130 
sexual selection: birds. 
domestic fowl and pigeon. The barbs coalesce ^ 
the extremity of the shaft to form the oval disc , 
ocellus, which is certainly one of the most bca« fI 
objects in the world. This consists of an irideS^ , 
intensely blue, indented centre, surrounded by a rl 
green zone, and this by a broad coppery-brown 0°" t 
and this by five other narrow zones of slightly-diff cl ' e 
iridescent shades. A trifling character in the disc 
haps deserves notice the barbs, for a space along ^ 
of the concentric zones are destitute, to a greater , 
loss degree, of their barbules, so that a part of the 
is surrounded by an almost transparent zone, "h 1 ^ 
gives to it a highly-finished aspect But I have ^ 
where described 47 an exactly analogous variation h‘ ^ 
hackles of a sub-variety of the game-cock, in 
the tips, having a metallic lustre, -‘are separated ^ 
“ the lower part of the feather by a symmetric®^, 
“ shaped transparent zone, composed of the naked f { 
“ t ! °ns ol the barbs.” The low er margin or ha ge i 
> 0 ^ 
t!ie dark-blue centre of the ocellus is deeply hide 1 * 
on the line of the shaft. The surrounding zones ly ' f 
wise shew traces, as may be seen in the dra" 1 ' 1 ^ 
(fig. S3), of indentations, or rather breaks. These ^ 
dentations are common to the Indian and Javan l 1 ' j 
cocks ( I’avo cristatus and P. muticus) ; and they 
to me to deserve particular attention, as probably | ;1 
nected with the development of the ocellus; hut 
long time I could not conjecture their meaning. $ 
It we admit the principle of gradual evolution, _ 
must formerly have existed many species which P' 
seated every successive step between the wonder*' 11 ' j, 
elongated tail-coverts of the peacock and the short & 
47 ‘Variation of Animals and Plants under Domestication 
p. 254. 
» fOl’ l ’ 
