37 



are set near ike leiitaele bases and are swollen 1(» ioriu 

 the well-marked eerebral ganglia. These are connected 

 by the cerebral coniniissure (forming the npper side of 

 the quadrilateral) which runs across very far forward 

 just beneath the dorsal outer lip. 



The right and left sides of the ([uadrilateral (continuous 

 above with the respective cerebral ganglia) have become 

 double by separation of the connectives going to the 

 })leural from those going to the pedal ganglia. 



The lower side of the quadrilateral is a very short pedal 

 commissure thickening at either end into the commence- 

 ment of the great pedal Jierve cord, Avhich is ganglionic 

 for a considerable ])ortion of its length. The outer side of 

 this anterior end of the pedal neive cord is continuous with 

 a short stout j)leuro-pedal connective, and this latter 

 thickens at the side and a little to the front into a pleural 

 ffanp-lion. From the o-ano'lionic centres a ]juml)er ol 

 nerves are given oif, as follows (see fig. 'So) : — 



{a) From each cerebral ganglion : 



(1) The cerebral commissure, the cerebro-labial con- 

 nective, and the cerebro-pedal and cerebro-pleural 

 connectives. 



{2) The branching tentacular nerve. 



(8) The hue optic nerve supplying the eye which is 

 placed on the posterior side of the base of the tentacle. 



(4) Fine nerves (•{ in number) going to the snout. 



(5) A nerve which, for some distance, runs along Avith 

 the cerebro-pedal connective, but which diverges from this 

 at about the level of the [)leural ganglia, going thence to 

 the dorsal body wall. 



(0) A nerve which is at hrst fused with the cerebro- 

 pleural connective but soon becomes distinct from it and 

 supplies the otocyst Avhich lies at the base of the pleural 

 ganglion against the pleuro-pedal connective. 



