VII.] THE MULLERIAN DUCT. 215 



Wolffian body there is formed in both sexes a duct, 

 which in the female becomes the oviduct, but which in 

 the male is functionless and usually disappears. This 

 duct, in spite of certain peculiarities in its development, 

 is without doubt homologous with the Miillerian duct 

 of the Ichthyopsida. 



The first rudiment of the Miillerian duct appears at 

 the end of the fourth day, as three successive open involu- 

 tions of the peritoneal epithelium, connected together 

 by more or less well-defined ridge-like thickenings of 

 the epithelium. It takes its origin from the layer of 

 thickened peritoneal epithelium situated near the dorsal 

 angle of the body-cavity, close to the Wolffian duct, and 

 some considerable distance behind the front end of the 

 Wolffian duct. 



In a slightly later stage the ridges connecting the 

 grooves become partially constricted off from the peri- 

 toneal epithelium, and develop a lumen. The condition 

 of the structure at this stage is illustrated by Fig. 70, 

 representing three transverse sections through two 

 grooves, and through the ridge connecting them. 



The Miillerian duct may in fact now be described as 

 a short but slightly convoluted duct, opening into the 

 body-cavity by three groove-like apertures, and con- 

 tinued for a short distance behind the last of these. 



In an embryo not very much older than the one last 

 described the two posterior apertures vanish and the 

 anterior opening alone remains as the permanent open- 

 ing of the Miillerian duct. 



The position of these openings in relation to the 

 Wolffian body is shewn in Fig. 71, which probably passes 

 through a region between two of the peritoneal openings. 



