The Blood Systems of Safoella and
Spirographis.
By
D. W. Ewer
(From the Zoology Department, University of Birmingham.)
With 10 Text-figures.
1. INTRODUCTION.
THE respiratory blood-pigment chlorocruorin is found only
in sabellid, serpulid, and chlorhaemid polyehaete worms. The
peculiarities and function of this pigment, together with the
physiology of respiration and blood circulation in sabellids, have
been studied by Fox and his collaborators (Fox, 1926, 1932,
1933, 1934, 1938; Eoche and Fox, 1933; E. F. Ewer and Fox,
1940). Before further work can be done on these lines it is
desirable to have a more detailed knowledge than hitherto of
the anatomy of the blood system in the animals concerned. It
was for this reason that the present investigation was undertaken. A study has been made of the anatomy of the blood
system of S a b e l l a p a v o n i n a Savigny, and this has been
compared with that of S p i r o g r a p h i s s p a l l a n z a n i i
Viviani. The latter species is so closely related to the former
that Claparede (1868-71, p. 418) remarked: 'les jeunes Spirographes sont done de vraies Sabelles.'
2. PREVIOUS WORK.
The anatomy of the blood system of S a b e l l a was studied
by Milne Edwards (1838). He described the arrangement of
blood-vessels which could be seen by means of a dorsal dissection. In the same year Grube (1838) gave an account of the
anatomy of the blood system of S p i r o g r a p h i s . His description was based on the observation of living material and the
dissection of fixed specimens. He made accurate observations
on the movement of the blood in the crown. Both authors
588
D. W. EWER
described a dorsal vessel running over the surface of the gut,
though Grube was very doubtful about the length of this vessel.
They both described the ventral vessel with the curious lateral
coilings of the paired ring vessels which lead out of it in each
segment. Grube described the vessels of the thorax, and, with
particular accuracy, the two longitudinal lateral vessels in the
abdomen.
In 1873 Clarapede redescribed the anatomy of the blood
system of S p i r o g r a p h i s . He appears to have used only
fine hand-cut sections. He was able to show that the earlier
authors had been wrong in describing a dorsal vessel over the
surface of the gut. He showed that the gut is surrounded by
a sinus, replaced anteriorly by a plexus over the oesophagus.
He stated that not only the vessels to the crown but also the
ventral vessel arise from this plexus.
Jaquet (1886) re-examined the blood system of S p i r o g r a p h i s . He rediscovered the paired lateral vessels which
had been missed by Claparede. In his description of the thorax
he followed that of Claparede in every detail.
Meyer (1888) once again described the blood system of
S p i r o g r a p h i s . He figured and described only the main
vessels. He confirmed' the existence of a gut sinus, and showed
that over the oesophagus the sinus concentrated to form a
dorsal vessel which carried the greater part of the blood from
the gut sinus to the crown. The blood from the crown returned
by definite circum-oesophageal vessels to the ventral vessel.
Meyer does not draw or describe the plexus found by Claparede
around the oesophagus, but it is apparent from his general
description that he was aware that it was there.
De Saint-Joseph (1894) published a description of Sab el la
in which he confirmed the presence of a gut sinus and also of
lateral vessels. He did not describe the thorax.
There have been a number of descriptions of the structure of
the crown filaments, which have been reviewed by Nicol (1930),
whose paper includes an accurate description of the structure
of the vessels of the filaments and pinnules of S a b e l l a .
The accounts of the blood systems of the animals described
as S a b e l l a a l v e o l a t a by Williams (1851) and of S a b e l l a
BLOOD SYSTEM OF SABEUA
589
a r e n i l e g a by Cosmovici (1879) have sometimes been compared with descriptions of S a b e l l a p a v o n i n a . They refer,
however, to S a b e l l a r i a a l v e o l a t a (L.) and B r a n c h i o m m a v e s i c u l o s u m (Montagu), respectively.
3. MATERIAL AND METHODS.
S a b e l l a was sent to Birmingham from Plymouth, and from
Millport in Scotland, while S p i r o g r a p h i s was collected at
Eoscoff in Brittany.1
Paraffin sections cut to a thickness of 10 and 20ft were used.
Material was fixed in Bouin-Hollande, Duboscq-Brazil, Schaudinn, Champy, Flemming, Hermann, and Camoy. The fixative
described by Keilin (1920) was also used. Of these the best
results were obtained with Duboscq-Brazil for S a b e l l a and
with Keilin'sfixativefor S p i r o g r a p h i s . Sections were stained
in Heidenhain's iron haematoxylin, Delafield's haematoxylin
and orange G or eosin, Mallory's triple stain, and Mann's methyl
blue and eosin.
A modification of the method of staining blood by the benzidine reaction described by Pickworth (1934) was used. Whole
worms were fixed in a 4 per cent, solution of formaldehyde in
sea-water for two days and then washed repeatedly in sea-water
to remove the formaldehyde. The material was afterwards stored
in sea-water saturated with thymol. Material thus preserved
has retained its staining power for at least a year. When
required the material was washed in running water and then
sectioned on a freezing microtome and stained as described by
Pickworth. Thick sections of 100-250/u. were used.
Small worms were stained by the modification of the benzidine
technique described by Slonimsky (1927). Living worms were
first washed in tap water before being treated with the reagents,
as sea-water produces a yellow incrustation. This method has
the disadvantage of being useful only for small and living
specimens. The reagents will not penetrate into large specimens.
Small living worms were used to observe the directions of
flow of the blood through the transparent tissues.
1
My thanks are due to the Director and StaS of the Laboratoire LacazeDuthiers at Roscoff for their hospitality and help.
NO. 328
Qq
590
D. W. EWER
4. THE ANATOMY OF THE BLOOD SYSTEM OF SABELLA.
The blood system of Sabella will be described in detail
and those differences which are found in S p i r o g r a p h i s will
then be given.
The body of Sabella is divided into two regions; anteriorly
the head and thorax, composed of a variable number of segments from six to twelve, and posteriorly the abdomen, with
segments up to the number of about three hundred. In
describing the anatomy of the blood system it is convenient
to start with the abdomen.
1. The A b d o m e n .
The general organization of the blood system in the abdomen
may be seen by an examination of Text-figs. 1 and 2.
The vascular system in the abdomen is organized into (a) the
longitudinal vessels—gut s i n u s , paired l a t e r a l vessels
and v e n t r a l vessel—and (b) the circular vessels of each
segment—ring v e s s e l s , l a t e r a l c o n n e c t i v e v e s s e l s ,
segmental dorsal vessels, notopodial vessels,
n e u r o p o d i a l v e s s e l s , t r a n s - s e p t a l v e s s e l s , and
ventral gland-shield vessels.
The Gut Sinus (or peri-intestinal sinus).—In a freshly
dissected specimen or in a small transparent worm the gut sinus
is immediately recognizable (Text-fig. 1, g.s.). The blood can
be seen to be carried forward by the peristalsis of the sinus wall.
The sinus runs the whole length of the worm from the hindmost
segment to the anterior septum of segment III. In each segment it receives a pair of ring vessels (Text-fig. 1, r.v.) which
come into it ventro-laterally.
The V e n t r a l Vessel.—The ventral vessel (Text-fig. 1,
v.v.) runs backwards along the whole length of the worm from
the posterior portion of segment II. It lies in the ventral
mesentery above the giant fibres and nerve-cord (Text-fig. 3,
v.v.). The vessel is circular in cross-section and may reach a
diameter of 100/L*. It is covered with black cells (Text-fig. 3,
&.C.).1 From the ventral vessel arise a pair of ring vessels as
1
These cells containing black granules have been called 'chloragogen
vm.b.
v.v.
TEXT-FIG. 1.
s.dv
rv.
L.v
tieu v.
S a b e l l a p a v o n i n a . Diagram of the vessels in the abdominal segments seen from the posterior aspect. The bodywall and septa of the right side, and the mesenteries, have been out away. Capillaries are omitted, d.m.b., dorsal
muscle block; g.s., gut sinus; I.e., lateral connective vessel; l.v., lateral vessel; neu.g., neuropodial gland; neu.v.,
neuropodial vessel; not.g., notopodial gland; not.v., notopodial vessel; r.v., ring vessel; a.d.v., segmental dorsal vessel;
t.s., trans-septal vessel; v.g.s., ventral gland shield; v.g.s.v., ventral gland-shield vessel; v.m.b., ventral muscle block;
v.v., ventral vessel.
neuc)
U
d.mb
as..
W
H
CD
H
H
GO
!
D
so
592
D. W. EWER
lateral branches immediately in front of each septum (Textfig, l.r.i?.; Text-fig. 3, r.v.).
The L a t e r a l Vessels.—These vessels (Text-fig. 1, l.v.)
can be seen through the skin in small living worms as two
zigzag lines running along the whole length of the body in a
latero-dorsal position. They run forward as far as the posterior
septum of segment II. The lateral vessels are joined to the ring
vessels in each segment by two lateral connective vessels (Textfig. 1, I.e.). On each side of each segment the lateral vessels
give off two blind-ending branches—the segmental dorsal and
the notopodial vessels (Text-fig. 1, s.d.v. and not.v.).
If one of the lateral vessels is followed forwards along the
dorsal muscle block beneath which it runs, its relations may be
understood. Immediately after passing through a septum the
lateral vessel is joined by the lateral connective vessel (Textfig. 1, I.e.) and then runs forwards and obliquely upwards. A
short distance farther on it gives off the segmental dorsal vessel
(Text-fig. 1, s.d.v.) which runs beneath the dorsal muscle block
towards the mid-dorsal line, ending there blindly. The lateral
vessel then changes its course and runs forwards and obhquely
downwards. Shortly before it reaches the anterior septum of the
segment it gives off the notopodial vessel (Text-fig. 1, not.v.)
which runs downwards beneath the dorsal muscle block to the
coelomie pouch of the notopodium (Text-fig. 2, note). After
giving off the notopodial vessel the lateral vessel again changes
its direction and, running forwards and obliquely upwards, it
passes through the septum to join the lateral connective vessel
of the next segment.
Along its course the lateral vessel gives off blind-ending
capillaries which project into the coelom (Text-fig. 2, l.v.).
The vessel may be as much as 80/z in diameter.
The E i n g Vessels.—The two ring vessels (Text-fig. 1,
r.v.) of each segment arise laterally from the ventral vessel
immediately in front of each septum and make a characteristic
S-shaped bend at their origin. Each of them runs along the
ventral muscle block towards the mouth of the segmental
cells' by Claparede (1873) and by de Saint-Joseph (1894). They are discussed by Meyer (1888) and by Evenkamp (1931).
TEXT-FIG. 2.
v.^.s.v
L.v.
neu.v
note.
nob.v.
S a b e l l a p a v o n i n a . Diagrammatic section of an abdominal segment seen from the posterior aspect. The vessels
in the muscles and glands of the right side are shown, c. capillaries joining the vessels of the neuropodial and ventral
glands; d.m.b., dorsal muscle block; l.v., lateral vessel; neu.g., neuropodial gland; neu.v., neuropodial vessel; not.c,
notopodial capillaries; not.g., notopodial gland; not.v., notopodial vessel; s.d.v., segmental dorsal vessel; v.g.s.,
ventral gland shield; v.g.s.v., ventral gland-shield vessel; v.m.b., ventral muscle block.
v.m.b
d.m.b.
s.d.v.
01
CO
OS
3
§
594
T>. W. EWER
organ. Although close to the septum it is not attached to it in
this region. The S-shaped bend is covered with black cells continuous with those covering the ventral vessel. On reaching the
segmental organ the ring vessel passes between the coelomostome and the septum, turns round, and runs obliquely upwards attached to the anterior face of the septum to join the
gut sinus in a ventro-lateral position. About three-quarters of
b.c.
vm.
vv.
TEXT-ITG. 3.
S a b e l l a p a v o n i n a . Section showing the relations of the ventral
vessel. Blood-vessels shaded grey, b.c, black cells; g.f., giant
fibres; n.c, nerve-cord; r.v., ring vessel; v.g., ventral groove;
v.g.s., ventral gland shield; v.m., ventral mesentery; v.m.b., ventral
muscle block; v.v., ventral vessel.
the way from the segmental organ along the upper limb of each
ring vessel there arises the lateral connective vessel (Text-fig. 1,
I.e.) which runs upwards and obliquely outwards on the septum
to join the lateral vessel of that side (Text-fig. 1, l.v.).
In many segments there are additional anastomoses on each
side between the lateral connective vessel and the dorsal limb
of the ring vessel, or reduplications of the latter. The form of
these additional vessels is very variable and they are of irregular
distribution. They do not necessarily occur on both sides of
the same segment. A number of these structures is shown in
Text-fig. 4.
The ring vessels may reach a diameter of 100/*.
BLOOD SYSTEM OF SABELLA
595
The S e g m e n t a l D o r s a l Vessels.—The two segmental
dorsal vessels of each segment (Text-fig. 1, s.d.v.) arise from the
lateral vessels as described above. The vessels curve upwards
Lv
rv.
TEXT-FIG. 4.
Sabella p a v o n i n a . Diagrams of four different types of anomalous organization of the ring vessels, g.s., gut sinus; I.e., lateral
connective vessel; l.v., lateral vessel; r.v., ring vessel.
beneath the dorsal muscle blocks. Along their length blindending capillaries arise and project into the coelom (Text-fig. 2,
s.d.v.). The segmental dorsal vessels are blind-ending; each runs
as far as the dorsal mesentery, but never joins the corresponding
596
D. W. EWER
vessels of the opposite side. The vessels may branch towards
their end. They reach a diameter of 40/*..
The N o t o p o d i a l Vessels.—The abdominal parapodia
have dorsal uncini and ventral chaetae. Each parapodium has
two parapodial glands (Text-figs. 1 and 2, not.g. and neu.g.),
the neuropodial gland lying beneath the chaetal bundle while
the notopodial gland surrounds the uncinal papilla of the notopodium on its ventral and anterior sides. The papilla itself
encloses a pouch of coelom which is filled with blind-ending
capillaries (Text-fig. 2, note). These capillaries are supplied
by the notopodial vessel (Text-fig. 2, not.v.) which arises from
the lateral vessel of that side as described above. The notopodial
vessel curves ventrally beneath the dorsal muscle block and
then runs upwards into the coelomic pouch of the notopodium.
Blind-ending capillaries which project into the coelom are given
off along the length of the vessel.
These vessels may reach a diameter of 30/*.
The V e n t r a l Gland Shield a n d T r a n s - s e p t a l
Vessels.—Along the ventral surface is a double series of
segmentally arranged rectangular blocks of glands known as
ventral gland shields (Text-figs. 1 and 2, v.g.s.). These are
liberally supplied with blind-ending capillaries.
From the ring vessel on each side of each segment, as it passes
from the ventral vessel to the segmental organ, is given off
a short vessel—the trans-septal vessel—which runs backwards
through the septum along the surface of the ventral muscle
block (Text-fig. 1, t.s.). Behind the septum the trans-septal
vessel forks to form the neuropodial vessel (Text-fig. 1, neu.v.)
and the ventral gland-shield vessel (Text-fig. 1, v.g.s.v.).
The ventral gland-shield vessel runs from the fork of the
trans-septal vessel transversely across the surface of the ventral
muscle block towards the midline. About two-thirds of the
way from the parapodium across the muscle block the vessel
turns ventrally and runs down through the muscle block (Textfig. 2, v.g.s.v.). In the ventral portion of the muscle block the
vessel divides into a number of branches which ramify in the
ventral gland shield. These branches lead to blind-ending
capillaries which can be seen through the skin of the worm.
BLOOD SYSTEM OF SABELLA
597
The ventral gland-shield vessel as it runs across the ventral
muscle block gives off blind-ending capillaries which project
into the coelom; there is a large clump of them where the vessel
turns down to run into the muscle (Text-fig. 2).
The N e u r o p o d i a l Vessels.—From the fork of the
trans-septal vessel, the neuropodial vessel (Text-fig. 1, neu.v.)
runs outwards for a short distance and then turns posteriorly
and runs along the inner side of the neuropodial gland. Along
its length it gives off blind-ending capillaries which ramify
among the muscles of the chaetal bundle and in the neuropodial
gland (Text-fig. 2, neu.v.).
In each segment vessels run across from the ventral gland
shield of each side beneath the ventral surface of the ventral
muscle block to the neuropodial gland, joining branches of the
neuropodial vessel (Text-fig. 2, c).
The B l i n d - e n d i n g Capillaries.—These capillaries
arise from all the vessels in the abdomen except the ring vessels,
the lateral connective vessels, and the gut sinus. They may have
a diameter up to 30/z.
The T e r m i n a l Segments.—The general form of organization described in the abdominal region is found as far
back as the last chaetigerous segment. In this region the
individual main vessels become smaller in diameter and the
gut sinus is not so well developed. Capillaries are not found
except in the ventral gland shields, where they are few in
number but no smaller in diameter than any of the other vessels
of this region.
The terminal projection on which the anus is situated is
devoid of blood supply.
2. The H e a d and T h o r a x .
The general organization of the main vessels in the head and
the thoracic segments is shown in Text-figs. 5 and 6. It is convenient to describe the thorax first and then the head,
(a) The T h o r a x .
The thoracic chaetigerous segments (the first of which is
segment II) are distinguished from the abdominal segments by
the inversion of the position of the uncini and chaetae of the
598
D. W. EWER
parapodia: in the thorax the chaetae are dorsal and the uncini
are ventral. There are no uncini on the first chaetigerous segment. In this region the basic plan of the blood system already
described for the abdomen is found except in segment II.
The Gut S i n u s , P e r i - o e s o p h a g e a l P l e x u s , a n d
L a t e r o - d o r s a l Vessels.—The gut sinus runs anteriorly
from the abdominal region as far as the anterior septum of
segment III (Text-fig. 5, g.s.). In segment II the gut sinus is
replaced by a plexus—the peri-oesophageal plexus—which lies
on the dorso-lateral and lateral surfaces of the oesophagus in
this segment (Text-fig. 5, p.o.p.). Above this plexus run two
latero-dorsal vessels (Text-fig. 5, l.d.v.) which unite at the
anterior margin of segment II to form a single dorsal vessel
which runs forwards in segment I (peristomium) over the dorsal
surface of the oesophagus (Text-fig. 5, d.v.). The peri-oesophageal plexus runs forwards and downwards through segments
II and I. The transition of gut sinus to plexus corresponds
exactly with the histological transition from stomach to oesophagus described by Nicol (1930).
The V e n t r a l Vessel.—The ventral vessel starts in the
thorax at the boundary between segments II and III. It is
formed at this level by the fusion of the ventral limbs of the
two circum-oesophageal vessels (Text-fig. 5, c.o.v.). The black
cells on the ventral vessel persist as far forwards as segment III.
The L a t e r a l and L a t e r a l C o n n e c t i v e Vessels.—
The two lateral vessels (Text-fig. 5, l.v.) run forwards in the
thorax as far as the anterior surface of the septum between
segments II and III. From segment VI forwards the vessels
may break up-into a number of smaller parallel vessels. The
connexion of each lateral vessel with the ring vessels by
the lateral connective vessels is found in all segments except
the first.
T h e E i n g V e s s e l s . — T h e two ring vessels of each segment
are found in normal form as far forwards as segment III. In
the majority of individuals the reduplications of the ring vessels
are more elaborate than those which have been described in the
abdomen.
In segment II the dorsal limb of each ring vessel is absent,
c.v
c.o.v.
p°p-
TEXT-FIG. 5.
s,cl.v
neu.w
u
ru.
S a b e l l a p a v o n i n a . Diagram of the vessels of the thorax seen in lateral view. The anterior end of the worm is to the
left. The body wall and septa of the left side, and the mesenteries, have been removed. Capillaries are not shown
except around the oesophagus. The segments are numbered in Roman numerals, b.v., branchial vessel; c.o.v., circumoesophageal vessel; c.v., collecting vessel of the peri-oesophageal plexus; d.v., dorsal vessel; g.s., gut sinus; I.e., lateral
connective vessel; l.d.v., latero-dorsal vessel; l.l.v., vessel supplying the lateral lip; l.l.v.1, vessel supplying the lateral
lip, ventral sac, and ventral collar fold; l.v., lateral vessel; neu.v., neuropodial vessel; not.v., notopodial vessel;
p.o.p., peri-oesophageal plexus; r.v., ring vessel; s.d.v., segmental dorsal vessel; s.in.v., vessel supplying the chaetal
muscles of segment I I ; l.v., transverse vessel; v.g.s.v., ventral gland-shield vessel; v.v., ventral vessel.
d.v.
u
5
td
H
03
CO
a
t
o
o
600
D. W. EWBK
the ventral limb connecting the anterior end of the lateral
vessel of that side with the ventral vessel by way of the lateral
connective (Text-fig. 5, I.e.). This absence of the dorsal limb
of the ring vessels of segment II is to be correlated with the
absence of the gut sinus in this segment.
The S e g m e n t a l D o r s a l Vessels.—These vessels
arise normally as far forwards as segment III (Text-fig. 5,
s.d.v.). The vessels are missing in segment II, the lateral vessels,
from which these vessels normally arise, ending at the posterior
septum of segment II.
The N o t o p o d i a l Vessels.—These vessels arise in the
normal manner as far forwards as segment III (Text-fig. 5,
not.v.). They are absent in segment II, in correlation with the
ending of the lateral vessels. The muscles of the notopodial
chaeta of segment II are supplied by a unique vessel which
arises from the ring vessel of each side of that segment more
laterally than the trans-septal vessel. This vessel runs forward
and upwards and breaks up into blind-ending capillaries around
the chaetal muscles on their ventral side (Text-fig. 5, s.m.v.).
The V e n t r a l Gland Shield and N e u r o p o d i a l
Vessels.—These vessels show their normal form as far forwards as segment III (Text-fig. 5, v.g.s.v. and neu.v.). The
system is absent in segment II, which has no neuropodium, and
there are no ring vessels in segment I from which neuropodial
vessels could arise. The ventral gland shields of segments II
and III are supplied by capillaries which run back from the
ventral collar fold.
In the abdomen the ciliated groove which runs along the
ventral surface of the worm divides the ventral gland shields
into two blocks in each segment. At the junction with the
thorax this ciliated groove runs round into a dorsal position
and so the ventral gland shields in the thorax are in the form
of single segmental blocks. This does not, however, alter the
arrangement of the capillary supply to the glands.
It will be noted that the inversion of the parapodia in the
thoracic region is not reflected in the organization of the blood
system.
There is no blood-supply to the large thoracic kidneys.
BLOOD SYSTEM OF SABELLA
601
(b) The H e a d . 1
The D o r s a l Vessel.—The dorsal vessel (Text-fig. 5, d.v.)
arises by the fusion of the two latero-dorsal vessels and runs
forwards over the surface of the oesophagus as far as the supraoesophageal ganglia, behind which it forks to form a T whose
cross limb is the transverse vessel (Text-fig. 5, t.v.). The vessel
has a diameter up to 80/x..
The T r a n s v e r s e Vessel.—The transverse vessel is
situated behind the supra-oesophageal ganglia and parallel to
their transverse axis. Above the root of the cireum-oesophageal
nerve commissure of each side it forks to form the branchial
vessel which runs forwards and the circum-oesophageal vessel
which runs downwards and backwards behind the nervous
commissure. The vessel reaches a diameter of 100/i.
The C i r c u m - o e s o p h a g e a l Vessels.—These two vessels run downwards and backwards behind the circum-oesophageal nerve commissures (Text-fig. 5, c.o.v.). The two vessels
do not join in segment I as do the nerve commissures, but run
backwards as far as the posterior portion of segment II where
they join to form the ventral vessel.
Shortly after their origin from the transverse vessel each
circum-oesophageal vessel gives off a vessel supplying the lateral
lip (Text-fig. 5, l.l.v.). Further back in segment I the circumoesophageal vessel of each side gives off a vessel which immediately divides into two branches supplying the lateral lip, the
ventral sac, and ventral collar fold (Text-fig. 5, l.l.v.1). In the
posterior portion of segment I the circum-oesophageal vessel
of each side also receives a vessel which drains the peri-oesophageal plexus (Text-fig. 5, c.v.). The circum-oesophageal
vessels reach a diameter of about 100/LI.
The P e r i - o e s o p h a g e a l Plexus.—This replaces the
gut sinus in segment II and is continued forward into segment I.
The plexus runs anteriorly and downwards to surround the
oesophagus on the dorso-lateral and lateral surfaces in segment
1
The head is composed of the peristomium (segment I), of wMcli the
collar fold is a part and of the prostomium and its appendages, the crown,
lateral lips, and ventral sac.
602
D. W. EWER
II and on the lateral and ventral surface in segment I (Textfig. 5, p.o.p.). The blood from the plexus is collected ventrally
on each side into a vessel which empties into the circumoesophageal vessel (Text-fig. 5, c.v.). At the sides of the
oesophagus the plexus extends outwards between the dorsal
and ventral muscle blocks of segment I.
The B r a n c h i a l , F i l a m e n t , and P i n n u l e V e s s e l s .
—The two branchial vessels arise from the transverse vessel
as described above and run forwards into the crown (Textfig. 6, b.v.). At the base of the crown each vessel swells out to
form the branchial vesicle (Text-fig. 6, b.ves.). From the inner
side of each branchial vessel just anterior to the branchial
vesicle arises a single slender vessel which runs to the palp ;x
it is blind-ending and has no branches (Text-fig. 6, p.v.).
From the branchial Aresicle the branchial vessel of each side
runs forwards. It sends off blind-ending vessels to each filament
of the crown in turn (Text-fig. 6, f.v.) and ends in supplying the
most distal filament.
The filaments of the crown give rise to numerous small appendages, the pinnules. Into each of these the filament vessels
send a short blind-ending vessel, the pinnule vessel (Text-fig. 6,
pn.v.).
The branchial vesicle may attain a diameter of 100ft, and the
branchial vessel 75/x. The filament vessel reaches a diameter
of 60ju, and the pinnule vessel 20/x..
The Vessels of t h e L a t e r a l Lips.—The lateral lips
are each supplied with a rich plexus of capillaries arising from
the circum-oesophageal vessels as described above. The plexus
is in the form of branching and blind-ending capillaries (Textfig. 6, U.v.).
The Vessels of t h e V e n t r a l Sacs and V e n t r a l
Collar Folds.—The vascular supply to these organs arises
from the circum-oesophageal vessels as described above. The
main trunk to the ventral collar fold of each side runs down the
1
Morphologically the whole crown represents the palps of other polychaetes (Pruvot, 1885; Johansson, 1927). The two processes referred to
here as palps are outgrowths of the dorsal lip; they are Fauvel's 'palpes'
(1927).
Pv-
TBXT-EEG. 6.
S a b e l l a p a v o n i n a . Diagram of the vascular system seen in a
ventral view of the head and thorax, b.v., branchial vessel;
b.ves., branchial vesicle; c.f.c, collar-fold capillaries; f.v., filament
vessel; I.I.V., lateral lip vessels; p.v., palp vessel; pn.v., pinnule
vessel; v.s., ventral sac.
604
D. W. EWER
posterior border of the collar fold. It also sends branches forwards to the ventral sac and backwards to the ventral gland
shields of segments II and III.
5. THE ANATOMY OF THE BLOOD SYSTEM OF SPIEOGRAPHIS.
All the main vessels which have been described in S a b e l l a
occur in identical form in S p i r o g r a p h i s . Such differences
as there are, are in points of detail. Only these detailed differences will be described here.
The L a t e r a l and A s s o c i a t e d Vessels.—The two
lateral vessels are similar to those described in S a b e l l a . The
segmental dorsal vessels, however, branch frequently. Additional vessels also arise from the lateral vessels and run up
beneath the dorsal muscle blocks parallel to the segmental
dorsal vessels. The notopodial vessels, too, occasionally branch.
In a few segments additional vessels coming from the lateral
vessels run down to the notopodia.
The E i n g Vessels.—The reduplications of the ring
vessels described in S a b e l l a (Text-fig. 4) are much more
highly developed in S p i r o g r a p h i s . The anterior face of
each septum is covered with a plexus of fine vessels joining not
only the dorsal limb of each ring vessel with the corresponding
lateral connective vessel, but also the two limbs of the ring
vessel. This plexus is an elaboration of the corresponding
reduplications in S a b e l l a .
The V e n t r a l G l a n d - s h i e l d Vessels a n d t h e i r
Derivatives.—Unlike the state of affairs in S a b e l l a there
are in the ventral muscle blocks of S p i r o g r a p h i s fine
capillaries, which run parallel to the longitudinal axis of the
worm. These ventral muscle capillaries (Text-fig. 7, v.m.c.)
originate in each segment from that portion of the ventral
gland-shield vessel which runs across the top of the ventral
muscle block. Most of these capillaries are continuous with the
corresponding capillaries arising from the ventral gland-shield
vessels of the adjoining segments, but some of them which run
out laterally in the muscle block are blind-ending.
The plexus of capillaries in each ventral gland shield runs up
on the median side of the ventral muscle block and forms a sub-
605
BLOOD SYSTEM OF SABELLA
neural plexus beneath the nerve-cord (Text-fig. 7, s.n.p.). In
some segments a prolongation of the horizontal coelomic portion
of the ventral gland-shield vessel runs over the ventral muscle
block to the midline and then downwards to join the subneural plexus (Text-fig. 7, ex.).
The T h o r a c i c C h a e t i g e r o u s Segments.—The vessels of the thoracic chaetigerous segments are similar to those
ex
vm.c.
sn
TEXT-FIG. 7.
Spirographis s p a l l a n z a n i i . Diagram of the vessels associated with the ventral muscle block. Cf. Sabella, fig. 2. ex.,
extension of the ventral gland-shield vessel; s.n.p., sub-neural
plexus; v.g.s.v., ventral gland-shield vessel; v.m.c, capillaries of
the ventral muscle block; v.v., ventral vessel.
in the abdominal segments, but the capillaries in the ventral
muscle blocks are missing.
T h e B r a n c h i a l a n d F i l a m e n t Vessels.—The vessels
in the filaments of the crown arise in pairs from the branchial
vessel, instead of singly as in S a b e l l a . Short reduplications
of the branchial vessel occur. There is no asymmetry of the
vessels at the base of the crown corresponding to the asymmetry
of the latter.
T h e N e u r a l P l e x u s .—Above the sub-oesophageal ganglia
and the ganglia of segment II there is a plexus of fine vessels,
NO. 328
Br
606
D. W. EWER
the neural plexus, arising from the circum-oesophageal vessels.
This is not found in S a b e 11 a.
6. THE BLOOD SYSTEM OF SMALL SPIROGBAPHIS.
S p i r o g r a p h i s grows to a larger size than S a b e l l a .
There is therefore the possibility that the differences which have
been noted above are connected with the greater size of S p i r o g r a p h i s and are not specific1 differences. The arrangement of
the blood-vessels in the abdomen of a number of small specimens
of S p i r o g r a p h i s was therefore examined.
Small worms, 4-5 cm. in length, showed no differences from
S a b e l l a as far as the blood system was concerned. There
were no capillaries in the ventral muscle blocks, no reduplication
of the ring vessels or of the segmental dorsal vessels.
In larger worms, 6-7 cm. in length, capillaries were found
in the ventral muscle blocks, reduplications of the segmental
dorsal vessels were observed, but the ring vessels were no more
complicated than the condition described for reduplications in
Sabella.
Some of the peculiar features of the blood system of
large S p i r o g r a p h i s are thus also found in these small
individuals of 6-7 cm. in length; these are much smaller than
some of the S a b e l l a studied, which were up to 20-30 cm. in
length. The differences between the vessels of S p i r o g r a p h i s
and S a b e l l a are therefore real and not due to the former
animal being the larger.
7. HISTOLOGY.
While no attempt has been made at a detailed examination
of the histology of the blood-vessels, it is possible to draw attention to differences between individual vessels which would
appear to be significant in the physiology of the circulation. The
structure of the vessels is the same in S a b e l l a and S p i r o graphis.
Claparede (1873) described the fine structure of the ventral
vessel of S p i r o g r a p h i s . He recognized a columnar endo1
The word 'specific' is written wittingly, since the division of Spirographis and Sabella into separate genera seems hardly justified by
the few anatomical differences between them.
BLOOD SYSTEM OF SABELIM.
607
thelium, a single layer of muscle-fibres and an outer layer of
peritoneal cells.
The histology of the ventral vessel was reinvestigated by
Hescheler (in Lang, 1903, p. 222). He agreed with Claparede's
description, but found in place of a columnar endothelium a
flattened endothelium separated from the layer of muscle-fibres
by a layer of connective tissue fibres.
I have found that the blood-vessels fall into two clear histological categories: (1) vessels with a muscular coat, and (2)
thin-walled vessels.
1. Vessels w i t h a M u s c u l a r C o a t .
These vessels include the A'entral vessel and the lateral
vessels, as well as the latero-dorsal vessels, the dorsal vessel,
the branchial vesicles, and the circum-oesophageal vessels. The
walls of these vessels are covered externally by a layer of peritoneal cells beneath which is a thin layer of circular muscle-fibres
lying on a structureless layer, on whose inner side are endothelial
cells. Text-fig. 8 shows the structure of the ventral vessel.
The gut sinus (Text-fig. 9) is a special case of this arrangement.
It is covered with a layer of peritoneal cells. Beneath this is
a single layer of circular muscle-fibres which is about 10\i thick.
This layer is, however, greatly thickened in the region of the
junction between the stomach and the intestine (Nieol, 1930)
and may there reach a thickness of 100/x. Beneath the musclelayer is a structureless layer, inside which are endothelial cells.
On the inner wall of the sinus is another layer of endothelial
cells lying on the basement membrane of the gut cells. I have
never observed cells free in the blood in this region as described
by Eomieu (1923) in S p i r o g r a p h i s .
This condition is similar to that described by Lee (1912) for
the intestinal sinus of serpulids. Evenkamp (1931) has, however, described a different arrangement in the gut sinus of the
sabelline L a o n o m e k r o y e r i , where he found a layer of
circular muscles lying between the basal membrane of the gut
cells and the endothelial cells of the inner wall of the sinus.
Across the lumen of the sinus runfinethreads of the structureless layer covered by scattered endothelial cells (Text-fig. 9,2>.c).
NO. 328
sr2
608
D. W. EWEE
The threads were first described by Claparede (1873) in Myxi cola i n f u n d i b u l u m and called 'brides contractiles'.
Similar structures have been described by Faulkner (1930) in
the serpulid F i l o g r a n a i m p l e x a , and by Lee (1912) in
a number of other serpulids.
rn
50 u
TEXT-FIG. 8.
Sabella p a v o n i n a . Section showing the structure of the wall of
the ventral vessel, b.c, black cells; b.g., black granules shed into
the coelom from the black cells; m./., muscle-fibres; n.e.c, nuclei
of endothelial cells; p.c, peritoneal cells; s.l., structureless layer.
It will be noted that all the longitudinal trunks are built
on the same principle.
2. T h i n - w a l l e d V e s s e l s .
All the remaining vessels have thin walls containing scattered
BLOOD SYSTEM OF SABELLA
609
nuclei but devoid of muscle-fibres. In S p i r o g r a p h i s the
larger of these vessels have in addition a thin structureless layer
lining the lumen; this has not been detected in corresponding
vessels in S a b e l l a .
e.c.
TEXT-FIG. 9.
Sabella p a v o n i n a . Section of the gut sinus at the level of the
junction of the stomach and intestine. The sinus is shaded grey.
6.c,' bride contractile'; 6.m., basement membrane of the gut cells;
e.c, endothelial cells; g.c, gut cells; m.f., muscle-fibres; p.c,
peritoneal cells; s.l., structureless layer.
8. THE COUESB OF THE CIBCULATION.
The main features of the circulation of S a b e l l a and S p i r o g r a p h i s have been described by Fox (1933, 1938).
Previously in S p i r o g r a p h i s Delle Chiaje (quoted in
Grube, 1838) regarded the ventral vessel as a vein and the other
vessels as arteries, but gave no reasons. Grube (1838) gave a
good description of the reversibleflowof the blood in the crown.
He considered that the blood flowed forwards in the lateral
610
D. W. EWER
vessels to the crown and backwards from the crown, by way
of the transverse vessel, into the dorsal vessel.
Claparede (1873) was of the opinion that all the blood which
was carried forward by the gut sinus flowed into the perioesophageal plexus. Prom this plexus the blood flowed into
the crown and then back again into the plexus which thus
contained mixed blood. Some of the blood from the plexus
flowed into the ventral vessel and into the vessels supplying
the ventral collar folds. Claparede speaks of the possibility of
some type of sorting mechanism in the plexus, but, he says,
'L'enchevetrement des vaisseaux dans le plexus est trop considerable pour qu'on puisse esperer une solution a cette question' (p. 82). It will be seen that this mistaken interpretation
of the anatomy of the thoracic vessels made the sorting
mechanism of the oxygenated and de-oxygenated blood seem
very complex.
Fox (1933, 193S) gives the following description. Almost all
the blood-vessels, both trunks and blind-ending capillaries,
contract rhythmically. Blood is forced out of the capillaries
and of the vessels in the crown by centripetal contractions of
the walls of these vessels; then after a short interval blood from
the continuous trunks flows back again into the capillaries.
In the continuous trunks blood is moved along by peristalsis.
Blood is propelled forwards in the gut sinus, from which it
flows into the dorsal vessel and circum-oesophageal vessels,
thus reaching the ventral vessel, through which it is forced
backwards (Text-fig. 10 A). In the abdomen blood moves from
the ventral vessel into the ring vessels of each segment, through
which part of the blood reaches the gut sinus, and part, by way
of the lateral connectives, reaches the lateral vessels (Text-fig.
10 B). It is then moved forwards along the latter as discrete
trains of blood starting from the posterior end of the worm,
the vessels being closed for some distance behind that section
which is full of blood. The notopodial vessels, segmental dorsal
vessels, and capillaries of each segment fill as the trains of
blood in the lateral vessels reach them, and empty again when
the train of blood passes on. There is no such regularity in the
emptying andfillingof the gland-shield capillaries. The rates of
611
BLOOD SYSTEM OF S A B E M J A
rhythmical contractions of the various vessels differ; for
S a b e l l a a t 19° C. the following times in seconds between
contractions are given; pinnule, filament, and branchial vessels
10-1, lateral vessels 84, ventral vessel 5-5, gut sinus 2-3. The
s.dv.
U
t-s
neo. v.
TEXT-FIG. 1 0 A.
S a b e l l a p a v o n i n a . Diagram of the outlines of the vessels seen
in fig. 1. The direction of the blood-flow is indicated byarrows.
Vessels in the abdominal segments seen from the posterior aspect
(cf. fig. 1). g.s., gut sinus; I.e., lateral connective vessel; l.v.,
lateral vessel; neu.v., neuropodial vessel; not.v., notopodial
vessel; r.v., ring vessel; s.d.v., segmental dorsal vessel; t-s.v.,
trans-septal vessel; v.g.s.v., ventral gland-shield vessel; v.v.,
ventral vessel.
contractions are not synchronous in the two sides of the crown
or in the two lateral vessels.
Fox (1933, p. 482) described the coelomic capillaries in a given
segment as all contracting at the same time, the contractions
in one segment being one or more seconds behind those in the
segment immediately posterior to it. It appears to me that this is
612
D. W. EWER
probably not due to a spontaneous rhythm of capillary contraction but to the fact that many of the coelomic capillaries arise
from the lateral vessel or its branches andfillperiodically as the
rhythmic trains of blood pass forwards along the lateral vessel.
I have made the following further observations on the cir-
Ld.v.
P°
d.v.
b.v.
LLv.
S a b e l l a p a v o n i n a . Diagram of the outline of the vessels seen in
fig. 5. The direction of the blood-flow is indicated by arrows.
Vessels in the head and thorax, the anterior end of the worm
being to the left (cf. fig. 5). b.v., branchial vessel; c.o.v., circumoesophageal vessel; c.v., collecting vessel of the peri-oesophageal
plexus; d.v., dorsal vessel; g.s., gut sinus; I.e., lateral connective
vessel; Ld.v., latero-dorsal vessel; l.l.v., vessel supplying the
lateral lip; l.l.v.1, vessel supplying the lateral lip, ventral sac, and
ventral collar fold; l.v., lateral vessel; neu.v., neuropodial vessel;
not.v., notopodial vessel; p.o.p., peri-oesophageal plexus; r.v.,
ring vessel; s.d.v., segmental dorsal vessel; s.m.v., vessel supplying
the chaetal muscles of segment I I ; t.v., transverse vessel; v.g.s.v.,
ventral gland-shield vessel; v.v., ventral vessel.
culation of S a b e l l a . As in the lateral vessels, so too in the
ventral vessels separate trains of blood are carried along by
peristalsis.
The neuropodial capillaries fill more frequently than the
BLOOD SYSTEM OF SABELLA
613
ventral gland-shield capillaries and blood passes across the
connecting capillaries to the ventral gland-shield vessels by
peristalsis. There is, however, no definite circulation from the
neuropodial to the ventral gland-shield vessels, for occasionally
blood may be seenflowingin the opposite direction.
In segments I and II the blood-flow is as follows (Textfig. 10 B). At the anterior end of segment III the blood from the
gut sinus passes into the two latero-dorsal vessels and into the
peri-oesophageal plexus on each side; from the peri-oesophageal
plexus it flows into the eircum-oesophageal vessels. At 13-5° C.
the following average periods of contractions in seconds were
found: gut sinus in thorax 9-1, latero-dorsal vessels and perioesophageal plexus 12-9. The greater frequency of the gut sinus
contractions causes a certain excess of blood to flow back from
the level of the peri-oesophageal plexus into the gut sinus after
each peristaltic wave of the sinus reaches the anterior end.
From the latero-dorsal vessels the blood is carried into the
dorsal vessel and thence into the transverse vessel. Some of
the blood then flows into the crown along the branchial vessels
and some runs directly into the circum-oesophageal vessels.
The blood whichflowsinto the crown is held in the blind-ending
filament and pinnule vessels for a short time and is then driven
back into the transverse vessel. This arrangement might result
in the same portion of blood flowing into the crown, back to
the transverse vessel, and into the crown again. There is no
valvular arrangement in the vessels which could separate the
aerated from the unaerated blood. If, however, the contraction
frequencies of the vessels are determined the method of separation becomes clear. At 14° C. the following average frequencies
of contraction were found: branchial vessel 16-6 seconds,
circum-oesophageal vessels 11-4 seconds. Fox (1933, p. 481)
has shown that the vessels of the crown remain empty for just
over half the period of the cycle of their contraction. As already
stated, I have found that the blood expelled from the branchial
vessels is returned to the transverse vessel. At the frequency
of contraction of the branchial vessels at 14° C. the blood would
remain in the transverse vessel for about 10 seconds. If one
of the circum-oesophageal vessels contracts during this period
614
D. \V. EWER
the blood will be carried away to the ventral vessel. The rates
of contraction of the branchial and circum-oesophageal vessels
given above show that this will happen at least for every
alternate contraction of the branchial vessel of each side.
While the gut sinus may be regarded as carrying deoxygenated blood, it is clear that the blood in the ventral vessel is
'mixed', for some of it is derived from the peri-oesophageal
plexus and the anterior end of the lateral vessels. Moreover,
the contraction frequency of the circum-oesophageal vessels
implies that some of the blood from the dorsal vessel is carried
directly to the ventral vessel without flowing into the crown.
Some of the blood in the circum-oesophageal vessels runs into
the capillaries in the lateral lips. These capillaries fill at each
contraction of the circum-oesophageal Aressels and empty again
rapidly. There is, however, no such periodicity recognizable in
the capillaries of the ventral collar folds and ventral gland
shields of segments II and III.
When the bloodflowingforwards in the lateral vessels reaches
segment II it must run downwards through the lateral connective and ring vessels of that segment and so into the ventral
vessel. This could not be seen, however, nor could it be ascertained whether blood runs upwards in all the thoracic ring
vessels as it does in those of the abdomen, or whether the
direction is reversed in the anterior lateral connective vessels
and ring vessels, thus helping to empty the lateral vessels.
In small worms it is possible to see that the normal direction
of circulation in the lateral and ventral vessels is reversible.
This shows that there is no 'polarization' of the blood-vessels
of S a b e l l a as Carlson (1908) has postulated to account for
the constancy of the direction of flow of blood in the dorsal
vessel of N e r e i s .
9. THE DISTRIBUTION AND FUNCTION OF BLIND-ENDING
VASCULAR STRUCTURES IN THE POLYCHAETES.
Blind-ending vessels are one of the peculiarities of the blood
system of sabellids. Similar vascular structures occur in a
number of other polychaetes. Excluding blind-ending vessels
BLOOD SYSTEM OF SABELLA
615
in gills, palps, and tentacles, they may be roughly divided into
four categories.
1. Blind-ending Vessels arising from the Eing
Vessels.
Allen (1904) has described bunches of contractile blind-ending
vessels arising from the ring vessels of the disomid Poeciiochaetus serpens Allen. Miiller (1858) andMclntosh (1878)
have found contractile sac-like structures in a similar position
in Magelona papillicornis F. Mull. Huxley (1883) and
Faulkner (1930) have shown the same type of structure in the
serpulid Filograna implexa Berkeley. A bulb-like structure in similar position was described by Grube (1838) in
Eunice harassii Audouin and Milne Edwards.
These structures might act as accessory hearts, serving to
drive the blood around the ring vessels. It is to be noted that
in Poecilochaetus Allen (1904) described the hearts as
blind-ending segmental pouches arising from the dorsal vessel
and lying over the intestine.
2. Blind-ending Capillaries Associated with the
Segmental Organs.
Fuchs (1907) described blind-ending vessels in the eunicid
Marphysa sanguinea (Montagu). I have examined this
form at Eoscoff and find that these vessels are limited to the
vessel supplying the segmental organ. In the terebellid
Polymnia nebulosa (Montagu), Jaquet (1886) described
blind-ending vessels associated with the anterior segmental
organs. In Lanice conchilega (Pallas) a similar condition
is described by Meyer (1888). I have observed these vessels to
contract.
In the family Arenicolidae Gamble and Ashworth (1900)
described short blind-ending vessels around the coelomostome
of the segmental organ of Arenicola grubii Clap, and
Arenicola ecaudata Johnston. Benham (1891) described
similar vessels in Arenieola marina (L.) and Jaquet (1886)
in Arenicola claparedii Levinsen. In the closely related
Ophelidae I have found in Travesia forbsii Johnston a
616
D- W. EWER
blind-ending vessel running the length of the segmental organ
and giving off short blind-ending capillaries. I have never
observed these vessels to contract. A similar vessel going to the
segmental organ was described by Schaeppi (1894) in Ophelia
r a d i a t a Delle Chiaje. This vessel itself gives off long blindending capillaries. On the ring vessels of this species there are
also blind-ending capillaries which are, however, much finer
than the vessels described in 1 above. It is of interest to note
that Brown (1938) failed to find any blind-ending capillaries in
Ophelia c l u t h e n s i s McGuire.
Among the Amphictenidae similar short capillaries associated
with the segmental organs were described by Eathke (1842)
in P e c t e n a r i a (Amphictene) a u r i e o m a (0. F. Mull) and
by Cosmovici (1879) in P e c t e n a r i a (Lagis) k o r e n i Malm.
In the absence of any definite knowledge even about the
contractility of the majority of these vessels it does not seem
advisable to speculate on their function.
3. B l i n d - e n d i n g Vessels S u p p l y i n g t h e G o n a d s . 1
Blind-ending capillaries arising from the ring vessels and
running into the mass of the gonads were described both in
N e p h t h y s h o m b e r g i i Audouin and Milne Edwards and
in the chlorhaemid P l a b e l l i g e r a d i p l o c h a i t o s Otto
by Jaquet (1886).
Ziircher (1909) described blind-ending ampullae arising
laterally in pairs from the ventral vessel of Owenia fusif or mis Delle Chiaje. These ampullae were observed to contract by von Drasche (1885). The gonads are attached to the
walls of these ampullae. In C h a e t o p t e r u s v a r i o p e d a t u s
(Eenier) Probst (1929) has described blind-ending vessels arising
from the ventral vessel and running to the gonads. In the
anterior region of the worm he also described blind-ending
ampullae arising from the ventral vessel. These he regards as
1
Hemplemann (1906) described blind-ending sacs on the ring vessels
of the archiannelid Polygordius lacteus Schneider. These project
into the next posterior segment and their walls are covered with gonads.
Similar structures are described by Fraipont (1887) in Polygordius
neapolitanus Fraipont.
BLOOD SYSTEM OF SABELLA
617
homologous with the hearts of the complete anterior ring
vessels described by Claparede (1873) in T e l e p s a v u s
c o s t a r u m Clap.
While it is probable that these vessels serve to carry oxygen
and nutrients to the developing gonads, the reason for their
ending blindly will not be understood until the mechanics of the
circulation in these forms has been further elucidated.
4. B l i n d - e n d i n g Vessels g e n e r a l l y D i s t r i b u t e d .
Such an arrangement of vessels has been reported in members
of two of the three sub-families of the Sabellidae. Among the
sabellines they occur in S a b e l l a , S p i r o g r a p h i s , L a o nome k r o y e r i Malm (Evenkamp, 1931), and I have observed
them in B r a n c h i o m m a v e s i c u l o s u m (Montagu). In the
Fabriciinae, Evenkamp (1931) reports their presence in
E u c h o n e p a p i l l o s a M. Sars. In the remaining sub-family,
the Myxicolinae, they are absent.
Fox (1938) has put forward two suggestions, not mutually
exclusive, about the function of the coelomic capillaries in
S a b e l l a . Drawing attention to the absence of any capillaries
in the muscles of this animal, he points out that part of the
oxygen supply to the muscles must come by way of the coelomic
fluid, in which a high oxygen concentration would be maintained
by diffusion of oxygen from the coelomic capillaries.1 He also
suggests that in the breeding season the capillaries may carry
oxygen to the genital products which lie free in the coelomic fluid.
In S p i r o g r a p h i s , as has been described above, there are
capillaries in the ventral muscle blocks, while in B r a n chiomma I have found both blind-ending coelomic capillaries
and capillaries in both dorsal and ventral muscle blocks. This
1
A similar idea was put forward by Wiren to explain the condition in
A r e n i c o l a in which he believed, incorrectly, that there was no capillary
supply to the body-wall. His ideas are expressed in the following manner
by Gamble and Ashworth (1898), p. 20. Wiren 'suggests that the assimilation of food and oxygen by the tissues is effected chiefly through the
mediation of the coelom, which he points out is parcelled off in the intermuscular spaces, by a channelling out of the subepidermic tissue into
"perihaemal c a n a l s " . . . . The extension of the coelom into the intermuscular
and subdermal spaces, has, however, all the appearance of acting as the
equivalent of lymph spaces in higher forms.'
618
D. W. EWEE
suggests that in these forms the supply of oxygen to the
muscles from the coelomie capillaries by way of the coelomic
fluid is not the only function of these capillaries.
The hypothesis that the coelomic capillaries may be important
in bringing oxygen to the genital products is strengthened by
the fact that in S p i r o g r a p h i s some of the coelomic blindending capillaries on the ventral gland-shield vessel run between
the cells of the ovary. In the coelom of S a b e 11 a and S p i r o g r a p h i s there are also fat-bearing eleocytes. In B r a n c h i o m m a are similar but smaller cells (Bomieu, 1923). It
may be that a further function of the blind-ending capillaries
is to carry food and oxygen to these cells.
It is not possible to make any estimate of the relative importance of the several proposed functions for the coelomic
capillaries of the Sabellinae.
My sincere thanks are due to Professor H. Munro Pox, F.E.S.,
who suggested the work and advised me during its progress,
and to Dr. D. P. Pielou and Mr. B. W. Bentley of this Department for drawing many of the figures.
10. SUMMARY.
1. The anatomy of the blood system of S a b e l l a p a v o n i n a
is described.
2. Differences from S a b e l l a found in the structure of the
blood system of the closely related S p i r o g r a p h i s s p a l l a n zanii are pointed out.
3. Very young S p i r o g r a p h i s show no difference in the
structure of the blood system from S a b e l l a . Certain of the
differences are, however, found in slightly larger specimens of
S p i r o g r a p h i s which are smaller than fully grown S a b e l l a .
The differences are therefore regarded as specifically significant.
4. A preliminary account is given of the histology of the
blood-vessels. The main longitudinal vessels show a distinct
muscular layer, which is absent in circular and capillary vessels.
5. The course of the circulation is described. An explanation
of the mechanism of the sorting of oxygenated and deoxygenated
blood is put forward.
6. Peristalsis in the main longitudinal vessels occasionally
BLOOD SYSTEM OF SABELLA
619
reverses its direction; there is thus no physiological polarization
of the direction of peristalsis.
7. The occurrence of blind-ending vascular structures in
other polychaetes is reviewed and suggestions put forward
concerning their function.
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