520 MR GREGG WILSON ON THE DEVELOPMENT 



Jungersen, too, denied that the segmental duct had any share in forming the Anlage 

 of the Miillerian duct of Rana and Triton, and ascribed it to the peritoneal epithelium ; 

 but speaking of Triton he says : "the mouth-part of the Miillerian duct is the first to be 

 laid down, and it is formed from the peritoneal-epithelium ; the development of the mouth 

 is not due to the high epithelium on the pronephros between the nephrostomes, for that is 

 inclosed within the capsule of the glomerulus." This seems to me to be only a partial truth. 

 It is the case that the epithelium in the line between the nephrostomes is not converted 

 into the anterior end of the Miillerian duct ; but the mouth is formed from the lateral 

 part of the plate of epithelium that first appears between the nephrostomes ; and the 

 "capsule of the glomerulus " is simply formed by the combined outgrowths of the 

 lateral wall and the radix mesenterii, and only partly divides the originally simple 

 Anlage. In the frog and Alytes there is no such division, and the anterior end of the 

 Miillerian duct is seen to arise from the lateral part of the simple plate and the back- 

 ward process that grows along the segmental duct. 



In summing up I may say, that though several of the authors referred to above 

 describe the first Anlage as being split off the segmental duct, all admit that the 

 anterior of the Miillerian duct develops out of the thickened epithelium of the prone- 

 phros region, and Hoffman's is the only description that is necessarily hostile to the 

 view that the part of the Anlage immediately posterior to the epithelial plate is a mere 

 backward process of the same. 



Formation of the Anterior Part of the Miillerian Duct. 



The first Anlage develops into the complete duct in two modes : anteriorly the 

 epithelial plate that lies on the pronephros forms first a thick band of cells, then a 

 ridge which becomes grooved, and finally closes to form a tube ; posteriorly a rod of 

 cells appears in the neighbourhood of the segmental duct, and in course of time 

 gradually becomes hollowed. I shall first give some particulars to illustrate the former 

 mode. 



An Axolotl of 37 mm. (7) shows the anterior end of the Miillerian duct Anlage 

 lying on the lateral body-wall, with the secondary attachment of the lung internal 

 to it. In the 1 8th section it begins to pass behind the lung, having now come to lie 

 dorsally. This is just on a level with the anterior end of the glomerulus of the 

 pronephros. Twelve sections further back, and posterior now to the glomerulus, the 

 band of epithelium approaches the centre, to lie outside the remains of the degenerate 

 pronephros. Six sections to the posterior a very marked thickening of the Anlage is 

 found, corresponding in appearance and probably in position with the cell-mass that 

 appeared lateral to the second ncphrostome in |3. From this point the Anlage passes 

 back as a thread of cells. A few sections further on the outgrowth of the radix 

 mesenterii comes to an end, and the Miillerian duct Anlage continues its course along 

 the outside of the segmental duct. 



