498 DEVELOPMENT OF ELASMOBRANCH FISHES. 



very obvious. In the first place, the ventral portion split off 

 from the segmental duct, instead of being as in the female 

 larger in front than the Wolffian duct, is very much smaller ; 

 while behind it does not form a continuous duct, but in some 

 parts a lumen is present, and in others again absent (PI. 21, fig. 6). 

 It does not even form an unbroken cord, but is divided in dis- 

 connected portions. Those parts with a lumen do not appear to 

 open into the Wolffian duct. 



The process of splitting extends gradually backwards, so that 

 there is a much longer rudimentary Miillerian duct by stage O 

 than by stage N. By stage P the posterior portions of the 

 Miillerian ducts have vanished. The anterior parts remain, 

 as has been already stated, till adult life. A second difference 

 between the male and female depends on the fact that, in the 

 male, the splitting of the segmental duct into Miillerian duct 

 and Wolffian duct never extends beyond the hinder extremity 

 of the small intestine. A third and rather important point 

 of difference consists in the splitting commencing far nearer 

 the front end of the segmental duct in the male than in the 

 female. In the female it was shewn that about 48 sections 

 intervened between the front end of the segmental duct and 

 the point where this became split, and that this region included 

 five or six segmental tubes. In the male the homologous space 

 only occupies about 7 to 12 sections, and does not contain the 

 rudiment of more than a single segmental tube. Although my 

 sections have not an absolutely uniform thickness, yet the above 

 figures suffice to shew in a conclusive manner that the splitting 

 of the segmental duct commences far further forwards in the 

 male than in the female. This difference accounts for two facts 

 which were mentioned in connection with the excretory organs 

 of the adult, viz. (i) the greater length of the Wolffian body 

 in the male than in the female, and (2) the fact that although a 

 nearly similar number of segmental tubes persist in the adults 

 of both sexes, yet that in the male there are five or six more 

 segments in front of the first fully developed segmental opening 

 than in the female. 



The above description of the formation of the Miillerian duct 

 in the male agrees very closely with that of Professor Semper 

 for Acanthias. For Scyllium however he denies, as it appears to 



