DEVELOPMENT OF ELASMOBRANCH FISHES. 267 



The above series of sections goes far to prove that the 

 posterior part of the oviduct is developed as a nearly solid ridge 

 split off from the under side of the segmental duct, into which 

 at the utmost a very small portion of the lumen of the latter 

 is continued. One instance has however occurred amongst 

 my sections which probably indicates that the lumen of the 

 segmental duct may sometimes, in the course of the forma- 

 tion of the oviduct and Wolffian duct, become divided into 

 two parts, of which that for the oviduct, though consider- 

 ably smaller than that for the \yolffian duct, is not so markedly 

 so as in normal cases (PI. XX. fig. 2). 



Professor Semper states that the lumen of the part of the 

 oviduct split off from the hindermost end of the segmental duct 

 becomes continuously smaller, till at last close to the cloaca it 

 is split off as a solid rod of cells without a lumen, and thus it 

 comes about that the oviduct, when formed, ends blindly, and 

 does not open into the cloaca till the period of sexual maturity. 

 My own sections do not include a series shewing the formation 

 of a terminal part of the oviduct, but Semper's statements 

 accord precisely with what might probably take place if my 

 account of the earlier stages in the development of the oviduct 

 is correct. The presence of a hymen in young female Elas- 

 mobranchs was first made known by Putmann and Garman^, y 

 and subsequently discovered independently by Semper ^ 



The Wolffian duct appears to receive its first segmental 

 tube at its anterior extremity. 



In the male the changes of the original segmental duct 

 have a somewhat different character to those in the female, 

 although there is a fundamental agreement between the two 

 sexes. As in the female a horizontal split makes its appearance 

 a short way behind the front end of the segmental duct, and 

 divides this into a dorsal Wolffian duct and a ventral Mullerian 

 duct, the latter continuous with the anterior section of the 

 segmental duct, which carries the abdominal opening. The 

 differences in development between the two sexes are, in spite 

 of a general similarity, very obvious. In the first place, the 



1 On the Male and Female Organs of Sharks and 'Skates, with special refer- 

 ence to the use of the claspers, Froceed. American Association for Advance- 

 ment of Science, 1874. 



' Loc. cit. 



18—2 



