NERVOUS SYSTEM. (Comparative Anatomy.) 
matter of which they are composed appears 
more dense and opaque in its texture.* 
Fig. 349. 
be 
aN 
IK 
f Ventral nervous cord of Mormo maura ( perfect state ), 
: 
magnified to about twice the natural size. 
a, infra-cesophageal ganglion. 6, large thoracic 
> ganglia. c¢, c, c, small abdominal ganglia. 
In Insects we observe a remarkable corre- 
 paled between the disposition of the ner- 
Yous system and the form of the animal, and 
_ this is conspicuous not only in the adult but 
“also in the larva state. Indeed the changes 
which take place in the arrangement of the 
_ hervous system as the creature passes from its 
‘immature to its mature condition, are sufficient 
to indicate that the same law which influences 
that alteration of form, promotes the adaptation 
of the nervous system to it; and yet, notwith- 
‘Standing its apparent complication, the nervous 
System of insects has the same physiological 
Signification as that of Mollusks. A cephalic 
Ganglion, with which are united the nerves of 
the organs of sense, is so connected with the 
Temaining ganglions, that its influence can ex- 
tend throughout the whole system. Each seg- 
ment is provided with a ganglion, which has 
no power beyond the limits of the segment, 
- which cannot act consentaneously with its 
fellows, except under the direction of the ce- 
ae ganglion. The pedal ganglion of Mol- 
usca is in insects represented by the aggregate 
of these ganglia of the segments, which are 
also doubtless the centres of the respiratory 
actions. And those nerves which, arising from 
the cephalic ganglion, are distributed to the 
ive organs, the stomato-gastric nerves, 
are analogous to the sympathetic or to the 
agus. 
baat has been supposed by some anatomists 
that a distinct isolation of motor and sensitive 
function occurs in the ganglionic and non-gan- 
glionic cords of the abdominal nervous chain of 
/ 
4 * This is, however, but a rough sketch of the 
interesting changes that take place in the nervous 
System during the progre s of the insect from its 
larva to its peifect s ate. Those who are interested 
in the matter, 1 beg leave to refer to Mr. Newport’s 
highly valuable paper, where, as I have before ob- 
served, the chanzes of the Sphinx ligustri are de- 
tailed with minute accuracy. See also INSECTA. 
613 
insects, as well as of other Articulatg (See 
Jig. 411, art. Insecta, vol. ii. p. 05a But 
there are many objections to this hypothesis, 
which, indeed, must be regarded as quite un- 
tenable. It has been founded upon the anato- 
mical fact, which is true as regards the verte- 
brata, that sensitive nerves have ganglions while 
the motor ones are devoid of them. But it is 
going too far to compare nerves and centres, 
and to argue from the nerves of vertebrata re- 
specting the centres of Invertebrata. More- 
over, as Prof. Owen remarks, the presence of 
ganglia on the sensitive roots of spinal nerves 
is not their constant character. This hypo- 
thesis also received some support from a doc- 
trine which was countenanced by Bell, namely, 
that the columns of the spinal cord of verte- 
brata corresponded in function with that of the 
roots of the nerves, the anterior columns being 
motor as the anterior roots were, and the poste- 
rior columns and roots being sensitive. But this 
doctrine is utterly without foundation, as will 
be shewn in a subsequent part of this article. 
Prof. Owen adduces an important fact respecting 
two nearly allied Crustacea, which further inva- 
lidates the supposed difference of function of the 
ganglionic and non-ganglionic columns. “ In 
the lobster ( Astacus) and in the hermit-crab 
(Pagurus) we have two opposite conditions 
of a large and important part of the trunk. In 
the lobster the abdomen or tail is encased in a 
series of calcareous rings forming a hard and 
insensible chain armour, but as it is almost the 
exclusive organ by which the animal swims, it 
enjoys considerable motor power, a large por- 
tion of the muscular system being devoted to it. 
In the hermit-crab, on the other hand, the mus- 
cular system is almost abrogated in the long 
abdomen, for this in fact takes no share in the 
locomotive functions of the body: it is occu- 
pied by part of the alimentary canal and by 
glandular organs: the sensibility of the external 
integument is not impaired or destroyed by the 
deposition of calcareous particles in its tissue, 
but it retains the necessary faculty of testing 
the smooth and unirritating condition of the 
inner surface of the deserted shell which the 
animal chooses for its abode: minute acetabula 
are developed in groups upon this sensitive 
integument, to which also delicate ciliated pro- 
cesses are attached. The muscular system is 
reduced to a few minute fasciculi of fibres regu- 
lating the action of the small terminal claspers. 
Now,” adds Professor Owen, “ if, as has been 
conjectured, the ganglionic enlargements of the 
abdominal cords monopolize the sensorial func- 
tions, and the non-ganglionic tracts the motor 
powers, we ought to find the nerves, which 
supply the muscles of tail constructed almost 
exclusively for locomotion, to be derived from 
non-ganglionic columns; whilst in the tail, 
which is almost as exclusively sensitive, the 
ganglions ought to have been large and nume- 
rous for the supply of nerves to the integument. 
The contrary, however, is the fact; six well- 
developed ganglions distribute nerves to the 
muscular fibres of the lobster’s tail; non-gan- 
glionic columns supply the sensitive tail of the 
