NERVES OF MOLLUSKS, 



13 



pair of ganglionic 

 swellings, which 

 are lodged in a 

 cartilaginous, cra- 

 nial cravity ; from 

 them arise tbe 

 nerves of the feet » 

 (Fig. 5). 



To recapitulate, 

 we see that, in this 

 class of animals, 

 ihe nervous sys- 

 tem is -essentially 

 comjwsed of a 

 medullaiy collar, 

 embracing the ali- 

 mentary tube, and 

 formed by the 

 communicating 

 cords of the tvt'o 

 pairs of ganglia, 

 which ai^ widely 

 separated in the 

 acephalous mol- 

 lusks, but approx- 

 imate more and 

 more as we ascend 

 in the series, form- 

 ed by the gaster-^ 

 opods and cepha- 

 lopods ; and the 



Fig. 5. NERVOUS SYSTKM OF T5IS OUTTSuE-FISH. 



Exphrmtion of Fig. 5. — Nervous system of the cuttle-fish ; — a. the ner- 

 vous collar which embraces the cesophagus, the course of wliich is indi- 

 cated by a bristle (s): — c, the nervous mass, situate in front oftheflesophagus, 

 and commonly called the brain : the upper surface is surmountied by a very 

 large cordiform tubercle, and from its anterior part arise two nerves that 

 soon terminate in a circular ganglion, which, in its turn, gives rise to 

 another pair of nerves, which descend beneath the mouth so as to embrace 

 thecesophagus again, and then form a small anterior ganglion from which 

 arise the labial nerves ;^-5. the tentacular ganglia, from v/hich arise the 

 nerves of the arm ; — o, tlie optic nerves which arise from the lateral parts 

 of the brain, and soon s%vell into a large ganglion ; — t. small nervous tuber- 

 cles, situate on the origin of the optie nerves; — g. the sub-oesophageal or 

 ventral ganglion ; — r, the great nerve of the viscera, one branch of which 

 presents asi elongated ganglion (r), and penetrates into the branchiae; — 7ft 

 nerves which also arise from the post-oesophageal ganglia, and which, in 

 their course, present a large star-Ukc ganglion (e), the branches of wi^ch 

 are distributed to the mantle. 

 2 



