CHAP. IV.] THE NERVOUS SYSTEM OF MOLLUSKS. 83 



of jerks, occasioned by the reaction of the respiratory 

 currents upon the surrounding water " these currents 



^Tn. 29. Nervous System of the Common Cuttle-Fish (Sepia officinalis). (Owen.) 

 1, Double supra-oesophageal ganglion developed from upper commissure ; p p, cut 

 surfaces of the cartilaginous cranium ; 2 2, optic ganglia ; 4 4, posterior sub-ceso- 

 phageal ganglia (anterior sub-oesophageal ganglia in connection -with nerves of feet 

 and tentacles, 6 6, not seen in this view) ; 7 and 8, ganglia in connection with the 

 pharynx and mouth, connected by nerves (5 5) with the cerebral lobes ; 13 13, great 

 motor nerves, of the mantle and other parts, with(d) their ganglia ; 14, c c, respiratory 

 nerves ; k k, smaU tubercles in connection with optic ganglia. 



being produced by the expulsive contractions of a powerful 

 muscular funnel continuous with a portion of the mantle. 

 In the Cuttle-fish one of the most striking character- 



G 2 



