MINUTE ANATOMY OF MEDITERRANEAN NEMERTEANS. 2 4 9

the oral surface of the disc; spiral of buccal cilia absent; mouthplaced in the angle formed by the junction of the body anddisc; body soft, changing in shape continually (?); ring with37 hooks, and radii; being of one piece throughout.

Cyclochata spongillce ; on the common fresh water sponge(Spongillafluviatilis). River Cherwell, Oxford. August.

A. Animal provided with a spiral of buccal cilia.a. Ring not hooked; marked by a spiral line.

1. Body ciliated— Trichodinopsis, 1 sp.2. Body naked; adoral spiral of cilia terminal— Urceolaria, 1 sp.

/3. Ring hooked; adoral spiral not terminal—Trichodina.B. Spiral of bnccal cilia wanting; animal famished with a row of sete

behind disc—Cyclochata,

Some REMARKS about the MINUTE ANATOMY of MEDI-TERRANEAN NEMERTEANS. By A. A. W. Hubrecht, of theLeyden Museum of Zoology. (With Plate XIII, figs. 6—8.)

A STUDY of some fifteen different species of Nemerteansfrom the Bay of Naples at Dr. Dohrn's zoological stationas well as an investigation of the scanty specimens inhabit-ing the Dutch coasts, have led me to results which have oftenconfirmed, but which have not seldom differed from andcontradicted the conclusions and views entertained by Mr.Macintosh in his latest monographical treatises on the sub-ject,1 in which the British species are exclusively alluded to.It is these points of confirmation and criticism which Iwant to put together in the following lines, although theyhave been incorporated already in the more extensive de-scription of my researches, published elsewhere.3 In thisbrief extract I will follow the arrangement of Mr. Macin-tosh's extensive treatise—yet without describing the Enoplaand Anopla separately as is done there, comparing successivelyhis principal observations with mine.

My observations extended for the greater part to speciesbelonging to the anoplan genus Meckelia, viz. Meckeliasomaiotomus (Leuck.), Meckelia (Nemertes) ligurica (Blanch),Meckelia Ehrenbergii (Dies.), Meckelia aurantiaca (Grube),and further to Polia delineata (Delle Ch.), Folia geniculata

1 'Transactions of the Royal Society of Edinburgh,' 1869, and RaySociety's publications, 1873 and 1874.

2 'Aontecheningen over de Anatomie Histologie en Ontwikhelingsgeschiedenis yaneeuige Nemertines,' Utrecht, 1874, and " Untersuchungeniiber Nemertinen," in Niederliindisdisches ' Archiv fur Zoologie,' Bd. I I ,Heft 2,1875.

2 5 0 A. A. W. HUBRECHT.

(Delle CL), Lineus longissimus (Sowerby), Lineus bilineatus(Delle Ch.), and Borlasia olivacea (Thompson).

From the enoplan sub-division I had at my disposalseveral species of the genus Ommatoplea (Dies.), as well asthree new species which I have put together iti the genusDrepanophorus (n. g.) and which are distinguished by thestructure of their stylet and stylet region differing entirelyfrom the typical form found in all other Enopla. Thiscurious deviation will be discussed in the proper place.

Dermal Tissues and Muscular Layers of the Body.The difference existing with respect to these tissues be-

tween the enoplan and the anoplan forms (Mr. Macintosh'sOmmatopleans and Borlasians) is great indeed, showingthat subdivision of the order (as first proposed by MaxSchultze) to be a very natural one. Yet the principal inves-tigators of the subject, such as Keferstein and Quatrefagea,confounded the structures in the one with those in the otherand it remained for Mr. Macintosh to point out with greatclearness the obvious differences. He reduces the numberof muscular layers in the Enopla to an external cir-cular one and an internal longitudinal one of greaterthickness, and shows that the Anopla are, on the con-trary, provided with an external as well as an internallongitudinal, with an interjacent circular layer. Keferstein'sexternal circular layer is shown to be a structureless basementlayer of the cutis. My observations tend fully to confirmthese views. Many preparations of unarmed Meckelias hadthe external epidermic layer thickly provided with flask-shaped glands opening externally, which are mentioned byKeferstein, but about which Mr. Macintosh is silent.

The interfascicular substance which plays so large a partin the structure of the body wall is rather undervalued byMr. Macintosh. It is a kind of fibrous connective tissue,surrounds the dermal structures, carries the pigment andforms layers between the cuticular and muscular layers cor-responding to that separate basement layer, confounded byKeferstein with a muscular one. From this stratum numerousseparate fibres can be traced entering into the interspacesbetween the fascicules of outer longitudinal muscles, con-tinuing their way downwards through the circular and in-ternal longitudinal layer, finally entering into the body-cavity, traversing this, and again completely piercing theopposite muscular body-wall, to find their way back into thedermal tissue.

Still the separate fibres of this fibro-elastic stroma do not

MINUTE ANATOMY OF MEDITERRANEAN NEMERTEANS. 251

penetrate at random into the body cavity, but mutually com-bine, giving rise to fibrous dissepiments (PI. XIII, fig. 8) placedat regular intervals—one between each intestinal caecum—and serving to attach and carry the intestine (g) and thesmall anastomotic blood-vessels (e). Moreover these verticalinterccecal septa are again composed of two separate layerslying close against each other in the normal condition andseparating when the sexual organs begin to develop.

Eggs and spermsacs (/) take their origin between theselayers. The fibrous septa might be regarded, on account ofall these peculiar functions, as a kind of primitive mesentery.

Cavity of the Proboscidian Sheath.Mr. Macintosh was the first to recognise this cavity with

its proper muscular wall and its characteristic corpusculatedfluid as entirely separated from the general body-cavity withwhich it had been confounded by Keferstein and Quatrefages.This cavity, extending through the entire length of theanimal, was present in all the species which came under mynotice. The muscular wall, ordinarily attached to the dorsalside of the body-cavity, was exceedingly thick in Drepano-phorus (n. gen.), being chiefly composed of circular fibresintermixed with longitudinal bundles. The inside was lined•with elongated papillae. This stronger development of thewalls no doubt stands in connection with the great facilitywith which these species extrude their proboscides.

Proboscis.

The minute structure of this organ as described by Mr.Macintosh could be verified in numerous specimens. Intransverse sections of the proboscis of Meckelia somatotomus(Leuck.), the curious deviation of fibres from the internaland external circular muscular layers presented a somewhatdifferent aspect, the mutual interchange of fibres not takingplace on one side only, but on two diametrically opposedpoints.

With respect to the anatomical structure of the armedproboscis, my conclusions, are chiefly based upon the differentspecies of Drepanophorus (n. g.)1

Mr. Macintosh distinguishes six different layers in theanterior part of the enoplan proboscis, and for the first timementions the presence of a separate layer with rather a puz-zling character (his reticulated or beaded layer), enclosed

1 For more details about this genus, vide Niederl., * Archiv furZoiilogie,' Bd. II, Heft 2.

2 5 2 A. A. W. HUBRECHT.

between the longitudinal muscular ones. This layer is veryconspicuous in the Drepanophorus species, and consists oflongitudinal columns, surrounded and united by bands offibrous elastic tissue which at the same time traverse thelongitudinal muscular coat in all directions, and originallydepart from the external and internal circular layers ofelastic tissue. (Plate XIII , fig. 6.)

These columns seem to consist of a very homogeneoustissue, no cut ends of fibres being visible in vertical sections,and carmine solution, which was strongly imbibed by theelastic tissue, never tinged them in the least. The curiousflask-shape of these columns in vertical sections at firstled me into the error of regarding this layer as a complexof small glands.

I am much in doubt as to the muscular character of thecircular layers e f, and if, which are held as such by Mr.Macintosh. The longitudinal layer I m, is decidedly mus-cular, traversed by a meshwork of interlaced elastic tissue asremarked above. Neither do I wish to follow Mr. Macintoshin regarding the external and internal portions of this layer astwo distinct muscular coats.

Externally this part of the proboscis, when extruded, iscovered with thickly-set papilla, which are composed of finetranslucent rods sticking together. They produce a gela-tinous mucus, and render the proboscis in a high degreesticky. A separate papilla is figured, Plate XIII, fig. 7.

The structure of the stylet region, central and lateralstylets, is treated in extenso by Mr. Macintosh. I only wishto point out the curious difference existing in this respectbetween Drepanophorus (n. gen.) and all other Nemerteanshitherto known. Instead of the usual transparent, straight,central stylet, with its swollen base and the peculiar mus-cular arrangement surrounding it, these species carry acrooked, dark-brown hook, pointed at the anterior, blunt atthe posterior end, and held in position by a ring-shapedinternal elevation of the proboscidean wall. A special mus-cular development in this region and natural stylet sacs aretotally absent, a reservoir filled with a greenish fluid as well astraces of an ejaculatory duct being visible.

Something analogous was very vaguely described by M»De Quatrefages for his Cerebratulus spectabilis, but neitherMax Schultze nor Mr. Macintosh (who incorporates thespecies in his genus Amphiporus) believed in the correctnessof the observations. The finding of three new species present-ing a nearly similar stylet-shape confirms the validity of M.De Quatrefages' statements.

MINUTE ANATOMY OF MEDITERRANEAN NEMERTEANS. 2 5 3

Digestive and Circulatory System.

In accordance with Mr. Macintosh's statements I found themouth in the Enopla situated before the ganglia, ventrally, alittle behind the opening for the proboscis. In Meckelia soma-totomus the ciliated oesophagus is distinct from the subse-quent part of the digestive cavity in which the coscal ap-pendages appear. The oesophagus is further provided withvery thick glandular walls. In Drephanophorus it is, on thecontrary, very short, provided with thick glandular walls evenbefore the ganglia, whilst the regular ccecal appendages maketheir appearance at no great distance behind these.

The circulatory system in Drepanophorus shows manypoints of resemblance with the same apparatus in Borlasiasplendida (Amphiporus spectabilis, Mclnt.) as describedby Keferstein. Besides the three longitudinal vessels agreat number of anastomotic vessels, perpendicular to thefirst, occur,'one in each interccecal space. The, containedfluid carries numerous red blood-corpuscles, which provedupon examination with the spectroscope to owe their colour-ing to haemoglobin. This fact was already ascertained forFolia sanguirubra by Mr. Ray Lankester.1

For the larger Borlasian forms, such as Meckelia soma-totomus (Leuck.), Polia geniculata (Delle Ch.), whose darkpigmentation prevents their being studied under compression,I could ascertain in longitudinal sections that here two fineanastomotic vessels—one for every intercoccal space—unitethe dorsal vessel with the two lateral ones.

As to Meckelia somatotomus (Leuck.), Cerebratulus margi-natus (Kef.), my observations confirm those of Mr. Macintosh,who found in this species the vessels in their ordinary place,close to the nerve-trunks, thus contradicting Keferstein'sstatements on this point. I cannot, however, agree with Mr.Macintosh in regarding the position of these blood-vesselsin the Borlasians as quite constant. Polia geniculata, forexample, carries its lateral vessels nearly in the middle of thebody cavity, suspended by connective tissue under the intes-tine.

Nervous System.

The difference which exists between Enopla and Anopla inrespect to shape and position of the ganglia and nerve-trunkswas already pointed out by preceding investigators, andclearly stated by Mr. Macintosh. A corresponding differ-

1 ' Proceedings of the Eoyal Society,' No. 140,1873.

2 5 4 A. A. W. HUBRECHT.

ence in the cephalic sacs (Keferstein's side organs) probablygoes alonir with this, as I will further on endeavour to show.

fr̂ n'M- ly the ganglia are of a red colour, paler in the Om-matopleans, much deeper and richer in the largeenoplan forms,suchas Meckeliasomatotomus,Meckelia Ehrenberg., &c. To thekindness of Mr. Ray Lankester, then also at the ZoologicalStation, I am indebted for the use of his excellent microspec-troscope, which, applied to the diffused colouring matter ofthese nerve-centres, left no doubts about its chemical con-stitution. It showed the two absorption-bands of oxyhsemo-globin with great distinctness. Mr. Lankester had found afew years ago haemoglobin in the ventral nerve-chain ofAphrodita, and the curious fact of its occurrence in nervetissue now stands isolated no longer. It must be observedthat in the same species which showed this so strongly theblood was quite colourless and devoid of corpuscles, whichare tinged by haemoglobin in some other Nemertean species,as mentioned above.

Investigations into the minute histological structure of thefour lobes of the ganglion, soldered together in front by thesuperior and inferior commissures, show that a thickbundle of exquisitely fine fibres occupies the middle of eachlobe. A thick layer of nerve-cells surrounds this kind ofaxis on all sides. These nerve-cells are imbedded in a neuri-lemma-sheath, as described by Leydig1, and vary in size. Thesmaller ones are the more numerous, still the larger onesoccur very regularly, often attaining a diameter of 66 mm.

The central fibrous bundles of each of the four ganglioniclobes unite in the commissures, forming a closed ring. Thoseof the inferior lobes continue their course backwards in thenerve-trunks, those of the superior lobes penetrate withoutinterruption into the tissue of the cephalic sacs, which liebehind these lobes in immediate contact with them, endingthere.

The lateral nerve-trunks, whose different position in theBorlasians and in the Ommatopleans has been clearly pointedout by Mr. Macintosh, show two different constituent ele-ments, viz., (1) the above-mentioned central bundle of fibres,and (2) a sheath of nerve-cells, thicker in the vicinity of theganglia, thinner further backwards, but accompanying thetrunk in its entire length. The size of the nerve-cells agreeswith that of the smaller cells in the central ganglia. Mr.Macintosh has not remarked this cellular coating. Hespeaks of a fibro-granular matrix of a reddish hue enclosingthe nerve-trunks. The red colour is caused by these nerve-

1 ' Vom Bau des thierischen Korpers,' p. 86.

ANATOMY 6P MEDITERRANEAN NEMERTEANS, 255

cells being like those of the ganglia, tinged -with haemo-globin.

In Drepanophorus (n. gen.) the position of the nerve-trunksreminds one of the genus Oerstedia (Quatref.), as they lieagainst the ventral wall of the body cavity, and have conside-rably approached the median axis of the animal. The state-ment of Mr. Macintosh as to the position of the nerve-trunksin the Meckelian type, viz., between the circular and the innerlongitudinal muscular coats (' Transactions of the RoyalSociety of Edinburgh'),was confirmed in none of the numerousMediterranean representatives of that genus, who all carriedthe nerve-trunks outside the circular layer.

The Cephalic Furrows, so conspicuous in the larger Mec-kelian species, often less distinct in the enoplan forms, areuniversally in connection with the cephalic sacs, which latterseem to take a different position in the Enopla and in theAnopla. The shape of these organs in the armed Drepano-phorus resembled that of the " side organs " in Keferstein'sBorlasia splendida, though they were situated more behindthe ganglia. They were connected with these by four com-missures, which passed uninterruptedly from the ganglionictexture into that of the cephalic sac. Furthermore, theyshowed pigmented spots and a small knotty elevation on oneside, which reached into the cephalic furrow. I could notmake out distinctly whether an internal ciliated canal waspresent or not. In other enoplan species the position of the" side organs" is generally in front of the ganglia, withwhich they are connected by only one commissure.

The Borlasian subdvision shows a rather different distribu-tion of the parts. The cephalic sacs lie behind the ganglia;they have a spherical or pyriform shape, and generally adistinctly visible internal ciliated canal, corresponding withthe cephalic furrows and permitting the sea-water to enterfreely. In their posterior portion they carry translucentglobules figured successively by Van Beneden, Macintosh,and myself.

The structure of the cephalic sacs in this subdivision wasstudied by me in several series of sections through themand through the ganglia, a reconstruction of the wholebeing in this way obtained. It then became evident thattheir constitution entirely corresponded with and immediatelypassed into that of the ganglionic lobes. Not only, as 1remarked above, do the central bundles pass from the oneinto the other, but the enclosing layer of nerve-cells is quiteas thick and conspicuous ; the central ciliated canal can betraced in these transverse sections with perfect accuracy. It

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256 A. A. W. HPBRECHf.

terminates in the central fibrous bundle, continues its waydirectly through the tissue of nerve-cells, passes upwards inthe space left free between the superior and inferior lobes(Meckelia somatotomus), finally to find its way into thecephalic furrows. The same sections with identical resultswere made by me of Borlasia olivacea from the Dutch coast;nerve-cells and canal were quite as distinct.

The cephalic sacs in the Borlasians must on these groundsbe regarded as belonging morphologically to the ganglionictexture with which they are in uninterrupted continuity.1

Now, as it is chiefly in this group that the ganglionic tissuecontains a considerable quantity of haemoglobin, with its well-known property of binding free oxygen, and as the oxygenatedsea-water has a free access to the hsemoglobinous nerve-cells by means of the cephalic furrows and ciliated canals, Ido not hesitate to regard the cephalic sacs as a special respi-ratory apparatus providing the cephalic haemoglobin withfresh supplies of oxygen.

How this respiratory process in the central nervous systemmay influence the organisation and the life of these ani-mals remains for the present unexplained, as long as similarobservations in other groups have not yet been made uponwhich comparative researches might be based.

Generative Organs and Development.I have little to add to what is mentioned by Mr. Macin-

tosh under this head. The change which takes place inthe interccecal dissepiments when the generative productsmake their first appearance, and the space occupied by thesebetween the constituent plates of these dissepiments has beenalready mentioned above (Plate XIII , fig. 8). Genital aper-tures giving access to these cavities were present on the dorsalside of the animal. Generally the emission of the eggs or thesperma took place by all the apertures simultaneously. Myobservations on the development of Borlasia olivacea agree,as far as they have been made, with those of Mr. Macintosh.Circumstances have prevented me from carrying on con-tinuous series of experiments on the development of otherspecies where the more interesting Pilidium larva makes itsappearance in the evolutional cycle.

March, 1875.1 The appearance sometimes presented in Borlasia olivacea as if they

lay independently behind the ganglia, must probably be ascribed to a nabnormal tension under compression, the elastic tissue so constantly dis-tributed along with the nervous permitting of this separation for a shorttime; similar disjunction was never observed in the Mediterranean speeies.