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ten large, much-branched tentacles. The pharynx, or the
portion corresponding to " Aristotle's lantern," of the sea-
urchin is broad and short, with five large retractor muscles
[f) originating from the ambulacral or longitudinal muscles
on the anterior third of the body. The stomach is short,
not much wider than the intestines, with well-marked trans-
verse folds within. The intestine («) is several times longer
than the body, with longitudinal small folds, and held in
place by a large, broad mesentery which accompanies the in-
testine through the greater part of its length. The intes-
tine terminates suddenly, in a large cloaca (c), from which

* In Eupyrgus and Echinocucumis it is difficult to perceive any radia-
tion in the body except in the unbroken circle of tentacles, while in
Sipunculus and alUed worms (Oephyrea) the tentacles fonn a complete
circle, and these worms have a ring-canal and an imperfect or rudi-
mentary system of vessels thought by some authors to correspond to
the water- vascular system of Echinoderms.



AN-ATOMT OF HOLOTHURIANS. 129

on one side arises the " respiratory tree," which has but one
main stem, and is only occasionally held in place by mus-
cular threads. The branches are numerous, and are smaller




Fig. S^.—Pentacta frondosa. t, tentacles; I, longitudinal muBcles; >■, retractor mus-
cles of the tentacular system; z, intestine; c, cloaca; 6, respiratory tree; vr, water-
vascular ring or nng-canal, v, radial water-vascular canal; m, madreporic body; pp,
polian vesicles; am, ampullae ; a, «', pseudo-hsemal coutractile vessels (from Carus);
0, ovary; ow, o\aduct. — Drawn by J. S. Kingsley from a dissection made by the author.

and paler than the ovarian tubes. The water enters the
cloaca (c), passes into the respiratory tree (5), oozes out of



130 ZOOLOGY.

tlie ends of the branches, filling the body, whence it is taken
up by the madreporic body and carried into the water-
vascular system by the spacious duct on the left side of the
pharynx. Besides being respiratory, this organ is supposed
to be depuratory in its function. In some Holothurians
certain organs (the Cuvierian organs), supposed by Semper
to be organs of defence, as they are readily thrown out when
the animal is disturbed, are attached either to the stem of
the respiratory tree or to the cloaca. The madreporic body
(to) forms a rosette, nearly surrounding the membrane at-
tached to one side of the pyloric end of the stomach, and
loads by the madreporic canal, which is closely bound down
to the pharynx, to the ring-canal {vr). Also connected
with the ring-canal are two enormous Polian vesicles {p, p),
which are nearly two thirds as long as the body ; by slitting
up their base with scissors they can be followed to the ring-
canal. The latter (vr) is a capacious canal surrounding the
mouth, and can be detected by laying open the oral-opening,
and then by cutting across the longitudinal muscles (as at?;)
the radial vessels may be followed along the body under the
muscles. Just above the ring-canal is situated the nervous
ring [nr], and its radial nerves (w) can be traced along and
outside of the radial water-vascular canals. The ampullae
(am) are red, conical, flask-shaped, conspicuous organs, lying
irregularly, a row on each side of each longitudinal muscle.
They are filled with water from supposed lateral vessels of
the radial water-vascular canals. The single ovary is com-
posed of a large mass of long tubes, which are larger than
and tangled up with the branches of the respiratory tree.
The oviduct is attached by a membrane to the stomach, and
opens between two of the tentacles on the edge of the
mouth.

The blood or pseudo-hffimal vessels * are difficult, without
very fine dissections, to be made out. The system consists
of a plexus of vessels lying next to the ring-canal, from
which two vessels {a, a') pass along opposite sides of the in-

* These vessels in Fig. 89 have been copied from Carus' Icones Zo-
otomicsB ; in other respects the drawing represents the anatomy of
P, f7-ondosa.



ANATOMY OF HOLOTHURIANS. 131

testine. A fluid containing nucleated cells fills both the
pseud o-hfemal and water- vascular canals.

Holothuria florldana Pourtales is a large, dark-brown
sea-cucumber, with the feet scattered irregularly over the
body, and with smaller tentacles than in Pentacta, which is
abundant just below low-water mark on the Florida reefs,
and grows to about fifteen inches in length. The aliment-
ary canal is filled with foraminifera and pieces of shells,
corals, etc. ; it is about three times the length of the body,
and ends in a much larger coecum than that of Pentacta.
There are two widely separated branches of the " respira-
tory tree," one being free, and the other, tied to the body-
walls by thread-like muscular attachments, extends to the
pharynx. The pharynx is calcareous, while in Pentacta it
is muscular. On the madreporic body is a group of about
thirty pyriform stalked bodies, the longest, including the
stalk, about a quarter of an inch in length. Succeeding
these bodies, and situated on the madreporic canal, leading
to the ring-canal, are a large number of Polian vesicles, the
largest one an inch in length. The duct passes spirally
nearly round the oesophagus, and empties into the ring-
canal by the ducts nearly a quarter of an inch apart. In
connection with the tentacles or branchiae are twenty long,
slender tentacular ampullae, not present in Pentacta and
Thyone. The ovarian tubes are very small, some enlarging
and bilobate at the end.

Closely allied in external form to Holothuria Jloridana,
though belonging to a different family (including Pentacta),
is Tliyone briareus (Lesueur), which lives just below tidal
marks, from Long Island Sound to Florida. In this genus
the ambulacral feet are not arranged in rows, but scattered
over the surface of the body. This species is very common,
and as it is more accessible to the student than any other of
the sea-cucumbers, we give some points in its anatomy as
compared with Pentacta, with which it is more closely allied
than to Holothuria. In a specimen about eight centi-
metres (three inches) long the intestine is over two metres
(about seven feet) long, the oesophagus opening into an
oval stomach less than an inch in length. The tentacles



132 ZOOLOGY.

are capable of being very deeply retracted, and as in
Pentacta there are no tentacular ampullae. The small
madreporic body is much as in Pentacta, and connects with
a duct (madreporic canal) leading to the ring-canal. There
are three Polian vesicles, one fusiform and an inch in
length, the two others slenderer. The cloaca is of mod-
erate size, as in Pentacta, and the respiratory trees divide
at once into two very bushy branches. The ovarian tubes
form a brush or round broom-like mass or tuft, about an
inch long, the tubes small, yellow, and of nearly uniform
length, the oviduct straight and bound down to the walls
of the body.

We might here mention the most aberrant type of Holo-
thurians, the Rhopalodina described by Semper, who states
that the body is flask-shaped, with the mouth and vent situ-
ated near each other on the smaller end of the body. The
mouth is surrounded by ten tentacles, and there are ten
papillse around the anus. There is a spacious cloaca or
respiratory tree. " Ten ambulacra diverge from the centre
of the enlarged aboral end of the body, and extend like so
many meridians to near the commencement of the neck of
the flask. In correspondence with each ambulacrum is a
longitudinal muscular band ; and it is an especial peculiarity
of Rhopalodina that five of these are attached to the anal
circlet, and five to the circum-cesophageal circlet" (Huxley).

The earlier stages of development of Holothurians, so far
as known, is like that of star- fishes. The larva when fully
grown is called an auricularla. It is transparent, cylindri-
cal, annulated, with four or five bands of cilia, and usually
with certain ear- like projections, from which it derives the
name originally given to this larval form. Before the auri-
cularla is fully formed the young Holothurian begins to bud
out from near the side of the larval stomach, the calcareous,
cross-like spicules appear, and the tentacles arise. The ear-
like projections disappear, the auricularia thus becoming
cylindrical. It is soon absorbed by the growing Holothurian,
which in some genera is strikingly worm-like, and it seems
that the Holothurian is more directly developed from the
larva than in the case of the star-fish and sea-urchins, the



METAMOnPHOSm OF H0L0THURIAN8. 133

metamorphosis being less marked — i.e., growth is more
continuous, as in the Crinoids.

In Holothuria tremula and Synaptula vivipara there has
been observed a very slight metamorphosis, the yonng de-
veloping directly in a marsupium, as in the star-fishes and
sea-urchins. Cladodactyla crocea Lesson, of the Falkland
Islands, according to Sir Wyville-Thompson, carries its
young in a sort of nursery, being " closely packed in two con-
tinuous fringes adhering to the water-feet of the dorsal am-
bulacra." He also found that in Psolus ephippifer^yy\\\&-
Thompson, which is covered with calcareous plates, there is
a dorsal group of larger tessellated plates, each supported
by a broad pedicel embedded in the skin. Under these
mushroom-like plates brood-cavities or cloister-like spaces
are left between the supporting columns, and in this archi-
tectural marsupium the embryos directly develop into sea-
cucr^mbers. It follows that in all free-swimming Eehino-
derm larvae, there is a true metamorphosis as distinct as in
the butterfly, while in other forms in which development is
direct the embryo is sedentary and lacks the cilia and Tari-
ous appendages so characteristic of the ordinary larval
Echinoderms ; thus there are different stages in the difEer-
ent classes of Echinoderms between direct development or
continuous growth, and a complete metamorphosis like that
of the star-fish or sea-urchin, in which the pluteus or larva
is but a temporary scaffolding, as it were, for the building
up of the body of the adult.

Turning now to the classification of the Holothurians,
and beginning with the lowest, simplest, most generalized
forms (which are also remarkably worm-like), and ascend-
ing to higher or more complicated forms, we find that there
are two orders, those without feet {Ajwcla) and those with
ambulacral feet {Pedata).*

* It is possible that the Holothurians should be divided into two sub-
classes, one Diplostomidea Semper, in which the body is spherical and
the mouth and anus are close together, with ten ambulacral rows, etc.,
and the normal, cylindrical, bipolar Holothurians. Semper's Diplostomi-
dea is based on BJiopalodina hcgeniformis Gray, from the Congo Coast,
and regarded by Semper as the tyiie of a fifth class of Echi.iodcrms.



134



ZOOLOGY.



Order 1. Apoda. — The simplest apodous form is the
Uupyrgus scaler Liitken, in which the body shows no
external signs of longitudinal muscles, though there are
five small ones, and is covered with spine-like, soft papillae
bearing calcareous plates. We have dredged it
frequently on the coast of Labrador in shoal-
water. It has a circle of fifteen unbranched
tentacles, and is about one centimetre long.
It also occurs in Greenland and Norwegian
waters. Myriotrochus has a transparent skin
dotted with minute white spots, which, when
magnified, appear to be wheel-like, calcareous
plates. It has a single Polian vesicle, and there
is no respiratory tree nor Cuvierian appendages
(Huxley). We have dredged this beautiful
form {M. Rinhii Steenstrup) in sand, in shoal-
water, on the coast of Labrador. A very com-
mon Labrador Holothurian is Ohirodota Icsve
Grube (Fig. 90). It lives in shallow, sandy,
retired bays, and is whitish-gray, with five dis-
tinct muscular bands and scattered white spots,
which are calcareous, wheel-like bodies situated
in the skin.

Near Synapta, is Leptosynapta Girardii
(Verrill), our common east coast species, which
II ll o lives in sand at low tide. The body is very
long, and the animal when disturbed constricts
its body and breaks up into several pieces. The
skin contains perforated plates and anchor-like
bodies (Fig. 91). In this genus and those pre-
viously mentioned, constituting the suborder
Apneumona and family Synaptidm, the sexes
are united in the same individual, and there
is no respiratory tree, while the tentacles are
simply digitated or lobulated.
suborder, Pneumophora, forming the family
is characterized by having a respiratory tree.
In Caudina the skin is rough with calcareous pieces, the



rodotalcuve. Half
natural size, a,
mouth, closed.

The next
Molpadidw,



DISTRIBUTION OF HOLOTEURIANS.



135



C. arenata
it is com-




• Hooks



plates



SyrMpta Oirardil.—Mter Verrill



body ends in a long, tail-like prolongation
Stimpson has fifteen four-pronged tentacles ;
monly thrown up on the beaches
of Massachusetts Bay. A deep-
water form, a member of the
abyssal fauna, is Molpadia tur-
gida Verrill, which we haye
dredged in over one hundred
fathoms in the G^^lf of Maine,
and which ranges sou.thward to
Florida. It has a head-end like
the neck of a bottle, and the end of the body suddenly con-
tracts into a tail, with a very small anus. There are fifteen
tentacles.

Oi'der 2. Pedata, or Holothurians with feet. The mem-
bers of the first family {Dendrochiroice) have tree-like,
branching tentacles, retractor muscles, without Cuvierian
organs. It is represented by Thyone and Pentacta, while
here belong also Lophotliuria Fabricii Diiben and Keren,
Psoitis pliantapus and P. squamatus, in which the body is
armed with heavy calcareous plates, and the feet are confined
to a ventral creeping disk.

In the highest family, AspidochirotcB, there are tentacular
ampullae ; the left respiratory tree is bound to the body-
walls, and there is a single ovary, while Cuvierian organs
are present. Holothuria is the type of the group. H. edulis
Lesson, of the Moluccas and Australia, and H. tremula
forms, when dried, the trepang sold in Chinese markets.
Our H. floridana has been dried and exported to China as
an article of food.

In their geographical distribution the Apoda are mostly
boreal and arctic. Of the Pedata, the Dendrochiroice are
mostly northern or arctic, while the highest group, Aspi-
dochirotcB, are mainly tropical. Certain genera {Holothuria,
Thyone, Psolus,Pentacta, Chirodota, and Synapta) are almost
cosmopolitan.

A few forms attain a great depth, and certain abyssal
forms are often highly colored. One species, Synapta



136



ZOOLOGY.



sitnilis, lives in brackish v/ater, according to Clans. Sup-
posed plates of Holothurians have been found in the
Jurassic rocks.



Class IV.— HOLOTHUROIDEA.

Wonn-liks, cylindriccd EchinofUrms, wUh a muscular body-wnU usually
containing calcareous bodies ; with a circle ofbranclied tentadss, a terminal
opening of the intestine, madreporie plate internal, and usually a res-
piratory ccecal appendage. Unisexual or bisexual, developing by a metamor-
phosis from cylindrical, auncvlatml, free-swimming larvm; or ametabolons.
OrcUrl. Apoda. — No ambulacral feet. Family 1. (%)ia;?fo'(to(Eiipyrgus,

Cliirodota, Syuapta). Family 2. MolpadidcB (Caudina, Mol-

padia).
Order 2. Pedata. — Respiratory tree present, and the ambulacral feet.

Bisexual. Family 1. Bendrochirotm {Thyone, Psolus, Eehi-

nocucumis, Pentacta). Family 2. Aspidochirotce (Stichopus,

Holothuria, Aspidochir).

Tabulae View op the CLASSEa and Obders of Echinodbbmata.

Pedata.
(Holothuria.)

Apoda.
(Chirodota.)



HOLOTHUBOIDBA.



Antechinida.
(Echinus.)



Palechinida.
(Melonites.)



EOHINOIDBA.



Asteridea.
(Apterias.)



Ophinridea.
(Ophiura.)



ASTBROIDBA.



Brachiata.

(Encrinus.)



Cystidea.
(Sphseronites.)



Blastmdea.
(Pentremites.)

I



Crinoidea.



ECHINODERMATA.



DISSECTION OF UOLOTUUlilANS.



137



Laboratory Work. — The Holothurians are easily dissected by cutting
the body open longitudinally, and pinning the specimen down In a
dissecting-pan, with wax on the bottom for holding the pins. The
calcareous plates can be extracted from the body-walls by being placed
in a solution of potash and mounted in balsam as microscopic objects.




Encrinus or Stone Lily.



CHAPTER V.

BRANCH v.— VERMES (Worms).

General Characters of Worms.— Having studied the
one-celled animals, or Protozoans, and the radiated animals,
or Ccelenterates and Echinoderms, we pass to an assemblage
of forms which even in the simplest types are seen to have a
dorsal and ventral, a right and left side, and a head and tail
end. It is rare that the form of a worm is so modified by its
habits or surroundings but that we are able to call it a worm,
though when we attempt to draw up a definition of the
branch or sub-kingdom Vermes, one which shall exclude the
worm-like Holothurians or the Mollusks, or certain low mites
and Crustacea, or even the AmpMoxus, we find it impossible
to lay down a set of characters which shall accurately and
concisely define them. This is due to the fact that the worms
are jJO'i' excellence a generalized, synthetic type, from which
the other branches of the animal kingdom above the Protozoa
and sponges have probably originated. It will be well for
the student not to trouble himself at first about a definition
of the branch, but to study with care the leading types, and
then, in a review of the group, he will have a more or less
definite idea of the sub-kingdom, and perceive where its bor-
ders, here and there, merge into other branches, and he will
be then able to understand the grounds for the speculations
regarding the phylogeny or ancestry of the other branches,
which have all an apparent starting-point from low or simple
forms resembling such worms as we are next to describe.

As a provisional definition of a ty^iical worm, we may say
that it is a many-celled, three-germ-layered, bilateral animal,
with a well-marked dorsal and ventral side and a head and
tail end, with the body in the higher forms divided at reg-



DIOTEMA. 139

ular intervals into segments (somites or arthromeres), with
usually a definite relation of the more important viscera to
the body -walls — i.e., a digestive tract extending from the
head to the end of the body, the nervous system consisting
of a brain, or supracesophageal ganglion, and a single or,
more commonly, double chain of ganglia, resting on the
floor of the body ; a dorsal vessel or heart is usually present
being situated above the digestive tract. True jointed
appendages are never present, and in the embryo the
blastoderm is usually without any " primitive streak " (the
Annulata excepted). This definition will exclude the worm-
like Actinozoa and Holothurians.

Before describing the lowest class of worms, we may call
attention to a small aberrant group called Mesozoa by E.
Van Beneden, the position 'of which is doubtful, though the
animals composing it are probably aberrant worms.

In 1830 Krohn observed in the liquid bathing the " spongy
bodies," or venous appendages, of different species of
Cephalopods certain filiform bodies, covered with vibratile
cilia, and resembling Infusoria. They were afterward named
Dicyema by Kolliker, who with others considered them as
intestinal worms. In 1876 Professor E. Van Beneden gave
a full account of their structure and mode of development.
He states that these organisms have no general body-cavity,
but that the body consists (1) of a large cylindrical or fusi-
form axial cell, which extends from the anterior extremity
of the body, which is slightly enlarged into a head, to the
posterior end ; (2) of a single layer of flat cells forming
around the axial cell a sort of simple pavement epithe-
lium. All these cells are placed in juxtaposition like
the constituent elements of a vegetable tissue. There is
no trace of a homogeneous layer, of connective tissue, of
muscular fibre, of nervous elements, nor of intercellular
substance. There is only between the cells a homoge-
neous substance, such as is found between epithelial
cells. The axial cell is regarded as homologous with the
endoderm of the higher animals (Metazoa). Van Beneden
designates as the ectodermic layer the cells surrounding the
large, single axial cell. There exists no trace of a middle



140



ZOOLOGY.



layer of cells, nor of any organs, all the animal and vegeta,
tive functions being accomplished by the activity of the
ectodermic cells and of the single axial cell. There is no
mesodermic cell or cells. On account of these characteris-
tics, Van Beneden
regards these or-
ganisms as forming
the type of a new
branch of the ani-
mal kingdom,
which he distin-
guishes as Mesozoa.
He places the
branch, or sub-
kingdom, between
the Protozoa and
all the many-celled
animals (Mefazoa),
and includes the
hypothetical Gas-
trceades of Haeckel
in the branch.
While this position
may prove to be
the correct one, we
should prefer, while
not overlooking the
resemblance of the
DicyemidcB to the
Infusoria, and even
the Gregarinse, to
wait for more light
on the development
of the parasitic
Platyhelminth
worms. It is not improbable, on the one hand, that the
Dicyemidce, retaining their j'arasitic life, are retrograde
forms, which have originated from some low Cestoid or
Nematoid worm, and bear the same relation to them, the




Fig. 93. — a, DicyemellaWagneri : g^ g. germigenes ; n,
Eucleii8 of the axial cell : 6, the epnencal germ of Dicye-
mella, with its striated nucleus ; c, the same beginning
to undergo self -division ; rf, final stages of self -division
(morula) ; e and /, infusoriform embryo; A, germs of
the vermiform embryos of IHcyema typus ; i, gastrula
of the same ; ky I, »i, o, different stages of vermiform
larvse of Licyema typus, all highly magnified. — After E.
Van Beneden.



FLAT- WORMS. 141

Cestoids especially, which have no body-cavity, as the Tar-
digrades or Linguatulm do to the higher Arachnida.

Each species of Dicyema and Dicyemella (Fig. 92) com-
prises two sorts of individuals, differing externally, one (the
Xematogeiie) producing vermiform embryos, the other
[BItombogene) infusoriform (but many-celled) young. The
Nematogenes produce germs which undergo total segmen-
tation, and assume a gastrula condition. After the closure
of the primitive opening, the body elongates, and the worm-
like form of the adult is finally attained, when it passes
through the body-walls of the parent.

The germs of the Rhombogenes arise endogenously in
special cells lodged in the axial cell, and called " germi-
genes." Tlie germ-like cells undergo segmentation, and
then form small spheres, which become infusoriform em-
bryos. The worm-like young is destined to be developed
and live in the Cephalopod where it has been born, while
the infusorian-like young probably performs the office of
disseminating the species. It is possible that in those ani-
mals, such as the Cetacea, which feed on cuttlefishes, these
worms (the Nematogenes at least) may pass into a genuine
vermian form.



Class I. — PLAXYHELiiiNTHES [Flat-ivorms, Tape-worms,
Fluke-worms, etc.)

Order 1. Turlellaria. — In any pond of standing water
one can find on the under side of sticks or stones, small
dark flat worms. These are Planarian
worms. The common dark-brown,
almost black Planaria torva Miiller «i|| Tga

(Fig. 93) is about six or eight milli- ii jlffl

metres long, oblong, flat, with two W V

black eve-spots, with an oblong oval Y\g. 93. rig. 04.

. * p J J.' 1 ^ \ 4?^^,,,. Planaria Dendroco'.iiivi

space m front 01 each. eye. A 101m ^^^.^ percmcMm.

allied to this is a perfectly white Plana-
rian called Dendroccelum lacteum Oersted, which lives under



142 ZOOLOGY.

svibmergeJ stones, sticks, and leaves in ponds. The body
is partly transparent, -with a dark area representing the
stomach, from which branch out at right angles a multi-
tude of ccBcal canals (gastric cceca). It has two small
black eye-specks. Closely allied to this flat worm is an eye-
less form inhabiting the streams of the Mammoth and ad-
joining caves, which may be called Dendrocmlum percmcum
(Fig. 94).

The foregoing forms are easily obtained by the student,
who can study their habits in confinement. They all be-
long to the order Turhellaria, which is characterized by the
flat, oval body, covered Avith cilia. The ciliary motion can
be detected, as Moseley has done, by placing a little arrow-
root meal or fine bits of paper on the back of the animal ;



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