DEVELOPMENT OF ELASMOBRANCH FISHES. 269 



parts of the Miillerian duct. He further asserts that the por- 

 tions of the Miillerian duct with a lumen open into the Wolffian 

 duct. The most important difference, however, between Pro- 

 fessor Semper's and my own description consists in his having 

 failed to note that the splitting of the segmental duct com- 

 mences much further forwards in the male than in the female. 



I have attempted to shew that the oviduct in the female, 

 with the exception of the front extremity, is formed as a nearly 

 solid cord split off from the ventral surface of the segmen- 

 tal duct, and not by a simple splitting of the segmental duct into 

 two equal parts. If I am right on this point, it appears to me 

 far easier to understand the relationship between the oviduct 

 or Miillerian duct of Elasmobranchs and the Miillerian duct of 

 Birds, than if Professor Semper's account of the development of 

 the oviduct is the correct one. Both Professor Semper and my- 

 self have stated our belief in the homology of the ducts in 

 the two cases, but we have treated their relationship in a 

 very different way. Professor Semper^ finds himself compelled 

 to reject, on theoretical grounds, the testimony of recent 

 observers on the development of the Miillerian duct in Birds, 

 and to assert that it is formed out of the Wolffian duct, 

 or, according to my nomenclature, 'the segmental duct.' In 

 ray account ^ the ordinary statements with reference to the 

 development of the Miillerian duct in Birds are accepted ; but 

 it is suggested that the independent development of the Miille- 

 rian duct ma}^ be explained by the function of this duct in 

 the adult having, as it were, more and more impressed itself 

 upon the embryonic development, till finally all connection, 

 even duriag embryonic life, betw^een the oviduct and the seg- 

 mental duct (Wolffian duct) became lost. 



Since finding what a small portion of the segmental duct 

 became converted into the Miillerian duct in Elasmobranchs, I 

 have reexamined the development of the Miillerian duct in 

 the Fowl, in the hope of finding that its posterior part might 

 develope nearly in the same manner as in Elasmobranchs, at 

 the expense of a thickening of cells on the outer surface of 



1 Loc. cit. p. 412, 413. 



2 The Urinogenital Organs of Vei-tebrates, Journal of Anatomy and Fhysiology, 

 Vol. X. p. 47. 



