SCYLLiEA.
into another. Here, however, the typical character of the Tritoniadce is. still sufficiently
preserved to allow of our retaining the genus in that family. This is the only nudibranchiate
mollusk in which any armature of the stomach, performing the functions of a gizzard, has been
detected.
The body of Scyllcea is elongated, very much compressed at the sides, and gibbous upon the
back, sloping down to the aiiterior and posterior extremities. It has* two tentacles;, which are
dorsal, but placed forwards nearly above the head. They are rather small, clavate, and
laminated, and areTetractile within large sheaths; these are wide near the top, tapering to a
narrow base, and are stated to be very contractile: the orifice inclines forwards, and there is
a thin, arched, crest-like appendage behind it. The head is sub-inferior ; the mouth fleshy,
. without oral tentacles, and covered by a slight velar expansion of the frontal margin. The
jaws are corneous. On each side of the back arise two or three erect flattened lobes of
irregular form. On the inside of these, as well as on the median portion of the back, are
placed the branchiae, which consist of small tufts of delicately branched filaments, disposed in
an irregular manner. The foot is linear and very narrow, with the sides thin and flexible,
formed for clasping the stems of sea-weeds. The anus is situated on the right side between
the first and second dorsal lobe, and nearly equally distant from the two extremities of the
body. The orifice of the generative organs is placed lower down and more forward on the
same side, being only a short distance behind the right tentacle.
On opening the animal from above, the buccal mass is seen to occupy the anterior
.extremity of the body. This organ is rather larger than usual, and is of an oblong ovate form,
. narrowest in front. It is furnished with horny, cutting jaws, resembling those of Uolis. The
tongue, however, is formed after the type of Tritonia : its anterior portion is convex, and
assumes a sub-conical form, with the apex turned upwards and forwards; posteriorly, it
becomes concave, the concavity being directed towards the oesophagus, and having the
appearance of a cylinder, capable of being turned inside out. The whole of this organ is
covered with denticulated spines, rising over the projecting part, and entering into the cavity:
they form about thirteen transverse rows, divided by a narrow groove down the centre, on
which, in each row, is a broad plate containing a central tooth, with three or four denticulations
on each side. The points of the spines are directed backwards and inwards, so that when the
tongue is advanced, and the margins of the concavity separated, it will become a powerful
prehensible apparatus, at once able to rasp down the food and carry it to the oesophagus.
The oesophagus is long and rather wide, and shortly after leaving the buccal mass, is
surrounded, for some little distance by a glandular layer of follicular organization, probably
salivary in its function: it then continues its course backwards, and, after dipping downwards,
bends upwards and empties itself into the posterior part of a small globular stomach, with the
ends somewhat flattened, situated on the left side of the body. The interior of this stomach
is lined with a broad transverse belt of dark, horny, lancet-formed plates, having their edges
and points sharp, and directed towards the centre of the cavity, which they almost fill. This
peculiar dental armature is well adapted to cut in pieces alimentary matters.
A wide intestinal tube is given off from this organ, opposite to the entrance to the
oesophagus, which tube, running forwards a short way, arches across to the right side of the
body, immediately in front of the h ea rt; it then passes backwards in contact with the skin,
and terminates at the constricted anal orifice a little in advance of the second branchial lobe.
SCYLLiEA.
The intestine is somewhat longer and wider than the oesophagus, and is not much less in
diameter than the stomach.
The liver holds the same central position as in Doris and Tritonia, and consists of six
or seven globular balls, seated on the ducts that empty themselves by three very large orifices
into the stomach just at the termination of the oesophagus. These glandular balls are made
up of convoluted tubes, regularly arranged in two concentric layers: the outer one has the
tubes small, frequently folded upon themselves, and placed in a radiating manner. The inner
layer, which is twice as thick as the outer one, has a like arrangement of the tubes, but they
are not so often folded upon themselves, and are much stouter; they are joined at the outer
extremities with the tubes of the external layer, and, uniting in pairs at their inner terminations,
give off fine transparent ducts, which, passing towards the centre of the ball, unite to
form a large central channel, which leads out of the gland and joins one of the ducts above
mentioned as emptying themselves into the stomach. Upon the peripheries of these balls,
several small tubes ramify in various directions: they appear to come from the convoluted
tubes of the gland, and, uniting, go to form a set of canals which lie loosely among the viscera,
and between the viscera and the skin ; and ramifying over the latter, the principal of them
pass into the dorsal lobes, and penetrate the branchial tufts. Six or seven minute branches
belonging to the same set of canals, are attached nearly, in a straight line along the anterior
border of the intestine, just below the stomach, and apparently enter that tube. All these
tubes and canals are opake, and of a yellowish colour like the gland itself; and when examined
with the microscope, are found to contain the same glandular substance.
The circulatory system is provided with a strong muscular ventricle, placed a little in
advance of the middle of the body, immediately below the dorsal skin. The auricle is united
to its posterior extremity, and, as in Tritonia Hombergii, is a broad transverse belt receiving
branches on each side from the skin. The aorta, as usual, passes from the anterior apex of
the ventricle, and divides into arteries for the supply of the viscera.
The nervous system is disposed much in the usual manner. The two central oesophageal
ganglia are large, elliptical, and slightly constricted in the middle; the lateral ganglia are
much smaller than the central ones, and are nearly circular. The eyes are placed near to
the junction of the central with the lateral ganglia.
The generative organs resemble those of Uolis. The ovary, however, is described by
Cuvier to resemble one of the liver masses, and to be placed with them in the abdominal,
cavity towards the right side. This we failed to detect in the specimen on which our observations
were made, as well as the several accessory parts.
EXPLANATION OF THE PLATES.
Fig. 1. General view of the viscera of Scylltea pelagica:—a, buccal mass; b, oesophagus; c, folliculated
gland surrounding the oesophagus, supposed salivary; d, stomach; e, intestine; f anal
nipple; g, g, g, liver masses; h, h> h, h, h, branches and tubes passing from the liver masses
to the skin and branchial tufts; i, ventricle of the heart j j , auricle; k, cerebral ganglia,
with nerves passing from the same; l, l, l, t, dorsal lobes, exhibiting branchial tufts; m,
retracted penis; n, convolutions of the testicle.
2. Side view of the buccal mass :•—a, channel of the mouth ; b, a portion of the corneous jaw,
uncovered by the muscle; c, oesophagus; d} follicular gland surrounding the oesophagus.