From the beginning of fertilization the oocyte completes the second meiosis, the sperm-egg union forms the embryo, which moves along the fallopian tube towards the uterus, on the way forming a two-cell embryo, a four-cell embryo, an eight-cell embryo, and a mulberry embryo. Cell division begins 26-30 hours after fertilization, with oogenesis taking place every 10-12 hours, and when it reaches 16-32 cells it is known as the mulberry embryo. At this time, it begins to reach the uterine cavity, and early blastocysts are formed on the 4th-5th day, the zona pellucida dissolves and disappears, and the blastocysts begin to invade the endometrium, and the implantation process is completed on the 11th-12th day, and the cells of the trophoblast layer of the blastocyst proliferate rapidly, and the cells of the follicular trophoblast layer turn from a single layer into a compound layer, the outer layer of cells fuses to form the merged trophoblast layer, and the deeper layer of cells has clear cell boundaries, which is called the cellular trophoblast, and the trophoblast layer grows outwardly after the implantation and is called the chorion. After implantation, the trophoblast grows outwardly with a number of chorionic villi, which gradually develop and differentiate to form the placenta. The trophoblast draws nutrients directly from the mother’s blood for the embryo’s development, and the embryo, which has settled down in the uterus, undergoes a continuous process of growth and development, forming a fetus, which then becomes a mature individual through childbirth.