1. Fertilization - when a sperm and egg meet. How does this happen? Remember that each month, a female ovulates and an egg moves out of the ovary. If the woman has sexual intercourse during this time, and sperm are deposited, the sperm will swim upwards to try to reach the egg. When one sperm enters the egg, the egg seals itself so that no more can enter.

2. Once the egg is fertilized, it is called a zygote. It moves to the uterus, where it is implanted. The zygote begins to go through cell division. It grows and develops in the uterus for a period of 40 weeks. This is pregnancy.

3. During the first two months of pregnancy, the unborn child is called an embryo. After that, it is called a fetus. The developing embryo.fetus is held inside a fluid-filled sac called the amniotic sac. It is connected to the mother by the umbilical cord. This cord carries nutrients and oxygen from the mother to the baby.

4. The umbilical cord connects to the placenta, which is the thickened, enriched lining of the mother’s uterus. (The development of the fetus is described in your text on Pages 712-714.)