cates a declining rate of growth and becomes a
cause of arrest in growth.

It has now to be noticed how complexity of organisation is hindered by
reproductive activity and conversely. The hydra's power to produce young
ones from nearly all parts of its body is due to the comparative
homogeneity of its body, while it is not improbable that the smallness
of human fertility, compared with the fertility of large feline animals,
is due to the greater complexity of the human organisation--more
especially the organisation of the nervous system.

Of the inverse variation between activity and genesis we have examples
in the contrast between the fertility of birds and the fertility of
mammals. Comparing the large with the large and the small with the
small, we see that creatures which continually go through the muscular
exertion of sustaining themselves in the air and propelling themselves
rapidly through it are less prolific than creatures of equal weights
which go through the smaller exertion of moving about over solid
surfaces. The extreme infertility of the bat is most striking when
compared with the structurally similar but very prolific mouse; a
difference in the rate of multiplication which may fairly be ascribed to
the difference in the rate of expenditure.

_Interpretation and Qualification_

Derived as the self-sustaining and waste-sustaining forces are from a
common stock of force, it necessarily happens that, other things being
equal, increase of the one involves decrease of the other. It may
therefore be set down as a law that every higher degree of organic
evolution has for its concomitant a lower degree of the peculiar organic
dissolution which is seen in the production of new organisms.

How is the ratio between individuation and genesis established in each
case? All specialties of the reproductive process are due to the natural
selection of favourable variations. Given a certain surplus available
for race preservation, and it is clear that by indirect equilibration
only can there be established that peculiar distribution of this surplus
which is seen in each case.

Here a qualification must be made. Recognising the truth that every
increase of evolution which is appropriate to the circumstances of an
organism brings an advantage somewhat in excess of its cost, the general
law, more strictly stated, is that genesis decreases not quite so fast
as individuation increases. The result of greater individuation-