Griffiths.—On Glaucocystis Nostochinearum , Itzigsohn . 429 
of Chroococcus macrococcus, or of Merismopedia elegans in its stage prepara¬ 
tory to division. Glaucocystis , however, shows a more elaborate structure 
in two ways, first in the possession of a definite nuclear membrane, 
and secondly in the formation of the very large mass of chromatin 
resembling a nucleolus in position, which I have referred to as the ‘ large 
karyosome ’. 
In stage (d) the behaviour of the nucleus is different from any other of 
the Cyanophyceae. The large karyosome gradually attains a considerable 
size by drawing to itself all, or nearly all, the chromatin of the nucleus. 
Nuclear division is initiated by the transverse fission of the karyosome, and 
is completed by a similar division of the nucleus. This division is shared 
in by the whole cell. The cytoplasm shows strain lines radiating from the 
two karyosomes in some cases. Similar phenomena have been observed in 
Lyngbya (Brown, Tl). Although the cytoplasm shows at first the Myxo- 
phycean character of division independent of the nucleus, it waits until 
nuclear division is complete before completing its transverse fission. This 
transverse fission is exhibited by such forms as Chroococcus macrococcus and 
Merismopedia elegans , but their nuclei remain in the stage of the simple 
chromatin reticulum, and there is no sign of the aggregation of chromatin 
material for purposes of equal division. In this respect Glaucocystis appears 
to have evolved a rough process of chromatin distribution comparable with 
the karyokinesis of high plants. The karyosome would be, according to 
this view, rather of the nature of a chromosome than of a nucleolus. 
The organism shows also a higher specialization in its formation of 
daughter-cells. Alone among the Cyanophyceae, it produces daughter- 
cells similar in outward form to those of the mother-cell and within the 
mother-cell wall (as in Oocystis). There is, however, a profound difference, 
as the mother-cell of Glaucocystis nearly doubles in volume before dividing, 
whereas in Oocystis this is not the case. 
In stage (e) the nucleus has finished its work of division and proceeds 
to take to pieces the structure it had elaborated. The large chromatin 
karyosome breaks up, the nuclear reticulum disappears, and once more the 
brilliantly staining metachromatin granules appear in the cytoplasm. The 
nuclear area increases in size, moves towards the side of the cell, and 
assumes the clear vacuole-like state of the resting condition. 
Glaucocystis shows, therefore, a near approach to the cytological struc¬ 
ture of higher plant cells, both in its actual nucleus and in the formation of 
daughter-cells. In higher plants the elaborate structure of the nucleus 
is retained permanently, but in this organism the nucleus reverts to the 
‘ open ’ condition, and for each division must reconstruct itself. 
That Glaucocystis is one of the Cyanophyceae is shown by the following 
characters : (1) The nucleus is of the ‘ open 5 type at one stage. (2) Nuclear 
division takes place by transverse fission, and the division of the cytoplasm 
