All the cells in our body arise from the solitary cell created by the fusion of a sperm, the male sex cell, and an ovum, the female sex cell. The union of these two cells forms the ~zygote~, or fertilized egg. Fertilization occurs in one of the Fallopian tubes. The cell divides to create more cells. The first cells created by the fertilized ovum are identical. These cells then divide and subdivide. A complicated ~process~ of differentiation occurs, creating cells of different shape, size, and texture, each of which has a specific task. As cell division progresses, the developing |embryo| moves down the Fallopian tube. After about three days it reaches the |uterus| and attaches itself to the uterine wall where the development of the human |embryo| continues.
