Stages of embryogenesis are cleavage, gastrulation and organogenesis.
1. Cleavage: The process by which the zygote divides to form a multicellular embryo is called cleavage. As a result of division, the zygote becomes a sterile sphere with 16-32 cells. This is the marula stage and the cells are called blastomeres. The process of morula formation is called morulation. The cells of the marula dasa are arranged in a layer and a cavity filled with fluid is formed inside. This stage is called blastula. The cell layer of the blastula stage is called the blastoderm and the cavity is called the blastocoel. Cleavage process ends with the development of blastula stage.
2. Gastrulation: The process by which gastrula stage is formed from blastula is called gastrulation. In this process, the cells change rapidly and are arranged in two layers. The outer one is called ectoderm and the inner one is called endoderm. Later mesoderm is formed from ectoderm. A fluid-filled cavity forms inside the gastrula. It is called archenteron. The opening through which the archenteron is released is called the blastopore.
3. Organogenesis: The process by which various organs are formed from the embryonic stage is called organogenesis. A specific cell mass forms a specific organ. First, rudimentary buds are formed from the embryonic layer. Later, specific organs are formed from the organelles.