Smith . — Cytological Studies in the Protococcales . /. 463 
same time, those at one end are not at the same stage of division as those at 
the other. The mass of chromosomes in the equatorial plate is always 
clearly recognizable, but the spindle fibres are not seen so easily. The 
number of chromosomes is about 10 or 1 The individual fibres of the spindle 
form a cone-shaped structure that ends in a small body (Figs. 15 and 16). 
In some division figures the small body at either end of the spindle can be 
seen even though the spindle itself is indistinguishable. This small body at 
the spindle pole was not observed excepting during the metaphases. The 
nature of this body is doubtful since there are no indications of polar radia- 
tions. In the telophase figures found, the spindle could not be seen, but the 
two groups of chromosomes were easily recognizable, forming deeply staining 
masses. The details of the reconstruction of the daughter-nuclei are also 
lacking, but there are frequently paired nuclei in the cell, indicating cases 
where nuclear division has just been completed. 
Formation of Zoospores. 
There is no definite stage in the development of the alga at which 
zoospore development takes place. Instances were not found, however, of 
the formation of zoospores in cells containing less than eight nuclei. The 
process of zoospore formation is that which has been called 4 progressive 
cleavage’ by Harper ( 3 ). The first indication may be a single transverse 
cleavage of the cytoplasm, or several transverse cleavages may take place at 
the same time. When there is a single cleavage plane formed it is not located 
in the middle of the cell but at either end (Fig. 2). The process of cleavage is 
a furrowing in, the furrow starting at the plasma membrane and gradually 
growing towards the centre. Cross-sections show furrows starting towards 
one another from opposite sides of the cell, but the furrows probably appear at 
first as a ring-shaped furrow in the plasma membrane and extending entirely 
around the cell. In some cases the protoplasmic masses formed by the 
cleavage furrows contain approximately the same number of nuclei (Fig. 3), 
while in others the number of nuclei is decidedly unequal (Fig. 2). The position 
of the pyrenoids remains unchanged during the formation of the first cleavage 
furrows, so that whether or not a protoplasmic segment will contain a pyrenoid 
when it is cut off is merely a matter of chance. Fragments may also be 
formed in which there are two pyrenoids (Fig. 3). The number of transverse 
cleavage planes formed varies, but the greater the number of nuclei in the 
cell the greater the number of transverse planes. After several transverse 
cleavage planes have been formed the cleavage furrows appear in the long 
axis of the cell. These do not extend from one end of the mother-cell wall 
to the other, but are formed between two transverse cleavage planes (Figs. 3 
and 4), the new furrows appearing first in the plasma membranes of the 
central protoplasmic masses. Furrows generally begin at opposite sides and 
