"We Breeders pay more attention to the bull because he can sire fifty calves yearly; while the cow can produce only one. One can afford to pay a thousand guineas for a bull, whereas one cannot afford fifty cows at the same price. And the purchase of a first-class bull is the cheapest way of getting a good herd. The history of practically every great herd is the history of some particular bull. As we say, '_a bull is half the herd_.' It is equally true to say that every great bull is the son of a great cow. With one highly-prepotent bull we can raise a high-class herd, even if we start with second-rate females; while a bad bull will ruin the best herd in the county. It is for this reason that we 'put all our money' on the bull." All of which supports my theory that the male is the impelling agency in Adaptation to Environment, or evolutionary development on the plane of physics, and that such progressive development is achieved by way of the male traits being Dominant upon this plane, and manifesting, accordingly, in the physical terms of stature and muscle and force-production. The male being the determinant agent in the physical characteristics of size and flesh and nervous energy--for which breeders of Live-stock are making--the bull is "half the herd." "With one highly-prepotent bull," a high-class herd may be raised, even though inaugurated with second-rate females. Whilst "a bad bull will ruin the best herd in the county." Akin to which is the circumstance that, in two generations, the improvement which occurs in the offspring of a New Forest pony-mare when mated with a horse, lapses; the descendants reverting to the type of the New Forest pony. If, however, the male, being the agent of Adaptation, determines progressive development in the direction of such physical traits as further fit species to its material environment, the female it is, that, being the agency of the Evolution of Life (and of the equipment of species in terms of Life, accordingly) supplies offspring with the Vital potential of living cells and vital organs--heart, lungs, digestive and assimilative organs and functions--which, by engendering the multiple functions and vital processes of Life, _sustain_ the existence and the powers of the organism in relation to environment. The female, moreover, provides it with the Vital potential of reproductive organs for the transmission of types ever further evolved and adapted, in terms both of Life and Adaptation. The male thus broadly sketches out the lines and supplies the initiative of structural development. The female supplements the sketch with the structural potential of living cells, whereby structural development is achieved; as too with the vital potential of organs whereby living organisation is sustained and transmitted.