538 
other in a longitudinal series, and generally 
furnished with lateral appendages of different 
kinds symmetrically disposed, which are sub- 
servient to many and very various purposes. 
The nervous system, moreover, throughout the 
entire range of this extensive series assumes a 
new and constant arrangement in itself, quite 
sufficient to characterize this sub-kingdom of 
animated nature, and with the different modifi- 
cations of this portion of their economy are 
intimately connected the progressive changes 
observable in the structure and habits of the 
different classes included therein. 
In the simplest conceivable condition under 
which a Homogangliate animal could exist, and 
doubtless among the lowest of the red-blooded 
worms and most imperfect forms of insect 
larve such a condition might be pointed out, 
the body would consist of a long succession of 
similar rings, each of which would contain an 
appropriate nervous apparatus consisting of a 
pair of ganglia symmetrically disposed on each 
side of the mesian line, from which nerves 
proceed for the innervation of the segment in 
which the brains or ganglia were placed. These 
ganglia in each segment communicate with each 
other and likewise with the pairs that precede 
and follow them by inter-communicating ner- 
vous filaments, and thus the entire series of 
individual brains or ganglia is united into one 
system made up of as many pairs as there 
would be rings entering into the composition 
of the body. There is, however, a remarkable 
difference between the anterior pair of ganglia 
and those placed in the succeeding segments. 
The first pair is invariably situated above the 
cesophagus on its dorsal aspect, while all the 
rest are arranged beneath the alimentary canal 
along the ventral region of the animal, so that 
the nervous cords that join the first and second 
airs of ganglia embrace the esophageal tube. 
The supra-esophageal pair of brains invariably 
communicates with the instruments of the 
senses whenever such exist, and therefore is 
very justly comparable to the encephalon of 
higher animals; while the succeeding chain of 
sub-cesophageal ganglia animate the muscles of 
the different segments of the body, and may 
therefore be looked upon with great reason as 
representing the spinal cord of the Vertebrata. 
But while the ganglia either of the head or 
of the ventral cord are thus numerous, as we 
have supposed them to be, in the lowest worm, 
they are as yet by far too small and devoid of 
energy in such a dispersed condition to corres- 
pond with organs connected with the higher 
senses, or even to wield muscles of sufficient 
power to support the weight of the body raised 
on articulated limbs. Therefore, before senses 
can be given or active limbs bestowed, a pro- 
cess of concentration must be gone through, the 
encephalic masses must be enlarged and thus 
rendered more perfect, the ganglionic centres 
that influence muscular movements reduced in 
number and made proportionately more ener- 
getic, and exactly in the ratio in which this 
improvement is effected in the nervous system, 
do the muscles become by degrees stronger and 
more efficient, and the limbs appended to the 
MUSCULAR SYSTEM. 
body more active and useful 1 ‘i 
agents. This, however, will be best i- 
fied by a rapid survey of the principal classes 
that compose the division of animals we 
now considering. a 
In the lowest Annelidans, as for example the 
Gordius or hair-worm, so impotent are the 
minute ganglia bestowed, that even the rings 
upon the exterior of the body are scarcely 
indicated, and not the least vestiges either o 
limbs, tentacula, or eyes are to be detec 
In the Leeches even, although the number o 
ganglia is in them considerably diminished, and 
rings of the body more strongly marked, extei 
nal limbs cannot as yet be given, their pl } 
being supplied by the suctorial dises of the 
head and tail; nevertheless, even in : 
aquatic Annelides, the encephalic masses are 
sufficiently advanced to permit organs of vision 
to be granted, and accordingly for the first time 
in the animal series (as far as our own belie 
goes) are real eyes met with. The muse 
system in these humble worms consists exelt 
sively of the contractile walls of the body, 
fibres of which are arranged in three stra 
superposed one upon the other, and pass 
different directions, one stratum being ce 
posed of longitudinal, another of oblige 
spiral, and another of annular fibres surrour 
ing the body of the animal; but these 
sufficient for progression, all the movements: 
contraction, elongation, or flexure of the bot 
being provided for by this simple arrangeme 
In the Nereis, Aphrodite, and other erra 
worms, external appendages become develop 
from the lateral aspects of the different 
ments, in the shape of bundles of seta, mor 
by muscles appropriated to each set, and th 
constitute the first rudiments of locomot 
limbs. The senses are at the same time — 
proved in their condition, tentacula or fet 
are found appended to the head, and the ey 
become larger and more conspicuous, althe 
still presenting the form of simple sg 
ocelli. 
In the Myrrapopa the limbs becon 
culated, and of sufficient strength to pern 
a terrestrial existence, each one of the f 
legs having a distinct set of muscles a 
priated to its movements, in addition 
muscular apparatus, whereby the 
the as yet flexible and elongated bo 
Iie Bre § with motion, and which of « 
represent the strata of the muscular cover 
the Leech, strengthened and endowed wi 
capability of more precise action, in pr 
as the cuticular skeleton has become 
dense and distinctly jointed. Anten 
moreover, now placed upon the head 
bling those of Toons no doubt cons 
organs of sense of a similar nature, a 
eyes in Scolopendre are found to be ve 
tinct and perfectly organized, but still 
ocelli resembling the simple eyes of Inst 
In the admirably constructed class ¢ 
SECTS, Creatures adapted to an aerial exis 
and consequently requiring the utmost é: 
of muscular power to sustain their bodi 
the air, the muscular system of the locon 
