The psychological information which is afforded by these remarkable facts of impregnation, which have only been properly observed during the last twenty-five years, is supremely important; its vast significance has hitherto been very far from appreciated. We shall condense the main conclusions of research in the following five theses: I. Each human individual, like every other higher animal, is a single simple cell at the commencement of his existence. II. This "stem-cell" (cytula) is formed in the same manner in all cases--that is, by the blending or copulation of two separate cells of diverse origin, the female ovum and the male spermatozoon. III. Each of these sexual cells has its own "cell-soul"--that is, each is distinguished by a peculiar form of sensation and movement. IV. At the moment of conception or impregnation, not only the protoplasm and the nuclei of the two sexual cells coalesce, but also their "cell-souls"; in other words, the potential energies which are latent in both, and inseparable from the matter of the protoplasm, unite for the formation of a new potential energy, the "germ-soul" of the newly constructed stem-cell. V. Consequently each personality owes his bodily and spiritual qualities to both parents; by heredity the nucleus of the ovum contributes a portion of the maternal features, while the nucleus of the spermatozoon brings a part of the father's characteristics. By these empirical facts of conception, moreover, the further fact of extreme importance is established, that every man, like every other animal, _has a beginning of existence_; the complete copulation of the two sexual cell-nuclei marks the precise moment when not only the body, but also the "soul," of the new stem-cell makes its appearance. This fact suffices of itself to destroy the myth of the immortality of the soul, to which we shall return later on. It suffices, too, for the destruction of the still prevalent superstition that man owes his personal existence to the favor of God. Its origin is rather to be attributed solely to the "eros" of his parents, to that powerful impulse that is common to all polycellular animals and plants, and leads to their nuptial union. But the essential point in this physiological process is not the "embrace," as was formerly supposed, or the amorousness connected therewith; it is simply the introduction of the spermatozoa into the vagina. This is the sole means, in the land-dwelling animals, by which the fertilizing element can reach the released ova (which usually takes place in the uterus in man). In the case of the lower aquatic animals (fishes, mussels, medusæ, etc.) the mature sexual elements on both sides are simply discharged into the water, and their union is let to chance; they have no real copulation, and so they show none of those higher psychic "erotic" functions which play so conspicuous a part in the life of the higher animals. Hence