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

16 MAECUS M. HARTOG.
COLEOCHJETE^: are also oogamous; the oosophere essentially
resembles that of Oedogoniese, but it is the direct transformation
of a superficial tissue-cell: its fertilising beak is
prolonged into a slender tube open at the apex, the "Trichogyne;"
the formative cytoplasm contained therein degenerates
as in Oedogoniese, while the rest of the protoplasm
in the body of the oogonium rounds off into the oosphere.
The spermatogonium undergoes two binary divisions, and
the cell-body of each of the cells so formed escapes as a biflagellate
spermatozoon. In certain species the four daughtercells
of the spermatogonium are budded off at its apex, and
though no information has been given we may well believe
the process to be that following as found in the spore formation
of Basidiomycetes. The nucleus of the basidium divides
by two mitoses, and each of the four nuclei so formed migrates,
accompanied by cytoplasm, into a bud formed at the apex,
which becomes shut off by a septum from the now sterile and
enucleate basidium. 1 That we are fairly justified in interpreting
budding here as a modification of segmentation is obvious when
we reflect on the behaviour of meroblastic ova or the zygote
of Noctiluca (infra, p. 41) in their segmentation.
In the MELANOPHYCEJE, or Olive Seaweeds, we have seen the
transition from isogamy through anisogamy to hypoogamy.
True oogamy occurs in the highest order of this group, the
FUCACEJE. 2 In these the oogonial nucleus divides by successive
mitoses into eight gametonuclei. In Fucus each of
these attracts round it one eighth of the cytoplasm, so that
there are eight oospheres. In Ascophyllum four of the
nuclei pass to the centre, and four lie at equal distances nearer
the surface of the cytoplasm.' The cytoplasm aggregates
around the four peripheral nuclei to form four oospheres,
leaving the four central nuclei as rejection-bodies in the
1
Possibly, however, the formation may take place as in the Meridian genus
Chondria (infra, p. 30).
* The following account is taken from Oltmanns' " Beitrage zur Vergleich.
Entwieklungsgesch. der Fucacese," in ' Sitzungsber. d. Berlin Akad.,' 1889,
p. 587.