The main features of the epiblast remain the same as during the last stages. It is still composed of a very distinct layer one cell deep. Over the segmentation cavity, and over the whole embryonic end of the blastoderm, the cells are very thin, columnar, and, roughly speaking, wedge-shaped with the thin ends pointing alternately in different directions. For this reason, the nuclei form two rows; but both the rows are situated near the upper surface of the layer (vide Pl. 7, fig. 5). Towards the posterior end of the blastoderm the cells are flatter and broader; and the layer terminates at the non-embryonic end of the blastoderm without exhibiting the slightest tendency to become continuous with the lower layer cells. At the embryonic end of the blastoderm the relations of the epiblast and lower layer cells are very different. At this part, throughout the whole extent of the embryonic rim, the epiblast is reflected and becomes continuous with the lower layer cells. The lower layer cells form, for the most part, a uniform stratum in which no distinction into mesoblast and hypoblast is to be seen. Both the lower layer cells and the epiblast cells are still filled with yolk-spherules. The structures at the embryonic rim, and the changes which are there taking place, unquestionably form the chief features of interest at this stage. The general relations of these parts are very fairly shewn in Pl. 7, fig. 5, which represents a section passing through the median line of the embryonic region. They are however more accurately represented in Pl. 7, fig. 5_a_, taken from the same embryo, but in a lateral part of the embryonic rim; or in Pl. 7, fig. 6, from a slightly older embryo. In all of these figures the epiblast cells are reflected at the edge of the embryonic rim, and become perfectly continuous with the hypoblast cells. A few of the cells, immediately beyond the line of this reflection, precisely resemble in character the typical epiblast cells; but the remainder exhibit a gradual transition into typical lower layer cells. Adjoining these transitional cells, or partly enclosed in the corner formed between them and the epiblast, are a few unaltered lower layer cells (_m_), which at this stage are not distinctly separated from the transitional cells. The transitional cells form the commencement of the hypoblast (_hy_); and the cells (_m_) between them and the epiblast form the commencement of the mesoblast. The gradual conversion of lower layer cells into columnar hypoblast cells, is a very clear and observable phenomenon in the best specimens. Where the embryonic rim projects most, a larger number of cells have assumed a columnar form. Where it projects less clearly, a smaller number have done so. But in all cases there may be observed a series of gradations between the columnar cells and the typical rounded lower layer cells[131].