360 OUTLINES OF CHORDATE DEVELOPMENT 



reproductive system in the Amniota. In these forms the 

 gonoducts are derived from the original mesonephric or Wolffian 

 duct, which is now represented by two longitudinal ducts, the 

 Wolffian duct, stricto sensu, and the Miillerian duct. As a 

 matter of fact, we shall see that the Miillerian duct develops 

 independently of the mesonephric duct, but phyletically it is 

 clear that both ducts are to be regarded as derivatives of a 

 common mesonephric duct. The mesonephros itself largely 

 degenerates, of course, but some part of it remains functionally 

 connected with the reproductive system in the male, and as a 

 purely vestigial structure in the female. Consequently in the 

 male Amniote the Wolffian duct proper is freed from excretory 

 function, and serves only as the gonoduct or vas deferens, 

 effecting a connection with the gonad through the remains of 

 certain mesonephric tubules; the Miillerian duct is either 

 vestigial or entirely wanting. In the female, on the contrary, 

 the Miillerian duct is the functional gonoduct, or oviduct, while 

 the Wolffian duct and mesonephros either disappear entirely 

 or remain as functionless vestiges. 



A. THE EEPRODUCTIVE DUCTS 



Nothing need be added to the account already given of the 

 development of the Wolffian duct. We shall see below how, in 

 the male, this connects with the testis; in the female the Wolffian 

 duct disappears along with the mesonephros. 



The Miillerian ducts develop similarly in the male and female; 

 they appear during the fourth day. Each is formed as a 

 thickened longitudinal band in the peritoneum, along the outer 

 surface of the mesonephros, near its attachment to the body 

 wall, i.e., just along the outer side of the Wolffian duct. This 

 band invaginates, forming first a groove and then a tube, lying 

 just beneath the surface of the anterior end of the mesonephros. 

 The extreme anterior end of this canal remains open into the 

 body cavity, as the rudiment of the ostium or infundibulum. 

 The greater part of the Miillerian duct is formed by the backward 

 extension of the tube thus formed. It grows posteriorly as a 



