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Show 150 SEXUAL SELECTION : BIRDR. PART ll. smaller and less perfect than on the other feathers, with the upper parts of the external black rings defi. cient, as in the case just mentioned. The imperfection here seems to be connected with the fact that the spots on this feather shew less tendency than usual to become confluent into stripes ; on tho contrary, they are often broken up into smaller spots, so that two or three rows run down to each ocellus. We have now seen that a perfect series can be followed, from two almost simple spots, at first quite distinct from each other, to one of the wonderful balland- socket ornaments. Mr. Gould, who kindly gave me some of these feathers, fully agrees with me in the completeness of the gradation. It is obvious that the stages in development exhibited by the feathers on the same bird do not at all necessarily shew us the steps which have been passed through by the extinct progenitors of the species; but they probably give us the clue to tho actual steps, and they at least prove to demonstration that a gradation is possible. Bearing in mind ~ow carefully the male Argus pheasant displays his plumes before the female, as well as the many facts rendering it probable that female birds prefer the more attractive males, no one who admits the agency of sexual selection, will deny that a simple dark spot with some fulvous shading might be converted, through the approximation and modification of the adjoining ~pots, together with some slight increase of colour, mto one of the so-called elliptic ornaments. These latter ornaments have been shewn to many persons, and all have admitted that they are extremely pretty, some thinking them even more beautiful than the ball-and-socket ocelli. As the secondary plumes became lengthened through sexual selection, and as the elliptic ornaments increased in diameter, their (;uAr. XIV. ·GRADATION OF CHARACTERS. 151 colours apparently became less bright; and .then the ornamentation of the plumes .had to be gained by improvements in the pattern and shading; and this process has been carried on until the wonderful balland- socket ocelli have been finally developed. Thus we .can understand-and in no other way as it seems to me-the present condition and origin of the ornaments on the wing-feathers of the .Argus pheasant. From the light reflected by the principle of grada< Uation; 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 more clearly see) 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 darkness. Mr. Gould several _years ago pointed out to me a humming-bird, the Urosticte benjamini, remarkable from the curious differences presented by the two 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 tailfeathers 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 curious is that, although tho colouring of the tail differs remarkably in both sexes of many .kinds of humming-birds, .Mr. Go-ald does not know a -single species, besides the Urosticte, in which the male has the four central feathers tipped with white. The Duke of Argyll, in commenting on this case,49 49 ' The Reign of Law,' 18G7, p. 2:1.7. |