402 THE DEVELOPMENT OF THE CHICK 



has not been supported by subsequent investigators. A short 

 distance in front of the growing point the Miillerian duct receives 

 a lumen, and mesenchyme presses in from above and below, 

 and forms a tunic of concentrically arranged cells around it 

 (Fig. 221). 



The Miillerian duct thus begins to project above the surface 

 of the Wolffian body, and, as it does so, the thickened epithelium 

 of the tubal ridge becomes flat and similar to the adjacent peri- 

 toneum; whether it is used up in the formation of the mesen- 

 chymatous tunic of the epithelial Miillerian duct is not known. 

 Up to this time the development is similar in both sexes and on 

 both sides of the body. 



In the male development of these ducts ceases on the eighth 

 day; retrogression begins immediately and is completed, or at 

 any rate far advanced, on the eleventh day. In this process the 

 epithelial wall disappears first, and its place is taken by cells 

 of mesenchymatous appearance, though it is not known that 

 transformation of one kind into the other takes place. Retro- 

 gression begins posteriorly and proceeds in the direction of the 

 head; the ostium is the last to disappear. The mesenchymatous 

 tunic shares in the process, so that the ridge is no longer found 

 (see Fig. 222). In the male the Miillerian ducts never open into 

 the cloaca. 



In the female the development of the right Miillerian duct 

 ceases after the eighth day, and it soon begins to degenerate. Its 

 lumen disappears and it becomes relatively shorter, so that its 

 anterior end appears to slip back along the Wolffian body. On 

 the fifteenth day slight traces remain along its former course and 

 a small cavity in the region of the cloaca. It never obtains an 

 opening into the cloaca (Gasser). 



With the degeneration of the anterior end of the Wolffian 

 body the ostium tubae abdominale comes to be attached by a 

 hgament to the body-wall (Fig. 231); farther back the ligamen- 

 tous attachment is to the Wolffian body. 



The fimbriae begin to develop on the eighth day on both 

 sides in both sexes. It is only in the left oviduct of the fe- 

 male, however, that development proceeds farther, and differ- 

 entiation into ostium, glandular part, and shell gland takes 

 place. This appears distinctly about the twelfth day. The 

 lower end expands to form the primordium of the shell- 



