Early stage of embryonic development At 7 weeks of pregnancy, the embryo enters the early stage of development. At this point, the embryo is only about 2 millimeters in size, similar to a bean. However, inside this tiny embryo, the foundation of the embryonic organs has already been formed. At this stage, there are three prominent parts of the embryo, namely the head, tail and heart. Development of the Head The head is the most obvious part of the embryo, containing the primitive forms of organs such as the brain, eyes, nose and mouth. In the process of forming the basic structure of the head, the