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REPORT

SCIENTIFIC RESULTS

VOYAGE OF H.M.S. CHALLENGER

DURING THE YEARS 1873-76

UNDER THE COMMAND OF ."

■'Jf -"V

Captain GEORGE S. NARES, R.N., F.R.S. /^//

AND THE I.ATE I'"'-'! ^

Captatn FRANK TOURLE THOMSON, R.N. V"

PREPARED UNDER THE SUPERINTENDENCE OF

THE LALE

Sir C. WYVILLE THOMSON, Knt, F.R.S., &c.

UEGHIS PROFESSOR OF NAIURAL HISTORY IN THE UNIVERSITY OF EDINBUROH
DIRECTOR OF THE CIVILIAN SCIENTIFIC STAFF ON HOARD

AND NOW OF

JOHN MURRAY

ONE OF THE NAIURAI.ISrS OF THE EXrEllI llON

Zoology — Vol. XIX.

PART LIV.— REPORT ON THE NEMBRTBA
By Dr. A. A. W. HUBRECHT, LL.D., C.M.Z.S.

}Publisl)eli bp (Bvntv of ^er iWajestp's ©obemment

PRINTED FOR HER MAJESTY'S STATIONERY OFFICE

AND SOLD BY

LONDON :— EYRE & SPOTTISWOODE, EAST HARDING STREET, FETTER LANE

EDINBURGH :— ADAM & CHARLES BLACK

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1887

J'n'ct' Ten Shillings and Sixpence.

PRINTED BY NKILL AND COMPANY, EDINBURGH,
FOR HER majesty's STATIONERY OFFICE.

EDITOKIAL NOTE.

On the return of the Expedition the specimens of Nemertea, along with the
Annelida, were placed in the hands of Professor W. C. M'Intosh, F.K.S., for
description. In the year 1884, however, Professor M'Intosh's time being fully
occupied with the Annelida, Professor A. A. W. Hubrecht of the University
of Utrecht, was requested to undertake the investigation and description of
the Nemertea, and the results of his labours are presented in this interesting
and valuable Report.

The Manuscript was received by me in instalments between the 12th
October and 18th November 1886

John Murray.

Challenger Office, 32 Cjueen Street,
Edinburgh, 9th Fehruavij 1887.

THE

VOYAGE OF H.M.S. CHALLENOEK.

ZOOLOGY.

REPORT on the Nemertea collected by H.M.S. Challenger during the
Yecars 1873-76. By Dr. A. A. W. Hubrecht, LL.D., C.M.Z.S.,

Professor of Zoology and Comparative Anatomy in the University
of Utrecht.

INTRODUCTION.

It was in September 1884 that the collection of the Challenger Nemertea was handed
over to me for investigation, on the express condition that the whole of the MS. and
plates were to be ready within fifteen months.

I mention this, not only with a view of finding an excuse for omissions and curtailings
which cannot fail to have been occasioned in this Eeport by its rather rapid elaboration,
but at the same time in order to be able at the earliest moment to express my thanks to
Professor W. C. M'Intosh of St. Andrews, in whose hands the Nemertea were placed on
the return of the Expedition, for his suggestion that the working up of this group should
be entrusted to me, his own time being fully occupied with the description of the Annelida
of the Expedition.

He moreover placed at my disposal such notes as he had already found occasion to
make upon the contents of the collection, some of them referring to species which he
recognised as new to science. When in the following Report these notes are made use
of, such passages will be specially indicated.

The material, as it was put into my hands, was contained in about thirty small bottles,
and was without exception preserved in spirit. It looked far from promising from a

(ZOOL. CHALL. EXP. — PART LIV. — 1886.) Hllh 1 -

2 THE VOYAGE OF H.M.S. CHALLENGEE.

systematist's point of view. Hardly any traces of coloration were visible, no external
appendages distinguished the diiferent species, no definite shape, marked out by hard
portions of the integument, which facilitate the recognition of rej^reseutatives of so many
other divisions of the animal kingdom, were anywhere noticeable.

The majority of the specimens in the collection were cylindrical or flattened fragments,
generally truncated, and rarely so intact that it was possible at first sight to distinguish
between head and tail. The cephalic slits of those specimens which belong to the group
of the Schizonemertea, and the mouths of many of the fragments, were the only external
marks that could serve both for the discernment of what was posterior and anterior,
and for a rough and provisional arrangement of the forms as they were probably related
to each other.

The various figures on PL I. will give a general impression of the appearance of the
fragments just alluded to. I more especially insist upon the poor aspect presented by
the preserved material of the Nemertea in order to impress the reader with the fallacy
of pronouncing an unfavourable judgment on a collection of marine invertebrates by
relying merely upon the external appearance of the specimens. For I can hardly
sufficiently emphasise the exceedingly good state of preservation of the large majority
of the Challenger Nemertea. They were, indeed, in so perfect a state that the
internal anatomy of all the fragments could be determined, and in very many cases
delicate histological details could be revealed with as much facility as if the specimens
had been captured a few days instead of ten years ago. I feel the more called upon to
make this statement, and to express my admiration for the extreme care which the
scientific staff have so evidently given even to unattractive and small-sized fragments,
as it has been occasionally stated (even in certain of these Reports) that the Challenger
material was sometimes unfit for the minute investigation of internal anatomical struc-
tures. So far as the collection of Nemertea is concerned, this statement is absolutely
unfounded.

The study of the fragments and complete worms constituting this collection was only
possible by aid of the microtome. This instrument was very freely made use of, and the
most important improvement to which it has been subjected by Caldwell, whose
automatic microtome was available, has enabled me to go into many more details than
would otherwise have been possible. The total number of sections through different
specimens of the Challenger material which have been prepared in the drawing up of this
Report amounts to 19,560. They were all of them stained with Ranvier's picrocarmine.

As already mentioned in the Narrative of the Voyage,^ the number of Stations from
which the Challenger obtained Nemertea is more than twenty. It cannot be said that
any of the three large subdivisions of the group is limited to any special region of the
globe, although representatives of the very lowest and most primitive genera of Palaeo-

1 Narr. Chall. Exp., vol. i. pt. ii. p. 831, 1885.

EEPORT ON THE NEMERTEA. 3

nemertea are as yet only on record from the Atlantic and the Mediterranean. It is,
however, very probable that these genera (the Carinellidse) are cosmopolitan, and have
as yet only escaped detection because even in the region from which they are known
they count among the rare forms.

I have here only to add that in drawing up the list of the Challenger Nemertea, I
will follow the subdivision into larger groups that was proposed by myself several years
ago (VII., p. 204),^ and will successively treat of the Palaeonemertea, Hoplonemertea, and
Schizonemertea. It may be remarked that in the first named groujj, which contains the
most primitive and least differentiated representatives, the genera Valencinia and Eupolia
( = Polia) were also provisionally placed. These two may be looked upon as, to a
certain degree, transitional forms. New light has been thrown by the Challenger
material upon at least one of these genera, and it appears advisable to let them stand in
that subdivision, however far they may differ in certain respects from the tjrpical
Palseonemertea, such as Carinella, Carinoma, Carinina, &c., and however strong their
affinities may be in other respects either to the Schizonemertea or to the Hoplonemertea.

1 The heavy numerals refer to the Bibliography at the end of the Report.

DESCRIPTION OF THE GENERA AND SPECIES.

NEMERTEA.
A. PALiEONEMERTEA.

Family Carinellid^.
Carinina, n. gen.

Closely allied to Carinella, from which it differs in the presence of a distinct
posterior brain lobe, situated with the rest of the brain and nerve-stems in the integu-
ment, outside of the body musculature. A ciliated canal jpenetrates into this posterior
brain lobe.

Carinina grata, n. sp. (PL I. figs. 1-3; Pis. II., III., IV.; PI. VI. figs. 1-3; PI. XL
figs. 1, 2).

Two specimens of this new genus and species were obtained in the dredge, both from
considerable depths, and from the same part of the Atlantic Ocean, namely, to the east
of the United States (Stations 45, 47). The bottom is recorded to be blue mud, and
the depth 1240 and 1340 fathoms respectively. This is the greatest depth from which
Nemertea have been brought to light, and it is worthy of notice that this deep-sea form,
which is at the same time the representative of a new and distinct genus, should be
characterised by peculiarities of structure, hereafter to be more fully recorded, which
are diametrically opjDosite to certain of the most striking features of the pelagic genus
Pelagonemertes and of other forms that generally occur close to the surface. The most
striking of these characters is the exceptionally strong development of muscular tissue
in the body-wall, and coincident with this, the considerable reduction of the inter-
muscular connective tissue, which in the surface forms becomes a gelatinous matrix in
which both the internal organs and the musculature are embedded.

It can hardly be doubted that this opposite line of development is to a large
extent influenced by the much more considerable resistance to be overcome by an animal
that has to move about at so great a depth of water.

Of the external appearance of the fragments of this new species little need be said.

6 THE VOYAGE OF H.M.S. CHALLENGER.

They are reproduced both in the Narrative of the Cruise (vol. i. pt. ii. p. 831) and
on PL I. figs. 1-3. There is no trace of longitudinal lateral slits— so characteristic of
the Schizonemertea — but a terminal crescentic groove (marked out by darker pigment and
by more profuse cUiation in one of the two specimens) was present in both. The pro-
boscidian opening could be easily detected in both specimens, the subterminal mouth in
one of them.

Incomplete as was the information that could be gathered from superficial examina-
tion, very interesting data came to light after the two specimens had been transferred to
the microscopic slides. From specimen a, which was dredged at Station 45, a con-
tinuous series of transverse sections was made, whereas specimen b, from Station 47, was
cut transversely along the region behind the brain, nearly horizontally through the
brain and tip of the snout, and longitudinally through that region of the body where
the nephridia are found.

It is very striking that in all these sections the cellular integument is of a consider-
able thickness when compared with the muscular (PL II.; PL XL figs. 1, 2). In it we
may distinguish several strata successively characterised (PL IV. fig. 1) by an accumu-
lation of nuclei, by profuse integumentary gland-cells, &c., which will be more fuUy
described in another chapter of this Report.

Curiously enough the contents of the deeper glands have a well-marked green
colour in the anterior portion of one of the body fragments of specimen b, whereas
they are brownish-red in the posterior portion, the whole fragment having first been
stained with picrocarmine.

A homogeneous basement-membrane separates the integument from the subjacent
muscles. This membrane is more deeply stained than other portions of the intercellular
substance and thus stands out very clearly.

In the outermost cellular layer, distinct unicellular, flask-shaped glands are present
(PI. IV. fig. 1), although they are not so numerous as in many Schizonemertea, These
facts authorise us to look upon the integument of Carinina as similar in aU its
essential elements to that of other Nemertea. We will further insist upon this similarity
when describing Eupolia and Cerebratulus.

Before we pass from the integument to the muscular investment of the body we have
to mention the central nervous system, which is found outside the homogeneous basement
layer just referred to. Where the tissue of brain and nerve-stems takes its course in
the deeper layers of the integument, it is directly applied against the subjacent muscles,
the basement-membrane being indistinct if not interrupted beneath these central parts of
the nervous system (PL III. fig. 7).

In addition to the two lateral stems, each transverse section reveals the presence of a
dorso-median thinner nerve-stem, corresponding to what I have formerly termed the
proboscidian sheath-nerve.

EEPORT ON THE NEMERTEA. .7

There is, moreover, positive evidence as to the presence of a delicate nervous plexus,
situated just outside of the basement membrane already alluded to, and which, judging
from the available fragments, is present throughout the whole length of the animal.
The transverse sections also show that a second nervous plexus may be presumed to be
present just outside the inner layer of circular muscles. The details of this will be
discussed hereafter when considering the nervous system.

Passing forwards along the lateral nerve-stems we iind them in every section fixed
to the subjacent muscles by semicircular fibres indicated in figs. 7 and 8 on PI. III.
Anteriorly the stems pass insensibly into the brain, which, as a mere thickening of the
lateral stems, has as yet only attained to a very low degree of difi"erentiation. In this
respect the brain much resembles that of Carinella, from which, however, it difters in a
very important point, viz., the presence of a posterior lobe into which penetrates a
ciliated duct ending blindly and communicating with the exterior.

This posterior lobe is situated, as is the anterior one, outside the muscles of the body-
wall (PL VI. figs. 1-3), the inner channel is coated by a ciliated epithelium, difi'ering in
texture from the surrounding nerve-cells. The latter, however, can hardly be sharply
distinguished from adjacent cells of a more indifterent character, and belonging to the
lower strata of the integument.

The muscular elements partaking in the formation of the body- wall are kept distinctly
apart from the tissue, which we have described as the integument, by the homogeneous
membrane above mentioned. Below this membrane we find a thin, circular, muscular
layer (PL XL figs. 1, 2, /3), then follows the much thicker layer of longitudinal fibres (a),
and finally an inner layer, thinner again, of circular fibres (S). The comparative thickness
of these two latter layers throughout the oesophageal region may be gathered from
PL 11. fig. 5. In the two circular layers the fibres appear to be more closely set than in
the longitudinal. In the outer circular layer the direction of all the fibres is, however, not
perpendicular to the body-axis, a very regular network of other fibres which have their
direction at an angle of 45^ both with the longitudinal and the transverse axis, being closely
interwoven with this layer. These are, however, not massive enough to form a distinct
layer by themselves. The homogeneous intercellular substance, which is also present here
between the bundles of muscular fibres, and which stains very distinctly with picro-
carmine, is of course best visible when the bundles are widest apart. Such a portion is
figured in PL III. fig. 6. This intercellular substance is also seen to be again traversed
by radial fibres passing between the two circular layers ; nuclei are, moreover, present
both in the intercellular substance and enclosed along with the bundles of fibres.

Within the muscular body-waU are lodged — (1) the proboscis and its sheath ; (2) the
intestine ; (3) the blood-spaces ; (4) the nephridia ; and (5) the generative sacs. The
space not occupied by any of these is entirely filled up by a tissue, which I wiU call the
gelatinous tissue, and regarding which more ample details will be given in the chapter

8 THE VOYAGE OF H.M.S. CHALLENGER.

dealing with the anatomy of the group. It is wholly continuous, and a body-cavity in
which the above-named organs may be said to float, or to be suspended, is totally absent.

A rapid survey of the peculiarities which these five systems present must complete
this descriptive account of the new genus. The aperture for the proboscis, which is
situated terminally, leads into an anterior cylindrical compartment, which remains passive
when the proboscis is protruded or retracted. It is coated by ciliated cells, and at the
posterior end the anterior insertion of the proboscis into the body musculature takes
place (PI. II. fig. 8 ; PI. III. fig. 5). Although the name is etymologically not wholly
adapted for the purpose, I still am inclined to adopt for this compartment, which is
present in all Nemertea, the name of rhynchodjeum. This name as clearly separates it
from the cavity of the proboscis or its sheath, as that of stomodseum and proctodseum
distinguishes certain portions of the intestine of other invertebrates from the mid-gut.

The rhynchodseum of Carinina has a great resemblance to that of Carinella, more
especially because of the wide and much distended blood-space which wholly surrounds
it, and in which it is kept in place by numerous strings of tissue starting from the
muscular body- wall and inserting themselves on the muscular investment of the
rhynchodaeum (PI. III. fig. 5 ; cf. IX., pi. i. fig. 2). From the same figure it may be
gathered that the internal cellular coating of the rh}Tichod8eum is more than one row
of cells thick, and that these cells have a clear and distended aspect, with a comparatively
small nucleus.

The proboscis itself is inserted in a very simple way in the muscular tissue of the
body-wall. The muscular investment of the proboscis curves round at an angle of 90°,
and becomes continuous with the longitudinal muscular layer of the body-wall. The
details of this arrangement may be gathered from PI. III. fig. 5, and it will there also be
seen how the protruded proboscis remains fixed to the body all along this annular point
of attachment. Thence it extends backwards as far as the proboscidian sheath permits,
which, in the forms allied to Carinella, is only the anterior portion of the body. It is
drawn back again by its retractor. How far backwards the proboscidian sheath reaches
in Carinina could not be made out, as I only possessed two small anterior fragments,
in neither of which the proboscidian sheath terminated. The proboscis itself could be
examined \dt[\ detail in the single specimen which was cut longitudinally. An anterior
and a posterior portion of diff"erent textures are exceedingly distinct. They are separated
from each other by a constriction. In the posterior portion the cells are eminently
glandular, high and flask-shaped ; in the anterior portion they are less high and appa-
rently less glandular (PI. III. figs. 1, 2). Great difi'erences in aspect, but not in actual
texture, are of course occasioned by the diff'erent stages of contraction in which the various
parts of the proboscis happen to be.

The mouth, situated ventrally close to the anterior extremity, was very small in both
specimens. The cellular coating of the oesophagus is very distinct, and the direct

REPORT ON THE NEMERTEA. 9

application of the oesojDliageal epithelium against the muscular tissue most marked
(PI. IV. fig. 3), not even a basement membrane separating the two, whereas a suspension
of the intestine by means of the gelatinous tissue is of common occurrence in other
forms. The longitudinal sections prove that further back the intestine does not con-
tinue as a straight tube as it sometimes does in Palaeonemertea, but is constricted
(PL IV. fig. 2), the constrictions and resulting caeca being, however, much less marked
and prominent than in the Schizonemertea and Hoplonemertea.

Eight and left of the intestine are situated the two longitudinal blood-spaces, which
are direct continuations of the blood-spaces already noticed in the head, and which com-
municate with these by passages that are encircled, together with the proboscis and its
sheath, by the annular nerve ring formed out of the right and left halves of the brain
and their superior and inferior commissures.

The arrangement of these spaces has been fully described for Carinella by Oudemans,'
and I may refer to that description, the arrangement being on the whole very much the
same. There is no median dorsal blood-vessel in Carinina, and there is a very distinct
internal epithelium to the longitudinal blood-spaces, two of which are figured on PI. IV.
figs. 2, 5, 6.

Transverse vessels of communication are not present in these two forms. I may
perhaps remark that my researches (XIV.) on the development of one of the Schizo-
nemertea have rendered it probable that also in the Palseonemertea we shall have to
look upon the blood-spaces in the same light as upon the cavity of the proboscidian
sheath, viz., as a direct derivative or continuation of the blastoccele, for which cavities
(in the adult state) I have proposed the name of archicoele.

The nephridia are situated partly in the anterior portion of the blood-spaces, another
portion traversing the muscular body-wall and leading to the exterior.

In the portion of the paired nephridia exclusive of this excretory duct we may
distinguish two distinct parts, one a continuous tube of varying dimensions, formed out
of very regularly arranged cells with large nuclei, but not in any way forming a series of
perforated cells such as are known in the nephridia of both Turhellaria and Discoj^hora,

These cells are distinctly ciliated and figured on PL IV. figs. 4-6, Nc. The structure
of the second part of the nephridium is not so easily unravelled, and my preparations
of the two specimens do not suffice to reveal all the details. I find it to consist of
a cellular mass of spongy appearance protruding along a certain distance into the blood-
space, here and there giving evidence of a tubuliform structure, no internal funnels being,
however, anywhere recognisable (PL IV. figs. 4-6, N. sj).).

I must here remark that the researches of Oudemans, who described in detail the
arrangement of the nephridia of Carinella and Carinoma,^ render it very possible that in

* Quart. Journ. Micr. Sci., Suppl. volume, 1885.
- Loc. cit., p. 71, pi. i. figs. 4, 5 ; pi. iii. figs. 56, 57.
(ZOOL. CHALL. EXP. — FAKT LIV. — 1886.) Hbh 2

10 THE VOYAGE OF H.M.S. CHALLENGER.

Carinma iuterual communications between the blood-spaces and the nephridian channels
exist, communications by which the cavity of the blood-spaces is thus directly connected
with the exterior. As I have, however, remarked, I could not detect the presence of
similar communications in my two specimens.

The aspect of the spongy portion of the nephridium and its connection with the
canalicular portion, as well as of this with the exterior, is represented in PI. IV.
figs. 1, 2, 4.

As to the generative apparatus of Cannina, I can only observe that one of the
Challenger specimens is a male, that the fragment contains only two sperm-sacs in its
posterior portion, and that these communicate with the exterior, each by a separate pore.
Whether in Carinina the sperm-sacs are disposed metamerically as in most Nemertea,
or irregularly distributed beneath the dorsal integument as in CarineUa, could not be
made out from this specimen.

The general distribution of integumentary and muscular tissue, as well as of the
cavities of the intestine {D), the proboscidian sheath {Ps), and the blood-space (bl) in the
body of Carinina is indicated by the various figures of PL II. The proboscis itself is
here indicated by Pr, the rhynchodseum by aPr.

Family Eupoliid.*;.

Eupolia, n. gen.
Folia, delle Chiaje.
Integument generally thick in comparison loith the body musculature, the two layers
of contractile fibres of the integument never coalescing with the outer larger one of longi-
tudinal body muscles as in certain Cerebratidi. Proboscis and proboscidian sheath thin
and inconspicuous. Brain-lobes comj^act, posterior lobe long, ivedged in between the
superior and inferior ones. Often a commisssure of the longitudinal nerve-stems beloiv
the anus. No longitudinal cephalic slits but transverse grooves as in many Hoplo-
nemertea.

The necessity for creating a new generic name for the species of Palseonemertea I
am now about to discuss is evident from the foUowiug considerations. The generic name
Polia, when it was applied by delle Chiaje to a genus of Nemertea which he introduced
into science {Polia delineata being the typical species of this genus) had already been
preoccupied in Zoology by Ochsenheimer, who in 1826 so designated a genus of
Lepidoptera. This reason alone sufiices to reject it henceforth from Nemertean nomen-
clature, and this rejection is also facilitated by the fact that the same generic name has
been used by other naturalists, such as Quatrefages (XXVIII.), Schneider (XXXI), &c.,
for Nemertea widely difi'erent from delle Chiaje's type. It was an error of judgment on

REPORT ON THE NEMERTEA. 11

my own part, when giving my critical revision of Nemertean genera and species (VII.),
to retain the name Polia in that list, although I was aware of its inapplicability according
to the accepted rules of nomenclature. I retain delle Chiaje's Polia delineata as the
type species for Eupolia.

Eiipolia delineata, (delle Chiaje) Hubrecht (PL VII. figs. 9, 10).

This species, which is very common in the Mediterranean, more especially at Naples,
is represented in the Challenger collection by one fragmentary specimen, captured at St.
Vincent, one of the Cape Verde Islands. The fragments showed no head, but the
characteristic colouring of the specimen by thin brown stripes on a lighter brown back-
ground, was stiU so distinct in the spirit specimen, that even in the absence of a head, I
do not hesitate to identify this form with the above-mentioned species, especially after com-
paring the sections through the fragments with those through Mediterranean specimens.

In one of the fragments, which is the tail, a terminal commissure between the two
nerve-trunks can be demonstrated ; by a curious twisting of the fragment the sections
seem to j)rove this commissure to lie above the intestine. Such a commissure is
found in other species of Nemertea {e.g. Ampliiporus, Drepanopliorus), but a close
inspection soon reveals that here, and also in other Ewpoli^, the posterior commissure is
indeed found heloio the posterior portion of the intestine instead of above it.

In M'lutosh's preliminary notes on the Challenger Nemertea, I find a notice made
of this specimen to the following effect : — " The specimen is incomplete, neither head nor
tail being present. The body is firm and rounded, measuring about 45 mm. in length
and about 8 mm. in diameter at the wider part anteriorly The body is closely
striated longitudinally, dorsally, and ventrally by alternate white and brownish belts, the
pigment constituting the latter being situated on the inner side of the basement layer of
the cutis, which forms a simple stratum."

Eupolia giardii, (M'Intosh) Hubrecht (PL I. figs. 7-9; PL V.; PL VI. figs. 4-11;
PL VIL figs. 4, 5, 8 ; PL X. fig. 6 ; PL XL fig. 12).
Euhorlada giardii, M'Intosh, in litt.

This new species, which shows interesting peculiarities, is represented by one
specimen, which was cut up into difierent portions when I first examined it, so that I
can only give a sketch of the head but no figure of the animal in toto.

A well-marked peculiarity of this species of Eiqoolia is its shortness, which even
surpasses that of Eupolia curta from Naples.

The head shows (see PL I. figs. 7-9) a faint annular constriction, not continuous in
the median ventral line. In this constriction the right and left external openings
leading into the posterior brain-lobe are situated. Judging from what we find in other

12 THE VOYAGE OF H.M.S. CHALLENGER.

Eupollse, I suppose that this constriction is not so marked in the living animal, but that
here, as in the Mediterranean species, two very shallow, strongly ciliated grooves in the
integument, curving laterally round both sides of the head, were present, and that, during
the process of preservation in spirit, the fold just mentioned made its appearance in the
region where normally these transverse grooves are situated.

What immediately distinguishes Eupolia giardii from its congeners is the thickness of
the circular muscular layer in the oesophageal region.

In M'Intosh's preliminary MS. notes on the Challenger Nemertea, I find the
following remarks upon this specimen, which he perfectly recognised as a new species
(the sjjecific name giardii is taken from M'Intosh's provisional label), without, however,
at that time referring it to delle Chiaje's Mediterranean genus.

" A comparatively large form, measuring about 40 mm. in length, with a diameter in
its widest part of 6 '5 mm. This specimen is colourless, bluntly rounded at each end
and somewhat fusiform in outline.

" The anterior end is almost truncate, with a dimple in the middle, caused by the
proboscidian aperture, and there are traces of a transverse and a vertical groove, thus
forming a cross at the tip of the snout.

" The latter is separated from the body by a well-marked fold which probably indicates
a furrow, and which on each side does not quite reach the mouth. The mouth occurs on
the ventral surface somewhat behind the foreo-oing; furrow and in the form of a triangular
dimple. A small aperture (anus) is situated at the dorsal margin of the blunt posterior

end The small size of the proboscidian slieath is remarkable. It has an

external layer of circular fibres and an inner layer of longitudinal muscular fibres. Both

are thin. It is continued to the posterior third In the middle and towards

the j)osterior third the body-wall presents a decided change from the foregoing — the
alimentary cavity forming a large central space and the solid wall is considerably
diminished in proportion."

In studying the sections of this species several additional points of interest came to
light. Those concerning the brain-lobes will be discussed in the paragraph treating of
the nervous system in general; the general aspect of the brain as it may be gathered
from a reconstruction of the sections is figured on PL V. The outline of the whole of
the lobes and that of the internal fibrous core are here figured side by side in order to
show the relations of the parts and the actual position of the ciliated canal that penetrates
into a separate part of tlie brain-lobes more clearly. There is a terminal commissure
between the longitudinal nerve-stems below the anus (PI. VII. fig. 8).

The right and left longitudinal nephridial ducts (PL VI. fig. 9, Nep.) communicate
by deferent ductules (PL VII. fig. 5, Nep.) with the exterior. Of the latter there are
several; in the available transverse series through the head and oesophageal region I
count five to the left and seven to the right, some of these (sections 298-325 left and

REPORT ON THE NEMERTEA. 13

303-308 right, as well as 448-485 left and 450-485 right) being unmistakably opposite.
The duplicity of these deferent ductules, as figured on PI. VII. fig. 5, is the exception ; it
was only noticed in this one case, all the other ductules being single.

As to the generative caeca I find in this specimen (which is a male) that they are
very full, and that dorsally and ventrally they assume a conspicuously lobed and arbor-
escent appearance.

The integument ofi"ers many points of interest which will not be detailed here as they
will be more fuUy described in the paragraph devoted to it.

Eupolia australis, n. sp. (PL I. fig. 6 ; PI. VII. figs. 1-3, 7).

From M'Intosh's notes on this specimen I copy the following : —

"Another type of a whitish colour, measuring about 19 mm. in length and about
2 mm. in its widest part in front. The body is tapered from the wide anterior region to
the fractured posterior end. It is rounded in front, somewhat flattened towards the pos-
terior region. The head having been retracted forms a short blunt cone projecting from
the folds of the wider nuchal region. No trace of furrows exists, but the mouth seems

to be at the bottom of the transverse dimple at the base ventrally The inner

longitudinal (muscular) layer is peculiar, for its fibres are somewhat regularly arranged,
in long, parallel, and occasionally pennate fasciculi, which in transverse section run
inward from the former coat. There is a slight hiatus in the dorsal middle line above the

proboscidian sheath The proboscidian canal is somewhat thin

The specimen is a male and the sperm-cells form large masses."

The sections showed that the species was distinct from Eupolia giavdii, which comes
from the same locality, as also from the Japanese Eupolia nipponensis, which will be
described below. They furnish the following data which it may be of use to recapitulate,
in order to facilitate identification of the species when it is again captured in the same
waters, and may then be described with its external coloration, of which no indication can
here be given.

The primary difference between every section of Eupolia australis and all the other
species of Eupolia here described is found in its integument. That portion of the integu-
ment which lies outside of the secondary basement membrane, B (PI. VII. figs. 1-3), is
by far the most prominent and the thickest portion, whereas in the other Eupolise it
attains only half or even less of the thickness of the whole integumentary layers that are
found outside the primary basement layer. Bet (PL VII. figs. 5, 9). In correspondence
with this the secondary basement membrane is much thinner in these latter species than
it is in Eupolia australis.

The regidar distribution of the blood-spaces round the oesophagus, and just behind it,
is such that in addition to the medio-dorsal and the two ventral blood-vessels (6r) it

14 THE VOYAGE OF H.M.S. CHALLENGER.

would appear as if there were two other longitudinal ones, situated right and left of the
proboscidian sheath (PI. VII. fig. 1). This may perhaps also turn out to be a special
feature of this species.

Certain other peculiarities observed concerning the intestinal system must for the
present be passed over in sUence, for want of material to verify them. It may, however,
be added that the nervous plexus and the dorso-median nerve are much less conspicuous
(though present) in Eupolia australis than in Eupolia nipponensis, where the plexus is
in some places very thick (PI. VII. fig. 11).

In this respect Eupolia australis more resembles Eupolia giardii, where the plexus
is not so very prominent, although the dorso-median nerve (PI. VII. fig. 4) is distinct
though not massive (c/.', PI. XL fig. 12).

Eupolia nipponensis, n. sp. (PI. I. figs. 4, 5, 10; PI. VII. figs. 6, 11, 12).

By this name I wish henceforth to designate a species of which fragments, partly
heads, partly posterior body regions, which obviously belonged to difierent specimens,
were collected by the Challenger in the Japanese waters.

The series of sections reveal enough of common characters to deter one from assigning
the fragments to different species.

The species is characterised by certain features already alluded to in the foregoing
description of Eupolia australis. If it resembles Eupolia giardii in the disposition of
the diff'erent layers of its integument, it difiers from this species in the absence of the
unusually thick circular muscular layer (PL VI. fig. 9) found in the oesophageal region
of the latter species. The deeper layers of the integument are most conspicuously
developed and vacuolated.

That its nervous plexus is more conspicuous than that of the other Eiipolise was
noted before, and I may add that in the availaljle sections a very good horizontal aspect
was obtained of the brain-lobes, which showed these to differ in certain minor but still
easily verifiable points from those of Eupolia giardii. The upper lobe appears to be
much more cylindrical ; so does the inner fibrous core. There is no superior additional
gyrus to the superior brain-lobe with special fibrous core corresponding to what is
described and figured for Eupolia giardii (PL V. figs. 1, 5, 7-9 ; PL VI. fig. 8).

The connection between the posterior brain-lobe carrying the ciliated canal and the
rest of the brain is, however, very intimate ; they are soldered together along a very
extensive surface.

As to the proboscidian sheath, one of the sections clearly demonstrates how exceed-
ingly thin and delicate it is, and how the separation of its cavity from that of the
blood lacuna is even difiicult to observe.

In this as in other species of Eupolia the distinction in the oesophageal epithelium

REPORT ON THE NEMERTEA. 15

between the layer of ciliated cells immediately surrounding the lumen and the deeper
layer of granular gland-cells is very marked.

There is no muscular layer in the oesophagus as in Euj^oUa giardii (PI. VI. fig. 9)
or in Cerebratulus corrugatus (PI. XIII. fig. 6) ; the thick layer of glandular cells just
alluded to may here and there show a longitudinal fibre in addition to the radial ones
that serve to suspend it in the circum-oesophageal lacuna ; for the greater part these cells
project freely into this cavity and are bathed by the fluid it contains.

B. HOPLONEMERTEA.

Amongst the Hoplonemertea collected by the Challenger none are so difi'erent from
those that are at present known as to necessitate the establishment of a new genus. Stdl
several of them present certain notable points of interest by which our knowledge of
this order of worms is extended, and which at the same time ofier valuable material for
more general speculations.

The three genera Drepaywjiho^'us, Am])hi20ovus and Tetrastemma, to which aU the
Challenger Hoplonemertea belong (when we except Pelagonemertes) appear to be very
cosmopohtan ; the same remark, however, applying to the Schizonemertean Cere-
bratulus, as will be shown in the sequel.

FamUy Amphipoeid^.

Drepanophorus, Hubrecht.

The mouth and the aperture of the proboscis are separate openings. The exceedingly
muscidar proboscidian sheath communicates with lateral spaces that are metamerically
placed, and have thin cellular or membranous walls. TJie armature of the proboscis
often conforms to an aberrant type.

Drepanophorus rubrostriatus, Hubrecht.

This species, although not represented by complete specimens, was dredged by the
Challenger ofi" St. Vincent, Cape Verde Islands, in July 1873. M'Intosh identified the
fragments before they came into my hands, and remarks upon them in his preliminary
notes as follows : —

" Two fragments of a form apparently closely related to Drepanophorus rubrostriatus,
the two measuring about 14 mm. by about 3 mm. in breadth. The colour of the animal
is reddish-brown on the dorsum, with longitudinal pale stripes

" The ganglia and cephalic sacs are remarkably distinct and the nerve-cords have a
cellular investment. A very remarkable feature is the presence of large granular tubes
which communicate with the cavity of the proboscis

16

THE VOYAGE OF H.M.S. CHALLENGER.

" The structure of the proboscidian sheath is peculiar, since the longitudinal fibres are
clasped in spaces made of the circular coat and in transverse section the lining is
papillose."

Not only the remains of the external coloration but also the internal anatomy

Fig. 1. — Armature of the proboscis of an adult Drepanophorus serraticollis. H, curved handle of stylets with muscle-
fibres attached to it ; st, nail-shaped stylets in action ; st', nail-shaped stylets in accessory reservoirs, the number of
these reservoirs more or less corresponding to that of the active stylets, and also increasing with age.

convinced me of the identity of this fragmentary specimen with the Mediterranean
species, which has, moreover, already been found by Langerhans at Madeira. Although

REPORT ON THE NEMERTEA. 17

the Challenger specimen contained no proboscis (which had apparently been expelled), I
cannot refrain from giving a woodcut of the curious and divergent armature of the
proboscis as it was observed by me both in young and in older specimens of Drepano-
phorus from the Mediterranean. In young specimens the number of pointed stylets
and of reserve sacs is less considerable. This proboscidian armature is certainly one of
the most marked and distinctive features of the genus, although, as we shall presently
see, I feel justified in assigning other species to it even when the presence of a similar
armature has not been definitely demonstrated.

The specimen was a female ; the generative products are, however, yet very far from
ripe.

Drepanophorus serraticolUs, Hubrecht (PL IX. figs. 5, 6 ; PI. X. fig. 5 ; PI. XI.
fig. 8 ; PL XII. fig. 6 ; PL XV. fig. 17).

Drepanoplu/rus serraticolUs, Hubrecht, Aanteekeningen over Anat. van eenige Nemertinen,

Utrecht, 1874.

Concerning the specimens here referred to this species, I find the following notice in
M'Intosh's preliminary MS. : —

" Two specimens were dredged at Station 162 (ofi" East Moncoeur Island, Bass Strait),
38-40 fathoms, sand, length about 30 mm., with a diameter of about 7 mm., but both
are broken.

" The ventral surface is marked by a median and two lateral longitudinal grooves.

" Externally the dorsum is tinted of a pale madder-brown without stripes. A darker
patch runs in the centre of the head in front of the cephalic furrows. The under surface
is pale.

" The head is wider than the neck and seems to have been somewhat bluntly conical.
The aperture for the proboscis is slightly inferior. It is marked by a prominent ridge
indicating the cephalic furrows, which slope slightly forward on each side to the middle
line, where they are separated by a short interval. Inferiorly they slope more distinctly
forwards and inwards, and are separated by a wide interval, from which a median ridge
goes forward to the proboscidian aperture. In front of this furrow, both dorsally and
ventrally, there are a series of secondary furrows about thirteen or fourteen in number,
running forward from the main groove

" In regard to the structure of the proboscis it agrees with the others of the genus,
presenting no stylets.

" The proboscidian sheath presents a regularly interwoven or basket-like pattern of
circular and longitudinal fibres, and the inner surface is pajDillose in transverse section.

No diverticula seem to be present Many ova are found partially projecting

through apertures a little external to the nerve-cord and corresponding to the very evident
raised line on the ventral surface."

(ZOOL. CHALL. EXP. — PABT LIV. — 1886.) Hhh 3

18 THE VOYAGE OF H.M.S. CHALLENGER.

It needs no comment that it is at the least rather hazardous to identify with the
Mediterranean species (which seems also to have been examined and figured by Quatre-
fao-es when he gave the description of his Cerehratulus crassus), a specimen in which the
proboscis, as well as its armature, is absent. StiU the transverse sections offer such a very
close resemblance to those of actual specimens of Drepanophorus serraticollis, that it
would be again hazardous to establish a new species for the fragments, of which the colora-
tion affords a less decisive clue than in the case of the foregoing DrejKmojohorus rubro-
striatns — the madder-bro^vTi hue referred to by M'Intosh being all that is preserved of
the uniform though bright coloration which the specimen must have had when alive, if
it agreed in this respect with the Mediterranean Drepanophorus serraticollis.

I have, moreover, hazarded the identification with the foregoing specimens of a third
fragment collected in the Kerguelen waters, of which not only the proboscis but also the
head was absent. Here, too, the internal characters enabled me to refer the specimen
to the genus Drepanophorus (the transverse cseca of the proboscidian sheath being in
this case the guiding feature).

The systematic position of this specimen thus only rests upon the similarity of the
transverse sections and on the general yellow hue of the fragment, darker on the dorsal
than on the ventral surface.

The very thick- walled proboscidian sheath with its delicate lateral sacs, different in
certain respects from that of a new species of Dreixinophorus hereafter to be described, is
fisured on PL X. fig. 5.

Drepanophorus lankesteri, n. sp. (PI. I. fig. 22; PI. IX. figs. 1, 2, 10; PI. X. figs.
2, 4 ; PI. XII. figs. 5 ; PL XIV. figs. 9, 10 ; PL XV. fig. 13).

Of the three species of Drepanophorus contained in the Challenger collection, this is
without doubt in several respects the most remarkable. One specimen measuring 30
mm. in length and 3^ mm. in breadth was obtained ; it was dredged at Station 49, in
the waters of Nova Scotia. As to its colour when alive, the spirit specimen allows of
no other certain conclusion than that the dorsal surface is darker than the ventral, which
may have been whitish. No special markings are now traceable on the dorsal integument,
and we may thus surmise that its natural colour, which has been only partly preserved
in spirit, was in life brown or red.

If I nevertheless feel justified in creating it a new species, it is because certain internal
characters are so well marked as to aUow of no confusion with the species of Drepano-
phorus hitherto known.

The two characteristic features which immediately attract attention in studpng a
series of sections through this species are, first, the presence of a series of transverse
commissures (PL IX. fig. 10) metamerically placed at intervals of about 0*2 to 0'15 mm.,
and connectinsr the two lonsitudinal nerve-stems all along their course below the intes-

REPORT ON THE NEMERTEA. 19

tinal caeca. Close to the posterior end of the body I cannot vouch for their presence ; their
extreme tenuity, and a fokling of the sections, preventing the transverse commissures, if
present, from being seen. Nor coukl I make out with certainty in the one specimen
available, whether the longitudinal stems themselves coalesce above the anus as they do
in the other Hoplonemertea, but on aj^riori grounds, I can hardly doubt their doing so.

Anteriorly, the transverse commissures were present even in the immediate neigh-
bourhood of the brain, up to the point where the so-called vagus nerve branches off and
stretches forwards towards the oesophagus.

Although, on the whole, they have a very regular course, and are situated at equal
intervals, still a few irregularities in these commissures must be noticed ; some of them
branching into two, others being connected with the preceding or the succeeding commis-
sure by a small bundle of nerve-fibres.

The significance of this nervous arrangement will be discussed further on.

The second characteristic to which I wish to draw attention is the presence of trans-
verse cgeca belonging to the proboscidian sheath. Although they are present in other
species of Drepanophorus, so that we are justified in looking upon their presence as one of
the typical generic characters, still I never found their walls so markedly developed as in
Drepanophorus lankesteri. Generally the walls are exceedingly thin and membranaceous
(e.g., Drepanophorus ruhrostriatus) ; here, however, they attract attention by the thick
cellular coating which immediately reveals its presence both in longitudinal and in trans-
verse sections. On PL X. fig. 4, the nature of this arrangement is clearly shown. Another
peculiar feature of these cseca of the proboscidian sheath is that I have found a few of
them coalescing peripherally with the one preceding or following them by means of a short
longitudinal extension, which allows these few successive caeca to intercommunicate not
only by means of the proboscidian cavity, but also by means of this distal connection.

The muscular body-wall of this, as of most other Hoplonemertea, may be shown to
contain, in addition to the two layers a and /S [cf. PL XL fig. 8), certain cross fibres
not forming a definite layer, but arranged at angles of 45°, and visible in sections parallel
to the surface. •

The openings of the longitudinal canals of the nephridia to the exterior are situated
ventrally, posteriorly, and at the same time terminally ; this constitutes another difi"erence
as compared with Drepanophorus ruhrostriatus which has been already described and
figured by Oudemans.^ On one side of the specimen investigated two openings of the
nephridial duct piercing the integument are at all events observable, although somewhat
more internally, before these deferent ducts have pierced the muscular body-wall, they
coalesce. There is a very close proximity between the anterior nephridial ramifications and
the lateral longitudinal blood-vessels. They do not, however, intercommunicate, nor do,
as was supposed by M'Intosh, the proboscidian sheath-caeca and the blood vascular system.

' Loc. cit., pi. i. fig. X.

20 THE VOYAGE OF H.M.S. CHALLENGER.

Eyes are present in Drepanoi^horus lankesteri. In the (detached) posterior lobes of
the brain there is a double canal as in most other Hoplonemertea, the one branch taking-
its course along the glandular cells, the other in the ganglionic part of this brain-lobe.

As to the sexual elements, they are in this species enclosed in sacs that are ventrally
situated, and although I have only one specimen at my disposal, which is just beginning
to ripen, I still believe I may lay it down as a rule for the species that the genital caeca
are arranged in pairs in the vicinity of each nerve-stem, so that four are very often
simultaneously met with in one section. This is, as we will presently see, a more compli-
cated arrangement than that which obtains in the other species of Drepanophorus, but it
is a simplification of the more profuse and less regular distribution of the genital sacs, as
it occurs in Amphiporus moseleyi.

Amphiporus, Ehreuberg.

Stylet in the prohoscis of the normal shape. Oral and proboscidian aperture con-
fluent. No lateral cseca to the proboscidian sheath. Numerous longitudinal nerves in
the proboscis as in Drepanop)horus.

Amphiporus moseleyi, n. sp. (PI. I. figs. 20, 21 ; PI. IX. figs. 4, 7-9, 11 ; PL X.
fig. 3; PL XV. figs. 11, 12, 20).

Professor M'Intosh has drafted the following notes on a provisional examination of the
specimens before they were handed over to me, which I may here be allowed to insert : —

" A large flattened species, the largest specimens about 68 mm. in length, and about
12 mm. at the broadest part. The body in those best preserved is somewhat flattened
and with an acute edge along both sides of the tip of the tail. Anteriorly the body is
thick and rounded both dorsally and ventrally, but posteriorly it is much flattened. In
the preparation the anterior end is more pointed than the posterior. The ventral surface
throughout is flatter than the dorsal.

" The larger specimens are deprived of much of their cutaneous tissue so that they
are comparatively pallid ; in one (the smaller) the dorsum is of a dull blackish-grey ;
while the ventral surface is either whitish or pale greyish. The lip of the snout is pale,
and from this a pale line runs backwards to the tail on each side. This is not altogether
due to jMgment, for in tho.se devoid of cutis a very evident whitish band is found along
the anterior third, but it becomes indistinct posteriorly.

" The head is somewhat truncated anteriorly and marked by a series of eyes which
are rather deeply seated. In the large specimens these form a marginal band on each
side along the antero-lateral margin of the snout. In the smaller a series begins on each
side of the median line of the snout and runs in a tolerably straight line backwards to
the slight narrowing of the furrow, while a somewhat triangular area superiorly is covered

REPORT ON THE NEMERTEA. 21

with similar eyes. The posterior boundary especially being so distinct as almost to
make a special row.

" Behind these a band of similar eyes runs upwards and slightly forwards, a consider-
able interval on the summit of the dorsum separating those of each side.

" The cephalic furrows slope outwards and backwards on each side to the margins
dorsally, and from the latter point are continued ventrally outwards and forwards.

" So far as can be observed in this form only a single aperture exists for the proboscis
and mouth. This forms a well-mar]i;ed slit in the ventral surface, a little behind the
tip of the snout

" In minute structure the proboscis corresponds to that of the typical form ....
the stylet is simple and normal."

To this description of the external characters I have nothing to add, but may proceed
to remark that the examination of the internal structure by means of sections has
revealed the significance of the white lateral stripe, noticed by Professor M'Intosh as not
beino- due to pigment. It is, indeed, a peculiar feature by which this species is
characterised, and which I have hitherto not observed in other Nemertea. All along the
extent of this lateral and longitudinal whitish line (PL IX. fig. 8) the sections show
the presence of numerous glandular (or sensory ?) cavities, opening to the exterior by very
numerous pores piercing the integument, and both accumulated at, and limited to, the
reo-ion where the dorsal musculature merges into the ventral (PL XV. fig. 11), and where,
as in so many Hoplonemertea, the muscularity of the body-wall is reduced to a minimum,
i.e., in the right and left lateral line. In the posterior portion of the body these organs
were no longer present ; anteriorly, however, they could be traced even in the head (PL X.
fig. 3, gls.). Further details about their structure will be given in the anatomical part of
this Report.

The other chief peculiarities of the species which are revealed by a study of the
sections, and which must be briefly enumerated in this summarising description, are : —
the situation of the longitudinal nerve-stems, in the portion of the body where the
intestinal cseca are clearly developed, above these cgeca about one-third or halfway
between the lateral margin and the proboscidian sheath. It should be remarked that
this arrangement is the opposite of what is observed in Drepanophorus, where the
longitudinal nerve-stems, as elsewhere described, have their course below the intestine, or
below the lateral cseca. The significance of this difi'erent arrangement wiU be elsewhere
discussed ; in itself it is a feature very much facilitating the discrimination of Amphi-
2)orus moseleyi from other Amphipori, where the nerve-stems are found much more
strictly laterally, at least in those hitherto known. There is a very distinct commissure
between the longitudinal stems above the anus.

Another most characteristic feature which may generally be distinguished in every
transverse section of the animal, especially when it is ripe for reproduction, is the situation

22 THE VOYAGE OF H.M.S. CHALLENGER.

of the numerous reproductive receptacles. These are not situated alternately between
each pair of intestinal caeca right and left, as we find in the majority both of Hoplo-
nemertea and Schizonemertea. In Ampliiporus moseleyi, the distribution of the genital
receptacles appears to follow a more primitive arrangement, and oifers many points of
similarity with what obtains in the Palseonemertean Cannella, where there is not yet a
regular metamerical arrangement of the genital sacs, but where there are short independent
cavities, irregularly distributed under the dorsal body-wall, which they pierce by means
of short ducts. The outer openings of these ducts are seen on the dark dorsal surface of
the animal as so many fine white dots irregularly spread between the transverse and longi-
tudinal white lines that form such weU-defined external markings in the species in question.

Ampliiioorus moseleyi, as will be seen on comparison of figs. 4 and 7 of PL IX., has its
generative sacs distributed very much in the same way, with this difference, however,
that generative pores are situated not only on the dorsal but also on the ventral surface
of the animal. When the animal is very ripe and the generative sacs are overfilled, it is
manifest that this specific character may be more easily detected in every transverse
section than in young or unripe specimens. As many as seven separate sacs in one
section were noticed. Both the male and female sex were found to agree in this respect.

Another character peculiar to nearly aU Am2:>]iipori — the coalescence of the oral and
the proboscidian aperture into a common wider opening, situated just below the tip of
the snout — is also met with in Amphijjorus moseleyi.

Ampliiporus marioni, n. sp. (PI. IX. fig. 3; PI. X. fig. 1; PI. XV. figs. 14, 15).

A second species of Ampliiporus is represented in the Challenger collections by two
specimens, the larger coming from Marion Island, and having been collected on December
26, 1873 ; the other from Christmas Harbour, Kerguelen, at a depth of 120 fathoms.

The place at which the first specimen was obtained was an inducement to dedicate
this species, in preference to any other of the novelties of the Challenger, to the indefatig-
able naturahst of Marseilles, so well known by his numerous researches in the field of
invertebrate morphology.

Ampliiporus marioni, was one of the larger sized sj)ecimens, measuring 5^ mm. in
diameter anteriorly in its widest region. The body musculature may be said to be
stronger than in most of the other Hoplonemertea {cf. PI. IX. figs. 1-6) ; the longi-
tudinal muscular layer shows a very marked pennate arrangement of the bundles (PI. X.
fig. 1) between which the gelatinous tissue penetrates, carrying with it massive nerve-
stems which assume a more or less flattened, plexus-like arrangement, just between this
longitudinal layer a and the circular layer /8 (PI. X. fig. 1, ne). The proboscidian sheath
is also very muscular ; the proboscis has the stylet of the normal Amphiporean shape.

The nephridial system is comparatively short and has one pair of deferent ducts

REPORT ON THE NEMERTEA. 23

situated at the posterior extremity ; the loBgitudinal canal is anteriorly very copiously
branched (PI. X. fig. 1, Nep).

There is a very thick, basement membrane {B) to the integument, and very strongly de-
veloped gelatinous tissue {Gt) inside the muscular body-wall. Curious granular enclosures
{inc) occurring in this tissue, both in the head and in the body, will be elsewhere described.

The longitudinal nerve-trunks are not wholly lateral but nearly so; there are no
ventral commissures between them.

The generative cseca assume the ordinary character of paired dorsal receptacles meta-
merically distributed between the intestinal caeca. The generative pores are dorsal and
situated above the nerve-trunks.

The ova, present in both specimens, are in both of them characterised by a curious
refractive body constantly present in addition to the nucleus, and staining deeply
with picrocarmine. This " paranucleus " can be seen to be present at the very earliest
stages of the development of the eggs which came under observation ; stages at which
the eggs could still hardly be distinguished from the surrounding cellular elements in
the wall of the generative caeca (PI. XV. figs. 14, 15).

Famdy Tetrastemmid^.
Tetrastemma, Ehrenberg.
Ei/es four ; arranged so as to indicate a square or ohlong. Specimens generally small.

Tetrastemma agricola, Wdlemoes Suhm.

Of this species, collected by Suhm in Bermuda (Mangrove swamps, Hungry Bay) and
which is the only Land Nemertean procured during the voyage, no specimens have been
preserved, although Suhm tells us that he collected a good many of them. So I must
content myself with reproducing the chief points of its anatomy as they were made out
by him in the Ann. and Mag. Nat. Hist, for June 1874. At the same time I have repro-
duced one of his figures in woodcut. Suhm writes {loc. cit., p. 409) : —

" The largest of these worms have a length of 35 mm. by 2 mm. in width. They are
of a milky-white colour. Their movements are slow and sometimes catterpillar-like ;
they shoot out their long proboscis, fix it at some distant point to which it adheres by
means of its papillse, and draw their body after them. Their skin is filled with rod-like
bodies as described by Max Schultze and others, and is covered on the outside all over
with cilia. In the front we find two pairs of eyes, one of them near the entrance of the
proboscis, the other smaller one further out ; they consist of a fine granulated pigment,
imbedded in a colourless substance, which holds these granules together, in which, how-
ever, a regular lens could not be observed; underneath these eyes is seen the prominent
centre of the nervous system (fig. l,g)\ it consists of two lobes and a ring which connects

24

THE VOYAGE OF H.M.S. CHALLENGER.

them and encircles the proboscis. From the lobes depart the two lateral nerves (n) and

some other cephalic nerves, which were not quite clearly visible The cephalic

fissures or ciliated sacs .... are either very small or wanting entirely. Sometimes
a folding of the skin seemed to indicate their presence ; but in the contractile bodies of
these worms it is very difficult to say whether you have a small cephalic fissure or a
folding of the skin before you.

" Underneath the ganglion, on the under surface, is the semicircular opening of the
mouth (o) leading into an intestinal tube (i), which runs through the whole length of the

animal, without showing anything particular, and is terminated by an anus (a)

The proboscis is divided into two portions —
the papilligerous part and the glandular part.
At the bottom of the former we find a peculiar
spine .... this spine is remarkable
because it differs in form accordina: to the sex
of its owner. In the male it has a rounded
base and is pear-shaped (fig. 2, pr^),^ while in
the female the base has sharpened angles (fig.
3, pr^)} I do not think that such sexual
differences have hitherto been observed in
Nemerteans.

" The ovaries and testes are, as usual, situ-
ated between the intestine and the walls of the

body I . . . . establish

for ifc the specific name of agricola, as
there is probably no described marine species
of Tetrastemma with which it could be
identified.

" I, however, do not attach much import-
ance to this point, as the object of these lines
is only to show that in America also land
Nemerteans exist. Hitherto they were only known from the Pelew Islands, where
Semper has found another, to which he has given the name of Geonemertes pala3ensis.
I think it is highly probable that land Nemerteans exist to a greater extent in tropical
countries than has hitherto been supposed, and that from their hidden life, and the
impossibility of preserving them, they have hitherto escaped the attention of travelling
naturalists. Especially in such islands as the Bermudas, where the earth of the lower
grounds contains a great deal of salt, it may easily be imagined how marine animals have
taken to terrestrial habits ; and it was interesting for me to see that one Tetrastemma

FiG. 2. — Tetrastemiiui agricola, WiUemoes buhm. o, mouth
_9, brain: n, lateral nerve; i, intestine; Pi 1, rhyn

chodjeuni ; Pt
the proboscis ;
reservoir.

papuliferous ; Pt 1, glandular part of
Pt'i and ctt, region of the stylet and

■ These figures referred to by Sutm have not been here reproduced.

REPORT ON THE NEMERTEA. 25

when put into salt water would live there for twenty-four hours, but when put into fresh
water died after a few hours time. Fresh water, however, poured over the earth which
contained them, did not damage them in the least."

Tetrastemma fascum, Willemoes Suhm {nee ffirsted).

A second species of Tetrastemma w-as noticed by Suhm during the first year of the
Challenger cruise. In the paper just referred to, in which he describes Tetrastemma
agricola, it is noticed in the following words :—

" I may here also add that on our cruise from the Bermudas to the Azores I found
parasitical Nemerteans on Nautilograpsus minutus, one of the gulf-weed crabs. They
were small brownish animals, and occupied especially the underside of the crab, under
the abdomen of which I found most of them. They did not exceed the length of 2 mm.
and in none of them could I see genital organs. In fig. 4 I have figured one of these
small parasites, which probably also belong to the genus Tetrastemma, though the second
pair of eyes is only punctiform, situated on both sides of the proboscis. Nervous system
and digestive apparatus do not present anything particular, and the proboscis
(fig. 4, 'pr^, pr^), is remarkable for its shortness.

" I do not think that these w^orms attain their full size on the crab, but believe them to
be young parasitical stages of some Nemertean which possibly lives on the gulf-weed."

In his journal, of which an abstract is given in the Narrative of the Cruise, vol. i.
p. 169, Suhm farther remarks about this species : —

" The worm presents no modification induced by j^arasitism ; it appears to be a new
species, and from its colour may be called Tetrastemma fuscum. . . . The ganglia are
especially large and conspicuous. . . . The proboscis is very short, and distinguished
from all other species I know of by having the stylet-sac placed close behind the ganglion
and just above the mouth. . . . Length 075 mm., breadth 0'25 mm."

Suhm was apparently not aware that the specific name which he gives to his specimen
was preoccupied for another Tetrastemma, as early as 1844, by (Ersted for the species
that is now known as Tetrastemma dorsalis.

No specimen being preserved, the special features enumerated by Suhm do not justify
me in proposing a new specific name. For completeness' sake it was, however, necessary
to mention his observations.

Family Pel xV gone mertid^.
Pelagonemertes, Moseley.
Pelagonemertes rollestoni, Moseley.

It was indeed a novel and startling fact when detailed news ^ appeared regarding the
capture by the Challenger naturalists of a pelagic Nemertean, which, in addition to other

1 Anv. and Mag. Nat. Hist., ser. 4, vol. xv. p. 165, 1875 ; vol. xvi. p. 377.

(ZOOL. CHALL. EXP. — PART LIV. 1886.) Hhh 4

26 THE VOYAGE OF H.M.S. CHALLENGER.

characteristic differences, was recognisable by a change in the constitution of its tissues,
similar to that which is noticed in pelagic animals belonging to other groups, when
compared with their non-pelagic allies, viz., the hyaline transparency of the body, with
undiminished, or even with rather increased bulk. The first specimen captured was a
ripe female, the second a very young female. No further specimens were met with. The
first specimen, though somewhat lacerated, was preserved ; the second w^as observed alive
and figured, but was destroyed. Before mentioning the results which have been obtained
by a careful microtomy of the available sjaecimen, I will here insert in full the interesting
descriptions with which Professor Moseley furnished us as early as 1875,^ soon after
the specimens were captured, and when he had been able to observe them in the fresh state.
His first article " On Pelagonemertes rollestoni runs as follows : —

" This remarkable form was found in the trawl, together with a number of deep-sea
animals, from 1800 fathoms, near the southern verge of the South Australian current,
lat. 50° 1' S., long. 123° 4' E., March 7, 1874. Its appearance at once pronounced it a
pelagic animal, the body being gelatinous and transparent as in Salpa, with the
exception of the alimentary canal, which stood out in relief, being of a deep burnt-sienna
colour (as is the nucleus in many Salpx), and the region of the sheath of the proboscis,
which was less transparent than the remainder of the body. The animal was living
when obtained, and when placed in fresh sea-water gave evidence of life by a feeble,
irregular, peristaltic contraction of the external muscular tunic, which increased on
irritation ; the proboscis was also protruded and retracted several times.

" The animal was about 4 cm. long and 2 broad, and 5 mm. in thickness. Hence its
dimensions, and especially its thickness, render it unfavourable for a perfect examination
of its structure under the microscope whilst in the entire condition. As only one
specim.en was procured, and as this was believed to be unique, no dissection was resorted
to, excepting the removal of a small portion of the epidermis and external muscular tunic
for microscopic examination. Hence the investigation of the structure of this Nemertine
necessarily remained an imperfect one, and the affinities of the animal amongst other
Nemertines could not be determined.

" The animal is leaf-like in shape, narrowing to a blunt point at the posterior
extremity, and commencing abruptly at the anterior. The proboscis is protruded from the
summit of a protuberance occupying the middle region of the anterior extremity. The
mouth is situate on the ventral surface of the body, just posterior to the aperture for the
proboscis. It is a simple aperture with a plaited margin composed of five or six folds.
It is the commencement of a short muscular tube, the oesophagus, which was seen to
pass behind the most anterior prolongation of the main mesial digestive canal, but the
communication of which with the latter was not traced. The digestive system stands

1 Ann. and Mag. Nat. Hist, 1875, No. 87 and No. 96.

^ The figures which accompanied the article have all been reproduced on PI. I. figs. 24-27.

REPORT ON THE NEMERTEA. 27

out very conspicuously in the fresh condition of the animal, from being of the deep
burnt-sienna colour already mentioned. It consists of a broad, flattened mesial canal,
somewhat broadest in the middle region of the body, anteriorly ending in a bluntly
■ terminated ctecal prolongation, and posteriorly narrowing gradually. As the posterior
part of the animal was somewhat injured it could not be determined whether the canal
terminates in an anus or not.

" The mesial canal receives on either side lateral tributaries in pairs, which tributaries
remain simple for some distance of their horizontal course, and then break up into
ramifications. The most anterior pair of lateral canals is split up into by far the most
ramifications. The ramifications become less and less in each pair towards the posterior
extremity of the body, some of the most posterior lateral canals being simply bifurcate,
and one merely enlarged at the extremity. There are thirteen pairs of lateral canals
in all.

" The nervous system was plainly seen in part. A pair of rounded ganglia lie on the
ventral and lateral surface of the sheath of the proboscis, being a little posterior in position
to the mouth. A commissure passes above the oesophagus and between it and the
proboscis-sheath. From the ganglia a pair of fine simple nerve-cords pass in a curved
course dowTi to the posterior extremity, where their termination could not be ascertained.

" The cords cross ventrally the lateral digestive cauals about the point where
ramification commences. Further connections of the ganglia could not be ascertained.

" The specimen obtained was a female. A series of ovaries, consisting of pear-shaped
masses of minute ova, were present, situate between each of the pairs of lateral digestive
tubes immediately external to the nerve-cord on each side. The masses of ova are
contained in small cavities in the gelatinous internal body-tissue. When pressure was
exerted the ova issued from small corresponding apertures on the ventral surface, and the
small empty cavities remained. The ova were spherical, about '28 mm. in diameter, and
appeared composed of fat-globules and granular matter.

" The proboscis-sheath, which is wide and capacious, is very plainly seen on the dorsal
aspect of the body, and dimly through the thickness of the body from the ventral aspect.
It has a firm muscular attachment at its orifice, and bundles of muscular fibres (apparently
retractor) are attached to it here on either side (ph xv. fig. B, 1 = PI. I. fig. 24). The
proboscis itself is, when retracted, coiled up in the usual manner within its sheath, as
seen in fig. D ( = P1. I. fig. 25). It could, unfortunately, not be ascertained whether the
proboscis is armed or not. It was never entirely retracted, but a small portion of it always
remained exserted.

" The outer surface of the body of the Nemertine is covered with a hyaline, very thin
integument, which is thrown into numerous folds and wrinkles, which are so arranged
along certain lines around small spaces nearly free from them as to produce on the surface
of the body an appearance of a series of small polygonal areas, separated by fine reticular

28 THE VOYAGE OF H.M.S. CHALLENGER.

network (fig. D = fig. 27). This condition of the surface was most conspicuous about the
anterior part of the body, but the body was much hxcerated by the meshes of the trawl,
and, therefore, I cannot say whether the whole integument is in this condition in the fresh
state or not. The folds and plaits in the integument are so sharp that they give the'
appearance under the microscope of somewhat spindle-shaped bodies with sharply pointed
extremities (fig. c, 1, 2, 3 = fig. 26). At first I supposed that these bodies were urticating
organs, resembling those of Bipalium, but on carefully teasing up a portion of the integu-
ment with fine needles, and being unable to isolate a single one, I concluded that they
were mere folds. They are, however, of remarkable appearance, from their extreme
abundance and the manner in which they cross each other at all angles. They are well
preserved in glycerine preparations of the skin hardened in picric acid.

" Beneath the integument is some granular glandular matter. Immediately beneath
the integument, and in close adherence to it, is the muscular tunic, evidently the
homologue of the cutaneous muscular system of Bipalium and other Planarians. As in
these, the outermost fibres are circular in direction, the inner longitudinal.

" The muscular tunic encloses the entire body. It is thin, and in the fresh condition
of the animal transparent and inconspicuous, but becomes opaque when the animal is
hardened in picric acid. The inner longitudinal layer consists of stout bands of fibres
running parallel to one another. The outer circular fibres are far less developed, and are
not gathered into bundles, but cross one another slightly obliquely in their transverse
course, forming a slight meshwork over the longitudinal fibres.

" Beneath the muscular tunic and between its meshes the body mass is filled up with
a gelatinous, hyaline, structureless matter, imbedded in which lie the viscera and the
muscles attached about the orifice of the sheath of the proboscis. Internal muscles, except
those referred to, were not observed.

" No eyes or other sense-organs were found, and ciliated sacs were not seen.

" From the circumstance of the only specimen of Pelagonemertes having been much
lacerated, and from the animal not having been dissected, it will of course require further
examination. In the specimen as procured there was a deep constriction of the body at
about the junction of the first with the second fourth of its length. This, it appeared
pretty evident, had been caused by the meshes of the net. The posterior extremity
was somewhat injured, and its form may not be quite correctly given. Ciliated sacs
may be present, and the structure of the proboscis might throw light on the afiinities of
the animal.

"The form of the digestive system is the most remarkable feature about Pelago-
nemertes in its close resemblance to that of Dendroccela. In other respects Pelago-
nemertes is thoroughly Nemertine in structure, being merely modified for pelagic existence.
It is remarkable that the gelatinous hyaline mass of the body is not tegumental in
character, but apparently homogeneous with internal structures.

REPORT ON THE NEMERTEA. 29

"The occurrence of a peculiar burnt-sienna colour in many very different pelagic
animals is remarkable. With many the colouring may be explained as protective
resemblance to the oceanic seaweeds. For its occurrence in others, such as Salpa and
Pelagonemertes, in an otherwise hyaline body, there may be some common cause, possibly
also protective.

" Diagnosis of the genus Pelagonemertes, H. N. M. : — Body leaf -shaped, gelatinous,
hyaline. The anterior extremity of the body broad and abrupt, the posterior narroiued
to a point. Tlie digestive canal with thirteen pairs of lateral ramifications, as in
Dendrocoela. Integument thin and hyaline, with a thin muscular tunic immediately
beneaih it, consisting of external circidar and internal longitudinal fibres. The animal
free-swimming, oceanic."

Moseley's second article, which appeai'ed nine months later, was again accompanied by
figures, which will be found reproduced on PI. I. figs. 23, 28-31. The contents were as
follows : —

"On June 5, 1875, in lat. 34° 58' N., long. 139° 30' E., about halfway between
Vries Island, Oosima, and Cape Sagami, the trawl was used by H.M.S. 'Challenger' in
from 755 to 420 fathoms. A young specimen of a peculiar pelagic Nemertean, which has
been described by me (Ann. and Mag. Nat. Hist., ser. 4, vol. xv. p. 165, March 1875)
under the name of Pelagonemertes Rollestoni, in honour of my friend and instructor
Professor Eolleston, was found by Dr. von Willemoes Suhm adhering to the net, and by
him handed over to me for examination. The adult specimen before procured and
described was in a similar manner found adhering to the trawl-net after a deep-sea
dredging by Dr. von Willemoes Suhm.

" The animal was very much smaller than the one obtained before, measuring only
13 mm. in extreme length, and 11 mm. in extreme breadth, and about 1 mm. in extreme
thickness. It was in good preservation when found, and living, and, being extremely
transparent, much more of its structure could be observed than in the case of the more
full-grown specimen. Unfortunately, an attempt to preserve the specimen by treatment
with perosmic acid and subsequent action of glycerine failed, and the specimen perished.
The trawl came up late in the evening, when only an hour of daylight remained ; the
examination made was thus a hasty one.

"The animal showed the same feeble pulsating movements which had been shown by
the adult.

" The external gelatinous investment of the body was perfectly transparent, and none
of the peculiar corrugations of a thin superficial epidermic layer were visible as in the
adult specimen. The contours of the body were well preserved, including those of the
hinder portion, which was broken in the specimen before obtained.

" The forepart of the body is wide, with rounded margins ; the posterior narrowed,
with a series of indentations on its margin corresponding to the successive pairs of

30 THE VOYAGE OF H.M.S. CHALLENGER.

diverticula of the digestive tract. At tlie extreme liiuder termination of the body is a
shallow notch, at the bottom of which is the anus.

" The mouth, which is a simple opening at the apex of a small, short, conical
protuberance, was situate just in front of the nerve-ganglia on the ventral surface of the
body (it is not shown in the figure, which represents the animal from the dorsal aspect).

"The central canal of the digestive tract terminated in front in a wide, rounded, blind
end, and tapered gradually to the anus at the posterior end of the body.

" The lateral diverticula in this young specimen were evidently in an immature
condition, and the successive pairs showed successive stages of development, the most
anterior being the most fully formed. This most anterior pair is the only one which
shows a commencement of ramification at the peripheral extremities. The ramifications,
so ample and well marked in the adult worm, are seen here to be developed as csecal buds
from the outer ends of the long diverticula. The diverticula themselves, of which five
pairs were present in the young s2oecimen here figured, arise, as can be seen from the
figure (pi. xi. fig. 1 = PI. I. fig. 23), as simple lateral buds from the central digestive tube.
These buds gradually increase in length, their peripheral csecal ends being always larger
than the tubes connecting these with the central digestive tract, and eventually these csecal
ends give ofi" buds and form ramifications. A slight enlargement in the rectum, situate
just anteriorly to the anus, and shown in the figure, probably represents the spot where a
sixth pair of diverticula were about to bud ofi" from the digestive tube. The diverticula,
with the exception of the first pair, were not placed exactly opposite one another, the
right diverticulum in each pair being situate anteriorly to the corresponding left one.

" The digestive tract was filled with a dark reddish-brown matter, consisting of large
granules and oU-giobules. The contents of the diverticula were darker and more opaque,
and contained numerous clear oily globules of a bright yellow and bright red colour,
mingled with similar opaque globules (fig. 4, « = fig. 28). The brightly coloured globules
exactly resembled those of the main tract. Similar coloured globules occur in larval
Nemertines, and I have observed them also in a marine Planarian larva, possibly that of a
Thysanozoon, or the Planarian larva described by Johannes Miiller from the Mediterranean,
sujjposed to be that of Eurylepta (Glaus, ' Grundziige der Zoologie,' p. 286).

"The sac of the proboscis corresponded exactly with that described in the adult. It
was here found to terminate posteriorly in a blunt point at a short distance from the
hinder end of the body. The fluid contained in it appeared transparent and without
corpuscles. The proboscis itself could be carefully examined in the present transparent
specimen. It was without stylets and quite simple, invaginated in the usual manner ; it
was not seen fully protruded, but when so protruded must be slightly longer than the
animal's body ; it has an outer pellucid gelatinous investment, and an inner muscular
layer (fig. 5 = fig. 29). No retractor muscle was observed to be connected with it.

" The nervous system consists of two pairs of ganglia, of which the up23er are by far

REFORT ON THE NEMERTEA. 31

the larger and give off the stout nerve-cords. The cords stretching backwards on either
side unite with one another above the rectum at the hinder end of the body. The nerve-
ganglia are shown enlarged in fig. 3 ( = fig. 30). No sense-organs of any kind were detected.
On the outer margin of the large superior ganglion (fig. 3) a series of elongate pellucid
cells were arranged side hj side perpendicularly to the curved surface which they form.
Abundant fine nerves were given off' from the entire length of the nerve-cords to the
surface of the body, the muscles, &c., arising both from the inner and outer margins of
the cords. At the origins of these nerves from the cords there are very slight swellings
on the margin of the cord, but these do not contain any nerve-cells. The nerves are very
fine, hyaline, with a nearly rectilinear course, and they generally divide into two near
their points of distribution ; they are never tortuous or much ramified. Terminal organs
on the surface of the body in connection with the nerves were carefully sought for but
could not be found.

" A pair of vascular trunks follow the course of the nerve-cords through the body, lying
internally to them and beneath them. The vessels unite with one another posteriorly, as
do the nerve-cords ; their course is undulating. J,ust behind the nerve-ganglia the
vascular trunks are enlarged into wide reservoirs. No branches of these vessels were
seen, and though the animal was living when examined, no pulsation in them was
observed. The vessels had a pellucid wall, in which were imbedded elongate oval nuclei
(fig. 4, & = fig. 28), but which otherwise appeared structureless. No motion of any fluid
within the vessels was seen.

" Although the specimen under description was evidently so immature, well-developed
ovaries were present, the specimen being a female, as was the adult one before obtained.
The ovaries follow in their disposition the vascular trunks so closely as to appear as if
connected with them. The ovaries are simple ovoid sacs with a distinct wall (fig. 2 = fig. 31),
filled with ova (in various stages of development) and granular matter. A dark irregular
fissure appeared on the centre of each ovary as viewed from the dorsal surface, which I
believe to be an opening by which the cavity of the organ communicates with the exterior,
thus dorsally. The ovaries were not quite regular in disposition, an extra anterior one
being developed on the right side of the body. In the interspace between the most
anterior and larger pair of intestinal diverticula and- the next posterior pair were four pairs
of ovaries, whereas in the succeeding corresponding interspaces were only single pairs of
these organs. In the adult specimen described in the 'Annals' (March 1875) a single
ovarian sac only was present in each interspace between the diverticula of the digestive
tract. It would therefore seem probable that on further development three pairs of
diverticula would have budded out between the first and second pairs in the present
specimen.

" The muscular system consists of a series of excessively fine transversely or circularly
disposed fibres, which are external in position to a series of broad band-like longitudinal

32 THE VOYAGE OF H.M.S. CHALLENGER.

muscles. The longitudinal muscular bands are in close relation with the proboscis-sac.
Their exact disposition was not made out, and their arrangement, as shown in the figure,
will possibly need correction.

" On the whole, Pelagonemertes is a form of considerable zoological importance. In
the flattened form of its body, and in its dendrocoelous digestive tract the animal
resembles Planarians. Amongst the Rhabdocoeles the Prostomew possess an exsertile
proboscis like that of Nemertines, but such an organ is present in no Dendroccele. In
all particulars — in being unisexual, in the simplicity of the generative organs, in the form
of the nervous and vascular systems and of the proboscis, in the jiosition of the mouth and
presence of an anus — in all essential structures Pelagonemertes is most distinctively a
Nemertine. Only in its remarkable dendroccele intestine does it differ from all other
Nemertines, and (but this is of far less importance) in the modification of its tissue into
the peculiar hyaline gelatinous condition which is characteristic of so many otherwise
most widely difi"ering pelagic animals.

" The development of the dendroccele intestine is very remarkable, in that the lateral
ramifications are apparently to be regarded as a series of buds occurring successively
from before backwards from a previously straight digestive tract, such as exists in other
Nemertines. In this the digestive tract difiers entirely from that of dendrocoelous
Planarians, such as Lejytoplana tremellaris, in which, as we know from the observations
of Keferstein (' Beitriige zur xA.natomie und Entwickelungsgeschichte einiger Seeplanarien
von St. Malo,' Abhandl. der k. Gesellschaft der Wiss. zu Gottingen, 4ter Band,
Gottingen, 1868, Taf. iii. figs. 19, 20, 21, text p. 34), 'the great yelkballs arrange them-
selves in the embryo with regularity and map out the form of the future digestive tract,' the
peripheral ramified part of the tract being formed at the same time as the central portion.

" The peculiar form of the front of the body of Pelagonemertes may be regarded as an
instance of the excessive formation of the head lappets of many Nemertines. In having
no ciliated sacs and an unarmed proboscis, Pelagonemertes resembles Cei^halothrix, but
the animal must evidently be placed in a new family of Nemertines, for which I propose
the term Pelagjonemertid^, thus characterised : —

" Animal pelagic in habit. Body gelatinous, hyaline, broad and flattened. Proboscis
unarmed. Ciliated sacs absent. Special sense-organs absent. Digestive tract dendro-
coelous.

" The occurrence of a second specimen of Pelagonemertes off Japan shows that the
animal has a wide distribution. It was found on both occasions adhering to the trawl-
net, and is, from its very slight consistency, easily overlooked. Hence it may have
been often missed by us, and probably is as widely distributed as other oceanic forms.
Since it has never been taken by former observers of pelagic animals nor by us in the
tow-net, it is very probable that it occurs only in deep water, and does not come to the
surface ; it is, however, most evidently not an inhabitant of the sea-bottom.

REPORT ON THE NEMERTEA.

33

" Postscript. — Since the above was written, my attention has been directed by
Dr. von Willemoes Suhm to Lesson's original figure of Pterosoma in the ' Zoology of the
Voyage of the Coquille ' (which work we have been able to consult, with a splendid series
of similar publications, in the Hawaian Government Library at Honolulu), and to the
many points of resemblance between Pterosoma and Pelagonemertes.

Fig. 3. — Pelagonemertes rollestoni, Moseley, enlarged, viewed from the dors.il surface ; the proboscis is partly extruded.
P, proboscis ; PrS, sac of proboscis ; IP, invaginated portion of proboscis within the proboscis-sac ; G, superior nerve-
ganglion ; NC, nerve-cords ; V, vascular trunk (the upper V points to an enlargement of the vessel lying just
posteriorly to the superior nerve-ganglion) ; I, intestine ; D, diverticula of intestine ; 0,0, ovaries ; CM, circular
muscles ; LM, longitudinal muscles.

" Pterosoma plana is described by M. Lesson, ' Voyage de la Coquille, Zoologie,'
Paris, 1830, p. 254, and figured, pi. iii. figs. 3 and 3 bis. Pterosoma was obtained in
great abundance by Lesson between the Moluccas and New Guinea, August 31, 1828.

"The animals measured 3 inches and some lines in length, 18 lines in breadth, and
3 to 4 lines in thickness. In general form and gelatinous structure Pterosoma resembles

(ZOOL. CUALL. EXP. PAET LIV. — 1886.)

Hhli5

34 THE VOYAGE OF H.M.S. CHALLENGER.

Pelagonemertes further, in that a series of polygonal areas are marked out on its surface.
The spirally wound organ, described as a tube, which is indicated in the figure of
Fterosoma, can scarcely be anything else than the proboscis of a Nemertine, the mouth,
at the extreme end of the body, being probably the aperture of the proboscis-sac, and the
fusiform nucleus the sac itself. On the other hand, it is ditiicult to conceive that Lesson,
with a number of specimens available for examination, could have missed seeing the very
conspicuously burnt-sienna-coloured ramified intestine of Pelagonemertes had such been
■present in his Fterosoma. Further, in Fterosoma, a pair of elongate, closely opposed
eyes are described and figured, having transparent coloured cornese.

" On the whole, now that a pelagic Nemertine is known to exist, there seems little
doubt that the animal seen and figured by Lesson was a Nemertine and not a Mollusc,
but it seems to have been a distinct form, with a pair of eyes and an unbranched digestive
tract."

For the sake of facilitating reference to Lesson's two figures of Fterosoma, in which
Moseley is so strongly inclined to see a second species of pelagic Nemertine from the
tropical seas — a supposition in which I entirely concur — I have reproduced these on
PI VIII. figs. 1, 2.

The single available specimen of Felagonemertes, when it came into my hands in
September 1884, was no longer entire, but consisted of two fragments of the body, and
of three small fragments of the proboscis. Both body-fragments were sht open on the
ventral side, the internal surface of the digestive tract, and partly that of the proboscidian
sheath, having thus been laid bare. The terminal portion of the body was missing
{vide Moseley, supra). My friend Professor M'Intosh, who made these incisions and
examined the specimen before it came to me to be sectionised, has made the following
notes: —

" The structure of the cutis corresponds with that of other forms. In the preparation
the transparent gelatinous basis-substance for the most part alone remained, the granular
cells and clear mucous or gelatinous contents of these spaces having escaped. Beneath
this layer is a remarkable deep investment of basement tissue, which forms an elastic
investment all round the body. Numerous ducts, often having a zig-zag appearance,
pass through this coat.

" The muscular layers of the body-wall, as Professor Moseley observes, are compara-
tively thin. The external circular fibres are hardly to be distinguished in ordinary
transverse sections, and form a thin layer outside the longitudinal. Such a condition
contrasts strongly with the well-marked circular coat in Amphiporus lactijioreus. The
longitudinal muscular coat is likewise comparatively thin, though it is better developed
than the circular.

" Frohoscis. — In the preparation the proboscis is partly extruded, and issues in the
same manner as in the ordinary form. It is streaked by longitudinal lines externally.

REPORT ON THE NEMERTEA. 35

" 111 minute structure the anterior region quite corresponds with the tj^jical form,
presenting externally a layer of elastic fibrous tissue, which in transverse section presents
a series of circular fibres. The external longitudinal muscular coat is well developed.
The reticulated layer cuts the foregoing layer into sections, as usual in most other forms,
and the connecting bauds seem to be broad, the longitudinal belts rounded in transverse
section. The condition of the specimen, which is imperfectly preserved, however,
probably causes this layer to be more prominent, and the separation between the two
lonoitudinal coats wider. The inner loneritudinal muscular coat has the usual thickness
and appearance, and the same may be said of the inner circular muscular coat. The
basement layer is verj^ largely developed, and fills up a considerable part of the central
area. It is somewhat regularly streaked by a radiating series of granular channels.
Occasionally tortuous and numerous granular cells occur in it. The central granular
glandular tissue has mostly disappeared, but in minute structure it corresponds with that
in other forms.

" The middle region of the organ presented no visible stylets, but otherwise it agrees
in general configuration with the typical form, though less definitely formed. The glands
of the posterior region are largely developed.

" The posterior part of the proboscis sheath had a quantity of flocculent material
microscopically presenting numerous granular, and often nucleated cells, mixed with
granular material ; such might be connected with the proboscidian gland.

" The mouth, as Professor Moseley observes, forms a well-marked aperture with a
frilled margin. It is proportionally the most distinct aperture yet observed. The
minute structure of the oesophageal region is similar to that of other forms, and it
terminates similarly.

"The dendritic arrangement of the digestive system. Professor Moseley states, is the
most remarkable feature about Pelagonemertes, indeed it diff'ers from all other
Nemerteans. The condition of the organ in the other forms, however, renders the
arrangement less striking. In Nemertes gracilis, for instance, it is considerably divided.
Microscopically it agi'ees with other forms in cells, &c. Professor Moseley describes a
distinct anus in the young form, but the specimen may have been incomplete posteriorly.
It is certainly unusuallj^ distinct. The vascular system offers no particular feature of
interest so far as observed, and seems to follow the ordinary arrangement. The lateral
vessels appear to vary a little from the ordinary relation to the nerve-cords, being often
internal rather than inferior, but probably such is due to the yielding nature of the
tissues. The inner lining of the vessels is granular, and a few granular cells ajipear in
the centre, but the nature of such is problematical

" The nerve-trunks are enveloped in a coating of nerve-cells. The branches from the
ganglia and nerve-cords are remarkably distinct, presenting a clear sheath and granular
axis cylinder. The gelatinous interstitial substance extends between the muscular

36 THE VOYAGE OF H.M.S. CHALLENGER.

substance and fills up tlie central area of the body in transverse section to an unusual
extent, as pointed out by Professor Moseley.

" Besides the organs mentioned by this author within the body-cavity, a large number
of granular nerve-cords run outwards to the surface (muscular wall), besides fine fibres,
which are very apt to assume a coiled or zig-zag appearance. Some of these much
resemble blood-vessels, but they are probably nerves, and they divide into fine branches
towards the muscular coat.

" The proboscidian sheath or chamber is very large, and its anterior aperture would
seem to be unusually distinct. The structure of the parts in unrolling of the organ is
the same as in the others, and the wall of the chamber presents continual circular internal
longitudinal fibres; the posterior region of the proboscis is firmly fixed as usual to the
internal wall of the proboscidian sheath at its narrow posterior end. The fibres of
attachment are short, so that the cul-de-sac of the posterior chamber is brought close to
the surface of the wall of the sheath. From the appearance of the parts posteriorly, it is
possible that the region is in process of repair after laceration. Indeed, it is not unlikely
that both anterior and posterior ends can easily be repaired after rupture, and that might
account for the absence of eyes (see Lesson's Pterosoma, 'Voyage of the Coquille').
Such gelatinous forms are especially prone to rupture, and sufficient is known of the
recuperative power of the Nemertean to render repair rather than permanent injury the
rule. The proportionate size and firmness of the proboscidian chamber, with its glistening
internal surface, are certainly remarkable, and, on the whole, my impression is that the
form is incomplete posteriorly."

All the fragments of Pelagonemei'tes that came into my hands were carefully treated
with stainino- reagents, hardened, imbedded and sectionised. The sections were all trans-
verse. PL VIII. fig. 3 represents one of the average sections with parts of aU the important
organs imbedded in the common gelatinous basis. No sufiicient sections of the brain
were available, nor were distinct traces found of a nephridial system. The integument
was in most parts of the surface wholly deficient ; in a few others its general correspond-
ence in transverse section with what is typical for the Hoplonemertea could be verified.

Certain other striking particulars, also visible in this section, and on the whole only
confirmatory of what we already knew by Moseley's and M'Intosh's observations, are
(1) the absence of a dorsal median blood-vessel; (2) the ventral openings of the generative
sacs; (3) the numerous transverse fibres, both contractile and nervous, running in
different directions through the body -jelly. Further, it may be observed, even with a
rather low power, that each of the ripe ova is surrounded by numerous small follicle cells
(PL VIII. figs. 3, 11), and that the nucleolus is often only represented by very numerous
small chromatin spheres.

By the aid of stronger powers the details also represented on PL VIII. by
figs. 4-13, can be more fully studied, and of these mention will succe.ssively be made in

KEPORT ON THE NEMEETEA. 37

the different paragraphs, which are more especially devoted to the internal anatomy of the
different representatives of the species, that are here described in their systematic
arrangement.

C. SCHIZONEMERTEA.

Family L i N E i D ^.

Cerehratulus, Ren.

To this genus I wisli to refer all the Schizonemertea collected by the Challenger. I
have elsewhere (VIIl) insisted on the difficulty of distinguishing the genera Cerehratulus,
Li7ieus, Micrura, &c., of which perhaps the two first may be distinguished by an
ontogenic difference {Pilidium or Z>esor-iarva). And even this distinction is not
definitely established. It is simply impossible to refer spirit specimens to any one of
these genera rather than to any other, and having formerly included Micrura as a
synonym amongst Cerehratulus, I now even feel inclined to do the same with Linens.
What value has a generic distinction when it can never be of any use to a taxonomist ?
And why should a developmental difference, such as that which obtains between a
Pilidium and a Desor larva, not be sufficiently honoured by a specific distinction ?

As to describing new species in this genus, it is even more diflicult than in any other,
because of the number already existing, which are partly solely distinguished by their
coloration in life, a character not available in determining the Challenger specimens.
Hence, only in seven cases can Ihold myself justified in referring the fragments to separate
species, six of which are new. The remaining fragments and heads, which clearly show
the Cerehratulus type (e.g., PI. XV. fig. 8), I will not specifically distinguish; what
remarks I have to make about them will appear when treating of the anatomy, and
will then be noticed as pertaining to the genus Cerehratulus in general.

Followino; the order of succession of the stations at which the Schizonemertea were
successively dredged diiring the expedition, we will now proceed to describe them.

Cerehratulus truncatus, n. sp. (PL I. figs. 11, 12).

This si:iecies, collected on the coast of Nova Scotia, and, as we refer a specimen from
Bermuda to it, also frequenting the ocean in the vicinity of those islands, was captured
May 8, 1873 (Le Have Bank), and once more, on May 20 of that year, when it came
from a depth of 85 fathoms at Station 49.

The anterior part of these two specimens is figured on PI. I. figs. 11, 12, the first
being a side view, the second a ventral view, the latter more considerably, the former
aljoutfour times enlarged. From both fioures it is. seen that the mouth is small and close

Ill Specimen a.

In

Specimen h.

30

34

35-39

38-44

43

51

55

60

84

103

97

11-2

38 THE VOYAGE OF H.M.S. CHALLENGER.

to tlie tip of the head, which is more or less truncated, that the cephalic slits are compara-
tively short, extending on to the anterior surface of the head, where they do not, however,
coalesce, but leave a small interval in which the proboscidian aperture is situated.

This is all that can be said of the external appearance.

The internal structure further confirms the supposition which the external characters
point to, viz., that these two specimens belong to the same sj)ecies. Thus, certain chief
points in the series of transverse sections made through both the specimens coincide to a
degree that may be judged of by the following table : —

The superior brain commissure is situated in section No.
The inferior brain commissure is situated in sections No.
Canal of the posterior brain lobe is situated in section No.
The mouth begins in section No.
The mouth ends in section No. . . .

First appearance of nephridia in section No. .

In specimen a (May 8, 1873) there are noticed four transverse deferent ducts to the
longitudinal nephridial duct on the left side (in sections 138, 175, 217 and 278), and four
on the right side (sections 147, 191, 217 and 278).

In specimen h (May 20, 1873) there is a less regular arrangement, some of the
deferent ducts being double, i.e., two at the same level or in the same section. Once in
this specimen this is so arranged that in the one section (No. 1 97) there are four deferent
ducts cut nearly throughout their whole length. In the portion of the oesophageal region
sectionised, which, however, does not embrace the whole nephridial region, I count in this
specimen on the left side six deferent ductules (sections 112, 144, 156, 159, 197, 207), and
to the right also six, which are only partly oj^posite to the left ductules (sections 142, 168,
178, 180, 197, 208). In judging of this apparent discrepancy it should not be lost sight
of that the short distance separating the two ductules 156 and 159 on the left is still
symmetrically repeated on the right side in 178 and 180, though somewhat further
backwards.

A commissure uniting the two vagus nerves after they have left the brain and before
they have yet reached the oesophagus was distinctly noticed.

The histological details of the integument fully correspond to the type of Cerehra-
tulus corrugatus, which will hereafter be more fully described and figured {cf. PL XIII.
fig. 6), and which is diagrammaticaUy represented in fig. 9 of PI. XL as differing from
figs. 10 and 11.

One of the specimens showed a very curious pathological degeneration, which I will
however, only touch upon very briefly. The muscular tissue on a restricted but ring-
shaped region not far behind the head, and only as far as the circular and longitudinal
rauscLilar coats are concerned, is replaced by (or gradually passes into) a homogeneous

REPORT ON THE NEMERTEA. 39

gelatinous mass, in which granular spherical bodies with large and distinct nuclei
(about one-fifth of the diameter of the body-wall on this spot) seem to be suspended.
Is this a local injury? Are these bodies enclosed gregarines or other parasitical
unicellular organisms ?

These questions can as yet only be formulated but not answered, and I would call
the attention of future observers dealing with fresh material to similar cases, which no
doubt must be accompanied by some externally visible distinction between the tissues.

Of the Bermuda specimen, which I refer to this species only with doubt, and which
measured 33 mm. in length by 2^ mm. in diameter, the integument was very imperfectly
preserved ; still it corresponds in the remaining characters with the other specimens of
Cerebratvlus truncatus. There are also points of agreement in the structure of the
proboscidian sheath.

The transverse blood-vessels are very thick-walled in this specimen, a feature more
particularly due to the basement-tissue below the inner epithelial lining.

Cerehratulus medullatus, n. sp. (PL XL fig. 10; PL XII. figs. 9, 10).

It is hardly consistent with the most lenient rules of zoological nomenclature, and it
is certainly not consistent with those which I havemyself advocated in my introduction, to
establish a new species on a fragment which has neither head nor tail ! Still, as I have been
rather careful on other occasions, and that especially with regard to genera, I may be trusted
to be anxious to guard against superfluous additions to an already cumbersome synonj'my.
The reasons by which I am guided in putting up this mutilated spirit fragment as the
type of a new species are purely morphological, and, as will be seen in the paragraph
treating of the nervous system, the peculiarities off"ered by this species are of sufficient
morphological interest to give it a place by itself, and (in at the same time naming it) to
direct the attention of collecting naturalists to this form.

It came up in the same haul of the dredge as did one of the specimens of Cerehratulus
truncatus just described, viz., at Station 49, off" Nova Scotia, from a depth of 85 fathoms.

In sections it is, however, immediately seen to be distinguished from the foregoing
species by several features, the first of which concerns the integument. Instead of the
integument being separated from the longitudinal outer muscular layer by a more or less
massive expanse of basement-tissue (PL XIII. fig. 6), the integument itself being divided
into a superficial and a deeper glandular layer (which are separated by a secondary
basement membrane and an expanse of fibres, such as is found in Cerehratulus
corrugatus, Cerehratulus truncatus, &c., also in the Challenger collection), our present
species has the superficial layer of the integument immediately applied to the outer
longitudinal muscles, from which it is thus only separated by the outer secondary basement
layer just alluded to (PL XII. fig. 10). This fact causes the integument in transverse

40 THE VOYAGE OF H.M.S. CHALLENGER.

sections to appear very thin in comparison to that of other species. However, closer
inspection reveals (as will be more fully discussed in the paragraph devoted to the
integument) that the deeper glandular layer is not wholly deficient, that it has only
become intercalated amidst the outer longitudinal muscular layer, which in this species is
not very massive, and that its cellulo-glandular elements thus reach amongst these muscle
fibres, even as far down as the nervous layer just outside the circular muscular coat
{cf., PI. XII. figs. 2, 10). The strong affinity which these gland-cells possess for staining
reagents brings this out in the sections very clearly.

Nor is this the only distinctive feature of Cerehratulus medullatus; the second, and
none the less important, is that in the nervous plexus just alluded to, the dorso-median
longitudinal thickening, which I shall presently, in the anatomical part of this Report,
designate as the medullary nerve, is exceptionally massive (cf., PI. XI. fig. 10 ; PI. XII.
fig. 9), being about one-third to one-fourth of the thickness of the fibrous core of the
lateral longitudinal nerve-trunks. Amidst the fibres of this dorso-median stem a few
nuclei, more faintly coloured and marking the presence of nerve-cells, are also seen.

In longitudinal sections through the same specimen, the unusual size, distinctness,
and marked individuality of this nerve-stem was also very obvious.

No other features of this species will for the present be enumerated. The specimen
on which it is founded was of the female sex.

I sincerely hope that the points here enumerated may enable American naturalists,
when recapturing specimens of the species, to recognise it and to give us indications of its
3olour and other peculiarities in life, of the shape of its head and cephalic slits, and of its
brain lobes and proboscis.

Cerehratulus lomjijissus, n. sp. (PI. I. fig. 16 ; PI. XV. figs. 1, 9, 10).

No other Schizonemertea were collected between the last-mentioned station and
Marion Island (Station 144a). A Cerehratulus was here brought to light, which it will
in future be easy to recognise by the fact of its having uncommonly long cephalic slits.
The specimen, which was perfect, and is also characterised by its comparative shortness, is
figured on PI. I. fig. 16. On inspecting it with the naked eye the mouth was found to
be small and to be situated anteriorly ; the proboscidian aperture occupied the place
indicated in the figure, whereas on the dorsum of the animal, just behind the end of the
slits, two rows of sublateral, very small pores were noticed, being visible as extremely small
white punctures. These rows were continued very far backwards. Although, on account
of their reaching so very far forwards, they might at first sight be taken for the exterior
openings of the nephridial system, the sections showed that they are indeed the
generative pores. Moreover, that the cephalic slits, though long, are comparatively
shallow, especially in their posterior portion, and that the canals leading into the posterior

REPORT ON THE NEMERTEA.

41

brain-lobes do not open out in the lower angle of the fissure but far forwards, in agree-
ment with the situation of those lobes.

It will perhaps best serve the purpose of conveying an idea of the relative situation
of the more important organs in the head and trunk to give, as was done for the fore-
going species, the number of the section of the whole transverse series (into which head
and anterior oesophageal region were cut up) in which these organs occur.

We then find: —

Section 30. First appearance of the lateral blood-
lacunse iu the head.

Sections 64-66. Superior commissure of the brain-
lobes.

Sections 71-78. Inferior commissure of the brain-
lobes.

Section 80. Left canal from cephalic fissure into
posterior brain-lobe.

Section 87, Right canal from cephalic fissure into
posterior brain-lobe.

Sections 84-104. Left posterior brain-lobe.

Sections 89-105. Eight posterior brain-lobe.

Section 71. The median blood-vessel enters the
proboscidian sheath.

Sections 350-360. It again leaves it.

Sections 129-159. Mouth.

Section 129. First appearance of the nephridial
canals just above the level of the longitudinal
nerve-trunk.

Sections 355-400. Left deferent ducts of nephri-
dial system.

Sections 329-335. Eight deferent ducts of nephri-
dial system.

These two deferent ducts (the only pair) are seen in the same section which still
shows the cephalic fissures. The ducts do not, however, open out into these fissures, but
just above them. This also proves how far the fissures reach, all along the oesophageal
region. In the 410th section the end of the cephalic fissures may be said to be reached,
the whole of the nephridial system, excretory ducts and all, being thus situated within
the region of the fissures.

Another specimen from the same locality was without a head, and though the
principal points of comparison are thus deficient, I feel confident, by the internal
characters which are shown by the sections, that we may look upon this specimen as
belonging to the same species. It was exceedingly well preserved and showed certain
interesting points with regard to the generative organs, which wiU be more fuUy discussed
in the paragraph devoted to those parts.

Another feature by which the species is — if not distinguished from its neighbours —
at least characterised as far as the fragments allow us to judge, is the great thickness
of the transverse connecting vessels between the medio-dorsal vessel and the two lateral
ones.

Cerebratulus cor7-«(/a^ws (M'Intosh), Hubrecht (PI. I. fig. 17 ; PI. XI. fig. 9 ; PI. XI F.
figs. 3, 4 ; PI. XIII. figs. 1-6 ; PL XIV. figs. 2-4).

This species, which was first described by M'Intosh in the Transactions of the Royal
Society for 1879 (extra vol., p. 262), has again been recognised by this author as occurring

(ZOOL. CHALL. EXP. — PART LIV. — 1886.) Hhll 6

42 THE VOYAGE OF H.M.S. CHALLENGER.

amongst the ChaDenger Nemertea. I have already indicated (p. 37) why I wish to bring
it under the genus Cerehratulus, rather than under Lineus, where M'Tntosh placed it.

The following notes were made by him concerning the Challenger specimens.

"Dredged in considerable abundance in Royal Sound, Kerguelen, January 27, 1874,
in 25 fathoms.

"Stat. 149, ofi" Christmas Harbour, Kerguelen, 120 fathoms, small specimens.

"Stat. 151, off Heard Island, 7th Febr. 1874, 75 fathoms. Some reach the length of
200 mm., and much contracted forms have a diameter of about 15 mm. In the oesophagus
of one was a blackish mass of sand-grains, sponge-spicules. Diatoms, and mud."

In M'Intosh's previous publications the description of Lineus {Cerehratulus) corru-
gatus contains the following characteristic features : —

"Body rather abruptly pointed anteriorly, and more gradually posteriorly. The
oesophageal region is marked externally by a series of prominent and somewhat regular
rugse, which sweep from the mouth dorsally and veutrally.

" Colour dark oHve throughout, with the exception of a white band, which crosses the
anterior border of the snout, and passes backward to the posterior third of the lateral
fissure, where it bends dorsally and terminates."

" The special characters are the very large mouth, with the prominent rugae, which
show that the animal probably possesses unusual powers of oesophageal protrusion — a
supposition borne out by the great development of the external circular muscular fibres,
the dorsal longitudinal coat, and the other fibres of the organ. The internal glandular
lining is also very firm."

A couple of figures are added, one a section of the proboscis, the other a section of the
ventral body-wall. The latter should be compared with our fig. 6 on PL XIII. It will
then be seen that M'Intosh's " pigmentary layer, divided by a definite black band," is
our superficial and deeper layers of the integument {Isg and Idg). The " black band"
between them is no other than our external secondary basement membrane. What
M'Intosh designates as the " curious translucent stratum cut into somewhat regular
spaces " is our basement layer proper [B), comparable to that of Eupolia and Carinina,
and radially traversed by bundles of contractile and nervous fibres, which bring about the
"regular sjDaces" alluded to.

On the whole, our two figures will be seen to correspond very well, only MTntosh
omits the nervous layer and the innervation of the CBSophagus. The large mouth and
folded lips were very conspicuous in the Challenger specimens, the head of one, seen from
the ventral surface to show the mouth, being figured on PI. XIII. fig. 5.

The different series of sections which I have made through four specimens of Cerehra-
tulus corrugatus were very instructive in several respects, although they all conform to
the well-known Schizonemertean type. It is especially the considerable development of
basement tissue of the integument (PI. XIII. fig. 6, B), which not only brings out the

REPORT ON THE NEMERTEA. ' 43

distinction between the outer longitudinal muscular layer y and the integument much
more clearly than is so often the case in other Schizonemertea, where these two have be-
come blended, but which also enables us to trace the course of radial nerve-fibres coming
from the plexus or the longitudinal stems, and innervating (after having traversed the
muscular layer 7 and this basement tissue) the glands and sense-cells of the integument.
Cerehratidus corrugatus is, moreover, the species in which, for this reason, I was able to
determine the direct part which the longitudinal nerve-trunks take in the innervation of
the skin (PL XIV. fig. 2), whereas, even in this very favourable specimen, I never
noticed the faintest trace of a similar participation of nerve-branches directly springing from
these stems in the innervation of the subjacent musculature. In that case such branches
would have to take an opposite course, and would have to traverse in the first instance
the circular muscular layer /3. This was never observed. It will be seen in the paragraph
more especially treating of the nervous system, as well as in the chapter devoted to
general considerations, that this fact is, in my opinion, not without morphological
importance.

The specimen of Cerebratulus corrugatus is also of great importance in demonstrating
the relation of the medio-dorsal medullary nerve and the branches springing from it at
right angles as so many thickenings of the plexus (PL XIII. fig. 2).

Cerebratulus parTceri, n. sp. (PL XIV. fig. 5 ; PL XV. figs. 5, 16).

A well-preserved specimen of a Schizonemertean was collected in the New Zealand
waters, which, I think, may safely be looked upon as belonging to a distinct species.

I have dedicated this species to the naturalist who of late years has done so much for
our knowledge of the New Zealand fauna, and whose anatomical preparations and zoologi-
cal collections from those regions have excited the admiration of visitors to the Colonial
and Indian Exhibition of 1886.

The head and anterior body fragments of Cerebratulus parkeri are thus described in
M'Intosh's preliminary notes : —

"A fragment of the anterior portion, measuring about 34 mm. in length, and about
7 mm. in diameter at its flattened and widest region. The cephalic furrows and mouth
conform to the ordinary type. The body is somewhat rounded anteriorly ; flattened
towards the posterior end of the fragment.

" Transverse sections of the rounded anterior region show that the muscular walls of
the body are greatly thickened .... the longitudinal muscular fibres form a very

thick coat all round, especially, as usual, opposite the nerve-cords The

circular muscular coat is uniformly thick, the longitudinal layer within it being excavated
superiorly by the large channel for the proboscis, and laterally by the very large and
very muscular vascular canals — a little below each nerve-trunk. The thickened part of

44 THE VOYAGE OF H.JI.S. CHALLENGER.

this coat is just beyond the proboscidian canal, while the thinnest part is in the median
line above it.

" The proboscidian sheath has a remarkably thick wall, which is chiefly composed of
an interwoven circular coat, presenting an irregular looped appearance in transverse
section. The fibres in thin sections seem to anastomose. On the inner surface of this
coat are some longitudinal fibres, with a glandular epithelial coat internally.

" Posteriorly the body-cavity is greatly dilated by the presence of a vast series of ova,
so that all the muscular coats are much thinned, and the digestive canal contracted. The
inner longitudinal coat is especially affected, three thickenings only being left, viz., one
on each side of the proboscidian sheath, and one in the middle line ventrally. The ova
are compressed into various angular forms, between vertical partitions which occur at
short intervals in the region, and which fill up the entire area, except the small sjjace for
the proboscidian and digestive canals superiorly."

For some farther particulars concerning this species, I refer to the description of Cere-
hratulus macroren that is still to foUow, and where the points of agreement and of difier-
ence between these two evidently closely related species will be more fully entered upon.

A second specimen, also from the New Zealand waters, shows that the conspicuous
development of the secondary basement layer of the integument, and the considerable
thickness of the medullary nerve, are further characteristic features of this species.

Cerehratulus angusticeps, n. sp. (PI. I. fig. 15 ; PI. XIV. figs. 1, 6 ; PI. XV. fig. 4).

This is another Schizonemertean from the New Zealand waters (Station 167a, Queen
Charlotte Sound, June 27, 1874 ; 10 fathoms). Its head is figured on PI. XV. fig. 4.
In M'Intosh's preliminary notes this fragment is referred to in the following words : —

" A fragmentary form, resembling in shape C. angulatus, and with an acutely pointed
snout. The diameter of the widest flattened region is about 4 '5 mm. The colour is dull

yeUow, with a darker stripe down the middle of the dorsum The vascular

trunks lie opposite the nerve-cords, and this in the angular lateral region. The external
longitudinal muscular coat is largely developed, and the fibres are uniformly fine. The
very much produced lateral angle of the body is mainly composed of this coat. In such
forms the lateral nerve-cord seems to be much flattened from above downwards."

The sections which I made of this fragment, horizontally through the head and trans-
versely through the trunk, were in many respects very instructive. To the flattened and
pointed shape of the head they added an internal distinctive feature of the species in the
unusual size of the posterior brain-lobes, which, although in intimate connection with
the superior brain-lobes in the same way as in the Schizonemertea, in general equalled
or even surpassed the latter lobes in length. PI. XIV. fig. 6, gives a representation of
this, illustrating, at the same time, how in a horizontal section the blood-space (c.oJ.)

REPORT ON TUE NEMERTEA. 45

surrounding the oesophagus may very evidently be seen to be in direct connection with
that in the head — a fact known to BLinchard, and for the first time fully described by
Oudemans {loc. cit.), but never adequately figured. This figure, at the same time,
demonstrates the projection of the posterior brain-lobe into this blood-space, by the con-
tents of which it is thus bathed.

Another figure reveals how the sections of Cerehratulus angusticeps were important in
another respect, viz., that of the medio-dorsal medullary nerve and the transverse branches
springing from it in metamerically arranged pairs (PI. XIV. fig. 1). Nor was this
regularity exceptional in the region figured ; it was characteristic wherever these trans-
verse nerve-tracts (which will be discussed more fully in their relation to the j^lexus in
the special paragraph) were met with, and was thus equally distinct ventrally and dorsally.
Ventrally, however, there is no median longitudinal stem.

On the other hand, the transverse tracts in Cerehrahdus angusticeps may be traced
as high up as the lower brain-lobes, which they connect till just behind the strong
ventral commissure of these lobes.

These transverse commissural trunks are distinctly separate from those by which the two-
stems of the vagus nerve are united close to their origin and in front of the mouth. The latter-
{cf. PI. XIV. fig. 5) are also present as distinct commissures in Cerebratulus angusticeps.

With respect to the nephridia, which often offer certain points of comparison for the
different species, I must state that the anterior part of the longitudinal duct is very
distinctly seen in the horizontal sections through the anterior extremity of the body, and
occupies its usual position in the circumoesophageal blood-space, whereas its size or its.
histological details showed no special features. The deferent ducts of the nephridial
system were not contained in this section, nor in those made through the remaining
fragments of the further portions of the body. They were very probably situated in the
intervening part, which was sacrificed by IM'Intosh in drawing up his preliminary notes,
and I cannot thus state with certainty whether these ducts were single or more
numerous, terminal or not.

To Cerehratulus angusticeps I must refer another specimen which came up in the
dredge at Station 168 from a depth of 1100 fathoms. It was much torn and lacerated
(PL I. fig. 15), a phenomenon which it would, however, be rash to attribute to the depth
from which it was brought up, although the possibility of that being the cause cannot be
wholly excluded. The reasons for identifying the specimens with Cerehratulus angusticeps:
are the following, and are deduced from the comparison of the sections : — (1) The length
of the superior brain-lobes stands to that of the posterior in the same (uncommon) rela-
tions as in the specimen above described ; (2) the ventral and parallel commissures of the
inferior brain-lobes are similarly very conspicuous; (3) certain histological details of the
superior brain-lobes and cUiated canal, and also of the nerve plexus, are identical ; (4) the
aspect of the rhynchodgeum is very similar.

46

THE VOYAGE OF H.M.S. CHALLENGER.

Cerebratuliis macroren, n. sp. (PI. I. figs. 13, 14, 18, 19; PI. X. figs. 8, 9; PI. XL
fig. 11 ; PI. XII. figs. 1, 2, 7, 8 ; PI. XIII. figs. 7-9 ; PL XIV. figs. 7, 8, 11 ;
PL XV. figs. 2, 3, 19).

From Japan, at Station 232a, a Schizonemertean has been brought home by the
Challenger Expedition, which I was first inclined to regard as identical with Cerebratulus
parheri, but which I have reluctantly been obliged to distinguish specifically — reluctantly,
because there being no possibility of giving outwardly visible distinctive features of
colour or shape, I must indicate an anatomical difference as the principal point of
distinction between the two ; and all the more reluctantly because of a second specimen,
which, dredged at 700 fathoms off" New Zealand (Station 169), was identical with the
Japan specimen, and differed from its much closer geograj)hical neighbour in this very
same point. I could not, however, evade assigning the latter specimen to the species
now about to be described, knowing by experience that if the confusion created by the
unnecessary multiplication of specimens is often very troublesome, the premature com-
bination under one name of forms that afterwards may be shown to be different is often
quite as apt to lead to inextricable confusion, when characters which, as a matter of fact,
only belong to one of them, are attributed to both.

About this second specimen M'Intosh's rough notes contains the following passage : — ■
" A small Lineus, presenting the ordinary external characteristics, and of a dull
yellowish hue, somewhat brownish on the dorsal surface in front. It was tapered from the
snout backwards. The cutis has a simple areolar structure ; the gelatinous contents were
slowly extruded in the sections after mounting, as cylindrical or clavate, translucent gela-
tinous processes. The basement tissue is largely developed as a translucent belt all round."
Of the larger specimen from Japan, the head is figured (PL I. figs. 18, 19). The
cephalic slits are perhaps comparatively a little longer than are
those of Cerebratulus parheri (PL XV. fig. 5), although the New
Zealand representative (PL I. figs. 13, 14) is again very similar,
even in this respect, to Cerebratulus parheri.

The internal anatomical character, to which I alluded just now
as being a distinctive feature, by which the species differs from
Cerebratulus parheri, is the size of the longitudinal nephridial
ducts, wliich are exceptionally conspicuous (both in the Japanese
and in the New Zealand specimens), and which have their deferent
ducts leading to the exterior situated at the very hindmost end,
whereas in Cerebratulus parheri there are two deferent ducts, the
one situated very closely behind the other, and placed about the
middle region of the longitudinal canal. The accompanying wood-
cut diagrammatically illustrates this difference between the two species. Oudemans
{loG. cit.) has already demonstrated that the number of deferent ducts to the nephridial

Fig. 4. — Nephridial ducts
and their communication
with the exterior, a, for
Cerebratulits parkeri ; b, for
Cerebrattdus macroren.

EEPORT ON THE NEMERTEA. 47

system increases with age ; there thus might remain one chance that the New Zealand
specimen of Cerebratulus macroren could still be assigned to Cerebratulus parkeri, if
we assume that increase in growth can have brought about a further extension backwards
of the principal nephridial duct, and at the same time the appearance of a second deferent
duct immediately behind the first. For the present this assumption appears to me to be
more strained than my own, which unites the New Zealand and the Japanese specimens
by laying more stress upon the large size of the longitudinal tube, combined with the
terminal situation of the deferent duct.

The further peculiarities that reveal themselves on studying the microscopic sections,
certainly show that the tw^o species, Cerebratulus macroren and Cerebratulus parhen,
cannot be very far apart. Both have in common the very thick and homogeneous secondary
basement layer beneath the outer glandular layer of the integument (PL XL fig. 11).

It would also be difiicult to point out salient points of disagreement in the muscular
body-wall, the proboscidian sheath, and the proboscis which would hold good when
respectively comparing the head, the oesophageal, or the posterior body region.

Cerebratulus, sp. inc. (PI. X. fig. 7; PL XV. figs. 6-8, 18.)

At the close of our systematic description of the Schizonemertea I must mention
certain fragmentary specimens, which have all the aspect of belonging to distinct species,
but which I cannot venture definitely to unite with any of the species here described, or
with such as have been published elsewhere. The fragments here aUuded to are mostly
without a head, and some of them of not inconsiderable size. I wUl discuss them in the
order of the stations at which they were obtained.

The first was procured in the Kerguelen waters. It is important, in consequence of
peculiarities in its integument, which will be more fully discussed in the paragraph devoted
to this system. A part of a section was figured on PL X. fig. 7, and from that section it
may also be gathered that the dorso-median medullary nerve is comparatively very massive.
This might eventually prove that it was related to Cerebratulus medullatus ; the difi'er-
ence in the integument, "though important from a morphological point of view, hardly
justifying the establishment of a diff"erent species, supposing all the other characters,
external and internal, might prove to be identical. That diff"erence might then be con-
sidered as indicative of a variety.

The second Cerebratulus, about which I must remain in doubt, was obtained among
the Philippine Islands (ofi" Zebu). MTntosh has made the following notes about
these fragments : — " Fragments of a large species. The fragments in all measure over

100 mm., with a diameter of 12 mm. at the widest part The carrying of

the vascular trunks far inwards towards the ventral middle line seems to be a feature
. in this form."

48 THE VOYAGE OF H.M.S. CHALLENGER.

There were further no particuhirs, nor auj features deviating from the general type
of Cerehratulus to be gathered from these fragments.

Numerous other fragments, of which one was a head, were obtained at Kobe (Japan).
Three of these are figured on PL XV. figs. 6, 7, and 8. Sections were duly made of these
fragments, but do not give much additional light beyond the general result that we have
a Cerehratulus before us, which cannot be definitely identified with any of the species
hitherto described. The vicinity of the Japanese waters to scientific centres from which
accurate descriptions of the Japanese marine invertebrates ma)^ probably be expected
ere long, makes it all the more advisable to refrain for the present from creating or
identifying species from these regions of which sufficient data cannot yet be obtained from
the available fragments. Still the specimen figured on PI. XV. figs. 6 and 7 deserves some
attention. The fragment, on which longitudinal and transverse white stripes were
visible, as indicated in the figure, was also distinguished by a peculiar rigidity. Trans-
verse sections (PI. XV. fig. 7) showed that this phenomenon was occasioned, or at all
events accompanied by, an extraordinary development of intermuscular gelatinous tissue.
The section figured, when compared with that of Pelagonemertes (PL VIIL fig. 3), will
demonstrate this, and at the same time show it to possess the arrangement of muscular
layers and other peculiarities that are typical for Schizonemertea. These muscular layers
are, however, exceedingly reduced in thickness, and occupy a very inconsiderable fraction
of the vertical or horizontal diameter. The proboscidian sheath is, in the fragments
investigated, thin and unimportant ; in more posterior sections there are indications
of its place being taken by more irregularly shaped, cellular material, without a lumen.
I am, however, not satisfied with the details that could be gathered from these fragments
concerning these important morphological points, and must refrain from more particularly
insisting upon them. The transverse blood-vessels are exceedingly numerous and tor-
tuous— the latter phenomenon causing their lumen to be transversely cut a large number
of times in every section ; these apparent perforations of the gelatinous tissue giving a
very peculiar appearance to most of the sections.

Another reason why I do not venture to establish a distinct species upon these
peculiar fragments, is the fact that I found them to be very considerably infested by a
large unicellular parasite (probably a Gregarine) which w^as not (as the Gregarines that
infest Nemertea generally are) found in the intestine, but which was present in consider-
able numbers in all the difi"erent tissues, both without and within the muscular layers.
When surrounded by gelatinous tissue, there was always a well-marked space round the
parasite in which it was contained.

There was no distinct capsule, and the free space may perhaps not have existed
during the life of both host and parasite. When first noticed, these unicellular parasites,
with very distinct nuclei and granular protoplasm, might have been mistaken for ova ;
not only their distribution throughout the animal as isolated individuals, but also the

REPORT ON THE NEMERTEA. 49-

presence of true ova in the fragments, which proved to have belonged to a female
individual, definitely excluded the possibility of any confusion on this head.

The question arises, whether the peculiar appearance of the different tissues recorded
above might be pathological, and somehow in causal relation to the infesting parasites.
It is this which necessitates extreme caution in the identification of these fragments. I
may here remind the reader that another case, presumably of a parasitic organism (also
unicellular, but of much smaller size) infesting the different tissues, was met with in
Amphiiwrus marioni.

The last fragmentary specimen which I wish to record may, for all I know, have
belonged to the common Cerebratulus marginatus. It was collected in the Atlantic
Ocean, at Station 321, off the Brazilian coast. It was a very large and flattened speci-
men, but without head or tail. In M'Intosh's notes I find these fragments referred to as
follows : —

"Two fragments, respectively 70 and 108 mm. in length, and with a transverse
diameter ranging from 21 to 24 mm., the vertical (in the centre) being only 5 or 6 mm.
The dorsal surface was dull olive, with a dark median band, the greater part of the
breadth being marked by fine transverse striae, leaving only the borders untouched.
Various transverse lines, passing quite across the body, also occurred ventrally. The
median line and the borders had each a smooth belt, the rest being marked by the closely
arranged and tranverse lines. A median ridge occurred along the ventral band."

The ova of this species, polygonal by recij)rocal pressure, and surrounded by a gela-
tinous outer layer (capsule), are figured on PI. XV. fig. 18.

(ZOOL. CUALL. ESP. — PART LIV. — 1887.) Hhli 7

50

THE VOYAGE OF H.M.S. CHALLENGEE.

List of the Stations at which the different Species of Nemeetea
collected by the challenger were obtained.

Distin-

guishing
No. of

Date.

Latitude and Longitude.

Depth in
Fathoms.

Nature of Bottom.

Species collected.

Station.

1873.

45

May 3

38° 34' 0"N., 72°10'0" W.

1240

Blue mud

Carinina grata.

47

„ 7

41''14'0"N., 65'45'0" "VV.

1340

Blue mud

)) )i

., 8

Lc Have Bank, N. Scotia

75

Ccrcbratulus truncatus.

49

„ 20

43°3'0"N., 63°39'0"W.

85

Gravel, stones

Drcpanophorus lankestcri, Cerebraiulus
tru'iuxdus, Cercbratulus -nudullatus.

June

Bermuda

Cerebraiulus trwicatus, Tetrastemiiia
agricola.

^^

Bermuda to Azores

Gulf weed

Tdrastemma fiiscum.

July

St Vincent, Cape Verde Islands

Eupolia delineata, Drepanophorus rubra-
slrialtis.

144a

Dec. 26
1874.

46°48'0"S., 37° 49' 30" W.

69

Volcanic sand

Cerebraiulus loncjifissus, Ampliiporus
marioni.

149

Jan. 9

49° 8' 0" S., 70° 12' 0" W. (Acces-
sible Bay)

20

Volcanic sand

AmpMporus raoscleyi.

149e

„ 21

49°37'0"S., 70°16'0"'W.

30

Volcanic sand

Cerebraiulus corrugatus.

" "

Royal Sound, Kerguelen
Christmas Harbour

Amphiporiis moseJaji, Drepanophonis scrra-
tieollis, Cerebraiulus corrugatus.

Cerebraiulus sp. inc. [mcduUatus?), A7nphi-
porus moscleyi.

151

Feb. 7

52° 59' 30" S., 73° 33' 30" E.

75

Volcanic sand

Cerebraiulus corrugatus.

158

Mar. 7

50° 1' 0" S., 123° 4' 0" E.

Pelagon^riicrtes rollcsloni.

162

Apr. 2

39° 10' 30" S., 146° 37' 0" E.

"38

Sand and shells

Drcpanoiihorus serraticollis.

lerA

June 27

41° 4' 0" S., 174° 19' 0" E.

10

Mud

Cerebraiuhis parlceri, Cerebraiulus angusii-

168

July 8

40° 28' 0" S., 177° 43' 0" E.

1100

Blue mud

ceps.
Cerebraiulus angusliccps.

169

„ 10
1875.

37° 34' 0" S., 179° 22' 0" E.

700

Blue mud

Eupolia giardii, Cerebraiulus inacrorcn,
Eupolia australis.

209

Jan. 22

10° 14' 0" N., 123° 54' 0" E.

95

Blue mud

Cercbratulus sp. inc.

232

May 12

35°11'0"N., 139°28'0"E.

345

Green mud

Cercbratulus -nuicroren, Cercbratulus sp.
inc. , Eupolia nipponensis.

June 5

34° 58' 0" N., 139° 30' 0" E. off
Japan

Pelagotieincrtes rollcsloni.

1876.

321

Feb. 25

35°2'0"S., 55°15'0"W.

13

Mud

Cercbratulus sp. inc.

A glance at the foregoing table shows that the very large majority of Nemertea were
captured in shallow water, and that they may, as a rule, be said to belong to the
littoral fauna. The most aberrant new tjrpes are the pelagic Pelagonemertes, and the
genus that has come from the greatest depth, Carinina grata.

The interesting peculiarity of a strongly developed medullary nerve, which is much
less conspicuous in the European species hitherto investigated, occurs in species so widely
apart as the waters of Nova Scotia {Cerebrahdus medullatus), of Kerguelen {Cerebra-
iulus sp. inc. {medullatus ?), of New Zealand {Gerebratulus parlceri), and of Japan {Cere-
hratidus macroren).

If we group the species according to geographical distribution, we find as novelties
in the American part of the Atlantic —

Carinina grata, Drepanophonis lanhesteri, Gerebratulus medullatus, and Cere-
bratulus truncatus.

EEPORT ON THE NEMERTEA. 51

Off Marion Island :

Amphiporus marioni, Cerebratulus longijissus.

Off Kerguelen :

Amphiporus moseleyi, Cerebratulus corrugatus.

Off New Zealand : ^

Eupolia giardii, Eupolia australis, Cerebratulus parkeri, and Cerebratulus
angusticeps.

Off Japan :

Eupolia nipponensis and Cerebratulus macroren.

It might Lave been expected that a collection of Nemertea from different parts of the
globe, preserved in .spirit, would prove to be less valuable for our intimate knowledge of
genera and species, and for our elaboration of the systematic arrangement of this group, than
it would be for anatomical and histological purposes. Where external specific characters
have come to be totally effaced, the details of the internal framework remain most per-
fectly preserved for microscopic investigation. In the preceding pages we have encoun-
tered difficulty in attempting specifically to determine the fragments forming this
collection, and we have at the same time seen that only in four cases {Eupolia
delineata, Drepanophorus rubrostriatus, Drepanophorus serraticollis and Cerebratidus
corrugatus) coincident with extraordinarily favourable circumstances, was identification
possible with species already known.

That nevertheless new species could be established with certainty must merely be
ascribed to the fact that the distinguishing internal specific characters, gathered by means
of microtomy, were so marked and so divergent. Still we cannot picture to ourselves
the appearance of these new species when alive and in the fresh state.

As just noted, we^ have in this collection a much more reliable basis for the
study of the anatomical and histological details. We must, indeed, recognise that we
have to thank the exceedingly well-preserved collection of Challenger Nemertea for
several new facts and suggestive results, to the description of which we will now devote a
new chapter.

1 Mention is made in M'Intosh's Monograph (XTX., p. 96) of a New Zealand Nemertean, distinguished by Baird as
Lineus novee--Mlandise. I have nowhere been able to find any description of this species by that author. After personal
inspection of Dr. Baird's specimen, which is preserved under that name in the British Museum, I do not, however, feel
justified in identifying with it any of the Challenger specimens from New Zealand. Externally it much more resembles
Cerebratidus ciirrugatus, and if this latter species is really encountered in New Zealand, Baird's name will have to be
dropped altogether.

ANATOMICAL INVESTIGATIONS.

INTEGUMENT.

By "integument" I wish to designate the cellular layers as they are found outside
the more or less stratified connective tissue, which is known as the basement membrane.
The latter is of very varying thickness, and, for reasons to be given subsequently, will be
treated in another paragraph. Glandular structures of the integument, whether enclosed
within the cellular layers just alluded to, or stretching inwards between the muscles
and piercing a secondary basement membrane, hereafter to be described, only by means
of their communicating ducts with the exterior, will also be treated of here.

Commencing with a description of the integument of the Palseonemertea, it will be well
to take the more important genus of which representatives are found amongst the Chal-
lenger Nemertea, viz., Carinina, as a type. This is all the more desirable as we shall here
find the central nervous system still clearly belonging to the integument, its constituents
imperceptibly merging into those of the deeper cellular layers of the skin, and also lying
outside of the basement membrane.

The two specimens of Carinina at my disposal revealed the same features with respect
to their integument, although in one of them the granular secretion in the glands that
form part of it is much more copious. When we leave out of consideration the basement
membrane, that can be easily detected in the sections by the uniform and deep red
tint it acquires by the staining reagent (picrocarmine), we can roughly distinguish four
constituent strata in the integument not in any way separated by sharp boundary lines,
but characterised by the presence of difi"erent histological elements which we will now
proceed to describe more fully. It will be understood that the absence of fresh material
and the scanty supply of spirit specimens has necessarily limited the exact discrimination
of these histological elements.

Of the four strata alluded to, the one adjoining the basement membrane is extremely
important, being the seat of those cellular modifications which must be looked upon
as the difierentiation of the central nervous system within the domain of the integu-
ment. This position — it was already noticed in the description of the species given

54 THE VOYAGE OF H.M.S. CHALLENGER.

above — remains the same in the adult, and we have in this more superficial situation of
the central nervous system one of the surest indications of the more primitive position
that ought to be assigned to Carinina and the allied genera, when compared with the
other Nemertea.

The intermixture of integumentary and nervous tissue is none the less evident
in the medio-dorsal longitudinal nerve than in the lateral stems. The first named nerve,
which in former publications (IX, X) I have, not wholly adequately [cf. p. 132), desig-
nated as the proboscidian-sheath-nerve, can readily be distinguished in my transverse
sections of Carinina as a delicate stem. It is not situated, as in the Schizonemertca, just
outside the circular and below- the outer longitudinal muscular coat, nor, as in Drepano-
2)Jiorus, Amphiporus marioni, &c., below the basement membrane just outside the same
circular muscular coat, but it lies in this case actually outside the basement memhrane,
and forms part of the deepest layer of the celhdar integument. Further, a plexus-like
distribution of nervous tissue between dorso-median and lateral nerve-stems obtains in
this species, as was more fully described elsewhere for the Schizonemertea, connecting
the three longitudinal stems and spreading round the body as a cylindrical investment.
It must be remarked that this plexus-like arrangement is thus necessarily situated in the
very layer of the integument with which we are occupied, and it may be added, that in
numerous transverse sections of Carinina the presence of fibrillar nerve-tracts in this layer
can be easily demonstrated, and these exactly resemble those that are met with in the
nervous plexus of Schizonemertca. This plexus has, since my first notice of its presence
(IX, x) been again observed by Dewoletzky (H) and other naturalists, and will be more
fully discussed in a succeeding paragraph.

The plexus here alluded to merges into the lateral nerve-stems. I may here once
more emphasize the fact that the whole system lies outside the basement memljrane. At
the same time, however, the lateral stems would seem to be separated, though very
incompletely, from the integument by bundles of fibres which bind them down to the
underlying layer of circular fibres (PI. III. figs. 7, 8.)

In the vicinity of the brain-lobes it is impossible to distinguish between the cells
of the deepest integumentary layer and the nerve-cells. With respect to this layer I
have further to state that its nuclei are less conspicuous, its cells paler, and the boundary
lines of the latter less easily distinguished than in the other layers. Extremely delicate
fibrillar tracts were already noticed as occurring in it.

The next layer to this, when we pass outwards, is the glandular layer of the integu-
ment. It is the thickest of the four, being alone often as massive as the three others
taken together. The large, flask-shaped, and tubular glands it encloses contain a thick
granular secretion, which is partly stained brownish-yellow, partly dark red in my pre-
parations (PI. HI. figs. 3, 7, 8, gi ; PI. IV. fig. 1 ; PI. VI. figs. 1-3). The ducts leading
to the exterior penetrate the two outermost layers. The presence in the most peripherally

REPORT ON THE NEMERTEA. 55

situated of the two latter layers of similar though much shorter glandular cells (PI. IV. fig. 1 ;
PL VI. fig. 2, E), immediately contiguous with others of a larger size, makes it a subject
for inquiry whether these are connected by transitional forms to those larger ones which
form the layer we are now describing. This involves the not unimportant question,
whether the glands constituting this layer are or are not unicellular. While I am inclined
to accept the latter proposition, I feel that the question can only be solved by the aid of
a careful inquiry into fresh specimens.

The layer external to the glandular is one in which very numerous and deeply stained
nuclei are heaped together. These nuclei occupy several rows in one section. The same
may be said to apply, as will be indicated further on, to the corresponding layer of deeply
staining nuclei in the integument of the Hoplonemertea.

The very outermost layer bearing the cUia clearly contains, in Carinina, the same
elements as will be described more in detail {TO(ie infra, pp. 58, 61) for the Schizonemertea,
i.e., nervous end-ceUs, alternating with supporting cells, " Stiitzzellen."

This layer, containing fewer nuclei and less granular protoplasm, is more transparent in
transverse sections, and distinguished by fine radial striae, indicating the boundary lines
between the contiguous cells. The four layers here described are not equally distinct in all
sections, nor are they equally well marked in all the sections figured. Thus, for example,
in fig. 4 of PI. III. the glandular layer is feebly developed, and the two external layers are
so indiiferently preserved that their distinctive character, just described, fails to attract
attention. The chief points enumerated can, however, even there, be easdy ascertained.
The partial absence, or, at any rate, temporary indistinctness of these gland-cells in certain
portions of the integument can also be observed in tangential sections, such as the one of
PL III. fig. 8. There, too, the groups of glandular cells to the right and the left are
separated by a band of integument, in which they are decidedly absent. The same figure
shows the difi"erent ways in which the contents of these gland-cells react on staining
agents ; those to the right in this section have decidedly yellowish contents, whereas the
contents of the group on the left had a deep carmine tint.

This description of the integument of Carinina must now be followed by that of
Eupolia, the only other genus of Palseonemertea contained in the Challenger collection.
The interesting genera Carinella, Cephalothrix and Carinoma, are not represented
in those collections and certain intermediate characters displayed by these genera, which
serve to justify the identification of the different layers, which as I am going to propose
can only be touched upon as far as they elucidate the phenomena. This I will defer
tUl after the detailed description of the integument of E^ipolia.

Instead of four layers it would not be difiicult to distinguish eight in the integument
of this genus, not all of them separately and clearly represented in every section, but
sometimes {e.g. PI. VII. fig. 5, 9) sufficiently distinct. This arrangement may be looked
upon as a further difierentiation of an earlier phase, corresponding to that of Carinina,

56 THE VOYAGE OF H.M.S. CHALLENGER.

the chief diflference being that the basement membrane upon which the whole integument
rests, is not here, at least not in all specimens, so clearly defined, nor comparatively so
structureless, as it is in Carinina, and as we shall again find it in the Hoplonemertea.
Moreover, identification is somewhat obscured hj the aj)pearance of a second, homo-
geneous, very thin basement membrane, which has also a strong affinity for the staining
reagent, and which we must be careful separately to distinguish, if we wish to establish
an adequate comparison between the parts in the difi"erent genera. This second basement
membrane (A in PL VII. figs. 2, 3, 5, 6, 9; h, in PI. XII. fig. 2 ; PL XIII. fig. 6) divides the
integument into two strata — an external one, comprising the peripheral sense-cells and
ciliated cells, the unicellular glands, and the layer of deeply-stained nuclei ; and an
internal one, containing the longer and more tortuous glands, the deepest integumentary
tissue, and, moreover, at least two very thin layers of fibres.

If we count the thin basement membrane alluded to for one layer, this makes three
strata externally and four internall}^ to it — eight altogether.

The difierent aspects of these strata may be gathered from the figures on PL VII. Fig. G
shows the three layers outside the membrane B, and though the histological elements
were not isolated, it was very obvious that large unicellular glands were here pouring
their secretion to the exterior. The very outermost layer was here, as in aU Nemertea,
formed of strictly radially arranged cells, with far less distinct nuclei, whereas between
and just below the secreting cells strongly stained nuclei give to this part of the integu-
ment the peculiar radially striped appearance which it has when viewed with lower
powers (figs. 2, 3, 5, 9). This same peculiarity is only less visible in fig. 6 because
of the very copious discharge of secretion in the gland-cells. From figs. 5 and 9
it is sufficiently obvious, however, that these glands are not the only ones, but that
in the layer indicated by Gi the darkly-stained secretion of more deeply Ipng, larger,
and more irregularly-shaped glands is unmistakable, and is also seen to communicate
with the exterior by fine tortuous tubes piercing the superposed membranous and cellular
strata, about ten of these ducts being specially indicated in fig. 5. Their direct passage
into the respective glands is not always visible in one section, the course of the tubes being
tortuous. The same glands, though also present in the sections shown in figs. 2 and 3, are
there less marked, because the secretion has not yet so distinctly accumulated. Here, too,
the reference letters Gi, point to the stratum in which we find them imbedded. A second
constituent of this stratum is seen in cells similar to the secreting cells in the unriije
stage (figs. 2, 3), but having afterwards a very distinctly vacuolated character, and
then forming the surrounding and sustaining tissue for the functional glands. They
might, then, best be designated as vesicular connective tissue (" blasenformiges
Bindegewebe"), with hardly any intercellular substance. The comparative thickness
to which this part of the integument may attain is best understood from PL VII.
figs. 5, 9, Gi. That there is a sharp line of demarcation between it and the gelatinous or

REPORT ON THE NEMERTEA. 57

lamellar connective tissue of the basement layer Bet, upon which the whole of the integu-
ment rests, may here be specially insisted upon, and is indicated in the same figures.

Finally, I have to mention the two layers of fibres which, though very delicate, form
in Eiqwiia very constant and characteristic parts of the integument. They are imme-
diately applied against the inner surface of the supernumerary basement layer B — an
outer layer of circular and an inner one of longitudinal fibres. Fig. 9 {Eupolia
delineata, long, sec.) shows them to be more conspicuous than figs. 2, 3 {Eupolia
australis). Fig. 9 moreover, serves to demonstrate that the pigment, to which in this
species the peculiar longitudinal brown stripes are due, is accumulated in the same
stratum of the integument, where these fibrous layers are found ; the section represented
shows an unpigmented zone between two pigmented ones. The pigment is granular, and
appears to be limited to this stratum. It was not met with in the other species of Eupolia.

That I am justified in looking upon the integumentary arrangement of Eupolia as a
higher differentiation of a lower tjrpe, which in general resembles the integument of Cari-
nina, must now be shown by a short account of the condition of things in Cephalotlinx
and Carinoma, two other Palseonemertea, both of them inhabitants of the European seas.

Cephalothrix shows an advance in differentiation upon Carinina, by the deeper
situation of the lateral nerve-stems (PI. XL fig. 15), imbedded in the outer longitudinal
muscular layer. Still it deserves special attention, that in this genus the medio-dorsal
nerve is stUl situated in the deepest layer of the integument (PI. XL fig. 5) outside
of the basement memljrane, and that, at the same time, the integument wholly answers
to the description that we have given of the integument of Carinina.

Carinoma, whilst generally agreeing with Cephalothrix in the situation of the lateral
nerve-stems, no longer retains the longitudinal medio-dorsal nerve as part of the integu-
ment, but in a somewhat deeper situation, enclosed in the basement-membrane. It
also shows very decided complications in the structure of the integument. Whereas the
basement layer is most closely similar to that of Carinina and Carinella, the outermost
integumentary layer is much more distinctly cellular, provided with unicellular glands,
and separated from the deeper glandular layer by the development of two layers of
muscular fibres that were first noticed by M'Intosh (XXIV), and by him interpreted as
two accessory muscular layers of the body-wall. They are such, in fact, although I feel
confident that we may look upon them as forming an integi-al part of the integument,
and as being, together with it, wholly of epiblastic origin. Not wishing to give a figure
of Carinoma, which does not form part of the Challenger collection (the diagrams on
PI. XL may, however, be consulted), I must needs appeal to the confidence of the reader
that a glance at a transverse section of the integument of Carinoma carries with it the
conviction that it is, in this respect, truly the most conclusive intermediate form between
Cariniyia and Eujiolia, so that we are amply justified (l) in declaring the basement
membrane {B of PL III. figs. 3, 4, 7 ; PI. IV. fig. 1) to be not homologous with the one

(ZOOL. CHALL. EXP. — PAET LIV. — 1887.) Hhh 8

58 THE VOYAGE OF H.M.S. CHALLENGER.

also lettered B on PI. VII., but to be so with the deeper layer, Bet of the latter plate ;
and (2) in comparing the glandular structures of Carinina more especially with the
deeper layer of glands of Eupolia, and in looking upon the unicellular glands of the
latter as more particularly developed in the outermost layer. These latter are then
comparable to the smaller and superficial unicellular glands which are met with in
Carinina {PI. IV. fig. 1). Similar considerations concerning the homology of the diff'er-
ent portions of the integument can be applied, as we shall see in the sequel, to the
Schizonemertea, their integument in so many points resembling that of Eupolia, and
being thus also linked to that of Carinina by intermediate forms, such as Carinoma.

Amongst the Hoplonemertea it is most difficult to obtain specimens in which the
integument is in a fair state of preservation. Even in the specimens that have been
treated with special care, it is a rare occurrence to find a portion of the integument in
which its difierent layers can be clearly made out.

From what I have noticed in the Challenger specimens, there is a certain amount of
uniformity which must first be noticed and compared with what obtains in Paleeonemertea
and Schizonemertea. Sharply distinct from the basement-membrane, which, after removal
of the integument, would even show a more or less honeycombed surface, are the deeper
eel] -layers of the integument, the rounded bases of these cells fitting into the honeycomb-
like pits in the basement-membrane just alluded to (PI. X. fig. 2). These cell-layers,
with very distinct nuclei, are in thin sections many rows thick. The nuclei are, however,
never so close together as they are in the subsequent layer, which is generally situated
about halfway between the basement-membrane and the ciliated surface (PL X, fig. 1).
On teasing out the elements of this layer, we find long spindle-shaped cells, considerably
thinning out at the ends, and only bulging at the spot where the deeply stained nucleus is
situated. Tliese nuclei, again arranged in several rows even in the thinnest transverse
sections, are there disposed so as to fit close between each other, the thin ends of the cells
being directed one towards the outer surface and the other towards the deeper layers
before mentioned. It cannot be doubted that sense-cells, which very generally have a
similar shape and position, are among these (cf. Dewoletzky, II). Towards the outer
surface, the remaining stratum of the integument has the peculiar radially streaked
appearance already described for the Palseonemertea ; nuclei being rarer in this layer
than in the two foregoing. Finally, the cilia are implanted upon the outer margin of
this region, and teased preparations reveal the presence of special cells with a nucleus of a
very much paler hue, and very faintly coloured. Only in a few preparations have the cilia
been well preserved ; a cuticula upon which they are implanted, as elsewhere (XIV)
described in embryonic stages, was also only noticed in certain favourable sections.

These are the principal features marking the integumentary system of the Hoplone-
mertea. A few further details, however, may still be added. The deepest layer (PI. X. fig. 2)
contains fibrous nerve elements, not distinctly indicated in the figure. The absolute

REPORT ON THE NEMERTEA. 59

thickness of the layers, above described as integument, does not vary very much in smaller
and larger-sized individuals. Also, in the tip of the tail, where growth is continually
going on, and where the newly formed parts are thus, in the first instance, found, the
integument is very much in advance of the underlying tissues in obtaining its definite
size. For example, in Drepanophorus lankesteri I find the cellular integumentary layer
(the basement membrane not included) to be on the thickest part of the body, 0'15 mm.
[i.e., one-tweutieth the horizontal diameter in this region), and close to the tail end 0"1
mm. (i.e., one-tenth the horizontal diameter in this region). In the largest specimens of
Ainphip)orus moseleyi, which have more than twice the length and more than two and a
half times the transverse diameter of Drepanophorus lankesteri, I find the integument
to measure 0"12 to 0"15 mm.

Both in specimens of Amphiporus moseleyi and in one of Amphiporus marioni, as
well as in one of Drepanophorus, it is easy to demonstrate glands in the integument by
the evident presence of the secretion, partly extruding towards the exterior, partly still
enclosed between the deeper layers (PI. X. fig. 2). These glands are, however, neither so
massive, nor do they form such a conspicuous layer as in Carinina, above described.
Whether they may be regarded as unicellular, and as comparable to the superficial ones
already mentioned in the integument of Eupolia, and also present in the Schizonemertea,
or whether they are more directly homologous to the deeper glands of that division,
is for the present difficult to decide by means of the preserved material in the Challenger
collection. Histological investigation of fresh specimens will be necessary to clear up
this point. Drepanophorus serraticollis would certainly tend to a direct comparison
with the flask glands of Cerebratulus, &c. In a general way, however, the Hoplone-
mertean integument ofi'ers more analogy to the more primitive arrangement than to the
higher diff"erentiation of the layers in Eupolia and the Schizonemertea.

One further detail deserving mention is the presence of a granular deposit (pigment?)
in the lower cell-strata of the integument of the last mentioned specimen of Drepano-
phorus. This deposit is different from the one hereafter to be mentioned in the tissues of
Amphiporus Tnarioni. A deposit comparable to the latter was absent in the specimen
of Drepanophorus here aUuded to. The granules have more resemblance to the pigment
granules of Eupolia delineata, described above, and may probably be looked upon as such.

While we see that the Hoplonemertean integument is directly connected — at least in
general outlines — with that of the Paleeonemertean genera Carinina and its allies, the
Schizonemertea are linked to the primitive stock by the intervention of Eupolia and
Carinoma.

Certain Schizonemertea {e.g., Cerebratulus corrugatus) in some portions of the
integument reveal a complete uniformity with what we have described for Eupolia ; a
stratified basement layer separating the outer longitudinal muscle-bundles of the body-
wall from the layer of vesicular tissue sustaining the deeper skin glands, these glands

60 THE VOYAGE OF H.M.S. CHALLENGER.

communicating by tortuous tubes with the exterior, and being separated from the outer-
most cell-layers with unicellular glands by a special secondary and continuous, though
thin basement layer (PI. XIII. fig. 6). Below the latter, longitudinal ahd circular fibres
proper to the integument are also present, corresponding, even in their more massive
develoi3ment, to those of Carinoma.

There apjDcars to me to be no doubt that this same arrangement holds good for the
great majority of Linei and Cey'ebratuli, and the only reason why the separation of
the parts is often less marked is the stronger development of the outer longitudinal
muscles of the body- wall, concordant with the disappearance of the connective tissue
separating the integument and body musculature, and also the fusion to a smaller or
larger extent of the longitudinal muscle-fibres proper to the integument with those of the
body-wall. From this it inevitably results that the line of separation between the
body-wall and the integument seems to be formed by the external, secondary basement
membrane, the deeper glands having the appearance of being imbedded within the longi-
tudinal muscles of the body (PL XI. figs. 10, 11 ; PL XII. figs. 2 and 10). That this
is a secondary arrangement, and that the real and original line of separation was another
one, has been demonstrated in the foregoing pages.

It is not necessary, after the detailed description of Eupolia given above, once more fully
to discuss the same details for those Schizonemertea that wholly correspond to the same
type of integument. In those species in which the more developed longitudinal muscular
layer more or less effaces the boundary line between integument and muscles (Cerehratulus
macroren, Cerehratulus medullatus, &c.), the characteristic and sometimes massive layer
of vacuolated cells surrounding the deeper glands is considerably reduced. The other con-
stituent parts have retained their original character, with the exception of the thin muscu-
lar strata of the integument, which are no longer separately recognisable (PL XII. fig. 10).

The integument is generally very completely preserved in the cephalic fissures; it
may here be noted that there, too, the deeper gland-structures of the integument may be
noticed, although they are much more sparingly set. In a few cases it would appear as
if they are wholly absent, and as if only the outer integumentary cell-layer is preserved in
the cephalic fissures ; others, again (PL XIV. fig. 11), offer special differentiations in the
region of the cephalic fissures of the glands, which may there be united in paired accumu-
lations. I must also mention a somewhat aberrant ty^Q of integument, as we find it
represented in a Cerehratulus?,^. inc. {medullatus f), from Kerguelen Island. The integu-
mentary layers offer more general resemblance to what obtains in the more primitive
Palaeonemertea {Carinina, Cephalothrix, &c.) than to Eupolia. Eventually it might be
said to retain a more primitive embryonic condition. I have at least described a develop-
mental phase of the integument very similar to what I am now about to describe for
adult forms, as occurring in the ontogeny of Linens ohscurus (XIV). The integument
m c[uestion may, however, also be looked upon in another light, i.e., as in no way

EEPORT OiSr THE NEMERTEA 61

more primitive, but rather as a special differentiation of the normal type of the Schizo-
nemertean integument, the result being an apparent simplification. This simplification
(PI. X. fig. 7) 'consists in the absence of the deeper layer of gland-cells below the
superficial secondary basement membrane h. The whole integument of this species would
thus only seem to correspond to the very outermost layer (the layer of the unicellular
flask glands) of the other Scliizonemertea. I have, indeed, the conviction, that far
from being more primitive, this condition may be linked with what obtains in other
Schizonemertea and in Eupolia b/ such transitional forms as Cerehratulus medullatus,
&c. (PL XII. figs. 10 and 2 ; PI. XL figs. 10, 11). These species have evidently well-
developed glands belonging to the deeper layer ; and whilst the glands are on aU sides
surrounded by the longitudinal muscles, they at the same time penetrate more deeply
into this layer, even at a few points touching the nervous stratum, which is superposed
upon the layer of circular muscular fibres (PL XII. fig. 10). The special character of the
integument of Cerehratulus sji. inc. (^medullatus ?), and the deceptive reminiscences it
evokes of the more primitive stages of the integument may well be said to be due to the
strong secondary basement membrane. Thus in this species the layer of the deeper
glands seems to have altogether disappeared.

Before passing to another paragraph, I cannot refrain from pointing out the many
points of resemblance that may be noticed between the integument of the Polyclada,
now so well known, thanks to A. Lang's beautiful monograph, and of certain Nemertea,
viz., those in which the integument is secondarily simplified as in those last discussed.
Our external layer of unicellular glands is evidently comparable to what Lang and Graff
call the " Schleimstabchenzellen " or " pseudorhabdites," and these in their turn are
compared by Lang, on very plausible grounds, with the '"' Rhabditeuzellen," in which the
peculiar rod-like enclosures of the integument are found. The highly refractive, uniform
contents of what I have called the unicellular glands, their general shape and properties,
wholly coincide in their semi-viscous nature with what are described by Lang as the
" Schleimkorper," and looked upon by him as merging into true glandular structures.

The Nemertean layer, of deep glands is also found in the Polyclada, below the
(also secondary ?) basement membrane. So is the layer of nuclei regarded by Lang as
belonging to a continuous stroma, by which both sense-cells and gland-cells are sustained
and which was recognised by me in all the subdivisions of Nemertea. The figure given by
Lang (XVIII ; PL XL fig. ll) would fit very well for different genera of Nemertea ; only
in Nemertea the rod-like viscous bodies are not subdivided into superposed blocks. More-
over, the tactile and sensory cells in the integument, as Lang describes and figures them,
more especially for the tentacular integument, ofler without doubt a close analogy to
that outermost layer of the Nemertean integument, with its triangular cells (tip down-
wards), which is also found in the vast majority of species where the skin is uninjured,
which is uniformly distributed over the body, and which, if indeed sensory, as appears

62 THE VOYAGE OF H.M.S. CHALLENGER.

to me most probable, would go a long way to explain the high degree of sensibility of
every portion of the Nemertean body-wall.

MUSCULAR SYSTEM AND CONNECTIVE TISSUE (GELATINOUS TISSUE,

BASEMENT MEMBRANE, &c.).

In describing in the foregoing paragraphs the integument and its varied constituents,
glands, sense-cells, cUiated cells, &c. , the tacit assumption has been made that the structures
there described might be looked upon as so many derivatives of the epiblast. Although
reliable embryological data are as yet very scanty, my own experience on this head
(XIV, XV) appeared to me to afford justification for this assumption. However, I agree
that the question, whether the thin layers of longitudinal or circular fibres, that, more
especially in Enpolia and Cerehrutulus corrugatiis (PL VII. figs. 5, 9 ; PI. XIII. fig. 6),
form so intrinsic and conspicuous a part of the integument, are also ei^iblastic derivatives,
or whether they are due to mesoblastic elements, is open to dispute, and cannot be solved
for the present on any other than the a priori arguments just alluded to. Hence, if I
look upon the tissues that are treated of in the present section as essentially meso-
blastic structures, I wish it to be well understood that this distinction may after all not
be a final one.

I have purposely omitted discussing the basement membrane of the integument under
the head of the iutegument, because it appears to find its more natural place amongst
what we are now going to describe : the tissues between the outer cell layers and the
intestinal epithelium, i.e., the muscular body-wall and the connective tissue (better,
gelatinous tissue, " Fiill-Gewebe"). The latter is not only present in the space between
the body-wall and the intestine (so far as it is not encroached upon by the generative,
blood-vascular, or nephridial systems), but also between the individual muscle-bundles,
when these are not very closely applied against each other, and outside of these, between
the muscles and the integument, as the so-called basement membrane above mentioned.

The question as to the exact nature of this tissue is, in my opinion, a very important
one. It represents the tissue which in Ccelenterata fills the space between epiblast
and hypoblast, the "jelly" of Medusae and Ctenophora, with its multifarious inclusions
of muscular, fibrous, and eventually nervous nature. This jelly is the more im-
portant since its distribution, in the way above defined furnishes a strong argument for
the view, also held by me, that the Nemertea are devoid of a body-cavity comparable to
that of Arthropods, Annehds, and of Vertebrates. The only body-cavity proper to the
Nemertea is the modified segmentation cavity, the archiccelome, as I have elsewhere pro-
posed to call it (XIII, XIV). Of the cavities of the generative sacs and of the nephridia
mention will be made in the respective paragraphs.

REPORT ON THE NEMERTEA, 63

It will be well to consider this connective tissue more closely before we pass to the
description of the muscular layers of the body- wall. From the foregoing it may already
be inferred that -there is a direct continuity between the different parts of this gela-
tinous tissue, be it situated close to the intestinal epithelium or to the integument, and
that this continuity is more or less completely interrupted by the muscular layers.
We may thus conclude that it wUl be most prominent in those species that have the
muscular body-wall reduced to a minimum, whereas it will be hardly visible in species
that have a very strongly and massively developed musculature. This is indeed the case,
Pelagonemertes offering a very striking example of the first category, Carinina of the
second.

Although the latter species is by far the most primitive, I would hesitate very much
in at the same time regarding the relation of the gelatinous tissue to the body-muscu-
lature of this deep-sea form as typically representing the original arrangement. Both
species mentioned represent an extreme ; the normal starting point may be more easily
derived from what we find in Eujwiia and in most Hoplonomertea. It then becomes
obvious that our gelatinous tissue, though uniform and continuous, still appears in three
principal modifications, which, however, are often connected by transitional phases having
the characteristic features of more than one of these modifications.

The first of these modifications is found between the muscles and the integument,
the second in the midst of the muscular bundles, the third between the muscular invest-
ment and the internal organs.

The first modification just alluded to appears in Cdrinina (as also in Carinella and
other Palaeonomertea not collected by the Challenger) as a wholly homogeneous base-
ment layer, on which the deeper cell layers of the integument are implanted, partially
honeycombing it in the way above noticed. It is strongly stained by picrocarmine, and in
Carinella traversed along circular and longitudinal tracts by nervous tissue. In Carinina
the corresponding tracts are still situated in the deeper layers of the integument itself.
Nuclei are very rare. What is a distinct basement layer in the more primitive Palseo-
nemertea just named, retains this character with but little change in the Hoplonemertea.
One change which is revealed at first sight is a distinct though exceedingly fine stratifica-
tion, that becomes apparent in the basement membrane of nearly all Hoplonemertea.
Along with this we very often find included in the Hoplonemertean basement layer
distinct and sometimes numerous nuclei. The other inclusions in it, as they are
figured on PI. X. fig. 1, B, appear to be parasitic unicellular organisms infesting
this particular specimen (see p. 49). Besides the exceedingly fine stratification which is
parallel to the surface of the body, and which is often thrown into wavy folds, there are
numerous radial tracts that would seem to transverse this basement layer, but are often
only due to slight differences in texture and coloration, or to hardly susceptible folding or
contraction (PI. VIII. fig. 13). Where actual radiating fibres can be demonstrated, they

64 THE VOYAGE OF H.M.S. CHALLENGEE,

sometimes are found to be extremely tliiu nerve-stems connecting the cellular integu-
ment with the central nervous system, whereas in other cases their spii-al coiling and their
affinity for staining solutions permits us to define them as contractile or elastic fibrils. It
is, however, not to these radial fibrils that the extreme pliability and continual change
in thickness of the basement membrane of the Hojjlonemertea can be ascribed. This
phenomenon must be an inherent quality of the tissue itself, and may be studied in every
transverse section, where the outer boundary line of the basement membrane is only
very rarely parallel to the inner one. Generally it is strongly undulated, in accordance
with the folds and wrinkles into which the integument may be thrown, not only during
life, but also when the animal is preserved in spirit. The consequence of this undulation
is, that in several places the integument much more closely approaches the muscular
body- wall than in others, where it is kept very widely apart, the basement membrane
being in the fii'st case compressed ; in the second, extended to its utmost limit.

Together with this extension and contraction, the fine parallel stratification changes
its aspect, becoming more coarse, and sometimes so coarse that it might be difficult not to
look upon the basement layer as composed of fibres. A confusion with subjacent mus-
cular layers would in some cases be pardonable. A comparison of longitudinal and
transverse sections reveals, however, the fact that it is indeed no fibrillar, but a stratified
condition. Another change accompanying these phenomena of extreme plasticity is the
change in colour, the staining appearing far more intense when the strata are in the
contracted than when they are in the expanded condition. The nuclei remain visible in
both cases. How the change of shape and the successive expansions and contractions
are actually brought about in this homogeneous though laminated tissue, which has more
the appearance of being intercellular ground substance than anything else, must here
remain an open question, which we shall again meet when treating of the contractions of
the muscular body-wall.

In PI. VIII. fig. 13, and PI. X. figs. 1, 2, different aspects of the Hoplonemertean
basement membrane are given. I will now pass to those of the Palseonemertean genus,
Enpolia, that in so many respects leads over to the Schizonemertea. In certain speci-
mens of this genus an arrangement, more or less corresponding to what has just been
described, was in a few cases met with, the basement membrane being of about the same
thickness aU round, finely striated, with imbedded nuclei, and sharply separated from the
integument (PI. VII. figs. 3, 9, Bet).

In other cases the membrane separating the muscles and the integument is much
more folded, more irregularly striated, and less characterised as a separate band of distinct
tissue (PI. VII. figs. 2, 5, Bet ; PI. X. fig. 6, B). Especially in these latter cases it is
quite clear that this band of tissue, to which the name of basement memhrane can only
be applied with particular restrictions, imperceptibly passes into the connective tissue
found between the longitudinal muscular bundles of the outer layer, where it is moulded

REPORT ON THE NEMERTEA. 65

between these bundles, aud also carries in the nephridial regions the terminal deferent
portions of the nephridial ducts (PI. VII. fig. 5, Nep). The originally cellular nature of
this connective tissue is retained in the head and in the anterior portion of the trunk,
where the outer longitudinal layer of muscles is not less thick, but certainly contains a
very much smaller number of fibres, because of the permanence of the intermuscular
cellular stroma just alluded to. A comparison of figs. 2 and 3, PL VII., the one taken
through an anterior, the other through a more posterior region of the trunk of a Eupolia,
will elucidate this, as will also the comparison of fig. 5, PI. VII., with the more enlarged
fig. 6 of PL X. (taken from the same specimen), which represents a section through the
region marked Bet in the former figure situated further forwards, and thus decidedly cellular
as far as concerns the intermuscular tissue. One important fact is clearly indicated in this
latter fig-ure, viz., that the cells situated between the muscle bundles of the outer longi-
tudinal layer {y.vl), although their general aspect, vacuolation and arrangement very
much resemble that of the similarly vacuolated cells of the deepest layers of the integu-
ment (Jdvl), may nevertheless be immediately distinguished from these by their much
larger nucleus. The same fact follows quite as unmistakably, though somewhat less clearly,
from PL VII. fig. 2. It gives some support to the hypothesis, that the whole of the deeper
cell-rows of the integument, vacuolated or otherwise, being substantially different from
the subjacent mesoblast cells, may be looked upon as epiblastic. However, this question,
which pertains more to an ontogenetic than to an anatomical investigation, may safely
be left out of further consideration. This basement tissue of Eupolia, much less
regularly arranged than in Hoplonemertea and in the Carinellidse, is thus still directly
homologous with that of the latter.

A secondary external homogeneous basement layer is found immediately below the
outer stratum of unicellular glands of the integument ; in the paragraph devoted to the
integument the comparison with Carinina, Carinella and Carinoma has been already
instituted, and it was at the same time shown in what way these different arrangements
may be identified with one another.

In the anterior portion of the body the stratified basement layer Bet (PL VII.) fuses
with the sparse intercellular tissue that is present round the vacuolated cells, and
appears to be a direct continuation of it. In the posterior portion, however, where the
muscular bundles are more strongly developed, this stratified tissue appears more limited
to the region between the muscles and the integument, principally because here the
character of the intermuscular tissue is also changed and becomes more homogeneous,
although it is here and there traversed by radial fibres, is also provided with nuclei, and
contains numerous nerve-tracts. The general aspect, and the effect of the staining
reagents, show this intermuscular tissue to be identical with the homogeneous,
more or less gelatinous tissue, that is observed between the outer longitudinal
bundles of Carinina (PL III. fig. 6). The cells, of which traces are found

(ZOOL. CHALL. ESP. — PART LIV. — 1887.) Hllll 9

66 THE VOYAGE OF H.M.S. CHALLENGER.

around the nuclei contained in this homogeneous intercellular substance, show a very
delicate granulation, and it is often very difficult to decide whether a given one
belongs to the nervous network, or whether it is a more indifferent cell, appertaining
to the gelatinous ground-substance. In the former case the connection with the ners^e-
plexus is of great advantage in the decision, and but for this such a decision would often
be wholly impossible. The fibres generally ofi"er less difficulty, the delicate nervous fibres
being sufficiently distinct from the elastic or contractile fibrils. The intermuscular
homogeneous tissue of Eupolia, and its inclusions in the region somewhat behind the head,
are figured in PI. VII. figs. 4, 5. In its deepest part, immediately surrounding the
circular muscular layer, we find the nervous stratum, that \at.U be more fully discussed
further on. We must mention this, because in certain of the Schizonemertea (PI. XII.
fig. 10), to whose basement membrane and intermuscular tissue we have now to direct
our attention, glandular structures belonging to the integument reach as far down as this
layer ; a factor which we have to keep well in view when discussing the tissues to which
this paragraph is devoted. This is all the more necessary, because in that case the other
deeper cellular components of the integument are reduced in number, whereas the
outer longitudinal muscular layer having become more compact and dense, the inter-
vening region between these two, the region Bet of PI. VII., has vanished from view.
The secondary basement membrane {B) is then the sole representative of such a
structure, and might easily, but as I hope I have demonstrated, injudiciously, be
looked upon as homologous with the basement membrane of Carinina, Carinella, Sec.
{cf. PI. XL).

An arrangement of the basement membrane, wholly comparable to what we have
described in Euiwlia, is found in such Schizonemertea as Cerehratulus corrugatus
(PI. XIII. fig. 6, B,h). In most of the others the strongly developed and massive
outer longitudinal muscular coat so much encroaches upon the deeper layers of the
integument in the way just noticed, that it is no longer possible clearly to distinguish
between the two integumentary muscular strata {Ilcm) and the subjacent one constituting
the body- wall (7). The extreme representatives of this development are figured on PI. X.
fig. 7, and PI. XII. fig. 10.

We now resume our examination of the gelatinous tissue, which we have as yet
only examined as subiutegumentary basement membrane [Carinina and Hoplonemertea),
or also as intermuscular substance [Eupolia and Schizonemertea) in its further partici-
pation in the muscular investment. In the circular and inner longitudinal layers gela-
tinous intermuscular tissue is unmistakably present, and its presence is revealed both by
the nuclei and by its peculiar homogeneous appearance, but at the same time, owing to
the far greater compactness of these last named muscular layers, when compared with the
outer longitudinal one of EujMlia, the position of the connective jelly is much more sub-
ordinate, and its presence less easdy demonstrable. Still it may be observed in the larger

REPORT ON THE NEMERTEA. 67

•species that, besides the distinctly granular ceUs included in it, striation in nearly every
direction forms a prominent feature of this intermuscular substance.

Inside the innermost muscular coat the gelatinous tissue appears in the third modifica-
tion which we have established for it. This modification is in many respects the most im-
portant, and at the same time most liable to a considerable amount of variation according to
the species we happen to examine. It has been already noticed that of all Nemertea Pelago-
nemertes shows it in its fullest development, whereas the eminently muscular Carinina is
only very sparsely provided with it. It will thus be safest first of all to examine it in
Pelagonemertes, and to indicate by what features the other genera difier and gradually
lead to grades of development as far down as Carinina.

The most striking feature in examining any section of Pelagonemertes, either with
low or high powers, with a special view to the gelatinous tissue inside the muscular body-
wall, is the homogeneity of this tissue, the comparative scarceness of nuclei, and the
uniform imbibition of the staining reagent, by which it has obtained a delicate rose colour.
A comparison mth the medusoid jelly, or, more distantly, with the intercellular substance
of cartilage, is here inevitable.

This general feature being established, the secondary characteristics are — (l) the
imbedded nuclei of this jelly; (2) the fibres forming part of its substance, other fibres tra-
versing it in apparently tubiform channels; (-3) difl'erences in the coloration of the jelly in
difi'erent regions, and lastly, a fibrillation of the utmost tenuity, only visible by the aid
of very high powers, which appears in different regions of the apparently homogeneous
jeUy, other and large portions, however, retaining the homogeneous aspect even with
these high powers, though then not apj^earing wholly limpid but cloudy, perhaps an indi-
cation of a yet finer fibrillation escaping the analysing power of our objectives when
studied, not in the fresh state, but in Canada balsam.

The difi'erent coloration of the jelly in difi'erent regions is partly arbitrary, i.e., darker-
coloured patches are irregularly scattered throughout the general lighter hue. At certain
places the darker staining is, however, constant, viz., contiguous to those regions where
the jelly is interrupted. Thus the channels above alluded to, in which nerve-fibres and
others take their course through the jelly, are marked by a double boundary line of
darker colour (PL VIII. fig. 6, n"), corresponding to the tract along which the continuity
of the jelly is interrupted for the passage of these fibres. These nervous tracts being
exceedingly numerous, the transversely or obliquely cut ends of similar distinctly red tubes
are discovered in every section (PI. VIII. fig. 3). Moreover, all round the two principal
nerve-stems (figs. 6, 8), and bounding the cavity of the proboscidian sheath (PI. VIII.
fig. 12, B), the blood spaces (fig. 8, hi), and the cavities in which the generative products
are lodged (fig. 8), the same continuous dark red tint, which that portion of the jelly has
acquired by the picrocarmine, is observed.

A peculiarity which I have further to notice in the sections, is the difi'erent hue that

68 THE VOYAGE OF H.M.S. CHALLENGED.

has been acquii-ed by two superposed layers of the basement membrane of Pelagonemertes
(PL VIII. fig. 13, B, B') ; the outer one being darker than the inner. I have no
explanation to oifer of this phenomenon, nor of the fact shown l>y the same figure
(PI. VIII. fig. 13) that the same phenomenon is repeated just below the basement
membrane, the jelly between the bundles of longitudinal muscles being much darker than
that which is found inside. The latter, into which the former gradually merges, is not
specially indicated in fig. 13. Mention ought here to be made of what is marked dr in
that figure, and what appears to be in several cases (PL VIII. fig. 5) a central cavity
enclosed by peculiar cells, of which the nuclei are specially distinct. I must leave it
undecided whether these structures, radially directed towards the surface of the body, are
the same as the masses dr (PL VIII. fig. 4), which I see in a glycerine preparation of the
integument made by Professor Moseley on board the Challenger from the fresh animals,
and also whether these structures might be looked upon as glandular, and comparable
to similar gland-masses in the jelly oi Amphipovus mosdeiji (PI. XV. figs. 11, 12).

That the course of the fibrils traversing the jelly is in no way strictly limited to
certain directions, but that we find them now parallel to the proboscidian sheath, now to
the intestinal wall, now convergingly directed against the generative ducts, is sufiiciently
demonstrated in PL VIII. figs. 3, 8. A very large number are, however, radially directed
towards the surface, and though it was not observed in one section, it might perhaps be
possible to find dorso-ventral fibres uniting both surfaces. That the nerve-stems, spring-
ing from the lateral cords N (PL VIII. fig. 3), are indeed encased in a tubular space
bounded by darker stained gelatinous substance, is best seen in fig. 6 of the same plate,
as well as the fact that in the immediate neighbourhood cells and fibres {f) form part of
that substance.

In the other Hoplonemertea this continuous jelly, though much less prominent, has
very much the same character as in CarineUa, with the exception that no special tubi-
form tracts for the passage of nerves, &c., are as distinct as they are in Pelagonemertes.
The passage of radial fibrous tracts through the gelatinous tissue is, however, everywhere
demonstrable (PL X. figs. 1, 2), as is also the origin of these fibres out of cells (PL X. fig. 2),
and the continuity of the gelatinous stroma with that contained between the muscular
bundles of the body-wall. The Challenger Nemertea not ofi"ering anything very special
in this respect, I will postpone a more circumstantial discussion of this tissue for the
monograph which I am preparing for the Naples series.

Similarly I may rapidly call to mind that, in the Schizonemertea, where this gelatinous
substance is best observed in the posterior region of the body, and better in large speci-
mens than in small ones (PL XV. figs. 7, 10), it ofiers the same characters. Anteriorly, where
the circumcesophageal blood-space is preseut, it does not play any conspicuous part ; pos-
teriorly, however, it carries not only the tubular continuations of this space (the three longi-
tudinal blood-vessels) but also the other internal organs, to all of which it is closely aj)plied.

REPORT ON THE NEMEETEA. 69

Here, again, its generally homogeneous character, with the addition of the same
cellular and fibrous inclusions (intermediate stages between the two being similarly
represented) as were noticed above, gives it an aspect similar to the corresponding tissue
in the other groups of Nemertea.

It cannot be denied, and has been already noticed above, that from a morphological
point of view there are certain strong points of resemblance between the gelatinous tissue
of the Nemertea and the jelly of the Medusse. I was very desirous to know whether this
would also apply to the chemical constitution, and owing to Professor Krukenberg's kind
aid I am now able to make definite statements on this head. Having sent him a small
quantity of the Nemertean jelly, he kindly examined it and writes as follows : —

" In accordance with your desire I have attempted, as far as it is possible, chemi-
cally to solve the question, whether the jelly of the Nemertea is more closely allied to
that of the Medusae or to the collagenous substances, such as I have with certainty
demonstrated in Sipunculus nudus (Vergl. physiol. Studien., i. 1882). As collagenous
tissue is digested by trypsine, only in case of its having before been treated with acids
or been boiled with water (Ewald and Kiihne), I tested the reaction of the Nemertean
jelly towards this ferment. It proved to be very easily digested by trypsine, and would
thus have to be regarded as a true proteid substance. Wholly in accordance with this
result is the intense red colour which the tissue acquires when boiled with Millon's
reagent ; whereas, on the contrary, tissues that contain more collagen are only faintly
stained, and pure collagen is not stained at all by Millon's reagent. Moreover, the
Nemertean jelly is not acted upon as are the coUagens (' leimgebendes Gewebe ') by
boiling water, nor does it furnish, when treated with diluted acids and soda, such reducing
solutions as are the so-called mucins (Hyalogene, mihi). The Medusa-jelly consists of true
proteid bodies.^ A similar substance is the vitreous body of the eye of vertebrates, and
I am thus fully prepared, after the experimental results obtained, to agree with you in
regarding the Nemertean jelly as an analogous product to the jelly of the Medusae, and
similarly of an albuminoid nature."

We now pass to a discussion of the muscular layers. We will first discuss the general
distribution of muscular tissue, and reserve histological remarks for the conclusion.

In discussing the muscular layers of the body-wall of the Nemertea, considerable
confusion still obtains in the writings of most of the older authors, and I must confess
that it took me a long time to see my way to a safe basis of comparison of the layers,
that may sometimes be only one, sometimes no less than five in number, three or two
being also very common occurrences. An outline of the homologies of the muscular layers
was given by myself in the article Nemertea in the recent edition of the Encyclopaedia
Britannica, and in the views there propounded I have no changes to make, only certain
further additions have been rendered possible by the aid of the Challenger material.

1 Krukenberg, Vergl. physioL Studien., ii., 1 Abth., pp. 23-34.

70 THE VOYAGE OF H.M.S. CHALLENGEE.

In all Nemertea, to whatever order or genus they may belong, there is one muscular
layer that is always present. This layer may, indeed, be looked upon as identical through-
out the whole series, and consists of longitudinal muscle-fibres. It is the longitudinal
layer of Cephcdothrix, in which genus definite or conspicuous circular layers sometimes
appear to be absent (PI. XL) ; it is the only longitudinal layer of the Carinellidje — the
longitudinal layer of muscle-fibres in the integument of Cariiiovia not being here taken
into account, as indeed belonging to another system — and it is the so-called inner longi-
tudinal layer of Polia, Valencinia, and of all Schizonemertea. In PI. XI. this laj^er has
uniformly been lettered a. I hold it to be the most primitive of all the Nemertean
muscular layers, both on account of its constant presence and on account of the fact that
in the posterior region of the body, where growth in length of the animal takes place, it
often appears before the other layers that are present in addition to it in the anterior
region of the body.

The layer second in importance to it (morphologically speaking) is a layer of circular
fibres marked yS, of very varying thickness, and which in the Carinellidse and the
Hoplonemertea is immediately subjacent to the basement membrane, and external
to the layer a. The very outermost fibres of this circular layer often take a differ-
ent course, making an angle of about 45° with the longitudinal body axis, instead of
being perpendicular to it. This, then, being the case in two directions, a decussation
of this exterior portion of the layer, especially in Hoplonemertea and Carinellid^, is
often noticed.

Outside of the circular layer yS there is in the Schizonemertea and in Polia and
Valencinia the outer longitudinal layer y, sometimes exceeding in thickness the two
layers just noticed, and offering very varying conditions as to the compactness of its
bundles. In most cases it remains entirely distinct from the two thin epiblastic muscular
layers (see pp. 57 and 60) that make their first appearance in Carinoma, and are very
generally present in Polia, Valencinia, and the Schizonemertea (PI. VII. figs. 5, 9, ef;
PI. XIII. fig. 6, Ilcm). In some of the latter, however, a fusion occurs between the
outer bundles of the longitudinal muscular layer y, and those that are decidedly of
integumentary origin and significance, as was already noticed in discussing the integu-
ment. It needs no exjjlanation that these latter species offer more difficulties in rightly
interpreting the relations between muscular system and integument than many others
(PI. X. fig. 7 ; PI. XII. fig. 10).

The difference in compactness just alluded to is often dependent upon the degree of
development of the deep glandular layers of the integument. Sometimes these glands
penetrate the whole depth of the muscular layer, reaching as far down as the nervous
stratum (PL XII. figs. 2, 10); sometimes the muscles are kept further apart by the
gelatinous ground substance, as was more fully discussed in a preceding paragraph.
Eupolia may on the whole be cited as an example in which the degree of compactness of

REPORT ON THE NEMERTEA. 71

this muscular layer remains at the lowest level (PI. VII. figs. 2, 5), in Cerebratulus
corrugatus I found it very compact, and composed of very delicate fibres (PI.
XIII. fig. 6).

Another additional muscular layer, which is not found in all but only in certain
Nemertea, is marked 8 in the figures of PI. XI. It is an inner circular layer, and in the more
primitive types (Cai'inina, Carinella, and Carinoma) it may even become exceedingly
massive. It is directly applied against the longitudinal muscular layer a ; it forms at the
same time the dorsal wall of the proboscidian sheath, the exceedingly thin ventral wall of
which is in these species formed by fibres of the same inner circular layer that branch ofi",
and are directed inwards between the space for the proboscis and the oesophagus or intes-
tine, thus creating a floor to that proboscidian space. The inner circular layer is continued
ventrally, and embraces the other internal organs as well. In Carinoma, where the
layer has such a considerable thickness in the proboscidian and oesophageal region, and
where it has disappeared in the posterior region of the body, leaving only the longi-
tudinal and outer circular layers, the conclusion is of course tempting that the special
development of this layer is in a certain functional connection both with proboscis and
oesophagus. And if we then find that in the Schizonemertea this layer is absent, but
that, on the other hand, there is a circular muscular coat to the proboscidian sheath and
that this sheath has been raised to greater independence, and remains dorsally connected
with the rest of the muscular body-wall in exactly the way it would be if it were the
modified remnant of a restricted portion of the inner circular layer, we are led to the
further hypothesis that these two may indeed be homologous. Thus all the transverse
sections of the dorsal body-waU of Schizonemertea on PI. XL, were they to be completed
by adding the circular muscular layer of the proboscis-sheath immediately applied against
them in the median line, would very strongly resemble the figures given of Carinoma
and Carinina.

I will not at present venture to decide whether any of the muscular layers of
the oesophagus, noticed both in Eupolia and Cei'ebratulus (PL VI. fig. 9, oe.m ; PL XIII.
fig 6, mto), may also be looked upon as derivatives of this inner circular layer, but will
only add that in Hoplonemertea such a musculature is hardly developed ; whereas, on
the contrary, the circular muscles of the proboscidian sheath have attained a very high
importance, and are even more independent of the dorsal muscular body-waU than they
are in Schizonemertea (PL IX. figs. 1-9 ; PL X. fig. 1).

Here, too, I would be tempted to hazard a comparison between the absent inner
circular layer and the musculature of the proboscidian sheath.

The detailed histology of the Nemertean muscular system is hardly in its place here,
and may perhaps be more fitly reserved for the monograph that will shortly appear
in the Naples series.

One point must, however, be mentioned, as its definite establishment seemed im-

72 THE VOYAGE OF H.M.S. CHALLENGER.

portant to the Hertwigs,'' -v^z., the question whether the delicate longitudinal fibres
composing the longitudinal muscular layers, and which in transverse sections are often
arranged in rings (PI. III. fig. 6 ; PI. XIII. fig. 6), have their matrix cells between them
or not. Having very often succeeded in demonstrating an evident nucleus in the midst
of this ring of cut fibres, and having constantly observed a difi'erence in the efiect of the
staining reagent upon this central space and upon the connective tissue surrounding the
muscle bundles, I must answer this question in the affirmative.

Finally, two points deserve a short notice in this place. First, that the layer a
of the longitudinal Nemertean muscles is very often separated into two, a right and a left
half, by a dorso-median, sometimes also by an additional ventro-median solution of con-
tinuity. It is very marked in the primitive Pateonemertea, especially in those cases
where this layer is the preponderating component part of the body musculature {cf.
PI. XL) ; it is very rarely wholly absent in Eupolia and the Schizonemertea ; it is less
marked or even absent in the Hoplonemertea. In how far this separation may have
general morphological significance, wiU be discussed in the chapter devoted to general
considerations.

The second point on which I shall ofi"er speculative remarks in that chapter {cf. p. 127)
has again reference to the same muscular layer. Sometimes it was observed that in this
layer darker patches of contracted fibres alternate with lighter ones in which these
contractions were absent (PI. XV. figs. 9, 10). As this phenomenon of contraction was
not wholly local but stretched all round the body in rings, the question must be considered
whether we have here successive waves of contraction preserved at the moment of death,
or whether the phenomenon has a deeper significance, is more permanent and indeed
allows of direct comparison with myotomes. The comparative rarity of the phenomenon
for the present prevents us from very emphatically advocating the latter view.

How the circular layer of the Schizonemertea onlj" stretches to the posterior brain-lobes,
how the longitudinal muscles decussate in all directions in the head, how the develop-
ment of the cephalic musculature is ontogenetically separated from that of the body
musculature, are points already known to former investigators of the anatomy and
embryology of the group. The fact of their having found ample discussion and mention
m other monographs, and the Challenger material not having furnished new points of
interest, will explain my silence in this Eeport on these and other points (such as the
muscular dissepiments, the musculature of the cej)halic slits, &c. ) connected with the
muscular system.

1 Die Coelomtheorie, p. 37.

EEPORT ON THE NEMERTEA. 73

NERVOUS SYSTEM.

With respect to the nervous system, I am indebted to the Challenger collection for
very valuable additional data. In former publications ( IX, X ) I have dwelt at length
on the peculiar arrangement of nervous tissue in the Nemertea as I had found it to exist
in specimens that were obtained at Naples ; I am now enabled to give a more exhaustive
description of this important system, and wall commence by a short account of certain
points in the latest investigations into the nervous apparatus of the lower forms of animal
life, in order the better to explain the bearing upon questions of general morphology
which the arrangements as we find them in the Nemertea may happen to have.

The general and important conclusions arrived at by Kleinenberg in his classical
Memoir on Hydra, conclusions which have since found their way into handbooks and
textbooks as Kleinenberg's Theory of the neuro-muscular cells, have of late years been
emendated by 0. and R. Hertwig. These investigators have propounded a general hypo-
thesis on the phylogenetic development of the nervous system, which in their treatise
Das Nervensystem und die Sinnesorgane der Medusen (Leipzig, 1878), is formulated
(p. 170) as follows : —

"We assume that in all Metazoa the ectoderm from which the (animal) nervous
system, with its motor and sensory terminal apparatus, has originated, was primitively
constituted of a simple layer of homogeneous cells in the same way as may be
noticed everywhere in the earliest ontogenetic stages. We further assume that these
cells, or at least part of them, have at an early period entered into mutual connection
by protoplasmic processes, and have thus formed a more closely connected cell-stratum.
According to our hjqwthesis, and on the principle of division of labour between the cells
thus connected, there has been gradually developed a primitive nerve system out of
this connected stratum. Whilst certain of these cells secreted contractile substance,
others were provided on their surface with tactile hairs, and a third set acquired very
numerous connections, tha simple epithelium cells of the one-layered ectoderm thus
becoming gradually and more or less simultaneously differentiated into epithelial muscle-
cells, sense-cells, and ganglion-cells. Their protoplasmic connections, modified into
specific nerve substance, have pari passu become converted into a plexus of nerve fibrils.
When, later on, the ectoderm became constituted of more than one layer, the ganglion-
cells were the first (of aU the three elements just mentioned) to separate from the
surface epithelium and to acquire a deeper situation."

Balfour, in his Comparative Embryology (vol. ii. p. 333), accepts the leading features of
this important hypothesis, partly substituting it for the earlier suggestion of Kleinenberg.

The latter, in his latest publication,^ revindicates his original theory against the

■" Zdtschr. f. wiss. Zool., Bd. xliv. p. 204.
(ZOOL. CHALL. EXP. — PAET LIV. — 1887.) ITIlll 10

74 THE VOYAGE OF H.M.S. CHALLENGER.

Hertwigs' objections, and maintains that these naturalists have furnished arguments in
favour of his hypothesis rather than of their own interpretation (Log. cit., p. 205). Kleinen-
berg holds that the naked nerve-cells of Hydra, that are in mutual and direct communica-
tion, may transmit a stimulus by contact without the intervention of a delicate network
of inter-cellular protoplasmic threads forming a network. He, moreover, holds that the
epithelial cells had all of them the double significance of nerve-cells and muscle-cells, i.e.,
were true neuro-muscular cells before further division of labour set in, whereas the
Hertwigs maintain that this division of labour took place between epithelial cells that were
not yet physiologically so far differentiated.

A nerve plexus, which covers a very large surface, was actually demonstrated by
the brothers Hertwig not only in Actinia and other Ccelenterata but also in the
Chsetognatha. Of the latter 0. Hertwig says :^ —

" By the fact of the nerve-fibres crossing and decussating in the most complex and
diverse ways, there is formed a nerve plexus which spreads over the whole surface of the
body, and in which the above described nerve-stems represent the single collecting tracts."

A more or less similar plexiform arrangement of nerve-tissue has since been demon-
strated in nearly all the lower gi'oups of invertebrates. Annelids ^ and Arthropods
excepted. Thus in the works of Loven, Greefi", Teuscher, Ludwig, and Carpenter the
nervous system of the Echinoderms is described as off'ering many analogies with the type
propounded as the most primitive by the Hertwigs.

Nemertea, Turbellaria, Trematodes, and Cestodes can now be very fuUy corapared, as far
as their nervous system is concerned, with Hertwig's starting point, when we consider the
results obtained by myself (IX, X) — which were afterwards confirmed (II) by Dewoletzky
— for Nemertea; by Lang, Grafi", and Pintner for TurbeUaria, Trematodes, and Cestodes.

Among aberrant forms one of the most striking examples of a thick epiblastic nerve-
plexus wdth longitudinal collecting tracts is oS'ered by Balanoglossus, as described by
Spengel and more lately by Bateson. We shall have occasion again to refer to this
interesting nervous system further on.

For MoUusca, remnants of a more or less plexiform arrangement were found to exist
in the Amphineura by myself^ [Proneomenia) and by Haller'' {Chiton), and also in other
groups of Mollusca by Semper,' Simroth,*' and others.

1 Die Chfetognathen, p. 34.

2 Lately Fraipont {Archives de Biologic, 1884, p. 274) has demonstrated the presence of an intermuscular nervous
plexus in Polygordim, Protodrilus, and Saccocirrus, and thus opened the possibility of also bringing the Annelids within
the region of comparison so far as this point of their organisation goes. Bergh describes a nerve-plexus in the larval
Aulostoma {Arbeit. Zool. Zoot. Inst. Wiirzhurg, Bd. vii. p. 238). As to Arthropods there are facts which also point in the
same direction, e.g., that Hoek mentions " a continuous network of ganglia and nerves " on the inner surface of the in-
tegument in Pycnogonida (Zool. Chall. Exp., pt. x. p. 116).

3 Niederland. Archivf. Zool, Suppl. Band, 1881. « Zool. Anzeiger, No. 76.

6 Archivf. Mikr. Anat, Bd. xix., p. 124, 1877; Arbeit. Zool. Zoot. Inst. Wurzburg, Bd. iii., 1877.
" Zeitschr.f. wiss. Zool., Bd. xxxii. p. 304.

REPORT ON THE NEMERTEA. io

For Vertebrates a plexiform arrangement is known to exist in the embryonic stages
of Amphibia, since the researches of Eemak and Strieker, and has lately been fully com-
mented upon by Goette and Baldwin Spencer.

The last writes :' — " 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 disappears
as these reach their full development." And further on : — " Along certain lines the cells
of the nervous layer proliferate, and it is by this proliferation that the rudiments of the
cranial nerves are laid down" (cf. p. 133).

The significance of this plexiform arrangement of the embryonic Vertebrate nervous
system will be discussed in the chapter devoted to General Considerations, and also the peri-
pheral plexus of the adult Am2)hioxit.s, which lately has been more fully described by Eohon.^

Hence, since my former publications above cited, the necessity has grown more and
more obvious of not looking upon the brain-lobes and the lateral nerve-stems of the
Nemertea as the nervous system, but, though recognising their significance as more highly
developed centres, to admit the presence of a most complicated and intricate network of
nerve-tissue, originally — and in the more primitive species still — belonging to the
integument. This network is most fully develoj^ed in the Schizonemertea. In Carinina
its situation in the integument makes it more difficult to observe ; still I succeeded in
demonstrating it both here {cf. p. 54) and in the other Carinellidae. In the Hoplonemertea
the plexus has been replaced for the greater part by distinct nerves, of which the majority
show a metameric arrangement.

We will now pass to a more detailed description of this network, thereby purposely
inverting the natural order by reserving the centres for the last. This apparent dis-
crepancy disappears, however, when we look upon the network as the most ancient
nervous arrangement, in which the centres have only gradually come forward.

When once the eye has been trained by repeated observation to notice this particular
nervous tissue of the Nemertea, it is comparatively easy to distinguish it from the
surrounding tissue. The peculiar punctate striation, the yellowish tint of the fibrous
elements, the very pale carmine hue of the nuclear ones, immediately reveal the presence
of nerve-tissue in sections, longitudinal or transverse, that have been made through
specimens stained with picrocarmine.

And when we take for our starting point, and as a basis for further description, one
of the Schizonemertea of the Challenger, e.g., Cerebratulus corrugatus (PI. XIV. figs. 3, 4 ;
PL XIII. fig. 6, pi), we observe in all transverse sections that the two lateral nerve-stems
are in continuous connection tvith each other by nervous tissue that spreads out all round
the circular muscular layer fi, both dorsally and ventrally. Immediately outside of

1 Some Notes on the Early Development of Rana temporaria, Quart. Jour Micr. Sci, SuppL, 1885.

2 Denkschr. d. k. Akad. d. IFiss. Wien {math.-nat. CI), vol. xlv.

76 THE VOYAGE OF H.M.S. CHALLENGER.

this nervous layer the longitudinal muscular coat 7 is situated. There is, moreover,
present a third longitudinal nerve-stem, also situated, as are the two lateral ones, in this
plexus, but medio-dorsally in the vertical plane that passes through the animal. It is
this nerve which I have in a former publication (ix) proposed to call the proboscidian-
sheath nerve, but of which I will, in the chapter devoted to General Considerations, offer
a modified interpretation (p. 131) and which I will henceforth call the medullary nerve.

The nerve-plexus uniting the three longitudinal nerve-stems, as a cylindrical coat of
tissue between the longitudinal and the circular layers of muscles, cannot be separated or
spread out flat, nor can we succeed in getting horizontal sections of it, just because of
this cylindrical curvature. A portion of it may, however, be contained in the few
consecutive sections passing in a horizontal plane through the medio-dorsal nerve or
elsewhere, tangential to the cylindrical surface of the nerve-plexus.

From such horizontal sections figs. 2, 3, and 4 of PI. XIII. and fig. 1 of
PI. XIV. have been taken, and where the plexus {n. 2^1) is touched right and left of the
medio-dorsal nerve m, it has wholly the appearance of a dense network, the meshes of
which are more especially due to the fact that radial bundles of contractile tissue — by
which the muscular layers and the integument are held together, and which may even
pass from the dorsal to the ventral body-waU of the animal — pierce the nerve-plexus.
The longitudinal dorsal nerve stands out very boldly in the midst of the plexus. It
is extremely important, and may be verified in any other surface section of the nerve-
plexus, that from this dorsal nerve spring, both right and left, at more or less regular
distances, thicker tracts of nerve-tissue {tr. n), also forming part of the plexus, but being
straight instead of tortuous, and having altogether the character of metamericaUy arranged
nerve-stems that are not yet recognisable as independent structures, but that are fairly
on the way to special differentiation as so many chief conducting tracts of nervous
energy in the midst of the plexiform nervous tissue which binds them together.

The presence of these transverse stems may also be noticed in transverse and longitu-
dinal sections as a local thickening of the plexus, but as the whole stem is rarely attained
in one transverse section, this thickening may be followed in consecutive sections, and is
found stretching from the medio-dorsal down to the lateral nerve-stems.^ How far these
transverse stems may be said to be metamericaUy arranged, everyone may judge for
himself by consulting fig. 1 of PI. XIV. The chief tracts are certainly symmetrical,
i.e., spring from the longitudinal dorsal medullary nerve at opposite points, and about
the same distance may also be seen to separate each successive pair from the foregoing.
Other transverse bundles, some thinner, some thicker, some more obliquely placed, &c., but
all similarly forming part and portion of the plexus, are, however, visible between the

1 Von Kennel, who lias so considerably advanced our knowledge of the Neniertea, appears to have observed, as early
as 1879 (Die in Deutschland gefundenen Landplanarien, p. 39), the presence of certain of these transverse dorsal
nerve-stems (commissures, v. Kenn.). He did not, however, notice or describe the nerve-plexus, nor the fact of the
existence of a ventral connection, both by means of the plexus and of ventral met^meric stems.

EEPORT ON THE NEMEETEA. • 77

principal ones, and it is this fact that more or less obscures the metamery here alluded to
(PL XIII. figs. 2, 4). This metamery in the nervous plexus is of the same character as
the metamery that is noticed in the intestinal arrangement, in the nephridia, in the
generative organs, and in the blood vascular system of the Nemertea ; it may indeed be
called incipient. To its significance, for the important question of the origin of segmen-
tation, we shall have occasion to return by and by.

Amongst the forms in which I found the metamery to be very distinct, Cerehratuhis
angusticeps stands foremost (PI. XIV. fig. 1). And I must here call attention to the fact
that the transverse stems here described are not only dorsally, but also ventrally, most
regular and conspicuous, uniting the longitudinal nerve-stems below the intestine by a
regular series of transverse commissures in the plexus, which is the primary connecting
medium. It is important to note that there is no ventro-median longitudinal stem in
Nemertea opposite the dorso-median one ; and not less important, that the same favourable
species just named enables me to establish with certainty that the ventral transverse stems
reach much further forwards than might originally be expected. The mouth alone inter-
feres with their course; they are, however, found immediately before as well as behind it,
and whilst in front of the mouth the lateral stems very soon merge into the lower brain-
lobes, it is clearly seen that the transverse commissures are still recognisable, i.e., that the
lower hrain-lobes are united by thin ventral commissures, separated by a very short
distance, tiU close up to the massive ventral commissure that has been hitherto regarded
as the only ventral connection between the brain-lobes. The thin commissures just
described are, however, not directly connected with the fibrous core of the brain-lobes,
which is, on the contrary, directly continued into the massive inferior commissure, but
they seem to derive then- fibres from the outer cellular coating of these lobes. They pass
underneath the two vagus stems, where these spring from the lower brain-lobes, and
where these are in their turn, in front of the mouth, united by transverse commissures,
as was noticed above (p. 38, 45 ; cf. PL XIV. fig. 5).

The histological description of the plexus may be very short, and has already been
touched upon in the beginning of this section. Fibrous and cellular nerve-tissue are
very regularly intermixed, the direction of the fibres follows that of the tracts in which
they are found, and the fibres are, on the whole, closer together than they are often found
in other Platyelminthes, where the designation of the nerve-stems — before they were
recognised as such — as " spongiose strands" (spongiose Balkenstriinge) was current, and not
inadequate. The nerve-fibres, however, are not so closely bound together, that the
bundles are not very frequently found to be pierced by radial contractile fibres, as was
noticed above, and is rendered evident by comparison of PL XIII. figs. 3, 4, rf. That
this intermixture is indeed a primitive character may safely be concluded, if we observe
that Lang in his monograph on the Polyclada (XVIII) specially mentions similar
features in the nervous arrangement of that group of Turbellaria, and also if we remem-

78 ■ THE VOYAGE OF H.M.S. CHALLENGER.

ber that in Carinella the passage of strong contractile fibres, even through the substance
of the brain, was already known (IX).

Of the cellular elements enclosed in the plexus the nuclei alone are conspicuous, and
it is rare to find, either in the plexus or in the medullary nerve, distinct cell outlines
(multipolar or other) round these nuclei, such as they are very often found in the brain.

The nuclei characteristic of medullary nerve and plexus have exactly the same dimen-
sions and shape as those that constitute by far the greater portion of the cellular coating,
both of the brain-lobes (PI. XIII. fig. 1 ; PL XII. figs. 1-4) and of the lateral nerve-stems.
The direct continuity between the nerve-fibres of the plexus, and those forming the axis
of the lateral nerve-stems, can be demonstrated in all well-preserved sections, at any rate
in those species where the plexus is well developed (PL XII. fig. 2). Nor is the continuity
with the fibres of the medullary nerve subject to any doubt (PL XII. figs. 3, 4).

This medullary nerve, a dorso-median thickening in the plexus, may be traced back-
wards down to the hindmost extremity of the bod)^ forwards up to the brain-lobes, and
even in front of these. A section of that foremost extremity of the medullary nerve can
hardly be distinguished from that of an ordinary cephalic nerve, but for its median
situation, and greater size and distinctness. It is here independent, i.e., not enclosed in
the plexus, which does not stretch further forwards than the brain-lobes, or than the
layer of circular muscles. The latter is known to cease in the region of the brain. The
connection of the brain-lobes with the plexus, and with the medullary nerve, is much more
intimate than I was hitherto inclined to believe. Certain specimens of Gerehratulus col-
lected by the Challenger (PL XII. figs. 7, 8 ; PL XIII. fig. l) permit me to form a definite
judgment on this question. We there see that the anterior prolongation of the medullar)^
nerve bends downwards in the region of the dorsal commissure of the brain-lobes, and
enters into connection with a nervous stratum which may, in this region, be either con-
sidered as a median portion of the brain, or as an anterior thickening of the jilexus.
Large ganglion-cells can be detected in it, also fibrous nerve-matter, both of them in the
most intimate connection with the nerve-cells and nerve-fibres of the brain-lobes (PL XII.
figs. 7, 8).

From this anterior thickened region of the plexus, in which a transverse core of fibres —
the dorsal commissure of the brain-lobes — takes its course (PL XIII. fig. 1), other fibres are
seen to start in the direction of the body-axis and to arrange themselves into a longitu-
dinal tract, which is also provided with nerve-cells, and which becomes the medullary
nerve (PL XIII. fig. 2). My former statement (ix), that the medullary or proboscidian
sheath nerve emerges from the dorsal commissure {loc. cit., pi. i. fig. l), although
exact, must thus be amplified in the way just described. I may add that a direct passage
of fibres of the medullary nerve into those of the commissure, though sometimes noticed,
is not always a constant phenomenon. Fig. 1 of PL XIII shows a state of things in
which the fibres belonging to the plexus and medullary nerve appear to be more or less

REPORT ON THE NEMERTEA. 79

independent from those of the brain commissure that is seen to pass under it, and to
have a different texture and arrangement.

Our observations on the nerve-plexus would not be complete if we did not allude to
the very elaborate branches that pass out from it into the superposed muscular layers
which they innervate. Some of them can even be traced as thick radial nerves piercing
these muscles, and spreading out into the integument (PI. XIII. fig. 6, n). Similarly the
underlying muscular layers receive fine nerve-twigs out of the plexus, which are thus
directed inwards as well, and first penetrate into the circular layer y8. For this reason
they are best seen in longitudinal sections. The peripheral nerve system of the Schizo-
nemertea has thus — as was already fully indicated in a former publication (x) — a totally
difierent character from that of the Hoplonemertea. The profusion of radial nerve-stems
springing from the plexus, every transverse section showing a great number of them, may
convince us of the high degree of elaboration to which the nerve system of this group
attains, and of which the great sensitiveness and quickly reacting movements of the worms
themselves are the outwardly visible tokens.

Nor may we omit to record the important fact, which was first observed in a Challenger
specimen of Cerehratuhis corrugatus, that in the region of the long slit-like mouth
and cesophagus (behind the region where the very strong nerve, to which the name of
vagus-nerve has been given (V, IX), leaves the inferior brain-lobes on its way to inner-
vate the oesophagus) we can observe that from the plexus distinct nerves become detached,
pierce the circular and inner longitudinal muscle layers (/3 and a), cross the circum-
cesophageal blood-space and enter the tissue of the wall of the blood lacunse and of the
cesophagus to assist in innervating these important organs. The morphological significance
of this fact wiU be further insisted upon later on {cf. pp. 134, 142). The phenomenon
is figured on PL XIV. figs. 3, 4.

We have now traced the facts concerning the plexus and the meduUary nerve. In a
general way these descriptions may be said to be applicable to the plexus of Carinina,
which, however, as was already noticedj is a less favourable object for study. It would
seem as if in this species the nervous tissue, passing inwards amidst the muscles, again
spreads out into a second plexiform arrangement between the muscular layers a and S.
This phenomenon, however, requires confirmation in more specimens than the two that
have been available for the present investigation.

One point alone requires a few words of further elucidation before we can pass from
the nerve plexus to another paragraph, viz., the question as to whether the name of
proboscidian sheath-nerve, formerly given by me to what I now propose to call the
medullary nerve or the Nemertean medulla, must for the future be dropped altogether.
It certainly must, if we wish to retain it for the longitudinal nerve originally so called ;
but, curiously enough, I have now been able to make out the presence of another longi-
tudinal nerve to which the name may very properly apply.

80 THE VOYAGE OF H.M.S. CHALLENGER.

This nerve is furnislied with fibres directly passing downwards out of the medullary
nerve (PL XII. fig. 9 ; PI. XV. fig. 1); it is situated below this, and is entirely parallel to it.

In one case of a very large specimen of Cerebratulus it appeared in its turn to
be splitting up into two parallel nerve-stems. This proboscidian sheath-nerve more
especially deserves its name because of its situation immediately above the muscular wall
of the proboscidian sheath, iato which it may be seen to give ofi" fibres. It is not noticed
in Carinina, Carinella, or the Hoplonemertea, bujf; it is iq Carinoma, Etipolia, and aU the
Schizonemertea. Its absence in the two first-named genera would appear unaccount-
able if we did not remember that in both of them the proboscidian sheath is of hardly
any importance, being extremely thin-walled {cf. PL II. figs. 4-7). And in this case it
is all the more natural that in the oesophageal region of Carinoma it has become specially
developed, being here even thicker than the raedullary nerve, and about as thick as
the lateral nerve-trunks of this species (PL XL fig. 6). This is another example
of sudden increase of a portion of the nervous system, and at the same time of the
existence of a very marked degree of supremacy to which certain apparently subordinate
parts of the organism may aU at once attain. This unexpected change of size of the
proboscidian sheath-nerve in one species is certainly a valuable fact for a hypothesis that
wiU in a further chapter be enunciated (p. 133), according to which the possibility of a
decrease in size of the lateral nerve-trunks is supposed to have been accompanied by an
increase in significance of the medullary nerve.

The fact that in this region of Carinoma the proboscidian sheath-nerve comes into
the foreground so strongly that it might easdy be mistaken for the medulla, may probably
be ascribed to the massive development of the inner circular muscvilar layer S, which in
Carinina, Carinella and Carinoma acts at the same time as part of the wall of the
proboscidian sheath. The fact was already noticed as a peculiar feature of the species
by M'Intosh (XXIV), when he first described Carinoma (under the name of Valencinia
armandi).

That a proboscidian sheath-nerve is wholly absent in the Hoplonemertea is stdl more
easily accounted for. Erom the moment the brain and longitudinal trunks of the ances-
tral Hoplonemertea were no longer lodged in the midst of the muscular tissue of the
body-waU, but have come to be situated within the gelatinous tissue that fills up the space
inside this muscular body-wall, not only has the plexus disappeared and been replaced
by the remaining metameric nerves described above, but at the same time the innervation
of the proboscidian sheath has altered. This innervation is now brought about by the
peripheral and metameric nerves, which, in favourable cases (Pelagoncmertes, &c.), may
be seen to send fine twigs into the muscular tissue of that wall. With this freer develop-
ment of the peripheral nerve-system, the special arrangement by which the innervation
of the proboscidian sheath is brought about, as long as the nerve-sheath is the source
from w^hich all peripheral nerve-fibres take their origin, has at the same time disappeared.

REPORT ON THE NEMERTEA. 81

It is certainly all the more remarkable that in the Hoplonemertea we nevertheless
find such very distinct traces of the medio-dorsal meduUary nerve, notwithstanding the
disappearance of the plexus. And more remarkable still that this remnant — not dis-
tinctly traceable in only one specimen of Amjyhiiwrus, whilst other specimens of the
same species still have it, and whilst it is even very conspicuous in Drepanophonis and
others — should occupy the same position as it does in the most primitive Palseonemertea,
i.e., in or even outside the basement membrane of the integument. This is another
argument for directly deriving the Hoplonemertea from the Palseonemertea. Cephaloihrix
may be said to fill up part of the distance which sepaxates Carinina and Carinella from
the Hoplonemertea as far as the situation of the nerve-system is concerned {cf. PI. XL
fig. 5), whereas Eupolia may be said to do the same with respect to the ciliated grooves
on the head, and partly also to the posterior brain-lobe, its glandular investment, and the
long duct leading from it to the exterior.

We must now pass on to the description of the brain-lobes and the lateral nerve-stems.

It is known that these offer the lowest degree of speciahsation in the more primitive
genera of Palseonemertea, e.g., Carinella. For this genus the brain- and nerve-stems
have been sufficiently described before (IX), and, in comparing this with what we find in

?.l.

Fig. 5. — Side view of the brain of Carinina m outline, reconstructed from the sections. The iibrous core is indicated by a
dotted line. A.I., anterior lobe ; P.I., posterior lobe ; Co., ventral commissure ; Ln, Lateral nerve-stem.

Carinina, the latter genus must be recognised as representing in this respect a somewhat
higher scale in the developmental series. This higher development finds its expression in
the presence of a posterior brain-lobe, comparable to the same lobe of the Schizonemertea
which was often designated as the side organ, although it is formed of nerve-substance
directly merging into that of the brain. Carinella inexpectata has been formerly
shown (VIII ) to possess a ciliated passage leading into the brain-substance, without any
special differentiation of that portion of the brain into which this cUiated channel pene-
trates. In Carinina such a differentiation has set in, and the braiQ-substance, into which
a ciliated canal leads, has become a separate lobe.^ In consequence of this we are,
moreover, enabled to draw a general — though by no means a sharply defined — distinction
between the portion of the brain-mass with which this accessory lobe is in contact, and

, 1 Chapuis has lately noticed posterior brain-lobes in a Cephaloihrix {Arch. d. Zool. Exp., vol. iv. p. xxi., 1886). His
description is, however, very incomplete.

(zOOL. CHALL. EXP. — PAET LIV. 1887.) Hhh 11

:^^Ai

82 THE VOYAGE OF H.M.S. CHALLENGER.

thatwhicli is continued into the lateral nerve-stems, i.e., an incipient distinction between
a pair of upper and a pair of lower lobes, respectively limited by the dorsal and ventral
brain commissure ; the whole forming a ring round the proboscis and its sheath. A
side view of the brain of Carinina — reconstructed from a series of sections — is given
in the accompanying woodcut, in which the very thin dorsal commissure is not
indicated. A comparison with figs. 4 and 7 of PI. V. will at once show the relation of this
stage of diflPerentiation to that to which Eiqoolia has attained. In the Schizonemertea
the separation between upper and posterior lobes is more marked still than in Eupolia
(PL XIV. fig. 6) ; in the Hoplonemertea they are definitely separated, and only con-
nected by one or more nerve-strands (PI. IX. fig. 10), their situation being then some-
times behind, and even sometimes before the rest of the brain.

The ciliated canal penetrating into the posterior lobe of Carinina is simple (not
divided in two as in certain Hoplonemertea), and provided with a high, ciliated epithe-
lium of its own. It is figured in figs. 1 to 3 of PI. VI. Certain glandular cells, gl. hr, are
seen in this same figure to have become specially developed in connection with this
posterior lobe and its ciliated canal. Similar glandular cells also form a characteristic
feature of the posterior brain-lobes of Schizonemertea and Hoplonemertea. In Carinina
it is evident that these glandular cells are derivatives, or at least morphological equiva-
lents, of the deeper glands Gi, of the integument.

The nerve- cells themselves, out of which the brain is built up, still undoubtedly
belong to the integument, and it is exceedingly difficult, if not impossible, to draw a
sharp distinction between the outermost brain-cells and the surrounding integument-cells.
In the figures just cited this difference has been artificially very much accentuated in order
to bring out more distinctly the outline of the brain ; for the same reason, the integu-
ment in this figure was on purpose not fully worked up.

The inner core of the brain is fibrous, so is the core of the longitudinal stems, where,
however, the attempt at a distinction between nerve-cells and cells of the surrounding
integument is equally hazardous (PL III. fig. 8). This fibrous core is in direct continuity
with the nerve-plexus, that spreads out in the deeper integumentary layers.

A vagus nerve passing from the lower portion of the brain on both sides towards the
oesophagus is also distinct in Carinina (PL VI. fig. 1, iVv).' The passage of contractile
fibres through the brain-substance is unmistakable, though less evident than in Carinella.

Passing on to the description of the nerve-centres of Eupolia, we immediately recognise
the difference resulting from the fact that here the brain is imbedded inside the muscular
layers, as is also the case in all Schizonemertea.

Our description of the brain of Eupolia maybe based upon the figures of PI. V., which
were obtained not de visu, but by reconstruction from a series of sections.^ Figs. 1-4

1 For the making of these and many other series of sections, and for assistance in the reconstruction above alluded to, I
am indebted to the kindness of Dr. Gudemans, my former assistant, now director of the Zoological Garden at the Hague.

REPORT ON THE NEMERTEA. 83

and 8 represent the whole of the brain tissue, figs. 5-7 and 9 the fibrous core, as it is
enclosed by the nerve-cells, the limit of this cellular investment being given in outline in
the latter figures. It must, however, from the first be remarked, that this outline should
be completed by the plexus, and by the median medullary nerve. They are not indicated
in these figures, although both of them are found along the whole length of the lateral
nerve-stems, and reach forward as far as the region of the dorsal brain commissure.

It is seen at a glance that the fibrous core repeats the external folds and prominences
of the brain-masses, that the lateral nerve-stem is continued into the lower lobe, and
that the upper lobe is distinguished by a prominent fold of its surface, a gyrus (fig. 1,
SL), into which a separate knob of the fibrous core is seen to pass, and by two other
fibrous projections — the one stretching towards the blunt end of the posterior lobe, the
other running forwards and accompanying the ciliated canal, which is also marked in
outline in fig. 6, and (in red) in fig. 5. The canal cc, in figs. 2, 3, 4, 8, is the exterior
portion of this duct. The difi'erent thickness of dorsal and ventral brain commissure may
be gathered from figs. 1, 3, 8, 9 ; from the latter two, the fact that the nerve-fibres are
very strongly preponderant in these commissures over the cells. Close behind the ventral
commissure the nerve for the oesophageal wall, vg, the so-caUed vagus nerve, is seen to
leave the common fibrous core of the brain, whereas the nerves for the proboscis (pn)
spring from the inner surface of the ring, where the fibrous core turns up from the ventral
to the dorsal commissure (figs. 5, 9). The vagus nerve is soon after its origin connected
by transverse fibres with its opposite neighbour ; this vagus commissure is sometimes
repeated ; it will be again referred to in the general considerations on the nervous system.
The cephalic nerves that leave the brain and innervate the head are only very imperfectly
rendered in these figures ; their number is far greater than might be concluded from
figs. 5, 6, an.

The aspect of several portions of the brain of Eupolia, in transverse section, is repre-
sented in PI. VI.

It will there be noticed that fig. 4 represents an anterior section through the inferior
brain commissure and ±he point of innervation of the proboscis, fig. 5 one just behind
this, cutting the dorsal commissure and the vagus root at the same time. The exact
situation of these sections will be best understood by comparing them with PI. V. fig. 9,
where the respective positions of the commissural ring, the proboscidian nerve, and the
vagus are clearly indicated. Fig. 7 is a transverse section lying further backwards,
almost in the level where the dotted line, SL, in PI. V. fig. 4 terminates, whereas the
section fig. 8 lies again somewhat behind this, at a point where the "gyrus" of the superior
brain-lobe actually divides the central fibrous nerve-substance into an upper and a lower
portion. These sections, at the same time, show the difi'erence in size between the
brain-cells and the glandular elements partaking in the constitution of the brain, along
the superficial part of what I have called the posterior brain-lobe (side-organ, auct.).

84 THE VOYAGE OF H.M.S. CHALLENGER.

The brain of the Schizonemertea was fully discussed in a former publication (ix). The
Challeno-er Schizonemertea all conform to this type, with the additional facts alluded to
above in connection with the medullary nerve. The difference in the size of the ganglion
cells in different regions of the brain, as it appears in PI. XII. figs. 7, 8, and PI. XIII.
fio-. 1, is much more marked in certain species of Cerehratulus than in others. The
laro-er sized nerve-ceUs appear to be principally peripherally and anteriorly situated ; that
they are absent, or less numerous, in certain other species, may be seen by comparing
PI. XII. fig. 1, with the above mentioned figures. The relative distribution of fibrous
and cellular nerve-matter in the brain need not be any further described in detail after
our foregoing description and figures of EicpoUa. The size and shape of the posterior
lobe is, however, somewhat difterent in the Schizonemertea. This will be obvious by com-
paring pi. i. fig. 1 of the treatise referred to (ix) with our present figures of Eupolia.

Not having been able to study any of the Challenger species alive, we should have to
be content with reconstruction from section series, if I were to enter more fully into the
discussion of the respective differences, and for that reason I wish to restrict myself
to these general remarks.

One other point connected with the posterior lobe and its ciliated duct deserves
special mention, viz., the observation I was able to make that the duct which leads from the
bottom of the cephahc shts into the nerve-tissue of the posterior brain-lobe (inside the
brain-lobe it very generally has an S-shaped, and, at the same time, a spiral twist, thus
being very often as in PL XIV. fig. 6, cut in three places, all in one section), and which is
clothed in the neighbourhood of its external opening with an epithelium directly con-
tinous with, and similar to, that of the outer surface, not only shows certain diff'erences
in its epithelium, as we pass further inwards (PI. XIV. fig. 11), but also ofi"ers certain
comphcations, which we have now to consider. These complications very distinctly con-
cern the participation of deeper cellular layers of the integument. As indicated by gl in
PI. XIV. fig. 11, these deeper layers segregate and form a ring-shaped or cushion-shaped
addendum to the simple epithelial tube. It must be doubted whether they communi-
cate with the exterior, as do the deeper glands of the integument, although this
deserves special attention, because of the glandular significance which must be attached,
according to Dewoltezky (ll), to the strongly refractive cells present on the posterior
surface of the hinder brain-lobe {cf. p. 94). The epithelium has undergone stUl more con-
siderable alteration when it passes inside the posterior brain-lobe. Its nuclei are distinct
(PL XIV. figs. 6, 7, 8), but instead of direct cell partitions we may observe a fine striation
vertical to the axis of the cUiated canal (fig. 8). This feature, known to former observers
(IX, figs. 35, 36), may here be more especially alluded to, because in Hoplonemertea
(PL XIV. fig. 10) we find that the discharge of glandular products from the deeper gland-
ceUs takes place between the interstices of this striated region. This discharge into the
lumen of the canal is a point that is put beyond doubt by numerous Challenger sections.

REPORT ON THE NEMERTEA. 85

The fact that the canal is single in the Schizonemertea, whereas it is double in the
Hoplonemertea, was known before (ix). It was also found to be confirmed in all the
Challenger species ; the bifurcation of the canal taking place in such a manner, that the
one branch passes through the distinct nerve-cells, forming the greater mass of the lobe,
whereas the other one immediately penetrates — more peripherally — amongst the much
larger glandular cells overcapping the foregoing. Carinina corresponds with the Schizo-
nemertea in having the canal single.

Having considered the central fibrous substance of the brain in the Palseonemertea and
Schizonemertea, we have only to add that the Challenger Hoplonemertea have also con-
firmed the fact that here this fibrous core is less complicated, the brain-lobes being
at the same time more compact, the cephalic nerves very numerous. In Cerebratulus angus-
ticeps (PI. XIV. fig. 6) the fibrous core is very massive and conspicuous also. As to the
innervation of the numerous eyes, I have no new observations to record (cf. V and IX),
nor as to that of the proboscis, with the exception of the fact that in Drepanophorus
and Amphiporus I could distinguish numerous nerves springing from the brain-ring and
corresponding to the numerous longitudinal trunks in that organ. This point, which was
left in doubt by v. Kennel (XVl), is thus definitely settled. The phenomenon was parti-
cularly distinct in one specimen of Amphiporus moseleyi that had retained its proboscis.
It has only been partly figured in PI. IX. fig. 10, where only two are indicated, so as not
to obscure the diagrams.

As to the innervation of the oesophagus, little need be said as far as the Schizo-
nemertea are concerned, the well-known strong and double vagus nerve being constantly met
with. Distinct nerve-branches are seen to take their course in the walls of the oesophagus
(PL XIV. figs. 3, 4) ; it was already noticed above (p. 79) that these may be partly
traced to separate branches springing independently from the nerve-plexus, whereas for
the other part they are ramifications of the so-called vagus.

Nerves to the intestinal canal, very easily detected in the oesophageal region, could
not be traced with the same accuracy and distinctness in the post-oesophageal region of the
intestine, most probably owing to the extreme tenuity which these fine and delicate nerve-
twigs may here have obtained. It cannot be determined at present whether this portion of
the intestine also receives branches from the oesophageal vagus system or only directly
from the plexus, now that the existence of such a double method of innervation {Cerebra-
tulus corrugatus) has been actually demonstrated for the anterior regions of the intestine.
On a priori grounds, I look upon the latter arrangement as by far the most probable.^

The course of the vagus is somewhat modified in Drepanophorus, and perhaps in
Amphiporus. I find the strongest nerve-stem, connecting the brain with the oesojihagus,
in Drepanophorus, running forwards instead of backwards (PI. IX. fig. 10). Other smaller

1 It should here be noticed that Kleinenherg {loc. cit., p. 114) has also failed to detect visceral nerve-branches to
the endodermal intestinal epithelium of the Annelid, Lopadorhynckus.

86 THE VOYAGE OF H.M.S. CHALLENGER.

stems leave the brain in corresponding regions of the lower brain-lobe, i.e., along the surface
turned towards the proboscidian sheath, and run in the direction of the oesophageal
epithelium. This secondary innervation, though different in morphological aspects, is
more or less homologous with the facts above disclosed in the case of Cerebratulus corru-
gatus. That the vagus proper — the massive and thick stem — is here turned forwards
may be a consequence of the change in the situation of the mouth, which in the Hoplo-
nemertea is no longer behind the brain, but in front of it. This gradual change of
position may very possibly have drawn the vagus-stem with it. In concluding our
remarks upon the brain I have only to add that the well-known difference between
Schizonemertea and Hoplonemertea with respect to the connection between anterior and
posterior brain-lobes (side organs) also obtains in the Challenger specimens. The latter
are connected in Drepanophorus and Amphip>07'us with the brain by one or more fibrous
commissures.

Another difference several times observed between the fibrous brain-tissue of these
two Hoplonemertean genera on the one hand, and Cerebratulus, Eupolia, &c., on the
other, is a marked increase in compactness of the fibres, so much so that the fibrous
character of the central portions of the brain has often more the aspect of Ley dig's
" Punktsubstanz," and even shows a still more delicate and more compact texture by
the appearance in this " Punktsubstanz " of regular patches with very faint outlines,
which apparently are still more compact regions of this tissue.

The longitudinal nerve-stems, which are the posterior continuations of the lower
brain-lobes, hardly need any special mention. It must only be insisted upon that in
them, as well as in the brain-lobes, there is no absolute distinction between the cellular
envelope and the fibrous core, but that inside this core nuclei are invariably scattered,
which bear testimony to the absence of any such definite boundary. Still, there is
generally a homogeneous and very thin layer between the cellular coating and the fibrillar
core, a kind of membranous neuroglia, through which the fine processes of nerve-cells may
be seen to take their course in groups, which then become lost amongst the fibres of the
core. Then, again, certain favourable sections (PI. XII. fig. 2) very distinctly show the
course of nerve-fibres inside this fibrous core that are not longitudinal, and thus puncti-
form in transverse sections, but that are interwoven at right angles with the latter and
continue their way into the nerve-plexus. The transparent sheath of the fibrous core
of the nerve-stem is more distinct in Cerebratulus than in either Palseonemertea or
Hoplonemertea. It is rarely encountered in the brain, where fibrous and nervous elements
are more intimately interwoven {cf. PL VI. figs. 4-8 ; PI. XII. figs. 7, 8 ; PI. XIV. figs. 7, 8).

Outside of the stems there is another accumulation of homogeneous connective
tissue arranged as a protecting envelope round the nerve-stems. This is much more
conspicuous in the brain-lobes, and more so in the Hoplonemertea (PL XII. fig. 5) than
in the Schizonemertea (PL XII. fig. 2 ; PL XIV. fig. 2). Still in the latter it is far more

EEPOET ON THE NEMERTEA. 87

conspicuous than in Carinina, where we have already pointed out the apj^arent absence
of any sharp or distinct boundary Une between the cellular brain- tissue and the sur-
rounding cellular tissue of the integument.

We cannot pass on to the description of the perijiheral nerves without first referring
to the terminal portion of the lateral nerve-stems, known to terminate at the posterior
end of the body, right and left of the anus in the Schizonemertea, but also known to
meet in a connecting commissure above the anus in several Hoplonemertea (IX). This
commissure was found by me in several Challenger species, but at the same time I was
able to verify the unexpected fact that in Eupolia the fibrous cores of the longitudinal
nerve-stems are also posteriorly united by a commissure. What most especially
deserves attention in this posterior commissure of Eupolia is, that it is found helow the
anus, the longitudinal stems and the commissure, together with the brain, thus forming
an immensely elongated ring round the intestine, whereas in most of the Hoplonemertea
alluded to, all the portions of the nerve-system may be said to remain above the intes-
tine. This is, indeed, very emphatically the case in Amphiporus moseleyi, where we find
(PI. IX. fig. 4) not only the brain and the anal commissure above the intestine, but also
the longitudinal stems, that take their course above the intestinal caeca. Nevertheless,
in Drepanophorus the anal commissure is above the intestine, although here the
longitudinal stems are diametrically opposite in position, i.e., below the intestinal caeca.
They were for this reason considered (IX) to furnish a transition stage to the ventral cord
and circumoesophageal ring of Annelids and Arthropods, a consideration which derives
very strong support from the existence of transverse commissures that will hereafter be
described. At all events, these very curious difi'erences — the anal commissure of Eupolia
is figured on PI. VII. fig. 8 — furnish another proof of the extraordinary plasticity which
we meet with in the group of the Nemertea, with respect to the morphology of the most
important com^^onents of the system ; a plasticity and diversity which are at the same
time indicative of the primitive and low scale on which the Nemertea may be said to
find themselves.

Coming now to the, peripheral nerve-system, I may note that I have already, some
years ago (X), stated that it is difiicult to apply this name in its generally accepted
significance to the arrangement which we find in Schizonemertea and in Palseonemertea.
It is, however, applicable to that of the Hoplonemertea. Here only we find distinct
metamerical peripheral nerves leaving the longitudinal nerve-stems at regular intervals,
and innervating the body musculature, the integument, the internal organs, &c.

In the Schizonemertea and Pala^onemertea the cephalic nerves, starting from the brain,
are directly comparable with those of the Hoplonemertea, but the rest of the peripheral
system is here represented by the plexus and its innumerable branches and twigs, which
are directed upwards and downwards, serve for the same purpose, and render the peripheral
arrangement in this group so primitive and so important. Still, in very large specimens

88 THE VOYAGE OF H.M.S. CHALLENGER.

of Schizonemertea (PL XIV. fig. 2) I could observe that from the thickened part of the
plexus, which forms the longitudinal stem, fine nerve-branches also take their origin, and
pass directly to the periphery. The essential difi'erence between Schizonemertea and
Hoplonemertea in this respect nevertheless remains the same as above formulated.

We may now turn to the Hoplonemertea. The difi'erent species contained in the
Challenger collection confirm the well-known facts about the metamerically placed pairs
of peripheral nerves of the Hoplonemertea, some of which are turned dorsally, others
ventrally, and which, dividing dichotomously, finally spread out in very numerous
bundles of nerve-fibrils, serving for the innervation of the environing regions. In addi-
tion they also furnished me with certain important new points. To begin with the latter,
I will first draw attention to the two longitudinal nerve-stems of Drepanophorus
lanhesteri, which are situated, as is characteristic of this genus, below the intestinal
caeca (PI. IX. figs. 1, 5, 6), about midway between the lateral margin of the body and
the median ventral line. These stems in transverse section very much resemble those
of other Hoplonemertea. One of them is figured on PL XII. fig. 5 ; from this it may be
seen that the nerve-cellular coating is generally not distributed as a sheath all round the
fibrous core, but as a double band applied upon this core at two diametrically opposite
points. The participation of this cellular coating in providing the outgoing peripheral
nerves with delicate nerve-fibres is distinctly seen in this section, as is also the direct
continuity of other portions of the peripherally directed nerve-fibres with those of the
core.

When in Drepanop>horus lanhesteri I followed some of these peripheral nerves in
their further course, by examining the consecutive sections in which they are continued,
I was struck by the very remarkable fact, never noticed before, that some of them
did not dichotomise — or at least very rarely — and did not taper towards the periphery,
but passed directly under the intestine from the one longitudinal nerve-stem into the
other, a distance in this specimen of 1^ mm. This was an unmistakable com-
missure, which could in no way be compared to the well-known commissure above
alluded to, which connects the two longitudinal stems above the anus. And not
only was one such ventral commissure present, but on closer inspection I found a
great number of them, and by registering the respective distances at which they
were present, the one behind the other (about \ mm.), I was forced to the conclusion
that we here have before us a system of very regular metamerically placed commis-
sures between the longitudinal stems, and forming a nerve-ladder (PL IX. fig. 10),
which is very directly comparable to that of Sahella and other species among Annelids,
and to that of Proneomenia and Cliiton among Molluscs. In a few of these commissures
I detected dichotomy and fusion of one of the branches thus formed with the fore-
going or with the following commissure, a peculiarity also known to exist in Chiton, but
evidently of rarer occurrence in Drepanop)horus lanhesteri. Moreover, I may also men-

REPORT ON THE NEMERTEA. 89

tion that in certain commissures it was clear that fine nerve-twigs spring from them and
serve to innervate the surrounding tissues, their significance thus not being solely com-
missural. The difi'erent facts just recorded are represented semi-diagrammatically on PI.
IX. fig. 10, which was reconstructed from the very large number of sections which I
have of this species. It is, moreover, seen in this reconstruction how other peripheral
nerves spring from the longitudinal stems as well, some being directed upwards or
downwards, some towards the side or inwards. These peripheral stems are metamerical,
as are the commissures, a metamery which, though not absolute, and sometimes broken
by certain irregularities, is still more advanced towards perfect regularity than is the
incipient metamery which we observe in the nerve-tracts that are noticed inside the
plexus of the Schizonemertea, and that were more fully described above. The transverse
commissures between the lateral stems may be noticed to go up quite close to the brain-
lobes, as indicated in the diagram on PI. IX. fig. 10. Both in this respect and in the
fact of their existence, they call to mind the ventral commissural tracts in the plexus of
Schizonemertea. I have no doubt that the two systems are homologous, the commissures
having subsisted in Drepanophorus lankesteri although the plexus has disappeared.
Finally, it must be mentioned that as yet I have looked for them in vain in other species
of Drepanophortis, or in other Hoplonemertea. My other specimens of Drepanophorus
are, however, less well preserved than is the one specimen of Drepanophorus lankesteri.

Another peculiar feature of the peripheral nerve-system of the Challenger Hoplo-
nemertea, which has also remained hitherto unnoticed, is most favourably observed
in Amphiporus marioni, although I afterwards noticed it in other Hoplonemertea. It
is figured on PI. X. fig. 1, ne, and consists in the fact of a peripheral stem, which
has taken its outward course away from the longitudinal nerve-trunk, and which
has penetrated amongst the pennate fasciculi of longitudinal muscle-fibres of the layer
a, spreading out in a plane parallel to that of the body-surface, and thus forming a kind
of local plexus between the muscular layers a and /3. It must for the present remain an
open question whether this arrangement, which can be noticed in different regions of the
same section, and which in no section was absent, must be regarded as a primitive
feature connected with the plexiform arrangement which must have obtained in the
ancestral forms of the Hoplonemertea, or whether it is merely a special adaptation,
having arisen in certain Hoplonemertea, and being in some way subservient to the
innervation of the muscular investment or the integument. At all events it is a peculiar
arrangement, and, as such, deserves special mention. ■»

How intricately and yet how regularly the peripheral nerve-system of the Hoplo-
nemertea may be said to be distributed can also be gathered from Moseley's figure of
Pelagonemertes, which we have copied on PI. I. fig. 23, where the peripheral nerves
are seen to spring, two at a time, from the lateral trunks, which here, too, are united
posteriorly by a commissure above the anus.

(ZOOL. CHALL. EXP. — PART LIV. — 1887.) Hhh 12

90 THE VOYAGE OF H.M.S. CHALLENGEE.

One peculiarity, finally, deserving special mention is the presence in the majority of
well-preserved specimens of Hoplonemertea of a medio-dorsal longitudinal nerve homo-
logous to the medullary nerve described above {cf. p. 81, and PL XL fig. 8). Its connection
with the rest of the nervous system could not be satisfactorily made out, although traces
of a connection with the dorsal brain commissure were not wanting in many specimens.
Its presence is, however, significant, and its retention in the Hoplonemertea, where the
arrangement of the nerve -system has so considerably deviated from the primitive Palaso-
nemertea and Schizonemertea, must prevent us from underrating its morphological
significance. This will be more fuUy entered into in the chapter of General Considera-
tions at the end of this Report.

SENSE-ORGANS, ACCESSORY GLANDULAR STRUCTURES, AND ORGANS

OF UNKNOWN SIGNIFICANCE.

The most conspicuous sense-organs of the Nemertea are without doubt the eyes.
Although eyes are absent in very many genera and species, and although in some species
pigment spots at the tip of the snout are regarded as such, other genera have very well-
marked and numerous eyes, with a hyaline hemispherical refractive body, a layer of visual
rods, and an optic nerve connecting the eye with the brain-lobes. These more highly-
developed eyes were previously known to occur in the Hoplonemertea, and the Challenger
material has confirmed these general conclusions. The most primitive of the Palseo-
nemertea, Carhiina, is not provided with eyes. Nor do I find traces of eyes in those
species of Eupolia which were contained in the collection, and of which the head was
studied in sections. EupoUa giardii is among these. However, it is known from
other researches (VIl) that different species of J^upolia have often very numerous eyes,
increasing in number with the growth and the age of the animal, and, moreover, that
these eyes resemble those of the Hoplonemertea in many respects. Nor were the Schizo-
nemertea of the Challenger provided with eyes that revealed their presence in the
microscopic sections, although I would not venture to afiirm the total absence of eye-
like structures or pigment spots. In this respect the fresh animal often shows at
a glance what is very difiicult to demonstrate in the series of sections, e.g., the
number and disposition of the eyes or pigment spots. As, moreover, these data can
hardly be of any taxonomic value for the determination of the Schizonemertea, I think
I may pass on to the discussion of the eyes of the Challenger Hoplonemertea.

They have the characteristic histological arrangement already described and figured
by myself in a former publication on the subject (IX, fig. 42). A posterior layer of rod-
like elements, which is in direct connection with the optic nerve, is enclosed by pigment,

REPOET ON THE NEMERTEA. 91

and the whole completed into a more or less oval enp-form of which the anterior part
shows very distinct cellular elements with nuclei. Distinct lenticular structures, which
were formerly noticed in Mediterranean Nemertea, could not be certainly made out
in the Challenger specimens. What varies most is the pigment coating the posterior
hemispherical surface. Sometimes this pigment is intensely black, and so extremely fine
that it looks almost homogeneous {Amphiporus moseleyi), whereas in other cases (Amphi-
porus marioni) the pigment granules are uncommonly coarse and large sized, the colour
being in this case a brownish-green rather than black.

In discussing the further sense-organs of the Nemertea, a great significance must
certainly be ascribed to the sensory elements distributed in the skin, and primarily
serving for tactile functions. With respect to this organ of sense, the spirit specimens at
my disposal have, however, revealed no new facts of importance. I have only convinced
myself — as has been already noticed both when describing the cellular integument and its
innervation — of the presence of distinct sense-ceUs in all parts of the integument. They
have the well-known form of the sense-cells described by the Hertwigs, by Lang, and by
others in the Coelenterata, in the Platyelminthes, &c., and it is to them that the
extreme delicacy of the tactile sense, which is revealed in living specimens of Nemertea,
must be ascribed. Bateson's fig. 77 ^ of Balanoglossus comes very close to what was
observed in the Nemertea in connection with these sense-cells. Their direct innervation
by nerve-fibres, starting radially from the plexus in the two more primitive groups, has
been noticed above (c/! PI. XIII. fig. 6 ; PI. XIV. fig. 2). Sense-cells with distinctly longer
and stifi'er hairs, such as I have been able to observe in living specimens from the Bay of
Naples, have not come under my notice in the Challenger sections. The similarity
with Balanoglossus, just alluded to, is increased if we consider Bateson's figs. 70, 75, and
79, and compare them with the integument of Carinina. The similarity is significant. In
sections of Balanoglossus made by myself I was very muck struck by this resemblance,
reaching from the cilia down to the nerve-plexus and subjacent muscles.

Another question I wish to allude to here, and which has been pressed upon me by
certain of the Challenger specimens, is whether the terminal transverse furrow which
is encountered at the tip of the head in Carinina (PI. I. fig, 1-3 ; PI. II. fig. 1), which
is also distinctly seen in certain A')np>hipori (PI. IX. fig. 9), has not also primarily a
tactile significance. And, in addition to that, I wish to ask whether we might not look
upon this terminal groove, which lies more or less in a horizontal plane passing through
the animal, as having preceded the paired longitudinal cephalic furrows which form the
distinctive feature of all the Schizonemertea. When considering the probability of this
suggestion, the following points should not be lost sight of — (l) that in certain
Cerehratuli these cephalic furrows do meet at the tip of the head (PI. I. figs. 13.
14, 18, 19) ; (2) that the furrows in this case are comparatively short (figs. 13, 14) ;

' Quart. Journ. Micr. Sci., June 1886.

92 THE VOYAGE OF H.M.S. CHALLENGER.

(3) that in Cannina the opening through which the proboscis is everted lies ventrally to
this furrow ; (4) that in most CerebratuU the proboscidian opening would similarly lie
ventrally to the point of meeting of the lateral cephalic furrows if we supposed these to
meet at the tip of the snout ; (5) that in a few cases the opening appears to have shifted
into the central part of the fissure ; (6) that in other Cerehratuli the fissures, though
continued on the anterior and apparently truncated portion of the snout, do not wholly
fuse (PI. I. fig. 12), but that just in the interval the proboscidian opening is situated;
(7) that again in other CerebratuU this anterior truncated portion is wholly devoid of
any continuation of the fissures, which in their turn may be exceedingly deep and long
(PL I. fig. 16); (8) that in the Amjjhipori alluded to (PI. IX. fig. 9) the common
opening for proboscis and digestive cavity is also situated ventrally to the terminal fold ;
(9) that in Eupolia transverse and very shallow cephalic fissures are found, which very
strongly resemble those of the Hoplonemertea (even in the presence of short and numerous
secondary grooves perpendicular to the principal groove), and which similarly contain the
opening that leads into the posterior brain-lobe, as is the case in Carinina and the
Hoplonemertea, and that even yet in certain Eupoliae a trace of a terminal horizontal
furrow has been retained (PI. I. fig. 7).

Tabulating these difi"erent facts, the case would appear to stand thus : —

Carinella annulata, one terminal shallow horizontal groove, two transverse lateral

ones, no cUiated canal.
„ inexpectata. (VIII) terminal groove uncertain, transverse lateral grooves,

ciliated canals into the brain-substance opening out into these

grooves.
Carinina, . . . terminal groove present, lateral grooves, with openings of

ciliated canal leading into a separate posterior brain-lobe.
Amphiporus, . . terminal groove present, lateral grooves, with openings of

ciliated canal leading into a separate posterior brain-lobe.
Eupolia, . . . hardly a trace of terminal horizontal groove, lateral grooves as

in the Carinellidse and Hoplonemertea.
Valencinia, . . no grooves at all, simple round opening for ciliated canal.
Schizonemertea, . two longitudinal (never transverse !) cephalic grooves which in

some cases are wholly separate, in other cases meet at the tip

of the snout, and might then in their entirety be compared to

a terminal horizontal groove such as that of Carinina.

If the latter conjecture be true, i.e., if we may suppose the lateral furrows of the
Schizonemertea to be derived from an ancestral phase, in which a terminal groove like
that of Carinina was separated into two halves which deepened and widened on both
sides of the head, reaching down as far as the opening of the ciliated canal into the

EEPORT OiSI THE NEMERTEA. 93

posterior brain -lobe, then, indeed, Caiinina may be said to represent — also with respect
to the fissures and grooves on the head — a stage of development in which both the
characteristic features of the Hoplonemertea and the Schizonemertea are still present in
combination. In deviating from the original arrangement, the Schizonemertea would
have gone a longer way than would the Hoplonemertea, some of wliich still answer to
the original type of structure found iu Ccmnina.

I now wish to consider more closely certain details of these difi'erent cephalic fissures,
which cannot be discussed in a more appropriate place than in the section treating of
the sense-organs, although their exact significance must for the present remain unsolved.
In spirit preparations the ciliated coating of the body is generally never better preserved
than in these furrows ; and the cells carrying the cilia, as well as their nuclei, are in most
cases exceedingly distinct. However, in a few cases it is only the superficial layer of
the integument that is thus continued as a clothing of the inner surface of these furrows.
In most cases I could observe the deeper layer of integumentary glands (Schizonemertea)
to be continued, although less compact, along the whole inner surface of the cephalic slits.
Generally these deeper glandular layers appear to have undergone some special modifica-
tion in connection with the canal that opens out at the bottom of the furrow, and leads
into the brain-substance, a modification which may already be noticed in so primitive a
genus as Carinina, which, however, with respect to this apparatus, may be said to be
more differentiated than the allied genus Carinella.

We find in Carinina (PI. VI. figs. 1-3) that all round the bottom of this groove {Cg)
there is a marked increase of the number of nuclei in the integumentary tissue ; and
although these nuclei can scarcely be said to belong to the layer of the deeper glands {cf.
PI. IV. fig. 1 E, and the paragraph on the integument), but rather to the one exterior to
this, the fact of their accumulation in this marked way, just along the inner surface of
the cephalic groove, is a most reliable indication that the integument is in some way
modified in adaptation to the significance of these grooves. In PI. VI. fig. 1 a distinctly
pointed shape is assumed by this wedge-like or horse-shoe-shaped accumulation of nuclei,
and a fibrous band connecting them with the intermuscular tissue is even visible, more or
less clearly, separating — at least in this section — a posterior brain-lobe -B?-', into which
the canal passes, from the anterior brain-mass Br {cf. woodcut, p. 81). The glandular
layer is, however, not indifi"erent or neutral during these changes in the exterior nuclear
one ; and although the two specimens at my disposal do not permit me to unravel the
whole of the modifications it undergoes, I may still be permitted to observe that in figs.
2 and 3 of PI. VI. its participation {Gi and gl.hr) cannot be denied, whereas a comparison of
all the three figures here given makes it appear very probable that these glandular elements
{gl.hr), derived from the deeper layer of the integument {Gi), play a part with respect
to the posterior brain-lobe of Carinina, which may best be compared to the glandular
investment of the posterior brain-lobe, as it is encountered in all the other Nemertea

9-4 THE VOYAGE OF H.M.S. CHALLENGER.

{cf. PL VI. figs. 7, 8 ; PI. XIV. figs. 6-8, 11). What the physiological meaning of this
glandular investment may be must remain unsolved for the present, although we will
return to this question further on. Carinina demonstrates that, as the brain-lobes are
direct derivatives of the integument, so is the glandular investment of the posterior one.
I may here note that, in studying the development of Lineus obscurus, I have (XIV)
been able to determine the fact that the glandular investment and the nerve-cells of the
posterior brain-lobes also arise in that species out of the same mass of embryonic
cells. Moreover, I must add that the glandular significance of this investment was for
the first time more emphatically brought forward by Dewoletzky in a short notice on the
Nemertea (II). Although I cannot accept all the conclusions to which this naturalist
arrives with respect to the apparatus of which we are here treating, and must demur
when he rejects the specially adapted respiratory significance which the brain canal must
necessarily have in very many species, still it is only fair to call attention to his inquiry
into the nature of this ceUulo-glandular investment.

The only jaoint which has still to be noticed, and which is partly a repetition of what
has been already described in the paragraph on the nervous system, is the fact of the actual
observation by myself in Drepano'phorus lankesteri, from the Challenger collection, of
the passage of the contents of part of these glandular investing cells into the lumen of
the canal (PI. XIV. fig. 10). Moreover, one point should not be lost sight of, viz., that
between the glandular cells that form an actual investment of the posterior lobe (and
which in Caniiina could be identified with the deeper glandular structure of the integu-
ment) and the actual integumentary glands, there exists in Schizonemertea a constant
and considerable difference, even with respect to the affinities for staining reagents, and
still more in the general aspect. The case of Carinina is on this account all the more
interesting. We must only be careful not to look upon the exceptional case which I was
able to observe and to figure (PI. XIV. fig. 11, gl), in which an additional glandular {Vj
ring surrounds the ciliated canal after it has passed out of the brain-lobe on its way to
the exterior, as one of transition. I hardly think that this special adaptation, which has
been already noticed above (p. 60), pertains to the layer of the deeper skin-glands ; and
though I am not prepared to offer a definite opinion, I am much more inclined to compare
this curious accumulation of distinct and nucleated cells with a similar accumulation
which we have also noticed in Carinina, and have there encountered more peripherally
but still surrounding the ciliated canal (PI. VI. figs. 1-3). In either case the physiological
significance of the arrangement cannot at present be decided.

And to a certain extent this may also be said to be the case with respect to the whole
of the posterior brain-lobe. As long as it went by the name of side-organ — which, how-
ever, did no justice to its intimate connection with the lirain — it was generally regarded
as a specific sense-organ of unknown function (Quatrefages, M'Intosh, &c.). Later on I
published a paper (IX) in which the attempt was made to show that, in a very large number

REPORT ON THE NEMERTEA. 95

of cases, the ciliated canal is adapted to give tlie oxygenated sea-water access to the
hsemoglobiniferous nerve-tissue. At the same time (loc. cit., p. 35) I did not deny all sensory
significance to the organ, but repeated that we had not found any specialised sensory
epithelium in it, and could not judge of what kind the sensory impressions might be that
were carried by the apparatus to the animal's sensorium. Since then I have been able
to fix the exact mode of origin of the apparatus in at least one species of Nemertea
(XIV, XV), and may here recall to mind that the central lining of the canal most
decidedly takes its origin as an invagination of the epiblast. This invagination second-
arily coalesces with the brain. In these two ontogenetic data we have only very vague
indications. They allow of a comparison both with olfactory and wdth auditory pits.
Strange as it may seem, I do not see that the first comparison has many more a priori
arguments for it than the second. Otoliths, it is true, have not been found in this lobe,
but who can tell what purpose the minute concretions, formed by the ensheathing
gland-cells, and sometimes accumulated inside the lumen of the canal, may serve 1

We have, however, to suspend our judgment. Graeffe's, Keferstein's, and Claparfede's
observations on the existence of special otolith capsules in the Nemertea require further
confirmation. They may, perhaps, have mistaken the highly refractive globules in the
gland-cells of the posterior brain-lobe for otoliths.

One more point may be mentioned, viz., that the comparison of the cavity of these
lobes with a branchial slit of Balanoglossus, &c. {cf. Bateson, loc. cit.), which I tenta-
tively attempted in a former paper (IX, p. 33) has to be definitely abandoned, now that
the epiblastic origin of the cavity has been indubitably shown by myself and afterwards
by Salensky (XIV, XXX), and since on this point the statements of earlier authors as to
the bypoblastic origin of this cavity (Barrois, &c.), which led to my former suggestion,
have to be definitely abandoned.

If the comparison with a gill-slit is no longer tenable on morphological grounds, this
in no way changes my views as to the physiological importance that must be attached to
the direct respiratory function of the nerve-tissue, which can nowhere be so perfectly
accomplished as in the posterior canalised lobe. I have no doubt, however, that in some
species — more especially of Hoplonemertea — its significance as an organ of sense may
supersede its importance as a respiratory chamber, the haemoglobin, though present in
these species, being there much more diluted, at any rate colouring the brain less intensely
red, and the connection between posterior and anterior lobes being at the same time less
intimate.

Having now discussed all those parts of the organism which we have any — though
sometimes even questionable — right to consider as sense-organs, I must pass on to those
which are of a still more dubitable nature, and which fall under the head for which the
further part of the superscription of this section was intended.

Since in some cases I find them in the head and directly innervated by the brain, since

96 THE VOYAGE OF H.M.S. CHALLENGER.

in another case they are at the sides of the head stretching backwards for a not incon-
siderable distance, but always exactly at the lateral margin, and because a glandular
epithelium plays an important part in their constitution, there is indeed some, though
of course very distant, analogy with the glandular parts of the posterior brain-lobes which
we have considered before. I do not wish to attach any importance or significance to
this analogy for the present, for we have no sutficient data ; but I mention it by way
of explanation as to how I come to intercalate the description of these parts of the
organism in this place.

The first structure which I have to mention occurs in the head of Drepanophorus
lanhesteri, and something analogous to it was noticed by former observers (XVl) in
Geonemertes palaee7isis. In the Challenger specimen the horizontal sections through the
precerebral region demonstrate, when viewed with low powers, the presence of a lobulated
mass which is imbedded in the gelatinous ground-substance and partly traversed by
contractile fibres that radiate through the head in so many directions. When higher
powers are applied, this mass is dissolved into groups of cells enclosing more or less
circular free spaces, which, being present in consecutive sections, represent a system of
canals coated by the cells just mentioned, the whole forming a kind of spongy tissue. A
branch by which this canalicular system communicates with the exterior could not be
made out in my specimen, although von Kennel has found such an opening in his
Geonemertes, and thus I do not wish to lay too much stress on the fact of my being
unable to rediscover it in the only Challenger specimen in which I found this structure.
The cells are much more granular and at the same time larger than the surrounding cells
of the intermuscular gelatinous mass ; the nuclei are large and distinct (PI. XV. fig. 13).
It must be noted that the character of the cells and the aspect of the organ differ very
essentially from von Kennel's description. It is the situation that is correspondent.

A similar precerebral glandular lobulated organ was found by me in Drepanophorus
ruhrostriatus from the Mediterranean, though not in the Challenger specimens of this
species, in which, as was remarked above, the head was deficient. A special innervation
by nerve-fibres belonging to the cerebral nerves was in both cases made out.

The second structure to which I alluded as occurring in Challenger Hoplonemertea
was found by me in the difierent specimens of Amphiporus moseleyi, both in transverse
and horizontal sections. It may shortly be characterised as being an accumulation of
short, saccular tubes, blind posteriorly and opening to the exterior by a distinct neck,
which pierces muscular layers as well as basement membrane, its internal epithelium then
fusing with the integument. These short flask-like sacs sometimes internally coalesce
with each other, the same interior cavity then communicating outwards by more than
one duct. This, however, appears to be more or less exceptional. They are very
numerous, though short, at the tip of the head (PI. X. fig. 3, gl.s). They become larger
when we follow them further backwards, where we find them situated laterally in that

EEPORT ON THE NEMERTEA. 97

region of the body where the dorsal musculature passes into the ventral, and where the
intervening layer of muscular tissue is either very thin or even (sometimes locally)
absent, at least as a special layer. In every transverse section some three or four of these
glandular flasks are simultaneously cut (PI. XV. fig. 11). They show no further variety
of structure, but are not found along the whole length of the body. In the hinder half
at least I have not detected them. The histological constitution of these flask-shaped
glands is difficult to make out in the spirit specimens. The epithelium clothing them
had a very much changed and deteriorated aspect, and only in certain favourable regions
could I definitely establish the fact that it was built up of largish cells with large nuclei
(PI. XV. fig. 12), the contents of the cells being granular like those of the cells of the
median precerebral organ before described. Innervation was not so clearly traced here,
though in the head these flask-shaped organs certainly receive fibres from the very
numerous cerebral branches there present.

Having once determined the presence of the organs just described and their situation,
it was found that their presence is even externally traceable in the specimens of Amphi-
porus moseleyi (see PI. IX. fig. 8) by a white line running backwards from the tip of the
head along the comparatively sharply edged margin of the body (see pp. 20, 21). When a
transverse section is made in this region with a razor, the naked eye can trace this white
line extending inwards for a short distance as if the pigment occasioning it were very
thickly applied. Viewed with the microscope, it is then easily seen that this white
spot breaks up into the accumulated flasks as above described, which are surrounded
and supported by the gelatinous tissue. In such a section the latter tissue is much more
transparent and homogeneous, thus bringing out the glands as white lateral spots in this
transparent imbedding mass, in which also the rest of the internal organs may be seen
to be suspended, and which is dorsally and ventrally limited by the body musculature
and the integument.

It may finally be noticed that I have never succeeded in finding the necks of these
flasks that lead to the exterior wholly free and open, as I have the canal of the posterior
brain-lobe or the excretory duct of the nephridia. These very numerous necks of the
flask-shaped organs are always filled with a mass that has a streaked and fibrous appear-
ance. I mention this because it partly contributes to establish my conviction that the
physiological significance may indeed be glandular, and that the secreted, viscid mass,
passing out perhaps more copiously when the animals are immersed in spirit, remains
fixed in this passage to the exterior.

If it be not premature — as I consider it to be — to establish any comparison between
these organs and parts of the organism of Vertebrates, one would certainly be reminded
of those canals in the head which are known as the " Schleimcauale," and which are
continued along the sides of the body as the lateral line. The significance which of late
has been -more and more definitely assigned to these organs in the Vertebrates, as

(ZOOL. CHALL, EXP. — PART LIV. 1887.) Hhh 13

98 THE VOYAGE OF H.M.S. CHALLENGER,

accessory to the sense-organs forming the system of the lateral line, a sensory epithelium
being protected by and combined with them, has no direct parallel in Amphiporus
moseleyi, although it cannot be denied that the flask-shaped glands are in the immediate
vicinity of and on a level with the lateral nerve-trunks.

The absence of these glandular structures in the Palseonemertea and Schizonemertea
hitherto observed, renders the suggestion of any close homology very hazardous. Still,
I would not wholly refrain from pointing out the distant kind of parallelism which may
be noticed, and which has certainly contributed to induce me to consider these
organs in the paragraph devoted to the sense-organs, a proceeding which future inves-
tigations may perhaps show to have been wholly unfounded. The significance of this
parallelism will once more be discussed, when, in the chapter of General Considerations,
there is further scope for speculation.

PROBOSCIS AND PROBOSCIDIAN SHEATH.

Concerning this important organ, so very fully described by M'Intosh in his
Monograph on the group (XIX), the Challenger material has not revealed any startling
peculiarities. Nevertheless, it deserves some closer consideration, because certain points,
e.g., the exact mode of the anterior attachment of the proboscis in these worms, could
be studied more favourably by me in certain of the Challenger sections than ever
before. Moreover, the Russian naturalist Salensky has lately^ propounded certain
views concerning the proboscis and its sheath which deserve consideration and refutation.

I will first describe the facts with respect to the proboscis which we notice in the
Challenger Nemertea.

Carinina has a proboscis which, in transverse section, reveals the remarkable
peculiarity that the primitive order of succession, according to which in the body-wall
we meet with (1) integument, (2) longitudinal nerves, (3) musculature, also obtains in
the proboscis, the innervation of which takes place through the intervention of two
longitudinal nerves, w^hich are so situated as to be enclosed by the internal cellular
epithelium (PI. II. figs. 11, 12), just as is the body nerve-stem in a section of the
trunk. This fact, though it cannot be looked upon as a direct confirmation of the
hypothesis advocated by me after I had become acquainted with Grafi's Monograph
on the Rhabdocoela, viz., that in the Nemertea also the proboscis should be looked upon as
a gradual derivative of an original continuation of the body-wall, which has become
introvertible like the snout of the Rhabdocoela proboscidea, still throws a very favourable
light on these views. And this is further the case when we notice that in many Schizo-
nemertea there is also an order of succession of the layers in the proboscis-wall which is

1 Zeitschr. f. triss. Zooh. Bil. xliii. p. 509.

REPORT ON THE ISTEMERTEA. 99

similarly more or less a repetition of the same arrangement in the body-wall (PL XV.
fig. 2, a', /3', npl, y').

In addition to the peculiarity just described, there is another morphological consider-
ation which tends to show that this interpretation of the significance of the proboscis
is indeed the right one. When we consider a horizontal section through the region of
insertion of the proboscis in the head (PI. III. fig. 5), we see that in Carinina the mode
of fixation of the proboscis is exceedingly simple, its longitudinal muscular coat being in
direct continuity with the longitudinal muscle-layer of the body-wall. Somewhat in
front of the transverse cephalic grooves, about on a level with the anterior brain-lobe,
we see certain of the fibres of this longitudinal coat, instead of pursuing their course
onwards towards the tip of the head, bending inwards, traversing the space which I have
termed (XIII, xv) the archicoele, and then rimning backwards as the longitudinal fibres
of the proboscis. Other fibres, parallel to those just referred to, do not contribute
towards the formation of the proboscis, but continuing in their original direction, take
part in the formation of the muscular wall of the head (PL III. fig. 5). It certainly
deserves remark that the same comparatively simple arrangement is met with in the
much more highly differentiated Hoplonemertea, as a glance at fig. 3, PL X. will show.
There, too, the longitudinal musculature (a) of the body-wall is partly continued towards
the tip of the head, where it partly bends round and largely contributes to the formation
of the muscular layers of the proboscis. I suppose this way of stating the facts is more
in accordance with their actual relations, than to say that the longitudinal musculature
of the proboscis is internally inserted upon that of the body. Here also the direct
continuity of body-waU and proboscidian-wall, the latter appearing merely as an inverted
portion of the former, is forced upon our attention, as is in the same way the direct
continuity of the exterior integument J, through that of the rhynchodajum Rh to that
which clothes the proboscis itself, and which on the eversion of that organ forms the
exterior surface.

We must now consider these difi"erent parts more in detail. Commencing with the
rhynchodseum {cf. p. 8)^ we find in the Palseonemertea and Schizonemertea its walls bathed
by the blood-spaces in the head, as may be gathered from a comparison of the figures in
Oudemans' paper (XXVIl) on the blood-vascular system. This is no longer the case in
the Hoplonemertea, where these blood-spaces are replaced by the distinct vascular loops.
The proboscidian walls, fusing anteriorly with the musculature and the external epithe-
lium of the head, are difi'erent in the difi"erent subdivisions. Contractile fibres and cellular
elements, the materials of which the rhynchodoeum is built up, are present in Carinina
in quite a difi'erent relation from that in which they occur in Cerehratulus or Amphvporus.

In Carinina, as a glance at PL III. fig. 5 wiU show, it is the cellular elements {APe)
that are extremely preponderant. These cells are vacuolated, more than one layer thick,
difi'erent in aspect from the true proboscidian epithelium, and held together by a fibrous

100 THE VOYAGE OF H.M.S. CHALLENGEE.

coating, wliich is attached by radial fibrous bands to the cephalic musculature. The
rhynchodseum is thus suspended in the cephalic blood-space, as was formerly (IX)
described by me in Carinella.

The histological difference between the vacuolated cells of the rhynchodseum of
Carinina and the cells of the outer integument, is less than that between the former and
the epithelium of the proboscis proper.

A comparison between figs. 3, 4 of PL III., fig. 1 of PI. IV., and figs. 1-3 of PI. VI. will
sufficiently demonstrate this, vacuolated cells playing a very prominent part in the outer
strata of the integument in Carinina. Still the three epitheUa (external, rhynchodseal,
and proboscidian) are immediately contiguous, the passage from the one to the other
being gradual and only in the latter case relatively abrupt.

In the rhynchodjeum of the Schizonemertea and Hoplonemertea the cellular and ciliated
layer of the rhynchodseum of the earliest Palseonemertea has been relegated to the back-
ground, and the whole has become more a muscular sheath, in which the muscles have,
however, a diff"erent arrangement in the first and in the second group. The increase in
muscularity is in the Schizonemertea more a regular thickening of the fibrous investment,
whereas in the Hoplonemertea it is much more massive in one region than in the other.
In this way an annular and massive muscular sphincter (as it may be adequately termed)
arises in the posterior part of the rhynchodseum (PI. X. fig. 3, Sp. Pr.).

In this muscular sphincter longitudinal and circular fibres are very intimately inter-
woven, more or less in basket fashion, as indicated in the figure. Moreover, the
connection with the general musculature of the head is again brought about by radial
bundles, also visible in the figure.

Of the Schizonemertean rhynchodseum no special figure is given ; it answers to the
short description which was given above, it can be well observed in several figures in
M'Intosh's monograph, and, like the rhynchodseum of the other groups, it reaches back-
wards just as far as the implantation of the proboscis in the musculature of the head.
The epithelium of the rhynchodseum is in most cases distinctly ciliated.

The proboscis itself has been the subject of so detailed study and so elaborate
description by M'Intosh and other investigators, that I must necessarily restrict myself
to those few points on which the Challenger material furnishes certain deviations or
additions.

The inner epithelium of the proboscis of Carinina shows considerable difierenccs
according to the region under observation. In front there are papillse of a more or less
arborescent shape, on which a coating of fairly large cells, with distinct nuclei, and
partly vacuolated, is present. Posteriorly the cells are lower and more closely set (PL
III. figs. 1, 2, Pc). This may be partially the result of a difi"erent state of contraction,
by which the anterior portion is thrown more into folds.

The difference is, on the other hand, further accentuated by the presence of a con-

REPOET ON THE NEMERTEA. 101

striction in the proboscis, which I observed in the longitudinal sections of the only specimen
of Carinina that had retained its proboscis.

I cannot affirm that this constriction was natural, i.e., that it would also be found in
fresh specimens. Since, however, I have formerly described (VIl) similar constric-
tions in the proboscis of Carinella and Valencinia, there are many a 2}r{ori grounds
for also accepting its normal occurrence in Carinina. At the same time it more or less
coincides with the change in the character of the epithelium just noticed.

The epithelium of the proboscis of certain Schizonemertea was known to be charac-
terised by the presence of nematocysts. In a former publication (VIl) I showed that
the observation of Max Miiller, who first noticed urticating elements in Cerebratulus
urticans, might be extended to nearly all Schizonemertea, although the size of these
elements is generally considerably below that of the type species just mentioned.
Miiller has given good figures of the shape of the elements in his species ; of the others
no figures have hitherto been given, and fig. 2 of PI. XV. is intended to show the situa-
tion of packets of urticating elements, batteries, as they might be called, in a transverse
section of the anterior part of the proboscis, rather than to furnish particulars concerning
the histology of these nematocysts. They are seen to be situated close to the free surface
of the cells, and to be of different sizes on the dorsal and on the ventral surface of the
proboscis. Three batteries are figured lying free in the lumen of the proboscis ; when
seen from the side they have the aspect of a brush with close hairs seen in the same way,
when seen from above they appear to be more or less circular, and each of the elements
composing the battery is then found to be represented by a fine dot instead of by a
straight line, as was the case in the side view.

In the spirit specimens of Cerebratulus more than these general facts could not be ascer-
tained. I may add that fresh specimens from the Mediterranean showed that each of the
elements out of which such a battery is composed has a spindle-shaped form, being more
or less pointed at both ends and somewhat bulging in the middle, and that from one of
the pointed ends — which in its natural position is directed away from the proboscidian
epithelium — the fine urticating thread may be observed to issue. This thread is, in most
cases, comparatively short. AVhile in Cerehratulus urticans there is hardly any doubt
that each urticating element may act independently of the others, it is not improbable that
in some species, as the one here described, they remain connected in batteries by whose
joint action, when the proboscis is projected, delicate animals may be wounded or para-
lysed upon extrusion of the proboscis, and may thus fall an easy prey to the proprietor
of this formidable weapon.

As to the more detailed histology of this epithelium, I wish to withhold further remarks
till I am enabled to publish the observations on the fresh specimens examined at Naples.
Similarly the curious and very adhesive epithelium of the foremost portion of the
Hoplonemertean proboscis which I have formerly described (IV, V), which was well

102 THE VOYAGE OF H.M.S. CHALLENGER,

known to M'Intosh, Graff, and other observers, and which I have again met with in
the Challenger Hoplonomertea, cannot be more circumstantially described. Moreover,
the stylets in the different Hoplonemertea did not offer any remarkable deviation from
the well-known tyjDe, and though the transverse sections gave very clear details regarding
the arrangement of the muscle-fibres in the muscular bulb, about the epithelium of the
glandular duct that conveys the probably venomous secretion of the posterior cavity to
the base of the stylet, &c., these are only confirmations of facts already known and
need not be recapitulated here. The shape of the stylets was mentioned when the
species were described ; those of Drepanophoriis, though not obtained from an actual
Challenger specimen, are represented in the woodcut on p. 16.

The muscular walls of the proboscis differ in the various genera, and these differences
speak for themselves when we compare figs. 11 and 12 of PI. II., and figs. 1, 2, and 5
of PI. III. (Carinina), fig. 11 of PL VI. {Eupolia), fig. 7 of PL VIII. (Pelagonemertes),
fig. 6 of PL XII. (Amphiporus) , and figs. 2 and 3 of PL XV. (Cerebratulus). These latter
show the muscular layers of the proboscis of the Schizonemertea to be a repetition of the
muscular layers of their body-wall : a circular layer between two longitudinal ones, the
circular layer giving off fibres at diametricaUy opposite poles to the external membranous
sheath (6), and moreover, a nervous plexus {ii.pl), which is also situated between the outer
longitudinal muscular coat y' (that just below the epithelium), and the circular one yS'.
This nerve-plexus does not go all round, at least it cannot be distinctly made out except
throughout one-half of the circumference. It is also traversed by radial fibres, and is again
replaced by definite longitudinal stems when we examine a transverse section of the
proboscis further back (PL XV. fig. 3). These longitudinal stems are characteristic of
certain species of Cerebratulus, and a plexus, even a far more complete and cylindrical
one than the one figured (PL XV. fig. 2) for Cerebratulus macroren, is characteristic of
others. The nerve-stems enter the proboscis at its point of insertion, and spring from
the right and left extremity of the ventral brain commissure.

In the posterior regions of the proboscis of Eupolia, of Pelagonemertes, and of nearly
all the other species, the musculature appears to be reduced to a simple longitudinal
layer, carrying the epithelium on one side, and being held together by an ensheathing
membrane on the other (PL VI. fig. 11, and PL VIII. fig. 7).

In Cannina there is an additional circular layer, and the remarkable fact, which has
been abeady noticed above, of the situation of the nerves still enclosed in the epithelium.

In Amphiporus, Drep)anophorus, and Pelagonemertes (anterior portion) the
proboscis-wall exhibits the notable complications corresponding with the curious dis-
position of the nerves in the proboscis, and which was described in sufficient detail
by M'Intosh (beaded layer) (XIX, XX), myself (IX), von Kennel (XVI), and
Graff (III). To von Kennel the merit is due of having definitely established
the nervous significance of the parts in question. The innervation may here l)e

EEPORT ON THE NEMERTEA. 103

said to represent a plexus witli numerous longitudinal thickened portions or stems.
The passage of the nerves from the brain into the proboscis can very rarely be well
observed, because the proboscis is nearly always extruded and torn off when the
animal is killed. I may, however, repeat what was noticed above (p. 85), viz., that in
Amphiporus moseleyi, more particularly, this doubt has now been dispelled. I can
observe in my sections that, instead of two strong nerves innervating the proboscis, as
in the Palseonemertea and Schizonemertea, a much larger number of branches leave
the brain-ring and enter the proboscis in the region of its attachment. That these may
dichotomise and give rise to a larger number of longitudinal stems has been already
stated by von Kennel (XVI).

This nervous plexus and the longitudinal stems subdivide the longitudinal muscle-
layer into an outer and an inner portion, the latter (when the proboscis is everted) being
again subdivided into as many longitudinal columns as there are nerve-stems in the
proboscis (PL XII. fig. 6). Outside and inside of this longitudinal layer there is a
circular layer of fibres, outside of the exterior one of these the epithelium.

As to the nerve-stems and the plexus, one specimen of Amphiporus marioni showed
very distinct cellular accumulations just between each nerve-stem, as if a longitudinal
tract of nerve-cells alternated with one of nerve-fibres in the plexus. For the study of this
phenomenon fresh specimens will be absolutely necessary. The phenomenon itself has
been already noticed, but has not yet been wholly understood, either by von Kennel (XVI)
or by Graft' (ill).

Just as it has been necessary to curtail our observations on the proboscis because of
the detailed information already available concerning this important organ, the probos-
cidian sheath need not be treated at any length in view of the data that are already furnished
by others. It is known to be a closed space surrounding the proboscis, having in the
majority of cases its own muscular wall, by the contractions of which the fluid contained
in the space is driven against the anterior proboscidian attachment. The muscular
sheath thus serves to protrude the proboscis as far as the length of the posterior portion
— acting as a retractor-muscle — will allow it.

There can hardly be any doubt, when we take into consideration all the morpholo-
gical data at our disposal, that the muscles composing the proboscidian sheath gradually
took their origin by the increase and modification of pre-existing muscular elements,
which belonged to the body-wall and to the body-parenchyma before the proboscis,
modified from a tactile organ, as it appears to have primitively been, had yet become
evolved, tlirough the growth inwards of the anterior tip of the body, into an aggressive
weapon, with stylet or nematocysts, &c. We find the shorter proboscides, and the less
significant proboscidian sheaths among the more primitive genera of Nemertea.

Carinella has a short proboscis ; the dorsal wall of its sheath is still a component part
of the musculature of the body-wall ; the ventral wall is thin, and only composed of a

104 THE VOYAGE OF H.M.S. CHALLENGER.

few fibres. So it is in Carinina (PL II. figs. 3, 6, 7, 9, 10 ; PI. IV. fig. 6, Ps). In Etqwlia
the proboscis is longer, but the sheath is stUl most insignificant, as may be gathered from
the figures (PI. VI. figs. 9, 10 ; PI. VII. fig. 10). It is a space having internally a cellular
coating very similar to that of the blood-spaces, the cells of this internal epithelial covering
often more or less projecting into the lumen of the sheath. Outside of these cells a few
circidar fibres are seen to have developed ; outside of these there is again the body-paren-
chyma, with the enclosed blood-lacunae. There is no doubt that from sections of Eupolia
alone nobody would be incliaed to look upon the cavity of the proboscidian sheath as a
very independent cavity, nor is it possible to aflirm that the mode of the protrusion of
the proboscis, as it was sketched above, is indeed full)' developed in Euj'^olia and
Carinella. There is no doubt that of all Nemertea observed alive, these two were
never seen to protrude their proboscis spontaneously, and very often even preserved
them in death, when the Hoplouemertea always forcibly expel and even spontaneously
detach their proboscis.

There is, on the other hand, no evidence at all which would justify us in regarding
the arrangement of these Palseonemertea as secondary or degenerated from a higher
difi"erentiated stage. The participation of the body musculature in bringing about
the movements of the proboscis in these lower forms renders this more intelligible.
Only in the more highly differentiated Schizonemertea, and especially in the Hoplo-
uemertea, the muscular walls of the proboscidian sheath undergo a very rapid increase
in bulk, and at the same time become more and more, and in the last-named group
even wholly independent of the body musculature. This increase of an organ so
eminently mesoblastic as the proboscidian sheath, by gradual addition of new fibres that
are even arranged in multiple layers, can thus be traced in all its various stages in the
different genera of Nemertea. Salensky would probably not have made his startling
hypothesis above alluded to,^ based on ontogenetical observations of a scission in the
proboscidian wall, by which (l) a muscular proboscidian sheath surrounding the proboscis
becomes separated fi-om, and independent of, the musculature of the proboscis itself, and
(2) an isolated ccelome — the proboscidian cavity — is originated, if he had been as well
acquainted with the comparative anatomy of the animals about which he ■sxiites as he is
with certain detads of their ontogeny.

Granting even that the development may, in the species observed by him,
follow the paths he has sketched (my own observations on the ontogeny of Lineus
ohsciirus (XIV) have led to wholly different results on this head), it is not yet per-
missible to base upon those two ontogenetic observations phylogenetic speculations
whoUy at variance with all the facts that are furnished by a comparison of the different
living genera. The woodcuts given by Salensky, in which a Rhabdocoele proboscis and a
Nemertean one are put side by side, look very tempting, but cannot be accepted by me.

^ Archives de Biologie, vol. v. p. 561 ; Zeitschr. f. iviss. Zool., Bd. xliii. p. 508.

REPORT ON THE NEMERTEA. 105

While fully recognising the importance of Graff's observations for our own interpretation
of the Nemertean proboscis, and the genetic relation of this organ to that of the Rhab-
docceles (not direct but collateral), I must as emphatically reject the proposed derivation
of the proboscidian sheath advocated by Salensky.

We must, indeed, represent to ourselves the gradual evolution of the proboscis as
that of an epiblastic organ reaching further and further inwards in successive genera-
tions, and strengthened and completed by a mesoblastic musculature ; and outside of this
the free and independent development out of other mesoblastic elements (primarOy
belonging to the body-wall) of the sheath. It has been abeady noticed elsewhere (XIV,
XV), that if these mesoblastic structures could be traced down to amoeboid mesoblast
cells derived in loco out of the subjacent hypoblast, an ontogenetic homology between
the tissues constituting the proboscidian sheath and those forming the notochord of
Vertebrates would be established.

Returning to the proboscidian sheath of the Schizonemertea, we find it to consist of
an outer layer of circular fibres and an inner one of longitudinal (PL X. fig. 8, mPrs;
PI. XV. fig. 1). The former sometimes, when the sheath is thick and contracted, shows
a wavy line. Radial fibres, piercing the two fibrous layers, insert themselves against the
inner epithelium, which covers the whole inner surface, looking towards the cavity of the
proboscidian sheath. Between this epithelium and the muscular layers there is a broad
band of transparent basement tissue (PI. XV. fig. 1, b) following the numerous longitu-
dinal folds of the epithelium just mentioned. These folds disappear when the proboscidian
sheath is in distension (PL X. fig. 8), a phase that may repeatedly be noticed, even
without any extrusion of the proboscis, e.g., as a consequence of complicated coilings of
the proboscis inside its sheath. It is easily understood that during such distension the
thickness of the subepithelial homogeneous basement layer and of the muscular layers is
considerably reduced. A maximum degree of distension is figured on PL X. fig. 9, where
the epithelium was no longer separately visible, and even the (Esophageal epithelium has
been flattened out, together with the proboscidian-sheath wall.

As will be seen from PL XV. fig. 1, we find outside of the outer circular layer of the
sheath the gelatinous body-parenchyma, a thin layer of this even separating the probos-
cidian sheath from the longitudinal muscular layer a, in the midst of which we notice the
true proboscidian-sheath-nerve (pr.sn). In addition, I think it is not unimportant to
remark, that just below this layer of longitudinal fibres, there are strands of circular fibres
which do not apparently belong to the proboscidian sheath, and which, after having been
closely applied against the dorsal musculature in the middle line of the back, radiate
amongst the parenchyma and the intestinal caeca. It is these fibres (and perhaps in
addition to them the circular layer of the sheath itself) which may possibly be looked
upon as representative of the layer 8 in the Carinellidae {cf. PL XL), and which there takes
such a conspicuous part in the dorsal delimitation of the proboscidian sheath.

(ZOOL. CHALL. EXP. PART uv.— 1887.) Hhh 14

106 THE VOYAGE OF H.M.S. CHALLENGER.

In many Schizonemertea the proboscidian slieath is tlius constituted ; in others I find
that a phenomenon, which receives its more final expression in certain Hoplonemertea,
is not wholly absent — I mean the presence of varicosities, in which the inner space of
the sheath is bulged out, without the musculature following. In this way more or less
irregular appendages are brought about, generally along the side or the lower corners,
having the aspect of accessory reservoirs. In Cerebratulus sp. inc. (PI. XV. fig. 6),
from Japan, it seems as if these appendages in the posterior region of the body
even surpass in size the sheath itself, which is not a very significant organ in that
region of the body, and, moreover, as if these two casca are filled with a sub-
stance of the nature of which the available spirit specimens do not enable me to
judge.

I do not wish to discuss here the significance of these facts, not having for the present
sufiicient material to study them more fully ; it is only my purpose to call the attention
of future investigators to the phenomenon, which may be so significant for a correct inter-
pretation of the posterior, often semi-rudimentary portion of the proboscidian sheath.

It has been observed that in certain Hoplonemertea the phenomenon just noticed
finds a more definite and more regular expression. The first observation of this is due to
M'Intosh, who detected in the proboscidian sheath of Drepanophoriis regular metameri-
cally placed openings, by which the space inside the muscular sheath communicated with
other cavities outside of it, that had no muscular walls (XX).

While M'Intosh supposed these accessory cavities to establish a communication
between the cavity of the proboscidian sheath and the blood-vascular system, I have
since demonstrated (VIl) that no such communication exists, but that Drepanojohorus
possesses closed membranous sacs communicating with the proboscidian sheath, and
probably serving as reserve spaces for the fluid contents of the proboscidian sheath
during the very powerful contractions and distentions which the organ may undergo. In
the Challenger specimens the same phenomenon was observed, and I have even ventured to
assign all those specimens in which these regular paired appendages of the proboscidian
sheath were found to the genus Drepanopliortis, even when I have not succeeded in deter-
mining the armature of the proboscis so characteristic of the genus.

Two sections through the proboscidian sheath of Challenger Drepanopliori are figured
on PI. X. figs. 4, 5.

The curious arrangement of circular and longitudinal fibres, having the appearance of
basket-work in the transverse section, may be understood from these figures, even without
any further description.

Between the musculature and the inner epithelial layer there is again a homogeneous
membrane, with longitudinal folds indicative of the contracted state in which the sheath
here figured was at the moment of its preservation. In neither of the two was the section
quite vertical, thus only one of the lateral diverticula is cut, instead of the pair that are

REPORT ON THE NEMERTEA. 107

opposite each other. The epithelium which coats the internal cavity of the sheath is seen
to be continued uninterruptedly in these lateral spaces, whereas the musculature is deficient,
and these caeca may thus with propriety be called membranous. There is a decidedly
thicker epithelial coating in the lateral sacs of fig. 4 [Drepanophorus lankesteri) than in
those of fig. 5 {Drepanophorus serraticollis). On the other hand, the musculature of the
proboscidian sheath of the latter is much more massively developed than that of the
former.

One remarkable detail concerning the lateral appendages in Drepanophorus lan-
kesteri, is the fact that I found a few of the anterior ones connected by a short longitu-
dinal communicating tube at their distal extremity, this connection being thus parallel to
the proboscidian sheath itself. Similar connections were not noted further backwards, nor
in any other species of Drepayiophorus.

While the proboscidian sheath of Ampihipoi'us marioni (PI. X. fig. l) is built on
the same plan as that of Drepanophorus, that of Pelagonemertes is seen to be much
simpler (PI. VIII. fig. 7). Both are quite freely suspended in the gelatinous tissue,
and only connected with the body musculature in the head (PI. X. fig. 3).

DIGESTIVE APPARATUS.

The digestive canal of the Nemertea cannot be said, from a morphological point of
view, to be very complicated.

Communicating with the exterior by a ventral mouth close behind the tip of the
head and by a terminal anus, it stretches along the whole length of the body, and only two
rather sharply defined regions may be distinguished in it : the oesophagus and the hind
gut or intestine proper. Still, even the mouth is not always an independent structure,
as it is known to become confluent with the opening through which the proboscis pro-
trudes, i.e., the terminal opening of the rhynchodjeum,^ in at least two genera (AmphijMrus
and Malacobdella^). In that case this common opening is either terminal or nearly so
(PI. IX. fig. 9), and generally larger than the separate openings in other Hoplonemertea.
This feature is clearly not primitive but derived from that condition in which the mouth
lies behind the brain-lobes on the ventral surface, as it does in the most primitive

1 Ehynchodseum (see p. 8) is the name that may conveniently be given to the passage stretching from the point of
insertion of the proboscis in the head to the level of the exterior opening on the surface of the body through which the
proboscis is seen to be thrust forth. Its walls are marked APe in fig. 5 of PI. III.; Eh. and .S)j. Pr. in fig. 3, PI. X.

' Salensky has lately {Biologisches Centralblatt, 1883, p. 740, and Archives de Eiologie, vol v.), in publishing embryo-
logical researches on a certain species of Nemertea, imagined that the feature here alluded to was then and there
discovered by him for the first time, and necessitated the creation of a new genus [Monopora). Although his attention
was drawn to the superfluity of this proceeding (XIV. p. 41), he still retains the name in a later publication {Zeitschr. f.
wiss. ZooL, Bd. xHii. p. 481). Still, I am afraid this will not extend its longevity, as aU the other anatomical characters
most decidedly conform to Amphiporus.

108 . THE VOYAGE OF H.M.S. CHALLENGER.

Carinellidse and in the Schizonemertea, in fact in all Nemertea, with the exception of
the Hoplonemertea. In the latter the mouth is always in front of the brain ; it has
thus shifted forwards, the extreme range of this shifting process being reached when
the mouth becomes confluent with the opening of the rhynchodseum just recorded.

Another difference between the Hoplonemertea and the two other orders of the class,
with respect to the digestive system, is found in the relative position of the CBSophagus and
hind-gut. "While in the two last-named groups these two subdivisions of the intestine
pass into each other along a straight line and do not overlap, we see that such an overlap-
ping does occur to a more or less considerable extent in the Hoplonemertea. In a number
of transverse sections the hind-gut is cut when the oesophagus is also still present in the
section, showing that the latter overlaps the former. Still, I should be inclined to adopt
the view that the gradual process by which this came about was not so much a further
extension backwards of the oesophagus, as a tendency of the hind-gut to sptead out
and to reach forwards below the oesophagus. This would seem to be indicated by the
fact that in these Hoplonemertea the intestinal caeca, that properly belong to the hind-
gut, but that have come to be situated below the oesojohagus (PL XV. fig. 20), may even
reach so far forwards as to become situated close to the brain-lobes, a phenomenon which
is never observed in the lower groups, where the whole length of the oesophagus separates
the brain-lobes from the hind-gut. Possibly the shifting forwards of the hind-gut and
its diverticula may be a phenomenon that runs parallel with (if not due to the same cause
as) the disappearance of the lacunar blood-spaces round the oesophagus, and the substitu-
tion for them of cylindrical blood-vessels communicating by transverse ducts with the
medio-dorsal vessel. The latter arrangement is also typical of the region of the hind-
gut in the Schizonemertea, where, however, the circumoesophageal portion of the blood-
system is eminently lacunar.

These speculations need not, however, be further insisted upon, and we may now
pass to a description of the oesophagus in the Challenger Palseonemertea. Here, again,
Carinina offers features of interest. In the first place, the exceedingly close application
of the oesophageal epithelium against the muscular body-wall below and the thin muscular
layer of the proboscidian sheath above is peculiar (PI. IV. fig. 3). There is no gelatinous
connective tissue between the cells and the bundles of circular muscles, not even a base-
ment membrane, and strong powers are wanted to demonstrate any intervening tissue
between the bundles themselves, so strongly are they interwoven, and so dense are the
muscular layers in this region of the body-wall. Anteriorly there is a sharp bend down-
wards where the mouth is situated, and in front of this a short bulging out forms a
prostomial extension to the oesophagus, which is seen to be cut through in PI. II. fig. 3.

The cells of the oesophagus, as seen from the section figured, are finely granular, and
below those which actually clothe the lumen there are sometimes seen others also with
large nuclei (PI. IV. fig. 7) but less granular and with less distinct boundaries. This

REPORT ON THE NEMERTEA. 109

figure at the same time reveals the presence of a conspicuous cuticula covering the free
surface of the oesophageal cells. It is not streaked, as the figure erroneously indicates,
but homogeneous. Ou it the cilia are implanted.

Concerning the behaviour of the intestine in the posterior body-regions of Carinina,
nothing can be said, as only anterior fragments were preserved.

In Eupolia the oesophagus has become more independent of the body-musculature
than in Carinina, and in addition to this a separate oesophageal musculature — at least
in Uupolia giardii — is present (PI. VI. fig. 9, oe.m). In this oesophageal muscular
investment an inner longitudinal and an outer circular layer may be distinguished ;
between the latter and the body -wall there is the gelatinous tissue, only locally inter-
rupted by the lacunar spaces of the vascular system (in which the nephridia [njj] are
suspended), by the dorsal blood-vessel, and by the proboscidian sheath. I mention this,
because there is no evidence that this splanchnic musculature has directly evolved out of
hypoblastic elements, whereas the evidence that it is enclosed in one continuous stroma
with the " somatic" musculature — which in Carinina was the only musculature noticed —
and not separated from this by a body-cavity, is very complete. It should, moreover,
be remarked that where this more prominent intestinal musculature makes its appear-
ance (certain Schizonemertea, Eupolia giardii, &c.), the internal circular muscular layer of
the body-wall of the Cariuellidse (8, PI. XL) is no longer present in that situation.
How far these two may be considered as homologous, must be left undecided as long as
we do not possess more complete ontogenetical data. This oesophageal musculature
was not noticed in all species of Exqoolia, and it is certainly curious that it should be_
present in Eupolia giardii, where the body musculature is so exceptionally thick, and
might be expected to serve the purpose of comjjressing and dilating the oesophageal wall
quite as efiiciently as we must suppose this body musculature to do in the Carinellidse.
M'Intosh, who detected it in Cerebratulus corrugatus, suggests (XXIl) that the
oesophageal musculature might assist in a partial protrusion of the oesophagus.

In Eupolia nipponensis and Eiipolia australis this special musculature is absent,
and we find, on the contrary, a much more considerable development of the deeper cellular
layers of the oesophageal wall (PL VII. fig. 12), and a comparatively sharp demarcation
between the internal ciliated epithelium [Je) and this thick cellular coating {Jin), this
demarcation even sometimes rising to the importance of an apparent basement membrane
{B). Between these cells radial fibres, starting from the body musculature, penetrate, and
solitary tangential fibres may be observed, but a separate muscular investment of the
CBSophagus can never be shown to exist. I am not inclined to believe that this diff"erence
may be caused by the age or the size of the individual, one of the specimens of Eupolia
nipponensis being indeed of considerable size and nearly as thick as Eupolia giardii.

The same deep cell-layer is met with in the oesophagus of the Schizonemertea
(PL XIII. fig. 6), and is no doubt of glandular significance. Generally many of the

110 THE VOYAGE OF H.M.S. CHALLENGER.

component cells are flask-shaped, the thinner extremity shoving in between the pallisade-
shaped inner cihated epithelium. Moreover, among the Schizonemertea there appear to
be differences in the development of muscular tissue in the oesophageal wall, sometimes
the circumcesophageal blood-lacuna directly bathing this cellular coating, sometimes
{e.g., Cerebratulus corrugatus) a special muscular investment of conspicuous development
(PI. XIII. fig. 6, mto) being again present together with very strong nerves {nv).

The passage from the oesophagus to the sacculated intestine is more or less gradual, in
the absence of any forward extension of the latter below the former, as was noticed for
the Hoplonemertea.

Macrosco^^ic dissection enables us, nevertheless, to make a clear distinction between
these two jaortions of the gut, although microscopic investigation of transverse sections
shows that, histologically speaking, the passage is tolerably gradual. The cell layers of
the posterior portion of the intestine have been more than once sufficiently described
(see von Kennel (XVI), pL xviii. fig. 11), and it is not always easy to show them to
be provided with a nucleus or with cUia. StiU I do not hesitate to declare that the
whole of the intestine is ciliated, both the central passage and the lateral, generally sym-
metrical caeca. But this ciliation is often rendered inconspicuous by the fact that the
very elongated cells, composing the wall of this portion of the gut, are so overfilled with
small spherical globules as not only to render the ciliation invisible, but even to efface the
traces of the boundaries between the cells, so that in certain cases — both amongst Schizo-
nemertea and Hoplonemertea — it would seem as if the intestinal wall were replaced by a
compact mass of those globules enclosing the intestinal lumen between them. Similar
phenomena were observed by Lang (XVIII) in the Polyclada, and have been described
by other naturalists for other groups of Invertebrates. I will not here enter upon the
question of the relation of this phenomenon to the process of intracellular digestion, which
on a priori grounds may also be presumed to exist in the Nemertea, but will only add
that the nuclei of these high and elongated cells may in favourable specimens be
discerned, and are deeply situated, far away from the surface.

Whilst strong vertical muscle-fibres pass from the dorsal to the ventral body-wall in
a lamellar arrangement, thus constituting what I have termed in a former publication (V)
the muscular dissepiments, placed alternately between the intestinal caeca, these caeca
themselves are destitute of any special musculature. The muscular lamellas just men-
tioned, together with the general body musculature, appear to be sufiicient to bring
about all the contractions in the intestinal wall needed for the progress along this
channel of the food swallowed. The intestinal epithehum itself is thus directly implanted
upon the gelatinous tissue, and this phenomenon is no less clear in the Schizonemertea
than in the Hoplonemertea (PL VIII. fig. 3; PI. IX. figs. 1-6; PL XV. figs. 7, 10).
-Among the latter Pelagonemertes is the most striking example of this, because of the
preponderance of the gelatinous tissue. It has been already noticed in a preceding

REPORT ON THE NEMERTEA. Ill

paragraph that this jelly appears to be somewhat denser, and that at any rate it
more strongly imbibes staining reagents, all round the circumference of the intestinal
epithelium where this is implanted upon it.

As to the oesophagus of the Hoplonemertea, I wish to observe that it is less thick and
massive than that of Eupolia and the Schizonemertea, and more resembles the simple
arrangement of Carinina. Its wall is generally only one cell-layer thick, and a distinct
cuticula, as was noticed in Carinma, may also be often observed here. Fig. 1, Oe, of
PI. X., representing a section of the oesophagus of Amphiporus marioni, gives a very fair
representation of it. Outside the oesophageal epithelium there are indicated in this figure a
layer of flattened cells which I at first expected to form an outer tunic to the oesophagus.
Closer investigation revealed the presence of these cells in all the tissues — they may also
be seen in the basement layer B of the same figure — and at the same time convinced me
that these unicellular bodies are parasitic organisms. They infest all the tissues of
their host, and are more abundantly heaped together just outside the oesophageal
epithelium, where nutritive substances may be expected to be more plentiful. Curiously
enough, they were also noticed in the smaller specimens of Amphiporus marioni.
Similar cases of specimens of Nemertea infected with unicellular parasites were noticed
by me on other occasions. There is another case amongst the Challenger material (see
p. 48), but there the parasite is much larger than in Amphiporus marioni, and
altogether difi"erently constituted. It agrees with the former only in the fact of its
presence in all parts of the tissues.

These parasites diff"er from others which are found in the lumen of the intestine, and
which have already been noticed by former observers.

Another view of the Hoplonemertean oesophagus is given (in longitudinal section)
in PI. XV. fig. 20. Here, too, the comparative thinness of the walls is conspicuous,
and the connection with the posterior gut portion which stretches forwards under it,
is clearly indicated.

In Pelagonemertes the last mentioned phenomenon could not be observed. The sec-
tions through the mouth^and oesophagus were, however, not intact, because of the macro-
scopic dissection to which the specimen had previously been subjected by M'Intosh.

As to the ca3ca of the posterior body region little remains to be noticed, but that they
are more regularly distributed as we approach the tail, i.e., the region where new caeca
are being continually formed. Their metameric and paired arrangement is here more
evident than further forwards, where the degree in which they are filled with food par-
ticles may be more or less difi"erent, and may thereby become the cause of a partial, but
not very common, asymmetry.

The innervation of the intestine was for the greater part described in the paragraph
treating of the nervous system. It may be remarked here, in addition, that in transverse
sections of the foremost portions of the oesophagus it is very easy to detect the consider-

112 THE VOYAGE OF H.M.S. CHALLENGER.

able nerve-stems, both of the vagus nerve and of the visceral nerves, by which this is
brought about, and that in longitudinal sections also (PL XIV. fig. 5) the vagus nerve
may often be followed uninterruptedly for a very considerable distance backwards, being
applied upon the outer surface of the oesophagus, and only gradually dichotomising and
sending delicate nerve-fibres amongst the CBsophageal epithelium {cf. PL XVL fig. 1).

Of the two sources of innervation of the intestine, the one by the nerve-stem directly
issuing from the brain-lobes (the so-called vagus nerve) is the most conspicuous, and can
be demonstrated in all species from Carinina to the more specialised Hoplonemertea
without exception. In Carinina it is represented in PL VI. fig. 1 , Nv ; in this species
the visceral nerves (PL XVI. fig. 1, vi.sy ; PL XIV. figs. 3, 4, vi.n) have not been
definitely demonstrated as yet in either of the two available fragments. These latter
nerves are more easily detected in larger Schizonemertea, where the thick nerve-plexus
is itself so much more conspicuous. Cerebratulus corrugatus especially answers this
purpose.

In the Hoplonemertea too the vagus is very evident, and already represented on
Quatrefages' figures (XXVIII) ; in Drepanophorus lankesteri I saw its principal stem
running forwards towards the anterior oesophageal portion that passes under the
brain.

In this species we find numerous thin nerves, both from the lower brain-lobes and the
lateral stems, further participating in the innervation of the oesophagus — a state of things
which may be directly compared to the mixed innervation described above for Cere-
bratulus corrugatus.

I cannot as yet supply any definite statement regarding the innervation of the
posterior region of the intestine.

NEPHEIDIAL APPAEATUS AND BLOOD-VASCULAR SYSTEM.

Our knowledge of the nephridia of the Nemertea is only of a comparatively recent
date. Though discovered by Max Schultze as early as 1851 in a Tetrastemma (XXXIl),
the observations of this naturalist concerning the Nemertean nephridia were for a long
time wholly unjustifiably disregarded, and this general scepticism made me very careful
in formulating any definite opinion, when I also discovered in Schizonemertea separate
lumina (iv), which I could hardly account for in any other way than by regai'ding them
as parts of a nephridial system.

This was afterwards more emphatically done by von Kennel (XVl), to whom is due
aU the credit of having rediscovered the nephridia, and of having described their histo-
logical appearance in several difi'erent genera. His results were later on confirmed by other
authors (ll, ill, xi). I have afterwards observed and described (xil) a special modifica-
tion of the nephridial system in Nemertea, in which an indubitable internal opening is

REPORT ON THE NEMERTEA. 113

present. This was found by me in the nephridial system of Carinoma, and these nephridia
thus establish a communication between the internal blood-spaces (archiccelome) and the
exterior. In other genera, Carinella excepted, similar internal communications were,
however, sought for in vain. A very notable and exhaustive contribution to our
knowledge of the Nemertean nephridia was then furnished by Oudemans (XXVIl), and the
Challenger material, which was partly made subservient to that publication, only furnishes
a few additional data here worth recording, most of the peculiarities having been already
mentioned by Oudemans. I hold it to be one of the principal results arrived at by this
author, that he definitely demonstrated the presence in numerous species of Nemertea of
a very large number of exterior openings, connected by short transverse branches with
the principal and longitudinal canals of the nephridial system, and that, at the same
time, he noticed that these transverse canals were paired and opposite, and showed an
arrangement which might most assuredly be compared to an incipient stage of metamery
in the nephridial system.

This fact is most distinctly borne out by the Schizonemertea. The Palseonemertea
(at any rate the Carinellidse) and Hoplonemertea show an arrangement which presents
different features, although, again, certain Hoplonemertea {Amphiporus lactifloreus)
answer very well to the Schizonemertean type.

A very remarkable form of nephridia is found in Carinina grata. The two fragments
of this species that form part of the Challenger collection both contain this important
structure in toto, so that I am able to figure both transverse and longitudinal sections.
These figures are brought together on PI. IV., and will first have to be discussed. Two
portions may be distinguished in the nephridia of Carinina : in the first place, a glan-
dular canalicular portion in which numerous delicate tubes appear to be closely applied
together into a larger lobulate mass, which is situated right and left in the blood-space,
not being freely suspended in it, but applied on one side against the muscular layers
(figs. 5, 6), and on the other side, offering a free surface towards the cavity of this blood
space. PI. IV. fig. 4 gives a more enlarged view (Nsp) of a longitudinal section through
this portion of the nephridial apparatus, and, at the same time, enables one to judge of
its extension, the whole of this glandular spongy portion having been reached in
this section. It is, of course, also present in other sections, but does not stretch either
further forwards or backwards.

The furthest blind ends of the anterior caeca of the digestive canal are found to pene-
trate between the lobes of this glandular mass {Jc, fig. 4). These lobes are, moreover,
subdivided by bundles of muscle-fibres detached from the inner circular layer (fig. 5),
against which the whole apparatus is so closely applied (fig. 4, Cm). The cells composing
the glandular portion are filled with a granular protoplasm, and have very distinct large
nuclei. However much I have looked out in my different sections for a definite opening
by which the canalicular system here described might enter into communication with the

(ZOOL. CHALL. EXP. PAET LIV. 1887.) Hllh 15

114 THE VOYAGE OF H.M.S. CHALLENGER.

blood-space (archiccelome) surrounding it, I did not succeed in demonstrating one. Con-
sidering that I had found such openings in Carinoma, and that Oudemans had afterwards
demonstrated them in Carinella, I expected they would also be present in Carinina.
For the present, however, the result of a very attentive search is that they are absent ; at
least no opening is visible which can be said to prove a similar communication beyond all
doubt and by which it might be demonstrated once for all. Questionable points of
communication, which might eventually be interpreted as such, I have not allowed to
influence my testimony, so that, for the present, I must answer the question in the
negative. The case stands in a similar light with respect to the Schizonemertea and
Hoplouemertea, as will be seen hereafter.

If this communication with the blood-spaces is thus not demonstrated, that with the
cavity of the second part of the nephridial system is subject to a much less degree of
doubt ; and though I did not actually see the lumen at the point of communication, I did
see the communication itself as represented in fig. 4. It is then seen that this second
portion is distinguished from the one just mentioned by the presence of a spacious cavity.
This cavity, which may be called the nephridial canal, is first found ventrally to the
glandular spongy portion (figs. 4-6), but then gradually bends upwards as it passes
further backwards along the animal, until it becomes a narrow channel with a very
distinct and ciliated epithelium (figs. 1, 2), which passes at a very strongly inclined angle
(fig. 1) through the successive muscular layers, then makes a very sharp bend towards
the exterior surface, and traversing also the basement membrane and the integument,
opens on the exterior. This exterior opening has not been figui'ed, but is found
in the sections following upon that which is represented in fig. 1. The two exterior
openings of the nephridial system lie on the dorsal surface of the animal, and at the
same time mark the point where the nephridial system reaches furthest backwards, the
glandular portion of it stretching forwards towards the head. That this nephridial canal
may, at all events in its proximal part, be more or less folded, is seen both in figs. 4 and
5, Nc, in the latter figure the lumen having an appearance as if it were doubled.

The nephridial system of our second Challenger genus of Paleeonemertea, Eupolia, is,
as was already known from Oudemans' researches, more comparable to that of the Schizo-
nemertea than to that which has just been described in Carinma. It offers certain
peculiarities which deserve special mention. Here, too, we may distinguish, as we may
throughout the whole class of the Nemertea, longitudinal and principal nephridial ducts
situated in the blood-spaces or enclosed by the gelatinous tissue (Hoplouemertea), and
transverse or deferent ducts placed perpendicular to the foregoing, varying in number
and somewhat in size, and bringing about a communication between the ducts before
mentioned and the exterior.

Of the aspect and situation of these two portions in a transverse section, a comparison
of figs. 9 on PI. VI. and 3 on PL VII. may convince us. Each of them represents

EEPORT ON THE NEMERTEA. 115

about one-half of the thickness of the body-wall of the animal, and though somewhat
differently magnified, the position of the nerve-stem and of the layer cm may easily
guide us how to combine them.

It is then seen that in PI. VI. fig. 9 the longitudinal trunk, situated in the circum-
cesophageal blood-space, is not only cut through, but that even more than one nephridial
lumen (hcj^) appears in this section, showing that there is a doubling or at least a
branching of the principal nephridial duct in this region. Internal openings of this
system, funnels or anything comparable to them, were not detected by me in Eupolia
giardii or any other Eupolia ; there were, however, very definite bends at right angles,
piercing first the inner longitudinal and then the circular muscular layer, next the
nervous plexus, and then arriving in the outer layer of longitudinal muscles. In this
position the deferent branches of the nephridial system are seen in fig. 5, PI. VII.,
which, moreover, reveals the important fact that sometimes more than one of them is
found at exactly the same level. I could not make out whether this duplication is in
any way related to that of the longitudinal tube ; I can hardly conceive it to be so, the
increase of the number of deferent vessels being also noticed in other cases, though hardly
as a regular phenomenon. In Eupolia giardii, too, I find it to be exceptional in this
sense, that most of the deferent ducts are single; one section of another species (Cere-
hratulus truncatus) contains the double duct on both sides, making the exceptional
phenomenon at the same time symmetrical. The number of deferent ducts observed in
the Challenger specimen of Eupolia giardii is seven on the right and five on the left
side, the latter being opposite to and symmetrically placed with five out of the seven on
the right. These numbers, however, only apply to that portion of the trunk behind the
head which was transversely cut, and belongs to the same series. I have not followed
up the nephridial apparatus to its posterior portion, but we may feel assured, on the
authority of Oudemans' researches, that it will on the whole answer to the diagram
given on pi. i. fig. 11 of his treatise. One point deserving mention is that the first
trace of the nephridial apparatus of this Eupolia is visible in about the ninetieth section
behind the tip of the^ snout. When I add that the upper brain-lobes occupy sections
25 to 45, the forward extension of the nejshridia can more easily be imagined. Nothing
special can be said of the deferent or of the principal ducts but that their epithelium is
distinctly one cell thick, nucleated, and unmistakably ciliated. Nor have I any special
discoveries to record with respect to the nephridial system of any of the Challenger
Schizonemertea, and may refer the reader for certain specific peculiarities, number and
disposition of deferent ducts, &c., to the description of the species where I have embodied
these details when they did not appear to have any general significance.

I should like, however, to refer a little more fully to the conspicuous development
at which the main, longitudinal canal of the nephridia has arrived in a certain species
of Cerebratulus [Cerebratulus macroren), where its walls are unusually massive {PI.

116 THE VOYAGE OF H.M.S, CHALLENGER.

XIII. figs. 7-9), although, when these walls are distended by the contents, theii-
thickness correspondingly diminishes (PI. XIII. fig. 8). In this species, moreover, it
could be observed that towards the anterior end of this massive nephridial canal it
subdi\'ides into smaller branches (PL XIII. fig. 9), applied against the wall of the blood
lacuna, and nearly escaping observation amongst the epithelial cells of these lacunae.
Here, again, no internal opening could be demonstrated ; whereas, at the posterior end,
the nephridial canal, making a sharp curve, passes outwards above the nerve-stems.
We thus observe difierences in the nephridial system of the Schizonemertea, which may
be classified under the following heads : —

(a) The nephridial canal may be massive and single throughout the greater part of
its course, only ramifying anteriorly [Cerehratulus macroren, &c).

{h) It may be very copiously subdivided, every transverse section showing a consider-
able number of lumina, the whole thus forming a kind of network, with certain principal
longitudinal ducts, and being suspended against the wall of the circumoesophageal blood
lacuna (EiipoUa).

(c) The meshes of this network may be situated in the region between the probo-
scidian sheath and the longitudinal nerve-stems (most Cerehratidi) , or they may stretch
ventrally to these nerve-stems {Eu2MUa).

(d) The ducts leading to the exterior may be one on each side, and these generally
terminal (posteriorly).

(e) There may be two on each side, and they may then communicate with the chief
longitudinal canal about its middle.

{/) They may be more numerous, often in various phases of distension, and arranged
more or less metamerically. The histological characters are fairly uniform, the lumen is
never excavated in a row of cells as is the case in so many Platyelminthes, in the
Discophora, &c., but is always bounded by a certain number of cells in every section.
Each of these cells has a large and distinct nucleus ; its protoplasm is granular, and the
free surface, which is turned towards the lumen, is ciliated.

We have now to examine the nephridia of the Challenger Hoplonemertea. In
Oudemans' paper several points concerning them have been already noticed ; other details
referring to the situation and the number of the deferent ducts were mentioned above
when the species were described.

Hence it may here be suflacient to call attention to the fact, made specially palpable
by certain of the Challenger preparations, that whereas the nephridia of the Hoplone-
mertea are no longer suspended in blood lacuntQ, but wholly surrounded by the gelatinous
tissue, they are at the same time much more intricately coiled and ramified, as
can be very easily seen from a comparison of fig. 1 {Nep), PI. X., with figs. 7, 9, PI.
XIII. This involves, however, no important change in the histology; what we have
noticed under this head in the Schizonemertea holds good for the Hoplonemertea as well.

EEPOET ON THE NEMERTEA. 117

Even less remains to be said when we consider the blood-spaces of the Challenger
Nemertea, be they the closed longitudinal and the metameric transverse vessels of the
Hoplonemertea and of the posterior body-region of the Schizonemertea, or the circum-
oesophageal and circumrhynchodaeal lacunae of the latter, or the two spacious lateral
longitudinal cavities of Carinina.

All these points have been dwelt upon at length by Oudemans (XXVIl), and the
Challenger material furnishes a general confii-mation of his results. Doubt cannot be any
longer entertained that these spaces are all clothed by an epithelium, — at any rate by a
special and continuous cellular coating, either applied against the muscular tissue when
this surrounds (PI. IV. figs. 5, 6 ; PL XIII. fig. 6 ; PI. XIV. fig. 4), or traverses (PI.
VII. fig. 10) the cavities or against the gelatinous tissue, when it is in this that the
vessel takes its course (PL X. figs. 1, 8). In the latter case the structure of the vessel
is still more complicated, so that, as described by Oudemans, there is constantly a tubular,
denser layer of the homogeneous tissue just outside the inner epithelial coating ; and
outside this tubular layer, which might be termed the basement layer of the vessel, we
find a second layer of generally more spherical ceUs, amongst which a layer of fibres, specially
belonging to the blood-vessel, may be seen to make its appearance (PL XV. fig. 1, dv).

This same description holds good for the longitudinal vessel, as far as it takes its
course inside the proboscidian sheath (PL X. fig. 8). The gradual narrowing of the
circumcesophageal lacunar space into the two ventral vessels shows the passage of the
epithelium of the one into that of the other very clearly.

The diff'erence in the distance along which the medio-dorsal vessel is enclosed in the
proboscidian sheath was mentioned and figured by Oudemans (xxvil) for different
species ; my own observations on the Challenger specimens fit into the same general
outlines ; a few additional data concerning these points are contained in the systematic
description of the species.

GENERATIVE ORGANS.

Certain not unimportant additions to our knowledge of the generative organs
of the Nemertea are due to the Challenger specimens. Among these facts I wish
successively to record :

{a) The irregular distribution in certain species of very numerous generative sacs
enclosed in the gelatinous tissue, and having each its separate external opening, which
are consequently neither paired nor metameric.

{h) The comparatively late period at which the definite external opening is formed,
although long before that time the sac is characterised by a pointed projection reaching
between the muscular tissue and foreshadowing the definite openings, dehiscence of
the body- wall being certainly not the normal way of exit of the generative products.

&

118 THE VOYAGE OF H.M.S. CHALLENGER.

As to the first point, it has been hitherto the current idea that in the Nemertea the
generative sacs, alternating with the intestinal caeca, are paired and more or less meta-
meric. This is no doubt the case in the very large majority, and relieves us from
the duty of further describing the position of the generative sacs in Eujiolia, the
Schizonemertea and most Hoplonemertea. In other Hoplonemertea, however, we find a
multiplicity of generative sacs in one transverse section (PI. IX. fig. 4) which cannot
possibly be made to answer to the type just aUuded to, and this irregularity reaches
its extreme expression in Amphiporus moseleyi. The specimens of this species are
Literally full of sacs, which I was able to notice in their first stages, as well as in their
later development and ripest stages. In each transverse section (PI. IX. fig. 4) a great
number of them may be seen; in horizontal sections (PL IX. fig. 7) the same irregular
multiplicity is met with. Externally I did not notice the openings, but it must be
remarked that only in very ripe specimens are these distinctly present.

Now this aberrant distribution is not wholly limited to Amphiiwrus moseleyi. There
are even reasons for considering it as an arrangement which has been retained in this species,
but which was common in the more primitive ancestral species of both the Hoplonemertea
and Schizonemertea. At least I find it in a similar condition in Carinella annulata, with
this difi"erence, (1) that it is here only in the dorsal half, above the intestine, that the gene-
rative products are found ; and (2) that the external openings are generally very distinctly
visible as numerous irregular whitish dots on the dorsal surface of the animal, in the dark
coloured space between the dorsal median white line and two successive transverse ones.
Whether in Carinina similar conditions exist could not be verified, because the
preserved fragments contain no generative products. At any rate the fact is fully
established for one of the most primitive genera of Palseonemertea, and this may justify
our insisting upon its having an archaic significance.

With the exception of Amphiporus moseleyi, Drep>anophorus lankesteri is perhaps
the only Hoplonemertean in which still another trace of it is preserved, at least if we
may consider the fact that in this species (PI. IX. fig. l) two ventral generative sacs
are present on each side, as a reduced phase of the phenomenon, which we have found
represented in Amphiporus moseleyi, instead of looking upon it as a secondary dupli-
cation of primarily simple generative cseca. For myself, I should feel inclined to take
the first view as rather the more probable.

The other Hoplonemertea have not this peculiarity. The generative sacs are paired
and metameric, and if in ripe specimens two of them are cut in one section (Pi. IX.
fig. 3) it is generally an indication that the section was not perpendicular. There is then
also found an adequate distance between the external pores.

This same figure clearly illustrates the fact that the generative products (in this in-
stance ova) may attain a considerable development and closely approach the ripe condition
before the generative sac itself communicates by a pore with the exterior, as indicated

REPORT ON THE NEMERTEA. 119

in the second of the two propositions above enumerated. At the same time we find the
spot where the pore will appear indicated by a pointed projection of the sac between the
muscles, and it is a fact very worthy of notice that the more we approach this preformed
outward duct, the less ripe are the ova (PI. XV. fig. 14). The same fact is noticed in
many other Nemertea ; Pelagonemertes even shows traces of it (PL VIII. fig, 8, ov.) In
Carinella I found it persisting even after the deBnite pore is established, and the most
plausible explanation appears to me to be this, that the deeper inwards the developing
generative products are situated, the more they are surrounded by the gelatinous tissue,
and the better their conditions of nutrition must be ; whereas those which are observed
close to the duct, piercing the muscles, wiU only gradually increase in size, when in
their turn similar favourable conditions are ofi"ered to them.

The fact of the occurrence of definite preformed ducts without pores was observed
by me in Amphiponis moseleyi, Amphiporus marioni, Brepanophorus lankesteri, and
Drepanophorus serraticollis, and of several of these I also had ripe specimens, in which the
fact could be determined that it is, indeed, in the places where these pointed projections
are found that the pores afterwards appear (PI. IX. figs. 5, 6).

In this place I may mention that according to embryological observations (XIV) the
generative sacs are primitively in connection, at least in the species investigated, with the
epiblast by means of a strand of tissue which is not indicative of the ultimate duct.
These strands, however, are situated on the other side of the nerve-stem, and thus are in
no way identical with the projections which were here described and discussed as preced-
ing the definite generative pores.

The duct which pierces the muscles to aff'ord a passage to the generative products is
generally shortened as maturity advances, through the distension of the body by the
ripening of ova or spermatozoa, and the consequent decrease in thickness of the mus-
cular body-wall. Still, in Cerehratulus macroren this duct presented an uncommon
feature, which must here be mentioned, and which is figured on PI. XV. fig. 19. After
having pierced the circular muscular layer yS, it distends in the layer 7 to a second
sac-like expansion, which in its turn communicates with the exterior by a small opening.
This was not a local disturbance, but was met with in very numerous generative ducts,
botb on the right and left sides of the animal.

In Eupolia and Schizonemertea the ripening sacs, developing in pairs between each
successive pair of intestinal caeca, are often wedge-shaped, with the sharp edge turned
outwards, and the broad end between the two intestinal cseca, where these emerge from
the principal longitudinal cavity of the intestine (see woodcut fig. 6, p. 120). And, in
addition to this, another fact is very marked in Eupolia giardii, viz., that dorsally
and ventrally the generative csBca become lobulated or arborescent, sending out short
lobes of indented and irregular shape.

It would, however, lead us too far, and hardly ofi'er any additional interest, to discuss

120

THE VOYAGE OF H.M.S. CHALLENGEE.

the changes in shape which the developing generative sac may undergo ; accordingly we
will now consider a few diverging peculiarities of the generative products themselves,
which I was able to observe in the Challenger Nemertea. That they are developed from

the epithelium of the generative sacs has long been known ; this
is figured on PI. XV. fig. 14, in a Hoplonemertean. It was
.particularly evident and very distinctly visible in Cerebratulus
longifisstis, where it was at the same time also demonstrable that
there is a very sudden decrease in ripeness of the generative
products close to the tail-end, where growth in length of the
animal is going on, and where new generative sacs are being
formed between the intestinal caeca. In this region all the most
diflerent stages of ripeness of the ova may be studied side by side
in the same longitudinal section. The ova of Amphiporus marioni
Fio. 6.-Portion of a horizontal ^ XV. fig. 15) are characterised by the presence, in addition to the

section of a Cerebrahdus. i.e. ^ o / J r '

latCTat'^cffica ! gjTihi''ieni^\ iiuclcus, of a round or reniform body, which is stained dark red by
T &'m'., mtl|iment"and m"usi picrocarmiuc, and but for this ofiers a certain analogy to the oil-drop
'^'^ ^*"™" in fish eggs, being also more refractive than the nucleus, though

not quite so highly as the latter. This paranucleus was already observed in the youngest
eggs (PI. XV. fig. 15, a) ; at that time its relative size, when compared to that of the whole
egg, was much more considerable. A second smaller specimen of Amphiporus marioni was
distinguished by the same peculiarity, which may thus in certain cases help to identify the
species, as I did not find the same feature in any other species of Hoplonemertea.

Of the eggs of Pelagonemei'tes it has already been recorded that they are distinguished
by an investment of follicle cells (PI. VIII. fig. 11) ; the development of this could also
be traced downwards to early stages, which were present in the same specimen (fig. 10)
side by side with the riper stages.

In the Schizonemertea two facts deserve mention, although their significance cannot
well be discussed as long as fresh specimens are not available. The one is the pre-
sence round the ripe eggs in Cerebiutuhis, sp. inc. (PI. XV. fig. 18), and Drepanophorus
serraticollis (PI. XV. fig. 17) of a hyaline, apparently mucous layer, which surrounds
each egg separately, and which is pressed into a polygonal shape when many ripe eggs
are enclosed together in the same sac. The layer is comparatively thick.

The second fact was observed in Cerehratuhis parJceri, where the peripheral proto-
plasm was much more darkly stained and more coarsely granular, all the eggs having
thus the aspect as figured on PI. XV. fig. 16.

As to the spermatogenesis I have no new observations to record, spirit specimens
alone rarely presenting favourable material for such researches. These phenomena have,
moreover, been recently fully studied by Sabatier (XXVIIIa).

Hermaphrodite specimens were not encountered by me in the Challenger collection.

GENERAL CONSIDERATIONS.

In venturing at the close of this Report on the Nemertea, collected by H.M.S.
Challenger, to leave the region of demonstrated facts and actual observations, and to
enter upon that of speculation and suggestion, I gladly avail myself of the permission for so
doing granted to me by the editor, Mr. John Murray. I thought it necessary to ask for
that permission, because general speculations on the ancestry of the Chordata hardly
appeared to me to fit into the framework of these Eeports. My desire in this case to
deviate from a rule which I held to be salutary, was due to the fact that of late these
speculations have been conducted along very varying channels, an entirely new one
having only very lately been ojDcned by Bateson's important series of papers on Bal-
anoglossus. An attempt to give more depth to one of these channels, and thus to lead
into it the attention of a greater number of my fellow-workers, especially commended
itself to me, since it was my conviction that the lines laid down by myself in former
publications derived considerable support from the Challenger material, and were thus
entitled to a renewed and full consideration.

I would formulate the proposition, to the further development of which this chapter is
to be devoted, as follows : —

More than any other class of invertebrate animals, the Nemertea have preserved
in their organisation traces of such features as must have been characteristic of those
animal forms, hy ivhich a transition has been gradually brought about from the archi-
ccelous Diplohlastic (Cailenterate) type to those enterocoelous Triploblastica, that have
afterwards developed into the Chordata [Urochorda, Hemichorda, Cephalochorda, and
Vertebrata).

It will be seen that this statement excludes the idea of any direct ancestral relations
between Nemertea and Chordata. If any such relation were proposed, it might with
good reason be asked — considering the very extensive variation which is met with
amongst Nemertea — which species or which genus was more particularly pointed to. The
question in itself condemns the proposition which leads to it.

It will, moreover, be seen that this statement accepts the outcome of Bateson's
researches and speculations, in so far as the points of agreement between Balanoglossus
and Amphioxus are fully recognised. A provisional link between these two, and an

(ZOOL. CHALL. EXP. PAKT LIV. 1887.) Hhll 16

122 THE VOYAGE OF H.M.S. CHALLENGEE.

arrangement of Balanoglossus amongst the Chordata, ajDpears to be quite as justifiable as
the elevation of the Urochorda to their new dignity in zoological classification.

There is, however, a great difierence between looking at Balanoglossus as a low type
amongst the Chordata (in which I fully agree with Bateson) and rejecting the signifi-
cance of the Nemertean tjrpe as one of transition in the way above indicated.

There is no doubt that the Nemertea represent a more primitive phase than the
Enteropneusta (Hemichorda). They have no enterocosle, and they have no gill-slits ;
but their nervous system shows certain unexpected analogies uith that of the higher
Chordata of more intrinsic value than those that obtain between Balanoglossus and the
Chordata in general. Also for the important question, which is so vital in any considera-
tion of the ancestry of the Vertebrates, viz., the origin of metameric segmentation, it
appears to me that the Nemertea offer points very worthy of consideration. The question
of the proboscis and its sheath, as comparable to hypophysis and notochord, was fully
treated by me in another pajDer, and will here only be very briefly touched upon. In
my opinion, this comparison is all the more forced upon us, now that in other respects
(nervous system, &c.) new evidence of genetic relationship is here brought forward.

The first point I wish to consider is that of metameric segmentation. It has been
specially treated of late years by various authors of renown, with whom I do not wish to
enter at this moment into any lengthy controversy, but will briefly state what may be
gathered for the theory in general, from a careful consideration of the incipient metamery
of the Nemertea.

If we start from a more or less radiate ancestor of the earliest diploblastic type, in
which neither a radial nor a serial repetition of organs or organ systems has yet come
about, and which may indifferently be considered to resemble either a more flattened
Trichoplax or a more spherical gastrula, we may assume that in the course of the
development of other internal organs (towards the formation of which the secondary
accumulation of cells between the two primary layers often so largely contributes) the
radial symmetry may either be further accentuated or may be replaced by a tendency
towards bilateral symmetry. In the latter case we are inclined to ascribe the first impulse
towards this bilateral symmetry to a preference, which slowly establishes itself in the
animal mechanism, for moving in one direction rather than in any other, i.e., for
genei-ally stretching forward, when moving about, one particular portion of the body.

One impulse of this sort will sufiice to lead us to understand, or rather to deduce, a
very considerable number of consequences, which cannot fail to make their appearance
under the influence of natural selection acting upon the organisms that have inherited
this tendency in different degrees. Thus we may understand the narrowing and
lengthening of an animal that moves in one direction in preference to any other ; and
similarly the development in the nervous system of a centralisation not far away from
the anterior extremity.

REPORT ON THE NEMERTEA. 123

All this has already been stated by Balfour in clearer terms in his Comparative
Embryology (vol. ii. pp. 308, 311), where he describes the gradual steps by which a
radiate medusa-like animal may have passed into a bilateral worm-like form, with two
longitudinal nerve-stems, which are regarded by Balfour as the stretched nerve-ring of
the Medusa.

I fully endorse these views ; only, with respect to the nervous system, I hold it to be
safer to leave out of comparison the already speciahsed nerve-ring of the Medusa, and
rather to go back to a Ccelenterate nervous system as primitive as that of the Actinia,
where the plexus, both of the epiblast and the hypoblast, with an increase in density in
the region of the mouth and the tentacles, may be said to be the fair representative of
one of the lowest starting points. In this the plexiform arrangement predominates.

Now we find in all the lower invertebrates various though distinct nerve tracts
that are being specialised in this plexiform nerve-tissue according to the modes of motion
of the animal, and according to the general shape of the body.

Thus in the Medusae, which move about in the water by annular contractions of the
lower portion of the bell-shaped body, one of the nerve-rings already alluded to was
demonstrated by the Hertwigs to innervate the musculature by which this is brought
about.

In the Ctenophora the nerve-system is less satisfactorily known, but still Lang does
not hesitate to bring them into genetic relationship with the Polyclada (XVIIl). Among
the latter, Gunda, with its two longitudinal lateral stems, may be looked upon as
an extreme term in this series.

Another series may indeed be supposed to have derived longitudinal stems from a
ring which became extended to form lateral cords, as the animal passed from the radial
to the bilateral symmetry, in the way suggested by Balfour. Still, even in this case, a
nerve-plexus may be expected to be co-existent with or to have preceded the nerve-ring.
The longitudinal stems originating from the anterior thickenings of the plexus that
innervate the sense organs and the tip of the head (specially sensitive in connection
with the forwardly- directed movements of the body), would all the more probably be
preserved and increase in development, as during this forward movement they form a
right and a left centre for the reception of outward stimuli. In the same way those
of the radially-arranged stems of the Polyclada that are parallel to the longitudinal
body-axis, and mark out right and left, are more strongly developed than the others,
presumably on account of their importance in connection with the well-directed movements
of the body in response to external agents.

In the ancestral MoUusca, I think we may assume with great probability the presence
of four longitudinal stems — two latero-dorsal, and two latero-ventral ones ; in the ances-
tral forms of Annelids and Arthropods two, which have gradually coalesced ventrally, as
was first suggested by Gegenbaur. Again, in Nematodes diff"erently situated longitudinal

124 THE VOYAGE OF H.M.S. CHALLENGER.

stems in what was originally a uniform plexus are preserved ; whereas, in ancestral
Nemertea, two lateral longitudinal trunks in the plexus were undoubtedly characteristic
features.

That one medio-dorsal stem in this plexus, in which all the impressions made by out-
ward agencies on both halves of the body might be concentrated, and from whence the
corresponding movements might be regulated, wlU more fuUy answer the purpose than
two lateral stems, however they may be united by an intervening plexus, is a priori
probable, and would explain the first impulse towards the formation of such a longitu-
dinal concentration in the uniform plexus.

And when once such a dorso-median stem is present, in addition to two lateral ones,
a struggle for supremacy, presided over by natural selection, may lead to a diminution
of the lateral stems, and to an increase of the dorso-median one.

This, in my opinion, as will be more fuUy developed below, was the case in the ances-
tors of the Chordata, traces of this struggle and of the competing structural elements
being duly preserved.

If we suppose the bilateral symmetry to be established in one of the lower re-
presentatives of the Metazoa, and the type to go on increasing in length va. the course of
generations ; then this increase, indeed, exposes it to very difi"erent, and perhaps more
numerous dansfers and enemies than would threaten it were the same bulk concentrated
in a spherical or radial circumference. And if, even in the latter case, injiuies to the
specimen might prove fatal were it not provided with strong powers of regeneration
[cf. Star-fishes, Ophiurids, Crinoids, &c.), stUl it needs no comment that, when bilateral
symmetry and increase in length so considerably enlarges the surface which is open to
attacks, and so enormously facilitates the rupture of the specimen, or the severing of
parts by rapacious enemies preying upon it, simdar regenerative powers are none the
less required to insure the persistence of the type.

These dangers, continually threatening the existence of the specimens, and thus in-
jurious to the species, counteracted as they are by regenerative processes (power of repro-
duction of lost parts), J ZioZc? to he at the base of all those cases of metamery in the animal
hingdom which do not fall under the head of strobilation, the latter being comparatively
rare with respect to the former. Incipient metamery, once established by this cause,
may further diff"erentiate in the most diverse directions (heteronomous segmentation, &c.),
even after the absolute cessation of the causes that in the fii'st instance have provoked it.

The explanation has, moreover, the advantage of being applicable to radial as well as
to serial metamery.

These propositions must now be more fully developed. The power of reproduction of
lost parts comes, without doubt, under the general laws of formation and growth. We
find it even in the lowest Protozoa. If the material which heredity has accumulated, either
in such a unicellular being or in the egg of a Metazoon, and out of which the elements of

EEPORT ON THE NEMERTEA. 125

the diflferent organ systems will gradually develop, is hereditarily so disposed that a
compensation for the loss of important parts is facilitated, this wdl, of course, constitute
an advantage. Such a compensation may, e.g., be obtained where the generative pro-
ducts are developed in very many separate centra, and not in one closed sac. Injury to
the latter wUl, ceteris j)ciribus, be more fatal than an equivalent injury destroying one
or more of the former. The same holds good for diffused instead of concentrated
nervous centra, for the case of liver saccules to the intestine, instead of one compact liver,
for numerous apertures and deferent ducts to the nephridial system instead of one, &c.
And all this is still more evident when we have before us a long, bilaterally symmetri-
cal animal, which is easily snapped in two. In this case it must be of pre-eminent
importance, that the remaining halves, which may in their turn be severed by the same
cause into smaller parts, possess sufficient power of reproduction to repair the damage.
Now, it cannot be doubted that an equal distribution of the important components of
the organism (nervous centra, generative organs, nephridia, intestinal appendages, &c.)
throughout the whole length of the animal meets this requirement. Any severed portion
will then be provided with these more important parts, and will be more or less adapted
for a separate and individual existence.

The formation of a new mouth and of new brain-lobes in a fragment of this descrip-
tion remains, of course, quite as wonderful and inexplicable as before, but still we cannot
fad to see that such an arrangement as here indicated must somehow be beneficial to the
species, and that we need not stop short with Bateson,^ when he says that " the repetition

of various structures is one of the chief factors in the composition of animal forms

The reason for their appearance is as yet unknown, and the laws that control and modify
them are utterly obscured." Obscurity is not exchanged for broad daylight, but some-
thing is gained when we can see that a growth of the principal organ-systems in separate
and more or less independent batches, which in an elongated and bilaterally s}Tnmetrical
animal insensibly passes into the phenomenon of incipient metamery, may be of the
highest value for the persistence of the species.

Now this is actually the way in which we find the important organ-systems distributed
in the lower Nemertea. And out of this more irregular distribution a gradual metamery, in
some incipient, in others more complete, is seen to evolve within the boundaries of the class.
Even the nephridial system, in the primitive forms provided with only one opening to
the exterior, participates in this tendency towards metamery, and acquires a greater
number of apertures, serially arranged in pairs, thereby also tending towards a diminution
of damage when artificial division into two takes place in the nephridial region. The meta-
mery, the regidar and serial repetition of parts, is thus seen to be of great importance in
aiding towards repair after damage to a lengthened bilateral form, in the same w^ay as
the radial repetition of parts facilitates repair in the Echiuodermata. In both cases the

I Bateson, The Ancestry of the Chordata, Quart. Journ. Micr. Sci., vol. xxvi. pp. 545, 54C, 1S8C.

12(5 THE VOYAGE OF H.M.S, CHALLENGEE.

destruction is only partial, the other homonodynamic portiona temporarily ministering,
thanks to their more independent relation to the injured region.

When the faculty of repair of damage, occasioned by the severing of the animal into
two or more portions, has in the course of generations become more and more complete, it
can be readily understood that it becomes at the same time a defensive instead of being
only a curative process. An animal that at the approach of danger can separate in two or
more parts, each of them capable of reproducing an entire new animal, evades this danger
very effectively by doing so ; whereas another that is attacked in the same way and does
not possess this faculty, is laid hold of, shaken about, and wholly or partly swallowed.
So in the Nemertea there is indeed a very strong faculty of spontaneous division
combined with the faculty of repair ^ ; and anybody who has observed a fresh and living
Cerehratulus, wdth its extremely delicate sense of touch, commence to rupture into two,
in preference at the spot where it was grasped with the forceps, cannot fail to see in this
a defensive action.

This mode of self-defence may in quite another respect be useful to the species,
because at the same time it serves for propagation. Thus we see that the passage of
this defensive process to that of reproduction by fission is so gradual, that it would be
impossible to decide in every case what name should properly be applied to it. It cannot
well be denied that in all probability ours is only a special case, in which the power of
reproducing the species by a process of fission, reaching down as far as the unicellular
ancestors, has come to be regulated by other motor forces than growth and — if it may
not be called voluntary fission — still may be regarded as sudden and spontaneous fission,
brought about by external influences, of a threatening nature to the further existence of the
specimen. This regulation is no doubt a consequence of selection. Schizogony having
once been established, it must have been further beneficial to the species, on the grounds
that were developed above, that the internal organs should be present in multiple num-
bers, and this having once come about it is easy to understand, that a regular, rigorously
metamerous arrangement of this multiple material, still more fuUy answers the same
purpose, and is gradually evolved under the influence of selection.

Thus we may be said to be able to follow the appearance of metamery in a bilateral
animal, along aU the gradual steps by which it is evolved, and many of these steps have
remained fixed and permanent in different Nemertean genera.

The last system that will participate in this metamery is the muscular system, and a
rash conclusion — such as is not rare in these days of ontogenetic fetichism — might lead
to the rejection of the views concerning metamery here developed, on the consideration
that it is exactly the metamery of the muscular system which appears first of all in the

^ Both 51'Intosli and Barrois have observed and described very peculiar cases of repair in Nemertea, where the
head, brain, side-organs, &c., were reproduced on a headless trunk-piece. These experiments are well worthy of careful
repetition. It mijjht be that only those fragments in which a portion of the oesophagus was retained were capable of
repair of the head.

REPORT ON THE NEMERTEA. 127

ontogenetic development of Vertebrates. I will not circumstantially refute this argu-
ment, but will only remark that in Polygordius and other ChEetopods, which are
representatives of a group of animals in which segmentation reaches such a very high
degree of perfection, the longitudinal muscular layer of the body-wall is as yet continuous
in the adult, and not divided into metameric sections, as it is in certain Arthropods and
in Vertebrates. Now let us consider contractions of the inner muscular layer a of the
Nemertea, the only layer that is common to all of them, from Carinella to Cerebratulus
and from Cephalothrix to Pelagonemertes. This layer also corresponds with the longi-
tudinal muscular layer just alluded to of other lower worms, such as Polygordius, and,
as was noticed in our paragraph on the muscular system (cf. p. 72), its contraction is
sometimes very distinct in favourable sections.

We then see the contraction marked out as so many successive blocks of contracted,
thickened fibres, separated by intervening pares of non-contracted fibrous tissue (PL XV.
figs. 9, 10). The sections demonstrate that the phenomenon persists throughout the
whole breadth of the animal, i.e., that successive rings of contractile tissue alternate with
interveninc rings in which no contraction is observed. This phenomenon is thus in a
certain degree comparable to an arrangement in distinct myomeres.

It is not unimportant that it was especially noticed in the fundamental muscular
layer, and it may at the same time be remarked that it appears, from what I have as yet
been able to observe myself, that the number of these rings in a given length of the
animal, is the same, or a multiple of the number of intestinal caeca and transverse
nerve-tracts in the plexus ; in other words, that the incipient metamery of the internal
organs is in a definite relation to these phenomena — which might also deserve the name
of incipient metamery — in the muscular layers.

For the present the fact is, however, not yet definitely demonstrated that these
successive blocks are indeed present as such in the living animal. The possibility is still
open that they may be waves of contraction which have been fixed at the moment of the
immersion of the animal in the preserving fluid. For this reason I will not lay any
undue weio-ht on this observation.

The ideas concerning the origin of metamery here expressed, and advocated for
several years in my university lectures, difi"er from those of Lang (XVIII) and
Sedgwick,^ in so far as they do not recognise the primary importance of the so-called
ccelomic sacs — the paired archenteric diverticula of Amphioxus — for the solution of this
question.

The question of the Vertebrate coelome, so full of obscurities and difiiculties, is
purposely left out of consideration here, where the relation to archica?lous ancestral
forms is discussed, and where an attempt is made to show that it is indeed probable that
the impulse towards the establishment of metamery is due to forces for which the

1 A. Sedgwick, On the Origin of Metameric Segmentation, Quart. Journ. Mici: Hci, vol. xxiv. p. 43, 1884.

128 THE VOYAGE OF H.M.S. CHALLENGEE.

archenteron was not the only, nor perhaps the most important part of the organism to
act upon.

Still more different are they from those advocated by Perrier ^ and Cattaneo/ who
have adhered to and extended the idea already held by others, but by them most actively
defended, " that the metamery of Arthropods, Vertebrates, and a great many Vermes,
has originated out of the multiplication by transverse fission of very simple primitive
worms which were not metamerous. The products of this transverse fission remaining
connected together have then formed a chain of individuals, or a linear colony ; later on
the unity of the chain has become more definitely established, the single individuals at
the same time becoming different both in form and in function, and the foremost
individual thus becoming the head of the series. Each segment (metamere) thus repre-
sents a reduced individual ; a metameric (segmented) animal is the result of the more or
less complete fusion of single individuals into an individual of higher order."

Emery, from whose paper ^ I have translated the foregoing sentence, has very success-
fully combated these propositions. This author, however, adheres to Lang's views in
ascribing to the archenteric pouches, the " gemmation " as Emery calls it {loc. cit., p. 18) of
the intestine, the most important and initial significance for the first origin of metamery,
" the sexual glands and excretory canals being in relation to the intestinal diverticula,"
and following the lead. I have above explained why I cannot adhere to this argumen-
tation, which brings the coelome and the sacculated intestine too strongly into the fore-
ground, and why I rather suppose incipient metamery to have been antecedent to either
of these {e.g., Carinella). On the other hand, many views contained in Emery's im-
portant paper coincide with my own. Thus he writes {loc. cit., p. 11), speaking of that
interesting marine Triclade, Gunda segnientata : —

" The metamery of Gunda is thus manifestly the consequence not of the ' symbiotic '
fusion of a colony of equivalent ' parts' (meridi), but of the 'autobiotic' differentiation
and perfectioning of one ' part ' (meride);" and further on (p. 15) : — " When I consider
the facility with which certain worms break into one or more pieces even spontaneously,
it appears to me that this capacity for rupture may well have been the origin of the
reproductive purpose of transverse scission in similar elongated organisms. The rupture,
in the first instance accidental, could have contributed to the more rapid multiplication of
the organism, being followed by the regeneration of the parts that were deficient in the
separate fragments. This process of rupture might further have been so perfected that the
spot best adapted for rupture, with a view to the best condition of the fragments, was
prepared in advance. In the more perfect evolutional phases of the process, which are at
the same time those that have till now been more carefully investigated, the new head is
formed anteriorly to the rupture, or at least its essential parts are pre-established."

^ E. Perrier, Les colonies animales, Paris, 1881.

^ G. Cattaneo, Le colonic lineari e la morfologia del Mollusclii, Milano, 1883.

' C. Emery, Colonie lineare e metameria, Napoli, 1883.

REPORT ON THE NEMERTEA. 129

My own views emphasise the presence of a peculiar process of development of the
internal organs, running parallel to this predisposition for rupture in a particular spot
— the spot which will correspond to the outwardly visible demarcation between the future
segments. They thus go one step further — and, in my opinion, a very essential step — •
in the attempt to explain the origin of metamery in the lower Platyelminthes, these
bilateral descendants of radiate Crelenterata, and at the same time predecessors of both
Chordata and Appendiculata.'

This view of the origin of metamery also affords an explanation for the very different
degrees in which we find metamery or segmentation expressed in the different divisions
of the animal kingdom. The incipient metamery which we have traced (and which we
have pictured to ourselves as arising through natural selection amongst those forms,
which, while developing in length, find metamery to be a protective peculiarity) imme-
diately creates, by the fact of its existence, new and variable material for selection,
again to be acted upon. And whilst metamery develops in one direction in one line of
descendants, the other line brings to the foreground a different set of advantageous
combinations, each of them again the stock of new and varied forms. In other words,
metamery once established in its most primitive form, and intimately connected with
.spontaneous fission under the influence of external agents, has been of very great
moment in the bringing about of new and endless variations of animal life. And it is
irrational, when we have before us, say one of the lowest Vertebrata, in which nobody
will deny the presence of distinct metameric segmentation, to conclude that this metamery
must necessarily be in many respects reduced, and that in the ancestral forms it must
have been far more complete, must have stretched forwards along the whole of the head,
must have been more forcibly expressed than it is now — in all the cephalic nerves, in
the nephridia, the gill-slits, &e. ; — all this on the presumption of the existence of an
ancestor so completely and exemplarily segmental as to throw no light on the origin of
segmentation and metamery, unless by the aid of Perrier's and Cattaneo's exaggerations.
Such conclusions must, however, necessarily be made by those who follow Dohrn's and
Semper's lead concerning the phylogeny of the Chordata.

Bateson, in takijig Balanoglossus as his starting-point, finds the acknowledged points
of resemblance in the metamerous gill-slits, &c., and adds to them important data con-
cerning the metamerous coelomic divertie-ula. Still, for a general view on the origin of
metamery, Balanoglossus offers no points that we do not find more strongly represented
and more forcibly expressed in the Nemertea. It certainly deserves mention that long

1 Gegenbaur, in his Grundriss der VergleiL-henden Anatomie (1878), hints at similar explanations to those advocated by
Emery and myself, when he says (p. 64) : — " Die Metamerie .... liisst Zustiinde des Beginnes und der nicht aus-
gefiihrten Beendigung mannichfach erkennen .... In dem Maasse als ein Metamer die Abhiingigkeit vom Gesammt-
organismus durch die Ausbildung seiner eigenen Organe aufgiebt emancipirt er sich vom Ganzen und gewinnt die
Befiihigung freier Existenz." Further on he speaks of incipient metamery as " eine stellenweise, fiir den Organismus
praktisch werdende AusbUdung " of the different organ systems.

(ZOOL. CHALL. EXP. — PART LIV. — 1887.) Hhh 17

130 THE VOYAGE OF H.M.S. CHALLENGER.

before Bateson drew renewed attention to the numerous points of agreement between
Balanoglossiis and the Chordata, M'Intosh had done the same for Bcdanoglossus and the
Nemertea, a separate paragraph of his monograph (XIX) being devoted to the discussion
of these homologies.

Sedgwick {loc. cit.) holds the unsegmented worms to be wholly " negligeablc
quantities," at any rate superfluous links in the chain that connects the Chordata with
the antecedent Diploblastic stages. In my idea both these authors, valuable as certain
of their suggestions are, have not been thoroughly aware of the necessity that, in all
discussions on the origin of metameric segmentation, we must attempt to grasp at data
that give a clue to the possible action of natural selection in the gradual evolution of
metamery. This clue appears to me to be far more distinctly contained in the ^dews here
advocated than in the other hj^otheses.

It may further be remarked, now that we have once more alluded to Bateson's
phylogeny of the Chordata, that even this naturalist does not feel justified in wholly
rejecting the Nemertea from the Vertebrate pedigree. Whilst in the text of his
article [loc. cit., p. 566) he does seem to prefer this negative alternative ; still,
in the subjoined diagram of the general relationships of Urochorda, Hemichorda,
Cephalochorda, and Yertebrata, the Nemertea are introduced — with a point of
interrogation, however — as a side branch lower down on the common parent stock.
Now, this being concordant with my own views of the Chordate phylogeny, —
the point of interrogation excepted, — ^it is necessary to inquire why there is this
discrepancy between Bateson's speculations in the body of his treatise and the
hypothetical pedigree at the end of it. It appears to me that this is due to his
hesitation {Joe. cit., p. 555) in accepting the views hitherto entertained and advocated
by myself as to the phylogenetic connection between the Nemertean and the Vertebrate
nervous system. For this hesitation Bateson has good reasons, and while I appreciate
the soundness of them, I hope in the remainder of this chapter to remove the relufctance
of him and others to accept the phylogenetic significance of the Nemertea, thanks to
new light that may be thrown on the evolution of the central nervous system of
the Chordata by the observations above recorded on the nervous system of the Challenger
Nemertea.

It is to these speculations on the nervous system that we now have to turn our
attention.

As will be seen from the terminology introduced in the paragraph on the nervous
system (p. 7G), and as it is now time more fully to develop, I am inclined to attach
considerable morphological imj)ortance to the arrangement of the diflerent constituent
parts of the nervous system in the Nemertea. In former publications (X, XI«) I have
repeatedly insisted on the significance of certain points in the anatomy of the Nemertea,
when considering the general question of the relationship of the Chordata to their

REPORT ON THE NEMERTEA. 131

unknown invertebrate ancestors, and I have insisted not only on the possibility of the
homology between the Nemertean proboscis and the hypophysis cerebri of the Verte-
brates, but I have, even earlier still, attempted to show that the nerve-system of these
two groups might be considered in a common light, as was first indicated by Harting
in his Leerboek van de Grondbeginselen der Dierkunde of the year 1874. Further
reference to the hypothesis here alluded to is found in Balfour's Monograj^h on the
Elasmobranch Fishes (pp. 170-172), in my own publications (IX, X), and in Balfour's
Comparative Embryology^ (vol. ii. ji. 258). I will not here enter upon this hypothesis
more fully, but will l^riefly state that it attempted to consider the central nervous system
of the Vertebrates as a possible median coalescence of two nerve-trunks, that were lateral
in the primitive ancestors of the Vertebrates, in the same way as the coalesced ventral
nerve-cord (Bauchmark) of Annelids and Arthropods may be considered with Gegenbaur
as having arisen out of a double lateral trunk, which in certain, still more highly differen-
tiated forms have fused ventro-medially.

A strong argument against the first-mentioned hypothesis is the fact that the spinal
cord ontogenetically always makes its appearance as a median unpaired plate or thicken-
ing, a very faint trace of a possible double origin of this plate being hitherto only
observable in one species of Amphibia, Triton twmatus ; whereas in all other vertebrates,
AmpMoxus and the Cyclostomata not excepted, the unjaaired origin is most evident.
The bilateral symmetry of the full-grown brain and spinal cord is a much later feature,
and can hardly be regarded as the expression of a primary coalescence of two separate
halves to form a median whole.

I am the more inclined to abandon this hypothesis, because I will attempt to show
that we can establish phylogenetic comparisons between the Chordate and the Nemertean
nervous system on a much more simple basis ; comparisons which at the same time cover
a far more extensive ground than did those of Harting, Balfour, and myself, which I
have just alluded to.

Since in the nervous plexus of all the Nemertea a median longitudinal tract, some-
times of comparatively large size, has now been detected, since even in the Hoplo-
nemertea, where the plexus has disappeared, the same medio-dorsal nerve-tract has in
most cases been preserved, and, finally, since from this dorso-median stem metameric and
paired nerve-tracks may be seen to emerge in Palseonemertea and Schizonemertea, we
must inquire in how far the direct comparison of this medio-dorsal nerve-stem with a
primitive spinal cord may be said to hold good.

In order to do this we must first consider the relation of this stem, to which we have
given the name of medullary nerve or medulla, to the rest of the nervous system, more

' It may here be remarked that Balfour has omitted to mention that Harting was the first to bring forward tliis
hypothesis : it is well to be reminded of this when Beard, Bateson, and others similarly ignore this claim to priority of
my venerated predecessor.

132 THE VOYAGE OF H.M.S. CHALLENGER.

especially the brain-lobes.' In a former publication (IX), where the medullary nerve
was for the first time noticed and described as the proboscidian-sheath-nerve, I traced its
orio-in to the dorsal commissure between the two lateral halves of the brain {loc. cit.,
pi. i. fig. 1). Thanks to certain very favourable specimens in the Challenger collection,
I have now been able to add new data to this statement. Sections through the brain of
Cerehratulus inacroren, CerehrxUulus corrugatus and Cerebratulus angusticeps (PI. XII.
figs. 1, 7, 8; PI. XIII. fig. 1) show that the condition of things is indeed less simple than
this original statement would imply, — that the medullary nerve is not an eminently fibrous
cord springing at right angles from the eminently fibrous upper brain-commissure, but
that the nerve-tissue constituting the foremost and uppermost portions of the upper
brain-lobes spreads out over a far more considerable surface than the fibrous tract which
is known as the dorsal commissure. This expansion of nerve-tissue, in which the cellular
elements are no less conspicuous than the fibrous, is posteriorly directly continuous
with the plexus above described, laterally with the brain-lobes, anteriorly with the
cephalic nerves springing from these lobes. It attains its fullest dev-elopment just
before and behind the region where a transverse bundle of fibres uniting the fibrous core
of the lateral brain-lobes forms the well-known dorsal brain-commissure. This commis-
sure is a transverse fibrous tract forming part of a more extensive nerve-plate. To this
expansion of nerve-tissue the presence of nerve-cells gives a more primitive, at any rate
a less specialised, character. These nerve-cells and nerve-fibres are directly continuous
with those of the medullary nerve and (backwards) with those of the nerve-plexus, of
which this nerve is only the median longitudinal thickening. There is even more reason
to look upon the fibres of this medullary nerve as a tract of the general fibrous stroma
not necessarily connected with the fibres of the brain-commissure. In other cases a more
direct continuity between the commissural and the medullary nerve-fibres was however
observed.

In order clearly to understand the relative importance of the difi"erent parts of the
nervous system here noticed, the primitive Palseonemertea ofi'er the best starting-point.

Thus in Carinella we find the brain-lobes not yet separated into distinct upper and
lower lobes, nor do we find a posterior lobe (side-organ). The brain is a double lateral
and anterior thickening in the nerve-plexus, situated like it and like the lateral nerve-
stems outside the muscular body-wall in the deeper strata of the integument. The only
difference between the medio-dorsal medullary nerve in this species and the lateral nerves
with their anterior enlargements (the brain-lobes) is its position and its greater tenuity
(PI. XVI. fig. 1), which, however, does not prevent its being very clearly observable in every
transverse section (PI. XL figs. 3, 4). Its connection with the brain-commissui'c was
already described (IX, p. 25), and figured by me {loc. cit., pi. iii. fig. 31). It must,

1 In the course of these considerations a certain amount of repetition of facts already noticed in the paragraph on

the nervous system cannot well be avoided.

REPORT ON THE NEMERTEA. 133

however, be remarked tliat in these most primitive Palseonemertea, the anterior dorsal
brain-commissure is less significant than in the Schizonemertea, and hardly anything else
than the foremost of those numerous transverse metameric tracts in the plexus {dvr,
PI. XVI fig. 1) which connect the lateral stems with the medullary nerve (dorsally) and
with each other (ventrally).

These important metnmeric nerve-pairs are most distinctly observed in CarineUa,
Here, as in the Schizonemertea, the medullary nerve is also continued forwards in front
of the brain thickenings. This continuation sometimes shows a short bend just on
the level of the commissure, so that both the medullary nerve and its anterior
continuation may be seen in one section. This explains at the same time the arrange-
ment traced on PI. XII. fig. 8. Posteriorly the medullary nerve can be followed down to
the hindmost extremity of the body. In Eu-polia and the Schizonemertea the arrange-
ment remains the same, the metamery of the transverse stems is perhaps more clearly
expressed, the whole plexus and the longitudinal stems are no longer in the integument,
but between the muscular layers. Still the whole of the nervous system also answers to
the general type as represented in the diagrammatic fig. 1 on PL XVI.

We have now seen enough of it to understand that a comparison with the central
apparatus of the Vertebrate nervous system cannot indeed be called a strained comparison.
On the contrary, the comparison is much less artificial than was the one which Balfour
was inclined to adopt, and which, as noted above, rendered necessary the acceptance of
the phylogenetic development of the Vertebrate medulla out of a double cord.

And so I do not hesitate to proclaim the medullary nerve of the Nemertea to be a
very important link in the phylogenetic chain, of which the Vertebrate spinal cord is the
outcome. Like the Nemerteau medulla, the Vertebrate spinal cord is median, unpaired,
and composed of nerve-ceUs and nerve-fibres ; like the Neraertean medulla, it is a thicken-
ing in a nervous plexus, originally wholly epiblastic, of which, among Vertebrates, the
Amphibian embryos ofier such a striking example. This instructive and suggestive case
was known to Remak and Strieker (as the " Nervenschicht" of the frog embryo), it was
more carefully studied and elaborately described by Goette (his " Grundschicht" of the
epiblast, in his Entwickelungsgeschichte der Unke), and it has been again recently
brought into the foreground by Baldwin Spencer, in his latest paper on the subject.'
The latter author compares the Amphibian plexus with that of Palseonemertea and Schizo-
nemertea (loc. cit., p. 134), as had already been done before him by my friend Professor
Ray Lankester, with whose suggestion I at that time (1880) did not yet venture fully
to associate myself

The numerous data that have since been accumulated for a direct comparison of
Nemertea with lower Vertebrates appear, however, now to fully justify that comparison

' Baldwin Spencer, Some notes on the early Development of Rana temporaria. Quart. Joum. Micr. Sci., vol. xxv.
Suppl., p. 123, 1885.

134 THE VOYAGE OF H.M.S. CHALLENGER.

which was first expressed in a footnote to a former paper of mine (X, p. 438). There
can hardly be any doubt as to the existence, consequent upon natural selection, of a
constant tendency in the different component parts of living organisms towards simplifi-
cation and increased efficiency (Eoux's Kampf der Theile im Organismus). This fact
enables us to understand the gradual supremacy of the median cord in the Nemertean
plexus over the two lateral ones. It seems as if it were mathematically demonstrable that
for the delicate adjustment of the impressions from the exterior to the co-ordinated
movements thereby occasioned, one longitudinal central stem in bilateral, lengthened
animals, would be more efficacious than two lateral ones. And if we ask if, at the final
stage of this struggle for supremacy between three longitudinal stems, any remnants of
the lateral cords are yet detectable in the Vertebrate embryos, perhaps even in the adults,
T am inclined to answer in the affirmative. Here I must be allowed to insert a reference
to the three figures on PI. XVI., which will facilitate the exposition of the further conse-
quences of the hypothesis I am here developing. Fig. 1 represents the chief points in the
nervous system of the Nemertea. The brain-lobes are simple lateral swellings of the
longitudinal stems, as in Carinella ; plexus, medulla and transverse stems, together with
brain-lobes and lateral stems, may be considered as forming part of the integument [cf.
Carinina). A double innervation of the respiratory portion of the intestine is indicated ;
one due to visceral branches {vi.sy) springing from the plexus (or from its transverse
tracts), the other to the more specialised nerve (v), which has above been indicated as
the Nemertean vagus nerve. The plexus and its innumerable radial fibres, both sensory
and motor, are not indicated in this figure, nor are the nerve-stems which, when present
(PL XIV. fig. 2), pass from the lateral stems directly to the integument.

This figure must now be compared with the two others. Of these, PL XVI. fig. 2,
diagrammatically represents the chief points that may be considered as characteristic
of the nervous system of a lower Vertebrate, in which the dorsal and ventral roots of the
spinal nerves {dr and w) are as yet separate nerve-tracts, in which the sympathetic nerve
system is as yet only represented by visceral branches given oft' by these dorsal roots
(vi.sy), and in which the polymerous character of a primitive vagus ( Vag) is established.

PL XVI. fig. 3, stands for Aynj>hioxus, as far as we know its nervous system, more
particularly through the researches of Rohon and others. It diSers from the foregoing by
the absence of a distinct brain swelling, and of a polymerous vagus. A number of spinal
nerves are considered as homologues to the vagus of Vertebrates by Eohon. The
commissural connections between the successive spinal nerves form a plexus, which is
peripherally even much more elaborate, according to Rohon's figures. This plexus does
not reveal the presence of any distinct lateral longitudinal nerve, nor any ganglia of
spinal or cephalic nerves. The latter (en) may be said to be three in number. Visceral
branches (vi.sy) are given oft" by the dorsal nerves (dr). The ventral ones, springing from
the lower edge of the medulla, are here represented as shorter stems (vr).

REPORT ON THE NEMERTEA. 135

The opposite half of the system, seen in transparent perspective, as given in the two
other figures, is purposely omitted here, because of the asymmetry of AmpMoxus in
this respect.

Now a glance at these figures will convince us that the situation of the Nemertean
medullary nerve in its plexus, and with its set of transverse nerves, is directly compar-
able to the Vertebrate medulla and spinal nerves. The nerve-plexus filling up the
intervening spaces in Nemertea is present as a transitory structure in Amphibian
embryos.

The ulterior appearance of an anterior enlargement forming the Vertebrate brain ;
the higher complication attained by the brain and spinal cord when its mass increases,
but not its dorsal expansion, by the appearance of medullary ridges ; and the formation of
a neural canal by infolding of the neural plate, all these are important developmental
facts which do not in any way weaken the grounds for comparison of the two structures.
They may be looked upon as adaptations to the much more considerable efiiciency
and concentration that is gradually attained by the central nervous system as we ascend
higher in the scale of the animal kingdom.

The fact that the neural ridge in so many Vertebrata precedes the appearance of the
spinal nerves, and is inserted along the top of the folds that bend together to form
the neural tube, may be thus interpreted, that during the phylogenetic process
of infolding, the transverse nerve-tracts (dorsal spinal roots) remain attached in the
same way to the medio-dorsal collecting trunk as they did in the ancestral forms, and
are dragged upwards by the infolding process. The ventral roots must be phylo-
genetically linked to the plexus as well ; inasmuch as the musculature originally lies
inwards of the nervous plexus, their deeper situation is not surprising.

In the points hitherto enumerated there is entire coincidence between Ainphioxus
and the other Vertebrata, as far as their comparability with the Nemertean diagram
goes. Another point of coincidence is the way in which the foremost portion of the
intestinal canal and adjacent blood-vessels are innervated by visceral nerve-stems,
indicated in all the three^ diagrams by vi.sy.

The claims to validity of the comparison here made between the spinal nerves of
the Chordata and the transverse stems of the Nemertea, should be again insisted on,
now that the researches of Eohon,^ Freud,^ Schneider, Ransom, and d'Arcy Thompson'

^ v. Eolion, Untersuchungen iiber Amphioxus lanceolatus, Denksch: d. k. Ahai. d. JFus. Wien, Bd. xlv.

- S. Freud, Ueber Spinalganglien und Riickenmark des Petromyzoii (Sitxungsb. niath.-nat. cl. k. Akad. Wiss. Wien^
Bd. Ixxviii., Abth. 3, 1878). This author says (p.l54) : " Ich kann wenigstensvon den letzten Wurzeln des Caudalmarks
sagen dass ihre Selbstandigkeit so gross ist, dass man von vorderen uud hinteren Spinalnerven, anstatt von vorderen
und hinteren Wurzeln reden konnte " ; and Wiedersheim in the 2d edition of his Lehrbuch der Vergleichenden
Anatomic (p. 321): "Vieles spricht dafiir dass die Vorfahren der heutigen Wirbelthiere getrennte dorsale und
ventrale Nerven wurzeln besessen haben miissen."

3 W. R. Ransom and d'Arcy W. Thompson, On the spinal and visceral nerves of Cyclostomata, Zool. Anzeiger, No, 227,
July 1886.

136 VOYAGE OF H.M.S. CHALLENGER.

have established for the lower Chordata (Cephalochorda and Cyclostomata) that the
typical chordate spinal nerve is not originally provided with a double root, but that this
double root apjaears to have arisen by the coalescence of what were primitively in the
groups just mentioned, separate and alternating dorsal and ventral nerve-tracts.
With these so much simpler spinal nerves the transverse nerve-stems of the Nemertea
undoubtedly offer points of comparison. These Nemertean nerves specially differ from
the Vertebrate spinal nerves in two respects : (l) they give off nerve-filires in different
directions, which are probably motor as well as sensory and visceral, according to the
different organ systems they terminate in ; and (2) they go round ventrally, each of them
forming a loop all round the body. As to the first point of difference just alluded to, it is
the expression of a low and primitive degree of differentiation, and when a step forwards
is made, differentiation of labour will tend to develop certain tracts more particularly con-
taining sensory and visceral nerve-fibres, which are more especially directed towards
the epithelia (the primitive dorsal or posterior roots), and others more particularly
containing motor nerve-fibres, and more especially directed inwards towards the muscles
(the primitive ventral or anterior roots), because the musculature, as was already
mentioned, is originally situated internally to the nervous system.

For the present we can only hold it to be established that the fibres of these three
categories are blended in the Nemertean plexus, •wdthout being able to determine in
how far the specialisation therein observed, of the appearance of transverse metameric
nerves, may at the same time be accompanied by a commencement of differentiation, such
as has just been alluded to. We may, in other words, not yet assume that among these
metameric stems there is already a tendency to an alternation between such as have
sensory and visceral, and such as have motor predispositions.

Only in a few cases may we be justified in saying that certain nerve- tracts belonging
to the Nemertean peripheral system are more especially sensory (PI. XIV. fig. 2) or
visceral (PL XIV. fig. 4), and these no doubt offer important analogies in their situation
and connections to similar nerve-tracts of the Vertebrata.

The second point of difference, viz., the continuity in the ventral median line of the
transverse tracts of the Nemertea, is no doubt a consequence (a) of their origin in a
perfectly continuous plexus, (6) of the cylindi-ical arrangement of the muscular layers,

which in most cases are uninterrupted both in the dorsal and in the ventral median line.

It is all the more important to notice, that more especially in the primitive Carinellidse,

the tendency is very marked towards a scission of this muscular body-wall into a right

and a left half (cf. p. 72). A comparison of figs. 4, 5 on PI. XI. will show this.

In the Schizonemertea, too, and in Eiqwlia it affects the primitive muscular layer (PI.

XL figs. 10, 12), in a more or less marked degree.

This longitudinal scission is no doubt the first expression of the phenomenon which

shows us the musculature of the right and left half of the body, developing quite inde-

EEPORT ON THE NEIIERTEA. 137

pendently in the Chordata. It is easily intelligible how, as this phenomenon gradually
becomes more and more marked, no more ventral connecting fibres across the non-
muscular region were required for the innervation of the musculature of the right and
left half of the body.

The process by which the transverse nerve-tract, with radial nerve-fibres leaving it at
short intervals, both centripetally and centrifugally gradually assumed the form of a
nerve-stem with a dorsal and a ventral branch, such as we find in the spinal nerves, must
have gone on 'pari passu with those numerous other changes, which we cannot as yet
fully trace, but which must have occurred when (1) the muscular metamery became
gradually established, (2) the dorso-median medullary tract became so preponderant
that an increase in mass, with economy of bulk, was only to be obtained by a process of
folding-in already discussed above, and (3) the attachment of the spinal nerves
(transverse tracts) to the medulla was modified in consequence of this process.

None of these phenomena, however, oflfer anything that is in any way inconsistent
with, or opposed to, the general theory here developed.

We have now sufficiently insisted on the chief point of comparison here proposed,
viz., that between the Nemertean medullary nerve and its metameric transverse nerve-
cords, and the Vertebrate cerebro-spinal axis and spinal nerves.

If Amjihioxus were the only Vertebrate known, we should, recognising the phylo-
genetie importance of the plexiform arrangement still met with in the adult of that
species, admit that, as far as we know at present, the primary lateral nerves with their
anterior swellings of the Vermian ancestors had disappeared in the same measure as the
dorso-median spinal cord had come more and more into the foreground.

But our consideration of other Vertebrates leads us to the conclusion that, when
once the general homology between the two nervous systems is admitted, there may
perhaps be secondary points in regard to which the comparison can be further extended.
And it must be recognised, that if we should also succeed in rendering more or less
probable a comparison in secondary details, this might again be favourably interpreted
for the primary and more important part of the hypothesis.

The search after these secondary points of agreement was instituted by me, when the
question above alluded to presented itself, viz., if any remnant could be traced of the
central nervous system of Nemertea-hke ancestors, i.e., of the brain-lobes and lateral
stems, in those Vertebrate descendants in which the medio-dorsal tract had become so
preponderant as to give rise to the unpaired medulla and brain.

It is clear that if it shall be possible to trace any such remnants, and to render their
homology with the Nemertean central nervous system probable, they will have to be
sought for — (o) in the head, as lateral more or less independent nerve-centra, innervating
sense-organs of the integument, and passing posteriorly into parallel longitudinal stems ;
or (h) in the trunk, as longitudinal nerve-stems, in which the central character should

(ZOOL. CHALL. EXP. PART LIV. — 1887.) Hhh 18

138 THE VOYAGE OF H.M.S. CHALLENGER.

be somewhat less marked than in the anterior swelling, but in which the original
significance as parts of the central system should still be indicated either by histological
or by embryological features.

To these latter conditions nothing can answer in the Vertebrate nervous system
excepting the so-called ramus lateralis vagi. It is present in all Vertebrates above
Amphioxus, long and important in the aquatic Ichthyopsida, gradually disappearing
when the aquatic medium is exchanged for an air-breathing existence, and finally only
retained in the higher Vertebrates as the inconspicuous ramus auricularis vagi.

Its course is indeed strictly lateral, and has always been a puzzle to anatomists.
Stannius^ characterises the existence and the course of this sensory nerve along the
trunk down to the tail as " one of the most interesting facts of anatomy."

None the less startling is its development. Whilst Balfour attempted in this respect
to bring it on one line with the other parts of the peripheral nervous system, the
corresponding results of Semper, Goette, van Wijhe, and Hofi'mann are all in the
contrary direction. They have seen the nervus lateralis appear as an independent
product of the epiblast, arising in loco along its whole length, its formation often even
preceding that of the spinal nerves. These results have again been fully confirmed and
definitely established by the latest investigator of the problem, Beard,^ who also gives a
detailed description and figures of the connection between the nervus lateralis and the
vagus ganglion, both of them so much more massive and conspicuous in early embryonic
stages than later on.

And now that we are attempting to find out whether there is a possibility of com-
paring the lateral nerve-stems of lower worms with the nervus lateralis of Vertebrata,
we are naturally led to consider, in the second place, the question whether the anterior
swellings of these lateral stems (the paired brain-lobes of the worm) may have their
morphological equivalents, their remnants, in the set of anterior nervous swellings that
are found in the head on a level with the nervus lateralis, and longitudinally connected
with it ; viz. , the variable set of ganglia of the cephalic nerves.

As to the origin of these ganglia of the cranial nerves I have no observations of my
own, and must rely on the data of other observers.

It is suggestive to give the opinion of the three latest investigators of the develop-
ment of these organs in different groups of Vertebrates in their own words.

Professor A. Froriep,^ who studied Mammalian embryos, writes {loc. cit., p. 35) : —
" The ganglia (of facialis, glossopharyngeus, and vagus) enter into a peculiar, very inti-
mate connection with the epiderm "; further (p. 40), '• these ganglionic connections with
the epiderm must probably be regarded as rudiments of organs which have phylogeneticaUy

1 Das peripherisehe Nervensystem der Fiache, p. 108.

' The System of Branchial Sense-Organs, &c., in Ichthyopsida, Quart. Journ. Micr. Sci, November 1885, p. 95.

' Ueber Anlagen von Sinneeorganen am Facialis, &c., Archivf. Aimt. u. Phys., 1885, Anat. Abth.

REPORT ON THE NEMERTEA. 139

disappeared, and wliicli are only now retained in the ontogenetic development"; then
(p. 43) "for the Gasserian ganglion there is no indication of a connection with the
epiderm"; and, lastly (p. 52), "it appears to be hardly any longer possible to look
upon these nerve-ganglia (Nerveuknoten) as simply homologous with spinal ganglia."

Baldwin Spencer ^ writes (Zoc. ai., p. 129) concerning Rana temporaria : — "Along
certain lines the cells of the nervous layer proliferate, and it is by this proliferation that
the rudiments of the cranial nerves are laid down" ; further (p. 130), "the development
of the ganglia at the level of the lateral line, and the fact of their long connection with
the epiblast at this point .... is of great interest in connection with certain
points in the development of the Elasmobranch nerves."

Concerning the developmental phenomena in the trunk-region at this period, the spinal
nerves are stated to be not yet visible, " though the nervous sheath is clearly developed
and in this the lateral line "

The author next mentions observations made by him on Dr. Beard's sections of
Elasmobranch embryos, and goes on to say (loc. cit., p. 131) : —

" The Gasserian ganglion is, at all events in part, formed directly from the epiblast
. . . . the same development takes place in the case of the ganglion of the third and
seventh nerve — in that of the ciliary ganglion the development is particularly clear —
. . The gcmglia arise cdong a level of the lateixd line continued on the head."

He next says : — " The curious origin of the ganglia of the cranial nerves points
strongly to the conclusion that .... their present condition and nature must

. . . 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 persistent parts of the lateral nerve .... in the head."

In the third place, extracts will be given from Beard's more extensive paper.^ He
writes (p. 97) as an introductory statement : — " At present we are acquainted with no
Invertebrate nervous system which is built upon the same plan as that of Vertebrates ";
and then passes to the results of his investigations chiefly carried out on embryos of
Torpedo and a few other Elasmobranchs. I make the following selections (p. 101) :—

" At the point of fusion" (of the cephalic nerve with the epiblast) " a local thickening
of epiblast has previously taken place. After the fusion has taken place a proliferation
of some of the cells composing the thickening ensues. The proliferated cells form a mass

of actively-dividing elements still connected with the skin This mass of

cells is the rudiment of the gangHon of the dorsal root."

On p. 110 he adds : — "Along with the separation of the (vagus) ganglion from the

1 Early Development of Rana temporaria, Qvxirt. Jotmi. Micr. Sci., Suppl., 1885.

2 Branchial Sense-Organs in Icbthyopsida, Quart. Journ. Mia: Sci., November 1885, No. cL

140 THE VOYAGE OF H.M.S. CHALLENGER.

skin, the sensory thickening begins to grow backwards along the lateral surface of the

trunk. This thickening is the rudiment of the so-called lateral line The

so-called lateral nei-ve is formed from the deeper portion of the sensory thickening.
. . . . That there is no actual growth backwards of the nerve is obvious enough."

Eecapitulating, we must acknowledge that the mode of origin of the ganglia of the
cephalic nerves, as described by these authors, is certainly a peculiar one — a mode of
development sui generis. One of Beard's accompanying diagrammatic figures, repro-
duced in Wiedersheim's second edition (1886) of the Lehrbuch der Vergleichenden
Anatomic as woodcut No. 265, moreover, shows how the position of the cephalic ganglion,
developing as an ectodermal proliferation, is in this early stage eminently lateral, a
conclusion corroborated by the figures of his actual sections. This primitive position is,
of course, gradually lost, and could never be predicted from a study of these ganglia and
their position and significance in the adult animal. Yet it is not without significance,
when seen in the light of the suggestion here brought forward. And that the interpre-
tation of the phenomena in question as given by these authors is not universally accepted,
thus leaving room for new suggestions, is proved by the following citation from Ransom's
and dArcy Thompson's latest article,^ running, as follows: — "Although the lamprey
presents a well-marked lateralis nerve, it has not also a regular lateral line, for the sense-
organs of the skin are scattered and without segmental arrangement. The sense-
organs do not, therefore, appear to be in direct relation with the sjiiual ganglia, and the
view of the close connection between them (Spencer, Beard, Froriep) does not receive

support It seems more natural to consider the lateralis as a relic of the

extensive and irregular commissure system connecting the posterior roots of Amphioxus."

Passing from a consideration of the embryonic ganglia to their connection in the
adults, I must mention the connection of the ramus lateralis vagi with cephalic nerves
anterior to the vagus. I will not here give a description of the numerous varieties pre-
sented by this nervous connection, but merely refer to the arrangement in Vertebrates so
low as the lampreys. We there find, according to Johannes Miiller, the ramus lateralis
originating from the seventh as well as from the tenth pair of cephalic nerves, and if we
compare the very satisfactory figure which was only lately" given by Ahlborn of this
arrangement, we must recognise that this nervous connection is important, and has more
the aspect of a direct forward continuation of the nervus lateralis than of a sensory branch
from the facialis, establishing a connection between it and the vagus.

Ahlborn mentions the existence of a similar connecting stem reaching further forward
still, and connecting the trigeminus and facialis. How these connections vary in the
different adult Vertebrata will not be discussed here.

The difi"erent facts and speculations here brought forward in connection with the

' Ou the Spinal and Visceral Nerves of Cyclostomata, Zool. Anzeiger, No. 227, July 18S6.
- Zeitschr. f. wiss. Zool., Bd. xl., pi. xviii.

REPORT ON THE NEMERTEA. 141

cephalic ganglia and the nervus lateralis vagi, may suffice for the present. They may
severally be brought to bear upon the question of the eventual homology of Vertebrate
cephalic ganglia and nervus lateralis, on the one hand, and Vermian paired brain-lobes
and lateral nerve-stems, on the other. The parts here compared, being indicated in figs. 1
and 2 of PL XVI. with corresponding letters, Lg and In, a glance at these figures may
further convey a notion of the purport of these speculations.

There is one fact, however, which is not indicated in these figures, which is never-
theless of very high importance for the views here considered, and which I must therefore
develop more in detail.

It is the connection between the successive spinal nerves and the ramus lateralis vagi.

The existence of similar connections between the (eminently sensory and cutaneous)
dorsal roots and the (similarly sensory and cutaneous) lateral nerve is for the first time
mentioned by Eansom and d'Arcy Thompson for Petromyzon in the following passage
{loc. cit., p. 422) :—

" The dorsal rami of the posterior roots pass up (over the lateralis nerve) to the skin
of the back, but appear also to send fibres into the lateralis. (For this statement we at
present rely only on sections, but we hope shortly to test it by dissections of the large
Petromyzon marinus. ) "

It hardly needs comment that if this observation should be confirmed the fact would
be of the utmost importance for the hypothesis under discussion. We should then be per-
mitted to consider these metameric connections between the dorsal roots and the nervus
lateralis of Petromyzon, as the reli-cs of an earlier stage, stiU permanent in the Nemertea,
where the metamerically consecutive transverse nerve-tracts similarly unite the medullary
nerve and the lateral stems.

This connection is, as we know, also brought about in the Nemertea by the plexus, in
those parts of it which spread out between the transverse tracts, and it may here be asked
if reHcs of such a plexus between the successive precursors of the spinal nerves are perhaps
retained, not only in Amphioxus (see above, p. 134, and Eohon, loc. cit., fig. 13), but also
in Osseous Fishes in the numerous superficial nerves described and figured by Stannius,^
or whether we must rather look upon this multiplication of lateral nerves (one of which
is called by Stannius the nervus lateralis trigemini, others, rami communicantes of the
dorsal branches of spinal nerves, &c.) as derivatives from the nervus lateralis vagi." This
question can, of course, only be solved by careful anatomical and embryological investiga-
tions. That the nervus lateralis was often (Stannius) observed in the Petromyzontidse
only along a part of the length of the body (Schneider and Born, according to Ahlborn,^

1 Das peripherische Nervensystem der Fische, 1849, pis. ii.-iv.

2 It should be remembered that Beard is inclined (loc. cit., p. 139) to look upon the superficial longitudinal nerve-
fibres, by which the successive epithelial modifications along the lateral line are often connected (Solger, Bodenstein), as
such derivatives (by longitudinal fission in its very early stages) of the nervus lateralis.

3 Zeitschr. f. wiss. ZooL, Bd. xl. pp. 303 and 301.

142 THE VOYAGE OF H.M.S. CHALLENGER.

observed it " bis an das Hinterende des Korpers") is not confirmed by modern investi-
gators. Alilborn's description ijoc. cit., p. 304) of the variable situation of this nerve in
Petromyzon is very suggestive in connection with the views here advocated. Eansom
and d'Arcy Thompson consider that the regularity of the integumentary sensory
apparatus is not yet established in Petromyzon, as may be concluded from the citation
given above (p. 140).

We have now considered the superficial ramifications of what I may call the lateral
nerve system, both in lower worms and in Vertebrates ; we must now turn to the
intestinal, to the visceral branches of this same system, from which other and important
data may be gathered for further elucidation of the hypothesis under consideration.

We have already seen that in Nemertea the typical innervation of the respiratory
portion of the intestine is brought about — (a) by a pair of nerves directed backwards and
springing from the anterior lateral swellings (the brain-lobes) of the lateral nerve-stems ;
Q)) by numerous visceral branches starting from the plexus, directed inwards as branches
that spread over the wall of blood-lacunae and intestine.

In the Vertebrata, Amjjhioxus excepted, we also find that the innervation of the
anterior respiratory portion of the intestine and of the circulatory apparatus is obtained
from two sources, viz., (1) the cephalic nerves, amongst which the vagus nerve is in this
respect the most important'; (2) the visceral branches of the spinal nerves, which are at
the basis of what is afterwards more highly difi"erentiated and separately recognised as
the sympathetic nerve-system.

In Nemertea it is very difficult to determine in the anterior part of the intestinal
wall, which tracts belong to the so-caUed vagus nerve, which to this system of visceral
nerve-branches.

So it is often in Vertebrata, and the blending together (in both divisions of the
animal kingdom) of two systems, each of them again mutually comparable when separately
considered, is an important point of agreement, and would, if no actual homology were
at the base of it, be a very puzzling coincidence.

It is in this respect highly suggestive that Born notices, as early as 1827, what was after-
wards confirmed by Ahlborn (loc. cit.) and others, that in Petromyzon, i.e., one of the lowest
Vertebrates, the spinal nerves send out connecting branches towards the pneumogastric
nerves. The existence of superficial metameric connections (Eansom and d'Arcy Thompson,
vide supra) as well as of this set of deeper connections between the transverse and the
latero-longitudinal nerve-stems (n. lateralis and n. pneumogastricus) of Petromyzon would
thus be a most remarkable repetition of the similar arrangement in the Nemertea,
as it has been here for the first time demonstrated.

' Ventrally these nerves (e.g., the n. hypoglossus) are sometimes commissurally united with their representative of
the opposite half of the body. It must remain an open question whether these commissures are in any way comparable
either to the Nemertean vagus commissures (<•/. p. 83), or to the general ventral commissural system of these worms.

REPORT ON THE NEMERTEA. 143

The facts as tliey lie before us do not, however, admit of any very circumstantial com-
parison so far as the nerves in particular are concerned, and I purposely refrain from
entering into any details. Yet it should be remarked —

(1) That the polymerous root of the Vertebrate vagus nerve is very readily explicable
if we take the Nemertean arrangement as a starting-point (PI. XVI. figs. 1, 2, vag),
as is also the mixture of sensory and motor elements in this root.'

(2) That similarly, if the anterior cephalic nerves (e.g., the fifth) should prove to be
polymerous, this would in no way be astonishing nor difiicult to bring into harmony with
that same starting-point.

(3) That the presence of superficial branches to the integument and to the muscu-
lature, and of deeper branches to the intestinal epithelium in those parts that will
contribute to form the cephalic nerves, is similarly foreshadowed in the Nemertea.

(4) That the equivalent of the Nemertean vagus nerve will have to be sought for
in such branches of the Vertebrate vagus as more especially innervate the intestinal
epithelium,^ whereas the innervation of the Vertebrate gill-slits, which marks a later phylo-
genetic stage, in which these perforations of the anterior trunk region have appeared,
may be as well put to the account of more superficial parts of the transverse tracts.

(5) That the common starting-point of the sensory, lateral, and the intestinal
portion of the vagus has also attracted the attention of former observers. Kansom and
d'Arcy Thompson write :- — " In the embryo dog-fish the second or ventral commissure
described by Balfour, &c., as uniting the roots of the vagus, ventral to the ganglia, is
essentially a sympathetic commissure, whose (visceral) fibres pass on, as described by
Balfour, to form the intestinal branch of the vagus. In that intestinal branch we have
an outflow of visceral fibres, quite comparable to, e.g. , a splanchnic branch of the dorsal
sympathetic system. The connection between the origin of the lateralis and this ventral
commissure connecting the vagus roots in the dog-fish, and similarly the relation of the
lateralis to the loops uniting the ganglia of the 5th, 7th, and 10th nerves in
Petromyzon may probably be described as indicating a fusion in this region of
the two great commissural systems which posteriorly are separate, viz., that of the
sensory branches (lateralis) and the visceral or sympathetic.

' Rohon, Ueber den Urspruiig des Nervus vagus bei Selacliiern, Arbeit. Zool. Inst. Wien, vol. i. p. 159.

^ I have good reasons, based upon actual observations made by my pupil, Mr. Dobberke, to believe that the ramus
intestinalis vagi in adult Elasmobranchs may lie traced centripetally from its region of innervation of the foremost portion
of the intestinal wall, towards the brain, as a bundle of nerve-tibres running parallel to and combined with those for the
branchial apparatus, but that, nevertheless, this bundle can be separately traced up to the vagus ganglion, without any
further intimate relation to those branchial branches (cf. Beard, loc. cit., p. 110). If this should^ actually be the case,
the possibility of a direct comparison between the Nemertean vagus nerve and the Vertebrate ramus intestinalis vagi, of
course, comes more closely within our reach. It need not be insisted upon that if these comparisons prove correct, the
separate intestinal nerve-systems (sympathetic nerve system) of other Invertebrates (Annelids, Arthropods, Molluscs)
camiot be looked upon as homologous with the sympathetic nerve system of the Vertebrates, but would rather be
homologous with that portion of the intestinal innervation of the latter which comes to the account of their cephalic
nerves, in so far as these represent derivatives of the Nemertean vagus, and are marked v in figs. 1 and 2 of PI. XVI.

144 THE VOYAGE OF H.M.S. CHALLENGEE.

" We agree with Gaskell tliat the term sympathetic should be suffered to fall iuto disuse,
as tending to perpetuate the old conception of the primary importance of the longitudinal
nerve-tract ; whereas the leading fact is the metamerically recurring outflow of visceral
fibres, which may or may not be united together by successive longitudinal commissures."

In the Nemertea this anterior " fusion of the great commissural systems " is
foreshadowed at the point where brain-lobe, lateral stem, and " vagus nerve " meet, or
rather diverge. It has been attempted in figs. 1 and 2 to indicate the points here
alluded to in a general way, special comparisons being, on the grounds that have been
stated, purposely avoided.

If we now turn to Dohrn's and Semper's hypothesis we must recognise that no such
satisfactory general comparisons are there possible. Even if we were inclined to accept
the " turning over " of Geoffroy St. Hilaire, by which back and beUy became exchanged,
and to admit the brain-piercing oesophagus, regarding the Annelid supracesophageal
ganglion and the ventral nerve-cord as respectively homologous to cerebrum and
medulla, it must still be conceded that we have not then in any way before us a nerve
system ofi'ering as many points of comparison with the Vertebrate system as does that of
the Nemertea.

Concerning the Annelids we have no observations by which the cephalic ganglia and
the cephalic nerves are so clearly foreshadowed, none which would throw light on the origin
of the vagus, its connection with the nervus lateralis and with the anterior cephalic
ganglia, none concerning the sympathetic system and its blending with the vagus system
in the lowest Vertebrates, indications of which are even retained in the highest. Nor is
the ventral nerve-cord of Annelids, with its undeniable double character and double
origin a match, so far as comparison goes, for the Nemertean medullary nerve, with its
transverse nerves preceding the spinal nerves of Amj^hioxus and the Cyclostomata.

And if we are then asked to consider the lens of the Vertebrate eye as a modified
ectodermal branchial invagination, as the outer portion of what was once a functional
gill-slit,^ we feel that the ground under our feet is becoming rather uncomfortable, and
that it is high time to reconsider whether all these ingenious speculations in which the
most beautifully pHable hyjjothetical and unknown Annelids play a too conspicuous part
should not be definitely abandoned, and a new departure made by those who are interested
in the phylogeny of the Chordata. In due time arduous and detailed morphological
investigations on the Platyelminthes in general, and on the Nemertea in particular, may
then lead us to more satisfactory conclusions than are the fata morgana that are so
temptingly evoked before our eyes by the ingenious manipulations of the indefatigable
founder of the first and foremost Zoological Station, when, following his lead, we find
ourselves wandering in the barren deserts of that province of phylogeny, in which he
attempts to establish a close connection between Chordata and Annelida.

1 Dohrn, Studien, x. p. 459, 1885.

REPORT ON THE NEMERTEA. 145

All these considerations have induced me to give this rapid outline sketch of the
degree of comparison which I hold to exist between Chordate and Nemertean (more
especially Paleeonemertean and Schizonemertean) nervous systems, although I am per-
fectly aware that there is a growing tendency among those authors at present occupied
with questions concerning the morphology of the Vertebrate nervous system (Froriep,
Baldwin Spencer, Beard, Cunningham, Kleinenberg, and many others) to accept
Semper's and Dohrn's views of the Anuelidan descent of Vertebrates. Wiedersheim,
in the new edition of his " Vergleichende Anatomic " (1886), does not even hesitate to
bring these results in their unripe phase before the more extensive public of students, and
this generally in acquiescent terms. It is curious to see how, e.g., the question of the
cephalic nerves and their comparison to spinal nerves, that of the nerve-roots, the
cephalic ganglia and their respective connecting trunks, have given occasion to the most
diverse twisting and retwisting of the facts in order to bring out a fixed scheme or
diagram, which might then be compared to what obtained in Annelids, and in which
the highest degree of similarity between the respective somites might be obtained, thus
establishing a preconceived idea of the Vertebrate ancestor as a most rigorously seg-
mented animah The value of these speculations has been already tested above, and I may
be allowed once more to express my conviction that our comparisons between the Chordata
and their lower Invertebrate predecessors may only be looked upon as in any way satis-
factory so long as they remain on a very broad and general basis, and that any very
special homology said to be demonstrated ougJit for that very reason to be more especially
suspected/

For my part I believe that, along the lines above indicated, a comparison between
Vertebrate and Invertebrate nervous systems will in future prove to be more fruitful, but
I wish to repeat that for the present we can only indicate general points of coincidence
between the two, and must rigorously refrain from making comparisons in detail.

On the other hand, it is suggestive once more to consider what has been recorded
above (p. 89) concerning the nervous system of Drepanophorus lanlcesteri, when
compared with that of certain Annelids ; and we may, I believe, safely come to the
conclusion which was formulated by me seven years ago, but which I now hold to be
much more solidly established, that we have in the Nemertea an important group
through which definite glimpses may be obtained at the sources from which both
Chordata and Appendiculata (Ray Lankester) have respectively sprung. The proposition

' Bateson {loc. cit., p. 562) seems to take a similar view of the efforts here alluded to. He says : — " No douht
the cranial nerves may, by arbitrary divisions and combinations, be shaped into an arrangement which more or less
simulates that which is supposed by some to have been present in the rest of the body, but little is gained by this
e.xercise beyond the production of a false symmetry." — Dohrn himself, whose suggestions have so largely contributed to
the accumulation of all this conflicting evidence, is now rather in the position of Goethe's Zauberlehrling, and writes
(Studien, x., p. 468, 1885) — " Auch auf diesem Gebiet (die Frage nach der Bedeutuiig der Hirnnerven)bildet die bisherige
vergleicheude Anatomie das BUd eines auf stiirmischer See steuerlos herumgeschleuderten Schifl'es."

(ZOOL. CHALL. EXP. — PART LIV. 1887.) Hhh 19

146 THE VOYAGE OF H.M.S. CHALLENGER.

first formulated by Gegenbaur, about the phylogenetie origin of the ventral nerve-cord
and oesophageal ring of the Annelida out of ancestors with lateral cords, has obtained new
support from the arrangement which was met with in the species just mentioned. And
just as we have before tentatively discussed the question, in how far remnants of the
lateral cords were retained in those descendants in which the median one had been raised
to the dignity of a medulla spinalis (the Vertebrata), we might now consider whether any
remnants of the median dorsal cord are retained in those descendants in which the lateral
cords have differentiated into brain-lobes, (Esophageal ring, and ventral cord (the
Annelida). To this question I have no definite answer to offer, but I may call attention
to the significant fact that the beautiful and exemplary investigations into the embryonic
development of LojiadorhyncMis, very recently published by Kleinenberg,^ have
demonstrated the existence in the larva of that Annelid, of a nerve-stem answering to the
conditions here required. It is dorsomedially situated, it is anteriorly connected with
the brain, or rather with a transverse nerve-tract (Kleinenberg's prototrochal nerve-ring),
which in its turn is connected with the brain,^ it appears to be connected close to the
anus with the ventral cord (the fused lateral stems), and though appearing in early
larval life, and having only a temporary existence, it is regarded by Kleinenberg as
having considerable physiological importance. If the fight in which I am inclined to
look at it is not deceptive, its morphological significance also can hardly be overrated.

In closing this chapter of general considerations, we may once more bring before
our minds the proposition with which it was opened. We have here and in the foregoing
chapters adduced facts and arguments which appear to speak in its favour ; we wiU once
more rapidly enumerate the common characteristics of Nemertea and Coelenterata, as
well as those of Nemertea and Chordata.

The Ccelenterate characteristics that are also found in the Nemertea are the fol-
lowing : —

a. The presence of nematocysts in the proboscidian epithelium.

b. The elaborate nerve-plexus in the integument, and its histological features.

c. The presence of epiblastic muscle-fibres separate from the general body-

musculature.

d. The presence and the chemical constitution of a sometimes very massive

intermuscular jelly, by which the other internal organs are at the same
time surrounded.

e. The mode of development of the mesoblast (at least in Linens obscurus),

which is less specialised than in most other Invertebrates.
/. The absence of any distinct enterocoele.

1 Zdtschr.f. vms. Zool, Bd. xliv., Heft, i, ii., October 18S6, p. 107 ; pi. vii. tig. 27a.

2 For comparison with the Nemertea, cf. ph xvi. fig. 1.

REPORT ON THE NEMERTEA. 147

The points of resemblance with the Chordata may be thus tabulated : —
a. The general features of the nervous system.

h. The presence of a homologue of the hypophysis cerebri as a massive and
important organ (the proboscis).

c. The presence of tissues which may have become converted into the notochord

(viz., the material of which the proboscidian sheath is built up).

d. The respiratory significance of the anterior portion of the alimentary tract.

At the base of all the speculations contained in this chapter lies the conviction,
so strongly insisted upon by Darwin, that new combinations or organs do not appear by
the action of natural selection unless others have preceded, from which they are gradually
derived by slow change and differentiation.

That a notochord should develop out of the archenteric wall because a supporting
axis would be beneficial to the animal may be a teleological assumption, but it is at the
same time an evolutional heresy. It would never be fruitful to try to connect the difi"erent
variations offered, e.g., by the nervous system, throughout the animal kingdom, if similar
assumptions were admitted, for there would be then quite as much to say for a. repeated
and independent origin of central nervous systems out of indifferent epiblast just as
required in each special case. These would be steps that might bring us back a good
way towards the doctrine of independent creations. The remembrance of Darwin's,
Huxley's and Gegenbaur's classical foundations, and of Balfour's and Weismann's
brilliant superstructures, ought to warn us away from these dangerous regions.

LIST OF AUTHORS REFERRED TO IN THE TEXT.

I. J. Barrois, Eecherches sur I'Embryologie des Nemertes, Ann. d. Sci. Nat., ser. 6, vol. vi., 1877.
II. R. Dewoletzky, Zur Anatomie der Ifemertinen, Zool. Ameiger, Jahrg. iii., 1880, pp. 372-306.
III. L. VON Graff, Geonemertes clialicophora, eine neue Landnemertine. Moryh. Jahrb., Bd. v.

p. 430.
IV". A. A. W. HuBRECHT, Aanteekeningen over de Anatomie, Histologic eu Oiitwikkelingsgeschiedenis
der Nemertinen, Utrecht, 1874.

V. Uiitersuchungen iiber Nemertinen aus dem Golf von Xeapel, Niederldndisches Archiv

fiir ZooJogie, Bd. ii. S. 99.

VI. Some Remarks about the Minute Anatomy of Mediterranean Nemerteans, QuaH. Journ.

Micr. Set., vol. xv. p. 249.

VII. The genera of European Nemerteans critically revised, with Description of Several New

Species. Notes from the Leyden Museum, vol. i. p. 193, 1879.

VIII. New Species of European Nemerteans. Notes from the Leyden Museum, vol. ii,

IX. Zur Anatomie und Physiologie des Nervensystems der Nemertinen, Verhandel. van de

KoninM. Alud. van Wetenschappen, Amsterdam, 1880, vol. xx.

X. The Peripheral Nervous System of the Pateo- and the Schizonemertea, one of the layers

of the body- wall. Quart. Joiurn. Micr. Sci., vol. xx., 1880.

XI. Zur Nemertinen Anatomie, Zool. Anzeiger, Jahrg. iii., 1880, p. 406.

XIa. On the Ancestral Forms of the Chordata, Quai-t. Journ. Micr. Sci., vol. xxiii., 1883.

XII. Der excretorische Apparat der Nemertinen, Zool. Ameiger, 1885, p. 51.

XIII. Zur Embryologie der Nemertinen, Zool. Anzeiger, Jahrg. viii., 1885, p. 460.

XIV. Proeve eener ontwikkelingsgeschiedenis van Linens obscurus Barr, Utrecht, 1885.

XV. Contributions to the Embryology of the Nemertea, Quart. Journ. Micr. Sci., vol. xxvi.,

1886.
XVI. J. VON Kennel, Beitrage zur Kenntniss de Nemertuien, Arbeit, zool.-zoot. Inst. Wiirzburg,
Bd. iv., 1878.

XVII. Die in Deutschland gefundenen Landplanarien, Arbeit, zool.-zoot. Inst. Wiirzburg,

Bd. v., 1882.
XVIII. A. Lang, Monographie der Polycladen, Leipzig, 1884.
XIX. W. C. M'Intosh, A Monograph of the British Annelids — A. Nemerteans, Ray Society Publica-
tions, 1873, 1874.

XX. On Amphiporus spectabilis, Quart. Journ. Micr. Sci., vol. xv. p. 273.

XXI. On the Central Nervous System, the Cephalic Sacs, and other points in the Anatomy of

the Lineidfe, Journcd of Anatomy and Physiology, vol. x. p. 231.

XXII. Marine Annelida from Kerguelen's Land, Phil. Trans. Roy. Soc. Lo7id., vol. cLxviii.

(extra vol.), London, 1879.

XXIII. Description of some New Species of Annelida from Kerguelen's Island, Ann. and 3Iag.

Nat. Hist., ser. 4, vol. xvii., 1876.

150 THE VOYAGE OF H.M.S. CHALLENGER.

XXIV. W. C. M'Intosh, On Valencinia Armandi, a New Nemertean, Trans. Linn. Soc. LoncL, ser. 2,

vol. i., 1879.
XXV. H. N. MosELEY, On Pelagonemertes rollestoni, Ann. and Mag. Nat. Hist, vol, xv., 1875.

XXVI. On a young specimen of Pelagonemertes, Ann. and Mag. Nat. Hist., vol. xvi., 1875.

XXVII. A. C. OuDBMANS, The Circulatory and Nephridial Apparatus of the Nemertea, Quart. Joxim. Micr.
Sei., Suppl., 1885.
XXVIII. A. DE QuATEEFAGES, Mdmoirc sur la famille des Nemertiens, Ann. d. Sci. Nat., (3), vii., 1846.
XXVIIIa- A. Sabatier, La spermatogen^se chez les Nemertiens, Revue Sc. Nat. Montpellier, (3), t. ii., 1883.
XXIX. W. Salensky, Recherches sur le d^veloppement du Monopora, Archives de Biologie, t. v.

XXX. Bau et Metamorphose des Pilidium, ZeitscJir. f. wiss. ZooL, Bd. xliii. p. 481.

XXXI. A. Schneider, Untersuchungen tiber Plathelminthen, Giessen, 1873.
XXXII. M. ScHULTZE, Beitrage zur Naturgeschichte der Turbellarien, Greifswald, 1851.
XXXIII. E- VON WiLLEMOES SuHM, On a Land-Nemertean found in the Bermudas, Ann. and Mag. Nat.
Hist., ser. 4, vol. xiii. p. 409.

INDEX.

INTRODUCTION, ....

I. DESCRIPTION OF THE SPECIES AND GENERA,

A. PALiEONEMBRTEA

Carinina grata, ....
Eiqwlia delineata,

„ giardii, .

„ australis,

„ ni]}])onensis,

B. HOPLONEMBRTEA

Drepanophorits ruhrostriattm,
„ serraticollis,

„ lankesteri,

Amphiporus moseleyi,
„ marioni,

Tetrastemma agricola,
„ fuscum,

Pelagonemertes rollestoni,

C. SCHIZONEMERTEA

Gerehratulus truncatvs,
medtdlafus,
longifissus,
eomigatus,
parkeri,
angusticeps,
maciwen,
sp. inc.,
List of Stations at which Nemertea were obtained,

II. anatomy-
Integument, .....
Muscular System, Connective Tissue, &c..
Nervous System,

Sense-Organs, AccEssoRy Glandular Structures,
Proboscis and Proboscidian Sheath,
Digestive Apparatus,
Nephridial and Blood- Vascular System,
Generative Organs,

III. GENERAL CONSIDERATIONS,

LIST OF AUTHORS REFERRED TO IN THE TEXT,

, and Organs of Unknown Significance

1
5

•5
11
11
13
14

15
17
18
20
22
23
25
25

37
39
40
41
43
44
46
47
50

53

62

73

90

98

107

112

117

121

149

PLATE I.

(ZOOL. CHALL. EXP. PART LIV. 1887.) Hhh.

PLATE I.

Fig. 1. Carinina grata, n. gen. et sp. A ventral view of one specimen. Terminal proboscidian opening visible, as well
as the terminal ciliated groove, the lateral ciliated groove and the ventral mouth, x about Si.

Fig. 2. CanuiiM grata, n. gen. et sp. A side view of same specimen, showing the terminal ciliated groove, the lateral
ciliated groove and the ventral mouth, x about 3J.

Fig. 3. Carinina grata, n. gen. et sp. A ventral view of another specimen, showing the terminal proboscidian opening,
and the terminal ciliated groove. x about 3J.

Figs. 4, 5. Eupolia nippmiensis, n. sp. Right and left lateral view of one of the specimens. Natural .size.

Fig. 6. Eupolia auslralis, n. sp. Venti'al view of the head. The mouth is very small, the surface transversely wriukled.
X 4.

Fig. 7. Eupolia giardii, n. sp. Tip of liead, viewed from above, x 2.

Fig. 8. Eupolia giardii, n. sp. Dorsal view of the head, x 2.

Fig. 9. Eupolia giardii, n. sp. Ventral view of the head, x 2.

Fig. 10. Eupolia nippmiensis, n. sp. Another specimen, seen from below. The mouth is very small.

Fig. 11. Cerebratulus truncatus, n. sp. Side view, x 4.

Fig. 12. Ccrcbratulics truncatus, n. sp. Another specimen, ventral view of tip of head, x 8.

Fig. 13. Cerebratultis macrorcn, n. sp. Ventral view of tip of head of New Zealand specimen, x 15.

Fig. 14. Cerebratulus macrorcn, n. sp. Lateral view of do. do. do. x 15.

Fig. 15. Cerebratulus angnsticeps, n. sp. Lateral view of the anterior portion of the lacerated specimen (.1100 fathoms).
Part of the proboscis protrudes through a rupture in the body wall, x li.

Fig. 16. Cerebrattilus longifissu^, n. sp. Lateral view. Natural size.

Fig. 17. Cerebratulus corrugatus, n. sp. Lateral view of a young specimen, x 2.

Fig. 18. Cerebratulus macrorcn, u. sp. Ventral view of the Japanese specimen. Natural size.

Fig. 19. Cerebratulus macrorcn, n. sp. Lateral view of do. do. do.

Fig. 20. Amphiporus moseleyi, n. sp. One of the specimens, seen in perspective. Natural size.

Fig. 21. Amphiporus moseleyi, n. sp. Anterior part, showing cephalic groove and subterminal opening (indicated by a
cross fold) which leads into the proboscis and the intestine. Natural size.

Fig. 22. DrepanopTionis lankcsteri, n. sp. Dorsal view. Natural size.

Figs. 23-31. Pelagonemertes rollestoni, H. N. M., after Moseley, who explains the figures as follows : —

Fig. 23. " Pelagoneinertes Rollestoni, enlarged, %iewed from the dorsal surface ; the proboscis is partly extruded ;
Pr.S., sac of proboscis ; IP., invagmated portion of proboscis within the proboscis sac : G, superior
nerve ganglion ; N.C., nerve cords ; T', vascular tnuik (the upper F points to an enlargement of the
vessel l>'iug .iust posteriorly to the superior nerve ganglion) ; J, intestine ; D, diverticula of intestine ;
A, anus ; 00, ovaries ; CJJ, circular muscles ; LM, longitudinal muscles.

Fig. 24. "' Pelar/07iemertes Rollestoni, from the ventrnl surface, x 2 diameters. 1, Mouth, with oasophagus ; 2, partly
protruded proboscis ; 3, nerve ganglia ; 4, nerve-cords ; 5, ovaries ; 6, digestive canal. The sheath of
the proboscis is seen through the body lying behind the digestive canal.

Fig. 25. " Sketch of the proboscis-sheath and contained retracted proboscis, from the dorsal aspect. Retractor
muscles inserted into the commencement of the sheath.

Fig. 26. "1, One of the polygonal areas, enlarged, showing the ^vrinkles of integument producing tlie appearance.
2, Peculiar appearance of some of the folds of the integument.

Fig. 27. " Reticular appearance of the integument observed in certain parts of the body. Natural size.

Fig. 28. "a, Groups of brightly coloured fatty globules forming the contents of the diverticula of the intestine;
6, portion of the vascular trmik, much enlarged.

Fig. 29. " Portion of the invagmated proboscis, much enlarged, a, External gelatinous layer ; b, interna] muscular
layer ; c, cavity continuous with that of the proboscis-sac ; within these the invaginated portion of the
proboscis with the layers reversed ; b, internal muscular layer ; a, e.xtemal gelatinous layer^ ; d, central
tube filled with dark amoi-phous matter (from the proboscis-sac ?).

Fig. 30. "The nervous ganglia and ring, much enlarged. A , Superior ganglion ; B, inferior ganglion.

Fig. 31. " One of the ovaries, enlarged. The dark irregular line on the centre represents what is probably an aperture
for the discharge of ova."

' This figure has been incorrectly lettered by tlie lithographer, a,b,c fm-thest to the right should be c,h,a.

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PLATE II.

PLATE 11.

J. Integument.

M. Musculature.

hi. Blood-.sjiace.

aPr. Kliynchodseum.

PiK Proboscidian opening.

Ps. Proboscidian sheath-cavity.

Pr, Proboscis.

D. Intestinal cavity.

C Brain-lohes.

Comm. Inferior brain commissure.

N. Lateral nerve-trunks.

Im, an. Musculature of the proboscis.

ie. Epithelium of do.

P. N. Nerve-stem.s of do.

Figs. 1-7. Cariiiina grata, n. gen. et sp. Transverse sections and parts of sections of one of the specimens in which the
proboscis vpas protruded and ejected from the body — drawn with the camera. The integument and what
pertains to it is tinted light sepia, the nervous system yellowish, the muscular investment of the body red,
the intestinal epithelium grey.

Fig. 1 . Section through the tip of the head and the anterior point of meeting (bl) of the two lateral blood-spaces.
The terminal furrow at the tip of the head (cf. PI. I. figs. 1, 3) has been touched in the left lower
corner of the section.

Fig. 2. Section somewhat further back in which the blood-space show.s a right and a left portion, and in which the
anterior wall of the rhynchod^um (cf. fig. 8, aPr) has been touched, the first indication of the opening
through which the proboscis is thrust forward being also visible in this section.

Fig. 3. Section through the brain thickenings (cc), the ventral commissure and the prsestomial blind portion of the
oesophagus.

Fig. 4. Section through the mouth region. To the left the blood-space ajipears to be locally subdivided by radial
strands of tissue.

Fig. S. Section through the ffisophageal region. The layer of longitudinal and imier ch-cular muscle fibres are
separated by a thin black line. The blood-spaces are more or less enclosed in the latter layer.

Figs. 6, 7. Two sections, still further back, of the inner circular muscular layer and what is encompassed by it.
These sections show the change m shape which both the proboscidian sheath-cavity and the blood-
spaces undergo in different portions of the body.

Fig. 8. Cariiiina grata, n. gen. et sp. A horizontal section through the head, brain-lobes and proboscidian insertion of
the second specimen, in which the proboscis had remained attached and inverted (t/. PI. III. fig. 4).

Fig. 9. Carinina grata, n. gen. et sp. Section further backwards {cf. fig. 3).
and the following are no longer horizontal but transverse).

(The specimen being curved this section

Fig, 10. Carinina grata, n. gen. et sp. Section further backwards still (cf. fig. 5).

Figs. 9 and 10, when compared vrith figs. 3 and 5, give an idea of the change effected upon the body musculature
by the inversion and eversion of the proboscis. Some latitude must, however, be left for the fact of the
specimens being different.

Figs. 1], 12. Carinina grata, n. gen. et sp. Two transverse sections through the proboscis, with the external thin homo-
geneous layer enclosing the outer longitudinal (brown) and inner circular (red) muscular layer. Inside the
latter is the proboscidian epithelium. The two strong nerves of the proboscis are still enclosed in this
epit^ielium, as are the nerve- trunks of the body in the integument.

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PLATE III.

(ZOOL. CHALL. EXP. PART LIV. 1887.) — Hllll.

PLATE III.

Fig. 1. Carinina grata, n. gen. et sp. Longitudinal section through a loop of the proboscis. In the
upper section the proboscidian epithelium {Pe) is much more columnar, in the lower one
it is thrown into folds and much more loosely applied against the musculature.

Fig. 2. Carinina grata, n. gen. et sp. A part of the last mentioned region, more considerably enlarged.

Fig. 3. Cariniim grata, n. gen. et sp. A longitudinal section through the body-wall. Cm, the inner
circular muscular layer (8 of PI. XI.); LM, the longitudinal muscles (a of PI. XI.); ec, the
outer ^circular muscular layer (/J of PL XL); B, the homogeneous basement membrane ; Nl,
the deepest layer of the integument, with plexiform nerve tissue (the lithographer has given
too stellate an appearance to these histological elements); Gi, the deeper glandular stratum ;
E, the outer stratum of the integument.

Fig. 4. Carinina grata, n. gen. et s,\). The same, in a region where the gland-cells of the glandular
stratum are all considerably reduced and the basement membrane contracted into waves.
The nervous plexus is not indicated in tliis figure. Lettering as in fig. 3.

Fig. 5. Carinina grata, n. gen. et sp. A horizontal section through the point of insertion of the pro-
boscis in the head. The cellular integument is coloured red. M, the musculature, chiefly
longitudinal, from which fibres emerge to pass backwards into the musculatui'e of the proboscis,
the epithelium of which is marked Pe. Other radial fibres attach the rhynchodeeuni in the
head, the cellular coating of which {APe) is thicker and more vacuolated than that of the pro-
boscis. Bl (upper), blood-space in the head ; Bl (lower), space of proboscidian sheath ; rf,
cephalic furrow.

Fig. 6. Carinina grata, n. gen. et sp. More enlarged figure of a transverse section of the body-muscu-
lature. Lettering as in fig. 3. Moreover, d, hyaline gelatinous tissue between the muscidar
bundles, carrying nuclei. Other nuclei are detected in the centre of the muscle bundles.
To the left of the layer Cm there is a faint iudication of what is possibly a second internal
layer of plexiform nerve-tissue.

Fig. 7. Carinina grata, n. gen. et sp. Enlarged figure of a transverse section of the lateral nerve-stem.
Nst, the fibrous core with sparse nuclei ; Nge, the cellular investment of the stem, continued
into Nl, the nerve plexus, all three stiU forming part of the deeper layers of the integument,
which by the basement layer B (not passing over the nerve-stem) is separated from the
subjacent muscular layers (ec); (H, the deeper gland-cells of the integument. The nerve-trunk
is attached by fibres' binding it down to the muscular layers.

Fig. 8. Carinina grata, n. gen. et sp. The same in tangential section. Lettering as in the preceding figure.
The attaching fibres are seen to be not continuous but arranged in closely set bundles. The
integumentary gland-cells show different colours in the left and in the right half of the
section ; in the intervening region they are not developed ; this would thus correspond to
such a region as is represented in fig. 4 in longitudinal section.

The Voyage of H M S Challen-^er"

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PLATE IV.

PLATE IV.

The basement membrane and the nephridial apparatus are on this plate indicated by a red tint.

Fig. 1 . Carinina grata, n. gen. et sp. A longitudinal section through the body-wall at the point where
the terminal dnct of the nephridia {Nc) pierces it. LJ/and ec, muscular layers (see PL III.
figs. 3, 4); J5,basement membrane; E, cellular integument, with superficial and deeper
gland-ceUs, separated by a layer of closely contiguous nuclei that belong to extremely
elongated cells, placed perpendicularly to the surface.

Fig 2. Carinina grata, n. gen. et sp. Section through a region where the nephridial canal {Nc) is still
enclosed in the blood-space {Bs) in which a distinct cellular coating is observable, and
which is separated from the intestinal caeca (Jc) by the inner circular muscular layer (cf..
Cm, figs. .5, 6); LM, the outer longitudinal muscular layer.

Fig. 3. Carinina grata, n. gen. et sp. A longitudinal section through the iL'sophagus (Oe). Jc, its ciliated
epithelium directly applied upon the muscular layers Cm, LM, and ec (see PI. III. fig. 3);
PSW, the proboscidian sheath-wall, very thin, with the oesophageal epithelium below
and its own nuclei above it. This fibrous wall is confluent superiorly with the layer of
circular muscles Cm (cf. PI. II. figs. 5, 9, 10).

Fig. 4. Carimna grata, n. gen. et sp. Section through the spongy and canalicular part of the uephi-idium
{N's^i), and the region where it communicates with the principal nephridial duct N'c ; Be, Jr,
LM, and Cm, as in the preceding figures.

Figs. 5, 6. Carinina grata, n. gen. et sp. Transverse sections of the same system. The nephridia he in
the blood-spaces {Bs) which have their own cellular coating, and are partly enclosed in the
circular muscular layer Cm. Ps and Oe indicate the respective situation of proboscidian
sheath and a?sophagus in relation to the nephridia ; JVsji and Nc as in fig. 4.

Fig. 7. Carinina grata, n. gen. et sp. A portion of the oesophageal epithelium under higher power. Je,
the granular epithelium cells ; c, the cuticula with the cilia.

The Voyage of RMS. Challenger"

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CARI NINA

PLATE V.

(ZOOL. CHALL. EXP. — PART LIV. — 1887.) — Hhll.

PLATE V.

dcm, Dorsarcoinniissure.
vcM, Ventral commissui'e.
.Si, Superior lobe separated into two
lappets by a sulcus.

PL, Posterior lobe.

cc, 'Ciliated canal to the exterior.
i»V, Lateral nerve-stem, with fibrous core
and cellular coating.

i«j, Innervation for the respiratory part

of the oesophagus (n. vagus).
pn. Innervation for the proboscis.
an. Cephalic nerves.

Figs. 1-9. Eupolia giardii, n. sp. Reconstructions of the brain-lobes from a series of sectiona

Figs 1, 2, 3, i, 8 represent the outward aspect, viewed from different sides.

Figs. 5, 6, 7, 9 represent the fibrous core ; the extension of the ganglion cells enclosing this core being

indicated by faint outlines.
Figs. 1, 5. Seen from above.
Figs. 2, 6. Seen from below.
Figs. 4, 7. Seen laterally and outwardly.
Fig. 3. Seen from behind.
Figs. 8, 9. Seen laterally and inwardly (after section of the commissui-e and removal of the left half).

In figs. 5 and 6 the course of the ciliated canal is specially indicated ; in the former figure

by a red outline.

The Voyao^e oF HMS Challeno^pr'

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PLATE VI.

PLATE VI.

Fig. 1. Carinina grata, n. gen. et sp. The brain as situated in the deeper strata of the integument,
seen in horizontal section (cf. woodcut fig. 5, p. 81). Br, Br, the anterior and the posterior
brain-lobes. The inner fibrous core of these lobes white ; in the anterior lobe traversed by
radial fibres, in the posterior one containing the ciliated canal cc, that opens out in fig. 2 into
the cephalic groove Cg ; Ngc, the nerve-cells of the brain-lobes (stretching outwards as far as
the red tint is applied in the hgui'e); gl.br, glandular cells connected with them ; E, the
outer layer of the integument ; Gi, the deeper one with gland-cells ; ec and LM, muscular
layers ; hs, blood-lacuna between the resophagus and the muscular bod,y-wall ; Oe, lumen,
le, epithelium of Oi^sophagus ; Nv, branches of the so-called vagus nerve.

Figs. 2, 3. Carinina grata, n. gen. et sp. The posterior brain-lobe in following and preceding sections.
Lettering as in fig. 1.

In all these three figures a marked increase of the nuclei in the immediate vicinity of the
cephalic groove is particularly distinct.

Figs. 4-8. Eupolia giardii, n. sp. Transverse sections through different parts of the brain. Com-
pare the figures on PI. V. The fibrous core white, the nerve-cellular coating light red.

Fig. 4. Section througli the lower commissure, just in front of the upper commissure. Pr, proboscis, the
innervation of which, proceeding from the two brain-lobes, is noticed in this section (cf. PI. V.
fig.s. 5, 9).

Fig. 5. Section through both commissures, i.e., a few sections fiu'ther back.

Fig. 6. A few sections still further back, through the point of oiigin of the vagus nerve (Nv). Prs,
anterior terminal portion of the proboscidian sheath.

Fig. 7. Section through superior, inferior and posterior lobe ; the latter coated by the granular glandular
cells gl.br, and with the ciliated canal a:

Fig. 8. In the superior lobe the fibrous core has again subdivided, giving off an uppermost stem, the
centre of the outwardly visible superior gjTUS (tf. PI. V. figs. 5, 7).

Fig. 9. Eupolia giardii, n. sp. Part of a transverse section through the oesophageal region.
an and Ihn, the circular and inner longitudinal muscular layer (/8 and a of PL XI. fig. 12);
PI, the nerve plexus just outside the former ; iV.s/, the lateral nerve-stem in this plexus ;
P;-.s, the proboscidian sheath with very thin walls ; dv, the dorsal blood-vessel, situated, as
are a dozen of circuma?sophageal lacunar spaces (that communicate with each other), in the
gelatinous tissue between body-wall and intestinal wall. Oe, the lumen of the oesophagus ;
le, its ciliated epithelium ; oe.m, its longitudinal and circular musculature ; nep, nephridian
tubes. The thin longitudinal nerve-stem above the proboscidian sheath has been omitted
in this figure.

Fig. 10. EapiMa giardii, n. sp. A transverse section of the dorso-median portion of the body- wall
at the furthest end of the body. cm, ilm, Prs, as in fig. 9. olm, outer longitudinal
muscular layer (y, PI. XL); Bd, the much folded primary basement layer ; ;/, the deeper
glandular layer of the integument ; ef, the longitudinal and circular fibres of the same ;
E, the outer layer of the integument {cf. PL VII. fig. 5 and PL X. fig. 6) ; hv, dorsal
blood-vesseL

Fig. 11. Eupolia giardii, n. sp. Transverse section through the posterior part of the proboscis,
with internal epithelium (Pre), longitudinal muscle-fibres {Lni), and external flattened epi-
thelium (e).

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CARININA EUPOLIA

PLATE VII.

(ZOOL. CHAt.r,. EXP. — PART LIV. — 1887.) — Hbh.

PLATE VII.

Fig. 1. Eupolia australis, n. sp. Diagram of a section through the posterior part of the cesophageal
region. Ps, proboscidian sheath with underlying dorsal lalood-vessel ; hs, lateral blood-
spaces, continued backwards, but not much further than the cesophageal region ; hv, ventral
blood-vessels; Oe, cavity of the cesophagus; Nsf, lateral nerve-stems ; JE, outer integumentary
layer.

Fig. 2. Eupolia australis, n. sp. Section of the body-wall about in the same region as the diagram of
fig. 1, and in the vicinity of the left ventral blood-vessel. E, outer epithelial layer with
unicellular glands ; B, its (secondary) basement membrane ; ef, scattered longitudinal and
circular fibres beneath this ; gi, subepithelial glandular layer ; olm, outer longitudinal
muscles, as yet very far from being a compact layer ; cm, cu'cular muscular layer ; ilm, inner
layer of longitudinal muscles ; ct, cellular coating of the circumcesophageal blood-space.
(Between ohn and gi the reference letter Bd, indicating the primary basement tissue
{cf. figs. 3, 5), should be inserted.

Fig. 3. Eupolia australis, n. sp. Section of body-wall of the same specimen, very much further back.
Lettering as in fig. 2. INIoreover, Bet, fibrous connective tissue (primary basement
membrane) between gi and ohn; Je, epithelium of the intestine ; br, left ventral blood-
vessel. The outer longitudinal muscular layer is thinner, but at the same time much more
compact than it was in the section of fig. 2. The blood-vessel and its surroundings, as well
as the intestinal epithelium, are only represented diagrammatically.

Fig. 4. Eupolia giardii, n. sp. A transverse section through the dorso-median (meduUary) nerve-
stem (dmN). The nerve-fibres are transversely cut ; the nuclei are distinct. Nl., the
nervous layer, continuous with the median stem ; olvi, outer longitudinal muscular layer
with a considerable amount of gelatinous connective tissue {cf) between the separate
bundles.

Fig. 5. Eupolia giardii, n. sp. Portion of a transverse section through the body-wall {cf. PL VI.
fig. 9). Only a small portion of the very thick circular muscular layer cm is here represented.
Lettering as in figs. 2 and 3. Nsf, longitudinal nerve-stem ; Nep, two radial ducts of the
nephridia leading outwards, one of them opening to the exterior at ne.o. The outer
longitudinal muscular layer is far from compact, the secretion of the sub-epithelial glands
gi can be traced piercing the layers, ef., B and E.

Fig. 6. Eupolia nipponejisis, n. sp. The outer ciliated epithelium {E) and unicellular glands (" Schleini-
stiibchenzellen ") secreting their product {u.g) to the exterior, supported by the basement
membrane B.

Fig. 7. EujMlia australis, n. sp. Longitudinal section in the posterior region of the body-waU, to show
the generative ducts {gd) leading from the generative sacs {gon) outwards and piercing the
muscular layers {ilm and cm) above the nerve-stem {Nsf).

Fig. 8. Eupolia giardii, n. sp. The sub-anal nervous commissures in a horizontal section. J, cavity
of intestine ; Je, epithelium of the same ; xV, N', the right and left longitudinal nerve-stem
communicating by the transverse commissure ; E, external epitheUum.

Fig. 9. Eupolia delineata, n. sp. Longitudinal section through the body-wall. Lettering as in figs. 2
and 3. efp, the external longitudinal and circular fibres that belong to the integument and
have the pigment between them.

Fig. 10. Eupolia delineata, n. sp. Section of the proboscidian sheath. Ps, the cavity of the sheath
lined by cells which are again encircled by a very attenuated circular layer ; bl, blood-spaces
outside of the proboscidian sheath ; cts, strings of connective tissue by which the proboscidian
sheath is suspended to the body-wall.

Fig. 11. Eupulia nipponensis, n. sp. Transverse section through the nervous layer {Nl). Nuclei are
found imbedded in the nerve-substance and fibrous nerve strings stretch out from it radially
at different points, ohn and cm, the muscular layers.

Fig. 12. Eupolia nipponensis, n. sp. The cesophageal wall, in transverse section, cm. and 27?;?, mu.s-
cular layers of body-wall ; hs, blood-scace inside of these. The wall of the cesophagus is
constituted of an inner ciliated epithelium Je, a basement layer B, and a thick layer of
glandular cells Jm.

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PLATE VIII.

PLATE VIII.

Figs. 1, 2. Pferosoma jilana, Less. After Lesson, supposed by Moseley to represent a species of Pe]a;/o-
nemertes.

Fig. 1. Seen from above.
Fig. 2. Seen from below.

Fig. 3. Pelagonemertes roUestoni, H. N. M. A transverse section, supposed to be not quite vertical to
the longitudinal body axis, so that to the right one of the digestive, to the left one of the
generative c»oa was touched in the section. £p, external epithelial layer ; B, basement
membrane; LM, layer of longitudinal muscles; J, intestine audits branching diverticula;
N, longitudinal nerve-stem ; b/, two lateral blood-vessels ; Gr, external opening of the
generative csecum ; P.S.C, the cavity of the proboscidian .sheath; Ps, the wall of that
cavity. All the internal organs are surrounded by and imbedded in a wholly continuous
gelatinous ground substance, in which a few cells and numerous fibres can be detected,
and which has more strongly imbibed the staining reagent in the immediate vicinity of
the different organs and tissues that traverse it.

Fig. 4. Pelar/onevierfes roUesfvni, H. N. M. A horizontal aspect of the muscular layers of the body-
wall, from a preparation made of the fresh animal by Professor Moseley. /»?, the
longitudinal muscles ; cm, the sparse circular muscular fibres, external to the foregoing ;
rh; granular patches, eventually glandular structures ; cf, the gelatinous connective ti.ssue
visible between the muscle fibres.

Fig. 5. Pelagonemertes rollestoni, H. N. M. A transverse section of what most probably corresponds
to one of the granular patches of fig. 4, furnishing arguments for looking upon the latter
as glandular. A central lumen (or fibre V), with nuclei surrounding it can be detected.

Fig. 6. Pelagonemeiiee rollestoni, H. N. M. The longitudinal nerve-stem N, in transverse section.
A branch n gives off smaller nerve-twigs n' and 7i". Nuclei are imbedded in the fibrous
nerve substance. The gelatinous connective tissue is more deeply stained all round, and
at ff has a distinctly fibrous appearance.

Fig. 7. Pelagonemertes rollestoni, H. N. M. The posterior region of the proboscis, in transverse
section. //, the longitudinal muscular fibres, externally invested by a basement mem-
brane ; E, the epithelium, of which no details could be made out.

Fig. 8. Pelagonemertes rollestoni, H. N. M. An empty genital caecum, in transverse section. In
the lower narrower part the epithelium is high and very distinct and a couple of epi-
thelium-cells are becoming converted into ova, ov. N, the nerve-stem; hi, the blood-
vessel ; Gc, the empty cavity ; etc, connective tissue cells in the gelatinous ground-
substance ; /, fibrous tracks in the same.

Fig. 9. Pelagonemertes rollestoni, H. N. jM. Isolated transversely striated cells from the wall of the
cavity, Gc, in fig. 8.

Fig. 10. Pelagonemertes rollestoni, H. N. M. A young ovum.

Fig. 11. Pdagonemeiies roUestoni, H. N. M. A larger ovum, surrounded by its follicle cells {cf.
tig. 3). No distinct nucleolus, but numerous chromatic granules inside the nucleus.

Fig. 1 2. Pelagonemertes rollestoni, H. N. M. Portion of the proboscidian sheath, in transverse section,
under higher power. B, the inner homogeneous limiting membrane ; tm, longitudinal ;
rm, circular muscular layer ; ct, the outer sheet of the gelatinous tissue immediately
applied against the muscles and again more deeply stained.

Fig. 13. Pelagonemertes rollestoni, H. N. M. Portion of the outer layers of the body-waU, under still
higher power. The external cellular epithelium has not been represented. B, the thick
basement membrane, below this epithelium, traversed radially by apparent glandular ducts
{cf. tigs. 4, 5); B', a deeper portion of the same, less affected by the staining solution, and
carrying connective tissue cells ; cm, isolated circular, LM, thicker bundles of longitu-
dinal muscular tibres ; dr, probable glandular ducts in the gelatinous ground-substance
penetrating through the muscles to the exterior.

The Voyage of H,M, S."Cliallenger"

Nemerlea Pl.VIII.

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PELAGONEMERTES

PLATE IX.

(ZOOL. CHALL. EXP. P4RT HV. 1887.) Hllh.

PLATE IX.

J+B. Integument and basement membrane.
M. Body musculature.
Ot. Gelatinous tissue.
Prs. Proboscidian theath.
LN. Lateral nerve-stem.

Int. Intestine.

Os. Genital sacs, in many cases not yet in open com-
munication with the exterior.
Prs.div. Lateral diverticula of proboscidian sheath.
br. Blood-vessel.

Figs. 1-6. Diagrams of different Hoploiiemertea to elucidate (1) the relative extent of integument,
muscular body-wall and internal gelatinous tissue; (2) the situation of the genital gland.s
and their respective openings to the exterior.

Fig. 1. Dr<"panoplwrus Icmlienferi, n. sp. Middle of the body, diverticula of proboscidian
sheath included in the section.

Fig. 2. Drejmnojjhonis lanJiesferi, n. sp. Towards the extremity of the tail, between two
pairs of diverticula of the proboscidian sheath.

Fig. 3. Ainphiporus marioni, n. sp.

Fig. 4. Aniphiporus moseleyi, n. sp. Numerous genital sacs, both dorsal and ventral,
contained in one transverse section.

Fig. 5. Drepanophorus serraticollis, Hubr.

Fig. 6. Drppano]jhorus geiTaficoUis, Hubr. In a further advanced stage of ripeness of
the genital products (with distinct genital openings to the exterior); the diver-
ticula of the probo.'^cidian sheath not touched in this section. In all these
sections the longitudinal blood-vessels are indicated, the median one below the
proboscidian sheath, the lateral ones close to the lateral nerve-stems. In
Aniphiporus inoseleyi the lateral nerve-stems are seen to lie above, in Drepano-
phoru-% heloie the intestinal cjeca.

Fig. 7. Ampihiporus moseleyi, n. sp. Diagram of a horizontal section through the body. The
intestine and its cseca are dark grey, the generative cfeca light grey. The latter are
seen to be very numerous and in no way regularly or metamerically arranged.

Fig. 8. Amphiparus moseleyi, n. sp. A specimen with flattened ventral surface. Natural size. A
whitish line from the tip of the snout backwards along the lateral margin marks the exterior
openings of the lateral glands (c/. PI. XV. figs. 11, 12).

Fig. 9. Amphipm-us moseleyi, n. sp. Head, seen from below. Longitudinal slit both for the
intestine and the proboscis ; terminal transverse sensory groove and lateral bent grooves
into which the cavity of the posterior brain lobe opens.

Fig. 10. Drepanoj)hortis lanliesteri, n. sjj. Diagram of the principal features of the nervous system.
B, brain-lobes; p.Br, posterior brain-lobes (side organs) with their cavity opening to the
exterior at e.o ; Ceplx.ne, numerous cephalic nerves to the tip of the head, the eyes, &c.,
only a few of them are here indicated in outline ; Prn, nerves for innervation of the pro-
boscis (they are more numerous than is here indicated); Va, outline of vagus nerve
springing from the lower brain-lolies and running forwards towards the resophagus. The
latter passes beneath the brain-lobes and their double commissure, but above the ladder
commissures (Comvi), which metamerically unite the longitudinal nerve-stems {LN) below
the intestine ; jie.ne, peripheral nerves springing from these nerve-stems.

Fig 11. AmpMpioriis ■tnoseleyi, n. sp. Stylet and accessory darts. A and //, V, the central stylet and
its two accessory sacs, in position ; //', bases of two accessory darts, viewed laterally (figure
to the left), and per.'ipectively (figure to the right).

The Voyage of H MS "Challenger

Nemertea PI IX.

Comjth.

HubrEcht i\ de Groot df.

FHuth,Lith'Eam^

AMPHIPORUS. DREPANOPHORUS,

PLATE X.

PLATE X.

Fig. 1. Ampliiporus marioni, n. sp. Part of a transverse section through the oesophageal region, indi-
cating the relative importance of the musonlature with respect to the integument and the
gelatinous tissue. Frs, proboscidian sheath in contracted state, the outline only partly
worked up to show the interlacement of muscular fibres, the basement layer and the internal
epithelium ; <ht, dorsal blood-vessel surrounded by gelatinous tissue, as is the proboscidian
sheath, and Ofi, the oesophagus with its cellular epithelium. Outside of this there is a layer
of dark'er fusiform bodies, which are most probably unicellular parasitic organisms. Gt, the
gelatinous tissue ; a, the longitudinal, /3, the circular muscular coat ; at ne, a bundle of nerve-
fibres spreads between a and (3 after having traversed the musculature between two of the
larger bundles of a ; B, thick basement membrane with only a few nuclei ; J, integument ;
LN', longitudinal nerve : Nep, nephridial tubules ; Nep.d, part of the communicating duct
of the nephridia with the exterior ; inc, peculiar crystalloid inclosures of a greenish colour,
irregularly distributed in the gelatinous tissue.

Fig. 2. DrepanojiJiontslankesteri,n.sp. Part of a section through the tail end. /, the integument, with
an outer layer of sense-cells and supjjorting cells ; granular glands leading to the exterior, a
layer of nuclei and one of deep lying cells with fainter nuclei ; B, basement membrane with
imbedded nuclei ; a, the longitudinal, f3, the circular muscular layer ; Gt, the gelatinous
tissue with nuclei and cells inclosed, certain of these being on their way of transformation
into fibres ; LN, longitudinal nerve-stem.

Fig. 3. Am.phiponcs moseleyi, n. sp. Horizontal section through the tip of the snout. Pr, proboscis
and its musculature passing into and being the direct continuation of a, the longitudinal
muscular layer ; Prs, the proboscidian .sheath: Sp.Pr, muscular arrangement in the wall of
the rhynchodfeuni constituting a sphincter ; Bk, external opening of the rhynchodaeum, which
is internally clothed by a layer of cells very gradually passing into the proboscidian epithelium,
and externally into J. the integument ; B, basement membrane ; yS, circular muscidar layer,
obliquely cut ; Gt, gelatinous tissue ; Br, Br', left and right brain-lobes ; B, eyes ; gh, lateral
glands, continued along both sides of the animal (cf. PI. XV. figs. 11, 12).

Fig. 4. Drepanophorus lankesteri, n. sp. Proboscidian sheath with diverticula (div.Prs). Prs.ep, epi-
thelium of the sheath, separated by folded basement tissue from the muscular wall.

Fig. .5. Drepanophorus serraficollis, Hubr. Proboscidian sheath with thicker muscular walls and thinner
walled diverticula (dh: Pr.i.).

Fig. 6. Eupolia giardii, n. sp. The boundary line between integument and body musculature. Jdvl,
deeper layer of vacuolated cells of the integument ; B, reduced and folded primary basement
membrane; y.vl, outer longitudinal muscular layer with large vacuolated cells and rare muscle
fibres. The vacuolated cells have larger nuclei than those of the integument {cf. PI. VII.
fig. 5).

Fig. 7. Cerebratul us sp. inc. (medtdlai us ?). Transverse section of medio-dorsal region. J, integument;
b, secondary basement membrane ; y, outer, a, inner longitudinal, fi, circular muscular layer ;
Prs.p.p, epithelium of the proboscidian sheath ; PrsN, longitudinal nerve of proboscidian
sheath ; ne, nervous layer with median medullary thickening.

Figs. 8, 9. Cerehratulus macroren, n. sp. The proboscidian sheath wall and intestinal epithelium wholly
(fig. 9) and half (fig. 8) di.stended by the proboscis, dv, dorsal blood-vessel (in fig. 8 still
within the proboscidian sheath cavity); Prs.ep, the epithelium of the proboscidian sheath,
supported by a homogeneous membrane, h, and surrounded by muscular layers m.Prs. Or.ep,
epithelium of the oesophagus.

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A IVl P H 1 PO RU S . D REPANOPH 0 R U S. EUPOLIA. C E R E B R A T U L U S.

PLATE XT.

(ZOOL. CHALL. EXP. PART LIV. 1887.) lihll.

PLATE XL

Diagrammatic figures to illustrate the situatiou of the dorso-median medullary nerve, and at the same
time the arrangement of the different layers of the body-wall and their respective relation as to size, &c.

The twelve upper figures are supposed to be taken as transverse sections just above the proboscidian
sheath, and are on purpose all reduced to the same scale, by which process the relative importance
of the integumentary layer is clearly brought out.

The corresponding muscular layers are indicated by the same Greek letters — a is the most important
longitudinal one, common to all ; ji, the circular ; y, the outer longitudinal ; 8 is a circular muscular
layer characteristic of the Carinellidse (figs. 1, 2, .3, 6, 13, and 14); it here forms the dorsal wall of the
proboscidian sheath and at the same time it forms part of the body-wall in the anterior part of the
body ; in all the others it has become detached and has possibly developed into the outer wall of the
proboscidian sheath, and as such is not indicated in figs. 5, 7-1 2. J, stands for the integument ; B, for
the primary basement membrane separating this from the muscles ; b, for the secondary basement layer.

The plexus and medullary nerve are indicated by a yellow tint.

Fig. 1. Carinina grata, n. sp.

Fig. 2. Carinina grata, n. sp. More posteriorly. i

Fig. 3. Carinella.

Fig. 4. Carinella. Further back in the region where the proboscidian sheath does not extend.

Fig. 5. Cej)halothrix.

Fig. 6. Carinoma armandi (M'Int.), Oud. Here the proboscidian sheath nerve lies below the
medullary nerve and is thicker than the latter.

Fig. 7. Carinoma armandi (M'Int.), Oud. Further backwards in the region where the pro-
boscidian .sheath does not extend.

Fig. 8. Amphiporus or Drepanophorun.

In figs. 9-12 the proboscidian sheath nerve is indicated and is seen to be less conspicuous than in
Caritioma.

Fig. 9. Cerehratidus corrugatus, M'Int.

Fig. 10. Cerebratulus medullatus, n. sp. The deeper glandular layer of the integument has
fused with the outer layer of longitudinal muscles, and the primary basement mem-
brane has thus disappeared.

Fig. 11. Cerehratidus macroren, n. sp.

Fig. 1 2. Eupolia giardii, n. sp.

The figs. 13-17 have reference to transverse sections of the body- wall in the region of the lateral
nerve-stem.

Fig. 13. Carinella (for Carinina, rf. PI. III. fig. 7).

Fig. 14. Carinoma armandi (M'Int.), Cud.

Fig. 15. Cephalothrix.

Fig. 16. Cerebratulus.

Fig. 17. Amphiporus.

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PLATE XII.

PLATE XII.

Fig. 1. Gerehratulus macroren, n. sp. Transverse seetioa tlirough a part of the brain-lobes of the New
Zealand specimen. The medullary nerve (m) is still in oounoction wtli the brain-lobes (hi);
prs, the proboscis, passing between the nervous ring formed by the brain-lobes and their
commissures. Superiorly two bundles of longitudinal muscle-fibres are enclosed by the
braiu-tissue.

Fig. 2. Cerebrafidtm macroren, n. sp. Transverse section of the body-wall in the region of the lateral
nerve-stem (Jajjanese specimen). a.;8.y, the three muscular layers, the latter with the deejjcr
integumentary glands embedded between the muscle-bundles (c/. PI. XL figs. 10, 11); id, the
nerve plexus ; h, the secondary basement membrane with the thin layers of integumentary
muscles just below it ; J, the cellular integument ; N, the lateral nerve-stem, into the fibrous
core of which part of the fibres of the plexus may be seen to be interwoven.

Fig. 3. Cerehratulug corrugatus, M'Int. Transverse section of the medullary nerve (»«) at a point
where a pair of transverse stems {cf. PL XIV. fig. 1) merge into it. n, these nerve-stems
(being thickened tracts in the plexus, pl)\ pf, nerve fibres radially emerging from these tracts
and having the significance of sensory or motor peripheral twigs ; fi, radial fibres (not
nervous) piercing the plexus (cf. PI. XIII. figs. 3, 4, rf).

Fig. 4. Cerehratulug forrufjaf II)!, M-'lnt. Transverse section of the medullary nerve of another specimen.
Lettering as in the foregoing figure.

Fig. .5. Drepanophorus lankesteri, n. sp. Transverse section of the lateral nerve stem (N), with two
peripheral nerves, jjf, springing from it. The fibres of the latter partly emerge from the
ganglion cells, partly from the fibrous core of the lateral stem.

Fig. 6. Drepanop'liorui>serraticollis,'iiahx. A portion of a transverse section through the proboscis. l.V,
the longitudinal muscle-fibres, in two strata, between which lies the nerve-plexus np, of
which In is one of the longitudinal thickenings (nerve-stems) ; v.c, the outer ; i.c, the inner
layer of circular filires ; /', transparent basement tissue.

Fig. 7. Cerebratulus macroren, n. .sp. Transverse section of the superior nervous connection between
the two brain-lobes (Japanese specimen). Nerve cellular elements predominate in this region
whence the medullary nerve is continued both backwards and forwards. 7d, the homcj-
geneous layer forming an investment to the nerve-tissue ; prs, the proboscidian sheath in
outline.

Fig. 8. Cerebratulus maeroreri, n. sp. A few sections fiu'ther backwai'ds. The medullary nerve m is
here more distinct, its anterior continuation m being on the point of coalescing with it.
Lettering as in fig. 7. pr, outline of the proboscis ; Br, fibrous core of the brain-lobe.

Fig. 9. Cmrhratulus medullatus, n. sp. Transverse section of the medullary nerve (m). pi, the plexus ;
/3 and a, the circular and longitudinal muscular layers ; (inner circular muscular fibres
are seen to form the outer layer of the proboscidian sheath) ; jjrn, the proboscidian sheath
nerve, receiving delicate fibres from the medullary nerve and situated just above the pro-
boscidian sheath musculature.

Fig. 10. Gerehratulus medullatus, n. sp. Integument and muscidar body wall. Lettering as in fig. 2.
'/'//, the deeper glands of the integument enclosed in the musculature.

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PLATE XIII.

Fig. 1. Cerebratulus comigafu^, M'Int. Transverse section through part of the superior brain-lobes and
dorsal brain commissure. Part of the fibrous core (h) is represented; its continuation into the
fibres of the commissure (f.co) being distinctly noticed on the left side. On the right this
connection is only visible a few sections further. The bulk of the brain-lobe is seen to con-
sist of nerve-cells of different sizes (n.cl); from these a cephalic nerve (en) is seen to emerge
on the left, whereas this cellular coating is also continued over the commissure, and there
forms the starting point (m) for the longitudinal dorso-median medullary nerve.

Fig. 2. Cerebratuhis corrwjatus, M'Int. Horizontal section of the same specimen through the medullary
nerve m. In this section only a portion of the cylindrical nerve-plexus (npJ), of which the
medullary nerve is only the median thickening, is visible. The transverse nerve-tracts tr.n,
paired and metamerical, being thicker than the plexus, are cut along a more considerable
surface and thus stand out as separate nerves. The openings in the plexus give passage
to radial, transverse, contractile fibres, as is specially indicated in fig. 4, rf.

Fig. 3. Cerebratulus corrugatiis, M'Int. Portion of a horizontal section through the ventral extension of
the nerve-plexus, n, the nerve-tissue of the plexus with nuclei of nerve-cells, and bundles
of radial fibres rf. piercing it.

Fig. i. Cereliratuhis corrui/atus, il'Int. Portion of the same section as fig. 2, more highly magnified.
/;, the tissue of the nerve-plexus with delicate fibres and distinct nuclei of nerve-ceUs, also
visible in the medullary nerve 7n ; rf, the bundles of radial, contractile fibres.

Fig. 5. Cerehratulus romigatus, M'Int. Ventral view of the head and long mouth with rugose lips of
large specimen. Natural size.

Fig. 6. Cerebrattdus ccrrrugatus, M'Int. Eadial strip out of a transverse section in the oesophageal region.
Jsg, the outer glandular layer of the integument (with " Schleimstabchenzellen "); h, the
secondary basement membrane below this ; JJcm, the longitudinal and circular muscle-fibres
peculiar to the integument ; Jdg, the deep glandular layer just below these ; B, the
primary basement membrane of the integument radially traversed by contractile fibres
(rf) and nerve-bundles (n) going towards the integument ; y, the outer longitudinal
muscles ; pi, the nerve-plexus with fibres and cells, pierced by the radial contractile
bundles rf; /3, the circular muscular layer; a, the inner longitudinal muscular layer; cos, the
circumffisopliageal intercommunicating blood-lacunse, clothed by a cellular endothelium ;
into, the cesophageal musculature ; nv, nerve-tissue in the oesophageal wall ; ^>a/), an
(Tsophageal papilla with deeper glandular and superficial ciliated cell-layers.

Figs. 7, 8. Cerebratuhis rnacroren, n. sp. Two sections through the principal nephridial duct of a
specimen from Japan. Contracted (fig. 7) and distended (fig. 8).

Fig. 9. Cerebratulus rnacroren, n. sp. Anterior tubuliferous proliferation of the nephridia. a, /3, mus-
cular layers as in fig. 6 ; Ne2), nephridian tubules applied against the ^vall of the circuin-
oesophageal blood-lacuna ; Oe, outline of resophagus wall.

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PLATE XIV.

Fig. 1. Gerehratulus angustieeps, n. .sp. The medullary nerve {m) and the transverse paired metamerical
nerve-stems {fni). Drawn with the camera. 1 mm. on the same scale is indicated on
the left of the figure.

Fig. 2. Cerebratulus cornir/atus, M'Int. Transverse section of the lateral nerve-stem (IN) and body-wall.
a, /3, y, the muscular layers ; B, the primary basement membrane, and /, the integument
in outline {cf. PI. XIII. fig. 6) ; rf, radial fibres piercing the muscular layers ; n and ]m,
nerve-tracts, of which one (p?i) is seen to emerge directly from the lateral nerve-stem and
to innervate the sensory layers of the integument ; njiJ, nerve-plexus.

Fig. ."i. Cerebratulus cornujatvs, M'Int. Diagrammatic figure of a transverse section in tlie mouth-region
to show the innervation of the resophagus and blood-lacunse. OeE, the oesophageal
epithelium; ft's, the proboscidian sheath ; ro.l, the circumcesophageal blood-lacuna. In
the nerve-plc.xus, which is indicated by a black line, m marks the medullary nerve, and
nl, the lateral nerve-stems ; vi.n, the visceral branches springing from the plexus; n.ca,
the vagus ramifications transversely cut and intermixed with the branches m.n.

Fig. 4. Cerebratulus corrugatus, M'Int. Part of the same section as fig. 3, more considerably enlarged.
Lettering as in fig. 3; ?;j:'Z, nerve-plexus ; ?/, radial, not nervous fibres ; a./3.y, the muscular
layers; c.o.l, the blood-lacunge with cellulur coating. The oesophageal epithelium (oe.E)
is not represented in its whole thickness.

Fig. .5. Cerebratulus parkeri, n. sp. Diagram, drawn with camera, of the inferior brain-lobes, Br, and
the vagus nerve (?.'«) springing from them, the two stems being united by a series of trans-
verse commissures co close to their origin. The brain-lobes merge into the lateral nerve-
stem {N) ; the ventral metameric connections of the latter are indicated by dotted lines,
v.tr.n, those of the brain-lobes being lettered e.tr.n; Oe, outline of the esophageal
epithelium.

Fig. 6. C'-rehratulua angustieeps, n. sp. Horizontal section of the left upper and posterior brain-lobes
{Br and PBr); col., rl, the free blood-lacuna between the brain, the proboscidian .sheath,
and the resophagus, the boundaries of these' two latter being only indicated by dark shading ;
a, /3, muscular layers ; In, anterior portion of lateral nerve-stem, the ganglion cells of the
cellular investment being here cut; cc, the outwardly directed portion of the ciliated
canal inside the posterior brain-lobes ; cc', re", the deeper portion of the same being cut
iu two places, because of the S-shaped curve which this canal makes inside the brain-lobe.
The relatively large size of the posterior brain-lobe, and the preponderance of fibrous
uerve-tissue in the upper lobe, are indicated in this figure.

Figs. 7, 8. Cerebratulus maeroren, n. sp. Two transverse sections (a few sections apart) through the
posterior brain-lobe and its investment of large granular glandular cells (g.d). m, the
outer membranous investment of the lobe ; 7i.cl, the ordinary ganglion cells with fibrous
core in the centre of the lobe ; '•(•, the ciliated canal with an epithelium of its own, more
distinct in fig. 8 than in fig. 7.

Fig. 9. Dre]ianophorus lankesteri, n. sp. Part of a horizontal section through the upper brain-lobe, with
interior fibrous core (p/.) and outer layer of ganglion cells, n.cl ; a few of which are much
larger {iiCl).

Fig. 1 0. DrepanopJioncs lankesteri, n. sp. Part of a horizontal section through the posterior brain-lobe.
Bm, the outer investment of the lobe ; 7i.cl, the nerve-cells ; cc, the ciliated canal with
its epithelium ; gel, the granular glandular cells ; the anterior ones pouring their contents
into the lumen of the ciliated canal.

Fig. 11: Cerebratmlus maeroren, n. sp. Part of a transverse section through the head, showing the ciliated
canal to the posterior brain-lobe in its course from that lobe {PBr) to the exterior.
gel, the granular glandul.-ir cells ; cc, the lumen of the canal, coated by an epithelium of
varied histological character as we pass outwards towards K, the externa! layer of the
integument. At gl. a sort of ring-shaped cushion of peculiar cells may be said to
embrace the canal \cf., PI. VI. figs. 1-3). Just behind this the epithelial cells are very
closely set and provided with elongated nuclei, further backwards they are seen to pass
without any sudden transition into those lining the canal, inside the brain-lobe.

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PLATE XV.

(ZOOL. CHALL. EXP. PART LtV. 1887.) Hhll.

PLATE XV.

Fig. 1. Cerebral ulii-i- lonf/ijissus, n. sp. Transverse section througli the proboscidian sheath, a, the
inner longitudinal muscular laj^er of the body wall; pr.sn, the proboscidian sheath nerve;
Pr.S, the lumen of the proboscidian sheath; e, its inner epithelial Uning; b, the homo-
geneous basement membrane of this epithelium, traversed by radial fibres and separatin.;
the aforesaid epithelium from the muscular layers (an inner longitudmal, and an outer
circular) of the proboscidian sheath ; Gi, the gelatinous tissue between the proboscidian
sheath, the intestine and the body wall ; dv, the dorsal blood-vessel.

Fig. 2. Cerebrafuhis marroren, n. sp. Transverse section of the proboscis, b, the ensheathing mem-
brane ; a and y', the two layers of longitudinal, /3', the layer of circular muscular fibres, the
latter connected crossways at two diametrically opposite points with the membrane b ; 7i.pl, the
nerve-plexus between /3' and y'; £, the very high inner epithelium with smaller (c) and
larger (C) batteries of nematocysts.

Fig. 3. Cerebraiulus macroren, n. sp. Transverse section of the proboscis much further backwards ;
the proboscis is thinner, the muscular fibres (a) only longitudinal, the epithelium (^E)
flattened, the nervous plexus replaced by two lougitudinal nerve-stems N.

Fig. 4. Cerebraiulus angusticepis, n. sp. Head, a, from below ; b, side view.

Fig. 5. Cerebraiulus parkeri, n. sp. Head, a, side view ; b, from below. x 1 i.

Fig. 6. Cerebraiulus sp. inc. Two fragments from Japan. x 2. a, dorsal view ; //, ventral view.

Fig. 7. Cerebraiulus sp. inc. Transverse section of one of the fragments of fig. 6. /, the integu-
ment ; a, /?, and y, the much reduced muscular layers ; N, the lateral nerve-stems ; Int, the
intestinal canal and cajca, suspended in the gelatinous ground tissue Ot ; Gi', the same tissue
expanded between the very sparse external fibres of the muscular layer y ; PrS, the probo.s-
cidian sheath ; bv, the blood-vessels.

Fig. 8. Cerebraiulus sp. inc. Lateral view of the head of another specimen from Japan (Kobe).

Fig. 9. Cerebraiulus loru/ijissus, n. sp. Longitudinal section of the tail end. /, the integument ;
l7ii, the intestinal epithelium ; a, /3, y, the muscular layers ; 712^1, the nerve plexus. This figure
is meant to show the general aspect of the muscular layer a, more highly magnified in fig. 10.

Fig. 10. Cerebraiulus lo7igifissus, n. sp. The muscle-fibres of the layer a are seen tojDresent a more con-
siderable diameter in successive vertical planes, forming rings round the intestine and alternating
with others in which this increase in diameter is not visible. Nuclei are also more numerous
in the former portions than in the latter ; Ep, the intestinal epithelium ; Gt, the gelatinous
tissue between this and the body musculature, with bundles of radial fibres.

Fig. 11. Am2>liiporus 7noseleyi, n. sp. Transverse .section of the lateral region with glandular cavities
(gl), arranged along the lateral line between the dorsal and ventral musculature a, piercing
the circular muscular layer fi at c, and suspended by the gelatinous tissue gt. I, integu-
ment ; B, basement membrane.

Fig. 12. A7uphiporus 7noseleiji, n. sp. One of the glandiilar caeca, more considerably magnified, with
granular epithelium and flattened nuclei exteriorly, the latter belonging to the surrounding
gelatinous tissue.

Fig. 13. Drepa7iopihorus lankesteri, n. sp. A section of similar glandiilar caeca in the dorso- median region
of the head.

Fig. 14. Amphiporus 7narioni, n. sp. A very unripe generative caecum, not yet ojjening to the exterior.
fi. Circular, a, longitudinal muscular layer. The caecum reaches down into the gelatinous
tissue, gt.

Fig. 15. Amphiporus marioni, n. sp. Ova in different stages of development.

Fig. 16. Cerebraiulus jjarkeri, n. s^i. An ovum.

Fig. 17. Dreiianophorus .ierraticollis, Hubr. An ovum.

Fig. 18. Cerebraiulus sp. inc. A batch of ova from a ripe generative cjecum of a specimen from Station

321. The ova are surrounded by a hyaline membrane (which has erroneously been dotted

by the lithographer) and pressed into polygonal shapes.
Fig. 19. Cerebraiulus marrore7i, n. sp. Part of a transverse section, in outline. Prs, The cavity of the

proboscidian sheath ; I, integument ; y, /8, the muscular layers ; N, the longitudinal nerve-slem ;

ge.c, the generative caecum ; o, its exterior opening. The duct to this opening, where it

pierces the layer y, is considerably extended in bulk.
Fig. 20. Ampjhiporiis moseleyi, n. sp. A longitudinal section through the greater part of the compressed

oesophagus Oe, and subjacent intestinal caeca (co).

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PLATE XVT.

PLATE XVI.

Tbree diagrammatic figures for the comparison of the nerve system of the l^emertea, of the Vertebrata,
and of the Cephalochorda.

Fig. 1. The chief points in the nervous system of the Nemertea. In, In', the lateral nerve-stems with
their anterior swellings, the brain-lobes, Lg. The latter are connected in front by a
strong ring-shaped commissure, the former by much thinner but unmistakable
commissures, dvr, metamerically placed both dorsally and ventrally in a continuous
plexus of nerve-tissue, that ensheathes the body. This plexus is no further indicated in
the figure. It moreover carries a longitudinal medio-dorsal nerve-tract m, which is
also continued forwards, in front of the brain commissure, with which it is connected.
Into this medullary nerve m the transverse tracts dvr converge. From the latter {sensu
strictiori from the plexus) radial nerve twigs of sensory and motor significance can be
traced both in centripetal and in centrifugal direction, but these are not indicated in the
* figure. Other similar nerve twigs, indicated by vi.sy, innervate in a similar way the

wall of the oesophagus and of the blood-lacuna surrounding it (rf. PI. XIV. figs. 3, 4).
The innervation of the resopliageal wall is, moreover, brought about by a paired nerve,
V, springing from the brain-lobes, and not strictly separate in its peripheral distribution
from that of the nerves vi.^y. ni, nerves to the tip of the head ; M, mouth.

Fig. 2. The chief points in the nervous system of the Vertebrata.

Instead of the medullary nerve we find here in the corresponding situation the
medulla spinalis m and its anterior enlargement, the brain. The spinal nerves are
represented in their primitive condition, i.e., with the dorsal (sensory) roots dr, and the
ventral (motor) roots vr, not yet connected into a spinal nerve of higher order.
Anteriorly is represented the union of more than one metameric transverse root into a
complex polymerous vagus nerve, Vag, motor and sensory branches of which are
represented as innervating the branchial pouches of the fore gut (the latter not specially
indicated in the figure). From the vagus ganglion also springs In, the ramus lateralis
nervi vagi or nervus lateralis ; hi', the left nervus lateralis. Tliis nerve is continued
forwards into other ganglionic swellings Lg, representing the series of ganglia of the
cephalic nerves. The visceral branches springing from the dorsal roots and inner-
vating vegetative organs are indicated by vi.sy ; they are supposed not yet to have united
into a longitudinal "sympathetic nerve." In front the region innervated by them
overlaps and fuses with that of the intestinal branch v. of the vagus, and of other
cephalic nerves. M, mouth.

Fig. 3. The chief points in the nervous system of Amphiuxus.

The medulla spinalis ?/i without any considerable anterior enlargement ; en, pairs of
cephalic nerves ; dr, dorsal roots ; vr, ventral roots ; the former springing from the
medulla at a higher level than the latter. The dorsal roots are connected together in a
plexiform arrangement; they give off visceral branches (vi.sy). M, mouth.

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