1 14 Bristol. — Life-history and Cytology of Chlorochytrium grande. 
and as many as 256 may be formed from a single cell. The inner cellulose 
layer of the wall of the mother-cell quickly becomes disintegrated to form 
a mucilaginous mass within which the aplanospores lie for some time 
(Fig. 32). The outer pectic layer of the wall retains its identity for a con- 
siderable time after this, only gradually undergoing dissolution. 
Preparatory to the formation of aplanospores the nucleus of the 
mother-cell, by successive divisions, forms a number of daughter- nuclei 
without the concurrent formation of daughter-cells ; the symmetry of 
the cytoplasmic network is disturbed (Fig. 25), and vacuoles appear. The 
apparent vacuolation of the living cell at this stage is probably due not only 
to the formation of true vacuoles in the cytoplasm, but also to the numerous 
dividing nuclei (Figs. 29 and 30). 
Figures of most of the stages through which the dividing nucleus 
passes have been obtained, showing that a fairly typical karyokinesis 
takes place. In the first stages the nucleolus completely disappears, 
breaking up to form a large number of chromatin granules which become 
dispersed throughout the reticulum of the nucleus (Fig. 25). A little 
later these granules become rearranged to form a coiled spireme (Figs. 26 
and 27), and at a still later stage each of the component granules is seen to 
be cleft longitudinally, so that the spireme is double (Fig. 28). The con- 
traction of the spireme and its division into chromosomes have not been 
observed. 
In Fig. 29 are seen the late prophases and the metaphases of division. 
Details of spindle-formation could not be followed, and the evidence avail- 
able is not sufficient to determine with certainty the number of chromo- 
somes, but there appear to be about seven. These arrange themselves upon 
an equatorial plate (Fig. 29, A) and each splits into two ; the halves separate 
and pass towards opposite poles of the spindle (Figs. 29, B and C ; 30, D and 
E). There the chromosomes become closely crowded together (Fig. 30, F), 
and the reconstruction of the daughter-nuclei begins. 
Each of the daughter-nuclei formed within the mother-cell becomes the 
centre of a little mass of protoplasm saturated with chlorophyll, and 
the formation of aplanospores takes place when each of these little masses 
rounds itself off from the rest with the simultaneous formation of as many 
daughter-cells as there are daughter-nuclei in the mother-cell. 
The young aplanospores begin their development within the covering 
provided by the wall of the mother-cell, and before long each acquires 
a cell-wall of its own, consisting of a thin layer of cellulose and a still thinner 
pectic layer (Fig. 32). As the wall of the mother-cell becomes completely 
disintegrated the developing cells are set free in the water, and they continue 
to hang together in a loose globular mass for a considerable time (Fig. 33). 
Each aplanospore develops directly into a vegetative cell like the 
mother-cell which produced it, and there is no intermediate period of 
