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GENESIS

of fertilisation/' In short, the germ-cells, separately con-
sidered, are cells in which the power of further asexual multi-
plication is exhausted, as it is known to become exhausted in
Infusorians and such body-cells as nerve-cells; there arises
a state which initiates a sexual union or amphimixis of the two
kinds of germ-cells, and the decrease in the chromatin is an
initial cause of that state.

We quote this speculation as a good instance of Spencer's
continual -endeavour to rationalise puzzling and exceptional
facts by showing that there is a general principle underlying
them. But the objections to his hypothesis are numerous.
Nature ova or spermatozoa will not normally divide if
left to themselves, but that is because they are special-
ised to secure amphimixis, not because their powers are in
any way declining or impoverished. A parthenogenetic ovum
gives off one polar body—though without reduction in the
number of chromosomes—and then proceeds by asexual
multiplication or ordinary cell division to build up a body.
The spore of a fern or a moss has only half the number of
chromosomes that the cells of its producer have, yet it
proceeds by asexual multiplication or ordinary cell-division to
build up the gametophyte or sexual generation.

Genesis.—Spencer attempted a classification of the
various modes of reproduction that occur among
organisms—asexual reproduction (agamogenesis) by
fission and budding, sexual reproduction (gamo-
genesis) by specialised germ-cells usually involving
fertilisation or amphimixis, and all the complications
involved in "alternation of generations" (metagenesis),
the development of eggs without fertilisation (par-
thenogenesis), and so on. But what gives particular
importance to the chapter on genesis is not the discus-
sion of the modes of reproduction, but the general
conclusion that nutrition and reproduction are
antithetic processes—a very fruitful idea in biology.

Where there is alternation of generation, sexual and
asexual, we find that asexual reproduction continues



	GENESIS of fertilisation/' In short, the germ-cells, separately con- sidered, are cells in which the power of further asexual multi- plication is exhausted, as it is known to become exhausted in Infusorians and such body-cells as nerve-cells; there arises a state which initiates a sexual union or amphimixis of the two kinds of germ-cells, and the decrease in the chromatin is an initial cause of that state. We quote this speculation as a good instance of Spencer's continual -endeavour to rationalise puzzling and exceptional facts by showing that there is a general principle underlying them. But the objections to his hypothesis are numerous. Nature ova or spermatozoa will not normally divide if left to themselves, but that is because they are special- ised to secure amphimixis, not because their powers are in any way declining or impoverished. A parthenogenetic ovum gives off one polar body—though without reduction in the number of chromosomes—and then proceeds by asexual multiplication or ordinary cell division to build up a body. The spore of a fern or a moss has only half the number of chromosomes that the cells of its producer have, yet it proceeds by asexual multiplication or ordinary cell-division to build up the gametophyte or sexual generation. Genesis.—Spencer attempted a classification of the various modes of reproduction that occur among organisms—asexual reproduction (agamogenesis) by fission and budding, sexual reproduction (gamo- genesis) by specialised germ-cells usually involving fertilisation or amphimixis, and all the complications involved in "alternation of generations" (metagenesis), the development of eggs without fertilisation (par- thenogenesis), and so on. But what gives particular importance to the chapter on genesis is not the discus- sion of the modes of reproduction, but the general conclusion that nutrition and reproduction are antithetic processes—a very fruitful idea in biology. Where there is alternation of generation, sexual and asexual, we find that asexual reproduction continues