their partners. This is the case with the common silk-moth (B. mori),
as I have been told by some continental and English breeders. Dr.
Wallace, who has had great experience in breeding Bombyx cynthia, is
convinced that the females evince no choice or preference. He has kept
above 300 of these moths together, and has often found the most
vigorous females mated with stunted males. The reverse appears to occur
seldom; for, as he believes, the more vigorous males pass over the
weakly females, and are attracted by those endowed with most vitality.
Nevertheless, the Bombycidae, though obscurely-coloured, are often
beautiful to our eyes from their elegant and mottled shades.
I have as yet only referred to the species in which the males are
brighter coloured than the females, and I have attributed their beauty
to the females for many generations having chosen and paired with the
more attractive males. But converse cases occur, though rarely, in
which the females are more brilliant than the males; and here, as I
believe, the males have selected the more beautiful females, and have
thus slowly added to their beauty. We do not know why in various
classes of animals the males of some few species have selected the more
beautiful females instead of having gladly accepted any female, as
seems to be the general rule in the animal kingdom: but if, contrary to
what generally occurs with the Lepidoptera, the females were much more
numerous than the males, the latter would be likely to pick out the
more beautiful females. Mr. Butler shewed me several species of
Callidryas in the British Museum, in some of which the females
equalled, and in others greatly surpassed the males in beauty; for the
females alone have the borders of their wings suffused with crimson and
orange, and spotted with black. The plainer males of these species
closely resemble each other, shewing that here the females have been
modified; whereas in those cases, where the males are the more ornate,
it is these which have been modified, the females remaining closely
alike.
In England we have some analogous cases, though not so marked. The
females alone of two species of Thecla have a bright-purple or orange
patch on their fore-wings. In Hipparchia the sexes do not differ much;
but it is the female of H. janira which has a conspicuous light-brown
patch on her wings; and the females of some of the other species are
brighter coloured than their males. Again, the females of Colias edusa
and hyale have orange or yellow spots on the black marginal border,
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