130 SEXUAL selection: birds. PartH 



various hideous deformities — deep scars on the face 

 with the flesh raised into protuberances, the septum 

 of the nose pierced by sticks or bones, holes in the ears 

 and lips stretched widely open — are all admired as 

 ornamental. 



Whether or not unimportant differences between the 

 sexes, such as those just specified, have been preserved 

 through sexual selection, these differences, as well as 

 all others, must primarily depend on the laws of varia- 

 tion. On the principle of correlated development, the 

 plumage often varies on different parts of the body, or 

 over the whole body, in the same manner. We see 

 this well illustrated in certain breeds of the fowl. In 

 all the breeds the feathers on the neck and loins of 

 the males are elongated, and are called hackles ; now 

 when both sexes acquire a top-knot, which is a new 

 character in the genus, the feathers on the head of the 

 male become hackle-shaped, evidently on the principle 

 of correlation ; whilst those on the head of the female 

 are of the ordinary shape. The colour also of the 

 hackles forming the top-knot of the male, is often cor- 

 related with that of the hackles on the neck and loins, 

 as may be seen by comparing these feathers in the 

 Golden and Silver-spangled Polish, the Houdans, and 

 Creve-coeur breeds. In some natural species we may 

 observe exactlv the same correlation in the colours of 

 these same feathers, as in the males of the splendid 

 Golden and Amherst pheasants. 



The structure of each individual feather generally 

 causes any change in its colouring to be symmetrical ; 

 we see this in the various laced, spangled, and pen- 

 cilled breeds of the fowl ; and on the principle of 

 correlation the feathers over the whole body are often 

 modified in the same manner. We are thus enabled 

 without much trouble to rear breeds with their plum- 



