360 
MOLLUSCA. 
Mollusca. rise to numerous biliary ducts, which proceed to the sto- 
—\~" mach. But it likewise gives rise to a duct which proceeds 
to a small bag plaited on the inside, and afterwards opens 
on the surface at a small hole near the anus. It yet remains 
to be determined, whether the fluid carried off by this con- 
duit be excrementitious matter, separated by the liver, or 
whether the gland which produces it be distinct from that 
organ, but so interwoven therewith as to elude the obser- 
vation of the anatomist. 
It is obvious, from the structure of the digestive organs, 
that the species subsist on soft food, requiring neither cut- 
ting nor grinding, and in this respect, differ remarkably 
from the species of the genus Tritonia, which were formerly 
arranged along with them. 
The organs of generation differ little from the other her- 
maphrodite gasteropoda. The vesicle furnishes two canals, 
one of which goes to the testicle, the other to the penis. 
There is likewise a minute bag connected with the canal of 
the latter. The spawn is deposited on sea-weeds and stones. 
It is gelatinous, of a white colour, and in appearance resem- 
bles the sponge denominated Grantia compressa. 
Genus Trrronta.—Branchie destitute of basilar sheaths. 
The branchiz are in the form of plumes, or imbricated pro- 
ductions, placed in a row on each side the back. The ten- 
tacula, which are partially retractile, have a sheath at the 
base. In some of the species there are indications of eyes. 
The mouth consists of two lips, which are placed longitudi- 
nally, and open into a short canal. The jaws consist of two 
corneous plates, united at the upper dorsal edge, slightly 
arched, and meeting at their upper margin, for the purpose 
of cutting. Within these is the tongue, which differs re- 
markably from the same member in the doris. In the lat- 
ter, the spines with which it is beset are reflected, and draw 
the food to the gullet, while in the former, the spines are 
deflected, and serve to keep the food within the reach of 
the jaws. The tongue of the doris, therefore, serves for 
deglutition, that of the tritonia for mastication. M. Cuvier 
describes the functions of both as similar. The salivary 
glands are placed on each side the gullet, and empty their 
contents behind the jaws. The gullet has a few longitudi- 
nal folds; the stomach is simple, scarcely diifering from the 
gullet ; and the intestine proceeds almost directly to the 
anus, situate on the right side. The liver is small, and situ- 
ate behind, enveloping the stomach, and intimately united 
with the ovarium. The organs of generation exhibit no- 
thing remarkable. The pedunculated vesicle has a simple 
canal. The external opening of the organs of generation 
is situate a little before and beneath the anus. The 7. 
Hombergii arborescens, pinnatifida, and bifida, are exam- 
ples of British species. 
~ Genus ScyLtiEa.—Branchie seated dorsally on the fins. 
Tentacula two. On each side of the back are two mem- 
branaceous expansions, and one on the tail, supporting on 
their dorsal surface scattered plumose branchia. Each of 
the tentacula is furnished with a large funnel-shaped sheath. 
The foot is very narrow, with a mesial groove, used in 
climbing up the stalks of sea-weeds. The mouth is placed 
at the base of the tentacula, and surrounded with a semi- 
circular lip. The tongue is in the form of a tubercle, with 
reflected points. The gullet is plaited longitudinally. The 
stomach is short and cylindrical, with a ring of hard, longi- 
tudinal scales. The liver consists of six unequal globules, 
and the bile is poured into the cardiac extremity of the gul- 
let. The Seyllea pelagica has been long known to naturalists, 
and appears to be very common in the equatorial seas, ad- 
hering to the stems of the Fucus natans. 
Genus Tuetnys.—Branchie forming a row on each side 
of the back, consisting of fringed processes, alternately larg- 
er and smaller. The body is ovate, with the cloak and foot 
continuous. The neck is distinct from the foot, and is nar- 
row. Above, the neck is continuous with the cloak, from 
which arises a large semicircular expansion, used probably Mollusea. 
asa fin. The margin of this expansion is fringed with nu- 
merous filaments, and on the upper surface, within the 
border, is a row of conical tubercles. The true tentacula 
are placed towards the base of this fin near the neck. Each 
of them consists of a small fleshy cone, striated across, with 
a semicircular sheath behind. The branchiz consist of a 
tapering, fleshy stalk, spirally twisted towards the summit 
with a series of filaments on one side. They are fourteen in 
number on each side,alternately and oppositely small and large. 
The anus opens in front of the third branchia on the right 
side. The orifice of generation is exhibited under the first 
branchia of the same side. In front of each of the larger 
branchiee, is a small cavity with a small filament in the cen- 
tre. The mouth is situate underneath the tentacula. It 
consists of a large funnel, covered within with soft papille, 
destitute of jaws or tongue. The gullet is short, the sto- 
mach simple, fleshy, and covered with a thick cuticle. The 
salivary glands are slender and branched, and open into the 
gullet. The intestine is likewise short, and proceeds di- 
rectly to the anus. The liver pours the bile into the canal 
at the pylorus; and likewise sends out another duct, which 
opens externally near the anus. The organs of generation 
are similar to the Doris. The 7. fimbria is the type of the 
genus, a figure of which, with its anatomical details, is given 
by M. Cuvier, in his Mémoire sur le Genre Thetys. 
Genus Vatvata.—In this genus are included several 
species which resemble in aspect the aquatic pulmoniferous 
gasteropoda. The branchize appear in the form of a fea- 
ther, with a central stem, and a row of compound branches 
on each side, decreasing in size from the base to the free 
extremity. This stem issues from the neck near the middle, 
ashort way behind the anterior tentacula. Near this plume, 
but towards the right side, is a single simple filament, like 
atentaculum. The antertior tentacula occupy the usual 
position, are setaceous, and have the eyes placed at the base 
behind. The spiral shell is capable of containing the body, 
and the aperture can be closed by a spirally striated oper- 
culum attached to the foot. The internal structure is un- 
known. 
Genus PatTELLA.—Shell entire. Mouth with tentacula. 
This genus differs from the others of the order to which it 
belongs. The back is covered by a conical shell, within 
the cavity. of which the animal is capable of withdrawing 
itself! The cloak is large, covering both the head and foot. 
It is united with the shell along its superior margin. The 
foot is fleshy, and furnished with numerous muscular fila- 
ments, which unite, in the superior part of the cloak, to 
form a strong muscle, by which the body adheres to the 
shell. The action of this muscle brings the shell close te 
the surface to which the foot adheres, or removes it to a 
distance. The head is furnished with a large, fleshy snout, 
supporting at the base two pointed tentacula. The eyes 
are placed on a small elevation at the external base of the 
tentacula. A little way behind the head, and below the 
cloak, on the right side, are two apertures, being the anus 
and orifice of generation. The gills occupy the same po- 
sition as in the preceding genera. In some, the branchize 
form a complete circle; in others, the circle is interrupted 
anteriorly at the head. 
Within the trunk, the mouth is fortified by two cartila- 
ginous cheeks, which, at their union anteriorly, support the 
base of the tongue. This last is a most singular organ. It 
is longer than the whole body, narrow, and covered with 
three rows of short reflected spines, interrupted longitudin- 
ally and transversely. Its fixed end only can be exercised 
in deglutition, its free end being coiled up the abdomen. 
On the upper side of the mouth is a semicircular osseous 
plate, or upper jaw. The gullet is furnished with a dilat- 
able pharynx. The stomach is elliptical, with the cardia 
and pylorus at opposite extremities. The intestines are 
