at Mr.
Darwin terms "sexual selection" appears to be shown by the otherwise
inexplicable fact, that in the groups which have a protection of any
kind independent of concealment, sexual differences of colour are either
quite wanting or slightly developed. The Heliconidae and Danaidae,
protected by a disagreeable flavour, have the females as bright and
conspicuous as the males, and very rarely differing at all from them.
The stinging Hymenoptera have the two sexes equally well coloured. The
Carabidae, the Coccinellidae, Chrysomelidae, and the Telephori have both
sexes equally conspicuous, and seldom differing in colours. The
brilliant Curculios, which are protected by their hardness, are
brilliant in both sexes. Lastly, the glittering Cetoniadae and
Buprestidae, which seem to be protected by their hard and polished coats,
their rapid motions, and peculiar habits, present few sexual differences
of colour, while sexual selection has often manifested itself by
structural differences, such as horns, spines, or other processes.

_Cause of the dull Colours of Female Birds._

The same law manifests itself in Birds. The female while sitting on her
eggs requires protection by concealment to a much greater extent than
the male; and we accordingly find that in a large majority of the cases
in which the male birds are distinguished by unusual brilliancy of
plumage, the females are much more obscure, and often remarkably
plain-coloured. The exceptions are such as eminently to prove the rule,
for in most cases we can see a very good reason for them. In particular,
there are a few instances among wading and gallinaceous birds in which
the female has decidedly more brilliant colours than the male; but it is
a most curious and interesting fact that in most if not all these cases
the males sit upon the eggs; so that this exception to the usual rule
almost demonstrates that it is because the process of incubation is at
once very important and very dangerous, that the protection of obscure
colouring is developed. The most striking example is that of the gray
phalarope (Phalaropus fulicarius). When in winter plumage, the sexes of
this bird are alike in colouration, but in summer the female is much the
most conspicuous, having a black head, dark wings, and reddish-brown
back, while the male is nearly uniform brown, with dusky spots. Mr.
Gould in his "Birds of Great Britain" figures the two sexes in both
winter and summer plumage, and remark