Gastrulation is a crucial phase in embryonic development that occurs after fertilization. During this process, the single-layered blastula transforms into a multi-layered structure called the gastrula. This transformation involves the movement and rearrangement of cells, leading to the formation of three primary germ layers: ectoderm, mesoderm, and endoderm. Each of these layers will eventually develop into different tissues and organs in the organism. The ectoderm will form structures such as the skin and nervous system, while the mesoderm gives rise to muscles, bones, and the circulatory system. The endoderm is responsible for developing internal organs like the lungs and digestive tract. Gastrulation is essential for establishing the body plan and ensuring proper organ formation in developing embryos.