Chap. VII.] THE GENESIS OF TISSUES AND ORGANS. 137 



and this cord becomes hollowed out so as to form a tube 

 which acquires an opening at its anterior end into the peritoneal 

 cavity, and in the female opens posteriorly into the cloaca, but 

 in the male ends blindly. This is known as the Mullerian duct. 

 From it the oviduct of the female is developed. In the male it 

 atrophies. The remainder of the segmental duct, from which 

 this new duct was separated off, is known as the Wolffian duct, 

 since it carries off the products of the kidney or Wolffian body. 



A further change has to be noted. In the anterior part of 

 the Wolffian body outgrowths from the primary segmental tubes 

 proceed to, and eventually open into, the testis of the male, the 

 products of which are thus carried by these vasa efferentia into 

 the Wolffian duct, which, therefore, is functional as the vas 

 deferens. As it conveys the urinary product it is also termed 

 the ureter ; but it is not strictly homologous with the ureter of 

 the rabbit. It is best termed the urino-genital duct. 



In the rabbit and the fowl there are notable differences in the 

 mode of development of the segmental, Wolffian, and Mullerian 

 ducts. There seems, at least in the fowl, to be a rudimentary 

 pronephros ; and in both a mesonephros is formed. The latter 

 organ, however, though it functions as a kidney during em- 

 bryonic life, does not persist as* the permanent kidney in either 

 of these types. 



From the dorsal aspect of the hinder part of the Wolffian 

 duct there is said to proceed an outgrowth which extends 

 forwards and sends out collecting tubes into a specially differ- 

 entiated portion of that mass of mesoblastic tissue from which 

 the mesonephros was previously formed. The outgrowth is 

 the ureter ; the glandular mass with which it enters into relation 

 is the metanephros, or permanent kidney of the bird and the 

 mammal. The ureter does not long remain attached to the 

 Wolffian duct, but, in the fowl, acquires a separate opening 

 into the cloaca, and, in the rabbit, , opens into that portion of 

 the allantoic duct which is persistent as the urinary bladder. 



In the fowl and the rabbit, as in the frog, a connection is 

 established in the male between the testis and the Wolffian 

 duct through the Wolffian body. The vasa efferentia thus repre- 



