stomach at the anterior end, and curving upwards, passes obliquely backwards, towards the
right side, and to the nipple-formed anus (e) amidst the branchial plumes.
The alimentary canal of D. pilosa differs considerably from the above. In this species
the (esophagus, at its origin, is dilated, forming a large membranous sac or crop (PI. 1, fig. 12ƒ),
and is again enlarged (g) before it reaches the liver {h): it then passes into that viscus,. and
shortly afterwards receives the biliary secretion by three or four enormous openings («). The
canal, now somewhat increased in diameter, and assuming the characters of a stomach (fig. 1 b,
and fig. 12 j), emerges from the liver at its upper surface, and turning suddenly backwards,
passes in the form of intestine (fig. 1 c) along the right side of the back to the anus, situated
as usual. The stomach is internally minutely plicated, and has a small pancreatic sac (d)
attached to its pyloric extremity.
The form of the alimentary canal in D. pilosa would appear to predominate in the genus.
In D. Johnstoni the type is the same, only the crop at the commencement of the oesophagus is
wanting. So it is with D. bilamellata, the crop being likewise deficient, unless the gizzard
opening into the buccal organ be considered as its homologue; a view which we do not
consider probable. In this species, too, the enlargement of the oesophagus (fig. 13ƒ), previous
to its entering the liver, has the walls of a glandular character. D. repanda, D. cocdnea,
D. aspera, and D. depressa have all the alimentary canal constructed after the same plan. In
most, the inner surface of the stomach, and in all, the intestines, are longitudinally plicated.
The liver is large (PI. 1, fig. 1 e, and fig. 2 d, d), filling the posterior part of the body; it
is pyriform, the broad end, which is usually bilobed, being in front. The ducts from its
different portions converge towards one or more short, very wide trunks in the interior.
These open so immediately and largely into the stomach, that the alimentary matters Cannot
fail of passing freely into them, as is the case in JEolis.
The organs of the reproductive system (PI. 1, fig. 2 e, ƒ, g, h) are remarkable for their
large size, high development, and complicated arrangement, being of the usual hermaphrodite
character of the order. The intromittent organ (PI. 2, fig. 7 6) is of considerable size, and,
in its contracted state, lies in front immediately within the common orifice. The testis (c) is a
long, simple, convoluted tube, with the extremities connected, one with the penis at its base,
and the other with the oviduct at the sudden turn which that tube makes before entering
into the channel of the mucus-gland, not far from the vulva, an arrangement identical with
that of JEolis. The ovarium (d) is spread over the liver, leaving generally a portion of the under
surface uncovered. The oviduct (e, e), passing from the anterior border of the liver-mass,
becomes suddenly dilated (ƒ), and passes sinuously to the front of the mucus-gland, and then
turns abruptly backwards. Here (g) it receives the testis, as before stated, and immediately
afterwards sinks into the mucus-gland, and being joined by the duct (/) from the androgynous
apparatus, debouches into the female channel.
The mucus-gland is a large, irregularly rounded, compressed mass, composed of two
parts; one {h, h) semi-pellucid and colourless, the other (i) opaque and reddish, the latter
being imbedded in the former; both these parts are made up of the folds of a convoluted tube,
which in the opaque portion is very minute. This portion receives the oviduct, and both
parts of the glands communicate with a common channel (j), which is very shorthand leads
to the external ovarian orifice.
There are two spermathecae and two channels; one of these latter leads from the
exterior to the spermathecae, the other from them to the oviduct. The orifice of the vagina
or external channel lies above and between the male and ovarian outlets. The vagina (n)
is large, longitudinally plicated internally, and opens freely into the principal spermatheca (/£)•
This is a large, globular sac of a purple-brown colour, lying between the male and female
parts. Just where the vagina opens into it, the channel (l) leading to the oviduct leaves it.
This channel is soon joined by the minute duct from the accessory spermatheca (m), and then
unites with the oviduct, where it sinks into the mucus-gland.
The reproductive organs are thus arranged in JD. tuberculata; and, notwithstanding
numerous modifications in the various species, the connexions of the parts are the same in all.
In JD. bilamellata, D. pilosa, D. repanda, and D. aspera, the testis diminishes in length, and
increases in thickness. In D. repanda it has appended to it a constricted duct-like tube, that
keeps up its connexion with the intromittent organ. In D. Johnstoni and D. cocdnea the
testis (fig. 8 c) is composed of a large, glandular, fusiform mass, bent upon itself, and made
up of a minutely convoluted tube. One end of this mass is connected to the intromittent
organ (a) by a short duct ($), and the other communicates with the oviduct (ƒ) at the usual
place of its union with the testis.
In addition to this interesting modification of the testis, D. Johnstoni is furnished with a
solid stiletto, contained within a sac (fig. 8 o, and fig. 10«, b) placed in front of the penis;
this stiletto (figs. 9, 10, 11) is capable of being protruded through an orifice (fig. 9 f ) proper
to itself, situated at the extremity of a long penis-like organ id), and the bottom of the sac
receives one end of a slender duct, which comes from a large glandular body (fig. 8 q). The
stiletto is probably an instrument of excitement, like the dart of the common snail.
Spermatozoa (fig. 12) are found in vast abundance in the spermathecae, and in the dilated
portion of the oviduct. In the principal spermatheca they are mostly in a state of development,
contained in large fusiform spermatophora; in thé accessory spermatheca, they are
always mature and arranged in parallel order, but in the dilated portion of the oviduct they
are confusedly crowded together. The head of the spermatozoa is slightly enlarged, fusiform,
and bent considerably to one side; the tail being very delicate, long, linear, and generally
undulated.
The heart lies upon the upper surface of the posterior part of the liver-mass, immediately
below the skin, and just in front of the branchial circle. It consists of an auricle (PI. 1, fig. 2 k)
and a ventricle {j) enclosed within a membranous pericardium (f). In addition to these parts,
there is another propelling organ (n) lying under the pericardium, and opening into it. The
great systemic artery (PI. 2, fig. 1 o) comes from the front or apex of the pyriform muscular
ventricle, and gives off branches to the various organs. The blood so distributed, with the
exception of that sent to the liver-mass ( /) , becomes extravasated among the tissues, and
thus finds its way into the general visceral cavity, and thence by orifices in its walls into the
regular network of sinuses or spongy tissue of the skin. It then passes into a great lateral
trunk-sinus running backwards on each side of the bodjr, and reaches the lateral angles of
the auricle by distinct systemic veins (PI. 1, fig. 2 1, l). This portion of the blood never
reaches the gills; it is only that which goes to supply the liver-mass that passes through the
specialised breathing organ. The blood supplied to this mass, which comprises liver, ovary,
and renal organ, passes into minute venous branches, which converge and unite into a