1g01-1902.] Report of the Microscopical Section. 381 
and are provided with delicate ducts which open into the 
atrial cavity. The mature ova and spermatozoa are thus 
carried out of the body by the current of water flowing 
through the atrial aperture. 
The type of Vegetable Life chosen for study was Codium, 
—No. IV. of “L.M.B.C. Memoirs.” Codium is a genus of the 
Siphonaceze (Confervoid Algx). It is a marine plant, with 
branched filaments interwoven into a spongiform frond of a 
dark-green colour. The species which came under observation 
was Codium tomentosum, a plant about eight inches or so in 
height, found at the south end of the Isle of Man. It grows 
in shallow rock-pools at or near low-water mark, and is 
attached to the substratum by numerous small rhizoids. The 
fronds are cylindrical, and usually dichotomously branched, 
and consist of a single multi-nucleated cell. They become 
thicker towards the apex, and end in a rounded point of a 
much darker colour than the lower part. Reproduction takes 
place by the discharge of the contents of certain sporangial 
cells in the form of numerous small ciliated zoospores. These 
sporangial cells are borne on the sides of the fronds, on what 
are called the palisade cells. 
Codium was chosen as the type of single-celled plants. A 
vegetable cell has been detined as “a closed sac composed of 
an (originally) imperforate membrane formed of the chemical 
substance called cellulose, this membrane enclosing fluid con- 
tents so long as the cell retains its vitality.” It is by the 
ageregation of cells that the plant is built up. Ordinarily 
the plant consists of an infinite number of cells, each with at 
least one nucleus, but in the type under consideration the 
plant consists of but a single cell with an indefinite number 
of nuclei. The branched filaments of Codium are thus but the 
extension and modification of the original cell. 
Mr Crawford, who conducted the demonstrations, had in 
addition specimens of allied genera, such as Botrydiwm, a 
microscopic plant found on damp clayey ground, in which the 
cell retains its original spherical form. It is attached to the 
substratum by a ramified filamentous base. Vaucheria, an 
interesting plant, growing in fresh or salt water or on damp 
ground, and in which the cell becomes filamentous. It is in 
