common hepatic trunk-vein, lodged in a median depression on the upper surface of the mass.
This trunk opens into an internal or venous branchial circle, closely surrounding the anus.
The blood thence, traverses the branchial leaflets, and falls into a second or external circular
canal at the base of the branchial crown ; from the anterior limb of this outer circle, a short
wide trunk (m), the true brancho-cardiac vein opens forward on the median line into the
posterior border of the auricle of the heart. Here the blood from the liver-mass, having been
fully aerated in the special respiratory organ, becomes mixed up with that from the other
viscera, which has been partially aerated on its return through the skin to the hea rt; the
whole surface of the cloak of Doris being covered with vibratile cilia, as well as the branchiae.
The surface of the crawling disc is likewise covered with these minute organs.
The additional propelling organ, situated, as before mentioned, underneath the pericardium,
is the organ which Cuvier calls “ a vesicle acting as reservoir to a canal, which,
coming backwards from the liver, opens at the external orifice placed close to the anus.”
This vesicle or heart (fig. 13 o) is pyriform, and has the interior plicated in a manner to
prevent the return of fluid that has once passed through the orifice (q), which is also capable
of being contracted like the mouth of a purse. The base or broad end opens into the
pericardium, the narrow end tapers to a tube (r), which, after perforating the wall of the
large sinus, to be presently described, turns suddenly forwards along the median fissure of
the liver, and, branching, goes to inosculate with a minute network formed by twigs of the
hepatic arteries. Venous blood from the general visceral cavity, finds its way by minute
orifices in the floor of the pericardium into the interior of that cavity, and is thence drawn
into the Cuvierian vesicle or heart, and then propelled by it along its tubes and branches,
which are arterial in disposition, into the network just described. This apparatus, then, has
a decidedly portal character. The blood traversing this network is conveyed through the
liver into the hepatic trunk-vein.
I t is evident from the above description, that the systemic circulation is divided into two
portions; one general, the other partial \ the latter being combined with a portal circulation.
I t is only from this hepatic course, in which the blood is more completely deteriorated, that it
is sent to the branchiae.
The small orifice (PI. 2, fig. 1 r, and PI. 1, fig. 13/) near the anus has no communication,
as Cuvier thought it had, with this vesicle or portal heart, but leads at once into an extensive
more or less ramified cavity or sinus (PI. 1, fig. 13 k, Jc), the trunk of which extends forwards
along the median fissure of the liver. This cavity is circumscribed by a delicate membrane,
which is found beneath the pericardium ; it has the aorta (n) running along its roof, and the
great hepatic vein along its floor, which is intimately adherent to, and undistinguishable from,
the capsule of the liver-mass.
In the wall of the cavity lies the network from the two sources already named; the
inner surface of the whole of this membrane is covered with a fine spongy-looking, glandular
tissue, which is most abundant over the tracts of the vessels. It is pretty evident that this
is an apparatus for the elaboration of some fluid from the blood, and as the sinus opens
externally by a small orifice close to the anus, it may be inferred that it is for excretion, and
is probably a renal organ.
The fine network of veins in the walls of the renal cavity varies in different species. It
is most developed in D. bilamellata (fig. 13), from which the above description is chiefly taken:
in D. repanda and D.pilosa (fig. Ip , p), it is also very extensive; but in D. tuberculata (PI. 2,
fig. 1 q, q) the arrangement of these vessels is probably much simpler, little more than the
main trunks being visible. The cavity, too, in this species is more branched than usual.
The nervous system of Doris comprises two portions:—a cephalic or cerebral, and a
sympathetic or organic. The cephalic, in D. tuberculata, is of an orange colour, and is made
up of two series of ganglia, supra- and infra-oesophageal, with their commissures and
numerous nerves. The supra-cesophageal ganglia are five pairs, and a single ganglion; the
pairs being symmetrically placed with regard to the median line. Three pairs predominate
in size. The anterior or sensorial (PI. 2, fig. 13«, a), the cerebroid of M. Blanchard, lie next
the median line, across which they are connected; they are pyriform, with the broad end
forward. Springing from about the middle of the anterior border, and from the upper surface
of these, is a pair of ganglia (d, d), corresponding to the pedunculated pair of Bolts,—the
olfactory. In Doris they are nearly sessile; and though in size much inferior to the cerebroid,
are nevertheless of notable dimensions. They give off each a large nerve to supply the dorsal
tentacles, which constitute the first pair. The next three pairs come off from the under
surface of the anterior border of the cerebroid ganglia, external to the attachment of the first
pair; the second and fourth run forward and supply the muscles and skin at the side of the
channel of the mouth and the lips. The third passes to the oral tentacles. The fifth pair comes
off close to the fourth, and soon divides into two branches; one goes on to the under part of
the channel of the mouth and lip, thé other courses round under the buccal mass, and unites
with the corresponding nerve of the opposite side to form the anterior collar (g), which is
slender and wide. External and close to the fifth pair, comes off on each side a nervous
trunk, which, curving under the oesophagus, joins the principal infra-oesophageal ganglia.
This trunk constitutes the second collar (/t). The nerves of the sixth pair are generally very
short, and come off from two minute elliptical ganglia, almost sessile, upon the external border
of the cerebroid ganglia; these are the optic nerves and ganglia. The seventh pair of nerves
appear to have no trunks, for the auditory capsules are sessile upon the same ganglia
immediately behind the eyes.
The posterior or branchial ganglia (b, b) are, when distinct, broadly ovate, and connected
with both the cerebroid and pedial ganglia. The eighth, ninth, and tenth pairs of nerves
belong to the branchial ganglia, and are distributed to the whole of the mantle; the tenth
sending a branch of communication to the branchial ganglia of the sympathetic system.
The lateral or pedial ganglia (c, c) lie on a plane beneath the others, with both of which
they are connected; and are generally in shape and size like the branchial. Three large
nerves, the eleventh, twelfth, and thirteenth pairs, pass off from these centres, and are for the
supply of the whole foot. Two small ones, the fourteenth and fifteenth pairs, appear to emerge
also from the same, and go to the sides of the body, between the mantle and foot.
The single supra-oesophageal ganglion, which we propose to term visceral, on account of
its nerves being in connexion with the ganglia of the viscera, is round, scarcely so large as
the olfactory, and sessile on the under surface and anterior border of the right branchial
ganglion, where it is in contact with the pedial. Four nerves (y, k, l, m) issue from this
ganglion; these go to the organs of reproduction, to the stomach, to the two hearts, and to
the branchiae, and can be traced, as has been just pointed out, into ganglia of the sympathetic
system belonging to these several organs. The only other nervous trunk in connexion with