BIRDS. 



495 



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 

 l)v 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 

 feather 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- 

 lique, almost pure white mark which shades off downward 

 into a pale-leaden hue, and this into yellowish and brown 

 tints, which insensibly become darker and darker toward 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 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, 

 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 the perfect shading of the ball* 



Figr. 58. Basal part of the seconflary 

 wing-feather nearest to the body. 



