The Descent of Man

eeds 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 topknot
of the male, is often correlated 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 exactly the same correlation in the
colours of these same feathers, as in the males
of the splendid Gold 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 pencilled breeds of the fowl; and