MULLERIAN AND WOLFFIAN DUCTS. 495 



which I differ from him. These are for the most part of a 

 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 seg- 

 mental duct 1 , commencing some little distance from its anterior 

 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 seg- 

 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. 511, where x represents the line along which the s.eg- 

 mental 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 juxtaposition, and immedi- 

 ately behind this a single duct. A series of sections through 

 the junction of two ducts is represented on Plate 21, figs. I A, 

 i B, i C, i D. 



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 evi- 

 dence of my earlier embryos appears to shew that the segmental 



1 For the development of the segmental duct, vide p. 34 5, et seq. 



