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Show 1±2 SEXUAL SELECTION: BIRDS. P .l.!l.T II. ball-and-socket effect, seems as incredible, as that one of Raphael's Madonnas should have been formed by the selection of chance daubs of paint made by a long succession of young artists, not one of whom intendeJ. at first to draw the human figure. In order to discover how the ocelli have been developed, we cannot look to a long line of progenitors, nor to various closely-allied forms, for such do not now exist. But fortunately the several feathers on the wing suffice to give us a clue to tho problem, and they prove to demonstration that a gradation is at least possible from n. mere spot to a finished ball-and-socket ocellus. The wing-feathers, bearing the ocelli, are covered with dark stripes or rows of dark spots, each stripe or row nmning obliquely down the outer side of the shaft to an ocellus. The spots are generally elongated in a transverse line to the row in which they stand. 'fhey often become confluent, either in the line of the rowand then they form a longitudinal stripe-or transversely, that is, with the spots in the adjoining rows, and then they form transverse stripes. A spot sometimes breal;:s up into smaller spots, which still stand in their proper places. It will be convenient first to describe a perfect balland- socket ocellus. This consists of an intensely black circular ring, surrounding a space shaded so as exactly to resemble a ball. The figure here given has been admirably drawn by Mr. Ford, and engraved, but a woodcut cannot exhibit the exquisite shading of the original. The ring is almost always slightly broken or interrupted (see fig. 56) at a point in the upper half, a little to the right of and above the white shade on the enclosed ball; it is also sometimes broken towards the base on the right hand. These little breaks have an important meaning. 'l'he ring is always much thickened, with the ·edges ill-defined towards the left-hand upper corner ·CHAP. XIV. GRADATION OF CHARACTERS. 1:13 the feather being held erect, in the position in which it is here drawn. Be- 11 n c neath this thickened part there is on the surface of the ball an~ oblique almost pure-~. white mark, which shade off downwards into a pale-leaden hue, and this into yellowish and brown tints, a which insensibly · become darker and darker towards the lower part of the ball. It is this shading which gives so admirably the ·effect of light shining on a convex surface. If one of the balls be examined, it will be seen that the lower part is of a browner Fig. 56. PurL of Secondary wing-feather of Argus tint and is indistinctly pucnsnnt, shewing two, a and b, perfect ocelli. d b d A, B, C, &c., dark stripes running obllquely down, separate y a curve each to un ocellus. oblique line from tho CMuch of the web on both gldPS, especially to the h . h . !elL of the shal'r, has been cut off.] upper part, w 1c IS yellower and more leaden; this oblique line runs at right angles to the longer axis of the white patch of hght, and indeed of all the shading; but this difference in the tints, which cannot of course be shown in tho woodcut, does not in the least interfere with the perfect shading of the ball.48 It should be particularly ob- 4~ When the Argus pheasant displays his wing-feathers like a great rfttn, those nearest to the body stand more upright than the outer ones, |
