Trow . — The Karyology of Saprolegnia. 6n 
are seldom to be found, while they have only been seen in 
.S. Thureti on very rare occasions. 
An oogonium produces from i to 40 or 50 oospheres. 
The antheridia give rise to small tubes — fertilization-tubes 
— which pierce the walls of the oogonium and apply them- 
selves closely to the naked oospheres. The oosphere then 
becomes clothed with a wall of cellulose and is now known as 
an oospore. In the young oospore De Bary noticed a clearer 
central speck, which he looked upon, at least provisionally, as 
a nucleus. In the mature oospore an oleaginous mass, which 
generally occupies a central position, is universally present. 
The oospore which usually remains in the resting condition 
for some time, ultimately germinates, and produces in most 
cases a hypha, which either forms a sporangium, or at once 
develops into a new generation. 
De Bary (’ 81 ) has given us an admirable account, with figures, 
of the stages in the development of the oogonium and oospheres 
in S. Thureti. The oogonium in the Saprolegnieae makes its 
appearance as a terminal swelling either on main or lateral 
branches, or occasionally is formed in an intercalary manner 
at some other point of a filament. Large quantities of proto- 
plasm pass into the swelling, which is then delimited from the 
rest of the mycelium by one or two transverse walls. The 
mass of protoplasm generally has the form of a hollow sphere 
and surrounds a large central vacuole, which is continuous at 
first with the vacuole of the filament upon which the oogonium 
is borne. After a time, peculiar shifting vacuoles make their 
appearance in the protoplasm. These fuse together and 
finally unite with the large central vacuole. The layer of 
protoplasm thus becomes denser and thinner and the central 
vacuole larger. The protoplasm then moves gradually towards 
certain points so as to form hemispherical heaps projecting 
into the vacuole, and attached to one another ultimately by 
an extremely thin layer at their bases. These heaps may 
be called the oosphere-rudiments. Ultimately the thin con- 
necting layer is ruptured and the oospheres lie free, in contact 
with each other, in the cavity of the oogonium. After a 
