KENAL AND EEPEODUCTIVE SYSTEMS 243 



8. The kidneys. Each kidney is, as in the female, divided 

 into an anterior part or mesonephros, forming about 

 half of its entire length ; and a posterior part or 

 metanephros. The mesonephros differs from that 

 of the female in being a well-developed lobulated 

 glandular body along its whole length. The meta- 

 nephros, as in the female, is a laterally compressed 

 mass of considerable size, especially thick at its 

 hinder end. 



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 the metaneph/ros from the body-wall 

 along its outer side, so as to see its full size. 



4. The mesonephric or Wolffian duct is a thick- walled tube 



running in a very sinuous course along the ventral 

 surface of the whole length of the mesonephros, from 

 which it receives numerous segmentally arranged 

 tubules. Opposite the junction of mesonephros and 

 metanephros it dilates rather suddenly into a wide 

 thin-walled tube, the vesicula seminalis, which runs 

 straight back along the ventral surface of the meta- 

 nephros to open into the urino-genital sinus, just 

 in front of the cloaca. The walls of the vesicula 

 seminalis are marked by close-set transverse lines, 

 corresponding to internal foldings of its lining 

 membrane. 



The mesonephric duct acts as vas deferens j. 

 conveying to the exterior the spermatozoa from the 

 testis, as well as acting as the excretory duct for the 

 mesonephros. 



Dissect off the mesonephric duct on one side from the ven- 

 tral surface of the mesonephros, noting the tubules it receives 

 from this ; and follow it back to the cloaca. 



5. The sperm sac is a thin- walled tube lying along the 



ventral surface and the outer side of the vesicula 

 seminaHs, to which it is closely attached, and which 



B 2 



