EXCRETORY ORGANS. 585 



Before dealing with the further changes of the Wolffian body it is 

 necessary to return to the segmental duct, which, at the time when 

 the pronephros is undergoing atrophy, becomes split into a dorsal 

 Wolffian and vential Muilerian duct. The process in Salamandra 

 (Fiirbringer) has much the same character as in Elasmobranchii, the 

 Miiilerian duct being formed by the gradual separation, from before 

 backwards, of a solid row of cells from the ventral side of the seg- 

 mental duct, the remainder of the duct constituting the Wolffian 

 duct. During the formation of the Miiilerian duct its anterior 

 part becomes hollow, and attaching itself in front to the peritoneal 

 epithelium acquires an opening into the body cavity. The process of 

 hollowing is continued backwards pari passu with the splitting of the 

 segmental duct. In the female the process is continued ti'l the 

 Miiilerian duct opens, close to the Wolffian duct, into the cloaca. In the 

 male the duct usually ends blindly. It is important to notice that 

 the abdominal opening of the Miiilerian duct in the Amphibia 

 (Salamandra) is a formation independent of the pronephros, and 

 placed slightly behind it ; and that the undivided anterior part of the 

 segmental duct (with the pronephros) is not, as in Elasmobranchii, 

 united with the Miiilerian duct, but remains connected with the 

 Wolffian duct. 



The development of the Miiilerian duct has not been, satisfactorily 

 studied 'in other forms besides Salamandra. In Cceciliida? its abdominal 

 opening is on a level with the anterior end of the Wolffian body. In other 

 forms it is usually placed very far forwards, close to the root of the lungs 

 (except in Proteus and Batrachoseps, where it is placed somewhat further 

 back), and some distance in front of the Wolffian body. 



The Miiilerian duct is always well developed in the female, and serves 

 as oviduct. In the male it does not (except possibly in Alytes) assist 

 in the transportation of the genital products, and is always more or less 

 rudimentary, and in Anura may be completely absent. 



After the formation of the Miiilerian duct, the Wolffian duct 

 remains as the excretory channel for the Wolffian body, and, till the 

 atrophy of the pronephros, for this gland also. Its anterior section, 

 in front of the Wolffian body, undergoes a more or less complete 

 atrophy. 



The further changes of the excretory system concern 1 1) the junction 

 in the male of the anterior part of the Wolffian body with the testis ; 

 (2) certain changes in the collecting tubes of the posterior part of 

 the mesonephros. The first of these processes results in the division 

 of the Wolffian body into a sexual and a non-sexual part, and in 

 Salamandra and other Urodeles the division corresponds with the dis- 

 tribution of the simple and compound segmented tubes. 



Since the development of the canals connecting the testes with 

 the sexual part of the Wolffian body has not been in all points 

 satisfactorily elucidated, it will be convenient to commence with a 

 description of the adult arrangement of the parts (fig. 4-00 B). In 

 most instances a non segmental system of canals the vasa efferentia 



