293 SUPPLEMENT 
With this brain communicates the ganglion of the organ of 
vision, which is always placed immediately behind the bulb 
of the eye, as well as that of hearing, when there is any, and 
from it proceed the different nerves, which repair to the ten- 
tacula as well as to the lips. 
Beside the communication more or less close which there 
is above the cesophagus, between the two parts of the brain, 
there is another inferior one, which passes under the ceso- 
phagus, and constitutes a sort of ring or collar surround- 
ing it. 
The nervous system of the sensitive and locomotive appa- 
ratus is formed only by a single ganglion situated on each 
side, sometimes tolerably distant from the brain, with which 
it always communicates by a cord, but most frequently so. 
near this organ that it really appears to form a part of it. 
In both cases it gives out the more or less numerous threads, 
which repair to all the parts of the musculo-cutaneous en- 
velope, and especially to those which serve essentially to 
general locomotion, as for instance, to the foot of the gastero- 
pods and trachelipods, to the sac of the brachiocephala, to 
the wings of the pteropods, &c. 
The visceral ganglia appear to be but two in number ; the 
one which appertains especially to the male excitatory organ 
is usually situated near the orifice through which that organ 
issues, and it furnishes threads to the organ as well as that 
by which it communicates with the brain. The other vis- 
ceral ganglion is more constant in its situation; it is usually 
placed towards the stomachal swelling, and the nervous 
threads which it furnishes are equally of two sorts, those 
which proceed to the intestinal canal and those which ascend 
to communicate with the brain, through the medium of the 
cesophageal ring. 
It is unnecessary to observe that the development of the 
different parts of this nervous system is proportional to that 
13 
