256 
W. J. Hodgetts. 
There is no cellulose cell-well, the cell being covered with a 
very delicate protoplasmic membrane, which appears to allow of a 
certain amount of change of form of the cell. Although such 
alteration in form was not directly observed in the motile 
individuals, yet the variability in the shape of the cells seems to be 
due in part to this power. In the non-motile state, as described 
below, the cells readily assume various forms, although they 
generally tend to become sub-globose. 
There is a single cup-shaped, bright green chloroplast, occupy¬ 
ing practically the whole periphery of the cell, leaving only the 
centre of the anterior end free and more or less hyaline. The 
anterior edge of the chloroplast is incurved and slightly thickened, as 
shown in the optical longitudinal section, Fig. 1, E, while the 
thickened base of the chloroplast contains a large conspicuous 
pyrenoid. A rather pale red stigma of elongated form is situated on 
the outer surface of the chloroplast in the anterior part of the cell, 
and invariably on the summit of one of the anterior lobes (Fig. 1, 
A—D), and projecting slightly above the general surface of the cell. 
The chloroplast appears to be quite entire at the anterior end. 
Even under very high powers (a 2 mm. oil-immersion objective was 
most frequently used in examining the minute structure of the 
cell), and in cells blistered with a drop of dilute formalin solution, 
or killed with iodine, or other reagents, the incurved anterior edge 
of the chloroplast never appeared to be divided into lobes 
corresponding to the four anterior lobes of the cell. 
The pyrenoid has a starch sheath, and minute grains of starch 
were frequently observed scattered throughout the chloroplast. 
The addition of a drop of dilute formalin solution causes the cells 
to become greatly swollen and distorted in the same way as that 
described by B. M. Griffiths in the case of Pyramimonas delicatulus.' 
Within the chloroplast and in the general cytoplasm of the 
anterior region of the cell are two (occasionally three) contractile 
vacuoles. They are very difficult to observe in moving individuals, 
although occasional glimpses of one or both of them can be 
obtained. They are more readily seen in the non-motile cells (Fig. 1, 
F), especially under a high magnification. The period between 
two successive disappearances of a vacuole is 18—22 seconds. 
Other small vacuoles were observed in different parts of the cell 
but these were never observed to pulsate. 
1 B. M. Griffiths. On Two New Members of the Volvocaceae, New 
Phytol., VIII, 1909, pp. 130—137. 
