MR. T. H, HUXLEY ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA. 55 
It seems possible that the series of lateral ganglia in certain Annelida {Amphinome) 
may correspond with the parieto-splanchnic ganglia of Mollnsks. 
On the other hand, the storaato-gastric nerves with their ganglia in Articulata 
appear to correspond with the visceral nerves of Mollusca. 
To what portions of the nervous system of the Vertebrata do these various ganglia 
answer? This is a problem which has been variously solved. Unless, with Von 
Baer, we deny the homology of the centres of the nervous system in the Invertebrata 
with those of the Vertebrata, an argument whose worth can only be decided by a 
careful and laborious study of development, it would seem clear that the cerebral 
ganglia are homologous with the corpora striata and thalami of Vertebrata. Their 
accessories, the buccal ganglia, answer to the trigeminal ganglia, and supply similar 
parts. 
The cephalo-pedal and cephalo-splanchnic commissures correspond with the crura 
cerebri ; the pedal and parieto-splanchnic ganglia answering to the spinal cord and 
medulla oblongata. The origin of the auditory nerves would then correspond with that 
of the seventh pair in Vertebrata,. and the pedal nerves with the spinal nerves in 
function and position. 
Again, if the parieto-splanchnic ganglia represent the medulla oblongata, their 
branches should, as I think they do, represent a pneumogastric nerve 
Finally, the visceral nerves answer to the sympathetic. 
The next question to be considered is, in what manner these typical ganglia are 
arranged and combined to form the almost infinite varieties in the actual nervous 
systems of the Cephalous Mollusca. 
We find — 
1. The ganglia concentrated into a mass above the oesophagus, e. g. Doris, Phyl- 
lirrhoU, the majority of the Nudibranchiata. 
2. The ganglia concentrated into a mass below the oesophagus, e. g. Pteropoda. 
3. The ganglia concentrated around the oesophagus, some above and some below, 
e. g. Buccimun, Helix, Onchidium, Cephalopoda. 
4. The ganglia scattered and separated in pairs, e. g. Heteropoda, Tectibraiichiata, 
and many Pectinibranchiata. 
Among these the parieto-splanchnic ganglia may either be united by apposition 
with the pedal ganglia, and with the cerebral by commissure, as occurs most com- 
monly, e. g. Octopus, Nautilus, Haliotis; or they may be united with the cerebral 
ganglia by apposition, and with the pedal by commissure, as in Strombus and 
Pteroceras. 
Patella, Aplysia and Bullcea, form a gradual transition from one of these condi- 
tions to the other. 
It will be seen at once from this enumeration that the concentration of the nervous 
* Von SiEBOLD compares the nerves which arise between the nerves to the ganglion stellatum in Cephalo- 
poda to a par vagum. Vergl. Anat. p. 379. 
I 2 
