If I go out into the sunshine I become tanned. This again is not a direct and purely chemical or physical result of the sun's rays, but these have stimulated the cells of the skin to undergo certain modifications. Any change in the living body under changed conditions is not passive, but an active reaction to a stimulus furnished by the surroundings. The same stimulus may excite very different reactions in different individuals or species. Early in this century a farmer, Seth Wright, found among his lambs a young ram with short legs and long body. The farmer kept the ram, reasoning that his short legs would prevent him from leading the flock over the farm-walls and fences. From this ram was descended the breed of ancon, or otter, sheep. Now the stimulus which had excited this variation must have been applied early in embryonic life, or perhaps during the formation or maturing of the germ-cells themselves. Such a variation we call a congenital variation. These cases are merely illustrations of the general truth that in every variation there are two factors concerned: the living being with its constitution and inherent tendencies and the external stimulus. The courses of the different balls in a charge of grape-shot, hurled from a cannon, are evidently due to two sets of forces--1, their initial energy and the direction of their aim; 2, the deflecting power of resisting objects or forces--or the different balls might roll with great velocity down a precipitous mountain-side. In the first case velocity and direction of course would be determined largely by initial impulse; in the second, by the attraction of the earth and by the inequalities of its surface. In evolution, environment, roughly speaking, corresponds to these deflecting or attracting external objects or forces; inherent tendencies to initial impulse. If we lay great weight on initial tendencies, inherent in protoplasm from the very beginning, we shall probably lay less stress on natural selection as a guiding, directing process.