9G BULLETIN: MUSEUM OF COMPAKATIVE ZOOLOGY. 



duct has generally degenerated nearly back to the region of the meso- 

 nephros before the Mtillerian duct arises. In one case only was a small 

 bit of the anterior portion of the Wolffian duct retained, and in that 

 case the posterior end of the Mullerian duct, although near by, was 

 clearly independent of it. What the relation of the two ducts is when 

 the Mtillerian reaches the undegenerated part of the Wolffian which 

 extends along the mesonephros, I have not observed. 



The processes which precede the establishment of the adult ostium 

 show a close similarity to those described for Amblystoma. During the 

 changes described above, the posterior evagination and its associated 

 (degenerating) nephrostome have migrated caudad. The anterior evagi- 

 nation where traces of it remain, is seen to have retained its position 

 near the root of the glomus. The posterior one, however, instead of 

 lying a short distance behind that point, as formerly, has migrated 

 sometimes as much as twenty sections, or about seventy-four micra, 

 caudad. The thickened band, which was mentioned as connecting the 

 two nephrostomes, being still present, has become greatly elongated. It 

 is also much more conspicuous than during the earlier stages, partly 

 because its cells have become higher, partly because the cells of the 

 adjacent peritoneal epithelium have taken on a squamous form. The 

 trough-like form of the band becomes more pronounced near the second 

 evagination. Since the band is continuous with that structure, a pro- 

 gressive fusion of its edges, beginning at the second evagination, results 

 in a displacement cephalad of the opening of the Mullerian duct, as 

 described for Amblystoma. The approximation of the edges of the trough 

 preparatory to their fusion is shown in Figure 101 (Plate 8). In the 

 ue:xt section posterior to the one figured the trough is closed to form 

 the Mtillerian duct, which extends thence caudad. In this case the 

 anterior migration of the opening has been but slight. The degenerating 

 common nephrostome is only three or four sections posterior to the one 

 figured and is dorsal to the opening of the duct. This is the only case 

 I have seen in which the evagination is ventral to the nephrostome, and 

 is important as an indication that the position of the evagination, dorsal 

 or ventral to the nephrostome, is not important. On the other side of 

 the body the evagination is dorsal, as usual. 



This is as far as my material allowed me to follow the ostial de- 

 velopment, but as the trough is continuous anteriorly with the thicken- 

 ing which curves ventrad, and as the adult ostium lies ventrally near 

 the base of the lung, there can be no doubt that the rest of the develop- 

 ment is essentially as in Amblystoma. 



