NERVES OF MOLLUSKS. 



pair of ganglionic 

 swellings, which 

 are lodged in a 

 cartilaginous, cra- 

 nial cravity ; from 

 them arise the 

 nerves of the feet * 

 (Fig. 5). 



To recapitulate, 

 we see that, in this rt 

 class of animals, 

 the nervous sys- 

 tem is essentially 

 composed of a * 

 medullary collar, 

 embracing the ali- 

 mentary tube, and 

 formed by the 

 communicating 

 cords of the two 

 pairs of ganglia, 

 which are widely v 

 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- 

 iopods ; and the 



Explanation of Fig. 5. Nervous system of the cuttle-fish ; a, the ner- 

 vous collar which embraces the oesophagus, the course of which is indi- 

 cated by a bristle (s): c. the nervous mass, situate in front of the oesophagus, 

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

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

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

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

 the oesophagus again, and then form a small anterior ganglion from which 

 arise the labial nerves ; b. the tentacular ganglia, from which arise the 

 nerves of the arm ; o. the optic nerves which arise from the lateral parts 

 of the brain, and soon swell into a large ganglion ; t. small nervous tuber- 

 cles, situate on the origin of the optic nerves ; g. the sub-cesophageal or 

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

 presents an elongated ganglion (r), and penetrates into the branchiae , m 

 nerve* which also arise from the post-cesophcgeal ganglia, and which, in 

 their course, present a large star-like ganglion (e), the branches of whirl* 

 %re distributed to the mantle. 

 2 



