Digestive System.—The pre-gastric casca are two in number, both being short and
broadly club-shaped. The third is transverse. All go deeply into the intermuscular
spaces at the feet. The movements of muscles and feet must thus have considerable
effect on the contents of the caeca.
Scales (Plate XXXIII, figs. 13—small example, and 14—larger example) fifteen
pairs. They vary in appearance according t,o the condition of the specimen; thus the
smaller race from the Channel Islands has the anterior scales dappled brownish with a
dark patch over the scar for attachment, and surrounded by a broad pale ring. In the
larger specimens from the Hebrides they heave a dark metallic (steel-like) iridescence.
When removed they - are translucent, pale anteriorly, marked by a dark belt, speckled
with translucent spots round the inner three-fourths of their circumference, and with a
pale centre. They vary, in any given specimen, in size according to state of development,
covering the dorsum in some nearly as far as , they extend, whereas in others with
developing scales an interval occurs betweén the pairs. In the large forms the first five
pairs cover the dorsum completely, the rest leave a space iff'the centre. The first pair
are rounded—with minute cilia anteriorly, the succeeding somewhat reniform, and the rest
more or less rounded ovoid. Though smooth under a lens they have a dense series of
minute papilla as a broad belt along the anterior region, and at the outer border a series
of minute papillas or cilia, and one or two also occur along the posterior border. Finely
branched nerves ramify throughout the scale from the scar for the pedicle. In the small
specimens from the Channel Islands the papillae (spinel) on the scales are proportionally
large, as observed in the sketch.
Feet.—The dorsal division of the first foot presents a single small dorsal bristle with
about seven or eight spinous rows, and a smooth tip.
The second foot has dorsally a group of somewhat tapered, short, slightly curved
bristles with well-marked spinous rows. Ventrally the slender bristles are also short,
the spinous regions being bent dorsally, and tapering to smooth bifid tips. The rows of
spines are well marked,—that is, are at moderate distances from each other.' The tips of
one or two of the inferior bristles are simple. The large ventral cirrus of this foot has
numerous cilia with clavate and-truncate tips. The bristles in the succeeding feet gradually
approach the typical form, which is found about the twelfth or thirtèenth bristled
foot. In shape the typical foot (Plate XXIX, fig. 17) presents dorsally the comparatively
short tapering cirrus, then the eminence for the dorsal bristles. The inferior division is
bifid, with a long anterior propess and a shorter posterior cushion, the margin beneath
having an inward slope from above downward. Even in the second foot the upper
ventral bristle is stouter than the others, with strongly bifid tip and spinous rows. It
increases in strength and becomes more boldly bifid as we proceed backward, attaining a
large size in the fifth and sixth, and then becoming simple about the tenth bristled foot,
while only traces of the spines remain. As a rule only one strong bristle occurs in thé
typical foot, which has below the dorsal cirrus the tuft of short, slightly curved, and little
tapered dorsal bristles arising from a small eminence (Plate XLI, fig. 4). These bristles
taper a little from the base, but end in a blunt tip (Plate XLI, fig. 7), which is curiously
wrinkled so as to appear bifid. The spinous rows are somewhat close, yet fairly distinct.
A careful examination of various specimens, however, shows that this condition of the
dorsal bristles is due to external influences, probably connected with commensalism.
The tip has evidently been destroyed, so that only the lower part of the bristle remains.
The stump, indeed, is often slightly thickened, and presents a furrow, giving the bifid
appearance already adverted to. In an example dredged off the Hebrides by Dr. Grwyn
Jeffreys the dorsal bristles are unusually complete, yet even in these the extreme tip
has disappeared and a probe-pointed end remains. This specimen shows, however,
that the normal condition of such a bristle is finely tapered to a filiform tip. The causes
of this remarkable change, which does not seem to affect the ventral bristles, may be the
secretions of the Terebella, or the friction of the bristles against the walls of the tube or
tunnel, the latter the most probable.
The ventral division forms a short triangular lobe, the process for the spine being at
the apex. In some a bar of dark pigment occurs near the tip of the foot, just at the
base of the bifid region. Above the spine is the single large bristle, the shaft of which
is about twice the diameter of those adjoining. The tip is hastate and the point acute
(Plate XLI, fig. 5). As already indicated, this bristle is formed from a bifid one, the
secondary process disappearing as we proceed backward, and likewise the spines—traces
of which, however, even far backwards, are left in the faint transverse lines on the
dilated region. The relative proportion of the two kinds of bristles is shown in figs. 4
and 5. All the bristles which follow.are bifid, with short spinous regions and moderately
stout shafts (Plate XLI, fig. 6, representing one of the superior forms with a longer tip,
and fig. 8 showing the tip more highly magnified).
Toward the posterior end the large superior ventral bristle disappears. Before this
change takes place, however, two strong bristles occur on the foot as in front. The
dorsal tuft becomes minute posteriorly, and in the terminal feet the bristles are slender
and tapered—with very distinct spinous rows.
The dorsal cirri, which in life are pale, extend in the preparations only a little beyond
the bristles, and gently taper to the slight swelling below the filiform tip. They have
numerous short cilia with clavate and truncate ends, and a few small cilia occur on the
base of the slender extremity. The ventral cirri are small and tapering, with similar
cilia. They do not reach the tip of the fleshy part of the foot. In some they are
rendered conspicuous by dark pigment at the base.
Nerve-cords.—In transverse section nucleated cells are found externally and beneath
the cords, especially at the ganglionic enlargements. Strands from the exterior fibrous
layer also passed into the area of the cord in section, and in many such fibres seemed to
join the nucleated cells lying in the median line below the cords.
Reproduction.—Females with well-developed eggs were found in the tube of Terebella
nebulosa at Herm in July, 1868, and in the chinks of rocks in tracks of Lysidice. In the
latter case males well advanced were also observed.
Habits.—This form is more sluggish in its habits than Harmothoe imbricata or other
ordinary type. I t is difficult also to conceive how the Terebella can be comfortable with
such a large commensalistic form in its tube, especially when the powerful bristles
of the Polynoe are considered. So far as observed it keeps its head towards the anterior
end of the tube, and thus its ordinary position is in agreement with that of the Terebella.
I t is brittle, breaking into several pieces in lifting from one vessel to another.