SEXUAL SELECTION 555 



Other ornaments, we ought to behold the long line of his 

 extinct progenitors; but this is obviously impossible. We 

 may, however, generally gain a clew by comparing all the 

 species of the same group, if it be a large one; for some of 

 them will probably retain, at least partially, traces of their 

 former characters. Instead of entering on tedious details 

 respecting various groups, in which striking instances of 

 gradation could be given, it seems the best plan to take 

 one or two strongly marked cases, for instance that of the 

 peacock, in order to see if light can be thrown on the steps 

 by which this bird has become so splendidly decorated. 

 The peacock is chiefly remarkable from the extraordinary 

 length of his tail-coverts, the tail itself not being much 

 elongated. The barbs along nearly the whole length of 

 these feathers stand separate or are decomposed; but this 

 is the case with the feathers of many species, and with 

 some varieties of the domestic fowl and pigeon. The 

 barbs coalesce toward the extremity of the shaft forming 

 the oval disk or ocellus, which is certainly one of the most 

 beautiful objects in the world. It consists of an iridescent, 

 intensely blue, indented centre, surrounded by a rich green 

 zone, this by a broad coppery-brown zone, and this by five 

 other narrow zones of slightly different iridescent shades. 

 A trifling character in the disk deserves notice; the barbs, 

 for a space along one of the concentric zones, are more or 

 less destitute of their barbules, so that a part of the disk is 

 surrounded by an almost transparent zone, which gives it a 

 highly finished aspect. But I have elsewhere described"" 

 an exactly analogous variation in the hackles of a sub- 

 variety of the game-cock, in which the tips, having a 

 metallic lustre, "are separated from the lower part of the 

 feather by a symmetrically shaped transparent zone, com- 

 posed of the naked portions of the barbs." The lower 

 margin or base of the dark blue centre of the ocellus is 

 deeply indented on the line of the shaft. The surround- 



"> "Variation of Animala and Plants, under Domestication," vol. i. p. 2S4. 



