512 MR GREGG WILSON ON THE DEVELOPMENT 



gauze nach hiuteu bis zur Kloake sich fortsetzende Theil, legt sich durch Neubildung an." 

 He also remarks that before the fission the segmental duct " auf den Namen einer Rokre 

 kaum Anspruch machen kann." The first statement renders his opinion alike difficult 

 to believe and difficult to disprove. The second indicates a possible source of error. 

 I shall deal specially with what Hoffmann said as to Triton when I have described my 

 own observations.* 



Since Hoffmann wrote, Marshall and Bles have investigated the development of 

 the frog without finding any splitting of the segmental duct ; Semon (1891), after a full 

 examination of Ichthyophis, has written : " Ich betrachte daher als sicher, dass bei 

 Ichthyophis der Miillersche Gang ohne Beziehung zum Vornierengang und zur Vorniere 

 entsteht." MacBride has described the development of the Miillerian duct of Rana as 

 due entirely to ccelomic epithelium ; and Jungersen has published an extensive account 

 of the facts in Rana and Triton, and comes to the same conclusion. 



Meanwhile, after it seemed proved by the works of Waldeyer, Gasser, Braun, 

 Renson, Janosik, Mihalkovics, Hoffman, Wiedersheim, and others, that the 

 Miillerian duct of Amniota was due to a proliferation of ccelomic epithelium, we have 

 this year two publications which aim at showing that this is not so. 



M. J. van Erp Taalman Kip, after studying various of the Insectivora and Rodentia, 

 has come to the conclusion that the two extreme modes of development, as found in 

 Selachians and Reptiles, are connected by others which exhibit partial splitting, partial 

 independent growth. He even holds that within such a group as the Birds, or within 

 a genus, there may be variability and a greater or less adherence to the original mode 

 of development by splitting from the segmental duct. He holds, for instance, that 

 the fowls investigated by Balfour and found to exhibit fission of the segmental duct 

 were " more primitive " than those made use of by continental zoologists and which 

 showed an independent origin for the duct. 



Burger writes in a very different strain ; but he, too, seeks to reduce to uniformity 

 the diverse modes of development of the Miillerian duct. He has worked on the duck 

 and Tadorna ; and having come to conclusions identical with those of Balfour and 

 Sedgwick concerning the fowl, he criticises the investigations of Mihalkovics and 

 Wiedersheim on Reptilia ; accepts Amann's evidence that in the sheep the Wolffian 

 duct takes part in originating the Miillerian duct ; and concludes that probably in all 

 the groups of Amniota, as well as in the Anamnia, the Miillerian duct arises by the 

 splitting of the segmental duct. 



The literature of the subject is thus in a state of confusion, from which further 

 investigation alone can free it. 



The First Anlage of the Duct. 



In an embryo (A) of Salamandra atra, 11*5 mm. in length, a little anterior to the 

 pronephros, one finds the body-cavity divided into five spaces (fig. 1). Dorsally on 



* See p. 518. 



