Figure 9_a_ represents a section through the anterior part of the head-fold; it shows one unusual condition: the head lies entirely beneath the surface of the yolk. This condition is quite confusing when the section is studied for the first time. The pushing of the head under the yolk is shown at its commencement in Figure 11. The process continues until nearly the entire anterior half of the embryo is covered; but when the embryo attains a considerable size it is seen to lie entirely above the yolk, as in the chick. According to Voeltzkow’s figures (78) this same condition is found in the crocodile, and Balfour also mentions it in connection with the lizard. The fusion of the medullary folds has made considerable progress, so that the entire anterior end of the canal is enclosed, except in the region where the folds are bent down and back, as in the preceding stage; here the folds are still distinct from each other, leaving the medullary canal open on the ventral side, as shown in Figures 9_a_ and 9_b_. In the section under discussion the ectoderm (_ec_) is a very thin membrane on top of a considerable mass of yolk, while no entoderm can be distinguished. The amnion (_a_) completely surrounds the embryo as an irregular membrane of some thickness in which no arrangement into layers can be seen. The epidermal ectoderm (_ep_) is composed of the usual loosely arranged cells, so that it is clearly distinguishable from the compactly arranged cells of the nervous layer (_nl_), from which it is separated by only a line. In Figure 9_b_, which shows a section a short distance posterior to the preceding, the medullary canal (_mc_) is somewhat deeper and is still open ventrally. There is a distinct space between the nervous (_nl_) and epidermal (_ep_) layers of the ectoderm, in which space a few mesoblast cells (_mes_) may be seen. The section is cut just posterior to the edge of the amnion, so that there is now neither amnion nor yolk above the embryo. Figure 9_c_ is about ten sections posterior to Figure 9_b_. The section passes through the anterior wall of the bent-under part of the medullary canal (_mc′_), so that the actual canal is shown only on the dorsal side (_mc_), where it is completely closed and begins to assume the shape of the typical embryonic spinal cord. The space between the superficial (_ep_) and nervous (_nl_) layers of the ectoderm is quite extensive and is largely filled by a fairly compact mass of mesoderm (_mes_).