Whatever may be said concerning the difference existing between dogs and foxes will not hold good in reference to dogs, wolves, and jackals. The wolf and the jackal are so much alike that the only appreciable distinction is that of size, and so closely do they resemble many dogs in general appearance, structure, habits, instincts, and mental endowments that no difficulty presents itself in regarding them as being of one stock. Wolves and jackals can be, and have repeatedly been, tamed. Domestic dogs can become, and again and again do become, wild, even consorting with wolves, interbreeding with them, assuming their gregarious habits, and changing the characteristic bark into a dismal wolf-like howl. The wolf and the jackal when tamed answer to their master's call, wag their tails, lick his hands, crouch, jump round him to be caressed, and throw themselves on their backs in submission. When in high spirits they run round in circles or in a figure of eight, with their tails between their legs. Their howl becomes a business-like bark. They smell at the tails of other dogs and void their urine sideways, and lastly, like our domestic favourites, however refined and gentlemanly in other respects, they cannot be broken of the habit of rolling on carrion or on animals they have killed.

This last habit of the domestic dog is one of the surviving traits of his wild ancestry, which, like his habits of burying bones or superfluous food, and of turning round and round on a carpet as if to make a nest for himself before lying down, go far towards connecting him in direct relationship with the wolf and the jackal.

The great multitude of different breeds of the dog and the vast differences in their size, points, and general appearance are facts which make it difficult to believe that they could have had a common ancestry. One thinks of the difference between the Mastiff and the Japanese Spaniel, the Deerhound and the fashionable Pomeranian, the St. Bernard and the Miniature Black and Tan Terrier, and is perplexed in contemplating the possibility of their having descended from a common progenitor. Yet the disparity is no greater than that between the Shire horse and the Shetland pony, the Shorthorn and the Kerry cattle, or the Patagonian and the Pygmy; and all dog breeders know 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 countries inhabited by the jackal often betray the jackal strain in their litters, and there are instances of men dwelling in lonely outposts of civilisation being molested by wolves or jackals following upon the trail of a bitch in season.

These facts lead one to refer to the familiar circumstance that the native dogs of all regions approximate closely in size, coloration, form, and habit to the native wolf of those regions. Of this most important circumstance there are far too many instances to allow of its being looked upon as a mere coincidence. Sir John Richardson, writing in 1829, observed that "the resemblance between the North American wolves and the domestic dog of the Indians is so great that the size and strength of the wolf seems to be the only difference. I have more than once mistaken a band of wolves for the dogs of a party of Indians; and the howl of the animals of both species is prolonged so exactly in the same key that even the practised ear of the Indian fails at times to discriminate between them."

As the Eskimo and Indian dogs resemble the North American wolf, so the dog of the Hare Indians, a very different breed, resembles the prairie wolf. Except in the matter of barking, there is no difference whatever between the black wolf-dog of the Indians of Florida and the wolves of the same country. The same phenomenon is seen in many kinds of European dogs. The Shepherd Dog of the plains of Hungary is white or reddish-brown, has a sharp nose, short erect ears, shaggy coat, and bushy tail, and so much resembles a wolf that Mr. Paget, who gives the description, says he has known a Hungarian mistake a wolf for one of his own dogs. Many of the dogs of Russia, Lapland, and Finland are comparable with the wolves of those countries. Some of the domestic dogs of Egypt, both at the present day and in the condition of mummies, are wolf-like in type, and the dogs of Nubia have the closest relation to a wild species of the same region, which is only a form of the common jackal. Dogs, it may again be noted, cross with the jackal as well as with wolves, and this is frequently the case in Africa, as, for example, in Bosjesmans, where the dogs have a marked resemblance to the black-backed jackal, which is a South African variety.

It has been suggested that the one incontrovertible argument against the lupine relationship of the dog is the fact that all domestic dogs bark, while all wild Canidae express their feelings only by howls. But the difficulty here is not so great as it seems, since we know that jackals, wild dogs, and wolf pups reared by bitches readily acquire the habit. On the other hand, domestic dogs allowed to run wild forget how to bark, while there are some which have not yet learned so to express themselves.

The presence or absence of the habit of barking cannot, then, be regarded as an argument in deciding the question concerning the origin of the dog. This stumbling block consequently disappears, leaving us in the position of agreeing with Darwin, whose final hypothesis was that "it is highly probable that the domestic dogs of the world have descended from two good species of wolf (C. lupus and C.