URINAL CLOACA. 50! 



It is, perhaps, just worth pointing out, that the blindness of 

 the oviduct of female Elasmobranchs, and its mode of develop- 

 ment from an imperfect splitting of the segmental duct, may 

 probably be brought into connection with the blindness of the 

 extremity of the Miillerian duct or oviduct which so often occurs 

 in both sexes of Sturgeons (Accipenser). 



I may, perhaps, at this point, be permitted to say a few 

 words about my original account of the development of the 

 Wolffian duct. This account was incorrect, and based upon a 

 false interpretation of an imperfect series of sections, and I took 

 the opportunity, in a general account of the urinogenital system 

 of Vertebrates, to point out my mistake 1 . Professor Semper 

 has, however, subsequently done me the honour to discuss, at 

 considerable length, my original errors, and to attempt to ex- 

 plain them. Since it appears to me improbable that the con- 

 tinuation of such a discussion can be of much general interest, 

 it will suffice to say now, that both Professor Semper's and my 

 own original statements on the development of the Wolffian 

 duct were erroneous ; but that both of us have now recognised 

 our mistakes ; and that the first morphologically correct account 

 of the development was given by him. 



With reference to the formation of the urinal cloaca there is 

 not much to say. The originally widely separated openings of 

 the two Wolffian ducts gradually approximate in both sexes. 

 By stage O (PL 19, fig. I b) they are in close contact, and the 

 lower ends of the two ducts actually coalesce at a somewhat 

 later period, and open by a single aperture into the common 

 cloaca. The papilla on which this is situated begins to make its 

 appearance considerably before the actual fusion of the lower 

 extremities of the two ducts. 



Formation of Wolffian Body atid Kidney proper. 



Between stages L and M the hindermost ten or eleven seg- 

 ments of the primitive undivided excretory 7 organ commence to 

 undergo changes which result in their separation from the 



1 Joitrnal of Anatomy and Pkysiolegy, VoL x. 1875. [This edition, Xo. VII. ] 



