ow it happens, that the
tracts in which distinct developments of colour appear, should so often
be marked out by the chief divisions of the bony structure in
vertebrates, and by the segments in the annulosa. There is, however,
another correspondence of even greater interest and importance.
Brilliant colours usually appear just in proportion to the development
of tegumentary appendages. Among birds the most brilliant colours are
possessed by those which have developed frills, crests, and elongated
tails like the humming-birds; immense tail-coverts like the peacock;
enormously expanded wing-feathers, as in the argus-pheasant; or
magnificent plumes from the region of the coracoids in many of the birds
of paradise. It is to be noted, also, that all these accessory plumes
spring from parts of the body which, in other species, are distinguished
by patches of colour; so that we may probably impute the development of
colour and of accessory plumage to the same fundamental cause.

Among insects, the most brilliant and varied coloration occurs in the
butterflies and moths, groups in which the wing-membranes have received
their greatest expansion, and whose specialisation has been carried
furthest in the marvellous scaly covering which is the seat of the
colour. It is suggestive, that the only other group in which functional
wings are much coloured is that of the dragonflies, where the membrane
is exceedingly expanded. In like manner, the colours of beetles, though
greatly inferior to those of the lepidoptera, occur in a group in which
the anterior pair of wings has been thickened and modified in order to
protect the vital parts, and in which these wing-covers (elytra), in the
course of development in the different groups, must have undergone great
changes, and have been the seat of very active growth.

_The Origin of Accessory Plumes._

Mr. Darwin supposes, that these have in almost every case been developed
by the preference of female birds for such males as possessed them in a
higher degree than others; but this theory does not account for the fact
that these plumes usually appear in a few definite parts of the body. We
require some cause to initiate the development in one part rather than
in another. Now, the view that colour has arisen over surfaces where
muscular and nervous development is considerable, and the fact that it
appears especially upon the accessory or highly developed plumes, leads
us to inquire whether the