4 Mr. A. Hancock on the Nervous System 



pair of large ganglions, the anterior suboesophageal of that 

 author; these ganglions are also in connexion with the optic 

 centres, although they are stated to come off from the " commis- 

 sure or brain " : the auditory organs were not determined. It 

 may therefore be concluded, that however divided in Ommastre- 

 phes, the anterior and median masses form essentially only one 

 centre. 



The position of the optic ganglions is also peculiar. In the 

 Gasteropods, when they exist, they are usually attached to the 

 sides of the cerebroids towards their posterior margins, and give 

 off their nerves upwards — the eyes being invariably placed on the 

 dorsal aspect. In the naked Cephalopods they are also inclined 

 towards the dorsal surface, and the ganglions are directly above 

 the alimentary tube, and they as well as the eyes are enormously 

 developed; had these ganglions therefore retained their usual 

 lateral position, the head must have been inconveniently en- 

 larged. In Nautilus, however, the optic ganglions may be said 

 to occupy their normal position, for they are placed at the sides 

 of the " anterior suboesophageal ganglions," and are apparently 

 connected with them as well as with the dorsal commissure or 

 brain. What are here denominated optic ganglions have been 

 called by some writers rudimentary optic lobes, by others the 

 rudiment of a brain. It is pretty evident, however, that they 

 are homologous with the optic ganglions of the Gasteropods, in 

 which the nervous element of the visual organ is divided into 

 three parts as in the Cephalopods. Thus, in Doris for instance, 

 there is first a minute ganglion, generally closely attached to the 

 cerebroid ; this is succeeded by a nerve, which, on reaching the 

 back of the eye, is in many Gasteropods, particularly in the Nu- 

 clcobranchs, spread out as an accumulation of nervous matter, 

 which, being the third portion, would appear to correspond to 

 the enlargement of the nerve at the back part of the eye in the 

 Cephalopods. 



The anterior suboesophageal mass of Ommastrephes gives off 

 from its posterior margin above two nervous cords (PI. I. figs. 1, 

 3 OT, & PI. II. fig. 2ff), one on each side of the median line ; these 

 passing upwards and forwards, one on each side of the oeso- 

 phagus, go to be united to the posterior margin of a pair of rather 

 small, depressed ganglions (PI. I. fig. Ij, & PI. II. figs. 1, 2d) 

 adhering to the outer capsule of the buccal mass, forming the 

 buccal retractors, to which these centres send all their nerves 

 (PI. I. fig. Ijo, & PI. II. fig. 2 e, e), which are numerous, and 

 passing forward spread out in a radiating manner. These gan- 

 glions are fused into a transversely elongated mass comprising 

 two lateral lobes, and are interconnected with another pair of 

 similar ganglions (PI. I. fig. I X;, & PI. II. fig. 1 e) lying on the 



