IV. REPRODUCTIVE SYSTEM. 



1. Seminal vesicles; composed of 3 pairs of white sacs arising 

 from a median portion below the oesophagus. This median portion 

 is subdivided into an anterior and a posterior part. 



2. Seminal receptacles ; 2 light colored sacs on the ventral surface 

 of the body-wall, on each side of the median line and attached to 

 septa betw r een the 9th and loth and loth and nth somites. 



3. Ovaries ; very small light colored bodies with pointed tips and 

 rounded bases on the anterior wall of the I3th somite, not very 

 far from the middle of the ventral surface, one on each side, right 

 and left. 



4. Oviducts ; these are also not easily seen, but form what appear 

 as thickenings of the wall between I3th and I4th somites. 



5. Cut off the lateral lobe of a seminal vesicle, cut open its 

 median part and carefully wash out its soft contents to show the 

 following structures ; great care in dissection and observation is 

 necessary, (a) Yasa Efferentia ; large folded or convoluted masses 

 which form the funnel-like openings, one on each side of the 

 median line in the loth and nth somites. From these, delicate thread- 

 like ducts pass back on each side to unite in somite 12 to form the 

 Vas Deferens, which passes along the body wall one on each side 

 of the median line, as far back as somite 15 where it opens to the 

 exterior. ( b ) Testes ; four small white bodies, a pair in each somite, 

 inside the seminal vesicles in part concealed by the funnels of the 

 vasa efferentia, and attached to the posterior surfaces of the septa 

 between somites 9 and 10, and 10 and n, two on the rght and two 

 on the left of the median line. 



V. XKRVOUS SYSTEM. 



1. The nerve cord; extending the whole length of body on the 

 median ventral line, lying in the body cavity but near the body wall. 

 In each somite it expands to form a ganglion and gives off three 

 pairs of nerves, (a ) Two large pairs arise from the ganglion, (b) 

 One smaller pair arises from the slender part of the cord (connec- 

 tive) near the anterior end of the somite. 



2. Circum-oesophageal nerve ring. Raise the oesophagus and 

 trace the nerve cord anteriorly to its division into right and left 

 halves which pass around the digestive tract to form a ring which 

 unites with the brain on the dorsal side of the oesophagus. 



3. Brain ; connected as above shown with the ventral nerve cord, 



42 



