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

60 . MABCTJS M. HABTOG.
nay, in some cases the oosperm or zygote in each archegonium
by early fission produces four embryos; and yet only one
embryo ripens in the seed. In Angiosperms the proportion of
matured seed to ovules and carpels varies very greatly. In
Anemone several ovular origins are formed, but only one
ovule attains full size in each carpel; in Drupacese two
ovules are present, but only one ripens into a seed, the exception
constituting the well-known " Philippina " of stone-fruit.
The one-seeded Acorn is the outcome of an ovary with three
biovulate carpels.
The fate of the central procarpia or oogonia of Co rail in a,
reduced to the position of mere agents for the transmission of
the male substance, finds a parallel in the peculiar transformation
undergone by the showy sterile peripheral flowers in the
inflorescence of Viburnum, Hydrangea, and some Composites,
into mere signboards, attracting the insects whose
visits fertilise the less conspicuous central flowers. The petals
of many flowers (e.g. Ranunculaceae) are merely the
degraded sterile outer stamens.
Iu the animal world severe competition exists between
embryos in those Molluscs which have numerous eggs in a
single capsule. Here the first larvae to hatch out in the veliger
stage eat up their more tardy brothers and sisters.
We may note that some of the nuclei produced by the
zygote nucleus of the exconjugate Ciliate are rejection-nuclei,
and fail to take any share in the life of its offspring.
D. Summary of Gametogenic Processes.
1. In many Protozoa the gametes are apparently ordinary
individuals or swarmers, the product of normal fission or
brood-formation.
2. In many Phytomastigopods and Protophytes the gametes
differ from ordinary zoospores in being produced by more
rapidly repeated acts of fission or segmentation, and in their
smaller size.