16 TADACHIKA MINOURA 



from pipped eggs, seven of which were female, and five laying 

 hens, and found that all of them had wolffian ducts. My own 

 observations agree with those of Boring and Pearl. I have 

 examined hundreds of embryos, and in all females without excep- 

 tion, the wolffian ducts were present. The wolffian bodies are 

 always found in a degenerating condition as the time of hatching 

 approaches and in some cases have almost completely disap- 

 peared at this time, but the wolffian ducts persist. 



It is therefore certain that the presence of the wolffian ducts 

 cannot be used as a criterion of the male condition. WTiether 

 the wolffian ducts eventually disappear in very late adult life 

 and whether they have some function during their existence in 

 the female are not known at the present time. 



A careful study was made to determine whether or not the 

 wolffian ducts are equally developed during embryonic life in the 

 two sexes and whether or not the right and left ducts in each sex 

 are of the same dimensions. It was found that in the male the 

 posterior portion of the wolffian ducts is generally of greater 

 diameter than in the female. This difference is noticeable in 

 the second week of incubation in most, if not all, cases. It was 

 further observed that in both male and female embryos after the 

 second week the left duct, especially near its posterior end, or 

 near its connection with the cloaca is distinctly larger than the 

 right duct. Sometimes the left duct of the male is nearly as 

 large as the ureter, while the right duct is always smaller than 

 the ureter. In the female the left duct generally runs dorsal to 

 the miillerian duct near its posterior end and is bound to the 

 latter by connective tissue. 



These points of difference between the wolffian ducts of male 

 and female, although slight, can nevertheless be utilized as 

 distinguishing sexual characteristics. 



d. Miillerian ducts. The fate of the miillerian ducts in embry- 

 onic life is quite characteristic in each sex. In the male these 

 ducts on both sides do not develop very far, but gradually retro- 

 gress and always disappear before hatching. In his book ''The 

 Development of the Chick," Lillie states that ''Retrogression 

 begins posteriorly and proceeds in the direction of the head; the 



