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Show 136 SEXUAL SELECTION: BIRDS. PART Il. domestic fowl and pigeon. The barbs coalesce towards the extremity of the shaft to form the oval disc or ocellus, which is certainly one of the most beautiful objects in the world. This consists of an iridescent, inteusely blue, indented centre, surrounded bf a rich green zone, and this by a broad coppery-brown zone, and this by five other narrow zones of sEghtly-different "'iridescent shades. A trifling character in the disc perhaps deserves notice ; the barbs, for a space along one of the concentric zones are destitute, to a greater or less degree, of their barbules, so that a part of the disc is surrounded by an almost transparent zone, which gives to it a highly-finished aspect. But I have elsewhere described 47 an exactly analogous variation in the hackles of a sub-variety of the game-cock, in which the tips, having a metallic lustre, "are separated from "the lower part of the feather by a symmett-icaUy" shaped transparent zone, composed of the naked por" tions of the barbs.'' The lower margin or base of tlw dark-blue centre of the ocellus is deeply indented on the line of the shaft. The surrounding zones likewise shew traces, as may be seen in the drawing (fig. 53), of indentations, or rather breaks. These indentations are common to the Indian and J a van peacocks ( Pavo cristat~ts and P. muticus) ; and they seemed to me to deserve particular attention, as probably connected with the development of the ocellus; but for a long time I could not conjecture their meaning. If we admit the principle of gradual evolution, there must formerly have existed many species which presented every successive step between the wonderfully elongated tail-coverts of the peacock and the short tail- 47 'Variation of Anima l~ and Plants under Dom~ sticution,' vol. i. p.254. .CIIAP. XJV. GRADATION OF CHAHACTERS. 137 coverts of all ordinary birds ; and again between the magnificent ocelli of the former, and the simpler ocelli or mere coloured spots of other birds ; and so with all the other characters of the peacock Let us look to the allied Gallinacero for any still-existing gradations. The species and sub-species of Polyplectron 'Fig. 53. Feather of l'cucock, a\Jout two·lh!rds of natural size, cnrPfnlly drawn by l\fr. Ford. The transparent zone lti represented by the outermost white zone, confined to the upper end of the disc. inhabit countries adjacent to the native land of the peacock; and they so far resemble this bird that they .are sometimes called peacock-pheasants. I am also informed by Mr. Bartlett that they resemble the pea. cock in their voice and in some of their habits. During |