DEVELOPMENT OF THE CHICK 137 



known as the germinal epithelium. The re- 

 productive tubes are the Wolffian and MUllerian 

 ducts. The former originates in connection 

 with the urinary organs (pronephros) as already 

 stated. The first trace of the Miillerian duct 

 is present on the fourth day in the form of a 

 thickened ridge of peritoneum on the lateral 

 aspect of the Wolffian body. The ridge becomes 

 grooved and the groove closes into a tube. 

 The tube grows slowly backwards and reaches 

 the neighbourhood of the cloaca on the seventh 

 day. In the male the development of this 

 duct ceases on the eighth day, and it never 

 opens into the cavity of the cloaca. In the 

 female the right duct ceases to grow after the 

 eighth day, and thereafter soon degenerates. 

 The left female duct ultimately opens into 

 the cloaca. 



In the male the gonads become testes ; the 

 Wolffian ducts develop into the deferent ducts ; 

 and the tubules of the anterior part of the 

 Wolffian bodies form the epididymides. The 

 Miillerian ducts become rudimentary and dis- 

 appear. 



In the female the left gonad becomes the left 

 ovary ; the right atrophies. The Wolffian ducts 

 disappear ; the left Miillerian duct develops into 



