bevelled divisions. Each of these lobes is a massive process which tapers in lateral view
anteriorly, has a twisted sulcus dorsally, and the firm margins of which have the slender
palem. Externally is a row of tapered papillae, as in other forms, which, commencing on
the edge behind the paleae, cease at the rounded anterior end of the lobe. The external
paleae (Plate CXXIII, figs. 1 and 1') form a single row of spatulate bristles which follow
the curve of the margin, and are slender posteriorly, stronger in front. Moreover, the
posterior bristles slope upward and forward, whereas the anterior are nearly proclivous.
Each of the posterior bristles starts from a rounded sac at the base, is much tapered, then
gradually dilates into a broad, flattened, translucent blade, after which it diminishes to
the finely-pointed tip (Plate CXXIII, fig. 1 a). The anterior bristles are larger, and, as
mentioned, they project nearly horizontally when the animal lies flat in a vessel. These
join the still more powerful anterior series of the inner row, which, in some cases,
extend boldly from the inner half of the anterior curve. The anterior end of the inner
Fig. 137 a.—Diagram of the anterior region of Tetreres murata. p., palps; membrane; ext., external border; int.,internal border; sep., separation fromc itl.hee., pcirloisattoemd icuhman pnre.l; fpoerrm., epde roi-f stomium (lower lip). After Arnold Watson.
row of paleae has the strong bristles just mentioned which present stout and not very
acute points (Plate CXXIII, fig. 1 b and 1 &'). When fractured long fibres hang from
the interior. These powerful bristles project considerably from the surface, but behind
the anterior edge the rest of them are deeply imbedded in the tissues, only the tip being
visible. All are directed obliquely forward and slightly upward. Attached to these is
a minute Campanularian with a ringed stalk, a comparatively large theca and a thick
rhizome. Next these powerful bristles are less robust forms with a tapered base, flattened
and pointed tip. Those deeply inserted in the tissues behind have the thickened chitinous
tips of the larger forms in front, whilst their hold of the tissues will enable them to act
as levers or protective organs. The base has a rim and abuts also on the rounded mass
seen in the outer posterior paleae.
Opposite the last and larger external papilla of the coronal row is, beneath the crest
of the ridge on each side, a strong, sharp, dark brown, curved hook which is guarded by
the flaps of a conical, fleshy papilla. The point of the hook in the preparations is directed
inward, but it probably can be moved in various directions. The long straight bristles
found in the tissues in this region in Sabellaria spinulosa may be the homologues of these
hooks. In the hollow in front of the hooks a series of symmetrical folds converge to the
margin of the fork in front of the mouth, whilst the groove behind has transverse or
curved furrows and much brown pigment.
The ventral face of each coronal lobe is slightly turned inward and densely covered
with proportionally small tentacles, which in their firm attachment and general aspect
resemble those of Phoronis rather them..Sabellaria. These are attached directly to the
surface of the lobes, and thus differ from the arrangement in Sabellaria. In some they
form oblique rows slanting from behind forward and outward at their commencement on
the external ridge posteriorly. After a short distance they spread to the inner border
and thus cover the. ventral surface with the exception of a belt internally, but the rows
are not evident either on the inner border or on the outer after the middle. Those in
front and internally do not present the same regularity in the rows ; indeed, in one they
were irregular. Both show a bare longitudinal stripe along the centre—that is, between
the outer and inner series—till near the tip. The tentacles are richly ciliated along one
surface, show an afferent and an efferent vessel, and are coloured of a deep brown. The
great length of the “ peristomial ” lobes and the extended surface covered by the tentacles
indicate a special function.
The mouth opens at the posterior end of the great lobes and behind the tentacles.
In contraction it forms a puckered longitudinal slit with two overlapping flaps in front,
whilst in partial dilatation it has a series of separate folds or “ cushions ” externally, and
internally the posterior folds of the hood; whilst in front the hood is folded forward in the
middle line like an epistome, and forms a collar at each side before joining the posterior
folds. The whole would thus form a characteristic funnel leading to the mouth. The
hood is fixed all round a little behind its margin. Mr. Arnold Watson, who at first
thought that the frilled membrane which runs from the extremity of each peristomial lobe
was an extension from the sides of the prostomium, has by careful examination of the
living forms now (1916) found that though this membrane is in its lowest (most posterior)
part united with the edge of the prostomium, yet it is distinctly and deeply separated at
its free upper edge. Its origin, therefore, is the same as the outer edge of the channel,
and both should be regarded as peristomial. On the dorsal aspect of the hood are
the two long tentacles which have a smooth dorsal edge and a deeply grooved ventral
surface with frilled margins—probably ciliated in life—and they occupy a smooth and
pigmented area of the pillars to the inner edge of the outer tentacles.
Besides the two lateral tentacles (palps of some) a median subulate one springs from
a slightly elevated and antero-posteriorly elongated base somewhat in front of the lateral.
This may have a function in connection with the forward frill of the hood. The parts
thus differ considerably from those of Sabellaria, especially in the great development of the
hood. The lobes overlapping each other and the hood present evidences of transverse
striation, so that the function is special. Externally is a large lanceolate lobe (Dr. Allen’s
neuropodial cirrus of the first segment) connected at its base by a frill with a small
elevation bearing bristles (ventral, Allen), as in Sabellana.
Allen thinks .the two tentacles have the same structure as those of the Spionidas and
Disomidze, beino- D-shaped in section with the grooved surface bordered by a crenate
171