18 
THE VOYAGE OF H.M.S. CHALLENGER. 
mantle which have overrun the shell. This union of the two primitive pallial nerves 
explains the origin of the “ commissure ” of the stellate ganglia, so well developed in all 
the (Egopsids, 1 already reduced in Loligo , 2 and still more so in the adult Sepiola 
(better marked in the embryos 3 ), and finally disappearing in the Sepiidse and Octopods ; 
by the disappearance of the pallial siphon and the primitive mantle, the median nerve 
has been lost, the “ commissure” not being then any longer carried forward by this nerve 
has not preserved its curvature, has become more posterior, and has passed into the 
mantle where it joins the two ganglia in a straight line. 4 
Behind the stellate ganglia, the pallial nerves, preserving sensibly their diameter (PI. 
Y. figs. 1, 2, 6, f.n; Fig. N, iii), are directed posteriorly in running along the wall of 
the shell-sac, but, immediately on leaving the ganglia, they give rise to a thinner 
latero-ventral trunk (PI. Y. fig. 6), innervating the mantle, and to another much larger 
one, which arrives at the fins, where it expands by dividing to an extraordinary extent, 
without, however, presenting ganglionic swellings (PI. Y. fig. 6). 
Stomato-Gastric System. —In the Challenger specimen (the only one examined which 
was provided with a head), the “ inferior buccal ” ganglia, or stomato-gastric ganglia, have 
not been seen ; they were apparently situated under the superficial muscular layer of the 
buccal bulb (as they are in some degree in certain Ommatostrephidse). There can be 
no doubt of their existence; two parallel stomato-gastric nerves run along the ventral 
face of the oesophagus and end in the large gastric ganglion (PL VI. figs. 2, 3, gl.). 
Sense Organs.— The olfactory pits, the otocysts, and the eyes are well developed. 
A. The olfactory pit is situated quite at the back of the ocular prominence, at 
the junction of the lateral and ventral faces of the head (PI. I. fig. 6, ol. ; PI. II. fig. 1, 
ol.). It is limited by a slightly elevated margin in the interior of which the bottom 
projects in the form of a papilla, the whole having thus the aspect of a “ circumvallate 
papilla” of the tongue of mammals (PI. VI. fig. II ). 5 
B. The otocyst is situated between the wings of the “ cranial ” cartilage and the 
1 For example, in Ommatostrephes (Hancock, op. cit.). 
2 Yon Jhering, Vergleichende Anatomie des Nervensystemes und Phylogenie der Mollusken, p. 257, 1877. 
3 Joubin, Recherches sur la coloration du tegument cliez les Cephalopodes {Arch, de Zool. Exper., s^r. 
2, t. x. p. 306, 1894). 
4 The pallial nerves may then be joined to one another on the dorsal side of the digestive tube, as they are 
likewise in the Lamellibranchs, behind and at the back of the rectum; this enables us to understand the supra- 
rectal commissure of the Amphineura {Chiton, &c.), in the identification of which were found certain difficulties 
(see especially Lang, Lehrbuch der Yergleichenden Anatomie, p. 711, 1892 ; Bouvier and Fischer, Recherches et 
considerations sur 1’Asym^trie des Mollusques univalves [ Journ. de Conchyl., t. xxxii. pp. 200, 201, 1892]; 
Grobben, Zur Kenntniss der Morphologie, der Verwandtschaftsverhaltnisse und des Systems der Mollusken 
[Sitzungsber. Akad. Wiss. Wien, Math. Naturw. Cl., Bd. ciii. p. 85, 1894]). It is only a junction like that, of 
the pallial nerves and in no way homologous to the visceral commissure ; the Amphineura thus re-enter into 
the common plan of organisation of the Molluscs. 
5 The central prominence is probably the point of departure of the rhinopliore in form of papilla of certain 
CEgopsids {Chiroteuthis, Doratopsis). 
