350 COMPARATIVE ZOOLOGY OF CHORD ATES 



whereas the sperms pass down a duct which serves for them as 

 well as for the evacuation of urine from the kidney. Thus, 

 while the Cyclostome has a single kidney-duct on each side in 

 both sexes, and the germ-cells do not pass through it, in the 

 fish and amphibia typically the females have two ducts on each 

 side. One of these is the Wolffian duct evacuating the urine, 

 the other is the Mullerian duct leading out the eggs. In the 

 males of fish and amphibia the Wolffian duct evacuates both 

 urine and sperms ; the Mullerian duct is reduced, and in the 

 Selachian is represented only by the funnel and the sperm- 

 sacs. This condition is typically represented in the frog and 

 newt. 



In several different groups of fish and amphibia, this 

 arrangement is slightly altered by the separation of a part of 

 the Wolffian duct conveying the sperms (vas deferens) from 

 another part which drains the kidney (mesonephric ureter, 

 not a true ureter). By this means, the sperms avoid going 

 through the excretory part of the kidney, and this condition 

 is found in the Dipnoan Protopterus, Polypterus, the Teleosts, 

 and in such toads as Alytes, in all of which it has been inde- 

 pendently developed. In Scyllium, it will be remembered 

 that only the hinder part of the mesonephros is excretory in 

 function, and the sperms pass through the anterior part. 



In Lepidosteus and many Teleosts, the ccelomic wall 

 surrounds the ovary forming a sac which joins on to the oviduct. 

 In this manner the ovary is completely shut off from the 

 ccelomic cavity, and consequently the eggs are not shed into 

 it, but led directly to the exterior. 



In the amniotes, the functional kidney in the adult is the 

 metanephros, and the metanephric duct or ureter is an out- 

 growth from the Wolffian duct. The Wolffian duct is therefore 

 spared the function of evacuting urine, and it persists only 

 in the male, where it functions solely as a vas deferens for 

 the sperm. The mesonephric tubules form the epididymis. 

 The Mullerian duct disappears in the male, and the Wolffian 

 duct disappears in the female. The Mullerian duct persists 

 in the female as the oviduct. In the adult bird, only the left 

 ovary and oviduct persist. 



