LIV
3005

Xtverpool flDarine Blologv (Toinmtttee,
LM.B.C. MEMOIRS

ON TYPICAL British Marine Plants &- Animals

EDITED BY W. A. HERDMAN. D.Sc, F.R.S.

XV.

ANTEDON

HERBERT CLIFTON CHADWICK,

Curator of the Port Erin Biological Station and Honorary Lecturer in
Marine Biology in the University of Liverpool.

(With 7 Plates)

Price Two Shillings and Sixpence

LONDON

Williams & Norgate
June, 1907

HARVARD UNIVERSITY.

L I B K A R Y

MUSEUM OF COMPARATIVE ZOOLOGY.

sU^t^

5UJI/v\AjI>i_

\n>'> '

L.M.B.C. MEMOIRS.

XV.

ANTEDON.

NOTICE.

The Committee desire to intimate that no copies of these
Memoirs will be presented or exchanged, as the prices
have been hxed on such a scale that most of the copies will
have to be sold to meet the cost of production.

The Memoirs may be obtained at the nett prices stated,
from Messrs. Williams and Norgate, 14, Henrietta Street,
Covent Grarden, London.

Memoir I. Ascidia — published in October, 18DU, GU pp.

and five plates, price 2s.
,, II. Cardiiim — published m December, 1899,

92 pp., six plates and a map, price 2s. 6d.
,, III. Echinus — published in February, 190U.

oG pp. and live plates, price 2s.
„ IV. Codium — published in April, 1900, 26 pp.

and three plates, price Is. 6d.
„ V. Alcyonium — published in January, 1901,

60 pp. and three plates, price Is. 6d.
„ YI. Lepeophtheirus and Lerntea — published in

March, 1901, 62 pp. and hve plates,

price 2s.
„ VII. Linens — published in April, 1901, 40 pp. and

four plates, price 2s.
,, YIII. Pleuronectes — published in December, 1901,

2G0 pp. and eleven plates, price 7s.
„ IX. Chondrus — published in July, 1902, 50 pp.

and seven plates, price 2s. 6d.
„ X. Patella — published in May, 1903, 84 pp. and

four plates, price 2s. 6d.
,, XI. Arenicola— published in March, 1904, 126

pp. and eight plates, price 4s. 6d.
,, XII. Gammarus— published in July, 1904,. 55 pp.

and four plates, price 2s.
., XIII. Anurida—published in October, 1906, 105 pp.

and seven plates, price 4s.
,, XIY. Ligia — published in January, 1907, 45 pp.

and four plates, price 2s.
„ XY. Antedon — published in June, 1907, 55 pp.

and seven plates, price 2s. 6d.

Ilipei'pool flDarine BiolC'<}\? (Xomiuittee.
L.M.B.C. MEMOIRS

ON Typical British Marine plants s- Animals

EDITED BY W . A. HeRDMAN. D.Sc, F.R.S.

XV.

ANTEDON

HERBERT CLIFTON CHADWICK,

Curator of the Port Erin Biological Station and Honorary Lecturer in
Marine Biology in the University of Liverpool.

(With 7 Plates)

Price Two Shillings and Sixpence

-' LONDON

Williams & Norgate
June, 1907

EDITOE'S PREFACE.

The Liverpool Marine Biology f'ommittee was constituted
in 1885, with the object of investigating the Fauna and
Flora of the Irish Sea.

The dredging, trawling, and other collecting expeditions
organised by the Committee have been carried on inter-
mittently since that time, and a considerable amount
of material, both published and unpublished, has been
accumulated. Twenty Annual Reports of the Committee
and five volumes dealing with the " Fauna and Flora "
have been issued. At an early stage of the investigations
it became evident that a Biological Station or Laboratory
on the sea-shore nearer the usual collecting grounds than
Liverpool would be a material assistance in the work.
Consequently the Committee, in 1887, established the
Puffin Island Biological Station on the North Coast of
Anglesey, and later on, in 1892, moved to the more
commodious and accessible Station at Port Erin in the
centre of the rich collecting grounds of the south end of
the Isle of Man. A new and larger Biological Station and
Fish Hatchery, on a more convenient site, has now been
erected, and was opened for work in July, 1902.

In these twenty years' experience of a Biological
Station (five years at Puffin Island and fifteen at Port
Erin), where College students and young amateurs form a
large proportion of the workers, the want has been fre-
quently felt of a series of detailed descriptions of the
structure of certain common typical animals and plants,
chosen as representatives of their groups, and dealt with by
specialists. The same want has probably been felt in other
similar institutions and in manv T'olleo-e laboratories.

Vl.

The objects of the Committee and of the workers at the
Biological Station were at first chiefly faunistic and
speciographic. The work must necessarily be so when
opening np a new district. Some of the workers have
published papers on morphological points, or on embry-
ology and observations on life-histories and habits ; but
the majority of the papers in the volumes on the '' Fauna
and Flora of Liverpool Bay " have been, as was intended
from the first, occupied with the names and characteristics
and distribution of the many different kinds of marine
plants and animals in our district. And this faunistic
work will still go on. It is far from finished, and the
Committee hope in the future to add still further to the
records of the Fauna and Flora. But the papers in the
present series, started in 1899, are quite distinct from these
previous publications in name, in treatment, and in pur-
pose. They are called " L.M.B.C. Memoirs," each treats
of one type, and they are issued separately as they are
ready, and will be obtainable Memoir by Memoir as they
appear, or later bound up in convenient volumes. It is
hoped that such a series of special studies, written by
those who are thoroughly familiar with the forms of Avhich
they treat, will be found of value by students of Biology
in laboratories and in Marine Stations, and will be
welcomed by many others working privately at Marine
x^atural History.

The forms selected are, as far as possible, common
L.M.B.C. (Irish Sea) animals and plants of which no
adequate account already exists in the text-books.
Probably most of the specialists who have taken part in
the L.M.B.C. work in the past will prepare accounts of one
or more representatives of their groups. The following
list shows those who have either performed or promised.

Memoirs from I. to XT. have now been published.

Vll.

Pecten, by Mr. AV. T. Dakin ; Cancer, by Mr. Pearson; and
Doris, by Sir C. Eliot, are now far advanced and ouglit to
be out during 1907. It is hoped that Cucumaria,
Buccinum, and the Uyster will follow soon.

Memoir I. Ascidia, W. A. Herdmau, 60 pp., 5 Pis., 2s.
„ II. Cardium, J. Johnstone, 92 pp., 7 Pis., 2s. 6d.
„ III. EcHixxiTs, H. C. Chadwick, 36 pp., 5 Pis., 2s.
„ lY. CoDiuM, R. J. II. Gibson and Helen Auld,

26 pp., 3 Pis., Is. 6d.
„ V. Alcyonium, S. J. Hickson, 30 pp., 3 Pis., ls.6d,
„ VI. Lepeophtheirus and Lern^a, Andrew Scott,

62 pp., 5 Pis., 2s.
„ YII. LiNEUs, E. C. Punnett, 40 pp., 4 Pis., 2s.
„ VIII. Plaice, F. J". Cole and J. Johnstone, 260 pp.,

11 Pis., 7s.
,, IX. Chondrus, 0. V. Darbishire, 50 pp., 7 Pis.,

2s. 6d.
„ X. Patella, J. II. A. Davis and II. J. Fleure,

84 pp., 4 Pis., 2s. 6d.
„ XL Arenicola, J. II. Ashworth, 126 pp., 8 Pis.,

4s. 6d.
,. XII. CrAMMARus, M. Cussaus, 55 pp., 4 Pis., 2s.
,. XIII. Anurida, a. D. Imms, 107 pp., 8 Pis., 4s.
„ XIV. LiGix, C. G. Hewitt, 45 pp., 4 Pis., 2s.
,, XV. AiNTEDON, H. C. Chadwick.
Cancer, J. Pearson.
Doris, Sir Charles Eliot.
Pecten, W. J. Dakin.
Cuci MARIA, E. n indie.

Oyster, W. A. Herdman and J. T. Jenkins.
OsTRACOD (Cythere), Andrew Scott.
Buccinum, W. B. Randies.
BuGULA, Laura II. Thornely.

Vlll.

ZosTERA, E;. J. Harvey Gibson.
HiMANTHALiA, F. J. Lewis.
Diatoms, F. E. Weiss.
Fucus, J. B. Farmer.
BoTRYLLOiDES, W. A. Herdmau.
Cuttle-Fish (Eledone), W. E. Hoyle.
Actinia, J. A. Clubb.
Hydroid, E. T. Browne.
Halichondria and Sycon, A. Dendy.

In addition to these, other Memoirs will be arranged
for, on suitable types, such as Pagurus, Sagitta, Pontoh-
della, a Cestode and a Pycnogonid.

As announced in the preface to Ascidia, a donation
from Mr. F. H. Gossage, of Wooltoii, met the expense
of preparing the plates in illustration of the first few
Memoirs, and so enabled the Committee to commence
the publication of the series sooner than would otherwise
have been possible. Other donations received since from
Mr. Gossage, Mrs. Holt, Sir John Brunner, and others,
are regarded by the Committee as a welcome encourage-
ment, and have been a great help in carrying on the work.

W. A. Heedman.

University of Liverpool,

June, 1907.

L.M.B.C. MEMOIRS.

No. XV. ANTEDON.

HERBERT C. CHADWICK,

Curator of the Port Erin Biological Station, Hon. Lecturer in Marine
Biology in the University of Liverpool.

ANTEDON" BIFIDA, Pennant ( = 6'omr/^W.z rosacea,
Linck, of Forhos nnd other autliors), is the most familiar
example of the Class C'Rinoidea found in British seas. Of
the six species of the p^eniis recognised as British, five
appear to be confined to the deeper waters of our seas, but
A. bifida has been recorded from depths of a few fathoms
only at many points around our coasts. In the L.M.B.C.
district it occurs in large numbers off Cemmaes Bay, North
Anglesey, at a depth of 10 fathoms, and also oif Bull
Bay. It is abundant around the South end of the Isle of
Man, and is often found clinging by means of its cirri to
the wicker creels used by fishermen for the capture of
lobsters and crabs. The fishermen state that specimens
are always more numerous on the creels after stormy
weather.

Witli abundant aeration and a moderate amount of
light, Antedon may be kept under observation in tanks
for months. It is not usually an active animal. By
means of its cirri it clings tenaciously to stones, algae,
Jiydroids, &c., the arms being widely spread horizontally
with the tips more or less flexed towards the disc (PI. I.,
fig. 1). When disturbed it swims actively and with
strikingly graceful movement, the two arms of each pair
being invariably flexed and extended alternately (PI. I.,

fig. 2). The colour of Antedon is very variable. Some
specimens are of a deep reddish purple, uniformly
distributed over both disc and arms, but the majority are
clouded and spotted with rose, orange, and yellow tints.
The colouring matter is highly soluble in fresh water,
alcohol, and glycerine, but not in ether. Its properties in
Antedon hifida and other species of the genus have
been described by Moseley (1), Krukenberg (2), and
MacMunn (3), to whose papers the reader is referred.*

External Characters.

Antedon is composed of a central disc and five pairs
of long and flexible arms fringed with pinnules (PI. I.,
fig. 2). The disc consists of a shallow cup or calyx,
composed of a number of calcareous plates firmly articu-
lated together, and a lenticular visceral mass, lodged
within the cavity of the calyx, and containing the central
parts of the ambulacral, nervous, and vascular systems in
addition to the alimentary canal. A number of jointed
appendages called cirri, each terminating in a claw, are
attached to the sloping sides of the central plate of the
calyx (PI. I., fig. 3, ci.). The opposite face of the disc is
the " tegmen calycis " (PI. II., fig. 24, tg. cl.). Near its
centre is the mouth (mth.), surrounded by five slightly
elevated valvular folds (PI. II., fig. 28, v.f.). The tegmen
calycis is traversed by five ambulacral grooves, fringed
with delicate tentacles (PI. II., fig. 24, cnnh. gr.), which
radiate from the mouth to the edge of the disc and there
bifurcate to enter and traverse the entire length of the
ten arms and all their pinnules except the first or
proximal one (fig. 24). In one of the five iuterradial

-'• The black numerals in brackets refer to the list of references
given at the end (p. 40),

portions into which the tegmen calycis is divided by the
ambulacral grooves there is a conical projection, the anal
funnel (PI. II., tig. 24, an. /?.), at the apex of which the
anus {(in.) is situated. The margin of the anal aperture
bears minute papillse. AVith the aid of a good lens a
number of minute pores may be detected in the tegmen
calycis. These are the external apertures of the ciliated
funnels of the water vascular system.

Orientation. — When Antedon is at rest with the
mouth directed upwards and the anal interradius nearest
to the observer, it is customary to call the opposite radius
anterior. The four remaining radii are thus right
anterior, right posterior, left posterior, and left anterior.
In correspondence with this designation of the radii
the interradii are called right anterior, right postero-
lateral, posterior (or anal), left postero-lateral and left
anterior respectively. To maintain this orientation when
the animal is viewed from the aboral surface the posterior
(anal) interradius must be turned away from the observer.

The Skeleton.

The skeleton of the calyx is composed of a centro-
dorsal plate (PI. I., fig. 3; PI. V., fig. 52; PL YL, fig. 59,
cnt. dr.), to the convex aboral surface of which the cirri
are articulated; five radial plates (PI. Y., fig. 52; PL YL,
fig. 59, rd.), which form a pentagon and rest upon the
plane oral surface of the centro-dorsal ; and five basal
plates which are fused together to form a single plate, the
rosette (PL I., figs 17 and 18; PL Y., fig. 52; PL YL,
fig. 59, ros.), which roofs over a bowl-shaped cavity in the
centro-dorsal (PL I., fig. 19). To these must be added, as
contributing to the support of the visceral mass, the two
most proximal joints of the arms, called respectively the
first and second primibrachials (PL I., fig. 3 ; PL Y.,

fig. 52; PI. YI., fig. 59, 2^mh. 1 mid iwih. 2). The laffer
joint is axillary, and supports, in each radius, two long
series of secundibrachials (PI. I., fig. 3, sec), which form
the skeletons of the five pairs of arms, and to these the
much shorter series of joints which support the pinnules
are articulated.

Several specimens of Antedon with only eight arms
have been observed by the writer, and one with twelve was
described by Dendy (4). The eight-armed condition results
from the absence of one of the radii, while the two extra
arms of the twelve-armed specimen resulted from the
bifurcation of two of the normal ones. In each of these
the second secundibrachial became an axillary, similar to
the second primibrachials, and of which each facet bore
the long series of, in this case tertibrachial, joints forming
the arms. In many species of Antedon one or both facets
of the primibrachial axillary bear a series of two or three
secundibrachial joints, the second or third of which is an
axillary, and may in turn bear two or three tertibrachial
joints, the second or third of which is also an axillary.
In this way the large number of arms borne by
many tropical species arise. All the skeletal plates are
composed of more or less densely reticulate calcareous
matter, to which the name " stereom " has been given.
This reticulate structure may be seen in its simplest form
in tlie skeletal plates of the larva (PI. VI., figs. 66, 67, and
69), in which the reticulations are all in one plane, but in
the much more massive plates of the adult they form a
sort of sponge work, the meshes of which vary in shape
and size even in the same plate.

The Centro-dorsal Plate. — The form of this plate
fPl. I., figs. 3 and 19) resembles that of a shallow bowl.
It is of considerable thickness; and its outer margin, as
well as that which bounds and slightly overhangs the

comparatively small cavity, is peutagoual, Avith rounded
and slightly upturned angles (fig. 19). In the peripheral
portion of the bottom of the cavity may be seen the
inner ends of a number of minute canals, through which
nerve cords pass to the cirri (PI. V., fig. 52; PI. VI.,
fig. 59). The central portion of the aboral face of the
plate is flat or only slightly convex (PI. I., fig. 20). The
peripheral portion is wholly occupied by a number of
sockets for the articulation of the cirri. Those which
border the flattened central portion of the plate have a
nearly circular outline, while the more peripheral ones
become more or less angular, owing to close approxima-
tion. At the bottom of each socket there is a minute
papilliform elevation, perforated in its centre by the
external opening of one of the canals already mentioned.
The oral face of the plate is nearly flat. Shallow grooves
traverse it at the interradial angles from the periphery to
the margin of the cavity, marking it out into five equal
and radia-l segments (fig. 19).

The Cirri.— These vary in number from twenty to
nearly forty. Each cirrus (PI. I., tig. o ; Pi. 111., fig. ;J8)
is composed of from ten to eighteen calcareous joints, the
terminal one being in the form of a claw, immovably
articulated with the penultimate joint. The proximal
and next succeeding joints are cylindrical and shorter
than the remainder, which are compressed from side to
side and slightly constricted about the middle of their
length, the latter character becoming less marked, almost
to disappearance, in the terminal joints. A minute canal,
continuous with one of the canals of the centro-dorsal
plate, traverses the whole series of joints and ends
blindly in the terminal claw (flg. 38, aa-. cji.). All the
joints, except the penultimate and terminal ones, are
united by elastic ligaments, and the interarticular spaces

6

between the joints are widest on the side nearest the
vertical axis of the animal, towards which the whole
cirrus is always more or less flexed.

Radial Plates.— These plates (PL V., fig. 52; PI. VI.,
figs. 56 and 59, rd.), closely adhering to each other by
their lateral faces and together forming a well marked
pentagon, are also adherent by their aboral faces
(figs. 52 and 59) to the oral face of the centro-dorsal plate.
Each radial plate is of triangvilar form. Its slightly
truncated apex, forming the internal face of the plate
(PI. I., fig. 4), is turned towards the vertical axis of the
animal, its base forms one of the sides of the radial
pentagon, while its lateral faces are in close contact with
its fellows on either side. The lateral faces are flat, and
each presents a fairly large aperture in the angle
formed by the aboral and internal faces (fig. G). Two
apertures of slightly larger size appear in the latter face,
which is small and irregular (fig. 4). The external
face (fig 5) presents an oval aperture in the middle
of its width, and a well marked transverse ridge divides
this face into upper and lower portions. The former is
divided into two pairs of fossse by an incomplete transverse
ridge and the continuation of two converging ridges, which
are more conspicuous on the oral face of the plate (fig. 7j.
The upper, deeper pair lodge the proximal ends of the
powerful flexor muscles, while the lower, shallow pair
aft'ord attachment for the proximal ends of the inter-
articular ligaments. The lower (aboral) portion of this
face is occupied by a single fossa which lodges the
proximal ends of an elastic extensor ligament. The
oral face of the plate presents two curved ridges (fig. 7),
the shorter ends of which approach each other along
the median line and form the median edges of the pair
of fossae which lodge the flexor muscles. The apertures

on the external, internal, and lateral faces of the radial
plates belong to a system of canals which radiate from
the central fnnnel-like space enclosed by the five plates,
and also form an annulus around it. These canals lodge
the radial cords and commissures of the apical nervous
system, and their courses will be more readily understood
in relation to that system.

The Rosette. —This plate (PI. I., figs. 17 and 18)
assumes the form of a disc with a circular aperture in the
centre, and a margin divided by deep clefts into ten
radiating processes. Of the latter, five are triangular and
lie in nearly the same horizontal plane as the disc
(fig. 8) ; whilst the alternating five have nearly parallel
margins, which are inflected in such a way as to form a
shallow groove, the whole process being markedly reflected
in the direction of the centro-dorsal plate. The exact
form of the rosette can only be made out after dissociation
from the radial pentagon by maceration in a solution of
caustic potash. When in situ it almost completely shuts
off the funnel-shaped cavity enclosed by the five radials
from the cavity of the centro-dorsal plate, the circular
aperture in its centre being the only communication
(PI. v., fig. 52; PL VI., fig. 59). The five triangular
processes are interradial, that is to say, they are directed
towards the sutures between the radials ; the alternating
processes are radial, and abut upon the axial faces of the
radials, from which also a number of irregular calcareous
outgrowths pass to the oral face of the rosette (PI. VI.,
fig. 59).

First Primibrachial Plates. — Each of these is an
ellipsoid disc-like plate of moderate thickness (PI. I.,
fig. 3, 2^»i&. 1 ; figs. 8 and 9), having two nearly parallel
faces, of which the inner, or axial, has much the larger
area (fig. 8), and articulates with the outer, or

abaxial, face of the correspondiug radial. The axial face
is divided transversely by a well-marked ridge into two
portions of unequal size. The larger portion is on the
oral, or upper, side of the ridge, and is sub-divided by a
median vertical and two oblique and less prominent ridges
into two pairs of fossfe, of which the upper pair are the
deeper. The smaller portion of the face is on the aboral,
or lower, side of the ridge, and is wholly occupied by a
broad and deep fossa. At the point of intersection of the
transverse, vertical, and oblique ridges is the oval opening
of a canal which traverses the plate from face to
face. The smaller abaxial face (hg. 9) is of simpler
character, and presents only one pair of fossse, divided by
a vertical ridge which passes round the opening of the
above-mentioned canal, and at its upjjer, or oral, end is
continuous with a slightly raised margin, which bounds
the fossie above. The oral margin of the plate presents a
well-marked notch when viewed from this face.

Second Primibrachial Plates. — These plates resemble
the radials in general form (PL I., fig. 3, 'pmh. 2; hgs. lU
and 11). Each one presents a triangular figure when
viewed from above or below, and has three articular faces.
Of these, the axial closely resembles the abaxial face of
the first primibrachial, with Avhich it is articulated, having
a single pair of lateral fossa* divided by a vertical ridge,
which also passes round the transversely oval aperture
of the axial canal. The surfaces of the lateral fosste slope
away slightly from the vertical ridge, so that when the
latter is in close contact with the corresponding ridge of
the first primibrachial the second primibrachial has a
slight range of lateral movement upon the first. A
median crest and a pair of divergent lamellee project from
the upper, or oral, margin of the axial face to form parts
of the two oblique surfaces of articulation (hg. llj.

lu general plan these latter correspond with the articular
faces of the radials and iirst primibraehials, there being
a strong transverse ridge that separates a deep fossa on its
aboral side from two pairs of fossae on its oral side
(fig. 10). The divergent lamella3 described above form
vertical dividing ridges between the latter. The radial
canal, which has been seen above to traverse the hrst
primibrachial, enters the second and immediately bifur-
cates, and the oval apertures of its two branches appear on
the corresponding oblique articular faces at the point
where the transverse ridge is joined by the vertical one.

Interradial Plates. — In some specimens of Antedon
three or four small interradial plates are found in the
interradii between the axillaries.

The Arms.— The arms (PL I., figs. 1, 2 and 3) are
rather slender and taper gradually to extreme tenuity.
Each arm is composed of a long series of joints or
segments (figs, o and 21), placed end to end and bound
together by muscular and ligamentous fibres (PI. V.,
fig. 50). These segments are termed secundibrachials,
and are of the same fundamental form throughout the
length of the arm, each one being a short cylindrical rod,
traversed by a minute axial canal (hgs. 12 to 10, also
fig. 21). The absolute length of the segments decreases
very gradually from the base to the tip of the arm, those
at the latter extremity being rather more than half the
length of those at the former. The proportion of length
to diameter presents considerable variation. Thus, at the
proximal end of the arm the length of the first few
segments is less than half their diameter; in the middle
region their length is less than twice their diameter ; while
at the distal extremity of the arm the segments become
more and more cylindrical in form, and their length is at
least four times their diameter. Viewed from the aboral

10

surface the oviter margins of the first secundibrachials
(PI. I., fig. 3) are seen to be considerably longer than the
inner, so much so that the angle of about 80° at which
their proximal articular faces incline towards each other
is widened out to one of about 130° between their distal
faces. The outer margin of the second joint also is longer
than the inner, and presents a shallow socket divided by
a transverse ridge, in which a minute perforation appears.
To this socket the first (oral) pinnule is articulated
(fig. 3). With certain exceptions to be presently described,
the succeeding joints present a similar inequality in the
length of their margins, but the longer margin is
alternately outer and inner, and the pinnule borne by
every such joint is articulated to it. Hence, when viewed
from the dorsal surface, the joints present the appearance
of triangles, the apices of which point alternately to one
side and the other (fig. 3). In the middle and more
distal parts of the arm the inequality of the margins
becomes less and less marked ; and while in the proximal
portion of the arm the articular socket of the pinnule
encroaches upon the distal articular socket of the segment
(fig. 14), in the middle and distal portions it is more
and more restricted to the lateral face (fig. 15). The
articular faces of the great majority of the secundi-
brachial segments present very similar characteristics
(figs. 12 to 10). A transverse ridge, pierced by the
opening of the axial canal, crosses each more or less
obliquely and separates a single deep fossa on its dorsal
side from a pair of shallower ventro-lateral fossse. A pair
of radial lamellae separates the latter from a second pair of
fosspp, which are deeper, occupy the ventral portion of the
articular face, and are themselves separated by a median
and more or less vertical lamella. The single dorsal fossa
lodges the elastic ligament which extends the arm ; the

11

ventro-lateral ones lodge ilie inter-articular ligaments;
while the ventral pair lodge the flexor muscles. Actual
contact between the successive segments of the arm occurs
only along the great transverse ridges. The distal
articular face of the first secundibrachial and the proximal
articular face of the second resemble the proximal face of
the second primibrachial and the distal face of the first in
having a vertical ridge separating a single pair of lateral
fossae.

Exceptions to this general rule are presented by the
distal faces of certain segments and the proximal faces
of the next succeeding ones, which are almost flat,
and the articular and muscular fossse are replaced by
a series of slightly elevated ridges and alternating furrows,
which radiate from the opening of the axial canal to the
dorsal and lateral margins (PI. I., fig. 16). Ligamentous
fibres only (PL V., fig. 50 j bind the two apposed faces
together. To this close and immovable union of two
segments, the direction of which is ahvays at right angles
to the axis of the arm, the name syzygy was given by
Joh. Mtiller (PI. I., fig. u, .^j/z.). Of the two segments
concerned in the formation of a syzygy only the distal one
(epizygal) bears a pinnule, the proximal (hypozygal)
never has one. In Anted on bifida syzygies occur between
joints 3 and 4, D and 10, 14 and 15, and then between
every fourth and fifth or sixth and seventh. Syzygies
appear to be points of least resistance, at which autotomy
very frequently occurs.

A transverse interbraehial muscle runs from arm to
arm of each pair, and its two ends are lodged in corre-
sponding rounded fossse excavated in the inner ends of the
proximal faces of the first primibrachials (PL I., fig. 12).

The pinnules, like the arms, are composed of
articulated segments, the diameter of which gradually

12

decreases from the base to tlie tip (PL I., fig. 0; PL II.,
fig. 24; PL III., figs. 32 and 38). The penultimate and
terminal segments are armed with minute hooks (PL III.,
hg. 34). The axial canal which traverses the arm branches
into all the pinnules and ends blindly in the terminal
segment of each. The movements of the pinnules are
effected by flexor muscles lodged in deep notches in the
ventral margin of each articular face, and extensor fibres
which pass from segment to segment on the dorsal margin.
Ligamentous fibres only bind the proximal segment to
the brachial segment that bears it. The pinnules borne
by the second brachial segments are usually twice the
length of the succeeding ones, and are distinguished as
the oral pinnules (PL L, fig. 3; PL II., fig. 24; PL III.,
fig. 32). They have no tentacles and no ambulacral
grooves, and during life are found more or less strongly
flexed over the tegmen calycis (fig. 24). The next
pair are quite short, but the succeeding pairs gradually
increase in length until the middle portion of the arm
is reached, beyond which the length decreases to its distal
end or growing point. Uichotomous division occurs
repeatedly at the latter, and one branch, on the right and
left sides alternately, remains short and constitutes a
pinnule. .

The external surface of the disc and arms is every-
where invested by a delicate cuticle, beneath which the
cells of the ectoderm are distinguishable only in the
ambulacral grooves, the inner faces of the oral and
marginal tentacles, and upon the pinnular tentacles, where
they form sensory 2)a2)ill8e.

In other parts, notably along the sides of the arms
and the lateral and dorsal surfaces of the visceral mass,
the most superficial cells beneath the cuticle have a more
or less regular arrangement, but no sharj) distinction can

13

be drawn between those of the ectoderm and those of the
cutis, except in young specimens. Where the subjacent
tissue is calcified, especially along the dorsal and dorso-
lateral surfaces of the apical plates and the brachial
segments, they become fusiform and still more regularly
arranged, and the delicate filamentous processes into
which their basal ends are divided are continuous with
similar processes of many of the cells of the deeper layer
(PI. IL, fig. 26).

Muscles and Ligaments.

The flexor muscles of the arms and pinnules (PI. Y.,
figs. 50 and 52, fix. m.) consist of large bundles of parallel
fibres which liave a strong affinity for aniline stains,
especially heematojcylin. Each fibre has a minute oval
nucleus, and is of uniform diameter throughout its length
(PI. III., fig. 36), but it is thicker along one edge than the
other, and thus presents a wedge-shaped figure in trans-
verse section. The ends of these fibres are sharply defined.
The extensor fibres are of extreme fineness and have less
affinity for stains (PI. III., fig. 35; PI. V., fig. 50). In
longitudinal sections they frequently possess a more or
less wav}^ appearance. Their ends are split up into a
variable number of fibrillsp, each of which may be traced
into continuity with the cells of the stroma which forms
the organic basis of the adjoining ossicles. The nuclei
are smaller and rather more rounded than those of the
flexor fibres. The fibres which form the interarticular
ligaments are not distinguishable from the extensor fibres,
and the interarticular fibres of the cirri are of similar
character.

14

Sacculi.

The sacculi (PI. II., figs. 24 and 28; PL III., figs. 32,
33, 34, and 40; PI. lY., figs. 41 and 47; PI. V., fig. 52;
PI. YIL, figs. Gl, 62, 66, 67, 69, and 71, sac.) are minute
globular or ovate sacs, which occur in great numbers
immediately below the external epithelium at the edges
of the ambulacral grooves of the disc, arms, and pinnules,
and occasionally in small numbers in the wall of the
intestine and mesenteries. Along the grooves of the disc
they may form a double or even a triple row, and are
especially numerous on the outer sides of the proximal
ends of the brachial grooves, on the periphery of the
disc (fig. 24). Along the arms and pinnules they form
a single row, and alternate regularly with the triad groups
of tentacles. Each sacculus consists of a delicate limiting
membrane of connective tissue, lodgecl in the mesoderm
and having no permanent aperture (PI. III., fig. 40). The
included space is almost invariably densely crowded with
groups of refractive spherules, consisting of an albuminous
substance, which are colourless during life, but turn
yellow or red after death, owing to absorption of the very
soluble pigment of the integument. They have a strong
affinity for stains.

Tliese spherules are the product of nucleated cells of
pyriform shape (fig. 40, rr), which clothe the inner face
of the lower wall of the sacculus, and are apparently
of mesodermal origin. The spherules make their appear-
ance in processes of the cells which grow upwards and
finally become attached in the form of filaments to the
upper wall of the sacculus. The spherule-containing
portion eventually separates from the base of the cell and
lies free in the sacculus. Sacculi have been successively
regarded as calcigenous glands, mucous glands, excretory

15

glands, symbiotic algoe, and nccumnlations of reserve
material to be nsed in tlie regeneration of injured arms
or pinnules. The value of the last view is somewhat
vitiated by the fact that sacculi do not occur in the allied
genus Actinometra, in the injured arms and pinnules of
which regeneration goes on quite as actively as in those
of Antedon. The present writer is inclined to regard the
function of the sacculi as excretory.

Digestive System.

The aperture of the mouth does not occupy the centre
of the disc, but is more or less displaced in the direction
of the anterior radius (PI. II., fig. 24, mth.). It opens into
a gradually widening resophagus, which runs obliquely
in the direction of the right posterior radius, and there
expands into a large sacculated intestine (PI. II., fig. 23,
int.). This, descending towards the aboral face of the
visceral mass, and gradually narrowing, makes a complete
coil around the vertical axis of the disc in the direction
of the hands of a chx*k. On re-entering the posterior inter-
radius it ascends the anal funnel and opens to the exterior
through the anal aperture. In addition to numerous
short diverticula which open into the intestine in the
first third of its course (fig. 23), there are two long
ones with finely-branched extremities, which open upoii
its inner border in the neighbourhood of the left anterior
radius (fig. 23, div.). The alimentary canal is of almost
uniform structure throughout. It consists of an
epithelium of fusiform, ciliated cells interspersed, in the
(psophagus, witli caliciform cells (PI. II., fig. 25), and,
throughout its length, with very minute rounded cells,
especially between the basal ends of the fusiform cells. A
layer of nerve fibres, continuous with the sub-epithelial
nerve ring, underlies the (esophageal epithelium and

16

gradually thins out as the oesophagus passes into the
intestine, in the walls of which it is difficult to trace.

The epithelium and subjacent nerve layer rest upon
a delicate basement membrane of connective tissue, which
is, however, enormously thickened in the rectal portion of
the intestine (PI. II., fig. 27, en. ts.). Thin but definite
layers of muscular fibre form sphincters around the
oesophagus and rectum (figs. 25 and 27, sj^h. fh.), but
the musculature is elsewhere feebly developed and less
definite.

The anal funnel has been observed to contract
rhythmically, doubtless in connection with the ejection of
water and excreta. The food of Antedon consists of
diatoms, radiolarians, foraminifera, and other small
organisms, which are captured by the tentacle-fringed
arms and pinnules and swept down the ambulacral grooves
to the mouth by the action of the cilia which line them.

The Blood-vascitlar or Lacunar System.

This system is highly characteristic of the majority
of the Echinodernia, and consists, in Antedon, of
a number of lacunar spaces, bounded by walls of
connective tissue scarcely distinguishable from that
which forms the numerous strands and trabecula?
of the body cavity (PI. Y., fig. 52). These lacunije
traverse the body cavity in all directions, and are
generally recognisable in sections by their albumi-
noid contents, Avhich are coagulated by the fixing
reagents and may even stain faintly. As will be presently
seen, some of the lacume simulate true vessels by the
assumption of a tubular form and considerable thickening
of their walls. The largest and most easily recognisable
lacuna is one to -svhich the name 'circumoral blood-vascular

17

ring ' lias been given by various authors. It depends
into the body-cavity from a point just below the circum-
oral water vessel (PI. TV., fig, 47; PI. Y., fig. 52, c.oM.r.),
and appears to attain its greatest development in the inter-
radii, especially the anal and right posterior ones. Its
wall consists of a thin sheet of connective tissue containing
rounded nuclei, and its form in sections depends largely
upon the quantity of coagulable fluid contained at the
moment of fixation. Generally speaking, however, it may
be said to expand gradually and irregularly from its point
of attachment to the wall of the oesophagus to its
periphery. Here it becomes much more sacculated ; and
the nuclei are not only more numerous but assume in
some parts a definite arrangement.

At one point in its circumference the lacunar walls
become thickened, very irregular, and confluent, so as to
form a roughly lenticular mass of connective tissue
traversed by numerous interlacing tubules. This is the
' spongy organ ' (PL Y., fig. 51). Its tubules are in direct
communication with a number of thick-walled trunks
(PI. lY., fig. 45), some of which run directly from the
spongy organ to the oral end of the axial organ, and,
branching and anastomosing, form a sort of vascular
envelope thereon (PI. Y., fig. 52). Others run on along-
side the axial organ towards the aboral face of the visceral
mass, and there branch and assume more irregular forms
upon the internal border of the intestinal coil. Other
similar trunks issue from the blood-vascular ring to be
distributed around the intestine and in the body cavity,
and others to ramify in the substance of the tegmen
calycis. Lastly, there is an annular lacuna which lies
outside the periphery of the blood-vascular ring and is in
communication therewith (PL Y., fig. 52, gen. hi. Ic).
From it a thin-walled tubular branch arises in each radius

c

18

to furnish the genital lacunse of the arms (PL lY., fig. 41,
gen. Ic).

Corpuscles. — Under the term " corpuscles sanguins,"
Cuenot (5) has described three kinds of amoeboid cells which
occur in the various tissues and coelomic fluid of Antedon :
(1) amoebocytes with short pseudopodia ; (2) amoebocytes
of extremely elongated form which are often found
migrating in the tissues, but which ultimately become
filled with rod-like bodies which have a special affinity
for salfranine, when the cell assumes a rounded form;
(3) very slightly amoeboid cells crowded with granules
which are golden yellow in the living animal. These are
the " oil cells " of Wyville Thomson, and they often occur
in numbers amongst the cells of the ectoderm, as well as
in the stroma of the skeletal plates. The rounded cells
described above as occurring amongst the fusiform cells
of the intestinal epithelium may possibly belong to the
first of these groups.

The Ccelom.

In Antedon, as in other Crinoidea, the cavity of the
coelom is not a clear space like that of the Echinoidea and
Holothuroidea, but is traversed in all directions by
trabeculse of connective tissue lined by coelomic endothe-
lium. The cavity is further partitioned by lamellae of
connective tissue which lie parallel to the body-wall into
two well-defined but intercommunicating sub-cavities —
the peripheral, or subtegumentary, and the peri-intestinal.
The latter encloses the intestine, which coils around a
central clear space which nearly coincides with the vertical
axis of the disc, and is known as the axial sinus (PL V.,
fig. 52, ax. si.). The upper, or oral, end of this sinus
communicates directly with the subtentacular canals of
the arms (fig. 52; PL III., fig. 29; PL IY.,fig. 41, s.te.ca.).

19

The peripheral cavity in like manner communicates
with the dorsal or coeliac canals of the same (figs. 29,
41, and 52, coeca.). These canals are, therefore, the
ccplomic cavities of tlie arms, and are lined by coelomic
endothelium (fig. 41, cce. en.). They traverse the arms
and pinnules to their extremities, and communicate
with each other at various points by minute openings in
the horizontal and vertical septa which bound them.
When viewed in a transverse section of an arm (fig. 29),
the dorsal or coeliac canal {cce. ca.) appears as a sub-
triangular space, bounded dorso-laterally by the flexor
muscles and ventrally by a horizontal septum. The latter
forms also the dorsal boundary of the subtentacular
canals, two quadrant-shaped spaces [s. te. ca.) separated by
a vertical septum, which, however, disappears before the
canals enter the disc. Immediately below the point where
the vertical septum merges into the horizontal there is a
small rounded or lenticular space, the genital lacuna
(fig. 41, gen. Ic), which encloses the genital cord or rachis.
Ciliated Pits. — In the median sagittal line of the
dorsal wall of the coeliac canal of the pinnules, and
immediately above the nerve cord, there are groups of two
to six bowl-shaped depressions with slightly raised
margins, and lined by modified cells of the coelomic
endothelium (PI. III., fig. 37, cil. jjt.). The cells which
line the bottom of the depression are flattened and non-
ciliated, while those which line the sides are columnar
and ciliated. The action of the cilia doubtless serves to
promote currents in the coelomic fluid, and on this
account the ciliated pits of Antedon have been compared
with the ciliated funnels of the Synaptidse and the ciliated
bands in the brachial cavities of the Ophiuroidea. Should
this be their only function their comparative rarity in the
coeliac canals of the arms is remarkable. Their linear

20

arrangement, in close proximity to the dorsal nerve cord,
is probably not without signiiicance, though no nervous
connection between the two has been traced.

The Chambered Organ.

This organ (PL V., fig. 52 ; PL YL, figs. 54, 55, 57,
59, ch. or.) is a division of the coelom, and is lodged for the
most part in the cavity of the centro-dorsal plate. It
consists of five radially situated chambers of roughly
equal size, lined by coelomic endothelium, and completely
enveloped on all sides by the central capsule of the apical
or aboral nervous system (fig. 57). In the vertical
axis, from which the connective tissue septa which divide
the chambers spring, there is a column-like prolongation
of the axial organ (PL V., fig. 52 ; PL VI., fig. 59) which
penetrates the central capsule and gradually tapers off in
the substance of the centro-dorsal. Tubular extensions
of the radial chambers, known as cirrus vessels (figs. 52
and 59, ci. v.), enclosed in corresponding extensions
of the central capsule, called cirrus cords {ci. cd.), and
divided throughout by a horizontal septum (figs. 58 and
59) traverse the thickness of the centro-dorsal and the
axial canals which have been described above as running
through all but the terminal joints of the cirri. The
horizontal septa cross the chambers, some to be inserted
in the vertical axis (PL YL, fig. 59), while others do not
reach it. They thus appear in sagittal and tangential
sections to divide the aboral ends of the radial chambers
into a number of super-imposed spaces. On the other
hand, the septa are not continued to the extreme ends of
the cirrus canals, so that a circulation of the coelomic fluid
therein is possible.

21

The Axial Organ.

This organ, variously known as " dorsal organ,"
" glandular organ," and " genital stolon," has already
been seen in connection with the chambered organ (PI. V.,
fig. 52; PL VI., fig. 59, aa;. or.). That portion which
forms the axis of the latter consists of a comparatively
slender cord, traversed by a few tubules lined with
epithelium (fig. 59), which finally merge into one in
the direction of the centro-dorsal (PI. VI., figs. 54, 55, and
57, ax. or.). In the opposite direction the organ passes
through the central foramen of the rosette plate, ascends
alongside the axial sinus of the coeloni towards the mouth,
and, in the adult animal, ends in a rounded extremity
some little distance below the tegmen calycis, in the right
anterior radius. This portion of the organ consists of a
complex mass of tubules lined with cylindrical epithelium
(PL IV., fig. 46), and enclosed in a stroma of connective
tissue. As already stated above, a part of the lacunar
system is in close relation with the axial organ ; but the
cord-like extensions of its free (oral) end w^hich have been
described as passing into the arms of the pentacrinoid
larva, there to form the genital rachids, do not persist in
the adult. A departure from the structural condition just
described appears to be associated with the breeding
season. The lumina of the tubules open into one another
much more freely than at other times (PL IV., fig. 44),
and the epithelial cells which line them break away from
the basement membrane and become amceboid. Various
stages of this process may be seen in serial sections of one
and the same organ.

22

The Water Yasculae, System.

This system consists of a circum-oral vessel and five
radial vessels which spring therefrom and bifurcate at the
base of the corresponding pairs of arms to traverse them
and their pinnules to their extremities. In addition to
these structures there are numerous water tubes which
depend from and open into the circum-oral vessel, and
still more numerous ciliated funnels which penetrate the
tegmen calycis and open into the body cavity.

The circum-oral vessel surrounds the mouth at the
base of the oral tentacles (PI. IV., fig. 47; PI. Y. fig. 52,
C.O.W.V.). In common with all other parts of the system,
it is lined with endothelium, the cells of which are here
rounded, non-ciliated, and have a central nucleus which
stains faintly (PL lY., fig. 47, cce. en.). Longitudinal
muscle fibres form a thin but well-defined band upon the
side of the vessel nearest to the cpsophagus (fig. 47, l.m.f.).

Tentacular branches are given off directly to the hve
interradial groups of oral tentacles, and at these points
the lumen of the vessel is traversed by little groups of
isolated muscle fibres (i.m.f.). Similar groups occur at
the points of origin of the radial vessels. The course of
the latter coincides exactly with that of the ambulacral
grooves of the disc, of the arms, and of the pinnules. A
lacuna-like space, the sub-neural sinus (PI. lY., fig. 41,
5.71. s.), separates the vessel (PI. III., fig. 29; PI. lY.,
fig. 41 ; PI. Y., fig. 52, r.w.v.) from the sub-epithelial
nerve band.

In traversing the arms the radial vessels follow a
slightly zigzag course, and give off, at each of the angles,
a lateral branch to a corresponding pinnule. Lateral
branches are given off also, which, after a short course at
right angles to the axis of the arm or pinnule (PI. III.,

23

fig. 29 ; PI. IV., tig. 41, f/i. vs.) divide into three to form
the cavities of the triad groups of tentacles which spring
from a common point in the centre of the hippets which
form the margins of the ambulacral groove. Tentacles
and tentacular vessels are wanting in the oral pinnules.
In its main features the histological structure of these
tentacles agrees with that of the oral ones (PI. IV., fig. 47,
or. in.). Passing from within outwards there is (1) an
endothelium of rounded cells {coe. en.) lining the lumen of
the tentacle and resting upon (2) a thin but well-defined
layer of longitudinally disposed muscular fibres (l.m.f.)
with which the epithelial cells are said to be connected ;
(3) a layer of connective tissue, scarcely recognisable in
the pinnular tentacles ; (4 j fibrils from the sub-epithelial
nerve band {sh. nv. f .) (on the inner face of the tentacle
only); (5) the external epithelium (ectoderm = ef<.). In
the case of the pinnular tentacles, however, the cells of
the external epithelium are grouped together to form stiff
projecting sensory papilla? (PL III., figs. 30 and 31,
sn. 'Pl^-)-

The water-tubes (stone canals of authors), to the
number of about thirty in each interradius, open into the
circum-oral vessel along its lower side (PI. IV., fig. 47 ;
PI. v., fig. 52, w.t.). The slightly expanded free ends of
the tubes depend and open into the peripheral portion of
the ccelom. Their lumina are lined by columnar cells
which are ciliated and have large oval nuclei which stain
deeply (fig. 47). The ciliated funnels (PI. II., fig. 22;
PI. v., fig. 52, cl. fn.) are scattered all over the tegmen
calycis to its extreme edge between the bases of the
arms, and are especially numerous along the borders of
the ambulacral grooves. Their slightly raised external
apertures, the water pores, are visible under a good hand
lens. Passing from without inwards the diameter of the

24

funnel gradually narrows (fig. 22), then widens again
to form a median dilatation. Here the columnar cells of
the epithelium with which the funnel is lined bear long
cilia which, in sections, are invariably directed towards
the body caYitj. Beyond the dilatation the cells lose their
cilia and gradually thin out, until, as the lumen of the
funnel gradually narrows, they are replaced by those of
the coelomic endothelium. Occasionally two adjacent
funnels unite before opening into the body cavity.

The water-vascular system of Antedon and its allies
differs functionally from that of the great majority of
Echinoderma in having no locomotor role. The function
of the delicate tentacles which fringe the ambulacral
grooves is probably respiratory ; and, as will be seen later
on, in the description of the nervous system, they are
highly sensory. The ciliated funnels and water-tubes
probably discharge the same function as the madreporites
and water-tubes (stone canals) of the majority of other
Echinoderma; but while, in the Echinoidea, Ophiuroidea,
and Asteroidea the surrounding water passes directly
through the madreporite and water-tube into the water
vessels, in Antedoji it must first enter the body-cavity
before passing through the numerous water-tubes into the
circum-oral water vessel.

The Nervous Systems.

There are apparently three well-marked nervous
systems in Ayitedon, known respectively as the Superficial
Oral, the Deeper Oral, and the Apical or Aboral. The
first of these consists of a nerve ring encircling the oral
aperture (PI. lY., fig. 47; PL V., fig. 52, c.o.nv.r.) in close
proximity to the circum-oral water vessel, and radial
nerves (PI. III. fig. 29 ; PI. lY., fig. 41 ; PI. Y., fig. 52,
arnb. nv.) which radiate from the rina: and traverse the

25

arms and j^iuniiles to their extremities. The ambulacra]
grooves are lined with an epithelium composed of fusiform
ciliated cells (PI. IV., figs. 42 and 43), beneath which
there is a well-marked band of longitudinally disposed
nerve fibres [amb. nv.), from which the inner faces of the
marginal tentacles are innervated (fig. 41). The band
is thickest in the median line of the groove and thina
out gradually towards the sides thereof. The filiform
basal ends of many of the overlying epithelial cells
penetrate the nerve band to the basement membrane upon
which it rests (figs. 42 and 43). Scattered between the
epithelial cells, just above the nerve band, are many bi-
polar and tri-polar cells, which are not improbably in
continuity with the epithelial cells and nerve fibres, and
similar cells occur in small numbers in the nerve band
itself, A layer of nerve fibres extends from the circum-
oral ring for some distance along the alimentary canal
(PI. lY., fig. 47; PL v., fig. 52, sh.nv.f.), but is not
readily traceable beyond the oesophagus.

The Deeper Oral system is situated, like the fore-
going, on the oral side of the disc and of the arms, but is
sub-epithelial in position, and consists of a circum-
oesophageal ring with cords radiating from it (PI. Y.,
fig. 52), lodged in the connective tissue of the tegmen
calycis and of the ventral faces of the arms. The circum-
oesophageal ring [d. o. nv. r.) is of irregular thickness, and
is not always readily traceable throughout a series of
sagittal sections of the disc. Of the nerve cords which
radiate from the ring Cuenot has described five principal
pairs, which are said to run one on either side of the five
ambulacral grooves of the tegmen calycis and from thence
traverse the arms in the same relative position. The
present writer has found the tracing of these nerves a
matter of very considerable difiiculty. In individual

26

sections of the arms in which a nerve appears in the
position indicated by Cuenot it may be seen to give o&.
twigs to the ambulacra! tentacles and to others which
run towards the dorsal face of the arm (PL III., fig. 29,
It. nv. c.) where they are said to unite with similar twigs
from the brachial cords of the apical system. Moreover,
it has not been shown how the single pair of nerve cords
which are said to run alongside the ambulacral grooves of
the tegmen calycis divide at the point of origin of each
pair of arms, so as to furnish a lateral nerve cord to their
inner faces. Nerves from the circum-oesophageal ring
are traceable to the oral tentacles (PL Y., fig. 52), and two
cords traverse the anal interradius to innervate the anal
funnel. Similar nerves occur in the other interradii, and
their branches appear to anastomose, thus forming a sub-
tegumentary plexus. From the latter, nerve twigs go to
innervate the bands and trabeculse of connective tissue in
the body cavity. It is highly probable that this sub-
epithelial system is in continuity with the su^Derficial
system as well as with the apical system.

The Apical system consists of a cup-shaped structure,
the central capsule, from which stout nein^e cords proceed
and eventually unite in pairs to form the apical or dorsal
nerve cords of the arms (PL Y., figs. 48, 49, and 52;
PL YI., figs. 54, 55, 56, 57, and 59, cen. caj).). The
central capsule is lodged in the concavity of the centro-
dorsal plate, to the walls of which it is closely applied,
and its oral or ventral face is covered by the rosette plate
(PL YI., fig. 59). Its thick walls form a close investment
around the chambered organ ; and, as has been already
stated above, the cirrus vessels which radiate from the
chambers are also invested by tubular extensions of the
capsule which form the so-called cirrus cords (figs. 52
and 59).

27

From the margin of the oral face of the capsule arise
five interradiallj^ situated and diverging pairs of cord-like
extensions of the capsule (PL V., figs. 48 and 49). Trend-
ing towards the oral face of the disc, and entering the
substance of the radial plates through the apertures seen
in fig. 4, PI. I., these cords unite to form five radial
nerves, the left cord of one interradial pair uniting with
the right one of the pair next to it. Just beyond the
points of junction of the cords the five radial nerves are
connected together by a pentagonal commissure (PL V.,
figs. 48 and 49 ; PL YI., fig. 56, 'pnt. com.) lodged in a
canal of corresponding shape which traverses the five
radials, in the lateral faces of which its openings may be
seen (PL I., fig. 6). Beyond the commissure the radial
nei'\'e cords pass out of the radial plates into the axial
canals of the first primibrachials, and from thence into
the second primibrachials or axillaries. On entering the
latter each nerve divides into right and left branches
(PL VI., fig. 53), which pass outwards through the
corresponding oblique facets of the plate to form the axial
cords of the arms. The two branches are connected
together just beyond their point of origin, and while still
within the axillary plate, by a transverse commissure
{tr. com.) and a chiasma {chi.), the latter occupying the
triangular space bounded by the former and the diverging
cords. Passing outwards from the Axillary plate, each
branch enters the arm of its own side to become the brachial
nerve cord of the apical system [hr. nv. c). Traversing the
whole length of the arm through the axial canal which
perforates all the calcareous joints, the cord gives off
alternately right and left branches to the pinnules, and
these arise from double roots (PL YL, fig. 60, cl. r. pn. hr.).
Further, the cord gives off in each joint two pairs of
nerves (PL III., fig. 29) which are considered to be

28

priucipally sensory. One pair arise from the oro-lateral
(ventral) border of the cord (y7i. nv.), and furnish principal
branches to the interarticular muscles, numerous twigs
which end in sensory cells of the external epithelium,
and branches which are said to unite with similar ones
from the lateral brachial cords of the deeper oral system.
The other pair arise from the dorso-lateral border of the
cord (dr. nv.), and the numerous branches divide again
and again until, as exceedingly fine twigs, they end
like some of those of the oral pair, in continuity
with the sensory cells of the external epithelium.
In longitudinal sections of the arms (PI. Y., fig. 50)
the brachial nerve cord [hr. nv. c.) presents a sort of
nodal enlargement between every two joints, those between
which a syzygy occurs excepted. These are the points of
origin of nerves which are distributed to the interbrachial
muscles and ligaments, and which are exceedingly difficult
to trace.

In histological structure the central capsule and its
radial cords are practically uniform. They consist of
extremely delicate fibrils, with numbers of very minute
ganglion cells intercalated between them. In the more
apical portion of the central capsule the fibrils have no
definite arrangement, but in the walls of its oral aspect
they are disposed for the most part concentrically around
the chambered organ (fig. 55). In the radial cords the
nerve fibrils do not form one homogeneous bundle, but are
bound together to form strands which are definite in
position and direction. Thus, the chiasma (PL YL, fig. 53,
chi.) is formed by two strands which run along the outer
lateral borders of the undivided cord, and from thence
cross over, one under the other, to be merged into similar
strands which run along the inner borders of the two
branches and, by the union of their proximal ends, form

29

the commissure. Transverse sections of the brachial nerve
cords (PL III., fig. 39) show that their fibrils form five
definite strands. Two of these run along the oral aspect
of the cord and are in contact in the middle line ; while
the remaining three traverse its dorsal face, one being
median and the other two lateral. Both the lateral
strands contribute fibrils to the pinnular branches. The
organic reticulum which forms the bases of the skeletal
parts is a definite investing layer around the capsule
and the cords.

Very little is known of the functions of the superficial
oral and deeper oral nervous systems. The sub-epithelial
bands which underlie the ambulacral grooves so closely
resemble, in histological structure and relation to the
ambulacral epithelium, the sub-epithelial bauds of the
Asteroidea, which are undoubtedly nerves, that there can
be little doubt of their nervous character ; but the experi-
ments of Carpenter (6), Milnes Marshall (7), and Jickeli (8)
show that neither the superficial oral nor the deeper oral
system plays more than a very subordinate part in
sensation and movement. In all probability the former
is concerned with the ambulacral epithelium and the
highly sensitive tentacles bordering the ambulacral
grooves, structures with which the system is in close
anatomical relation. The experiments cited above show
that the apical system is the principal one. That the
central capsule is a centre from which the complex co-
ordinated movements of swimming and righting are
controlled is shown by the fact that when this organ is
entirely removed the movements cease ; on the other hand,
evisceration, with consequent removal of the circum-oral
ring of the ambulacral system, has no effect whatever
upon them. The commissure lodged in the pentagonal
canal of the radial plates co-ordinates the movements of

30

the whole inimber of arms, as is shown by the partial or
complete failure of co-ordination when the commissure
is injured or wholly destroyed; while the commissure and
chiasma which connect the bifurcating nerve cords in the
second primibrachial in like manner co-ordinate the
movements of each pair. The brachial cords are the
paths along w^hich afferent and efferent impulses travel
to and from the central capsule. If the cord only be
severed at any one point of an arm, leaving the
ambulacral nerve band intact, even the severest irritation
applied to the distal portion of the arm beyond the injury
fails to excite any response in the disc and the remaining
uninjured arms. Irritation applied to the cut end of the
cord in the proximal part of the arm causes immediate
and strong flexion of that and all the uninjured arms,
while irritation applied to the cord in the distal part of
the arm causes similar movements in that part of the arm
alone.

The Genital Organs.

The genital organs, testes and ovaries, are specialised
portions of a system of sterile cords which radiate from
the disc and traverse the arms and pinnules. In a
transverse section of an arm (PI. IV., fig. 41) there may
be seen in the horizontal partition which divides the
coeliac from the subtentacular canals another rounded
coelomic space, lined like its neighbours with endothelium
{gen. Ic). This is the genital lacuna or sinus. It encloses
another tube, the genital strand or rachis {gen. ra.), which
is suspended to its walls by slender filaments of connective
tissue. At first a solid cord, the rachis eventually
becomes a hollow tube lined with germinal epithelium.
In its course along the arm it supplies a branch to each
^jinnule with the exception of the first. In the pinnules

31

the branches widen out enormously to form ovate cavities,
the gonads (PL VI., fig. 61, tes.\ fig. 62, ov.), which equal
in length five or six of the piunular joints, and, at the
period of sexual maturity, are filled with spermatozoa, or
ova, derived from the germinal epithelium.

The testes are invested by a delicate layer of con-
nective tissue in which there are oblique muscular fibres ;
on the inner side this layer is thrown into many project-
ing folds, which greatly augment the surface upon which
the spermatoblasts are developed. The mature sperma-
tozoon has a conical head and a middle piece to which the
tail is attached. Many of the germinal cells which line
the ovaries remain small and form a follicular investment
around the developing ova (fig. 62, fol. c).

The course of the genital sinuses and the included
genital strands in the disc is very difficult to trace. The
sinuses almost certainly open into the circum-cesophageal
plexus, but, in the adult animal at least, the genital
rachids are not traceable into continuity with the oral
end of the axial organ, from which they are said to arise
in the larva. A sexually mature Antedon may be easily
recognised by its swollen pinnules, to which the extruded
ova, which are fertilised externally, adhere in little
groups for four or five days, and until the embryo within
has developed the rudiments of its skeleton. The gonads
of the more proximal pinnules appear to be the first to
ripen. The eggs probably escape from the ovaries by
rupture of their walls at one or more points of least
resistance, while the spermatozoa are discharged through
a small funnel-like projection upon one or both sides of
the gonad (fig. 01). Sexual maturity occurs in the
months of May and June around the Isle of Man, but
the time difi'ers a little according to geographical position.
According to Cuenot, it occurs in March and April in the

32

Mediterranean, and from the end of May to the end of
June at Trieste.

Segmentation of the egg results in the formation of
a spherical embryo, which consists of a single layer of
cells enclosing a cavity filled with gelatinous matter.
This is a coeloblastula. Immediately after the completion
of this initial stage, a depression, due to invagination of
the wall of the cceloblastnla, appears at one pole, and the
invaginating portion soon becomes bilaminar. The slit-
like aperture of the invagination is the blastopore. The
embryo is now a gastrula. The cells of the inner layer
of the invagination migrate into the gelatinous matter to
form mesenchyme (PI. YI., fig. 63, mes.). The external
surface of the embryo is covered with cilia, the action of
which causes it to rotate within the egg membrane.
Presently the blastopore closes completely, and the
archenteron becomes a closed vesicle. A circular furrow
now appears in its walls and, gradually deepening,
eventually separates the archenteric cavity into two
distinct vesicles, of which the anterior is slightly the
larger (fig. 63). The latter gives rise to the intestine
and the hydrocoel, while from the posterior vesicle the
coelom and the chambered organ are derived. The
posterior vesicle elongates transversely ; and concurrently,
the anterior one is produced into horn-like dorsal and
ventral extensions (fig. 64, me. hy. V5.), which grow around
it until they touch, but do not communicate. The
two ends of the posterior vesicle now enlarge, while the
median portion, encircled by the horns of the anterior
vesicle, becomes more tubular. The embryo is now
bilaterally symmetrical, and begins to assume an oval
form. A ventral outgrowth from the anterior vesicle now
forms the rudiniient of the hydrocoel {ru. hy.), and the
vesicle itself becomes the intestine. The enlarged ends of

33

tlie posterior vesicle coutiniie to increase in size, and by
the eventual disappearance of the median connecting
portion, become right and left enteroccelic sacs. About
the fourth day the embryo assumes a still more elongated
form, and at its anterior end a tuft of long cilia appears.
This is borne by a thickened and slightly depressed area
of the ectoderm known as the neural plate, in the deeper
laj'ers of which the rudiments of the larval nervous system
appear. Close behind the neural plate, on the antero-
ventral face of the embryo, is a slight depression, the
adhesive pit, by means of which the' free swimming larva
eventually attaches itself. The right enteroccelic sac
invades the segmentation cavity and spreads dorsally
forwards and over the intestine. The left sac enlarges
in the opposite direction and surrounds the posterior
border of the intestine. The rudiment of the hydroccel
is now separated from the intestine, but remains for a
short time in open communication with a small outgrowth
from its anterior wall, the parietal sinus. The intestine
undergoes changes of shape and becomes a vesicle. The
rudiments of the skeletal system now make their appear-
ance in the form of five oral plates, five basals, from three
to five infrabasals, and about eleven segments of the stalk
(fig. 65, jt. sk.). Externally the embryo is encircled by
five ciliated bands (cI. v.), and there is a depression in
the ventral ectoderm, known as the vestibule (vs.), the
significance of which will appear later. At this stage the
embryo is hatched out and becomes a free-swimming
larva, Avith the tuft of long cilia directed forwards.
Between the third and fourth ciliated rings there is a
minute aperture, the primary water pore. During the
free swimming stage the larval nervous system attains its
highest development, and the adhesive pit enlarges and
becomes glandular. The vestibule becomes tubular, owing

34

to the fusion of its lateral edges in tlie median line, a
small anterior aperture being retained. The intestine
assumes the form of a hollow plate, and the hydrocoel lies
in its ventrally directed cavity (fig. 65). The rudiments
of the chambered organ now appear as five tubular out-
growths from the right enterocoel vesicle ; and the skeletal
joints of the stalk, which are at first horse-shoe shaped,
surround them. The hydrocoel vesicle separates from the
parietal sinus and assumes a horse-shoe shape. Five
outgrowths of its Avail appear, each of which eventually
gives rise to three primary tentacles, while the primary
water tube (stone canal) appears at the blind end of the
left limb of the vesicle. The parietal sinus takes up a new
position in front of the hydrocoel and finally communicates
with the exterior through the hydropore. Soon after the
larva attaches itself the ciliated rings and tuft and the
neural plate disappear. The vestibular aperture dis-
appears and the vestibule itself takes up a new position at
the posterior end of the larva, and by the assumption of
a pentagonal form, determines the radiate structure of the
adult. It is accompanied in its movements by the
hydrocoel, so that the two structures maintain their relative
positions. Communication between the hydrocoel vesicle
and the parietal sinus is re-established by the water tube,
which breaks through into the former. Concurrently with
these changes a store of nutritive material is accumulated
within the intestinal vesicle by numerous cells which
become detached from its wall and finally completely fill
it. A funnel-like depression of the floor of the vestibule
passes through the hydrocoel ring and forms the
(Esophagus. A corresponding p?ocess of the intestinal
vesicle eventually fuses with it. The left ccelomic sac
becomes the oral coelom, and the right sac the aboral or
apical coelom.

35

The axial organ arises as an epithelial thickening
upon one of the primary mesenteries — the longitudinal
accessory — formed by the approximation of the cnelomic
sacs. Concurrently with the shifting of the vestibule to
the posterior end of the larva a re-arrangement of the
skeletal plates takes place.

The five orals (PI. YII., fig. 66, or. p.) form a pyramid
on the roof of the vestibule, while the five basals (has. p.)
form a similar but inverted pyramid in the body wall of
the calyx. The plates forming both pyramids are inter-
radial in position. Around the uppermost joints of the
stalk there are from three to five small infrabasals, which
are said to eventually fuse with the centro-dorsal. During
subsequent development of the larva the definitive mouth
is formed by perforation of the vestibule, and radial
grooves soon divide the vestibular roof into five interradial
valves, in each of which lies an oral plate. Between these
the five groups of primary tentacles and five primary
sacculi make their appearance (fig. 66). The superficial
oral nervous system appears as a multilaminar ring of
ectoderm, the deeper cells of which give rise to the nerve
tissue. The anus, in the formation of which the ectoderm
takes no part, breaks through in the posterior interradius,
in which also the primary ciliated funnel (hydropore)
appears (fig. 68, Jnjp.) The chambered organ is now
shut off from the aboral coelom, and the axial organ
becomes an independent strand of cells, at first solid,
but subsequently hollow. The horse-shoe-shaped hydrocoel
(fig. 68, hyd. r.) becomes completely closed and forms the
circum-oral water vessel. Four new ciliated funnels and
four water tubes (stone canals) make their appearance, so
that there is one of each in all five interradii. The larva
now consists of a well-marked stalk, composed of from
eight to fen cylindrical joints, and a more or less expanded

36

calyx, supported, as we have already seen, by the circlets
of basal and oral plates. The lowest joint of the
stem (figs. GH, 67, and 69) assumes a discoid or lobate
form, so as to afford firm attachment to the substratum
upon which the larva has fixed itself, whilst the highest is
also somewhat expanded as a support for the calyx. In
the latter the basal and oral plates are now fully
developed.

As will be seen in fig. (i6, the oral plates usually stand
almost erect, thus exposing the underlying oral apparatus,
but they can be closed down upon it. Five pairs of
tentacles make their appearance between the groups of
three primary ones (fig. 68, se.ten.), making twenty-five
in all; and whereas at first the five tentacles in each
radius are connected by a common tentacle canal arising
from the circum-oral water vessel, they eventually arise
separately from the latter. Another circlet of plates, the
radials, now make their appearance in the spaces left
between the contiguous angles of the basal and oral plates
(fig. 67, 69, and 70, rd.). As their name implies, they
are radial in position. A small asymmetrical plate, the
anal, also appears between two of the radials, and on a
level with them, but this undergoes resorption at a later
period. The next plates to appear are the first primi-
brachials, which, supported by the radials, project upwards
and slightly outwards between the orals (fig. 67, j^mh. 1).
These are soon followed by the second primibrachials or
axillaries {pmh. 2), upon the distal extremities of which
the first pair of secundibrachials [sec. 1) appear in due
course. Eventually the basal plates fuse to form the
rosette, which covers in the chambered organ and central
capsule. By the outward growth of the arms and the
consequent enlargement of the circumference of the
tegmen calycis, the oral plates are left upon the oral

37

surface, and at a later period undergo resorption. When
fully developed tlie larval stalk consists of about twenty
joints, of which the two or three uppermost are short and
disc-like (fig. 69). The first whorl of cirri, numbering
five, is developed, interradially, upon the under surface
of the uppermost joint, which ultimately fuses with the
centro-dorsal. The members of the next formed whorl
alternate in position with the first, and to these a third
whorl is generally added before the young Antedon
detaches itself from its stalk and becomes free. The first
pinnules are formed before the larva detaches itself from
its stalk, and when each of the arms consists of about
twelve secundibrachial joints. A bifurcation now presents
itself at the growing extremity of the arm, one ramus of
which grows more rapidly than the other, and in a line
continuous with that of the axis of the arm. The shorter
ramus diverges at an acute angle and becomes the primary
pinnule. With the exception of the second secundi-
brachial, upon which an oral pinnule early appears, the
first formed and more proximal joints of the arm do not
bear pinnules until the larva become free.

The larva is capable of considerable movement. Its
stalk can be bent from side to side or thrown into a short
spiral, while the arms are repeatedly extended and flexed
with considerable vivacity. Detachment of the young
Antedon from its stalk is not an accidental circumstance,
resulting merely from atrophy of the upper joints of the
latter. It is preceded by the appearance, at a point
immediately below the centro-dorsal plate, of a narrow
band of fine fibrils which run parallel to the axis of the
stalk, and unite two layers of very minute cells. The
plane of rupture passes between these two layers.
Detachment does not take place until the cirri are
sufficiently developed to enable the animal to attach itself

38

to siirrouuding objects, such as Laminaria, Delesseria,
Hydroids and Polyzoa.

Eegeneration.

Antedon has long been kuuwii to pustsess considerable
power of regeneration. The risceral mass may often be
detached with great ease, and, as shown by Dendy (9), may
be completely regenerated in the course of a few weeks.
Specimens are occasionally found (10) only partially evis-
cerated, and the original visceral mass remains, more or
less displaced, but Avith a new one developed in the normal
position. Przibram (11) found that the visceral mass could
be transplanted Avith success from one individual to
another. Regeneration and transplantation cannot occur,
however, in the absence of the apical nervous system.
Regeneration of the arms is of very frequent occurrence,
and not uncommonly results in monstrosity. Perrier (12)
has fully discussed regeneration of the arms.

Parasites.

Antedon bifida is the host of a number of parasites
and commensals, of which the best known are two species
of Myzostomidse, Myzustuma glahruni and M. cirriferum.
The former is found fixed in the neighbourhood of the
mouth in specimens from the Mediterranean and the
Adriatic, and the latter occurs in large numbers on the
disc and arms of specimens from the same localities as
well as from various parts of the British coasts, including
the Isle of Man. A small (iastropod, Stylina comatulicola,
is not uncommonly found attached by means of its pro-
boscis to the anal funnel or to the cirri of specimens from
the Mediterranean. Several Copepoda, including Collo-
cheres (jracilicauda, Brady, have been found attached to

39

the surface of the disc of specimens from various localities,
aud other Crustacean parasites have been found sunk in
the tissues or inhabiting the alimentary canal. A pear-
shaped holotrichous Infusorian is frequently abundant in
the alimentary canal of specimens ccdlected oft' the Isle of
Man and in the neighbourhood of lloscoft, and a
peritrichous form, Hemuyclroj^jsis aiitedoiiis infests the
surface of the body of Mediterranean specimens.

Methods.

Antedon may be killed rapidly and with the arms
fully extended by immersion in fresh water. Corrosive-
acetic mixture is a good fixative, but the Avriter's best
results were obtained by the use of corrosive-acetic
mixture o vols, and 10 per cent, solution of formalin 1 vol.
For sectioning, specimens which have died with the arms
fully extended laterally should be selected, so that
the primibrachials and proximal secundibrachials may
be as nearly as possible in the same plane as the
radials. After fixation, the specimens should be well
washed in several changes of 70 per cent, alcohol.
Decalcification may be effected by the addition of 3 per
cent, of strong nitric acid to !)7 c.c. of TO per cent, alcohol ;
and the specimens, especially if large, should remain in
this for at least twenty-four hours after bubbles of gas
have ceased to escape from them. All trace of the nitric
acid should then be removed by liberal washing in TO per
cent, to 90 per cent, alcohol. For staining sections the
writer has used Heidenhain's iron hajm-alum method
with excellent results, and methyl-blue-eosin is also good.

40

List of Works Referred to in the Text.

1. MosELEY. On the Colouiing Matters of Various Animals, &c.
Quart. Journ. Micr. Science, Vol. XVII., 1887.

2. Krtjkenberg. Ueber die Farbstoiie von Comatula mediter-
ranea (Lam.), Antedon rosaceus (Frem.), ' Vergl. phj'siol. Studien,'
zweite Reihe, dritte Abth., 88-91, 18S2.

3. MacMunn, C. A., Contributions to Animal Chromatology.
Quart. Jom-n. Micr. Science, Vol. XXX., 1889.

4. Dendy, a. Description of a Twelve-armed Comatula from
the Firth of Clyde. Proc. Roy. Physic. Soc, Edin., 1886, Vol. IX.,
pp. 180-182.

5. CuENOT, L. La Comatule. Zoologie Descriptive, T. I.,
chap. X., pp. 227-264.

6. Carpenter, W. B. On the Structure, Physiology and
Development of Antedon rosaceus. Proc. Roy. Soc, Lond., Vol.
XXIV., 1876, pp. 211-231.

7. Marshall, A. Milnes. On the Nervous System of Antedon
rosaceus. Quart. Journ. Micr. Science, N.S., Vol. XXIV., 1884,
pp. 507-548.

$• JiCKELi, C. F. Uber das Nervensystem und die Sinnes-
organe der Comatula mediterranea. Zool. Anzeiger, Jahrg. VII.,
1884, pp. 346-349 and pp. 366-370.

9. Dendy, A. On the Regeneration of the Visceral Mass in
Antedon rosaceus. Stud. Biol. Lab. Owens College, 1886, Vol. I., pp.
299-312.

10. Chadwick, H. C. On an Abnormal Specimen of Antedon
rosaceus. Ann. & Mag. of Nat. Hist., Series 6, Vol. XII., Sept. 1893.

11. Przibram, H. Experimentelle Studien iiber Regeneration.
Arch. Entwickmech., XL, pp. 321-345.

12. Perrier, E. Recherches sur 1' Anatomic et la Regeneration
des Bras de la Comatula rosacea {Antedon rosaceus, Linck). Archives
d. Zool. exper., T. II., 1873, pp. 29-86.

41

DESCEIPTION OF THE PLATES.

List of Eefer

amb. ep. — Ambulacral epithe-
lium.

amh. gr. = Ambulacral groove.

awh. nv. — Ambulacral nerve.

an. = Anus.

an. fl. = Anal funnel.

arc. = Archenteron.

ax. en. = Axial canal.

ax. or. = Axial organ.

ax. si. = Axial sinus.

has. = Basal plate.

bl. Ic. = Blood lacuna.

br. nv. c. = Brachial nerve cord.

cal. d. = Cahciform cell.

cen. cap. = Central capsule.

chi. = Chiasma of radial cords.

ch. or. = Chambered organ.

ci. = Cirrus.

ci. cd. — Cirrus cord.

cil. pi. = Ciliated pit.

ci. V. = Cirrus vessel.

d. fn. = Cihated funnels.

d. r. = Cihated ring.

cnt. dr. — Cen tro -dorsal plate.

en. ts. — Connective tissue.

c. o. bl. r. = Circum-oral blood
vessel.

coe. ca. = Coeliac canal.

COS. en. = Coelomic endothehum.

cog. — Coagulum.

c. o. nv. r. = Circum-oral super-
ficial nerve ring.

c. 0. w. V. = Circum-oral water

vessel.
ct. = Cuticle.
cv. p. = Covering plate.

d. 0. nv. = Nerves of deeper oral

system.

ExcE Letters.

d. o. nv. r. = Circum- oesophageal

deeper nerve ring.
dr. nv. = Dorsal nerves from

brachial cord.
d. r. pn. br. — Double root of

pinnular branch of brachial

cord.
ect. = Ectoderm.
ep. = Epithelium.
ex. ch. or. = Extension of cham-
bered organ.
ex. lig. = Extensor Ugaments.
fix. m. = Flexor muscles.
gen. bl. Ic. = Genital blood lacuna.
gen. ra. = Genital rachis.
hyd. = Hydroccel.
hyd. r. = Hydroccel ring.
hyp. = Hydropore.
i. m. /. = Isolated muscular fibres.
int. = Intestine.
int. ep. = Intestinal epithelium.
int. lig. = Interarticular hga-

ments.
jt. pn. — Calcareous joint of

pinnule.
jt. sk. — Calcareous stalk joint.
I. COS. — Left ccelom.
/. m. f. = Longitudinal muscular

fibres.
It. nv. c. = Lateral cord of deeper

oral nervous system.
me. hy. vs. = Mesentero -hydroccel

vesicle.
mes. = Mesenchyme.
mth. = Mouth.
nv. I. = Nerve layer.
or. = Oral plate.
or. pn. — Oral pinnule.

4-2

or. in. = Oral tentacle.

ov. = Ova.

ovr. — Ovary.

pd. = Pedal plate.

•pmb. 1. = First primibrachial.

pmh. 2. = Second primibrachial.

pn. = Pinnule.

pnt. com. = Pentagonal com-
missure.

pr. ten. — Primary tentacles.

r. cce. — Right ccelom.

tad. nv. = Radial cords of apical
nervous system.

rd. — Radial plate.

ros. — Rosette plate.

rii. hi/. = Rudiment of hydroccel.

r. w. V. = Radial water vessel.

sac. — Sacculus.

sb. c. nv. /. = Sub-epithehal nerve
fibres.

sec. 1. = First secundibrachial.
s. te. ca. = Sub -tentacular canal.
se. ten. = Secondary tentacle.
sn. pp. ^ Sensory papilla.
5. n. s. = Sub-neiural sinus.
sph. jb. = Fibres of sphincter

muscle in transverse section.
sp. or. = Spongy organ.
st. = Stomach of larva.
syz. -^ Syzygy.
ten. — Tentacle.
^e.s. = Testis.
t(j. cl. = Tegmen calycis.
tn. vs. = Tentacular vessel.
tr. com. = Transverse commissure

of radial cords.
V. f. = Valvidar fold.
vn. nv. = Ventral nerves from

brachial cord.
w. t. = Water tube.

Plate I.

Fig. 1. Antedon hifida, vsKowiug the attitude assumed by
the animal wheu at rest. Natural size.

Fig. 2. Antedon hifida, shoAviug the disposition of the
arms in swimming. Natural size.

Fig. 3. Antedon hifida, viewed from the aboral surface.
The cirri were removed from two-thirds of the
periphery of the centro-dorsal to show the
bases of the arms. x 5.

Fig. 4. A radial plate, viewed from the axial face, x 8.

Fig. 5. Abaxial (outer) face of a radial plate. x 8.

Fig. 6. Lateral face of a radial plate, x 8.

Fig. 7. Oral face of a radial plate, x 8.

Fig. 8. Axial face of a hrst primibrachial. x 8.

43

Fig. 9. Abaxial face of a first primibracliial. x 8.

Fig. 10. Lateral face of a second primibracliial axil-
lary). X 8.

Fig. 11. Ural face of a second primibracliial. x 8.

Fig. 12. Proximal face of a first secundibrachial. x 8.

Fig. 13. Proximal face of a secundibrachial joint from
tbe base of an arm. x 8.

Fig. 14. Distal face of a secundibrachial joint from the
base of an arm. x 8.

Fig. 15. Distal face of a secundibrachial joint from near
the tip of an arm. x 8.

Fig. IG. Distal face of the hypozygal joint of the first
syzygial jiair. x 8.

Fig. IT. llosette plate, from the oral surface. x 12.

Fig. 18. Lateral view of rosette plate. x 12.

Fig. 19. Oral face of ceutro-dorsal plate showing its
cavity. x 10.

Fig. 20. Half of aboral face of centro-dorsal plate,
showing the sockets for the articulation of the
cirri. x 10.

Fig. 21. Side view of four secundibrachial joints from
the base of an arm, with the proximal joints of
two pinnules in situ. The soft parts had been
removed by maceration in caustic potash
solution. X G.

Plate II.

Fig. 22. Portion of a vertical section of the tegmen
calycis, showing two ciliated funnels. x 320.

Fig. 23. Oral face of the disc, with the alimentary canal,
reconstructed from serial sections, seen by
transparency. x G. Adapted from L. Cuenot.

Fig. 24. Oral face of the disc and the bases of the arms
of Antedon bifida. x G.

44

Fig. 25. Longitudinal section of the lower portion of the

oesophagus, x 320.
Fig. 26. Section of the ectoderm of the dorsal face of an

arm. x 400.
Fig. 27 Portion of a longitudinal section of the anal

funnel, x 320.
Fig. 28. The central portion of fig. 24. x 12.

Plate III.

Fig. 29. Transverse section of an arm. x 40.

Fig. 30. A pinnular tentacle, in optical section. x 300.

Fig. 31. Transverse section of pinnular tentacle, x 300.

Fig. 32. An oral pinnule, x 12.

Fig. 33. An ordinary pinnule, with ovary containing

nearly ripe eggs. x 25.
Fig. 34. Distal end of a pinnule from the distal end of

an arm. x 177.
Fig. 35. Fibres of extensor ligaments, x 400.
Fig. 36. Fibres of flexor muscle, x 400.
Fig. 37. Portion of longitudinal section of a pinnule,

showing three ciliated pits. x 320.
Fig. 38. A cirrus, x 14.

Fig. 39. Transverse section of brachial nerve cord, x 180.
Fig. 40. a & h. Vertical sections of two sacculi, showing

stages in the formation of the masses of

granules, x 320.

Plate IV.

Fig. 41. Ventral portion of a transverse section of an

arm. x 110.
Fig. 42. Transverse section of ambulacral epithelium

and the sub-epithelial nerve band, x 650.

45

Fig. 43. Longitudinal section of ambulacial epithelium

and tlie sub-epithelial nerve band, x 650.
Fig. 44. Portions of two transverse sections of the axial

organ, x 320.
Fig. 45. Transverse sections of a group of tubular blood

lacunae, x 180.
Fig. 46. Transverse section of the axial organ, x 180.
Fig. 47. Portion of a sagittal section of the disc, passing

through the anal interradius. x 180.

Plate V.

Fig. 48. Side view of central capsule and pentagonal

commissure of the apical nervous system,

reconstructed from serial sections. x 20.
Fig. 49. Aboral view of central capsule and pentagonal

commissure of the apical nervous system,

reconstructed from serial sections, x 20.

The cirrus cords are not represented in this

figure.
Fig. 50. Sagittal section of an arm. x 40. The

structures on the ventral side of the cceliac

canal are not represented.
Fig. 51. The " spongy organ," as seen in a horizontal

section of the disc, x 122.
Fig. 52. Diagram of a sagittal section of the disc, partly

after Ludwig.

Plate VI.

Fig. 53. Horizontal section of a radial nerve cord at the
point of bifurcation to form the brachial cords,
showing the commissure and chiasma. x 55.

Fig. 54. Horizontal section of the central capsule and
the chambered organ, at about the level of the
line * in fig. 59. x 40.

4fi

Fig. 55. Horizontal section of the central capsule and
the chambered organ, at ahont the level of the
line * * * in fig. 59. x 40.

Fig. 56. Horizontal section of the pentagonal com-
missure, at about the level of the line t in
fig. 59. X 40.

Fig. 57. Horizontal section of the central capsule and
the chambered organ, at about the level of the
line * * in fig. 59. x 40.

Fig. 58. Transverse (a) and longitudinal (b) sections of
a cirrus cord and the included cirrus vessel.
X 350.

Fig. 59. Portion of a sagittal section of the disc, showing
the central capsule, radial and cirrus cords,
chambered organ and axial organ. x 40.

Fig. 60. Horizontal section of the base of an arm passing
through the first four secundibrachials, and
showing the double roots of the two first
pinnular branches of brachial nerve cord, x 30.

Plate YII.

Fig. 61. Horizontal longitudinal section of a pinnule,
with a ripe testis showing the lateral papilli-
forra projection through which the sperm-
atozoa would eventually escape. x 56.

Fig. 62. Transverse section of a pinnule, with a nearly
ripe ovary. x 40.

Fig. 63. Horizontal longitudinal section of an embryo,
fifty-seven hours old. After Seeliger, from
Lang.

Fig. 64. Posterior end of an embryo, sixty hours old,
seen from the right side. After Seeliger,
from Lang.

47

Fig. 05. 'Free-swimming' larva, from the right side, x 177.
Fig. 66, A young attached larva, showing the basal and

oral plates, the primary tentacles and the

primary sacculi. x 40.
Fig. 67. An older attached larva, showing the radial

plates interposed between the basals and orals,

and supporting the two primibrachials in each

of the radii, x 40.
Fig. 68. The calyx of a decalcified attached larva, five

weeks old, viewed from the left side. After

Seeliger, from Lang.
Fig. 69. A still older attached larva, showing the five

pairs of arms as they appear before the

development of the first pinnules, x 22.
Fig. 70. The calyx and part of the stalk of a nearly

fully developed attached larva, showing the

developing cirri, x 12.
Fig. 71. Portion of one of the arms of the specimen

represented in fig. 70, showing the " covering "

plates.

C. Tinliiig & Co., I.td., Printers, 53 Victoria Street, Liverpool.

L.M. B. C. Memoir XV

Fi^.l9

M-Fa.rlan« iEr.krae Lith Tim

ANTEDON

L.M. B. C. Memoir XV. Plate II

0 * § W ' ' " f f e » . If -"^.

■ • ■ ■ i/ -=^

i ■ •- :i « ■■ ^0 ■ , ; » s» r," , tit

-,.,,/ / ^ =, " „' \ ' '«. ^ /^ '^ wv

fig. 22. ""^^_ \- ' ^

ini.ep. coe.en.. XX-^-f /
;, .. . ••■ . '^"- "<«^

1^ .■•«.; •;.--i^ A'-- Fig 28 -.^ ^^.

Kg, 27 X 320 ^;^j^ ,,A.y<. ',• ,•.'«'

cnd.cl. . 5

■■■■-■■ ^ ^•■■^ ■ -T^:-i-^ %^ \ /^\*^W M -'^ / ' ^^

"'"^ "^ m '^

^^^- 26- , ^^- ^^ f/^i f/iJ It - ^lY^^ \W

__^ ''"Q \ f/z/^I/^/'/u} RaV^Vx^

"jr. If ir" # ^' ^^J<m I f^^

" *- C -del. M<F»rliLa. lErAinf I..t!,,EJ.t

ANTEDON.

L.M. B. C. Memoir XV.

Plate HI.

Fig, 38

Fi^. 40. X 320 »

MTirlann itl-rslmclith Edin''

ANTE DO

L.M. B. C. Memoir XV.

or. tn. - yW*-

Fig. 47. X 180 yi^ ■'''•'■' -^

oi.o. nv. »*-.'. /y y'"?/

Pl.ATK IV

•:-■:'/.' ■/':-" .^ f^l I'A

' t, ' " ' / ' coq. coe en.T-—/; J-

cn.ts. J ' J : ■ / -

a,mb.ep. sph.jh-/-' ' r .^

(Ui,.,.'"^'' ' ': ' ''!" ■'■!''::'.' f'rr-.^:^. nut.

a-mb. &p.

'Tf[nniiW'"ir]rrilnT!:i':;mS'-t;r!i>nrf

W^M'^^'''^^''''§ "^'" W:^^^s;i:y^:^,m

^-'lliifiiiliiiyiiiii illilll!!(/JW/iiv;;i

liininn u

'1,'rig. 42.

X 650

;:-)&. 4' 3>

amb. nv.-^-

^

Fij^.45. X 180

Fig. 44.x 320

ANTED ON.

M'FirUnc i^ Erskinc Lith Edit

L.M.B. C. Memoir XV

Plate Y

ToLciL nv

pnt COTTV

Tad

"r. Thv. c. ex. Li

\9-

pnt. cor.

•^2/'

^

"^

'Tad, nv '

Fig. 49. X 20

Fig f)l X 12^

Fi^. 52.

cK.o

H, C C d-;.

I'^FfcrlaDe Jl. Erslnne.LitTi Edif

ANTEDON.

L.M.B. C. Memoir XV.

Plate VI.

cd.

OLX.OT.

Fig. 57.

X 40

'^^^m& pnt.com..

rd

Fi^.53.x 55

^'^--^^' Fig. 55

-iK.

<X'

rd.

m.

l^Ap rd q

pnt com.

^^Z^

Vf

f 0%

W R^. 56.

,>?^ X 40

.{?

i

* * *-

* *-

r^e

fiS 59

^^ 40

^ rad-nv:\

'-r'~\.

■-SUX.

'r

,' » znt-Liq.

d.r. pn.br. -y.-,-- ■_-' ' -"X-

f in.t h^i

rjiii

^''^^W

cen cup X 30 ir. nv. C.'

H^FarUntt &."Ersl\in«, Lithldirf

ANTED ON

LM, B. C. Memoir XV.

ect rcae ru h.u

Plate Vll.

Fi^. 68 •'

X 40

pd^^^

M'r«jliii. lErskinelith Eiu

ANTED ON

3 2044 093 366 490

s