"!MM«<««i»iW««^^ ■ < '2' l^j; ;'i !.^" (W. 'h^^'^u K\ , -,w w '<»rrtv.fiM''Kv;>xwAiR'/Ay^'.y.w; un QOI^AL IS£ANDS% Wi^MMi WUi'iii|iiii>iiYii:iiiJMiiiiii>ii>^^ JSPSSSJS PM»i>w,iimtvm,itoi iSSSi - u TKci>vvsf^.^>u^ 4o 1350 HARVARD UNIVERSITY / * LONDON R. CI AY, SONF, AND TA\I.OR, PRINTERS, BREAD STREET HILL. PREFACE TO THE ENGLISH EDITION. In presenting this volume to English readers, the prominent part which the science of Britain has borne in the develop- ment of the subjects discussed comes naturally to mind. The remarkable works and memoirs of Ellis, from 1754 to 1786, which forced Linn/eus and Pallas ultimately to admit that corals belong to the animal kingdom, gave the earliest great impulse to the study of this branch of Zoology. On the other hand, Darwin's admirable investigations first made known the true nature and theory of coral reefs and islands. The publications of Ellis were constantly by my side in the preparation of my " Report on Zoophytes ; " and the theory of Darwin — as I have stated in my general preface — gave mc, in my ocean journeyings, not only light, but delight, since facts found their places under it so readily, and derived from it so wide a bearing on the earth's history. In later years have appeared the works of Johnston, Gosse, and HiNCKS, and the many memoirs of Gray, Forbes, Wright, Duncan, and other workers in science, which have aided largely in giving this department of Zoology its present advanced position. Since the subject of polyps is only incidental to the main topic of this volume, I have not had occasion to refer to the details of these memoirs. But the name of Gosse appears often in connection with passages cited from his " British Sea-Anemones ; " and I heartily com- mend his work to all who would appreciate the beauties ot PREFACE TO THE ENGLISH EDITION. these flower-like animals, and are able to enjoy science when well set forth by a genial author. Justice to France requires that these allusions to the science of polyps in Great Britain should be followed by a mention of the eminent names of Milne Edwards and Jules Haimr, of Paris, chief among the makers of the science of polyp- corals ; and by a reference also to the fact that France, through Peysonxel, was ahead in establishing by investigation the animal nature of corals, this observer proving his point at Marseilles, in 1723, on specimens of the very species that had just before been declared to be flowering plants by Marsigli, and afterward confirming his results by thirty years of study among the reef-corals of Guadaloupe. It should be added, also, that the rest of P'.urope has made large contribu- tions to the science, through Pallas, Esper, Ehrenberg, and other later investigators. If France, in past times, has taken the lead, she has had the advantage of a sea-coast of more than a thousand miles on the ocean, and of a long line also on the warmer and more prolific Mediterranean. The discovery of deep-sea corals by recent dredging expedi- tions has opened up a new field for coral investigations, no less important to (icology than to Zoology. But while so much attention has been absorbed in this direction, it should be remembered that the interest of the old coral-fields is far from exhausted, and that one great and most important sub- ject, the rate of growth of corals, and of the increase of reefs, waits for investigators. James D. Dana. New Haven, Conn., March i, 1872. PREFACE TO THE SECOND EDITION. The principal additions wliich have been made to this work in the preparation of the second edition are : an abstract of an important paper on the Bahamas, by Captain (now Major- General) Nelson, R.E., read before the Geological Society of London in 1852 ; an account of the interesting observations of Mr. J. Matthew Jones, from Nature of August 1872, bearing on the former extent of the Bermudas; facts stated by Mr. S. J. Whitnell with regard to some Pacitic coral islands ; and a report of the planting, by MM. Le Clerc and De Benaze, of slabs of coral rock at Tahiti, near the slab placed by Admiral Wilkes, to aid in future determinations of the rate of growth of the Dolphin Shoal, together with a Map of the region. Other minor changes have been made which it is not important here to enumerate. James D. Dana. March, 1875, h PREFACE. The object in view in the preparation of tins work has been to present a popular account of " Corals and Coral Islands," without a sacrifice of scientific precision, or, on the main topic, of fulness. Dry details and technicalities have been avoided as far as was compatible with this restriction, explana- tions in simple form have been freely added, and numerous illustrations introduced, in order that the subject may have its natural attractiveness to both classes of readers. 1 have opened the volume with a chapter on " Corals and Coral Makers,"" describing, under it, the forms and structure of Polyps ; how they Hve and grow and hold their own in a world of enemies ; how coralmaking species secrete their coral ; how they multiply, and develop their large clusters, spreading leaves and branching forms, so much like those among plants ; and in what seas they thrive, and under what conditions produce the coral plantations. All this is prefatory to the following part of the volume on Coral Reefs and Islands, which comprises a description of the features and structme of these reef-formations, an account of their mode of accumulation and increase, and a discussion of the origin of the included channels and lagoons, and of the distribution of reefs, together with a review of the facts with reference to their geological bearing. viii PREFACE. , The observations forming the basis of the work were made in the course of the cruise of tlie Wilkes Exploring Expedi- tion around the world during tlie four years from 1838 to 1842. The results then obtained are published in ,my Report on Zoophytes, which treats at length of Corals and Coral Animals, and in a chapter on Coral Reefs and Islands form- ing part of my Cieological Report. The opportunities for investigations in this department afforded by the Expedition were large, ^^'e visited a number of the coral islands of the Paumotu Archipelago, to the north of east from Tahiti ; also some of the Society, Navigator, and Friendly Islands, all remarkable for their coral reefs ; the P'eejee Group, one of the grandest regions of growing corals in the world, where we spent three montlis ; several islands north of the Navigator and Feejee Groups, including the Gilbert or Kingsmill Group ; the Sooloo sea, between Borneo and Mindanao, abounding in reefs ; and, finally, Singaj)ore, another P^ast India reef-region. Most agreeable are the memories of events, scenes and labours, connected with the cruise : — of companions in travel, both naval and scientific ; of the living things of the sea, gathered each morning by the ship's side and made the study of the day, foul weather or fair ; of coral islands with their groves, and beautiful life, above and within the waters ; of exuberant forests, on the mountain islands of the Pacific^ where the tree-fern expands its cluster of large and graceful fronds in rivalry with the palm, and eager vines or creepers intertwine and festoon the trees, and weave for them hangings of new foliage and flowers ; of lofty precipices, richly draped, even the sternest fronts made to smile and be glad, as delights the gay tropics, and alive with waterfalls, gliding, leaping, or plunging, on their way down from the giddy heights, and, as they go, playing out and in amid the foliage ; of gorges explored, mountains and volcanic cones climbed, and a burn- ing crater penetrated a thousand feet down to its boiling PREFACE. ix depths ; and, finally — beyond all these — of man emerging from the depths of barbarism through Christian self-denying, divinely-aided effort, and churches and school-houses standing as central objects of interest and influence in a native village. On the other hand, there were occasional events not so agreeable. Even the beauty of natural objects had, at times, a dark back-ground. When, for example, after a day among the corals, we came, the next morning, upon a group of Feejee savages with human bones to their mouths, finishing off the cannibal feast of the night ; and as thoughtless of any impro- priety as if the roast were of wild game taken the day before. In fact, so it was. Other regions gave us some harsh scenes. One— that of our vessel, in a tempest, fast drifting toward the rocks of Soutliern Fuegia, and finding anchorage under Noir Island, but not the hoped-for shelter Irom either winds or waves ; the sea at the time dashing up the black cliffs two and three hundred feet, and shrouding in foam the high rocky islets, half-obscured, that stood about us ; the cables dragging and clanking over the bottom; one breaking; then another, the storm still raging: finally, after the third day, -near midnight, the last of the four cables giving way, amid a deluge of waters over the careering vessel from the breakers astern, and an instant of waiting among all on board for the final crash ; then, that instant hardly passed, the loud calm command of the Captain, the spring of the men to the yard-arms, and soon the ship again on the dark, stormy sea, with labyrinths of islands, and the Fuegian cHffs to leeward ; but, the wind losing some- what of its violence and slightly veering, the ship making a bare escape as the morning dawned with brighter skies. And still another scene, more than two years later, on a beautiful Sunday, in the summer of 1841, when, after a cruise of some months through the tropics, we were in full expecta- tion of soon landing joyously on the shores of the Columbia ; X PRE FACE. of the vessel suddenly striking bottom ; then, other heavier blows on the fatal bar, and a quivering and creaking among the timbers ; the waters rai)idly gaining, in spite of the pumps, through a long night ; the morning come, our taking to the boats, empty handed, deserting the old craft that had been a home for three eventful years, for '* Cape Disappointment " — a name that tells of other vessels here deceived and wrecked ; and, twenty hours later, the last vestige of the old Peacock gone, her upper decks swept oft" by the waves, the hulk buried in the sands. But these were only incidents of a few hours in a long and ahvays delightful cruise. If this work gives pleasure to any, it will but prolong in the world the enjoyments of the " Exploring Expedition." In explanation of some allusions in the following pages, I may here state with regard to the Exploring Expedition, that Captain (now Admiral) Charles Wilkes, U.S.N., the Com- mander of the Expedition, was in charge of the Slooi)-or-war Vincenucs ; Capt. W^l L. Hudson, U.S.N., of the Sloop-of- war Peacock; Capt. A. K. Long, U.S.N., of the Storeshi]) Relief (the vessel which encountered the dangers in the Cape Horn sea, above related) ; and Eieut.-Commandant C. RiNGGOi>D, of the Brig Porpoise ; and that my associates in the "Scientific Corps" were Dr. Charles Pickering, J. P. CouTHOUY, and Titian R. Pkale, Zoologists ; Wm. Rich and J. D. Breckenridge, Botanists; Horatio Hale, Philologist : Joseph Dravt(3N and A. T. Agate, Artists. Our cruise ltd us partly along the course followed by Mr. Charles Darwin during the years 183 1 to 1836, in the voyage of the Peagie, under Captain Fitzrov ; and, where it diverged from his route, it took us over scenes, similar to his. of corq,l and volcanic islands. Soon after reaching Sydney, Australia, in 1839, a brief statement was found in the papers of Mr. Darwin's theory with respect to the origin of the atoll and barrier forms of reefs. The paragraph threw a flood of PREFACE. xi light over the subject, and called forth feelings of peculiar satisfaction, and of gratefulness to Mr. Darwin, which still come up afresh whenever the subject of coral islands is men- tioned. The Gambler Islands, in the Paumotus, which gave him the key to the theory, I had not seen; but on reaching the Feejees, six months later, in 1840, I found there similar facts on a slill grander scale and of more diversified character, so that I was afterward enabled to speak of his theory as estab- lished with more positiveness than he himself, in his philosophic caution, had been ready to adopt. His work on Coral Reefs appeared in 1842, when my Report on the subject was already in manuscript. It showed that the conclusions on other points, which we had independently reached, were for the most part the same. The principal points of difference relate to the reason for the absence of corals from some coasts, and the evidence therefrom as to changes of level, and the distribution of the oceanic regions of elevation and subsidence — ^topics which a wide range of travel over the Pacific brought directly and constantly to my attention. In the preparation of the present work my former chapter on Coral Reefs and Islands has been greatly extended by the addition of facts from numerous sources. The authorities cited from are stated in the courseof the volume, and need not here be rementioned. I have occasion, however, for special ac- knowledgments to our excellent Yale Zoologist, Professor A. K. Vp:rrill, who now stands first in the country in the depart- ment of Zoophytes. Through his recent memoirs on the subject, and also by his personal advice, I have been greatly aided in acquainting piyself with the present state of the science : — my own special labours in this branch of Zoology having ended in 1850, when both the Reports referred to above had been published, and the last of my Expedition departments — that of the Crustacea — forced my studies in another direction. The illustrations of the following pages have been drawn mainly from my Expedition Reports. Those not my own are xii PREFACE. from the works or memoirs of Gosse, Mubius, Verrill, Pour- tales, L. Agassiz, a. Agassiz, Smitt, Edwards and Haime, Wilkes and Hartt. In addition, the volume is indebted for a few cuts to the beautifidly ilhistrated popular works, " Le Monde du Mer " and '" La Vie et les Moeurs des Animaux ; " but nearly half of these were engraved from m.y plates. Tlie sources of all the figures are given in the List of Illustrations. James D. Dana. New Haven, Conn., Feb, 12, 1872. CONTENTS. . CHAPTER CORALS AND C(H 3^> Bunodes gemma. Author's Zoophyte Atlas, Plate 4, 3a, the polyp contracted. PAGE 6. Paractis Rapiformis, Edw. From a drawing by the Author, made in 1852. 7. Cancrisocia expansa. Verrill, Amer. Naturalist, from Proc. Essex Institute, vol. vi. 9. fig. I, Peachia hastata. Gosse's Actin. Brit, Plate viii. fig. 2, Edwardsia callimorpha ; and 3, Halocampa chrysanthellum. Ibid., Plate 7. 10. Section of Actinia. From a drawing by the Author, made in 1856, on the basis of a study ([852) of the Actinia figured on p. 6. 14. Lasso-cells. Dr. K. Mobius, Abh. Nat. Ver. Hamburg, vol. v., 1866. 22. Caryophyllia cyathus. Le Monde du Met. 23. Thecocyathus cylindraceus. Pourtales on Deep Sea Corals, Plate 2. Flabellum Povonium. 25. Ctenactis echinata, one-third natural size. La Vie et les Moeurs des Animaux. 26. Fungia lacera, living and expanded. Author's Zoophyte Atlas, Plate 18. 27. Enlarged view of tentacle of F. lacera, and profile, natural size, of one of the calcareous septa. Ibid., Plate 18. 29. Madrepora aspera, living and expanded. Author's Zoophyte Atlas Plate 38. 31. Dendrophyllia nigrescens, living and expanded. Author's Zoophyte Atlas, Plate 30. 32. Goniopora columna. Ibid., Plate 56. 33. Porites mordax. Ibid., Plate 53. 34. Cladocora arbuscula. Ibid., Plate 30. 35. Orbicella cavernosa. L. Sanford, from specimen. 36. Spontaneous fission. Author's Repoit on Zoophytes. 37. Astraea pallida. Author's Zoophyte Atlas, Plate 10. 37. Caulastrasa furcata. Ibid., Plate 9. b X vi ii LIST OF ILL USTRA TIONS. lAGE 40. Epizoanthus Americanus, Verrill, Amer. Naturalist, vol. iii., p. 248. View of single polyp. From a drawing by Prof. Verrill. 41. Antipathes arborea. Author's Zoophyte Atlas, Plate 56. , 42. Enlarged view of polyp of A. arborea. Ibid., Plate 56. 43. Astra-a pallida. Author's Zoophyte Atlas, Plate lo. 44. Diploria cerebriformis. Le Monde du Mer. 45. Fungia Danw. L. Sanford, one-sixth the natural size ; from a photo- graph by Prof. A. Y.. Verrill. 46. Caryophillia Smithii, one of the figures with the" animal expanded ; the other with it contracted. Gosse's Actinologia Britannica, Plate 10. 47. Astrangia Uanae; fig. a one of the polyps enlarged; c, coral with the polyps expanded, natural size. Agassiz, Seaside Studies, fig. b, surface of corallum, natural size. L. Sanford, from specimen. 69. Phyllangia Americana, a Florida species. Edwards and Haime, Corallieres. fig. I, Oculina varicosa, extremity of a branch. Author's Report on Zoophytes, page 67, corrected from specimen, figs. 2, 3, Stylaster erubescens ; 2, corallum, natural size ; 3, extremity of a branch enlarged. Pourtales, Deep-Sea Corals, figs. 4, 5, Stylophora Dana; ; 4, extremity of a branch ; 5, one of the calicles enlarged. Author's Zoophyte Atlas, Plate 4Q. fig. 6, Polyp, enlarged, of St. mordax. Author's Zoophyte Atlas, Plate 49. fig. 7, Pocillipora grandis. L. Sanford ; from an Exploring Expe- dition specimen ; portion of one of the large, flattened branches of the corallum. An entire clump is figured in the Author's Zoophyte Atlas, Plate 51. fig. 8, cell, enlarged, of Pocillipora elongata. Author's Zoophyte Atlas. Plate 50 fig. 9, cell, enlarged, of Pocillipora plicata. Ibid. Plate 50. fig. 10, vertical section of corallum of P. plicata, showing the tabular stnicture. Ibid., Plate 50. 50. Polyp of Madrepora cribripora, enlarged. Author's Zoophyte Atlas, Plate 31. 51. Madrepora formosa. Author's Zoophyte A.tlas, Plate 38. 52. Polyp of Dendrophyllia nigrescens, enlarged. Ibid., Plate 30. 53. Dendrophyllia nigrescens, natural size. Ibid., Plate 30. 54. Alveopora Verril.Uana, natural size ; the corallum covered below with a peritheca. Author's Zoophyte Atlas, Plate 48. The species is here named after Prof. A. E. Verrill, as it is not the true A. dedalea. Alveopora spongiosa, vertical section of corallum, and upper view of calicle, much enlarged ; the diameter of the cell being about a fifteenth of an inch. Author's Zoophyte Atlas, Plate 48. 55. Polyp of Porites levis, enlarged. Author's Zoophyte Atlas, Plate 54. 6. Porites levis, with the polyps of one of the branches expanded, natural size. Author's Zoophyte Atlas, Plate 54. 59. Xenia elongata. Author's Zoophyte Atlas, Plate 57. 60. Anthelia lineata. Verrill, Proceedings of the Essex Institute, vol. iv., Plate 5. From a drawing by Dr. Stimpson. 60. Telesto ramiculosa. Verrill, Proceedings of the Essex Institute, vol. iv., Plate 6 ; the second figure an enlarged view of expanded polyp. From drawings by Dr. Stimpson. LIST OF ILLUSTRA TIONS. xix '6^ Tubipora syringa ; fig. i. part of a clump, natural size ; 2, one of the polvps expanded. Author's Atlas, Plate 59. . v •• 1 , Tubipora fimbriata (3rd figure) polyp, expanded. Author s Zoophyte Atlas, Plate 59. , • a .1 ' v •• 62. Gorgonia (?) flexuosa, part of zoophyte, natural size. Author s Zoo- 6:; SpFcSes^f c'orgo^^,''much enlarged. Verrill, Transactions of the Connecticut Academy of Sciences, vol. 1., Plates 4 and 5. 6:;. Isis Hippuris. La Vie et les Moeurs des Annnaux. 66. CoralUum rubrum, the coral, natural size. L. Sanford, from specimen. Extremity of branch of C. rubrum, enlarged, with some of the ani- mals expanded. Lacaze-Duthiers, from La Vie et les Moeurs des Animaux. , ^ 1 j • r ^„ 68 Cophobelemnon clavatum ; the small figure, enlarged view of one of the polyps. Verrill, Proceedings of the Essex Institute, vol. iv , Plate «;. From a drawing by Dr. Stimpson. Veredllum Stimpsoni, enlarged 3 diameters. Verri 1, Proceedings of the Essex Institute, vol. iv., Plate 5. From a drawing by Dr. Stimpson. 71. Caulastrrea furcata. Author's Zoophyte, Plate 9. 77. Hydra. Le Monde du Mer. 78. Hydramania falcata. Le Monde du Mer. 79 Millepora alcicornis. La Vie et les Moeurs des Animaux. 80. Animals of M. Alcicornis, enlarged. L. Agassiz, Contributions to the Natural History of the United States ; vol. 111., Plate 15. 81. Hornera lichenoides: I, natural size ; 2, part of branch enlarged. Smitt's Mem. des Bryozoaires. , tt.- 1 Discosoma Skenei, part of a group much enlarged, ibid 103. High Island, with Barrier and Fringing Reefs. Author s Geol. Report, 106 Map of New Caledonia. Darwin on Coral Islands. III. The Lixo Coral Abrolhos. Harrt's Brazil, p. 202. 119. Coral Reefs off the North Shore of Tahiti. Author's Exp. Geolo- crical Report, from the Wilkes Expl. Maps. 131. Coral Island, or Atoll. Wilkes's Narr. Expl. Exped. 133. Map of Gilbert or Kingsmill Islands. Authors Geol. Rep.; from Expl. Exp. Maps. ^ . , t 1 i 1 13=:. Maps ot Taiara, Henuake, Swain's Island, Jarvis s Island, and Fakaafo. Author's Geol. Rep. ; from Expl. Exp. Maps. ^ 137. Map of Menchikofif Atoll. Darwin on Coral Reefs ; from Kotzebue s Atlas 142. Section of the rim of an Atoll. Author's Exp. Geol. Report. 145. Blocks of Coral on the shore platform of Atolls. Authors Geol. Report. 1 T> f 1 1,2 Map of Maldive Archipelago. Darwin on Coral Reels. 153. Map of Mahlos Mahdoo Atoll, one of the Maldives. Darwm on Coral Reefs. 155. Map of Great Chagos Bank. Darwin on Coral Reels. I «;6. East and West Section across the Great Chago^Bank. Ibid. 158. Metia, an elevated Coral Island. Wilkes's Narrative of Expl. Exp., 183 Map of the Bermuda Islands. Reduced from an English chart. 197. The "Old Hat." Author's Exp. Geol. Report. X X LIS T OF ILL US TRA TIONS. PAGE 204. Harbour of Apia. Author's Exp. Geol. Rep. ; [from charts of the Wilkes Expl. Exped. 206. Part of North Shore of Tahiti. Ibid. 208. Harbour of Falifa. Ibid. 210. Whippey Harbour. Ibid. 217. Map of the Coral reefs in Matavai Bay, Tahiti; from a chart by MM. Le Clerc and Minier. 223. Section illustrating the Origin of Barrier Reefs. Ibid. 224. Map and Ideal Section of Aiva Island. Ibid. 227. Map of Gambler Islands. Darwin on Coral Reefs. 229. Section illustrating the Origin of Atolls. Author's Exp. Geol. Rep. 230. Menchicofif Atoll. Darwin on Coral Reefs. 235. Fakaafo. Author's Geol. Rep., from Charts of Expl. Exped. At close of vohime : — Isocrymal Chart of the World. Author's Report on Crustacea. Map of the Feejee Islands. Wilkes's Narrative of the Expl. Exped. Map of the Florida Reefs, and the Seas between them and Cuba. De Pourtales on Deep-Sea Corals. ( I CORALS AND CORAL ISLANDS, CHAPTER I. CORALS AND CORAL MAKERS. A SINGULAR degree of obscurity has possessed the popular mind with regard to the growth of corals and coral reefs, in consequence of the readiness with which speculations have been suppUed and accepted in place of facts ; and to the present day the subject is seldom mentioned without the quali- fying adjective mysterious expressed or understood. Some writers, rejecting the idea which science had reached, that reefs of rocks could be due in anyway to "animalcules," have talked of electrical forces, the first and last appeal of ignorance. One author, not many years since, made the fishes of the sea the masons, and in his natural wisdom supposed that they worked with their teeth in building up the great reef. Many of those who have discoursed most poetically on zoophytes have imagined that the polyps were mechanical workers, heaping up the piles of coral rock by their united labours ; and science is hardly yet rid of such terms as polypary, polypidom, which imply that each coral is the constructed hive or house of a swarm of polyps, like the honeycomb of the bee, or the hillock of a colony of ants. B 2 CORALS AND CORAL LSL.AhWS. Science, while it penetrates deeply the system of things about us, sees everywhere, in the dim limits of vision, the word mystery. Surely there is no reason why the simplest of organ- isms should bear the impress most strongly. If we are aston- ished that so great deeds should proceed from the little and low, it is because we foil to appreciate that little things, even the least of living or physical existences in nature, are, under God, expressions throughout of comprehensive laws, laws that govern alike the small and the great. It is not more surprising, nor a matter of more difficult com- prehension, that a polyp should form structures of stone (car- bonate of lime) called coral, than that the quadruped should form its bones, or the mollusk its shell. The processes are similar, and so the result. In each case it is a simple animal secretion ; a secretion of stony matter from the aliment which the animal receives, produced by the parts of the animal fitted for this secreting process ; and in each, carbonate of lime is a constituent, or one of the constituents, of the secretion. This power of secretion is then one of the first and most common of those that belong to living tissues ; and though dif- fering in different organs according to their end or function, it is all one process, both in its nature and cause, whether in the Animalcule or Man. It belongs eminently to the lowest kinds of life. These are the best stone-makers ; for in their simpli- city of structure they may be almost all stone and still carry on the processes of nutrition and growth. Throughout geological time they were the agents appointed to produce the material ot limestones, and also to make even the flint and many of the siliceous deposits of the earth's formations. Coral is never, therefore, the handiwork of the many-armed polyps ; for it is no more a result of labour than bone making in ourselves. And again, it is not a collection of cells into which the coral animals may withdraw for concealment any more than the skeleton of a dog is its house or cell ; for every part of the coral — or corallum, as it is now called in science — of a polyp, in most reef-making species, is enclosed within the polyp, where it was formed by the secreting process. i CORALS AND CORAL MAKERS. 3 It is not, perhaps, within the sphere of science to criticise the poet. Yet we may say in this place, in view of tlie frequent use of the Hnes even by scientific men, that more error in the same compass could scarcely be found than in the part of Montgomery's "Pelican Island" relating to coral formations. The poetry of this excellent author is good, but the facts nearly all errors — if literature allows of such an incongruity. There is no "toil," no " skill," no " dwelling," no " sepulchre " in the coral plantation any more than in a flower-garden ; and as little are the coral polyps shapeless worms that " writhe and shrink their tortuous bodies to grotesque dimensions." The poet oversteps his license, and besides degrades his subject, when downright false to nature. Coral is made by organisms of four very different kinds. These are : First^ Polyps, the most important of coral-making animals, the principal source of the coral reefs of the world. Second, Animals related to the little Hydra of fresh waters, and called Hydroids (a division under the Acalephs), which, as Agassiz has shown, form the very common and often large corals called Millepores. Thh'd, The lowest tribe of MoUusks, called Bryozoans, which produce delicate corals, sometimes branching and moss-like (whence the name from the Greek for moss animal), and at other times in broad plates, thick masses, and thin incrustations. Although of small importance as reef-makers at the present time, in a former age of the world — the Paleozoic — they so abounded over the sea bottom that some beds of limestone are half com- posed of them. Fourth, Algai or sea-weeds, some kinds of which would hardly be distinguished from corals, except that they have no cells or pores. I. POLYPS. A good idea of a polyp may be had from comparison with the garden aster ; for the likeness to many of them in external form as well as delicacy of colouring is singularly close. The 4 CORALS AND CORAL LS LANDS. aster consists of a tinted disk bordered with one or more series of petals. And, in exact analogy, the polyp flower, in its most common form, has a disk fringed around with petal-like organs called tentacles. Below the disk, in contrast with the slender pedicel in the ordinary plant, there is a stout cylindrical pedicel or body, often as broad as the disk itself, and sometimes not much longer, which contains the stomach and internal cavity of the polyp ; and the mouth, which opens into the stomach, is at the centre of the disk. Here then the flower-animal and the garden-flower diverge in character, the difference being required by the different modes of nutrition and other characteristics in the two kingdoms of nature. The coral polyp is as much an animal as a cat or a dog. The figures of the frontispiece, and others on pages 6, 7, 9, sustain well the description here given, and afford some idea also of the diversity of form among them. The prominent subdivisions of polyps here recognized are the following : — I. AcTiNoiD Polyps. — Related to the Actinia, or vSea- anemone, in tentacles and interior structure, and having, as in them, the number of tentacles and interior septa a multiple of six. The name Actinia is from the Greek ray. II. CvATHOPHYLLOiu PoLYPS. — Like the Actinoids in tenta- cles and interior structure, except that the number of tentacles and interior septa is a multiple of four. Ludwig and De Pourtales state that the number in the earliest young state is six, and that therefore the fundamental ratio is the same as in the Actinoids ; and that they pass from this ratio by develop- ments of tentacles and septa more rapidly on one side than the opposite, and in such a manner that the number becomes after the first stage a multiple of four. The Cyathophylloid polyps hence combine this characteristic of the Actinoids with one fea- ture of the Alcyonoids. The Cyathophylloids were the earliest of polyps, and the most abundant species in Paleozoic time. HI. Alcyonoid Polyps. — Having eight fringed tentacles, and other characters mentioned beyond ; as the Gorgonix and Alcyonia. CORALS AND CORAL MAKERS. 5 I. ACTINOID POLYPS. 'J'he highest of Actinoid Polyps are those of the Actinia iKiBE — the species that secrete no coral to clog vital action and prevent all locomotion. The details of structure may be best described from the Actinia or Sea-anemone, and aftei- ward the distinguishing characters of the coral-making polyps may be mentioned. In external aspect and in internal charac- ters all are essentially identical. I. NON-CORAL-MAKING POLYPS. As the figures on the frontispiece, and also the following, show, the external parts of an Actinia are — a subcylindrical body— a disk at top — one or more circular series of tentacles making a border to the disk — a mouth, a merely fleshy, tooth- less opening, at the centre of the disk, sometimes at the summit of a conical prominence — a basal disk for attachment. The upper extremity is called the actinal end, since it bears the tentacles or rays, and the lower or base, the abadhial. Sea-anemones vary greatly in colour, and in the distribution of their tmts. The lower figure on the frontispiece represents one variety of the Fhy?tiaclis clematis from Valparaiso. Another variety of the same lias a rich deep green colour. The upper species on the same plate is one of the gorgeous varieties of the Phymadis florida from Callao, Peru. Another is green throughout ; and another has a pale bluish-green disk with purplish tentacles, and the papillae of the body dark sap-green on a pale reddish ground. The other species is the Biuiodcs ganma, from Porto Pray a. Cape Verd. It is one of the warty species, and is but partly expanded. The same is shown un- expanded m figure 3^;, on the right, with disk and tentacles, as usual in this state, wholly concealed. While often brilliantly coloured, especially in the tropics, other Actiniai are nearly colourless. This was the case with that represented in the following cut, a species from Long Island Sound near the New Haven Lighthouse, figured some twenty years since by the author, but left undescribed. The 6 CORALS AXD CORAL ISLANDS. body in this species had a delicate texture throughout, its walls being so transparent that the organs within could be seen through them. It was exceedingly flexible and passed through various shapes, imitating vases of many forms, wine glasses, goblets, &C. It was generally very slow^ in its changes, and sometimes continued in the same vase-attitude for a whole day. I'AKACrib KAl'IFOK.MIS, KUW. Actiniae vary immensely in size— from an eighth of an inch and smaller in the diameter of the disk to over a foot — though commonly between half an inch and three inches. One species from the Paumotu Coral Archipelago in the COKALS AND CORAL MAKERS. 7 Pacific, a coloured figure of which is given in the Atlas of the Author's Report on Zoophytes (Plate HI.)? had a diameter across its disk o( four tee? i inches ; and it was also one of the most beautiful in those seas, having multitudes of tentacles with carmine tips and yellowish bases, around the open centre, gathered into a number of large groups or lobes. With rare exceptions. Actiniae live attached to stones, shells, or the sea bottom, or are buried at base in the sand or mud. The attached species have the power of locomotion, through the muscles of the base, but only with extreme slowness. The loose stones on a sea-shore near low tide level often have Actiniae fixed to their under surface. A very few species swim or float at large in the ocean. CAXCRISOCIA EXPANSA St., ON THE BACK OF DORII'I'E FACCHINO. Now and then an Actinia puts itself on the back of a crab, and thus secures rapid locomotion, but only at the will of the crab, which may at times give it some hard rubs : — a kind of association styled cotnmensalisju by Van Beneden, as the two in a sense live at the same table, without preying one upon the other. In the above example, from the China seas, the Actinia has mounted a Dorippe. The figure is from the Proceedings of the Essex Institute, where an account of it is 8 CORALS AND CORAL LSLANDS. published by Prof. Verrill ; the specimen was collected by the Zoologist, Dr. W. Stimpson. As Prof. Verrill states, the Dorippe carries, for its protection when young, a small shell over its back, which it holds in this position by means of its two reversed pairs of hind legs. The Actinia appears to have fixed itself, when young, to the shell, and afterwards, by its growth, spread over the back of the crab, taking the place of the shell. This case of commensalism, like most others, is not a mere chance association of species, for the two always go together, the Actinia, according to Dr. Stimpson, never being seen except upon the crab's back, and the crab never without its Actinia. The fact shows an instinctive liking on the part of the Actinia for a Dorippe courser, and for the roving life thus afforded it. And the crab is undoubtedly conscious that he is carrying his fortress about with him. It is not a solitary case ; for there are many others of Actiniae attaching themselves to locomotives — to the claws or backs of crabs, or to shells in possession of soldier crabs, or to a Medusa ; and frequently each Actinia has its special favourite, proving an inherited instinctive preference for rapid change of place, and for just that kind of change, or range of conditions, which the pre- ferred commensal provides. Prof. Verrill has an interesting article on this subject, with especial reference to crustaceans, in the third volume of the Aino'ican Naturalist. Species living in sand are often unattached ; and then the base is rounded or tapering, and sometimes balloon-shaped ; some of them are long and almost worm-like, and even burrow like worms. The following are figures of three species : one, figure 3, exhibiting simply the tentacles and disk of the Actinia, the only parts visible above the sand ; the others showing the whole body removed from the sand, and consequently a little out of shape. They are from Gosse's " British Sea-Anemones," in which they are given with the natural colours. Figure i re- presents the Peachia hastata of Gosse, a beautiful species hav- ing twelve large tentacles; figure 2 the Edwardsia callvnorpha COKALS AND COITAL MAKERS. 9 ().; figure 3, Halocampa chrysa?ithcUum G. Most of these sand- dwellers bury themselves like the Halocampa, and often hide all the disk but the mouth. The Edwardsia is peculiar in having, above the hollow bladder-like basal portion, a firm opaque exterior to the body, making for it a kind of case or jacket, into which the upper extremity, which is soft and delicate in texture, may be retracted. I'he thickening of the epidermis in this middle portion is produced through the entanghng of disintegrated cells and minute foreign particles, sometimes in part spores of Confervae, by means of the mucus of the surface ; and if the layer is removed, as it may be, the skin will again become covered. This species, like others of the genus, Uves buried to its neck in the sand, that is, with the soft upper extremity protruding. If disturbed, the head is suddenly drawn in, together with more or less of the following jacketed part of the body. lO CORALS AND CORAL ISLANDS. The warty prominences on some warty species have the power of clinging by suction to a surface, and such Actiniae often cover their sides thus with bits of shell or of other sub- stances at hand. Where there are no warts the contracted exterior skin, reticularly corrugated, occasionally becomes a surface of suction-warts, as in many Sagartiae. The hiteriial sti'iidure oi the Actinia is radiate like the ex- ternal, and more profoundly and constantly so. The mouth, a fleshy toothless opening in the disk, opens directly into a stomach, which descends usually about a third of the way to the base of the body ; its sides are closed together unless it be in use. The general cavity of the body around and below the stomach is divided radiately by fleshy partitions, or septa, into narrow compartments ; the larger of these septa connect the stomach to the sides of the animal, and, besides holding it in place, serve to pull it open or distend it for the reception of food. The above figure represents in a general way a horizon- tal section of the body through the stomach, and shows the posidon of the radiating septa and the intermediate compart- ments. It presents to view the fact that these are in pairs, and another fact that the number of pairs of partitions in the ordinary Actinoid polyps is regularly some multiple of six, although other numbers occur during the successive develop- ments that take place in the growth of a polyp, and are CORALS AND CORAL MAKERS. ii occasionally persistent in the adult state. There are six pairs in the first series ; six in the second ; twelve in the third ; twenty-four in the fourth ; forty-eight in the fifth, and so on. The compartment between the two septa of each pair opens at top into the interior of a tentacle, and thus tlie cavity in each tentacle has its special corresponding compartment below. This tentacular compartment is properly, as first recognized by Prof. Verrill, the a?nbulacral, since each corresponds in position and function to an ambulacral or tentacle-bearing section in the Echinoderms and other Radiate animals. Although polyps are true Radiates, they have something ot the antero-posterior (or head-and-tail) polarity, with also the right-and-left, which is eminently characteristic of the animal type. This is manifested in the occurrence in some polyps of a ray on the disk different in colour from the general surface ; of one tentacle larger than the others, and sometimes peculiar in colour ; of two opposite septa in a calicle or polyp-cell larger than the others, and sometimes meeting so as to divide the cell into halves. The first of these marks the author has observed in a Zoanthid, as mentioned in his Report on Zoophytes at page 419, and represented on plate 30 : and the last is very strongly developed in the cells of many Pocillopor^ (ib. p. 523)- Gosse and many other authors have drawn attention to the one large tentacle, and the fact that it lies in the direction of the line of the mouth. Prof H. James Clark, in his "Mmd in Nature," states that the order in which the fleshy septa and the tentacles in an Actinia are developed has direct reference to the right and left sides of the body, and that there is only one plane in which the body can be divided into two halves, and this is that corresponding with the longer diameter of the stom- ach, or the direction of the mouth. Mr. A. Agassiz has shown that in Actiniae of the genus Arachnactis, the new septa and tentacles are developed on either side of the one chief or anterior tentacle : and Prof. Verrill, that in Zoanthids they are formed principally on either side of this anterior tentacle and also ot the opposite or posterior one, and much less rapidly, if at all, along the sides intermediate. This chief-tentacle marks properly 12 CORALS AND CORAL LS LANDS. the true front or anterior side of the polyp. A fore-and-aft structure is also very strongly marked in some of the ancient cyathophylloid corals, and hence it belonged to the type from early Paleozoic time. The way leading out from the Radiate structure is thus mani- fested *by these flower-like polyps. In fact perfect circular series in organs or parts do not belong to any living organism, not even to the true flower ; for growth is fundamentally spiral in its progress, and there must be always an advance end to the spiral of growth ; all apparent circles are only disguised spirals. The walls of the body contain two sets of muscles, a circu- lar and a longitudinal, the latter becoming radial in the disk and base. Similar muscles exist also in the tentacles, and cor- responding muscles in the fleshy partitions or septa of the in- ternal cavity. By means of these muscles an Actinia, whenever disturbed, contracts at once its body ; and most species make of them- selves a spheroidal or conoidal lump, showing neither disk nor tentacles. One example of this contracted state is presented on the frontispiece in figure 3<^. After a brief period of quiet the polyp commonly reassumes its full expansion. The ex- ])ansion depends on an injection of the structure with salt water, which is taken in mainly by the mouth. As the whole body is thus filled and injected, the flower slowly opens out, and shows its petal-like tentacles. On contraction the water is suddenly expelled through the mouth, and by pores in the sides of the polyps, and at the extremity of the tentacles, and the tentacles disappear, along with the disk, beneath the adjoining sides of the body which are. drawn or rolled in over them. The Actinia appears, at first thought, to be well prepared for securing its prey through its numerous tentacles. Bat these are generally too short for prehension. Yet the disk often aids them by rolling over the captured animal, and pushing it down into the stomach. At the same time, the mouth and stomach are both very extensile, so that an Actinia may swallow an animal nearly as large as itself; it gradually stretches the CORALS AND CORAL MAKERS. 13 m.irgins of the mouth over the mollnsk or crab, until the ^' .:oIe is inclosed and passed into the digestive sac ; and when tl, estion is complete, the shell and any other refuse matters are easily got rid of by reversing the process. But the Actinia owes nearly all its power of attack to its concealed weapons, which are carried by myriads. These are what Agassiz has called lasso-cells^ because the little cell-shaped sheath contains a very long slender tubular thread coiled up, which can be darted out instantly when needed. As first observed by Agassiz, the tubular lasso escapes from the cell by turning itself inside out, the extremity showing itself last, and this is usually done " with lightning-like rapidity." Then follows the poison. The lasso-cells (called often nettling cells, and by Gosse cnidcs, and thi-ead capsules) are usually less than a 200th of an inch in length ; but they are thickly crowded in the larger part of the skin or walls of the tentacles, and about the mouth ; also in the walls of the stomach, and within the visceral cavity in white cords hanging in folds from the edge of the septa. Thus the polyp is armed inside and out. The mollusk or crab that has the ill luck to fall, or be thrown by the waves, on the surface of the pretty flower is at once pierced and poisoned by the minute lassos, and is ren- dered incapable of resistance. The following figures, by Dr. Karl Mobius, of Hamburg, illustrate admirably these organs. The views are magnified 700 diameters. Figure i represents one of the lasso-cells of the Actinia, Corynactis viridis^ with its lasso coiled up within ; its actual length is about a 350th of an inch. Figure 2 is the same with the lasso out, though less than half of the long thread is shown. Figure 3 is the lasso-cell of the polyps of a European coral, the Caryophyllia Smithii. It differs from figure I in having the basal part of the lasso within the cell or sheath strait and stout ; it is this part which makes the first portion of the extended lasso. A view of part of the latter is represented in figure 4, and of the extremity of the same in figure 5. The lasso-cells in the above species are from a 240th to a 360th of an inch in length. In the Aletridmm viargina- CORALS AND CORAL LSLANDS. tum^ an American Acti- nia occurring along the coast of the United States, north of New York, the length of one of the lasso-cells, ac- cording to Dr. Leidy, was about a 400th of an inch, and the charac- ter of the extended lasso was much like that ot figure 4. The lower part of the lasso, for a length \\ times or more longer than the cell or sheath, is usually thick- ened, and sometimes slender ly spindle- shaped, while the rest is an even slender thread ; and the thickened part, and sometimes all the rest, as above shown, is spirally wound by a slender line, sometimes elevated, set with short hairs or bristles. The thread-like portion may be wanting or very short. The lasso is often twenty times as long as the cell or sheath, and occasion- ally forty times ; but if the thread-like part is absent, only one and a half to two times. A lasso cell once used CORALS AXD CORAL MAKERS. 15 is afterward worthless ; for the tube cannot be returned to tlie sheath. But those thus expended are not missed, as the ])olyp has indefinite suppUes of such weapons, and also ready means of refurnishing itself Figures 6, 7,8, 9, 10, pp. 14, 15, illustrate different stages in the development of a lasso-cell (figure ro) out of a com ^^m mon spherical cell, as made out by Dr. Mobius in his j^B careful microscopic investigations. The Actinia afford- IH^ ing the results was the Urticina crassicornis, found in ■^|i both European and American seas. The actual size of B|y the cell represented in figure 6 is about a 5000th of an K^ inch. In figure 7 the lasso-cell has already taken form 1^9 but is folded on itself; in 8, there is a second infold- iBI ing ; 9 shows a return to a single fold, and further ^SA progress in the forming cell; and 10, the straightened- Wtm lasso-cell. Thus the work of replenishing, throughout the body wherever lassos are used, is always going on. The radiating partitions or septa in the internal cavity ot the polyp have along the outer free edge what looks like a slender white cord attached to it by a much convoluted or mesentery-like membrane ; and this cord contains vast num- bers of lasso-cells radiately arranged. These white cords through the multiplied plaitings of the mesenteric membrane have great length ; and they sometimes extend up through the stomach and pass out of the mouth ; or they are extended in loops through the walls wherever they may happen to be torn. There are often also bunches of somewhat similar white cords full of lasso-cells appended to the septa, which are ex- tended from the body through some natural orifices near the base of the Actinia (especially those of the Sagartia family), (iosse calls these cords Acontia. They extend out usually two or three inches, and sometimes six inches, and thereby widen much the stinging range of an Actinia, both for the purposes of defence and attack. Gosse, in his " British Sea- Anemones," gives the results of some experiments with regard to the action of these lasso-cells {cnidce)^ from which a few paragraphs may be here cited. i6 CORALS AND CORAL ISLANDS. " It has long been known, that a very slight contact with the tentacles of a polyp is sufficient to produce, in any minute animal so touched, torpor and speedy death. Since the dis- covery of these c/iida; (lasso-cells) the fatal power has been supposed to be lodged in them. Baker, a century ago, in speaking of the Hydra, suggested that ' there must be some- thing eminently poisonous in its grasp ; ' and this suspicion received confirmation from the circumstance that the Entomos- traca which are etiveloped in a shelly covej'lng frequently escape unhurt after having been seized. The stinging power possessed by many Medusae, which is sufficiently intense to be formid- able even to man, has been reasonably attributed to the same organs, which the microscope shows to be accumulated by miUions in their tissues. " Though I cannot reduce this presumption to actual cer- tainty, I have made some experiments, which leave no reason- able doubt on the subject. First — I have proved that the edhorceum (tubular thread of the lasso-cell) when shot out, has the power of penetrating, and does actually penetrate, the tissues of even higher animals. Several years ago, I was examining one of the purple acontia of Adamsia palliata ; no pressure had been used, but a considerable number of cnidcc had been spontaneously dislodged. It happened that I had just before been looking at the sucker-foot of an Asterina, which remained still attached to the glass of the aquatic box, by means of its terminal disk. The cilia of the acofitiiim had, in their rowing action, brought it into contact with the sucker, round which it then continued slowly to revolve. The result I presently discovered to be, that a considerable number of cnidce. had shot their ecthorcea into the flesh of the sucking-disk of the Echinoderm, and were seen sticking all round its edge, the wires (lassos) being imbedded in its substance even up to the very capsules, like so many pins stuck around a toilet pin- cushion. '' To test this power of penetration still farther, as well as to try whether it is brought into exercise on the contact of a foreign body with the living Anemone, I instituted the follow- CORALS AND CORAL MAKERS. 17 ing experiment. With a razor I took shavings of the cuticle from the callous part of my own foot. One of these shavings I presented to the tentacles of a fully-expanded Tealia crassi- cornis {Urlicina crassicornis of Europe and America). After contact, and momentary adhesion, I withdrew the cuticle, and examined it under a power of 600 diameters. I found, as 1 had expected, cnidce standing up endwise, the wires in every case shot into the substance. They were not numerous — in a space of -Qi inch square, I counted about a dozen. . . . " These examples prove that the slightest contact with the proper organs of the Anemone is sufficient to provoke the dis- charge of the cnidcE; and that even the densest condition of the human skin offers no impediment to the penetration of the cct/iorcea. "As to the injection of a poison, it is indubitable that pain, and in some cases death, ensues even to vertebrate animals from momentary contact with the capsuliferous organs of the Zoophyta. ... I have elsewhere recorded an instance in which a little fish, swimming about in health and vigour, died in a few minutes with great agony through the momentary con- tact of its lip with one of the emitted acontia of Sagai'tia para- sitica. It is worthy of observation, that, in this case, the fish carried away a portion of the acontium sticking to its lip ; the force with which it adhered being so great, that the integrity of the tissues yielded first. The acontium severed, rather than let go its hold. " Now, in the experiments which I have detailed above, we have seen that this adhesion is effected by the actual impene- tration of the foreign body by a multitude of the ecthonea whose barbs resist withdrawal. So that we can with certainty associate the sudden and violent death of the little fish with the intromission of barbed edhorcea!' The following observation by J. P. Couthouy, from the author's Report on Zoophytes (p. 128), if it is beyond question, shows power even in the Actinia's presence. " Having a number of Monodontas (a genus of univalve Mollusca allied to our Trochi) too much crowded in a large jar of water, 1 c i8 CORALS AND CORAL LSLANDS. took out half-a-dozen, and placed them in a jar with an Actinia {Ant/iea Jias;el/ifera). On looking at them about three hours after, I found that, instead of climbing like the others to the top of the water, they remained just where they had fallen, closely withdrawn into their shells. Supposing them to be dead, they were taken out, when they directly began to emerge; and w^hen returned to the jar with the other Monodontas, they were in less than five minutes clustered round its mouth. On placing them again in the jar with the Actinia, though kept there for two hours, they did not once show themselves out of the shell. Once more placing them along with the other shells, they exhibited their former signs of life and activity. The ex- periment was repeated several times with a large Littorina, with the same result, evincing fear of the Actinia on the part of the Mollusks." Gosse gives the following fish story, which is much to the point. Speaking of the Aiithca cercus, or Opelet, a British species, he says (p. i68) : — " I one day saw an amusing exam]jle of its power of passive resistance. A beautiful little specimen of the variety alabastrijia., which had been sent to me by Mr. Gatehouse, I had occasion to remove from one tank to another. There was a,half-growm Bullhead (Coitus bubalis) at the bottom, which had been in captivity rather more than a fortnight. As he had not been fed during that time, I presume he was some- what sharp-set. He marked the Anthea falling, and before it could reach the bottom, opened his cavern of a mouth and sucked in the hojine boucJie. It was not to his taste, however, for as instantly he shot it out again. Not discouraged, he re- turned to the attack, and once more sucked it in, but with no better success ; for, after a moment's rolling of the morsel around his mouth, out it shot once more ; and now the Bull- head, acknowledging his master, turned tail, and darted into a hole on the opposite side of the tank in manifest discomfiture." He adds : — " But if you, my gentle reader, be disposed for exploits in gastronomy, do not be alarmed at the Bullhead's failure : only take the precaution to ' cook your hare.' Risso calls this species ' edidis^ and says of it — * On le mange en CORALS AND CORAL MAL'CERS. 19 friture^ and I can say, ^ Probatum est.^ No squeamishness of stomach prevents our volatile friends, the French, from appre- ciating its excellence ; for the dish called Rastcgna, which is a great favourite in Provence, is mainly prepared from AntJiea cefeiis. I would not dare to say that an Opelet is as good as an Omelet ; but diacun a son goiit — try for yourselves. The dish is readily achieved." The stomach, although without a proper sphincter muscle at its inner extremity, appears to be closed below during the process of digestion. When digestion is complete, the refuse from the food is pushed out through the mouth, the only ex- ternal opening to the alimentary cavity, and the digested material passes downward into the interior cavity; and there, mixed with sea-water from without, it is distributed through all the interior cavities of the polyp for its nutrition. The polyp has no circulating fluid but the results of digestion mixed with salt water, no blood vessels but the vacuities among the tissues, and no passage-way for excrements excepting the mouth and the pores of the body that serve for the escape of water on the contraction of the animal. Actiniae have usually no gills or bra?ichice for the aeration of the blood, the whole surface of the body being ordinarily sufficiently soft and delicate to serve in this function. Some species Uve half buried in the sand, and, as this in large spe- cies would prevent the skin of the sides from aiding in respira- tion, there are sometimes very much lobed and crimpled organs, attached to, or alongside of, the tentacles, which give the animal-flower much greater beauty, and at the same time in- crease the extent of surface for the purposes of aeration ; they are set down as branchial by Prof. Verrill. In one tribe of polyps closely related to the Actiniae, the Zoanthids, in which the outer skin is usually somewhat corria- ceous, or is filled with grains of sand, there are narrow gills arranged vertically, one on either side of the larger radiating septa, figures of which are given in the author's Zoophyte Atlas. As to senses, Actinia, or the best of them, are not quite as C 2 20 CORALS AND CORAL ISLANDS. low as was once supposed. For, besides the general sense of feeling, some of them have a series of eyes, placed like a necklace around the body, just outside of the tentacles. The yellow prominences in this position on the larger figures in the frontispiece are these eyes. They have crystaUine lenses, and a short optic nerve. Yet Actiniae are not known to have a proper nervous system : their optic nerves, where they exist, are apparently isolated, and not connected with a nervous ring such as exists in the higher Radiate animals. Reproduction is carried forward both by ova and by buds, though the latter method is mostly confined to the coral-making polyps. The ovarian and spermatic functions belong to the radiating septa in the interior cavity of the Actinia, and to the part of a septum, mesenteric in character, at or near the outer margin. They have the aspect of a pulpy mass, or look like clusters of ovules. The ova have no chance for escape except through the stomach and mouth. They are covered with vibratile cilia, and rove about free for a while. As the development of the embryo goes forward, a depression begins at one end, which deepens and becomes a stomach, with the entrance to it as a mouth. Concurrently, septa grow out from the inner wall, and a few tentacles commence to rise around the mouth. Not unfrequently, the young has already some of its tentacles before it leaves the parent. There is at first but a single row of tentacles ; the number increases with the size until the full adult limit is reached, the newer series being successively the outer. In the budding process, which is of rare occurrence. Actiniae grow young ones on their sides near the margin of the base. A protuberance begins to rise and soon shows a mouth, and then becomes surrounded by tentacles ; and, thus begun, the new Actinia continues to grow, usually until its tentacles have doubled their number, when finally it separates from the parent and independent animal. At times, as Prof. H. James Clark has observed, small pieces of the base of an Actinia separate by a natural process before a trace of a tentacle has CORALS AND CORAL MAKERS. 21 appeared, and in this case " they do not at first show any signs of activity, but on the contrary remain for a long time in a quiet state, having the appearance of artificially separated pieces, seeming to be undergoing, as in the latter, a recupera- tive process after the shock of a separation." After a while they commence to develop and grow into perfect individuals. Prof. Verrill mentions the case of an Actinia from Puget's Sound (the Epiactis prolifera, V.) which had three rows of young individuals attached to it around the middle of its body ; but whether the young Actiniae were produced by bud- ding from this part of the body, or whether they had colonized there after being produced in the ordinary way, he was unable to determine. In all cases the young ultimately separate from the parent. These polyps have also the faculty of reproducing lost parts ; and to such an extent that a mere fragment, if it be from the lower part, and include a portion of the base, will repro- duce all the rest of the Actinia, even to the disk, tentacles, and stomach. Thus the mere forcible tearing of an Actinia from the rock to which it is attached may result in starting a crop of new Actiniae. Although Actiniae have no internal coral secretions, they sometimes make a thickened epidermic plate at the base, and also in a few cases around a part of the body. This is how- ever not a result simply of an epidermic secretion, but arises from an exudation of mucus from the surface, and the entang- ling thereby of minute particles of foreign or dead matters. A case of the kind, in an Edwardsia where the body is thus encased, is mentioned and explained on page 9. The above are the more prominent characters of the Actinia tribe of polyps. The special features distinguishing them from the coral-making polyps are the following : (i) They are simple animals, or, if they bud, the buds early separate from the parent; (2) They have a muscular base; (3) They are generally capable, more or less perfectly, of locomotion on the base by means of its muscles ; (4) They sometimes possess rudimentary eyes; (5) They have no internal coral secretions. 22 CORALS AND CORAL LSLANDS. Each of these characters is evidence of the superior grade of this division of polyps. II. CORAL-MAKING ACTINOID POLYPS. Of the form, tentacles, mouth, stomach, fleshy septa, lasso- cells, food, digestion and respiration of the coral-making polyps here included, nothing need here be said, these characters being the same as in the Actinise. Their more striking pecu- liarities depend on the secretion of coral, making them fixed species, and involving an absence of the base ; and, in the CAKVOPHYLLIA CYATHUS. case of the majority of the species, on the extent to which they multiply by buds, in imitation of species in the vegetable kingdom. The coral skeleton which the secretions of polyps form is called the coi-allum. These secretions take place among the tissues of the sides and lower part of the polyp, but never in the disk or stomach, as this would interfere with the functions of these organs. In the above sketches of a simple coral, CORALS AND CORAL MAA'ERS. from the Mediterranean, the upper extremity is a depression, or caliclc, inclosed by a series of radiating calcareous (coral) septa. Each of these septa is secreted between a pair of the radiating fleshy partitions, or septa, of the polyp (see figure ]). lo); and thus the radiate structure of ordinary corals is nothing but an expression of the internally. radiate structure ot the polyp. When aUve, the top, and usually the sides, of the coral were concealed by the outer skin of the polyp, including, above, the disk and tentacles ; and into the depression or calicle at top, descended the stomach. Whether these radiating septa of the coral are secreted from the sur- faces of the fleshy septa, or trom a ]jrolongation inward of the mem- brane forming the walls of the inter- nal cavity, has not been directl}' ascer- tained. The latter view is sustained by Professor Verrill, on the ground that the coral septa contain fibres of animal tissue. The secretion does not always commence at the central plane of a septum, for the septa are sometimes hollow within, just as the surface spines of some ■HEC0CVATHL:S CVLINDKACCrS. FLABELLL'M I'AVONINUM. species (e.g., Echinopora irjfcxa) are hollow. The exterior surface of the corallum, that is, the part outside of the calicles, 24 CORALS AND CORAL LSLANDS. is often ribbed, and the ribs are ordinarily only an outer ex- tension of the interior septa ; so that surface spines are in fact but the outer margins of septa. The first of the preceding figures, representing Thecocyathus cylindraceus, Sourt, exhibits another of the forms of these simple corals. It is described by Pourtales, from specimens collected by him at a depth of loo to 200 fathoms off the Florida reef The actual size was one-third that of the figure. The second figure represents a living species, the Flabellutii pavonifiuf/i, described and figured by the author from specimens obtained at Singapore. The bottom of the calide, or polyp-cell, in the corallum is sometimes made simply by the meeting of the radiating septa ; occasionally by the same, with the addition of a point or columella at the centre ; often by a twisting together of this part of the radiated septa. Very often, also, it is a mere porous mass. Sometimes there is a circle of prominent points about the centre, as seen in the figure of a Caryophyllia on page 22, which are the extremities of narrow vertical strips (called /(?//) lying in the planes of the septa. Similar points exist in the Thecocyathus on the preceding page, though not in sight in the figure. In many cases the bottom is quite solid ; and this may be so either (i) because the coral secretions fill up all the pores as the polyp increases in age, and thus make the interior of the corallum solid or nearly so; or (2) because there are formed periodically, as the polyp grows upward, solid horizon- tal plates across the bottom, so that beneath, in the interior of the corallum, there is a series of plates or tables with spaces between. The Pocilloporae, among recent corals (page 70),, and the Favosites among ancient, are examples. Increasing solidity with the increasing age of the polyps is also produced at times by additions to the exterior of a corallum. In many species, the skin, over part or all of the exterior, gradually disappears or dies away and leaves the corallum bare, while all is living within ; and in such cases the skin, before disap- pearing, often adds a layer of stony material to the exterior. CORALS AND CORAL MAKERS. 25 giving greater firmness to the whole. An example is shown in the figure on i)age 22. In such a case, there is no skin or animal tissue over the outside of the corallum, excepting at its upper extremity, above this calcareous coating. Another form of a corallum. the secretion of a single polyp, is illustrated in the following figure of a species of the Fungia family, so-called in allusion to a resemblance to the mushroom. The long mouth occupied a considerable part of the longi- tudinal central line. From the line at the centre, there is the same radiated arrangement of calcareous septa as in the preceding species, though the animal difi"ers greatly in its LNACTIS ECHINATA. extreme shortness in proportion to the breadth. The corals of this group are also peculiar in having the radiated upper surface flat, or nearly so, instead of concave. The figure is a fourth the natural size. These corals, of the genus Fungia, often exceed a foot in length ; and thus coral animals are sometimes as large as the largest of Actiniae. Another species of this genus, the Fungia lacera, V. (for- merly Fimgia echinata^ D., from the Feejees), is represented as it appears when living (excepting a part left off to suit the page) in the following figure. The coral in the perfect state of the animal is wholly concealed, though often showing the points of the teeth of the septa in consequence of the skin being broken. FUNGIA LACERA, V. CORALS AND CORAL MAKERS. 27 An enlarged view of one of the tentacles is given below. They are very small, compared with the size of the polyp ; and this is true of all the living Fungiae studied by the author. It is plain that the ])ovver of such tentacles must reside wholly in their lasso-cells. TENTACLE OF FUNGIA LACERA. The tentacles are scattered over the disk, instead of being in regular circles. It is evident from the figure that the ap- parent circles, where there is more than one, in Actiniae, arise from the crowding of the series of tentacles together ; and also that the inner row of tentacles in polyps is the older. It will be noticed also that each of the tentacles stands where a new ridge (or calcareous septum in the coral) begins. The Fungi?e, unlike most corals, are not fixed animals except in the young state. They are common in coral-reef seas, lying over the sandy or rocky bottom between the other corals. Other varieties of corals and coral animals are illustrated in the figures on the following pages. They represent compound gj'oups, in which great numbers of polyps are connected in a single zoophyte — a result, in part, of the process of budding already alluded to, and partly of different modes of growth connected therewith. This budding is very similar to the budding process in vegetation. One common method is the same that is occa- 28 CORALS AND CORAL LSLANDS. sionally met with in Actinias, the description of which is briefly given on page 20. The bud commences as a sHght prominence on the side of the parent. The prominence enlarges, a mouth opens, a circle of tentacles grows out around it, and increase continues till the young finally equals the parent in size. Since in these species the young does not separate from the parent, this budding produces a compound group ; and the process often condnues until in some instances thousands, or hundreds of thousands, have proceeded from a single germ, and the colony has increased to a large size, sometimes many feet, or even yards, in breadth or height. Such is the species of Dendrophyllia represented in the figure on page 31, and the Madrepora figured on page 29 ; in both of which, and in all such coral zoophytes, each stellate cavity or prominence over the surface corresponds to a separate one of the united polyps. The compound mass produced by budding — which consists of the united polyps with the corallum as their united secre- tion— was called in the Author's Report, a Zoophyte, it being truly animal in nature, though under a plant-like form through the plant-like process of budding. But the word to many minds conveys the idea that the species is something between a plant and an animal, which is totally false ; and besides, it is often used distinctively for the division of animals in- cluding the sponges. As a substitute the term Zoofhome may be employed, derived from the Greek L,u)oy, animal, and Ow/jiog, a /ieaj> — a term applicable also to compound groups in other classes, as, for example, those of Rhizopods, Bryozoans and Ascidians. The term zoophyte, where employed beyond, signifies a zoothome formed of united polyps, or a polyp- zoothome. The coral of the zoothome being the corallum, that of each polyp in the compound corallum may be called a corallet — the term calicle, formerly used by the author for the same, being now restricted to the polyp-cell. It is obvious that the connection of the polyps in all com- pound groups must be of the most intimate kind. The several polyps have separate mouths and tentacles, and separate CORALS AND CORAL MAKERS. 29 stomachs ; but beyond this there is no individual property. They coalesce, or are one, by intervening tissues ; and there is a free circulation of fluids through the many pores or lacunes. The zoothome is hke a living sheet of animal matter fed and nourished by numerous mouths and as many stomachs. MADREPORA ASPERA, D. Polyps thus clustered constitute the greater part of the flowering zoophytes of coral reefs. Only a few are simple animals, like the Caryophyllia figured on page 22, or the Thecocyathus, page 23, or the Fungia, page 26. This kmd of budding may take place from the sides of the polyp at different heights ; either (i) from the base, as in the Actinia mentioned on page 20 when it is basal ; or (2), above 30 CORALS AND CORAL ISLANDS. the base, when it is called lateral ; or (3) at the upper margin outside of the tentacles, when it is called marginal ox superior ; or (4) from the disk inside of the tentacles. Sometimes a shoot grows out from one point only of the base of a polyp, like the stolon iferous stem from a strawberry plant, and at short intervals gives off biids ; and thus makes a linear zoophyte with a row above of flower-animals. In other cases, the base spreads in all directions and buds at the edge, or in the upper surface near the ^^g^., and so makes an in- crusting plate consisting of a multitude of polyps. If the germ polyp, or that from which the compound zoophyte proceeds, has the property of growing upward be- yond the adult height — which the existence of coral renders a possibility, and even to an indefinite degree — various otlier forms may result. Sometimes the first polyp gives out buds from its sides, and continues so to do when it grows upward ; and thus a rising stem is formed with one parent polyp at the extremity of the stem, and a terminal corallet to the corallum, or to each branch of it. This is the case in the genus Madrepora, a species of which is represented on the preceding page. Each branch in the living state had at its extremity the parent polyp of the branch, or that whose budding made the other polyps of the branch. In such species, a new lateral branch is commenced by one, among the many polyps over the surface of a branch, beginning to grow and bud. Thus branch after branch is added, and the little tree produced. Another kind of coral, growing and budding in the same manner, is represented on page 31. It is a species of Dendro- phyllia, from the Feejees — a genus often representing tree-like forms, as the name implies. In other cases, budding goes on until a cluster of some size is formed, and then the older or marginal polyps of the cluster cease budding while the rest continue the process ; in this way a stem rises, with the budding cluster of polyps at its summit, and the more aged, or non-budding polyps, about its sides ; and the breadth of the stem depends on the size of DENDROPHYLLIA NIGRESCENS, 32 CORALS AND CORAL ISLANDS. the budding cluster. Below a case of this kind is represented, in which the stem is a laro:e column. GONIOPORA COLUMN A, D. The polyps, in this beautiful Pacific species, as seen, stand up prominently over the coral when expanded, which is due POKITES MUKDAX, D. to the feet that only the lower parts of the polyp secrete coral, as a moment's consideration will make apparent. D 34 CORALS AND CORAL ISLANDS. In other cases, the budding cluster is small, and hence makes small branches, as in the annexed figure of a species of Porites, from the Feejees. The cells in this genus are very small and nearly or quite superficial, as the figure shows. New branches are made in such species by a forking of an old one. The budding cluster enlarges as it grows, and, when it is just beginning to pass the regular or normal size for the species, a subdivision of the budding cluster commences at the extremity of the branch. It is a process of spontaneous fission of a branch or stem. In this way the forking in the coral of the figure on page 32 was produced, and also the branching in that on page t,-^. Sometimes, again, the budding cluster is a linear series; and then a coral with erect, flattened or lamellar branches is made. Again, sometimes each branch of the corallum is only the corallet of a single polyp ; and new branches are added by the budding of new polyps from its sides, each to length- en out into a new branchlet. In this manner the coral here figured, and many like it, were grown. It is a common species of the West Indies. When the budding is not confined to any particular polyp, or cluster of polyps, but takes place univer- CLADOCORA ARBUSCULA. n i i i • i sally through the growmg mass, the coral formed is more or less nearly hemispherical ; and often the process goes on with such extreme regularity that these hemispheres are perfectly symmetrical, even when enlarged to a diameter of ten or fifteen feet. A portion of the surface of one of these massive species, called Orbicella cavernosa, from the West Indies, is represented in the annexed figure. In the growth of these hemispheres, the enlargement takes place in the spaces between the polyps ; and whenever these spaces CORALS AND CORAL MAKERS. 35 ORBICELLA CAVERNOSA. begin to exceed the width usual to the species, a new mouth opens, commencing a new polyp ; and thus the growth of the mass involves multiplication by buds. The small calicle near the centre of the figure is from one of the new interstitial buds. Species of Pontes also grow into hemispheres and rude hil- lock-like forms, through the same method of budding, and some of the masses in the tropi- cal Pacific have a diameter ot even twenty feet. Myriads ot living polyps are combined in a single such mass, for each is but a fifteenth or a twentieth of an inch in diameter. Often there is a lateral growth of the polyp and thereby of the zoophyte without much upward growth; and spreading leaves are thus made, and bowl-like shapes. Where there is lateral budding, the leaves have generally an edge of young polyps from the new buds that are there opening, as in the Gemmipores, and some foliaceous Madrepores ; where there is superior budding, and sometimes in the case of inferior, the new polyps appear some distance from the edge, the growing margin spreading on in advance of the buds that open in it, as in the Echinopores. Besides the method of budding explained in the above re- marks, there is also a kind of superior budding called sponta- neous Jission^ which consists in a spontaneous subdivision of a polyp, by which two are made out of one. In such cases the disk of the polyp has not a distinct limit of growth, as in the above, but tends to enlarge indefinitely ; and when there is a beginning of an increase beyond the proper adult size, a new mouth opens in the disk, a short distance from the old one, and at the same time its edges extend downward and make a new stomach beneath it; finally tentacles are developed between the two mouths, and then each polyp separates with its part of D 2 36 CORALS AND CORAL LSLANDS. the old tentacles, as illustrated in the following figure. It is not, as is seen, a subdivision strictly into halves, as one carries off the old mouth and stomach. The figure to the left represents a polyp of the Astraea tribe, with already two mouths, through a commencement of the process of subdivision. In the next figure there are tentacles between the two mouths, so that each SPONTANEOUS KISSiON IN POLYPS. mouth has its own circle ; and in the third, the separation has gone so far as to complete the circles and make two inde- pendent polyps. This dividing one's self in two, for the sake of an increase of population, is the process called spontaneous fission or fissiparity. This mode of budding does not belong exclusively to coral polyps, for it has been observed among a few Actiniae. Gosse describes its occurrence in a British species, the Anthea cereus, in which it results in two distinct animals. He says "the fission begins at the margin of the disk, and gradually extends downward until the separation is complete, when each moiety soon closes and forms a perfect animal." The same author alludes to the occurrence of double-disked individuals of the genera Actinoloba, and Actinia as illustrating the process with- out a separation of the spontaneously developed pair. This spontaneous fission is the conmion kind of budding in the large Astraea tribe. The following figure represents a species of living coral of the Astraea family, from the Feejees, the Astrcsa pallida, D. which grew, and multiplied its polyps as it grew, by this method. In such species some of the disks of the polyps will COKALS AND CORAL MAKERS. 37 be found to liave two mouths. This is the first step in the ASTR.KA I'ALI.IDA, D. process. In others, the two mouths will be found to be partly divided from one another by new-formed tentacles ; and finally each will have its own circle complete and all else in polyp per- fection. Many of the Astr^ea hemispheres of the Paci- fic, grown by this method, have a diameter of ten to fifteen feet. In other Astraia-like species, this spontaneous fission ends in a complete separation of the two polyps formed ; and con- sequently in a forking of an old branch. The caulasth^a furcata, d. figure annexed, of a Caulastrsea, from the Feejees, illustrates 38 CORALS AND CORAL LSLANDS. this mode of branching. In the left-hand polyp there are already two mouths, and the work of subdivision is consequently begun ; while in those to the right, which have a single mouth, the subdivision has just been completed, and also the forking of the old branch. Thus spontaneous fission goes forward, and branches accordingly multiply. By this method some of the most magnificent clumps of coral zoophytes found in tropical seas have been, and are being, developed each from a single germ. Many of them have the perfect hemispherical symmetry of the solid Astraeas. Sometimes, when a new mouth forms in an enlarging disk, there is not at once a separation of the two, but the disk con- tinues to enlarge in one direction and another, and then another mouth opens, and so on until a string of mouths exists in one elongated disk ; and finally, a separation occurs, but only to commence or carry forward another long series. In this way the corals with meandrine furrows are made, some kinds of ^\^hich are popularly called " Brain coral," and pertain to the Meandrina family (figure on page 4-4). The same may take place in the ramose corals, and so make flat branches, each with a long sinuous line of polyp mouths at top. In all such species the tentacles stand in a line either side of the line of mouths. By the simple methods here explained all of the various forms of Actinoid zoophytes have been produced ; and, equally so, those of the Alcyonoids described beyond. The tree, shrub, clusters of coral leaves, hemispheres, and coral net-work require for the explanation of their origin only the few princi- ples which have been mentioned. The germ-polyp, growing upward and more or less outward, and budding as it grows, makes thus the rising stem — that of the Madrepore or Dendro- phyllia, with its summit polyp (figures p. 29, 31), or that of the Pontes, with its terminal budding clusters (p. 2iZ) 'i *^'* the rising, massive dome of the Astrsea and Mcneandrina (pp. 37, 44), in case budding is symmetrical in all directions ; — or, if growth in the germ-polyp is upward exclusively, it forms a rising stem bearing at top the single polyp that originated it, CORALS AND CORAL MAKERS. 39 or crowded clusters of such stems branching variously and having each branch surmounted with its one polyp (figure j). 32) ; or, if there is lateral growth and but little of upward, it produces leaf-like forms and graceful groups or clusters of leaves, vases, and other shapes ; or, if the germ-polyp is capa- ble of lateral growth alone, the results are simple lines of polyps creeping over the supporting rock, like the creeping stolons of a plant, or else encrusting plates, spreading outward like a lichen. In the descriptions of corals the following terms have the significations annexed. Those aheady mentioned are here repeated to bring them all together. Zo'dthotne. — The compound animal mass produced by budding. Corallum: — The coral either of the compound mass, or of the solitary polyp. Corallet (in Latin, corallulum). — The- coral of a single polyp in a com- pound corallum. Calide. — The polyp cell in the top of a corallet, or of a solitary coral- lum, within the walls of the cells ; it is sometimes flat at top, that is, without the usual depression. Septa. — The radiated plates of the cell or calicle. Dissepiments.— '^xcidXX cross plates between adjoining septa (sometimes wanting). Synapticulce. — Minute cross bars uniting the surfaces of adjoining septa. Ccenenchyma. — The common mass of the corallum between its differ- ent polyp cells or corallets, as in the Madreporae, Gemmiporae and Den- drophyllioe. Epitheca. — The coral layer sometimes deposited over the exterior of the corallum during the life of the polyp by the outer skin before it dries away, as explained on page 25. Peritheca. — The epitheca of a compound group or zoothome (fig. p. 50). Exotheca. — The portion of the corallum outside of the walls of cells in many coralla of the Astraea family, and some others, in which the polyps of the mass ai;e properly in contact, and there is consequently no true ccenenchyma. Endotheca. — The portion of the corallum inside of the walls of the cell. We may now state briefly the characteristics of the grander divisions of the Actinoid polyps, several of which have been illustrated in the preceding figures. The tribes adopted are those recognized by Prof Verrill, and have the limits he has assigned to them. The classification SS COKALS AND CORAL ISLANDS. diverges from his system in uniting the non-coral making and coral-making species into one grand division, that of the Actinoids (on the ground of the close resemblance of the polyps), and also in separating from the latter the Cyatho- phylloid corals, for the reasons mentioned on page 5. Some of the figures of corals on former pages are here repeated in order to present together those of like relations. 1. Species iciifhont internal Coral Secretions. Actinaria of Verrill. 1. The Actinia tribe, or Actinacea, secrete no coral inter- nally, and moreover have a muscular base, with some degree of locomotion by means *of it. The Acdniae of the frontis- piece, and of pages 6, 9, are examples. 2. The Zoanthus tribe, or Zoanthacea. The species here included are like the Actiniae in secreting no coral. But while they have a base, it is not muscular, and they are never capable of locomotion. The i)olyps have a thick or somewhat lea- El'IZOANTHL'S AM ERICA ^• US, V., WITH EirACa'KrS Pi: BESCEIsS, Sx. thery exterior, and, as already observed (p. 19), have gills, or branchiae. Some of the species are solitary polyps ; but gener- ally the>' form compound masses or zoothomes, by budding; sometimes making simple lines of polyps over a supporting surface ; at other times incrusting plates, or irregular masses. The preceding figure (from Verrill) re])resents a species found in American seas off the coast of New Jersey, in deep water, and also in Massachusetts Bay, v/hich has a habit of fixing on a shell for its support and of always taking one containing a COKALS AND COKAL MAKERS. 41 soldier crab. The shell finally becomes dissolved away — how, it is not known— by the growing Zoanthid ; but the crab holds on to its house, although at the expense of transporting wher- ever it goes a colony of flowering polyps. I'he polyps are but partly expanded in figure i, and wholly so in figure 2. i^<;r7!VWir ANTIPATHES AKIiOREA, D. The animals of the Zoanthus tribe have broad, radiated disks, with an edging of short tentacles, in one or more rows. Although not secreting coral, the mucus of the surface in some 42 CORALS AND CORAL ISLANDS. of the species entangles the sand that falls on it, and thus gives a degree of firmness to the mass of the zoophyte. 3. The Aiitipathus tribe, or Antipathacea. In this tribe the polyps never have locomotion, and, as far as known, always produce compound groups by budding. These groups have the forms of delicate shrubs and long twigs ; and some of them are three feet or more in height. The branches consist of a horny axis, usually spiny or hispid over its surface, sur- rounded by an animal coating, which is made up of united polyps. An example is shown in the following figure of a living species from the Feejees. A view of one of the polyps, much enlarged, is given in the following figure. Its tentacles are closely like those of the Actinia. The height of the entire POLYP OF A. AKBOKEA, MUCH ENLARGED. shrub, collected by the author, was three feet, and the trunk at base was half an inch thick. The polyps had a brownish- yellow colour, not particularly beautiful, and the tentacles were in general, as in another species described by the author, rather awkwardly handled by the polyp. The number is commonly six ; but in one genus, Gerardia,.it is as great as hventy-fo2ii\ 2. Polyps having infernal calcareous secretions. Madreporaria of Verrill. i^TJie Cyathophylloid species excluded). 4. AstrcEa tribe, or Astr^.acea. — In this tribe the polyj)- cells or calicles are distinctly lamello- radiate within, and gener- ally so outside. Moreover, budding is always by division of the disks, or spontaneous fission. The figure of the Caulastraea, on CORALS AND CORAL MALy'ERS. 43 page 37, illustrates one section of this family, that in which each branch of the corallum is made by a single' polyp, and branch- ing is by furcation through spontaneous fission. In other related genera, as Mussa, the polyps sometimes have a diameter of two inches, being as large as ordinary Actiniae. ASTK/KA PALLIDA, D The Astrcea pallida is a good representative of the massive Astraeas. The colour of the polyps in this species is quite pale, the disks being bluish-gray, and the tentacles whitish. In others, the tentacles are emerald-green, or deep purple, or of other shades. Another range of forms is represented by the following figure of one of the Meandrine corals, already referred to as often called " Brain coral.'' In the figure, the coral is reduced one-half lineally. The difference betw^een its mode of for- mation and that of an Astraja has been stated on page 38. This species is common at the Bermudas, where it grows to a diameter of three feet. It is also found in the West Indies. The ridges in this species are double, and hence the name Diploria, from the Greek for double. A common large West India species of Brain coral is called Meandrina labyri7ithica. 44 CORALS AND CORAL ISLANDS. It is readily distinguished from the Diploria by the ridges between the furrows, these being simple and triangular. Still other forms of the Astraea tribe are foliaceous, or such as would result if the growing margin of an Astrsea, or of a Meandrina, were to spread out into folia instead of thickening DIPLORIA CEKEHRIFOKMIS, E. AND H. upward in the ordinary way. The groups ot gracefully curv- ing leaves thus made are sometimes very large and sym- metrical. 2. Fungia tribe, or Fung ace a. — The general character of the simple species of this tribe is mentioned on page 25, and the character of the living Fungia, with its tentacles, is shown in the figure of a Feejee species on page 26. The corallum of another large species, the Fungia Dance, is represented CORALS AND CORAL MAKERS. 45 in the annexed figure one-sixth the actual diameter. Large, com- pound groups, both massive and foliaceous, are formed by- budding, and the budding is always superior. There are no margins to the disk in this tribe, and in the corallum of FCXGIA DAN^, E. & H., Rf-DICEI) TO ONE-SIXTH MNKAI.I.V; a,l>, TEETH OF UI'l'ER AND LOWER MARGINS OF SEPTUM, NATURAL SIZE. the compound kinds no wall or partition between the adjacent stars, and no walls to adjoinmg polyps, or only imperfect ones. The polyps consequently coalesce throughout by their disks. The simple Fungise are attached when young, and then would hardly be distinguished from a simple or solitary species of the Astraea tribe. 3. Oadina tribe, or Oculinacea. — These species occur eitner simple or compound, and the latter are often branched, massive, or encrusting, never thin, foliaceous. Budding is either superior, lateral, or basal ; never by spontaneous fission. The coralla are remarkable for the solid walls and lamellae of the cells ; and often for having the coenenchyma nearly or quite solid. Transverse septa between the lamellae are some- times wanting. The calicles are usually striated externally, but seldom dentate. The polyps, moreover, are small ; and very commonly they stand prominent above the corallum when expanded. The Orbicella, figured on page 35, is an example of one of the massive Astraea-like forms, constituting the Orbicella family, or OrbicellidcE^ in the Oculina tribe. 46 CORALS AND CORAL ISLANDS. The Caryophyllia here figured is one of the solitary species of the tribe found in European Seas, and on the coast of Great Britain. The figure is from Gosse's " British Actinology." It also grows much longer in proportion to the breadth. The CARVOrHYI.I.IA SMITHII, StOKES. figure to the right is of one unexpanded. One of its lasso- cells, in different states, is shown in figures 3, 4, 5, on page 13. The corallum of a related species is given on page 22. The walls and , septa are remarkably solid. This species, the Caryophyllia cyat/ms, has been found not only in the Mediter- ranean, but also at the Azores. Another species, the C. davus, has a wide distribution, occurring in deep water in the Florida straits and off the British coasts as well as m the Mediterranean. Another example of this tribe, as defined by Professor Verrill, is the species of Astrangia occurring alive along the southern shores of New England, and on the coast of New Jersey. Specimens are not uncommon in the vicinity of New Haven, on the rocks by the Light-House, and at other places in Long Island Sound, and when alive it is an exceedingly beautiful object. The accompanying figures of the animal are from the drawings made to illustrate a yet unpublished memoir by Professor Agassiz. They are copied from the "Sea-Side Studies" of Mrs. Agassiz and Alexander Agassiz. In figure COKALS AND CORAL MAKERS. 47 c, the polyps are of the natural size, while figure a represents one of them enlarged, The polyps, as is observed, stand very j)rominent above the cells of the corallum, because only the bases of them secrete coral ; and the buds, which open between the calicles, are hence lateral buds ; the coral has much resem- blance to that of an Orbicella, in which budding is marginal. ASTKANGIA DANyE, Ag. The tentacles have minute warty prominences over them, which are full of lasso-cells, each about a 500th of an inch in length, or about two-thirds larger than those of the ivhite cords that edge the internal septa. The corallum, though mas- sive, is somewhat irregularly lobed above, and grows to a diameter of two or three inches. It is covered with stars an eighth of an inch to a sixth across (figure b), which are usually crowded the intervening being very thin and solid. The author alluded to the crowd of stars in the name Pleiadia, which he proposed for the genus in his Report on Zoophytes (page 722). The genus Cladocora, containing slenderly branching ram.ose zoophytes, is closely related in its polyps, according to together, wall PHYI.LANGIA AMEKICANA, E. & H. 48 CORALS AND CORAL LSLANDS. Professor Verrill, to the Astrangiae, and belongs to that family. Its cylindrical stems are gathered into crowded clumps. The C. arbtcscula is figured on page 34. A West India species of another genus of the group, the Fhyllangia Americana^ is represented in the preceding figure. In the following cut, figure i represents the extremity of a branch of an Oculina, the O. varicosa, of the family Ocnlinidce. The species of this genus grow in clumps of round branches, and have very solid corolla, so white and firm when bleached CORALS OF THP: OCl'LINy\ TRIIiF. as to go by the popular name of " white coral," and to be sometimes pohshed for beads and other such ornamental purposes. Figure 2 is a branch of a beautiful little coral called Sty- laster eriihescens Pourt., and 3, a portion of the same enlarged. It has the firmness, and something of the habit of an Oculina, but is rather like a miniature Oculina, its calicles never exceed- ing a twentieth of an inch in breadth. There are a number of genera in this Stylaster family, the Stylasteridce, and the corals are among the most delicate of species. CORALS AND CORAL MAKERS. 49 Figure 4, in the same cut, represents a portion of a branch of the Stylophora Dance E. and H. The corals of the genus are remarkable for their small, crowded calicles, and for the very distinct six-rayed star in each calicle (as shown magnified in figure 5), and usually have a prominent point or columella at the centre of the star. The polyp of a Feejee species, 6". mordax, is represented in figure 6. The name of the family, StylophoridcE (signifying style-bearer), alludes to this columella. The corals grow in regular hemispherical clumps consisting of flattened or rounded branches, and are sometimes a foot or more across. In another family under this tribe, the FocilliporidcB^ very common in coral-reef seas, the cells of the corallum are always very small and crowded, as shown in figure 7. The corals are branching, and in Pocillipora, the surface is often irregular and warty, the little prominences, like the rest, being covered with polyp cells ; while in Seriatopora, the branches are slender, even, and pointed. The corallum in both is very firm and soHd. In the larger part of them the number of tentacles is only twelve, and formerly they were referred on this account to the Madrepore tribe ; a few have as many as twenty-four tentacles. The Pocilliporje form hemispherical clumps like the Stylo- phorae ; and the branches vary from the flattened and broad form shown in figure 7 (which represents the upper part of a branch of the P.grandis D.), to irregularly cylindrical branches, looking rough on account of the very short branchlets. The cells are usually stellate, as in figure 8, from P. elongata D., and often one of the septa, and sometimes two opposite ones, extend to a columella at the centre, as illustrated in figure 9, from P. plicata D. ; dividing the cell into halves. The cell in the interior of the corallum is crossed by thin plates or tables, as shown in figure 10, and hence they have been called tabulate corals. Agassiz, after the discovery of the Hydroid character of the animals of the Millepore corals, whose cells also are tabulate, referred the Pocilliporae to the same Hydroid type. But recent study of the polyps has shown that they are 50 CORALS AND CORAL ISLANDS. true polyps ; and Professor Verrill remarks on the resemblance of the tentacles to those of the Oculinae. The stellate character of the calicle also proves that the animals must be polyps. Madrepore tribe, or Madreporacea. — In this tribe tlie coralla, even to the walls of the corallets, are remarkable for being porous, and the radiating lamellae of the polyp-cells are narrow, often perforated or imperfectly developed, and frequently mere points. The coralla are either branched, mas- sive, or foUaceous. Budding is lateral, and in the branching species there is either a parent polyp, as in Madrepora and Dendrophyllia, or a terminal budding cluster. This peculi- arity has been already illustrated in the figure of Madrepora aspera, on page 29. On the following page there is an outline sketch of another species, the Madrepora formosa D., common in the Feejees, and also in the East Indies. The two species here mentioned give a good idea of the ordinary character of the Madrepore corals. One of the polyps of the Madrepora cribripora D., a species collected in the Feejees, is represented much enlarged in the accompanying figure. The natural size of the expanded polyp in this genus is generally from an POLYP OF M. CKIDKIPOKA, D. eighth to a twelfth of an inch across the star. The disk of the polyp is quite small, and the number of tentacles is always twelve. The most common colour of the polyps is green, while that of the general surface between is ordinarily a pale or a dark umber. In many species of Madrepora the branches spread out laterally from a central or lateral trunk, and coalesce together into a complete net-work, having the form of a shallow vase ; and the interior of the vase is filled with multitudes of short, . cylindrical coral stems, rising from the reticulating MADREPORA FORMOSA. E 2 52 CORALS AND CORAL LS LANDS. branches, which, when alive, have literally the aspect of sprigs of flowers in the vase. In certain kinds, closely related to Madreporae, the calicles are reduced to points, or spiniform or angular prominences, or fail altogether, and there are sometimes rounded prominences between the cells ; these degraded Madrepores belong to the genus Montipora (Manopora of the Author's Report). The genus Dendrophyllia is also referred to the Madrepore tribe. The budding, as already explained, is of the same kind as in the Madrepores. But the tentacles exceed twelve. One of the polyps of D. nigresce?is D., enlarged, is shown in the accompany- ing figure. This Pacific species grows to a height of at le.ist three feet, and is peculiar in having a very dark blackish green or almost black colour, while the polyps have the tentacles nearly colourless, and the disk has a circle of emerald green around the mouth. DeiidrophyUia arborea is the name of a common species of his genus found in deep water in the Mediterranean ; it is equally large with the preceding, and somewhat similar in its mode of branching, but a little stouter. It has also been found in the Atlantic about the Azores. Another common Mediterranean spegies is the D. cor?ngera. It is sparingly branched, and has very long and stout corallets, sometimes as long and large as the finger. The genus Gemmipora contains porous corals, of foliaceous, bowl-like, and massive forms, covered by prominent cylindri- cal, porous calicles, and having many short tentacles to the polyps, usually in a single circle. Here belongs also the large Porites family (Poritidse), the corals of which are very porous, and sometimes almost spongy, and whose polyp-cells are exceedingly shallow, and usually only imperfectly radiated. POLYP OF DENDROPHYLLIA NIGRESCENS. DENUKOl HYLLIA NIGRESCENS, D. 54 CORALS AND CORAL ISLANDS. One of the genera in this family is Alveopora. It contains the h'ghtest of known corals, the texture being exceedingly porous, and the walls of the cells, which are continued regularly through the coral! um, are like delicate lace- work. As stated long since by the author, " they are intermediate in character between the Montiporse and the Favosites group " — as shown by the texture and the horizontal par- titions across the cells, giving them the " tabu- late " character of the ALVEOPORA vEKRiLLiANA, D. aucicnt T avositcs, as represented by the au- thor in the annexed figure exhibiting a section of the coral- lum of a Feejee species. On account of this tabulate structure. VERTICAL SECTION OK CORALLUM, AND UPPER VIEW OF CALICLES, ENLARGED, OF ALVEOPORA SPONGIOSA, D. the genus was referred by the author to the Favosites family. A related species, of unknown locality, has been made the CORALS AND CORAL MAKERS. 55 type of a new genus, called Favositipora^ by Mr. W. S. Kent, on the ground of its tabulate character (Ann. Mag. Nat. Hist., 1870), thus confirming, though overlooking, the author's conclusions. In the genus Pontes, the corals are frequently branching, as in the Forites viordax D., sometimes more slenderly, but oftener less so, and at times massive and monticulose in form. Another species of Porites is represented on the following page, with one of the branches fully expanded, but the others in outline ; a polyp, much enlarged, having twelve tentacles as in the Madrepor^e, is shown in the accompanying figure. The cells ^^^^^ ^^ ^^^^^^^ ^^^,3 of the corallum are superficial, and hence the name of the species, Forites levis. Another form, different in the size and character of its polyps, is exemplified in the genus Goniopora. In the species figured on page 32, the colour of the projecting polyps was lilac or pale purple, and the number of tentacles eighteen to twenty-four, yet all were in a single series. The columns grow to a height of two feet or more, with only the summits for two or three inches alive. The dead portion is usually encrusted with nullipores, sponges, serpulse and various shells, which protect the very porous corallum within from wear and solution by the moving waters. II. CYATHOPHYLLOIDS. It is not necessary to dwell here at length upon the ancient Cyathophylloids. The corals have a close resemblance to those of the Astraea tribe in general aspect, varieties of form, and range of size ; the methods of multiplication by buds were the same that are now known in the Oculina tribe. Some of the larger kinds of simple corals, such as those of the genera Zaphrentis and Heliophyllum, had at times a diameter of three or four inches, so that the breadth of the polyp flower was probably at least six inches. Hemispherical masses of soHd 56 CORALS AND CORAL ISLANDS. PORITES LEVIS, D. CORALS AND CORAL MAKERS. 57 corals attained, in some species, a diameter of several feet. No doubt the colours, among the coral polyps and other life of the ancient seas, were as brilliant as now exist. Nature's economist here puts the question — Why all this beauty when there were no eyes to enjoy it? But beauty exists because, " in the beginning," " the Spirit of God moved upon the face of the waters;" and man finds delight therein inasmuch as he bears the image of his Maker. A single recent species has been obtained by Mr. L. F. de Pourtales, in dredging at a depth of 324 fathoms, near the Florida reef, which may be a Cyathophylloid, although it has been supposed that the species of the tribe have been extinct since the middle of the Mesozoic era. It was half an inch high and broad, and the polyp-cell had eight septa — a multiple of four, as in the true Cyathophylloids. The discoverer has named it Haplophyllia paradoxa. F)Ut he observes that it may after all be only an abnormal Actinoid. III. ALCYONOID POLYPS. The name Alcyo?uum, given to some of the species of this group, is derived from Alcyone, the fabled daughter of Nep- tune. It is sometimes written with an initial H, in conformity with the aspirate of ihe Greek word ; but Latin authors usually omitted the H, and this has been good enough authority for Linnaeus and the majority of later writers. The Alcyonoids include some of the gayest and most deli- cate of coral shrubs. Almost all are flexible, and wave with the motion of the waters. They contribute but little to the material of coral reefs, but add largely to the beauties of the coral landscape. Not only are the polyps of handsome tints, but the whole shrub is usually of a brilliant orange, yellow, scarlet, crimson or purple shade. Dun colours also occur, as ash-grey, and dark brown, and almost black. Some kinds, the Sponggodiae, are too flexible to stand erect, and they hang from the coral ledges, or in the coral caves, in gorgeous clusters of scarlet, yellow, and crimson colours. 58 CORALS AND CORAL ISLANDS. The species of this order spread from the tropics through the colder seas of the globe, and occur at various depths, down to thousands of feet. The two following are the most striking external peculiarities of the polyps : the number of tentacles is always eight ; and these tentacles are always fringed with papillae, though the papillae are sometimes mere warts. Some of the various forms of the polyps are shown in the figures on the following pages. But besides these characteristics, there is also the following : the existence of only eight internal septa, and these septa not m pairs; consequently, the interior is divided into only eight compartments (octants), and with each a tentacle is connected. Hence in the Alcyonoids, as Prof. Verrill has observed, the areas externally, and the compartments within, are all ambu- lacral, or tentacular, which makes a wide distinction between them and the Actinoids (p. ii) in which only the alternate are tentacular. The solid secretions of these polyps are of two kinds : Either (i), internal and calcareous; or (2), epidermic, from the base of the polyp. The latter make an axis to the stem or branch, which is either horny (like that in Antipathus, p. 42) or cal- careous. A few species have no solid secretions. All the species are incapable of locomotion on the base ; yet there are some that sometimes occur floating in the open ocean. The three following divisions of the Alcyonoids are those now generally recognized : — I. The Alcyo?iiu7n tribe, or Alcyonacea. — One of the forms under this tribe is represented in the annexed figure. It is from the Feejees (like most of the zoophytes figured by the author), and in the living state the polyps had the middle por- tion of the tentacles pale brown, with the fringe deep brown. In another more beautiful species of the genus, from the same region, the Xenia fioi'ida D. (made Xenia Dance by Verrill, as it proved to be distinct from Lamarck's species to which the author referred it), the polyps are as large, but shorter, and the colour is a shade of lilac. These species differ from the larger CORALS AND CORAL MAKERS. 59 part of the Alcyonia in having the polyps not retractile ; the tentacles fold together, if the zoophyte is disturbed, but cannot hide themselves. The following figure represents another related species obtained by Dr. W. Stimpson, near Hong Kong, and called by its discoverer Anthelia lineata; the polyps are but partly expanded. 6o CORALS AND CORAL LS LANDS. Other Alcyonoids are much branched, with die branched thick and finger-like, and soft or tlexible, and the polyps small and wholly retractile into the mass. The branches, bare of polyps, are usually of some dull pale colour, and on account of this fact some of these Alcyonia go by the common name of dcad-jnetis fingers. Some of the species form thick lobed plates over the rocks ; and occasionally they are brightly coloured, even when the polyps are unexpanded. The above kinds secrete granules or spicules of carbonate of lime in the tissues, and are harsher or softer in texture according to the proportion of these granules. Some species form branching tubes, rising from an incrusting base, which are rather firm owing to the calcareous spicuh^s present. Such species are referred to the genus Telesto — one ANTHEl.IA LINEATA, S F TEI/fCSTO RAMICULOSA, V. of which, from Hong Kong, from the collection made by Dr. Stimpson, is here figured (from Verrill). The second figure shows the form of the expanded polyps. The unbranched species of this kind make up the genus Cornularia. CORALS AND CORAL MAKERS. 6i In one family of this tribe the polyps form red calcareous tubes ; sometimes a slender, creeping tube, with polyps at intervals, as in a species referred by the author to the genus Aulopora ; but generally vertical tubes, grouped into large red masses, called, popularly, Orga?i- pipe coraL A portion of one of the latter — Tiibi- pora syringa D. — is re- presented in the first of the annexed figures, with its expanded polyps ; and a polyp from the group much enlarged in the sfcond figure. The papillse of the fringe are arranged closely together in a plane, so that it is not at first apparent that there is a fringe. The third figure represents, enlarged, the polyp of another Feejee species, the Tubipora fiinbriata I). Such coral masses are sometimes a foot or more in diameter, and the living zoophyte, with its lilac or purple polyps fully expanded, looks much like a large cluster of flowers from a lilac bush, plates at intervals. . 2. Gorgo/iia tribe, or Gorgonacea. — The following figure re- presents a species of this tribe from the Kingsmill or Gilbert Islands. It is one of the net-like or reticulated species, the The tubes are united by cross 62 CORALS AND CORAL LSLANDS. reticulation being a result of the coalescence of the branchlets. The general colour of the species was crimson \ but when alive and expanded it was covered throughout with yellowish polyps of the form in figure a, though much smaller, the natural size not exceeding a twelfth of an inch. The common sea-fan of the West Indies, Go?^goma fiabellum, is much more finely re- ticulated, the meshes of the net-work being ordinarily not over CORALS AND CORAL MALCERS. 63 a fourth of an inch in breadth ; while the fan often grows to a height and breadth of a yard. Other species of the Gorgonia family are like clusters of slender twigs, and others like many-branched shrubs or minia- ture trees. The exterior of the stem or branch in a Gorgonia is a layer of united polpys, with minute calcareous spicules dis- tributed through the tissues and giving the layer some firm- ness. It is like a bark to the axis of the stem or branch, and may be peeled off without difficulty, and hence is often called the cortex. The outer surface of the dried cortex is often smooth, or nearly so ; but sometimes covered with small pro- minences. Over it there may be seen numerous oblong points (one to each of the prominences if there are any) ; each of these is the spot where a polyp opened out its tentacles when the zoophyte was alive. SPICULES OF GORGONI/E, MUCH ENLARGED. Kolliker and others have shown that genera, and sometimes species, of the Gorgonacea, may be distinguished by the forms of the calcareous spicules. Some of these knobby spicules are represented in the annexed cut, from figures published by Professor Verrill. The most common forms are those of figures i, 4, 5 ; they occur, with small differences, in the genera Gorgonia, Eugorgia, Leptogorgia, etc. Figure i is from the Leptogorgia eximia V. Figure 2, in which one side is smooth (from the Gorgonia quercifolia V), is characteristic of the genus Gorgonia, but occurs in the species along with forms much like figure i. The forms represented in figures 64 CORALS AND CORAL LSLANDS. 3, 4, 5, are all from Eugorgia aiiraiitiaca V., the peculiar kind shown in figure 3 occurring with the other more common form, in species of this genus. In species of Plexaurella many of the spicules are beautiful crosses of various fancy shapes. In Eunicellae the cortex is covered with an out- side layer, in which the spicules are club-shaped, though or- nately so, and have the smaller end pointed inward. These spicules afford valuable distinguishing characters also in all Alcyonoids. The spicules are often brilliantly coloured, and sometimes variously so in the same individual. Yellow, crimson, scarlet, and purple are common colours, and they occur both of dark and pale shades. Viewed under a compound microscope by transmitted light, a group of these spicules from some species, part bright yellow and part crimson, or of some other tints, produces an exceedingly beautiful effect. It gives still greater interest to this subject that all Gorgoniae owe the various colours they present to the colours of their spicules. Spicules are usually wholly internal, or they only come to the surface so as to make the exterior slightly harsh. But in other cases, as in the genus Muricaea, they project and give a somewhat bristly look to the coral. The calcareous spicules are internal secretions, like those of ordinary coral, and the constitution is the same, — mere car- bonate of lime. But the secretion of the axis of the branches is epidermic^ from the inner surface of the cortex, as in the Antipathus before described (page 42). In the ordinary Alcy- onoids that make no horny axis, the stolons, or budding stem or mass, creeps or spreads over the supporting body. But in these Gorgonige, the budding cluster, which would make a stolon if there were no horny secretions, has the form of a tube about a horny axis ; and as this tube elongates and secretes the axis within, it gives out buds externally; thus the branch rises. New branches commence at intervals over the sides of the rising stem or branch through the starting of new budding centres, and so, finally, the Gorgonia zoophyte is completed. ALCYONOID POLYPS. ^'5 In a few species, the axis is partly or wholly calcareous. In the Isis family, it is made up of a series of nodes and inter- nodes. The former, in the genus Isis, are white, calcareous, furrowed or fluted pieces ; and the latter are smaller and horn- ISIS HiriT like in nature, as illustrated in the preceding figures. In the branching stem here figured, the main stem and the branch on the left are smiply the axis, bare of the polyp-layer or cor- tex ; while the branch on the right, with the surface dotted, has the cortex complete, and the dots are the sites of the con- tracted polyps. The circular figure below is a transverse sec- F 66 CORALS AND CORAL LSLANDS. tion of the stem enlarged, showing the cavities occupied by the retracted polyps. In the genus Melitaea, and some others related, the inter- nodes are porous and somewhat cork-like or suberous instead CORALI.RTM RUBRUM. of horny. The species of this group are often bright-coloured and much brancherl, and resemble, in aspect, ordinary Gor- gonicX ; but they are very brittle, breaking easily at the inter- nodes. . ALCYONOID POLYPS. 67 In the Corallidae, the axis is wholly calcareous, and firm and solid throughout, with usually a red colour, varying from crim.- son to rose-red. Here belongs the Corallium riibrum, or pre- cious coral. The polyp-crust or cortex, which covers the red axis or coral, is thin, and contains comparatively few calca- reous spicules, and consequently it readily disappears when the dried specimens are handled. In an uninjured state, the polyp centres may be distinguished over it by a faint six-rayed star, A branch from a specimen obtained by the author at Naples, is represented, of natural size, in the cut on page 66. The polyps, as the enlarged view, by Lacaze Duthiers, shows, are similar to those of other Alcyonoids — the tentacles being eight in number and fringed. The figure represents the extremity of a branch, magnified about four times lineally, with one polyp fully expanded, two partly, and the rest unexpanded. In the living Corallium, they open out thickly over the branches, and make it an exceedingly beautiful object. The coral grows in branching forms, spreading its branches nearly in a plane ; and sometimes the little shrub is over a foot in height. The author just mentioned states that, among the polyps, those of the same branch are often all of one sex alone, and that besides males and females, there are a few that combine both sexes. The precious coral is gathered from the rocky bottom of the borders "of the Mediterranean, or its islands, and niost abundantly at depths of 25 to 50 feet, though occurring also even down to 1,000 feet. There are important fisheries on the coast of Southern Italy ; of the island of Ponza, off the Gulf of Gaeta ; of Sicily, especially at Trapani, its western ex- tremity ; of Corsica and Sardinia, in the Straits of Bonifacio ; of Algeria, south of Sardinia, near Bona, Oran, and other places, which in 1853 afforded 80,000 pounds of coral; and on the coast of Marseilles. The rose-coloured is the most highly valued, because the rarest. Another species of Corallium was obtained by the author at the Sandwich Islands (Atlas of Zoophytes, plate 60) ; but, while probably from the seas of that region, its precise locality is not known. F 2 68 CORALS AND CORAL LSLANDS. 3. Pennatnla tribe, or Pennatulacea. These are com- pound Alcyonoids, that, instead of being attached to rocks or some firm support, have the base or lower extremity free from polyps and buried in the sand or mud of the sea-bottom, or else live a floating life in the ocean. Their forms are very various. In the Veretillum family (Veretillidae) they are stout and short club-shape. One of the species from Hong Kong is C01'H()I5K1.E.MN()X t I.AVATf.M, V. , AND VERETII.LI;M STIMl'SONI, V shown in the figure on the left, with its polyps fully expanded, and the small figure represents one of the polyps enlarged. The third figure represents a polyp of another species, from Hong Kong, a true ^'eretillum, enlarged three diameters ; the specimens, obtained by Dr. Stimpson, and described by Prof. ALCYONOID POLYPS. 69 Verrill, were six to eight inches in lengtli, and, where thickest, were three inches or more in diameter. A common Mediterranean species is the Vcretillum cynonio- rium; and it has been recently found, of a length of ten inches, in the depths of the Atlantic off the coast of Spain. Mr. VV. S. Kent observes, with regard to its polyps and their phos- phorescent qualities, as follows : — " Nothing can exceed the beauty of the elegant opaline polyps of this zoophyte when fully expanded, and clustered like flowers on their orange-coloured stalk ; a beauty, however, almost equalled by night, when, on the slightest irritation, the whole colony glows from one extremity to the other with undulating waves of pale green phosphoric light. A large bucketful of these Alcyonaria was experimentally stirred up one dark evening, and the brilliant luminosity evolved produced a spectacle too brilliant for words to describe. The support- ing stem appeared always to be the chief seat of these phos- phorescent properties, and from thence the scintillations travelled onward to the bodies of the polyps themselves. Some of the specimens of this magnificent zoophyte measured as much as ten inches from the proximal to the distal extremity of the supporting stalk, while the individual polyps, when fully exserted, protruded upward of an inch and a half from this inflated stalk, and measured as much as an inch in the diameter of their expanded tentacular discs." In several genera of the Pennatula tribe there are two kinds of polyps over the surface, and this was the case with the Veretillum Stimpsoni^ as observed by Professor Verrill. Between the large and well-developed polyps, there were multitudes of small wart-like prominences, each of which proved to be a polyp, but very small and imperfectly developed, having only two lamellae in the interior instea<3 of the usual eight, and without distinct tentacles, or the ordinary nettling cords within. Among the other forms of Zoophytes in the Pennatula tribe are those having a stout axis, with branches either side, arranged regularly in plume-like style (the Pennatulidse) ; or a very slender stem and verv short lateral polyp-bearing 70 CORALS AND CORAL ISLANDS. pinnules or processes along it (the Virgularidse) ; or a thin reniform shape (Renillidae). Others differ from the preceding in having the polyps not retractile ; and some of these have a slender stem and the polyps arranged along one side of it (the Pavonaridae) ; and still others a terminal cluster of polyps (the Umbellularidce). The most of the species secrete a slender, horny axis, and have slender calcareous spicules among the tissues, somewhat like those of the Gorgonidje. In conclusion, it may here be stated that the reader will find very full illustrations of most of the forms of recent corals, and of their animals, with their natural colours, in the author's Report on Zoophytes. It is with regret that he has to add, that owing to the special action of the Congressional Commit- tee in charge of the publications of the Wilkes Exploring Expedition, only one hundred copies of this Report were pub- lished by the Government, and also of the others of the series, and that but i^\N have been issued besides. The Atlas contains sixty-one folio plates, many of them coloured. The works on " British Sea Anemones," by Mr. Philip Henry Gosse, contains figures and descriptions of a large number of Species, and gives an excellent idea of the most of the forms of Actiniae, and also presents well their colours. Professor A. E. Verrill has published, in the Memoirs of the Boston Society of Natural History, Vol. I., a " Review of the Polyps of the Eastern Coast of the United States," with a plate illustrating a few of the species. IV. LIFE AND DEATH IN CONCURRENT PROGRESS IN CORAL ZOOPHYTES. The large, massive forms of stony corals would not exist, and the tree-shaped and other kinds would be of diminutive size, were it not for the fact that, in the living zoophyte, death and life are going on together, pari passu. This condition of growth is favoured by the coral secretions ; for these give a LIFE A ND BE A TH IN CONCUR REN T PR OGRESS, 71 chance for the polyp to mount upward on the coral, as it lengthens it by secretions at the top. But, to be successful in this ascending process, either the polyp must have the power of indefinite elongation, or it must desert the lower part of the corallum as growth goes forward ; and this last is what hap- pens. In some instances, a polyp, but a fourth of an incli long, or even shorter, is finally found at the top of a stem many inches in height. The following figure represents a case of this kind ; for all is dead coral, excepting less than an inch at the extremity of each branch. The tissues that once filled the cells of the rest of the corallum have dried away, as increase went on above. Another example is shown on page 34, in which the living part had a length of one eighth of an inch. The Goniopora, on page 32, is still another example of the process ; but here the living part com- bines a great number of polyps : these are growing and budding with all the exuberance of life, while below, the old polyps gra- dually disappear, and even their cells become superficial and fade out. Trees of Madrepores may also have their limits — all below a certain dis- tance from the summit being dead ; and this distance will differ for different species. But this is not a limit to the existence of the zoothome, even though a slender tree or shrub, or of its flourishing state ; for the dead coral below is firm rock itself, often stronger than ordinary limestone or marble, and serves as an ever-rising basement for the still expanding and rising zoophyte. CAULASTR^A FURCATA, D. 72 CORALS AND CORAL LSLAXDS. But this death is not in progress alone at the base of the cokimn or branch. Generally the w/iole ititerior of a corallum is dead, a result of the same process with that just explained. Thus, a Madrepora, although the branch may be an inch in diameter, is alive only to the depth of a line or two, the grow- ing polyps of the surfoce having progressively died at the lower or inner extremity as they increased outw^ard. The large domes of Astrseas, which have been stated to attain sometimes a diameter of ten or fifteen feet, and are alive over the whole surface, owing to a symmetrical and unlimited mode of budding, are nothing but lifeless coral throughout the interior. Could the living portion be separated, it would form a hemispherical shell of polyps, in most species about half an inch thick. In some Porites of the same size, the whole mass is Hfeless, excepting the exterior for a sixth of an inch in depth. With such a mode of increase, there is no necessary limit to the growth of zoophytes. The rising column may increase upward indefinitely, until it reaches the surface of the sea, and then death will ensue* simply from exposure, and not from any failure in its powers of fife. The huge domes may enlarge till the exposure just mentioned causes the death of the summit, and leaves only the sides to grow, and these may still widen, it may be indefinitely. Moreover, it is evident that if the land supporting the coral domes and trees were gradually sink- ing, the upward increase might go on without limit. In the following of death after life "aequo pede," there is obedience to the universal law. And yet the polyps, through this ever yielding a little by piecemeal, seem to get the better of the law, and in some instances secure for themselves almost perpetual youth, or at least a very great age. Of the polyps over an Astrsea hemisphere, none ever die as long as the dome is in a condition of growth ; and the first budding individual, or at least its mouth and stomach, is among the tens of thou- sands that constitute the living exterior of the dome of fifteen feet diameter. In the Madrepore, the terminal parent-polyp of a branch grows on without being reached by the deatli- rROTECTION A GAINST INJUR ] ; 73 warrant that takes off at last the commoners about the base of the tree ; it keeps growing and budding, and the tree thus continues its increase. The death of the polyps about the base of a coral tree would expose it, seemingly, to immediate wear from the waters around it, especially as the texture is usually porous. But nature is not without an expedient to prevent to some extent this catastrophe. In the first place, there is often a peritheca over the dead corallum — that is, an outer impervious layer of carbonate ot lime, secreted by the lower edge of the series of dying polyps, a fact in the Gouiopoi'a co/u?nna figured on page 32. Then, further, the dead surface becomes the resting-place of number- less small encrusting species of corals, besides NuUipores, Serpulas, and some Mollusks. In many instances, the lichen- like Nullipore grows at the same rate with the rate of death in the zoophyte, and keeps itself up to the very limit of the living part. The dead trunk of the forest becomes covered with lichens and fungi, or, in tropical climes, with other foliage and flowers ; so among the coral productions of the sea, there are forms of life which replace the dying polyp. The process of wear is frequently thus prevented. The older polyps, before death, often increase their coral secretions also within, filling the pores as the tissues occupying them dwindle, and thus render the corallum nearly solid ; and this is another means by which the trees of coral growth, though of slender form, are increased in strength and en- durance. The facility with which polyps repair a wound, aids in carrying forward the results above descri' ed. The breaking of a branch is no serious injury to a zoophyte. There is often some degree of sensibility apparent throughout a clump even when of considerable size, and the shock, therefore, may occasion the polyps to close. But, in an hour, or perhaps much less time, their tentacles will again have expanded ; and such as were torn by the fracture will be in the process of complete restoration to their former size and powers. The 74 CORALS AND CORAL LSLANDS. fragment broken otf, dropping in a favourable place, would become the germ of another coral plant, its base cementing by means of new coral secretions to the rock on which it might rest ; or,, if still in contact with any part of the parent tree, it would be reunited and continue to grow as before. The coral zoophyte may be levelled by transported masses swept over it by the waves ; yet, like the trodden sod, it sprouts again, and continues to grow and flourish as before. The sod, however, has roots which are still unhurt ; while the zoophyte, which may be dead at base, has a root — a source 'or centre of life — in every polyp that blossoms over its surface. Each animal might live and grow if separated from the rest, and would ultimately produce a mature zoophyte. V. COMPOSITION OF CORAL, Ordinary corals have a hardness a little above that of com- mon limestone or marble. The ringing sound given, when coral is struck with a hammer, indicates this superior hardness. It is possible that it may be owing to the carbonate of lime being in the state of aragonite, whose hardness exceeds a little that of ordinary carbonate of lime or calcite. It is a common error of old date to suppose that coral when first removed from the water is soft, and afterward hardens on exposure. For, in fact, there is scarcely an appreciable difference ; the live coral may have a slimy feel in the fingers ; but if washed clean of the animal matter, it is found to be quite firm. The water with which it is penetrated may contain a trace of lime in solution, which evaporates on drying, and adds slightly to the strength of the coral ; but the change is hardly appreciable. A branched Madrepore rings on being struck when first collected ; and a blow in any part puts in hazard every branch throughout it, on account of its elasticity and brittleness. The specific gravity of coral varies from 2-5 to 2-8 : 2-523 was the average from fifteen specimens examined by Prof. Silliman. Chemically, the common reef-corals, of which the branching Madrepora and the massive Astr^eas are good examples. PHOSPHATE WATER AND OR- OF LIME. GAN IC MATTERS. . 0-84 . 379 • 0*50 • 2-96 . 053 . 164 . 0-28 . 2-42 . 0-32 . 1-93 . 078 . 2-8i COMPOSITION OF CORAL. 75 consist almost wholly of carbonate of lime, the same ingredient which constitutes ordinary limestone. In 100 parts, 95 to 98 parts are of this constituent; of the remainder, there are i^ to 4 parts of organic matter, and some earthy ingredients amounting usually to less than i per cent. These earthy ingredients are phosphate of lime, with sometimes a trace of silic;a. A trace of fluorine also has been observed. S. P. Sharpies found the following constitution for the species below namec^ {Afji. Jou?\ Sci., III., i. 168). CARBONATE OF LIME. Oculina arbuscula, N. Car. . . . 95 '37 . Manicina areolata, Florida . . . 96'54 . Agaricia agaricites 9773 • Siderastrtea radians 97*30 . Madrepora cervicornis 98'07 . Madrepora palmata 97 "19 • Forchhammer found 2*1 per cent, of magnesia in Corallium rubriim, and 6*36 in Isis hippuris. The sea-water, and the ordinary food of the polyps, are evidently the sources from which the ingredients of coral are obtained. The same powers of elaboration which exist in other animals belong to polyps ; for this function, as has been remarked, is the lowest attribute of vitality. Neither is it at all necessary to inquire whether the lime in sea-water exists as carbonate, or sulphate, or whether chloride of calcium takes the place of these. The powers of life may make from the elements present whatever results the functions of the animal require. The proportion of lime salts which occurs in the water ot the ocean is about -^V to ^^ of all the ingredients in solution. The lime is mainly in the state of sulphate. Bischof states that the proportion of salts of all kinds in sea-water averages 3-527 per cent.; and in 100 parts of this, 7579 are chloride of sodium, 9-i6 chloride of magnesium, 3*66 chloride of potassium, I'lS bromide of sodium, 4-62 sulphate of lime or 76 CORALS AND CORAL LSLANDS. gypsum, and 5*597 sulphate of magnesia, = 100. This cor- responds to about 16^ parts of sulphate of lime to 10,000 of water. Fluorine has also been detected in sea-water ; so that all the ingredients of coral are actually contained in the waters of the ocean. It has been common to attribute the origin of the lime of corals to the existence of carbonic-acid springs in the vicinity of coral islands. But it is an objection to such a hypothesis, that, in the first place, the facts do not require it ; and, in the second, there is no foundation for it. The islands have been supposed to rest on volcanic summits, thus making one hypothesis the basis of another. Carbonic-acid springs are by no means a universal attendant on volcanic action. The Pacific affords no one fact in support of such an opinion. There are none on Hawaii, where are the most active fires in Polynesia ; and the many explorations of the Society and Navigator Islands have brought none to light. Some of the largest reefs of the Pacific, those of Australia and New Caledonia, occur where there is no evidence of former vol- canic action. The currents of the Pacific are constantly bringing new supplies of water over the growing coral beds, and the whole ocean is thus engaged in contributing to their nutriment. Fish, mollusks, and zoophytes are thus provided with earthy ingredients for their calcareous secretions, if their food fails of giving the necessary amount ; and, by means of the powers of animal life, bones, shells, and corals alike are formed. The origin of the lime in solution throughout the ocean is an inquiry foreign to our present subject. It is sufficient here to show that this lime, whatever its source, is adequate to explain all the results under consideration. II. HYDROIDS. The annexed sketch represents a Hydra as it often occurs attached to the under surface of a floating leaf — that of a species of Lemna. The animal is seldom over half an inch HYDRO IDS. 77 long. It has the form of a polyp, with long slender tentacles ; and, besides these tentacles with their lasso-cells, it has no special organs except a mouth and a tubular stomach. Like the fabled Hydra, if its head be cut off another will grow out ; and any fragment will, in the course of a short time, become a perfect Hydra, supplying head, or tail, or whatever is want- ing : and hence the name given to the genus by Linnaeus. The Hydra is the type of a large group of species. It buds, but the buds drop off soon, and hence its compound groups are always small, and usually it is single. But other kinds multiply by buds that are persistent, and almost indefinitely so ; and they thus make mem- branous coralla of considerable size and often of much beauty. The species figured on p. 78, the Hydrallmania Falcata, is one of them ; in allusion to its deli- cate plumes, it is called Plumu- laria. Along the branches, there are minute cells, each of which was the seat of one of the little Hydra-like animals (in this not a fourth of a line long), and usually with short tentacles spread out star-like. Other kinds are simple branching threads, and sometimes hvuka. the cells are goblet - shaped and terminal. The Tubulariae grow in tufts of thread-like tubes, and have a star-shaped flower at top, often half an inch in diameter, with a proboscis-like mouth at the centre. In Coryne, a closely-related genus, the tentacles are shorter, and somewhat scattered about the club-shaped or probosciform head of the stem, so that the animal at top is far from star- shaped or graceful in form ; it is in fact a very clumsy unshapen thing for a Radiate. To the animal of the Coryne, that of the very common, and often large, corals, called Millepores, is closely related, as first 78 CORALS AND CORAL LSLANDS. detected by Agassiz on one of his cruises to the reefs of Florida. HYDRALLMANIA FALCATA. The autlror often had Millepore corals under study in the HYDROIDS. 79 Pacific, and waited long for the expansion of the animals, but was never gratified by their making their appearance. Agassiz observes that they are very slow in expanding themselves. When expanded, they have no resemblance to true polyps. There is simply a fleshy tube with a mouth at top and a few small rounded prominences in place of tentacles, four of KILLEPORA ALCICORNIS. them sometimes largest. The next figure, from Agassiz, shows, much enlarged, a portion of a branch ot the Millepora alcicoiiiis with the animals expanded, and the small figure en these grow so abundantly on some coasts, that, when broken up and accumulated along the shore by the sea, they may make thick calcareous deposits. Agassiz has described such beds as having considerable extent in the Florida seas. V. THE REEF-FORMING CORALS AND THE CAUSES IN- FLUENCING THEIR GROWTH AND DISTRIBUTION. I. Distribution in Latitude. Reef-forming species are the warm-water corals of the globe. A general survey of tlie facts connected with the temperature of the ocean in coral-reef seas appears to sustain the con- clusion that they are confined to waters which, through even the coldest winter month, have a mean temperature not below 68° F. Under the equator, the surface waters in the hotter part of the ocean have the temperature of 85° F. in the Pacific, and 83" F. in the Atlantic. The range from 68° F. to 85° F. is, therefore, not too great for reef-making species. An isothermal line, crossing the ocean where this winter temperature of the sea is experienced, one north of the equa- tor, and another south, bending in its course toward or from the equator, wherever the marine currents change its position, will include all the growing reefs of the world ; and the area of waters may be properly called the coral-reef seas. This isothermal boundary line, the isocryme (or cold-water line) of 68° F., extends, through mid-ocean, near the parallel G 2 84 CO.?.^/.S AND CORAL ISLANDS. of 28°; but in the vicinity of the continents it varies greatly from this, as explained beyond in the course of remarks on the geographical distribution of reefs. It is to be observed that the temperature of 68° F. is a temporary extreme — not that under which the polyps will flourish: Except for a short period, the waters near the limits of the coral seas are much warmer; the mean for the year is about 731" F. in the North Pacific, and 70° F. in the South; from which it maybe in- ferred that the summer mean would be as high at least as 78° and 74° F. Over the sea thus limited coral reefs grow luxuriantly, yet in greatest profusion and widest variety through its hotter portions. Drawing the isocryme of 74° F. (that is, the iso- therm for 74° F. as the mean for the coldest month) around the globe, the coral-reef seas are divided, both north and south of the equator, into two regions, a torrid, and a subtorrid, as they are named by the author (see Chart beyond, from the Author's Report on Crustacea) ; and these correspond, as seen below, to a marked difference in the corals which they grow. Further, the torrid region should be divided, as the distribu- tion of corals show, into a warmer and a cooler torrid, the isocryme separating the two being probably that of 78". But, before considering the facts connected with the geo- graphical distribution of existing coral-reef species, it is important to have a correct apprehension of what are these reef species as distinct from those of colder and deeper seas. The coral-reef species of corals are the following : — 1. In the Astraea tribe (Astrseacea), ail the many known species. 2. In the Fungia tribe (Fungacea), almost all known species, the only exceptions at present known being two free species found much below coral-reef depths, in the Florida seas, by C. F. de Pourtales, one of them, at a depth of 450 fathoms. 3. In the Oculina tribe (Oculinacea), all of the Orbicellids ; part of the Oculinids and Stylasterids ; some of the Caryo- phyllids, Astrangids and Stylophorids ; all of the Pocillo- porids. GEOGRAPHICAL DISTRIBUTION OF CORALS. 85 4. In the Madrepora tribe (Madreporacea), all of the Madreporids and Poritids ; many of the Dendrophyllia family or Eupsammids. 5. Among Alcyonoids, numerous species of the Alcyonium and Gorgonia tribes, and some of the Pennatulacea. 6. Among Hydroids, the Millepores and Heliopores. 7. Among Alg?e, many Nullipores and Corallines. The corals of colder waters, either outside of the coral-reef seas, or at considerable depths within them, comprise, accord- ingly, the following : — 1. A very few Fungids. 2. Some of the Oculinids ; many of the Astrangids and C'aryophyllids ; many Stylasterids ; a few Stylophorids. 3. Many of the Eupsammids. 4. Some of the Gorgonia and Pennatula tribes, and a few of the Alcyonium tribe. 5. A few Milleporids of the genus Pliobothrus. A large proportion of the cold-water species are solitary polyps. Through the torrid region, in the central and western Pacific, that is, within 15° to 18° of the equator, where the tempera- ture of the surface is never below 74° F. for any month of the year, all the prominent genera of reef-forming species are abundantly represented — those of the Astr^acea, Fungacea, Oculinacea, Madreporacea, Alcyonoids, Millepores and Nulli- ])ores. The Feejee seas afford magnificent examples of these torrid region productions. Astraeas and Maeandrinas grow there in their fullest perfection ; Madrepores add flowering shrubbery of many kinds, besides large vases and spreading folia ; some of these folia over six feet in expanse. Mussa*. and related species produce clumps of larger flowers ; Meru- linae, Echinoponx, Gemmiporse and Montiporae form groups of gracefully infolded or spreading leaves ; Pavonise, Pocilli- porae, Seriatoporae and Pontes, branching tufts of a great variety of forms ; Tubipores and Xeniae, beds or masses of the most delicately-tinted pinks; Sponggodiae, large pendant clusters of orange and crimson ; and Fungiae display their 86 CORALS AND CORAL LSLANDS. broad disks in the spaces among the other kinds. Many of the species may be gathered from the shallow pools about the reefs. But with a native canoe, and a Feejee to paddle and dive, the scenes in the deeper waters may not only be enjoyed, but boat-loads of the beautiful corals be easily secured. The Hawaian Islands, in the North Pacific, between the latitudes 19° and 22°, are outside of the torrid zone of oceanic temperature, in the siibton'id^ and the corals are consequently less luxuriant and much fewer in species. There are no Madrepores, and but few of the Astraea and Fungia tribes ; while there is a profusion of corals of the hardier genera, Porites and Pocilliporae. The genera of corals occurring in the East Indies and Red Sea are mainly the same as in the Central Pacific ; and the same also occur on the coast of Zanzibar. To the eastward of the Pacific coral islands, the Paumotus, which are within the limits of the torrid region, the variety of species and genera is large, but less so than to the westward. Special facts respecting this sea have not been obtained. The author's observations were confined to the groups of islands farther west, the department of corals having been in the hands of another during the earlier part of the cruise of the Govern- ment Expedition with which he was connected. The Gulf of Panama and the neighbouring seas, north to the extremity of the California peninsula and south to Guay- aquil, lie within the ior7'id region ; but in the cooler part of it. The species have throughout a Pacific character, and nothing of the West Indian ; but they are few in number, and are much restricted in genera. There are none, yet known, of the Astra^acea, and no Madrepores. Prof. Verrill, through the study of collections made by F. H. Bradley and others, has observed that there are, near Panama, a few species of Porites and Dendrophyllise, a Stephanaria (near Pavonia), two species of Pocilliporae, two of Pavonise, one of them very large and named P. gigafitea V., several Astrangids, and a few other small species, besides a large variety under the Gorgonia tribe. At La Paz, on the California peninsula at the entrance GEOGRAPHICAL DISTRIBUTION OF CORALS. 87 to. the Gulf, occur a small but beautiful Fungia {F. elegans V.), three Porites, a Dendrophyllia, a Pocillipora, some Astrangids, and many fine Gorgoniae. The character of the species is that of the cooler torrid region, rather than that of the warmer torrid. Owing to the cold oceanic currents of the eastern border of the Pacific — one of which, that up the South American coast, is so strong and chilling as to push the southern isocryme ot 68^, the coral-sea boundary, even beyond the Galapagos, and north of the equator — the coral-reef sea, just east of Panama, is narrowed to 20°, which is 36° less of width than it has in mid-ocean ; and this suggests that these currents, by their temperature, as well as by iheir usual westwa7'd direction, have ])roved an obstacle to the transfer of mid-ocean species to the Panama coast. In the West Indies the reefs lie within the limits of the isocryme of 74° F., or the torrid region ; and yet the variety of species and genera is very small compared with the same in the Central Pacific. The region contains some large Madre- pores, the /)/. paimata, a spreading foliaceous species that forms clumps two yards in diameter ; M. cervicornis, a stout, sparsely-branched tree-like species, which attains a height of fifteen feet ; M. proli/era, a handsome shrub-like species, of rather crowded branches ; besides others ; and these are marks of the existence of the warmer torrid region ; yet the sea has not as high a temperature as the hottest part of the Pacific. The species of the Astrsea tribe are few in number, and among the largest kinds are the Maeandringe (the Diploria being here included). None of the free Fungidae are known excepting the two species in deep water, and none of the Pavonioe among the compound species ; but the massive Siderinaj (Siderastr^ece) are common, and the foliaceous Agaricias and Mycedia. Of the Oculina tribe, species of Oculina, Cladocora and Astrangia are relatively more numerous than in the Central Pacific ; but there are none of the Pocilliporids, which are common bodi in the torrid and subtorrid regions of the Pacific. Millei)ores are very common. Gorgonice, are of many species. 88 CORALS AND CORAL LS LANDS. Professor Verrill observes that not a single West Indian coral occurs on the Panama coast, although, on the opposite coast, at Aspinwall, there are found nearly all the reef-building species of Florida, viz. : Porites asti-ceoides Lmk., P. davaria Lmk., Madi'epora pabnata L., M. cervicoi'nis L., M. prolifera L., MffMJidrida divosa V., M. /aby7'i?tthica, M. sinuosa Les., with other species of Mseandrina, Manidna areolata Ehr., Sider- astriEa {Sidcrind) radiata V., 6". galaxea BL, Agarida agari- dtes, OrbiceUa cavernosa V., O. ajimilaris D. Moreover no West Indian species is known to be identical with any from the Pacific or Indian Ocean. The reefs of the Brazilian coast south of Cape Roque lie in the subtorrid region of oceanic temperature, or between the isocrymes of '74° and 68°. The reef corals extend as far south as Cape Frio, according to Professor C. F. Hartt. The species, as determined by Professor Verrill, from Professor Hartt's collections, resemble the West Indian. All species of Madrepora, Mseandrina, Diploria, Manicina, Oculina, genera eminently characteristic of the West Indies, appear to be want- ing, while the most important reef-making genera are Faina, Acanthastrcea^ Oflncelia, Siderastraa, Porites, and Millep07-a, and also, of less importance, Mussa and some others. A few species, viz. : Siderastrcea stdlata V., OrbiceUa aperta V., Astrcea gravida V., and Porites solida V., are very close to West Indian species ; and Millepora alcicoi'iiis is an identical species, though different in variety. The Bermudas are in the North Atlantic subtorrid region, in the range of the Gulf Stream. The few reef-making species that occur there are all West Indian, viz : The species of the Astrsea tribe, Isophyllia dipsacea, /. rigida, Diploria cerebri- for mis ; of the Oculina tribe, Oadina diffusa, Ocidina varicosa, Oculina pallens, Oculina Valenciejinesii ; of the Fungia tribe, Siderastrcea radians, Alycediurn fragile ; of the Madrepora tribe, Porites davaria; also the Millep07'a alcicornis, and the common West India Alcyonoids, Gorgojua flabellum, Plexaura a-assa Lx., PL flexuosa Lx., PL homomalla Lx., Pterogorgia Ameri- cana Ehr., Pt. ace?'osa, Ehr. RANGE IN DEPTH OF CORALS. 89 The facts presented are sufficient to show that temperature has much to do with the distribution of reef-corals in latitude^ while proving also that regional peculiarities exist that are not thus accounted for. II. Distribution in Depth. Quoy and Gaymard were the first authors who ascertained that reef-forming corals were confined to small depths, contrary to the account of Foster and the early navigators. The mis- take of previous voyagers was a natural one, for coral reefs were proved to stand in an unfathomable ocean ; yet it was from the first a mere opinion, as the fact of corals growing at such depths had never been ascertained. The few species which are met with in deep waters appear to be sparsely scat- tered, and nowhere form accumulations or beds. The above-mentioned authors, who explored the Pacific in the Uranie under D'Urville (and afterward also in the As- trolabe), concluded from their observations that five or six fathoms (30 or 36 feet) limited their downward distribution. P^hrenberg, by his observations on the reefs of the Red Sea, confirmed the observations of Quo}' and Gaymard ; he con- cluded that living corals do not occur beyond six fathoms. Mr. Stutchbury, after a visit to some of the Paumotus and Tahiti, remarks, in Volume I. of the West of England Journal, that the living clumps do not rise from a greater depth than sixteen or seventeen fathoms. Mr. Darwin, who traversed the Pacific with Captain Fitzroy, R.N., gives twenty fathoms as not too great a range. In his soundings ofT the fringing reefs of Mauritius, in the Indian Ocean, on the leeward side of the island, he ob- served especially two large species of Madrepores, and two of Astraea ; and a Millepora down to fifteen fathoms, with pIso, in the deeper parts, Seriatopora ; between fifteen and twenty fathoms a bottom mostly of sand, but partly covered with the Seriatopora, with 'a fragment of one of the Madre- pores at twenty fathoms. He states that Capt. Moresby, in 90 CORALS AND CORAL LSLANDS. his survey of the Maldives and Chagos group, found, at seven or eight fathoms, great masses of Hving coral ; at ten fathoms, the same in groups with patches of white sand between ; and, at a litde greater depth, a smooth steep slope without any living coral ; and further, on the Padua Bank, the northern part of the Laccadive group, which had a depth of twenty- five to thirty-five fathoms, he saw only dead coral, while on otlier banks in the same group, ten or twelve fathoms under water, there was growing coral. In the Red Sea, however, according to Captain Moresby and Lieutenant Wellstead, there are, to the north, large beds of living corals at a depth of twenty-five fathoms, and the anchors were often entangled by them ; and he attributes this depth, so much greater than reported by Ehrenberg, to the peculiar purity, or freedom from sediment, of the waters at that place. Kotzebue states that in some lagoons of the Marshall group he observed living corals at a depth of twenty-five fathoms, or one hundred and fifty feet. Professor Agassiz observes that about the Florida reefs the reef-building corals do not extend below ten fathoms. Mr. L. F. de Pourtales states that he found species of Ocu- lina and Cladocora off the Florida reefs living to a depth of fifteen fathoms. It thus appears that all recent investigators since Quoy and Gaymard have agreed in assigning a comparatively small depth to growing corals. The observations on this point, made during the cruise of the Wilkes Explormg Expedition, tend to confirm this opinion. The conclusion is borne out by the fact that soundings in the course of the various and extensive surveys afford no evi- dence of growing coral beyond twenty fathoms. Where the depth was fifteen fathoms, coral sand and fragments were almost uniformly reported. Among the Feejee Islands, the extent of coral-reef grounds surveyed was many hundreds of square miles, besides the harbours more carefully examined. The reefs of the Navigator Islands were also sounded out, with others at the Society group, besides numerous coral RANGE IN DEPTH OF CORALS. 91 islands ; and through all these regions no evidence was obtained of corals living at a greater depth than fifteen or twenty fathoms. Within the reefs west of Viti Lebuand Vanua Lebu, the anchor of the Peacock was dropped sixty times in water from twelve to twenty-four fathoms deep, and in no case struck among growing corals ; it usually sunk into a muddy or sandy bottom. Patches of reef were encountered at times, but they were at a less depth than twelve fathoms. By means of a drag, occasionally dropped in the same channels, some fleshy Alcyonia and a few Hydroids were brought up, but no reef-forming species. Outside of the reef of Upolu, corals were seen by the writer growing in twelve fathoms. Lieutenant Emmons brought up with a boat-anchor a large Dendrophyllia from a depth of fourteen and a half fathoms at the Feejees ; and this species was afterwards found near the surface. But Dendrophyllia, it may be remembered, is one of the deep-water genera. These facts, it may be said, are only negative, as the sound- ing-lead, especially in the manner it is thrown in surveys, would fail of giving decisive results. The character of a growing coral bed is so strongly marked in its uneven surface, its deep holes and many entangling stems, to the vexation of the sur- veyor, that in general the danger of mistake is small. But allowing uncertainty as great as supposed, there can be little doubt after so numerous observations over so extended regions of reefs. The depth of the water in harbours and about shores where there is no coral, confirms the view here presented. At Upolu, the depth of the harbours varies generally from twelve to twenty fathoms. On the south side of this island, off Falealili, one hundred yards from the rocky shores, Lieutenant Perry found bare rocks in eighteen and nineteen fathoms, with no evidence of coral. There is no cause here which will explain the absence of coral, except the depth of water ; for corals and coral reefs abound on most other parts of Upolu. Below Falelatai, of the same island, an equal depth was found, with no coral. Off the east cape of Falifa harbour, on the north 92 CORALS AND CORAL ISLANDS. side of Upolu, Lieutenant Emmons found no coral, although the depth was but eighteen fathoms. About the outer capes of Fungasa harbour, Tutuila, there was no coral, with a depth of fifteen to twenty fathoms ; and a line of soundings across from cape to cape afforded a bottom of sand and shells, in fifteen to twenty-one and a half fathoms. About the capes of Oafonu harbour, on the same island, there was no coral, with a depth of fifteen fathoms. Similar results were obtained about all the islands surveyed, as the charts sadsfactorily show. There is hence little room to doubt that twenty fathoms may be received as the ordinary limit in depth of reef corals in the tropics. It may however be much less, possibly not over half this, on the colder border of the coral-reef seas, as, for example, at the Hawaian Islands and the atolls northwest of that group. It is natural that regions so little favourable for corals on account of the temperature should differ in this respect from those in the warmer tropics. It may be here remarked, that soundings with reference to this subject are liable to be incorrectly reported, by persons who have not particularly studied living zoophytes. It is of the utmost importance, in order that an observation supposed to prove the occurrence of living coral should be of any value, that fragments should be brought up for examination, in order that it may be unequivocally determined whether the corals are living or not. Dead corals may make impressions on a lead as perfectly as living ones. As to the origin of this small range in depth — about 120 feet — temperature must be admitted as one cause, it having been proved to be predominant with regard to distribution of life throughout the extent and depths of the ocean. Yet it can hardly in this case be the only cause. The range of tempera- ture 85° to 74° gives sufficient heat for the development of the greater part of coral-reef species ; and yet the temperature at the 100 foot plane in the middle Pacific is mostly above 74.° CAUSES AFFECTING GROWTH OF CORALS. 93 III. Local Causes influencing Distribution. Coral-making species generally require pure ocean water, and they especially abound in the broad inner channels among the reefs, within the large lagoons, and in the shallow waters outside of the breakers. It is therefore an assertion wide from the fLict that only small corals grow in the lagoons and chan- nels, though true of lagoons and channels of small si7e, or of such parts of the larger channels as immediately adjoin the mouths of fresh-water streams. There are undoubtedly species especially fitted for the open ocean ; but as peculiar conveniences are required for the col lection of zoophytes outside of the line of breakers, we have not the facts necessary for an exact list of such species. From the very abundant masses of Astrseas, Mseandrinas, Porites, and Madrepores thrown up by the waves on the exposed reefs. It was evident that these genera were well represented in the outer seas. In the Paumotus, the single individuals of Porites lying upon the shores were at times six or eight feet in diameter. Around the Duke of York's Island, the bottom was observed to be covered with small branching and folia- ccous Montipores, as delicate as any of the species in more ])rotected waters. Species of the same genera grow in the face of the breakers, and some are identical with those that occur also in deeper waters. Numerous Astraeas, Mseandrinas, and Madrepores grow at the outer edge of the reefs where the waves come tumbling in with their full force. There are also many Miile- l)ores and some Porites and Pocillipores in the same places. But the weaker Montipores, excepting incrusting species, are found in stiller waters either deep or shallow. Again, the same genera occur in the shallow waters of the reef inside of the breakers. Astraeas. Mseandrinas and Pocilli- pores are not uncommon, though requiring pure waters. There are also Madrepores, some growing even in impure waters. One species was the only coral observed in the lagoon of 94 CORALS AND CORAL ISLANDS. Honden Island (Paumotus), all others having disappeared, owing to its imperfect connection with the sea. Upon the reefs inclosing the harbour of Revva (Viti Lebu), where a large river, three hundred yards wide, empties, which during freshets enables vessels at anchor two and a half miles off its mouth to dip up fresh water alongside, there is a single porous species of Madrepora {M. cribripord), growing here and there in patches over a surface of dead coral rock or sand. In similar places about other regions, species of Porites are most common. In many instances, the living Porites were seen standing six inches above low tide, where they were exposed to sunshine and to rains ; and associated with them in such exposed situations there were usually great numbers of Alcyonia and Xeniae. The Sideringe endure well exposure to the air. The exposure of six inches above low tide, where the tide is six feet, as in the Feejees, is of much shorter dura- tion than in the Paumotus, where the tide is less than half this amount; and consequently the height of growing coral, as compared with low- tide level, varies with the height of the tides. Porites also occur in the impure waters adjoining the shores ; and the massive species in such places commonly spread out into flat disks, the top having died from the deposition of sediment upon it. The effects of sediment on growing zoophytes are strongly marked, and may be often perceived when a mingling of fresh water alone produces little influence. We have mentioned that the Porites are reduced to flattened masses by the lodg- ment of sediment. The same takes place with the hemispheres of Astraea ; and it is not uncommon that in this way large areas at top are deprived of life. The other portions still live unaffected by the injury thus sustained. Even the Fungiag, which are broad simple species, are occasionally destroyed over a part of the disk through the same cause, and yet the rest remains alive. It is natural, therefore, that wherever streams or currents are moving or transporting sediment, there no corals CAUSES AFFECTING GROWTH OF CORALS. 95 grow ; and for the same reason we find few living zoophytes upon sandy or muddy shores. The small lagoons, when shut out from the influx of the sea, are often rendered too salt for growing zoophytes, in consequence of evaporation, — a condition of the lagoon of Knderby's Island. They also are liable to become highly heated by the sun, which likewise would lead to their depopulation. Coral zoophytes sometimes suffer injury from being near large fleshy Alcyonia, whose crowded drooping branches lying over against them, destroy the polyps and mar the growing mass. Again* the dead parts of a zoophyte, though in very many cases protected by incrusting nullipores, shells, bryo- zoans, &c., as already explained, in others is weakened by boring shells and sponges. Agassiz states in his paper on the Florida Reefs (Coast Survey Report for 185 1) : " Innumerable boring animals establish themselves in the lifeless stem, piercing holes in all directions into its interior, like so many augurs, dissolving its solid connection with the ground, and even pene- trating far into the living portion of these compact communi- ties. The number of these boring animals is quite incredible, and they belong to difterent families of the animal kingdom ; among the most active and powerful we would mention the date-fish or Lithodomus, several Saxicavae, Petricolce, Acae, and many w^orms, of which the Serpula is the largest and most destructive, inasmuch as it extends constantly through the living part of the coral stems, especially in the Mseandrina. On the loose basis of a Maeandrina, measuring less than two feet in diameter, we have counted not less than fifty holes of the date fish — some large enough to admit a finger — besides hun- dreds of small ones made by worms. But however efficient these boring animals may be in preparing the coral stems for decay, there is yet another agent, perhaps still more destruc- tive. We allude to the minute boring-sponges, which pene- trate them in all directions, until they appear at last completely rotten through. ' On the other hand, Serpulas and certain kinds of barnacles 96 CORALS AND CORAL LSLANDS. (of the genus Creusia, &c.) penetrate living corals without injury to them. They attach themselves when young to the surface of the coral, and finally become imbedded by the in- crease of the zoophyte, without producing any defacement of the surface, or affecting its growth. Many of these Serpulas grow with the same rapidity as the zoophyte, and finally pro-