EXCEETOKY AND REPEODUCTIVE SYSTEMS 237 



delicate folds of peritoneum which are very readily 

 torn, so that in many specimens the testes appear to 

 lie free in the body-cavity. 



2. The vasa efferentia are a number of very slender ducts 



which arise on each side from the dorsal surface of 

 the testis, and run forwards in the fold of peritoneum 

 to the mesonephros, which they enter close to its 

 anterior end. 



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



into an anterior part or mesonephros, forming about 

 two-thirds of its entire length ; and a posterior part 

 or metanephros, forming the remaining third. The 

 mesonephros differs from that of the female in being 

 a well-developed lobulated glandular^^ddy along its 

 whole length. The metanephros, 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 hindef^end dissect away the metanephros from the body- 

 wall, 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 tubules. Opposite the 

 junction of mesonephros and metanephros it dilates 

 rather suddenly into a wide thin-walled tube, which 

 runs straight back along the ventral surface of the 

 metanephros to open into the urino-genital sinus, 

 just in front of the cloaca. 



The mesonephric duct acts as vas deferens, 

 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. 



