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PRE-OOULAR AND POST-OOULAR TENTACLES OF NAUTILUS. 197
The Pre-ocular and Post-ocular Tentacles and
Osphradia of Nautilus.
By
Arthur Willey, D.Sc.
With Plate 10.
THE occurrence of a special tentacle in front of the eye and
another behind the eye in Nautilus is well known. These
tentacles resemble the large number of remaining tentacular
appendages in being ringed, and also in being retractile within
sheaths, but differ from them in almost every other respect.
In the first place, most of the tentacular appendages of
Nautilus have essentially an adhesive function, to which is
related a prehensile function. They are employed for seizing
hold of food and for attachment to surfaces.
Attachment is effected by the definite suctorial ridges on
their lower and inner sides (fig. 3). When attached by its
tentacles, Nautilus holds on with considerable tenacity j 1 and
sometimes in forcibly detaching it some of the tentacles
break off, and remain fixed to the surface of attachment. The
shape of a section of the tentacular processes of Nautilus is
that of a spherical triangle, the base of which corresponds to
the suctorial ridges, while the apex and sides are directed
1
In the next number of tbis 'Journal' Dr. Willey's figure of a pearly
Nautilus crawling on a glass surface by means of its tentacles will be published, as also some notes on the ccelom and pericardium of Nautilus. His
discovery of the deposited] eggs of the Nautilus has been published with
figures of the eggs in the ' Proc. Roy. Soc*
198
ARTHUR WILLEY.
outwards, and are distinguished by a deep brown pigment.
The suctorial ridges have a pale neutral tint. We may, therefore, speak of those tentacles which are used for prehension
and attachment as the adhesive t e n t a c l e s . Their function
speaks for the pedal nature of the tentacular processes of
Nautilus, as does also their innervation; and further, their
function allows them to be compared with the arms of the
Dibranchiata. If the comparison is carried into detail the
suctorial ridges of the former would correspond with the
definite suckers of the latter.
That prehension as well as adhesion is a function of the
Molluscan foot is well illustrated by the method of capture of
a species of Oliva at Lifu. This species can be obtained in
large numbers by employing a line baited with the animal of
a land-shell (Placostylus). The Oliva wraps its foot round the
bait, and so can be lifted out of the water and landed.
Recently arguments have been brought forward by Kerr 1
against the supposed pedal nature of the Cephalopod arms in
general and the tentacular processes of Nautilus in particular.
If embryological data are not to be trusted on account of the
large quantity of food-yolk in Cephalopod ova, we are obliged
to consider, among other things, function and innervation.
With regard to the latter, Kerr throws doubt on the generally
accepted identification of the sub-cesophageal ganglionic
masses of Cephalopods. It is well, however, to remember
that in Dentalium the ganglionic centres have the same
topographical relations as in Nautilus, the undoubted pedal
ganglion being placed far in front of the pleural and visceral
ganglia.
Returning to the tentacular appendages of Nautilus, it will
not be surprising to learn that the adhesive tentacles are not
ciliated; but it is necessary to mention this negative fact,
because the pre-ocular and post-ocular tentacles are ciliated.
On the side corresponding to the suctorial ridges of the adhesive tentacles the annulations of the pre- and post-ocular
1
J. Graham Kerr, " On some Points in the Anatomy of Nautilus pompilius," 'Proc. Zool. Soc.,' 1895.
PBE-OOULAR AND POST-OOULAR TENTACLES OP NAUTILUS. 199
tentacles form deep grooves, between which the ridges project
as prominent lamellae. The upper and lower surfaces of the
lamellae and the bases of the grooves are covered with vibratile
cilia (fig. 2). There can be little doubt that the pre-ocular and
post-ocular tentacles of Nautilus represent tentacular processeSj homologous with the adhesive tentacles, which have
been modified to serve an accessory olfactory function. We
will therefore speak of them as the olfactory tentacles, in
contrast to the adhesive tentacles. As is well known, there is
a rhinophore in Nautilus, placed directly below the eye, corresponding to the rhinophore or olfactory groove of the Dibranchiata. In Nautilus there is a small tentacle as well as a
fossa in connection with the rhinophore, but it is not annulated
and not retractile.
The olfactory tentacles (apart from the rhinophore) when
extended stand out from the body nearly at a right angle, the
pre-ocular tentacle being directed slightly forwards, and the
post-ocular tentacle usually tending backwards (fig. 1). The
ciliated olfactory lamellae are directed strictly forwards.
In the living Nautilus the olfactory tentacles otherwise offer
a strong contrast to the adhesive tentacles by their almost
uniform white colour. When examined under the microscope
there is found to be a little brown pigment in the annulations
and at the edges of the lamellae, but when viewed in to to
under water the general colour effect is white.
Moreover the adhesive tentacles can be touched without
necessarily being retracted, but at the slightest contact with a
foreign body the olfactory tentacles are instantly retracted
within their sheaths.
The presence of accessory olfactory tentacles in Nautilus
can, I think, be related to an essential bionomical difference
between the existing Tetrabranchiata and the Dibranchiata.
Nautilus finds its food chiefly by the sense of smell, while
it is a matter of more or less common observation that the
Dibranchiata with their remarkably perfect eyes pursue their
quarry by the sense of sight. This difference, which is to a
certain extent evident from the facts of organisation, is further
200
AETHUB WILLEY.
emphasised by the different modes adopted by the natives for
trapping these animals.
One of the surest ways of obtaining Nautilus, and, in fact,
the method by which I have obtained most of my specimens
at Lifu, is to bait the fish-basket with the cooked and bruised
exoskeleton of Palinurus or an allied form. The strongly
scented " potage" so produced is then wrapped up in cocoa-nut
fibre like a small parcel, and placed in the fish-trap o*. ernight.
There is therefore nothing to be seen, but on the other hand
there is something to be smelt, and by this means I have
obtained as many as ten Nautilus at one time.
For taking Octopus the natives of Lifu employ a very different method. A rounded oval piece of stone backed by a
well-fitting piece of the shell of a species of Cyprsea, to which
are added pieces of leaf to simulate legs and tail, is dangled
along the surface of the water at the end of a line. The
natives say that the Octopus mistakes this for a rat, against
which it has a special grudge; but whatever the reason may
be, the fact remains that Octopus attacks this singular nonscented contrivance, and so is captured.
THE OSPHRADIA OF NAUTILUS.
In an article published in ' Natural Science' for June, 1895
(vol. vi, pp. 405—414), I suggested that the post-anal papilla
represented a pair of osphradia—namely, the inner osphradia,
in addition to the outer osphradia which were originally described by Lankester and Bourne. The nerve to the outer
osphradium on each side is bound up together with the nerves
to the branchiae into a common trunk, the respective nerves
separating out from the trunk towards the base of the branchiae.
The nerve supplying the inner osphradium has a generally independent course close beside the above-mentioned common
nerve-trunk. I cannot believe that this slight difference in
the behaviour of the osphradial nerves constitutes an obstacle
PltE-OOULAB AND POST-OOULAE TENTACLES OF NAUTILUS. 201
to the identification of the post-anal papilla as a pair of
osphradia, as has been recently suggested.1
However, by means of macroscopic sections of fresh material
the presence of vibratile cilia on the sensory epithelium of both
the inner and outer osphradia can be demonstrated, and this I
regard as the final proof of the osphradial character of the
so-called post-anal papilla (figs. 4, 5). The sensory epithelium
of both osphradia is distinguished from the surrounding ectoderm both by the presence of the cilia and by the general
absence of goblet-cells.
The olfactory lamellae of the accessory olfactory tentacles
and the sensory epithelium of the osphradia are the only
places where I have observed vibrating cilia in Nautilus
hitherto.
EXPLANATION OF PLATE 10,
Illustrating Dr. Arthur Willey's paper on " The Pre-ocular and
Post-ocular Tentacles and Osphradia of Nautilus."
FIG. 1.—View from above of the "hood" and tentacles of Nautilus
during life.
PIG. 2.—To show the ciliated ridge of the olfactory tentacles.
FIG. 3.—To show the suctorial ridges of the ordinary tentacles.
FIG. 4.—The ciliated structure of the surface of one of the anterior
osphradia.
FIG. 5.—Ditto of the posterior.
FIG. 6.—Outline sketch of the Gastropod Aplustrum to show "laminate
organ " comparable to the olfactory tentacles of Nautilus.
1
W. Garstang, "The Morphology of the Mollusca," in 'Science Progress,' vol. v, March, 1896.
VOL. 40, PAKT 1.—NEW SEE.
PreocuZar ol/adcrj
tentacle
ist - ocular olfactory
tentacle,
Fur.
suctorial' riaiges
slurAt/y tsndricatinq