How is an animal embryo formed?

Let’s consider everything on the example of a person. We belong to mammals and the development of embryos in us is the same as in many other species. It all begins after the fertilization of the egg with the sperm. Only two gametes are needed to form a zygote. The zygote then begins to divide. After a while, the embryo is formed. In humans, the period of intrauterine development takes three trimesters. This is nine months. In the first, an embryo is formed, in the second, the embryo becomes a fetus. Other animals develop in the same way, but the timing of intrauterine development is different.