parts resembling the background and invisible; a
Membracid (Homoptera) is entirely unlike an ant, but is concealed by an
ant-like shield. When we further realize that in this and other examples
of mimicry "the likeness is almost always detailed and remarkable,
however it is attained, while the methods differ absolutely," we
recognize that natural selection is the only possible explanation
hitherto suggested. In the cases of aggressive mimicry an animal
resembles some object which is attractive to its prey. Examples are
found in the flower-like species of _Mantis_, which attract the insects
on which they feed. Such cases are generally described as possessing
"alluring colours," and are regarded as examples of aggressive
(anticryptic) resemblance, but their logical position is here.

_Colours displayed in Courtship, Secondary Sexual Characters, Epigamic
Colours._--Darwin suggested the explanation of these appearances in his
theory of _sexual selection_ (_The Descent of Man_, London, 1874). The
rivalry of the males for the possession of the females he believed to be
decided by the preference of the latter for those individuals with
especially bright colours, highly developed plumes, beautiful song, &c.
Wallace does not accept the theory, but believes that natural selection,
either directly or indirectly, accounts for all the facts. Probably the
majority of naturalists follow Darwin in this respect. The subject is
most difficult, and the interpretation of a great proportion of the
examples in a high degree uncertain, so that a very brief account is
here expedient. That selection of some kind has been operative is
indicated by the diversity of the elements into which the effects can be
analysed. The most complete set of observations on epigamic display was
made by George W. and Elizabeth G. Peckham upon spiders of the family
_Attidae_ (_Nat. Hist. Soc. of Wisconsin_, vol. i., 1889). These
observations afforded the authors "conclusive evidence that the females
pay close attention to the love-dances of the males, and also that they
have not only the power, but the will, to exercise a choice among the
suitors for their favour." Epigamic characters are often concealed
except during courtship; they are found almost exclusively in species
which are diurnal or semi-diurnal in their habits, and are excluded from
those parts of the body which move too rapidly to be seen. They are very
commonly directly associated with the nervous syst