MOLLUSCA. 
Mollusca. variously folded, and are several times longer than the body. 
~~ The salivary glands are minute. 
The liver is intimately 
united with the stomach and intestines. The heart is situ- 
ate on the left side, in the anterior part of the body. The 
auricle receives the aérated blood from one vein when the 
circle of the gills is complete, and by two when interrupted. 
This auricle is placed on the anterior side of the heart. An 
aorta arises from each side, to convey the blood to the body. 
The ovarium is placed underneath the liver ; and, as it ex- 
hibits some differences of organization, M. Cuvier infers 
that it likewise contains the male organs. The species be- 
longing to this genus are numerous, “and appear to admit of 
distribution ante sections; the first having the branchial 
circle complete, the second interrupted. 
cated dorsal plates. The body is elipical The cloak 
is firm and cartilaginous, and variously marked on the mar- 
gin. The dorsal plates are arched, and occupy the middle 
and sides of the back, where they are implanted in the 
cloak, in an imbricated manner, the posterior margin of the 
first valve covering the anterior margin of the second. The 
foot is narrow. The mouth is surrounded with a semicir- 
cular curled membrane, and is destitute of tentacula. The 
anus consists of a short tube, placed at the posterior ex- 
tremity of the cloak. The external orifice of generation 
has not been detected. 
The mouth is capable of forming a short proboscis. The 
tongue is short, and armed with strong, reflected spines. 
The gullet is short, and the stomach, which is lengthened 
and folded, is membranaceous. ‘The intestine is several 
times longer than the body, and much folded. The liver 
is aevideds into numerous lobes, and intimately united with 
the stomach and intestines. The heart is situate at the pos- 
terior part of the body. The auricle is placed posteriorly, 
and receives the aérated blood from two veins. Each vein 
descends along the base of the gills, collecting the aérated 
blood from the particular side of the body to which it be- 
longs ; and,’ what is most remarkable, when opposite the 
ventricle, it is suddenly enlarged, and sends off a branch 
which communicates with it, and again contracts and unites 
with its fellow from the opposite side, to form the auricle. 
A single aorta arises from the anterior side. The ovarium 
is conical, and divided into numerous lobes.- Behind, two 
ducts seem to arise, and to proceed one to each side; but 
it has not been determined whether they open externally. 
No male organs have been detected ; nor is there any thing 
accurately known with regard to the peculiar nature of their 
hermaphroditism. 
Genus Puyrimr1a— Anus placed dorsally near the ex- 
tremity of the cloak. The body, in the animals of this 
genus, is ovate. The foot is narrow in front. The cloak 
is broad, coriaceous, and destitute of a shell. Towards its 
anterior extremity are two cavities, from which issue the 
retractile superior tentacula, as in the genus Doris. Nearly 
at the posterior extremity is another cavity, containing the 
anus. ‘This opening, though similar in situation to that of 
the Doris, is mer ely a short simple tube. The head is im- 
mediately above the anterior margin of the foot, above which 
is the mouth, having a small conical feeler on each side. 
Under the margin of the cloak on the right side, and about 
half way between the mouth and the middle of the body, 
are two openings, in a tubercle, for the organs of genera- 
tion. The branchize consist of slender complicated . leaves, 
which surround the body between the foot and the cloak. 
The circle is interrupted at the head and at the tubercle of 
generation. The mouth is destitute of jaws. The gullet is 
simple, ending ina membranaceous stomach. The ‘pylorus 
is placed near r the cardia, and the intestine goes directly to 
the anus. The salivary glands are small, and placed near 
the mouth. ‘The liver is large in proportion. The heart is 
situate in the middle of the back. The auricle is simple, 
VOL. KY. 
361 
placed on the side next the tail, and supplied by the two Mollusca. 
systemic veins which collect the aérated blood from the == 
branchiz on each side. There isa simple aorta arising from 
the opposite side of the heart. The organs of generation 
appear to be similar to those of the preceding class; but 
they have not as yet been minutely examined. The exist- 
ence of eyes is not satisfactorily determined. The animals 
of this genus appear to be inhabitants of the tropical seas. 
Cuvier has given descriptions and figures of three species, 
which differ remarkably from one another in the protuber- 
ances of the cloak. 
Genus Apiysra.—Branchiz with a corneous lid. The 
body of the Aplysia is ovate, acuminated behind, and pro- 
duced before to form a neck. The foot is narrower than 
the body. In the middle of the back is a corneous plate 
inclosed in a bag in the skin, and on each side, and be- 
hind, there is a fold by which this part may be concealed. 
The head is slightly emarginate, with a feeler on each side. 
The superior feelers are situate on the neck. In front of 
each of these is a small black point or eye. The branchize 
are situate underneath the dorsal plate, on the right side, 
and exhibit a complicated plumose ridge, capable of expan- 
sion beyond the edge of the plate. The anus is situate im- 
mediately behind the.branchize, and before these is the ori- 
fice of generation, from which proceeds a groove along the 
neck to the inferior base of the fore feeler, on the right side, 
where there is an opening for the penis. Within the longi- 
tudinal lips there are two smooth, corneous plates, the sub- 
stitutes for jaws; the tongue is rough, as in. many of the 
other gasteropoda. The gullet is short, and suddenly ex- 
pands into a large subspiral crop, with membranaceous walls. 
To this, a gizzard with muscular walls succeeds, the interior 
of which is armed with numerous pyramidal teeth, with ir- 
regular summits, of a cartilaginous nature. The connection 
beta, een these teeth and the integuments is so slender, that 
they are displaced by the application of the smallest force. 
They, however, project so far into the cavity, as to offer re- 
sistance to the progress of the food. There is yet another 
stomach, armed on the one side with deflected, pointed, car- 
tilaginous teeth. At the pyloric extremity are two mem- 
branaceous ridges, between which are biliary orifices, and 
the opening into a long narrow ccecum, with simple walls, 
which is contained within the liver. The intestine is sim- 
ple, and after two turns ends in a rectum. The salivary 
glands are very long, and, as usual, empty their contents 
into the pharynx. The liver is divided into three portions 
by the folds of the intestine, each of which consists of seve- 
ral lobes. The biliary vessels are very large, and open at 
the mouth of the ccecum into the last stomach. The food 
of the Aplysia consists of sea-weeds and minute shells. 
The circulating organs are remarkable. On each side 
the body, in the region of the dorsal plate, there is a large 
vessel, which receives blood from different parts of the body, 
and which likewise, by various openings, has a free com- 
munication with the cavity of theabdomen. In this respect 
there is a resemblance to the spongy, glandular bodies of 
the venze cavee of the Cephalopoda. These two vessels, or 
vene cave, unite posteriorly, and transmit their contents to 
the gills. The aérated blood is now conveyed to an auricle, 
of large dimensions, and uncommonly thin walls, situate be- 
neath and towards the front of the dorsal plate, and empty- 
ing its contents through a valve, into the right side of the 
ventricle. The aorta, which issues from the left and an- 
terior side, divides into two branches, the smallest of which 
proceeds to the liver on the left. The larger branch is again 
divided, the smaller branch proceeding to the stomach. ‘The 
largest trunk that remains, before it leaves the pericardium, 
has two singular bodies attached to it, consisting of com- 
paratively large vessels, opening from this aortic branch. 
The use of these glands is unknown. The organs of gener- 
ation likewise exhibit some remarkable peculiarities. The 
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