n of feathered legs and membrane
between the two outer toes.

Andrew Knight[810] has remarked that the face or head and the limbs vary
together in general proportions. Compare, for instance, the head and limbs
of a dray and race-horse, or of a greyhound and mastiff. What a monster a
greyhound would appear with the head of a mastiff! The _modern_ bulldog,
however, has fine limbs, but this is a recently-selected character. From
the measurements given in the sixth chapter, we clearly see that in all the
breeds of the pigeon the length of the beak and the size of the feet are
correlated. The view which, as before explained, seems the most probable
is, that disuse in all cases tends {324} to diminish the feet, the beak
becoming at the same time through correlation shorter; but that in those
few breeds in which length of beak has been a selected point, the feet,
notwithstanding disuse, have through correlation increased in size.

With the increased length of the beak in pigeons, not only the tongue
increases in length, but likewise the orifice of the nostrils. But the
increased length of the orifice of the nostrils perhaps stands in closer
correlation with the development of the corrugated skin or wattle at the
base of the beak; for when there is much wattle round the eyes, the eyelids
are greatly increased or even doubled in length.

There is apparently some correlation even in colour between the head and
the extremities. Thus with horses a large white star or blaze on the
forehead is generally accompanied by white feet.[811] With white rabbits
and cattle, dark marks often co-exist on the tips of the ears and on the
feet. In black and tan dogs of different breeds, tan-coloured spots over
the eyes and tan-coloured feet almost invariably go together. These latter
cases of connected colouring may be due either to reversion or to analogous
variation,--subjects to which we shall hereafter return,--but this does not
necessarily determine the question of their original correlation. If those
naturalists are correct who maintain that the jaw-bones are homologous with
the limb-bones, then we can understand why the head and limbs tend to vary
together in shape and even in colour; but several highly competent judges
dispute the correctness of this view.

The lopping forwards and downwards of the immense ears of fancy rabbits is
in part due to the disuse of the muscles, and in part to the weight and
length of the ears, which have been