Lloyd Williams,— Studies in the Dictyotaceae. 157 
when it swells, becomes angular, and finally its membrane disappears and 
the fibrillae are allowed to disperse through the nuclear cavity. 
The stages of the ‘reduction ’ nucleolus are the following : — 
1. The nucleolus is uniformly fibrillar, and probably contains the bulk 
of the chromatin. 
2. It becomes vacuolate and the spherule forms. 
3. It is much distorted and attached to the spirem ; the staining power 
becomes gradually less. 
4. A large vacuole appears, with fibrillar inclusions. 
5. It becomes spongy and more deeply stained. 
6 . It swells, becomes angular and fibrillar. 
7. It disintegrates into fibrillae and a nucleolar globule, which are both 
excluded from the daughter-nuclei. 
The distorted nucleus accompanying the ‘knotted’ spirem, and its 
frequent actual attachment to the thread, irresistibly suggest that the 
nucleolus nourishes the spirem at this stage. This view is strengthened 
by the fact that about this time the nucleolus becomes less responsive to 
chromatin stains. 
In the succeeding stage the very large vacuole occupying the greater 
part of the diameter seems to show that the nucleolus has been deprived 
of much of its substance. The significance of the included fibrils is not 
clear. 
The spherule accompanying the reduction spirem is most probably 
a derivative of the nucleolus. It stains intensely with most chromatin 
stains, but shows some distinctive reactions, especially its retention of 
Carbol Fuchsin. Very often the spherule remains bright red when the 
colour has been extracted from all the other constituents. It is not homo- 
geneous — very frequently deeper stained bodies can be seen within it. It 
shows no definite relation to other nuclear structures and its role cannot 
at present be explained. 
The disintegration stage shows that the nucleolus contains two very 
different substances, the fibrillar chromatin-like constituent, and the globule 
— plasma-like in its colour reactions. If the former substance be not chro- 
matin, then a third constituent must be added, for it is exceedingly probable 
that part of the chromatin is stored up in the nucleolus previous to karyo- 
kinesis. 
It was shown that in the reconstruction of the daughter-nuclei the 
process in the stalk-cell division is different from that in all the others. In 
the tetrasporangium nucleus all the chromatin is at first stored up in the 
nucleolus, and there is no second body within it. This may be part of the 
elaborate preparation for the reduction of the chromosomes. In the telo- 
phase of the next division the chromatin is aggregated in a separate mass 
of fibrils which, however, become dispersed through the nuclear space and 
