266 THE DOG-FISH. 



is abortive, and appears as an ill-defined tract of soft 

 yellowish-brown degenerate gland-tissue, arranged 

 in patches corresponding to the vertebrae. 



The posterior third or so of the kidney is a 

 well-developed, compact, laterally compressed, and 

 lobulated mass of a brownish colour, extending 

 back as far as the level of the cloaca. 



Dissect off the 'peritoneum from the ventral surface of one 

 of the kidneys, so as to expose it along its whole length. At 

 the hinder end dissect along its outer side from the body- 

 wall, so as to see its full size. 



4. The Wolffian ducts are a pair of straight narrow tubes 



lying on the ventral surface of the kidneys along 

 their whole length. Their posterior ends are en- 

 larged to form a pair of tubular sacs, the urinary 

 sinuses, which run back side by side, unite together 

 posteriorly, and open into the cloaca at the apex of 

 the small urinary papilla in the posterior margin of 

 the opening of the oviducts. 



Find the opening at the apex of the urinary papilla : pass 

 a seeker through the opening and forwards along the urinary 

 sinus of one side : slit up the ventral wall of the sinus along 

 its whole length. 



5. The ureters are slender tubes, usually four to six in 



number on each side, which run from the meta- 

 nephros to open into the dorsal surface of the 

 urinary sinus by four to six slit-like apertures lying 

 along the septum between the two sinuses. The 

 anterior ureter is much longer than the others. 



Find the ureters, lying on the ventral surface of the meta- 

 nephros, and trace them back to the urinary sinus. Slit up 

 the sinus, unless this has already been done, and examine its 

 dorsal wall to see the openings of the ureters. 



6. The cloaca is a shallow depression between the pelvic 



fins. In the female there are three openings into 



