File:The descent of man, and selection in relation to sex (1874) (20867508625).jpg

Title: The descent of man, and selection in relation to sex
Identifier: descentofmansele1874darw (find matches)
Year: 1874 (1870s)
Authors: Darwin, Charles, 1809-1882
Subjects: Evolution; Natural selection; Heredity; Human beings; Sexual selection in animals; Sexual dimorphism (Animals); Sex differences
Publisher: New York : A. L. Burt
Contributing Library: Harold B. Lee Library
Digitizing Sponsor: Brigham Young University

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BIRDS, 49J bi-eaks up into smaller spots, which still stand in their proper places. It \^ill be convenient first to describe a perfect ball-and- 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 well en- graved, but a wood-cut cannot exhibit the exqui- site shading of the original. The ring is almost always slightly broken or inter- rupted (see fig. 57) at a point in the upper half a little to the right of and above the white shade on the inclosed ball; it is also sometimes broken toward thebase on the right hand. These little breaks have an important meaning. The ring is always much thick- ened, with the edges ill- defined toward the left- hand upper corner, the featlier being held erect in the position in which it is here drawn. Beneath this thickened part there is on the surface of the ball an ob- I lique, almost pure white mark which shades off downward into a pale-leaden hue, and this into yellowish and browp tints, which insensibly become darker and darker toward the lower part of the ball. It is this shading which gives sc admirably the effect of light shining on a convex surface, If one of the balls be examined it will be seen that ihk lower part is of a brown tint and is indistinctly separated by a curved oblique line from the upper part, which is yel- lower and more leaden; this curved oblique line runs at right angles to the longer axis of the white patch of light, i and indeed of all the shading; but this difference in color, which cannot of course be shown in the wood-cut, does not in the least interfere with tlie perfect shading of the balL
Text Appearing After Image:
Fig:. 58. Basal part of the secondary wing-feather nearest to the body.

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