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

SOME PROBLEMS OF BEPBODUCTTON. 17
centre. In Pelvetia six of the nuclei pass towards the
equator of the oogonium, and two lie towards the ends of
its axis. The cytoplasm separates into two oospheres, each
containing one of the axial nuclei, while the six equatorial
nuclei are left out as rejection-nuclei. Finally, in Halidrys
and Himanthalia, and also Cystoseira, seven of the
nuclei pass to the periphery as rejection-nuclei, while the
eighth remains in the centre of the cytoplasm of the oogonium
which is thus directly resolved into the single oosphere.
Oltmanns, who gave the first correct account of these processes,
rightly remarked on their close identity with the formation
of polar bodies in the Metazoa. It is obvious that the
formation in Fucus is primitive, and that the advantages due
to the increased size of the oospheres in the other genera
are obtained by the abortion of half, three quarters, or seven
eighths of them, and that this physiological advantage is a
relative gain and not an absolute necessity.
B. APOCYTIAL FORMS.
1. Green or Algal Types.
CLADOPHORA has septate filaments with many nuclei in each
joint, and forms zoospores, ordinary or isogametal, by the resolution
of these apocytia into uninucleated swarmers. In both
cases a portion of the cytoplasm is eliminated at the boundaries
of these cells, and takes no further part in the living processes.
From Berthold's description 1 it appears certain that
he is correct in regarding this excretion of " epiplasm" as
derived from a primitive formation of cell-wall, a process
which has been lost in the evolution of the group. We may
note that this confirms the propriety of our using Vuillemin's
term "apocytial" instead of Sachs' "non-cellular."
The gametes of Cladophora are biflagellate, the ordinary
zoospores quadriflagellate, a distinction which we interpret as
1
Op, cit., p. 302. He expressly notes (p. 305), in opposition to Dodel-
Port, that such formations, occurring also in asexual spore-formation, can have
no relation to fertilisation-processes as such.
VOL. XXXIII, PAET I.—NEW SER. B