w
how easy it is to produce a variety in type and size by studied
selection.

In order properly to understand this question it is necessary first
to consider the identity of structure in the wolf and the dog. This
identity of structure may best be studied in a comparison of the
osseous system, or skeletons, of the two animals, which so closely
resemble each other that their transposition would not easily be
detected.

The spine of the dog consists of seven vertebrae in the neck, thirteen
in the back, seven in the loins, three sacral vertebrae, and twenty
to twenty-two in the tail. In both the dog and the wolf there are
thirteen pairs of ribs, nine true and four false. Each has forty-two
teeth. They both have five front and four hind toes, while outwardly
the common wolf has so much the appearance of a large, bare-boned
dog, that a popular description of the one would serve for the other.

Nor are their habits different. The wolf's natural voice is a loud
howl, but when confined with dogs he will learn to bark. Although
he is carnivorous, he will also eat vegetables, and when sickly he
will nibble grass. In the chase, a pack of wolves will divide into
parties, one following the trail of the quarry, the other endeavouring
to intercept its retreat, exercising a considerable amount of
strategy, a trait which is exhibited by many of our sporting dogs
and terriers when hunting in teams.

A further important point of resemblance between the _Canis lupus_
and the _Canis familiaris_ lies in the fact that the period of
gestation in both species is sixty-three days. There are from three
to nine cubs in a wolf's litter, and these are blind for twenty-one
days. They are suckled for two months, but at the end of that time
they are able to eat half-digested flesh disgorged for them by their
dam--or even their sire.

We have seen that there is no authenticated instance of a hybrid
between the dog and the fox. This is not the case with the dog and
the wolf, or the dog and the jackal, all of which can interbreed.
Moreover, their offspring are fertile. Pliny is the authority for
the statement that the Gauls tied their female dogs in the wood that
they might cross with wolves. The Eskimo dogs are not infrequently
crossed with the grey Arctic wolf, which they so much resemble, and
the Indians of America were accustomed to cross their half-wild dogs
with the coyote to impart greater boldness to the breed. Tame dogs
living in countrie