| NERVOUS SYSTEM. (Comparative Anatomy ) 
merous forms and degrees of organization. 
! In the common Talitrus, an inferior genus, 
it consists of a regular series of ganglia, 
developed at an equal distance from each 
other, united by two distinctly separated 
longitudinal cords, from which are given 
off transverse nerves. 1 have found the same 
arrangement in the genus Oniscus, in which 
also a close analogy to the nervous system 
_of the Annelides was apparent. In the 
_ Cymothoa, an animal a little higher in the 
seale, these longitudinal columns have become 
closely approximated, and the ganglia have 
coalesced transversely. Rising higher in the 
Seale, we find a still greater degree of concen- 
_ tration and coalescence in the Decapoda, this 
_ being directed to two ponies points—the 
thorax in the long-tailed Decapods, and the 
_ thorax and abdomen in the short-tailed ones. 
_ With regard to the former, I have examined 
the nervous system in the genera Crangon, 
Processa, and Pagurus, in all of which it pre- 
sented a similarity in developement. In the 
lengthened abdomen the longitudinal cords 
were very closely approximated, and the gan- 
‘glia developed were nearly of an equal size, 
‘and équidistant from each other; from them 
‘were given off transverse nerves. In the thorax, 
the ganglia were very closely approximated 
eed, longitudinally, so as nearly to have 
@ appearance of one nervous mass, from 
a hich were given off large transverse nerves to 
part of which there passed off two long nervous 
_ ¢ords, which encircled the esophagus, and de- 
os a ganglion on its superior part. In 
the short-tailed Decapods, as in the common 
_ edible crab, the abdominal ganglia have co- 
al into one large nervous mass, from 
which radiate nerves to the legs, &c ; from its 
anterior part there pass two long filaments, 
— it with the coalesced ganglia in the 
There is a supra-esophageal gan- 
_ glion, as in the precedihg, but it is compara- 
_ tively small. 
2. Myriapoda.— Amongst the Myriapoda, 
he next class, we find the nervous system 
pinning by a low state of organization, 
milar to the lower Crustacea, this being prin- 
ee ee 
cipally characterized by a considerable number’ 
ganglions. In the Scolopendra morsitans, 
the nervous system consists of a series of 
twenty-one double ganglia, situated on the 
ventral surface of the body, connected by in- 
tervening distinctly double longitudinal cords. 
fom each ganglion are given off lateral nerves 
to supply the neighbouring muscles, viscera, 
and feet. Those ganglia are nearly all equal 
mM Size excepting the first, which is the largest, 
and ftom which are given off additional nerves 
to supply the maxilla, &c. Beyond this first 
Sub-esophageal ganglion, and from its anterior 
part, proceed the longitudinal connecting cords, 
which diverge to encircle the esophagus, above 
_ which they meet and develope a bilobate supra- 
esophageal ganglion. (See Myrrapopa, (. Fig. 
313.) [Mr. Newport’s recent researches on 
the nervous system of Myriapoda favour the 
— that a distinct series of excitomotory 
OL. III. 
‘the neighbouring parts, and from the anterior . 
609 
fibres connected with the ganglia of te seg- 
ments (and not with the cerebral ganglion) exist 
in these animals. See the forthcoming volume 
of the Philosophical Transactions, 1843.] 
3. Arachnida—lIn the Arachnida the ner- 
vous system is more concentrated, and the gan- 
glia are fewer; they may be considered, indeed, 
as intermediate in the developement of this sys- 
tem between the Insecta and Crustacea. In the 
Scorpions, according to Dr. Grant,* ** the gan- 
glia of the trunk have formed one large nervous 
mass, from which all the nerves of the legs and 
the surrounding parts take their rise as from 
a single ganglion.” The cerebral ganglion is 
comparatively small, and, according to Cuvier 
and Carus,+ the two nervous cords, proceeding 
thence, unite at intervals to form seven gan- 
glions, the last of which belongs to the tail. 
Grant observes,} that the motor column is very 
loosely connected with the two inferior or sen- 
sitive columns, particularly in the region of the 
abdomen, and that this conformation is more 
obvious here than in any other of the Articu- 
lata. In Spiders, the nervous system consists, 
according to Professor Owen’s description, of a 
brain, a bilobed ganglion which supplies the 
optic nerves, and also two large nerves to the 
mandibles. From it a short and thick collar, 
embracing the gullet, extends to a second very 
considerable stellate or radiated ganglion, si- 
tuate below the stomach upon the plastron. 
From this ganglion five! principal nerves are 
sent off on each side, “the first to the pedi- 
form maxillary palpi, the second to the more 
pediform labial palpi, which are usually longer 
than the rest of the legs, and used by many 
spiders rather as instruments of exploration 
than of locomotion; the three posterior nerves 
supply the remaining legs, which answer to the 
thoracic legs of Hexapod Insects. The ner- 
vous axis is prolonged beyond this great gan- 
glion, as two distinct chords, into the beginning 
of the abdomen, where, in the Epira diadema, 
it divides into a kind of cauda equina; but in 
the Mygale a third ganglion of very small size 
is formed from which the nerves diverge to 
supply the teguments of the abdomen and its 
contents.” * * * “ The stomatogastric nerves 
are sent off from the posterior and lateral parts 
of the brain and form on each side a reticulate 
ganglion, which distributes filaments to the 
stomach.” § 
4. Insecta—We have now to examine the 
last and highest class of articulated animals— 
the Insecta, in which we shall find the nervous 
system very highly organized, leading us by 
strict analogies to the Vertebrata. It consists, 
in almost every order, of a ganglionic nervous 
cord, running along the abdominal surface, as 
in the preceding classes, and of a similar supra- 
cesophageal nervous mass, called by Cuvier the 
brain, from which are given off eight pairs of 
nerves and two single ones. This nervous cord 
consists of a varied number of ganglia, giving 
off lateral nervous filaments, and connected to 
* Lectures on Comparative Anatomy. 
+ Op. cit. 
t Op. cit. ; 
§ Owen’s Lectures, by White, p. 255. 
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