NERVOUS SYSTEM 



333 



the former of a well-developed nervous system (p. 311) 

 consisting of an arrangement of peculiarly modified cells, 



was seen to be due. It is 



to which automatic action 



such an active and otherwise 

 as the earthworm a nervous sys- 



^.■prcst 



y'y- 



natural to expect in 

 highly-organised animal 

 tern of a considerably 

 higher degree of com- 

 plexity than that of a 

 medusa. 



The central ner- 

 vous system consists 

 of two parts, the braiji 

 and the ventral nerve- 

 cord. The brain (Fig. 

 79 br, and Fig. 81, 

 cer. gang) 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 

 (n. c and ne. cd) 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 (esophageal connectives (com) which 

 pass respectively right and left of the buccal sac, and thus 

 form a nerve-collar. 



Fig. Si. — Anterior portion of nervous s^'stem of 

 Liifjibricrcs. 

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

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

 prost. prostomium. (From Parker and Has- 

 well's Zoology^ after Leuckart.) 



