342 



THE EARTHWORM 



motive medusa and the fixed polype was the presence in 

 the former of a well-developed nervous system (p. 319) 

 consisting of an arrangement of peculiarly modified cells, 

 to which automatic action was seen to be due. It is 

 natural to expect in such an active and otherwise 

 highly-organised animal as the earthworm a nervous sys- 

 tem of a considerably 

 higher degree of com- 

 plexity than that of a 

 medusa. 



The central ner- 

 vous system (Figs. 

 82, 83, and 85) con- 

 sists of two parts, 

 the brain and the 

 ventral nerve - cord. 

 The brain consists of 

 a pair of white pear- 

 shaped swellings or 

 ganglia situated on 

 the dorsal side of 

 the buccal sac where 

 it is continued into 

 the pharynx. The 

 ventral nerve - cord 

 is a longitudinal band 

 extending along the whole middle ventral line of the 

 body, internally to the longitudinal muscular layer, from 

 the third to the anal segment, and slightly swollen in each 

 segment. The brain is connected with the anterior end of 

 the ventral nerve-cord by a pair of nervous bands, the 

 cesophageal connectives, which pass respectively right and left 

 of the buccal sac, and thus form a nerve-collar. 



FIG. 85. Anterior portion of nervous system of 

 Lumbricifs. 



cer.gang. cerebral ganglia or brain ; com. oeso- 

 phageal connectives ; ne. co. ventral nerve-cord ; 

 prost. prostomium. (From Parker and Has- 

 well's Zoology, after Leuckart.) 



