To obtain the earliest stages, I watched the newly made nests until the eggs were laid, and in this way a number of eggs were obtained within a very few hours after they had been deposited, and all of these eggs contained embryos of a more or less advanced stage of development. Gravid females were then killed, and the eggs removed from the oviducts. These eggs, although removed from a “cold-blooded” animal, generally contained embryos of some size, and only one lot of eggs thus obtained contained undeveloped embryos, which embryos refused to develop further in spite of the most careful treatment. Voeltzkow (78) found, in the same way, that the earlier stages of the crocodile were extremely difficult to handle; so that, in order to obtain the earlier stages, he was reduced to the rather cruel expedient of tying a gravid female and periodically removing the eggs from the oviducts through a slit cut in the body wall. The older embryos are hardy and bear transportation well, so that it is comparatively easy to obtain the later stages of development. For the stages up to the formation of the first four or five somites, I am indebted, as I have already said, to Professor Clarke, and, since I have had opportunity to examine only the sections and not the surface views of these stages, I shall quote directly Clarke’s paper in the _Journal of Morphology_ (17) in description of these surface views. STAGE I FIGURES 2-2_f_ (PLATES VI., VII.) The youngest embryo that we have for description is shown in Figures 2 and 2_a_. Of Figure 2 Clarke says: “The limiting line between the opaque and pellucid areas is clearly marked, and within the latter is a shield-shaped area connected by the narrower region of the primitive streak with the area opaca. The blastopore is already formed near the posterior end of the shield. “A ventral view of another embryo of the same age (Fig. 2_a_), seen from the ventral side, shows that the blastopore extends quite through the blastoderm, in an oblique direction downwards and forwards, from the dorsal to the ventral side. The thickened area of the primitive streak is here very prominent. There is, too, the beginning of a curved depression at the anterior end of the shield, the first formation of the head-fold.” Transverse sections of this stage are shown in Figures 2_b_-2_f_. Figure 2_b_, through the anterior region of the blastoderm, shows a sharply defined ectoderm (_ec_) which is composed of three or four layers of cells in the median region, while it gradually thins out laterally. Closely underlying this ectoderm is a thin sheet of irregular cells, the entoderm (_en_). Figure 2_c_ is about one fifth of the length of the blastoderm posterior to the preceding and represents approximately the same conditions, except that there is an irregular thickening of the entoderm in the median region (_en_). This thickening apparently marks the anterior limit of the mesoderm, to be discussed shortly.