340 PHYSIOLOGY OF THE INVERTEBRATA. 



off nerves to the anterior portion of the pallium ; to the 

 anterior adductor muscle ; to the labial palps, &c. ; and to the 

 branchiee. (&) The pedal ganglia are situated in the foot, or 

 in the corresponding part of the body when the foot is absent, 

 as is the case in some of the Lamellihranchiata. These ganglia 

 are fused together on the naedian line of the body, and are 

 connected by commissures with the cerebral ganglia. The 

 pedal ganglia send off nerves to the foot.(c) The parieto- 

 splanchnic or visceral ganglia lie on the ventral side of the 

 posterior adductor muscle. They are united with the cerebral 

 ganglia by commissures (Fig. 68 A), which traverse the organ 

 of Bojanus (kidney). These ganglia send off nerves to the 

 branchiae ; to the posterior and middle parts of the pallium ; 

 to the posterior adductor muscle ; to the heart ; to the siphons 

 — as in Mya ; and to the viscera generally. 



In the Gasteropoda, represented by Helix, the nervous 

 system consists of the following parts : (a) The cerebral or 

 supra-cesophageal ganglia, lie on the dorsal side of the oeso- 

 phagus, and are joined close together by a transverse nervoua 

 band (Fig. 68 B). Each ganglion sends off a commissure to 

 the pedal ganglia, which are situated close together on the 

 ventral side of the oesophagus. Commissures also join the 

 cerebral ganglia with the so-called parieto-splanchnic ganglia 

 (a group of paired ganglia), which come into close relationship 

 with the pedal ganglia ; in fact, they are fused together with 

 the latter ganglia. The cerebral ganglia supply nerves to 

 the eyes, tentacula, &c., and also give off a pair of nerves — 

 one on either side of the oesophagus — ^to the buccal ganglia. (V) 

 The pedal ganglia are closely united, (c) As already stated, 

 the parieto-splanchnic ganglia are fused with the pedal gangha. 

 They send off nerves to the nephridia, heart " lung," sexual 

 and olfactory organs, and pallium, (d) The small paired 

 buccal ganglia are situated above and below the buccal mass. 

 These regulate the movements, &c., of the mouth ; and they 

 have been regarded by some investigators as sympathetic in 

 function. 



