When the sexual act takes place, there is deposited into the vagina a secretion known as semen. According to Sutkowsky, each deposit or ejaculation contains 50,000,000 of spermatozoa. About the same time in the act there occurs in the female, spasmodic contractions of the muscles of the uterus which draws in a small amount of the sperm which the male has left there. The sperm cell of the male under the microscope shows that it contains both head and tail. The tail enables it to move and advance with a tadpole-like motion toward the ovum. As in the lower forms of life, the male cell has within it the instinct to chase and capture the female cell. Consequently, it does not depend upon the uterine contractions of the female to enable it to reach the ovum for fertilization. The vagina being a corrugated or wrinkled tube, hides and secretes the sperm cell for days, unless it is removed with water or killed by poisonous injections. When, however, the sperm comes near the ovum it is drawn to it as to a magnet. The ovum being carefully protected by nature within the ovaries, leaves its sister cells and travels alone. The sperm cell, however, having more dangerous paths to travel, must provide against the uncertainty of doing its great work by going in numbers, though it takes but one single cell to produce human life. A number of the male cells go to meet the ovum, but only one enters it. Almost at the moment the head enters the ovum it becomes completely absorbed by the ovum and all trace of it is lost. This union of the two cells is called fertilization, fecundation, impregnation, or conception. Any of these terms may be used. This union usually takes place in the tube, but the fertilized egg does not remain there; it wanders along and finds its way into the uterus. Now that the ovum has been fertilized, it readily becomes attached to the soft lining of the uterus which has been specially prepared to receive it. No menstruation occurs. The woman is now pregnant. A new being is created, and marvelous changes will now take place within the tiny cell clinging so weakly to the lining of the uterus. At this time the ovum is so small it can scarcely be seen by the naked eye, but in two weeks it has grown to the size of a pea; in four weeks to the size of a walnut, and in eight weeks to the size of a lemon. At this time it is three inches long and is completely formed, the head being much larger in proportion to the rest of its body. What has happened to the ovum in these few weeks is briefly this: All the changes in the evolution of the animal kingdom, that man had to pass through to arrive at his present shape, the human embryo goes through step by step within the uterus in a very short period. Immediately after fertilization the ovum begins to divide into sections or lobes, into 2, 4, 8, 16, 32, etc. cells until they are almost countless. Each cell splits in the middle of the nucleus, forming two complete new cells and so on.