C68 THE DESCENT OF MAN 



than usual to become coaflnent into stripes; they are, an 

 the contrary, often broken up into smaller spots, so that 

 two or three rows run down to the same ocellas. 



There still remains another very curious point, first ob- 

 served by Mr. T. W. Wood," which deserves attention. 

 In a photograph, given me by Mr. Ward, of a specimen 

 mounted as in the act of display, it may be seen that on the 

 feathers which are held perpendicularly the white marks on 

 the ocelli, representing light reflected from a convex sur- 

 face, are at the upper or further end, that is, are directed 

 upward; and the bird while displaying himself on the 

 ground would naturally be illuminated from above. But 

 here comes the curious point: the outer feathers are held 

 almost horizontally, and their ocelli ought likewise to ap- 

 pear as if illuminated from above, and consequently the 

 white marks ought to be placed on the upper sides of 

 the ocelli; and, wonderful as is the fact, they are thus 

 placed 1 Hence the ocelli on the several feathers, though 

 occupying very different positions with respect to the light, 

 all appear as if illuminated from above, just as an artist 

 would have shaded them. Nevertheless they are not illu- 

 minated from strictly the same point as they ought to be; 

 for the white marks on the ocelli of the feathers which are 

 held almost horizontally are placed rather too much toward 

 the further end; that is, they are not suificiently lateral. 

 We have, however, no right to expect absolute perfection 

 in a part rendered ornamental through sexual selection, 

 any more than we have in a part modified through natural 

 selection for real use; for instance, in that wondrous organ, 

 the human eye. And we know what Belmholtz, the high- 

 est authority in Europe on the subject, has said about the 

 human eye: that if an optician had sold him an instrument 

 so carelessly made, he would have thought himself fully 

 justified in returning it." 



n The "Field," May 28, 1870. 



62 "Popular Lectures on Scientific Subjects," Eng. trans., 1873, pp. 219, 

 821, 269, 390. 



