158 THE URINOGENITAL ORGANS OF VERTEBRATES. 



duct is probably to be looked upon as an embryonic abbre- 

 viation of the process by which these two ducts are formed in 

 Amphibians. The fact that this separation into Miillerian and 

 Wolffian ducts proceeds further in the females of most Amphi- 

 bians than in the males, strikingly shews that it is the oviductal 

 function of the Miillerian duct which is the indirect cause of its 

 separation from the Wolffian duct. The Miillerian duct formed 

 in the way described persists almost invariably in both sexes, 

 and in the male sometimes functions as a sperm reservoir ; 

 e.g. Bufo cinereus. In the embryo it carries at its upper end 

 the glandular mass described above (Kopfniere), but this gene- 

 rally atrophies, though remnants of it persist in the males of 

 some species (e.g. Salamandra). Its anterior end opens, in most 

 cases by a single opening, into the perivisceral cavity in both 

 sexes, and is usually ciliated. As the female reaches maturity, 

 the oviduct dilates very much ; but it remains thin and incon- 

 spicuous in the male. 



The only other developmental change of importance is the 

 connection of the testes with the kidneys. This probably 

 occurs in the same manner as in Selachians, viz. from the 

 junction of the open ends of the segmental tubes with the 

 follicles of the testes. In any case the vessels which carry off 

 the semen constitute part of the kidney, and the efferent 

 duct of the testis is also that of the kidney. The vasa effe- 

 rentia from the testis either pass through one or two nearly 

 isolated anterior portions of the kidney (Proteus, Triton) or 

 else no such special portion of the kidney becomes separated 

 from the rest, and the vasa efferentia enter the general body 

 of the kidney. 



In the male Amphibian, then, the urinogenital system con- 

 sists of the following parts (Fig. 6) : 



(1) Rudimentary Miillerian ducts, opening anteriorly into 

 the body-cavity, which sometimes carry aborted Kopfnieren. 



(2) The partially or completely formed Wolffian ducts 

 (ureters) which also serve as the ducts for the testes. 



(3) The kidneys, parts of which also serve as the vasa 

 efferentia, and whose secretion, together with the testicular 

 products, is carried off by the Wolffian ducts. 



