Some Problems of Reproduction: a Comparative Study of ...

62 . MARCUS M. HAHTOG.
either directly or after preliminary division of the nuclei
(Cladophora).
11. In some Apocytial Plants the gametonucleus (whether
of iso- or oo-gametes, but not of spermatogametes) is the product
of the union of several nuclei, either the ordinary vegetative
nuclei (Dasycladus), or the offspring of the vegetative
nuclei by antecedent mitotic divisions (Peronospora). In
both cases the gametes are obligatory.
12. Hence preliminary nuclear division is not a necessary
antecedent to the differentiation of obligatory gametes.
13. Since the nuclei formed in heterogeneous gametogeny
(§§ 5—7) are all similar, and contain (in every case when the point
has been worked out) an equal number of chromatic elements,
we conclude that the difference between an arrested and a
functional gamete lies in their cytoplasm, not in their nuclei
(0. Hertwig).
14. The alleged "processes of excretion" antecedent to
fertilisation and incidental to gametogeny are neither universal
nor uniform. Under this head we may group the following
processes, which I have made to include all cases where part
of the gamete takes no share in the formation of the zygote.
(a) Part of the oogamete is utilised in the formation of a
receptive or transmitting organ for the male; of this character
is the trichogyne in Coleochseteaa and Floridese;
the beak with its mucified cytoplasm in Oedogoniese (and
Vaucheria?).
(b) The formation of non-nucleated epiplasm by isogametes,
originally referable to a formation of cell-walls, which remains
in abeyance, in some apocytial plants (Cladophoreae and
Protomyces ; found also in similar formation of the asexual
zoospores).
(c) The cutting off of a wall of cytoplasm around the central
vacuole of an apocytium or cell (Acetabularia, Botrydium,
and Ulothrix).
(d) A similar excretion to (b) of non-nucleated protoplasm
from the oospores of Saprolegniese, afterwards resumed by
them; the same process occurs with the asexual zoospores.