510 MR GREGG WILSON ON THE DEVELOPMENT 



The current controversy, as to whether the Miillerian duct arises independently 

 from the coelomic epithelium or by the splitting or budding of the segmental duct, 

 dates from the time of publication of Semper's great work, " Das Urogenitalsystem 

 der Plagiostomen " (1875). For fifteen years subsequently each but one of the few 

 workers who studied the development of the duct in Amphibia supported an origin 

 similar to what had been described by Semper for Selachians ; in 1890 Marshall and 

 Bles stated that they had not been able to observe any such splitting of the segmental 

 duct as had been asserted for Rami; and since 1890 three papers have appeared 

 supporting the independent origin of the duct in Gymnophiona, Urodela, and Anura. 

 The literature on the development of the Miillerian duct in Amphibia thus falls into 

 three groups : such as was published before 1875, from 1875 to 1890, and from 1890 

 onwards. 



With the first period I need not concern myself much. Marcusen (1851) believed 

 in the direct conversion of the segmental duct into the Miillerian duct ; Leydig and 

 Wittich, proceeding on a more accurate knowledge of the comparative anatomy of 

 Amphibia, thought that only the anterior part of the segmental duct was employed in 

 the formation of the Miillerian duct. Wittich founded on his observations on male 

 Urodela and female Anura the opinion : " dass ein und dasselbe fotale Organ hier zu 

 den ausfiihrenden weiblichen, dort zu den ausfuhrenden mannlichen Geschlechtsapparaten 

 umgewandelt wird, in beiden Fallen aber auch als harnleitender Apparat fungirt, bei 

 jenen in seiner ganzen Lange, bei diesen nur in seinem hinteren Theile." This view 

 that the segmental duct is divided into a sexual and a urinary channel has often been 

 repeated. 



As late as 1875 the opinion advanced by Wittich and Leydig seems to have been 

 unquestioned. In that year Gotte, in his " Entwickelungsgeschichte der Unke," 

 simply says, as to the genital ducts, that he holds a repetition of their researches to be 

 unnecessary. 



But work on other groups had already prepared the way for a change. In 1867 

 Bornhaupt, investigating the fowl, found for the first time the independent formation 

 of the Miillerian duct from a thickening of the epithelium of the mesonephros. In 

 1870, too, Gegenbaur had argued for a splitting of the segmental duct ; but he rested 

 his case entirely on Comparative Anatomy, rather than on direct observation. Finally, 

 in 1875, Semper's work on the urogenital-system of Plagiostomes appeared; and in it 

 he showed that " Bei den Plagiostomen theilt sich der primiire Urnierengang wenigstens 

 im weiblichen Geschlccht vollstiindig in zwei anclre Canale, deren einer als Miillersclier 

 Gang oder Tube den vorderen Trichter des Urnierengangs sich aneignet, sich aber gleich- 

 zeitio- oiinzlich von der Niere trennt ; deren andrer nun Ausfuhrgang der Niere wird 

 und sich abermals in Leydig'schen Gang und eigentlichen Harnleiter spaltet." 



Spengel (1875), a pupil of Semper's, working in the Zoological Institute at Wiirz- 

 burg, was the first actually to describe a splitting in the segmental duct of Amphibians. 

 At the end of a short " vorlaufige Mittheilung " on the " Segmental-organc der 



