ELEDONE. 535 
cerebral ganglia are distinguishable from the remaining, 
sub-oesophageal ganglia, yet the three pairs which build 
up this latter mass cannot be definitely marked off 
externally one from another. Similarly any two ganglia 
of a pair are intimately fused, so as to appear like one 
mass only. The ganglion cells in these ganglia form 
an external layer round a central fibrous mass. 
The Cerebral ganglia form a supra-oesophageal mass 
oval in dorsal view, triangular when seen laterally 
(Pl. IX, figs. 76 and 70, C.G.). Three transverse grooves 
mark the ganglionic mass externally into four divisions 
which increase in size from the front, backwards. The 
last and largest division is marked with longitudinal 
alternating bands of white and grey matter, and the 
regions of the above grooves are also grey. The anterior 
division of this mass also bears a groove running antero- 
posteriorly, along its dorsal middle line. 
The Brachial ganglia form the anterior third of the 
sub-oesophageal mass. They exceed in size the pedal 
ganglia, and together with these form a mass which is 
morphologically equivalent to the pedal ganglia of other 
Molluses (fig. 70, Br.G.). As the arms are so greatly 
developed, while the remaining portion of the foot, the 
funnel, is comparatively small, so the brachial ganglia 
exceed the pedal ganglia in size. The former are also 
connected above the oesophagus by a slender supra- 
oesophageal commissure. 
The Pedal ganglia form the central and smallest 
portion of the sub-oesophageal mass, and innervate the 
funnel (epipodium) (fig. 70, Ped. G.). 
The Visceral ganglia lie behind the pedal. Accord- 
ing to Pelseneer, there are really two pairs of visceral 
ganglia—an anterior pair (the pleural ganglia) lying 
dorsally and giving off the pallial nerves, and a more 
