They are quiet and good-natured, never inclined to roam or neglect their duties, and as little disposed to injure the animals intrusted to their keeping. They have almost the intelligence of the shepherd in discerning the vagaries of the flock, and ten times his efficiency in driving it. No extensive sheep-walks, unless closely hemmed in by impassable fences, should be without one or more of these useful animals. The Drover's Dog. This animal is shown in the annexed figure. He is closely allied to the sheep-dog, from which he derives all his intelligence and capacity, differing only in being somewhat larger and heavier, which is essential to his controlling the sturdier bullocks under his charge. His additional size is acquired by crossing with some of the stouter races, such as the Newfoundland or the pointer, and even the bull-dog and large shaggy terrier have sometimes been resorted to for a strain of that indomitable courage and game, which is frequently requisite to the proper discharge of his duties. He requires more training than the sheep-dog, as his peculiar instincts are rather to the management of the flock than the herd; but when fairly broken in, he is equally expert in its management. The drover's dog may also be useful for watching, if crossed with a reference to this object, which the sheep-dog seldom is. [Illustration: Fig. 39. Drover's Dog.] The Terrier. This, in addition to the foregoing, is the only dog necessary to the farm. He is needed principally for his great sagacity and indefatigable perseverance in exterminating rats and other vermin, that frequently congregate in swarms around the farmer's premises, producing such an aggregate of annoyance and devastation. Other dogs may occasionally be good ratters, but the terrier takes to them from instinct, as the Newfoundland does to the water, or the sheep-dog to his flock. He has great ingenuity and activity in ferreting out and capturing his prey, and whenever a fair opportunity is afforded, he seldom fails of success. The famous English terrier, Billy, on two occasions, killed 100 rats in a ring at each time, in an average of less than six and a half minutes. The terrier is usually below the medium size, but sometimes fully comes up to or even exceeds it. He is smooth-haired or rough according to the breed, of which there are several, each claiming to be equally pure. Besides his capacity for the destruction of small game, his innate love for the sport renders him a valuable assistant in keeping off vagrant cattle from the premises; and his quick ear, habitual watchfulness, and prompt courage, fully qualify him, to the extent of his size, for an excellent watch-dog.