EXPLANATION OF PLATES 22, 23. xxxiii 



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 commenc- 

 ing 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. 



9 A. 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!. (VIII. p. 168.) 

 PLATE 22. 



Fig. A. Section through the dorsal region of an embryo of Scyllium stellare, with 

 the rudiments of two visceral clefts. The section illustrates the general features at a 

 period anterior to the appearance of the posterior nerve-roots. 



nc. neural canal, mp. muscle-plate, ch. notochord. x. subnotochordal rod. 

 ao, rudiment of dorsal aorta, so. somatopleure. sp. splanchnopleure. al. alimentary 

 tract All the parts of the section except the spinal cord are drawn somewhat 

 diagrammatically. 



Figs. B I, B II, B in. Three sections of a Pristiurus-embryo. B I is through 

 the heart, B n through the anterior part of the dorsal region, and B III through 

 a point slightly behind this. Drawn with a camera. (Zeiss CC, ocul. 2.) 



In B III there is visible a slight proliferation of cells from the dorsal summit of the 

 neural canal. 



In B II this proliferation definitely constitutes two club-shaped masses of cells (/>r), 

 both attached to the dorsal summit of the neural canal. The masses are the rudi- 

 ments of the posterior nerve-roots. 



1 The figures on these Plates give a fair general icfea of the appearance presented by the 

 developing spinal nerves ; but the finer details of the original drawings have in several cases become 

 lost in the process of copying. 



The figures which are tinted represent sections of embryos hardened in osmic acid ; those without 

 colour sections of embryos hardened in chromic acid. 



