The document summarizes the key stages of embryonic development from fertilization to differentiation of organs. It begins with fertilization, where the genetic material from sperm and egg cells combine to form a zygote. The zygote then undergoes cleavage, forming a solid ball of cells called a morula. Further cleavage results in blastulation and the formation of a hollow ball of cells called a blastula or blastocyst. During gastrulation, the blastula undergoes differentiation into three embryonic layers - ectoderm, endoderm, and mesoderm. Neurulation follows, forming the neural tube from neural folds. Finally, organogenesis occurs as organ rudiments develop and differentiate into mature organs.