Part II. of Volume II. will be published on November 75, igo^. The Fauna and Geography of the Maldive and Laccadive Archipelagoes Being the Account of the Work carried on and of the Collections made by an Expedition during the years 1899 ^^^ 1900 Edited by J. Stanley Gardiner, M.A. Fellow of Gonville and Caius College and late Balfour Student of the University of Cambridge. VOLUME II. PART I. With Plates XXVI—XXXIV Cambridge : at the University Press. London: C. J. Clay and Sons, Cambridge University Press Warehouse, Ave Maria Lane. Price Fifteen Shillings net. The Fauna and Geography of the Maldive and Laccadive Archipelagoes VOLUME li. PART I. HonUon: C. J. CLAY and SONS, CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, AVE MARIA LANE, AND H. K. LEWIS, 136, GOWEE STREET, W.C. ©lasgoto: 50, WELLINGTON STREET. Uripng: F. A. BROCKHAUS. ilrlD gorit: THE MACMILLAN COMPANY. ISomtia!) anl) Calrutta: MACMILLAN AND CO., Lid. [All Rights reserved.'] ' 4^ liS The Fauna and Geography of the ^^ Maldive and Laccadive Archipelagoes Being the Account of the Work carried on and of the Collections made by an Expedition during the years 1899 and 1900 Edited by J. Stanley Gardiner, M.A. Fellow of Gonville and Caius College and late Balfour Student of the University of Cambridge. VOLUME II. PART I. With Plates XXVI—XXXIV Cambridge : at the University Press. 1903 r o a :n-i : CAMBRIDGE PRINTED BY J. AND C. F. CLAY, AT THE UNIVERSITY PRESS. CONTENTS OF VOL. II. PAET I. Reports. PAGE 1. The Alcyonaria of the Maldives. Part I. The Genera Xenia, Telesto, Spongodes, Nephthya, Paraspongodes, Chironephthya, Siphonogorgia, Solenocaulon, and Melitodes. With Plates XXVI and XXVII 473 By Prof. Sydney J. Hickson, M.A., D.Sc, F.R.S. 2. The Alcyonaria of the Maldives. Part II. The Genera Sarco- phytum, Lohophytum, Sclerophytum, and Alcyonium. With Plates XXVIII—XXXI 503 By Edith JI. Pratt, M.So. 3. Nudibranchiata, with some Remarks on the Families and Genera and Description of a New Genus, Doridomorpha. With Plate XXXII 540 By Sir Charles Eliot, M.A., K.C.M.G. 4. Marine Crustaceans. IX. The Sponge-crabs (Dromiacea). With Plate XXXIII 574 By L. A. BORRADAILE, M.A. 5. On a Land Planarian from Hulule, Male Atoll, with a note on Leptoplana pardcdis Laidlaw . 579 By F. F. Laidlaw, B.A. 6. Lagoon Deposits. With Plate XXXIV. I. General Account . 581 By J. Stanley Gardiner, M.A. II. Report on Certain Deposits . 584 By Sir John Murray, K.C.B., F.R.S. THE ALCYONAPJA OF THE MALDIVES. PART I. THE GENERA XENIA, TELESTO, SPONGODES, NEPHTHYA, PARASPONGODES, CHIRONEPHTHYA, SIPHONOGORGIA, SOLENOCAULON, AND MELITODES. By Sydney J. Hickson, M.A., D.Sc, F.R.S., Beyer Professor of Zoology in the Oivens College, Manchester. (With Plates XXVI and XXVII.) INTRODUCTION. This collection of Alcyonaria from the Maldive archipelago is of more than ordinary interest. In most cases the species of Alcyonaria have been founded on a single specimen obtained from a single dredging or on two or three specimens obtained from a single locality. The interest of the present collection lies in the fact that specimens were obtained from a considerable number of dredgings made in several of the atolls or off the reefs of a very extensive archipelago, and consequently an opportunity is afforded for the study of the variation of form, colour, and other features within the limits of a wide area. I have no hesitation in saying that the general impression gained by the study of single specimens of the different genera from a reef is usually an erroneous one, because it cannot give due weight to the important facts of the possible variations of a species living in surroundings and under conditions which are, wthin certain limits, identical. If we were to take at random, for example, a specimen of Tuhipora from the reef off N. Celebes, and compare it with another specimen taken at random from the reef at Ternate, it is probable that so many differences would be found in the shape of the colony, the size of the tubes, the distance of the platforms, etc. in the two specimens that it would be thought necessary to make two species, one for the Celebes specimen and one for the Ternate specimen ; but anyone who walks along the N. Celebes reefs at low tide will find in one morning not only the reputed Ternate species but a complete series leading from that up to the reputed Celebes species, and beyond it. When I went out to Celebes the first thing I did was to collect specimens of Tuhipora, having already obtained a knowledge of the genus in Europe from books and museums, but the conclusion I came to was that there is only one species which varies on the one reef within limits almost as wide as the limits of all the hitherto described species of the genus. G. II. 61 474 SYDNEY J. HICKSON. The collection made by Mr Gardiner in the Maldives affords an opportunity of judging of the extent of variation possible in one group of islands of some other genera that are widely distributed. In the case of the genera Spongodes and Solenocaidon, for example, it is clear that there is a very great range of variation in form, colour, and in the size and shape of the spicules. They exhibit a number of " facies " which form an almost uninterrupted series between the types that have been described as distinct species. Now these facies are not confined to any one island of the Maldive archipelago, nor are they clearly separated from similar facies found in other parts of the tropical Indian and Pacific Oceans. If each facies represents a distinct species, then we have the very remarkable phenomenon of a large number of closely related species distributed over a very wide geographical area and competing in the struggle for existence, with approximately equal success, in many localities of this wide area. If, on the other hand, all the facies together represent but one species, then we have an example of a species that is capable of an extraordinary range of variation in circumstances which are approximately identical. As it is impossible to prove either one of these propositions without recourse to experiments in cross breeding, the only course to pursue, as a temporary measure, is to place in a separate species those facies which appear to be discontinuous with others in their form and distribution, and to collect into one species those facies that are connected by sufficiently continuous series of intermediate links. This is the course I have adopted in this paper. As an example of the method I may refer to the genus Solenocaidon, in which we have no less than eight specimens from different islands of the Maldive archipelago connected together to form a series, and one specimen which I have called S. ramosa distinguished from them in the tube-formation of the stem, the retractility of the polyps and other characters. This last I regard as a distinct species at present, but I think it is quite possible that a series of intermediate forms between it and S. tortiiosum may be found which will ultimately necessitate the abandonment of the specific name. It is a question of very great importance as bearing upon the species problem, whether the varying forms and colours of these Alcyonarians are due to sporadic variation irrespective of their environment or to distinct inherited characters. If we were to trace the history of 20 eggs of a brown divaricate Spongodes fertilised by the spermatozoa of another brown divaricate Spongodes, and settled down within a restricted area of a single reef, should we expect to find that all the young Spongodes developed from them were brown divaricates (BD), or should we expect to find that .some of them were red conglomerates (RC), others yellow flabellates (YF), etc.? If they are all BD, with of course variations in minor particulars, then we should be justified in believing that the brown colour and the divaricate manner of branching are not only transmissible by inheritance, but are so transmitted because they are of some importance to the species in the struggle for existence. If on the other hand the young Spongodes are of the facies BD, RC, YF, etc., then we should be justified in believing that the characters of the colour and mode of branching are of little or no importance for the species in the struggle for existence, but are due to the direct action of the environment (e.g. sunlight, food supply, strength of currents, proximity of neighbouring zoophytes, presence of epizoic Crustacea, etc.). THE ALCYONARIA OF THE MALDIVES. 475 Conversely, we may argue that if the colour and mode of branching are of little importance in the struggle for existence of the species the offspring of a single pair of parents will probably show a great range of variation in these characters, BD x BD gi"ving rise to BD's, R(Ts, YF's, etc. in varying proportions. It is impossible to believe that the struggle for existence has much influence upon the colour of these Alcyonarians. There is no evidence that the colours can be of assist- ance to the species either as apatetic colours, hiding the individuals from their enemies by resembling the suiToundings or some other dangerous zoophyte, or as aposematic colours, signalising some dangerous sting or abhorrent taste. Spongodes are, so far as my experience goes, extremely conspicuous in their proper surroundings, and do not mimic any other zoophyte that is usually associated with them on the same reef.