CEPHALOPODA. 



549 



which they perforate, but there are no columns bility, the centre of nervous impression and 

 prolonged backwards from the lateral parts of volition is proportionally developed, and exhi- 

 the brain to form pallial ganglia as in the bits the highest conditions which the brain pre- 

 higher Cephalopods ; the structure and func- sents in the Invertebrate series of animals, 

 tions of the cloak to which these ganglia are Except in some of the smaller species, as 

 subservient, not being enjoyed by the shell- the Sepiola, in which the surrounding sub- 

 clad Nautilus. The nerves corresponding to stance still retains the consistency of a mem- 

 the large visceral nerves of the Dibranchiates brane, the brain, together with the anterior 

 are, however, proportionally developed; for in and posterior oesophageal collars, is entirely 

 the organs of plastic life the Nautilus is upon surrounded by a thick cartilage. The portion 

 an equality with its naked congeners. These of oesophagus which is thus enclosed is sepa- 

 nerves, which combine the functions of the rated from the surrounding medullary matter 

 sympathetic and par vaguin, consist of a large by a thin layer of softer substance. The cere- 

 pair derived from the lower part of the pos- bral cavity is larger than the brain itself, and 

 terior oesophageal collar, and extending back- the intervening space is filled with a gelatinous 

 wards on each side of the vena cava ; and of fluid. In the Cuttle-fish the supra-oesophageal 

 smaller twigs (17) coming off between the mass is transversely shortened, as compared 

 origins of the preceding nerves, and forming a with the Nautilus, and supports a smooth, 

 plexus upon the parietes of the vein. The rounded, heart-shaped medullary mass, slightly 

 larger chords swell into ganglions at the termi- divided into two lateral lobes by a mesial Ion- 

 nation of the vena cava, (16, 16,) and send off gitudinal furrow (1, fig. 232); from the lower 

 ramifications to the branchiae, (15,15,) the and lateral parts of this body proceed the broad 

 contents of the pericardium, and the viscera of bands of cerebral substance which afterwards 

 digestion and generation. dilate into the large reniform optic ganglions 



In the Dibranchiate Cephalopods which (2, 2); upon each of these bands is placed a 

 possess instruments for varied and active loco- small spherical medullary body ( k, k). These 

 motion, where the visual organ is of large size, bodies, which we first discovered in the Sepia, 

 and attains a complexity of structure equal to we have since ascertained to exist in Loligo. 

 that of the Vertebrate animals, where a distinct From the anterior apices of the cerebral 

 acoustic organ is developed, and where the lobes small nerves are continued, which almost 

 whole surface of the body is the seat of sensi- immediately dilate into a round flattened gan- 

 glion (a, Jig. 233); this is closely 



Fig. 232. applied to the back part of the fleshy 



mass of the mouth above the pharynx; 

 it sends off nerves to the oral appa- 

 ratus (i, i, Jig. 233), and two fila- 

 ments descend and form a pair of 

 small closely approximated ganglions 

 (8, 8, Jig. 232) below the mouth, 

 analogous to the labial ganglions of 

 the Nautilus. 



From the inferior, lateral, and an- 

 terior parts of the brain two large 

 chords (k, Jig. 233) descend, and 

 unite and dilate below the oesopha- 

 gus to form the anterior suboeso- 

 phageal ganglion, or pes anserinus of 

 Cuvier, from which the nerves of the 

 feet and tentacles arise. Two still 

 larger bands (I, fig. 233) descend 

 from the brain behind the preceding 

 to form, by a similar enlargement and 

 union, the posterior cesophageal gan- 

 glionic collar. From a comparison 

 of these with the corresponding gan- 

 glions of the Nautilus, it will be seen 

 that by their approximation in the 

 transverse direction the distinction 

 of the ganglions at the lower part 

 of the collar is lost ; and a corre- 

 sponding approximation in the antero- 

 posterior direction, being accompa- 

 nied by an additional accumulation 

 of nervous substance, has produced 

 a blending together of the four gan- 

 glions into one large continuous sub- 

 oesophageal mass. The portions of 



ii this mass corresponding to the four 



Nervous system of the Cuttle.fish. ganglions and double cesophageal 



