LUMBRICUS 113 



not visible otherwise. If possible, remove an ovary and ex- 

 amine it with a microscope 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 commissure. In what somite do they lie? 



2. The remainder of the ganglia lie ventral to the ali- 

 mentary 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 connectives. 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 

 reproductive system. 



Notice the sacs that inclose the setae 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 from grit, before they are preserved for sectioning. It is well to 

 narcotize them by placing them in a small quantity of water and add- 

 ing a little alcohol from time to time (never enough to make the worms 

 squirm violently) until they cease to move. They may then be killed 

 with sublimate acetic or other killing agent and treated in the usual 

 manner. 



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