SEXUAL SELECTION 497 



tiful voffs and collars. The tail-feathers are frequently 

 increa&tsd in length; as we see in the tail-coverts of the 

 peacoci, and in the tail itself of the Argus pheasant. 

 With the peacock even the bones of the tail have been 

 modified to support the heavy tail-coverts." The body of 

 the Argus is not larger than that of a fowl; yet the length 

 from the end of the beak to the extremity of the tail is no 

 less than five feet three inches," and that of the beautifully 

 ocellated secondary wing-feathers nearly three feet. In a 

 small African night-jar ( Cosmetornis vexillarius) -one of the 

 primary wing-feathers, during the breeding season, attains 

 a length of twenty-six inches, while the bird itself is only 

 ten inches in length. In another closely allied genus of 

 night-jars, the shafts of the elongated wing-feathers are 

 naked, except at the extremity, where there is a disk."' 

 Again, in another genus of night-jars, the tail-feathers 

 are even still more prodigiously developed. In general the 

 feathers of the tail are more often elongated than those of 

 the wings, as any great elongation of the latter impedes 

 flight. We thus see that in closely allied birds ornaments 

 of the same kind have been gained by the males through 

 the development of widely different feathers. 



It is a curious fact that the feathers of species belonging 

 to very distinct groups have been modified in almost exactly 

 the same peculiar manner. Thus the wing-feathers in one 

 of the above-mentioned night-jars are bare along the shaft, 

 and terminate in a disk; or are, as they are sometimes 

 called, spoon or racket-shaped. Feathers of this kind oc- 

 cur in the tail of a motmot {^Eumomota superciliaris), of 

 a kingfisher, finch, humming-bird, parrot, several Indian 

 drongos (Dicrurus and Edolius, in one of which the disk 

 stands vertically), and in the tail of certain birds of para- 

 dise. In these latter birds, similar feathers, beautifully 



«« Dr. W. Marshall, "Ueber den Vogelsebwanz, " ibid., B. I. Heft 2, 1812. 

 " Jardine's "Naturalist Library: Birds," vol. xiv. p. 166. 

 «8 Sclater, in the "Ibis," vol. vi., 1864, p. 114. Livingstone, "Expedition 

 to the Zambesi," 1865, p. 66. 



