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JU | : BR 1 he a a rl rt {+e Kwe a oe peeg =, et a SO - fo Pepet Oye LK, a Crh Syren ig es REPORT” 7-186 £ ON THE i j SCIENTIFIC RESULTS Me ia OF THE VOYAGE OF H.MS. CHALLENGER DURING THE\ YEARS 1873-76 \ UNDER THE COMMAND OF Cartan GEORGE S. NARES, R.N., F.RS. AND Captain FRANK TOURLE THOMSON, R.N. PREPARED UNDER THE SUPERINTENDENCE OF THE LATE om COW VILLE THOMSON, Knt.\ F.RS., &c. REGIUS PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF EDINBURGH DIRECTOR OF THE CIVILIAN SCIENTIFIC STAFF ON BOARD AND NOW OF JOHN MURRAY, BRE SE. ONE OF THE NATURALISTS OF THE EXPEDITION ZOOLOGY VOL. V1. jPublished bp Order ot er Majesty’s Government PRINTED FOR HER MAJESTY’S S STATIONERY OFFICE AND SOLD BY LONDON :—LONGMANS & cO.; JOHN MURRAY ; MACMILLAN & CO.; SIMPKIN, MARSHALL, & CO, TRUBNER & CO.; E. STANFORD; J. D. POTTER; AND KEGAN PAUL, TRENCH, & Co. EDINBURGH :—ADAM & CHARLES BLACK AND DOUGLAS & FOULIS. DUBLIN :—A. THOM & CO. anD HODGES, FIGGIS, & CO. 1882 Price Forty-two Shillings. PRINTED BY NEILL AND COMPANY, EDINBURGH FOR HER MAJESTY’S STATIONERY OFFICE. CONE NES. L—Report on the ActintariA dredged by H.M.S. Cuatiencer, during the years 1873-1876. / By Professor RicHaRD Hertwiec. (Received February 1, 1882.) I.—Report on the TunicaTa coltected_ during the Voyage of H.M.S. CHALLENGER, ASCIDLANSIMPLICES. during the years 1873-76.— ~ See = SS By WittraxmA. Herpman, D.Sc., Kalinos eee of Natural History “in University College, Liverpook ~~ : = (Received November 1, 1882.) el vatow sy sore * pay isle DW Al eeg bani bear ve : Wid A ui "Ay scien swindling au . re ‘reaper ane s- i a | Sees anit i144) Vasari? it) aca vwoligle rn a mmo bane dit vied ffenea Trail ape aah ain welt eae y ermal ee 1: ‘a hoa 7 5 Mupyerti nti seca py ANI aid s ee mee ee |: e ty ‘ a an - PEORIA NOTE. Tue first Memoir in the present volume is a Report on the AcriniariA of the Expedition, by Professor Richard Hertwig, of Koenigsberg. This Report is not complete, in so far as it does not embrace the whole of the Challenger collection. A considerable number of specimens did not reach Professor Hertwig till some time after he had completed the examination of the collection originally sent to him, indeed, not till the present paper was in type. Professor Hertwig has kindly undertaken to prepare a short supple- mentary Report on the additional specimens here referred to. The Memoir has been translated from the German by Miss Nellie Maclagan. The second Memoir is the first part of a Report on the Tunicava of the Expedition, by Professor W. A. Herdman, of University College, Liverpool. As Professor Herdman had completed the examination and description of the Ascidiz Simplices, he consented to the separate publication of this portion of his Report. The second part of his Report, which will consist of a description of the Ascidiz Composite and the Pelagic Tunicates, will, it is hoped, be ready for publication within a year from the present time. The above Reports form respectively Parts XV. and XVII. of the Zoolo- gical Series. Part XVI. was published in Vol. V., Zoology. Joun Murray. = Bt ae ae 2 i er ad pe4ae nh. AGT WW? TLS, i : ‘ £, alld il ots ae a ra aa Uae \ Sencar ry, Lite lia Valid Men iain Jy. eS lds Co aries # el ay 4 el AL ae walvinhdunge: we “Se iy cE uidgey and Re aeees COV art, cis al is ae aia TR b LTR, AG ah eT hole rev ast, “AE SRR, Gidyo sellout, what gut, Sebati RN Ere irs nett 5 cilia me ate et oe ay tiliet! wi Pach) ey BE aent ane ile : iy Ls * abe * : ; ‘ WF ea WTAOLE nf UST * 4: hay oe 3, set Gayl, Wi, -. agra | 5 stigt as ie fear Yi iz svadihs re $8 is : ‘Wai Ee CURL att ae (bit detalapaprrd ne annant ‘ a ae ‘in Hi ywAltbet ai ieee” ok Ch baie ae * ‘ . Ay liptsy AN iy sae } ol tye ee ee ji A Lares rn wish dam at | ial fount art ti gh! My inane peda’ ave hua sity RY Be tah aly A BAG ste s eRAG Ne PROS Ben viel Peis SGT Bike at aga oe by THE VOYAGE OF H.M.S. CHALLENGER. ZOOLOGY. REPORT on the Acriyiaria dredged by H.M.S. Challenger during the years 1873-1876. By Prof. Ricuarp Herrwic. NER OD CEUON. In investigating the Anthozoa the majority of earlier naturalists were content to give the most exhaustive description possible of the parts which are externally visible in the living animal, and of the skeleton where such a structure existed; on the other hand, they only went slightly into more exact anatomical details, as the observation of these presented great difhculties. The majority of the Anthozoa are not sutliciently transparent to allow of the recognition of the form and arrangement of the organs in the living animal, whilst after death they are so contracted that all the parts become mis- placed in many ways and pressed one against the other, and can only be demonstrated, with great care, by means of knives and scissors. Up to the present time the systematic survey and characters of the orders, families, and genera are founded upon external characteristics which are of less morphological importance. In this way many errors arose, which have only become intelligible from the work of the last decades. Following the steps of Agassiz (Contrib. to the Nat. Hist. of the United States, vol. iii.), Moseley (Phil. Trans., vol. clxvi. pt. 1, p. 91, 1876; vol. elxviil. pt. 2, p. 425, 1878) has shown in the most convincing fashion that many hydroid polyps which form skeletons have been long placed among the reef-forming corals, and that, moreover, in consequence of the skeletal formation alone having been taken into consideration, many Octocorallia have been disconnected from their natural systematic place, and united to forms entirely remote. It cannot by any means be asserted that (ZOOL. CHALL, EXP.—PART xv.—1882.) PA 2 THE VOYAGE OF H.M.S. CHALLENGER. recent discoveries have led to the exhaustion of the more comprehensive reforms of the system of Corallia, as up to the present time we only know the structure of the soft parts of the body, especially of the septa, from a comparatively small number of species, and our knowledge, even of such forms as have been most thoroughly investigated, is far from satisfactory. This also holds good for the soft-membraned Anthozoa, the Actiniaria or Malaco- dermata. In this section the structure and arrangement of the septa are of the highest importance for the proper comprehension of the structure ; they will probably require to be taken pre-eminently into consideration in the classification, not only of the Actinize but also of the other Hexacorallia. But how little do we know on this point. In a reeently published work (Studien zur Blittertheorie, Heft i., die Actinien, Jenaische Zeitschrift, Bd. xi. p. 457, 1879) my brother and I have tried to show that all the important charac- teristics have hitherto been properly estimated only in a treatise by Schneider and Rotteken (Ann. Mag. Nat. Hist., ser. iv., vol. vii. p. 437), and that, on the other hand, both v. Heider (Sitzungsber. d. Kaiserl. Acad. z. Wien, Math. Nat. Classe, Bd. Ixxv., Abth. 1, p. 367, 1877), in his otherwise very elaborate anatomy of Sagartia troglodytes, and Jourdan (Annales d. Sciences Nat., Zool., ser. vi., t. x., No. 1, 1880), in his treatise on the Actiniz of Marseilles, remain far behind the two first-named naturalists. As, however, we have only a short report in a preliminary publication on the researches of Schneider and Rotteken, which extend over a large number of species, it is impossible to make any systematic use of their material, and therefore the number of more detailed anatomical studies of Actiniz, which, taken from different species, would enable us to form an exhaustive plan of the variations of the type common to all, is still incomplete. These anatomical studies we must have before we can deem it possible to settle an accurate point of view from which to determine the relations of the Actinize both to each other and to the other Anthozoa. Since it appeared to me a grateful task to make a beginning myself in the direc- tion just mentioned, I accepted with pleasure the offer made to me to undertake the working out of the Actinize collected by the Challenger Expedition. I wish at the same time to express my most hearty thanks to the late director of the Challenger Commission, Sir Wyville Thomson, and his first assistant and successor, Mr. John Murray, for the great liberality with which they placed the rich material collected at my free disposal. Before going into a description of the separate species, I think it advisable to determine in a few words the requisites, which, according to my view, ought to be fulfilled by the anatomical description of an Actinia if this is to be of any systematic value. I shall therefore preface the description by a sketch of the structure of this animal, in which I shall lay stress upon the points which are most subject to variation, and to which the special attention of the describer must be directed. Such an attempt is also to be recommended for the further reason that in this way the reader will at the same time REPORT ON THE ACTINIARIA. 33 become familiar with the nomenclature, which, taken partly from earlier authors, and founded to some extent upon my own observations, will be adopted in the following pages. I shall also be able to imterweave short remarks upon the most serviceable methods of investigation. The body of the Actinia is shaped like a hollow cylinder, which is usually very long in proportion to its breadth, but which can also be shortened to a discoid form under certain circumstances. It is limited by two terminal surfaces, the “oral disk” or “ peristome,” and the “ pedal disk ” or “‘ base,” whilst the body wall corresponding to the outer surface of the cylinder is termed the “ mural layer,” or shortly, the “wall”; the wall is usually separated from the pedal disk, always from the oral disk, by a sharp margin, the two surfaces here meeting at a right or even at an acute angle; the wall occasionally passes gradually inwards into the base, in such a way that we cannot speak of a separate pedal disk. Towards its periphery the oral disk bears the tentacles, which are simply hollow evaginations of the disk. Besides these ‘‘ marginal” tentacles there are also “ circumoral” tentacles, which are united in a corona round the oral opening, and “intermediate” tentacles, which occupy a position between the oral opening andthe margin of the disk. As the first are always present, and the last two only exceptionally, those may be termed the “ primary” or “ principal” tentacles, these the “secondary ” or ‘‘ accessory ” tentacles. The oral opening, placed in the middle of the oral disk, leads into a tube which hangs down a little way into the hollow space of the body, and in the older descrip- tions was held to be a stomach, a name which we may now suitably abandon and replace by the term “esophagus.” This ends before it reaches the pedal disk in a free margin, ? and communicates by a wide opening, the “gastric orifice” or “cardia,” with the large hollow space which occupies the inside of every Actinia, and is developed from the primitive intestine of the gastrula, whilst morphologically and physiologically it replaces the intestine and body cavity (enteroccele) of the bilaterals. Leuckart’s term “ceelenteron,” or “ ccelenteric space,” is therefore specially appropriate to the Actiniz. The cesophagus hanging down in the ccelenteron is fastened to its place by the numerous septa (sarcosepta, Heckel) which spring from the oral disk, wall, and pedal disk, and are attached superiorly to the cesophagus, whilst they end in a free margin below. ‘They therefore divide the peripheral part of the ccelenteron into simple radial chambers, which are closed where they surround the cesophagus and where they pass into the hollow spaces of the tentacles, but which open downwards between the free margins of the septa into the “central stomach,” 7.e., into that part of the ccelenteron which lies under the cesophagus and is no longer divided into chambers by the septa. All the above-mentioned walls and septa of the body of the Actinia are lamelle of no great thickness, and in many species the wall only is a tough sheath. The firmness of the lamella depends upon their fundamental substance of connective tissue, + THE VOYAGE OF H.M.S. CHALLENGER. which, according to the degree of their histological differentiation, may be homogeneous and not enclosing cells, homogeneous and enclosing cells, or, finally, fibrous and containing cells. The framework of connective tissue gives us an accurate figure of the corporeal form of the Actinia even when the epithelial parts have been removed by maceration ; from the standpoint of the “ Blittertheorie,” it must be termed the middle layer of the body or mesoderm. All the lamelle of connective tissue are covered on either side by a single layer of epithelial cells, which are distinguished by extraordinary length and thinness, and may, moreover, be placed in different categories according to their different functions. The most usual form is seen in the “ supporting cells,” in which, despite their fineness in an isolated condition, we can recognise a distinct, triangular, basal expansion. The most common after these are the “ urticating cells ” and “ gland cells.” In the former the body is expanded by the presence of the thread, in the latter it is distended by glandular secretion stored up in it. The form of the nematocysts, and the nature of the thread contained in them is not the same everywhere, and may, perhaps, some day become of systematic importance. The glandular secretion is also of different kinds; it sometimes fills the body of the cell, as a homogeneous, glassy mass, sometimes it is deposited as a mass of closely compacted granules, greedily absorbing colouring matter. The fourth form of cells is that of the “sense cells,” which have the same fine, filamentous nature as the supporting cells, from which, however, they can be distinguished in an isolated condition by their central end giving off two or more fine nerve threads, which have a tendency to become varicose. With the exception of the glandular cells, all the cells bear appendages at the peripheral end; the sense cells, and probably also the urticating cells, have fine, long, tactile bristles, of which each cell usually possesses only one; the supporting cells bear a buneh of cilia, or a simple flagellum. Ciliated cells and flagellate cells may be present in the same animal, e.g., in most Actiniz the ectodermal epithelium is made up of the former, the endodermal of the latter, whilst in Cerianthus we find only flagellate cells. We have as yet no satisfactory knowledge of the manner in which the two forms of cells are distributed among the Actinize. The epithelial coverings are derived immediately from the two primitive layers of cells of the gastrula larva, the endoblast and the ectoblast, and in the developed animal are therefore to be distinguished as separate body layers, as endoderm and ectoderm, even when they hardly vary in their histological character. The ectoderm covers the outer surface of the body and the inside of the cesophagus ; the endoderm covers everything else, 7.e., the inner wall of the whole ccelenteron, and the inner spaces of the tentacles. The supporting lamelle of the wall, of the cesophagus, &e., are therefore covered with ectoderm on one side and with endoderm on the other; the septa only form an exception, as they bear endodermal epithelium on both sides. REPORT ON THE ACTINIARIA. — 5 Among the histological elements of the Actinia we must finally mention the muscle cells, nerve cells, and reproductive cells; we shall merely discuss the two former here from a general point of view. The muscles originate either from the ectoderm or the endoderm, and usually continue to belong to both these epithelial layers. They consist of flat, fusiform, muscular fibrillee, to one side of which the cell from which they were originally produced is attached. This latter is usually at the same time an epithelial cell, and with the fibre belonging to it represents an epithelio-muscular cell, or it is a cell lying in the deeper layers of the epithelium, and no longer extending as far as the surface, an epithelial cell, whose peripheral end has undergone retrograde formation, or a subepithelial muscle cell. The principle of arrangement of the fibrillee is the same in both cases ; they are placed on the borders of the epithelium and the mesodermal connective substance, and form a thickly apposed simple layer, a muscular lamella. The muscles are not strengthened by the deposition of new layers of fibres, but by the “ pleating” of the single-layered lamellee. The underlying connective substance also comes into play, supporting all the folds of the muscular lamella by fine leaf-like processes (Pl. V. figs. 7-10; Pl. VI. figs. 4, 6). The pleating of the epithelial, or subepithelial muscular lamella, becomes in many cases the starting-point for the development of a third form of the muscular fibres, the “ mesodermal ” fibres. When the surfaces of the supporting substance, which borders a muscular fold laterally, approach so that here and there they touch and become fused, the connection of the lower part of the pleating with the epithelium is dissolved, and it becomes completely enclosed in the mesoderm (PI. VII. fig. 8). In this way are found in transverse sections, circular figures, whose periphery is occupied by the divided fibrille, whilst the centre contains the muscular corpuscles belonging to it. The trans- formation of the epithelial muscular elements into mesodermal can go so far that considerable masses of muscles lie in the mesoderm (PI. IV. figs. 5-8; Pl. VI. figs. 1-3, 5). In describing the muscles of the Actiniz we must, therefore, be careful to note whether they are ectodermal, endodermal, or mesodermal, whether they extend simply in a smooth lamella, or are disposed in folds; as we shall see, they present in this way many characteristics of systematic value. This cannot be said of the nervous system, which I only go into here for the sake of completing my description. Nerve fibres and ganglion cells are found, in thoroughly examined Actiniz, in nearly all the epithelial lamine, where they form a layer between the bases of the epithelial cells. The layer is extremely thin in the ectoderm of the pedal disk, and usually also in that of the wall, whilst it is very strong in the ectoderm of the tentacles, of the oral disk and of the cesophagus. Nervous elements are usually less frequent in the endoderm, and only produce visible cords in the mesenteric filaments and acontia. We may lay down as a rule, that, where muscular filaments are present, the layer of nervous filaments lies over the former, and is most easily found in that place. 6 THE VOYAGE OF H.M.S. CHALLENGER. I have as yet only given a general survey of the anatomical and histological parts composing the organisation of the Actiniaria ; it now remains for me to discuss the differentiations shown by the histological elements in their nature, distribution, and arrangements in the various parts of the body, and to show how we may thereby acquire a knowledge of the more accurate characteristics of these parts. The pedal disk does not present much worthy of notice; it has a slightly developed endodermal muscular layer, always running circularly, which is often even wanting ; in the centre there are sometimes, but rarely, one or more small openings, through which the water can find entrance and exit; as yet, however, such openings have only been ~ observed where the pedal disk and wall pass continuously the one into the other, which condition is usually described as absence of the pedal disk. Radial furrows may also run on the outside of the pedal disk, and usually correspond to the insertions of the septa on the inside (Pl. IV. fig. 2; Pl. IX. fig. 5). The wall is much more complicated both on its endodermal and its ectodermal sides; on the former there often lies a layer of cireular muscular fibres, which appears everywhere as a flat or slightly folded lamella, but is also often more strongly developed in certain places, and forms a special muscular cord acting as a sphincter. The sphincter or circular muscle usually hes immediately below the upper margin of the wall, which it draws together like a bag over the oral disk and the tentacles if the latter require shelter from any threatened danger, A second sphincter, lying further down, may also be added to the upper sphincter. The nature of the sphincters varies greatly. We talk of a “ diffuse” sphincter when it merely arises from repeated pleatings of the muscular lamella; because in that case it is not sharply defined at the upper and lower margins (PI. V. fig. 8), it does not strike the eye in looking at the surface, and is shown in transverse section only by the local thickening of the wall in whose substance it is completely embedded. A “ cireum- scribed” sphincter is formed when the pleated muscular mass projects above the inner surface of the wall, with which it is connected only by a narrow band, so that an annular swelling arises which is easily observed both in looking at the surface and in transverse section (Pl. VII. figs. 2, 4). Finally, in the “mesodermal” sphincter, the muscles have left their original position in the epithelium, and are completely hidden in the supporting substance, which consequently increases doubly or trebly in thickness (PI. VII. fig. 7; Pl. VI. figs. 1-8). The complete absence of the sphincter is comparatively rare. I have only observed it in a few species (e.g., in the representatives of the genus Corallimorphus), almost invari- ably animals which are not capable of contracting the upper margin of the wall over the oral disk. This is, however, also the case in animals with a weak sphincter, such as the Antheadz. On the other hand, the existence of a strong circular muscle can often be inferred with tolerable certainty from a high degree of contraction. The capacity for concealing the oral disk plays an important part in the systematic division of the REPORT ON THE ACTINIARIA. 7 ce Actiniaria; this is generally most inappropriately expressed by the term “ retractile tentacles.” It would be decidedly more rational to make the anatomical reason, and not the physiological appearance, of systematic value. We shall therefore talk of Actiniaria without sphincter, and of Actiniaria with weak and with strong sphincter, and further distinguish in the latter case whether the muscle is endodermal or mesodermal. The systematic value of the circular muscle does not end here, as it furnishes a character not to be undervalued, for determining the species. The extraordinary variations of the circular muscle are shown by a glance at Plates VI. and VII. ; in the endodermal forms the shape and mode of branching of the muscular folds vary, in the mesodermal the shape and grouping of the bundles formed by the fibres, and also their position in the more superficial or deeper layers of the wall. I lay stress upon this point, as the circular muscle can be examined in the preserved animals even when their state of preservation is not very favourable, and because, moreover, a small piece of the wall, which can be eut away without essential damage to the whole animal, is sufficient for such an investigation. Muscles, especially longitudinal muscles, are rarely present on the ectodermal side of the wall, whilst, on the other hand, it is not unusual to find “marginal spherules” and different forms of papille. The marginal spherules (‘ bourses marginales,” Hollard, Ann. d. Sci. Nat., Zool., ser iii, t. xv. p. 257) follow immediately outside the tentacles, and are evaginations of the mural membrane, just as the tentacles are evaginations of the oral disk. All the layers of the body participate in the evagination, though the ectoderm alone undergoes modification of its structure, being extraordinarily rich in nematocysts. The papille, to which such importance was attached in earlier investigations of the Actinie, are formations of very subordinate value ; they are caused by mere local growth of the supporting plate, and are not distinguished by a single special property of the covering epithelium (Pl. VIII. fig. 4). Hence the observer often found himself on the horns of a dilemma when he had to decide whether papillee were present or not. A smooth surface may become papillose in consequence of contraction, and, on the other hand, small papillee may disappear when, as often happens, the Actinia becomes distended like a drum. It would, therefore, be better in future only to make the papillose or smooth nature of the membrane of value in distinguishing species, or at most of genera, and to disregard it in the formation of larger divisions. The comportment of the epidermis appears to me much more important. The majority of the Actiniz have a smooth surface, on which particles of mucus become secreted when the animal is irritated ; histological investigation then shows an active ciliated epithelium composed of extremely long, thin cylindrical cells. Besides this, two varying modifications of the integument haye already been specially observed. In the one case, in Cerianthus, the epithelium is covered externally by a tough membrane, consisting of mucus, nematocysts, and scattered foreign bodies, which can be stripped off, but which 8 THE VOYAGE OF H.M.S. CHALLENGER. is rapidly regenerated, and in which the animal is concealed as in a sheath; in the other case there is a membrane present which cannot be stripped off, and which gives the surface a rough, bark-like appearance ; this has received the very unsuitable name of “epidermis.” In fact, we have to deal with a cuticular formation. In the most simple cases, where the epithelium does not bear cilia, it is covered loosely by a thin, irregular fibrous membrane, outside which is a layer of mucus, traversed by all sorts of foreign bodies (Pl. VIII. figs. 1 and 6). This cuticular secretion rarely becomes a broad, stratified mass resting firmly on the epithelium, and recalling completely the cuticula of the worms (Pl. XII. figs. 1 and 2). The wall can also be traversed like the pedal disk by furrows, which run in a longitudinal direction from the base to the border of the oral disk, and likewise correspond to the septa. The possible presence of “ cinclides” must finally be taken into consideration ; this is the name applied by Gosse (Actinologia Britannica, 1860) to openings in the wall through which water and the acontia, which we have still to describe, can be ejected from the inside of the body. Such cinclides can be observed in Calliactis parasitica, even in spirit specimens, where they are arranged in a circle at a little distance from the pedal disk. In other cases, on the contrary, we see that acontia issue from the interior of the living animal through the wall, but it is impossible to find performed openings, even if we take a protruded acontium as guide. Whether the opening is difficult to find out, or whether it is not performed, but arises afresh each time by rupture, as v. Heider assumes, must still be regarded as an open question. That is a point which essentially lowers the systematic value of the cinclides. Gosse has certainly made light of the question, and assumed the presence of cinclides wherever he noticed the passage of the acontia, even though he did not find any openings. Such a method of treatment, however, can be properly carried out only in the living animal, as spirit material leaves the question undecided. The oral disk is furnished on both sides with muscular fibres, running radially on the ectodermal side, circularly on the endodermal ; the latter are connected immediately with the muscular fibres of the wall, with which they form a continuous layer. Whilst the endodermal muscular fibres possess no further interest, and comport themselves, so to speak, in the same manner throughout, the development of the ectodermal muscular fibres is subject to numerous variations, which, like the nature of the sphincter, can be turned to good account for more accurate determination of the species. In all cases we must distinguish whether the muscular fibres maintain their original place in the epithelium, or whether they have passed wholly or partially into the mesoderm. We must, moreover, pay attention in the first instance to whether the muscular lamella is smooth or pleated, and in the second instance to the form and arrangement presented by the mesodermal bundles of fibres. REPORT ON THE ACTINIARIA, . 9 The same questions recur in the tentacles, which are merely evaginations of the oral disk. Here the endodermal circular muscular fibres are always uniform, whilst the ectodermal longitudinal cords vary. Moreover, there are usually, if not always, open- ings present in the tentacles through which water is ejected when the animal becomes contracted ; they occupy the point of the tentacles, and are easily observed in the living animal. In order to find them out in the spirit material I fastened a tentacle, which had been cut off, to a tube and inflated it with air under water ; if an opening were present the air bubbled out through it. According to their shape the tentacles are distinguished as “ knobbed,” “club-shaped,” “branched,” “conical,” &c., terms which do not require further explanation. Their mode of arrangement, of which I shall speak in connection with the septa, is also of importance. On the other hand, their length and shortness is a characteristic which is not capable of exact definition, and cannot be determined with any certainty in the spirit specimens, as it is impossible to judge to what extent the length has been influenced by a greater or lesser degree of contraction. This characteristic cannot, how- ever, be dispensed with for systematic purposes. Whether the tentacles in the Actiniz may be entirely wanting, without being morphologically replaced in some way or another, seems to me questionable, as no such case 1s known up to the present time. The tentacles may, however, undergo a peculiar retrograde metamorphosis, progressing so far that only the terminal opening is left in the form of a fissure, which is enclosed by thickened lips, and, lying in the periphery of the oral disk, shows the spot where we might have expected to find the tentacle. I have observed different stages of this retrograde formation in species of Actinize coming from great depths. We see the beginning of it in Polysiphonia tuberosa (Pl. IL figs. 7, 9), also Sicyoms crassa (Pl. IV. fig. 4), and the advanced stages in Polyopis striata (PL II. fig. 11), and Polystomidium patens (Pl. V. fig. 6). The oral opening is only exceptionally round; it has usually the form of a fissure whose longitudinal diameter les in the same direction in all Anthozoa. It is therefore of the greatest importance for distinguishing the axes which may be drawn through the body of the Actiniz. If the Actinize were animals possessing perfect radial symmetry, then the longitudinal axis, determined by its passing through the oral and aboral poles, would be the only constant one, and all radial axes lying perpendicular to the longitudinal would then be perfectly equivalent to one another. By the constant form of the oral opening, the radially symmetrical fundamental form becomes more definite, and is at least transformed into the biradially symmetrical form. In all cases, two of the radial axes strike us as specially distinguishable, the sagittal axis running in the direction of the oral fissure, and the transverse axis perpendicular to it. We can even exceptionally recognise a dorsal and a ventral side at the ends of the sagittal axis, and a right and a left side at the ends of the transverse axis, and hence the (ZOOL, CHALL, EXP.—PART xv.—1882.) P2 10 THE VOYAGE OF H.M.S. CHALLENGER. biradially symmetrical fundamental form is transformed into the bilaterally symmetrical. I lay great stress upon this apparently unimportant consideration of the form of the mouth, as it is the expression of a fundamental character in the architecture of the body of the