134 SEXUAL SELECTION : BIRDS. [Part II. 



convcrixeiit ocelli would manifestly leave a much deeper 

 indentation at the divergent than at the convergent 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 species of peacock are entire- 

 ly destitute of ocelli, and this apparently is related to 

 their being covered u}) and concealed by the long tail-cov- 

 erts. In this respect they differ remarkably from the 

 tail-feathers of Polyi>lectron, 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 showed any 

 tendency to disappear, and, to my great satisfaction, I was 

 successful. The central tail-feathers of P. N'apoleonis 

 have the two ocelli on each side of the shaft perfectly de- 

 veloped ; but the inner ocellus becomes less and less con- 

 spicuous 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-feathers, 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-colored ocelli, the 

 ocelli having completely disappeared from the inner sides 

 of all the other tail-feathers. Consequently the tail-cov- 

 erts and tail-feathers of this species of Polyplectron make 

 a near approach 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 magniflcent train of the pea- 

 cock has been acquired, hardly any thing more is needed. 



