140 SEXUAL SELECTION : BIRDS. Part IL 



deeper indentation at the divergent than at tlie con- 

 vergent end. It is also manifest that if the convergence 

 were strongly pronounced and the confluence complete, 

 the indentation at the convergent end would tend to be 

 quite obliterated. 



The tail-feathers in both sj)ecies of peacock are en- 

 tirely destitute of ocelli, and this apparently is related 

 to their being covered up and concealed by the long 

 tail-coverts. In this respect they differ remarkably from 

 the tail-feathers of Polyplectron, which in most of the 

 species are ornamented with larger ocelli than those on 

 the tail-coverts. Hence I was led carefully to examine 

 the tail-feathers of the several species of Polyplectron 

 in order to discover whether the ocelli in any of them 

 shewed any tendency to disappear, and, to my great 

 satisfaction, I was successful. The central tail-feathers 

 of P. Na^oleonis have the two ocelli on each side of the 

 shaft perfectly developed ; but the inner ocellus becomes 

 less and less conspicuous on the more exterior tail- 

 feathers, until a mere shadow or rudimentary vestige is 

 left on the inner side of the outermost feather. Again, 

 in P. malaccense, the ocelli on the tail-coverts are, as we 

 have seen, confluent ; and these feathers are of unusual 

 length, being two-thirds of the length of the tail-fea- 

 thers, so that in both these respects they resemble the 

 tail-coverts of the peacock. Now in this species the two 

 central tail-feathers alone are ornamented, each with two 

 brightly-coloured ocelli, the ocelli having completely 

 disappeared from the inner sides of all the other tail- 

 feathers. Consequently the tail-coverts and tail-feathers 

 of this species of Polyplectron make a near aj^proach 

 in structure and ornamentation to the corresponding 

 feathers of the peacock. 



As far, then, as the principle of gradation throws 

 light on the steps by which the magnificent train of 

 the peacock has been acquired, hardly anything more 



