These results we may attribute to the lessened use of the wings.
CORRELATION OF GROWTH.
I will here sum up the few facts which I have collected on this obscure, but important, subject. In Cochin and Game fowls there is perhaps some relation between the colour of the plumage and the darkness of the egg- shell. In Sultans the additional sickle-feathers in the tail are apparently related to the general redundancy of the plumage, as shown by the feathered legs, large crest, and beard. In two tailless fowls which I examined the oil-gland was aborted. A large crest of feathers, as Mr. Tegetmeier has remarked, seems always accompanied by a great diminution or almost entire absence of the comb. A large beard is similarly accompanied by diminished or absent wattles. These latter cases apparently come under the law of compensation or balancement of growth. A large beard beneath the lower jaw and a large top-knot on the skull often go together. The comb when of any peculiar shape, as with Horned, Spanish, and Hamburgh fowls, affects in a corresponding manner the underlying skull; and we have seen how wonderfully this is the case with Crested fowls when the crest is largely developed. 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. Gunther 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 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. It would therefore appear that the same law has regulated the state of the feathers on the head and body, both with species living under natural conditions, and with birds which have varied under domestication.
CHAPTER 1.VIII.
DUCK--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. INHERITANCE OF CHARACTERS. IMPERFECT WINGS. LOST INSTINCTS. CORRELATED CHARACTERS.
I will, as in previous cases, first briefly describe the chief domestic breeds of the duck:--
[BREED 1. COMMON DOMESTIC DUCK.
Varies much in colour and in proportions, and differs in instincts and disposition from the wild duck. There are several sub-breeds:--
1. The Aylesbury, of great size, white, with pale-yellow beak and legs; abdominal dermal sack largely developed.
2. The Rouen, of great size, coloured like the wild duck, with green or mottled beak; dermal sack largely developed.