114 Organs of Bearing [^ZnlL.rrMS 
YI.— 0^^ the Or gam of Hearing in MoUushs. By M. Laoaze- 
DUTHIERS. 
It is well known that the auditory organ of moUusks is reduced 
fundamentally to a nervous vesicle filled with liquid, in which float 
and vibrate calcareous particles, and that this vesicle is analogous 
to portion of the membranous labyrinth of vertebrate animals, 
in which is contained the otolites. Authors assign various func- 
tions to this apparatus in the different groups of animals, and thus 
lead to some confusion of the physiological attributes of the various 
ganglia of the nervous centres. A priori, this proposition is diffi- 
cult to admit. Nevertheless, the works of the most eminent 
anatomists, such as Claparede, Leydig, and Huxley, express no 
doubt upon the point, and indeed I myself have in more than one 
paper confirmed the common error, which is due to the great diffi- 
culty of making suitable preparations, and to the method of 
conducting observations. 
It is necessary to bear in mind the fact that the central nervous 
system of Gastropods (that is of the animals we are now considering) 
is composed of three groups of ganglia, whose physiological attributes 
are evidently distinct. In relation to the digestive tube, one is 
dorsal, or posterior, and supplies nerves to the organs of sight, of 
touch, and to the lips — in a word, to the head and its appendages, 
parts all endowed with an exquisite sensibihty. The two others, 
abdominal, or anterior, send nerve filaments, the most anterior and 
superior, to the foot or organ of locomotion ; the most inferior, to all 
the other parts of the body. I leave the sympathetic nerve out of 
consideration. The question then arises, With which of these nervous 
centres are the otolites connected ? 
In some gastropods in the Eolidae and the Heteropoda, the 
auditory vesicles are evidently connected with the dorsal gangha, 
which, as far as can be determined, are associated with sensation. 
In the Heteropoda especially, the otolites are suspended from the 
brain (?) (cerveau) as if from a long delicate thread. 
In all the other gastropods, the auditory vesicles are figured 
and described as being intimately united to the pedal, or locomotor 
ganglia. On this point all writers express a distinct affirmative. 
Herr Adolf Schmidt alone has described a canal which establishes 
a communication between the cavity of the organ and the external 
surface of the body; but this is a further error founded on an 
appearance, but not on a demonstrated fact.* 
In studying the histology of the central nervous system of a 
very small gastropod, the Ancylus of our streams, I found sus- 
* Giebel und Heintz's Zeitschrift fiir die Gesammtem Naturwissenschaft. 1856. 
