54 MR. T. H. HUXLEY ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA. 
digital ganglia, developed to meet the wants of certain elongations or expansions 
of the foot. , , T 1 
Such are the ganglia at the bases of the arms of the Cephalopoda, and such appe i 
to me to be the ganglia which supply the - labial” processes of Nautilus 
HI. Under the name oi Parieto-splanchnic system of ganglia, I include the b^i'anc m 
and visceral ganglia of most authors, and the cervical, branchio-cardiac, and angeia 
ffanslia of M. Blanchard. This system consists of two primary ganglia, which are 
always to be found at the side of the oesophagus, connected with both the pedal an 
cephalic ganglia, and for which I reserve specially the term parieto-splanchnic 
ganglia ; from these nerves are given olf 
1. Parietal, to the sides of the body, as distinct from the foot. 
2. Columellar, to the shell-muscle or muscles, of which there are two m Octopus, 
Nautilus, and Cymhulia ; one in the shelled Gasteropoda. 
3. Branchial, to the branchicE. 
4. Angeial, to the heart and great vessels and generative organs. . • .i. 
Separate ganglia, answering to the three latter sets of nerves, may be oun in 
dibranchiate Cephalopoda; to the two last in the Heteropoda; a single gang ion 
corresponding to all of them is found in Aplysia, Buccinum, Turbo, Paladma, &c. 
Two such exist in Stromhus and Pteroceras. 
The angeial ganglia, wherever they exist separately, are placed above the aorta 
and united by a commissure. 
The visceral or sympathetic nerves ramify extensively ovei t le intes ina 
Hancock and Embleton upon Doris). They are connected anteriorly with the buccal 
ganglia, posteriorly with the parieto-splanchnic system. 
To sin, up, the typical number of ganglia in the Cephalous Mollusca is three pair, 
• with which accessory ganglia and visceral ganglia may be connected in variable 
number. The primary ganglia are united by com missures which form 1 , two g, ea e/ 
nervous rings, the cephalo-pedal, connecting the cephalic and the pedal ganglia, an 
the cephalo-splanchnic, connecting the cephalic and parieto-splanchmc ganglia : lese 
rings surround both the msophagus and the aorta. 2, Two lesser nervous rings, the 
cephalo-buccal, uniting the cephalic and buccal ganglia, and encu-chng the oesophagus, 
and the parieto-angeial, uniting the parieto-splanchnic and angeial ganglia and some- 
times surrounding the aorta alone: this ring does not seem to be invariab y present. 
The homology of these ganglia with those of other animals does not, tim^, pie 
sent any very great difficulty. .it 
It is needless to point out their identity with those of the Acephala La 
’"T^thTArticulata we have corresponding cerebral ganglia, while the suboeso- 
nhageal ganglionic chain answers to the pedal and parieto-splanchnic ganglia united 
The nerves of the latter system appear in a distinct form as the transverse nerves of 
Insects. 
