PSEUDOSPORA VOLVOCIS, CIENKOWSKI. 220 
A later stage (fig. 15) shows a very considerable increase 
in the nuclear material; about eight to thirty nuclei larger 
in size than the original masses can be seen in the sphere. I 
am unable to say how the increase in the number of nuclei 
takes place; this much, however, seems certain that all the 
nuclear material of the sphere is derived from the thickened 
rays of the original nucleus. The sphere increases still 
further in size (fig. 16) and the nuclei break up apparently 
into minute particles, as for some time before segmentation 
begins they can no longer be detected in my preparations. 
When the sphere has reached its full size, ‘(007 mm.—011 mm. 
in diameter, segmentation occurs. A constriction appears 
which divides the sphere into two equal segments (figs. 
17-18). The parts, however, remain closely apposed to one 
another. Hach of these now divides. After this the division 
of the segments is not quite regular, and the spherical shape 
is usually lost. Finally a very large number of segments are 
formed —in one case I counted a hundred and sixteen, and even 
in very small single-sphered individuals I have never found 
fewer than sixteen. The process of segmentation occupies as 
a rule from ten to thirty minutes. After the segmentation 
is complete (fig. 19) the segments lie motionless for a while, 
and then move a little apart before actually becoming motile. 
If the protoplasmic body which surrounded the sphere has 
not already broken down they pierce through it and escape. 
The segments set free are small oval or round uniflagellate 
gametes, varying in size from ‘00116-00186 mm. The flagel- 
lum is thick (average length ‘0046 mm.) and slightly curled ; 
it arises from a point about half way from the anterior end 
and propels the animal forwards. Hach gamete appears to 
possess a nucleus, that is to say, in stained specimens a spot 
that stains more deeply than the rest of the creature can just 
be discerned with the highest powers of the microscope. 
This probably is the nucleus, but I can say nothing as to its 
structure. 
Shortly after becoming free the gametes fuse in pairs, 
forming zygotes with two flagella (fig. 20). Gametes arising 
