Monthly Microscopiral"] 
Journal, Feb. 1, 18G9. J 
in Mollush 
115 
pended to the cerebral, or sub-oesophageal ganglion, a vesicle wbicli 
it was difficult to make out distinctly. I was led by this observation, 
and by my repugnance to admitting that an organ of sense may 
derive its nerve indifferently from either a motor or sensory centre, 
to researches which led me to this conclusion. The acoustic nerve 
invariably takes its origin from the sub-oesophageal or cerebral 
ganglion. The auditory vesicle may, it is true, rest on the pedal 
ganglion ; but it never takes its nerve from this centre. 
In order to study the otolites, it has been customary to raise 
the pedal ganglia, and to compress them under the microscope. 
This mode of preparation displays the vesicle ; but it is seldom 
sufficient to demonstrate its relations, and the acoustic nerve can 
only be shown by the most delicate and careful dissection and 
manipulation. Tinting with carmine is of great advantage in these 
cases. 
In cases where the otolites are at a distance from the pedal 
ganglia, they are extremely difficult to find, since they are buried in 
the cellular tissue of the general cavity. This is so in Cyclostoma, 
Calyptrea, Lamellaria, Natica, and in certain species of Murex and 
Paludina. I have had recourse to a chemical reaction, which 
immensely assists and simplifies researches. By plunging the animal 
into a solution of oxalic acid, the lime of the otolites forms a very 
white and very insoluble oxalate, and the tissues become more 
transparent. By this means the position of the auditory vesicle is 
very distinctly seen. 
In very small species, a system of compression by a series of 
blows on the covering-glass will display the otohthic granulations 
penetrating into the acoustic nerve. If in these cases oxalic acid be 
employed, a white fine may be seen, which leads to the cerebral and 
not to the pedal ganglion. 
My researches have been made on more than thirty species, 
and I have never failed to demonstrate the relation I have pointed 
out ; and I therefore regret to have to be compelled to oppose the 
opinions of Messrs. Leydig, Claparede, and Huxley, which express 
so distinctly the connection of the otolite with the pedal ganglion. 
In a recent excursion along the sea-coast, I have had the satisfac- 
tion of finding all the new species discovered by me range them- 
selves under the following law:* — The position of the organ of 
hearing may vary, but its connection with the central nervous 
system remains always constant in the Gastropods, Heteropods, and 
Cephalopods. The acoustic nerve always arises from the sub- 
oesophageal or cerebral ganglion, which has therefore aU the sense- 
* These are the genera in which it is constant :— Limax, Arion, Helix, 
Zonites, Clausilia, Succinea, Physa, Lymneus, Ancylus Neratina, Paludina, Tes- 
tacella, Cyclostoma, Pileopsis, Calyptrea, Natica, Nassa, Trochus, Murex, Cassi- 
daria, Purpura, Patella, Haliotis, BuUeea Aplysia, Lamellaria. 
