margin of the rudimentary cloak is more or less dilated, bearing on the margin tubercles,
digitations, or tentacular filaments. A ridge of tubercles, sometimes connected by a slight
membrane, extends along each side of the back, from the margin of the veil to the branchiae,
terminating in one or more simple or lobed branchial appendages on each side. The tentacles,
two in number, are dorsal, placed in the usual position; they are subclavate, laminated
on the upper portion, and non-retractile; without sheaths or basal filaments. The branchiae
are plumose, and surround the vent about two thirds along the back, whence a central ridge
extends to the tail. The foot is nearly linear. The aperture of the generative organs is simple,
and placed on the right side.
The genus may be divided into two sections as follows:—
Section 1. Veil dilated into tentacular filaments; branchial appendages linear, one on
each side.; Type. P. quadrilineata.
Section 2. Veil short, bilobed and tuberculated: branchial appendages tubercular, more
than one on each side. Type. P. Lessonii.
Polycera quadrilineata is generally found on Fuci, P. Lessonii on flexible zoophytes: the
former is therefore probably herbivorous, the latter carnivorous.
There is not much diversity in the anatomy of the three British species of Polycera,
though, in some respects, P. quadrilineata differs in its organisation from its congeners. The
channel of the mouth is exceedingly short, leading almost immediately from the external
opening, situated in the inferior surface of the head, into a rather large and powerful buccal
organ, provided with corneous jaws, which (PI. 17, fig. 11 b) in the species of the second
section are small, and of a sub-triangular form, with the cutting edge (d) ■ feebly developed.
In P . quadrilineata, they (fig. 10) are larger, and are pretty efficient cutting instruments,
having their upper margins concave and bearing each in front a lengthened, well-arched,
cutting blade (a). The tongue is moderately broad, generally of an amber colour, occasionally
dark: the posterior portion is tubular, and protrudes a little behind the buccal organ. In
P. quadrilineata there are fifteen rows of plates, with twelve plates in a row,—six on each
side. Two on each side, next, the median line, bear bicuspid spines ; the innermost of these
have the spines considerably smaller than the others: the external plates are of an elongated
form, a little elevated in the centre, and diminish in size towards the external border. The
tongue is divided down the centre by a naked space, the central plate being wanting. In
the other two species, the lingual organ is similar to the above, but in them the spines are
shorter and stouter, and the innermost are proportionally smaller. In P. ocellata, the rows of
plates are sixteen in number, with seven in a row on each side: in P. Lessonii there are only
thirteen rows, eight plates on each side, and the naked space down the centre of the tongue is
of considerable width.
The oesophagus (fig. 9c) is a rather long, simple tube, and has at its origin on either side
a small salivary gland, (b) which opens into the buccal organ (a): these glands are tubular and
are more or less folliculated. The oesophagus, passing backwards, enters the anterior border
of the liver on its way to the stomach, which is small, and is buried in that viscus, the upper
wall (d) being visible at the surface above and towards the left side. Here the intestine (e)
leaves the gastric pouch, and passing across the liver to the right, arrives at the anal termination
(ƒ) in the midst of the branchial circle. The intestinal tubl is rather short, and in
P. Lessonii is a little dilated just before it terminates. A small oval sac, apparently the
same as the pancreatic organ in Loris, opens into the stomach near to the oesophagus in P .
ocellata: a similar organ probably exists in the other species, but has escaped observation.
The liv.er (y) is of a brownish yellow colour, of an oval form, with the anterior extremity truncated
; its secretion passes into the stomach through three or four openings.
The reproductive apparatus in P. quadrilineata is much like that of Idalia. The testis is
divided into three portions; that '(«') next the intromittent organ (7i) is moderately thick and
tubular: the inner extremity of this portion is swelled a little, and is succeeded by an attenuated
tube (i") having a duct-like appearance, which leads to one end of a large, irregularly
oval, glandular organ (*), presenting the semblance of a laminated structure; the other extremity
of this portion is united by a short tube (i"') to the oviduct. The ovary is spread out
as usual over the liver, and the oviduct is at first slender, {j) and afterwards much dilated (ƒ)
as it reaches the testis. The vaginal tube \l) is rather long and slender; it opens into the
obtuse end of a very large pyriform spermatheca (ni); A long, delicate duct (n), passes from
the same point to the oviduct, and has attached to it a small oval sac—a second spermatheca
(o). The mucus-gland (£) is much convoluted.
The generative organs, in P. ocellata and P.Lessonii are similar to those of P. quadrilineata,
differing only in unimportant modifications. In the former, the glandular portion of the testis
is smaller and fusiform, as in Goniodoris, and the principal spermatheca is roundish and much
diminished in size.
The vascular system is apparently as highly developed in Polycera as in any of the
Lorididce. The heart is contained within a pericardium, and is composed of a ventricle (p)
and an auricle; the latter receiving the blood from the gills and skin, the former distributing
it again by a large artery from the anterior apex in the usual manner. The portal heart lies
below the pericardium, and is rather small. In P. quadrilineata there is a folliculated glandular
organ in connexion with the arterial system, lying on the right side in front of the reproductive
organs. This is similar to what has been observed in Idalia and Ancula, and will probably
be found in all the Polycerince. The heart beats sixty-two times in a minute in P. Lessonii; in
P. ocellata, from seventy-two to eighty-eight times ; and in P. quadrilineata from ninety to a
hundred times.
The renal organ is distinctly visible in P. Lessonii, and is copiously supplied with vessels ;
the margins have a dendritic appearance, and the external orifice is placed to the right in front
of the anus. In the other species this organ has been less perfectly observed.
The nervous system is provided with three pairs of oesophageal ganglia, besides the accessory
ones. They may all be considered as placed above the alimentary tube, though the
pedials droop a little on its sides. In P. quadrilineata, the cerebroids (fig. 12, a, d) are
irregularly quadrilateral, inclined to pyriform, with the broad ends united across the median
line. They give off from the frontal margin three pairs of nerves, (2,3,4), which go to the
lips, the oral appendages, and channel of the mouth. The olfactory nerves (1) pass from the
upper surface of the anterior margin, and have each at their origin a small round ganglion,
and another {j), which is considerably larger, is connected with them as they reach the
laminated portion of the tentacles: from the latter, several nerves pass up the tentacles. The
branchial ganglia (b, b) are round, and closely adherent to the posterior extremity of the
cerebroids; they give off eac'h two nerves, one (7) of which goes to the skin of the back, and