dissepiment. Branchiae two pairs, on the second and third segments,1 pectiniform,
lamellae diminishing from within outward and attached to a tapered basal stem—often
coiled, situated near the feet. Anterior heart connected with peri-intestinal sinus.
Bristles commence on the sixth segment, arranged in two series, viz., three in the
first region and twelve to fourteen in the second, the latter stronger, and accompanied
by lamellae forhbo'ks. The structure throughout is the same, viz., strong, simple, tapering
bristles with traces of wings on the tips, and a shorter series with spear-like dilatations at
the end of the shaft, and a tapering, hair-like tip. Some forms have hooks with long
shafts anteriorly (Hessle). Pectiniform hooks, commencing on the ninth segment, and in a
single row (Hessle). Bristle-like hooks (probably ventral, though in young dorsal—Hessle)
on each side of the base of the caudal appendix (scapha). Tube free, tapered, nearly straight
or very slightly curved, composed of neatly arranged sand-grains and secretion, or in one
genus of fragments of shells. Feet reduced as in all tubicolar forms. Nerve-cords
comparatively free. Tentacles innervated from the anterior ganglia (Nilsson), from the
middle ganglion (Hessle), the former homologising them with the palps. Nerves for
tentacular membrane from the middle ganglion. Nuchal organ, as in the Ampharetidae,
raised (Hessle). A groove between tentacles and mouth.
In the Ampliictenidae Schneider found a heart-body, and Cunningham1 2 (1888)
mentions that an anterior heart is present, and is connected with a blood-sinus on the
walls of the intestine.
Some authors, like Eisig and Picton, think the heart-body equivalent to the ehlora-
gogenous coat of the vessel pushed in. Picton considered it mesoblastic in Polymnia, and
analogous to the liver of vertebrates, but glycogen is absent so that its complete analogy
is not proven, though other products may be present and stored. The functions of the
pigment and the chitinous bodies are unknown. It has been suggested that waste
products may be carried through the heart-wall and thence to the nephridia and leucocytes.
Beddard and Horst, again, are of opinion that the Heart-body is hypoblastic. Bisig
views it as modified peritoneal tissue, though Schaeppi has found it of different chemical
composition. It is in the blood-stream as the liver is, and hence Fauvel considers it hepatic
in function, and that it has no connection with amoebocytes. Its occurrence in so many
families of Polychsets is noteworthy, for besides the Amphictenidae, it is present in the
Opheliidge, Chloraemidae, Cirratulidae, Ampharetidae and Terebellidge, whilst in the
Arenieolidge it is paired, and unites the gastric plexus with the ventral. Functionally
some are inclined to the view that it prevents regurgitation.
In the anterior region of Oystenides hyperborea, Malmgren, the cuticle is tough, but
the hypoderm is comparatively thin. A thin circular muscular coat lies beneath the
basement-membrane. The dorsal longitudinal muscles are elongated in section, stretching
from the feet at each side to the dorsal middle line, where they are connate. The ventral
longitudinal muscles are thicker, but have, a wide space between them occupied by the
transverse muscle formed by the circular coat augmented by other fibres. The nerve-
cords form an ovoid mass in section above the transverse muscular fibres, and there is
1 According to Nilsson, the fourth and fifth segments.
2 ‘ Quart. Journ. Micr.Sci./ N.s., vol. xxviii, p. 261.
no neural canal. The oblique muscles pass by the blunt inner end of the ventral
longitudinal muscles and thus are widely separated from the nerve-cords—a rare condition.
The apparent absence of neural canals in the group is interesting in connection
with the supposed special functions of the so-called “ giant-fibres.”
Cunningham1 (1888) describes three pairs of nephridia in Pectinaria belgica, the
first the largest, each consisting of a tube bent on itself, and provided with a nephrostome
and nephridiopore. The nephrostome of the first, is on the anterior side of the septum
separating the buccal from the next segment. The others occur on the fifth and
sixth segments, the third and fourth being devoid of them. They are brown or black in
colour. Between the nephridiopore of the first and the base of the branchia is the
aperture of the special glandular organ of the species. The nephrostomes are simple,
elongated funnels with the apertures directed forward, and the gonads (undifferentiated
cells) are attached to their inner side.
Linnæus (1767) included Pectinaria along with the Terebellids, the forms he alluded to
being P. grannlata and P. capensis. G-melin (1788) somewhat improved on the foregoing
by aid of O. F. Muller’s labours in the ‘Zoologiæ Danicæ Prodromus,’and the ‘ Zoologia
Danica ’ itself. He, however, did not render the position of the Pectinarians and the
Terebellids clear, including for instance P. belgica under the genus Sabella.
Cuvier separated the Amphictenidæ from the Terebellæ and Sabellæ of Muller,
Bruguière, Gmelin and Lamarck, and constituted thé group Amphitrite, containing not
only the Amphictenidæ but the Hermellidæ. Under this head» he enters a protest, so
needful in modern times, against the perpetual changing of names, rendering the study
of nomenclature much more difficult than that of facts. In Amphitrite the head is
furnished with two series of stout bristles having a metallic lustre and resembling combs,
whilst above them are the tentacles. The plumose anterior gills do not exceed four.
The Amphictenidæ were relegated by Grube in 1851 to the Terebelliformia — the
practice usually followed up to that date, ifjn 18712 he reviewed the characters which
linked Terebella, Pectinaria and Amphicteis together, but he followed Malmgren in
making each a separate family. He divided the Amphictenea into two groups, the one
including Pectinaria, Lam., having two pairs of comb-like branchiae on the third and fourth
segments, and Scalis, Grube, whilst Petta had three pairs. The number of bristle-bundles
and the lateral processes differ in each.
This group followed the Hermellidæ, and was termed the “ Pectinairiens ” by De
Quatrefages (1865). He regarded these annelids as only partly sedentary, since they
can carry their tubes about like those of the Phryganidæ. He was at one time inclined
to link them on to the Terebellidæ, but the disposition of their branchiae and their
definite anatomical characters caused him to separate them. Amongst other structural
features he mentions that there are two dorsal blood-vessels, and that the chief trunks
joining the dorsal with the ventral have pedicled sacculations on each side. He arranged
them according to the number of the branchiae, Pectinana having two and Scalis three
pairs.
Claparède (1868) thought that the separation made by Malmgren between Pectinaria
1 ‘ Quart. Journ. Micr. Soi./ N.s., vol. xxviii, p. 254.
2 f Schles. (resell./ 6th April, 1870.