iv UKINOGENITAL CONNEXION 281 



duct (Dixcoglossus, Alytes, anterior vasa efferentia of Bombinator). 

 In Alytes the single vas efferens with its continuation becomes 

 completely emancipated from the kidney tissue and lies in the adult 

 some distance from the anterior end of the kidney. 



The same phenomenon is seen in Elasmobranchs and Amniotes 

 where the opisthonephric tubules connected with the vasa efferentia 

 never reach the length and complicated convolution of the normal 

 tubule and the Malpighian bodies either degenerate (Scyllium, Pris- 

 tiurus, Birds) or are eliminated entirely from ontogeny (Skates). 



On the other hand the simplification of the route from testis to 

 Wolffian duct may come about in a different fashion, as is seen in 

 Amia, where the opening of the vas efferens has become shifted from 

 the Malpighian body down the course of the tubule, in some cases 

 till it has come to open directly into the duct. 



A careful study of the method by which these various modifica- 

 tions come about during ontogeny is greatly needed. 



Application of the general principles outlined above seems to 

 afford a probable explanation of the remarkable arrangement in 

 Teleostean fishes, where the testis is continued back into a special 

 sperm duct which opens to the exterior near the opening of the 

 kidney duct (Fig. 143). 



The presence of a urinogenital network along the whole length 

 of the testis in Ganoids (Acipenser, Lepidosteus) justifies the assump- 

 tion that the ancestral Teleost possessed this primitive arrangement of 

 the network. In the case of Polypterus the testis is continued back 

 as a duct which opens into the urinogenital sinus formed by the 

 hinder ends of the Wolffian ducts. The duct, however, is not, except 

 near its termination, a simple tube but contains a network of cavities 

 continuous with those of the testis. It is in fact not a simple duct 

 but a portion of the testis which has become sterile. 



Similarly in the case of various typical Teleosts it has been shown 

 (Jungersen, 1889) that the duct is formed by the hinder part of the 

 genital ridge, that it contains for a time a network of cavities con- 

 tinuous with those 'of the functional testis that it is in other words 

 the modified and sterile hinder portion of the testis and, finally, 

 that posteriorly it opens into the Wolffian duct. 



Now the method by which the condition met with in Polypterus 

 or in the young Teleost has arisen is probably indicated by what 

 has happened in the two Lung-fishes Lepidosiren and Protopterus. 

 In the former the testicular network is reduced to the extent that 

 only about half a dozen vasa efferentia persist at the hind end of 

 the series. In Protopterus these are still further reduced to a single 

 vas efferens which passes from the hinder end of the sterile portion 

 of the testis " sperm duct " of the older descriptions into the hind 

 end of the kidney and communicates with the Wolffian duct through 

 the hindermost kidney tubules. 



The only further step needed from the condition exemplified 

 by Protopterus to that of Polypterus or the young Teleost is that 



