356 NERVOUS SYSTEM OF ARTICULATED ANIMALS. 
the Moth being much shorter than that of the Caterpillar), 
and that great changes have taken place in the relative sizes 
of the ganglia. The cephalic 
ganglia, being now connected 
with much more perfect eyes and 
other organs of sense, are greatly 
enlarged; the thoracic ganglia, 
^ 1 1 from which the legs and wings 
are supplied, are enlarged and 
^3 2 concentrated; whilst the abdomi¬ 
nal ganglia are relatively dimi¬ 
nished in size, the 7th and 8th 
being entirely wanting. 
442. When the structure of 
the chain of ganglia is more par¬ 
ticularly inquired into, it is found 
to consist of two distinct tracts; 
one of which is composed of 
nervous fibres only, and passes 
backwards from the cephalic 
ganglia, over the surface of all 
the ganglia of the trunk, giving 
off branches to the nerves that 
proceed from them; whilst the 
other connects the ganglia them¬ 
selves. Hence, as in Mollusca, 
every part of the body has two 
Fig. 186.— Ner- , J 
vous System of sets oi nervous connexions ; one 
with the cephalic ganglia, the 
other with the ganglion of its 
own segment. Impressions made upon it, being conveyed by 
the fibrous tract to the cephalic ganglia, become sensations; and 
by the influence of the conscious power, operating through 
these same ganglia, the general movements of the body are 
harmonised and directed. It is obvious that, as the motions 
of an animal are chiefly guided by its sight, the cephalic 
ganglia would have a governing influence over the rest, if 
only from their peculiar connexion with the eyes; but there 
is good reason to believe that their functions are still more 
different from those of the ganglia of the trunk, and that 
sensation resides in them alone. The motions produced by 
Fig. 185. —Ner¬ 
vous System of 
Larva of Sphinx 
LIGUSTRI. 
Sphinx 
LIGUSTRI. 
