Figure 11_c_ is twenty sections, about one tenth the length of the embryo, posterior to the one last described. The large mass of overhanging yolk (_y_) is still present, as is also the amnion (_a_), though the latter no longer passes entirely around the embryo; only the true amnion could be made out. The thickened walls of the medullary canal have reduced that cavity to a narrow, Y-shaped slit (_mc_). The notochord (_nt_) is very slender in this region, compared to its diameter farther toward the posterior end. The enteron (_ent_) is a large cavity, whose wall is made up of loosely arranged cells except around a median, ventral depression where the cells are more compact. This depression may be traced through ten or fifteen sections and may represent the beginning of the thyroid gland, though this point was not worked out with certainty. Surrounding the notochord and enteron is a loose mass of typical, stellate mesoblast cells (_mes_), which are cleft on either side to form the anterior limit of the body cavity (_bc_). Between the body cavity below and the enteron above, on each side, is a small blood-vessel (_bv_) which when followed caudad is found to open ventrally and medially into the anterior end of the heart. Figure 11_d_ is about a dozen sections posterior to the preceding. The appearance of the overhanging yolk (_y_), of the amnion (_a_), and of the notochord (_nt_) is about as in the more anterior section. The medullary canal (_mc_) is a straight, vertical slit, and the depression in the floor of the pharynx (_ent_) is much more shallow. The body cavity (_bc_) is much larger and extends across the mid-ventral line beneath the heart (_ht_), which is cut through its middle region. The heart may be traced through about twenty sections (one tenth the length of the embryo); its mesoblastic wall (_mes′_) is thin and irregular, and is lined by a distinct endothelium (_en′_) whose exact origin has not yet been worked out. Figure 11_e_ is just back of the heart, and shows in its place the two vitelline veins (_vv_). The depression in the floor of the enteron (_ent_) is entirely distinct from the one that has been mentioned above, and is simply the posterior limit of the head-fold of the entoderm; the fifth section posterior to this shows where this depression opens ventrally to the yolk sac. The other structures shown in the figure are not markedly different from what was seen in Figure 11_d_.