THE EARTHWORM 163 



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of the pharynx a short distance behind the mouth. 2. The 

 ventral cord. When the two commissures have united they 

 form a cord which passes to the posterior end in the median 

 line of the body, closely attached to the body wall beneath 

 the intestines; this is the ventral cord, v. In each segment 

 the cord is slightly enlarged to form what is called a ganglion; 

 see Fig. 80 vc. At the posterior end of the body this cord 

 becomes smaller and finally terminates. 



The peripheral system. The nerves which form the per- 

 ipheral system are numerous. From the cerebral ganglion 

 two large nerves arise, which soon divide into many branches 

 and pass forward to the prostomium, giving it a very large 

 nerve supply and making it a very sensitive organ; Fig. 79. 

 From the commissures extending around the oesophagus arise 

 the nerves that supply the second and third segments of the 

 body. From the ventral cord in each of the segments, from 

 the fourth to the posterior end of the body, there arise three 

 pairs of nerves. Two pairs arise from the ganglionic enlarge- 

 ment and one pair from the sides of the ventral cord behind 

 the septum that separates each segment from the next. 



Reproductive System. The only method of reproduction in 

 the earthworm is by sexual process.* The two sexes are, how- 

 ever, combined in the same individual, so that the earthworm 

 is what is called an hermaphrodite; see page 251. 



Female reproductive organs. In the thirteenth segment 

 there is a pair of small glands called ovaries, situated on the 

 ventral side of the body cavity close to the middle line; Fig. 

 80 ov. In the same segment is the opening of a funnel which 

 leads into a short tube passing through the septa into the next 

 posterior segment. Here it is slightly enlarged to form an egg 

 sac, and from the sac a small duct extends through the body 

 wall to the exterior, opening upon the ventral surface of the 

 fourteenth segment. These ducts are the oviducts, od, and 

 through them the eggs produced by the ovary pass to the 



The earthworm has a slight power of regeneration of lost parts, but this power is far less 

 developed than in Hydra. If it is cut into two pieces two individuals are formed. 



