Figure 9_j_ is about twenty sections posterior to Figure 9_i_. The medullary groove (_mg_) is considerably larger than in the more anterior regions, and its folds are somewhat inclined toward each other, though still wide apart. The notochord and entoderm are fused to form a large, compact mass of tissue close under the ventral wall of the medullary groove. On the ventral side of this mass of cells a groove (_blp_) marks the anterior and ventral opening of the blastopore shown in the next figure. The mesoblast shows no sign of cleavage. Figure 9_k_ shows the medullary groove (_mg_) in about the same position as in the preceding section. The blastopore (_blp_) is here seen as a small cavity in the center of the large mass of cells that was noted in the last figure. The entoderm (_en_) is continuous from side to side, but is not so sharply differentiated from the other germ layers as is represented in the figure. Figure 9_l_ is four sections back of the preceding; the wide, dorsal opening (_blp_) of the blastopore or neurenteric canal into the medullary groove (_mg_) is shown. The blastopore or neurenteric canal, then, is still at this stage a passage that leads entirely through the embryo, the medullary canal being in this region unenclosed above. Ventrally it is seen as a narrow opening through the entoderm; it then passes upward and backward, behind the end of the notochord, as a small but very distinct canal, which may be traced through about ten sections. The enclosed portion of the canal lies, as has been stated (Figure 9_k_, _blp_), in the center of the mass of cells that is fused with or is a part of the floor of the medullary groove. The above-described neurenteric canal is essentially like that described by Balfour in the _Lacertilia_. He does not say, however, and it is not possible to tell from his figures, whether there is a long, gradually diminishing groove posterior to the dorsal opening of the canal, as in the alligator. He says that the medullary folds fuse posteriorly until the medullary canal is enclosed over the opening of the neurenteric canal; also that “the neurenteric canal persists but a very short time after the complete closure of the medullary canal.” In Figure 9_m_, for about thirty sections (one tenth the entire length of the embryo), behind the section represented in the last figure, there is a very gradual change in the embryo, converting the deep groove, _mg_ in Figure 9_l_, into the shallow slit, _pg_, Figure 9_m_.