XII 



PHYLUM MOLLUSCA 



769 



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

 .ganglia (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 off to the 



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



immediate contact with the pedal behind 

 j the oesophagus. 



Besides the optic nerves the cerebral 

 I ganglia also give off a pair of slender 



nerves which join a smaller pair of closely 



united buccal ganglia (Fig. 666, buc.\ 



situated close to the buccal mass on the 

 [anterior aspect of the oesophagus. The 

 [buccal ganglia again (which are some- 

 I times looked upon as separated portions 



of the cerebral) are connected by slender 

 | connectives with a pair of stomato gastric 

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

 limited, situated on the posterior aspect 

 I of the oesophagus. Besides the ten 



brachial nerves, each of w r hich, expanding 



at the base of the arm into a brachial 

 I 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 

 jgive off two visceral nerves (Fig. 667, 

 \visc. n.) supplying the various internal 

 j organs, one pair of branches, the branchials, 

 [having each a branchial ganglion at the 

 jbase of the ctenidium, and running along 

 jits 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 Cuttle-fish are much more 



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



Fio. 664. Sepia officinalis, 

 longitudinal section of ink- 

 sac, n. an vis ; tl. ink-duct ; 

 i. ft. ink-gland ; i. r. cavity 

 of ink-sac ; o. orifice of ink- 

 gland ; ';% rectum ; up. sphinc- 

 ter muscles. (From the Cam- 

 bridge Xatv.rat History, after 

 Girod.) 



