744 



Pig. 21. 



Md. 



S.d 



M.d.. 



Fig. 22 



S.d. 



a change may be seen. At the same level, i. e., immediately anterior 

 to the line of attachment of the lung, the plate of epithelium is found 

 to be undergoing conversion into the mouth of the Miillerian duct. 

 Only in the first section in which the thickened epithelium occurs do 

 we find the relations similar to those in earlier stages (Fig. 17); the 

 next shows an undermining of the plate by an extension of the body- 

 cavity ; and after four sections the epithelial plate is seen to have lost 

 its attachment to the lateral wall, and to persist only in connection 

 with the dorsal wall (Figs. 18 — 20). In the next eleven sections a 

 projecting remnant of the epithelial plate is seen on the lateral wall 

 (Fig. 20 r). Meanwhile the epithelial plate raised from the dorsal wall 

 of the body-cavity becomes grooved. On one side the groove extends 

 forwards to the still lateral, undermined portion of the plate; on the 

 other side the groove begins a few sections further back. 



It thus appears that the anterior end of the Miillerian duct is 

 formed in Axolotl from the lateral plate of thickened epithelium that 

 lies between the nephrostomes of the pronephros. 



In the 45 mm specimen, though the anterior plate of epithelium 

 is not undermined, the part of the Anlage that is immediately 

 posterior to the rudimentary pronephros shows a gradual elevation. 

 Where the Anlage comes to lie near the mid- dorsal line it is seen to 

 be raised on a slight ridge; and as we go further back, we find the 

 ridge increasing till it is higher than it is broad. Anteriorly it is 

 not grooved (Fig. 5) ; then a distinct furrow appears along the thickened 

 epithelium that formes the top of the ridge (Figs. 6 and 7); and still 

 further back — 43 sections from the beginning of the Anlage — there 

 is a closing over of the edges, and (on one side) for one or two 

 sections a distinct tube appears, only to be followed, however, by a 

 dense mass of cells, in which, again, a rod of cells appears as the 

 immediate precursor of the Miillerian duct (Figs. 8 — 14). 



I have been unable to determine exactly where the formation of 



