is the first small shield or scute. The first bristle-tuft is opposite the last branchia, only
a short interval separating it from the base of the organ. It springs from a setigerous
papilla at the dorsal edge of the ridge for the hooks. The bristles form a vertical row
of considerable depth, and in structure agree with the succeeding tufts, no rudimentary
forms marking the commencement of the series, as in various groups. Each tuft consists
of a longer series with stout, straight and long shafts, the free portion of which is slightly
diminished in. diameter toward the commencement of the winged, finely tapered and
curved tip (Plate CXXV, figs. 10 and 10 a, and Plate. CXXV a, fig. 1). The tips of
the bristles are directed upward and backward in their normal condition. The shorter
series consists of those with shorter and less tapered winged tips, which have an accessory
terminal blade carried at an angle to that beneath, and is broad at the base and tapered
to a slender, slightly curved tip. Such a bristle approaches that of certain Accetidaa,
such as Panthalis. The structure of these bristles remains the same from the first tuft
to the last, but the setigerous processes increase in prominence in their progress backward.
The serratures at the tip cause them to cling tenaciously to the cuticle.
No hooks or their homologues occur in the ridge running downward from the first
bristle-tuft and the ridge itself is intermediate in character. The ridge from the second
pair of bristles presents a lateral border and a median linear elevation containing the
single row of hooks, the ridge terminating ventrally in a rounded border at some distance
from the ventral shield'; the ridges which follow gradually approach the ventral scutes
or shields until at the eighth they touch. The third ridge has a double row of hooks,
but they appear to be less regular than those which follow. As a rule the ridges
for the hooks are longest in front, and diminish a little toward the twenty-fourth
bristle-bundle. Each leaves the setigerous process as a slightly flattened ridge with
an anterior, a median, and a posterior fillet, the median bearing the rows of hooks.
On the cessation of the bristles the thick and rather long ridge for the hooks increases
in prominence and presents a free edge dorsally and ventrally. It diminishes in
depth, while increasing in prominence posteriorly. The rows of hooks in life are
terminated ventrally by a brownish speck. In the posterior processes the hooks are
in a single row.
The hooks, which commence at the second bristle-tuft and continue to the posterior
end (Plate CXXV a, fig. 1 a), differ from those of A. cirrata in the less oblique base and
in the curves of the anterior outline below the main fang. Usually four teeth occur in
lateral view on the crown above the fang, but when examined in front the crown appears
to have several transverse rows. These hooks are very similar to those of Amphitrite
variabilis, Risso, as figured by Marenzeller, but the latter has only seventeen pairs
of bristles.
The coelomic corpuscles immediately after extrusion in spirit are ovoid or elliptical
bodies, reddish in mass, the larger of a certain uniformity of size, filled with rather coarse
granules and with a nucleus. Amongst these are many smaller rounded bodies, some with
two large nuclei—it may be in process of fission—and, indeed, the process of division is seen
in others. The smallest are minute, translucent, elliptical bodies, though some are
fusiform with a nucleus in the centre, and a number may be strung together in a small
coagulum. From these the larger corpuscles seem to be developed, numerous divisions
apparently taking place during their growth, groups of three after division occasionally
occurring. On reaching the full size division seems to be rare. Each large cell has
a cell-wall which sometimes is ruptured or dissolved, and the coarse granules form a
botryoidal surface.
Reproduction.—In May the pale salmon-coloured ovaries occurred in the anterior
region, extending to the seventh or eighth bristle-tuft as a series of lobate folds crowded
with very minute ova. The nephridia are large and numerous. In the same month
(May) a large example had in the coelomic cavity a quantity of a dull purplish gelatinous
fluid, the colour being apparently due to the minute granules of purple oil in the ova,
which measured '046 mm. in long and ’037 mm. in short diameter. There were besides
numerous coelomic corpuscles, elongated or spindle-shaped bodies, which by-and-by
disappeared from the fluid.
Habits.—It is less active than T. nebulosa, and lies rolling in a vessel moving branchiae
and tentacles. Dalyell says it is phosphorescent, but this has not been observed at
St. Andrews..
The tube in a Hebridean example is earthy and rather friable. In confinement it
rapidly forms a membranous tube in the vessel of sea-water, both ends of the tunnel being
open. From this shelter it stretches its attenuated tentacles along the bottom. In
tangle-roots the tube is formed of mucous lining with sandy mud externally. A tube
from Bantry Harbour (R. I. A. Expedition, 1885) consists of mud and dark fragments
like peat, the whole forming a thick friable coating. At St. Andrews the tubes are
composed of sand-grains and mud (and they retain their shape), part being attached to
stones and part to the mud beneath. In one instance the tube was a foot and a half in
length, and contained in addition the commensal, Gattyana cirrosa.
Commensals.—The ordinary commensal at St. Andrews is Gattyana cirrosa, though
at least on one occasion large examples of Sthenelais boa were obtained near the mouth of
their tubes at low-water mark. De St. Joseph found the former also in the tubes on the
shores of France (Croisic).
If Montagu’s Terebella constrictor proves to be this form, then his title has priority.
Dalyell’s (1853) description and figure are perfectly clear, so that there is no
dubiety as to the species which he called the potter from its predilection for mud in the
construction of its tube. He pointed out the thick, heavy and friable nature of the tube in
contrast with that of Lanice conchilega, and the fondness of the annelid for empty shells
in deep water. A small specimen which from injury had only twelve bristle-tufts,
regenerated its body in five or six weeks. The versatility of the annelid, he noted,
was surprising. “ Many tentacula are searching for materials, many in collection,
many bearing them to the edifice, some quitting their hold, others recovering the
load, while the architect itself seems occupied in kneading masses in its mouth, disgorging
them successively, or in polishing the rude workmanship resulting from its
labours.” ♦
So far as can be gathered from Claparede’s description and figures (1870), his
Amphitrite nana would not appear to offer substantial differences from this species.
Cunningham and Ramage (1888) state that there are fifteen to seventeen pairs of
nephridia in the first fifteen to seventeen post-buccal segments, and that there are median