354 NERVOUS SYSTEM OF MOLLUSKS. 
side. Of these, one passes through the ganglionic masses o c, to 
communicate with the ganglion b, which is the one connected 
with the respiratory movements. The others are distributed 
with the branches of the ganglia cc, the function of which is 
double ; for one set of branches from each is distributed to 
the mantle in general, every part of which (in these shell-less 
Mollusks) is capable of contracting and giving motion to the 
body; whilst another set is distributed to that thick and 
fleshy part of it which is called its foot, and on which the 
animal crawls (§ 107). There is another ganglion, d, lying 
in front of the cephalic ganglion, and also receiving branches 
of communication from it; this ganglion is specially connected 
with the actions of mastication and swallowing, and is called 
the phary ngeal ganglion. 
439. Thus we see that the cephalic ganglion sends branches 
to all the other ganglia, though these having different functions, 
do not communicate with each other; and thus every part 
has two sets of nervous connexions, one with the cephalic 
ganglia, and the other with its own ganglion. By the former, 
the animal becomes conscious of impressions made upon it, 
these impressions being converted in the cephalic ganglia into 
sensations ; and the influence of its conscious power is exerted 
through them upon the several parts of its body, causing 
spontaneous motion. By the latter are produced those reflex 
actions of the several organs, which do not require sensation, 
but which depend upon the simple conveyance of an im¬ 
pression to the ganglion, and the transmission of the resultant 
motor impulse from it to the muscles supplied by its nerves. 
A small part only of the Nervous System of Mollusks 
ministers to the general movements of the body; and this 
corresponds with what has been elsewhere stated (§ 107) of 
the inertness which is their general characteristic, and of the 
small amount of muscular structure which they possess. 
440. On the other hand, in the Articulated classes, in 
which the apparatus of movement is so highly developed, and 
whose actions are so energetic, we find the Nervous System 
almost entirely subservient to this function. Its usual form 
has been already described (§ 94) as a chain of ganglia con¬ 
nected by a double cord, which commences in the head, and 
passes backwards through the body. In general, we find a 
ganglion (or rather a pair of ganglia united on the middle 
