l the number of the vertebrae and
the forms of the cervical vertebrae have been changed. In certain pigeons
the shape of the lower jaw, the relative length of the tongue, the size of
the nostrils and eyelids, the number and shape of the ribs, the form and
size of the oesophagus, have all varied. In certain quadrupeds the length
of the intestines has been much increased or {409} diminished. With plants
we see wonderful differences in the stones of various fruits. In the
Cucurbitaceae several highly important characters have varied, such as the
sessile position of the stigmas on the ovarium, the position of the carpels
within the ovarium, and its projection out of the receptacle. But it would
be useless to run through the many facts given in the earlier chapters.

It is notorious how greatly the mental disposition, tastes, habits,
consensual movements, loquacity or silence, and the tone of voice have
varied and been inherited with our domesticated animals. The dog offers the
most striking instance of changed mental attributes, and these differences
cannot be accounted for by descent from distinct wild types. New mental
characters have certainly often been acquired, and natural ones lost, under
domestication.

New characters may appear and disappear at any stage of growth, and be
inherited at a corresponding period. We see this in the difference between
the eggs of various breeds of the fowl, and in the down on chickens; and
still more plainly in the differences between the caterpillars and cocoons
of various breeds of the silk-moth. These facts, simple as they appear,
throw light on the characters which distinguish the larval and adult states
of natural species, and on the whole great subject of embryology. New
characters are liable to become attached exclusively to that sex in which
they first appeared, or they may be developed in a much higher degree in
the one than the other sex; or again, after having become attached to one
sex, they may be partially transferred to the opposite sex. These facts,
and more especially the circumstance that new characters seem to be
particularly liable, from some unknown cause, to become attached to the
male sex, have an important bearing on the acquirement by animals in a
state of nature of secondary sexual characters.

It has sometimes been said that our domestic productions do not differ in
constitutional peculiarities, but this cannot be maintained. In our
improved cattle, pigs, &c.,