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 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 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) 



