The Anatomy of Alcyonium Digitatum. by Sydney J

THE ANATOMY OF ALOYONIUM DIGITATUM. 343 The Anatomy of Alcyonium digitatum. By Sydney J. Hickson, M.A., D.Sc, 3eyer Professor of Zoology in the Owens College, Manchester; Fellow of Downing College, Cambridge. With Plates 36—39. INDEX OF CONTENTS. PAGE PREFACE ........ 344 Section I.—HISTORY OF OUR KNOWLEDGE OF THE ANATOMY OF ALCYONIUM ...... 344 Section II.—GENERAL FORM AND NATURAL HISTORY OF THE COLONY 349 Shape—Size—Colour—Expansion and contraction of the polyps —Contraction of the colony as a whole—Sexuality—Geo- graphical and bathymetrical distribution—English species of Alcyonium. Section III.—GENERAL ANATOMY ..... 354 The composition of the colony—The individual polyps and the colony—The appearance of the extensible portion—Size— Tentacles—Mouth—Disc — Stomodeeum — Mesenteries— Ventral mesenterial filaments—Dorsal mesenterial filaments —Gonads—Communication between individual polyps— The endodermic canals—Distribution of the spicules. Section IV.—MINUTE ANATOMY . .363 The ectoderm—Nematocysts—Stomodseum—Mesenterial filaments—Mesogloea—Spicules — Endoderm — Ovaries and testes—The buds. Section V.—NOTES ON THE CIRCULATION OF THE FLUIDS IN THE COLONY AND THE DIGESTION . 380 VOt. 37, PART 4. NEW SEE. A A 344 SYDNEY J. HIOKSON. PREFACE. THE work that is recorded in these pages has occupied a considerable portion of my time for the past two years, and was entirely conducted in the morphological laboratory at the University of Cambridge and the Marine Biological Asso- ciation's laboratory at Plymouth. In some respects it is not so complete as I had hoped it would be. My original inten- tion was to publish with the account of the anatomy of the species a description of its development and spermatogenesis, but unforeseen difficulties presented themselves, and I have decided to postpone the publication of the results I have already obtained until they are more complete. The development of Alcyonium can only be studied in the months of December and January, when the investigations are frequently interrupted or delayed by storms and rough weather. I have experienced very great difficulty in keeping the young embryos alive when I have been successful in effecting artificial fertilisation of the ova. If I am successful this winter in obtaining the stages in development that I have not hitherto obtained, I hope to publish an account of the maturation and fertilisation of the ovum and the development in the course of next year. As I felt that the determination of the chemical constitution of the homogeneous substance composing the bulk of the mesogloea required considerable skill and time, which I did not possess myself, I entrusted this portion of the work to Mr. W. L. Brown, of St. John's College, Cambridge, and his paper, which accompanies this, is a valuable addition, to our knowledge of the chemical constitution of the Ccelenterate tissues. Section I.—HISTORY OF INVESTIGATIONS. The common " dead men's fingers" of our coasts was considered by the ancients to be one of those substances formed by the churning of the sea waves. It received its name Alcyonium probably from Alcyone, daughter of iEolus and THE ANATOMY OP ALOTONIUM DIGITATUM. 345 Enarete, who threw herself into the sea for grief on the death of her husband, Ceyx, in a shipwreck. In the middle of the last century a great controversy arose as to the nature of the so-called zoophytes, of which Alcyonium was one. Peysonnel (1727), de Jussieu (1742), Reaumur (1742), Ellis (1754), and others, all maintained that they were animals, notwithstanding the vigorous opposition of the great Linnaeus, who considered them to be partly animal and partly vegetable in nature, of Baster and others. It is not necessary, however, to give an account of this controversy here, as the reader will find a most interesting account of it in the first edition of Johnston's ' Zoophytes.' In the course of the controversy, however, de Jussieu paid a visit to Honfleur to study these forms in the living state, and the result was (19) that he produced for the first time a description and some fairly good figures of the polyps of Alcyonium digitatum. He says, " Nous avons soin de tremper dans nos bocaux une branche de chacun des ces plantes en particulier, et nous fumes sur- pris au premier aspect d'apercevoir, sans secours d'aucun in- strument, de petits insectes qui avoient chacun pour loge une des petites cellules formees dans le tissu de ce qui nousparois- soit la feuille d'une plante." It is to be noted that in this memoir de Jussieu uses the term "polype:" " J'appelle et dans la suite j'appellerai en general polype, une famille d'insectes de la nature des vers plus ou moins longs, dans les uns desquels la te"te et dans les autres le corps sont ou environnez ou parsemez de cornes, qui servent aux uns connue de mains pour prendre des choses dont ils font la nourriture, et outre cet ouvrage tiennent e.ncore lieu aux autres de pieds pour se mouvoir." It is difficult to say, however, whether he or Reaumur was the first to apply the word polype to the Coelenterate individual. The following passage in Reaumur's great work (34) is interesting as showing the reason for its adoption. Writing of Hydra he says, " De concert avec M. de Jussieu qui en avoit observe" aux environs de Paris et fait dessinez une espece du m§me genre, mais plus grande et d'une autre couleur je leur imposai 346 SYDNEY J. HICKSON. lenom de polype parceque leurs comes nousparurent analogues aux bras d'animal de mer qui est en possession de ce nom." The term was subsequently adopted by Trembley (36), and used by him in his classical work on ' Hydra.' At the commencement of the present century, however, the name Alcyonium was used to include a considerable number of marine fleshy, gelatinous, and spongy zoophytes, which are now known to belong to widely different groups of the animal kingdom. The description given by Ellis (8) of the genus is as follows: " Animal, plantae forma crescens. " Stirps fixa, carnosa, gelatinosa, spongiosa, vel coriacea; epidermide cellulosa poris stellatis s. osculis pertusa, hydras tentaculatas oviparas exserentibus." . Baster (1) describes the genus quite briefly as follows: " Die Alcyonia zyn zagte dog vaste zeegewassen die als een middelsoort tussen de Kruidige (Herbacea) en Hoornagtige (Keratophyta) entmaken." Included in the genus, as denned by Ellis, were a large number of Ascidians, sponges, and probably also some Bryozoa and Hydroids. In the systems of Miiller (177G) (31), Fabricius (1780) (10), Berkenhout (1795) (2), Turton (1809), Bosc (1807) (3), and others, we find the same conglomeration of animals included under the name Alcyonium. It must not be supposed, however, that because these natu- ralists included all these different forms of animals under the one generic name they were necessarily ignorant of more easily discerned characters of Alcyonium digitatum; it was rather their want of knowledge of the anatomy of the Ascidians, Bryozoa, &c, which led to the confusion. Ellis's (7) description of his figure runs as follows:—" A piece of Alcyonium manus marina cut perpendicularly through the middle to show that it is formed of tubes, which branch out into others, each ending on the surface in a starry opening of eight rays; in each of these openings is a polype- like figure or sucker with eight claws, fastened to the inside of the tube at its lower part by eight fine, tender filaments, by THE ANATOMY OF ALOYONIUM D1GITATUM. 347 which it can raise or sink itself at pleasure in its tube; all these tubes that compose this Alcyonium are connected to- gether by minute reticulated fibres; these enclose a stiff gelatinous substance which seems to be the flesh of this com- pound animal, and these fibres, with their enclosed contents, to be the muscles; for by the excretion of these it assists in opening or closing the stars on the surface, while the suckers or polype-like figures are pushing themselves out in search of food, or when they are retreating to secure themselves from danger." In 1816 Savigny clearly pointed out that the species Alcyonium digitatum, A. exos, and A. arborea, in the possession of eight pinnate tentacles, must not be classed with the Ascidians, the anatomy of which he described in some detail. Alcyonium exos was probably the Alcyonium palmatum of the Mediterranean, and Alcyonium arborea the Paragorgia of Norway. In Cuvier's ' Regne Animale' it is stated that in Alcyonium, as in the Pennatulese, we observe polyps with eight denticu- lated tentacles, and a stomach prolonged into the ovaries; but the first detailed description of an Alcyonid was that given by Milne Edwards in 1835 (9). This distinguished naturalist obtained some specimens of Paralcyonium (?), to which he applied the generic name " Alcyonide," at Cape Matifou, in Algeria, and he gave to the Academie des Sciences a description of the anatomy, which, considering the simplicity of his methods, is remarkably accu- rate and detailed. He pointed out the individuality of the polyps, and that each of them is capable of independent action, although acting in response to stimuli with its neighbours. He cut off a single polyp, opened it longitudi- nally, and discovered the stomodseum, with its free opening into the coelenteron, the eight mesenteries with their attach- ments, the ovaries, and the cavities in the tentacles. With regard to the structure of the colony, he pointed out that tubes (loges) running down into the colony are really the continua- tion of the polyps, " II suffit d'un examen superficiel pour se 348 SYDNEY J. HIOKSON. convaincre que ces loges ne sont autre chose que la continua- tion du corps des polypes eux-me'ines;" and asserted that the polyps do not retreat into their tubes like the Serpulse, &c, do, but into themselves by a sort of invagination.

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