Nevertheless, be
this as it will, whether they exist in two or in twenty species, the
occurrence of these peculiar hook-like processes is certainly very
limited.
Now our two species live sheltered beneath slightly tilted stones in the
neighbourhood of the shore: one of them, Melita Messalina, so high that
it is but rarely covered by the water; the other, Melita insatiabilis, a
little lower; both species live together in numerous swarms. We cannot
therefore suppose that the loving couples are threatened with
disturbance more frequently than those of other species, nor would it be
more difficult for the male, than for those of other species, in case of
his losing his female, to find a new one. Nor is it any more easy to see
how the contrivance on the body of the female for insuring the act of
copulation could be injurious to other species. But so long as it is not
demonstrated that our species are particularly in want of this
contrivance, or that the latter would rather be injurious than
beneficial to other species, its presence only in these few Amphipoda
will have to be regarded not as the work of far-seeing wisdom, but as
that of a favourable chance made use of by Natural Selection. Under the
latter supposition its isolated occurrence is intelligible, whilst we
cannot perceive why the Creator blessed just these few species with an
apparatus which he found to be quite compatible with the "general plan
of structure" of the Amphipoda, and yet denied it to others which live
under the same external conditions, and equal them even in their
extraordinary salacity.
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