COMPARATIVE ANATOMY 



Fig. 1 8 



A. Nervous system of Helix aspersa, an example of the euthyneurous condition in 

 which the pleural, visceral, abdominal and pedal ganglia are fused to form a 

 suboesophageal ganglion mass. B. Nervous system of Limntea, an example of 

 the short-looped euthyneurous condition in which the ganglia are separate 

 (after de Lacaze Duthiers). C. Nervous system of Paludina vivipara, an 

 example of the streptoneurous condition, abd, abdominal ganglion ; bucc, 

 buccal ganglia ; cer, cerebral ganglia ; cpc, cerebro-pedal connective ; cvc, 

 cerebro-pleural connective ; gd, conjoined genital duct ; nf, facial nerve ; 

 ngt genital nerve ; nle, exterior labial nerve ; /z, internal labial nerve ; 

 nop, optic nerve ; np, pedal nerves ; npl, left pallial nerve ; npm^ median 

 pallial nerve ; /, penial nerve ; npr, right pallial nerve ; o, osphradium ; 

 oe, oesophagus ; otc, otocyst ; ped^ pedal ganglion ; ph, pharynx ; //, pleural 

 ganglion ; rs, radula-sac ; sbg^ suboesophageal ganglion mass ; sb, sub-intestinal 

 ganglion; sp t supra-intestinal ganglion; vis, visceral ganglion; vn, visceral 

 nerve. 



