92 bulletin: museum of compakative zoology. 



(Fig. 67), similar to those which formed the evaginations in Amblystoma. 

 From this disk a thickened baud runs ventrad and cephalad to join 

 that from the first evagiuatiou. The opposite side of the body presents 

 the normal condition of a single irregular evagiuation ventral to the 

 common opening of the three nephrostomes. 



It was stated above that even where the three nephrostomes have 

 fused, the fundament of the Mtilleriau duct may show signs of being 

 formed of separate proliferations or evaginations. I have represented 

 ten successive sections through such a fundament in Figures G8-77 

 (Plates 6, 7). 



In Figure 68 the proliferation (evg. 1) may represent the first evagi- 

 nation, although it is also possible that it is the posterior end of the fold 

 of the thickened band which is described below. If it is really the first 

 evagination, the mass of cells marked dt. 1, in Figures 69 and 70, would 

 seem to represent the duct which in Amblystoma extends caudad from 

 the first evagination. In Figure 70 the epithelial thickening shows no 

 evagination or special proliferation. In Figures 71 and 72 the cell 

 proliferation immediately beneath the common nephrostome is well 

 marked and takes the form of a distinct evagination, whose lumen is 

 shown in Figures 73 and 74 {ev(j. 2). These sections also show a group 

 of cells {(It. 2) which may represent the duct from this second evagina- 

 tion. Owing to the thickness of the sections, this group of cells is 

 longer than one would at first imagine. Figure 75 passes through 

 the posterior margin of the second evagination. Directly ventral to it 

 is the thickest point in the peritoneal epithelium, which marks the level 

 at which the third evagination takes place. The opening of the third 

 evagination is shown in one section only (Fig. 76, evg. 3). Tlie next 

 section (Fig. 77, Plate 7) passes through its posterior prolongation, and 

 in the two following sections (not figured) is seen its duct, which is 

 free from the peritoneum. This duct dwindles to a cord, which is short 

 and ends in contact with, but independent of, the peritoneal epithelium. 

 This cord forms the Mtilleriau duct, but whether alone or witli the addi- 

 tion of anterior ducts (by fusion, as in Amblystoma), I was unaVile to 

 determine. I must also leave undecided the important question whether 

 the developing Miillerian duct comes into relationship with the Wolfiian 

 duct or not. Two factors render the determination of these points very 

 difficult : the fold which contains the ducts turns mediad behind the 

 pronephros, so that it is cut very obliquely in cross-sections of the body ; 

 this fold, like the degenerating pronephros, is filled with densely packed 

 lymph cells. That the Mtilleriau duct takes cells from the "Woltfian 



