8 Mr. A. Hancock on the Nervous System 



Each of the branchial ganghons (PI. I. figs. 1, 2, Sf, & PI. II. 

 fig. 1 o) of Ommastrephes gives off posteriorly a large nervous 

 cord (PI. I. fig. 1 hf h)j which on its passage to what has been 

 called the stellate ganglion distributes two or three nerves. 

 The first (PI. I. fig. 1 u) of these passes off almost immediately 

 to the muscles of the mantle a short way behind the head ; a 

 little further down another branch (w'') is given off, which, divi- 

 ding into two portions, sends one of them to the mantle — the 

 membrane investing the viscera. The other (w;), which is the 

 larger, becomes attached to the anterior aorta; and after sup- 

 plying this great vascular trunk with numerous twigs, follows 

 a branch of it into the liver, where it was lost. This is the 

 course of this nerve on the right side. A similar nerve (?/;'), 

 from the cord of the left side, is also applied to the aorta ; but 

 how it terminates was not ascertained. Close to the root of the 

 great nervous cord, on the inner side, another pair of nerves (w') 

 leaves the branchial ganglions. These nerves go to the muscles 

 forming the sides of the mantle in front, and to the posterior 

 portion of the funnel. Professor Owen considers these muscles 

 in the Cuttle-fishes to represent the shell-muscles of Nautilus ; 

 accordingly this nerve, and the two above described as going 

 from the great cord to the mantle, are all that in Ommastrephes 

 represent the numerous nerves given from the posterior '^ sub- 

 cesophageal " (branchial) ganglions to the shell-muscles in Nau- 

 tilus, The comparative, almost rudimentary, condition of these 

 nerves in the naked Cephalopods is naturally accounted for by 

 the rudimentary state of the muscles they supply. A similar 

 reduction of the nervous element is always found when the organ 

 is imperfectly developed, as can very easily be proved by the dis- 

 section of a few Gasteropods whose organs are of unequal deve- 

 lopment. There are, however, other two or three small nerves 

 (PI. I. figs. 1, 3 V, V, & PI. II. figs. 1, 3 m) given off from either 

 side, apparently from the upper surface of the optic nerve, 

 close to a small, round, ganglionic enlargement (PI. II. fig. 3 /), 

 which nerves, perhaps, should be considered as belonging to the 

 branchial ganglions ; and if so, the ganglionic enlargements must 

 be accessory branchial ganglions. These nerves go to the skin 

 of the head above and behind. The ganglionic enlargements 

 may, however, represent the olfactory ganglions, which, in the 

 Gasteropods, are not uncommonly confounded with the optic 

 nerve, as for instance in the BullidcB ; and if so, the olfactory 

 organ is probably situated in the vicinity of the eye; — a conclusion 

 not altogether improbable, for in Nautilus the ophthalmic ten- 

 tacles have the structure of the dorsal tentacles of Doris, which 

 tentacles are assuredly the seat of olfaction. I did not succeed. 



