system of the bee is adapted to its congenital instinct of honeycomb building, just so truly is the brain of the dog adapted to its now congenital instinct of following and obeying a master. The habit of attaching itself to a particular human being is nowadays engrained in the nerves of the modern dog just as really, though not quite so deeply, as the habit of running or biting is engrained in its bones and muscles. Every dog is born into the world with a certain inherited structure of limbs, sense-organs, and brain: and this inherited structure governs all its future actions, both bodily and mental. It seeks a master because it is endowed with master-seeking brain organs; it is dissatisfied until it finds one, because its native functions can have free play in no other way. Among a few dogs, like those of Constantinople, the instinct may have died out by disuse, as the eyes of cave animals have atrophied for want of light; but when a dog has once been brought up from puppyhood under a master, the instinct is fully and freely developed, and the masterless condition is thenceforth for him a thwarting and disappointing of all his natural feelings and affections. Not only have dogs as a class acquired a special instinct with regard to humanity generally, but particular breeds of dogs have acquired particular instincts with regard to certain individual acts. Nobody doubts that the muscles of a greyhound are specially correlated to the acts of running and leaping; or that the muscles of a bull-dog are specially correlated to the act of fighting. The whole external form of these creatures has been modified by man's selective action for a deliberate purpose: we breed, as we say, from the dog with the best points. But besides being able to modify the visible and outer structure of the animal, we are also able to modify, by indirect indications, the hidden and inner structure of the brain. We choose the best ratter among our terriers, the best pointer, retriever, or setter among other breeds, to become the parents of our future stock. We thus half unconsciously select particular types of nervous system in preference to others. Once upon a time we used even to rear a race of dogs with a strange instinct for turning the spit in our kitchens; and to this day the Cubans rear blood-hounds with a natural taste for hunting down the trail of runaway negroes. Now, everybody knows that you cannot teach one sort of dog the kind of tricks which come by instinct to a different sort. No amount of instruction will induce a well-bred terrier to retrieve your handkerchief: he insists upon worrying it instead. So no amount of instruction will induce a well-bred retriever to worry a rat: he brings it gingerly to your feet, as if it was a dead partridge. The reason is obvious, because no one would breed from a retriever which worried or from a terrier which treated its natural prey as if it were a stick. Thus the brain of each