THE URINOGENITAL ORGANS OF VERTEBRATES. 157 



tremity. This process is not always carried out with equal 

 completeness. In the tailless Amphibians, however, the process 

 is generally 1 completed, and the ureters (Wolffian ducts) are of 

 considerable length. Bufo cinereus, in the male of which the 

 Mullerian ducts are very conspicuous, serves as an excellent 

 example of this. 



In the Salamander (Salamandra maculosa), Figs. 6 and 7, 

 the process is carried out with greater completeness in the 

 female than in the male, and this is the general rule in Amphi- 

 bians. In the male Proteus, the embryonic condition would 

 seem to be retained almost in its completeness so that the 

 ducts of the kidney open directly and separately into the still 

 persisting primitive duct of the kidney. The upper end of 

 the duct nevertheless extends some distance beyond the end 

 of the kidney and opens into the abdominal cavity. In the 

 female Proteus, on the other hand, the separation into a Mulle- 

 rian duct and a ureter is quite complete. The Newt (Triton) 

 also serves as an excellent example of the formation of distinct 

 Mullerian and Wolffian ducts being much more complete in the 

 female than the male. In the female Newt all the tubules 

 from the kidney open into a duct of some length which unites 

 with the Mullerian duct near its termination, but in the male 

 the anterior segmental tubes, including those which, as will be 

 afterwards seen, serve as vasa efferentia of the testis, enter the 

 Mullerian duct directly, while the posterior unite as in the 

 female into a common duct before joining the Mullerian duct. 

 For further details as to the variations exhibited in the Amphi- 

 bians, the reader is referred to Leydig, Anat. Untersuchung, 

 Fischen u. Reptilien. Ditto, Lehrbuch der Histologie, Menschen 

 u. Thiere. Von Wittich, Siebold u. Kolliker, Zeitschrift, Vol. 

 IV. p. 125. 



The different conditions of completeness of the Wolffian 

 ducts observable amongst the Amphibians are instructive in 

 reference to the manner of development of the Wolffian duct 

 in Selachians. The mode of division in the Selachians of the 

 segmental duct of the kidney into a Mullerian and Wolffian 



1 In Bombinator igneus, Von Wittich stated that the embryonic condition was 

 retained. Leydig, Anatom. d. Amphib. u. Reptilien, shewed that this is not the case, 

 but that in the male the Mullerian duct is very small, though distinct. 



