13G SEXUAL SELECTION: BIRDS. [Part IL 



eftcct, seems as incredible, as that one of Raphael's Ma- 

 donnas sliould have been formed by the selection of 

 chance daubs of paint made by a lonor succession of young 

 artists, not one of whom intended at first to draw the 

 human figure. In order to discover how the ocelli have 

 been develo])ed, we cannot look to a long line of progeni- 

 tors, 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 clew to the problem, and they 

 prove to demonstration that a gradation is at least pos- 

 sible from a mere spot to a finished ball-and-socket ocel- 

 lus. 



The wing-feathers, bearing the ocelli, are covered with 

 dark stripes or rows of dark spots, each stripe or row run- 

 ning obliquely down the outer side of the shaft to an ocel- 

 lus. The spots are generally elongated in a transverse 

 line to the row in which they stand. They often be- 

 come confluent, either in the line of the row — and 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 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 admi- 

 rably drawn by Mr. P^'ord, and engraved, but a w^oodcut 

 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 5 it is 

 also sometimes broken toward the base on the right hand. 

 These little breaks have an im]>()rtant meaning. The ring 

 is always much thickened, with the edges ill-defined 



