DEVELOPMENT OF ELA6M0BRANCH FISHES. 271 



the development of the rudimentary Miillerian duct in the male 

 Elasmobranchs. 



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 sys- 

 tem of Vertebrates, to point out my mistake^. 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 moq^hologically 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 open- 

 ings of the two Wolffian ducts gradually approximate in both 

 sexes. By stage (PL xviil. fig. 1 h) they are in close con- 

 tact, 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. 



Forrnation of Wolffian Body and Kidney proper. 



Between stages L and M the hindermost ten or eleven 

 segments of the primitive undivided excretory organ commence 

 to undergo changes which result in their separation from the 



1 Journal of Anatomy and Physiology, Vol. x. 1875. 



