NUTRITION AND REPRODUCTION 125

ffient of sexual reproduction until the rate of growth
begins to decline. " For so long as the rate of growth
continues rapid, there is proof that the organism gets
food with facility—that expenditure does not seriously
check assimilation 5 and that the size reached is as
yet not disadvantageous: or rather, indeed, that it is
advantageous. But when the rate of growth is much
decreased by the increase of expenditure—when the
excess of assimilative power is diminishing so fast as
to indicate its approaching disappearance—it becomes
needful, for the maintenance of the species, that this
excess shall be turned to the production of new in-
dividuals 5 since, did growth continue until there was
a complete balancing of assimilation and expenditure,
the production of new individuals would be either
impossible or fatal to the parent. And it is clear that
* natural selection * will continually tend to determine
the period at which gamogenesis commences, in such
a way as most favours the maintenance of the race."

That natural selection punctuates the life to advan-
tage does not imply that it works directly towards
such a remote goal as species-maintaining; it means
that the arrangements which do secure this end most
effectively are those which tend to establish themselves.
Those that do not secure this end are eliminated.

Nutrition and Reproduction.—Spencer's doctrine of
the antithesis between Nutrition and Reproduction
is of great importance in biology, and we must dwell
on it a little longer.

The life of organisms is rhythmic. Plants have
their long period of vegetative growth, and then
suddenly burst into flower. Animals in their young
stages grow rapidly, and as the growth ceases re-ce to the chapter on genesis is not the discus-