Perhaps the most interesting of the early variations induced among dogs is that which has arisen from the pastoral habit. We do not know when this custom of keeping sheep in large flocks was first instituted, but it is evidently of exceeding antiquity, probably far older than the pyramids of Egypt. The custom could hardly have been instituted without help of the shepherd's mate, the sheep-dog. Although the creatures of this breed are probably in form very near to the original wild species whence our canines came, the variety has as regards its instincts been, by a process of education and selection, led very far away from the original stock. The wild forefathers of this species were clearly natural born sheep-slayers, and the motive abides to this day in all the breeds which have the strength to assail our unresisting flocks. The spirit is so ingrained that even the most civilized of our house-dogs, which may for generations never have tasted blood and which show no disposition to attack the other animals of the barn-yard, cannot be trusted alone with sheep. When two or more of them are together the old instincts of the wild pack return, and they will slay with insensate brutality until they are fairly exhausted with their fury. Their behavior on such occasions reminds one of the actions of their masters when possessed with the blind rage of a mob. Yet in the shepherd-dog we find this ancestral motive, once a large part of the life of the creature, so overcome by education and selection that they will not only care for a flock with all the devotion which self-interest can lead the master to give to the task, but they will cheerfully undergo almost any measure of privation in order to protect their charges from harm. The annals of shepherd districts, especially those where winter snows fall deeply, as in Scotland, abound in anecdotes of a well-attested nature which show how profoundly the dogs which tend the flocks are imbued with the love of the animals committed to their care. This affection is more curious for the reason that it is never in any measure returned by the sheep. To them the custodian is ever a dreaded overseer. He seems to bring to them nothing but the memories of danger derived from the experience which their species acquired in far-away times.