The spermatozoön is composed of protoplasm and is one of the smallest cells in the animal body. The seminal fluid is called “sperm” or “the male seed.” Sperm, like saliva or blood, is not a simple fluid, but is a thick agglomeration of innumerable cells swimming about in a comparatively small quantity of fluid. It is not the fluid, but the independent male cells, which swim in it, that cause conception. They have, as a rule, “a peculiarly lively motion.” In most animals, the spermatozoä have a very small naked body, inclosing an elongated nucleus and a long thread like tail, hanging from it. It was long before we could recognize that these structures were simple cells. We now know that the spermatozoä are nothing but simple and real cells of the kind we call “ciliated” cells, equipped with cilia or “lashes.” The body of the spermatozoön is divided into “head,” “trunk” and “tail.” The head is merely the oval nucleus of the cell; the body or middle part is an accumulation of cell matter and the tail is a thread-like prolongation of the trunk or body. The form of the spermatozoön is not peculiar to it; cells with similar forms are found in various other parts of the body. Such forms as the spermatozoön are called caudate or tailed cells. See Haeckel, _Evolution of Man_, p. 52-53. “The spermatozoä,” says Professor Martin, “are motile bodies about 1/500th of an inch in length; they have a flattened, clear body or head and a long vibratile tail or cilium; the portion of the tail nearest the head is thicker than the rest, and is known as the neck. The mode of development of a spermatozoön shows that the head is a cell-nucleus and the neck and tail a modified cell-body.”--(Martin, _Human Body_, p. 651.) According to Haeckel, the spermatozoön is about 1/10,000th of an inch in diameter. See _Evolution of Man_, p. 53, fig. 22. “The striking differences,” says Haeckel, “of [between] the respective cells, in size and shape … are easily explained on the principle of division of labor. The inert motionless ovum grows in size according to the quantity of provision it stores up in the form of nutritive yelk for the development of the germ. The active swimming sperm-cell is reduced in size in proportion to its need to seek the ovum and bore its way into its yelk.”--Haeckel, _Evolution of Man_, p. 57. These statements appear to be true; but the work described by Haeckel, cannot be done by man nor woman; nor by their sexual organs; nor by the blind unthinking atoms which go to build up the spermatozoön and the ovum. The Creator only, can make them! “The phenomena we have described,” he says, on another page, “can only be understood and explained by ascribing a certain lower degree of psychic activity to the sexual principles. They feel each other’s proximity and are drawn together by a sensitive impulse (probably related to smell); they move towards each other and do not rest until they fuse together.” (Haeckel, _Evolution of Man_, p. 58.)