fs) ¥. E. FRITSCH. 
end was acutely pointed (figs. 1, 3, 4), but in some cases it was more or less 
completely rounded off (figs. 2, 5). The cells are frequently somewhat asymmetrical 
about the longitudinal axis (fig. 1), sometimes even to a marked extent (fig. 4), 
but in other cases (fig. 3) the cell was quite symmetrical, the pointed termination 
being median. The shape of the individuals thus varies a good deal, but the 
elongated form figured by Wille (op. cit., figs. 12, 13, 14) was rare (cf. my fig. 5). 
The position of the nucleus is variable, as the figures show; in some cases it 
is quite near the front end of the cell (see especially fig. 2), in others much 
nearer the pyrenoid (fig. 3). The latter was always situated near the middle of 
the cell, but obviously in the posterior half. In many individuals the longitudinal 
ribbing of the chloroplast was very prominent; the chloroplasts were often charged 
with numerous small starch-grains. Division-stages were not uncommon, division 
being effected by oblique planes as recorded by Wille and the Wests. 
In a considerable number of the individuals encystment had taken place 
(figs. 6-11). Within the colourless membrane of the mother-cell the contents had 
become rounded off into an oval or spherical mass and surrounded by a rather 
thick and often stratified wall (figs. 6 and 7). Laterally this new envelope is 
almost in contact with the old cell-membrane, but at the front and back ends 
of the cell there is a considerable space between the two (figs. 6 and 7). The 
pointed posterior end of the old cell-membrane is often very distinct (fig. 6). 
The contents undergo no apparent change in this process of encystment, the 
pyrenoid retaining its posterior and the nucleus its anterior position, and the shape 
of the chloroplast is often quite recognisable (fig. 6). The cilia are evidently 
drawn in or cast off prior to the occurrence of encystment, as no traces of them 
could be found in these individuals. Perfectly similar encysted individuals were 
found in which the membrane of the cyst showed protrusions of various kinds 
(figs. 8-10). These protrusions are either single (fig. 8) or there are two of them 
(figs. 9, 10), and, as the figures show, they are developed to a very varying extent. 
Sometimes they cause protrusions of the old mother-cell membrane (fig. 10) and 
lead to the assumption of very irregular shapes. Free cysts, which had escaped 
from the enveloping mother cell-membrane, were abundant among the ordinary 
Chlamydomonas-individuals, appearing as circular or oval cells with a rather thick 
and stratified membrane and the characteristic angular pyrenoid of the species 
(figs. 11-13). Occasionally in these cells the membrane is much more markedly 
thickened on one side than on the other (¢/. fig. 11). Now and again a cell 
of this kind with two pyrenoids was observed (fig. 14), thus possibly indicating 
the commencement of division. Stages like that shown in fig. 20, in which the 
contents of the cyst have undergone division into four parts, were extremely 
rare. It is not known what the further fate of these cysts is. 
Similar cysts are known for other species of Chlamydomonas and its allies ; 
Dill (Die Gattung Chlamydomonas und ihre niichsten Verwandten,” Berlin, 1895) 
