Chap. XIV. GRADATION OF CHARACTEES. 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 ball- 

 and-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- 

 dation ; from Avhat we know of the laws of variation ; 

 from the changes which have taken place in many 

 of our domesticated birds ; and, lastly, from the cha- 

 racter (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 pro- 

 bable 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 

 Urostide henjamini, remarkable from the curious dif- 

 ferences 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 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 curious is that, although the colouring 

 of the tail diff'ers remarkably in both sexes of many 

 kinds of humming-birds, Mr. Gould 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 ' The Reign of Law,' 1867, p. 247. 



