In gastruladon the cells of the inner surface of embryonic knob distinguish as endodermal cells. The cells of the primitive streak fan out laterally, forming a distinct cell layer the mesoderm. After the formation of mesoderm the remaining cells of epiblast form ectbderm. Gastrulation involves cell movements that help to attain new shape and morpholpgs of the embryo. These cell movements are called, morphogenetic movements. The embryo forms a distinct endodermal tube by gastrulation, that constitute the early gut. The space enclosed within the gut is the gastrocoel or archehteron. Blastomeres are formed by the early cleavage.