x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 291 
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 magnifi¬ 
cent 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 oidy 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 same cause has not primarily determined the development 
of these plumes. The immense tuft of golden plumage in the 
best known birds of paradise (Paradisea apoda and P. minor) 
