136 SEXUAL SELECTION: BIRDS. [Part IX 



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

 donnas should have been formed by the selection of 

 chance daubs- of paint made by a long 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 developed, 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. 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 toward the base on the right hand." 

 These little breaks have an important meaning. The ring 

 is always much thickened, with the edges ill-defined 



