the feathers having nearly the same structure and manner of development, and consequently tending to vary in the same manner. We often see a tendency to analogous variability in the plumage of our domestic breeds belonging to distinct species. Thus top-knots have appeared in several species. In an extinct variety of the turkey, the top-knot consisted of bare quills surmounted with plumes of down, so that they resembled, to a certain extent, the racket-shaped feathers above described. In certain breeds of the pigeon and fowl the feathers are plumose, with some tendency in the shafts to be naked. In the Sebastopol goose the scapular feathers are greatly elongated, curled, or even spirally twisted, with the margins plumose.[125] [Illustration: Fig. 47. Paradisea rubra, male (from Brehm)] [Illustration: Fig. 48. Lophornis ornatus, male and female (from Brehm).] In regard to colour hardly anything need here be said; for every one knows how splendid are the tints of birds, and how harmoniously they are combined. The colours are often metallic and iridescent. Circular spots are sometimes surrounded by one or more differently shaded zones, and are thus converted into ocelli. Nor need much be said on the wonderful differences between the sexes, or of the extreme beauty of the males of many birds. The common peacock offers a striking instance. Female Birds of Paradise are obscurely coloured and destitute of all ornaments, whilst the males are probably the most highly decorated of all birds, and in so many ways, that they must be seen to be appreciated. The elongated and golden-orange plumes which spring from beneath the wings of the _Paradisea apoda_ (see fig. 47 of _P. rubra_, a much less beautiful species), when vertically erected and made to vibrate, are described as forming a sort of halo, in the centre of which the head “looks like a little emerald sun with its rays formed by the two plumes.”[126] In another most beautiful species the head is bald, “and of a rich cobalt blue, crossed by several lines of black velvety feathers.”[127] [Illustration: Fig. 49. Spathura underwoodi, male and female (from Brehm).]