The figures shew that the lumen of the developing ureter is enclosed in front by an independent wall (fig. 3A), but that further back the lumen is partly shut in by the subjacent Wolffian duct, while behind no lumen is present, but the ureter ends as a solid knob of cells without an opening into the Wolffian duct. Fig. 4. Section through the ureters of the same embryo as fig. 3, but nearer the cloaca. Zeiss B, ocul. 2. The figure shews the appearance of a transverse section through the wall of cells above the Wolffian duct formed by the overlapping ureters, the lumens of which appear as perforations in it. It should be compared with fig. 9A, which represents a longitudinal section through a similar wall of cells. Fig. 5. Section through the ureters, the Wolffian duct and the oviduct of a female embryo of Scy. canicula belonging to stage P. Zeiss B, ocul. 2. Fig. 6. Section of part of the Wolffian body of a male embryo of Scyllium canicula belonging to stage O. Zeiss B, ocul. 2. The section illustrates (1) the formation of a Malpighian body (_mg_) from the dilatation at the end of a segmental tube, (2) the appearance of the rudiment of the Müllerian duct in the male (_od´_). Figs. 7_a_, 7_b_. Two longitudinal and vertical sections through part of the kidney of an embryo between stages L and M. Zeiss B, ocul. 2. 7_a_ illustrates the parts of a single segment of the Wolffian body at this stage, vide p. 491. The segmental tube and opening are not in the plane of the section, but the dilated vesicle is shewn into which the segmental tube opens. 7_b_ is taken from the region of the kidney proper. To the right is seen the opening of a segmental tube into the body-cavity, and in the segment to the left the commencing formation of a ureter, vide p. 502. Fig. 8. Longitudinal and vertical section through the posterior part of the kidney proper of an embryo of Scyllium canicula at a stage between N and O. Zeiss A, ocul. 2. The section shews the nearly completed ureters, developing Malpighian bodies, &c. Fig. 9. Longitudinal and vertical section through the anterior part of the kidney proper of the same embryo as fig. 8. Zeiss A, ocul. 2. The figure illustrates the mode of growth of the developing ureters. 9A. More highly magnified portion of the same section as fig. 9. Compare with transverse section fig. 4. Fig. 10. Longitudinal and vertical section through part of the Wolffian body of an embryo of Scyllium canicula at a stage between O and P. The section contains two examples of the budding out of the vesicle of a segmental tube to form a Malpighian body in its own segment and to unite with the tubulus of the preceding segment close to its opening into the Wolffian duct. EXPLANATION OF PLATES 22 AND 23[3]. (VIII. p. 168.)