THE OEGANS OF THE MIDDLE GBEM-LAYEE. 



373 



«f figure 212 exhibit this condition. Figure B shows the place 

 •where tho ventral wall of the mesonephric duet is thickened into 

 a ridge (md) by an increase of the epithelial cells ; upon a cross 

 section (A) made farther forward the thickened part has become 

 ■detached as a cord 

 {md), which subse- 

 quently becomes still 

 more isolated and ac- 

 quires a cavity of its 

 •own. The condition 

 recalls very clearly 

 the appearances 

 which the cross sec- 

 tions through embryo 

 Selachians (fig. 209) 



igave. 



According to the 

 ■observations of Sedg- 

 wick, therefore, the 

 anterior end of the 

 Miillerian duct would 



he derived from the pronephros, but the posterior end by a splitting 

 off of cells from the mesonephric duct. Thus an agreement with 

 the conditions in the non-amniotic Vertebrates would be established. 



Fig. 212, — T-vo sections to show the union of the solid terminal 

 part of the Uiillerian duct with the mesonephric duct in 

 the Chick, after Balfour akd Sedgwick. 



In A the terminal part of the duct is still quite distinctly 

 separate ; in .S it has united with the wall of the mesone- 

 phric duct. 



mtZ, Miillerian duct ; Wd, Wolffian duct. 



Fig. 213,— Cross sections through the WoU&an and Uiillerian ducts of two human emhryos, after 



Naoel. 

 A A female embryo 21 mm. long. 

 £, A male embryo 22 mm. long. 

 W.g-t Wolffian duct ; M.g.^ end of the Miillerian duct in process of development. 



It still deserves to be especially mentioned that in human embryos 

 also the Miillerian ducts (fig. 213 A and B M.g.) during their 

 development have their posterior ends fused for a short distance with 

 the mesonephric duct {W.g.). Nagel, to whom we are indebted for 

 this fine observation, expresses himself, it is true, against a splitting 



