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The fertilized eggs are called a zygote. After the egg has been fertilized the next step is implantation. While the zygote begins to undergo mitoses. As the embryo grows a cavity forms in the center until the embryo becomes a hollow ball of cells known as a blastocyst. About six or seven days after fertilization, the blastocyst attaches to the wall of the uterus and begins to grow into the tissues of the mother. This process is called implantation. Then after the gastrulation come which is key events in early development include gastrulation, which produces the three cell layers of the embryo and neurulation, which leads to the formation of the nervous system. The result of gastrulation is the formation of three cell layers called ectoderm, mesoderm and endoderm. After the gastrulation is followed by another important step in development is called nurulation. During neurulation, the ectoderm undergoes changes that lead to the formation of a neural tube the develops into the brain and the spinal cord. Neural crest cells develop into many types of nerves. Then the next stage is the placenta. The placenta connection between the mother and the developing embryo or fetus is called the placenta. It is through the placenta that the embryo gets oxygen and nutrients and excretes wastes. The chronic villi from the fetus extend into the mothers uterine lining. The after 8 weeks the embryo is called a fetus. From 4-6 months the 4,5 and 6 months after fertilization the tissues of the fetus become more complex and specialized, and begin to function. The during 7-9 months during the last three months before birth, the organ systems of the fetus mature and the fetus grows in size and mass. By 14 weeks the hands feet and
