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New Series, Supplement, 1885. Price 10s.

THE

QUARTERLY JOURNAL

MICROSCOPICAL SCIENCE.

E. RAY LANKESTER, M.A., LL.D., F.BS.,

Fellow of Exeter College, Oxford, and Jodrell Professor of Zoology in University College,
London ;

WITH THE CO-OPERATION OF

W. T. THISELTON DYER, M.A., C.M.G., F.B.S.,

Assistant Director of the Royal Gardens, Kew,

E. KLEIN, M.D., F.BS.,

Joint-Lecturer on General Anatomy and Physiology in the Medical School of St. Bartholomew's Hospital,
London.

H. N. MOSELEY, M.A., LL.D., F.R.S.,
Linacre Professor of Human and Comparative Anatomy in the University of Oxford,
AND

ADAM SEDGWICK, M.A.,

Fellow and Assistant-Lecturer of Trinity College, Cambridge.

WITH LITHOGRAPHIC PLATES AND ENGRAVINGS ON WOOD.

LONDON:

J. & A. CHURCHILL, 11, NEW BURLINGTON STREET.

Sav
MDCCCLXXXV.

J. EB. Adlard.] [Bartholomew Close.

CONTENTS OF SUPPLEMENT, 1885.—New Series.

MEMOIRS:

The Circulatory and Nephridial Apparatus of the Nemertea. By A.
C. OupEmans, Conservator at the Zoological Museum of the Uni-
versity of Utrecht. (With Plates I, II, and III) .

The Later Stages in the Development of Balanoglossus Kowa-
levskii, with a Suggestion as to the Affinities of the Enteropneusta.
By W. Barsson, B.A., Scholar of St. John’s College, Cambridge.
(With Plates IV, V, VI, VII, VIII, and IX)

Some Notes on the Early Development of the Rana temporaria.
By W. Batpwiy Spencer, B.A., Scholar of Hxeter College, Oxford.
(With Plate X)

Notes on Hehinoderm Morphology, No. IX. On the Vascular System
of the Urchins. By P. Herpert Carpenter, D.Sc., Assistant
Master at Eton College

PAGE

—!

81

123

139

The Circulatory and Nephridial Apparatus of
the Nemertea.

By

A. C. Qudemans,
Conservator at the Zoological Museum of the University of Utrecht.

With Plates I, II and II.

THIs paper was originally written in the Dutch language
and served as a “ specimen inaugurale”’ for obtaining the Doc-
torate in the Faculty of Natural Science at the University of
Utrecht.

The subject has been subdivided by me under the following
heads :

a. History of the subject.

b. Enumeration of the investigated species and description
of the method applied.

c. Description of the new genus Carinoma (=Valen-
cinia Armandi, MclInt.), and comparison of Carinoma
with Carinella, Cephalotrix and Valencinia.

d. Results of the investigation.

e. Summary.

f. Literature of the subject.

g. Explanation of the plates.

a. History oF THE SUBJECT.

It was DELLE Cutage (1, 2) who first discovered the blood-

vessels or circulatory apparatus of the Nemertea. In the
1

9 A. CG. OUDEMANS.

description of his Polia siphunculus (=Cerebratulus
marginatus, Ren.) he describes it as follows :

“Dalla fine della bocca principia una piccolissima vena, che
sull’ intestino manda un vasellino ad ogni sua borsa laterale”’
(1. p. 434).

His figure (Tav. xxviii, fig. 3) very clearly shows both the

dorsal vessel and the smaller transverse vessels situated one
above each diverticulum of the intestine.
‘Ducks (3) is the next to mention blood-vessels in the dif-
ferent species of his genus Prostoma (=Tetrastemma).
He mentions one median and four (!) lateral longitudinal
vessels, two on each side, communicating with each other in
the head.

Jounston (4) erroneously regarded the brain as a double
heart, the longitudinal nerve-stems as vessels. Several later
authors have fallen into the same error.

RatuHKeE (5) carefully avoided it and describes the median
and the two lateral longitudinal vessels of Lineus.

QuaTREFAGES (7) in his splendid treatise on this group of
worms has given an accurate description of the circulatory
system of certain Hoplonemertea. He, however, too
peremptorily looked upon this description as applying
to all Nemertea, whereas most considerable differences
obtain in the other groups. However, his figures have
found their way into most of the text-books of zoology as
correctly illustrating the vascular system of the Nemertea
indiscriminately.

His colleague Brancuarp (6, 8, 9, 10) minutely describes
injections made by him of the Nemertean vascular system as
well as their results. It is hardly probable that he indeed suc-
ceeded in injecting the true blood-vessels ; on the contrary, it
may be fairly inferred that it was the proboscidian sheath
which he operated upon.

The results with respect to the Nemertean vascular sys-
tem to which Max Scuutrze (11, 12), Kererstetn (14),
vaN Brnepen (13), and Cuaparepe (15) have been led
by their respective researches, have been carefully recorded

CIRCULATORY APPARATUS OF THE NEMERTEA. 3

by McInrosH in his splendid Monograph on the group
(18); I can here be satisfied with referring to, that standard
work.

McInrosH himself made a very marked advance in our
knowledge of the subject here treated, by detecting and clearly
describing the difference between the vascular apparatus of the
Hoplo- and of the Schizonemertea, more especially with
respect to an interesting particularity obtaining in the ceso-
phageal region of the latter group where a system of
spacious lacunz surrounds this portion of the intestine,
merging into the three typical vessels at a point further
back towards the tail. He, however, erroneously looks upon
these lacunze as the direct continuation of the median
blood-vessels. He ascribes a respiratory meaning to this
lacunar arrangement.

McIntosu similarly discriminated the differences occurring
in certain Paleonemertea, where he mentions the two
spacious lateral vessels of Cephalotrix and Carinella
being the only portions that constitute the circulatory ap-
paratus.

Ray Lanxkester (17) and Husrecur (19, 20, 21) have called
attention to the presence of hemoglobin in the circulatory
fluid of Nemertea. It is, however, not improbable that the
former operated not upon Polia sanguirubra, Quatr., as he
indicates, but upon Cerebratulus urticans (J. Mill.),
Hubr. In the latter species it is, however, not the blood but
the proboscidian fluid that contains hemoglobin, as demon-
strated by Husrecut. The latter found it impregnating the
blood-corpuscles of Drepanophorus. |

In 1875 MclIntosuH (24) describes a communication which
he says exists between the proboscidian chamber and the
cavity of the vascular apparatus. This observation has hither-
to remained unconfirmed, although I have myself tried to test
it in all the different species I investigated.

_ This author’s description of the circulatory channels of
Valencinia Armandi (=Carinoma mihi) (25) is noticed
further on. In 1876 he figures the curious passage (26) of

*

4 A. ©. OUDEMANS.

the median dorsal vessel into the proboscidian chamber (the
cavities, however, remaining separate) in the cesophageal
region, without, however, following up the further course of this
vessel anteriorly.

The description which Barrors (29) gives of the blood-ves-
sels of the Nemertea is eminently fantastic and in no respect
borne out by direct observation of sections. He denies the
presence of transverse vessels in the unarmed species (although
DELLE CuHIasE, BLANCHARD, KerersteIn, McInrosn, and
Husrecut vouch for them!), and looks upon the genital sacs
as establishing a direct and metamerically arranged communi-
cation between the longitudinal vessels ; these sacs thus form-
ing part of the circulatory apparatus! He, moreover, mentions
a posterior communication between the proboscidian sheath
and the median blood-vessel. I would venture to suggest that
it is the more or less complicated lacunar arrangement in
the esophageal region that has led astray in this respect so
conscientious and accurate a naturalist.

The circulatory apparatus of Malacobdella has been in-
vestigated by Buancuarp (6), Szmper (28), Horrmann (80),
and Von Kennex (81). The latter furnishing by far the
most accurate description.

GrarF (37), GuLLIvER (36), and Dewoterzky (38), have not
materially added to our knowledge of the circulatory apparatus.

With respect to the nephridia this historical introduction
can be very concise. It is the merit of Von Kennex (81)
to have correctly traced this system in different species,
and to have given most satisfactory histological descriptions
of it.

There is reason to suppose, however, that already DELLE
CuiasE (1, 2) was aware of its existence, and actually observed
it in one of his species (Descrizione, p. 128, vol. iii). It has
since been noticed by Max Scuutrze (11, 12), and more
reservedly been referred to by Husrecut (19).

McInrosu (18) denies its existence, and suggests that Max
ScHuLtzE has confounded the circulatory with the excretory
apparatus.

CIRCULATORY APPARATUS OF THE NEMERTEA, 5

Semper (28) was the first to notice the nephridia of
Malacobdella.

6. ENUMERATION OF THE SPECIES INVESTIGATED AND DEscRIP-
TION OF THE Metuop APPLIED.

The Nemerteans are divided by Husrecut (35) into
Palzonemertea, Schizonemertea, and Hoplonemer-
tea. I will adhere to this division, as it seems to me to be
more natural than that of Max Scuuttzz (11, 12), who divide
the Nemerteans into Enopla and Anopla, the proboscis being
armed with a central stylet or not. In regard to the fourth
group, that of the Malacobdellide, formed by Von
Kennex (31), I can hardly agree with the creation of this new
subdivision, the anatomical characters of Malacobdella show-
ing it to be a Hoplonemertean, which, probably by its para-
sitical habit, has lost stylet and eyes, and has obtained in the
hindmost part of its back an attaching apparatus wherewith
to fix itself to its hosts (Mya, Pholas, &c.). The absence
of cephalic sacs cannot be a reason for removing it from the
Hoplonemertea, as Amphiporus hastatus, MclInt., a
true Hoplonemertean, is also deprived of these organs.

Of each of these three groups I have examined examples.
All the specimens I have used are from the collection of Prof.
Hubrecht, who with the greatest kindness not only put the
specimens in spirit at my disposal, but allowed me to examine
his numerous collection of microscopical slides and series of sec-
tions. I was thus enabled to examine specimens of all the ten
families: Cephalotricideg, Carinellide, Poliide, Valen-
ciniide, Lineide, Langiide, Amphiporida, Tetras-
temmidz, Nemertide, and Malacobdellide. Only of
the genera Borlasia, Oken (emend. MclInt.) (Lineide),
Prosorhochmus, Kef. (Tetrastemmide), and Oerstedia,
Quatr. (Nemertide), I have not examined representatives.

The new automatic microtome of Caldwell from Cambridge
has very much facilitated my research. As the Nemerteans
are animals which cannot be submitted to the usual methods of

6 A. C. OUDEMANS.

dissection, but can only be satisfactorily studied when cut into
microscopical slices, it is easily understood that such research
can only be made by examining a complete series of slices of
the same animal. This may be performed very easily when
using the microtome of Caldwell, and the sticking-method of
Giesbrecht.

The thickness of the slices varied between 7, and ;i>
millim. So I obtained series of

Cephalotrix linearis (Rathke), Oerst., one specimen,
transversally, the foremost part to the intestine (230 slices).

Carinella annulata (Mont.), McInt., three specimens
transversally, of each, the foremost part to the intestine
(behind the nephridial system), (resp. 730, 800, or 2550
slices).

Valencinia Armandi, MclInt., one specimen, trans-
versally, the foremost part to the intestine (behind the nephri-
dial system) (880 slices), and the tail.

Valencinia longirostris, Quatr., one specimen, trans-
versally, totally (2300 slices) cut up.

One specimen, partly sagittally partly transversally (1940
slices).

One specimen, the head transversally (200 slices), a piece
of the intestinal region sagittally (138 slices), and the tail
transversally (130 slices).

Polia curta, Hubr., one specimen, in toto, transversally
(1150 slices).

Lineus sanguineus (Rathke), McInt., one specimen,
with a large piece of the intestinal region, transversally (735
slices).

One specimen, young, zn toto (720 slices), transversally.

One specimen, young, the head, transversally (150 slices),
the cesophageal and a piece of the intestinal region sagittally
(120 slices) and the tail transversally (200 slices).

One specimen, intestinal region, sagittally (140 slices).

Lineus gesserensis (O.F.M.) McInt., one specimen, the
foremost part with a large portion of the intestinal region,
transversally (1125 slices).

OIRCULATORY APPARATUS OF THE NEMERTEA. 7

Amphiporus lactifloreus (Johnst.), McInt., one speci-
men, in toto (840 slices), transversally.

Amphiporus pulcher (Johnst.) McInt., one specimen,
in toto, tranversally (700 slices).

Amphiporus hastatus, MclInt., one specimen, trans-
versally (1200 slices).

Drepanophorus rubrostriatus, Hubr., two specimens,
transversally, in toto (resp. 800 and 1300 slices).

Tetrastemma candidum (O.F.M.), Oerst., one specimen,
transversally, in toto (580 slices).

Malacobdella grossa (O.F.M.), Blainv., two specimens,
transversally (resp. 423 and 428 slices), and one specimen, the
foremost half horizontally (130 slices). :

Total, 20,639 sections.

Moreover, from the collection of Prof. Hubrecht I made
use of preparations of Cephalotrix linearis (Rathke),
Oerst., Carinella annulata (Mont.), McInt., Valencinia
longirostris, Quatr., Polia curta, Hubr., Cerebratulus
marginatus, Ren., Cerebratulus hepaticus, Hubr.,
Cerebratulus urticans (J. Miull.), Hubr., Cerebratulus
roseus (d. Chiaje), Hubr., Langia formosa, Hubr., Am-
phiporus pulcher (Johnst.), McInt.,. Amphiporus mar-
moratus, Hubr., Amphiporus hastatus, McInt., Dre-
panophorus rubrostriatus, Hubr., and Nemertes
gracilis, Johnst.

c. DESCRIPTION OF THE NEW GENUS CaRINOMA (= VALENCINIA
ARMANDI, MclInt.), anp Comparison oF CaRINOMA
witH CARINELLA, CEPHALOTRIX, AND VALENCINIA.

Amongst the above-mentioned Nemerteans there also occurs
the name of Valencinia Armandi, McInt. Of this species
I was able to examine a specimen which was caught and
named by McIntosh himself (one of the type specimens)
and presented to Professor Hubrecht. Even after a
superficial examination, it appeared necessary to remove it from
the genus Valencinia, Quatr. By the situation of the

8 A. C. OUDEMANS.

mouth behind the ganglia, and by the absence of one or more
stylets in the proboscis, and of deep lateral furrows on the
head, this species, it is true, is a Paleonemertean; but by the
absence of diverticula of the intestine, of posterior lobes, and
of cephalic sacs, it approaches more closely to the group
wherein Hubrecht has placed the families of the Carinellide
and Cephalotricide. Iam compelled to make a new genus
for this species, to which genus I will give the name of Cari-
noma. The species thus is called Carinoma Armandi
(McInt.), Oud. In the following pages this proceeding will
find its justification.

The chief reason McIntosh (25) had for placing this species in
the genus Valencinia was a certain agreement between this
species and the one formerly described by him as Valencinia
lineformis (18). McIntosh, however, made a mistake in,
arranging a new worm in a genus (Valencinia, Quatr.) which
he did not know by personal investigation. Sections through
a specimen of Valencinia longirostris—the species which
had served as type to the genus Valencinia—would have
convinced him very soon that Valencinia Armandi can in
no case be placed in this genus, whilst V. lineformis, McInt.,
probably is a synonym of V. longirostris, Quatr. —at least is
considered so by Hubrecht (31).

It will suffice if I explain by what facts especially V. Ar-
mandi and V. longirostris differ from one another, facts
which can at the same time serve to characterise the new
genus which is created for V. Armandi, and to show that
the relation to Carinella is more intimate.

McIntosh describes V. Armandi in detail, so that I can
here be satisfied with a short recapitulation.

1 In my opinion it is certain, both from the description of V. lineformis
in his Monograph (18), as from the anatomical facts given in his treatise
on Val. Armandi (25), that V. lineformis is, just as little as the other,
a Valencinia, but a form which approaches closely to Cephalotrix
linearis (Rathke), Oerst. V. lineformis, viz. has two muscular layers
(one circular and one longitudinal) within its basal membrane, only two great

longitudinal vascular trunks and two lacune in the head, and the lateral
nerves are situated between the fibres of the longitudinal muscular coat.

OIRCULATORY APPARATUS OF THE NEMERTEA. 9

Along the whole length of the body there are two muscular
coats within the basal membrane, a circular layer and a longi-
tudinal one. In the head and in the esophageal region a third
layer occurs between the outer (circular) layer and the basal
membrane, viz. a layer of isolated bundles of longitudinal mus-
cular fibres. The bundles are separated from one another
by hyaline basal tissue. In the cesophageal region a number
of fibres of the circular muscular coat of the proboscidian
sheath direct themselves round the esophagus. Further back-
wards they increase in number, whilst they diminish beneath
the proboscidian sheath. At last there is no muscular fibre
between proboscidian sheath and intestine, and a little more
backwards the process repeats itself in a reverse manner, so
that the proboscidian sheath is again surrounded by its circular
muscle, and no more fibres go round the intestine. Further,
here and there in the head and the post cerebral region more
transverse bands of fibres appear, which, however, are of
secondary importance.

The brain is situated outside of the two characteristic mus-
cular coats, though the above-mentioned layers of isolated
longitudinal bundles are situated externally to the brain.

Also the two lateral nerves lie in the cesophageal region
outside of the two muscular coats, penetrate a little further
backwards into the circular coat, and gradually come to lie
between the longitudinal muscular fibres, moving still a little
further again outwards, remaining, however, between the two
layers.

The intestine has no diverticula.

Of the vascular system I will treat afterwards. In truth,
in regard to this system, I can correct McIntosh only in one
respect, viz. in regard to the mutual communication of the
six vascular trunks.

The mouth is situated behind the ganglia.

The proboscis has no stylet.

The head has no deep lateral longitudinal furrows.

Posterior lobes (brain respirators, cephalic sacs) are ab-
sent,

10 A. CO. OUDEMANS.

Now let us repeat in a few words what McIntosh says con-
cerning his V. lineformis: to show (1) how little it agrees
with V. Armandi, and (2) how at the same time it differs
from the type of the genus Valencinia, Quatr.—V. longi-
rostris, Quatr.—which I hope to describe hereafter.

Through the whole length of the body we find two muscular
coats within the basal membrane, a circular layer and a longi-
tudinal layer (also in Cephalotrix). Of a third layer in the
head (this is absent in Cephalotrix) and of a fourth layer in
the cesophageal region, nothing is mentioned (this I have found
in Cephalotrix).

How the brain is situated in respect to the muscular layers
is not mentioned (these lie in Cephalotrix within the inner
(longitudinal) muscular layer, just as in the Hoplonemer-
teans), but the lateral nerves through the whole length of the
body lie between the longitudinal muscular fibres (just as in
Cephalotrix).

The vascular system consists of two lacunz of the head and
two longitudinal tubes. This is typical in the Cephalo-
tricide, and one has only to consult my description of this
system in Cephalotrix linearis (Rathke), Oerst., to obtain
an idea of the vascular system of V. lineformis.

McIntosh has not mentioned diverticula of the intestine
(Cephalotrix has none).

The mouth is situated behind the ganglia, the proboscis has
no stylet, the head has no lateral furrows, and the cephalic
sacs are absent (all characters of Cephalotrix as well).

Now let us consider how these points are arranged in
Carinella.

Through the whole length of the body there are two mus-
cular coats, a circular layer and a longitudinal layer, both
within the basal membrane. A special layer between the
circular layer and the basal membrane is absent. On the
other hand, we find in the cesophageal region the same layer as
in V. Armandi, and this layer also here originates from the
circular layer of the proboscidian sheath. Although this layer
is in the cesophageal region more visible than elsewhere, it is

OCIROULATORY APPARATUS OF THE NEMERTBEA. 11

continued even further backwards. But there are always some
fibres between the proboscidian sheath and the intestine, even
in the cesophageal region.

The ganglia and the lateral nerves are always outside of the
circular coat and within the basal membrane.

The intestinal tract has no diverticula. The mouth is
situated behind the ganglia. The proboscis has no stylet, the
head no lateral furrows, the brain no posterior lobes.

We shall see that the vascular system occurs in two forms.
The first approaches that in Cephalotrix, the second that of
V. Armandi. But this will hereafter be noticed.

I will now sum up in a few words the characters of Valen-
cinia (borrowed from the typical species longirostris of
Quatrefages) to justify my first assertion that V. Armandi
can in no case be placed in this genus.

Within the basal membrane there are, through the whole
length of the body, three muscular coats, viz. an outermost
layer of longitudinal fibres, then a circular layer, and finally an
innermost longitudinal one. There is no trace of an inner-
most circular layer inclosing the proboscidian sheath and the
intestine.

The whole central nervous system lies between the circular
muscular coat and the outer longitudinal one.

The whole intestinal tract has, with the exception of the
cesophagus, diverticula. The mouth is placed behind the
ganglia. The proboscis has no stylet, the head no lateral
longitudinal furrows. But posterior lobes are present, even
large, and are directly continuous with the brain.

When describing the vascular system we shall see how extra-
ordinarily that of Valencinia deviates from that of Cari-
nella, Cephalotrix, and the new genus Carinoma. And
whoever chooses to form an opinion on this point ueed only
compare the figures 1 (Cephalotrix), 2 and 4 (Carinella),
5 (Carinoma), with 13—16 (Valencinia).

In none of the four genera can any point of special import-
ance be derived from the proboscidian sheath and proboscis.
In the one the proboscidian sheath is long, in the other (Cari-

12 A, C. OUDEMANS.

nella and Carinoma) short, and the same is the case with
the proboscis. .

We must now enumerate those characters which Carinoma
does not share with Valencinia, and which are common to
one, two, or three of the other above-mentioned genera.

In all the four genera the mouth is situated behind the
ganglia, there are no stylets in the proboscis, and the lateral
longitudinal furrows are absent. Thus they are all Palzo-
nemertea.

In Valencinia well-developed posterior lobes occur, coa-
lesced with the ganglia. Also well developed intestinal diver-
ticula, and through the whole length of the body three well
developed muscular coats. These characters at once are absent
in the genera Cephalotrix, Carinella, and Carinoma.

In Valencinia the cesophageal constrictor muscle is
absent, but it occurs in the three other genera. In Cari-
nella and Cephalotrix only a part of, in Carinoma all the
fibres. of the proboscidian sheath are used to form it. In
Carinella it extends much further backwards; there is thus
formed an intestinal constrictor.

The third muscular coat of Valencinia (the first from
without inwards) which is situated exteriorly to the brain,
occurs in Carinoma, but much less developed and only in
the head and the cesophageal region. (This, and certain
peculiarities of the vascular system in the head are the only
characters which are common to Carinoma and Valen-
cinia, and not common to Carinoma and the other two
genera.)

The ganglia (excluding the posterior lobes) are placed in
Valencinia, Carinoma, and Carinella outside of the
circular muscular coat, in Cephalotrix within this and the
longitudinal one. The lateral nerves always remain to the
exterior of the circular muscular layer in Valencinia and
Carinella. In Carinoma they penetrate, in the hindmost
half of the cesophageal region, the circular layer till they lie in
the midst of the longitudinal layer, a little further backwards
again moving outwards, and finally remaining between the

CIRCULATORY APPARATUS OF THE NEMERTEA. 13

longitudinal and circular layers. And in Cephalotrix, lying
already within the muscular coats, they go outwards, but do
not go farther than the midst of the longitudinal layer, where
they remain.

Of the vascular system I will here only note one peculiarity,
viz. that Valencinia has a median dorsal vessel, which is
absent in the three other genera.

Carinoma Armandi (MclInt.), Oud., has the following
external characters: Length to 20 c.m., width that of a stout
thread (contracted and in spirits 1 mm.). Body cylindrical
except the flattened head and the also flattened tail, which
terminates in a long point. The foremost part of the body is
whitish, the hindmost pale buff and the tail translucent. Eyes
are absent.

d. REsuLts OF THE INVESTIGATION.
1. Cephalotrix linearis (Rathke), Oerst., figs. 1, 19—22.

The vascular system of Cephalotrix consists in two longi-
tudinal trunks, which communicate in the tip of the snout and
in the tail. I had no opportunity of convincing myself of the
latter fact by personal examination.

Before the ganglia we find two lacunar spaces, one on each
side of the proboscidian sheath (fig. 19), which communicate in
the tip of the snout (fig. 1) by means of an arch above the
proboscidian sheath. This arch, too, is lacunar, that is to say,
irregular in shape, and when cut transversally does not show a
circular or ellipsoidal form. There are, moreover, no muscular
or other fibrillar walls, though the blood-fluid, as one would be
inclined to think from the expression lacunar, does not wash
directly the longitudinal muscular layer, nor even do the
lacunz present themselves as gaps in the gelatinous tissue
that fills up the room between the proboscidian sheath and the
longitudinal muscular coat. On the contrary, though the
lacune are imbedded in the gelatinous stroma, this is—where
it forms the lining of the lumen of the lacuna—changed so
that it absorbs more colouring material than elsewhere farther

14 A. O. OUDEMANS.

from the lumen. On the inner side of these cavities I have
seen here and there small flattened nuclei.

Thus the lacune have a wall consisting of a layer of cells with
flattened nuclei, and a layer of hyaline basal tissue. McIntosh
(26) makes use of the terms “granular layer” and “ basal
layer ” or “layer of basal tissue,” where he describes the wall
of the proboscidian sheath.

I did not observe a communication of the two lacunz beneath
the proboscidian sheath.

On following the lacunze backwards one sees that they pass
with the proboscidian sheath through the brain ring, formed
by the ganglia and their two commissures, still resting on the
sides of the proboscidian sheath (fig. 20). They then descend
to a lower level. The mouth and the csophagus next become
visible. First the lacune remain where they are (fig. 21), that
is to say, they do not descend any further, but lie in the hori-
zontal plane, between the stomodzum and the proboscidian
sheath. A few slices further backwards they are separated
from the proboscidian sheath by the cesophagus which assumes
a semilunar shape, the two horns extending between the pro-
boscidian sheath and the blood cavities. Now, these cavities
lie against the intestine above the plane of the nerve trunks,
which are perfectly lateral. Behind the cesophageal region the
lacune descend till they come to lie against the intestine,
beneath the level of the lateral nerves, but still imbedded in
gelatinous stroma. However, they have become somewhat
changed, having obtained outside of the hyaline basal layer a
layer of circular fibres. Intentionally I use here the term
“fibres” because I have not been able to make out whether
they are muscular or not. It appeared to me that they were
still “in statu nascenti.”’ They are still primitive, and I
cannot say anything definite concerning them. They appear
to be of the same nature as those which I shall describe after-
wards in Carinoma Armandi (see fig. 74). I have not seen
longitudinal fibres. Probably the fibres add to the contrac-
tility of the vessel.

I have seen nothing of the water-vascular, better called ne-

CIRCULATORY APPARATUS OF THE NEMERTEA. 15

phridial system. Hubrecht mentions (35) in the living animal on
the level of the mouth a lateral opening, and adds (“of the
water-vascular system ?”): I can only mention that the blood
spaces, seen on transverse section, here send a diverticulum
towards the periphery above the lateral nerves. But I have
never seen an opening, nor anything that could represent a
nephridial system, such as I shall describe below in Carinella.

2. Carinella annulata (Mont.), McInt., figs. 2, 4, 19—27.

The vascular system consists chiefly of two longitudinal
vessels, which communicate in the tip of the snout and in the
tail. I have not verified the presence of this last-named com-
munication. Two longitudinal vessels in the proboscidean
sheath, never, however, extending any further than the cesopha-
geal region, are perhaps only of secondary importance. I
will henceforth call the individuals which are deprived of
these vessels those of the first form, the others I will designate
as the second form. (See the Explanation of the Plates.)

In the head we find two great lacunar spaces, one on each
side of the probiscidian sheath (fig. 19). They fill up the
head—before the ganglia—and have the proboscidian sheath
between them. Besides these two lateral lacunz one some-
times finds (not, however, seen by me in all the specimens) a
broad and flattened lacuna above the proboscidian sheath,
which has the whole width of the proboscidian sheath, but is
tolerably flat in transverse sections, and which is temporarily
separated from the other lacunz by transverse muscular bands.
In the tip of the snout the two lateral lacunze communicate by
an arch above the proboscidian sheath. When the lacune
above the proboscidian sheath is present, it also opens in the
above-mentioned arch. Further backwards this process is
repeated just behind the supra-proboscidian commissure, and
in front of the infra-proboscidian one. A broad arch is here
situated above the proboscidian sheath. But between the two
arches the lacuna above the proboscidian sheath has already
had occasion here and there to mix its fluid contents with that

16 A. ©. OUDEMANS.

of the two lateral lacunez, the transverse bands which separate
them being here and there interrupted.

The two great lateral lacune are surrounded by a thin layer
of transverse muscular fibres. Still, I am inclined to call
these spaces ‘‘lacune,” reserving the name of vessel for those
that are in transverse section of a circular ellipsoidal shape.
Bands of dorso-ventral muscles traverse the lacune, slanting
backwards or forwards. They are so strongly inclined, that in
transverse sections of ;+, mm. I never saw a band from one
wall to the other, but always found it cut off, so that in section
they resembled finger-like protuberances from the walls.
Bands which were twice cut through thus produced in sections
an insular patch in the lacune. McIntosh gives a similar
description of this arrangement in his “Great Canadian
Carinella” (25).

As in Cephalotrix, I have here found a very thin layer of
hyaline basal tissue, against which on the inner surface are
found very distinct small round or ellipsoidal cells, with rela-
tively large nuclei.

We now follow the lacune backwards. We have passed
the supra-proboscidian commissure of the brain, and have seen
that the supra-proboscidian lacuna, which occurs only in some
individuals, is already coalesced with the other, and dis-
appears.

Now, in those specimens which have a lacuna above the
proboscidian sheath, there is also a lacuna below it. This, too,
is wide and flattened, and becomes visible all at once, it
evidently terminates blindly in front. The blind end lay in
the same slice, wherein the infra-proboscidian commissure of
the brain became visible. Close behind this region the inner-
vation of the proboscis by two large nerve-trunks becomes
visible. Just behind these the lacuna dilates, and then
appears a broad arch (turned downwards) as a commu-
nication between these three lacunz. This broad arch also
is now and then traversed by large bands of transverse
muscles.

lt appears to me that all these transverse bands can co-

CIRCULATORY APPARATUS OF THE NEMERTHA. 17

operate, and not in an insignificant manner, considerably to
diminish the lumen of the lacune.

These two different types of communication of the lacune
in the head I have described from specimens cut into trans-
verse sections, but it would not surprise me if there are more
types or variations, having found these two types in only four
specimens. I must remark that these two types occur as well
in the first form as in the second. (See the beginning of this
description, p. 15.)

We now approach the csophageal region. In those indi-
viduals where there is a large communication between the
lacune of the head beneath the probiscidian sheath the
mouth becomes visible when this lacuna disappears. The
lacune, which down to this point have been situated on the
sides of the probiscidian sheath, now descend to a level between
the probiscidian sheath and intestine (figs. 19 and 20), as in
Cephalotrix (fig. 21). They have not lost their circular
fibres, and also preserve their inner investment of the thin
hyaline basal layer, and the beautiful epithelium of little
round cells, with relatively large nuclei. Still further back-
wards the lacunz descend still further, and now lie on each
side of the intestine, but so that their upper wall is just as
high as the upper limit of the intestine.

In the esophageal region I have to mention apeculiarity which,
as far as I know, has not yet been seen in other forms. The
lacune show numerous dorsal dilatations, a portion of which
is separated from the bulk of the lacuna by a sometimes
thin, sometimes large band. This band consists for the greater
part of hyaline basal tissue, but some of the circular fibres
also enter the band. I have represented it in figs. 2 and 4
diagrammatically. On the ventral border of the lacune
arches, as indicated in the figure, only now and then occur,
A transverse section through such a region is shown in the left
half of fig. 23, and the more common case of arches directed
upwards, in the right half of fig. 23 and in fig. 24. Rarely
an arch directed upwards and one downwards were seen in the

same section. In a younger specimen these separating bands
9

ow

18 A. O. OUDEMANS.

were more numerous in one and the same transverse section,
but the bands were much thinner and the lacune reached lower
down under the intestine than in an older specimen; but they
never coalesced beneath the intestine.

In figs. 4 and 24 we still see two other thin longitudinal vessels
in the cesophageal region. The form of Carinella annulata,
where this occurs, I have called (see above) the second form.
These two vessels lie in the proboscidian sheath. They ter-
minate blindly in three of the four specimens examined, both
in front and behind. They become visible gradually, not at
once, and disappear also by degrees. In one of the specimens
of the second form, I saw at the point where these vessels
originate a trace of a communication of these vessels with the
longitudinal blood-vessels, consisting in a pointed diverticulum
of the blood-lacunz towards the vessel in the proboscidian
sheath, this point finishing in the hyaline basal layer of the
proboscidian sheath, whilst the vessel of the sheath had not
yet a lumen there, but only a little further behind. In a
second specimen I noticed a space becoming visible above the
horn of the semi-lunar section of the cesophagus, but lying
within the cesophageal constrictor muscle. This space seemed
to me to communicate with the vessel in the proboscidian
sheath (the latter lying nearly on the same level as the horns
of the cesophagus), and a few slices more forwards or back-
wards to communicate with the lateral blood lacuna. It is
with due reserve that I mention this, the more so because I have
seen this only on the right side of the animal, and never on the
left.

I have stated that the two vessels in the proboscidian sheath
lie on the same level as the two horns of the cesophagus. In
the hindmost part I saw one of the vessels going down a little,
approaching the median line which I have represented as seen
from above in fig. 4. Similarly, with due reserve, I will
mention what I have seen in a third specimen of the second
form, of which I had only a small portion. Five times on the
left side and twice on the right side, the vessel in the probos-
cidian sheath sent out a pointed diverticulum through the

CIRCULATORY APPARATUS OF THE NEMERTEA, 19

muscular wall of the proboscidian sheath in a direction slanting
downwards, the lacunz doing so in the opposite direction, so that
a connection between these two spaces may exist. In a slice
which was very thick, the connection was complete, but the
section was so thick that the whole canal, if it was one, lay in
it. I have distinctly seen a lumen in it. The walls of this
narrow canal were limited by fibres which were directed from
the wall of the proboscidian sheath towards the walls of the
blood-lacuna. Fig. 24 shows us a section through the ceso-
phageal region of the second form.

In regard to the histological structure of these vessels I
must be very brief. Sometimes both the epithelium layer and
the hyaline basal layer of the proboscidian sheath, the latter
being tolerably thick, covered them, so that the vessel cannot
be said to lie in the lumen of the proboscidian sheath. Some-
times they were considerably swollen, and I saw neither hyaline
basal layer nor epithelium layer covering them and separating
them from the lumen of the proboscidian sheath. In such
cases their wall was very thin, and their lumen divided into little
compartments, more or less resembling certain portions of the
nephridial system to be mentioned below. In both cases they
lay upon the hyaline basal layer of the proboscidian sheath.
Sometimes they were in no way of a peculiar colouring, some-
times they distinctly showed two colours, one part being ex-
tensively yellow. Of their cellular structure I can say nothing.

If nevertheless I were to make a hypothesis as to their
possible physiological signification, I should be inclined to ask:
Could they perhaps have any significance with respect to nutri-
tion, oxygenation, &c., of the fluid of the proboscidian sheath ?
In this opinion I was strengthened when I noticed their
probable connection with the vascular system, which, as we
will soon see, communicates with the exterior by means of the
nephridial system. This very provisional hypothesis will be
further discussed in the description of the arrangements which
we find in the following species.

Gradually going backwards we have now approached a
region where the singular arches formed by the lacune

20 A. CO. OUDEMANS.

cease. This lacunar region I have called the esophageal
region. The blood-spaces have now changed their form
into one which in transverse section is circular or ellip-
soidal, so that now the name of vessels can be applied.
Internally they are clothed with the cellular epithelium, next
follows a hyaline basal layer and externally a layer of circular
muscular fibres. I have nowhere observed a longitudinal layer
of fibres. The region which follows the cesophageal one I will
call the nephridial region, because we meet here with organs
visibly belonging to that type of excretory apparatus of the
Evertebrata, which Ray Lankester has united under the name
of nephridia.

Above the blood-vessel, directly applied against it in a slanting
direction, and only separated from it by a thin wall, hes a
second large longitudinal canal, the nephridial canal (see figs. 4,
25, 26, 27). Its walls are similar to those of the blood-vessels.
Thus the thin wall that separates them consists of five layers:
epithelium, hyaline basal tissue, circular muscular fibres,
hyaline basal tissue, epithelium. Indeed, a highly primitive
nephridium, which is, as it were, a part of the blood-vessel
separated from it! Now,in the whole nephridial region a
spongy organ lies in the blood-vessel, placed on its outer wall, of
which to my regret I could not make out sufficient histological
details, at least none which I would venture to communicate as
yet. This organ, which presents itself as a spongy gland, I will
call the nephridial gland (see figs. 4, 25 to the left and to the
right, and fig. 26 to the right). The nephridial canal has at its
front end an open communication with the blood-vessel (see
fig. 4 and fig. 25 on the right). Also at the other end where its
lumen gradually becomes smaller (see fig. 4 and fig. 26 to the
left). The nephridial canal further at intervals has open com-
munications with the nephridial gland (see fig. 4 and fig. 25 on
the left, and fig. 26 on the right). The lumen or the lumina of
this gland are always separated from the lumen of the blood-
vessel by a very thin wall. I have clearly noticed two excretory
ducts, one on each side, by which the lumen of the nephridial
canal communicates directly with the exterior, consequently also

CIRCULATORY APPARATUS OF THE NEMERTEA. 21

that of the vascular system (see figs. 4, 24).! These excretory
ducts lie above the lateral nerves. The epithelial layer and
the hyaline basal layer clothe the whole duct. The epithelial
layer passes gradually into that of the skin. The hyaline basal
layer coalesces with the basal membrane of the skin, which
deviates outwards, and the layer of circular fibres passes into
that same layer which lies within the basal membrane. The
whole is remarkable as bearing a very primitive character.
The skin shows in the living animal a hardly perceptible cup-
shaped deepening. In a transverse section this is seen to
correspond with the outer infundibulum of the duct.

Behind the nephridial region I have followed the vascular
system much further. The vessels in the intestinal region lie
sometimes beneath, sometimes above the level of the lateral nerves
(figs. 21, 22), are large and wide, and their wall again consists of
the three layers already described. Here, too, I searched in
vain for an exterior layer of longitudinal fibres to the vessel.

I have not had occasion to observe the connection of the
two vessels in the posterior extremity of the animal.

3. Carinoma Armandi (MclInt.), Oud.; figs. 5, 28—37,
56—61, 72—75.

Of this species the vascular system, neglecting a few smaller
vessels, consists of four large lacune in the head, which com-
municate in the tip of the snout, and form two lacune in the
cephalic region, passing into six longitudinal vessels further
backwards, two of which are situated in the proboscidian
sheath, terminating blindly behind two others above and out-
side of the proboscidian sheath, which also terminate blindly
behind, whilst two others, which extend along the whole length

1 Inducement to search for the nephridia of Carinella, unknown till to-
day, and to hope to find a communication with the vascular system, was
given me when Professor Hubrecht communicated to me that he had met with
nephridia in two genera closely related to Carinella (the still inedited genus
Carinina dredged by the “Challenger,” and Valencinia Armandi;,
MciInt.), and that he had succeeded in finding in the latter the internal and
direct communication of the nephridium with the vascular system.

22 A. OC. OUDEMANS.

of the body, remain beneath the level of the nerve trunks, and
finally communicate in the tail.

In the tip of the snout, already in the third section, where
the thickness of the sections is about ~; mm., the communi-
cation of the lacune (fig. 28) is visible. A few sections
further the spacious lacuna is already traversed by vertical
bands, extremely thin, consisting of transverse muscular
fibres, which again diverge amidst the tissue that surrounds
the lacuna. In the thirteenth section the lumen of the pro-
boscidian sheath penetrates between these lacune, and is situ-
ated in the axial line, but with one of the lacune above it.
The two lacunar spaces on the sides of the proboscidian sheath
gradually lose their thin bands, whilst they become divided,
each by a broad vertical band (fig. 29). The lacuna above the
proboscidian sheath becomes gradually flatter (seen in trans-
verse sections, not marked in fig. 29), and is at every moment,
sometimes to the left sometimes to the right, in connection
with the lacunz on the sides of the proboscidian sheath,
sometimes even with both of them at once. In the meantime
a thick, circular, muscular layer is formed, surrounding all the
lacunze, the contractions of which may aid in driving the fluid
backwards. The circular muscular layer is closed entirely,
and not, as asserts McIntosh, half open on its sides. Within
this circular layer longitudinal fibres become visible, as well
lining the four lacune as further backwards, between the
fibres of the transverse bands which separate them. In this
species, too, the fibres are not directly bathed by the fluid.
Here and there the epithelium was visible very distinctly ; it
has the same character as that of the foregoing species, con-
sisting of little round cells with relatively large nuclei. A
little before the brain-ring the two lacune on each side of the
proboscidian sheath coalesce into one, so that when they
pass through the brain-ring only one great lacuna lies on
each side of the proboscidian sheath. Just before the upper
brain - commissure the broad band of circular muscular
fibres diminishes so suddenly that one is inclined to think
it disappears there. The same is seen when the brain-masses

CIRCULATORY APPARATUS OF THE NEMERTEA. 25

and the lower brain-commissure become visible laterally and
ventrally. By a more accurate contemplation with objectives
of higher power, it can, however, be demonstrated that
the circular muscular layer, which now consists of only a very
few fibres, passes through the brain-ring at the same time
with the lacunze and the proboscidian sheath, whilst the
number of longitudinal fibres has increased remarkably ; and
this circular muscular layer is the same which, behind the
ganglia, will enclose the cesophagus, and thus is the same as the
circular muscular layer of the body wall. The longitudinal
fibres will form the layer of longitudinal muscular fibres, so
that the circular layer which surrounds the lacune in the head
of Carinoma is in no case comparable with the transverse
fibrillar layer which surrounds the lacune in the head and
other blood-spaces in Carinella. In the lacune of Cari-
noma, however, I have found the same hyaline basal layer
and the same epithelium cells as in Carinella.

Immediately behind the ganglia the lacune grow down-
wards, but both are divided by a common horizontal band of
transverse muscular fibres. The upper lacuna is the larger,
and lies on the side of the proboscidian sheath, slanting down-
wards. The lower, or smaller, lies beneath the proboscidian
sheath, and both of them between the two brain-masses. The
broad band that separates the upper lacune from the lower
consists of muscular fibres, which run from the left to the
right, these fibres passing amongst those of the circular
muscular layers. The two lower lacune are separated by a
broad vertical band of hyaline basal tissue, in which numerous
vertical transverse muscular fibres are visible, in the upper
portion passing into the horizontal band, and in the lower
diverging into the third (outermost) layer of isolated muscular
longitudinal bundles, which layer penetrates here more inwards
than elsewhere. The horizontal band disappears soon, thus the
four lacunz again become only two, lying on each side of the
proboscidian sheath. The mouth becomes visible, and presses
the lacune still further from one another and upwards.

The two lacune now extend dorsally (figs. 31 and 58), and

24 A. 0. OUDEMANS.

the uppermost portion, which is bent outwards, is suddenly
separated from the lacune by a portion of the gelatinous
stroma that everywhere fills up the spaces between the different
organs in the body of the Nemerteans (figs. 31 and 59). Thus
there are now formed four lacunar spaces. McIntosh has not
seen this connection between the four blood-spaces. These
two supra-proboscidian sheath-vessels soon obtain a distinct hya-
line basal layer and an epithelium (fig. 73), and extend to the
nephridial region, where they terminate blindly. I have seen
no other communications with the blood-vessels of these two
supra-proboscidian sheath-vessels.

Though they were very variable, and appeared to be subject
to immense dilatation or contraction, they had, besides the two
layers noted, no third layer of circular or longitudinal fibres.
Their situation through the whole cesophageal region was the
same laterally above the proboscidian sheath. Once I saw
the left vessel extraordinarily dilated; once the right one
divided into two, but sixty slices further these again merged
into one (figs. 72 and 73). The blind end appears gradually,
not abruptly.

We have seen that in Carinella there is a tendency in the
cesophageal region of the longitudinal blood-spaces to give off
arch-shaped portions directed upwards. If we suppose a similar
separation to have taken place along the whole length of the
vessel in the cesophageal region, then we have the two supra-
proboscidian-sheath-vessels of the genus Carinoma. (Com-
pare the fig. 4 with 5, and 24 with 32.)

In the same vertical section, where the two supra-probos-
cidian-sheath-vessels spring from the two great lacune, I saw
very clearly on the left side—on the right side only a tendency
to it was visible—how the left vessel in the proboscidian sheath
communicates with the lacuna. I have therefore exactly
figured the left half in figs. 583—61 of four subsequent slices.

Let us now call to mind for a moment what I have men-
tioned, with due reserve, of what I have seen in the second
specimens of the second form (see p. 18), and let us then
compare fig. 59. The band of transverse fibres, which sepa-

CIRCULATORY APPARATUS OF THE NEMERTBEA. 25

rates the larger lumen from the neighbouring smaller one,
passes upwards into the circular layer of the proboscidian
sheath, and below it surrounds the esophagus. It thus proves
to be the constrictor muscle of the cesophagus, and the smaller
lumen lies within this constrictor, the same as I have seen
in Carinella.

On the right side I only saw a similar communication
between the vessel in the proboscidian sheath and the lumen
within the cesophageal constrictor faintly indicated; but a
connection between this and the great lumen I have not seen.
McIntosh says that the two vessels in the proboscidian sheath
have no connection with the blood-vessels anywhere. It is
thus probable that this connection disappears when the animal
becomes older, or that it only appears when the animal has
reached a certain age; this only is sure, I have seen the con-
nection. These two vessels are not very long. In the speci-
men I have examined, they are about one fifth of the cesophageal
region. They terminated blindly, but not as in Carinella,
gradually, but at once. Perhaps this is to be ascribed to the
posterior end being filled with fluid or not. In regard to the
histological structure, I cannot mention more than that they
are invested on the inner side with the same layer of small
cells as the blood-vessels and the proboscidian sheath; that their
hyaline basal layer sometimes passes into that of the probos-
cidian sheath, sometimes is separated from it by the same cells,
and that the epithelium layer of the proboscidian sheath
always covered the vessels on their outside.

We now return to the region of the mouth, to the two great
lacunze with which the four last mentioned vessels are con-
nected. These two great lacune, seven slices further back-
wards, are already surrounded by a circular layer of muscular
fibres. This circular layer is well developed. A few slices
further backwards the circular layer becomes thinner and
thinner, but it still exists. Not before the midst of the
cesophageal region some longitudinal fibres become visible
outside of the circular, which are also not very sharply limited
there. An immersion objective very soon showed that they

26 A. C. OUDEMANS.

possess a very primitive character. After a few efforts, I suc-
ceeded in finding a very beautiful section through the longi-
tudinal vessel, which section, being cut partly at an angle,
furnished a very good picture of the two layers, which, as we
see in fig. 74, have a thickness of only two or three cells, and
consists of cells which have not yet lost their protoplasmatic
character, and nevertheless give rise to a distinct fibre. Espe-
cially an isolated cell on the right side of the figure shows
which cells give rise to the outermost investment of the blood-
vessels. A whole section through a vessel and vertical section
I have figured in fig. 75. This section lay just before the
nephridial region, to which we will pass immediately, after
having mentioned that the two great vessels that take their
course from the level of the mouth till far behind, are al-
ways provided with a well-developed hyaline basal layer, and
an epithelium with large nuclei (see figs. 74 and 75); and that
in contracted portions of the vessels the basal layer forms
protuberances towards the lumen, so regularly arranged that
the whole has the appearance of a saw. These must be longi-
tudinal folds lying side by side.

Only a very few sections (four in this specimen) before we
see a true nephridial canal, we see that the lower portion of
the blood-vessel changes its structure. A portion of its wall
now is lined by palisade-shaped cells, regularly placed by the
side of each other. We soon see a section in which a furrow
pierces this changed wall-portion, and in the following slice we
see this furrow cut off from the vessel by similar cells, and
the nephridial canal is ready. There is thus an open anterior
communication between the nephridial and the vascular
system. The blood-vessel retains this changed ventral wall from
section 718 to section 768. The nephridial canal, once separate,
remains small when compared to the vessel, and lies next to it.
Here and there I distinctly saw cilia, which were so long that
they touched the opposite wall of the canal. A little further
backwards we see the nephridial canal again in connection with
the blood-vessel (see figs. 5 and 57: the communication took
place in slice No. 762). At first, behind this connection the

CIRCULATORY APPARATUS OF THE NEMERTEA. 27

canal becomes larger, also the cells, the nuclei in their base,
and the cilia at their top. By-and-by it moves away from the
vessel, descends, and finally is partly situated in the longi-
tudinal muscular layer (fig. 33). A little further backwards a
second canal suddenly appears on the side of the vessel, which
soon divides into two canals, the upmost of which gradually
goes upwards till above the level of the nerve-stems, then goes
to the periphery, piercing the basilar membrane and the skin,
and communicates with the exterior. The second undermost
canal of the two coalesces further backwards with the chief
canal beneath the blood-vessel. It is thus a branch which,
rising from a certain branch of the nephridial canal, goes for-
wards, then a little backwards, and communicates with the
exterior above the nerve-trunk (see fig. 5: fig. 84 is an ideal
transverse section cut along the dotted line in fig. 5). There
are thus a few slices which show six cut canals, on each side
three, then a larger number with four canals (fig. 35). This
point of rising of the branch we see in fig. 36. Still further
backwards the canal again lies close to the vessel, and is finally
connected with it (figs. 5 and 37), thus forming the hindmost
open communication with the vascular system.

Let us now compare the nephridial system of Carinoma
with that of Carinella. We find a striking resemblance in
their design, but an extraordinary progress in the structure
of that of the former. Both have in front and behind an open
communication with the blood-vessel, both have one single
excretory duct ou each side, which rises from the hindmost
part of the nephridial canal, goes directly outwards in Cari-
nella, and in Carinoma first tends forwards a little before
communicating with the exterior. Both have the excretory
ducts lying above the nerve-stems. In Carinella the
nephridial canal has occasion to communicate from time to
time with the nephridial gland, which lies in the blood-vessel ;
in Carinoma it is connected in its whole course once with the
blood-vessel, thus forming a third direct communication. The’
nephridial gland is absent in Carinoma, but we may perhaps
suggest that its function has passed over to the cells of the

28 A. ©. OUDEMANS.

wall of the canal itself. Its cells have a typical glandular
structure and design. A transverse section through the
nephridial canal shows, in regard to the form and habitus of the
cells (without their cilia), a perfect resemblance to all glandular
ducts or glands of the stomach or other glands. The nephridial
canal has more the appearance of a blood-vessel, with the same
histological structure as the blood-vessel lying next to it,
and thus probably serves as a reservoir for the materials
excreted from the blood by the nephridial gland. In Cari-
nella, cilia were absent; but a circular muscle layer sur-
rounded the nephridial canal. In Carinoma, cilia are
present, even in the extremity of the excretory duct; but the
layer of circular muscular fibres is absent. All the cilia are
directed outwards. In Carinoma, too, the excretory duct
has the appearance of having progressed outwards, for the
basal membrane, and even a small part of the circular muscular
layer inside of it, are pressed outwards, as in Carinella. As
far as close to the surface the duct is invested with its epi-
thelium, and only at the rim of the opening there are cells that
are intermediate between skin epithelium cells and nephridium
glandular cells. Thus, the structure indicates that the nephridial
system of Carinoma has a higher development than that of
Carinella.

I have examined only a few sections behind this region, the
body being still several centimetres longer. The blood-vessels
do not show anything peculiar. In the tail their communica-
tion is very peculiar. They can indeed be followed till nearly to
the tip of the tail, where, however, they do not coalesce directly
but gradually increase in size, becoming lacune which com-
municate above the proctodeum. But anteriorly to this
connection already many lacunz, for the most part also above
the intestine have become visible, which communicate from
time to time with the vessels themselves, forming thus rudi-
mentary transverse contracting vessels! It is very probable

‘that these lacune also communicate with one another.
Laterally to the vessels I have also seen lacunar spaces, but I
could not find any communication, either with the vessels, or

CIRCULATORY APPARATUS OF THE NEMERTBEA. 29

with the blood-lacunez, or with the exterior. Perhaps they are
genital spaces.

4, Valencinia longirostris, Quatref. Figs. 13—16,
41, 45—47, 50—55, 63, 67.

The vascular system of Valencinia longirostris resem-
bles in the head that of Carinoma Armandi, consisting of
longitudinal lacunze which coalesce into two, when passing
through the cerebral ring. But for the rest its principal traits
are also common to all Schizonemertea and Polia. There
is a median dorsal vessel, which lies in the cesophageal
region in the proboscidian sheath, and behind it between the
proboscidian sheath and the intestine. It communicates with
the lacunze above the inferior brain-commissure and it leaves
the proboscidian sheath towards the hindmost part of the
cesophageal region. This region is characterised by two pecu-
liarities, (1) the whole cesophagus is surrounded by lacune with
the exception of that portion which lies close to the probos-
cidian sheath, and (2), this region is the seat of the nephridial
system. Behind this region two lacune are still visible at the
sides of the proboscidian sheath, above the foremost half of the
intestinal tract. Beneath the intestine we find two vessels, so
that on a transverse section we see five blood-canals, of which
three have muscular walls and two not. These five blood-
spaces are united together by transverse vessels. The hind-
most half of the intestinal region only shows three vessels, the
lacunz next to the proboscidian sheath having disappeared.
Here, too, transverse vessels are present. All the transverse
vessels lie above the diverticula of the intestine. The commu-
nication of the three longitudinal vessels takes place in the
tail before the anal commissure of the nerve-trunks and both
lie above the rectum.

A series of transverse sections of Valencinia, when
examined from head to tail, shows in the tip of the snout (in
my specimen in the ninth section) the beginning of the circular
muscular layer in the shape of a small curve with its convexity

30 A C. OUDEMANS.

directed upwards ; a few sections further backwards this little
arch becomes larger, sending two horns downwards; again, a
few sections further and the circular muscular layer is closed.
Meanwhile we see within the little arch the beginnings of the
lacune, for there are more than one, all situated against the
circular layer, so that when this is closed there is also a circular
arrangement of the lacunz, which of course are all more or
less triangular, with their bases against the circular layer and
with their tops turned towards the centre (fig. 53). The
lacunz are separated from one another by transverse muscular
fibres, which not only take their course from the one side of
the circular layer to the other, so that they form in the centre
a median chord, transversing each other in all directions, but
which also extend further outwards than the circular layer, so
that they appear to run radially from the centre to the skin.
I seldom saw any communication between the lacunee whenever
a transverse band was partly absent. As in Carinoma longi-
tudinal muscular fibres also took part in the limitation of these
lacune, being placed both against the circular layer and against
the transverse muscular bands, and also in the angles of the
triangular lacune. Even between the transverse fibres of
the bands, as in Carinoma, longitudinal fibres occurred.
However, the blood did not directly bathe these fibres, but was
separated from them by a richly developed beautiful epithelium
of small round cells with relatively large granular nuclei as in
Carinoma. On a sagittal section (fig. 67) going from above
downwards we find the circular muscular layer (not indicated
in the figure), a few longitudinal fibres, epithelium, lacuna,
epithelium, longitudinal fibres, then the chord or cylinder of
transverse fibres, and then the same arrangement in inverse
order.

Where the epithelium cells were present in large numbers,
the very thin and nearly colourless hyaline basal layer was
not visible. It was clearly seen where the epithelium was
torn off.

Though we cannot say that in Carinoma the opening of
the proboscidian sheath is not wholly terminal, yet in Valen-

CIRCULATORY APPARATUS OF THE NEMERTEA. 31

cinia it is placed still further backwards. In my specimen it
becomes first visible in the fifty-sixth section, thus nearly on
1 mm. from the tip of the snout (in the preserved specimen),
goes upwards till it reaches the circular muscular layer, and
penetrates this a few slices further backwards, finally remain-
ing in the centre of this ring-shaped layer. When the pro-
boscidian sheath first touches the circular muscular layer the
number of the lacunze diminish by communicating with one
another, and deviate more from the median line; but after the
circular layer has given a passage to the sheath and has
enclosed it, the number of the lacune is diminished to two,
lying on the sides of the proboscidian sheath. There is no
lacuna above the latter. One may thus say that in Valen-
cinia the lacune in the head communicate not directly above
the proboscidian sheath but indirectly. The brain-commis-
sures now become visible, and the circular layer, the longitu-
dinal fibres, the lacunz and the proboscidian sheath protrude,
as in Carinoma, through the cerebral ring. The lower half
of the cerebral ring being very thick is seen in many slices.
In the hindmost three sections, where it was visible, the two
lacunz slant downwards, and the fibres of the proboscidian
sheath cut off a part of the left lacuna and enclose it between
them. (Fig. 54, referring to Lineus sanguineus, may also
serve for this species.) I believe this is abnormal, for in all
Nemerteans where this process takes place, and which I
examined also on transverse sections, both the lacune, except
in two other cases, participated in this process. For the
moment we leave the dorsal vessel in the proboscidian sheath,
only pointing out that here as in Carinoma, a part of the
lacunz as it were penetrates the muscular wall of the probos-
cidian sheath, and extends further backwards as a vessel in
the latter. This process I have also been able to follow in
sagittal sections.

The lacune again remove to the sides of the proboscidian
sheath. Now, beneath the latter a lacuna becomes visible,
which terminates blindly in front, and in a following section is
broad and flattened and thus may be compared with the “‘infra-

$2 A. CO. OUDEMANS.

proboscidian channel” of McIntosh (26) (better “infra-pro-
boscidian-sheath-channel”). It is separated from the two
others and from the sheath by a horizontal broad band of
transverse fibres (cf. Carinoma).

The next section shows us six lacune, for each of the three
lacunz is divided into two by transverse fibres, viz. the lacunz
on the sides of the proboscidian sheath are divided into an
upper and a lower one, whilst that beneath the sheath into one
right and left.

A little further backwards the transverse bands in the
lacunz on the sides of the proboscidian sheath disappear, and
so we have again four lacunz, one on each side of the sheath,
and two beneath it, just as in Carinoma.

At the same time we see on each side a great ganglionic
mass penetrating the circular layer. These are the posterior
lobes (brain respirators). As soon as they are within the
circular layer they are surrounded by a thin lacunar space,
thus they are bathed (McIntosh) by a lacuna. These lacune
as soon as the posterior lobes disappear, immediately unite
with the two lacunz beneath the proboscidian sheath, which in
the meanwhile have moved from one another.

Besides the two brain respirators, still two smaller club-
shaped ganglionic masses penetrate into the two lacune on the
sides of the proboscidian sheath (are they brain processes ”).

The two lacune on the sides of the sheath are wholly sepa-
rated from the other lacune, even from those in which the
two posterior lobes bathe, by the above mentioned horizontal
band of transverse muscular fibres. After the disappearance
of the lobes this band also disappears and the four lacune now
coalesce into two.

This coalescence, however, is of very short duration, for they
are again divided by transverse bands. The mouth becomes
visible. The circular muscular layer in its lower portion is
interrupted, deviates outwards, and finally encloses the ceso-
phagus. The lacune and the longitudinal muscular layer,
which always remain against the inner side of the circular
layer, do the same as the circular layer (fig. 50), so that as

CIRCULATORY APPARATUS OF THE NEMERTEA. 33

soon as the cesophagus is inclosed by the circular layer, it is at
the same time surrounded by the longitudinal muscular layer
and the lacune (fig. 5]). The small transverse bands which
continue to divide the lacune, are also present round the ceso-
phagus and keep it connected with the circular layer, at an
almost equal distance all round, of course not on its dorsal side
where the proboscidian sheath lies, which is at the same time
the cause, that on its sides through the whole length of the
cesophageal region, a lacuna is visible, larger than the others.
I shall call them proboscidian sheath lacune.

I have carefully examined all the little transverse bands of a
small portion of the oesophageal region, with respect to their
width and situation, but did not find any indication of meta-
merism or segmentation, so distinctly expressed behind the ceso-
phageal region, both in the intestine as well as in the vascular
system.

In the specimen examined the lacunar or cesophageal region
took up nearly one third of the whole length of the animal.
The lacune in the hindmost part of this region become
gradually larger, at the same time diminishing in number,
especially ventrally.

In this region, at the same time, a little more forwards the
vessel in the proboscidian sheath penetrates through the wall
of the sheath, and now lies below it, but so closely against it
that I could not distinguish the two muscular layers, for the
vessel too has now a very thin circular muscular layer. Also
the intestine lies so closely against the blood-vessel that no
space is seen between them. The process takes place within
five slices, and it appears as if the circular layer of the
proboscidian sheath moved upwards from below.

The median vessel, when lying in the sheath, shows an inner
epithelium layer of the same cells which everywhere limit
blood-spaces ; then follows a hyaline basal layer. It always
lay above the epithelium layer of the sheath, and the dorsal
half of the wall of the vessel had quite another histological
character than the ventral half. The layer outside the hyaline
basal layer showed on the dorsal half glandular cells, as if the

8

34 A. OC. OUDEMANS.

median vessel in the proboscidian sheath has, as I suggested
from the two vessels in the sheath of Carinella and Cari-
noma, some important bearing on the material interchange of
the fluid in the proboscidian sheath. In accordance with this
view the hyaline basal layer of the dorsal half is thin, of the
ventral one thick. I further saw (see above) that in Cari-
nella they were sometimes swollen and spongy. ‘Their
surface was thus enlarged. In Carinoma I have never seen
them so swollen, but here too their surface was on all sides
surrounded by the fluid of the sheath, because their attachment
on the inner surface of the sheath only takes place along a very
small base; whilst in Valencinia the vessel is not only lifted
up and supported by little bands, but is also washed on its
ventral surface by the fluid of the proboscidian sheath. The
preparations, however, were not sufficiently preserved to give
a representation of it. In sagittal sections I have also seen
the median vessel leave the proboscidian sheath.

In this region the lacunz, as we have mentioned above,
diminish in number, especially ventrally. However, not all
the ventral lacunz disappear. The intestine shows here, on the
sides of the median line, an inward fold, in which a lacuna
remains visible, which further backwards obtains a layer of
circular muscular fibres, so that finally these lacune have
become vessels. Not so the proboscidian lacunz, with which
all the remaining lacune have gradually coalesced. They
remain running, on the sides of the proboscidian sheath,
without muscular or fibrillar walls, through the whole foremost
half of the intestinal region. Now and then they seem to be
lied with fibres, but on closer examination these prove to be
only transverse bands, which temporarily only limit them on
their upper or lower side. They disappear as soon as they
have come.

In the foremost half of the intestinal region thus there are
five longitudinal blood-spaces. These are united together by
transverse vessels, which are extremely thin, and run regularly
over each diverticulum (figs. 14, 15, 52). These transverse
vessels I have seen both in transverse and in sagittal sections,

CIROULATORY APPARATUS OF THE NEMERTEA. 35

but in none of my preparations did I see circular fibres sur-
rounding them, only a thin hyaline basal layer, and occasionally
epithelium. They stuck, as it were, to the diverticula; their
wall, at the same time, was the wall of the intestine.

In the hindmost half of the intestinal region the lacunar
spaces of the sides of the proboscidian sheath are absent. They
have gradually disappeared (fig. 15), and now only three longi-
tudinal vessels occur (figs. 16,41) with their transverse vessels,
which are visible down to the hindmost communication of the
three longitudinal vessels above the proctodeum; sometimes
this latter communication is invisible.

The lacune surrounding the esophagus and the two long
lacunar spaces next to the proboscidian sheath in the foremost
half of the intestinal region are always internally limited by
the epithelium cells already mentioned; externally by an
extremely thin hyaline basal layer. In the dorsal vessel, as soon
as it lies beneath the proboscidian sheath outside the hyaline
basal layer, a thick layer of circular muscular fibres are seen ;
also in the two ventral vessels. In vain did I look for longi-
tudinal fibres. The two ventral vessels lay in a fold, turned in-
wards, of the intestine amidst a gelatinous stroma that filled up
this fold. This stroma has a radiating arrangement round the
vessel. Probably these rays are local thickenings arising from
the violent contraction of the vessel. In the stroma great
granular nuclei were visible. The whole looked almost like
fig. 63.

Let us now, with respect to the vascular system, compare
Valencinia with Carinoma and Carinella. We have seen
that Carinoma in its head (except in the arrangement of the
lacune) greatly resembles Valencinia, and that the remain-
ing body bears a likeness to that of Carinella, with some
differences in the csophageal region and in the nephridial
system. Both in Carinoma and Carinella there is an @so-
phageal region which differs from the rest of the body by the
blood-spaces in this region having here a strong tendency to
detach from themselves portions (Carinella), or have even
already finished this process (Carinoma), especially Cari-

36 A. ©. OUDEMANS.

uella, shows on transverse sections in its blood lacunze some-
thing indefinite, and the lacunze sometimes go down very far
beneath the intestine. Asto Valencinia, if we are in a region
where the lacune have not yet wholly surrounded the ceso-
sophagus, we are struck by the resemblance of the situation
and habitus of the lacunze with those of Carinella. More-
over, we are inclined to compare the arches of the lacunar
spaces in Carinella, and the supra-proboscidian sheath-vessels
in Carinoma with the proboscidian sheath lacune of Valen-
cinia, for they are all separated portions of the blood-vessels,
which have moved upwards, and are placed next to the probos-
cidian sheath; and they are all in direct communication with
the vascular system. The different situation which they seem
to have in Carinoma and Valencinia may not be of im-
portance. In Valencinia they lie within the longitudinal
muscular layer, and in Carinoma they appear to lie in the
longitudinal layer—but I say they appear, for, properly speak-
ing, they lie also within this layer, but their high triangular
shape makes it appear as if they were placed between the fibres
of this layer. Further backwards they lose their triangular
shape, descend to a lower place, and in habitus and situation
more resemble the proboscidian sheath lacune of Valencinia.
In Valencinia the intestine is comparatively wrge, and the
blood-vessels lie beneath it; in. ©urinoma the intestine 1s
comparatively small, and *’ne ‘nlood-vessels lie next to it.

Let us now zumpare the two vessels in the proboscidian
sheath i=. Carinella and Carinoma with the median dorsal
vessel, of Valencinia. Suppose that the points of origin of
{he two vessels in the two former are moved forwards, and at
the same time approach the median line, and even reach this,
so that they coalesce, then there is no reason that two
proboscidian sheath-vessels will be formed. Only one will be
formed, viz. a median dorsal vessel, lying in the median line,
and at the bottom of the proboscidian sheath, and communi-
cating with the two great lacune on the sides of the sheath,
which now, in accordance with this simpler origin of the
median vessel, will temporarily reach one another beneath the

CIRCULATORY APPARATUS OF THE NEMERTEA. 37

proboscidian sheath, as is the case in Valencinia. If the
two lacunz become vessels, then we have a bidentate fork,
a pitchfork, and we have the form that occurs in all the
Hoplonemertea. The median dorsal vessel will, however, not
go farther than the cesophageal region in the proboscidian
sheath as in Carinella and Valencinia, and several higher
forms mentioned hereafter; and suppose now that from the
point where it finishes a groove is formed by the proboscidian
sheath down its whole length, communicating with the vessel
in the sheath, and is now cut off, then we have the median
dorsal vessel of all the Schizonemertea and Hoplone-
mertea. Simultaneously with the formation of diverticula
on the intestine, there are formed transverse vessels over these
diverticula between the longitudinal vessels.

The reason that I do not treat the nephridial system at the
same time with the vascular system is that I have nowhere
seen open or direct communication between these two
systems.

The nephridial system is situated on the sides of the cso-
phagus, in the lacunar spaces between cesophagus and longi-
tudinal muscular layer, and against the latter. It consists
(and this is very plainly visible on sagittal sections) of two
longitudinal canals, which are united by transverse canals, just
like a ladder. The foremost part was about one mm. from the
hindmost point of the opening of the mouth, the hindmost part
a little before the point where the median vessel leaves the
proboscidian sheath. The whole length was fifteen mm. in a
specimen of four cm. in length (in spirits).

The nephridial system in Valencinia offers us an im-
portant peculiarity, viz. there are more than one pair of
excretory ducts. I have found in the specimen cut in trans-
verse sections twenty-six pairs of excretory ducts, all lying
above the nerve-trunks, nearly touching them. The slices in
which I found them were the following :

38 A. O. OUDEMANS.

On the Left. On the Right.
277 , : : : ; . 805
361 ; ; . . ; . 336
421 : ; ° : 5 » 423
452 : : : : : . 462
493 : t : ; : En
554 . ‘ > 3 5 . 533
599 4 : : : : . 603
623 : : : 5 : . 620
638 : ; A : ; . | \Gpe
662 : : ; . ; . | eee
684 i 5 ‘ : ; - 700
697 : 3 i i i Fee
719 : : : ; ‘ ot | G22
736 ‘ 4 ; ; : . 738
744 : : : ; “Doe
765 : : : : : . 165
776 : j : . Right side damaged.
803 : : : ; : . 803
838 : : : : : . 814
874 : : ‘ . Right side damaged.
885 A : . , . . 885
912 : : : : ; . 903
959 : ‘ ; : ; ae ae
1010 : j : : ; . 1021
1057 5 ; : : - . 1052
1070 : 5 - . - - O70

P 1090

Probably the ducts run quite straight outwards ; this was to
be seen especially in regard to the very small hindmost ducts,
whilst the foremost, which were much larger, sometimes ran
obliquely forwards, sometimes backwards, or were curved.
Some of them had a small lumen, others a lumen which was
visible through many sections, and locally dilated. As a rule,
the ducts were smaller as they lay further backwards. If we
reflect that the numbers I have given of the slices are those in
which I at first saw anything of a duct, either its beginning, or
aperture, or the knee of a crooked duct, then some irre-
gularities in the arrangement of the ducts are already ex-
plained. But let us take for a moment the two most remote

CIRCULATORY APPARATUS OF THE NEMERTEA. 39

ducts of one pair, e.g., 277 and 305, or 361 and 366, which
are removed twenty and twenty-four sections from one another ;
and if we now know that sixty-six sections form 1 mm., then
we see that these ducts were removed only between 3 and ¢ =
= of a millimetre from one another. And we may conclude
that such irregularities are the results of the high con-
tractility of such worms as Nemerteans. If we reflect on
all these causes, it is indeed striking how the ducts are
arranged by pairs.

The canals themselves in the transverse sections were very
faintly coloured, and in the beginning I did not see them, not
in any way thinking of a water-vascular system. (It was the
first Nemertean I ever examined.) Already I had found and
noticed more than one pair of ducts, and seen that they always
began close to the inner longitudinal muscular coat, without
comprehending their significance. It was Professor Hubrecht
who not only drew my attention to the nephridial system, but
who also decided as to the connection between these ducts and
that system. When I had once observed this organ I saw it
wherever it was present, and I immediately found even the
smallest ducts of 4—6 mikrom. Shortly afterwards I could
also very well see the connection of the ducts with the system
of canals.

The ducts have a wall of one single row of palissade-shaped
cells, with granular contents placed side by side, somewhat
obliquely bent outwards. Each cell is provided with a cilium
of up to 200 mikrom. in length. It may be remarked that the
excretory ducts are all open towards the basal membrane, then
suddenly narrow, as if the basal membrane contracts them.
Outside the basal membrane they widen again, but here I rarely
saw their lumen. Where it was visible I again saw large
cilia, and the cells were still more granular, and their limits
were not sharply visible and they were not so well coloured as
the cells of the duct within the basal membrane. Although I
saw distinctly in Carineila and Carinoma that the basal
membrane was pressed outwards, in Valencinia longirostris
I saw neither this nor the reverse. The basal membrane was

40 A. C. OUDEMANS.,

simply perforated, neither pointing towards the periphery
nor inwards.

In a specimen, cut sagittally, the nephridial canals were better
coloured, but neither in transverse nor in longitudinal sections
could I observe cilia in the canals. On the sagittal sections I
could not find any openings in the skin, but I did find the
ducts within the basal membrane. If I have seen well, these
ducts open into the upper longitudinal canal where a transverse
canal also falls into it.

On these better coloured sagittal sections I saw that
tke canals have walls of one single row of cells, the nuclei
of which, intensely coloured, lay on the bottom of the cells,
as Von Kennel represents it, of Notospermus (Cere-
bratulus).

Already I have mentioned that the foremost ducts were wider
and better developed than the hindmost, so that the first were
easily found, the latter only with difficulty. It appears that
with the growth of the animal also the cesophageal region
grows, and probably preserves the same relative length to the
whole body, e.g. one third of its total length. The nephridial
system appears to grow gradually with the esophageal region.
We are further inclined to conclude, if we observe the differ-
ence between the foremost and hindmost ducts, that the fore-
most part of the cesophageal regions and thus also of the
nephridial system, is the oldest, the hindmost the youngest.

At any rate Valencinia displays, not only in its diverticula
of the intestine, in its transverse vessels and in its genital
organs, a clear internal segmentation, but also in the cesopha-
geal region a certain degree of metamerism is visible in the
nephridial system, which is formed like two ladder-shaped
systems on each side, having on the level of each step a pair of
excretory ducts.

5. Polia curta, Hubr. Figs. 11, 12, 43—51.
Two lacunz in the head, which terminate blindly anteriorly,
communicate above the proboscidian sheath, then beneath at,
spread themselves over the brain, inclose the posterior lobes and

CIRCULATORY APPARATUS OF THE NEMERTEA. 41

the cesophagus. There is a tendency to form five longitudinal
blood-spaces. Behind the cesophageal region there are three
vessels, united by transverse vessels. Communication of the
three vessels occurs in the tail before the anal commissure, and
like this, above the intestine. In the foremost half of the ceso-
phageal region the median vessel lies in the proboscidian sheath.
Its foremost communication is with the lacunes above the lower
brain-commissure.

In the head the vascular system becomes visible not at the
tip of the snout but a little distance from it; in the specimen
I examined, in the twenty-first slice, that is, about two-fifths
mm. from the tip, the specimen had (in spirits) a width of
one and a half, and a length of twenty-three mm. Quite in
front there is no communication, two lacunz becoming visible
at once. They are flat (fig. 43). The circular muscular layer
is already well formed dorsally and ventrally from the
lacunz. On the sides, however, the fibres cross one another
and extend divergingly in the surrounding tissue to the skin.
A similar crossing of transverse fibres, but in a higher degree
and number, also takes place in the middle of the area between
the two layers of circular fibres, so that it appears as if the
lacune lie in a transverse muscular band in the shape of an
8 ( c© ) lying sideways.

As the upper lobes protrude forwards and have on their
foremost part the upper brain-commissure, which is very thick,
we obtain a figure as if the lacune with the circular layer lie
beneath the brain.

Behind the upper brain-commissure the brain on both
sides increases in size, and the proboscidian sheath, which in
the meantime has become visible, has penetrated the circular
muscular layer, and taken up a position between the two
lacune, and is gradually placed, with the lacune and the
circular muscular layer, between the two brain-masses. Here
is found the lower brain - commissure. Just before this
becomes visible the lacunz coalesce above the proboscidian
sheath (fig. 44), and gradually spread over the brain. On
both sides of the sheath two small lacune remain; these go

42 A. CO. OUDEMANS.

downwards, coalesce beneath the proboscidian sheath, com-
municate with the median dorsal vessel in the sheath, remain
a moment in their places, and descend still further behind the
lower brain commissure, to unite with the lacunz, which have
now totally enclosed the large posterior lobes, and seem to
come from above, whilst the circular muscular layer, which
has always followed all the movements of the lacune, now
closes again (figs. 45, 46, 47, 48). A little further backwards the
posterior lobes gradually become smaller, and two short diver-
ticula of the cesophagus, directed forwards and terminating
blindly, now become visible (figs. 49 and 50). What in
Valencinia I saw only once I here saw continually, even on
the lateral nerve trunks, viz. club-shaped ganglionic masses
projecting into the lacune. Behind the mouth the lacune
again coalesce and embrace the cesophagus, but next to the
proboscidian sheath two distinct uninterrupted lacunar spaces
are always visible (fig. 51). But these latter extend beyond
the point where the median vessel leaves the proboscidian
sheath, whilst already the number of the lacune round the
cesophagus diminishes, and two lacune present themselves
constantly at the same places beneath the intestine, so that
we have here again a figure of five longitudinal blood-spaces. I
have not seen in Polia curta that these five longitudinal blood-
spaces are united by transverse vessels. At first, when the
two proboscidian sheath lacune have disappeared, and thus
when there are only three vessels, transverse uniting vessels
become visible, one over each diverticulum. The communica-
cation of the three longitudinal vessels in the tail is the same
as in Valencinia. .

Just behind the lower brain-commissure the first longitu-
dinal muscular fibres occur within the circular muscular coat.
I have not seen a longitudinal fibre in the precerebral region.
This is very anomalous.

As to the internal coating of the lacune and vessels, it is
the same as in Valencinia; also here the median dorsal
vessel, when it lies in the proboscidian sheath, shows its dorsal
side formed otherwise than its ventral arch; also here it is

OIRCULATORY APPARATUS OF THE NEMERTEA. 43

held up by ligatures, of which the remotest on the left and
right sides are the most solid; and also here from time to
time lumina are distinctly visible beneath the vessel, and it
appears that the proboscidian sheath fluid also bathes its
ventral surface. In another specimen I saw a part of this
vessel, quite at its commencement, still before the mouth,
where it seems not te be as described above. I have repre-
sented it in fig. 68. The hyaline basal layer everywhere is the
same as in Valencinia, but the vessels of Polia I have not
observed to be surrounded by circular muscular fibres. In the
median vessel beneath the proboscidian sheath I have seen out
of the hyaline basal layer large nuclei in the gelatinous stroma,
heaped up against the hyaline basal layer, just as is seen in
fig. 65 of a transverse vessel in Cerebratulus marginatus.
The two ventral vessels fill the whole space of the longi-
tudinal grooves in the intestine and between it and the longi-
tudinal muscular layer, so that the radially developed stroma,
visible in Valencinia and Langia (figs. 62—64), was absent
here, at least in the specimens examined by me. The dorsal
vessel beneath the proboscidian sheath was pressed against the
intestine, but not against the wall of the"proboscidian sheath.
There was a little stroma between them.

The nephridial system here is also situated in the cesopha-
geal region. It commences near the mouth, and finishes when
the first transverse vessel is seen; thus in a region where
three longitudinal vessels are already present without lacune
it penetrates even into the intestinal region.

I cannot say how it appears when viewed obliquely.

Openings and ducts of this system I found in the following
slices :

4,4, A. O. OUDEMANS.

Left. Right.
125 ; 5 ; : 125?
134 ? : : ; ; 135
145? . : : ‘ 146
157 : : ‘ : 166
188 : : : 3 184
199 ; ; . 4 200
213 ; ; : ’ 213
222 ‘ : 4 : 223
Nothing . : : : 231
285 : : : . Nothing.
290 : : : : 294
309 ; ‘ : ; 310

The excretory ducts, as in all the foregoing species, are
projected above the nerve stems, and, as in Valencinia,
nearly touch them; but, as to their further course through
the outer longitudinal muscular coat, I saw some running
straight to the skin, some downwards, and others even very
obliquely rising upwards.

The excretory ducts for the most part were well developed
(probably I had a nearly full grown individual) ; some of them
were extraordinarily enlarged, but all were contracted by the
basal membrane and in the skin, so that the external opening
was only a few mikromillimetres. The cells in the walls are
smaller than those of Valencinia, and placed otherwise, not
shaped like palisades but like a pavement, and not pressed
against one another but apart. Their nuclei seen from the
side were flat and rectilineal, and from above ellipsoidal ; but
all these appearances may be the results of a stretching of the
outer muscular layer. The histological structure of the canals
of the system is the typical one (cf. Von Kennel). I have not
seen cilia in them, nor direct communication with the lacunar
blood-spaces.

6. Lineus sanguineus (Rathke), MclInt., figs. 17, 18, 54.

In the main the same vascular system as Polia curta,
except in the head, of which the lacune are arranged other-
wise.

CIRCULATORY APPARATUS OF THE NEMERTEA. 45

In all sections through the precerebral region the lacuna is
only one, horse-shoe shaped, having between its legs the pro-
boscidian sheath, which become visible at the same time with
this lacune. The circular muscular layer, the lacuna and the
proboscidian sheath, I saw together in the sixth slice (j; mm.
from the tip of the snout). The former was present only on
the dorsal side, and the fibres diverge on the sides, extending
and diverging through the surrounding tissue nearly to the
basal membrane. At first in the eighteenth slice the lower
arch of the circular muscular layer presents itself, also diverg-
ing in the sides and thus crossing with its fibres those of the
upper arch. So the proboscidian sheath in Lineus has not
penetrated through the circular muscular layer, as in the other
species, for it was already present when the lower arch of this
layer formed itself. Already from the beginning I saw longi-
tudinal fibres occurring within the circular muscular layer, as
in Valencinia (see, however, Polia). Just before the upper
brain commissure the lacune united beneath the proboscidian
sheath, whilst they parted above it. The horseshoe is now
turned, with its legs upwards. Now also it breaks beneath the
sheath, forming thus two lacunz, one on each side of the
proboscidian sheath. The left of these (in my specimen) (fig.
54) communicates with the median vessel in the proboscidian
sheath. But this I regard as absolutely abnormal. (In the
two other specimens I examined, the proboscis much interfered
with my observations of this process.) My specimen was
greatly contracted, but it seems to me, that in general the
region that follows closely resembles that same region in
Valencinia, both with regard to the form and extent of the
circular muscular layer, the longitudinal fibres, the transverse
bands, lacunz, proboscidian sheath, &c. Also with regard to
the manner of embracing the posterior lobes and the ceso-
phagus.

Better than in the two former species, the lacunze on the
sides of the proboscidian sheath remain visible. In transverse
sections they are round, their hyaline basal layer well coloured,
their epithelium well developed. They are separated from the

46 A. CG. OUDEMANS.

other lacunar spaces, especially in the foremost half of the
esophageal region, by transverse fibres, and only now and then
communicate with the other lacune. At first in the hindmost
half the separation is less distinct, they lose their vascular
character and unite more with the other lacune. They always
remain within the longitudinal muscular layer.

About the region where the median vessel leaves the probos-
cidian sheath, two ventral lacunze become larger than the rest,
aud are always visible at the same point. A hundred slices
further on there are some small lacunar spaces, but after-
wards no more. These two lacune are the foremost portions
of the ventral vessels. In the meanwhile the two proboscidian-
sheath-lacune have disappeared, and the remaining lacune
arrange themselves so that they bear a likeness to the rudi-
ments of transverse vessels, so that I cannot precisely note
where the foremost well-defined transverse vessel may be said
to occur. When the first well-defined vessel is visible the two
proboscidian sheath lacunz have already disappeared. The rest
is entirely similar to Valencinia and Polia.

The inner coating of the blood-spaces with the epithelium
and the thin hyaline basal layer was everywhere the same. In
none of the three specimens examined did the median vessel
beneath the proboscidian sheath lie against the intestine or
against the proboscidian sheath, but freely amidst the gelati-
nous stroma. Outside the hyaline basal layer, nuclei were
grouped. The same is the case with the ventral vessels.
From what I have seen further on in the intestinal region, I
may state that they have only a thin layer of circular and a —
thick one of longitudinal fibres.

The dorsal vessel in the proboscidian sheath displays the
same peculiarities which I mentioned in speaking of Valen-
cinia and Polia.

The transverse vessels, as in Valencinia, were so closely
attached to the wall of the intestinal diverticula that they
appeared to have a common wall.

The situation of the nephridial system is the same as in
Valencinia and Polia. To the left and to the right it lies

OIRCULATORY APPARATUS OF THE NEMERTEA. 47

against the inner surface of the inner longitudinal muscular
coat, and stretches no farther back than the dorsal vessel in
the proboscidian sheath. The canals are very thin, with a very
small lumen and relatively thick walls. Anteriorly the system
does not reach the mouth. Also in Lineus sanguineus I
found many more than one pair of excretory ducts.

I have only traced it in two specimens, an old one (X) and a
young one (Y). All the excretory ducts lay above the nerve
trunks in the sections here enumerated :

X. ¥:
Closure of the Mouth-slit 210. Closure of the Mouth-slit 75.
Left side. Right side. Left side. Right side.
228 5 : 240 99 : Nothing.

? - : 309 121 : : 121
341 ‘ ; 325 Nothing : 125
358 : : 353 133 é ‘ 134
Bee |... ; 373 ? 136 ; Nothing.
Nothing. : 377 ? 143 : Nothing.
405 : 3 4.04 147 : ‘ 146
419 : - Ald 153 : Nothing.
437 : : 437 The dorsal vessel leaves the pro-
447 ‘ : 446 boscidian sheath in 155.
476 : : 472

The dorsal vessel leaves the pro-
boscidian sheath in 479.

Also this observation points to the increase of the number
of excretory ducts in proportion to the growth and age of the
animal.

T could not see ciliain the canals. In Lineus sanguineus
—at least in the two specimens examined by me—the excretory
ducts were not so close to the lateral nerves. If we trace a
horizontal line through the centrum of the transverse section
of the body the nerve stems lie just beneath this line, and the
excretory ducts of X lay at an angle of 45°, that of Y at an
angle of 5°10° inclined against the horizontal line.

Though X was older than Y the excretory ducts of X were
limited by smaller cells and less visible, that of Y by larger
cells, contiguous, as in Valencinia, and immediately visible,

48 A. ©. OUDEMANS.

even with a glass of magnifying power of 30—40 times, having
been better coloured (picro-carmine of Ranvier).

In neither of the two specimens were the excretory ducts
open. They were sometimes filled by a granular secretion, so
that I could not observe the cilia. Here I did not see any
difference between the foremost and hindmost ducts. On
observing the two lists one is inclined to conclude that
they arise here irregularly, though always segmentally projected
in pairs.

7. Lineus gesserensis (O. F. M.), McInt.

Similar to the foregoing species, but the two proboscidian
sheath lacune, even in the foremost part of the cesophageal
region, are not so well separated by transverse bands from the
remaining lacune.

The specimen, owing to the insufficient preservation of the
microscopical slices, was not suitable for closer examination of
the nephridial system.

8. Cerebratulus marginatus (Ren.), fig. 65.

In the main resembling Lineus sanguineus.

The lacune, which go downwards to communicate with the
dorsal vessel, first form a true vessel, which only a few sections
further backwards penetrates the wall of the proboscidian
sheath. More than elsewhere this vessel displays a different
character in its upper and lower arch. The cells of the upper
side are stretched, are situated against each other, and are
fan-shaped in their arrangement. Next to the proboscidian
sheath in the brain region lie two large lacune, separated from
those that embrace the mouth by a horizontal transverse band
of muscular fibres, as in Lineus. In these large lacune the
posterior brain lobes bathe, which extend far backwards, even
behind the slit of the mouth.

In another fragment, which belonged to the cesophageal
region, but was situated further backwards, I saw, next to the
proboscidian sheath, in the angle formed by its wall and the
longitudinal muscular coat on both sides, a longitudinal vessel,

CIRCULATORY APPARATUS OF THE NEMERTBEA. 49

which resembled a blood-vessel. Once a transverse vessel ran
from it to the circumference of the intestine, but as the sec-
tions were made only through the upper quarter of this
region I cannot say anything more on the further course of
this vessel.

Somewhat on one side of the upper half of the intestine I
saw a second longitudinal vessel, which is undoubtedly a
nephridial canal. ;

Over the intestinal diverticula transverse vessels run from
the median vessel to the two ventral ones. Fig. 65 gives us
a representation of a transverse section through such a transverse
vessel, around which the surrounding stroma is radially
folded, with numerous nuclei heaped in the immediate
neighbourhood.

9. Cerebratulus hepaticus, Hubr., fig. 66, 69, very similar
to C. marginatus.

In the head there are within the circular muscular layer
three large lacunz (one above the proboscidian sheath), sepa-
rated from one another by two massive bundles of longi-
tudinal muscular fibres. In the region of the cerebrum the
longitudinal fibres have increased in number, lying against the
circular muscular coat. The proboscidian sheath, at first lying
against the lower arch, has removed towards the upper arch of
the circular coat. The lacune have united to one, which is
horse-shoe shaped, with its legs upwards. The lacuna com-
municates directly with the median vessel in the proboscidian
sheath. Behind this section, some fibres of the circular layer
of the proboscidian sheath to the left and to the right take
their course downwards, very obliquely, however, so that they
cross one another, and cut the horse-shoe shaped lacuna into
three. The one lying beneath the proboscidian sheath is
triangular with its top turned upwards. The circular muscular
layer of the proboscidian sheath increases considerably, so that
the lacunz are pressed sidewards, and the lower lacuna very
far downwards. In the meanwhile the two lateral lacunz em-
brace the posterior cerebral lobes, and the sides of the tri-

4

50 A. CG. OUDEMANS.

angular lower lacuna become gradually horizontal, forming a
horizontal band, which separates the lateral lacune and the
posterior lobes from the two smaller lower lacune (the one
being now divided by vertical transverse muscular fibres into
two). The mouth-slit becomes visible. The two lower lacune
gradually slant downwards round the cesophagus, leaving
behind in its folds from time to time small lacune. *The two
upper lacunz gradually become very small, and, as the hori-
zontal band has disappeared, they now lie on what may be
called in the transverse section the two horns of the half-moon
shaped intestine. The mouth-slit is now closed, and the
cesophagus is, except the ventral side and the side towards the
proboscidian sheath, surrounded by lacune. The upper surface
of the median vessel in the proboscidian sheath again differs
from the lower, rests upon the inner (longitudinal) layer of the
sheath, is, however, not held up by small bands. It touches the
wall of the sheath only along a very thin base (see fig. 69).

The part in which the nephridial system is situated was not
represented in the series I examined. The part that follows
now lies in the intestinal region. Generative organs could be
detected. The median vessel lies beneath the proboscidian
sheath, and not far from the median line, on the ventral side of
the intestine, the two ventral vessels are visible. Sometimes
transverse vessels were very plainly to be seen, opening into
one of the three longitudinal ones.

From a section which was situated still further backwards,
and very well preserved, I give a representation of one of the
ventral vessels in fig. 66. The inner epithelial layer is dis-
tinctly visible, also the large hyaline basal layer, thickened
here and there by contraction, and better coloured. Following
upon this there is a distinct layer of circular fibres, but no
longitudinal. The stroma is radially contracted. Some cells
in the stroma have a very distinct protoplasmic aspect.

In a tail-portion transverse vessels were observed, even over
the hindmost diverticulum.

CIRCULATORY APPARATUS OF THE NEMERTEA. 51

10. Cerebratulus urticans (J. Mill), Hubr., fig. 48.

Quite at the tip of the snout there is only one lacuna. The
proboscidian sheath lies beneath it. A circular muscular layer
surrounds them. This layer is already formed on its dorsal
part, when the lacuna and the proboscidian sheath become
visible. So here, too, the proboscidian sheath does not pene-
trate a circular layer. Already, at the foremost part, longi-
tudinal fibres are visible within the circular muscular coat,
which in the meanwhile is closed. The proboscidian sheath
rests on the ventral side of the circular layer. In the medial
line dorsally a bundle of longitudinal fibres increase in
number, and finally touch the probiscidian sheath, so that the
lacuna is divided into two, one on each side of the probos-
cidian sheath. But we may as well say there are in the head
of C. urticans two lacunz, which communicate anteriorly by
a broad arch above the proboscidian sheath, as occurs in so
many Nemertea. A Jittle further backwards the wall of the
proboscidian sheath increases so that it pushes away the
longitudinal bundle on its two sides, and touches the dorsal
arch of the circular muscular layer. Now the lacune are each
surrounded by longitudinal fibres. Immediately before the
cerebral ring both the circular layers greatly diminish; one
would not recognise them, especially that of the proboscidian
sheath. The two lacune approach each other ventrally, finally
unite, lying beneath the sheath. They communicate directly
with the dorsal vessel in the sheath, but remain one single
lacuna beneath the preboscidian sheath, between this and the
lower brain-commissure. The proboscidian sheath again
acquires a thicker circular layer. The upper arch of the
medial vessel is again different from the lower. It is held up
by a spongy tissue.

As soon as the lower brain-commissure has disappeared, the
lacuna beneath the proboscidian sheath goes down still further,
and acquires a trapezoidal figure, limited above by the sheath ;
to the left and right by the lower lobes (from which the lateral
nerves arise), and beneath by the outer longitudinal muscular

52 A. C. OUDEMANS.

coat. It is, as well as the proboscidian sheath, always sur-
rounded by the two well-known muscular coats, sending, as it
were, two branches between the proboscidian sheath and the
brain masses; it next gradually embraces the posterior lobes
(as in fig. 48).

The mouth then becomes visible and presses the circular
muscular layer a little upwards. Transverse vertical muscular
fibres appear between this layer and the proboscidian sheath,
so that the lacuna is divided into two. These two lacune are
again divided into four by a horizontal band of muscular fibres
between the proboscidian sheath and the stomodeum.

The two lacune beneath the horizontal band will again
embrace the stomodzum, leaving here and there little lacune.
The two lacune above the band, after the disappearance of the
posterior lobes, acquire a circular layer of muscular fibres and
diminish in size. The lacunz round the stomodzum here and
there disappear, as if they terminated blindly ; some of them
are still to be recognised, but the only distinctly visible lacune
are the above-mentioned two with a circular layer and next to
the proboscidian sheath: caetera desunt. (Two heads have
served for this description; there was no difference between
them.)

11. Cerebratulus roseus (delle Ch.), Hubr.

The precerebral region so strikingly resembles that of
Cer. urticans, that I at first believed there was an error in
the determination. As soon, however, as the circular muscular
layer with its contents passes through the cerebral ring, differ-
ences are to be seen.

The two lacunze on the sides of the proboscidian sheath
unite beneath the sheath, but instead of communicating di-
rectly with the medial vessel, a part of the now single lacuna
is cut off by the circular muscular fibres of the proboscidian
sheath, so that a flat lacuna lies between this wall. This
lacuna rises between the fibres, finally comes within the cir-
cular coat, and is now the median vessel. So that the median
vessel here, as in Cerebratulus marginatus, goes further

CIRCULATORY APPARATUS OF THE NEMERTEA. 53

forwards beneath the proboscidian sheath, and communicates
indirectly with the lacune. For a few slices the great lacuna
retains its horse-shoe shape. Then a horizontal band of trans-
verse fibres divides the lacuna into three, two on the sides of
the proboscidian sheath, and one beneath it. The lower
brain-commissure is passed by, and the mouth becomes
visible, and still the whole figure is the same. Now the
two lacune next to the proboscidian sheath embrace the
posterior lobes. The horizontal band is still present and also
the lacuna beneath it. On the sides of this lacuna two others
arise, which of course terminate blindly forwards. These three
are separated by vertical muscular fibres, passing into those of
the proboscidian sheath. So the area of the circular muscular
coat is divided into two unequal parts by the horizontal band.
The upper or larger and the lower or smaller are now divided
by the same two vertical bands into three, so that there are
three large and three small compartments. The central one of
the larger is filled by the proboscidian sheath with the median
vessel. The two larger on the sides are the lacunz with the two
posterior lobes bathing in them, and the three smaller are
flat lacune. [Each lacuna besides its own coating of epithe-
lium and its hyaline basal layer, is surrounded by longitudinal
muscular fibres. Now the middle one of the three smaller is
pushed away by a mass of transverse and longitudinal mus-
cular fibres which cause the lacuna to communicate with the
two others next to it. (In my specimen, however, it opened
‘nto the left one, but this seems to be abnormal.) So we here
meet again the ordinary arrangement; two lacune, one on
each side of the proboscidian sheath, separated by a horizontal
band from two smaller beneath the sheath, which in their turn
are separated by a vertical transverse band. The lower or
smaller embrace the stomodeum. Here and there between its
folds small lacune remain visible. In Cerebratulus urti-
cans I already had an opportunity of remarking that several
of these lacune terminate blindly backwards, at least they
disappear. The same now is the case here behind the mouth,
so that only a few sections further backwards there are no

54 : A. ©. OUDEMANS.

other lacunz visible than the two above the cesophagus and on
the sides of the proboscidian sheath. These gradually turn to
one side a little, and come to lie in a fold of the cesophagus,
which protrudes comparatively far into its lumen. Their
proper lumen was filled with a coagulum that did not show
any blood-corpuscles. Exactly the same coagulum here and
there presented itself in little traces on the folds of the ceso-
phagus, especially a little to the left and right of the median
line ventrally, so that I am convinced that round the ceso-
phagus the lacunar system occurs, though reduced to a mini-
mum. The hindmost part of the cesophageal region and the
rest of the body were absent.

From another specimen I could examine some sections which
were probably from the hindmost part of the cesophageal
region. Here the cesophagus is surrounded by lacune. Above
the cesophagus, at the sides of the proboscidian sheath, two
larger ones were present. In the lacune surrounding the
cesophagus here and there parts of the nephridial system were
distinctly visible. In the lateral angles of the lacunz above
the esophagus a longitudinal nephridial canal was distinctly
to be seen lying partly in the longitudinal muscular layer.
Everywhere the lacunz were richly coated by the epithelium
that rested on a relatively massive layer of hyaline basal
tissue.

In both the specimens the vessel in the proboscidian sheath
again showed the remarkable difference of structure in its dorsal
and ventral half.

In a third specimen, in which only the head and the fore-
most half of the cesophageal region were cut sagittally, I
convinced myself of the presence of even very large lacunz in
this part of the cesophagus.

12. Langia formosa (Hubr.), figs. 62—64.

The vascular system corresponds to the type of that of the
Schizonemertini.
The aperture of the proboscidian sheath is nearly terminal,

CIRCULATORY APPARATUS OF THE NEMERTEHA. 55

In the same slice in which this aperture lay I also saw the first
trace of the lacunar space above it. The circular muscular
layer is at first only present as an upper arch, which gradually
grows round and closes beneath the proboscidian sheath. This
now lies against the lower arch of the circular muscular layer,
Here again the proboscidian sheath has not to penetrate the
circular layer. The lacuna is single and horseshoe shaped,
with its legs downwards. Already quite anteriorly longitudinal
fibres are visible, which are everywhere numerous. The sheath
leaves its position, going upwards, the lacune thereby taking
the shape of a circle in transverse sections. This is only appa-
rently abnormal, for we may say here that the arch of the
lacune above the sheath is very broad—so broad that it disap-
pears when the lower arch is already visible. This lacunar
ring is only really visible in three slices, for the proboscidian
sheath reaches the upper arch, and the lacuna is again horse-
shoe-shaped, with its legs upwards. Exactly above the lower
brain-commissure the median vessel in the proboscidian sheath
communicates with the lacuna. Nowhere did I see this pro-
cess so distinctly as here. The vessel was swollen, filled with
blood-corpuscles ; the opening was so large that it seemed that
the wall of the proboscidian sheath was broken there. After
this the horizontal band again becomes visible, dividing the
lacuna into three—two on the sides of the proboscidian sheath,
which gradually embrace the posterior lobes, and the third
lying beneath the sheath. This third lacuna is soon divided by
three vertical bands going from the sides of the proboscidian
sheath downwards. Soon, however, these three lacune are
pushed sideways by a mass of transverse and longitudinal
fibres, and whilst the horizontal band disappears communicate
with the two large lacune on the sides of the proboscidian
sheath. The posterior lobes are still visible in these latter
lacune. The mouth of Langia, as it seems to me, lies further
backwards than in other genera. The two lacune have by this
time coalesced with those two in which the posterior cerebral
lobes bathe, and now surround the esophagus. As in Cere-
bratulus in all the lacune, except in those ventrally from the

56 A. 0. OUDEMANS,

cesophagus, the nephridial canals float. They are not attached
against the longitudinal muscular layer (or this is a peculiarity
of the specimen I examined?). The nephridial canals here
are thicker and more distinct than I have ever seen, but have
the same character as all the nephridial canals hitherto examined
(of course with the exception of Carinella). In one of the
canals I very distinctly saw cilia a little longer than the
cells.

I have found only one pair of excretory ducts. They were
very easily to be observed, not only lying above the nerve
stems, but were even directed straight upwards, and their
pores lay in the longitudinal dorsal groove or fold formed by
the upwards-turned edges of the body (cf. Hubrecht, 35).
About the region of the two pores the medial vessel left
the proboscidian sheath, having shown again, as in all
Schizonemertea, the different character in its upper and
lower wall. Behind the pores the nephridial system extends
still a little further backwards.

In the meantime the lacune surrounding the cesophagus
have gradually become larger, and afterwards again smaller,
till they pass into the two vessels situated beneath the intes-
tine. Thus in the intestinal region we find three longitudinal
vessels ; they are usually united by transverse vessels, and
though the diverticula are narrow I saw very distinctly a
transverse vessel over each diverticulum. But these trans-
verse vessels do not lie so closely against the diverticula as in
Valencinia. In Langia they lie free amidst a gelatinous
stroma with large nuclei (figs. 62—64), as do also the three
longitudinal vessels. These nuclei are generally arranged
round the vessel. Several of the nuclei had about them an
irregular protoplasmic substance, generally showing offshoots
arranged radially round the vessel. The stroma, too, pre-
sented radial arrangement, which is probably to be ascribed to
local thickenings caused by the contraction of the vessel in the
gelatinous tissue. Fig. 62 shows us one of the lateral (ventral)
vessels cut transversely ; fig. 63 the same, with an outlet of a
transverse vessel, the latter, of course, cut longitudinally ;

CIRCULATORY APPARATUS OF THE NEMERTEA. 57

fig. 64a portion of a transverse vessel, drawn with different
focussing of a microscope.

13. Amphiporus pulcher (Johnst.), McInt., figs. 6, 7, 9, 38.

Of this type of Hoplonemertea I cannot give any sum-
mary, not having been able to examine all the details. By
analogy we may, however, conclude that it is essentially the
same as of Amph. Jactifloreus (Johnst.), McInt., which
will be treated subsequently.

In a head of a specimen of this species which I was able to
examine, I saw very distinctly that there was only one single
aperture to both the proboscidian sheath and the mouth (see
also Hubrecht 35); the upper curve of the aperture is that
of the proboscidian sheath, and the lower one that of the
mouth. How the cephalic vascular loop (for here are no
lacune but two vessels, which communicate anteriorly, figs.
6,7,9) is situated in relation to the proboscidian sheath I have
not seen. In some slices I believe I saw the two vessels ; they
lay laterally (see fig. 38) and within the longitudinal muscular
layer. In this area also the whole nervous system is situated.
I have not observed whether the two vessels go through the
cerebral ring, nor how the dorsal vessel communicates with it.
But I could very well see that the dorsal vessel lies in the
proboscidian sheath, but only for some twenty sections ; it then
leaves it. A little behind the brain I first saw very distinctly
the two lateral vessels. They lie through the whole length of
the body, beneath the level of the nerve-stems.

In two portions of the intestinal region [ did not see trans-
verse vessels. In a tail-piece I found them lying above each
diverticulum. The mutual communication of the three longi-
tudinal vessels is the same as in the Schizonemertea,
above the intestine and before the anal commissure of the
lateral nerves.

Of the nephridial system I may mention that Prof.
Hubrecht has found in one specimen that the excretory ducts of
the system lie just behind the ganglia. He had noted it down
on the preparation. These ducts are very easily to be seen,

58 A. ©. OUDEMANS.

for they have very thick walls. I have examined the prepara-
tion very closely, but I did not see any more ducts. Thus, in
this species, there is but one single pair of ducts, not in the
posterior part but quite anteriorly. In front of the excretory
ducts there is no trace of nephridial system. I have no
histological facts to record.

14. Amphiporus lactifloreus (Johnst.), McInt., figs. 9,
10, 388—40.

The mouth and the proboscidian sheath have together only
One aperture, nearly terminal and on the ventral side. This
was first seen by Prof. Hubrecht, who noted it down on his
preparation. I saw very distinctly in this preparation that the
proboscidian sheath falls into the stomodzum ; and this is, as
we know, not behind but far before the ganglia. Above this
stomodeum, thus also above the proboscidian sheath, goes the
loop which unites the two vessels of the head (fig. 9). Of this
loop we at first observe an ellipsoidal lumen, then a dumb-bell
shaped one; and, finally, two lumina, being the transversally
cut vessels. These two are gradually placed wider apart.
Their wall consists of a very thick hyaline basal layer. They
finally lie laterally to the proboscidian sheath and the eso-
phagus (fig. 38).

The brain respirators are very small. Their aperture is the
foremost part of the whole organ. (They lay in the slice
No. 31. The slices had a thickness of ;mm. The specimen,
in spirits, measured 17 mm. in length and 2 mm. in thickness.)
The canals run backwards, lying beneath and contiguous to
the vessels. A thick nerve-stem connects them with the
ganglia. They soon disappear (slice No. 41).

The blood-vessels go upwards (No. 37), just before the lower
brain commissure, between the two brain-masses and the
proboscidian sheath ; but in their former place they have left
two remnants which soon disappear (slice No. 42). These two
terminate thus blindly posteriorly (see fig. 9). Exactly above
the lower brain commissure the vessels move beneath the
proboscidian sheath, unite, and communicate with the dorsal

CIRCULATORY APPARATUS OF THE NEMERTEA. 59

vessel in the proboscidian sheath (No. 47). Meanwhile, I saw
all at once, on the sides of the sheath and above the ganglia
(No. 42 and No. 46), a vessel cut transversally. There, then,
are two branches, terminating blindly forwards (see fig. 9).
The two vessels, after having communicated with the median
vessel, go directly towards these little branches, coalesce, and
go back to their former place between the brain-masses and the
proboscidian sheath, leaving no trace of these peculiar blood-
spaces (Nos. 49—51). The median vessel soon leaves the pro-
boscidian sheath. It remains in the sheath only in five sections
of +, mm. Ina younger specimen only three sections. The
two lateral vessels remain on the inner side of the lateral
nerves, but swing up and down, now being above and then
beneath their level. I have twice closely examined the 800
slices, made through the whole animal, and I have nowhere
seen a transverse vessel. In a tail-portion, horizontally cut,
however, they were present. The communication of the three
longitudinal vessels in Amphiporus lactifloreus I saw
very distinctly. It occurred again before the anal commissure,
and above the intestine.

With respect to the nephridial system, I may mention the
following points. It lies, as all other organs in this species,
free in the gelatinous stroma, in which I could nowhere observe
nuclei. It begins in the cerebral region (slice No. 42), just
there where I saw the foremost point of the strange branches
of the vascular system (figs. 9 and 39). The first canal I saw
lay so close to this branch that it will not surprise me if another
naturalist finds there an open communication between the two
systems. At all events, 1 have not seen it myself, though I
believe I have seen that the tissues were here intimately
jomed. The canals showed the well-known structure. They
swung very irregularly round the lateral nerves, remaining
always next tothem. I have found here again more than one
pair of excretory ducts. These lay in the following sections.

60 A. C. OUDEMANS.

To the Left. To the Right.
BOUDS AGA BG ic. hep aallie: 55, 56, 57
a : : : : 57, 58, 59) 60
62, 63, 64 : 3 : , 62, 63
— : : : =» 65, 66,67, He
— ; : : . 65, 66, 67, 68
— F : ; : 73, 74, 75
717, 78 ; : : : —
—- A ; . : 84, 85
85 : ; : : 85
_ : : ; : on
97, 98 : : ; : —
— ‘ : : P 101

In No. 110 the nephridial system ceased, and the first genital
organs became visible. This is the limit then between the
cesophageal region and the intestinal. We clearly see how
irregularly even the excretory ducts are arranged. Properly
speaking, there are only three pairs, the other seems to be
uneven. I have written in a row the numbers of the slices, in
which the same duct was to be seen (running obliquely to the
periphery). Two ducts on the right are twice united by an
accolade. ‘These are peculiar phenomena not hitherto observed
by me in other Nemerteans. The ducts 65, &c., in the first
accolade were parallel to each other (fig. 40), visible on the
right side of four subsequent sections, and one beneath the
nerve-trunk. The second peculiarity is this that the ducts
84 and 85 on the right had one and the same aperture
through the basal membrane and the skin !

15. Amphiporus marmoratus, Hubr., fig. 38.

The mouth and the proboscidian sheath have a common
aperture. I could not, however, ascertain to which this aper-
ture belongs, because the proboscidian sheath was widely stretched
by the extruded proboscis. The cephalic loop was very distinctly
visible. It ran above the common aperture, thus also above the
proboscidian sheath. The two vessels then ran on the sides of
the proboscidian sheath and the intestine (as in fig. 38). The
brain-respirators lie beneath them, but do not touch them.

CIRCULATORY APPARATUS OF THE NEMERTEA. 61

They move just before the cerebrum, a little upwards, next
to the proboscidian sheath, and whilst going with this through
the cerebral ring, they protrude downwards between the sheath
and the brain-masses. In the specimen I examined something
abnormal took place. The left vessel did not reach the ventral
surface of the sheath, the right one did; it was very much
enlarged, and filled with blood-corpuscles (diastole ?) and com-
municated with the vessel in the sheath. The vessels remain
where they are, they do not go upwards, because the brain-
masses move sideways and diminish, and the lower commissure
disappears. The vessels go downwards but remain above the
level of the lateral nerves. The median vessel left the sheath
after twenty-four slices (I estimate them to be one thirtieth of a
mm. Thebody hada widthof onemm.),andsome ten slices behind
the lateral vessels move beneath the level of the lateral nerves.

With regard to the nephridial system, it lies behind the
ganglia. It consists of a very crooked canal above the lateral
nerves. After twenty-five slices it disappeared, and thus it is
very short. I did not see any communication with the vascular
system. At the first appearance of the system on contemplating
the slices from the front to the hind part, the two excretory
ducts were very distinctly visible. Thus they are as much as
possible in the front. Together with the whole system they
are situated above the lateral nerves, but instead of running
nearly horizontally towards the skin, they proceed almost
vertically downwards, and so these ducts have ventral
apertures.

Neither of the vascular, nor of the nephridial systems, can I
mention any histological particulars.

16. Amphiporus hastatus, Mc.Int., figs. 8, 13,
538, 63, 64, 70, 71.

The mouth and the proboscidian sheath have again a common,
almost terminal aperture. The proboscidian sheath falls into
thestomodeum just before the lower brain commissure. Brain-
respirators absent.

I did not find a vascular loop in the head, nor the two vessels

62 A. C. OUDEMANS.

which in other Hoplonemertea form such a loop. And yet
the whole head (fifty-seven slices of +> mm. in thickness) was
very well preserved, judging from certain other peculiarities.

Between the stomodezeum (which has three distinct layers, an
inner epithelium layer, a hyaline basal layer, and a circular
muscular layer) and the muscular layer of the skin (which
consists here only of the circular muscular layer, outside which
lie the basal membrane and the skin) we meet in the anterior
sections (e. g. the tenth) with three layers. Both against the
circular muscular layer of the stomodeum and against the
circular muscular layer of the skin we find situated a layer of
large vesicular cells, with large nuclei, and between these two
gelatinous stroma occurs. The twolayers of large cells are not of
one row of cells; the layer against the skin had from two to three,
the other from four to six rows of cells. The cells are arranged
more or less radially in both layers. At the common aperture
we see that the epithelium of the stomodeum passes into that
of the skin, the hyaline basal layer into the basal membrane of
the integument, the two circular muscular layers and the two
layers of large vesicular cells into one another. (The layer of
gelatinous stroma between the two latter of course ceases in
front.) The more we go backwards the more in the two layers
of cells do longitudinal muscular fibres become visible. In the
layer next to the skin this happens through the whole thickness
of it, but not in the inner layer. In the inner layer the
arrangement is thus that we can distinguish an internal layer
of numerous nuclei (as are figured in figs. 63 and 64. of Langia)
and an external layer of longitudinal muscular fibres, which
are arranged in groups. The number of the nuclei just men-
tioned diminishes on approaching the brain, so that this layer
close to the brain obtains more the character of gelatinous
stroma. Gelatinous stroma thus fills the space between the
two layers of longitudinal muscular fibres, and also the area
within the inner longitudinal muscular layer, in which area lie
the central nervous system, proboscidian sheath, intestine,
vascular system, and generative organs.

The outer layer of gelatinous stroma is relatively the

CIRCULATORY APPARATUS OF THE NEMERTEA. 63

broadest in the tip of the snout, is still uninterrupted in the
cerebral region, but becomes further backwards ever narrower,
more so ventrally than dorsally, so that about slice 110 the
two longitudinal muscular layers ventrally unite. In section
160 the same takes place on the sides and dorsally, so that
further backwards Amphiporus hastutus is in the main
not to be distinguished from any other Hoplonemertean.

In the layer of gelatinous stroma before the brain and
between the two layers of vesicular cells are seen isolated
single or groups of the same cells. These are, when isolated,
round or ellipsoidal, but when in groups, like soap-bubbles,
more polygonal; their size varied from fourteen to thirty
micmm. Their contents are transparent, however, with a
fine granulation, which apparently is protoplasm, and which
sometimes, as in vegetable cells, lay round the nucleus, and
sent threads to the walis of the cells, thus forming irregular
star-shaped figures. I also saw cells in which the protoplasm
was distinctly arranged against the inner side of the cell
membrane. Then the nucleus also lay against the wall. These
groups of cells diminished backwards, so that in the cerebral
region still a few groups are visible, and still further backwards
none occur. The more these groups disappear the more very
small vessels become visible, which, occurring even in the tip
of the snout, bear a highly primitive character. Sometimes,
but rarely, they appear to be simple lumina in the gelatinous
stroma; their wall is merely a modified hyaline gelatinous
tissue, which absorbs more colouring matter than the sur-
rounding. Sometimes, outside the hyaline basal layer, a few
large nuclei are situated, exactly resembling those of the vesi-
cular cells. Most frequently, however, these lumina are limited
by some, often by a closed ring of vesicular cells (see fig. 70).
Such a vessel seen in profile has the appearance of fig. 71.

I was not able to trace these vessels. They seem to pass into
one another, forming a reticulum. I have illustrated it in
fig. 8. A transverse section, however, through the head has a
totally different appearance from one through the head of
Valencinia longirostris (see figs. 13 and 53).

64. A. ©. OUDEMANS.

In the slices between the regions of the upper and lower
brain commissures I observed in the gelatinous tissue between
the proboscidian sheath and the brain-masses a larger vessel
than the other. They approach each other til] they come
beneath the proboscidian sheath, and communicate with the
dorsal vessel, which only in this single slice lay in the
sheath, the four following in its circular muscular layer, and
in the fifth already beneath the sheath.

Behind the lower brain commissure I saw the vessels again
separated, running downwards till they lie beneath the level of
the nerve-trunks.

Behind the brain we again have an cesophageal and an intes-
tinal region.

In the cesophageal region I again observed the same small
vessels in the two layers of gelatinous tissue, uniting with one
another by branches traversing the inner longitudinal layer.
The vessels within this layer also communicate with the three
longitudinal vessels. They are all arranged in certain regions.
Beneath the cesophagus transverse vessels run from the one
lateral vessel to the other. From the median vessel to these
transverse vessels, rarely directly to the lateral, other transverse
vessels occur. But also transverse vessels, hitherto never
seen, running over and above the proboscidian sheath, con-
necting the two lateral and passing towards the nerve-chords,
are everywhere to be observed. It is very probable that
between all these transverse vessels, which all resemble one
another (as fig. 71), there still exist connecting vessels, so that
the whole is a vascular network. This, however, is not easily
to be demonstrated in transverse sections.

In the cesophageal region two longitudinal vessels are very
often visible above the nerve-trunks, therefore dorsolateral.
These did not always occur, so that 1 do not believe that there
is (on each side) one uninterrupted longitudinal vessel, but
fragments of it. The transverse vessels which go over the
proboscidian sheath, always opened into the longitudinal vessels
above the nerve-stems, where they occurred. These longitu-
dinal vessels thus are connecting vessels between the transverse

OIROCULATORY APPARATUS OF THE NEMIERTEA. 65

ones. From these dorsolateral vessels I often observed delicate
branches running almost straight to the periphery, above the
lateral nerves. Never, however, did I succeed in finding a
piercing of the basal membrane or of the skin. Do they
terminate blindly ? It is to be hoped that some later observer
may find the excretory ducts of this nepridial system, for I do
not doubt but this system of fine canals and dorsolateral vessels
belongs to a nephridial system. (Compare the nepridial
system of all Hoplonemertea in which the principal (longi-
tudinal) canal also always lies more or less above the nerve-
trunks!) I hesitated to represent the system in my illustration
(fig. 8) on account of its complicated character.

In histological structure the nephridial (?) canals do not
deviate from the transverse vessels of the vascular system
(figs. 70, 71), even the dorsolateral, and the transversely cut
connecting points occasionally visible between the transverse
vessels above the proboscidian sheath, had the same structure
only they were larger. They all exhibited an outer ring of
large vesicular cells, round a hyaline basal layer, in which were
some large granular nuclei, which were not to be distinguished
from all other nuclei in the gelatinous stroma of the head or of
the vesicular cells themselves. The nuclei lay in a fine granular
layer. Are these nuclei blood-corpuscles and is this fine
granular layer blood-coagulum, or do they both belong to the
coating of the vessels? This I could not decide.

The median and the two ventrolateral vessels had between the
basal layer and the ring of vesicular cells a layer of circular
muscular fibres.

In the intestinal region the transverse vessels run over only
a few of the diverticula. Inthe tail, however, they occur more
frequently, yet here and there skipping a diverticulum.

The lateral vessels always lie beneath the nerve-stems, not
beneath the intestine.

17. Drepanophorus rubrostriatus, Hubr., fig. 7, 42.
The vascular system consists of a cephalic loop, running
above the proboscidian sheath. (Proboscidian sheath and
5

66 A. ©. OUDEMANS.

mouth have each their own aperture, nearly terminal.) The
passage through the cerebral ring and the communication with
the median vessel, which only in the cesophageal region lies in
the sheath, are similar to what occurs in all Hoplonemertea
with cephalic loops. In the cesophageal region no transverse
vessels occur, in the intestinal region, however, they do. The
communication in the tail is normal.

The nephridial system lies, in the cesophageal region, entirely
above the nerve-trunks, and always has numerous windings, so
that nearly always more than one transversely cut canal is seen
in sections. If we bear the fact in mind that a winding canal
must always show three, five, or seven sections, and if we than
see in a slice four sections of canals, we must conclude that at
least one of these canals is a branch. As I often observed an
even number, so I suggest that there are many branches, as I
have represented in fig. 7. The excretory ducts lie in the
midst of the cesophageal region, above the nerve-trunks,
and curve downwards, having ventral apertures. Fig. 42
exhibits a section through the cesophageal region of Dre-
panophorus.

From the proboscidian sheath lateral sacs proceed between
the intestine and the nerve-trunks, arranged in pairs and
ranging from the ganglia to the end of the proboscidian sheath.
McIntosh was the first (24) who observed this peculiarity of
the sheath of Drepanophorus. He saw on sagittal sections
openings through the lateral walls of the proboscidian sheath,
and represents them, but without further tracing what these
Openings are. He, however, concluded that these openings
(stomata) form the connection between the vascular system
and the proboscidian sheath. Hubrecht (35) recognised the
true nature of these organs, calling them “membranaceous
sacs.” I have exerted myself to trace, on transverse as well
as on horizontal sections, these peculiar spaces. They are
only blindly terminating tubes, sometimes very much dilated
and at their extremities sac-shaped. They generally run with
a downward curve. Only once I found a communicating
branch (longitudinal) between two of these sacs. Their open-

OIROULATORY APPARATUS OF THE NEMERTEA. 67

ing into the sheath was sometimes wide; most frequently,
however, so closely contracted that only a high power enabled
me to see any aperture.

It is not my purpose to give an explanation of these sacs
or to trace their histological structure, but they are not
connected with the vascular system.

The medial blood-vessel in the proboscidian sheath is
attached with avery small base, so that it is almost totally
bathed by the fluid of the sheath. But I did not observe that
its upper wall had a different structure from that of the lower
one. The epithelium of the sheath covers the vessel. The
hyaline basal layer of the proboscidian sheath passes into that
of the vessel, and just beneath the vessel a few longitudinal
muscular fibres are situated. The median vessel, when beneath
the proboscidian sheath, and the two lateral vessels, have outside
the hyaline basal layer some circular muscular fibres. Within
the hyaline basal layer the common epithelium is again
present. The nephridial canals exhibit the same structure as
in all other species.

18. Drepanophorus serraticollis, Hubr., fig. 65.

The mouth and the proboscidian sheath have each their own
aperture. I could see the cephalic loop distinctly above the
proboscidian sheath. Transverse vessels were present in a
tailpiece at the tip of the tail, where the three longitudinal
vessels pass into one another. The transverse vessels cut
transversely resemble those of Cerebratulus marginatus
(fig. 65).

19. Tetrastemma candidum (O. F. M.), Oerst.,
figs. 6, 38.

I did not observe that the cephalic loop went over the
proboscidian sheath. The preparation was not sufficiently
preserved to enable me to see it. I clearly saw the two vessels
of the loop (fig. 38). In the usual way they protrude between
the brain and the proboscidian sheath, descend along the sides
of the sheath, and communicate just below the proboscidian

68 A. C. OUDEMANS.

sheath and behind the lower brain commissure with one
another and with the median vessel, which in Tetrastemma
never lies inthe proboscidian sheath. The two lateral
vessels descend further between the lateral nerves and the
cesophagus, and lie beneath the level of the nerve-stems, so that
they are ventral, the nerve-stems already being situated ven-
trally. The preparation was too imperfect to allow of the de-
tection of transverse vessels. Perhaps they exist.

20. Nemertes gracilis, Johnst.

The specimen was cut sagittally, and about 23 mm. in
length.

In the hindmost part I distinctly saw transverse vessels
running over the diverticula. They have no circular muscular
fibres round the basal layer.

The nephridial system is of unusual length, for in a specimen
about 23 mm. long and 1 mm. wide I saw behind the ganglia
one nephridial canal, and about 8 mm. from the tip of the
snout two canals. Concerning their histological particulars I
can make no definite statements.

21. Malacobdella grossa (O. F. M.), Blainv., fig. 3.

Tam unable to correct Von Kennel’s description, either of
the vascular or of the nephridial system. I will merely give
some additional observations.

The cephalic loop runs over the proboscidian sheath, as in
all other Nemertea. Not only from the two lateral vessels,
but also from the cephalic loop numerous branches arise. In
my specimen the median vessel had none.

I could observe cilia, both in the two chief canals and in
the excretory ducts of the nephridial system. The chief
canals anteriorly lie above the nerve-trunks, then backwards ;
they assume a more lateral position, and finally send the ex-
cretory ducts with a little curve round above the nerve-stems ;
they thus communicate ventrally with the exterior.

|
!

CIRCULATORY APPARATUS OF THE NEMERTEA, 69

SuMMARY.

We have seen that there are three types of vascular system
in the Nemertea. Though the families of the Valenci-
niidz and the Poliide belong to the Paleonemertea,
they, with respect to their vascular and nephridial system,
already approach the Schizonemertea. To avoid con-
fusion, I will here employ the expressions, ‘ Paleo-type,”’
““ Schizo-type,” and “ Hoplo-type.”’

In the Palzo-type we have two longitudinal blood-spaces,
which communicate forwards in the head above the probos-
cidian sheath, are lacunar in the head and the- cesophageal
region. They have in the cesophageal region a tendency to
enlarge their surface, but are true vessels in the intestinal region,
and communicate in the tail above the intestine.

In the head also, lacunar communications may occur beneath
the proboscidian sheath. In the cesophageal region the surface
is enlarged, owing either to the fact that the lacune are large
(Cephalotrix), or that portions are constantly being detached,
which, however, remain in open connection with the principal
lacune (Carinella), or that along the whole csophageal
region the lacunez have divided into two stems, which only in
the foremost part permanently communicate (Carinoma).

The vessels in the tail of Carinella open directly into one
another, thus forming a loop above the intestine. In Cari-
noma lacunar spaces communicate above the proctodeum,
representing rudimentary transverse vessels.

Moreover, in some forms of the Palzo-type (Carinella,
second form of Carinoma) two other vessels occur in the weso-
phageal region and in the proboscidian sheath. Their con-
nection with the vascular system could only be demonstrated
with certainty in exceptional cases.

In the Schizo-type we find: in the head, lacunar spaces
which communicate both above and beneath the proboscidian
sheath; in the esophageal region also, lacunar spaces which
coalesce round the @sophagus on the ventral side. Two lacune
on the sides of the proboscidian sheath are more permanently

70 A. 0. OUDEMANS.

distinct and separate from the rest. In the remaining portion
of the body, three longitudinal vessels, connected by trans-
verse vessels, are present. The communication in the tail lies
above the intestine.

In the cesophageal region we find only one single vessel in
the proboscidian sheath. Anteriorly, this is connected with
the lacunar communication beneath the proboscidian sheath,
piercing its lower wall. Posteriorly, it also pierces the lower
wall of the sheath, and is continued into the median vessel
lying under the proboscidian sheath.

In the lower forms (Valenciniide) the two lacune on
the sides of the proboscidian sheath continue further back-
wards. The transverse vessels, which otherwise only connect
the three longitudinal vessels, in that case also enter into com-
munication with these lacune.

The third type, the Hoplo-type, is especially characterised
by the absence of lacunar spaces. Here there is a closed
vascular system. Here we find (excl. Amphiporus
hastatus, McInt.) in the head two vessels which communi-
cate in front, forming a vascular loop, above the proboscidian
sheath. These vessels also communicate within the cerebral
ring, but now beneath it. From this point down to the tail
three longitudinal vessels occur, of which the median vessel
in the cesophageal region often lies partly in the proboscidian
sheath. In the intestinal region generally the three longi-
tudinal vessels are united by transverse vessels. The com-
munication in the tail les above the intestine.

The cephalic loop may form branches (fig. 8, Malacob-
della). The portion of the median vessel which lies in the
proboscidian sheath, in this type gradually becomes shorter
and shorter. There are even forms in which it no more enters
the sheath, but remains beneath it along its whole length.
(Nemertes, Tetrastemma, Malacobdella.) In the in-
testinal region, along the whole length, or only in the posterior
portion, transverse vessels occur. In some cases, branches
arise from the longitudinal vessels (more especially from the
lateral ones) during sexual maturity (fig. 3, Malacobdella).

CIRCULATORY APPARATUS OF THE NEMERTEA. 71

In the posterior sucker of Malacobdella numerous vascular
branches are developed.

In all Nemertea the foremost communication of the
vascular spaces occurs above the proboscidian sheath, the
hindmost above the intestine. In all Nemertea the blood-
spaces are everywhere coated internally with a layer of epi-
thelium, then a layer of hyaline basal tissue follows always.
Outside this basal layer there may lie either large vesicular
cells (figs. 70, 71), or protoplasmatic cells with large nuclei
(figs. 62—65), or circular muscular fibres are formed by these
cells (figs. 66), or, but more rarely, longitudinal fibres are
present in addition (figs. 74, 75).

With regard to the nephridia in Carinella, a portion of
the lateral vessels is changed into such an apparatus. This
apparatus here is distinctly a portion of the blood-space, sepa-
rated from it, just as in the cesophageal region other portions
detach themselves; it communicates both directly and in-
directly with the vascular system. Indirectly, because a por-
tion of the walls of the blood-vessel changes into a gland, the
function of which appears to be to convey the superfluous matter
from the blood-fluid towards a reservoir, the portion separated
from the blood-vessel. This has two open communications
with the blood-vessel. Thus, the separation is, as it were,
still imperfect, and the points of communication appear to
diverge from one another with the growth of the animal. The
secretions of the nephridial glands must be removed, therefore
an excretory duct is developed on each reservoir. The two
excretory ducts lie nearly on the same transverse level, so that,
if the animal were a segmented one, they would be found in the
same segment. They are generally contracted by the basal-
membrane and the skin, so that no sea-water can enter the
reservoir but by an inner impulse caused by the muscular walls
of the reservoir the ducts may open. I suppose that the
removal of the secretions happens periodically. Thus the
nephridia of Carinella, the lowest type of Nemerteans, in
which up to this time a nephridium has been found, is highly
primitive.

72 A. C. OUDEMANS.

Of higher development is the nephridial system of Cari-
noma. The function of removing the waste products is here
transferred to the canals of the system itself. Here we no
more find a nephridial gland. The canals, however, are coated
with an epithelium, consisting of pure glandular cells. The
removal of the secretion outwards would seem not to happen
periodically but permanently, as each cell is provided with a
long cilium directed outwards, The system, though changed
so much that it cannot possibly be confounded with the
vascular system, in Carinoma, however, still shows its
primitive relation to it. There are three open connections on
each side, and the whole lower arch of the blood-vessel
between the first and the second communication is changed
into a tissue which closely resembles that of which the
nephridial canal consists. Thus, we have here also a por-
tion of the nephridium, which is, as it were, separated from
the blood-vessel, of which the traces are still present! The
two excretory ducts here lie also in the same transverse
plane.

In the Schizo-type the nephridium lies wholly in the lacunar
spaces of the cesophageal region. In some species it extends
still a little further into the intestinal region. The whole
system is generally situated against the inner side of the
inner longitudinal muscular coat. There are, however, types
where it seems to float in the lacune (Langia). In most
species I could not distinguish the exact arrangement. In
Valencinia, however, the form is that of a ladder, and on the
level of each step there is an excretory duct. Thus there are
two longitudinal canals and numerous transverse ones. They
are, however, all of the same size. The whole indicates a seg-
mental arrangement. The same is found in Polia and
Lineus. In these two genera I could not, however, trace the
form of the system, but it seems to me that here too the canals
are all of the same size. In Cerebratulus and Langia,
however, a thicker longitudinal canal is distinctly seen, and
several thinner ones. Here I could not find more than one
single pair of excretory ducts. Thus, the lower the types the

CIRCULATORY APPARATUS OF THE NEMERTEA. 79

more numerous are the paired ducts; the higher the types the
fewer, till they are reduced to one pair.

The nephridial system of the Hoplonemertea also shows
several degrees of complexity. It consists of numerous small
canals, which are connected with a longitudinal canal on each
side. These send their excretory ducts outwards. The excre-
tory ducts are either two in number (D repanophorus,
Nemertes, Malacobdella, Amphiporus pulcher, &c.)
or more [Amphiporus lactifloreus (and hastatus?)].
Where two occur these may be quite anteriorly situated
(Amphiporus pulcher), in the middle (Drepanophorus
rubro-striatus), or posteriorly (Malacobdella).

Thus the nephridial system of all the Nemertea consists of
one or more canals, directly communicating or not with
the vascular system, provided or not with cilia, and com-
municating with the exterior by means of excretory ducts.
These excretory ducts all lie above the nerve-trunks.

I now wish for a moment to summarise the very provisional
hypothesis, which I have ventured to make respecting the
physiological function of the two proboscidian sheath-vessels
in the Paleo-type of the median vessel, lying in the probosci-
dian sheath in the two other types, and of the membranaceous
sacs of Drepanophorus.

McIntosh was the first who, both in the Schizo-type and
the Palzo-type, mentioned a vessel which lay in the probosci-
dian sheath. Dewoletzky was the first to mention this median
vessel in the sheath in a representation of the Hoplo-type
(Drepanophorus). In Lineus marinus, in the foremost
part of the cesophageal region, McIntosh found one median
vessel lying in the sheath, and described in Carinoma
Armandi two vessels in the sheath. In his description of the
latter he says: “ The physiological signification of these two
vessels is clear since the discovery of a regular series of vessels
which communicate with the proboscidian sheath.”

This passage can hardly be said to clearly explain what
physiological significance McIntosh ascribes to this arrange-
ment, and as far as it applies to the existence of an open com-

74 A. C. OUDEMANS.

munication between the vascular system and the proboscidian
sheath, I must distinctly negative it as far as my own experience
goes. I therefore wish to suggest another hypothesis, viz. that
the two blindly terminating vessels in the proboscidian sheath of
the Palzo-type, as well as that portion of the median vessel
which lies in the proboscidian sheath in the Schizo- and Hoplo-
type, and “‘ the membranaceous sacs” (Hubrecht) in Drepano-
phorus, are intended for purposes of respiration, nutrition,
and excretion of the fluid contained in the proboscidian
sheath.

It is superfluous here to resume all the reasons which have
led me to this supposition. I beg to refer the reader to what

has been stated above, where this subject was more extensively
alluded to.

LITERATURE OF THE SUBJECT CONTAINING REFERENCES EITHER
TO THE VASCULAR OR THE Excretory Systems OF THE
NEMERTEA.

1. Dette Cutase.—‘ Memoria sulla storia e notomia degli animali senza
vertebre del regno di Napoli,’ volume ii, p. 408, 1828.

2. Dretie Cutase.— Descrizione e notomia degli animali invertebrati delle
Sicilia citeriore osservati vivi negli anni 1823-30, vol. iii, p- 128.

3. DuegEs.—Apercu de quelques observations nouvelles sur les Planaires
et plusieurs genres voisins,”’ ‘ Ann. Sc. Nat.,’ xxi, 1830.

4. Jounston.—* Miscellanea Zoologica,” ‘Magazine of Zoology and
Botany,’ i, 1837.

5. Raruxe.—* Beitriige zur vergleichenden Anatomie und Physiologie,”
Neueste Schriften der Naturf. Ges. zu Danzig, iii, 1842.

6. BuancHarp.—“ Mémoire sur un animal appartenant au sous-embranche-
ment des vers. (Le genre Malacobdelle de Blainville),” ‘ Ann. Se.
Nat.’ (3)—* Zool.,” iv, 1845.

7. De QuatreracEs.—‘ Etudes sur les types inférieurs de l’ébranchement
des Annelés, mémoire sur la famille des Némertiens,” ‘ Ann. Se. Nat.
(3)—* Zool.,” vi, 1846.

8. Brancuarp.— Recherches sur l’organisation des Vers.,” chap. v et chap.
ix, ‘Ann. Se. Nat.’ (3)—“ Zool.,” viii, 1847.

9. BuancHarp.— Recherches sur l’organisation des Vers.,” chap. xii, ‘ Ann.
Se. Nat.’ (3)—* Zool.,” xii, 1849.

10.

ll.

12.

13.

14.

15.

16.

Wi

18.

19.

20.

21.
22.

23.

24.

25.

26.

27.

28.

OIRCULATORY APPARATUS OF THE NEMERTEA. 75

Biancuarp.— Seconde mémoire sur l’organisation des Malacobdelles,”’
‘Aun. Sc. Nat.’ (3)—* Zool.,” xii, 1849.

Max Scuurze. —‘Beitrige zur Naturgeschichte der Turbellarien,’
Greifswald, 1851.

Max Scuuttze.— Zoologische Skizzen.,” ‘ Zeitschr. f. wiss. Zool.,’ v,
1852.

Van BenepEN.—“ Recherches sur la faune littorale de Belgique,” ‘ Mém.
Acad. Sc. Belge,’ xxxii, 1861.

Kererster.— Untersuchungen iiber niedere Seethiere ;” vi, ‘* Unter-
suchungen iiber die Nemertinen,” ‘ Zeitschr. f. wiss. Zool.,’ xii, 1862.

Craparnpr.—‘ Beobachtungen iiber Anatomie und Entwickelungsge-
schichte wirbelloser Thiere, Leipsig, 1863.

Frepscuenxo.— Protocolle der Gesellschaft der Freunde der Naturwissen-
schaften zu Moscau,’ Bd. x, Heft 2, 1872.

Ray LanKester.—‘ A Contribution to the Knowledge of Heemaglobin,”
‘Proc. Roy. Soc. Lond.,’ xxi, 1872.

McInrosu.—“‘ A Monograph of the British Annelids,’ part i, “The
Nemerteans,” 2 vols., London, ‘ Publications of the Ray Society,’
1873-74.

Husrecut.— Aanteekeningen over de Anatomie, Histologie en Ont-
wikkelingsgeschiedenis van eenige Nemertinen,” ‘ Utrecht,’ 1874.

Husrecut.— Untersuchungen iiber Nemertinen aus dem Golfe von
Neapel,” ‘ Niederl. Archiv. f. Zool.,’ i, 1874.

Husrecut.— Some Remarks about the Minute Anatomy of Mediter-
ranean Nemerteans,” ‘ Quart. Journ. Micr. Sci.,’ xv, 1875.

Marron.— Anatomie d’un type remarquable du groupe des Némertiens :
Drepanophorus spectabilis,” ‘Compt. rend.,’ Ixxx, 1875.

Marion.—* Anatomy of a Remarkable Type of the Group of Nemer-
teans: Drepanophorus spectabilis,” ‘Ann. and Mag. of Nat.
Hist.,’ xv, 1875.

MclIwrosu.—‘‘ On Amphiporus spectabilis and other Nemerteans,”
‘Quart. Journ. Mier. Sci.,’ xv, 1875.

MclIntosu.—*‘ On Valencinia Armandi, a New Nemertean,” ‘ Trans.
Linn. Soc. Lond.,’ 2nd ser., vol. i—* Zool.,” Dec., 1875.

MclIntosu.—“ Onthe Central Nervous System, the Cephalic Sacs, and
other points in the Anatomy of the Lineide,” ‘Journ. of Anat. and
Physiology,’ x, Jan., 1876.

Mosetey.— On a Young Specimen of Pelagonemertes Rollestoni,”
‘ Ann. and Mag. Nat. Hist.,’ xvi, 1876.

SmmpER.— Die Verwandtschaftsbeziehungen der gegliederten Thiere,”
‘Arb, Zool. zoot. Inst. Wirzburg,’ ii, 1876.

76 A. C. OUDEMANS.

29. Barrors.—‘ Recherches sur Vembryologie des Nemertes,’ Lille, 1877.

30. Horrmann.—“ Zur Anatomie und Ontogenie von Malacobdella,” ‘ Vers}.
Med. Kon. Acad. Wet. Afd. Nat.,’ xi, 1877.

31. Vow Kennet.— Beitrage zur Kenntniss der Nemertinen,” ‘ Arb. Zool.
zoot. Inst. Wiirzburg,’ iv.

32. Giarp.—“ Sur l’Avenardia Priei, Némertien geant de la cote occi-
dentale de France,” ‘ Bull. Sc. Dép. Nord.,’ Ann. i, 1878.

33. Giarp.—(Idem.) ‘ Compt. rendu,’ Ixxxvii, 1878.

34, Grarp.—On Avenardia Priei, a Gigantic Nemertean,” ‘Ann. and
Mag. Nat. Hist.,’ ii, 1878.

35. Huprecut.—“The Genera of European Nemerteans Critically Revised,

with Descriptions of Several New Species,” ‘Notes from the Leyden
Museum,’ i, No. 44, 1879. X

36. GULLIVER.—“‘ On a New Land Nemertine, Tetrastemma roderica-
num, ‘ Phil. Trans.,’ el xvii, 1879.

37. Grarr.—*Geonemertes chalicophora, eine neue Landnemertine,”
‘Morph. Jahrg.,’ 1879, vy.
38. DeworeTzxy.—‘ Zur Anatomie der Nemertinen,” Vorlaufige Mitthei-
lung, i, ii, ‘ Zool. Anz.,’ iii, p. 375 u. 396, 1880.
39. Husrecut.— Der Excretorische Apparat der Nemertinen,” ‘ Zool. Anz.,’
26 Januar, 1885.
For nomenclature Nos. 18 and 35 have served me.

EXPLANATION OF PLATES I, II, and Ts

Illustrating Mr. A. C. Oudeman’s Memoir on “The Circulatory
and Nephridial Apparatus of the Nemertea.”

In Plates I and II the blood-spaces are marked red, the nephridia
blue. The short lines accompanying the figures in Plate I show the levels
at which the transverse sections have been obtained which are figured in Plate
IJ. The numbers placed on these lines correspond to the numbering of the
figures in Plate IT.

Plate II only contains figures of transverse sections. All that is grey
belongs to the nerve system. J. Intestine, and Ps. Proboscidian sheath.

The figures in Plate III are all drawn by means of the camera lucida,
Figs. 55—61 with a Zeiss, obj. 8, oc. 2, and Figs. 62—75 with a Siehert, obj.
imm. No. 7, Periscopic ocular,

CIRCULATORY APPARATUS OF THH NEMERTBA. ee

PLATE I.

Fic. 1.—Diagram of the vascular system in the head, the cesophageal region,
and the intestinal region of Cephalotrix linearis (Rathke), Oerst.

Fie. 2.—Diagram of the vascular system (1st form) in the head and cso-
phageal region of Carinella annulata (Mont.), McInt.

Fic. 3.—Diagram of the vascular system and the nephridial system of
Malacobdella grossa (O. F. M.), Blainv.

Fic. 4.—Diagram of the vascular system (2nd form) and the nephridial
system in the head and the cesophageal region of Carinella annulata
(Mont.), McInt.

Fic. 5.—Diagram of the vascular system and the nephridial system in the
head and the cesophageal region of Carinoma Armandi (Melnt.), Oud.

Fies. 6 and 10.—Diagram of the vascular system of Tetrastemma can-
didum (O. F. M.), Oerst.

Fries. 7 and 10.—Diagram of the vascular system and the nephridial system
of Drepanophorus rubrostriatus, Hubr. The portion of the median
vessel drawn in the figure between two white interruptions lies in the
proboscidian sheath.

Fies. 8 and 10.—Diagram of the vascular system of Amphiporus hasta-
tus, McInt.

Fics. 9 and 10.—Diagram of the vascular system and the nephridial system
of Amphiporus lactifloreus (Johnst.), Mclnt. The portion of the me-
dian vessel drawn in the figure between two white interruptions lies in the
proboscidian sheath.

Fic. 10.—See Figs. 6, 7, 8, and 9.

Fis. 11 and 12.—Diagram of the vascular system and the nephridial system
of Polia curta, Hubr. The portion of the median vessel drawn in the
figure between two white interruptions lies in the proboscidian sheath.

Fies. 13, 14, 15, and 16.—Diagram of the vascular system and the nephridial
system of Valencinia longirostris, Quatr. The portion of the median
vessel drawn in the figure between two white interruptions lies in the pro-
boscidian sheath. Fig. 14 immediately unites with Fig. 13.

Fics. 17 and 18.—Diagram of the vascular and the nephridial systems of
Lineus sanguineus (Rathke), McInt. The portion of the median vessel

drawn in the figure between two white interruptions lies in the proboscidian
sheath.

PLATE II.
Transverse Sections.
Figs. 19—21.—Cephalotrix linearis (Rathke), Oerst. See Fig. 1.
Fie. 19.—Through the precerebral portion.
Fic. 20.—Through the cerebral portion (cerebral ring).

78 A. C. OUDEMANS.

Fie. 21.—Through the cesophageal region.

Figs. 22—27.—Carinella annulata (Mont.), McInt. See Figs. 2 and 4.

Fic. 22.—Through the intestinal region.

Fic. 23.—Through the cesophageal region to the left, curving downwards,
and to the right upwards, thus becoming partially lacunar.

Fic. 24.—Ditto, with two vessels in the sheath. The lateral vessels, each
with an arch upwards, partially lacunar.

Fic. 25.—Through the nephridial region. The left half of the figure shows
a blood-vessel with the spongy nephridial gland lying in it, and a nephridial
canal. The right half shows the same as the left one, but, in addition, the
foremost open communication between blood-vessel and nephridial canal.

Fic. 26.—Ditto. The left half shows the blood-vessel and the hindmost
open communication between this and the nephridial canal. The right half
shows the blood-vessel with the spongy nephridial gland lying in it, and a
communication of the nephridial canal with this gland.

Fie. 27.—Ditto. The two only excretory ducts of the nephridial system
are situated in this section.

Figs. 23—37.—Carinoma Armandi (MclInt.), Oud. See Fig. 5.

Fic. 28.—Through the tip of the snout. Point of junction of the four
large lacune.

Fic. 29.—Through the precerebral region. Four large cephalic lacune are
visible, two on each side of the proboscidian sheath.

Fie. 30.—Through the cerebral portion. The four lacune have coalesced
to form two, and with the proboscidian sheath protrude through the cerebral
ring.

Fic. 31.—Through the postcerebral region. The mouth lies in this section.
Mutual connection between the six vessels: two lateral vessels, two supra-
proboscidian sheath-vessels, and two vessels lying in the sheath.

Fig. 32.—Through the esophageal region. The six longitudinal vessels are
visible,

Fic. 33.—Through the nephridial region. The vessels above and in the
sheath have disappeared, terminating blindly. The two blood-vessels and the
nephridial canals are visible.

Fic. 34.—Ditto. The two only excretory ducts are visible in this section.
The dotted line in Fig. 5 shows the direction of the imaginary sections
represented in our Fig. 34.

Fig. 35.—Ditto. On each side a blood-vessel and two nephridial canals,

Fie. 36.—Ditto. The two nephridial canals coalesce.

Fic. 37.—Ditto. Hindmost communication between blood-vessel and
nephridium.

Fic. 38.—Through the precerebral region of Tetrastemma candidum
(O. F. M.), Oerst. See Fig. 6.

Figs. 39 and 40.—Amphiporus lactifloreus (Johnst.), McInt. See
Fig. 9.

CIRCULATORY APPARATUS OF THE NEMERTEA. 79

Fie. 39.—Through the precerebral region.

Fie. 40.—Through the cesophageal region. Excretory ducts of the nephri-
dial system, both above and below the nerve-trunks.

Frc. 41.—Through the intestinal region of Hoplonemertea (excl. Mala-
cobdella), Schizonemertea, Valenciniide, and Poliide. See
Figs. 10, 12, 16, and 18.

Fie. 42.—Through the cesophageal region of Drepanophorus rubro-
striatus, Hubr., with two membranaceous sacs of the proboscidian sheath,
and the two only excretory ducts of the nephridial system.

Figs. 43—51.—Polia curta, Hubr. See Fig. 11.

Fre. 43.—Through the precerebral region. The foremost lacune do not
communicate with one another.

Fic. 44.—Through the cerebral region. Communication between the
cephalic lacune above the proboscidian sheath.

Fic. 45.—Ditto. The lacune on the sides of the proboscidian sheath at
first coalesce beneath the sheath and then divide into three parts, one of which
lies beneath the sheath.

Fie. 46.—Ditto. Communication between the cephalic lacune and the
median vessel in the proboscidian sheath.

Fic. 47.—Ditto. Communication of all the lacune, which now spread over
the brain lobes.

Fic. 48.—Through the postcerebral region. The posterior lobes bathe in
the lacune.

Fic. 49.—Ditto. The forward projecting part of the stomodeum bathes in
the lacune, partly lying above the posterior lobes, which are still visible.

Fic. 50.—Ditto. The mouth lies in the section. Two lacune, one on
each side.

Fic. 51.—Through the cesophageal region. The lacune surround the
esophagus, except on its dorsal surface. ‘The nephridial system lies in the
lacuna against its outer border. Two of the excretory ducts are severed by
the section.

Figs. 52, 53. —Valencinia longirostris, Quatr. See Fig. 14.

Fic. 52.—Through the foremost part of the intestine. The csophageal
lacune are continued into the two lateral (ventral) vessels, and the two lacunse
on the sides of the proboscidian sheath. (The median vessel here lies beneath
the sheath.) The five vessels are united by transverse vessels.

Fic. 53.—Through the precerebral region, in front of the opening of the
proboscidian sheath. Numerous cephalic lacune.

Fic. 54.—Through the cerebral region of Lineus sanguineus (Rathke),
MclInt. (cerebral ring). The abnormal method of communication between the
cephalic lacune and the median vessel. See Fig. 17.

80 A. C. QUDEMANS.

PLATE III.

Fre. 55.—The median vessel leaves the proboscidian sheath in the cesopha-
geal region : drawn from a preparation of Valencinia longirostris, Quatr.

Fic. 56.—Foremost open communication of the nephridial system with the
blood-vessel in Carinoma Armandi (McInt.), Oud. The true nephridial
canal arises from the tissue of the wall of the vessel, which in the neighbour-
hood of the opening is of totally different structure from the rest.

Fie, 57.—Second open communication of the nephridial system with the
blood-vessel in Carinoma Armandi (McInt.), Oud.

Fies. 58, 59, 60, and 61.—A series of four transverse sections through
Carinoma Armandi (MclInt.), Oud., to justify the sketch No. 31. ;

Fic. 62.—Transverse section through one of the lateral vessels of Lan gia
formosa, Hubr.

Fic. 63.—Transverse section through one of the lateral vessels of Langia
formosa, Hubr., with a longitudinally-cut transverse vessel.

Fic. 64.—A transverse vessel seen lengthways in a transverse section of
Langia formosa, Hubr.

Fic. 65.—Transverse section through a transverse vessel of Cerebratulus
marginatus, Ren.

Fic. 66.—Transverse section through one of the lateral vessels of Cere-
bratulus hepaticus, Hubr.

Fic. 67.—Longitudinal section (vertical) through the precerebral region
(before the opening of the proboscidian sheath) of Valencinia longiros-
tris, Quatr. An upper and a lower lacuna are visible in this section. Com-
pare Fig. 53.

Fic. 68.—Transverse section through the foremost part of the median
vessel, lying in the proboscidian sheath of Polia curta, Hubr.

Fre. 69.—Transverse section through the median vessel, lying in the pro-
boscidian sheath of Drepanophorus rubrostriatus, Hubr.

Fic. 70.—A small vessel in the gelatinous tissue of Amphiporus hasta-
tus, McInt., transversely cut.

Fic. 71.—Ditto, as seen lying in a transverse section.

Fic. 72.—The supra-proboscidian-sheath-vessel from the right side in
Carinoma Armandi (Mclat.), Oud., transversely divided into two.

Fic. 73.—The same, normal.

Fic. 74.—The lateral vessel of Carinoma Armandi (McInt.), Oud. Partly
obliquely severed. An inner epithelium-layer, a hyaline basal-layer, a layer of
protoplasmic cells passing into fibres which run round the vessel, and a
layer of the same kind of cells which run along the vessel are distinctly
visible.

Fic. 75.—The lateral vessel of Carinoma Armandi (McInt.), Oud.,
transverse section.

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 81

The Later Stages in the Development of Bala-
noglossus Kowalevskii, with a Suggestion
as to the Affinities of the Enteropneusta.'

By

William Bateson, B.A.,
Scholar of St. John’s College, Cambridge.

With Plates IV, V, VI, VII, VIII, and IX.

In the ‘ Quart. Journ. Micr. Sci.’ for April, 1884, I described
the early stages in the development of a species of Balano-
glossus, common on the shores of the Chesapeake Bay.
I am led from various reasons, which I hope to detail
when an opportunity occurs for discussing the classification of
the Enteropneusta, to regard this species as identical with
that described by Alex. Agassiz, and called by him B.
Kowalevskil.

I was again enabled, during the summer of 1884, by the
great kindness of my friend Dr. W. K. Brooks, to pursue my
investigations into the morphology of the Enteropneusta. My
warmest thanks are due to Dr. Brooks for once more
_ affording me the hospitalities of the Chesapeake Zoological
Laboratory, which was this year situated at Beaufort, North
Carolina. While there I collected a number of specimens of
a large undescribed species of Balanoglossus resembling B.
salmoneus (Giard). This species, a description of which

1 A note on the subject-matter of this paper appeared in the ‘ Proc. Roy.
Soc.,’ No. 235, 1885.

6

82 WILLIAM BATESON.

will I hope shortly appear, I propose to call B. Brooksii. My
attempts at rearing this species from the egg were unsuccessful,
and I was prevented by illness from making any additional
observations on its development.

On leaving Beaufort, N. C., I returned to Hampton, Vir-
ginia, in the beginning of September, in the hope of finding
the later stages in the development of B. Kowalevskii, and
was fortunate enough to procure a complete series of larve
from Stage H to individuals possessing ten gill-slits, in which
condition the generative organs are first present. It is intended
in this paper to give a general account of these stages, together
with the histology of the animal, until two pairs of gill-slits are
developed (fig. 1). From this point the further histological
differentiation of the various organs will be described under
separate headings.

With this account of the organogeny of B. Kowalevskii
will be given, as far as possible, a comparative description of
the same parts in all the species which I have hitherto
examined,

External Changes.—The larva of B. Kowalevskii was
described (loc. cit.) as leaving the egg in an elliptical form,
divided by two transverse constrictions into three segments.
The surface of the body was ciliated, a special tuft of long
cilia being developed at the anterior end, while the posterior
region was surrounded by a transverse band of long cilia.

From further observations it seems probable that this period
(Stage D) assigned as the time of hatching is too early ; for
embryos kept in aquaria do not break the membranous shell
before Stage G is reached. Probably, therefore, the larve
found swimming in Stage D had escaped owing to an artificial
rupture of the shell during the process by which they were
found, an account of which is given in an appendix.

The formation of the mouth as a ventral pore in the anterior
groove was described (No. 3, fig. 41). It opens directly into
the archenteron, which was previously a closed sac, from which
five mesoblastic pouches had been given off, forming the
anterior, middle, and posterior body cavities respectively,

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 83

The external relations of the parts then become changed
until finally the larva has the shape shown in No. 3, figs. 16
and 17. In this stage the proboscis is conical and the middle
segment much shortened. In the anterior dorso-lateral region
of the third segment are the openings of the first pair of gill-
slits, which are simple circular pores leading into the
archenteron.

The larva is still opaque, and pale yellowish-brown in colour.
In this condition it remains for about ten days, at the end of
which time the second pair of gill-slits is formed. The body
has become partly transparent, especially in the region of the
proboscis, through the walls of which muscle-fibres are visible.
Other external changes which occur at this period are the loss
of the anterior tuft of cilia and the gradual disappearance of
the posterior ciliated ring. At the commencement of this
period the larve are to be found in Stage G at a depth of
about six to eight inches in the sand, but towards its close they
work their way into the higher strata of mud, and do not again
go down again until the adult condition is reached.

As the cilia disappear a peculiar organ is formed as a small
papilla, bearing long cilia and mucous glands, situated at the
central part of the posterior surface (fig. 1, sk.). This organ
serves as a sucker, by which the animal can attach itself to
foreign bodies sufficiently firmly to prevent itself being washed
off by a stream of water from a pipette. The anterior surface
of the proboscis is also slightly suctorial, and by thus fixing
itself posteriorly and extending the proboscis it is able to creep
slowly about, somewhat in the manner ofaleech. The appear-
ance of this organ bears some resemblance to the terminal
sucker described by Graaf as occurring in certain Rhabdo-
ceeles. It subsequently attains a considerable size, and is
traversed by several wrinkles (figs. 3 and 4, sk.). This organ
afterwards entirely disappears, but as to its mode of disappear-
ance I have no certain observations. It would appear to occur
very suddenly at the stage when the animal possesses seven to
eight gill-slits. I have found animals with eight gill-slits
which possess this sucker, and also animals of apparently the

34 WILLIAM BATESON.

same age without it ; hence it may be inferred that it undergoes
a rapid atrophy at this point.

Similar suckers! occur as larval organs in Tunicata, Ganoids,
and Amphibia.

With regard to the meaning of the sucker, considering the
time of life at which it appears, it is probably not ancestral in
origin; as the animal is already, from Stage G onwards, a
distinct Balanoglossus in all its characters. It is more rea-
sonable to conjecture that it is of purely developmental
importance, and indeed its use to a larva of this kind is suffi-
ciently obvious; for the creatures inhabit shallow pools on the
sand-flats, being just buried in the mud, from which position
they would be in danger of being washed away by the incom-
ing tide and so be dried up by the great heat of the sun at low
tide. On attaining a larger size the body can be, and always
is, coiled round a spindle of sand and thus is kept in position,
hence the sucker is no more required. In connection with
this sucker I observed that nearly all the animals found in
these pools were such as are provided with similar means of
fixing themselves, which power is probably essential to life in
such a habitat. An account of the histology of this sucker will
be given subsequently.

During the period which elapses between the appearance of
the first and second pair of gill-slits the body gradually
acquires, as was mentioned above, a considerable degree of
transparency. Owing to this fact several points of internal
structure may be observed. ‘This is especially marked in the
case of the alimentary canal, which can now be clearly per-
ceived to consist of three regions—an anterior branchial tract,
a middle digestive portion, and an intestinal section posteriorly.
The digestive section may be at once recognised by the bright
yellow-brown colour of the secretion which it contains. This
fluid is evacuated after a time when the animal is irritated, but
no experiments were made to determine its physiological pro-
perties.

1 Balfour was of opinion that in these forms they might be an ancestral
feature (Balfour, ‘Comp. Emb.,’ vol. ii, ‘“ Tunicata”’).

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 85

The partial transparency of the body wall permits also an
indistinct view of the curious supporting rod of hypoblast
which projects into the proboscis cavity. For reasons given
later in this paper I propose to speak of this structure as the
notochord (Nch.). The general appearance of the animal at
the time when the second gill-slit appears, is shown in fig. 1.
The animal is drawn as seen from the actual left side and dis-
plays the increased flexion of the body on its ventral surface.

The second gill-slit is shown as a small circular pore.

It will also be observed that that part of the body which lay
between the two grooves constituting the middle segment of
the body has now assumed an altered shape. At Stage H is
found little more than a circular ridge on the body separating
the proboscis from the trunk, while in fig. 1 (two gill-slits) it
forms a kind of phlange enveloping the base of the proboscis.
This change in shape is due to the operation of several causes,
which are of great importance in interpreting the processes by
which the final form of the adult is reached.

In the first place, after the formation of the mouth as a pore
on the ventral surface, the constriction by which the proboscis
is segmented off becomes deeper and deeper, until at last it is
only attached by the exceedingly slender stalk shown in figs. 2
and 3. As a consequence of this process coupled with a
forward growth of the ventral lip of the collar, the mouth
comes to be directed anteriorly instead of ventrally (cp. figs.
7,46 and 57). By this process the anterior phlange of the
collar acquires the relation shown in fig. 1, et seq. In
addition to these changes a most important structure is first
formed at this time, namely, the cavity, which from the rela-
tions which it afterwards possesses I shall speak of as the
atrial cavity.

In the later conditions of Stage H the body is perceptibly
wider in the region of the body immediately anterior to the
gill-slits than it is behind them. This increase in width, which
is still very slightly marked, is due to a circular thickening
which passes all round the animal, being most developed at the
sides. By the time of the appearance of the second pair of

86 WILLIAM BATESON.

gill-slits this thickening has considerably increased, and in the
contracted condition of the body is a very marked structure
(fig. 2, op.). As development proceeds, this thickening in-
creases, and at the same time grows backwards in the lateral
regions until (five gill-slits) it has covered half the first gill-
slit. The degree of contraction of the body of course alters its
relations, but in the extended condition in adult specimens its
posterior margin is about on a level with the fourth gill-slit.
As then this structure is a process of the body wall which
forms an opercular fold over the foremost gills, it appears
reasonable to institute a comparison between it and the atrial
walls of Amphioxus, &c. It will therefore be alluded to as the
operculum, and the cavity between it and the body wall as
the atrial cavity.

As previously described, the first gill-slit on its appearance
is a simple circular pore. In this condition it remains for
some days, but gradually, on about the tenth day, its form
changes owing to the growth of a process from the dorsal
margin of the pore, which renders the aperture somewhat
kidney-shaped (fig. 1). Whilst this process is continuing the
second gill-slit appears as another circular pore, similar to the
original aperture of the first gill-slit. I was unable to discover
any priority in the appearance of the gill-slit of either side in
particular, but incline to believing that they appear syn-
chronously on the two sides of the body, as previously
mentioned.

After the appearance of the first gill-slit a definite series of
changes is undergone, and these form a definite period in the
history of the development of the animal, which may be con-
sidered as closing with the formation of the second pair of gill-
slits.

At this point it may be well to recapitulate these changes.
The embryonic life terminates with hatching, and the free
larva with one pair of gill-slits escapes, moving about in the
mud by means of cilia.

Before the second pair of gill-slits appear, it has undergone
the following changes :

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSEII. 87

(1) Disappearance of ciliated band and apical tuft.

(2) Body walls have become semi-transparent.

(3) Animal has changed its habitat, creeping into the upper
layer of mud.

(4) A fixing organ has formed as a ventral posterior sucker.

(5) Owing to growth of collar-fold, and constriction of pro-
boscis-stalk, the mouth comes to be directed forwards.

(6) Differentiation has occurred in the hypoblast cells,
marking out the alimentary canal into three regions, VIZ.
branchial, digestive, and intestinal.

(7) Notochord is distinctly visible.

(8) Anal perforation present.

(9) Second pair of gill-slits arise.

(10) Opercular fold forms, as a circular thickening.

From this point onwards the principal changes in external
features consist chiefly in an increase in size, and in continual
progress towards transparency. This latter is so marked a
feature that when three pairs of gill-slits are formed the walls
of the body behind the collar, which were originally opaque,
become perfectly clear and glassy, so that the internal struc-
tures are quite distinguishable. The walls of the proboscis
and. of the collar never entirely lose their primitive opacity.
An attempt is made in figs. 1, 2, and 3 to show this gradual
transition. It is presumably due to the consumption of the
food particles which in the earlier condition were distributed
almost uniformly among the cells of the body. This great
transparency is not usual among forms that do not lead a free-
swimming existence, and is possibly, so to speak, accidental,
and correlated to the rapid growth which now occurs. Nume-
rous glandular patches and spots are to be seen in the skin.
They are developed chiefly ou the proboscis, collar, and sucker,
those on the latter being refractive and differing somewhat in
appearance from the rest.

The increase in size seems to be rapid, but as to the length
of time that is taken in passing through subsequent stages I
have no record, as the specimens were caught from time to
time, and not reared in aquaria.

88 WILLIAM BATESON.

As the body grows, the number of gill-slits increases. They
are always added in pairs behind the last formed. The newest
has a circular orifice, while the growth of the “ valves ” (fig. 4)
from the dorsal margins of the anterior ones continues to
modify their shape. From being circular they then become,
first, kidney-shaped, then horseshoe-shaped, and next, by a
diminution in width from before backwards; together with a
great elongation dorso-ventrally, their openings are made
U-shaped. When this condition is attained, the ‘ valve”
continues to grow downwards, its free end lying inside the
pharyngeal cavity, as will be described when the histology of
the gills 1s treated of. Frequently, in contracted specimens,
these valves are washed outwards through the gill-slit, and
hang freely out in the water. This condition often occurs
during life. The gill apertures are from the first strongly
ciliated. The cilia move in a constant direction, driving a
current dorsalwards on the anterior line of the U, then down
the anterior margin of the “valve” and up the posterior, and
finally ventralwards on the hinder edge of the gill-slit. The
currents have the same course before the formation of the
‘‘ valve,” viz. on looking at a circular gill-slit of the left side,
if the animal’s head is directed to the observer’s left, the course
will be round the aperture in the direction of the hands of a
watch. By this current the water which passes in at the
mouth is carried out of the pharynx; probably, therefore, the
motion of the cilia is in a sort of spiral converging outwardly,
and not circular as it appears to be on looking down upon a
gill-slit.

From the fact that the number of gill-slits varies with the
length of the animal, together with the constant presence in
the posterior branchial region of a regularly arranged series of
gills in all stages from a complete U-shaped opening to a
terminal one which is always circular, I am led to believe that
these structures increase in number throughout the greater
part, if not the whole, of the life of the animal. The greatest
number of slits which I have observed was fifty-seven pairs.
Figures illustrating the development of the branchial

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 89

skeleton, &c., will be given when the histology of the gills
is described.

Together with the increase in number of the gills the differ-
entiation between the digestive and intestinal region becomes
more prominent, the bright yellow-brown of the former show-
ing through the transparent body wall, being a most striking
feature in the appearance of the animal. When first per-
ceptible, the digestive tract is a simple tube, separated by a
slight constriction from the intestine. As growth proceeds
this constriction becomes more marked, and when the second
gill-slit is fully formed the separation between the two is
sharply defined (fig. 2). Subsequently a fold arises in the
digestive region which gives it the appearance of being made
up of two saccules (two gill-slits). This condition becomes
more and more marked, and then a third saccule appears
posteriorly (4—5, gs.). When, however, the animal is seen
from the dorsal side the alimentary canal is seen to have a
wavy contour, the two saccules being thus parts of a slightly
bent tube. Moreover, in longitudinal sections the divisions
between the saccules are parts of a spiral fold which traverses
the whole digestive region. When five gill-slits are formed
there are three saccules, and in animals with ten gill-slits they
are five in number. After this the body walls become much
more opaque, attaining the condition which they present
throughout adult life. It is consequently not possible to follow
the internal development after this stage by means of surface
views.

The walls of the intestinal region are also thrown into folds,
but their arrangement would appear to be irregular. The cells
in this tract bear long flagelliform cilia which appear to drive
a current through the anus.

The anus is first found at about the time of the formation of
the second gill-slit. As previously mentioned it is almost if
not quite in the position in which the blastopore closed, being.
posterior, median, and dorsal. When the tail is formed the
anus is immediately dorsal to it, in fact, its ventral margin is
formed by the dorsal side of the tail. In ordinary conditions

90 WILLIAM BATESON.

the anus remains open widely, but when the animal is irritated
it contracts its body and draws in the intestine, closing the
anus, over which there project two flaps of the body wall.
These flaps are very thin and transparent presenting an appear-
ance as of a posterior vesicle (fig. 3a).

In some specimens a curious separation between the meso-
blast and epiblast occurs in this place, which may be due to
re-agents or may have some significance ; this structure will be
treated of together with the other formations in the third
body cavity.

In the transparent animal pulsatory contractions can be seen
in a vesicle lying on the dorsal side of the notochord, but
owing to the imperfect transparency of the body walls in this
region nothing more could be definitely affirmed as to the course
of the blood. As will be seen in considering the internal
structure, a large trunk appears (2—3, gs.) in the dorsal
mesentery ; pulsations could also be observed in this structure,
which seemed to pass from behind forwards, but occasionally
an appearance was produced as of a reversal in the direction.
But in consideration of the fact that the ventral wall of this
vessel is by the nature of the case adherent to the splanchno-
pleura, while the dorsal wall was fixed in the somatopleura,
no very certain importance can be attached to any observa-
tions of pulsation in the dorsal vessel, since any peristalsis in
the gut might produce this appearance. The same applies to
the ventral vessel, which is said to be contractile in B.
minutus (Spengel). On the whole, however, the balance of
evidence was distinctly in favour of postero-anteror pulsa-
tions in the dorsal vessel. No corpuscles were discovered in the
blood which is colourless. In preserved specimens it appears
as a homogeneous coagulum, which in specimens preserved in
Perenyi’s fluid shows a slight tendency to granulation.

Large ameeboid-looking cells are visible, floating about in
the body cavities, especially in the second.

After about seven to eight gill-slits are formed the general look
of the animal changes, mainly owing to the fact that the walls
of the body become more and more opaque. This seems to be

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 9]

due to thickening of the ectoderm and the appearance of
numerous mucous glands on the skin. The whole skin is
uniformly ciliated from the time when the blastopore closes
throughout life.

At about seven to eight gill-slits the suctorial tail disappears,
probably atrophying rapidly, but as to this process nothing more
can be predicated. It is to be found in some larve with eight
gill-slits, while others in the same stage are without it. The
anus is then terminal, circular, and permanently open.

At ten gill-slits the ovaries are first perceptible, but as yet
are not marked enough to appear in a surface view. In older
animals they form large yellowish-grey projections from the
sides of the body. Their minute structure, together with that
of the testis, will be given later.

The body of the adult is very highly coloured, the proboscis
being of a yellowish-white tint. The collar is a brilliant red
orange (especially in males), with a white line round the edge
of the operculum, while the rest of the body is of an orange
yellow, shading to pale green yellow in the intestinal region,
which is semi-transparent throughout life. The distinction
between the colour of the males and females is very well
marked in B. Kowalevskii, the genital regions being grey in
females and yellow in males. The sexes are of different colour
in all the Enteropneusta, most prominently so in B. sal-
moneus (Giard), in which the males are chrome yellow and
the females salmon coloured.

It may be well, before passing to the internal development,
to mention the peculiar odour which the creatures possess.
This odour is very penetrating and persistent, resembling that
of chloride of lime with a fecal admixture. All the species of
Enteropneusta which I have examined alive possess more or
less offensive odours. This peculiar property is most developed
in B. Brooksii (new species), in which the smell is very
distinct after the animals have been months in spirit, which
has been often changed. The smell of this species is strongly
suggestive of iodoform. It is so powerful as to be a con-
siderable drawback to investigating the species.

92 WILLIAM BATESON.

Another feature which ought not to be overlooked in a
general account of this species (B. Kowalevskii) is its extreme
vitality. In a bucket of unaérated water in which all other animals
had died some days before, in a hot climate, these creatures were
able to carry on their existence, and parts of the body may be seen
moving about by means of the ciliated skin to which a com-
pletely macerated skeleton of the branchiz is attached. Lobes
of the testis, torn off, will likewise swim about for days. To
what extent the body is capable of regeneration I cannot say.
Specimens were found in which there was at all events an
appearance suggesting that the proboscis had grown again.
Spengel has alluded to regeneration of tissues as occurring in
B. minutus, and I have little doubt that it is also common in
B. Kowalevskii.

With regard to the specific name of this form, it appears
that the figure and description given by Agassiz of B. Kowa-
levskii identify it with the form which is the subject of this
paper. The mode of development ascribed by him to the
species is of course entirely different. Seeing, however, that
he was unable to show the connection between the animals
found by him in the beach and the Tornaria which he reared,
it does not seem by any means certain that these Tornaria
were the larve of B. Kowalevskii. On the whole, it is
at least possible that they were the young of some other
species, e.g. B. Brooksii, which occur at least as far
north as the Chesapeake, and probably higher still on the
coast.

From a general survey of the group Enteropneusta, which I
hope subsequently to attempt, I think it will appear likely that
B. Kowalevskii stands, in many respects, in a group differing
in several features from the other members, which agree with
one another in these points, e.g. short proboscis, complicated
branchial skeleton, operculum small, liver saccules present, eggs
minute, &c. It is to the latter division I am inclined to
believe that Tornaria alone belongs.

In studying. the anatomy of Balanoglossus by means of
sections difficulty arises owing to the variable amount of con-

DEVELOPMENT OF BALANOGLOSSUS KOWAILEVSKII. 93

traction which the body may undergo in preservation. The
trouble chiefly occurs in the case of the proboscis-stalk and
folds of the collar. By comparing figs. 3 and 4, which were
drawn from living specimens in the extended state, with fig. 5,
which is taken from a preserved specimen, these relations will
be understood. In the contracted animal the gill-slits are
always more or less obscure, owing to the great shortening
which takes place in the branchial region, together with the
protrusion of the valves (fig. 5, viv.).

In older animals this contraction is not nearly so great,
probably owing to the increased firmness of the branchial
skeleton.

Internal Structure.

Stages Fand G—Skin.—The ectoderm is composed of long
fusiform cells arranged two to three deep over the body, except
in the dorsal side of the collar groove, where they are colum-
nar and one layer thick. Also in the posterior dorsal region
the skin is thinner than that of the rest of the body. The
whole surface is ciliated. Beyond the fact that the cells are
more compressed, and closely arranged, the structure is
similar to that of the previous stage.

Nervous System.—The solid cord which began to separate
from the skin in the middle dorsal line at Stage F continues to
sink inwards. No lumen is as yet present in it. Throughout
its length it still remains in contact with the skin, fusing with
it at both ends (figs. 10 and 20—24).

Towards the end of Stage G a differentiation begins between
the upper and lower parts of this cord, the upper being formed
of cells, while the lower part consists of lightly stained sub-
stance, which in older animals is distinctly made up of fibres.
Its fibrous nature cannot in this condition be certainly affirmed,
probably owing to defect in preservation. The formation of a
nervous network over the whole body, which afterwards
occurs, is not yet begun.

Hy poblast.—The mouth is ventrally directed (fig. 7), and

94 WILLIAM BATESON.

_ the anterior wall of the gut (Stage E to F) runs at right angles
to the long axis of the body. As will afterwards appear this
feature is of importance. In longitudinal section, a commenc-
ing differentiation between the branchial and digestive region
is perceptible. The cells of the former are columnar, while
those of the latter have irregular ameeboid processes which
give the inner wall of the gut an irregular contour. The anus
is not yet formed.

In the front end of the third segment of the larva (Stage F),
anterior to the ring of cilia, the sides of the gut give rise to a
pair of dorso-lateral evaginations ; these pouches are the first
indications of the gills. No change has occurred in the skin
covering them. Subsequently they come in contact with the
skin, the walls fuse and then a perforation is formed through
the fused portion, apparently occurring by a process of degene-
ration of the tissue. Fig. 29 is from a section taken through
the side of one of these evaginations. The subsequent appear-
ances are shown in figs. 41 and 42, which are from an older
larva.

Notochord.—In the later stages of F and G in the
anterior dorsal wall of the gut, arises a most remarkable struc-
ture. For reasons which will appear when its later develop-
ment and fate is considered, I propose to compare this organ
with the notochord of the Chordata, and by this name it will
be subsequently spoken of.

In Stage E it was stated that the anterior wall of the hypo-
blast came vertically to join the skin at the mouth (figs. 7 and
10). As, however, development proceeds, the dorsal wall of
the pharynx becomes partly constricted from the remainder
(figs. 20 and 22). As this process of separation of the dorsal
wall proceeds, the part so separated grows forwards so that it
comes to project slightly in front of the anterior end of the gut
(fig. 30). By this means a hypoblastic tube is formed dorsal
to the gut, with a lumen which opens into the archenteric
cavity (figs. 21, 22, and 30).

Mesoblast.—The lining of the anterior body cavity in
Stages E and F is composed of rounded cells arranged in con-

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 95

tact with the ectoderm. These cells are in some parts only
one layer thick (anterior and posterior walls) (fig. 8), while in
others (ventrally) they proliferate rapidly (fig. 9), forming loose
masses of cells, the outer elements of which are elongated,
with rounded heads from which the spherical cells which form
the inner portion are budded. This proliferation continues
until the proboscis cavity is partially filled up. But in the
later phases of Stage F elements are formed other than the
rounded cells above mentioned, in the shape of fibres (fig. 13)
which appear to arise in a curious way, as is shown in figs. 9,
10, 12, &c. The elongated cells gradually become pyriform,
the round ends being for the most part central, while the fine
ends are drawn out into peripheral fibres. The round heads
then appear to separate from the fibres, so that in examining
the mesoblastic structure lining this cavity in late larve of
Stage G, the elements are arranged in the following order :
centrally, a small empty cavity surrounded by a ring of sphe-
rical granular cells; next a layer of pear-shaped cells con-
tinued into peripheral fibres, and externally a layer, composed
almost, and later in life entirely, of radial fibres. Some of
these are inserted into the lower layer of the skin, and are
probably a peculiar form of connective tissue. In the heads of
the pyriform cells brightly refractive granules may be seen;
whether these are food or waste products cannot be affirmed.
Such then is the lining of the proboscis-cavity. In the
anterior third it is evenly distributed over the inner surface,
but at the back of the posterior third, where the proboscis
tapers abruptly to its stalk, the layer of mesoblastic tissue is
much thinner dorsally than laterally and ventrally (compare
fig. 13 which is through this region with figs. 12 and 11 which
are anterior to it). On passing further backwards, the cavity
in Stage Gis divided into two by a great proliferation of
mesoblast from the dorsal surface, which grows downwards
until it meets the ventral mesoblast. The position occupied
by this structure at first coincides with the point at which the
anterior mesoblastic pouch closed off from the archenteron.
In that stage the anterior body cavity was a simple sac con-

96 WILLIAM BATESON.

tinued backwards into two lateral horns. The mass of cells
which now arise at the original point of separation, therefore,
constitutes a continuation of the division between these two
horns into the anterior simple cavity (fig. 14). As will
shortly be seen, this division of the back of the anterior cavity
into two is correlated to the forward growth of the notochord.

In this septum, which is composed of roundish, hexagonal
cells containing many granules (fig. 16), appears the first
rudiment of a peculiar organ which subsequently is a con-
spicuous and characteristic structure in the proboscis of all
the Enteropneusta, viz. the proboscis-gland (“ heart” of
Spengel'). This gland has at first the relations shown in
fig. 10, gl. It consists (Stage F) of a triangular mass of loose
tissue containing nuclei in which but few cell-outlines can be
seen, and would appear to be formed by a sort of degeneration
of the mesoblast of the septum. As yet it contains no cavity.
Immediately behind and ventral to it is the anterior end of
the notochord (fig. 17).

Fig. 18 is taken through the posterior apices of the meso-
blastic horns behind the gland.

Middle Body Cavities.—These are (Stage E) a pair of
simple cavities divided by a dorsal and a ventral mesentery,
completely closed from both the anterior and posterior cavities,
as they remain throughout life. They are lined by round or
crescentic mesoblast cells. As the proboscis-stalk is con-
stricted, the anterior parts of these cavities are compressed.
into two forwardly directed horns. The horn of the left side is
shown in fig. 18. From an early period it projects in front of
that of the right side.

In Stage F a histological differentiation occurs in the
splanchnopleure at the place of union between that part of the
hypoblast which is destined to form the notochord and the
lower section of the pharynx: This appearance is shown in
fig. 25, #). It consists in the prolongation of the ends of the

1 For reasons which will subsequently appear this term is somewhat in-
&pprop riate.

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 97

mesoblast cells which are in contact with the hypoblast into
curious tails, which are refractive.

I was at first led to suppose that these tails were mus-
cular, and this undoubtedly is the fate of many of the
mesoblastic elements of this region, but no direct evidence of
the contractile nature of these pear-shaped cells was attained
beyond the general suggestion of their shape; on the other
hand, when the notochordal sheath is developed in this region,
an appearance is presented which suggests the possibility of
their having taken part in its formation. Their histological
characters are, however, strikingly similar to those of the cells
which occur at the sides of the notochord in the same region
in Amphioxus at the time when it has eleven pairs of meso-
blastic pouches (Hatschek, No. 4, figs. 124, 126, &c.). These
cells are stated by Hatschek to be muscle-fibres; by analogy
it seems, therefore, likely that this may be the real nature of
the same cells in Balanoglossus.

As development proceeds, proliferations of mesoblast are
formed in the ventral region of the middle body cavities. From
each side in the posterior region of these cavities a tubular
portion is separated off from the rest (fig. 28).

The fate of these parts is not quite certain. It seems, how-
ever, likely that they unite with two forward growths from the
posterior body cavities to form the tissue space in which the
dorsal blood-vessel is ultimately enclosed throughout the collar
region. This tissue space I propose to call the perihema
cavity (fig. 60, &c., Ph. c.).

The posterior body cavities are simple cavities, similar
to the middle pair. The dorsal and ventral mesenteries
persist throughout life. As yet they contain no special
differentiations.

Period between the Formation of the First and
Second Pair of Gill-Slits.

Skin and Nervous System.—The histology of the skin
in the proboscis and collar regions has not undergone material
7

98 WILLIAM BATKHSON.

alteration since the last stage. The epiblastic cells are some-
what smaller and more closely packed. In the posterior
regions, however, the ectoderm is thinner than in the
younger animals, owing to the rapid growth which occurs at
this time in the trunk region (fig. 46). Unicellular mucous
glands occur at rare intervals in it. But in the lower layer of
the skin at the posterior surface of the proboscis is formed the
beginning of that network of nerve-fibres which is such a pro-
minent feature in these regions of the body in later life.
Though a network of this kind eventually is formed on the
inner surface of the skin all over the body to a greater or less
extent, it is as yet only to be seen in the base of the pro-
boscis. The exact process by which this layer is deposited is
not certain, but it would appear that cells of the inner layer
elongate and form multipolar cells with long, thread-like, anas-
tomosing tails (fig. 32).

At this stage nuclei are still visible in this fibrous layer,
though in later stages they have almost entirely disappeared
from it (fig. 54, &c.). From this point in development on-
wards these fibres constitute a perfectly defined layer of tissue.
Projecting into it may be seen some of the fibres which were
described as being formed from the mesoblastic lining of the
proboscis cavity. These fibres are presumably supporting
structures. Occasionally an appearance is presented as of an
anastomosis occurring between them and the tails of the nerve-
fibres. Whether this is really the case or not, it can scarcely
be doubted that the muscle-fibres, which are now forming in
the proboscis cavity, receive their innervation from the fibrous
layer of the skin, to which many of them are attached, and
thus such an anastomosis is not @ priori improbable. On the
other hand, the structure of the mesoblastic fibres is rather in-
dicative of a supporting than of a contractile function. But,
as will afterwards appear, there are eventually present in the
mesoblastic elements of these animals cells which present
almost every shade of variety between undoubted contractile
fibres and obvious connective tissue, so that it is by no means
easy to determine the nature of these fibres with precision.

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 99

On the whole I am inclined to regard them as supporting
structures.

The separation of the dorsal nervous system is much
more marked during this period than it was before it. It is
now completely separate from the point of junction of the pro-
boscis with the trunk to almost the level of the first pair of
gill-slits. At its anterior end (fig. 36) may be seen the be-
ginning of the process by which the anterior lumen is formed.
This is effected by a forward growth of the collar, together
with a continual sinking and horizontal invagination of the
nerve-cord.

This lumen, thus formed, never extends for more than a
short distance into the cord, which, however, in its middle and
posterior regions in older animals, contains remarkable spaces
lined by columnar cells, more or less separated from each other
by strands of tissue, which will be described, together with the
later development and histology of the nervous system.

The nerve-cord, as always, fuses with the skin at both ends,
but from its posterior point of junction the rudiment of its
dorsal continuation in the skin may already be seen in section
as a small area of fibrous tissue in the base of the skin in the
middle dorsal line (fig. 42). A similar strand (fig. 42) may
also be seen on the ventral side, beginning a little in front of
the first gill-slits. The two cords are still quite unconnected.

The Proboscis Pore.—The first appearance of this struc-
ture is a thickening on the inner surface of the epiblast in the
proboscis stalk, which soon becomes hollow while still attached
to the skin (fig. 34, p. pr.). This epiblastic sac is from the
first asymmetrical, being on the dorso-lateral aspect of the
left side. From the first, the cells of which it is formed are
columnar, and it has no communication as yet (two gill-slits)
with the exterior or with the body cavity.

Hypoblastic Structures.
Branchial Region and Notochord.—The process by
which the mouth comes to be forwardly directed has already
been described. In larve with one to two gill-slits it has already

100 WILLIAM BATESON.

begun (fig. 45). The walls of the branchial region are
distinctly differentiated from those of the rest of the gut,
consisting of long, solid-looking cells arranged in layers of one
to two deep. The lumen of the gut is very small anteriorly
and has an irregular outline in preserved specimens (figs. 36
and 37), but in the middle of the collar region as at present
marked out, its lumen is continuous dorsally with that of the
notochord (fig. 39).

This notochord, which is now a very prominent feature in
sections of the anterior end of the body, arose in the first
instance, as already stated, by a forward growth of the anterior
dorsal wall of the pharynx, which thus shuts off a short diver-
ticulum of hypoblast (fig. 30). The part of the pharynx with
which the walls of this diverticulum are continuous, then
separates itself from the rest by longitudinal constriction, which
at first causes the lumen of the gut to take an 8-shaped figure,
the separation of the dorsal part of the 8 becoming finally
complete from before backwards. This process gives rise to the
appearance seen in fig. 37. The part thus constricted off
becomes then entirely separated except at its posterior end,
where throughout life its lumen opens into the pharynx.

In its anterior region the lumen of the notochord is always
suppressed at this stage, owing to the compression of the ventral
against the dorsal wall. Moreover, in larve of this, as of all
subsequent stages, the lumen is altogether obliterated in part
of its course. This obliteration does not appear to occur pro-
gressively from before backwards, but more or less irregularly,
so that, as in fig. 38, the lumen may have already disappeared
while still present in a region anterior to this (fig. 36). As,
however, in older animals the lumen is always continued far
into the notochord of the proboscis cavity (namely, to a point
anterior to that where it is already obliterated in two-gill
larve), it is almost certain that the subsequent increase in the
length of the notochord is due to a growth from behind for-
wards, and that all the notochord which is as yet formed
(two gill-slits) is pushed bodily forwards by a proliferation,
probably occurring at the point of union with the gut. The

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 101

alternatives, that the growth occurs at the apex or at any point
intermediate between the two ends is unlikely, from the fact
that almost immediately after two gill-slits the tissue of which
it is composed becomes vacuolated and irregular, undergoing
the “degeneration” characteristic of notochordal substance,
presenting therefore by no means the appearance of a growing
tissue.

The length and proportions of the notochord at this stage are
indicated in fig. 45, which is, however, not a truly median
section. Its anterior end already projects far into the anterior
body cavity, pushing in the mesoblastic lining. Fig. 45 is from
a specimen slightly older than that from which figs. 37, &c.,
are taken, and the commencing degeneration of the notochord
tisssue is already begun.

To recapitulate: the growth of the notochord is due to:

1. A forward growth of the dorsal anterior portion of the
archenteron (fig. 30). This is supplemented by—

2. A longitudinal constriction of the dorsal region of the
pharynx, which gradually travels backwards (cp. figs. 21 and 22
with figs. 38 and 389), separating a hollow hypoblastic tube
which remains open to the gut behind.

3. A forward growth from the point of junction with the gut.

In connection with the notochord must be mentioned the
skeletal rods, which now just appear, though it cannot be
positively affirmed that they are of hypoblastic origin. When
first visible, they are two short rods of a deeply-stained, struc-
tureless substance, which lie in the angles between the noto-
chord and the dorsal wall of the pharynx. As first seen in this
position they appear to be formed externally to the hypoblast
cells, against the ends of which they lie. Their posterior ends
are enclosed in the hypoblast (fig. 39), and it is difficult to
understand how this can have been brought about if they were
secreted by the mesoblast cells. This would involve an outward
growth of the hypoblast to inclose them, of which there is no
appearance. As will afterwards be seen the view that they are
of hypoblastic origin is supported by the fact that they con-
tinue growiug with the growth of the animal, and that their

102 WILLIAM BATESON.

thickness is, so to speak, inversely proportional to that of the
cellular tissue of the notochord, which becomes thinnest in the
region where they attain their maximum size. This, therefore,
suggests that they are formed at the expense of the notochord.
An analogy moreover at once occurs of the secretion of such
a substance from notochordal tissue in the case of Amphioxus,
in which discs are deposited of very similar histological
character to these masses in Balanoglossus. These two rods
posteriorly bend downwards and then slightly forwards lying
in the hypoblast. They are therefore each cut twice in sections
through this part of the body.

Behind the end of the notochord are the gill-slits, which are
still only circular pores leading to the exterior (fig. 43). The
lumen of the gut in the branchial region is (in contracted
specimens) much suppressed, and its ventral side, however,
always is grooved, and in this groove the cilia which line the
branchial region are well developed.

When the animal contracts, the branchial region of the gut
posteriorly projects over the front of the digestive region on
the dorsal side (fig. 44).

The digestive region is quite distinct from this point
in development onwards. Its cells have the appearance shown
in fig. 45, being large cells with amoeboid processes containing
large granules. From the back of the digestive region the
intestinal region is now marked out. Its walls are thinner,
and the cells composing it are long and ciliated at their inner
ends. The anus is a large aperture, permanently open when
the animal is expanded, situated dorsal to the tail. There is
no epiblastic proctodzum.

Mesoblastic Structures.

Anterior Body Cavity. The mesoblast of this tract may
now be divided into two parts—(1) a peripheral portion
which lines the body walls of the proboscis, and (2) a central
portion which is pushed in by the forward growth of the
notochord ; between these two portions there is a body cavity
which retains a clear central space throughout life.

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 103

(1) The peripheral part consists of cells and fibres. The cells
are mostly pyriform similar to those of one-gill larve. They
contain few granules and are much reduced in number. The
fibres are more numerous. They are of several kinds: thick
strands that are obviously muscular, running as yet only in a
longitudinal direction, having their ends inserted in the skin:
and also thinner fibres, which are arranged circularly, as in
the periphery of the middle third; longitudinally, only
occurring asa sort of sheath separating the circular fibres from
the general connective tissue, and occasionally in the central
portions; radially, as over the whole periphery of the pro-
boscis cavity, and finally, very fine fibres forming a loose
network connecting all the mesoblastic elements together. As
may be seen in figs. 31, &c., there is as yet no suggestion of
the peculiar concentric arrangement of the longitudinal fibres,
which gives a section of the adult proboscis its curious appear-
ance. The radial fibres are mostly inserted into the skin
(fig. 32), their possible connection with the epiblast has been
already discussed.

There are still present a few of the large spherical cells
which formed the inner layer of mesoblast in one-gill-slit
larvee, but they contain fewer granules, and are only found in
the posterior parts of the cavity.

(2) The central portion in the one-gill-slit larva was made
up of a mass of spherical and polygonal cells surrounding a
central part filled with loose tissue (fig. 16). As the noto-
chord grows forward, this structure, which, from its subsequent
fate may now be termed the proboscis gland, is prolonged with
it. As this forward growth occurs, a basement membrane
forms between the mesoblast outside the proboscis gland and
the loose tissue contained in it. Fig. 46 shows a section ante-
rior to the part where this basement membrane is formed.
The mesoblastic cells are here large and granular, having
irregular shapes. The proboscis gland now is hollowed out,
so that it contains a space which extends from the proboscis
stalk to the front end of the notochord. This space contains a few
mesoblastic cells, which are as yet not obviously differentiated.

104. WILLIAM BATESON.

The position of this space is shown in fig. 45. It will be seen
in the sequel that the mass of the secreting tissue of the gland
is formed from the cells covering this space, and forming the
sides of this central portion of the mesoblast. The space itself
contains eventually but few of these secreting cells, and will
be spoken of as the sac of the proboscis gland (fig. 52, gl. s.).

The heart is as yet not represented.

Middle Body Cavities.—The tissue lining these cavities
does not exhibit more than a general progress of differentiation.
Owing to the increased narrowing of the proboscis stalk the
two anterior horns of the cavities are more distinct. In the
dorsal and ventral mesenteries basement membranes occur.
The cells lining these cavities are generally pyramidal or
crescentic, some of them being radially directed and fusiform.

Posterior Body Cavities.—The tissue of the posterior
mesoblastic pouches has undergone the same proliferation and
progressive differentiation as that of the middle cavities. These
processes are not, however, quite so far advanced. The two
horns (peri-hemal cavities) which began to grow forwards
above the gut in the one-gill larva are now much more de-
veloped. They now extend into the back of the collar region,
in front of the first gill-slit. They are filled more or less with
loose mesoblastic tissue containing a few fibres. As before
stated, in the mesentery between them is formed the dorsal
blood-vessel. This structure appears as a split in the
mesentery, and is as yet quite empty in preserved animals.
This split extends already through the whole course of the
perihemal cavities. On the ventral side also a split is formed
in the lower mesentery of the posterior body cavity to form
the ventral blood-vessel. There is as yet no connection
between the dorsal and ventral vessels.

From this point the details of the subsequent development
and anatomy of the parts will be given in the section dealing
with the separate organs ; but, before doing so, it may be well
to describe briefly the general course of the later history of the
internal structures.

Notochord.—As will be seen, this structure increases

DEVELOPMENT OF BALANOGLOSSUS KOWALEBVSKIL. 105

greatly in size, and assumes a vacuolated appearance closely
resembling that of the notochord of young Lampreys and
Elasmobranchs.

The skeletal rods attain a considerable size. Their anterior
ends unite, forming a single bar, while their posterior ends
diverge, partially enclosing the gut. This whole structure
forms the support of the proboscis.

From its development, position, relations to surrounding
parts, histology and function it appears to me to be com-
parable with the notochord of the Chordata, and this name is
strictly appropriate to it. Even if the suggestions which will
be made hereafter as to its phylogenetic significance be not
accepted, this rejection would in no way militate against the
fact that this structure is to all intents and purposes a noto-
chord, which can only be designated as a longitudinal dorsal
supporting rod, derived from the hypoblast.

The nervous system afterwards attains a great develop-
ment (fig.60). The dorsal cord in the collar sinks further and
further from the skin, being (in B. Kowalevskii) connected
to it by a mesentery. The lumen is in this form less developed
than in B. minutus, &c. The ventral cord is the next to
appear, and almost simuitaneously with it arises the deposit of
nervous tissue in the skin at the base of the proboscis. This
deposit afterwards attains a great extent, forming a thick band
round the proboscis stalk. It may be noticed that this nerve-
ring has practically the same relation to the proboscis that the
ring of ganglia in Nemertines presents, the proboscis of Balano-
glossus being, however, permanently protruded, and the nerve-
ring still in the skin. Both these nerve-rings agree in being
traversed in Nemertines by two and in Enteropneusta by one
pore communicating from the exterior to sacs which were
originally archenteric diverticula.

Body Cavities.—As before mentioned, the left horn of the
anterior body cavity comes to open by the proboscis pore to
the exterior. This opening is median and dorsal in other
species, but in B. minutus it is on the left side throughout
life. In all species it perforates the nerve-ring of the stalk.

106 WILLIAM BATESON.

Nearly all the proboscis cavity is eventually filled up with
loose tissue. This is composed of a number of concentric rings
of longitudinal fibres and connective tissue. These rings
attain the maximum number of eight. In fig. 51 the general
appearance of an older proboscis cavity is shown. The con-
centric arrangement is, however, not yet attained in the stage
there figured.

A free space is always present between these rings of tissue
and the central structures in preserved specimens.

The proboscis gland becomes a large mass of tissue com-
posed of anastomosing blood-vessels covered with conical cells
fixed on the vessels by their apices. Many of these cells
contain remarkable yellow granules, which are also to be
found outside the cells, sometimes presenting a couglomerate
arrangement. They would seem to be formed in the cells and
thrown out. They are also to be found in the sac of the
proboscis gland. This sac is blind posteriorly, but anteriorly
the loose tissue which it contains passes into unbroken con-
nection with the remarkable cellular layers covering the blood-
vessels. Hence the sac is in communication with the central
body cavity through the tissue spaces of the gland. The
function of this gland is quite unknown. Spengel suggests
that it is an “internal gill.” It does not seem probable to me
that an animal with some sixty pairs of true branchial clefts
would also possess another large and complicated organ of
entirely different structure also for respiratory purposes. The
presence of the brown granules suggests that it may be excre-
tory. If this were so, the excreta might be expected to pass
out by the proboscis pore which opens into the cavity in which
the gland lies. No direct evidence was obtained as to the
normal direction of the flow through this pore. Spengel and
other observers state with regard to B. minutus that water
is taken into the body cavity at the proboscis pore, but my
own observations do not confirm this statement. On the
contrary, particles of Indian ink or carmine held in suspension
in the water in which the animals have lived for days, cannot
be found to enter the proboscis cavity, while similar particles,

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 107

if placed in the tissue spaces of the proboscis, are certainly
expelled by the pore. This evidence does not of course
demonstrate, beyond doubt, that inwardly directed currents
never enter the pore but only gives a presumption against
them.

Spengel’s statement of the absence of the pore described by
Kowalevsky and Agassiz, at the apex of the proboscis, is true
for all the species which I have examined.

The Heart.—As mentioned by previous observers, a large
vesicle may be seen pulsating above the water-vessel in Tor-
naria; such a pulsation may be observed in the dorsal side of
the base of the proboscis in B. Kowalevskii at the stage of
two to three gill-slits. Spengel states that this contractile sac is
the upper of the two cavities lying above the notochord (figs. 51,
53, &c.); this he calls the “heart.” In consideration of the
fact (which he also admits) that it contains no blood, gives off
no vessels, and has no muscular walls, this name seems open
to misconstruction. As this so-called ‘‘ heart” is merely a
space filled with loose tissue which is part of the proboscis
gland I have preferred to call it the sac of the proboscis gland,
and to reserve the name “heart” for the sac which lies
between this space and the notochord (figs. 50 and 51, At.).
That this is the actual heart can I think hardly be doubted.
It arises at about three gill-slits as a single horizontal split in
mesoblast between the notochord and the sac of the proboscis
gland. It acquires muscular walls and is always nearly full of
a coagulum similar to that which is found in the remaining
blood-vessels of the body, which can all be traced into connec-
tion with it.

These peripheral vessels are (1) a longitudinal dorsal one,
running from the heart to the tail in the dorsal mesentery
from the back of the collar, and in the collar as a blood-space
surrounded by the perihemal cavities (fig. 60); (2) a ventral
longitudinal vessel running from the back of the collar to the
tail in the ventral mesentery. These two are connected by
blood sinuses in the skin and in the wall of the gut. I have
uot seen the definite circular vessel which other observers state

108 WILLIAM BATESON.

surrounds the gut anteriorly. The principal skin sinuses are a
pair of large ones which extend on each side of the dorso-
lateral regions of the proboscis (fig. 51).

The Collar Pores.—On the outer wall of each atrial cavity
appears a thickening at about eight gill-slits. This thicken-
ing acquires a perforation which leads from the collar body
cavity to the atrial cavity. These perforations acquire a
curious folded lumen and become ciliated constituting the
collar pores. Their opening into the atrial cavity is con-
tinuous with that of the first gill-slit. From analogy it may
be expected that these pores are of an excretory character.
With regard, however, to the direction of the flow through
them, the evidence is as unreliable as that as to the currents
in the proboscis pore. Spengel states that water is taken into
the body cavity at these points, while 1 was unable to find that
coloured particles ever entered it. Similarly, however, such
particles placed artificially in the collar body cavity were
washed out at these points.

The Middle and Posterior Body Cavities.—These
cavities become in adult life more or less filled with connective
tissue, &c. The cavity of the middle pair becomes practically
obliterated owing to the great development of loose tissue in
it. But in the posterior cavity this proliferation is never so
great. The middle pair of body cavities is far more choked
up in B. Kowalevskii than in B. minutus, but in B.
Brooksii the amount of connective tissue is even greater.
This fact is interesting in the present state of views as to the
morphological meaning of ‘‘ ceelom,” as presenting an example
of a body cavity arising in a most typical “ mesodermic ”
manner, assuming ontogenetically precisely such an appear-
ance as is presented by the “mesenchyme” of Platyhel-
minths, &c.

A statement as to the origin of the generative organs
is reserved for the present, as some doubt exists as to the layer
from which they are derived. The general appearance is, how-
ever, suggestive that they are of epiblastic origin.

Before beginning a detailed account of the later development

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 109

it may be desirable to discuss briefly the new light which these
facts throw upon the affinities of the Enteropneusta.

In 1881 Metschnikoff published a detailed comparison of
Balanoglossus with the Echinoderms, comparing Tornaria with
Bipinnaria, showing that the resemblance is close, and con-
cluding with the suggestion that Balanoglossus should be in-
cluded among the Echinodermata in a separate division,
“ Bilateralia.”” The branchial structures he compared to the
openings from the body cavities of Echinoderms. This view,
as thus expressed, receives no support from further observa-
tions, and would now appear to be untenable.

As mentioned above, all the Enteropneusta possess a sup-
porting structure which is comparable with the notochord in
every way, except in extent and in the persistence of its con-
nection with the alimentary canal. Its resemblance to that of
Amphioxus is especially striking, for in Amphioxus the noto-
chord projects a long way in front of the mouth. It moreover
possesses gill-slits which are not only without parallel, except
among the Chordata, but also in structure, position, and de-
velopment, agree exactly with those of Amphioxus, in which
the slits acquire the same U-shaped form.

The agreement in the position of the blood-vessels and
skeleton of the gill bars is also very close. The fact of their
gradual increase in number from before backwards throughout
life is another common feature.

The position and mode of origin of the central nervous
system is also similar in both forms; the invagination of the
dorsal cord in Balanoglossus being, however, only partial, while
that of Amphioxus is complete.

The mesoblastic pouches suggest the same resemblance,
differing oniy from those of Amphioxus in number, being one
median and four lateral, while those of Amphioxus are one
median and twenty-eight lateral. As I have already pointed
out, the fate of this anterior pouch is in the two animals closely
similar. In both it is divided into two as the notochord grows
forward. In Amphioxus the division is complete, while in
Balanoglossus it is partial. In both, the backwardly-projecting

110 WILLIAM BATESON.

horn upon the left side becomes lined by ciliated co umnar
cells, and opens to the exterior. Moreover, in both animals
this opening has a definite relation to the nervous system. In
Amphioxus it becoms the “olfactory” pit (Hatschek), while
in Balanoglossus it is surrounded by a mass of nervous tissue.
Finally, the collar folds, especially of B. Kowalevskii, would
appear to be comparable with the commencing atrial folds of
Amphioxus, for the most anterior gill-slits open into the cavity
which is thus enclosed. .

The pair of ciliated funnels opening from the collar body
cavities to the atrium has been compared above to the excre-
tory tube mentioned by Hatschek in a similar position in
Amphioxus.

A pair of tubes has been described by Lankester in
Amphioxus opening into the back of the atrial cavity, com-
municating with the dorsal body cavities. It may be remarked
that if the collar fold of B. Kowalevskii were prolonged
backwards, as the atrial folds are in Amphioxus, the two collar
funnels would then be carried backwards, and have relation
similar to that of these tubes, which, as suggested by Lankester,
may be excretory.

To recapitulate: striking resemblances to the Chordata, and
especially to the Cephalochord type, are to be found in the
following structures :

(1) The notochord.

(2) The gills and branchial skeleton and blood supply.

(3) The central nervous system.

(4) The origin of the mesoblast.

(5) The peculiar fate and remarkable asymmetry of the
anterior pouch.

(6) The atria.

(7) The excretory funnels.

In each of these cases, excepting that of the branchial struc-
tures and the excretory funnels, the condition is that which
would be produced by a partial or arrested development of the
corresponding structure in Amphioxus.

The above considerations appear to justify us in including

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 111

the Enteropneusta among the Chordata. I would, therefore,
tentatively suggest the following table :
Chordata.—Hemichordata (Enteropneusta).
Urochorda (Ascidians).
Cephalochorda (Amphioxus).
Vertebrata.

It is not now proposed to enter into a more detailed dis-
cussion of the morphology of the group, or of the light which
an acceptance of this suggestion throws on the origin of the
Chordata. A fuller examination of these points is reserved for
a subsequent occasion.

It may nevertheless be advisable to point out that since,
according to Spengel, the tissue of the “‘ water vessel” of Tor-
naria forms the lining of the proboscis cavity of B. minutus,
this “ water vessel” is therefore the same structure as_ the
anterior body cavity in the form just described. If, then, the
“water vessel”? of Tornaria is comparable to the “ water
vessel” of Bipinnaria, which has a similarly asymmetrical de-
velopment upon the left hand side of the body, which view has
been held by all previous observers, it would therefore appear
to follow that the water vessel of Bipinnaria is primd facie
comparable with the asymmetrical anterior body cavity of
Amphioxus.

Later Development and Comparative Account of
the Organs in the various Species.

The species which I have examined are the following :
B. Kowalevskii (Alex. Agazziz.) (Coastof North America).
B. Brooksii, n. sp. (ditto).
B. minutus (Kowalevsky.) (Bay of Naples).
B. salmoneus (Giard.) (Iles de Glenans, off South Coast
of Britanny).
B. Robinii (Giard.) (ditto).
B. Kowalevskii differs from all the others in having—
(1) a relatively long proboscis ;
(2) no hepatic sacculations ;

112 WILLIAM BATESON.

(3) a simple branchial skeleton, not connected by longi-
tudinal bars, as in the other forms ;

(4) very short collar funnels, the external opening of
which is directed transversely instead of posteriorly,
as in the others, in consequence of

(5) the greater extent of the backwardly-directed atrial
fold.

As far as can be determined from Agassiz’ account, his
species agrees in these points with the one which is the subject
of this paper.

The Notochord and Axial Skeletal Rods.

B. Kowalevskii.—The general course of development of
the notochord has been already described. Fig. 47 shows the
histological characters of the cells at two gill-slits, when they
are still large full-looking cells with large nuclei.

Fig. 48 is from a section of the proboscis stalk in the region
of the pore of a larva with three gill-slits. It exhibits the
commencing degeneration of the notochordal tissue and the
increase in size of the structureless deposit which constitutes
the skeletal rods.

In this region the skeletal rods unite to form a single
median rod, which is continuous with the notochordal sheath.

In figs. 49—53 the appearance of the notochord at four gill-
slits is illustrated. The degeneration is now far advanced.
Nuclei are rare in the notochord, and the cells are vacuolated,
as shown by the fact that the nuclei occur in the nodes of the
cell outlines. The protoplasm of the cells merely forms a kind
of network containing a few nuclei. The remainder of the
space is probably occupied by some homogeneous non-proto-
plasmic substance, such as may be supposed to fill up the
notochordal tissues of other forms.

Figs. 49—52 are from sections taken in front of the lumen
(cp. fig. 57). In fig. 53 the lumen is reached. It will be ob-
served that the lumen at this point still ends asa fine tube. In
later life a great thickening of the notochord takes place at this
point, and the lumen then acquires a downward extension

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 113

(figs. 57 and 56). Immediately behind this downward exten-
sion lies the anterior end of the united skeletal rods, which
here attains its greatest thickness, almost filling the sheath of
the notochord, the tissue of which is here almost suppressed.

In old specimens the shape of the anterior parts of the
notochord becomes rather irregular in section.

In that part of its course which lies behind the proboscis the
notochord in the adult is more or less elliptical in section,
containing a large and somewhat irregular lumen. Its tissue
is here greatly reduced, and this reduction appears to progress
regularly as the animal grows older. In fig. 60 the appearance
of the notochord in such an old adult is shown. Degeneration
has progressed far, leaving the notochord as a space surrounded
by vacuolated cells enclosed in asheath. With this sheath are
connected the skeletal rods, which attain a great size. Cen-
trally, on the dorsal side, between the notochord and the gut,
lies the principal rod ; this is formed by the uniting of the two
rods (figs. 37, 38, &c.), whose development has already been
described. This fused portion is now diamond-shaped in sec-
tion ; its lower angle causes a dorsal ridge to project into the
mouth cavity. Laterally are placed two long rods, which
are continued into the central rod and notochordal sheath
anteriorly. To these lateral rods are attached large bunches
of longitudinal muscles, by which, doubtless, the notochord
may be pulled backwards, and the proboscis retracted so as to
shut the mouth (fig. 60).

Posteriorly the median rod divides into two, and the opening
from the notochordal lumen into the gut lies in the angle
formed by the separation of these two diverging rods
(fig. 57).

A considerable deposit of ‘ structureless”? substance takes
place, filing up the spaces in the proboscis stalk, and forming
a partial sheath around the perihemal cavity. Whether this
substance is chitinous or of some other material I am unable
to say. The ensheathing parts of it have exactly the histolo-
gical appearance preseuted by the “structureless” substance,
which in Amphioxus is continued from the notochordal sheath,

8

114 WILLIAM BATESON.

&c., between the myotomes. The rods, however, are seen in
adult specimens to have concentric markings in section, sug-
gesting that they are formed by a deposit around a central
core. In that part of the rod which lies just in front of the
point of divergence of the two horns there are two such cores.
The cores stain more deeply than the rest of the rods.

In B. minutus the position and general appearance of the
notochord is similar to that in B. Kowalevskii, with the
exception that the lateral rods are not developed to the same
extent. The histology, however, is somewhat different. In
figs. 61—63 the appearance of the tissue is shown. Spengel
has stated that he is unable to find, in B. minutus, any
structure resembling the notochord of the Chordata, figuring
that organ as though composed of columnar cells. My own
observations give no support to this statement. No specimen
of notochord of any of the species which have been examined
by me present the appearance indicated by Spengel. On the
coutrary, specimens preserved severally in picric acid, corro-
sive sublimate and acetic acid, Perenyi’s fluid and osmic acid,
all equally show this body as made up of vacuolated tissue
strongly suggestive of the notochord of Chordata. This is
especially the case with regard to that of B. minutus. Fig.
61 is taken from a section of B. minutus in front of the lu-
men. The sheath is here very slightly developed. It will be
observed that the nuclei are fewer in number than in B. Kowa-
levskii, and that they are gathered round the upper centre. The
section shown in fig. 62 is from the same in the region of the
proboscis stalk. It shows the diamond-shaped section of the
skeletal rod and the concentric markings upon it. The noto-
chord itself is here elliptical in section, and the strands of
protoplasm running across it are well seen.

Fig. 63 shows its appearance in front of the point at which
it opens. Dorsally its wall is very thick and solid, while
ventrally it is comparatively thin. Behind this part the
skeletal rod divides into two divaricating horns as in B.
Kowalevskii.

In the other species the structure of the notochord is

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 115

essentially the same as in B. minutus. In the anterior
region of the notochord of B. Brooksii there are hardly any
nuclei at all. I hope to publish figures illustrative of the later
development and anatomy of the other parts at no distant date.

APPENDIX.

Methods.—From the characters of the unfertilized egg
of B. Kowalevskii it was extremely improbable that the
earliest stages of development could be passed anywhere else
but in the mud which the parents inhabit. Though the exami-
nation of Agassiz had failed in the attempt to find any but
adult Balanoglossus in this situation it seemed worth repeating.
Accordingly a large quantity of mud inhabited by Balanoglossus
was placed in a glass vessel of water and worked up, avoiding
rotatory currents, until the whole was in suspension. A number
of Balanoglossus which had previously been minced very finely
were then thrown in and the whole was then left to settle for a
few minutes. I then siphoned off the water and lighter parti-
cles in suspension, which consisted chiefly of vegetable débris,
stopping the siphon when the layer of chopped Balanoglossus
was reached, which could easily be seen by the bright orange
colour of the fragments. This portion was drawn off and
examined separately. It was found to contain great numbers
of larve and embryos of Balanoglossus, minute Nemertines,
free Nematodes, &c. In this manner all the animals
living in several hundredweight of mud may, in an hour or
two, be collected into about a pint of water and sorted with a
simple microscope. This was generally performed by rotating
a little of the water in a shallow saucer with a slight peripheral
groove. The larve then all lie in the groove which may be passed
under the lens by rotation. After a little practice it is of
course unnecessary to discolour the water with fragments of
the animal required, as of course the right layer can easily be
detected by the size and character of the particles composing
it. It appeared to be worth mentioning this mode of obtaining
mud larvee as its application on a large scale does not seem to
be generally employed. It should be remarked that small

116 WILLIAM BATESON.

Nemertines, &c., are usually found still suspended long after
most of the mud is precipitated. The water should then of
course be poured off and left to settle separately. The degree
to which any particular animals required may thus be easily
separated off from the rest is very great. The disadvantage of
such a method is that a certain number of larve are sure to be
broken in the stirring necessary to effect suspension. I have
little doubt that the larvee which were observed free-swimming
earlier than stage F were thus liberated from the egg-shell.

Preservation.—All my specimens of B. minutus were
obtained from Naples, being very kindly prepared for me by
Mr. Weldon with picric acid.

Most of the larve of B. Kowalevskii were placed for
less than a minute in corrosive sublimate sat. sol. two parts,
mixed with one part glacial acetic acid, washed with water and
successively passed through 380 per cent., 50 per cent., 70 per
cent., and 90 per cent. spirit. On the whole the results
given by this reagent were the best. The softer parts, however,
are best preserved in those specimens which were treated with
Perenyi’s fluid one hour, then 90 per cent. spirit for twelve hours,
the 90 per cent. spirit being then changed. In the case of
adults preserved with Perenyi’s fluid, the fluid was changed
once or twice.

Osmic acid did not give good results, but probably this was
due to bad manipulation. The sections were cut in continuous
series with Caldwell’s automatic microtome.

List or Papers REFERRED TO.

1. Acassiz, ALEx.— Hist. of Balanoglossus and Tornaria,” ‘Mem. Amer.
Acad.,’ vol. ix.

. Batrour, F. M.—‘ Monograph on Elasmobranch Fishes,’ 1878.

3. Bateson, W.—“ Early Stages in Dev. of Balanoglossus,” ‘Quart. Journ.
Mier. Sci.,’ April, 1884.

4. Hatscnpx, B.—‘“ Stud. tb. Entw. d. Amphioxus,” Claus’s ‘ Arbeiten,
Wien, 1881.

5. Hatscnek, B.—“ Mitth. ib. Amphioxus,” ‘ Zool. Anz.,’ Sept. 29th, 1884.

iS)

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 117

6. Kowatevsky, A.—‘ Anatomie des Balanoglossus,” ‘Mem. Acad. Imp.
Sci.’ St. Petersburg, 1866.

7. LanxesterR, B, Ray.— New Points in Structure of Amphioxus,”
* Quart. Journ. Micr. Sci.,’ xv, p. 257.

8. Merscunrkorr, E.—“ Ueb. d. Metam. einiger Seethiere,” ‘Z. f. W. Z.,’

20, 1870.
9. Murscunixorr, E.— Ueb. d. Syst. Stell. v. Balanoglossus,” ‘Zool.
Anz.,’ 1881.
10. Scorr, W. B.—* Beitrage z. Entw. d. Petromyzonten,” ‘ Morph. Jahrb.,’
Bad. vii.

11. Spence, J. W.— Bau. u. Entw. v. Balanoglossus,” ‘Tag. d. Naturf.
Ver.,’ Miinchen, 1877.

12. Spencen, J. W.—*Z. Anat. d. Balanoglossus,” ‘ Mitth. a. d. Zool. Sta.
z. Neapel.,’ Bd. v, Hft. 3 and 4.

EXPLANATION OF PLATES IV—IX,

Illustrating the “ Later Stages in the Development of
Balanoglossus Kowalevskii, with a Suggestion as to
the Affinities of the Enteropneusta.”?

Complete List of Reference Letters.

a. Anus. Ac. Archenteron. A/. Alimentary canal. a. 7. Anal lappets.
bc.1, 2, 8. The anterior, middle, and posterior body cavities respectively. The
letters Z and 7 affixed to these letterings denote that the parts are of the left
or right side. 47. Branchial chamber. C. Apical tuft of cilia. C. WV. S. Cen-
tral nervous system. c.g. Groove between the collar and the trunk. cil,
Transverse band of cilia. Cl. Collar. CU’. The posterior fold of the collar,
which eventually forms the operculum. C7/.sé. Skinof collar. D. 4. v. Dorsal
blood-vessel. D. mes. Dorsal mesentery. D. x. s. Dorsal nervous system.
dig. Digestive tract of alimentary canal. #. Ectoderm. ex. g. Refractive
granules in mesoblastic cells. /- Mesoblastic fibres. g.s, Gill-slit. g.s.7.
Branchial supporting rod. g/. Proboscis gland. gi. s. Sac of proboscis gland.
gn. Ganglion (?) cells. #. Hypoblast. At. Heart. nt. Intestine. 1. 7.
Lateral rods of the skeleton. 7. Lumenof notochord. I’. M". M'. Meso-
blast derived from the anterior, middle, and posterior pouches respectively.
Mo. Mouth. msc. Muscle-fibres. mz. Mucous gland. z.s. Nervous system
n. enl. Neural canal. We. pr. Pore by which the notochord lumen opens into

118 WILLIAM BATESON.

the pharynx. Neh. Notochord. JV. pr. Neural pore. Op. Operculum.
pkt. Fibrous substance of the nervous system. P. pr. Proboscis pore.
P.h.b.c. Perihemal body cavity. P. sk. Skin of proboscis. Sep. Septum
between the horns of the anterior body cavity. SA. Sheath of notochord.
Skr. Sucker. Sé. Skin. S.7. Supporting rod. 8%. Skin. Sp. Tissue-space
in the proboscis cavity. és. Testis. V.vs. Ventral vessel. V. 2. s. Ven-
tral nervous system. Viv. Valve of gill-slit. «. Pyriform cells of splanch-
nopleure of middle body cavity.

With the exception of Figs. 5 and 6, the outlines were all drawn with
Zeiss’s camera lucida. I have to thank Mr. Edwin Wilson of the Lithographic
Department of the Cambridge Scientific Instrument Company for drawing for
me two beautiful figures (Figs. 5 and 6) of the whole animal from preserved
specimens, and also for Figs. 1, 2,3, and 4, which he has prepared for me
from my own sketches, the original outlines of which were traced from living
specimens.

Fic. 1.—Whole animal seen from the side, immediately after the appearance
of the second pair of gill-slits. (Obj. A, oc. 2.)

Fre. 2.—Similar view of an older animal, with two gill-slits. (Obj. A, oc. 2.)

Fie. 3.—Similar view of a three-gill-slit larva. (Obj. A, oc. 2.)

Fic. 3a.—Posterior end of the same in a retracted state, seen in profile
(from a preserved specimen). (Obj. A, oc. 2.)

Fic. 4.—Side view of larva with five pairs of gill-slits. The fold of the
operculum covering part of the first gill-slit is semi-transparent. (Obj. A, oc. 2.)

Fic. 5.—Side view of preserved specimen with nine pairs of gill-slits.
Owing to the contraction of the body and the protrusion of some of the
valves, few only of these are visible. (Obj. AA, oc. 2.)

Fic. 6.—The adult animal (¢). (x 2 diameters.)

Fig. 7.—Longitudinal vertical section (not quite median) of a larva in
Stage F. (Obj. C, oc. 2.)

Fie. 8.—Cells of mesoblast of anterior pouch, from a transverse section of
a larva shortly after this pouch is closed off from the hypoblast. (Obj. F,
oc. 2.)

Fic. 9.—The same tissue from the posterior third of the proboscis of a
rather older larva, showing the proliferation and commencing differentiation of
the mesoblastic elements. (Obj. D, oc. 2.)

Fic. 10.—Section similar to Fig. 7, from a rather older larva to show
anterior, dorsal structures (Stage G—H). (Obj. D, oe. 2.)

Figs. 11—20 represent transverse sections of a larva in Stage G—H, with
the exception of Figs. 12 and 16, which were drawn under Obj. F, oc. 2. All
these figures were drawn under Obj. CC, oc. 2, In most of these figures the
ectoderm is only indicated ona short arc of the circle of the whole section,
They are numbered from before backwards,

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSKII. 119

Fic. 11.—Transverse section of proboscis cavity. Mesoblastic elements
distributed nearly uniformly all round the interior.

Fie. 12.—Portion of these mesoblastic elements more highly magnified, to
exhibit the differentiations.

Fic. 13.—Section taken behind Fig. 11. The mesoblastic layer is thinner
dorsally than elsewhere.

Fig. 14.—In this section the septum separating the two horns of the cavity
is reached.

Fic. 15.—Still further back the first rudiment of the proboscis gland is
reached (cp. Fig. 29).

Fie. 16.—The rudiment of the gland lying in the septum more highly
magnified.

Fic. 17.—Section across the proboscis stalk. The anterior end of the
notochord is reached. The back of the gland is nearly passed. The meso-
blastic horn of the left side is apparently divided into two parts, this appear-
ance is due to shrinking.

Fig. 18.—The lumen of the notochord is reached. The extreme ends of the
two anterior mesoblastic horns and the posterior apex of the left horn from
the first cavity are all cut in this section. (The irregular folds of skin
are due to the contractions of the body; it will be understood by comparing
the figures of the whole animal that only the central part within the folds is
the real stalk of the proboscis.)

Fic. 19.—The section crosses the end of the archenteron, lying in front of
the mouth. (The whole of this part of the archenteron becomes eventually
pushed forward to form the notochord.)

Fic. 20.—The mouth is here traversed, as also the anterior end of the
nervous system. (A space, due probably to shrinking, is visible in the dorsal
mesentery.)

Figs. 21—29 are transverse sections of a larva, slightly older than the fore-
going. Fig. 25 was drawn under Zeiss’s Immersion 2 and oe. 2; the others were
drawn under Obj. D and oc. 2. They are numbered from before backwards.

Fie. 21.—Section taken just behind the mouth, The lumen of the noto-
chord is here shut off from the archenteron.

Fic. 22.—The notochord still open to the archenteron.

Fic, 23.—The nervous system is attached to the skin.

Fic. 24.—The nervous system is already nearly separated from the skin.

Fic. 25.—Part of the foregoing enlarged, to show the peculiar pyriform
cells of the splanchnopleure (2).

Fic. 26.—Nervous system still in the skin,

Fic. 27.—The nerve-cord is separated from the skin.

Fic. 28.—Two parts of the middle body cavities may be here seen separat-
ing from the rest, probably forming part of the perihemal cavities,

120 WILLIAM BATESON.

Fic. 29.—The anterior ends of the third pair of body cavities are here cut
as a solid mass of mesoblast on each side.

Fic. 30.—A longitudinal vertical, nearly median, section of a larva, in the
same stage as that shown in Figs. 21—29. The differentiation of the walls of
the digestive tract may be here seen.

Figs. 31—44 are from transverse sections of a larva which has just
acquired the second pair of gill-slits. They are numbered from before
backwards.

Fic. 31.—Transverse section of the proboscis cavity. The loose tissue in
the sac of the gland is shown. The membrane which is deposited round it is
visible (ep. Fig. 47). (Obj. D, oc. 2.)

Fic. 32.—Small portion of skin and mesoblast on a larger scale, to show
structure of the nervous layer. (Obj. F, oc. 2.)

Fie. 33.—Region behind that shown in Fig. 31. (Obj. D, oc. 2.)

Fic. 34.—Through the proboscis stalk. The anterior horns of the middle
body cavities are here cut.

Fic. 35.—Through the proboscis stalk and the anterior phlange of the
collar which forms the lower lip.

Fie. 36.—Through the anterior end of the nervous system (in the region
of the mouth), showing the manner in which the lumen arises in the
nerve-cord.

Fic. 37.—Through the anterior part of the collar, showing the nearly com-
plete separation of the notochord with the hypoblast.

Fic, 38.—Section taken behind the previous one. The nervous system is
here separated from the skin.

Fic. 39. Through the junction of the lumen of the notochord with that of
the gut. The skeletal rods, which here bend downwards, backwards, and
then slightly forwards, are therefore cut twice on each side.

Fic. 40 is taken rather in front of the branchial sacs; it shows the two
anterior horns of the posterior body cavities, which form the perihemal
cavities.

Fie. 41,—Section through the gill-sacs in front of the clefts. The nervous
system here is fused to the skin dorsally.

Fic. 42.—Through the extreme posterior end of the second body cavities,
and the anterior end of the ventral blood-vessel and nervous cord.

Fic. 43.—(Section not quite transverse.) Through the left gill-slit.

Fie, 44.—Section taken through the extreme posterior end of the branchial
region of the gut, showing how this overlaps the digestive region. ‘The dila-
tation in the sides of the branchial region here shown are parts of the second
pair of gill-slits.

Fie. 45.—A longitudinal vertical section of the whole animal. (Two gill-

DEVELOPMENT OF BALANOGLOSSUS KOWALEVSEKIT. 121

slits.) (The section is not truly vertical, as*it cuts the gill-slit.) It exhibits
the relation of the notochord and other parts. (Obj. CC, oc. 2.)

Fic. 46.—By an oversight no figure bearing this number appears in the
plates. The figure referred to as such in the text at pages 85, 98, and 103,
is Fig. 45.

Fic. 47.—A transverse section of the extreme tip of the notochord, &c.,
in the larva from which Figs. 31—45 were taken. It shows the histology of
the notochord and the arrangement upon it of the mesoblastic tissues, which
are pushed in by it. (Obj. D, oc. 2.)

Fic. 48.—Transverse section across the proboscis pore of a larva with three
gill-slits. The two skeletal rods are here fused and have attained a considerable
size. (Obj. F, oc. 2.)

Figs. 49—53 represent transverse sections taken from B. Kowalevskii,
at the stage of four pairs of gill-slits. (When the remaining structures are
dealt with a fuller explanation will be given of these and of the subsequent
figures ; on the present occasion they are only introduced to explain the account
of the notochord given in the text.) Figs. 49—53 are numbered from before
backwards.

Fies. 49 and 50 illustrate the histology of the anterior end of the notochord.
(Obj. F, oc. 2.) These sections are in front of the heart.

Fic. 51 shows a section of the whole proboscis, to illustrate the relations of
the parts. The body cavity may be seen to be nearly filled up with muscle-
fibres and connective tissue, with the exception of a small central space, in
which lies the notochord bearing the central mesoblastic structures, viz. the
heart and proboscis gland with its sac. (Obj. C, oc. 2.)

Fic. 52 exhibits the central structures of Fig. 51. (Obj. F, oe. 2.)

Fie. 53.—Here the lumen of the notochord is reached. At this point the
sac of the proboscis gland is attached dorsally to the skin of the proboscis.
(Obj. F, oc. 2.)

Fig. 54.—Transverse section of proboscis stalk of an older animal, taken
behind the epiblast sac of the proboscis pore, the back of which appears in
section. The skeletal rod has still in this region two central “cores.” (Obj.
D, oc. 2.)

Fic. 55.—A transverse section of the notochord of an adult B. Kowa-
levskii, taken in front of its lumen (ep. Fig. 57). (Obj. CC, oe. 2.)

Fie. 56.—Transverse section of the same as foregoing, through the dilated
lumen in front of the skeletal rod.

Fic. 57.—Longitudinal vertical median section of the back of the proboscis
and the front of the collar of B. Kowalevskii, to show the relation of the
notochord. The other parts are diagrammatic. (Obj. A, oc. 2.)

Fic. 58.—Transverse section of the junction of the proboscis stalk with
the collar. (Semi-diagrammatic.) Exhibits relations of the notochord and its
sheath to the skeletal rods, nervous system, &c. (Obj. A, oc. 2.)

122 WILLIAM BATESON.

Fie. 59.—A diagram of a transverse section taken through the anterior
region of the collar, to show the relation of the parts figured in Fig. 60.
(Obj. A, oc. 2.)

Fic. 60.—The dorsal structures of the anterior part of the collar shown in
Fig. 59, viz. the nervous system, notochord, perihzmal cavities, &c. (The gut
is torn away from the skeletal rod, presumably by shrinking.) The lateral rods
are here connected to the notochordal sheath. (Obj. D, oc. 2.)

Figs. 61—63 show transverse sections of parts of B. minutus.

Fic. 61.—The notochord in transverse section in front of its lumen. (Obj.
CC, oc. 2.)

Fic. 62.—The same in the region of the proboscis stalk.

Fic. 63.—Through the notochord, &., in the front of the collar, showing
the thickened dorsal half of the organ. (Obj. CC, oc. 2.)

ERRATUM.

In the body of the preceding paper (not in the Description of the Plates),
for Fig. 45, read Fig. 44, and for Fig. 46, read Fig. 45.

BARLY DEVELOPMENT OF RANA TEMPORARIA. 123

Some Notes on the Early Development of
Rana temporaria.

By

W. Baldwin Spencer, B.A.,
Scholar of Exeter College, Oxford.

With Plate X.

Tuer following work has been carried on chiefly in the
laboratory of the University Museum, Oxford; and I must
here acknowledge the kindness and assistance received from
Professor Moseley.

This paper deals firstly with the question of the fate of the
blastopore, and secondly with some points in connection
with the early development of the cranial nerves. I hope
before long to publish a further paper dealing with the latter
subject.

(1) Fare or THE BLastopore.

Up to very recent times it was stated, in accordance with the
well-known investigations of Gétte on Bombinator and Scott
and Osborne on Triton, that in both anurous and urodelous
Amphibians, the blastopore was enclosed by the growth of the
neural! folds, and thus formed a means of communication

1 Would it not be much simpler, if instead of using the term “ medullary ”
in connection with the development of the central nervous system, the word
‘“‘ neural” were used throughout? We should then have a complete, uniform
series of terms, viz. neural plate, neural folds, neural groove, neural canal,
neural ridge, and also neurenteric canal. In this article I have adopted the
above nomenclature.

124 W. BALDWIN SPENCER.

between tae neural and alimentary canals, whilst the anus was
subsequently formed as a proctodeum.

Miss Johnson,! however, has shown that the neural folds do
not thus enclose the blastopore in Triton, but that in this form
it remains open and forms the permanent anus.

Some little time previously Oskar Schulze published an
account of his investigations with regard to the early develop-
ment of Batrachians, and his paper is accompanied by a careful
series of drawings, which, however, consist exclusively (save
one small diagrammatic section) of external views of Rana
fusca.

He states? that the blastopore closes up, and that the anus
is formed as a proctodeum very closely behind the posterior
end of the neural folds.

As before said, however, he figures no sections, and more
lately an investigation of the egg of Rana temporaria, both
by means of external views and of numerous series of consecu-
tive sections, has given me a very different result, and one
which differs also in important details from that described by
Miss Johnson for Triton.

The neural folds, as is well known, stretch back on the dorsal
surface as far as the blastopore, and though but very slightly
raised in this part they appear to pass round and join each
other behind, as seen in figs. 2 and 3.

Figs. 1, 2, and 3 show different stages during the growth of
the folds, and in the last of these they are seen to have met,
though the line of union is distinctly marked, and—most
important—the blastopore is not enclosed.

So far the account agrees with that of Gotte for Bombinator,
the figures from which are copied in Balfour’s ‘Embryology.’
When this stage has been reached, however, according to
Gitte, and after the blastopore has remained open to the ex-
terior for some little time, the neural folds continue to grow
and enclose it, whilst still later a proctodeeum is formed some
distance anterior to this upon the ventral surface.

1 * Quart. Journ. Mic. Sci.,’ Oct., 1884.
2? « Archiv. fiir Mikr, Anat.,? Oct., 1883, part i.

EARLY DEVELOPMENT OF RANA TEMPORARILA. 125

I have, however, in Rana, been unable to find any trace of
this closure, and in fig. 4 is given a view of the ventral surface
of an older embryo, in which the tail is just beginning to grow
out, and the line of union of the folds is but faintly marked,
whilst at the end of the latter, and occupying the same position
as in figs. 2 and 3, is yet the blastopore.

At this stage the line of union may or may not be traceable,
but the aperture retains the same relative position, and as
growth proceeds remains open, and can be traced through still
older specimens until the adult stage is reached.

This gradual transformation is shown by external views in
figs. 1—4, whilst it is fully confirmed by the series of sections
in figs. 5—15.

Figs. 5, 6, and 7 represent transverse sections through an
embryo of the age shown in fig. 1, whose neural folds are yet
open.

Fig. 7 is the most anterior section, and shows the open
neural groove on the dorsal surface, while the alimentary canal
is cut in section in the middle of the yolk.

Fig. 6 represents a more posterior section through the neural
groove dorsally and the blastopore ventrally, while in fig. 5
the two folds are cut through as they pass round the posterior
end of the egg. (The section is oblique, and hence more is cut
through on one side than the other.) The sections show
that the neural groove runs right back to the blastopore.

Figs. 8—11 are from similar sections of an older embryo
(such as fig. 3 represents), whose neural folds have met, their
line of union being seen in the most posterior section (8), while
one (9), just anterior to this, cuts through the posterior part
of the neural canal which runs round the hinder part of the
egg to open at the blastopore. Owing to the direction in which
it runs a transverse section, such as is represented in fig. 9,
cuts through a considerable part of its length.

The two anterior sections show the neural canal dorsally
and the alimentary canal ventrad of this.

After this stage has been reached a further important de-
velopment takes place; the hinder part of the neural canal,

126 W. BALDWIN SPENCER.

which opens into the blastopore, becomes closed though the
blastopore itself remains open. This apparently is caused by
growth of the epiblast cells lining the neural canal, and, inas-
much as they contain much pigment, the position of the former
canal, connecting the neural and alimentary canals, is plainly
indicated by a line of dark cells seen well in section.

Figs. 12—14 represent transverse sections through an embryo
of the age of fig. 4, in which the primitive blastopore still opens
into the alimentary canal, but yet no open connection exists
between this and the neural canal, which posteriorly ends in a
solid cord of cells. At this period, as is well seen in fig. 15,
which represents a longitudinal vertical section of an embryo,
there is, at the posterior end around the blastopore, a fusion of
the different cell layers. Into this fused mass appear to enter
the cells of the external epiblast, of the neural canal, of the
notochord, of the hypoblast of the alimentary canal, and of the
yolk, whilst at a slight distance anteriorly the mesoblast grows
out of this.

Thus both sections and external views lead to the same con-
clusion, that in Rana, as in Triton, the blastopore is transformed
into the permanent anus, though there is the not unimportant
difference between the two, that in Triton no connection exists
between the neural and alimentary canals, whilst such a struc-
ture is well marked in Rana.

Balfour! (after Gotte) figures a longitudinal section of
Bombinator at a stage considerably after the neural folds have
met and fused, and when, according to this older theory, the
blastopore has been enclosed and a neurenteric canal formed.
The same section shows the formation of a proctodzum, and
the presence of a so-called post-anal gut. In no section out
of the numerous series cut have either of these structures been
seen in Rana, and yet, inasmuch as, by means of dorsal growth,
the blastopore is carried round the posterior end till it lies
some little distance anteriorly on the ventral side, there is a
time at which the hinder end of the neural canal opening into
the blastopore occupies exactly the position of the post-anal

1 ©Comp. Embryolog.,’ vol. ii, p. 107.

EARLY DEVELOPMENT OF RANA TEMPORARIA. 127

gut of Gotte: not only is this the case, but the blastopore also
is situated in precisely the same position in which, according
to him, the proctodeeum is being formed.

May it not thus be possible that what Gotte calls the post-
anal gut, and which, according to him, closes up after forma-
tion of the proctodzum, is in reality the posterior part of the
neural canal which in early stages opened into the blastopore,
but which, later on, disappeared ?

It is further rather difficult perhaps to say whether, strictly
speaking, a neurenteric canal is present in Rana, as this term
is usually used in connection with the enclosure of the blasto-
pore, and when this itself forms a means of communication
between the alimentary and neural canal. Perhaps, however,
the term “ neurenteric canal ”’ may be applied to all structures
which allow of communication between the two canals, and
which itself, in subsequent development, closes up and dis-
appears: using the term in this sense one is clearly present
and well developed in Rana.

(2) Some Points ConnEecTED witH THE Harty DeEvetor-
MENT OF THE CRANIAL NERVES. :

The following are a few notes connected with the early
development of the cranial nerves of the Amphibia, and I must
acknowledge my indebtedness to Professor Marshall for kind
assistance, and for his permission to use the laboratory and
materials of the Owens College.

Sections of eggs of Rana as early as the close of segmenta-
tion show that the epiblast is formed of two distinct layers of
cells, the outer of which is one cell deep, whilst the inner
varies much in thickness in different parts and continues to do
so during development.

Of these the first is the epidermic and the second the nervous
layer, and the development of the whole of the nervous system,
save the lining of the neural canal, is concerned solely with
the latter.

On what will ultimately be the dorsal surface of the embryo

128 W. BALDWIN SPENCER.

is formed the neural plate by a great proliferation of cells in
the nervous layer; this plate becomes first of all grooved
longitudinally by the primitive groove, and then in the well-
known way the neural folds grow up dorsally, enclose the
neural groove, and finally, after meeting each other, the neural
canal.

During this course of development the greatly thickened
neural plate as it becomes transformed into the walls of the
neural canal retains its primitive connection with the nervous
layer of the epidermis as is well shown in figs. 7, 11, 16, &e.;
in the first of these the neural folds have not yet fused dor-
sally and the groove is wide open.

The axolotl differs, however, in one respect from the frog,
agreeing with the newt in having at first the epidermis of one
cell thick, though after closure of the neural folds the two
layers appear, and further development seems to be similar to
that of Rana.

This inner nervous layer is intimately connected with the
development not only of the central nervous system, but also
with that of the sense organs of the body, the auditory sac,
the olfactory organ, the sense organs of the lateral line, and,
most important of all, it is, as I hope to show, intimately related
to the formation of the peripheral nervous system.

Without taking the latter into account at the present
moment there may be said to exist in the Amphibian embryo
a complete superficially placed nervous sheath out of which
not only the central nervous system, but all the sense organs
of both head and trunk are formed and which gradually dis-
appears as these reach their full development.

The following notes refer to the origin of the cranial nerves,
and I hope shortly to publish a complete account of these and of
the spinal nerves. Owing tothe great difficulty in distinguish-
ing the cells of the various germinal layers at early stages it
is no easy matter to ascertain the manner in which the nerves
develop and in the sections figured the mesoblast has been
omitted for the sake of clearness.

Before the closure of the neural canal no development of

EARLY DEVELOPMENT OF RANA TEMPORARIA. 129

nerves can be perceived; there is simply the nervous sheath of
the epiblast surrounding the whole body and connected with
the lateral edge of the neural plate, and(as this gradually bends
up on each side) with the dorsal lips of the neural groove
(fig. 7), and finally, with the dorsal surface of the neural canal
(figs. 11 and 14).

In the chick! before closure of the neural canal a neural
ridge is present on each side of the brain, and from this as
outgrowths the nerves are formed; in Elasmobranchs,” though
developed somewhat later, a well-marked neural ridge is present
and the origin of the peripheral nervous system apparently
corresponds closely with that of the chick, but in Amphibia I
have been unable to discover any such structure as a neural
ridge, and it is only when the neural folds have met and fused
completely, and the neural canal quite separated off from the
epidermic layer that the earliest rudiments of nerve appears.

This earliest appearance does not assume the form of a
direct outgrowth from the substance of the neural canal, but
a series of consecutive transverse sections shows that along
certain lines the cells of the nervous layer proli-
ferate, and it is by this proliferation that the rudi-
ments of the cranial nerves are laid down.

This is most clearly seen in the case of the trigeminal and
facial nerve, and figs. 16—20 represent stages in the develop-
ment of the former nerve.

In fig. 16, on the left side, the nervous layer of the epi-
dermis is seen to have proliferated (for, save at the part where
nerves are formed and along the lateral line, it is only one cell
thick on the sides of the embryo), and it is seen further
that this proliferation extends for almost the whole length of
the side.

The section is an oblique one so that one side passes through
the optic vesicle, and here the nervous layer is only one cell
thick except where at the level of the lateral line the very
front part giving rise to the Gasserian ganglion is cut through.

1 Marshall, ‘ Quart. Journ. Mic. Sci.,’ vol. xviii, 1878.
2 Balfour, ‘Monograph on Elasmobranch Fishes,’ London, 1878.

9

130 W. BALDWIN SPENCER.

Section 19, which is taken from an axolotl, shows the same
proliferation, and also that this is greatest at the level of the
lateral line. In course of development the string of cells thus
formed becomes gradually separated off from the nervous layer
of the epidermis, which retains its normal thickness of one cell
and for some time afterwards the exact boundary of the nerve
is ill-defined, while the mesoblast grows in between it and the
epiblast, the only point at which it remains connected with the
latter being that at which the Gasserian ganglion is developed.

This is seen in section 17, where the main strand of the tri-
geminal is seen separated from the epiblast, while in fig. 18, a
slightly more anterior section, the Gasserian ganglion is yet
connected with the epiblast ; in fig. 17 the nerve should be
represented as lying somewhat nearer to the surface.

In further development the whole nerve and ganglion comes
to hie within the mesoblast, and, as seen in fig. 20, the latter
quite loses its connection with the epiblast.

This development of the ganglia at the level of the lateral
line, and the fact of their long connection with the epiblast at
this point, when all the rest of the nerve has been separated
off, is of great interest in connection with certain points in
the development of the Elasmobranch nerves to be shortly
noticed.

With regard to the development of roots, I hope to be able
soon to publish some detailed account. At the earliest period
at which they can be recognised they appear to arise from the
dorsal summit of the brain, and, as shown in figs. 16 and 19,
to originate by proliferation from the nervous layer, which
afterwards separates entirely from the brain, and can be traced
running right across the head dorsally.

In the region of the trunk, a considerable period after the
cranial nerves are well formed and recognisable, there seems
to be no development of spinal nerves, though the nervous
sheath is clearly developed, and in this the lateral line.

Through the kindness of Dr. Beard I have been enabled to
examine several beautiful series of sections of Elasmobranch
embryos, and he has also allowed me to introduce into this

EARLY DEVELOPMENT OF RANA TEMPORARIA. 131

article one or two points of interest derived from the study of
them, and which are of some importance in connection with
the development of the cranial nerves.

They are, moreover, conclusions at which Dr. Beard has
himself also arrived.

Fig. 21 represents a transverse section through the head of
an Elasmobranch embryo, and, owing to cranial flexure, the
three divisions of the brain are all cut through. Arising from
the dorsal surface of the hind brain may be seen the two rudi-
ments which will give rise in development to the trigeminal
nerve. These arise apparently quite independently of the
epiblast, with which, at this early stage, they have no connec-
tion, but are connected solely with the nervous matter of the
neural canal.

Figs. 22, 23, and 24, however, are similar sections through
the head of a somewhat older embryo, the first-mentioned
being the most anterior section, and the other two being cut
at slight intervals posterior to this. In these three is seen
part of the course of the trigeminal nerve, which at one point
has become clearly fused with the epiblast. It is at this point,
after the fusion has taken place, that the Gasserian ganglion is
formed.

In the sections the cells of the epiblast at this point seem to
have undergone considerable proliferation, and an examination
leads to the conclusion that the Gasserian ganglion is, at all
events in part, formed directly from the epiblast.

The importance of this origin and relation to the epiblast of
the Gasserian ganglion, and the fact that the same development
takes place in the case of the ganglia of the third and seventh
nerves—in that of the ciliary ganglion the development is par-
ticularly clear—becomes still more important when taken in
connection with the particular part of the epiblast with which
the ganglia are so intimately connected in early stages.

The ganglia arise along the level of the lateral line
continued on to the head.

Professor Marshall has previously described! the ciliary and

1 “Qn the Head Cavities and associated Nerves of Elasmobranchs,”

132 W. BALDWIN SPENCER.

Gasserian ganglia as arising from the first as swellings of the
third and fifth nerves respectively, which are, from the earliest
time of their appearance, hemmed in between the first and
second and second and third head cavities. This description
must now be modified, as primitively these ganglia arise in
immediate connection with the epiblast, and only come to
occupy their previously-described position at a later stage of
development.

This curious origin of the ganglia of the cranial nerves points
strongly to the conclusion that primitively they arose as
ganglia of the sense organs of the lateral line in the
head, and that their present position and nature must there-
fore be regarded as a secondary, and certainly not primitive,
condition.

In passing, I may just notice that on this supposition an
explanation is offered as to the origin and meaning of the two
curious branches! which unite respectively the ganglia of the
fifth and seventh and fifth and third cranial nerves; they may
be regarded as the persistent parts of the lateral nerve which
united the ganglia of the sense organs along the lateral line in
the head, and which, separating from the skin, have come in
the course of development to occupy a much deeper position,
together with the ganglia, with which they preserve their
primitive connection.

The development (though taking place, partly at all events,
directly from the epiblast) of the ganglia and nerves above
given, varies considerably and in very important points from
that given by His for the chick.

According to this investigator’ the ganglia are developed
from an “intermediate cord” (Zwichenstrang), which is de-
veloped out of the floor of an “intermediate groove”
(Zwichenrinne), which is itself derived from the epiblast, and
not from the neural folds whilst these are closing over.

‘Quart. Journ. Mic. Sci.,’ Jan. 1, 1881; also Marshall and Spencer, “ Obser-
vations on Cranial Nerves of Scyllium,” ‘Quart. Journ. Mic. Sci.,’ July, 1881.
1 See Marshall and Spencer, op. cit., July, 1881, fig. 10, We’ and Ne.
? «Arch, fiir Anat. und Phys.,’ 1879.

EARLY DEVELOPMENT OF RANA TEMPORARIA. 135

The position of this “ Zwichenstrang” varies in different
parts of the body and in the head where it lies between the
neural canal and the epiblast; after uniting with the central
nervous system! it gives origin to the Gasserian, auditory,
glosso-pharyngeal, and vagus ganglia.

This origin hence differs essentially from that given above
in Elasmobranchs, where the nerve first grows out of the brain
(i.e. from the neural ridge), and only subsequently fuses with
the epiblast where the ganglia are formed, and, moreover, this
fusion takes place at a very different level from that described
by His as occurring in the chick, and shown by him? also in
in the section which he figures of Scyllium. He also draws
two sections of frog embryos, and marks on them the position
of the “ Zwichenrinne,” but his figures do not show the very
clear double nature of the epiblast, and it is to this that is due
the method of development of the peripheral nervous system
above described.

It is possible that the condition which obtains in the
Amphibia* may be an exceedingly primitive one. ° The pos-
session of what must be regarded as a complete nervous sheath
points in this direction, and the development in such forms as
the chick and Elasmobranch, where the epiblast does not sepa-
rate into its two constituent parts, may be regarded as a con-
siderably modified one. It is important to notice also in this
connection that, where in Elasmobranchs the nervous layer of
the epidermis may be regarded as most developed—that is about
the level of the lateral line—the cranial nerves here fuse with
the epiblast, and at the point of fusion the ganglia are
produced.

Possibly the neural ridge which grows out from the central
nervous system may be taken as representing, in a highly-
modified form, the nervous layer which in Amphibians sur-

1 Op. cit., figs. iil, a—*

2 Op. cit., fig. xi, 2.

3 It is exceedingly likely that in Teleostei and Lepidosteus where the epi-
blast is also double, that the peripheral nervous system will be found to
originate in the same way.

134 W. BALDWIN SPENCER.

rounds the whole body. In Elasmobranchs the whole epiblast
does not divide into two layers, and hence the nerves must be
developed in some different way. After formation of the neural
canal the nervous matter of its walls grows very rapidly, and
gives off on each side the neural ridge, from which as lateral
outgrowths the nerves are formed by cell proliferation, the
parts of the ridge not used in development of the nerves disap-
pearing, just as in the Amphibia, after formation of the nerves
and sense organs, the remainder of the nervous layer gradually
atrophies, and finally disappears as a distinct structure.

This will, at all events, explain the fact of there being a con-
tinuous neural ridge along the dorsal surface of the central
nervous system, the intermediate parts of which disappear after
formation of the nerves.

The proliferation of nerves in Amphibia shows a remarkable
resemblance to that of the lateral and pedal nerve-cords which
has recently been described by Kowalevsky as occurring in
Chiton.! Fig. 25 is copied from one of his figures (fig. 60)
and shows the thick epiblast on the ventral surface giving rise
by simple proliferation to the nerves, and when compared with
figs. 16 and 19 of Amphibian sections the process will be seen
to be an essentially similar one in the two cases.

It is interesting further to observe that a neural sheath is
actually found existing throughout life in some of the inverte-
brates, in which sheath greater or less differentiation for the
formation of nerves takes place.

Thus in some Ceelenterates a rudimentary and ill-defined
sheath may be present; in the schizo- and palzo-Nemertines
one is well developed and in the latter les close to the epiblast,
whilst long lateral nerve-cords are developed from the sheath,
though they retain their connection throughout life, while
finally, Professor Marshall has suggested that the Echinoder-
mata may be supposed to have had a nerve-sheath immediately
below the epidermis surrounding the whole body, and out of
which both the nerve-cords of crinoids may be formed, the

1 Memoire No. 5, ‘Annales du Musée Histoire Naturelle de Marseille,’
** Embryogenie du Chiton Polii.”

EARLY DEVELOPMENT OF RANA TEMPORARIA. 185

dorsal one having been separated off whilst the ventral
still retains its primitive connection with the persistent neural
sheath.

The Amphibian embryonic neural sheath may possibly hence
represent a primitive condition, and the formation from it of
sense organs and nerves, resembling as it does that which is
found in certain Invertebrates, may reveal a more ancestral
process than the method of their formation in Elasmobranchs

and birds.;

DESCRIPTION OF PLATE X,

Illustrating Mr. W. B. Spencer’s Paper on “Some Notes on
the Early Development of Rana temporaria.”

Alphabetical List of References.

al, Alimentary canal. az. Anus. 4/. blastopore. ep. Epiblast. ep’. Epi-
dermic layer. ep". Nervous layer. f. 4. Fore brain. gass. Gasserian ganglion.
h. 6. Hind brain. Ay. Hypoblast. Jat. Lateral line. mes. Mesoblast. x.
Pedal nerve. 2’. Lateral nerve. x. c. Neural canal. 2.7. Neural folds.
n.g. Neural groove. z.7. Neural ridge. xe. c. Neurenteric canal. zo.
Notochord. o/f. Olfactory organ. op. v. Optic vesicle. sc. Suckers present
in embryo frog. ys. Yolk. 2. Second head cavity. V. Trigeminal nerve.
zx. Point of fusion of layers.

Fies. 1—4 represent external views of embryos of Rana temporaria.

Fig. 1.—From the dorsal surface. The neural folds have not yet closed,
and are especially wide open in the head region.

Fig. 2.—The posterior end of an older embryo, seen from the ventral
surface. The folds are just meeting, but not obliterating the blastopore.

Fig. 3.—A similar view of a slightly older embryo. The folds are still
closer, but the blastopore persists.

Fig. 4.—Ventral view of a considerably older embryo, in which the tail
is just beginning to grow and the line of union of the folds is but very
faintly marked, the blastopore persisting as the anus at its end,

136 W. BALDWIN SPENCER.

Fics. 5—7 represent transverse sections through an embryo of the age of
Fig. 1 in the posterior region.

Fig. 5.—The most posterior section and cut somewhat obliquely through
the medullary folds, showing the groove between these running to the
blastopore.

Fig. 6.—Cuts through the blastopore below and the open neural groove
above.

Fig. 7.—A more anterior section shows the groove still open above, and
the alimentary canal lying in the midst of the yolk-cells. The nervous
layer is seen continous round the body, and connected with that portion
which has become much enlarged to form the neural folds.

Figs. 8—]1.—Transverse sections through an embryo intermediate in age
between those in Figs. 3 and 4. The folds have closed over and the neural
canal opens into the blastopore.

Fig. 8.—The most external and posterior section shows the line of union
of the folds.

Fig. 9.—Cuts through the part of the neural canal which opens into the
blastopore.

Figs. 10 and 11 are more anterior sections and show the alimentary canal
and neural canal cut in sections, fig. 10 passing through the blastopore
below.

Fics. 12—14 represents sections through an embryo of the age of Fig. 4.

Fig. 12.—Most posterior section passing through the blastopore.

Fig. 13.—More anterior section, showing the alimentary canal into which
the blastopore has opened below, and a line of dark cells leading up to
the dorsal surface where the neural canal is seen dimly outlined. The
dark cells represent the open passage of Fig. 9.

Fig. 14 represents a more anterior section of the same embryo.

Fie. 15.—A vertical longitudinal section through an embryo of the same
age as in Fig. 4. The fused layers are seen at x, and the hinder part of the
nervous system is solid and has lost its opening into az., which corresponds
to the blastopore which has not closed up.

Fic. 16.—Transverse section through an embryo of Rana temporaria,
showing proliferation of the cells of the inner nervous layer of the epidermis
to form the fifth cranial nerve. On the right side the Gasserian ganglion is
seen in course of’ formation.

Fies. 17 and 18.—Transverse sections through a somewhat older embryo to
show the position of the fifth nerve after separation from the epiblast, except
at the point where the Gasserian ganglion is formed.

Fic. 19.—Transverse section through an axolotl embryo, showing the for-
mation of the fifth nerve on each side. a tae,

Fic. 20.—Transverse section through a much older embryo of Rana

EARLY DEVELOPMENT OF RANA TEMPORARIA. 137

temporaria, to show the complete separation of the Gasserian ganglia from
the epiblast.

Fie. 21.—Transverse section through the head of an Elasmobranch embryo,
to show the early origin of the fifth nerve. fap

Fics. 22—24.—Transverse section through the head of a somewhat older
embryo, to show the fusion of the fifth nerve with the epiblast and the forma-
tion at this point of the Gasserian ganglion.

The Figs. 21—24 are drawn from sections kindly lent to me by Dr. Beard.

Fig. 25.—From Kowalevsky. Transverse section through a developing
Chiton polii, to show the formation of the nerve-cords by proliferation.

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NOTES ON ECHINODERM MORPHOLOGY. 139

Notes on Echinoderm Morphology, No. IX. On
the Vascular System of the Urchins.

By

P. Herbert Carpenter, D.Sc.,
Assistant Master at Eton College.

EIGHTEEN months ago I published a note in this Journal,!
which contained a partial analysis of the excellent memoir by
Koehler upon the minute anatomy of the Echinoidea.? I was
led more particularly to discuss those of his observations which
dealt with the vascular system, and their bearing upon the
two theories as to its anatomical relations which are current
among morphologists. Many of these observations go far to
support the views of Ludwig respecting the general morphology
of the Echinoderm vascular system; while others seem as
decidedly opposed to them, and in favour of Perrier’s theory
as to the fundamental unity of the double vascular system of
an Echinoderm, and the communication of the so-called
“heart” with the exterior through the pores of the
madreporite.

At the same time I ventured to notice what appeared to me
to be certain weak points in Koehler’s chain of evidence—
points which it was desirable to have thoroughly established,
as being those on which the theory of Perrier and Koehler
mainly rested.

If the French zoologists are in the right we must either

1 “ Notes on Echinoderm Morphology, No. VI. On the Anatomical Re-
lations of the Vascular System,” ‘ Quart. Journ. Mier. Sci.,’ vol. xxiii, 1883,
pp- 597—616.

2 * Recherches sur les Hchinides des Cotes de Provence,” ‘ Ann. du Mus.
d’ Hist. Nat.de Marseille, Zoologie,’ Mémoire No. 3, pp. 1—167, pl.i—vii, 1883,

140 P. HERBERT CARPENTER.

admit that the results of their German colleagues, and more
especially those of Ludwig, are in many respects very incor-
rect; or else that the vascular system of an Urchin is far
more different from that of a Starfish than has been hitherto
supposed.

The zoological group Echinodermata is so extremely well
defined, and has so few direct relations with other classes of
animals, that we are justified in expecting a close correspon-
dence in fundamental characters among the different members of
the group. Readers of this Journal will not need to be reminded
of the detailed homologies which have been recently demon-
strated in the Apical Systems of the three classes of Brachiate
Echinoderms. The same may be said of the nervous system
throughout all the Echinodermata, and, as I fully believe, of the
vascular system too. But where one author tells us that the oral
blood-vascular ring of a Starfish is in direct communication
with an elaborate system of genital and visceral vessels beneath
the dorsal surface, while another asserts that the correspond-
ing structure in an Urchin communicates with the exterior
through the madreporite, it is difficult to avoid the suspicion
that further observations, conducted by the same method in
both cases, may reveal an error somewhere.

In the note to which I have referred allusion was made to a
few points of this nature, in the hope that the authors con-
cerned might take up the question again, so as to bring out
more clearly the points of agreement or difference between
them.

Stimulated by my criticisms of what I, rightly or wrongly,
conceived to be certain possibilities of error in Koehler’s treat-
ment of his subject, he has returned to it again with the fol-
lowing results! :—“ Quoiqu’il en soit de cette discussion, je
ne puis que maintenir les résultats auxquels je suis arrivé.
J’ai répété mes injections un assez grand nombre de fois vou-
lant vérifier les faits que j’avancais, surtout au sujet des dis-
positions sur lesquels Carpenter émet des doutes, pour croire

1 ©Quelques mots sur les relations du Systeme circulatoire chez les
Echinides,” ‘ Zool. Anzeiger,’ viii Jahrg., 1885, p. 83,

NOTES ON ECHINODERM MORPHOLOGY. 141

ne m’étre pas trompé.” To this I can make no further reply
than that the injection method should not be relied on too im-
plicitly in the decision of a disputed point of minute anatomy.
Apart from the divergent results of Perrier and Koehler
respecting the anatomy of the vascular system in the Urchins,
there is along series of statements about that of the Star-
fishes, which are principally based upon the results of injection,
and are hopelessly at variance with one another.

_ Besides maintaining the truth of his previous descriptions,
Koehler discusses some of the points wherein we differ. He
expresses himself as utterly unable to find the pharyngeal
blood-vessels which Teuscher described as uniting the oral
blood-vascular ring (auct) with the radial vessels; and he
says point-blank that these vessels do not exist,! although their
presence appeared as theoretically probable to him as it has to
me. For this reason I may have somewhat overrated the
value of Teuscher’s observations; but, on the other hand,
Koehler seems to me to have depreciated them very consider-
ably when he says:

J] dit qu’ayant remarqué sur les coupes du pharynx cing lacunes il a pensé
que ces lacunes correspondaient a cing vaisseaux, que ces cing vaisseaux
devaient probablement aller se jeter dans un anneau péribuccal et qu’ils
feraient ainsi communiquer cet anneau avec son vaisseau perinervien. Com-
ment? il ne le dit pas. Carpenter parle de suppositions dans sa note; on peut
juger par ce qui précéde la valeur réelle des observations de Teuscher dont il
défend les conclusions.”

Teuscher’s description? ofa horizontal section of the pharynx
(fig. 5) 1s as follows :

“Zwischen je zweien dieser Ligamente, auf der Mitte jeder Leiste,
erscheint an jeder derselben eine Gefassdffnung (47.). Nach meiner ueber-
zeugung gehoren diese Oeffnungen fiinf Blutgefassen an, welche nur aus dem
Blutgefassring entspringen konnen. Nach unten (fig. 6) sieht man diese
Gefasse sich von der Wand des Pharynx entfernen, um tber den an der
Mundbasis liegenden Nervenring (wr.) (wovon unten) hinwegzutreten.”

Now it does not appear to me likely that Teuscher can have

1 * Zool. Anzeiger,’ 1885, p. 80.
2 « Beitrage zur Anatomie der Echinodermen,” iv, ‘ Jenaische Zeitschrift,’
Bd. x, pp. 520, 521, Taf. xx, figs. 5, 6.

142 P. HERBERT CARPENTER.

inserted these vessels in the figures of his vertical and trans-
verse sections of the pharynx, without having seen something
which he might have mistaken for vessels. But, according to
Koehler, nothing of this kind is present; nor will anyone ever
discover such vessels, even with the eye of faith. ‘ Les deux
vaisseaux radiaux ne communiquent qu’avec l’un des deux
anneaux,” that, namely, which communicates with the exterior
through the water-tube and madreporite, and is generally
known as the water-vascular ring.

Unfortunately, however, Koehler’s statements upon this
point have not been supported by any figures; and in reply to
my remark to this effect Koehler says: “ En ce qui concerne
les figures, je crois en avoir donné d’assez nombreuses et
d’assez démonstratives, mais 4 propos de la circulation de
Voursin il m’a semblé inutile de représenter 4 nouveau des
dispositions déja figurées par Perrier.” But since the second
radial vessel (the blood-vessel, as I regard it) was entirely
unknown to Perrier, Koehler would have done well to give a
figure showing its (supposed) junction with the radial water-
vessel which was described and figured by Perrier.! Such
a figure would go far to support Koehler’s assertion, which,
if true, must necessitate a considerable change in the generally
received ideas respecting the morphology of the Echinoderm
vascular system. I presume that it would not be difficult to
obtain a series of sections through the part where the double
radial vessels “ become simple.” But the figure illustrating
this point, whether of an injected preparation or of a section,
has yet to be drawn; and we must content ourselves for the
present with Koehler’s bare statement of the fact.

He is surprised at my representing him as considering the
“‘ madreporic canal ” which runs from the organ of excretion of
Spatangus towards the madreporite as the water-tube. I
must apologise if I have misunderstood him; but I used the
word water-tube=Steincanal=canal du sable, as denoting the
vessel by which the oral vascular ring that supplies the

1 « Recherches sur l’appareil circulatoire des Oursins,” ‘ Arch. de Zool.,
Exp. et gén.,’t. iv, 1875, p. 621, pl. xxiv.

NOTES ON ECHINODERM MORPHOLOGY. 143

ambulacral vessels communicates with the exterior. I believe
this to be the generally accepted meaning of these three
equivalent terms.

Now Koehler’s injections passed out from the madreporic
canal to the exterior; while he describes its inner end as in
perfect structural continuity with the organ of excretion.1 He
speaks of “ le canal du sable, qui présente chez les Spatangues
une structure glandulaire sur une partie de son trajet ;”? and
the tubular communication of the organ of excretion with the
oral ring in which the radial (blood-) vessels originate is contin-
ually referred to by him® as the “canal du sable.” Thus, then,
the madreporic canal and its continuation through the organ of
excretion towards the oral vascular ring form the only commu-
nication between the latter and the exterior, according to
Koehler’s views. He himself calls one part of this line of
communication by the French equivalent for “ water-tube ; ”’
and I cannot see, therefore, why he is surprised at my supposing
him to take the same view of that other part of it which lies
immediately beneath the madreporite, and is described by
himself as opening to the exterior through its pores. In what
other way can the following sentence be explained? “ J’étu-
dierai plus loin les relations du canal du sable avec cet organe
(of excretion) et sa termination vers la plaque madre-
porique.”4

It is just possible that as Koehler does not believe in the
general independence of the water-vascular and blood-vascular
systems, the expression ‘‘ water-tube or stone-canal” has not
the definite meaning for him which is attributed to it by those
who regard the stone-canal as a part of the water-vascular

1 § Recherches,’ pp. 98, 99.

2 Thid., p. 110.

Ibid., p. 98. ‘*C, canal du sable,” on pl. i, figs. 1—3 ; pl. ii, figs. 6, 8,
10,11; pl. ii, figs. 14, 15.

* Op. cit., p.91. The italics are mine. If Koehler does not consider his
*madreporic canal” as the water-tube or stone-canal, he would have done
well not to call it by this name, which has been used by many writers instead
of stone-canal (Huxley’s ‘ Invertebrata,’ pp. 558, 576).

144 P. HERBERT CARPENTER.

system only, and would not give this name to any vessel con-
nected with either end of the ovoid gland.

I do not regret my remark, however, as it has drawn from
him a definite statement of his views; and if I interpret them
aright, I am glad to find them more in accordance with those
which I expressed in my previous note than I had any reason
to expect. He says:

‘* Je considére le canal du sable,! la glande et le canal madréporique chez le
Spatangue comme respectivement homologues au canal glandulaire, a la glande
ovoide et son conduit excréteur chez l’oursin, et que le canal du sable de ce
dernier est représenté chez le spatangue par le canal onduleux qui accompagne
’oesophage * plus le canal a épithélium cylindrique dont il était question tout
a Vheure. Ces deux canaux ne représentent que les deux extremités du canal
du sable dont la région moyenne aurait disparu et dont l’extrémité apicale
aurait perdu les relations qu’elle a chez |’Oursin avec la plaque madréporique.”

With the exception of the second half of the last sentence
this is precisely the position which I took up in my previous
note®. Our only point of difference appears to be the follow-
ing one. The canal with columnar epithelium is described by
Koehler, on the results of injection* as losing itself “ dans
les lacunes du tissu conjonctif.”’ Teuscher> spoke of it as
“Der Steincanal, welcher an seinem Cylinderepithel leicht
kenntlich ist; and he supposed it, though erroneously so, as
Koehler has shown, to be continuous with the tube which
unites the organ of excretion with the oral blood vascular-ring,
i.e. Koehler’s “ canal du sable.” 'Teuscher evidently assumed,
though he nowhere demonstrated, that it opened to the exterior
through the madreporite; but this connection is denied by
Koehler,® though he does not support his statements by figuring
any sections which show the gradual subdivision of this canal,
as described by him.

Like myself, however, he considers it as homologous with the
dorsal end of the water-tube (canal du sable) of Echinus;
1 This is coloured blue and lettered C, on pls. i—iii of Koehler’s memoir.

2 C’ of Koehler’s figures.
§ This Journal, vol. xxiii, pp. 607—609.
4 * Zool. Anzeiger,’ 1885, p. 82.

5 Loe. cit., p. 532.
6 « Recherches,’ p. 99.

NOTES ON ECHINODERM MORPHOLOGY. 145

while we both regard the ventral end of this water-tube as
represented in Spatangus by the incomplete sinuous canal
(C’ of Koehler’s figures) which lies along the gullet and starts
from the water-vascular ring (auctorum).

Koehler attributes no special functional importance to this
discontinuous water-tube ; whereas I have suggested that its
two ends may correspond respectively to the water-pores on
the disc of a Crinoid and the water-tubes by which the water-
vascular ring communicates with the body cavity. There
would be a difficulty about this, however, if Koehler is right
in saying that the tube with columnar epithelium, Teuscher’s
Steincanal, “ne débouche pas au dehors et ne tarde pas Ase
perdre au milieu des interstices du tissu conjonctif.””!

At the beginning of Koehler’s statement of his views which I
have just quoted, he uses the term “ canal du sable” for an organ
in Spatangus which he and I both believe to be homologous,
not with the similarly named vessel in Echinus, but with the
“ glandular canal” that unites the ovoid gland with the oral
blood-vascular ring of this type. I rather wonder, therefore,
at his giving the same name to two vessels which he does not
consider as homologous. According to his views they have the
same function, viz. that of effecting the communication between
the conjoint vascular system and the exterior, the work of the
glandular canal and water-tube in Echinus being performed
in Spatangus by the former alone, owing to the incomplete
development of that part of the system which is homologous
with the water-tube of Echinus. But would it not have been
more rational to call the ‘‘ canal du sable” of Spatangus by
the name of that organ, the glandular canal, to which it is
unquestionably both homologous and analogous in Echinus?
As it is, however, Koehler has preferred to use the name
“canal du sable” for this tube; and most readers would
therefore regard him as attributing to it the function of admit-
ting water into the vascular system. This, be it remembered,
must take place through the organ of excretion, if Koehler’s
views are the true ones. But, if he will pardon me for saying

' * Recherches,’ p. 99.
10

146 P. HERBERT CARPENTER.

so, there is still a certain amount of doubt respecting the
communication of this organ with the exterior. Even if this
be admitted, however, the fact still remains that the “canal du
sable” of Echinus, and the tube to which Koehler gives the
same name in Spatangus, do not communicate with the same
vascular ring. The former joins the water-vascular ring
(auct) which communicates with the tentacular system ; while
the latter is connected, not with the water-vascular ring of
Spatangus, but with the blood-vascular ring ; so that even if
the community of the two vascular systems be admitted, the
“canal du sable” of the two genera are not homologous, and
it therefore seems to me very undesirable that they should
both receive the name which is strictly applicable to one of
them only.

Partly in consequence of this want of precision in his
nomenclature, and partly by the omission of half a dozen
words in one of my sentences, Koehler has been led to
comment on what he believes to be an inconsistency between
two passages which he quotes from my previous paper. In the
first one,! I expressed the belief that the canal which joins the
excretory organ in Spatangus with the oral ring, and is
called by Koehler the “‘ canal du sable,” does not really belong
to the water-vascular system, but corresponds to the “ glan-
dular canal” of Echinus. Koehler? remarks that he had
already pointed out this latter homology, as indeed I had
stated in my earlier note. But then he goes on to say, “ Puis
i la page suivante Carpenter ajoute. ‘ Koehler regards the
stone canal of Spatangus as homologous with the glandular
canal of Echinus;’” and he endeavours to find in my subse-
quent remarks an expression of a theory inconsistent with his
belief and my own.

What I really wrote was—‘‘ Koehler regards the organ
which is commonly called the stone canal of Spatangus,
as homologous with the glandular canal of Echinus, on

! This Journal, vol. xxiii, p. 607.
* § Zool. Anzeiger,’ 1885, p. 81.
> This’ Journal, vol. xxiii, p. 609,

NOTES ON ECHINODERM MORPHOLOGY. 147

account of its relation to the excretory gland. It appears to
me, however, that Teuscher’s identification of the canal with
columnar epithelium, found by him at the apical pole, as the
water-tube, is more correct than Koehler’s view of what is
evidently the same structure.”

The words in italics were omitted by Koehler in his quota-
tion, and he thus entirely altered the meaning of my sentence.
I never referred directly to ‘‘the stone canal” of Spatangus,
as would appear from Koehler’s quotation; and had I done so,
I should never have given this name to a tube which commu-
nicates, not with the water-vascular ring (auctorum), but
with the excretory gland at one end, and with the oral blood-
vascular ring at the other. Not wishing to be dogmatic, I
avoided giving a definite name, as Koehler has done, to either
of the canals between the oral rings and the madreporite.
Koehler, however, first attributes to me an expression which I
purposely refrained from using (7.e. in propria persona),
and then interprets it according to his own ideas, which I am
far from sharing.

In writing of ‘the organ which is commonly called the
stone-canal of Spatangus,” I was merely referring to the
homologue of the glandular canal of Echinus. ‘Teuscher!
calls it the ‘‘ Steincanal,’”’ and noted the presence of a second
vessel by its side where it les along the gullet. Hoffmann?
gave this name to the two vessels together, not having been
able to differentiate them; while Koehler’ speaks of the “canal
du sable” as double along the whole length of the gullet, but
as single for the rest of its course until it joins the organ of
excretion, just like the glandular canal of Echinus, with
which both he and I believe it to be homologous.

I was perfectly right, therefore, in referring to it as the stone-
canal of authors. But as all agree in describing its connection
with the ovoid gland, and I do not believe that this organ

1 Loe. cit., p. 534.

2 “Zur Anatomie der Echinen und Spatangen,” ‘ Niederl. Archiv f. Zool.,’
Bd. i, 1871, pp. 85, 86.

> * Recherches,’ p. 92.

148 P, HERBERT CARPENTER.

communicates with the exterior, I certainly never spoke of it
as the stone-canal, as quoted by Koehler. On the other hand,
I believe that Teuscher was right in giving this name to the
canal with columnar epithelium at the apical pole. Koehler
agrees with both Teuscher and myself in considering it as
homologous with the dorsal end of the “ canal du sable” in an
Echinus. But he nevertheless prefers to give this name to
the homologue in Spatangus of a totally different structure,
viz. the glandular canal of Echinus. ‘This appears to me to
be very undesirable. The expressions stone (or sand) canal,
water-tube, Steincanal, canal du sable, &c., have hitherto been
understood as referring to the tube which joins the primary
“dorsal pore” of an Echinoderm larva with the developing
water-vascular ring and its tentacular apparatus. This
remains as a continuous tube in Echinus, alongside the
ovoid gland and its connections at bothends. In Spatangus,
however, only the extremities of this primary tube are left, the
middle portion having disappeared. Koehler admits this ;! but
nevertheless he transfers the name “canal du sable” to
another structure altogether, which, on his own showing, is in
no communication whatever with the water-vascular ring and
tentacular apparatus; and for the undoubted homologue of
which in Echinus he would not think of using the name
canal du sable.

We have already seen that Perrier’s statements respecting
the relation of the ovoid gland of Echinus with the exterior
have been repeated by Koehler, who now speaks of them as
“relations qu’on ne peut nier puisqu’on voit dans les injec-
tions, la matiére se répandre au dehors a travers les pores de
la plaque madréporique.’’® I hope that I shall not be con-
sidered discourteous if I still avow myself a sceptic upon this
point; and I will try to explain my reasons for my doubts.
They are of two kinds, partly theoretical and partly practical.

In the present state of morphological teaching it is the
general practice to put before the student a series of typical

1 *Zool. Anzeiger,’ 1885, p. 82.
? * Zool. Anzeiger,’ 1885, p. 81.

NOTES ON ECHINODERM MORPHOLOGY. 149

animals, with whose morphology he may make himself thor-
oughly acquainted. This method depends upon the very
general assumption that the other members of the group of
animals to which each type form belongs will resemble it in
all those essential characters by which it differs from the other
types. Next to the radial symmetry and the peculiarities of
the skeleton, there is, I take it, no feature which is so emi-
nently characteristic of Echinoderms as the presence of two
sets of radial vessels, the water-vessels and the blood-vessels of
authors ; and of two corresponding vascular rings, the one
communicating with the exterior through the stone-canal, and
the other connected with the cavities of the remarkable glan-
dular organ which was formerly considered as a heart.

Now the most careful observations which have yet been
made upon the Starfish (the typical Echinoderm of every
teacher) go to show, not only that the so-called water-vascular
and blood-vascular systems are fundamentally independent of
one another, but also that the latter does not communicate
with the exterior through the madreporite, as the former does ;
and I have a strong conviction that equally careful observa-
tions, conducted by the same rigorous methods, will show
that these characters exist in the Urchins. They have been
described as presenting themselves in Ophiurids and in Cri-
noids. But although the accuracy of these descriptions has
been called in question by the French zoologists, no proof has
yet been furnished that they areincorrect. Thus, for example,
Ludwig describes the single water-pore of Ophiurids as leading
(directly or indirectly) into the stone-canal; while the so-
called heart “endigt iiber der Innenseite der Madreporenplatte
neben der Stelle, an welcher sich der Steinkanal mit der
Madreporenplatte verbindet.!. He figures some selected hori-
zontal sections through the madreporite, which, as usual, fully
bear out his statements.

Then comes Apostolidés’? who tells us how “ Chez les

1 “Neue Beitrage zur Anatomie der Ophiuren,” ‘ Zeitschr. f. wiss. Zool.,
Bd. xxxiv, 1880, p. 351. Taf. xiv, figs. 1—3.

2 « Anatomie et Developpement des Ophiures,” ‘Arch. de Zool. exp. et
Gén.,’ vol. x, 1881, p. 25 (of separate copy).

150 P. HERBERT CARPENTER.

Ophiocoma le canal aquifére vient aboutir directement a
Vextérieur, par un pore unique sans canal. Le canal du pore
suit directement le canal aquifére, dont il n’est qu’un pro-
longement qui se rencontre chez les individus adultes. Chez
les Ophiothrix, les choses ont lieu comme chez lOphio-
coma nigra.” But then he goes on to tell us how in
Ophiothrix rosula it is easy to expose the heart or piriform
gland by slitting up the envelope which surrounds it and the
stone-canal ; and it is then ‘ impossible de ne pas voir la com-
munication directe de la glande piriforme avec l’extérieur.”
Farther on again he says, ‘Son conduit est extrémement
apparent, et ainsi aucune erreur ne peut exister sur ce point.”

But if the single pore-canal of the madreporite is the direct
continuation of the stone-canal, how can the duct of the
piriform gland open externally? Apostolidés is silent upon
this point; and his figures! (like that given by Perrier of the
corresponding parts in an Urchin’) merely show the termina-
tion of both “ duct” and stone-canal on the inner side of the
madreporite. There is no indication whatever that the former
opens externally through the pore, although Apostolidés’ injec-
tions have caused him to have no doubt whatever concerning
the existence of this communication. He tells us that he has
confirmed the results of his injections by the section method.
But he does not figure a single section showing how the duct
of the piriform gland opens externally ; and I much doubt
whether he or any one else will ever do so.

I feel therefore that we are fairly entitled to use our present
knowledge of the vascular system in the Brachiate Hchi-
noderms as a basis for criticising the descriptions of its
peculiarities in the Urchins which have been published by
Perrier and Koehler. The researches of these authors have
been principally carried on by means of injections, and not by
the section-method which has been chiefly employed in the
investigation of the Brachiate Echinoderms. Lach plan has
its advantages ; but it will be generally admitted that the

1 ¢ Arch. de Zool. exp. et Gén.,’ vol. x, pl. viii, fig. 6, and Pl. ix, fig. 8.
2 Thid., vol. iv, pl. xxiii, fig. 1.

NOTES ON ECHINODERM MORPHOLOGY. 151

former is less satisfactory, when used singly, than the latter ;
and that its results require to be checked by a careful
anatomical investigation before they can be trusted too im-
plicitly.

I am well aware of the danger of placing too much reliance
upon a theoretical morphology of Echinoderms: and I have so
often alluded to it in discussing the nervous system of Crinoids!
that I am not surprised to be told that my doubts as to the
accuracy of the French observations respecting the communi-
cation of the ovoid gland of an Urchin (or Ophiurid) with the
exterior are due to the influence of preconceived theoretical
ideas. But, all the same, I find it difficult to believe that there
should be such a difference between the vascular systems of
Urchins and Starfishes respectively as is revealed by a compari-
son of the results of Perrier and Koehler on the one hand, and
of Ludwig on the other. .

The statements of the French authors are based upon the
results of injections. So were the assertions of Hoffmann,
Greeff, and Teuscher respecting the communication of some of
the pores in the madreporite of a Starfish with the tubular
space which surrounds both the ovoid gland and the stone-
canal. Ludwig, however, working with four different species,
made sections of the madreporite in three different planes, and
dissected out its surroundings under a lens: “In allen Fallen
war das Resultat dasselbe. Nicht eines der Porencanilchen
fihrt wo anders hin als in den Steincanal (oder dessen
nachher zu besprechende ampullenformige Erweiterung); das
gesammte Canalsystem der Madreporenplatte steht
einzig und alleinin Zusammenhang mit dem Stein-
canal, aber nicht mit dem schlauchformigen Canal, noch
auch mit irgend einem anderen Hohlraum.’’?

This very definite statement has never been contradicted,
even by Messrs. Perrier and Poirier, who while asserting

1 The present position of this question has been described by a distin-
guished biologist as “ the triamph of physiology over morphology.”

2 “ Beitrage zur Anatomie der Asteriden,” ‘ Zeitschr. f. wiss. Zool.,’ Bd.
xxx, 1878, p. 104.

b52 P. HERBERT CARPENTER.

the glandular nature of the so-called heart of a Starfish! say
not aword respecting its communication with the exterior
through the madreporite, although Perrier had previously de-
scribed this communication in the Urchins. This omission is
a significant one. Then, again, Jourdain,? who seems to have
been the first to describe the glandular appearance of the sup-
posed heart, not only gave no account of its having any com-
munication with the exterior through the madreporite, but
positively asserted that the pore-canals of this plate have no
internal connection otherwise than with the water-tube, just
as described by Ludwig some years later.

The latter author devoted some attention to the dorsal ter-
mination of the ovoid gland of a Starfish, and he found that,
after passing through the aboral vascular ring, it entered
“die kleine Hohlung welche die Ampulle der Madreporen-:
platte enthalt . . . . Das Herzende durchsetzt diese Hohlung
(fig. 9) und befestigt sich dann schliesslich in ihr und zwar in
ihrem zumeist dem Centrum der Ruckenhaut zugekehrten -
Theile (figs. 10,11). Soweit meine Beobachtungen reichen,
gehért derjenige Theil der Hohlenwandung, an welchem sich
das Herz inserirt, nicht mehr der Madreporenplatte selbst an,
sondern dem unmittelbar daran anstossenden Bezirke der
Korperwand.””’

Let us compare with the above statements the description
given by Perrier and confirmed by Koehler respecting the
dorsal termination of the ovoid gland in an Urchin. Both
authors rely principally on the injection method. Perrier
tells us that ‘La matiére colorante, aprés avoir rempli la cavité
cardiaque, passe dans un canal qui fait suite 4 la pointe supé-
rieure du cceur et va remplir un espace infundibuliforme compris
entre la plaque madréporique et la membrane de revétement

1 «Sur Appareil circulatoire des Etoiles de mer,” ‘Comptes Rendus,’
March 6th, 1882, t. xciv, pp. 658—660.

2 “Recherches sur |’Appareil circulatoire de ’Etoile de mer commune
(Asteracanthion rubens),” ‘Comptes Rendus,’ t. lxv, 1867, pp. 1002—
1004.

3 Loe. cit., pp. 130, 131.

NOTES ON ECHINODERM MORPHOLOGY. 158

du test, qui, en ce point, n’est pas adhérente 4 la plaque mad-
réporique.” He then goes on to say that the pores of the
madreporite open into this space, which “semble étre tout
@abord une sorte de cloaque dans lequel viennent s’ouvrir le
canal du sable et le canal issu de la pointe supérieure de
Porgane que l’on considére comme un ceeur.”’!

Definite as these statements are, they appear to me to rest
upon insufficient evidence, as did those of Hoffmann respecting
the Starfishes. If the pores of the madreporite in an Urchin
really do lead into a cavity which lies beneath it, and receives
the ends both of the stone-canal and of the duct issuing from
the ovoid gland, Perrier or Koehler could surely have obtained
sections or other preparations? in proof of their assertions.
They may have done so; but, as the fact is one of considerable
importance, they would have done well to illustrate it by
figures. Ludwig figures several sections through the madre-
porite of a Starfish, and they completely bear out his statements
which I have quoted above. Had Messrs. Perrier and Koehler
done the same, the solution of the problem of the Echinoderm
vascular system would have been very materially advanced.

Ludwig’s remarks*® upon the possible fallacies of the injection
method are very much to the point, and if the internal connec-
tions of the pore-canals in the madreporite can be demonstrated
in a Starfish a similar demonstration is surely possible in the
case of an Urchin. But we have not had it as yet; and in the
absence of this much-to-be-desired proof of the statements of
MM. Perrier and Koehler I prefer to believe that the relations
of the ovoid gland to the madreporite are the same in the
Urchin as they are in the Starfish, according to Ludwig,
i.e., that the ovoid gland does not communicate with the
exterior.

I have therefore practical reasons, besides the purely theo-

1 * Arch. de Zool. Exp. et Gén.,’ t. iv, p. 613.

? The dissection which is represented in fig. 1, of Perrier’s memoir, only
shows: this infundibuliform space from the outside. A larger figure of its
internal arrangements would be interesting.

3 Loe. cit., p. 103.

1]

154 P. HERBERT CARPENTER.

retical ones on which Koehler comments, for doubting his
description of the communication of the two vascular systems
of an Urchin, both with one another and with the exterior.
But at the same time I am fully prepared to abandon my doubts
and to admit the truth of his views, when he can demonstrate
the following propositions by the same methods as Ludwig
employed in his work on the Starfishes.

1. The communication of the so-called excretory canal of
the ovoid gland in an Urchin with the space beneath the
madreporite, into which the pore-canals and the water-tube
both open.

2. The connection of both the radial vessels of an Kchinus
with one oral ring (water-vascular, auctorum).

3. The connection of the intestinal vessel of Spatangus
with both the oral rings.

In these days of an intensely elaborated technique and self-
acting microtomes, it must surely be possible to obtain such a
series of sections as would put the truth of Koehler’s views
beyond the reach of doubt; but if obtained they have not yet
been figured. We are indebted to him for the rediscovery of
the “ glandular canal” of Echinus, by which the ovoid gland
communicates with an oral blood-vascular ring. This con-
nection was positively denied by Perrier,! as the result of
unsuccessful injections. Koehler’s injections were more for-
tunate, however, and he confirmed his results by making
tranverse sections of the combined water-tube and glandular
canal,? which place his discovery upon a sure foundation. Can
he not do the same for the three anatomical points mentioned
above ?

I trust that what I have written above will not be considered
as wanting in courtesy to Mons. Koehler. Weowe him such a
heavy debt of gratitude for the advance which he has made in
our knowledge of the Echinoid vascular system, that it seems
almost ungracious to ask for further information. His des-
criptions of the radial blood-vessels, and of the glandular canal

1 Arch. de Zool. Exp. et Gén.,’ t. iv, p. 613.
? * Recherches,’ pl. vi, fig. 40.

NOTES ON ECHINODERM MORPHOLOGY. 155

between the ovoid gland and the oral blood-vascular ring only
sugggest the possibility of an even closer resemblance between
the vascular systems of Urchins and Starfishes than has hitherto
been thought possible.

Will he not complete his work, and give a convincing
demonstration of the truth of his own statements, so as to
disprove the views of those morphologists, like myself, who
believe in the fundamental distinctness of the two vascular
systems throughout the Stellerids, Crinoids, and Urchins?

Postscript.—Two more notes upon Crinoid Anatomy have
been published by Professor Perrier! since I last wrote upon
the subject in the pages of this Journal.? The second one,
which has only appeared quite recently, closes as follows :—
“‘ Chez les Comatules comme chez les Oursins, ce qu’on a appelé
Vappareil vasculaire est en communication avec le systéme des
canaux ambulacraires.”

As regards the Urchins, the nature of the evidence on which
Professor Perrier relies has been explained above, while I have
discussed his statements about the Crinoids in my report upon
the “ Challenger’ Crinoida.* When his illustrated memoir
upon the Anatomy of Comatula has appeared, I intend to go
into the whole question again, and I will only say at present
that I have seen no evidence of a communication between
water-vascular and blood-vascular systems in any of the five
genera of Crinoids which I have examined, while neither Greeff,
Teuscher, nor Ludwig make any mention of it. At the same
time I am bound to confess that I never thought of looking
for it at all until its existence was asserted by Professor
Perrier, and I shall await his demonstration of it with very
great interest.

1 Anatomie des Echinodermes ; sur l’organisation des Comatules adultes,’’
‘Comptes rendus,’ tom. xcvili, No. 23, June 9th, 1884, pp. 1448—1450; and

Sur le développement de l’appareil vasculaire, et de l’appareil genital des
Comatules,” ibid., tom. c, 16th February, 1885.

2 «Notes on Hchinoderm Morphology,” No. 3, “On Some Points in the
Anatomy of Larval Comatule,” ‘Quart. Journ. Micr. Sci.,’ vol. xxiv, 1884,
pp. 8319—327.

3 «Zool. Chall. Exp.,’ part xxxii, pp. 106, 40— 407.

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