bristles are on the ventral side of the cirrus. He also mét with a specimen having a
double cirrus on the second segment, the bristles emerging between them. Another
example had two sets of collar-bristles on the right, whilst the left was devoid of them
and the process reduced in size.
The anterior (“ thoracic ”) region of the body includes three segments with
transversely elongated lamellae, each, moreover, having a pair of flattened, ligulate,
crenate bran chi as which taper to a point and somewhat resemble the horns of a goat or
antelope, from their transverse ridges, the large cilia of which have a bold hook-like
curve directed toward th^jtip of the organ. The branchias are supplied with long,
powerful cilia on their ridges, which make a vortex in the water around them, and thus
are in marked contrast to the delicately ciliated tentacles. Two vessels occur at their
base, apparently afferent and efferent, and between these are a series of parallel
transverse branches. They are less sensitive than the pale purple tentacles, since a more
violent contraction takes place when the latter are touched with a needle. The first,
viz., that in front of the anterior region proper, is a rather broad tongue-shaped process,
shorter than the succeeding, which are elongated horn-shaped organs, the sixth
apparently being the longest. They continue to the posterior end, but gradually diminish
in size.
Each of the three prominent lateral lamellae below the branchiae carries a series of
spatulate golden bristles (Plate CXXIII, fig. 2 d) arranged in a single line, the first
•having seven or eight, the second nine, and the third ten. They are generally directed
straight outward, though in life the points are directed backward, and have a flattened
translucent tip like the blade of a paddle, the upper end of the shaft gradually dilating
into the broad blade, the dilated part, moreover, showing in some short oblique striae
on one side—as if a trace of the striae so common in wingèd forms. Those of the first
set have a narrower tip and longer fringes, the outer fringes, moreover, being split into
finer processes on the margin. Those of the third series have broader tips and the
brush-like filaments at the extremity are shorter. Each bristle diminishes in size from
the tip to the base, and the shaft is striated. Mingled with the foregoing bristles are a
few simple forms (Plate CXXIII, fig. 2 c), the curved slender tapering tips of which
with their sparse spikes project from the skin between the stronger forms. If anything,
the first series has slightly narrower tips and more slender shafts than the third, which
sometimes shows truncated tips from wear.
A fold, marked by the purple-brown pigment from each of the dorsal setigerous
lamellae, continues the segment ventrally and ends in a papilla with a minute tuft of
golden bristles (Plate CXII, fig. 1 b), which, although small, have a similar structure to
the larger. They are translucent bristles with long shafts deeply inserted in the tissues,
the dilatation of the shaft distally being more gradual, whilst the fringes at the tip
of the blade pass much more deeply, so that the whole tip forms a more perfect brush.
They are also accompanied by the simple spinous bristles, which are considerably shorter,
but go more deeply into the tissues. The physiological importance of the two sets of
bristles is unknown, but it may be conjectured that the oar-shaped forms, having performed
their functions of fashioning the tube, could be slightly retracted, or the slender
ones may be slightly protracted, so that both might act in a brush-like manner. The
anterior tuft is the largest and the third the smallest, the opposite condition occurring in
the large dorsal bristles. The direction of these bristles is forward and slightly inward,
the angle of inclination being thus different from that in the next series. The last
(third) set shows faint serrations or striae at the sides just below the flat tip.
Between the ventral edge of the lamella for the hooks and the ventral bristles in the
second (abdominal) region of the body is a small filiform papilla, longest in front and
diminishing to a minute process in the caudal region.
The succeeding region of the body is characterised by the increase in the depth
of the lateral lamellae, the first being about three times that of the next in front
(Plate CXII, fig. 1); but they gradually diminish in depth in their progress backward,
Avhilst they increase in prominence, those in the distal part of the region, for no dorsal
bristles are visible, projecting like cirri. The bristles of the region are thus pushed
ventrally, so that even the long posterior forms are not, as a rule, seen at the sides in a
dorso-ventral view. They are situated to the inner side of the prominent, coloured
lamellae forming the dorsal region of each segment. The longest bristles in each tuft
are in front, since, instead of being arranged in a transverse row, they form an oblique
one. The typical bristles (Plate CXXIII, figs. 2 ƒ and 2 cj) are long and translucent
with smooth shafts, which taper from the skin to the delicate and flexible tip covered
with whorls of spikes directed distally. Their usual direction is forward and inward,
and they fall smoothly under a needle carried from behind forward, but rise against it
when passed in the opposite direction. As rudimentary bristles of the same kind appear
in the first region of the body between the bases of the spatulate forms, their distri-.
bution is thus uniform throughout. Moreover, the bristles of the first series of this
region present a transition stage, having stouter shafts and a broader and shorter spinous
part at the tip, the latter, indeed, resembliDg a short villous region. . Accompanying
these is usually a slender tapering spinous bristle, and this is also a transition form.
The posterior bristles form a conspicuous series ventally, but though longer their
structure remains the same.
The prominent transverse or lateral lamellae formerly alluded to bear the numerous
hooks, their tendons and muscles. In shape the hooks (Plate CXXIII, fig. 2 h) are
elongate, with a single tendon at the distal end and two at the rounded base. In lateral
view five teeth usually characterise them, though when viewed from the front each
represents only one of two or three in the row, of which six may occur in both anterior
and posterior feet, the latter, however, having smaller hooks. The slender cirriform
lamellae of the posterior feet have the interior largely occupied by the bundles of tendons
from the hooks, and to these muscular fibres are attached. At the base of each elongated
lamella posteriorly is a deep brownish pigment-spot.
The narrow posterior end of the body is continued as a long tubular process
(Plate CXII, fig. 1), which fits into the dorsal groove when the animal is quiescent in
the tube, but which can be elongated or shortened at will, and forms a very efficient
means for passing the faecal matter out of the aperture of the tube without necessitating
the turning of the annelid. At its tip is the vent with a more or less distinct rim, which
in some is oblique. It is noteworthy that in the preparations this tube is generally
dorsal, whereas that of 8. alveolata is doubled forward in the ventral groove. The