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

SOME PROBLEMS OP REPRODUCTION. 41
V. COMPARATIVE GAMETOGENY IN THE ANIMAL KINGDOM.
A. PROTOZOA.
1. Flagellata.
Our chief knowledge of the gametogeny in the true Flagellata
is due to the researches of Dallinger and Drysdale.
After repeated acts of fission karyogamic unions occur, always
binary.
In CEKCOMONAS DUJARDINII and TETRAMITUS ROSTRATUS the
gametes resemble the ordinary forms, and are isogamous.
BODO SALTANS is anisogamous; the larger gamete, produced
by the longitudinal fission habitual in this species, has the
specific form; the microgamete is smaller, and produced by
transverse fission. BODO CAUDATUS and MONAS DALLINGERII
are also anisogamous, the microgamete having the same form
as the megagamete, and only differing in size. In DALLINGERIA
DRYSDALII the gametes are equal in size, but dissimilar, the
one being like the ordinary individuals, triflagellate, the
other uniflagellate; so that in this group we already find tendencies
to anisogamy, and indications of the specialisation of
gametes by peculiar forms of bipartition.
In NOCTILUCA, belonging to the Cystoflagellates, conjugation
is isogamous between individuals of the ordinary type.
In this case we shall describe the behaviour of the zygote,
which affords a most instructive parallel to certain forms of
spermatogeny in the Metazoa. The nucleus of the zygote
comes to lie peripherally below an elevation of the cytoplasm;
and as the nucleus divides, so the cytoplasmic elevation is
parted by crucial furrows into hillocks, into which the daughternuclei
pass one to each. By some eight or nine bipartitions
256or 512 buds are formed, grouped into a disc-like elevation.
By a basal thinning the buds are abstricted as uninucleate
flagellates, while the body of the zygote is left, containing a
residue of cytoplasm but no nucleus, and obviously incapable