66 
THE VOYAGE OP H.M.S. CHALLENGER. 
The anterior suboesophageal mass gives off the nerves to the arms, and hence has been 
called “ brachial.” 
The middle suboesophageal mass, from which arise the nerves of the siphon, has been 
universally regarded as constituted by the pedal ganglia. 
Lastly, the posterior suboesophageal mass innervates the mantle and the viscera; 
hence it corresponds with the combined visceral ganglia of other Mollusca . 1 
The supraoesophageal mass (cerebral ganglia) is united to the infraoesophageal masses 
by two connectives on either side ; the anterior is rather thin and passes to the brachial 
ganglion ; the posterior is very large and thick, and joins the cerebral ganglion to the 
two posterior infraoesophageal masses, that is the pedal and visceral ganglia. 
It has already been stated that all observers are agreed as to the interpretation of 
the supraoesophageal and the two posterior suboesophageal masses. The disagreement 
relates only to the brachial ganglia, which are regarded by one party as pedal and by the 
other as cerebral. We shall now proceed to discuss this point. 
Those zoologists who maintain that the brachial ganglia are part of the cerebral 
ganglia explain their position below the oesophagus by saying that on either side a part 
of the cerebral ganglia has been displaced from the upper to the lower surface of the 
oesophagus, still remaining united to the cerebral ganglion, and that these two nervous 
masses have fused below the oesophagus and formed the brachial ganglia. In this 
manner the brachial ganglia are cerebral in origin, and the arms which they innervate 
are similarly cephalic. 
Against this interpretation the following arguments may be adduced : — 
I. It is eminently unlikely that in order to innervate the crown of arms which 
surrounds the buccal aperture on all sides ( lateral and dorsal as well as ventral) a 
portion of the cerebral ganglia should have descended on either side to the lower aspect 
of the oesophagus, and that it should be just this particular part of the cerebral ganglia 
situated entirely below the oesophagus that innervates the arms situated dorsally to and 
at either side of the latter. 
If the arms were really cephalic in origin, the nervous mass which innervates them 
would not have descended entirely to the lower surface of the digestive tract, and those 
arms, which are situated above the oesophagus, would surely be supplied directly from 
the supraoesophageal cerebral mass, even if all were not so innervated as in the case of 
the six cones of Clione. 
If the muscular mass of the arms had all been displaced from the upper aspect of the 
head in order to locate itself entirely below the mouth, then it would be reasonable to 
suppose that a portion of the cerebral ganglia had followed this movement, and descended 
on either side of the digestive tract. But nothing of the kind is the case. On the 
1 See Paul Pelseneer, Recherches sur le systeme nerveux des Pteropodes, Arch. deBiol., t. vii. p. 121. 
