and choice of either sex. Nevertheless some few apparent exceptions
occur; thus, as I hear from Dr. Baird, the males of certain Entozoa, or
internal parasitic worms, differ slightly in colour from the females;
but we have no reason to suppose that such differences have been
augmented through sexual selection. Contrivances by which the male
holds the female, and which are indispensable for the propagation of
the species, are independent of sexual selection, and have been
acquired through ordinary selection.
Many of the lower animals, whether hermaphrodites or with separate
sexes, are ornamented with the most brilliant tints, or are shaded and
striped in an elegant manner; for instance, many corals and
sea-anemones (Actiniae), some jelly-fish (Medusae, Porpita, etc.), some
Planariae, many star-fishes, Echini, Ascidians, etc.; but we may
conclude from the reasons already indicated, namely, the union of the
two sexes in some of these animals, the permanently affixed condition
of others, and the low mental powers of all, that such colours do not
serve as a sexual attraction, and have not been acquired through sexual
selection. It should be borne in mind that in no case have we
sufficient evidence that colours have been thus acquired, except where
one sex is much more brilliantly or conspicuously coloured than the
other, and where there is no difference in habits between the sexes
sufficient to account for their different colours. But the evidence is
rendered as complete as it can ever be, only when the more ornamented
individuals, almost always the males, voluntarily display their
attractions before the other sex; for we cannot believe that such
display is useless, and if it be advantageous, sexual selection will
almost inevitably follow. We may, however, extend this conclusion to
both sexes, when coloured alike, if their colours are plainly analogous
to those of one sex alone in certain other species of the same group.
How, then, are we to account for the beautiful or even gorgeous colours
of many animals in the lowest classes? It appears doubtful whether such
colours often serve as a protection; but that we may easily err on this
head, will be admitted by every one who reads Mr. Wallace s excellent
essay on this subject. It would not, for instance, at first occur to
any one that the transparency of the Medusae, or jelly-fish, is of the
highest service to them as a protection; but when we are reminded by
Haeckel that not only the Medusae, but many floating Mollusca,
crustaceans, and even small oceanic fishes partake of this same
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