No. 3-] THE PRONEPHRIC DUCT IN SELACHIANS. 129 



given correspond with those of Ruckert (p. 215) in so far as 

 the union of the Anlage of the pronephros with the ectoderm 

 is concerned. Apparently Rabl describes the same thing in 

 his " sichelformige Masse " or Strang " (637), but the appear- 

 ance of the ectoderm in his drawings, though somewhat dia- 

 grammatic (XIII, 3, 4, 5, 11, 12), seems to support Ruckert's 

 interpretation of the immediate relations rather than his own. 

 The phylogenetic conclusions might be the same. In regard to 

 the genetic connection between the ectoderm and duct the 

 results harmonize with those of Ruckert and van Wyhe. It 

 seems impossible, however, to draw so sharp a line as Ruckert 

 has drawn between the end of the pronephros and the begin- 

 ning of the duct, and to say that the duct is derived only from 

 the ectoderm. On the appearance of the paper by Rabl, my 

 preparations were again examined carefully, but without find- 

 ing any grounds for abandoning the view that there is a genetic 

 connection between the duct and the ectoderm in Selachians. 



UNIVERSITY OF CHICAGO, 

 May 8, 1897. 



