78 ANNELIDA. 



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. 



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 ? 



2. The remainder of the ganglia lie ventral to the alimentary 

 canal. The first ventral ganglia are connected with the cerebral 

 ganglia by connectives that pass around the sides of the pharynx. 

 Adjacent ganglia of the ventral chain are united by connec- 

 tives. The ganglia of each somite, and the cords that connect 

 those of adjacent somites, are fused so that the original paired 

 condition is not very apparent. How far does the ventral chain 

 of ganglia extend ? Where do nerves leave it ? 



Draw the nervous system into the figure that shows the repro- 

 ductive system. 



Notice the sacs that inclose the setse and indicate them in 

 the above figure. 



Examine prepared serial microscopic sections. 1 



1 Small worms should be kept in a dish and fed on clean moistened 

 filter-paper, which they will eat readily, until the alimentary canal is free 



