of Ommastrephes todarus. 5 



buccal mass immediately below the origin of the oesophagus ; 

 the cords (PI. I. fig. 1 /) which unite them pass therefore down- 

 wards inclosing that tube, and are joined to the external margins 

 of both pairs. The under pair of buccal ganglions give to the 

 buccal organ four pairs of nerves ; the pair (r) next the median 

 line go to the tongue and the fleshy laminae on each side of it, 

 which laminae being in connexion with the salivary glands and 

 themselves glandular, must be looked upon, if not entirely, at 

 least to some extent, as auxiliary to them ; the next pair (</) go 

 to the muscles of the under jaw and anterior part of the buccal 

 organ ; the outer or external pair (g') supply the muscles of the 

 upper jaw. These three pairs come off from the anterior margin ; 

 the fourth pair {s) pass off' from behind on the median line, and 

 are applied to the under surface of the oesophagus, and accom- 

 panying that tube backwards they form a plexus of minute twigs 

 on it, and go to be united to a ganglion on the stomach. This 

 pair of nerves is similar to that which in Doris has been consi- 

 dered to represent the par vagum of the higher animals. It 

 appears that these four ganglions are the homologues of the 

 buccal ganglions, — the centres which in the Gasteropods sup- 

 ply the tongue, the muscles of the buccal mass, and the salivary 

 glands, and also give off" the two oesophageal nerves. But here 

 again, as with the centres which supply the brachial nerves, 

 there are two pairs instead of one, and one of them is placed 

 below the alimentary tube. It is pretty certain, however, 

 that they are only the buccal ganglions, broken up, pro- 

 bably on account of the peculiar arrangement of the parts they 

 supply. 



In Nautilus, " the parts immediately surrounding the mouth, 

 the muscles of the jaws, and the tongue," take their nerves from 

 the broad " rounded chord or commissure " placed transversely 

 above the oesophagus, and connected by its extremities to the 

 optic and to the great ganglions below that tube. This com- 

 missure Professor Owen calls the brain, and considers it ana- 

 logous with what we have denominated the optic ganglions in 

 the Cuttle-fishes. It would seem, however, that as this commis- 

 sure in Nautilus gives its nerves, four pairs, to the buccal mass 

 and tongue, it is homologous with the four buccal ganglions of 

 Ommastrephes. And thus it appears that the buccal ganglions of 

 Nautilus are situated above the oesophagus. In the Gasteropods 

 they are always below it. 



In the Cephalopods the buccal ganglions are also connected 

 to the optic. A delicate cord (PI. II. figs. 1, 2 h) is given off 

 from the anterior apex of these ganglions in Ommastrephes ; it 

 passes from the upper side on the median line, and is composed 



