Now that we know something of the place where the baby’s life begins and how the way is prepared for his growth, we are ready to follow the interesting course of events that occur from the time the seed, a tiny egg-like cell, bursts from an ovary until the beautiful, fully developed baby comes into the world. You will remember that when the ovum is expelled from an ovary it may float about in the abdominal cavity and be lost or it may enter the near-by mouth of a tube. Also that if it enters a tube it is carried downward toward the uterine cavity by the sweeping motion of the hair-like projections on the lining of the tube. This journey of the ovum through the tube is of enormous consequence, for during its course occur the events which decide whether the ovum shall, like most of its fellows, be simply swept along to no end and lost, or whether by chance it is to receive the mysterious impulse which begins the development of a new human being. The amazing power which enables this cell to reproduce itself, and to develop with unbelievable complexity is acquired somewhere in the tube, usually in the upper end, by meeting and fusing with a _spermatozoon_, the germinal cell of the male. The spermatozoa are attracted to the ovum much as bits of metal are drawn to a magnet, but although the ovum that is destined to be fertilized is surrounded by several spermatozoa, only one actually enters and fuses with it. This fusion is termed =fertilization=, or, in lay parlance, =conception=, and the instant at which it occurs marks the beginning of pregnancy. The establishment of this fact is of considerable importance, since it does away with any possible controversy concerning the time at which a new life begins. The origin of the baby is exactly coincident with the fusion of the male and female cells. Furthermore, the sex of the child and any inherited traits and characteristics are also established at this decisive moment. No amount of dieting, exercise or mental effort on the part of the expectant mother can alter or influence them in the smallest degree, for the father has made his complete contribution toward the creation of the new being and the mother, also, has made hers, except for nourishment which she provides throughout pregnancy. All told, probably more than five hundred theories have been advanced to explain what it is that decides of which sex the forthcoming child is going to be. But as the results of applying these theories have scarcely borne out the claims of their advocates, they are given but scant attention to-day.