436 THE DESCENT OF MAN. 



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 beauti- 

 fully 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 

 adisk.f 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 ditferent 

 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 occur 

 in the tail of a motmot (Eumomota siiperciliaris), of a king- 

 fisher, finch, humming-bird, parrot, several Indian drongos 

 (Dicrurus and Edolins, in one of which the disk stands 

 vertically), and in the tail of certain birds of paradise. 

 In these latter birds, similar feathers, beautifully ocellated, 

 ornament the head, as is likewise the case with some galli- 

 naceous birds. In an Indian bustard (Syplicotides auritus) 

 the feathers forming the ear-tufts, which are about four 

 inches in length, also terminate in disks.]; It is a most 

 singular fact that the motmots, as Mr. Salvin has clearly 

 shown, give to their tail-feathers the racket-shape by 

 biting off the barbs, and, further, that this continued 

 mutilation has produced a certain amount of inherited 

 effect. 



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



| Sclater, in the " Ibis," vol. vi, 1864, p. 114. Livingstone, "Expe- 

 dition to the Zambesi," 1865, p. 66. 



JJerdon, "Birds of India," vol. iii, p. 620. 



"Proc. Zoolog. Soc.," 1873, p. 429. 



