It is a wise precaution, therefore, to regard with apprehension an increase in the amount of the menstrual flow of any woman past thirty, and not to accept it as a normal forerunner of the menopause. In the dark womb where I began My mother’s life made me a man. Through all the months of human birth Her beauty fed my common earth. —JOHN MASEFIELD. PART II THE DEVELOPMENT OF THE BABY CHAPTER III. DEVELOPMENT OF THE OVUM, EMBRYO, FETUS, PLACENTA, CORD AND MEMBRANES. The Ovum. The Spermatozoon. Fertilization. Heredity. Sex-determination. Most Favorable Age for Motherhood. The Morula. Growth in the Uterus. The Decidua. Ectoderm. Mesoderm. Entoderm. The Chorion and Placenta. The Amnion. The Umbilical Cord. The Fetus. Growth by Months. Factors Influencing the Size of Child. Multiple Pregnancy. Extra-uterine Pregnancy. CHAPTER IV. GROWTH AND PHYSIOLOGY OF THE FETUS. Circulation. Kidneys. Bowels. Head. Fontanelles. Occipital Measurements. CHAPTER V. SIGNS, SYMPTOMS, AND PHYSIOLOGY OF PREGNANCY. Duration of Pregnancy. Date of Labor. Signs of Pregnancy: Presumptive, Probable, and Positive. Physiological Changes in the Maternal Organism: Uterus. Cervix. Vagina. Tubes and Ovaries. Abdomen. Umbilicus. Breasts. Cardio-Vascular System. Respiratory Organs. Digestive Tract. Urinary Apparatus. Bony Structures. Skin. Carriage. Temperature. Mental and Emotional Changes. Ductless Glands. CHAPTER III THE DEVELOPMENT OF THE OVUM, EMBRYO, FETUS, PLACENTA, CORD AND MEMBRANES As we learned in the last chapter, some of the ova which are discharged into the peritoneal cavity enter the fimbriated end of the tube, while very many others perish. As a rule an ovum enters the tubal opening adjacent to the ovary from which it has been discharged, but it is possible for this tiny cell to travel across the body and enter the tube on the opposite side. This migration of the ovum, as it is termed, has been demonstrated in cases in which pregnancy has followed removal of the ovary on one side and the tube on the other. [Illustration: FIG. 17.—Diagram of spermatozoa, the male cells of germination. ] There are various theories as to how and why an occasional migrating ovum, floating around in a relatively large cavity, ever enters the tubal opening, which, after all, is not large. The most widely accepted belief is that the motion of the cilia lining the tubes creates a suction which draws the microscopical cell into the opening, the same cilia being the means by which the ovum is later propelled downward through the tube to the uterus.