426 Griffiths.—On Glcincocystis Nostochineartim , Itzigsohn. 
outer edge. The deeply staining bodies in the cytoplasm lie at the inter¬ 
section of the threads of the reticulum. The threads are very delicate and 
not granular at this stage. 
( b ) The clear space, which may be denoted the ‘ karyoplasmic area ’, 
now begins to contract and to move towards the centre of the cell. It 
becomes more deeply stainable, the staining being diffuse. Its reticulum, 
previously extremely delicate and difficult to see, becomes coarser and 
more visible. At the same time, the number of darkly staining bodies 
in the cytoplasm diminishes, and the whole cytoplasm becomes diffusely 
stainable. The karyoplasmic area does not possess a definite membrane at 
this stage (Fig. 2). 
(1 c ) The karyoplasmic area contracts further until it reaches a diameter 
of 6 or 7 /x, and a well-marked membrane forms. The cell as a whole 
increases in size also. The threads of the karyoplasmic reticulum become 
thick and stain more deeply. Deeply staining granules of chromatin 
appear at the intersections of the threads (Fig. 3). One granule becomes 
very much larger than the rest. It is circular or roughly polyhedral in 
outline. It is not homogeneous in structure, but is composed of many 
granules fused together. The dark bodies of the cytoplasm disappear 
completely, and the threads of the cytoplasmic reticulum become finely 
granular. These granulations do not stain deeply (Fig. 4). At this stage, 
the cell bears a striking resemblance to the cell of higher plants. There is 
a definite nucleus bounded by a membrane, and possessing darkly staining 
granules of chromatin. The large karyosome, roughly circular in form, 
resembles a nucleolus in position, but, as will be seen later, its behaviour is 
quite different from that of the nucleolus of higher plants. 
(d) The concentration and definition of the nucleus is a preparation for 
division. The nucleus elongates to a length of about 11 /x, but the diameter 
remains about the same (Fig. 5). The nucleolus-like karyosome becomes 
a very conspicuous object. It grows very large, probably by the addition 
of the smaller granules of chromatin previously scattered on the nuclear 
reticulum. The nuclear reticulum itself ceases to be visible, and the 
nucleus becomes uniformly diffusely stainable, with the large karyosome 
lying in it. The karyosome now divides by a transverse fission into two 
equal parts semicircular in outline, which separate a short distance. No 
case was observed among the very large number of dividing nuclei in which 
there was anything in the nature of a polar separation of chromatin 
substance or the formation of a chromatic figure. In every instance 
the process consisted of the aggregation of chromatic material into a large 
karyosome, which subsequently divided by simple transverse fission. After 
the division of the karyosome, the nucleus divides in a precisely similar 
manner (Figs. 6 and 8). A large number of specimens were in this stage. 
Each half of the nucleus is semicircular or semi-elliptical, with a very distinct 
