No complete series of figures, representing the various stages in development of an Elasmobranch Embryo, has hitherto been published. With the view of supplying this deficiency Plate 8 has been inserted. The embryos represented in this Plate form a fairly complete series, but do not all belong to a single species. Figs. A, B, C, D, E, F, H, I represent embryos of Pristiurus; G being an embryo of Torpedo. The remaining figures, excepting K, which is a Pristiurus embryo, are embryos of Scyllium canicula. The embryos A-I were very accurately drawn from nature by my sister, Miss A. B. Balfour. Unfortunately the exceptional beauty and clearness of the originals is all but lost in the lithographs. To facilitate future description, letters will be employed in the remainder of these pages to signify that an embryo being described is of the same age as the embryo on this Plate to which the letter used refers. Thus an embryo of the same age as L will be spoken of hereafter as belonging to stage L. A. This figure represents a hardened blastoderm at a stage when the embryo-swelling (_e.s._) has become obvious, but before the appearance of the medullary groove. The position of the segmentation cavity is indicated by a slight swelling of the blastoderm (_s.c_). The shape of the blastoderm, in hardened specimens, is not to be relied upon, owing to the traction which the blastoderm undergoes during the process of removing the yolk from the egg-shell. B. B is the view of a fresh blastoderm. The projecting part of this, already mentioned as the 'embryonic rim', is indicated by the shading. At the middle of the embryonic rim is to be seen the rudiment of the embryo (_m.g._). It consists of an area of the blastoderm, circumscribed on its two sides and at one end, by a slight fold, and whose other end forms part of the edge of the blastoderm. The end of the embryo which points towards the _centre_ of the blastoderm is the head end, and that which forms part of the _edge_ of the blastoderm is the tail end. To retain the nomenclature usually adopted in treating of the development of the Bird, the fold at the anterior end of the embryo may be called _the head fold_, and those at the sides the _side folds_. There is in Elasmobranchii no tail fold, owing to the position of the embryo at the periphery of the blastoderm, and it is by the meeting of the three above-mentioned folds only, that the embryo becomes pinched off from the remainder of the blastoderm. Along the median line of the embryo is a shallow groove (_m.g._), the well-known medullary groove of vertebrate embryology. It flattens out both anteriorly and posteriorly, and is deepest in the middle part of its course. C.