ied with
abundant nourishment. Nevertheless there can be little doubt that our
domesticated animals have been modified, independently of the increased
or lessened use of parts, by the conditions to which they have been
subjected, without the aid of selection. For instance, Prof.
Ruetimeyer[692] shows that the bones of all domesticated quadrupeds can
be distinguished from those of wild animals by the state of their
surface and general appearance. It is scarcely possible to read
Nathusius's excellent 'Vorstudien,'[693] and doubt that, with the
highly improved races of the pig, abundant food has produced a
conspicuous effect on the general form of the body, on the breadth of
the head and face, and even on the teeth. Nathusius rests much on the
case of a purely bred Berkshire pig, which when two months old became
diseased in its digestive organs, and was preserved for observation
until nineteen months old; at this age it had lost several
characteristic features of the breed, and had acquired a long, narrow
head, of large size relatively to its small body, and elongated legs.
But in this case and in some others we ought not to assume that,
because certain characters are lost, perhaps through reversion, under
one course of treatment, therefore that they had been at first directly
produced by an opposite course.

In the case of the rabbit, which has become feral on the island of
Porto Santo, we are at first strongly tempted to attribute the whole
change--the greatly reduced size, the altered tints of the fur, and the
loss of certain characteristic marks--to the definite action of the new
conditions to which it has been exposed. But in all such cases we have
to consider in addition the tendency to reversion to progenitors more
or less remote, and the natural selection of the finest shades of
difference.

The nature of the food sometimes either definitely induces certain
peculiarities, or stands in some close relation with them. Pallas long
ago asserted that the fat-tailed sheep of Siberia degenerated and lost
their enormous tails when removed from certain saline pastures; and
recently {280} Erman[694] states that this occurs with the Kirgisian
sheep when brought to Orenburgh.

It is well known that hemp-seed causes bullfinches and certain other
birds to become black. Mr. Wallace has c