towards the right side in front of the heart: it then dips down and terminates in an anal
nipple situated about midway along the side immediately below the mantle. The alimentary
tube is longitudinally plicated throughout; , in the stomach the plicse are strong and much
wrinkled.
The liver (ƒ) is a large pyriform body with the obtuse end forward and hollowed for the
reception of the posterior portion of the stomach. The left side is much prolonged, forming
a lobe which advances a considerable way forward. The colour is a yellowish rose, caused
chiefly perhaps by the ovary which envelopes the organ. The hepatic fluid enters the
posterior end of the stomach by a single large duct.
The alimentary system varies only a little in T. plebeia, in which the oesophagus is dilated
into an anterior stomach or crop; and the stomach itself is almost concealed by the liver, the
anterior lobe of which is large and passes quite in front of it. The gastric organ has therefore
the appearance of lying in a transverse cleft.
The reproductive organs seem to be arranged more on the plan of Eolis than of Doris.
They are composed of the usual three parts,—male, female and androgynous, which open into
a common vestibule having a single outlet on the right side of the body, about half way
between the head and the anal nipple. The intromittent organ (fig. 2k), which is situated in
front of the other parts, is long and tapering; and the testis (/), a convoluted tube of no great
length, is connected with it by one extremity and by the other to the oviduct. The ovary is
firmly attached to the liver over which it is spread. The oviduct, at first very delicate (n),
dilates and forms a widish tube (m), a little convoluted. Before reaching the testis it
contracts to its former diameter, and after its junction with that organ, it suddenly turns upon
itself and sinks into the mucus-gland (0, 0). This latter organ, like that of Eolis, is very bulky,
and is formed of two lateral masses made up of convoluted tubes, which open into the female
channel (p ). The androgynous apparatus is very simple, being composed of a mere elongated,
pyriform sac, or spermatheca (q) terminating a rather short vaginal tube (r). This tube
opens as usual into the common Vestibule above and between , the male and female orifices.
There is here no accessory spermatheca nor special duct leading from the androgynous parts
to the oviduct as in Doris. The seminal fluid hoarded in the spermatheca must, therefore,
pass again down the vaginal tube, and fertilise the ova as they pass out; or it must find its
way by the same tube into the female organs; in which case it will penetrate the oviduct and
perhaps reach even as far as the ovary.
The generative organs are a little modified in T. plebeia, in which the testis is composed
of two portions; one thin and tubular, the other a little enlarged and fusiform. From the
inner extremity of this latter portion, a constricted duct leads to the oviduct, the dilated part
of which is very wide and doubled upon itself. The spermatheca is large and oval; the
vaginal tube short and distinct.
The organs of circulation differ in some respects from those of other Nudibranchs. The
heart as usual lies immediately below the dorsal skin, about half way down the body, and is
enclosed within a delicate, transparent pericardium, which extends the whole width of the
back (fig. l,y). The ventricle (k) is strong and muscular, with the sides much produced,
giving it externally very much the appearance of being composed of two chambers. The
aorta passes from the frontal apex, and gives branches to the various organs. The auricle {l)
is comparatively delicate; it is narrow, transversely elongated, reaching from side to side of
the pericardium, and has the anterior margin produced into a lobe at each side; it lies,
immediately behind the ventricle, and receives at each end a trunk vein {rn, m) from the skin.
These trunk veins bifurcate within the skin, one branch (n). passing forward, the other (ri)
backward close to the margin of the mantle, and drain the blood from the sinuses or cellular
tissue of the skin, and from the gills; consequently returning to the heart a stream of
imperfectly aerated blood. These trunks are therefore efferent branchial veins.
The systemic circulation is two-fold as in Doris,—general and partial. By the former
all the blood sent to the various organs, except that which is distributed to the liver mass
(comprising liver, ovary, and renal organ) must as usual reach the system of inter-visceral
sinuses, and so find its way into the cellular tissue of the skin, and from thence to the heart by
the lateral or efferent branchial veins just mentioned. By the partial or hepatic circulation,
which is probably supplied with a complete set of capillaries, the blood which is transmitted
to the liver mass, and that only, is conveyed to the branchim by six trunk veins (0 , 0, 0 ); three
passing from each side of the organ. These trunks are formed by the convergence of
numerous branches on the surface of the liver, and each on reaching the skin is divided into
two portions (p,p), one of which passes forward, the other backward: these run along within
the skin, immediately below the efferent branchial veins, and give branches to the branchial
plumes. It would seem, then, that the branchial circulation is probably as complete as in
Doris, the blood being conveyed to and from the gills by a system of afferent and efferent
vessels; but the latter, we have seen, are not distinct, for they carry to the heart also the
blood from the skin, which here, as well as in the Dorididce and Eolididce, undoubtedly assists
in aerating the blood.
The hepatic circulation has in connexion with it a portal circulation, evinced by the
presence of a portal heart (q), which lies as .usual below the pericardium, a little to the right,
and is related to it as in Doris. This heart is very large, being not much inferior in size to
the systemic ventricle ; it is of a cylindrical form, with the ends truncated, and the interior is
strongly plicated longitudinally as in Doris.
The renal organ has not been examined, but its presence is proved by the renal orifice,
which is situated close above the anal nipple. It is apparently connected with the liver as
the great vessel from the portal heart enters that viscus.
The cerebral ganglia resemble those of Eolis. The oesophageal are all placed above the
alimentary tube; of these there are apparently at first sight only two principal pairs,—the
cerebroid (fig. 9 a, a) and branchial (b,b) being fused so as to form two elongated masses, one
on each side the median line, across which they are united by a short commissure. The
component parts are, however, distinctly defined by a constriction near the centre of the
masses. The olfactory nerves are given off from the upper surface of the anterior portion or
cerebroid ganglia. They (1) are long, and, on reaching the dorsal tentacles, each swells out
into a rather large roundish ganglion,—the olfactory (d), from the upper aspect of which,
numerous filaments pass up the tentacle. A small twig from each of these nerves apparently
goes to the veil next the median line. Three pairs of large nerves (2 ,3 ,4 ) go from the
anterior margin of the same ganglia and supply the vdil; one of these (2) sends a large branch
to the channel of the mouth; and another (4) gives a twig to the tentacular point below the
veil. Two pairs of small nerves (5, 6) are given off apparently from the commissure, uniting
the cerebroid and pedial ganglia; these go to the skin of the sides of the body. The