divided up, 
so that there is an apex in each lobe. But no simultaneous 
division into four nuclei follows, even in these latter extreme 
cases, and thus the four spindle-arms when present act in 
pairs. The chromosomes agree in shape with those met with 
in the first division of the pollen-mother-cell of Lilium , that 
is they exhibit two processes which lie along the spindle, and 
a humped portion which is directed outwardly from it. The 
same mode of division of the chromosome as has been 
