The existence of a protoplasmic network in the yolk has already been mentioned. This in favourable cases may be observed to be in special connection with the nuclei just described. Its meshes are finer in the vicinity of the nuclei, and its fibres in some cases almost appear to start from them (Pl. 7, fig. 12). For reasons which I am unable to explain the nuclei of the yolk and the surrounding meshwork present appearances which differ greatly according to the reagent employed. In most specimens hardened in osmic acid the protoplasm of the nuclei is apparently prolonged in the surrounding meshwork (Pl. 7, fig. 12). In other specimens hardened in osmic acid (Pl. 7, fig. 11), and in all hardened in chromic acid (Pl. 7, fig. 2_a_ and 2_c_), the appearances are far clearer than in the previous case, and the protoplasmic meshwork merely surrounds the nuclei, without shewing any signs of becoming continuous with them. There is also around each nucleus a narrow space in which the spherules of the yolk are either much smaller than elsewhere or completely absent, vide Pl. 7, fig. 2_b_. It has not been possible for me to satisfy myself as to the exact meaning of the lines dividing these nuclei into a number of distinct areas. My observations leave the question open as to whether they are to be looked upon as lines of division, or as protoplasmic lines such as have been described in nuclei by Flemming[126], Hertwig[127] and Van Beneden[128]. The latter view appears to me to be the more probable one. Footnote 126: "Entwicklungsgeschichte der Najaden," _Sitz. d. k. Akad. Wien_, 1875. Footnote 127: _Morphologische Jahrbuch_, Vol. 1. Heft 3. Footnote 128: "Développement des Mammifères," _Bul. de l'Acad. de Belgique_, XL. No. 12, 1875. Such are the chief structural features presented by these nuclei, which are present during the whole of the earlier periods of development and retain throughout the same appearance. There can be little doubt that their knobbed condition implies that they are undergoing a rapid division. The arguments for this view I have already insisted on, and, in spite of the observations of Dr Kleinenberg shewing that similar nuclei of Nephelis do not undergo division, the case for their doing so in the Elasmobranch eggs is to my mind a very strong one.