130 
sexual selection: birds. 
p.if 
various hideous deformities — deep scars on 
the 
& 
with the flesh raised into protuberances, the 
of the nose pierced by sticks or bones, holes in th® , |V . 
the f 
-are all adroit 
and lips stretched widely open 
ornamental. t t’ 
Whether or not unimportant differences betw®® 1 ’ V ,J 
sexes, such as those just specified, have been p re “ j r 
through sexual selection, these differences, as "' L > 
0 .... .. . C iTlV 
all others, must primarily depend on the laws of 
tion. On the principle of correlated development ’ ' $ 
plumage often varies on different parts of the jf 
body- 
I n . A V 
over the whole body, in the same manner. " Ji) 
this well illustrated in certain breeds of the «l 
all the breeds the feathers on the neck and 
the males are elongated, and are called hackles , j 
when both sexes acquire a top-knot, which is ! ( ] f 
character in the genus, the feathers on the 
head 
„ ■ 
male become hackle-shaped, evidently on the p rI ; J 
of correlation ; whilst those on the head of the > l , ^ 
are of the ordinary shape. The colour also 0 ^ 
hackles forming the top-knot of the male, is oi'ff 1 ! 
related with that of the hackles on the neck auo 
a K 
as may be seen by comparing these feathers 111 ^ 
Golden and Silver-spangled Polish, the Houduri’ 
Creve-coeur breeds. In some natural species " e -f 
colc^'jl 
observe exactly the same correlation in the 
these same feathers, as in the males of the S P 
Golden and Amherst pheasants. ^ 
The structure of each individual feather 
causes any change in its colouring to be sym' ||(J 
we see this in the various laced, spangled, 
aud * (i 
cilled breeds of the fowl ; and on the prim'd ^ 
correlation the feathers over the whole body 
modified in the same manner. We are thus 
ei lil 
vithout much trouble to rear breeds with then 
r 
