Bristol— Life-history and Cytology of Chlorochytrinm grande, 1 1 7 
external projections very different in shape from the internal ones. They 
are composed of pectic substances and are solid, striated, and frequently 
very broad, and their surface is rounded. They vary considerably in 
position and shape (Text-fig. 1, A-H), and there are usually not more than 
two on any cell, frequently only one being present. In a few cases (Text- 
fig. 1, G) the projection is seen to take the form of an elongated ridge in the 
median plane, sometimes extending as much as half-way round the circum- 
ference of the cell. It frequently though not invariably happens that the 
pectic projection is opposite to the cellulose projection, and where this is the 
case there is sometimes a small air-space between the two layers, probably 
formed as a result of the strain produced in the wall by the unequal 
thickening. 
At the same time as the cell-wall is undergoing the above changes, the 
cell increases greatly in size, and, as a result of the unequal thickening 
of the wall, it sometimes assumes a somewhat irregular shape (Text-fig. 1, C). 
The size to which the zoogonidangium may attain varies in different 
individuals. A fully grown zoogonidangium probably measures on an 
average about 1 30 /x in diameter, but specimens have been observed measur- 
ing as much as 303 /x long by 127 /x broad, and 162 y long by 140 /x broad 
respectively, and as little as 65 jtx long by 54 jtx broad, including the thickness 
of the wall, while the production of zoogonidia was observed on a zoogonid- 
angium only 82 jtx in diameter. 
The formation of the internal cellulose projections from the cell-wall 
produces corresponding depressions in the cytoplasm of the cell. That 
these depressions are of secondary development, caused by the invagination 
of the surface of the protoplast, is shown by the fact that the arrangement 
of the cytoplasm bordering on the depressions is identical with that of 
the peripheral cytoplasm of the cell ; the lobes of the chloroplast are, how- 
ever, obliterated by mutual pressure and the colourless film of cytoplasm, 
which elsewhere lines the cell-wall, appears to be absent from the depressions 
near their base. Funnel-shaped depressions can be seen in the cytoplasm 
of the living cell at the surface (Text-fig. 1, B), but owing to the dense colour 
of the cell it is impossible to trace either the course or the extent of the 
tubular passages to which they lead except by means of sections. 
In consequence of the invagination of the surface, the more or less 
regular arrangement of the cytoplasmic reticulum characteristic of the 
vegetative cell becomes disturbed, and in an old zoogonidangium the mesh 
of the reticulum is usually much smaller than in a young one. Where the 
internal projections are long an actual splitting of the cytoplasm must even- 
tually take place, because the nucleus, which in vegetative cells is central 
in position, is frequently seen to lie close to the side of the depression 
(Fig. 13 ). 
The zoogonidangium contains large quantities of yellow oil, and very 
