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SEXUAL selection: birds. 
Part II. 
ball-and-socket effect, seems as incredible, as that one 
of Eapliael’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 in- 
tended at first to draw the human figure. In order to 
discover how the ocelli have been developed, we can- 
not 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 the problem, and they prove to 
demonstration that a gradation is at least possible from 
a 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 
running 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. They 
often become confluent, either in the line of the row — 
and then they form a longitudinal stripe — or trans- 
versely, that is, with the spots in the adjoining rows, 
and then they form transverse stripes. A spot some- 
times breaks up into smaller spots, which still stand in 
their proper places. 
It will 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 engraved, but a wood- 
cut 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. The ring is always much thickened, with the 
edges ill-defined towards the left-hand upper corner 
