ISO THE URINOGENITAL ORGANS OF VERTEBRATES. 



The kidneys extend along the whole length of the body- 

 cavity ; and the ureter, which does not reach the whole length 

 of the kidneys, is a thin-walled wide duct lying on the outer 

 side. On laying it open the numerous apertures of the tubules 

 for the kidney are exposed. The Miillerian duct, which opens 

 in both sexes into the abdominal cavity, ends, according to 

 Leydig, in the cases of some males, blindly behind without 

 opening into the ureter, and Miiller makes the same statement 

 for both sexes. It was open on both sides in a female specimen 

 I examined 1 , and Hyrtl found it invariably so in both sexes in 

 all the specimens he examined. 



Both Rathke and Stannius (I have been unable to refer to 

 the original papers) believed that the semen was carried off by 

 transverse ducts directly into the ureter, and most other ob- 

 servers have left undecided the mechanism of the transportation 

 of the semen to the exterior. If we suppose that the ducts 

 Rathke saw really exist they might perhaps be supposed to 

 enter not directly into the ureter, but into the kidney, and 

 be in fact homologous with the vasa efferentia of the Selachians. 

 The frequent blind posterior termination of the Miillerian duct 

 is in favour of the view that these ducts of Rathke are really 

 present. 



In Polypterus (vide Hyrtl, Ganoideii) there is, as in other 

 Ganoids, a pair of Miillerian ducts. They unite at their lower 

 ends. The ureters are also much narrower than in previously 

 described Ganoids and, after coalescing, open into the united 

 oviducts. The urinogenital canal, formed by coalescence of 

 the Miillerian ducts and ureters, has an opening to the exterior 

 immediately behind the anus. 



In Amia (vide Hyrtl) there is a pair of Miillerian ducts 

 which, as well as the ureters, open into a dilated vesicle. This 

 vesicle appears as a continuation of the Miillerian ducts, but 

 receives a number of the efferent ductules of the kidneys. There 

 is a single genito-urinary pore behind the anus. 



In Ceratodus (Giinther, Phil. Trans. 1871) the kidneys are 

 small and confined to the posterior extremity of the abdomen. 

 The generative organs extend however along the greater part of 



1 For this specimen I am indebted to Dr Giinther. 



