DEVELOPMENT OF ELASMOBRANCH FISHES. 265 



secondary importance ; but they have a certain bearing on the 

 homology between the Miillerian duct of higher Vertebrates 

 and that of Elasmobranchs. The following account refers to 

 Scy. canicula, but so far as my observations go, the changes in 

 Scy. stellare are nearly identical in character. 



I propose treating the development of these ducts in the 

 two sexes separately, and begin with the female. 



Shortly before stage N a horizontal split arises in the 

 segmental duct\ commencing some little distance from its an- 



O 'CD 



terior extremity, and extending backwards. This split divides 

 the duct into a dorsal section and a ventral one. The dorsal 

 section forms the Wolffian duct, and receives the openings of 

 the seo'mental tubes, and the ventral one forms the Miillerian 

 duct or oviduct, and is continuous with the unsplit anterior 

 part of the primitive segmental duct, which opens into the 

 body-cavity. The nature of the splitting may be gathered 

 from the woodcut, fig. 6, p. 281, where ^represents the line along 

 which the segmental duct is divided. The splitting of the 

 primitive duct extends slowly backwards, and thus there is for 

 a considerable period a single duct behind, which bifurcates 

 in front. A series of transverse sections through the point of 

 bifurcation always exhibits the following features. Anteriorly 

 two separate ducts are present, next two ducts in close juxta- 

 position, and immediately behind this a single duct. A series 

 of sections through the junction of two ducts is represented 

 on Plate XX. fig. 1A,1B,1C,1D. 



In my youngest example, in which the splitting had com- 

 menced, there were two separate ducts for only 14 sections, and 

 in a slightly older one for about 18. In the second of these 

 embryos the part of the segmental duct anterior to the front end 

 of the Wolffian duct, which is converted directly into the oviduct, 

 extended through 48 sections. In the space included in these 

 48 sections at least five, and I believe six, segmental tubes with 

 openings into the body-cavity were present. These segmental 

 tubes did not however unite with the oviduct, or at best, but 

 one or two rudimentary junctions were visible, and the 

 evidence of my earlier embryos appears to shew that the seg- 

 mental tubes in front of the Wolffian duct never become in 

 1 For the development of tlie segmental duct, vide p. 127, et seq. 

 B. 18 



