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XXIII. — The Development of the Miillerian Ducts of Reptiles. By Gkegg Wilson, D.Se. 

 Communicated by Professor J. C. Ewart, F.Pl.S. (With Two Plates.) 



(Read 5th July 1897.) 



We have already accounts of the development of the Miillerian ducts of reptiles from 

 Braun (1), Mihalkovics (2), Hoffmann (3), and Wiedeesheim (4). All of these 

 writers agree in saying that the Mullerian ducts arise quite independently of the seg- 

 mental ducts ; but in view of recent attempts to show that in the other groups of verte- 

 brates there are forms in which the Mullerian ducts are derived from the segmental 

 ducts, it seemed expedient to reconsider this conclusion,* and I have accordingly 

 examined the development of the ducts in Crocodilus biporcatus, Chelone viridis, and 

 Lacerta agilis. 



As regards the derivation of the Miillerian ducts from ccelomic epithelium, I can only 

 confirm the above-mentioned authorities ; but I am able to supplement what they say as 

 to the first foundation and the formation of the anterior end. I find that the anterior 

 end is formed in reptiles, very much as in amphibians, by a modification of the ccelomic 

 epithelium in the region of the pronephros. Backward growth proceeds independently 

 alike of the segmental duct and of the epithelium of ,the body-cavity posterior to the 

 ostium abdominale. 



Braun examined all stages of the development of the ducts in Lacerta agilis, Anguis 

 fragilis, and Tropidonotus natrix, and controlled his results by observations on Coronella 

 leevis. He found essential uniformity in all. 



In Anguis fragilis he described two anterior diverticula of the ccelom, separated by 

 a bridge of connective tissue. These are, of course, lined by peritoneal epithelium, and 

 Braun remarked that this, at one place on the pleura costalis, near its transition to the 

 pleura visceralis, shows an incomprehensible thickening — eine mir vbllig unverstdnd- 

 liche Verdickung. Braun made no suggestion as to the significance of this thickening, 

 and did not attempt to connect it with the origination of the Mullerian duct. He 

 described the first Anlage of this as further back, where the diverticula open into the 

 ccelom proper, and the mesonephros projects freely into the body-cavity. Here he de- 

 scribed the peritoneal epithelium as being thickened and raised on a longitudinal ridge 

 that has appeared on the excretory organ. Most anteriorly this ridge is almost quite 

 ventral, but it passes gradually in a spiral till it comes to lie dorsal to the mesonephros. 

 It then accompanies the Wolffian duct to the posterior end of the ccelom. In the 

 thickened epithelium at the anterior end of this ridge an invagination appears, and the 

 funnel so formed grows back along the ridge. Braun is emphatic as to the independent 



* Burger (5) suggests that probably the Mullerian ducts of reptiles are derived from the segmental ducts. He even 

 makes the statement that there is no evidence of independent origin. 



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