8 F. 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. l), 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 

 CMamydomonas-iudividuals, 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 (cf. 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 Cldamydomonns and its allies ; 

 Dill ("Die Gattung Cldamydomonas und ihre niichsten Verwandten," Berlin, 1895) 



