ANCULA.
determining most points of importance, and in ascertaining that the internal structure
bears out its relationship to Idalia on the one hand, and to Polycera on the other.
The oral channel is very short; it opens externally on the inferior surface of the head,
and leads to a buccal organ, which is well developed, compact, and muscular, though of no
great s iz e a n d has connected with its upper surface a gizzard, constructed in the same
manner as in Idalia and Goniodoris. The tongue is long and narrow, having from twenty-five
to twenty-seven rows of spines ; there are four spines in each row, those next the median line
being large, excessively broad, and flat, with their inner margins denticulated; the external spines
are much smaller and plain; there is no central spine. The posterior portion of the tongue is
tubular, and protrudes a little from behind the buccal organ in a sheath. The buccal lip is
provided with a very formidable, spinous prehensile collar, (PI. 17, fig. 7), which is wide, and,
narrowing upwards, terminates on each side of the median line in a sharpish point. The spines,
(fig. 8) are arranged in indistinct transverse rows; they are simple, curved, and much larger
than is usual in the Nudibranchs.
The oesophagus is very long and slender: it has on each side, as it passes from the
buccal organ, a small, oval, salivary gland, which pours its secretion into the mouth through
a very short duct. At its origin, the oesophagus is swelled out into a crop, with delicate walls;
it then, suddenly contracts, and in the form of a constricted tube, passes through the nervous
rhjg; immediately afterwards it again dilates a little for a short distance backwards, and
contracting once more, is continued as a simple tube to the anterior border of the liver, into
which it plunges on its way to the stomach. This latter viscus is small, and is buried just
within, the frontal margin of the hepatic organ. The intestine is given off from its upper
surface, and, passing up through the liver, crosses over to the right side in front of the heart,
and, after a short course, terminates in the anal nipple, within the branchial circle. There is
a glandular enlargement of the intestinal tube just after it emerges from the liver, which is
apparently the same as that which has been designated a rudimentary pancreas in Doris. The
liver, of a yellowish brown colour, is rounded behind and truncated in front, and passes backwards
beyond the branchiae; the anus being situated comparatively further forward than
usual.
The reproductive organs resemble, in the arrangement of their parts, those of Goniodoris,
and the other Polycerinte. The three component parts of the testis are not very distinctly
marked | the glandular or fusiform portion exceeding the tubular only a little in caliber. The
vaginal tube and spermathecae are small.
A delicate pericardium contains a ventricle and an auricle, and below it is the portal
heart. The. ventricle gives off in front, in the usual manner, a large artery, which branches to
the various organs,- and there is a folliculated glandular body, overlying the genitalia, which
is apparently connected with the arterial system, and is probably similar to that described in
Doris, as. situated in the vicinity of the oesophageal ganglia.
The branchial leaflets exhibit, in a high state of de velopment, that curious internal struc-
ture> which in Doris we consider as an elastic apparatus to aid respiration by keeping the
gibs, to sgme extent, in a state of expansion when out of water; and such an apparatus would
seem of peculiar advantage to Aneula cristafaT as it lives between tide-marks, and is liable to
be left dry by the receding tide. In this species, the apparatus in question is formed of a
double row of roundish vesicles, set on a central stem, and is situated in the trunk and prinANCULA.
cipal branches of the leaflet, appearing in these parts as a double row of white dots. The
walls of the vesicles are firm, and undoubtedly possess some degree of resiliency.
The oesophageal ganglia are not so much concentrated as in Idalia, in this respect
agreeing with Polycera. In Aneula there are six principal ganglia, in three pairs. The
cerebroids are placed above the alimentary tube, and are broadly fusiform, with their apices
united across the median line. These supply nerves to the channel of the mouth, the lips, and
dorsal tentacles; the channel and labial nerves are three in number; the olfactory or tentacular
have each a small round ganglion at the origin, and from the root of these latter nerves
there is also a minute twig given off, which goes apparently to the tentacular filaments at the*
base of the dorsal tentacles. The branchial ganglia are spherical, and are cemented to the
under side of the cerebroids; they are placed at the sides of the oesophagus, and give off each a
large nerve from behind, which supplies the dorsal skin. The right branchial also supplies, from
the anterior margin, a nerve which goes to the root of the penis, and there joins a minute ganglion
from which three or four small twigs are given to the intromittent organ. The pedial ganglia
are situated below the alimentary tube, and are of the size and form of the branchial; they
are closely united to the other two pairs above, and to each other below; thus completing
a constricted collar of ganglia round that tube; they send three or four nerves to the foot.
A small visceral ganglion is attached to the right branchial, at its junction with the pedial.
Two or three nerves issue from it, which will, there can be no doubt, go to the viscera; but,
from the minuteness of the species, we have failed to trace them. A delicate cord likewise
passes from this ganglion, and, going to the branchial of the opposite side, forms the
branchial collar.
There is nothing peculiar in the buccal ganglia, except that the commissure which unites
them across the median line is rather long. The gastro-cesophageal ganglia have not been
observed.
The eyes have the usual development; they are seated each on a minute round ganglion,
which is sessile on the outer margin of the cerebroids. The auditory capsules contain numerous
otolithes, but we have not succeeded in determining to which ganglia 'they belong.
Vibratile cilia appear to clothe the whole surface of the animal; they have been detected
along the margin of the foot, and ridge of the back, on the gills and lateral papillae, on the
dorsal and oral tentacles, and on the tentacular processes.
The skin is smooth, soft, and delicate, with scattered imbedded spicula of a cylindrical
form, bent in the centre and a little enlarged at the ends.