THE ORGANS OF THE MIDDLE GERM-LAYER. 



371 



of its own cells, and gives rise to a solid cord, which lies directly 

 between the mesonephric duct and the peritoneal epithelium, which 

 is here somewhat thickened. The funnel produced by the invagina- 

 tion now becomes the ostium abdominale tubse, but the solid cord of 

 cells, which is soon hollowed out and finally opens behind into the 

 the 



Miillerian duct. 



If the representa- 

 tion just given is cor- 

 rect in all particulars, 

 the Miillerian ducts 

 in the Anamnia and 

 the Amniota, al- 

 though possessing 

 the same location, 

 form, and function, 

 would still be non- 

 homologous organs, 

 because their develop- 

 ment is different. 

 For the one is split 

 off from the meso- 

 nephric duct, the 

 other is formed in- 

 dependently by a 

 new invagination of 

 the epithelium. 



Such a surprising 

 result appears to 

 us, however, upon 

 grounds of compara- 

 tive anatomy, to be 



Fig. 210, Cross section through the mesonephros, the funda- 

 ment of the Miillerian duct, and the sexual gland of a 

 Chick of the fourth day. after WALDEYER. Magnified 160 

 diameters. 



m, Mesentery ; L, somatopleure ; a', the region of the germinal 

 epithelium from which the Miillerian duct (z) has been 

 invaginated ; a, thickened part of the germinal epithelium, 

 in which the primary sexual cells, C and o, lie ; E, modi- 

 fied mesenchyme out of which the stroma of the sexual 

 gland is formed ; WK, mesonephros ; y, mesonepbric duct 



very improbable, and 



therefore the attempt made by some investigators to refer back 

 the conditions found in the Amniota to such as exist in the 

 Anamnia deserves every attention. This would be possible if 

 the statements of BALFOUR AND SEDGWICK, which have however 

 been called in question by others (JANOSIK), should be confirmed. 

 As we have previously seen, there are two different regions to 

 be distinguished on the Miillerian duct an anterior, which is 

 the degenerated pronephros and bears the orifice of the tuba, 



