st. abe! m cu cote ee ces ies _* Sear Cornell Mniversity Library BOUGHT WITH THE INCOME FROM THE SAGE ENDOWMENT FUND THE GIFT OF Henry W. Sage 1891 CIRO) Bo eens oe ee A MOMS. Date Due CAT.|NO. 23233 | ‘ornell U | oF 3.H98 “Toque iit olin,ove1 Cornell University The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924024759759 THE SCIENTIFIC MEMOIRS OF THOMAS HENRY HUXLEY THE SCIENTIFIC MEMOIRS OF THOMAS HENRY HUXLEY EDITED BY PROFESSOR MICHAEL FOSTER, M.A., M.D., LL.D., F.R.S, AND BY PROFESSOR E. RAY LANKESTER, M.A., LL.D., F.R.S. IN FOUR VOLUMES VOL. I London MACMILLAN AND CO. LimirTep NEW YORK: D. APPLETON AND COMPANY 1898 All rights reserved ¥ RicuarD Cay anp Sons, LimirEb, LONDON AND BUNGAY. PREFACE WHEN, after the death of the late Professor Huxley, the question of the form of a memorial to him was being discussed, among the proposals made was one to republish in a collected form the many papers which, during well nigh a half century of scientific activity, he contributed to scientific societies and scientific periodicals. It was felt that while his scientific treatises in the form of books, as well as his more popular writings, might safely be entrusted to the usual agencies of publication, there was a danger lest his exact scientific writings, scattered among many journals, might be in part over- looked or at least not gain that prominence in the eyes of students of biological science in times to come which was their due. And it was suggested that the financial responsibilities, by no means light ones, of publishing in an adequate form these collected scientific memoirs might be met out of the fund subscribed for a memorial. The Messrs. Macmillan, however, who for many years had had close relations as publishers with Professor Huxley, very generously, as a contribution to the memorial, undertook all the financial responsi- bilities of the republication, provided that we would be willing to bear such editorial labours as might be necessary. This of course we were delighted to do; the reprinting and the reproduction of the illustrations were at once begun, and we are now able to offer the first volume, which will be followed as rapidly as possible by the others. So far as we can judge, the work will be completed in four volumes. The papers are arranged in chronological order, and the present volume contains fifty memoirs originally published between 1847 and 1860. The list of papers which we propose to republish (and we have done our best to make the list complete) contains about two vi PREFACE hundred titles, exclusive of the memoir on The Oceantc Hydrozoa, published by the Ray Society in 1859, which, from its size and character, we have considered as an independent publication. Huxley produced so great an effect on the world as an expositor of the ways and needs of science in general, and of the claims of Darwinism in particular, that some, dwelling on this, are apt to overlook the immense value of his direct original contributions to exact science. The present volume and its successors will, we trust, serve to take away all excuse for such a mistaken view of Huxley’s place in the history of biological science. They show that quite beyond and apart from the influence exerted by his popular writings, the progress of biology during the present century was largely due to labours of his of which the general public knew nothing, and that he was in some respects the most original and most fertile in discovery of all his fellow-workers in the same branch of science. Older naturalists will, we feel sure, welcome this complete and convenient collection of writings which they have long known and long treasured. To our younger brethren we offer it as a most valuable mine in which searching they will find a most interesting history of the birth and growth of general ideas which seem to them now the most elementary truths of their science, while at the same time they will be brought to know models of style, patterns of sin- cerity and lucidity of exposition, which haply they may set before themselves as standards towards which they may strive. As a frontispiece to the present volume we present a photograph of Huxley, taken in 1857, when he was thirty-two years of age, a time corresponding to the middle of the period covered by the memoirs contained in the volume. Our thanks are due to the Royal, the Medico-Chirurgical, and other societies for the use made, for the purposes of reproduction, of periodicals contained in their libraries. M. F. Ee. RSL. January, 1898. CONTENTS I PAGE ON A HITHERTO UNDESCRIBED STRUCTURE IN THE HUMAN HAIR SHEATH . I London Medical Gazette, vol. 7. p. 1340, July, 1845. Il EXAMINATION OF THE CORPUSCLES OF THE BLOOD OF AMPHIOXUS LANCEO- LATUS. . bee 4 ; 4 Lritish Assoctation Report, 1847, pt. tt. p. 95. III DESCRIPTION OF THE ANIMAL OF TRIGONIA, FROM ACTUAL DISSECTION 6 Proceedings of the Zoological Society, vol. xvit. 1849, pp. 30-32, also in Annals and Magazine of Natural History, vol. v. 1850, pp. 141-143. IV ON THE ANATOMY AND THE AFFINITIES OF THE FAMILY OF THE MEDUSZE 9 Philosophical Transactions of the Royal Society, 1849, pl. 72. p. 413. Vv NOTES ON MEDUS AND POLYPES.. . é Satie es CES em ge Sy Annals and Magazine of Natural History, vol. vt. 1850, pp. 66-67. VI OBSERVATIONS SUR LA CIRCULATION DU SANG CHEZ LES MOLLUSQUES DES GENRES FIROLE ET ATLANTE 2 ij se, 36 Lxtrattes d'une lettre adressée d MW. ALilne-Edwards Annales des Sciences Naturelles, vol. xiv. 1850, pp. 193-5. VII OBSERVATIONS UPON THE ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA - 38 Philosophical Transactions of the Royal Soctety, 1851, pt. 22. Pp. 507-594 5 also tn Annals and Magazine of Natural History, vol. tx. 1852, Dp. 242-244. viii CONTENTS VIII PAGE REMARKS UPON APPENDICULARIA AND DOLIOLUM, TWO GENERA OF THE TUNICATA . : <2 69 Philosophical Transactions of the Royal Society, 1851, pt. 22. Pp. 595-606. IX ZOOLOGICAL NOTES AND OBSERVATIONS MADE ON BOARD H.M.S. “ RATTLE- SNAKE” DURING THE YEARS 1846-50 . ‘ : inh i 86 Annals and Magazine of Natural Hestory, vol. vit. ser. it. 1851, pi. 304-6 5 370-45 vol. vit2. Pp. 433-42. x OBSERVATIONS ON THE GENUS SAGITTA . . 96 British Association Report, 1851, pt. 77. pp. 77-78. (Sectional Transactions.) XI AN ACCOUNT OF RESEARCHES INTO THE ANATOMY OF THE HYDROSTATIC ACALEPHE wt F 98 British Assoctatzon Report, July, 1851, pt. 22. pp. 78-80. (Sectional Transactions.) XIl DESCRIPTION OF A NEW FORM OF SPONGE-LIKE ANIMAL . 102 British Association Report, July, 1851, pt. a7. p. 80. (Sectional Trans- actions.) XIII REPORT UPON THE RESEARCHES OF PROF. MULLER INTO THE ANATOMY AND DEVELOPMENT OF THE ECHINODERMS na a 103 Annals and Magazine of Natural History, ser. tt. vol. viit, 1851, pp. 1-19. AIV UEBER DIE SEXUALORGANE DER DIPHYDAE UND PHYSOPHORIDAE . 122 Miiller’s Archiv fiir Anatomie, Physiologie, und Wressenschaftliche Medicin, 1851, pp. 380-4. XV LACINULARIA SOCIALIS : A CONTRIBUTION TO THE ANATOMY AND PHy- SIOLOGY OF THE ROTIFERA ‘ ; 126. Transactions of the Macroscopical Society of London, new ser. vol, 2. 1853, Pp. 1-19. (Read December 31, 1851.) XVI UPON ANIMAL INDIVIDUALITY . 7 146 Proceedings of the Koyal [nstitution, vol, %. 1851-4, pp. 184-9. (Abstract ofa Friday Evening Discourse delivered on April 30, 1852.) CONTENTS 1X XVII ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA, AS ILLUSTRATED BY THE ANATOMY OF CERTAIN HETEROPODA AND PTEROPODA COLLECTED DURING THE VOYAGE OF H.M.S. “ RATTLESNAKE” IN 1846-50... 152 Philosophical Transactions of the Royal Soctety, vol. cxlizd. 1853, pt. 2. pp. 29-66. PAGE XVIII RESEARCHES INTO THE STRUCTURE OF THE ASCIDIANS ....... +6 I94 British Assoctation Report, 1852, pt. 12. pp. 76-77. NIX ON THE ANATOMY AND DEVELOPMENT OF ECHINOCOCCUS VETERINORUM . 197 Proceedings of the Zoological Soctety, vol. xx, 1852, Pp. 110-126. AN ON THE IDENTITY OF STRUCTURE OF PLANTS AND ANIMALS oe ee BO Abstract of a Friday Evening Discourse delivered at the Royal [nstitution on April 15, 1853; Proceedings of the Royal Instttution, t. 1851-4, fp. 298-302; Edinburgh New Philosophical Journal, litt. 1852, pp. 172-177. e NXI OBSERVATIONS ON THE. EXISTENCE OF CELLULOSE IN THE TUNIC OF ASCIDIANS © §. a ao x cay Bor ae a Ce ae ae 22 Quarterly Journal of Alicroscopical Sctence, t. 1853. XXII ON THE DEVELOPMENT OF THE TEETH, AND ON THE NATURE AND IMPORT OF NASMYTH’S “PERSISTENT CAPSULE” ‘ ‘ » 224 Quarterly Journal of Mécroscopical Sctence, t. 1853. XXIII THE CELL-THEORY (REVIEW) .... . F F 242 British and Foreign Medico-Chirurgwal Review, vol. x%z. 1853, pp. 285-314. XXIV ON THE VASCULAR SYSTEM OF THE LOWER ANNULOSA........ . 279 British Assoctation Report, 1854, pt. it. ~. 109. XXV ON THE COMMON PLAN OF ANIMAL FORMS. . es & Raa ee we BI Abstract of a Friday Evening Discourse delivered at the Royal Lustitution on May 12,1854. Proceedings of the Royal Institution, vol. 2. 1851-4, PP. 444-446. x CONTENTS XXVI ON THE STRUCTURE AND RELATION OF THE CORPUSCULA TACTUS (TACTILE CORPUSCLES OR AXILE CORPUSCLES) AND OF THE PACINIAN BODIES . Quarterly Journal of Mfécroscopical Sctence, vol, tt. 1854, pp. 1-7- XXVII ON THE ULTIMATE STRUCTURE AND RELATIONS OF THE MALPIGHIAN BODIES OF THE SPLEEN AND OF THE TONSILLAR FOLLICLES Quarterly Journal of Microscopical Sctence, vol. 17. 1854, pp. 74-82. NXVITI ON CERTAIN ZOOLOGICAL ARGUMENTS COMMONLY ADDUCED IN FAVOUR OF THE HYPOTHESIS OF THE PROGRESSIVE DEVELOPMENT OF ANIMAL LIFE IN TIME Proceedings of the Royal Institution, vol. ¢. 1854-58 (Abstract of a Dés- course delivered on 'riday, Aprtl 20, 1855), Pp. 82-85. NNIN ON NATURAL HISTORY AS KNOWLEDGE, DISCIPLINE, AND POWER ... . Royal Institution Proceedings, vol. 77. 1854-58 (Abstract of a Déscourse delivered on Friday, February 15, 1856), pp. 187-195. GLa ON THE PRESENT STATE OF KNOWLEDGE AS TO THE STRUCTURE AND FUNCTIONS OF NERVE .. . ols Procecdings of the Royal Institution, vol. 17. 1854-58 ( Abstract of a Discourse delivered on Friday, Alay 15, 1857), Pf. 432-437. ANNXI ON THE PHENOMENA OF GEMMATION Proceedings of the Royal Institution, vol. t2. 1854-58 (Abstract of a Dis- course delivered on Lriday, Alay 21, 1858), Pp. 534-5385 Szleman, Journal, xxvizt. 1859, pp. 206-209. NXANII CONTRIBUTIONS TO THE ANATOMY OF THE BRACHIOPODA ae Procecdings of the Royal Society, vol. vei. 1854-55, PP. 106-117, 241-242. XNNIII ON HERMAPHRODITE AND FISSIPAROUS SPECIES OF TUBICOLAR ANNELID& (PROTULA DYSTERI) . ; Ledinburgh New Philosophical Journal, vol. 7. 1855, pp. 113-129. XAXIV ON THE STRUCTURE OF NOCTILUCA MILIARIS Quarterly Journal of Microscopical Science, vol. td. 1855, Pp. 49-54. PAGE 284 Uo is) uw 35 CONTENTS x1 AXAV ON THE ENAMEL AND DENTINE OF THE TEETH , . ‘ ‘ - 357 Quarterly Journal of Microscopical Sctence, vol. ti. 1855, Pp. 127-130. AXAXAVI MEMOIR ON PHYSALIA F q 361 Proceedings of the Linnean Soctety, vol. t7. 1855, pp. 3-5. NXXVII ON THE ANATOMY OF DIPHYES, AND ON THE UNITY OF COMPOSITION OF THE DIPHYID® AND PHYSOPHORIDA, ETC. . . . 363 Proceedings of the Linnean Soctety, vol. 17. 1855, pp. 67-69. NNNVITI TEGUMENTARY ORGANS . 365 The Cyclopedia of Anatomy and Physiology, Edited by Robert B. Todd, M.D., LLR.S. (The fascicules containing this article were published between August, 1855, and October, 1856.} NXNNIX ON THE METHOD OF PALEONTOLOGY os OD to Annals and Magazine of Natural History, vol. xvii?. 1856, Pp. 43-54. XL OBSERVATIONS ON THE STRUCTURE AND AFFINITIES OF HIMANTOPTERUS 445 Quarterly Journal of the Geological Society, vol. xt7. 1856, Ap. 34-37. SLI FURTHER OBSERVATIONS ON THE STRUCTURE OF APPENDICULARIA FLABEL- LUM (CHAMISSO) . . . : 449 Quarterly Journal of Microscopical Science, vol. 2v. 1856, fp. 181-191. XLII NOTE ON THE REPRODUCTIVE ORGANS OF THE CHEILOSTOME POLYZOA . 461 Quarterly Journal of Microscopical Science, vol. tv. 1856, Pp. 191-192. XLIII DESCRIPTION OF A NEW CRUSTACEAN (PYGOCEPHALUS COOPERI, HUXLEY) FROM THE COAL-MEASURES é ea . 463 Quarterly Journal of the Geological Society, vol. xztz. 1857, pp. 363-369. XLIV ON DYSTERIA, A NEW GENUS OF INFUSORIA 471 Quarterly Journal of Mécroscopical Science, vol. v. 1857, pp. 78-82. xii CONTENTS XLV REVIEW OF DR. HANNOVER’S MEMOIR: “UEBER DIE ENTWICKELUNG UND DEN BAU DES SAUGETHIERZAHNS” Se Sst Quarterly Journal of Microscopical Sctence, vol. wv. 1857, pp. 166-171. XLVI LETTER TO MR. TYNDALL ON THE STRUCTURE OF GLACIER ICE . Philosophical Magazine, vol. xiv, 1857, pp. 241-260. XLVII ON CEPHALASPIS AND PTERASPIS Quarterly Journal of the Geological Soctety, vol. xiv. 1858, pp. 267-280. XLVIII OBSERVATIONS ON THE GENUS PTERASPIS British Association Report, 1858, pt. 72. pp. 82-83. NLIX ON A NEW SPECIES OF PLESIOSAURUS (P. ETHERIDGI) FROM STREET, NEAR GLASTONBURY ; WITH REMARKS ON THE STRUCTURE OF THE ATLAS AND AXIS VERTEBRZ AND OF THE CRANIUM IN THAT GENUS Quarterly Journal of the Geological Soctety, vol. xiv. 1858, pp. 281-294. L ON THE THEORY OF THE VERTEBRATE SKULL Proceedings of the Royai Society, vol. tx. 1857-59, Pp. 381-457 5 Annals and Magazine of Natural History, vol. 777. 1859, PP. 414-439. PAGE 476 502 517 538 LISt OF PLATES To face page THOMAS HENRY HUXLEY, 1857. From a photograph by Maull and Polyblank........., e 4 ae . 2... Frontispiece PLATE 1. DESCRIPTION OF THE ANIMAL OF TRIGONIA FROM ACTUAL DISSECTION. Figs. 1-6. .00«=~2~« ae Seiki k wo Woely 8 PLATE 2. ON THE ANATOMY AND THE AFFINITIES OF THE FAMILY OF THE MEDUS&. ‘Figs. 1--17— Thaumantias— Mesonema—Oceania 29 PLATE 3. ON THE ANATOMY AND THE AFFINITIES OF THE FAMILY OF MEDUS&. Figs. 18-28—Phacellophora—Rhizostoma mosaica. . . vr. 30 PLATE 4. ON THE ANATOMY AND THE AFFINITIES OF THE FAMILY OF THE MEDUS&. Figs. 29-49—- Rhizostoma mosaica—Cephea ocellata — Diphyde—Sertu- IQVIIG nis ee we 88 PLATE 5. OBSERVATIONS UPON THE ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA. Figs. 1-9—The Structure of the Salpa. . , : 78 PLATE 6. OBSERVATIONS UPON THE ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA. Figs. 1-8—The Structure of the Salpa. . . . ios 78 PLATE 7. OBSERVATIONS UPON THE ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA. Figs. 1-1o—The Anatomy of Pyrosoma 78 PLATE 8. REMARKS UPON APPENDICULARIA AND DOLIOLUM. Figs. 1-9—Appendicularia flagellum—Doltolum denticulatum . 78 PLATE 9. REMARKS UPON APPENDICULARIA AND DOLIOLUM. Two Genera of the Tunicata—Sectional Diagrams of the Tunicata . . 78 PLATE 10. ZOOLOGICAL NOTES AND OBSERVATIONS ON BOARD H.MLS. “RATTLESNAKE” DURING THE YEARS 1846-50. Figs. 1-1o—The Auditory Organs in the Crustacea 82 PLATE 11. ZOOLOGICAL NOTES AND OBSERVATIONS ON BOARD H.MLS. “ RATTLESNAKE” DURING THE YEARS 1846-50. Figs. 1-6—T7x%. punctata—Th. nucleata : ‘ , 2 86 XIV LIST OF PLATES To face page PLATE 12. REPORT UPON THE RESEARCHES OF PROF. MULLER INTO THE ANATOMY AND DEVELOPMENT OF THE ECHINODERMS. Figs. 1-11, i-xiii—_ Bipiénnaria — Brachiolaria— Tornaria—A uricularia Stpunculus. — . : rane Se Ah : 120 PLATE 13.—UEBER DIE SEXUALORGANE DER DIPHYDAE UND PHYSO- PHORIDAE. Figs. 1-17 — Eudoxia — Diphyes — Athorybia — Physalia — Velella— Stephanomia 4 . : 4 124 PLATE 14. LACINULARIA SQCIALIS. A CONTRIBUTION TO THE ANATOMY AND PHYSIOLOGY OF THE ROTIFERA. Figs. 1-19—Lacinularta soctalis . : soe 144 PLATE 15. LACINULARIA SOCIALIS. A CONTRIBUTION TO THE ANATOMY AND PHYSIOLOGY OF THE ROTIFERA. Figs. 20-37—Lacinularia soctalis—Melicerta ringens—Brachtonis polya- canthus—Philodina, sp. (2) . 7 , 144 PLATE 16. LACINULARIA SOCIALIS. A CONTRIBUTION TO THE ANATOMY AND PHYSIOLOGY OF THE ROTIFERA,. The diagrams illustrate Mr. Huxley’s paper on Adult Rotifera, and on Larval Annelids and Echinoderms . 144 PLATE 17. ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA, AS ILLUSTRATED BY THE ANATOMY OF CERTAIN HETEROPODA AND PTEROPODA COLLECTED DURING THE VOYAGE OF H.M.S. ‘f RATTLE- SNAKE,” 1846-50. Figs. 1-8—Firoloides Desmarestit 192 PLATE 18. ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA, AS ILLUSTRATED BY THE ANATOMY OF CERTAIN HETEROPODA AND PTEROPODA COLLECTED DURING THE VOYAGE OF H.M.S. “ RATTLE- SNAKE,” 1846-50. Figs. 1-6—-Adlanta Lesuertt — : 192 PLATE 19. ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA, AS ILLUSTRATED BY THE ANATOMY OF CERTAIN HETEROPODA AND PTEROPODA COLLECTED DURING THE VOYAGE OF H.M.S. “ RATTLE- SNAKE,” 1846-50. Figs. 1-7—Pneumodermon-—Euribia Gaudichaudii—Cleodora curvata— Cleodora aciculata 192 PLATE 20. ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA, AS ILLUSTRATED BY THE ANATOMY OF CERTAIN HETEROPODA AND PTEROPODA COLLECTED DURING THE VOYAGE OF H.M.S. “ RATTLE- SNAKE,” 1846-50. Figs. 1-17—Aplysta—A tlanta—Patella—Pteroceras PLATE 21. ON THE ANATOMY AND DEVELOPMENT OF ECHINOCOCCUS VETERINORUM. Figs. 1-5 192 ? Sess 215 PLATE 22. ON THE ANATOMY AND DEVELOPMENT OF ECHINOCOCCUS VETERINORUM. Figs. 6-9, A—E—Development of Echinococcus. LIST OF PLATES XV To face page PLATE 23. ON THE DEVELOPMENT OF THE TEETH, AND ON THE NATURE AND IMPORT OF NASMYTH’S “ PERSISTENT CAPSULE.” Figs. I-12 . 240. PLATE 24. ON THE STRUCTURE AND RELATION OF THE CORPUSCULA TactTus (TACTILE COPUSCLES OR AXILE CORPUSCLES), AND THE PACINIAN BODIES. Figs. I-10, A-F ar 290 PLATE 25. ON THE ULTIMATE STRUCTURE AND RELATIONS OF THE MALPIGHIAN BODIES OF THE SPLEEN AND OF THE TONSILLAR FOLLICLES. Figs. I-10 299: PLATE 26. ON A HERMAPHRODITE AND FISSIPAROUS SPECIES OF TUBICOLAR ANNELID. Figs. 1-11—Protula dysteri ‘ 350 PLATE 27. ON THE STRUCTURE OF NOCTILUCA MILIARIS. Figs. 1-6—Noctiluca milzaris . a 356 PLATE 28. FURTHER OBSERVATIONS ON THE STRUCTURE OF APPEN- DICULARIA FLABELLUM (CHAMISSO). Figs. 1-4—Appendicularia flagelluin 460 PLATE 29. DESCRIPTION OF A NEW CRUSTACEAN (PYGOCEPHALUS CoOOPERI, HUXLEY) FROM THE COAL-MEASURES. Figs. 1-6—Pygocephalus Cooperi 470 PLATE 30. ON DySTERIA; A NEW GENUS OF INFUSORIA. Figs. 13-15—Dysteria armata . 475 PLATE 31. ON CEPHALASPIS AND PTERASPIS. Figs. 1-5—Cephalaspis 518 PLATE 32. ON CEPHALASPIS AND PTERASPIS. Figs. 1-4—Preraspis . 518. THs SCIENTIFIC. PAPERS OF THOMAS HENRY HUXLEY I ON A HITHERTO UNDESCRIBED STRUCTURE IN THE HUMAN HAIR SHEATH London Medical Gazette, vol. t. p. 1340, July, 1845 IN Professor Henle’s “Bericht ueber die Leistungen in der His- tologie,” for 1846, the following passage is contained :— “Kohlrausch and Krause describe the inner layer of the sheath of the root (of the hair) which I depicted as a glossy soft fenestrated membrane, to be a layer of pale longish and flat cells, which firmly adhere in the longitudinal direction, whilst transversely they may be separated by manipulation, and then present the appearance of a membrane with irregular gaps. This same membrane separated and folded they considered to form the transverse striae on the root of the hair. I venture to affirm that these observers have not even seen any inner layer of the sheath of the root. I beg of them to treat a hair torn out with both layers of the sheath adhering, with acetic acid ; carefully to strip off the granular outer layer, which by this means is rendered brittle, and then to adjust the focus of the microscope to the most superficial part of the hair. They will then see, not only the round holes with very even sharp borders described by me, but also, by altering the focus, they will see beneath this the transverse strips, which, as Meyer justly stated, are formed by the borders of imbricated scales. I have also at times seen a layer consisting of anastomosing longitudinal fibres, which perhaps is composed of elongated scales but I cannot say whether this was in the place of my fenestrated membrane. Certainly it is not ordinarily present.” VOL. I B 2 HITHERTO UNDESCRIBED STRUCTURE IN HUMAN HAIR Perhaps some light may be thrown upon the contradictory opinions here set forth, by some observations made by myself in the beginning of the present year, and since repeated so frequently, as, I hope, to avoid all source of error. If the sheath of the root be split longitudinally with needles or a fine knife—removed, and laid out flat with the inner surface upper- most, the fenestrated membrane will be at once seen, when the focus of the microscope is adjusted to its upper surface. If some part where the sharp well-defined edge of this membrane is free, be now more carefully examined there will probably be seen extending for some little distance beyond, and lying above it, a single layer of very pale epithelium-like nucleated cells. If the eye be now carried again over the fenestrated membrane (the focus being carefully adjusted), this layer will be found to be traceable over the fenestrated membrane, and to be in close connection with it. The individual cells composing the layer are very delicate and pale, readily escaping observation when not separated from the other structures ; they are more or less polygonal or rounded, 1-6o0oth to. HITHERTO UNDESCRIBED STRUCTURE IN HUMAN HAIR 3 I-1200th of an inch in diameter; they are applied edge to edge or nearly so. The nuclei are elongated, broader at their extremities than in the middle, and sometimes more or less prolonged at their angles ; their average long diameter may be about 1-2000th of an inch, but in this respect they (as the cells) vary a good deal. They appear more or less granular, but do not present any distinct nucleolus. Acetic acid renders both cell and nucleus extremely indistinct ; the latter would sometimes appear to become corrugated after the manner of the pus corpuscles, &c. The position of this layer of cells is between the fenestrated membrane and the cortical scales; clear proof of this is obtained when the cortical scales happen to peel off from the shaft and adhere to the inner surface of the sheath. If the focus be adjusted to them, depressing it brings into view, Ist. the layer of nucleated cells; 2nd. the fenestrated membrane. Subjoined is a drawing of the inner surface of a hair sheath, illustrating this. Possibly it is the layer of cells here described which has been confounded by Kohlrausch and Krause with the fenestrated membrane, which has been described by Henle as consisting of anastomosing longitudinal fibres, and by Meyer (cited in Professor Henle’s “ Allge- meine Anatomie,” p. 295), as a stage of development of the cortical scales. II EXAMINATION OF THE CORPUSCLES OF THE BLOOD OF AMPHIOXUS LANCEOLATUS British Association Report, 1847, pt. 2, p- 95 In September last I was furnished, by the kindness of Professor Edward Forbes, with one of the living specimens of Amphioxus /anceolatus, which that gentleman exhibited at the meeting of the British Association at Southampton. On the succeeding day I proceeded to examine the blood of the animal, but it unfortunately no longer exhibited any signs of life, and it was with difficulty that I obtained two drops for that purpose ; the one by making an incision into the skin (having first carefully dried the surface), the other by cutting off the extremity of the tail. This difficulty will, I trust, be a sufficient excuse for the want of that com- pleteness about the following statements, which more frequently re- peated observations might have given them; at the same time I believe they will be found correct as far as they go. The blood was thin and had a very slight rusty tinge. Under the microscope (objective 4th of an inch, Ross) it presented the following appearances: in both specimens a number of large, irregular, pale greenish granule-cells, rather more than ;,!;,th of an inch in diameter ; these contained a few scattered strongly refracting granules, were shot out into one or two irregular processes, and adhered together into masses. Besides these there were ofhers having much the same characters, but possessing cither more or fewer granules, so that there was a complete gradation exhibited from those which were full of coarse granules, to those which had quite a fine texture without any granules at all. CORPUSCLES OF THE BLOOD OF AMPHIOXUS LANCEOLATUS 5 By the action of water the processes became obliterated, and the granules all assumed the form of a very pale and colourless globular cell, with large granules here and there, and a very pale nucleus occupying rather less than half its diameter. In one part of the field I perceived such a nucleus floating about attached only toa number of granules, which appeared bound together by an inter- mediate substance invisible from its transparency. The whole mass appeared to have become free by the bursting of the cell-wall, which was nowhere to be detected. In one specimen only (that obtained by puncturing the skin) I observed two roundish or slightly oval corpuscles, rather more than zg5gth of an inch in diameter, with a nucleus occupying three-fifths of that extent. This nucleus was greenish-looking, and refracted light strongly, while the cell-wall was of a pale reddish colour and exccedingly delicate, so much so that it seemed more like a reddish halo round the nucleus than a distinct structure. Altogether, with the exception of the last-mentioned corpuscles, the blood of the Amphioxus had a most remarkable resemblance to that of an invertebrate animal, and that in every particular. [This communication was illustrated by figures.] III DESCRIPTION OF THE ANIMAL OF TRIGONIA, FROM ACTUAL DISSECTION! Zoological Society Proceedings, vol. xvit. 1849, Pp. 30-32, also in Annals and Magazine of Natural History, vol. v. 1850, Pp. 141-143 THE accompanying account of the animal of 77zgonza was for- warded to me by Mr. Huxley, Assistant-Surgeon to the Ratélesnake, now surveying in the Eastern and Australian Seas, under the able command and scientific zeal of Captain Owen Stanley. The great number, beauty and geological importance of the species of this interesting genus have made especially valuable a knowledge of the structure of its animal. Quoy and Gaimard were the first to give any account of it, and a figure and description of the animal of Trigontia were published from their drawings and notes in the zoo- logical division of the Voyage of the Astrolabe? Since then 1 am not aware of this curious creature having been re-observed, though much has been written respecting its systematic position. As in such a case a verification of the evidence we possess, through a new and accurate set of observations, is of almost as much importance as the description of an unobserved animal, the Zoological Society may con- sider Mr. Huxley’s notes in the light of a valuable contribution to malacology. Both accounts confirm the idea suggested by the shell of its position among the Avcacee, and its close affinity with Macula and Arca. The degree of union of the mantle-lobes, and the development of siphonal tubes in this family, as among the neighbouring J/ytc/ide, is of generic and not sectional significance. 1 The paper is by Prof. E. Forbes. The part headed Description of Trigonia is written by Huxley.—£Zas. * Vol. iii. p. 476, Mollusques, pl. 78, f. 5. DESCRIPTION OF THE ANIMAL OF TRIGONIA 7 I add the description of the animal given by the French naturalists for comparison :— “L’animal a le manteau ouvert dans les trois quarts de sa circon- férence inférieure. Il est frangé sur ses bords, avec de petites taches ou lunules blanches qui alternent avec des stries rayonnées. On voit, au sommet de ce manteau, les impressions denticulées de la charniére, et en avant et en arriére, les muscles qui unissent les valves. Le pied est grand, robuste, sécuriforme, trés recourbé en arriére, tranchant et denticulé sur son aréte, de chaque cété de laquelle sont des laciniures au tiers antérieur seulement. Il ne nous a pas paru se dilater comme dans les muscles. Les branchies sont grandes, libres, subtriangulaires, €n pointe, reposant, de chaque cété de la racine du pied, leur doubles lamelles. Les palpes buccaux sont excessivement petits, réunis dans une partie de leur étendue. L’anus est a l’extrémité d’un court pédicule. La disposition du manteau et le manque de tubes rap- prochent ce mollusque de celui des Nucules, dont il différe cependant par la disposition des branchies ect la briéveté des appendices de la bouche.” Description of Trigonia. The mantle-lobes are rounded and plaited, to correspond with the ribs of the shell. The edges of the mantle are marked with white spots; posteriorly, opposite the anus they are provided with short convex appendages. The mantle-lobes are disunited throughout, not joining until they reach the upper surface of the posterior adductor, some distance above the anus. The gills are somewhat triangular, extending backwards almost horizontally on each side of the visceral mass. Each gill is formed of three stems, fixed at one extremity, free and pointed at the other, and giving attachment throughout their whole length, on one side to depending filaments, which become shorter as they are more posterior. The filaments are formed of a tubular horny thread, supporting on one side a broad membranous fringe. I could perceive no trace of vessels in this fringe, but it appeared to be covered by an epithelium (ciliated ?). The mouth is placed at the anterior and superior part of the animal, between two thickish horizontal lips. The labial tentacles are two on each side, rather long, lanceolate, and slightly pectinated. The anus is placed posteriorly and superiorly between the gills, and just about the posterior adductor muscle. The so-called “foot” is composed of two portions, an upper and 8 DESCRIPTION OF THE ANIMAL OF TRIGONIA quadrilateral (properly the abdomen), and a lower pointed part (the true foot), the two being set at right angles to one another. The first portion is sharp-edged and slightly pectinated posteriorly, marked by a groove bounded by two folded lips anteriorly. The second portion is slightly pectinated along its lower edge, pointed anteriorly, prolonged behind into a curved process, where it joins the superior portion. Visceral mass——The mouth opens by a very short cesophagus into a wide pyriform stomach, surrounded by a dark dendritic liver. The stomach narrows into a long intestine, which descends for the whole length of the abdomen, and forms one or two loops in the substance of the generative gland; then passes up again above the stomach, penetrates the heart, and passing between the two small lateral muscles of the foot, terminates in the anus. [Plate 1.]? Fig. (1). View of the animal with the right valve of the shell removed, and the right lobe of the mantle turned back. w, mouth; 4, anus; ¢, filamentous appendages of mantle ; d@, gill; e, grooved superior part of foot. Fig. (2). View of the animal from behind, with the valves separated. Letters as before. Fig. (3). Visceral cavity laid open. «, stomach, surrounded by the liver; 4, intestine ; ¢, heart ; @, generative gland. ? The word Plate accompanied by a number and printed within brackets refers throughout to the plate-number assigned to each plate in the present reprint of Huxley’s papers, and not to the original numbering of the plates as published in transactions or journals.—Eps. Proc ZS Mollusca II! IV ON THE ANATOMY AND THE AFFINITIES OF THE FAMILY OF THE MEDUS Philosophical Transactions of the Royal Society, 1849, pt. 2, p. 413- I. PERHAPS no class of animals has been so much investigated with so little satisfactory and comprehensive result as the family of the Medus@, under which name I include here the Weduse, Mono- stomat@, and Rhizostomide ; and this, not for the want of patience or ability on the part of the observers (the names of Ehrenberg, Milne- Edwards, and De Blainville are sufficient guarantees for the excellence of their observations), but rather because they have contented them- selves with stating matters of detail concerning particular genera and species, instead of giving broad and general views of the whole class, considered as organized upon a given type, and inquiring into its relations with other families. 2. It is my intention to endeavour to supply this want in the present paper—with what success the reader must judge. I am fully aware of the difficulty of the task, and of my own incompetency to treat it as might be wished ; but, on the other hand, I may perhaps plead that in the course of a cruise of some months along the east coast of Australia and in Bass’s Strait I have enjoyed peculiar oppor- tunities for investigations of this kind, and that the study of other families hitherto but imperfectly known, has done much towards sug- gesting a clue in unravelling many complexities, at first sight not very: intelligible. . 3. From the time of Peron and Lesueur downwards, much has been said of the difficulties attending the examination of the Meduse. I confess I think that they have been greatly exaggerated ; at least with a good microscope and a good light (with the ship tolerably 10 ON THE ANATOMY OF THE FAMILY OF THE MEDUS/A# steady), I never failed in procuring all the information I required. The great matter is to obtain a good swccess¢ve supply of specimens, as the more delicate oceanic species are usually unfit for examination within a few hours after they are taken. SECTION I.—Of the Anatomy of the Meduse. 4. A fully-developed Medusa has the following parts :—1. A disc 2. Tentacles and vesicular bodies at the margins of this disc. 3. A stomach and canals proceeding from it; and 4. Generative organs, either ovaria or testes. The tentacula vary in form and position in different species, and may be absent; the other organs are constantly present in the adult animal. 5. Three well-marked modifications of external structure resuit from variations in the relative position of these organs. There is either—Ist, a simple stomach suspended from the centre of a more or less bell-shaped disc, the disc being traversed by canals, on some part of which the generative organs are situated, e.g. Geryonta, Thauman- tias ; or 2ndly, a simple stomach suspended from the centre of a disc ; but the generative organs are placed in cavities formed by the pushing in, as it were, of the stomachal wall, eg. Aurelia, Phacellophora ; or 3rdly, the under surface of the disc is produced into four or more pillars which divide and subdivide, the ultimate divisions supporting an immense number of small polype-like stomachs; small apertures lead from these into a system of canals which run through the pillars, and finally open into a cavity placed under the disc; the generative organs are attached to the under wall of the cavity, eg. Rhisostoma, Cephea. 6. To avoid circumlocution I will make use of the following terms (employed by Eschscholtz for another purpose) to designate these three classes, viz. Cryptocarpe for the first, Phanerocarpe for the second, and Rhizostomide for the third. 7. In describing the anatomy of the Medusze it will be found most convenient to commence with the stomach, and trace the other organs from it. Of the Stomach—This organ varies extremely both in shape and in size in the Cryptocarpe and Phanerocarpe. But whatever its appearance, it will be always found to be composed of two mem- branes, an inner and an outer. These differ but little in structure ; both are cellular, but the inner is in general softer, less transparent, and more richly ciliated, while it usually contains but few thread-cells, The outer, on the other hand, is dense, transparent, and either dis- ON THE ANATOMY OF THE FAMILY OF THE MEDUS-% II tinctly cellular or developed into a muscular membrane. It may be ciliated or not, but it is usually thickly beset with thread-cells, either scattered through its substance or concentrated upon more or less raised papillae developed from its surface. 8. I would wish to lay particular stress upon the composition of this and other organs of the Medusz out of two distinct membranes, as I believe that it is one of the essential peculiarities of their structure and that a knowledge of the fact is of great importance in investigating their homologies. I will call these two membranes as such, and inde- pendently of any modification into particular organs, “foundation membranes.” g. When the stomach is attached to the disc, the outer membrane passes into the general substance of the disc, while the inner becomes continuous with the lining membrane of the canals. There is a larger or smaller space between the inner aperture of the stomach and the openings of the canals, with which both communicate, and which ] will therefore call the “common cavity.” 10. In the Rhizostomidz the structure of the stomachs is funda- mentally the same, but they are very minute, and are collected upon the edges and extremities of the ramuscules of a common stem ; so that the Rhizostomide, guoad their digestive system, have the same relation to the Monostome Medusz as the Sertularian Polypes have to the Hydre, or the Coralline Polypes to the Actiniz. 11. If one of the ultimate ramuscules be examined, it will be found to consist of a thick transparent substance, similar in constitution to that of the mass of the disc, through which there runs, nearer one edge than the other, a canal with a distinct membranous wall ciliated internally. From this ‘common canal” a series of parallel diverticula are given off_at regular intervals, and run to the edge of the branch, where they terminate by rounded oblique openings. It is not always easy to see these ees but I have repeatedly satisfied myself of their presence by passing a needle or other delicate body into them, figs. 28, 2c. aA 12. The difficulty in seeing the openings arises in great measure from the presence of a membrane which surrounds and overlaps them, and being very irritable, contracts over them on being touched. The membrane consists of two processes, one from each side of the per- forated edge of the branch, fig. 28. In RAzzostoma these two processes generally remain distinct, so that their bases form a common channel into which all the apertures open ; but in Cephea they are frequently united in front of and behind each aperture so as to form a distinct polype-like cell, figs. 35, 36. I2 ON THE ANATOMY OF THE FAMILY OF THE MEDUSA: 13. Each membranous process is composed of two membranes ; the outer of these is continuous with and passes into the thick trans- parent outer substance above mentioned (11); the other is less trans- parent, more richly ciliated, and continuous with the lining membrane of the canals through the apertures. The two membranes are con- tinuous at the free edge of the fold, and are here produced into numerous tentacula. The latter are beset with great numbers of thread-cells, and are in constant motion while the part retains its vitality,! fig. 29. 14. Of the Drse—In the Meduse monostomate the outer membrane of the stomach is, as I have said, continueus with the thick trans- parent mass of the disc, as the inner membrane is with the lining membrane of the canals which traverse it. The disc, therefore, is com- posed of two membranes inclosing a cavity variously shaped. 15. I have examined the minute structure of the disc in RAzz0- stoma. The outer surface of the transparent mass is covered with a delicate epithelium composed of polygonal nucleated cells joined edge to edge. Among these there are many thread-cells. Beneath this there is a thick gelatinous mass which is made up of an apparently homogeneous substance containing a multitude of delicate fibres interlacing in every direction, in the meshes of which lie scattered nucleiform bodies. On the lower surface of the disc, the only differ- ence appeared to be that the epithelium was replaced by a layer of parallel muscular fibres. 16. It might be said that the gelatinous substance here described is a new structure, and not a mere thickeniig of the outer membrane ; but a precisely similar change is undergone by the outer membrane in the Diphyde, and here it can be easily traced, ¢,g. in the formation of the bracts and in the development of muscular fibre in the outer wall of the common tube. 17. The structure of the inner membrane of the disc and its canals resembles that of the corresponding tissue in the stomach, &c., but in the ultimate ramifications of the canals it becomes more delicate. In these points there exists no difference between the Monostome and Rhizostome Medusze. 18. The three divisions, however, vary somewhat in the arrange- ment of the cavities and canals of the disc. 1 M. Milne-Edwards, in his ‘‘ Observations sur la Structure de la Méduse Marsupiale,”’ describes the fringe and its tentacles, but having altogether overlooked the true digestive apertures, he ascribes to the tentacles the function of villi. ‘Les franges qui garnissent les bras des rhizostomes sont donc bien certainement des organes @absorption, et leur structure les rend en effet tres propres a remplir cette fonction, qui ici dépend probablement tout entier d’un phénoméne analogue a celui désigné par M. Dutrochet sous le nom d’endosmose.” ON THE ANATOMY OF THE FAMILY OF THE MEDUS& 13 In the Cryptocarpe, the common cavity may be either small (Thaumantias) or large (Oceania): from it there proceed a number of straight unbranching canals which open into a circular canal running round the margin of the disc. In the Phanerocarpz the general arrangement is similar, but the canals frequently branch (Medusa aurita, Phacellophora) and anasto- mose in a reticulate manner. In many of the Monostome Medusz the centre of the under sur- face of the disc projects into the “common cavity ” as a rounded boss (fig. 11 @.), and according to its form and size will seem to divide the former more or less into secondary cavities. This appears to me to be the origin of the multiple stomachs of AZedusa aurita as described by Ehrenberg. 19. In the Rhizostomide, the canals of the branched processes unite and open by four (Rhisostoma, Cephea) or eight (Casscopea?) distinct trunks into a wide curiously-shaped cavity, from whence anastomosing canals are given off to all parts of the disc (figs. 26, 26 a.). The circular vessel exists, but is not particularly obvious in consequence of anastomosing branches being given off beyond it. 20. In very many of the Cryptocarpee (Caryédoa, Oceania (fig. 5 a. and &.), Polyxenia) there is a circular, valvate, muscular membrane developed from the inner and under edge of the disc. In the Phanero- carpze such a membrane does not seem to be present, but in Rhzzostoma, and Cephea it is evidently replaced by the inflexed edge of the disc fig. 26 a. 21. Of the Marginal Corpuscles—In the Cryptocarpe the marginal corpuscles are sessile upon the circular vessel, figs. 8,9, 10. They are spheroidal vesicles, containing a clear fluid, and one or more spherical strongly-refracting bodies occasionally included within a delicate cell. The marginal vesicles are placed between the inner and outer mem- branes of the circular vessel. In the Phanerocarpe (Phacellophora) the marginal corpuscle (figs. 28, 25 a.) is placed at the extremity of a short double-walled tubular pedicle projecting downwards or towards the ventral surface of the disc; the under margins of the fissure in which it is lodged are pro- longed into two overlapping fringes. The cavity of the pedicle is con- tinuous with that of a canal which runs from the common cavity directly towards the corpuscle. Its walls are continuous, the inner with the inner wall of the canal, the outer with the substance of the disc. The pedicle is in fact a mere process of the system of canals, so that the position of the marginal vesicle is relatively to this system 14 ON THE ANATOMY OF THE FAMILY OF THE MEDUSA! the same as in the Cryptocarpe. A similar remark holds good with regard to the Rhizostomide. 22. In Cephea and Rhizostoma the organ is placed ina notch between two lobe-like processes of the margin of the disc, and looks upwards. On the upper surface a semilunar fold extends from one lobe to the other and covers in the corpuscle ; below, the edges of the lobes are thinned and overlap, figs. 33, 34. 23. There are some peculiarities in A/zzostoma which deserve to be noticed more fully. On the dorsal surface, behind the semilunar fold above mentioned, there is a large heart-shaped depression (fig. 33) with its base towards the corpuscle. Its surface is thrown into prominent arborescent folds, and is very richly ciliated. The deepest part of the depression is towards its base, and seems to take the direction of the base of the pedicle of the marginal corpuscle, which is just below it. I could not pass a needle from the depression into the cavity of the pedicle, but I have no doubt that they communicate, as on a lateral view the deepest part of the depression seems to project into the cavity of the pedicle. Furthermore, on pressure, the granules usually contained in the cavity of the pedicle sometimes passed into the depression. 24. Ehrenberg describes apertures in Mfedisa aurita by which the system of canals communicates with the exterior, but they are alternate with the marginal corpuscles, not under or above them. In Cephea Wagneri, again, according to Will, the canals open beneath the marginal vesicles. I did not observe this in the Cephea ocellata. 25. On the ventral surface a much slighter semilunar fold connects the base of the two lobes, fig. 34. In the centre, behind this, there is an elevation of the substance of the disc, to which the muscular bands which run along the under surface of the disc converge. 26. The canal which runs to the marginal vesicle gives off branches on each side, then opposite the base of the vesicle forms a dilatation rather larger than the cordate depression ; from this a ceecal process passes off into each lobe, and so terminates. The termination of the canal in Cephea and Phacellophora is similar, but in the latter the caca gives off lateral anastomosing branches, fig. 25. 27. In Rkesostoma the pedicle is somewhat bent and enlarged at its upper half. The inner membrane is richly ciliated, and the cavity which it encloses usually contains a number of rounded cell-like bodies floating about in incessant motion. There is a considerable space between the inner and outer membranes, which are thick, and there- fore, when viewed by transmitted light, appear like four thick fibres. The vesicle is about ;45th of an inch in diameter, more spherical ON THE ANATOMY OF THE FAMILY OF THE MEDUS/ 15 in small than in large individuals ; it contains a closely-packed mass of strongly-refracting granules 3 455th of an inch, more or less, in diameter. The outer membrane of the pedicle can be traced over the vesicle, and the inner probably passes under it, separating the cavity of the pedicle from the vesicle: the dense mass of granules prevents this from being actually seen, but from analogy with Mesonema, &c., I have no doubt of the fact. 28. Ehrenberg, in his description of the J/edusa aurtta, says, “ Le pédoncule est attaché a une vésicule, dans lequel on remarque, sous le microscope, un corps glanduleux, jaunatre lorsque la lumiere le traverse et blanchatre lorsque cette derniere est réfléchie. De ce corps il part deux branches qui se dirigent vers le pédoncule du corps brun jusqu’a son petit bouton ou téte”” And further on, “Le corps bifurqué placé a la base du corps brun parait étre un ganglion nerveux, et ses deux branches peuvent étre regardées comme des nerfs optiques.” I must confess that, judging by what I have observed in Rhzzostona and Phacellophora, it appears to me that these so-called nervous branches passing on each side of the pedicle towards its head, are nothing more than the optical expression of the thickness of the two membranes of which the pedicle is composed; and a very similar explanation may, I think, be given of his intertentacular ganglia, which appear to be nothing more than the optical expression of the thickened walls of the circular canal. 29. Of the Tentacles-—The tentacles of the Medusee are of two kinds :—1, those which are processes of the outer foundation mem- brane alone ; and 2, those which are processes of both inner and outer membranes, and therefore contain a cavity continuous with the common cavity of the body. Under the former class must be included the knob-like processes on the convex surface of many Meduse con- taining thread-cells; the papillae on the generative and stomachal membranes of Phacellophora ; the thickened margin of the stomachal membrane in Oceanza ; the buccal tentacles of AZesonema ; the tentacles of the fringe of Rhzzostoma and Cephea, and probably the marginal tentacles of Thaumantias. I will proceed to describe some of these more in detail. 30. The papillz scattered over the generative and stomachal mem- branes of Phacellophora are spherical, and connected with the membrane by a somewhat narrower neck. The substance of this, as well as of the body itself, is made up of large clear cells, but the surface of the body is covered with an immense number of round thread-cells, figs. 20, 20 a. In Mesonema, the perpendicular membrane, which depends from 16 ON THE ANATOMY OF THE FAMILY OF THE MEDUSA! the orifice of the central cavity, is prolonged at its edges into a great number of short tentacles. Fach of these is composed of an outer wall, in which immense numbers of thread-cells are imbedded, and a central axis made up of large transparent cells. This cellular axis extends for some distance beyond the base of the tentacle into the substance of the membrane, fig. 7. 31. The tentacles of the fringe of RAzzostoma and Cephea have already been described, fig. 13. The tentacles which beset the gener- ative membrane closely resemble them, and consist of a single mem- brane, containing many smal] thread-cells, ggygth of an inch in diameter. Their cavity is filled with a homogeneous substance, some- times containing nuclei, similar to those of the disc (15); the inner membrane takes no part in their formation, fig. 30. 32. The marginal tentacles of 7aumantias are very similar (fig. 3) to the buccal tentacles of A7esonema ; they consist of an outer mem- brane, in which numbers of thread-cells are imbedded, and an inner axis composed of clear cells arranged end to end; they have a peculiarity, which has been already pointed out by Prof. E. Forbes, in being placed above the marginal vesicles instead of being alternate with them, as in the nearly allied genus Geryonza ; and from this fact, and from their totally different structure, I believe that they have a totally different origin. In Geryonza the tentacles belong to the second class—are processes of the circular canal; in 7haumanttas they are simple processes of the outer foundation membrane, zc. of the substance of the disc. Perhaps this difference in structure among the tentacles may turn out to be a good means of generic distinction among other members of the class. 33- As to the second class of tentacles. Such are the marginal tentacles of AZesonema, of Geryonia (Will), of Oceanta and of Jledusa aurita (Ehrenberg) ; the tentacles of the under surface of Phacellophora, and the interbrachial tentacles of Cephea. 34. In the specimens of //esonema 1 obtained, there were not more than eight tentacles, placed at equal distances round the disc, which had attained their full development. The interval between every two was filled up by a series of bud-like rudimentary tentacles, and mar- ginal corpuscles alternate with them. Each tentacle, in its bud-like rudimentary form, is simply a cecal process of the circular canal, and has therefore, like it, a double wall and an internal cavity, usually filled with granules in rapid motion, produced by the cilie of the inner wall; the outer wall contains large thread-cells. The structure of the adult tentacle is essentially the same, but in the course of its growth it has become divided into a lower filamentous portion and ON THE ANATOMY OF THE FAMILY OF THE MEDUS/ 17 an upper dilated sac, by which it communicates with the circular canal, fig. 8. The marginal tentacles of Oceanta resemble these in all points ; they are double-walled, communicate freely with the circular canal, and contain an immense number of minute thread-cells in their outer wall, fig. 15. 35. In Phacellophora there is no distinct marginal circular canal, but the sixteen radiating canals are very wide and sacciform, and com- municate only by anastomosing marginal branches. Eight of the canals are narrower and run to the marginal corpuscles. The alternate eight are very much wider, and their outer, under surface is beset with a curved series of long tentacles, fig. 18. Now the lower wall of the canals is composed of the two “foundation membranes,” and the tentacles are simply prolongations of these membranes; they are therefore double-walled, and contain a cavity continuous with that of the canal. At their upper part they are thicker than below, where their outer membrane is developed into spherical processes containing multitudes of thread-cells and closely resembling those on the genera- tive membrane (30).'. The inner cavity becomes obliterated at the lower part of the tentacle, fig. 19. 36. The large interbrachial tentacles of Cephea are processes of the branched arms. For the greater part of their length they have the same structure as the arms, z.c. consist of a dense, thick, transparent outer substance and an inner membranous wall inclosing a tubular canal; but at the extremity they are thickened, and the outer wall is raised into a number of small pyriform processes, ;45th of an inch in diameter, thickly covered with minute spherical thread-cells, =j4,th of an inch in diameter. At the same time the central canal becomes branched out into a kind of plexus, which occupies the interior of the enlarged end of the tentacle, fig. 37. These tentacles are two inches or more in length and jth of an inch in thickness, but other smaller tentacles, #ths of an inch in length by th of an inch in diameter, depended from the arched concavity of the brachiferous plate. Their general structure much resembled that of the foregoing, except that the central canal terminated in a blind simple extremity, and that the pyriform bodies extended rather further up the stem. Beside these there was a third small kind of tentacles, which appeared as small blue points among the stomachs. These were clavate bodies placed without any regular order in the axils between the stomachs, and containing an internal cavity which communicated with the nearest branch of the common canal. A series of pyriform processes, exactly resembling in form those above described, was VOL. I G 18 ON THE ANATOMY OF THE FAMILY OF THE MEDUS/E arranged round their hemispherical extremities. As the individual I observed was a young one (the generative organs not being developed), I conclude that these were young forms of the longer tentacles, fig. 36. 37. Of the Generative Organs—lIt has been already noticed with regard to the Cryptocarpe by Will (in Geryonza, Thaumantias, Cyt@ts, Polyxenia), and by Milne-Edwards (in 4 gworea), that the generative organs are connected with some part of the system of canals, but they do not attempt to define the nature of this connection. I shall en- deavour to do this, and to show that the generative organs, both in these and in the Phanerocarpe and Rhizostomide, are always portions more or less developed of the wall of this system; and therefore con- sist of the two “foundation membranes,” in or between which the generative elements, whether ova or spermatozoa, are developed. 38. In Thaumantias there are four canals radiating from the centre of the disc, at right angles to one another, and terminating in a circular vessel at the edge of thedisc. Near its termination each has a rounded body seated upon it. In most of the specimens I examined this body was distended with ova, and its structure was thereby obscured ; but in one instance it was replaced by an elongated, somewhat pyriform body, which on close examination was found to be simply a dilatation of the canal on which it was seated, having double walls continuous with those of the canal, only much-thickened, and a central cavity communicating freely with that of the canal. This was without doubt a young generative organ, fig. 4. 39. In Oceanza the canals are very numerous, and radiate from the wide central cavity to the circular vessel at the margin of the disc. In young individuals these canals are narrow and nearly equal through- out, but in adults their inferior wall, for the middle three-fifths of their extent, is greatly enlarged and hangs down in folds or plaits, fig. 15. Under the microscope the wall exhibits an immense number of ova, of all sizes and stages of growth, lying in its substance; and if the edge of a fold be examined, these are seen to be placed between the inner and outer membranes. The inner membrane is thick, and composed of projecting cells with very long cilia ; the outer membrane is dense, thinner, and much more transparent, figs. 16, 17. 40. This account agrees in its general details very closely with that given by M. Milne-Edwards of the generative organs of Eguorea’ : and I regret the less not having been able to obtain male individuals, as he expressly states that in d2:guorea the spermatozoa are developed ? Annales des Sciences Naturelles, t. xvi., quoted verbatim in Lesson’s Histoire Naturelle des Zoophytes Acalephes. ON THE ANATOMY OF THE FAMILY OF THE MEDUS/E ce) in the same position. There is, however, one discrepancy. M. Edwards states that the generative lamelle “sont tout a fait distincts de la cavité digestive centrale.” J think that on repeating his exami- nation he would find this not to be the case. In Oceania, at any rate, I could readily introduce a needle from the stomach into the canals, and show that the lamellz were mere dilatations of their wall. In Polyxenia, where the canals are very short and the central cavity very large, the ova are situated in the under wall of the cavity, according to Will; but this author enters into no particulars as to the structure of the wall. 41. The generative organs of the Phanerocarpe have been much investigated. The general result arrived at appears to be, that they are plaited tubular bands attached to the concave wall of a depression existing between the pillars of attachment of the stomachal membrane ; that they are altogether separate from the central cavity; that the spermatozoa are developed in pyriform sacs opening externally, and that the ova lie free in the substance of the ovarial band. 42. The structure of the generative organs in Phacellophora is as follows :—The voluminous folded and plaited stomachal membrane is attached by four thick pillars to the under surface of the disc. The edges of the pillars are connected by a thin membrane, which is con- cave externally so as to form a sort of shallow depression or generative cavity, but the central and some of the marginal parts of this mem- brane are produced into long plaited processes, which hang far out of the cavity, fig. 18. Each process is a sort of 'sac communicating freely at its attached extremity with the cavity of the stomach, air, &c., passing readily from the one to the other. It is in fact a sort of ever- sion of the walls of the stomach, or more properly, of the central cavity. It consists in its upper or attached part of nothing more than the two “foundation membranes,” and here they are smooth, but at their lower or free edge they become much plaited, acquire a deeper colour, and exhibit the characteristic generative elements. Short tentacles, similar to those of RAzzostoma (31), are scattered over the. inner surface of each process, fig. 21. 43. In the ovardum, the two membranes develope between them immense multitudes of ova with a dark granulous yelk and clear germinal vesicle. The ova are attached to the outer surface of the inner membrane, the outer membrane passing quite freely over them, fig. 24. 44. The ¢estzs is similarly composed of two membranes with an intervening space. The inner membrane is produced into a vast number of thick pyriform sacs, which lie between the two membranes, C 2 20 ON THE ANATOMY OF THE FAMILY OF THE MEDUSA! with their blind ends towards the inner surface of the outer membrane ; internally, they open each by a distinct aperture on the free surface of the inner membrane. 45. The contents of the sacs are spermatozoa, and cells in every stage of development towards spermatozoa. These stages are—I. Spherical cells, ygyath of an inch in diameter, filled with smaller nucleated cells (fig. 23 a). 2. Cells exactly resembling these included cells but free,and about ;,/;5th of an inch in diameter (4). 3., Similar cells, occasionally united into masses with long filiform productions (c). 4. Similar cells with a short process in the opposite direction also; these swim about freely and sometimes move their tails (7). 5. Perfect spermatozoa with elongated heads (;3';5th of an inch), rather larger below than above, where they are not more than z5ggath of an inch in diameter, with very long tails of immeasurable fineness, extending from the larger extremity (¢). From the existence of these different stages, I conclude that the spermatozoa are formed by the elongation of the secondary cells contained in the large cells first mentioned. 46. I have not been fortunate enough to meet with any description of the generative organs of the Rhizostomide except that of these organs in Cephea by Will; and as what I have observed differs some- what from his statements, I will describe those of RAzsostoma mosaica somewhat fully. In this Acalephe, the eight arms which bear the stomachs are inserted into the lower angles of a thick square plate, which I have thence called the “ brachiferous plate,” fig. 27. From the upper angles of this plate there arise four pillars, of the same structure as the peduncles of the arms, and are inserted into the under surface of the disc rather externai to the middle point between its centre and margin. The “brachiferous plate” has no other attachment to the disc, so that it forms the floor of an arched cavity, with four entrances between the suspending pillars of the plate. The suspending pillars expand at their attachment to the disc into three thickened ribs or crura, two of which are lateral and external, and one central and internal: these are united by a thin membrane. The central crura meet and form a cross under the centre of the disc ; the lateral crura are continuous with the substance of the disc above, and each meets with its fellow external to the centre of the disc, fig. 26. The central crura are united with these and thence with the disc by the thin membrane only. It thence follows that there exists above the central crura and the connecting membrane a wide crucial cavity ; into this the canals of the suspending pillars open, and from it radiate ON THE ANATOMY OF THE FAMILY OF THE MEDUSA 21 the canals which are given off to the circumference of the disc: the crucial cavity then is only a portion of the great system of canals. 47. The external surface of the outer half of the thin uniting mem- brane (which is composed solely of the two “ foundation membranes”), is ‘produced into a vast number of transverse folds of a grayish-green colour in the male, but of a deep orange-red in the female, fig. 26. These give rise to the appearance of a coloured cross shining through when the disc is viewed from above. The inner side of the folds is beset with a series of tentacles, the generative tentacles described above (31), fig. 30. In young specimens, not more than 3 inches in diameter, the generative organs were undeveloped ; the outer portion of the thin membrane being as smooth as the inner, but the series of tentacles already existed. In adults the margins of the folds contain the spermatozoa in the male, the ova in the female. 48. In the ovarium the ova lie between the inner and outer founda- tion membranes, which are both ciliated on their free surfaces. The ova are attached to the outer surface of the inner membrane by a kind of pedicle, which expands into the thick vitellary (?) membrane ; this chorionic coat is distinctly cellular in middle-sized ova, in larger ones it is thicker and homogeneous. If the inner surface of the inner membrane be examined, a depression will be seen opposite each ovum : the yelk of the ova is granulous and of a bright orange colour. The germinal vesicle is clear and thin-walled, and is ;$5th of an inch in diameter ; the germinal spot is a thick-walled cell 5,,th of an inch in diameter, fig. 32. 49. So far as the structure of the inner and outer membranes is concerned, the ¢estzs resembles the ovary. But the spermatozoa are contained in ovoid or pyriform, thick-walled sacs, about jth of an inch in long diameter placed between the two, fig. 31. In one indi- vidual the sperm-sacs were more ovoid in shape, and did not appear to have any particular attachment to either membrane, but in the rest they were all connected with the inner membrane, and when its inner 1 It appears to me that M. Milne-Edwards must have had a young individual of RAzzostoma before him, when he says (Observations sur la Structure de la Méduse Marsupiale), ‘‘ Nor does the plaited membrane, which forms a sort of partition between the central and the four lateral cavities, appear to be an organ of reproduction. If we examine one of these mem- branes superficially with the naked eye, we see towards its upper part a kind of woollen fringe, which at first sight might be taken for a series of glandular sacs, but by the aid of the microscope it is found that this appearance is due in fact to a multitude of suckers (sagoers), having the greatest similarity in form to those appendages which are observable in certain parts of the body of different Zoophytes, such as V7tella, clctenca, &c. From this it would appear that these membranes are much more fitted for absorption or respiration, as is the opinion of M. Eysznhardt, than for the formation of ova.” 22 ON THE ANATOMY OF THE FAMILY OF THE MEDUSE surface was turned towards the eye, the openings of the sacs could be perceived : the sacs were filled with spermatozoa with triangular heads, about ;g25,th of an inch in diameter, and very long, fine, delicate tails, ig. 31 a. The course of their development appeared to be as in Phacellophora. 50. Rhisostomaand Phacellophora then agree in having the sperma- tozoa developed in sacs connected with the inner “ foundation mem- brane” and opening internally. It would appear from this that the exit for the spermatozoa is through the mouth of the animals, though this course in RAZzestoma would certainly be a rather circuitous one. 51. The individual of Cephea (C. ocellata) which I examined resembled, with regard to the generative organs, a young RAzzostoma. The line of generative tentacles was present, but the generative organs were undeveloped. According to Will, the structure of the testis in Cephea Wagneri closely resembles that of RAzzostoma. He says that there is a cavity under the dise into which the canals of the arms and disc open ; that the floor of this cavity is formed by a thin membrane covered with fine tentacular appendages, and that the band-like testes are attached to the under free surface of the membrane ; they consist of pyriform sacs (flaschenformigen Driischen) closely applied together, and each opening independently below. The spermatozoa are elon- gated and cylindrical, and have a very long, fine appendage. 52. With regard to the muscular system of the Meduse, such observations as I have made lead me to believe that the muscular fibres are always developed in the outer “foundation membrane.” In Khezostoma the muscular fibres of the under surface of the disc are flat, pale, and from 731;5th to gijth of an inch in diameter. They run parallel to one another, but the lines of separation between them are not continuous throughout, but thus: each fibre is made up of very small and indistinct fibrils, which >_> are transversely striated, the striation being most distinct at the edge of the fibres. - ci 53. I have not observed any indubitable trace of a nervous system in the Meduse. 54. Will has described a blood-vascular system, consisting of a system of canals inclosing the water canals and containing a distinct fluid with cells floating in it. I have paid particular attention to this point in all my examinations of ,the Medusa, but notwithstanding that I have had species of the very same genera (Crdippe, Cephea, Lhaumantias) under my hands, I have never observed any trace of it. I am at aloss even to understand what he means, unless, as I strongly suspect, he has taken the outer foundation membrane, which occa- ON THE AFFINITIES OF THE FAMILY OF THE MEDUSAE 23 sionally is thick and distinct from the inner, especially about the circular marginal canal, for the walls of a distinct vessel. Even if this be the case, what are the blood-corpuscles ? 55. The thread-cells resemble in all respects those of the Diphyde, which I have described elsewhere, consisting of a delicate outer cell inclosing another thick-walled cell, with a spiral filament of greater or less length, coiled up in its interior and capable of protrusion on pressure. , SECTION I].—Of the Affintties of the Meduse. 56. Certain general conclusions are deducible from the facts stated in the preceding section. It would appear,— Ist. That a Medusa consists essentially of two membranes in- closing a variously-shaped cavity, inasmuch as its various organs are so composed (7, 8, 14, 21, 22, 29, 33, 38, 39, &c.). 2ndly. That the generative organs are external, being variously developed processes of the two membranes (38, 39, 42, 48, 49) ; and 3rdly. That the peculiar organs called thread-cells are universally present (7, 15, 31, 32). Now in these particulars the Meduse present a striking resem- blance to certain other families of Zoophytes. These are the Hydroid and Sertularian Polypes, the Physophoridz and Diphyde, with all of which the same three propositions hold good.? 57. But in order to demonstrate that a real affinity exists among different classes of animals, it is not sufficient merely to point out that certain similarities and analogies exist among them; it must be shown that they are constructed upon the same anatomical type, that, in fact, their organs are homologous. Now the organs of two animals or families of animals are homo- logous when their structure is identical, or when the differences between them may be accounted for by the simple laws of growth. When the organs differ considerably, their homology may be deter- 1 “Tes parois du tube nutritif sont formées d’une double membrane toujours rondée intimement dans cette partie du polype, externe répond aux téguments ; l’interne est une continuation de la membrane digestive de la capacité alimentaire.” —Cuvier, Org. de Généra- tion des Zoophytes, Legons d’Anat. Comp. t. viii. 2nd edit. I have elsewhere pointed out that the same circumstance obtains among the Diphydz and Physophoride. That the generative organs are external in the Sertularian and Hydroid Polypes has been long known. Milne-Edwards has shown that they have a similar position in one of the Physophoridz (.4folemza). 1 have observed it myself in the Diphydee. The presence of the thread-cells has been determined by Will in the Diphydz, by Milne- Edwards in Afolemia, by myself (only ??) in Physalia, Physophora, Athorybia, and other Physophoridz, and in the Sertularian Polypes. Da: ON THE AFFINITIES OF THE FAMILY OF THE MEDUSA! mined in two ways, either—1, by tracing back the course of develop- ment of the two until we arrive by similar stages at the same point ; or, 2, by interpolating between the two a series of forms derived from other animals allied to both, the difference between each term of the series being such only as can be accounted for by the laws of growth. The latter method is that which has been generally employed under the name of Comparative Anatomy, the former being hardly applicable to any but the lower classes of animals. Both methods may be made use of in investigating the homologies of the Medusz.! 58. A complete identity of structure connects the “foundation membranes” of the Medusz with the corresponding organs in the rest of the series ; and it is curious to remark, that throughout, the outer and inner membranes appear to bear the same physiological relation to one another as do the serous and mucous layers of the germ; the outer becoming developed into the muscular system and giving rise to the organs of offence and defence; the inner, on the other hand, appearing to be more closely subservient to the purposes of nutrition and generation. 59. The structure of the stomach in the Meduse is in general identical with that of the same organ in the rest of the series. The Rhizostomide offer an apparent difficulty, but it appears to me that the marginal folds in them answer to the stomachal membrane of the Monostome Meduse ; the apertures to the inner orifice of their stomach, and the common canal to their “common cavity.” Just as in a polygastric Diphyes the common tube answers to the chamber into which the stomach of a monogastric Diphyes opens; and in Cephea IVagnera (Will) these resemblances are still more striking. He says that each cotyledon “has at its apex a small round opening, the mouth, which leads to an ovate cavity, occupying the whole interior of the cotyledon. I consider this as the proper digestive or stomachal cavity, and believe that the cotyledons have the same relation to the vessels as the so-called suckers (Sangrohren) of the Diphydz to the common tube (Sa/trohre).”? 60. The disc of a Medusa is represented by the natatorial organ among the Diphyde and Physophoride. Take for instance the disc of Oceania or Cyteis. It is here a more or less bell-shaped body, traversed by radiating canals, lined by a distinct membrane, united ' The above definitions may be thought needless and even trite, but the establishment of affinities among animals has been so often a mere exercise of the imagination, that I may be pardoned for pointing out the guiding principles which I have followed, and by which I would wish to be judged. ? Hore Tergutine, p. 60. ON THE AFFINITIES OF THE FAMILY OF THE MEDUSA‘ 25. by a circular canal at the margin. In the centre the radiating canals communicate freely with the chamber into which the stomach opens. The inner margin of the disc is provided with a delicate, circular, valvate membrane. The same description applies, word for word, to the natatorial organs of the Diphydz and Physophoride ; the only difference being, that in the latter the stomach is ou¢szde the cavity (fig. 47) of the organ, instead of being, as in the Meduse, suspended from its centre zzside, fig. 49. And even if the different texture of the two organs should give rise to any doubt, the genus Kosacea, in which the natatorial organ is perfectly soft and gelatinous, furnishes the needful intermediate form. 61. The disc of the Meduse has no representative among the Hydre and Sertulariade. The cell of the Sertularian Polype rather resembles the “ bract” of the Diphydz than the ‘“ natatorial organ” in its structure and function, and in this manner the Diphyde form a connecting link between the Meduse and the Physophoride. 62. Of the two kinds of tentacles of the Medusa, the first is repre- sented, in the Physophoridz and Diphydea, by the thickenings, richly beset with thread-cells, that frequently occur in the lip of the stomach ; in the Sertularian Polypes (Plumularia, Campanularia) by the ten- tacles of the margin of the mouth, which precisely resemble the tentacles of the fringe of RAzzostoma, or the marginal tentacles of Thaumantias, in being composed of a single membrane covered with thread-cells, and having a cellular axis. 63. The second kind of tentacle is homologous with the prehensile organs of the Diphydz and Physophoridz with the peculiar clavate processes of Plumularia, and so far as 1 can judge from descriptions of their structure, with the tentacles of Hydra. All the organs here mentioned commence their development as bud-like processes of the two primary membranes, elongating and attaining the forms peculiar to their perfect state as they grow older. The tentacles of the Medusz are usually developed (as in most Monostomate) from the circular vessel of the disc, sometimes (Phacellophora) from the diverging canals, sometimes, finally, from the neck of the stomach (Lymmnorea, Javonia). The prehensile organs of the Physophoride also have considerable variety in position. In Porpita, Vitella, Angela (?), they are developed from the margin of the float ; in PAysophora and many others from the base or the pedicle of the stomach. The prehensile organs of the Diphydz are always developed either from the base or the pedicle of the stomach. The peculiar clavate organs of Plwmularia are developed from the common tube independently of the stomach. 26 ON THE AFFINITIES OF THE FAMILY OF THE MEDUS-E 64. The adult forms of these organs have all the same structure, being composed of two membranes, with a vast number of thread-cells of larger or smaller size, seated in the substance of the outer membrane or between the inner and the outer. 65. The “clavate organs” of Plmularia deserve especial notice, as I am not aware that they have been hitherto described, and as they exemplify in a very beautiful manner the “unity of organization - manifest among these families. I have found them in two species of Plumularia obtained by the dredge at Port Curtis ; they were of two kinds, the one attached to the cell of the polype, the other to the pedicle of the ovary, figs. 43, 44, 45. In each species there were three processes of the former kind, two above proceeding from near that edge of the aperture which is towards the stem, the other below from the front part of the base of the cell ; they were conical in the one species, club-shaped and articulated in the other, and consisted of an external horny membrane open at the apex, and an internal delicate membrane inclosing a cavity, all these being continuous with the corresponding parts of the stem. At the apex of each, and capable of being pressed through the aperture, lay a number of thread-cells ; with moderate pressure the threads only of these organs were pressed out. I found the second kind of organ in the species with conical pro- cesses. It consisted of a stem proceeding from the pedicle of the ovary, bearing a series of conical bodies having the same constitution as those just described, fig. 45. The perfect resemblance between these and the prehensile organs of the Diphydee cannot be overlooked. 66. The structure of the generative organs is still more instructive. In the Meduse I have endeavoured to show that there are always processes of the two foundation membranes, the generative elements being developed between them, figs. 1 a, 11 a, 18 a, 26 a. 67. In the Diphydz (and as I have good reason for believing in the Physophoride also) the generative organ commences as a simple process of the common tube (fig. 39 @), and undergoing great changes of form in the course of its development (0, ¢), it becomes at last exactly similar to an ordinary natatorial organ with a sac composed of two membranes suspended from its centre, fig. 39. In external form it greatly resembles such a JZedusa as Cytezs, and this resem- blance is much heightened when, as in some cases, it becomes detached and swims freely about, fig. 41. The ova or spermatozoa, as the case may be, are developed between the two membranes of the sac, the inner of which at any rate is a continuation of the inner membrane of the common tube, fig. 39. ON THE AFFINITIES OF THE FAMILY OF THE MEDUS.E 27 68. The ovarium of the Plumularta above mentioned (65), com- mences as a dilatation of the apex of its pedicel, which again is a process of the common stem. It then becomes lenticular with a horny outer wall, glassy and transparent externally, but internally coloured by pigment masses. Internally it has an oval cavity communicating with that of the stem and lined by a distinct membrane, fig. 45. Between the two membranes is a thick layer of ova, more or less oval in shape, and about 535th of an inch in diameter, with a germinal spot about s),5th of an inch in diameter, seated in the middle of a clear space about twice that size, which doubtless represents the germinal vesicle. 69. The account given by Lowen of the generative organs of Campanularia differs considerably from the foregoing. After all, however, his “female polypes” may be nothing more than ovaria similar to those of Dzphyes or Coryne, but having the production of tentacles from the margin carried to a greater extent than in the latter. If this be a correct explanation, the idea promulgated by Steenstrup, that there is an “alternation of generations” among the Sertularian Polypes, must be given up. 70. In Hydra, the ova are developed in similar processes of the lower part of the body. But among the Hydroid Polypes the ovaries of Coryne, Syncorine and Coryimorpha, as described by Sars, Lowen and Steenstrup, are most interesting. They commence as tubercles of the stem, afterwards become bodies, precisely resembling the ovaria of the Diphydz, and finally (fig. 42) detaching themselves develope regular tentacles from their margin. The ova are formed between the two membranes of the inner sac.” 71. What has now been advanced will perhaps be deemed evidence sufficient to demonstrate,—tIst, that the organs of these various families are traceable back to the same point in the way of develop- ment; or 2ndly, when this cannot be done, that they are connected by natural gradations with organs which are so traceable, in which case, according to the principles advanced in 57, the various organs are homologous, and the families have a real affinity to one another and should form one group. 1 M. Dujardin, Annales des Sciences Naturelles, November 1845, states on the authority of Ehrenberg, Corda and Laurent, that the ova of the freshwater Polype are ‘produits dans Vépaisseur méme du tissu sans ovarie ni ovule préalable.” 2 «The axis of the bell is occupied by a membranous sac, which is a prolongation of the nutritive canal, and answers to the alimentary cavity of the alimentary Polypes. The ova are developed in regular series in the interval between this alimentary capsule and the parietes of the outer sac, in an intermediate membranous sac, distinguished by its yellowish brown colour.” —Cuvier, Lecons d’Anat. Comparée, t. viii. Organs de Generation des Zoophytes, p- 860. See also Duvernoy, Annales des Sciences Naturelles for November 1845. 28 ON THE AFFINITIES OF THE FAMILY OF THE MEDUSA 72. Perhaps the view that I have taken will be more clear if I throw it into a tabular form, placing opposite one another those organs in the different families, for the homologies of which there is, I think, sufficient evidence, thus :— Stomachs identical in Structure throughout. Meduse. Physophoride. Diphyde. Sertularidé Hydre. DASE: stoeuahecvaaatdters Natatorial organ ...Natatorial organ. Catials: mscisancinn Canals of natatorial OIG jamehiwsrornand Canals of natator- ial organ. Common cavity... Canals of branches ;Cominon tube ...... Sacculus and com- (Rkzzs) ss assur J mon tube ...... Cavity of stem. Bra ticaawirdimanses cas vane Polype-cell. Tentacles, 1.0.0.0... Thickened edge of SIGIMACh: layalocisi emo amautapattes Oval tentacles. 2 casas Prehensile organs 20.0.0... ....ceee eee es Clavate organs ...Tentacles (?). GENETALIVE SAE ges scenarinsscoanaantces Generative organ.Generative organ. Generative organs Natatorial organ of PEN CLALINE Sa Ciaarnnaiganrsactins mimataniatnns wioniaanddiedaicla Natatorial organs (Coryne). Marginal vesicle iiss vivses vc B. mscayln atlas omen cavannl sate Sits naa 2) esasanait Enea Dass eae Ge 73. It appears then that these five families are by no means so distinct as has hitherto been supposed, but that they are members of one great group, organized upon one simple and uniform plan, and even in their most complex and aberrant forms, reducible to the same type. And I may add, finally, that on this theory it is by no means difficult to account for the remarkable forms presented by the Medusz in their young state. The Meduse are the most perfect, the most mnaividualized animals of the series, and it is only in accordance with what very generally obtains in the animal kingdom if in their early condition they approximate towards the simplest forms of the group to which they belong. 74. | have purposely avoided all mention of the Beroidz in the course of the present paper, although they have many remarkable resemblances to the animals of which it treats : still such observations as I have been enabled to make upon them have led me to the belief, that they do not so much form a part of the present group as a link between it and the Anthozoic Polypes. But I hope to return to this point upon some future occasion. Sydney, April 24th, 1848. *,." Since the above was written I have had an opportunity (by the kindness of W. MacLeay, Esq., to whose advice I am much [PLATE Ii Pha. Trans MDCCCXLIX Fate XXXVI, OK > aN : am WMHS \ tN Y AToozop0y WW ODDY! ee Me TTT (0 Ma Zi ON THE AFFINITIES OF THE FAMILY OF THE MEDUS 29 indebted), of reading M. Dujardin’s “Mémoires sur le Développement des Méduses et des Polypes Hydraires,” contained in the Annales des Sciences Naturelles for November 1845. This author has, as it appears to me, been misled by the great analogy between the structure of a Medusa and that of the generative organ of a Coryniform Polype, into taking the detached organ of the Polype for a real Medusa. He does not hesitate to say that the Claviform Polypes are “only a first stage of development of the Acalephe.” He hints that each clavate Polype has its corresponding Acalephe, and he does not hesitate to give the latter distinct names as independent genera (Sthenyo, Cladoneia). Here, as in many other instances, the study of the Diphyde throws light upon the matter. The detached free-swimming testis or ovary of a species of Sphenza has just as much claim to a distinct generic name as has Sthenyo or Cladonema, and yet in what respect does this differ from the persistent ovary of Ewdoxia, which surely is an organ, and nothing but an organ? Would it not be as reasonable to give a distinct name to Needham’s sperm-sacs because they exhibit certain independent motions external to the body of the Cephalopod ? The point is of consequence, because it is anything but desirable that ¢rue polypes with medusiform generative organs should be con- founded with the Polypiform larve of true Meduse. DESCRIPTION OF THE PLATES. * * In all the sectional diagrams the letters have the same meaning, viz. 7. Stomach. mn. Common cavity. v. Canals. %. Generative organ. g. Natatorial organ. ¢ Tentacle. u. Marginal vesicle. .«. Outer membrane. 2’. Bract. x”. Valvular membrane. PL. XXXVII. [Plate 2.] Thaumantias ? Fig. 1. Disc seen from above. Fig. 1 a. Imaginary vertical section. Fig. 2. Opening of the stomach into the canals seen from above. Fig. 3. Marginal tentacles. Fig. 4. Young generative organ. Aesonema? Fig. 5. Lateral view of the animal. Fig. 5 a. Vertical section. Fig. 6. View of a segment of the disc ; under surface. a. Buccal tentacles. 6. Canals. «. Marginal membrane (20). 30 ON THE AFFINITIES OF THE FAMILY OF THE MEDUSA: Fig. 7. A single buccal tentacle much magnified. lig. 8. A portion of the marginal canal with a tentacle and two marginal corpuscles. Vig. 9. Portion of the marginal canal (a) with young tentacle (4), and a marginal vesicle containing two corpuscles, each enclosed within a delicate cell-wall. Vig. 10. A marginal vesicle highly magnified; the two corpuscles do not appear to have attained their full development, as they refract less, and the cell appears more opake. Oceanta Vig. 11. Lateral view of the animal. Tig. 11 «. Vertical section. Fig. 12. Part of the under surface of the disc. a. Marginal membrane. 6. Canals and generative organs. «. Common cavity. Fig. 13. Part of the membrane surrounding the mcuth. Fig. 14. The edge of this much magnified. lig. 15. Part of the margin of the disc much enlarged. a. Marginal membrane. 6. Canal and generative organs. «. Tentacles. @. Marginal corpuscles. e. Circular canal. Vig. 16. Portion of the ovarium so folded as to have its inner membrane (a) outwards. Fig..17. Sectional view of the ovarium. a. Inner membrane. 6. Outer membrane. «. Ovum. d@. Germinal vesicle. e. Germinal spot. PL. NXXVITI. [Plate 3.] Pracelloj hora ——? Tig. 18. View of a segment of the under surface. a. Marginal vesicles. 6, Tentacles in this individual very much shorter than usual. c. Ovary or testis. d. Buccal membrane. lig. 18 a. Vertical section. Tig. 19. Tentacle. lig. 20. Portion of the buccal membrane. Fig. 20 a. Round processes containing thread-cells scattered over its outer surface. lig. 21. Portion of the testis. a. Generative tentacles. Vig. 22. Sectional view of part of the testis. uw. Outer membrane. 6. Sperm-sacs. ¢ Inner membrane. Vig. 23. Stages of development of the spermatozoa (45). lig. 24. Ovarium. a. Outer membrane. 6. Ova. c. Inner membrane. [PLATE 111] ON THE AFFINITIES OF THE FAMILY OF THE MEDUSA Fig. Tig. Tig. Fig. Fig. Fig. Vig. lig. Fig. 31 25. Marginal vesicle from the under surface. a. Dilatation of the canal. 25 a. Marginal vesicle and pedicle very much enlarged. Rhisostoma mosatca. - 26. View of the under surface of the disc, the brachiferous plate being cut away. a. Marginal vesicles. 4. Cut extremity of the suspending pillar of the brachiferoys plate. «. Central crura. @ Lateral crura. e. Generative folds. 7 Connecting membrane. 26 a. Vertical section of the Rhizostoma. 27. Side view of the brachiferous plate detached. PL. NNNIX. [Plate 4.] Rhisostoma mosaica. 28. Extremity of one of the ultimate ramifications of the arms. a. Thick substance of the outer membrane. 6. The central common canal. ¢. The lateral canals leading to the apertures. ad. The fringes. 29. Lateral view of one of the apertures much magnified. a. Thick outer membrane. 6, Inner membrane. c. Lateral canal. d. Tentacles. 30. Portion of the testis slightly magnified. a. Generative tentacles. 31. Sectional view of testis much magnified. «. Outer membrane. 6. Inner membrane. ¢. Sperm-sacs. . 31 a. Spermatozoa. . 32. Ovarium. au. Outer membrane. b. Inner membrane. c. Ova. g. 33. Marginal vesicle, upper surface. u, 6. Lobes connected by the arched membrane, ¢. «. Ceeca of the canal f d,. Vesicle on its pedicle. e. Cordate depression. 34. Marginal vesicle from below, much magnified. aa. Lobes. 4, Inferior connecting membrane. Cveca. Elevation of the outer memLrane. e. Muscular fibres. SS) 32 ON THE AFFINITIES OF THE FAMILY OF THE MEDUSE Cephea ocellata. Fig. 35. An aperture surrounded by its membrane. Fig. 36. Portion of the extremity of an arm, with a young interbrachial tentacle (a). Fig. 37. Extremity of one of the large interbrachial tentacles. Diphyde. Fig. 38. Vertical section of a monogastric Diphyes. Fig. 39. Attached ovarium. a. Natatorial organ, 6. Ovisac, Fig. 39 a. Youngest stage of ovarium. a. Simple process of the common cavity. 6, . Ovaria further advanced. Fig. 40. Prehensile organ. a, 6, Early stages. Fig. 41. Free-swimming ovarium. a. Natatorial organ. 6. Ovisac. Fig. 42. Free-swimming ovarium of Coryne (from Steenstrup) to compare with fig. 41. Sertularidé. Fig. 43. Cell of Plamzlaria ? a. Peculiar clavate organs. 6, Large thread-cells. Fig. 44. Cell of another Plumularia, letters as before. Fig. 45. Ovarium of fig. 43. a. Organs containing thread-cells similar to fig. 43 a. 6. Ova. Fig. 46. Section of Plumularia. Fig. 47. Section of Polygastric Diphyes. Fig. 48. Section of Rhizostoma. . Section of Monostome Medusa. V NOTES ON MEDUSZ AND POLYPES Annals and Magazine of Natural History, vol. vi. 1850, pp. 66-7 A.AML.S. Rattlesnake, CAPE YORK, October 1849. My DEAR S1r,—You will probably be interested in knowing what I have been about for the last year. I have examined (in most cases very carefully) species of the following genera of Acalephe and Polypes: PHYSOPHORIDA, Velella, Porpita, Physalia (a good many new points), Stephanomza, Athorybia, Agulina, Rhizophyra ; DIPHYD, Resacea, Cuboides (two species), Adbyla (three species), Enneagonea ; MEDUSID#, Sinope (?), Xanthea, Geryonia, Cytwis, Cephea, Oceania, * Bugainvillea, Tima, Aglaura (2), Pelagia, * Willsia; POLYPES, Tubularia, besides some genera altogether new. The two I have marked thus * will interest you, as you describe them in your “ Vaked- eyed Meduse.’ Bugainvillea, | may mention, has its generative organ in the thickness of its outer membrane of the stomach; Wel/sza develops bodies mostly resembling those in Sarsza prolifera and gemmitfera, at the angle formed by the two first divisions of each of the four radial canals. The structure of the Zwdularia is also very interesting. I was for a long time astonished at what appeared to be its very wide geographical distribution, until I discovered one day that it was attached in large masses to the ship’s bottom ! I have found much that was new to me in all respects, but nothing that contradicted in any important matter the results at which I arrived in the paper on the J/eduse@. On the other hand, I can speak much more confidently on some points advanced only with hesitation before. I believe that I shall be able to show you on our return evidence amply sufficient to prove,—Ist, that the Hydroid and Sertu- larian Polypes, the Hydrostatic and ordinary Acalephe, and the Helianthoid Polypes form one large family, which from their invari- VOL. I D 34 NOTES ON MEDUSA! AND POLYPES ] able and peculiar “thread-cell,” I propose to call the “ Nematophora” ; 2nd, that this great family consists further of two subdivisions, the number of which as affixed, if we consider one subdivision, and strictly analogous and parallel if we consider the two subdivisions as thus :— Nematophora. Hydroide. Actinide. Corynide. Zoanthide. Sertularide. Sarcoidea. Physophoride. Pennatulide. Diphyde. Madreporide. Meduside. Beroide. I believe that I have already evidence enough on the “ Hydroid ” side, but on the other I have done nothing, or next to nothing. It is a very difficult investigation, but if this intolerable heat leaves me energy enough I will do something towards it. I am unwilling to write hastily or without due evidence on this matter (especially since the establishment of my views must, as it seems to me, necessitate the total re-arrangement of the ‘ Radiata”), and I mean therefore merely to go on making observations until we return to England. If then I find any means offer itself of publishing my results on an appropriate scale, well and good; if not, I suppose I must content myself with feeling like a‘ mute inglorious Hampden,” and like a good philanthropist, pity the public for its loss. I have a great advantage in the society and kind advice (to say nothing of the library) of Mr. MacLeay in Sydney. Knowing little of his ideas, save by Swainson’s perversions, I was astonished to find how closely some of my own conclusions had approached his, obtained many years ago in a perfectly different way. I believe that there is a great law hidden in the " Circular system” if one could but get at it, perhaps in Quinarianism too; but I, a mere chorister in the temple, had better cease discussing matters obscure to the high priests of science themselves. Keeping well in mind the old adage about “too many irons in the fire,’ I have nevertheless been able to make a few scattered observa- tions on other animals than the Acalephe, and I mean to embody those on the Mollusca—comet-wise—making the “anatomy of Firola and Atlanta” the nucleus whereunto to append a tail of observations on the genera, which will I think possess some interest, referring to the nervous system, structure of buccal mass, and the existence of a peculiar urinary system. I will send this from Sydney to the Secre- NOTES ON MEDUS. AND POLYPES 35 tary of the Zoological Society, with a request that you may, if so inclined, have the first perusal of it. Our return appears to be very uncertain, perhaps not for a couple of years. If in this remote corner of the earth I can be of any service to you either in a scientific or any other way, pray consider my best exertions as at your command. A letter addressed to me at Sydney will always reach me. Yours very faithfully, THOMAS H. HUXLEY. To Pror. E. FORBES. Ae ot Vi OBSERVATIONS SUR LA CIRCULATION DU SANG CHEZ LES MOLLUSOQUES, DES GENRES FIRGLE EY ATLANTE EXTRAITES D’UNE LETTRE ADRESSEE A M. MILNE-EDWARDS Annales des Sciences Naturelles, vol. xiv. 1850, Pp. 193-5 AYANT navigué pendant cing années a bord du batiment de S. M. B. the Rattlesnake, dans les eaux de la Nouvelle-Hollande et de la Nouvelle-Guinée, j’ai eu loccasion d’étudier anatomic et la physiologie de beaucoup d’animaux marins. Je viens de publier un Mémoire sur la structure des Méduses, et je me propose de porter prochainement a la connaissance du public les résultats de mes recherches sur les Tuniciers; mais j’ai pensé qu'il vous serait peut-étre agréable d’apprendre dés aujourd’hui que j’ai ¢tudié egale- ment le mode de circulation du sang chez les Firoles, dont le corps, comme vous le savez, est d’une transparence hyaline, et que j’ai obtenu ainsi une confirmation enti¢re de vos vues relatives a la maniére dont cette fonction s’exerce chez les Mollusques. Chez la FIROLE, le cceur est placé pres de l’extrémité postérieure du corps a cété de la portion redressée de l’intestin. L’oreillette est supérieure et ses parois sont composées d’un lacis de fibres muscu- laires striées et ramifiées, entre lesquelles on apercoit de grands espaces ouverts. Le ventricule situé au-dessous est un sac a parois transparentes, mais fortes et denses ; il communique avec l’oreillette par un orifice garni de valvules, et donne naissance a une aorte, qui, a son origine, présente également un apparceil valvulaire. Cette artere a la forme d’un tube a parois minces et transparentes ; elle fournit de suite une branche qui porte le sang a la masse viscérale (ou nucleus), formée par le foie et les organes générateurs ; puis elle se dirige en avant en décrivant diverses courbures sur le tube digestif. Parvenue sur les ganglions sous-cesophagiens ou pédieux, elle donne naissance a une artere pédieuse qui descend dans la nageoire ventrale, et s’y termine d’une maniere tout a fait brusque; son extrémité est tronquée et béante, et l’orifice ainsi formé est susceptible de se dilater beaucoup et de se contracter. CIRCULATION DU SANG CHEZ FIROLE ET ATLANTE 37 Avant de pénétrer dans le pied, ou nageoire ventrale, cette derni¢re artére fournit une branche récurrente qui se porte, en arriére, paralléle- ment a l’aorte, et se termine dans l’'appendice tubulaire de l’extrémité postérieure du corps de l’animal. L’aorte, aprés avoir fourni l’artére pédieuse, se dirige en avant, et se termine dans la masse buccale; pendant ce trajet, son calibre reste a peu prés le méme, et l’on n’en voit naitre aucune branche. Par suite de la parfaite transparence du corps de ce Mollusque a létat vivant, rien n’est plus facile que de suivre tout le cours du sang en circulation.—J// n’eriste point de veines quelconques.—On voit les globules du sang sortir en foule de l’orifice terminal de l’artére pédieuse, pénétrer dans la substance du pied, et passer aussi de la masse buccale dans la grande cavité péri-intestinale ; enfin c’est par cette cavité quils retournent lentement, et en s’arrétant souvent, vers le cceur. Quelquefois on en voit qui pénétrent directement dans Yoreillette a travers les espaces inter-fibriilaires déja mentionnés, et quelquefois aussi on voit des globules qui, pendant un certain temps, se trouvent arrétés au milieu de ce lacis. Lorsque l’animal commence a s/affaiblir, et que la circulation se ralentit, il devient possible de suivre de l’ceil un globule pendant tout son trajet a travers la cavité péri- intestinale et le coeur jusque dans I’aorte. Dans! ATLANTE, l'appareil circulatoire est tout a fait semblable a ce qui existe chez la Firole, si ce n’est que l’artére pédieuse en pénétrant dans le pied se divise en trois branches, dont l’une (qui correspond a l’artére récurrente de la Firole) est destinée 4 la portion postérieure du pied; la seconde de ces branches se rend a la ventouse, et la troisieme se porte en avant, et appartient au lobe antérieur du pied ; mais aucune de ces arteres ne se ramifie, et toutes les trois se terminent brusquement par un orifice béant, a travers lequel le sang s’échappe comme chez la Firole, et se répand dans les lacunes d’alentour. J’ai constaté une disposition analogue dans l’appareil circulatoire des Cléodores, des Crésus, observés a l'état vivant ; j’ajouterai que je me suis également assuré de |’existence d'une circulation en partie lacunaire chez divers Crustacés, tels que des Alimes, des Leuciferes, des Zoés et de petits Palémons. En résumé, je suis porté a croire que l’absence plus ou moins com- plete de la portion veineuse du systéme vasculaire, loin d’étre un cas exceptionnel, est I’état normal dans Ja plupart des classes de la grande division des animaux sans vertebres. VII OBSERVATIONS UPON THE ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA Philosophical Transactions of the Royal Society, 1851, pt. tt. Pp. 567-594 » also in Annals and Magazine of Natural History, vol. 1x. 1852, pp. 242-244 1. THE Salpe, those strange gelatinous animals, through masses of which the voyager in the great ocean sometimes sails day after day have been the subject of great controversy since the time of the pub- lication of the celebrated work of Chamisso, De Animalibus quibusdam é classe Vermium Linneana. In this work were set forth, for the first time, the singular pheno- mena presented by the reproductive processes of these animals,— phenomena so strange, and so utterly unlike anything then known to occur in the whole province of zoology, that Chamisso’s admirably clear and truthful account was received with almost as much distrust as if he had announced the existence of a veritable Peter Schlemihl. In later days an opposite fate has fallen upon the statements in question. They have been made the keystone of a revived! theory, and the phenomena presented by the Sa/pe have been cited as “glaring instances” of a law governing the vast majority of the lower invertebrata—the law of the “ Alternation of Generations.” 2. There appeared then to be two main points to be kept in view in examining the Sa/pc :—1st. Are the statements made by Chamisso correct? and 2ndly, if they be correct, how far is the “alternation theory ” a just and sufficient generalization of the phenomena? 3. These questions, however, could not be entered upon without a thorough preliminary study of the structure of the Sa/pe, the oppor- tunities for which are granted but to few. Such opportunities were afforded to the writer of the present paper at Cape York, in November 1849: for a time the sea was absolutely 1 Not new, see (70). ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 39 crowded with Sa/pa, in all states of growth, and of a size very con- venient for examination. At subsequent periods the writer had occa- sion repeatedly to verify the results at which he had arrived, and to find strong analogical confirmation in the structure of Pyrosoma and other allied genera! 4. It is proposed in the following pages to consider— I. The structure of the species of Sa/pa examined. Il. The structure of Pyrosoma. III. The homology of structure of Sa/pa and Pyrosoma, and of these with the ordinary Ascidians. IV. The history of our knowledge of the Safe. SECTION Il—The Structure of Salpa. s. Before entering upon this question, there is a point of some im- portance to be determined, as to the upper and lower surfaces, the anterior and posterior extremities of the Sa/g@. Observation will not decide this apparently simple matter, for as the writer has frequently seen, they swim indifferently with either end forward and with either side uppermost ; and the determinations of authors are most contra- dictory. Throughout the present paper, that side on which the heart is placed will be considered as the dorsal side ; that on which the ganglion and auditory vesicle are placed, as the ventral side. That extremity to which the mouth is turned will again be considered as the anterior extremity, the opposite as the posterior. Such a view of the case appears to be more harmonious with the determinations of corres- ponding parts in other animals than any other. In all the inverte- brata the mouth end is always considered as the anterior, the heart side as the dorsal side. 6. The two so-called species of Sa/ga examined were the S. democratica of Forskahl, spzxosa of Otto, and the S. mucronata of 1 Those who are acquainted with the nature of the service on which H.M.S. Rattle- snake was engaged, will readily comprehend that the author's investigations were almost necessarily original, and independent of anything going on in Europe. It is the more necessary to state this, as it will be seen, in the historical part of this paper, that M. Krohn, in the Ann. des Sciences for 1846, has completely anticipated the chief results arrived at, a fact of which the author was totally unaware until his arrival in England in the end of 1850. Still, as M. Krohn gives merely his conclusions without details or figures, his promised memoir not having appeared (so far as the writer of the present paper is aware), it is hoped that this anticipation will, by showing that perfectly independent observers arrive at the same result, rather tend to increase than to diminish any weight that may be attached to the present researches. AO ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA by Sars as S. spénosa and S. mucronata, or rather as S. spinosa, proles solitaria, and S. spinosa, proles gregaria. This, however, begs the question as to the truth of Chamisso’s theory, and I shall therefore prefer to name the two forms I observed simply Sa/~a A and Salpa B. At Cape York, and only there, these two forms were always obtained together. They were of about the same size, but so totally distinct in appearance, that, had they belonged to any other genus, they would have been justly regarded as separate species. 7. Salpa A, Plate XV. [Plate 5], fig. 1—The body is gelatinous, transparent, and colourless, except the nucleus (2), which has a deep reddish-brown tint. It has a general square prismatic shape, and is abruptly truncated and somewhat convex at each extremity. The posterior extremity is provided with eight horn-like processes, which project backwards. Two of these are short and hook-like, placed one before the other in the median line at the posterior part of the superior surface. On the upper part of the lateral surfaces there is, on each side, a short process. From about midway between the upper and lower edges of this surface, a long, conical process curves upwards and backwards ; these processes are distinguished from the others by containing a czcal process of the system of sinuses in their base (7). Close to the lower edge of the lateral surfaces there is another short process like the uppermost one. The respiratory apertures are wide and provided with valvular lips. The posterior (0) is narrower, and has the valvular lip more marked. The ganglion (d@ ) is less than one-fourth of the length of the body distant from the anterior respiratory aperture. The otolithes are four in number, hemispherical, and with a dark blackish brown coloured spot on their external surface, Plate XVI. [Plate 6] fig. 5. The endostyle (c) is nearly half the length of the body (reaches as far as the sixth muscular band, counting from before backwards). The outer surface of the integument is everywhere covered with minute asperities, like little prickles. The muscular bands (£) are seven in number, and, with the excep- tion of the anterior and posterior, completely encircle the body of the animal. This form was always free and solitary.t 8. Salve B, Plate XV. [Plate 5] fig. 2, on the other hand, is thus characterized. The body is subovoid, smaller at the posterior ex- ' The statements of Meyen (of. c2¢.) to the contrary are certainly erroneous. ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 41 tremity than at the anterior (a) ; the former ends in a point, the latter in a small square facet. The sides are flattened into several irregular facets, and the upper and lower edges are sometimes somewhat carinated. The apertures are similar in general structure to those of the form A, and the anterior and posterior extremities project considerably beyond them. The ganglion (d@) is placed at about one-fourth of the length of the body from the anterior extremity. The otolithes resembled those of A. The endostyle (c) is not nearly equal in length to half the body ; it does not extend so far back as to the third muscular band. The outer surface of the integument is smooth. The muscular bands (#) are five in number, and none of them encircle the body of the animal, the dorsal extremities being always separated by a considerable interval. This form, when young, was sometimes found in chains; the adults were always separate. These forms, it will be observed, are widely different, and the difference is as great between the youngest forms of each as between the adults, so that they are not derived from one another by any species of metamorphosis, properly so called. Whatever be their external differences, however, their internal organization is so similar that the same description applies to both. g. The Sala, then, may be considered as a hollow cylinder, consisting of two tunics, an external and an internal (a, 8), the former (a) forming the mantle, the latter (@) the wall of the respira- tory cavity. These tunics are continuous with one another at the respiratory apertures, but elsewhere they are separated by a more or less wide space. In very young Salpe this space is like the cavity of a serous sac, but in the older forms it becomes broken up into smaller channels by the adhesion of the inner and outer tunics to one another at various places, and so constitutes a system of sinuses ; it may be conveniently called the “sinus system.” 10. Running obliquely from behind forwards and downwards, a thickish column or band (e) crosses the respiratory cavity ; it is hollow, and its cavity opens above and below into the sinus system. This is the “gill.” It presents an edge anteriorly and superiorly, and on each side of this, the lateral surfaces are beset with a series of small, oval, ciliated spaces. In this species the gill has but a single grand sinus running through it, and presents no appearance of vascular ramifica- tions. The name gill has been applied to this structure somewhat 42 ANATOMY AND PAYSIOLOGY OF SALPA AND PYROSOMA too exclusively, as there can be little doubt that the whole respiratory cavity performs the branchial function. It is proposed, therefore, to call it the Aypopharyngeal band, on the supposition that the proper respiratory cavity of the Ascidians answers to an enlarged pharynx. 11. The muscular bands (/) are closely adherent to the inner tunic ; they are composed of flattened fibrils, about 755th of an inch in diameter, which are very distinctly transversely striated, the strize being about ;js5th of an inch apart. The bands appear to possess no sarcolemma. 12. The intestinal canal (Plate XV. [Plate 5] figs. 5 and 6) com- mences by a wide somewhat quadrangular mouth (7) opening into a flattened cesophagus, and placed at the re-entering angle formed by the hypopharyngeal band and the upper wall of the respiratory cavity. The intestine passes backwards, then becomes suddenly bent upwards upon itself, and curving slightly to the right, terminates in a wide flattened anus, close above and to the right side of the mouth (s). A wide czecal sac (¢), given off on the left side of the intestine and bending upwards and to the right side, constitutes the stomach. 13. There is a very peculiar appendage to the intestinal canal hitherto, it is believed, quite undescribed, and consisting of a system of delicate, transparent, colourless tubes, with clear contents, arising by a single stem from the upper part of the stomachal caecum, and thence ramifying over the surface of the intestine (5, 6, ~), on what may be called the rectum, that is, the terminal portion of the intestine ; it forms a sort of expansion of parallel anastomosing vessels, which all terminate at the same distance from the anus anteriorly, and from the bend of the intestine posteriorly, either by uniting with one another or in small pyriform ceca, Plate XV. [Plate 5] figs. 5 and 6. Do these represent a hepatic organ, or are they not more probably a sort of rudimentary lacteal system, a means of straining off the nutritive juices from the stomach into the blood by which these vessels are bathed ? The intestine is connected with the parietes of the sinus in which it lies by innumerable delicate short threads, like a fine areolar tissue. 14. In Salpa A, the only other organ contained in the circum- visceral sinus, besides the intestine and “system of tubes,” is a mass of clear cells (@), rendered polygonal by mutual pressure, and placed at the upper and back part of the sinus; to this body the name of ‘“eleoblast” has been given by Krohn. It has by some authors been confounded with a liver, an organ to which it certainly has no analogy whatever. The eleeoblast is much larger and more conspicuous in the ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 43 young than in the adult Sa/pe, and frequently, but not always, its cells contain an oily matter. There would seem to be no clue either to the homology or to the function of this eleoblast. Without hazarding a conjecture, it may be remarked, as a curious fact, that these animals, so remarkable for possessing in the foetal state a true though rudimentary placental circulation, possess an organ which in structure and duration some- what calls to mind the thymus gland. 15. The nervous system consists of a single subspherical ganglion (d@), situated in the space between the inner and outer tunics, just where the anterior and lower extremity of the hypopharyngeal band joins the ventral paries. It gives off two delicate branches forward to the “languet” (16), and a great many in all directions to the parietes of the body. There were no branches traceable specially to the mouth or towards the cesophagus. A delicate but strong vesicle attached to the anterior and lower surface of the ganglion, and containing four subhemispherical cal- careous bodies, with black pigment spots on their outer surface, evidently represents the auditory vesicle and its otolithes in the gasteropod and acephalous Mollusca: and a conical depression in the outer tunic leading towards this auditory vesicle, would appear to be intended to bring it into closer relation with the surrounding medium, Plate XVI. [Plate 6] fig. 5. 16. There would appear to be yet another organ of special sense, composed of the “languet” (7) and the “ciliated fossa” (w), called by Eschricht the “langliches organ.” The “languet” (Plate XVI. [Plate 6] fig. 5) is a long tongue-shaped or conical process, fixed by its base to the ventral surface of the respiratory cavity where this is joined by the anterior extremity of the gill, and for the rest of its extent floating freely in the respiratory cavity : it is curved so as to be convex anteriorly and concave pos- teriorly, and its anterior surface is marked by a shallow vertical groove ; at the base this groove is wider, and where it becomes con- tinuous with the surface of the respiratory cavity, it presents a narrow median slit, which leads into a small purse-shaped cavity, flattened from side to side and richly ciliated within, Plate XVI. [Plate 6] fig. 5 w. The posterior contour of this ciliated fossa is formed by a delicate thickened band or filament, much more distinct in some other species than in the present. It would appear probable that the languet and the ciliated fossa subserve in some manner the performance of the gustatory function. 17. From each side of the base of the languet a narrow “ ciliated Ap ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA band” (x) runs upwards, until it meets with its fellow of the opposite side, the two thus encircling the anterior aperture of the respiratory cavity. 18. The dorsal wall of the respiratory cavity is marked by two longitudinal folds, running from before backwards to the mouth. These are the dorsal folds of Savigny and others ; but there is an organ to which the name of “ Endostyle” may be given (¢), very distinct from these, and yet which has been invariably confounded with them, consisting of a long tubular filament, with very thick strongly refracting walls, Plate XV. [Plate 5] fig.4¢ This body lies in the dorsal sinus; its anterior extremity is slightly curved down- wards, somewhat pointed, and looks stronger and more developed than the posterior extremity, which is paler, more delicate and truncated. By its ventral surface this “ endostyle” is attached to a ridge of the inner tunic, which rises up into the dorsal sinus. 19. It has been stated that the circulatory system consists, not of vessels with distinct parietes, but of more or less irregular sinuses. However irregular in form, the position of several of these is very constant. There isa dorsal sus running along the dorsal surface and enclosing the internal shell ; there is a vex¢ral stnus opposite to this and containing the ganglion; there are /ateral sinuses connecting these. Then there is the sinus in which the intestine and generative organs lie, the pert-zxtestinal sinus, and, finally, the sinus which, connecting the dorsal and ventral system of sinuses, traverses the gill and con- stitutes the dranchial sinus. These sinuses all communicate together round the cesophagus, and above and in front of this, the heart (g) is developed. The heart lying obliquely at the posterior extremity of the dorsal sinus, is not tubular, as it has been described ; it forms not more than three-fifths of a tube; nor is it correct to say that it lies in a pericardium. Its true nature will be best conceived by supposing the inner surface of a sinus to have become developed for about three-fifths of its circumfer- ence into a free muscular membrane, Plate XV. [Plate 5] fig. 9. This membrane is exceedingly delicate, and is composed of a single layer of flat striated muscular fibrils. 20. The direction of the circulation depends entirely upon the order of contraction of the muscular fibrils of the heart. If they contract successively from behind forwards, the blood is forced in that direc- tion ; after a certain number of such contractions, they all become simultaneously, as it were, paralysed for a short period, and then they begin to contract again, but in the inverse order, and of course with an opposite effect upon the direction of the circulation. ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 45 The blood, in its alternate flux and reflux, bathes all the internal organs—the intestine, the endostyle, the brain and the generative organs, the corpuscles finding their way as they best may among the interstices. When the force of the heart diminishes, they frequently accumulate around the intestine in consequence of becoming en- tangled among the meshes of the areolar tissue (13) connecting the intestine with the parietes. 21. So far, the structure of the two forms A and B has been identical ; but in proceeding to examine the reproductive organs, it will be necessary to treat of each separately. The form A is always found to possess a connected series of young forms, the so-called Sa/pa chain, encircling its visceral nucleus ; the form B, on the other hand, never possesses the Sa/pa chain, but generally contains a solitary foetus, pendent from the upper and posterior part of its respiratory cavity. It is clear therefore that in each of these forms reproduction takes place. But is the mode of reproduction in each case similar or different? Are both, processes of gemmation, or processes of sexual reproduction, or is one process of the one description, the other of the other description? To come at the solution of this question, it will be necessary to know first, the nature and relations of the chain of young in A, then the nature and relations of the solitary fcetus in B, and, finally, to trace back the development of both to their first origin. 22. Salpa chain of A (Plate XV. [Plate 5] fig. 1% Plate XVI. [Plate 6] fig. 1. Plate XV. [Plate 5] fig. 9). The chain is formed of a double series of foetuses, commencing on the right side of the nucleus, curving under it, then turning upwards and over it to the right side, and finally terminating in the middle line by a free extremity midway between the two long posterior horns. The chain is enclosed in a proper cavity, hollowed out in the sub- stance of the outer tunic, and this sometimes opens externally opposite the free extremity of the chain, Plate XV. [Plate 5] fig. 9. 23. The foetuses do not form a chain by mere apposition ; they are all attached by pairs to one side of a cylindrical double-walled tube, which is connected, at its anterior or proximal extremity, with the system of sinuses of the parent, to the right of the heart. The tube is in fact merely a diverticulum of the sinus system, Plate XV. [Plate 5] fig. 9, and the blood contained in the sinuses passes freely into it. It is divided by a partition (y) into two canals, which are distinct for the whole length of the tube, except at its very extremity, where they communicate just as the two scale of the cochlea do; and it thence happens, that in the living animal, a constant current passes up on one 46 ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA side of the partition and down on the other, the direction of the two currents being generally, but not always, reversed with the reversal of the general circulation. If the fcetuses be traced back upon this tube, it will be found that towards the proximal end of the tube they lose their distinctive form and become mere buds, processes of its wall, Plate XV. [Plate 5] fig. 9. It may thence be conveniently termed the “ gemmiferous tube.” 24. The proximal extremity of the gemmiferous tube is simply transversely striated, Plate XV. [Plate 5] fig.9; further on, two eleva- tions become apparent on either side of the median line in each of these striz. These elevations are rudiments, the inner, of the nucleus, the outer, of the ganglion of a foetal Sa/pa. Still more towards the distal end of the tube, the young Sa/p@ are much larger in proportion to the tube ; the internal organs become marked, the heart becomes visible by its contractions, and the body itself, although the respira- tory apertures are as yet only marked out, not open, contracts occa- sionally. Finally, the otolithes make their appearance, the body becomes larger relatively to the nucleus and ganglion, and the respiratory orifices open, Plate XVI. [Plate 6] figs. 1, 2. 25. The cavity of the gemmiferous tube communicates with the dorsal sinus system of the foetus. Apparently the inner canal com- municates by two canals, a wider and a narrower (Plate XVI. [Plate 6] fig. 1), with the anterior portion of the dorsal sinuses of the fcetus, and the outer canal communicates with the middle of the dorsal sinuses of the foetus. However this may be, it is quite easy to watch the blood- corpuscles of the parent making their way from the gemmiferous tube into and out of the sinus system of the foetuses. The writer has seen one of the large blood-corpuscles of the parent entangled in the heart (which was not more than =45th of an inch long) of a very young feetus. It is not exactly true that a gradual series in the development of the foetuses is to be traced along the gemmiferous tube. The tube is rather marked out into sharply-defined lengths (generally three in number), in each of which the foetuses are nearly at the same stage of growth, while they are much further developed than in the “length ” on the proximal side, much less advanced than in the “length” on the distal side. 26. In this species the young Sa/pe@ thus produced were extruded, when fully developed, from the aperture mentioned in (22); but it rarely happened that even two or three adhered together, and they never formed the remarkable free-swimming chain of other species. Generally they were found solitary, presenting only on their lateral faces traces of their former adhesion. Those which were connected ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 47 adhered together in a single series, the left antero-lateral extremity of the one being applied to the right postero-lateral extremity of the other ; and when they became free the traces of the connection were visible as angular processes of the sinus system. It is not correct to say that the Sa/pa chains have organs of attach- ment. At first they are attached by the whole length of their lateral faces, the sinus system of one being continuous by a wide channel with the sinus system of the other; but as they grow these communi- cating channels become more and more narrowed until they are mere points of connection ; all communication then ceases, and the Se/pe become free from one another and move about independently. 27. Having thus determined the nature and relations of the Sadpa chain, it remains only to be said, that the young when freed, have a sub-ovoid, posteriorly-pointed form, five muscular bands, facetted sides, and in short are identical in form, and ultimately in size, with the form described as Sa/pa B. One-half, therefore, of Chamisso’s theory is clearly correct ; the solitary Salpa (Salpa A) produces the aggregate form (Salpa B); and we may add, that this takes place by a process of gemmation from the walls of a tube in free continunication with the circulatory system of the parent. 28. Solitary Fetus of Salpa B.—Whilst this form still forms part of the chain or is but just freed, it is sure to contain a solitary fcetus ; and frequently one may be found in it when it has attained its full size, but as often not. When the solitary foetus exists, it hangs freely in the respiratory cavity (Plate XV. [Plate 5] figs. 4, 8) by means of a pedicle attached to the upper and posterior part of its wall, on the left side of the mouth of the parent. In its youngest and most rudimentary state it is a somewhat conical papilla (Plate XV. [Plate 5] fig. 7) or bulging of the inner tunic, consisting of an inner oval or pyriform cellular mass, enveloped in a delicate transparent membrane, which appears to be a continuation of the inner tunic. As development proceeds the inner mass becomes divided into two portions, a larger turned towards the respiratory cavity, and which projects more and more into it, and a smaller subspherical, turned towards and lying in the cavity of the sinus, and bathed by the parental blood. 29. The whole mass goes on enlarging, but the former portion faster than the latter. The former becomes somewhat ovate, with its long diameter in the same direction as the long diameter of the parent, and gradually assumes the form of a Sa/pa. The muscular bands, the gill, the ganglion and its otolithic sac become distinct, and 48 ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA eventually the heart is obviously seen pulsating close behind the pedicle of attachment, Plate XVI. [Plate 6] fig. 6. In the meanwhile the smaller subspherical mass has undergone a remarkable change. It has likewise become thrust from the sinus towards the respiratory cavity, so that it no longer lies in the former, but is situated in the thick pedicle of the young Sa/pa. It has furthermore become hollow, and contains two perfectly dis- tinct cavities or sacs; of these the outer is concave and cup-shaped and envelopes the inner, which is subspherical, Plate XVI. [Plate 6] fig. 6 #. Now the outer sac is in free communication by a narrower neck, divided into two channels by a partition, with the dorsal sinus of the feetus ; and the inner sac is in equally free communication by a neck similarly divided, with a short sinus arising immediately behind the heart ; and as there is no communication between the two sacs, it follows that the current of blood in each is perfectly distinct from and independent of, that in the other. A more beautiful sight indeed can hardly be offered to the eye of the microscopic observer than the cir- culation in this organ. The blood-corpuscles of the parent may be readily traced entering the inner sac on one side of the partition, coursing round it, and finally re-entering the parental circulation on the other side of the partition ; while the foetal blood-corpuscles, of a different size from those of the parent, enter the outer sac, circulate round it at a different rate, and leave it to enter into the general cir- culation in the dorsal sinus. More obvious still does the independence of the two circulations become when the circulation of either mother or foetus is reversed. 30. Whether this body perform the function or not, it can hardly be wrong to give it the name of a placenta. It is identical in structure with a single villus contained in a single venous cell of the mammalian placenta, except that in the Salpian placenta the villus belongs to the parent, the cell to the fcetus; the reverse ob- taining in the Mammalia. As the young Sa/pa increases in size, the placenta, ceasing to grow, becomes proportionately smaller, until the pedicle gradually narrowing the communication with the parent ceases and the foetus becomes free, Plate XVI. [Plate 6] fig. 3. The remains of the placenta are traceable for some time as a small diverticulum of the dorsal sinus of the young Sa/pa, Plate XVI. [Plate 6] fig. 3 7. 31. The latter as it grows nowise resembles its parent. It has a prismatic form, has seven muscular bands, and developes processes from its posterior extremity. It becomes indeed perfectly similar to the form which has been described as Sa/pa A. ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 49 It thence appears that the other half of Chamisso’s theory is also perfectly true, viz., the aggregate form of Salpa (Salpa B) produces the solitary form (Salpa A), and the circulatory system of the foetus in this case is connected with that of the parent, xof zmmedtately, but by means of avery distinct and well-developed placenta. Here is one very clear distinction between the two processes of re- production. Are there any other differences? To answer this ques- tion we must proceed to trace back both processes to their origin. 32. It has been seen that the young Sa/pe B are developed by a process of gemmation from the gemmiferous tube of Salpa A. Whence comes the tube itself? The smaller the individual of the form A examined, the shorter is the gemmiferous tube, and the less developed the buds upon it. In individuals just free, or about to be free, it is a very short cylindrical tube, arising on the right side and just in front of the heart, and curving downwards and backwards, Plate XVI. [Plate 6] figs. 3, 3 a. In still smaller attached specimens it appears as avery short, some- what conical process (imperfectly divided by a partition) of the dorsal sinus, close to the heart; its walls are smooth, and the blood-cor- puscles are easily seen passing up one side and down the other of the partition, Plate XVI. [Plate 6] fig. 4. It is clear, therefore, that the gemmiferous tube is nothing more than a stolon, containing a diverticulum of the circulatory system of the parent, and the whole process of reproduction as it is mani- fested in Sa/pa A is one of gemmation. Salpa Bis a bud of Salpa A. 33. Following the same course of investigation with regard to the young Sa/pa A (which it has been seen is produced from Sa/pa B), it is found, that in Sa/@ B, which are either still adherent to the gem- miferous tube or just set free, there is no protuberance of the inner tunic into the respiratory cavity; but where this afterwards exists, a pedicle of greater or less length is attached, and running backwards, carries at its extremity an oval cellular mass, Plate XVI. [Plate 6] fig. 8. This hangs suspended by its pedicle in the cavity of the sinus, and is freely bathed by the blood. In one specimen the length of the pedicle was z}jth of an inch, the long diameter of the oval body about ;2,5th of an inch. In still younger forms of the Sa/pa B, and indeed as soon as the separate organs are distinguishable, the outer tunic bulges slightly in the middle line behind the outline of the posterior aperture and beneath the nucleus, Plate XVI. [Plate 6] figs. 1, 2; this protuberance is caused by the presence of a spherical body (g) about zg5,5th of an inch in diameter, containing a clear vesicle z7j;5th of an inch in VOL. I iE 50 ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA diameter, which again frequently contained a round opake spot or nucleus about ,;lssth of an inch in diameter; the latter sometimes appeared as a thick-walled vesicle. This is plainly an ovum; a narrow pedicle (g') is attached to its upper extremity and runs upwards, curving slightly forwards to the same point as in the preceding forms. It would appear then that the Sa/pa B developes a single ovum, which is at first placed in the median line in the ventral sinus ; that partly by the increase in size of the body, and partly in consequence of a shortening of its pedicle which acts as a gubernaculum, it becomes drawn from this position upwards and to the left side; and that in the meanwhile, probably in consequence of fecundation, it becomes altered in structure, and precisely similar to and identical with the cellular mass which has been seen to form the rudiment of the young Sa/pa A, Plate XVI. [Plate 6] fig. 7. In this case #he Salpa A would be a true embryo developed by a process of sexual generation. 34. Sexual generation however presupposes a male fecundating organ, and this is found in Sal/pa B as a ramified body, hitherto generally called a liver (f), Plate XV. [Plate 5] figs. 6 and 7, closely surrounding the intestinal canal with a network, solid in the younger form, but in the older tubular, with very thin walls, and containing a vast number of pale-greenish circular cells, from sjg5th to y-ggth of an inch in diameter ; and besides these detached spermatozoa, with very thin tails and long narrow heads, about y55th of an inch in length. The testis has no visible excretory organ, but such might well escape notice. Nothing at all resembling this body is found in the form A; its contents sufficiently demonstrate its real nature, and its existence on the other hand is strong confirmatory evidence, if any be needed, that the pediculate body described above is a true ovum. One curious circumstance needs to be remarked ; the testis does not develope part passu with the ovum and attain its full development at the same time, as might be imagined. The testis is always behind the ovum in its progress, and does not, indeed, seem to have attained its full development until the latter has become freed from the parent. Without carefully tracing the form B through all its stages, it might readily be supposed to be always male ; in fact, fully-grown specimens, while they always possess a well-developed testis, rarely contain any embryo, this being generally set free when the parent is about half or two-thirds grown. The careful observer will, however, be always able to detect a trace of its former attachment, in a sort of cicatrix, left at the corresponding part of the respiratory chamber. ANATOMY AND PHYSIOLOGY OF SALP.A AND PYROSOMA 51 35. It is not clear by what channel fecundation takes place, whether each Sa/pa B impregnates its own ovum by discharging the contents of its own testis into the circulatory fluid, which would be a procedure altogether anomalous ; or whether, on the other hand, impregnation do not rather take place from without, a presumption which is strengthened by analogy, and by the fact, that the testis does not seem to attain maturity early enough to fecundate its own ovum. The spermatic fluid may have access to the ovum by the gubernaculum becoming hollow and tubular, as will be seen to be the case in the Pyrosomata, and indications of such an occurrence have occasionally manifested themselves. 36. To recapitulate—The form A (Salpa solitarta) produces a stolon, from which, by gemmation, arises the form B (Salpa gregata). This contains a testis and a single ovum attached by a pedicle or “cubernaculum ” to the wall of the respiratory chamber. Fecunda- tion takes place in a manner not yet clearly ascertained, and the “gubernaculum ” shortens until the ovum is brought into close contact with the respiratory wall or inner tunic. The latter then protrudes into the respiratory canal, enveloping the ovum in a close sac ; the ovum becomes developed into an embryo, which is connected by a genuine placenta with its parent, and ultimately assuming the form of Salpa A becomes detached and free. 37. While Chamisso’s formula, then, expressed the truth with regard to the generation of the Sa/pz, it does not express the whole truth. True it is, that the Sadpa solitaria always produces the Salpa gregata, and the Sala gregata the Salpa solitaria ; but it is most important to re- member that the word “ produce” here means something very different in the one case, from what it means in the other. In the Salpa solitarta the thing produced is a dud, in the Salpa gregata a true embryo. There is no “alternation of generations,” if by generation sexual generation be meant ; but there is an alternation of true sexual generation with the altogether distinct process of gemmation. It would be irrelevant to discuss here the wide question of the “ alternation of generations” in all its bearings ; but the writer may be permitted to express his belief, founded upon many observations upon the Polypes, Acalephe, &c., that the phenomena classed under this name are always of the same nature as in the Sa/pe@; that under no circumstances are two forms alternately developed by sexual gene- vation; but that wherever the so-called “alternation of generations ” occurs it is ax alternation of generation with gemmeation. 38. Using the terminology of insect metamorphosis, as Chamisso Bie 2 52 ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA has done (70), the larva never produces the imago by sexual genera- tion, the imago again producing the larva by sexual generation. But a pseud-imago, which is indeed nothing more, homologically, ¢han a highly individualised generative organ, is developed from the larva, ova are produced by it, and from these the larva again is developed ; the whole process differing from that common to animals in general, in nothing but the independence and apparent individuality of the generative organ. 39. It cannot be too carefully’ borne in mind that zoological indi- viduality is very different from metaphysical individuality, and that the whole question of the propriety of the “alternation theory” as a means of colligating the facts (for at best it can be nothing more), turns upon the nature and amount of this difference. If the true definition of the zoological individual be (as the writer believes it to be) “the sum of the phenomena successively manifested by, and proceeding from, a single ovum, whether these phenomena be invariably collocated in one point of space or distributed over many,” then there is no essential difference between the reproductive pro- cesses in the higher and lower animals, and the alternation theory becomes unnecessary. In accordance with this definition, neither the form A, nor the form B would be a zoological individual; not either of their forms, but both together, answer to the “individual” among the higher animals. In strictness both Se/fa Band Sa/pa A are only parts of individuals, —are organs ; but as we are unaccustomed to associate so much inde- pendence and completeness of organization with a mere organ, to give them such a name would sound paradoxical. It is proposed, there- fore, to call them, and all pseudo-individual forms resembling them, “ zodids,” bearing in mind always that while the distinction between zooid and individual is real, and founded upon the surest zoological basis,—a fact of development,—that between zodid and organ is purely conventional, and established for the sake of convenience merely.t 40. In the Sa/pa, then, the parent and the offspring are not dis- similar, but the individual is composed of two zodids. In Cyanea, the individual is composed of two “ zooids,” a medusiform and a polypiform zodéid. ? For a further consideration of this subject the author begs to refer to Dr. Carpenter’s “Principles of Physiology,” in which the whole question of individuality in plants and animals is treated in a very clear and masterly manner; to Mr. Thwaites’s papers in the Annals of Natural History ; and to an attempt to apply the principles advocated in the text to the metamorphosis of the Echinoderms in a Report by himself. —mza/s, July 1851. ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 53 In the Zrematoda there are frequently three “zodid” forms to the individual. In the Aphidae the sum of from nine to eleven “ zodids ” composes the individual, the great number of zodid forms in this case being simply an instance of that “irrelative repetition” of parts so common among the lower animals. A similar irrelative repetition exists among the so-called “com- pound” animals, the Polypes and compound