745 



the anterior groove ends. In my 51 mm specimen the groove ends 

 in the 27 th section after the beginning of the Anlage, almost im- 

 mediately behind the place where the ridge approaches the middle. It 

 forms no tube, but gradually closes, and is followed posteriorly, first 

 by a superficial, then by a somewhat deep-lying rod of cells. The 

 transition from the anterior furrow to the posterior epithelial thicken- 

 ing seems to be a gradual one. 



The position of the Müllerian duct in relation to the segmental 

 duct is similar to what was described in the early forms. Anteriorly 

 the Müllerian duct is lateral as well as ventral to the segmental 

 duct ; but it soon comes to lie almost opposite it ; while posteriorly it 

 is again lateral. The segmental duct is seen well-defined and distinct, 

 running along the base of the ridge that carries the Müllerian duct, 

 both anterior and posterior to the inclosing of the furrow (S. d. 

 Figs. 7 — 14). In the 51 mm form, though degeneration of the seg- 

 mental duct is seen to be in progress, its position is well-marked, and 

 in neither specimen is there any indication of its originating or cooper- 

 ating in the origination of the Müllerian duct. 



It thus appears that the Müllerian duct of Axolotl is first 

 represented by a columnar epithelium that lies on the pronephros 

 between the nephrostomes, and extends backwards opposite the seg- 

 mental duct; that subsequently the part that covers the pronephros 

 forms the mouth of the duct, while the posterior portion becomes 

 thicker, and gives rise to a rod of cells, which form the Mülle- 

 rian duct. There is no room for doubt either as to the formation of the 

 anterior end from coelomic epithelium, or as to the non-participation 

 of the posterior part of the segmental duct in the formation of the 

 posterior region of the duct ; and in Axolotl I have found no evidence 

 that even "ein kleines Stück" (Hoffmann, speaking of the frog) 

 arises by the splitting of any intervening part. On the contrary I have 

 seen the Anlage of the duct essentially completed, in the only region 

 concerning which there could be difficulty, without any participation 

 of the still perfect segmental duct. 



49 



