EXPLANATION OF PLATE XX. 



Complete list of reference letters. 



ca. V. cardinal vein. ge. germinal epithelium. 



mg. Malpighian body. od. oviduct or Miillerian duct of the female. 



od\ Miillerian duct of the male. 



2)j.\ growth from vesicle at the end of a segmental tube to join the 

 collecting tube of the preceding segment. 



I'u. ureter commencing to be formed. 



s. d. segmental duct. s. t. segmental tube. 



sur. suprarenal body. u. ureter. w. d. "WolflBan duct. 



Fig. 1 A, 1 B, 1 C, 1 D. Four sections from a female Scyllium canicula 

 of a stage between M and X through the part where the segmental duct be- 

 comes split into Wolffian duct and oviduct. Zeiss B, ocul. 2. Fig 1 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 pro- 

 longation 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 

 pa.ssing 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. 



Fig. 3 A, 3 B, 3 0. Three sections illustrating the formation of a 

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



Fig. 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. 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. 9 A, which represents a longitudinal section through a similar wall of 

 cells. 



