election, to the effects of which, acting alternately with regression
or degradation as above explained (p. 328) must be imputed the
development of the countless floral structures we now behold. Even the
primitive flowers, whose initiation may, perhaps, have been caused, or
rendered possible, by the irritation set up by insects' visits, must,
from their very origin, have been modified, in accordance with the
supreme law of utility, by means of variation and survival of the
fittest.]

[Footnote 212: In an essay on "The Duration of Life," forming part of
the translation of Dr. Weismann's papers already referred to, the author
still further extends the sphere of natural selection by showing that
the average duration of life in each species has been determined by it.
A certain length of life is essential in order that the species may
produce offspring sufficient to ensure its continuance under the most
unfavourable conditions; and it is shown that the remarkable
inequalities of longevity in different species and groups may be thus
accounted for. Yet more, the occurrence of death in the higher
organisms, in place of the continued survival of the unicellular
organisms however much they may increase by subdivision, may be traced
to the same great law of utility for the race and survival of the
fittest. The whole essay is of exceeding interest, and will repay a
careful perusal. A similar idea occurred to the present writer about
twenty years back, and was briefly noted down at the time, but
subsequently forgotten.]

[Footnote 213: The outline here given is derived from two articles in
_Nature_, vol. xxxiii. p. 154, and vol. xxxiv. p. 629, in which
Weismann's papers are summarised and partly translated.]

[Footnote 214: There are many indications that this explanation of the
cause of variation is the true one. Mr. E.B. Poulton suggests one, in
the fact that parthenogenetic reproduction only occurs in isolated
species, not in groups of related species; as this shows that
parthenogenesis cannot lead to the evolution of new forms. Again, in
parthenogenetic females the complete apparatus for fertilisation remains
unreduced; but if these varied as do sexually produced animals, the
organs referred to, being unused, would become rudimentary.

Even more important is the significance of the "polar bodies," as
explained by Weismann in one of his _Essays_; since, if his
interpretation of them be correct, variability is a necessary
con