How does a multicellular embryo arise from a fertilized cell?

It arises through multiple divisions. This whole process is divided into stages. So, an egg after fertilization is called a zygote, it contains a double set of chromosomes. Then this cell begins to divide into two, four, eight, etc. cells. This set of cells is called a morula. As a result of further division of all cells, the next stage is obtained – blastula, a feature of which is the formation of an embryo consisting of many cells with a cavity inside. Cell diploidy remains unchanged at all stages. Then comes the next stage, when the ball begins to bulge inward, forming a two-layer, cupped embryo. At this stage, it is called gastrula. Then the third layer of cells is formed, and the name is changed to neurula.