nd separating into several parts, each
one constituting a new individual.

The sexual organs are formed on special branches, and their
arrangement is such as to make the species instantly recognizable.

The first sign of their development is the formation of a short
branch (Fig. 21, _A_) growing out at right angles to the main
filament. This branch becomes club-shaped, and the end somewhat
pointed and more slender, and curves over. This slender, curved
portion is almost colorless, and is soon shut off from the rest of
the branch. It is called an "antheridium," and within are produced,
by internal division, numerous excessively small spermatozoids.

As the branch grows, its contents become very dense, the oil drops
especially increasing in number and size. About the time that the
antheridium becomes shut off, a circle of buds appears about its
base (Fig. 21, _B_, _og._). These are the young ooegonia, which
rapidly increase in size, assuming an oval form, and become
separated by walls from the main branch (_C_). Unlike the
antheridium, the ooegonia contain a great deal of chlorophyll,
appearing deep green.

When ripe, the antheridium opens at the end and discharges the
spermatozoids, which are, however, so very small as scarcely to be
visible except with the strongest lenses. They are little oval
bodies with two cilia, which may sometimes be rendered visible by
staining with iodine.

[Illustration: FIG. 22.--_A_, non-sexual reproduction in _Vaucheria
sessilis_. _B_, non-sexual spore of _V. geminata_, x 50.]

The ooegonia, which at first are uniformly colored, just before
maturity show a colorless space at the top, from which the
chloroplasts and oil drops have disappeared (_D_), and at the same
time this portion pushes out in the form of a short beak. Soon after
the wall is absorbed at this point, and a portion of the contents is
forced out, leaving an opening, and at the same time the remaining
contents contract to form a round mass, the germ or egg cell
(Fig. 21, _E_, _o_). Almost as soon as the ooegonium opens, the
spermatozoids collect about it and enter; but, on account of their
minuteness, it is almost impossible to follow them into the egg
cell, or to determine whether several or only one enter. The
fertilized egg cell becomes almost at once surrounded by a wall,
which rapidly thickens, and forms a resting spore. As the spore
ripens,