hall: MESONEPHKOS and arULLERIAN DUCT IX AMPHIBIA. 101 



of cells to form a mass [evidently corresponding to the " first evagina- 

 tion " after its caudal migration has begun] in the middle of Avhicli a 

 rod appears. This rod is continued back for some distance, but is occa- 

 sionally interrupted by merging with the cell mass, — or it may be 

 represented by only a few heightened cells of the peritoneal epithelium. 

 The cord is entirely distinct here, as always from the Wolffian duct. 



In still older specimens the rod becomes more marked, but shows the 

 same irregularity as before ; that is, the cord merges at times with the 

 cells of the oviducal welt, or, if development has gone so far that a 

 distinct tube is present, there are places where it is just appearing. In 

 all cases the posterior end is continued as a simple epithelial thickening. 

 During this caudad growth the anterior end of the thickening loses its 

 connection with the degenerating nephrostomes. The thickening now 

 extends from the region of the pronephros caudad and mediad almost 

 to the mid-dorsal line. At this point, in a larva forty-five millimetres in 

 length, the thickening begins to be raised into a ridge, and still farther 

 back, grooved. Forty-eight sections behind the beginning of the funda- 

 ment, the edges of the groove close over [probably the ''second evagina- 

 tion " is here described] to form a rod, or, on one side of the body, a 

 distinct tube for one or two sections, followed by the interrupted rod 

 above described. 



It is worth}^ of note that in the forty-five millimetre larva, the thick- 

 ening begins to be raised to form a ridge at the point where it approaches 

 the mid-dorsal line, the grooving beginning farther back, while in a spe- 

 cimen of fifty-one millimetres in length (which shows an advance in the 

 differentiation of the MtlUerian duct and hence really is older and not 

 simply longer) the grooving begins at this point. Although the author 

 does not call attention to the fact, there has evidently been ^progression 

 cephalad in the raising and infolding of the epithelium to form the duct. 



The fact just alluded to makes me suspect that Wilson saw the ostium 

 only after it had begun its forward migration^ that is, some time after its 

 first appearance. The free portion of the duct, unconnected with the 

 ostium and present before that structure had appeared, and the isolated 

 bits of duct might be explained as in my criticism of Furbringer's de- 

 scription. It is needless to say that I consider Wilson in error in 

 describing the posterior end of the developing duct as continuous with 

 the peritoneal epithelium of the oviducal welt. 



In Triton punctatus Gemmill ('97) describes the fundament of the 

 Mtillerian duct as first appearing while the pronephros is still com- 



