in valves of Pecten opercularis (W. 0. M.). Dredged off the Hebrides in considerable
numbers; 9 miles off Balta (J. G. J.) ; Yalentia Harbour in 2 fathoms amongst soft
mud (J. Gr. Jeffreys and A. C. Had don) ; Torquay (Elwes) ; Plymouth (Spence Bate,
B. Rowe and Crawshay) ; Blacksod and Clew Bays, etc. (Southern).
It is elsewhere found in the Mediterranean (Delle Chiaje, Milne-Edwards, G-rube,
da Costa, Panceri, Claparède, Fauvel) ; Adriatic (Grrube), amongst stones and nullipores
as well as in a brown sponge; shores of France (Milne-Edwards, Grube, De St. Joseph) ;
Azores and Gibraltar,Isles of Gambia (Fauvel) ; Finmark (Norman) ; North Sea; Gulf of
St. Vincent, Australia (Fauvel).
The cephalic region is distinguished by the great size of the upper collar or arch,
and by its frilled inward curve at each lower edge. Its upper surface is somewhat
flattened, that is to say, only a shallow groove is present, the mass, of tentacles springing
from the posterior half near the rim. These tentacles are pale orange in life, and spotted
with white so as to give them a barred appearance, and their movements are remarkable,
for not only do they aid in the construction of the tube, but hoist the animals up the
perpendicular side of a glass vessel or in any direction, and are continually moving as a
series of complex threads. All are deeply grooved. When the annelid is hidden amongst
shells and tufts of Ceramium the long spreading tentacles resemble independent Nemerteans,
and in large examples stretch nearly a foot from the body. Below the mouth is a
transversely elongated fold, and then follows the broad lower lip, which ceases at the
dorsal fold on each side.
Behind the dorsal collar are a large number of dark pigment-spots—the so-called eyes.
These are generally concealed by the posterior fold of the collar. In a small variety met
with under stones between tide-marks at St. Peter Port, Guernsey, they are both
numerous and distinct, and, moreover, remain in spirit. They form in a large Irish
example a conspicuous brown band below the collar.
Body 9—10 inches or more in length, and as thick as the little finger behind the
bristles, soft and mobile, with numerous (sixty to ninety) narrow segments, the anterior
region being enlarged, and the posterior tapered to a comparatively large terminal anus
with a crenate margin. Though the dorsum as a rule is convex, the preparations are
generally marked by a slight median groove anteriorly. Ventrally, a deep median groove
runs from one end to the other. In large examples the swollen anterior end is tessellated,
whilst in the smaller posterior region this is less evident.
Each segment consists of two rings, one at the bristle-tuft and one in front of it
dorsally, and these are continued ventrally, the groove in the ridge for the hooks being
opposite the bristle-tuft, and only a narrow space occurring between them (the ridges).
Posteriorly the segments are more definitely marked, the broader division containing the
lamella for the hooks, a narrow ring being in front of it. Then the two rings are only
indicated laterally above the lamellæ for the hooks, and finally for some distance at the
tail each segment is undivided, and moreover, the segments become more and more
minute as they approach the last, which is broader than those in front of it and has
a minutely crenate margin. The ventral surface in this region is considerably diminished
whilst the dorsal arch is increased. The ventral glandular shields are narrow and long
in front, broader and shorter from side to side from the fifth backward, and they often
present a median process laterally in front of the point of contact of the hook-row. They
are usually fourteen or fifteen in number, the anterior narrow shields being ridged
(two-ringed), the posterior flattened. Occasionally an abnormality occurs in the
arrangement of the two rings anteriorly, the broad posterior ring ceasing like a fold
in the middle line. Reproduction of the tail is common.
The mucous glands form a dense series of orange tufts in the thoracic region on
each side of the middle line and extend forward to the anterior end. They are long
and much folded and frilled anteriorly, and the contents tinge the long anterior ones
white with the exception of the orange tips. The contents consist of granular cells,
granules and protoplasmic threads and vesicles. In the small forms from the Channel
Islands the five posterior ventral shields in well-preserved examples present a symmetrical
arrangement, each being broadly fan-shaped in front, constricted posteriorly, and sending
out a spur on each side in front of the succeeding shield.
The Hebridean forms are orange-red, sometimes inclining to brown, speckled all
over (tentacles, body and branchise) with white (on tubercles, Dalyell), and the larger
examples are darker than the smaller. The oral region is purplish-red, also spotted with
white. Those from the Channel Islands are paler than the foregoing, but also speckled
with white on both body and branchise. The tentacles in the latter are irregularly barred
with white, and in young specimens from Herm they are milk-white. The specks rapidly
disappear in spirit.
The branchise are three in number on each side, and have a dull red colour spotted
with white. The first pair are about 1 inch long in large specimens, and arise from the
second body-segment, which has a spout-like fold at each side. The main stem is often
unbranched for some distance, whilst in others (large) a small branch or two occur
close to the base. The whole organ is sub-dichotomously divided, the short terminal
divisions giving a character to the mass which appears to form a dense arbuscle. In
many of the divisions the branches spring from one side only, but this does not appear
to hold in the distal divisions. The. ring at the base of the first branchia trends evenly
away from it to the frill near the external margin of the mouth. A small papilla
sometimes occurs close to the base of the second branchia—it may be only on one side—
whilst ventralward the anterior fillet of the segment has a free process like a flat papilla.
Close to the outer base of the third branchia is the first setigerous papilla, and a
short distance ventralward is a similar free flattened process to that described in the
previous segment.
In young examples the branchise are comparatively simple, though the terminal
divisions correspond in general structure with that of the adult, and in a small littoral
variety from St. Peter Port, Guernsey, the branchise are likewise less bushy, though the
terminal branches are typical.
The setigerous processes are seventeen in number,; commencing, as indicated, at
the third branchia and continuing for sixteen segments thereafter. Each is a somewhat
flattened papilla with the bristles arranged in a vertical row in the centre. The first
tufts of bristles are smaller, the bristles themselves shorter, but they show two groups,
as in the posterior, viz., a shorter series in this case without evident wings, and a longer
series also without evident wings, and with slightly curved and tapered tips. In the