Nuclear Division in the Hepaticae. 48 1 
a small central space common to them all. The nucleus is 
always found to be situated in this central common region 
(Figs. 17-20). 
If the nucleus be examined at a stage in which the cell 
as a whole has reached rather less than one-third of its final 
size, it will be seen to possess a well-marked wall, within 
which is contained a very distinct linin thread. The latter is 
very much convoluted, and lies just within the wall, though 
some parts of the filament are also visible in the more 
central regions of the nucleus. It is very easily differentiated 
at this period, as it still possesses a considerable amount of 
chromatin which is distributed through its substance. There 
is also present one (seldom more than one) large nucleolus. 
As the sporogonium increases in size the spore-mother-cells 
also become larger, but the process is one which takes con- 
siderable time as compared with the cells during what may 
be termed their archesporial period, in which both growth 
and division proceed rapidly. The linin next loses its 
definiteness, owing to the disappearance of its chromatic 
constituents as such, but pari passu the nucleolus becomes 
more clearly prominent. It now absorbs greedily those stains 
used for differentiating chromatin, although in its reactions 
to these substances it is not quite similar to chromatin. 
It shrinks somewhat in size and occupies the centre of the 
nucleus. Indeed at this period it is easy to mistake it for 
the real nucleus, for the extra-nucleolar portion now hardly 
differs from the cytoplasm save in its rather denser and more 
uniform consistency. This peculiarity is one which is shared 
by a large number of liverworts at the stage in question, and 
it is also a familiar one in the vegetative nuclei of many Algae. 
In the next stage, that is, when the spore-mother-cells have 
reached their mature size, the nucleus again begins to alter 
its appearance preparatory to the two final mitoses ; the 
nucleolus becomes less chromatic in character, and assumes 
a more peripheral position, whilst at the same time the linin 
thread is again clearly distinguishable. It is in nearly all 
cases seen to be specially aggregated and convoluted in the 
