THE ELASMOBRANCH FISHES 233 



each side which arise from the ventral and outer side of the 

 metanephros and joining together form a single wide duct 

 which opens into the urogenital sinus just behind and to the 

 inside of the opening of the Wolffian duct. 



The Miillerian ducts are aborted and disappear in the 

 adult male, except for a small median pouch situated in the 

 suspensory ligament of the liver on the ventral side of the 

 oesophagus. This pouch represents the conjoined openings of 

 the oviducts of the female, and in some specimens rudiments 

 of the Miillerian ducts can be traced along the walls of the 

 oesophagus. 



In the female the mesonephros is degenerate and function- 

 less, being represented by two streaks of brown tissue occupy- 

 ing the same position as the more fully developed mesonephros 

 of the male. These streaks are traversed by the Wolffian ducts, 

 which in the anterior part of their course are straight and 

 narrow tubes, but posteriorly are dilated to form a pair of 

 sacs, the urinary sinuses. Still further back the urinary 

 sinuses unite together and open into the cloaca by a median 

 aperture placed on the end of a urinary papilla. The 

 metanephros of the female resembles that of the male, but 

 its ducts, instead of uniting to form a single duct on each side, 

 open separately by five or six small apertures situated on each 

 side of the septum dividing the anterior ends of the urinary 

 sinuses. The ovary of the female varies a good deal in size 

 according to the age and condition of the specimen. It 

 occupies the same relative position as the right testis of the 

 male, and is attached to the dorsal wall of the peritoneal cavity 

 a little to the right of the median line by a double fold of 

 peritoneal membrane, the mesovarium. The left ovary appears 

 to be aborted. The ovary is full of ova in various stages of 

 maturity. When ripe, the ova are distended with food-yolk 

 and form very prominent projections of the ovarian walls. 

 There is no direct communication between the ovary and the 

 excretory system as there is between the testes and the 

 Wolffian ducts in the male. The ova, when ripe, escape into 

 the peritoneal cavity by rupture of the ovarian walls, and are 

 passed forward by contractions of the abdominal walls to its 

 anterior end, where they pass into the capacious aperture of 

 the oviducts. The latter, which, as has already been explained, 

 are formed from the Miillerian ducts of the embryo, are two 



