d. With the protuberance of
the frontal bones the shape of the internal surface of the skull and of the
brain is greatly modified. The presence of a crest influences in some
unknown way the development of the ascending branches of the premaxillary
bone, and of the inner processes of the nasal bones; and likewise the shape
of the external orifice of the nostrils. There is a plain and curious
correlation between a crest of feathers and the imperfectly ossified
condition of the skull. Not only does this hold good with nearly all
crested fowls, but likewise with tufted ducks, and as Dr. Guenther informs
me with tufted geese in Germany.

Lastly, the feathers composing the crest in male Polish fowls resemble
hackles, and differ greatly in shape from those in the crest of the female.
The neck, wing-coverts, and loins {275} in the male bird are properly
covered with hackles, and it would appear that feathers of this shape have
spread by correlation to the head of the male. This little fact is
interesting; because, though both sexes of some wild gallinaceous birds
have their heads similarly ornamented, yet there is often a difference in
the size and shape of feathers forming their crests. Furthermore there is
in some cases, as in the male Gold and in the male Amherst pheasants (_P.
pictus_ and _Amherstiae_), a close relation in colour, as well as in
structure, between the plumes on the head and on the loins. Hence it would
appear that the same law has regulated the state of the feathers on the
head and body, both with species living under their natural conditions, and
with birds which have varied under domestication.

* * * * *

{276}

CHAPTER VIII.

DUCKS--GOOSE--PEACOCK--TURKEY--GUINEA-FOWL--CANARY-BIRD--GOLD-FISH--
HIVE-BEES--SILK-MOTHS.

DUCKS, SEVERAL BREEDS OF--PROGRESS OF DOMESTICATION--ORIGIN OF, FROM
THE COMMON WILD-DUCK--DIFFERENCES IN THE DIFFERENT BREEDS--OSTEOLOGICAL
DIFFERENCES--EFFECTS OF USE AND DISUSE ON THE LIMB-BONES.

GOOSE, ANCIENTLY DOMESTICATED--LITTLE VARIATION OF--SEBASTOPOL BREED.

PEACOCK, ORIGIN OF BLACK-SHOULDERED BREED.

TURKEY, BREEDS OF--CROSSED WITH THE UNITED STATES SPECIES--EFFECTS OF
CLIMATE ON.

GUINEA-FOWL, CANARY-BIRD, GOLD-FISH, HIVE-BEES.

SILK-MOTHS, SPECIES AND BREEDS OF--ANCIENTLY DOMESTICATED--CARE IN
THEIR SELECTION--DIFFERENCES IN THE DIFFERENT RACES--IN THE EGG,
CATERPILLAR, AND COCOON STATES-