THE UR1NOGENITAL ORGANS OF VERTEBRATES. 151 



the length of the abdominal cavity. In both male and female 

 there is a long Miillerian duct, and the ducts of the two sides 

 unite and open by a common pore into a urinogenital cloaca 

 which communicates with the exterior by the same opening 

 as the alimentary canal. In both sexes the Miillerian duct 

 has a wide opening near the anterior extremity of the body- 

 cavity. The ureters coalesce and open together into the urino- 

 genital cloaca dorsal to the Miillerian ducts. It is not abso- 

 lutely certain that the semen is transported to the exterior 

 by the Miillerian duct of the male, which is perhaps merely a 

 rudiment as in Amphibia. Dr Giinther failed however to find 

 any other means by which it could be carried away. 



The genital ducts of Lepidosteus differ in important par- 

 ticulars from those of the other Ganoids (vide M tiller, loc. cit. 

 and Hyrtl, loc. cit.}. 



In both sexes the genital ducts are continuous with the in- 

 vestments of the genital organs. 



In the female the dilated posterior extremities of the ureters 

 completely invest for some distance the generative ducts, whose 

 extremities are divided into several processes, and end in a 

 different way on the two sides. A similar division and asym- 

 metry of the ducts is mentioned by Hyrtl as occurring in 

 the male of Spatularia, and it seems not impossible that on 

 the hypothesis of the genital ducts being segmental tubes these 

 divisions may be remnants of primitive glandular convolu- 

 tions. The ureters in both sexes dilate as in other Ganoids 

 at their posterior extremities, and unite with one another. 

 The unpaired urinogenital opening is situated behind the anus. 

 In the male the dilated portion of the ureters is divided into 

 a series of partitions which are not present in the female. 



Till the embryology of the secretory system of Ganoids has 

 been worked out, the homologies of their generative ducts are 

 necessarily a matter of conjecture. It is even possible that 

 what I have called the Miillerian duct in the male is function- 

 less, as with Amphibians, but that, owing to the true ducts of 

 the testis having been overlooked, it has been supposed to 

 function as the vas deferens. Gunther's (loc. cit.} injection ex- 

 periments on Ceratodus militate against this view, but I do 

 not think they can be considered as conclusive as long as the 



