2 
NERVOUS SYSTEM. (Comparative Anatomy.) 
Council of the College of Surgeons under the 
judicious direction of Professor Owen. The 
beautiful preparations of the nervous system of 
the mussel and other animals by our friend 
Mr. Goadby, cannot fail to excite the delight 
and admiration of every friend to the advance- 
ment of Physiology. One is not less asto- 
nished at his remarkable power of manipu- 
lation, as displayed in the dissection of the 
soft and fragile nerves of these delicate animals, 
than at the great ingenuity with which he has 
displayed and perpetuated these witnesses to 
his anatomical skill. We hope, for the sake of 
science, that, under the liberal patronage of 
the College Council, Mr. Goadby will be able 
to form a large collection of dissections of the 
Invertebrate Nervous System; and sure we 
are, that in nothing can the Council contribute 
more to promote the designs of John Hunter 
than in making his Museum the depository of 
such a series by such an artist. 
3. Gasteropoda.—{In this order of Mollusks 
the locomotive function is freely enjoyed, and 
is effected in many of the genera.by a powerful 
muscular organ, which generally acts as a 
Sucker and enables the animal to adhere forci- 
bly to the surface and draw itself on in a 
crawling manner—the well known mode of 
progression of the common snail and slug. In 
_ other genera the foot is modified according to 
the objects to which the animals adhere, or loco- 
_ Motion is performed by portions of the mantle 
_ adapted to act as oars or fins in swimming. 
- The respiratory function, whether adapted to 
an aquatic or a terrestrial mode of existence, 
‘is much more highly developed in these animals 
than in the Sieeceding order. Their digestive 
System, too, is more perfect, the accessory 
organs being more fully developed. We per- 
ceive, too, the unequivocal existence of a 
visual organ. There are also special organs 
(tentacles) for the exercise of the sense of 
touch, and it has been supposed that the power 
of smell and that of hearing existed, although 
the respective seats of these senses cannot be 
determined. 
It is well known that if the surface of a 
Snail or slug be touche ever so slightly, a con- 
traction of the part so stimulated will imme- 
diately take place. This is probably due to 
the inherent irritability of the subdermic mus- 
cular layers, or it may result from the 
reflexion of the impression upon the motor 
organs from some nervous centre with which 
the nerves of the skin are in connexion. It 
Seems very unlikely that we can refer it to a 
Sensibility of the surface, for the observations 
of Ferussac clearly imply that the terrestrial 
Gasteropods present no signs of pain when 
injured or wounded. We cannot, therefore, 
agree with Professor R. Jones in assigning 
tactile sensibility to the general cutaneous sur- 
face of these animals, nor do we think it neces- 
Sary to regard the phenomenon in question (as 
Dr. Carpenter suggests) as an example of 
motion excited by a reflected impression, which 
1s not accompanied with sensation; but rather 
as an instance of muscular contraction, pro- 
duced by the immediate influence of the stimu- 
lus on the irritable fibre. 
605 
Now this more active exercise of certain 
functions necessarily implies a greater develop- 
ment of the nervous system; but the same 
general plan as that described in the Conchifers 
prevails. The principal part of the nervous 
apparatus is connected with the csophagus, 
and has communications with the other ganglia. 
There is also a centre of locomotion, and a 
respiratory centre.* 
The cesophageal nervous centre is developed 
either as two small ganglia, situate on either 
side of the «esophagus, or as a single large 
ganglion placed on the median line and above 
the esophagus ; or, lastly, a single ganglion is 
formed beneath the esophagus. In each of 
these varieties the common type of a nervous 
ring or collar around the esophagus is pre- 
served, however the situation of the cephalic 
centre or the number of its ganglia may differ. 
The centre of locomotion consists of two 
ganglia, from which nerves proceed to the foot 
and to the mouth; which latter, however, is 
sometimes supplied from distinct ganglia. These 
ganglia are connected to each other by com- 
missural nerves and also to the cephalic centre, 
The respiratory apparatus and the viscera 
receive nerves from a proper centre, which 
sometimes is formed by one ganglion, some- 
times by two separate ones, which, however, 
have a connexion with the cephalic ganglia. 
The branchial and the pedal ganglia are some- 
times conjoined, and in some genera there is a 
still further concentration, so as to form a com- 
mon centre from which nerves are distributed 
to all the organs. 
The following examples will serve to illus- 
trate the principal points in the nervous system 
of these animals :— 
In Patella (limpet) there are two ganglia 
situate on either side of the esophagus (A, fig. 
339). From these ganglia the tentacles and 
A, cerebral ganglia. B, 
pedal ganglion. C, bran- 
chial ganglion. a, fila- 
ment of communication 
from cerebral to bran- 
chial ganglion. 4, fila- 
ment of communication 
from cerebral to pedal 
ganglion. E, labial gan- 
glia. D, connecting band 
liq between labial ganglia. 
Nervous system of Pate 
vulgaris ( Limpet). 
eyes are supplied with nerves, and they are 
connected to each other by a simple nervous 
band which passes above the esophagus. From 
the posterior part of each ganglion two nerves 
pass back : the outer one terminates in the bran- 
chial ganglion, and theinneronein the pedal. The 
apparatus for mastication in this animal being 
complicated, it is supplied from a transverse 
band or two ganglia, situated beneath the 
cesophagus, and connected with the anterior or 
cerebral ganglia. This band is connected with 
two ganglia that supply the lips, called labial 
* See article GASTEROPODA, p. 394, vol. ii., 
and Dr. Carpenter’s Lectures on the Nervous Sys- 
tem, Lond. Med. Gazette for 1841. 
