100 ANNELIDA. 



ward, so underlying organs will not be disturbed. In this way 

 free the alimentary canal to the position of the pharynx. 



You can now see the extent of the nephridia, and possibly 

 see where they perforate the septa. 



Reproductive System. 1. The seminal vesicles are large 

 white bodies, united in the median line. They send three lobes 

 on either side, that normally overlap the posterior part of the 

 esophagus. In what somites do the lobes occur? 



2. Carefully open the seminal vesicles near the median dor- 

 sal line and examine their contents microscopically. 



3. With a pipet wash out the contents and notice the two 

 pairs of convoluted funnels, the inner openings of the vasa defe- 

 rentia. The testes are hard to find, as they are the same color 

 as the coagulated mass that filled the seminal vesicles. Thev 

 are attached to the septa just anterior to the funnels. The 

 narrow tubes of the vasa deferentia may sometimes be seen leav- 

 ing the seminal vesicles. They open externally on somite fifteen. 



4. The ovaries are a pair of very small organs attached to the 

 posterior surface of the septum that separates the twelfth from 

 the thirteenth somite, near the mid-ventral line. They may 

 sometimes be found with a lens, but are not usually visible other- 

 wise. If possible, remove an ovary and examine it with a micro- 

 scope to see its shape, and to find which portion has the most 

 mature eggs. The oviducts open into the cavity of the thirteenth 

 somite and externally through the ventral wall of the fourteenth 

 somite, in line with the nephridia. They can seldom be seen in 

 dissections. 



5. Between the ninth and tenth and the tenth and eleventh 

 somites, on the ventral side, are two pairs of white, rounded 

 pouches, the seminal receptacles, that open externally but not 

 internally. Understand their function. Make a drawing of 

 the reproductive system. 



Nervous System. 1. On the dorsal surface of the pharynx, 

 near its anterior end, are the two cerebral ganglia. They lie on 

 either side of the median line and are connected by a stout com- 

 missure. In what somite do they lie ? 



