NUTRITION AND REPRODUCTION 1*7

tlon be carried on in all cases, as it is in many cases,
by asexual reproduction ?

As yet, he says, biology is not advanced enough
to give a reply, but a certain hypothetical answer
may be suggested. ** Seeing, on the one hand, that
gamogenesis recurs only in individuals which are
approaching a state of organic equilibrium; and
seeing, on the other hand, that the sperm-cells and
germ-cells thrown off by such individuals are cells
in which developmental changes have ended in
quiescence, but in which, after their union, there
arises a process of active cell-formation; we may
suspect that the approach towards a state of general
equilibrium in such gamogenetic individuals is accom-
panied by an approach towards molecular equilibrium
in them; and that the need for this union of sperm-
cell and germ-cell is the need for overthrowing this
equilibrium, and re-establishing active molecular
change in the detached germ—a result probably
effected by mixing the slightly different physiological
units of slightly different individuals."

Now, while Spencer was probably right in saying
that fertilisation promotes change, we cannot think
that he succeeded in finding what he was seeking,
namely a primary physiological reason why sexual
reproduction should occur. It may be pointed out
that it is only in a limited sense that sperm-cells or
egg-cells can be spoken of as in a state of " quiescence/'
and that it is only in a limited sense that the organism
which has finished growing and is beginning to be
sexual can be spoken of as in a state of general or
molecular equilibrium. An egg-cell is quiescent, as
a seed lying in the ground is quiescent, awaiting its grow rapidly, and as the growth ceases re-ce to the chapter on genesis is not the discus-