hall: MESONEPHROS and MLJLLERIAN DUCT IN AMPHIBIA. 103 



irregular mass of cells constituting the oviducal welt. The caudad 

 prolongation of the duct, which is at first a solid cord, is formed by a 

 rearrangement of the cells of the oviducal welt. 



It will be seen that, contrary to what might have been expected in an 

 animal which shows so many primitive characters in the urino-genital 

 system, Ichthyophis has as yet thrown no light on the origin or develop- 

 ment of the Miillerian duct in other forms. 



Anura. 



The conditions in Anura have been carefully studied by Hoffmann 

 ('86) in the cases of Eana temporaria, R. esculenta, Bufo cinereus, by 

 MacBride ('91, '92) in Rana, and by Gemmill ('97) in Rana temporaria 

 and Pelobates fuse us. 



According to the statement of Hoffmann, his was the first description 

 of the development of the Miillerian duct in Anura. The first change 

 preparatory to its development is a histological alteration of the pro- 

 nephric duct between the pronephros and the mesonephros. This change 

 consists in the transformation of its flat epithelial cells into those of a 

 columnar shape and a reduction in the size of its lumen. The anterior 

 end of the duct then separates from the degenerating pronephros and 

 fuses with its peritoneal covering, — which is now also composed of 

 cylindrical cells. A little anterior to the mesonephros, the segmental 

 duct divides oblicpiely. Of the two portions thus formed, the posterior 

 one, which ends blindly in front, retains its connection with the meso- 

 nephros and is the "Wolffian duct. The anterior portion, connecting with 

 the pronephric epithelium in front and ending blindly just lateral to the 

 anterior end of the Wolffian duct, is the fundament of the jNIiillerian 

 duct. The caudad growth of the Miillerian duct is independent of the 

 Wolffian duct and is probably accomplished by the proliferation of a 

 solid cord of cells from the neighboring thickened peritoneal epithelium, 

 although of this Hoftniann is not certain. 



Turning to the behavior of the anterior end of the Miillerian duct, its 

 fusion with the peritoneal epithelium is converted into an opening. 

 This is not, however, the ostium abdominale. From this opening a 

 thickened band passes laterad and ventrad around the base of the lung 

 and then turns caudad for some distance. By a folding of this band 

 and a fusion of the lips thus formed the anterior opening is carried 

 outward and downward, and then caudad. With the degeneration of 

 the glomus, the duct moves niediad, and at the same time the edges 

 of its cephalic opening begin to flatten out again to form a part of the 



