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.