XII 



PHYLUM MOLLUSCA 



769 



au 



pedal and pleuro- visceral ganglia, which lie behind. The pedal 

 <lnglia (Fig. 667) are, like the cerebral, united into a single 

 mass ; orally this is prolonged and expanded into a broad mass 

 from which the ten brachial nerves (br. n.) are given oft 1 to the 

 arms. The pleuro-visceral ganglia, also united into one, are in 

 immediate contact with the pedal behind 

 the oesophagus. 



Besides the optic nerves the cerebral 

 ganglia also give off a pair of slender 

 nerves which join a smaller pair of closely 

 united luccal ganglia (Fig. 666, buc.}, 

 situated close to the buccal mass on the 

 anterior aspect of the oesophagus. The 

 buccal ganglia again (which are some- 

 times looked upon as separated portions 

 of the cerebral) are connected by slender 

 connectives with a pair of stomatogastric 

 ganglia (Fig. 660, g. stow.), also closely 

 united, situated on the posterior aspect 

 of the oesophagus. Besides the ten 

 brachial nerves, each of which, expanding 

 at the base of the arm into a brachial 

 ganglion, runs along the axis of the arm 

 to its extremity, the pedal ganglia also 

 give off nerves to the funnel, and also a 

 pair to the statocysts ; but the latter are 

 found, when their fibres are traced to 

 their origin, to be derived from the cere- 

 bral ganglia. The pleuro-visceral ganglia 

 give off two visceral nerves (Fig. 667, 

 vise, n.) supplying the various internal 

 organs, one pair of branches, the branchials, 

 having each a branchial ganglion at the 

 base of the ctenidium, and running along 

 its axis to its extremity. Two other 

 ganglia of considerable size the visceral 

 and the gastric occur in the course of 

 this system. The pleuro-visceral ganglia 

 also give off two very stout pallial nerves 

 (pall, n.) which run through the neck to 

 the inner surface of the mantle-cavity, 

 where each expands into a large, flat, pallial or stellate ganglion 

 (Fig. 658, /. st. g.), which is visible in front of the ctenidium when 

 the mantle -cavity is opened. From the outer edge of this arise a 

 number of nerves supplying the various parts of the mantle. 



The organs of special sense of the Cattle-fish are much more 

 highly developed than those of Triton. The eyes (Fig. 668) are 



,-.7.7' 



m 



Fin. 664. Sepia officinalis, 



longitudinal .section of ink- 

 sac, a. anus ; d. ink-duct ; 

 i. <i. ink-gland ; 2. r. cavity 

 of ink-sac ; o. orifice of ink- 

 gland ; r. rectum ; j>. sphinc- 

 ter muscles. (From the Cam- 

 Iniilije Natural History, after 

 Girod.) 



