In many cases especially large cells are to be seen on the floor of the cavity (Pl. 7, fig. 2, _bd_). In my preliminary paper[122] the view was expressed that these are probably cells formed around the nuclei of the yolk. This view I am inclined to abandon, and to substitute for it the suggestion made by Dr Schultz, that they are remnants of the larger segmentation cells which were to be seen in the previous stages. Footnote 122: _Qy. Journal of Micros. Science_, Oct. 1874. [This Edition, No. V.] Plate 7, figs. 2, 3, 4 (all sections of this stage) shew the different appearances presented by the floor of the segmentation cavity. In only one of these sections are there any large number of cells upon the floor; and in no case have cells been observed imbedded in the yolk forming this floor, as described by Dr Schultz[123], but in all cases the cells simply rested upon it. Footnote 123: _Loc. cit._ Probably Dr Schultz, here as in other cases, has mistaken nuclei for cells. Passing from the segmentation cavity to the blastoderm itself, the first feature to be noticed is the more decided differentiation of the epiblast. This now forms a distinct layer composed of a single row of columnar cells. These are slightly more columnar in the region of the embryonic swelling than elsewhere, and become less elongated at the edge of the blastoderm. In my specimens this layer was never more than one cell deep, but Dr Schultz[124] states that, in the Elasmobranch embryos investigated by him, the epiblast was composed of more than a single row of cells. Footnote 124: _Loc. cit._ Each epiblast cell is filled with yolk-spherules and contains a nucleus. Very frequently the nuclei in the layer are arranged in a regular row (vide Pl. 7, fig. 3). In the later blastoderms of this stage there is a tendency in the cells to assume a wedge-like form with their thin ends pointing alternately in opposite directions. This arrangement is, however, by no means strictly adhered to, and the regularity of it is exaggerated in Plate 7, fig. 4. The nuclei of the epiblast cells have the same characters as those of the lower layer cells to be presently described, but their intimate structure can only be successfully studied in certain exceptionally favourable sections. In most cases the yolk-spherules around them render the finer details invisible. There is at this stage no such obvious continuity as in the succeeding stage between the epiblast and the lower layer cells; and this statement holds good more especially with the best conserved specimens which have been hardened in osmic acid (Pl. 7, fig. 4). In these it is very easy to see that the epiblast simply thins out at the edge of the blastoderm without exhibiting the slightest tendency to become continuous with the lower layer cells[125].