442 Tlie Descent of Man. Part J I. 



spots, together with some slight increase of colour, into one of the 

 so-called elliptic ornaments. These latter ornaments have been 

 shewn to many persons, and all have admitted that they are 

 beautiful, some thinking them even more so than the ball-and- 

 socket ocelli. As the secondary plumes became lengthened 

 through sexual selection, and as the elliptic ornaments increased 

 in diameter, their colours apparently became less bright; and 

 then the ornamentation of the plumes had to be gained by an 

 improvement in the pattern and shading ; and this process was 

 carried on until the wonderful ball-and-socket ocelli were finally 

 developed. Thus we can understand — and in no other way as 

 it seems to me — the present condition and origin of the orna- 

 ments on the wing-feathers of the Argus pheasant. 



From the light afforded by the principle of gradation — from 

 what we know of the laws of variation — from the changes which 

 have taken place in many of our domesticated birds — and, lastly, 

 from the character (as we shall hereafter see more clearly) of the 

 immature plumage of young birds — we can sometimes indicate 

 with a certain amount of confidence, the probable steps by which 

 the males have acquired their brilliant plumage and various 

 ornaments ; yet in many cases we are involved in complete 

 darkness. Mr. Gould several years ago pointed out to me a 

 humming-bird, the Uroslicte benjamini, remarkable for the curious 

 differences between the sexes. The male, besides a splendid 

 gorget, has greenish-black tail-feathers, with the four central 

 ones tipped with white ; in the female, as with most of the allied 

 species, the three outer tail-feathers on each side are tipped with 

 white, so that the male has the four central, whilst the female 

 has the six exterior feathers ornamented with white tips. What 

 makes the case more curious is that, although the colouring of 

 the tail differs remarkably in both sexes of many kinds of 

 humming-birds, Mr. Gould does not know a single species, be- 

 sides the Urosticte, in which the male has the four central 

 feathers tipped with white. 



The Duke of Argyll, in commenting on this case, 53 passes over 

 sexual selection, and asks, " What explanation does the law of 

 " natural selection give of such specific varieties as these ?" He 

 answers " none whatever ;" and I quite agree with him. But 

 can this be so confidently said of sexual selection ? Seeing in 

 aow many ways the tail-feathers of humming-birds differ, why 

 should not the four central feathers have varied in this one 

 species alone, so as to have acquired white tips ? The variations 

 may have been gradual, or somewhat abrupt as in the ?&se 



53 < The Reign of Law,' 1867, p. 247. 



