69 



statocysts whereas the visceral ganglion lies above the statocysts and behind the 

 rest of the ring , blocking the oesophageal canal so that the oesophagus makes a 

 Sharp turn upward to pass above this ganglion. The upper and posterior surfaces 

 of the visceral ganglion are covered by a fascia which extends from the edges 

 of the large foramen of the skull to the oesophagus and so separates the brain 

 and the oesophageal canal from the liver. 



The cerebral ganglion gives off two pairs of connectives, the cerebropedal 

 and the cerebro-buccal. The former pass downward and forward around the 

 oesophagus to the propedal ganglion , the latter pass forward above the oesophagus 

 to the suprabuccal ganglion. This gang- 

 lion also receives a connective from the 

 propedal ganglion (propedo-buccal connec- 

 tive) and gives off a connective which 

 passes around the oesophagus to the in- 

 frabuccal ganglion. A long pair of connec- 

 tives passes from the infrabuccal ganglion 

 to the splanchnic ganglion. 



A short large bundle of fibres passes 

 from the pedal to the propedal ganglion, 

 which also receives the above mentioned 

 connectives (cerebro-propedal and propedo- 

 buccal connectives) and gives off five 

 pairs of connectives to the five pairs of 

 brachial ganglia. Connectives unite the 

 first and second , the second and third , 

 the third and fifth brachial ganglia , and 

 with the commissures between the gang- 

 lia of the first pair and the fifth pair 

 form the branchial nerve-ring. Careful search has failed to reveal any connection 

 between the ganglia of the fourth arms (tentacles) and this ring. 



The pleural ganglion ; viewed externally, is well marked and is readily 

 distinguished from the cerebral ganglion on one hand and from the pedal and 

 visceral ganglia on the other , but a study of the minute anatomy of the so 

 ■called ganglion shows that there is very little ground for calling the mass of 

 fibres in which a few nerve cells are scattered a ganglion. It is really a mass 

 of nerve tracts passing, a) between the optic lobes through the base of the 

 cerebral ganglion , b) from the optic ganglion to the cerebral and pedal ganglia , 

 and c) from the cerebral to the pedal and visceral ganglia. Nevertheless , it is 



Bc.G 



Fig. 15. 



