172 
W. B. Grove. 
was an artefact, produced by the mutual pressure of the gelatinous 
capsules surrounding each cell at a certain stage. There are no 
cell connections in Pleodovina and no contiguous polygonal 
compartments such as Volvox possesses. 
The outer coat frequently showed slight irregular projections 
at the posterior end, which occasionally assumed the form of three 
regular manielons placed at the corners of a triangle (Fig. 3). When 
they occurred, these mamillae were rendered more conspicuous by 
a number of minute highly refringent colourless granules, attached 
to them as well as to the rest of the outer surface : these granules 
might be nothing but particles of debris adhering to the mucus, 
although they seemed to be too regular in size for such a description 
—weak acids had no effect upon them. 
The most striking point about the colonies was the inequality 
in size of the cells of which they were composed, the four anterior 
cells being always distinctly smaller than the others (Figs. 1,2): in 
many cases, but not in all, it could be seen that the four posterior 
cells were also larger than those in the intermediate zones. The 
ratio of the diameters of the smallest and largest in a colony varied 
from an average of about 1:1£ to 1:2 in the few extreme cases. 
There was oftentimes, in addition, a certain wider spacing apart 
of the front rows which caused the anterior half of the colony to 
show decidedly more of the hyaline mucus than the posterior half. 
The measurement of the cells in one individual gave such sizes as, 
e.g., 25, 24, 22, 21 and 17/a, or 18, 15, 14, 13-5, 12-5/a, taking the rows 
respectively from back to front, although the decrease was not 
always so regular. 
Each cell was approximately spherical, containing a hollow 
cup-shaped chloroplast, with a nucleus occupying nearly the whole 
of its central cavity and a conspicuous nucleolus; the anterior 
portion of the protoplasm was hyaline and bore at its upper end 
(not infrequently on a short projecting neck) two flagella of the 
usual kind. The chloroplast contained, in the mature cell, from 
one to eleven (most often three or four) roundish pyrenoids, but no 
pyrenoid could be detected in the cells of the very young daughter- 
colonies. 
Another striking feature of the colony related to the red eye- 
spots situated near the base of the flagella. These varied 
considerably in size, being largest (3 /a) in the four anterior cells, and 
thence diminishing gradually in each zone, until in the posterior 
cells they were minute or even completely absent (Fig. 1). Their 
