68 
THE VOYAGE OF H.M.S. CHALLENGER. 
If it be admitted that cephalic appendages may surround the buccal aperture and 
unite below the alimentary canal (as is demanded by the arguments of von Jhering and 
of Grobben), then it ought also to be allowed that pedal appendages, such as those of 
Vermetus, may encroach upon the sides of the mouth and unite above the oesophagus, 
and embryology teaches us that this is what must have taken place in the case of the 
Cephalopoda. 
IV. If, now, these appendages should undergo great development, it is natural that 
a pair of special ganglia (the brachial ganglia) should be formed for their innervation 
at the expense of the pedal ganglia. The formation of accessory ganglia in consequence 
of the great development of certain organs is often observed in the Mollusca, and here we 
find a case almost identical with that of the Cephalopoda. 
In two groups of Gastropoda we find that the head carries a muscular mass as large 
in proportion as the brachial mass of the Cephalopoda; these are the Bullidse (“ Aceres” 
of Cuvier) and the Naticidse. 
1 . In the Bullidse there is a “ cephalic hood,” which seems to be analogous to the 
hood of the Nautilus and to the dorsal arms of the Dibranchia ; it arises from the 
fusion of the four tentacles (two labial and two nuchal) of the Euthyneura, and 
assists these animals in digging. The cephalic nature of the hood is thus beyond 
doubt. 
Is then the nervous system of the Bullidse similar to that of the Cephalopoda, and do 
we find there in front of the pedal ganglia other suboesophageal ganglia which innervate 
this cephalic mass ? By no means. Here, as in Ampullaria, the innervation of this 
mass has its source in the supraoesophageal or cerebral ganglia. 
On other grounds, too, it is impossible to regard the arms of the Cephalopoda as 
similar in origin to the cephalic tentacles of the Gastropoda. For even if the tentacles 
do not any longer exist in the adult Dibranchia, I may point out that they are still present 
in Nautilus (which is incontestably more primitive), though their homology has not 
hitherto been perceived. The structures in question are the ophthalmic tentacles, situated 
in front of and behind each eye ; as a matter of fact these tentacles are innervated by 
the supraoesophageal ganglia, 1 whilst all the other appendages (whose mass corresponds 
morphologically to the arms of the Dibranchia) are innervated by the anterior infra- 
cesophageal ganglia, which also give off the nerves to the funnel. 
2. In Natica the muscular mass which covers the head can be reflected in front so 
as to expose the buccal opening. It is the anterior part of the foot, but physiologically 
is the same part as the cephalic hood of the Bullidae, and like it aids in burrowing. 
1 Valenciennes, Nouvelles recherches sur le Nautile flambe, Archives Mus. Hist. Nat. Paris, t. ii. p. 288, pi. viii. 
figs. 2, 3, 6 and 7. It is inaccurate to state, as does von Jhering (Vergleichende Anatomie, &c., p. 262), that the anterior 
ophthalmic tentacle is innervated by the anterior infracesophageal ganglion, as also the olfactory organ. Its nerve 
issues from the extreme lateral part of the supraoesophageal ganglion. Compare the figures of Valenciennes above 
quoted. 
i 
