Figure 7_h_ represents the region of the primitive groove (_pg_) and primitive streak (_ps_). The section shows the typical structure for this region--a thick mass of cells is proliferating from the ventral side of the ectoderm (_ec_) and is spreading laterally to form a distinct mesoderm (_mes_). The entoderm (_en_) is entirely distinct from the other layers. STAGE V FIGURES 8-8_j_ (PLATES XII., XIII., XIV.) On opening the egg this embryo (Figs. 8 and 8_a_) was found to lie on the end of the yolk, near the center of the irregular, lighter area which was mentioned in connection with the description of the egg. The length of the embryo proper is 3 mm. This was the youngest stage found in 1905, and approximates quite closely the condition of the chick embryo after 24 hours’ incubation. The dorsal aspect of this embryo, viewed by transmitted light, is shown in Figure 8. The medullary folds (_mf_) have bent over until they are in contact, though apparently not fused for a short distance near their anterior ends. As will be described in connection with the sections of this stage, the medullary folds are actually fused for a short distance at this time, though in surface views they appear to be separated from each other. In the Madagascar crocodile (78) the first point of fusion of the medullary folds is in the middle region of the embryo, or perhaps even nearer the posterior than the anterior end of the medullary groove. Throughout the greater part of their length the medullary folds are still widely separated; posteriorly they are merged with the sides of the very distinct primitive streak (_ps_), which seems, owing to its opacity, to extend as a sharp point toward the head. Extending for the greater part of the length of the primitive streak is the primitive groove (_pg_), which, when the embryo is viewed by transmitted light, is a very striking feature at this stage of development and resembles, in a marked way, the same structure in the embryo chick. Clarke (17) figures the blastopore at this stage as a small opening in front of the primitive streak, but does not mention any such condition as above described at any stage of development. Five pairs of somites (_s_) have been formed and may be seen, though but faintly outlined, in both dorsal and ventral views of the embryo; they lie about half-way between the extreme ends of the embryo. The head-fold (_h_, Fig. 8_a_) shows plainly in a ventral view as a darker, more opaque anterior region, extending for about one fourth the length of the embryo. The still unfused region of the medullary folds may be seen also in the ventral view at _mg_. The head-fold of the amnion (_a_) forms a very thin, transparent hood over the extreme anterior end of the embryo. The tail fold of the amnion has not made its appearance, and in fact is not apparent at any stage in the development. This is true also of the Madagascar crocodile. The notochord (_nt_) may be seen in a ventral