EXPLANATION OF PLATES 2O AND 21. 519 



Fig. 7. The anterior four vasa efferentia of a nearly ripe embryo. Connected 

 with the foremost one is seen a body which looks like the remnant of a segmental 

 tube and its opening (r si ?). 



Fig. 8. Testis and anterior part of Wolffian body of an embryo of Squatina 

 vulgaris. 



The figure is intended to illustrate the arrangement of the vasa efferentia. There 

 are five of these connected with a longitudinal canal in the base of the testis, and 

 with another longitudinal canal in the Wolffian body. From the second longitudinal 

 canal there pass off four ducts to as many Malpighian bodies. Through the Mal- 

 pighian bodies these ducts are continuous with the several coils of the Wolffian body, 

 and so eventually with the Wolffian duct. Close to the hindermost vas efferens is 

 seen a body which resembles a rudimentary segmental tube (r st?}. 



PLATE 21. 



Figs, i A, i B, i C, i D. Four sections from a female Scyllium canicula of a stage 

 between M and N through the part where the segmental duct becomes split into 

 Wolffian duct and oviduct. Zeiss B, ocul. 2. i A is the foremost section. 



The sections shew that the oviduct arises as a thickening on the under surface of 

 the segmental duct into which at the utmost a very narrow prolongation of the lumen 

 of the segmental duct is carried. The small size of the lumen of the Wolffian duct in 

 the foremost section is due to the section passing through nearly its anterior blind 

 extremity. 



Fig. 2. Section close to the junction of the Wolffian duct and oviduct in a female 

 embryo of Scyllium canicula belonging to stage N. Zeiss B, ocul. 2. 



The section represented shews that in some instances the formation of the oviduct 

 and Wolffian duct is accompanied by a division of the lumen of the segmental duct 

 into two not very unequal parts. 



Figs. 3 A, 36, 3 C. Three sections illustrating the formation of a ureter in a 

 female embryo belonging to stage N. Zeiss B, ocul. 2. 



3 A is the foremost section. 



The figures shew that the lumen of the developing ureter is enclosed in front by 

 an independent wall (fig. 3 A), 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. i. 



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. 9 A, 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. 



