*- ■^ jl : r 1^ m »ar- ••:: ^-^y^.^^ • 1 ■ • •- ## MATNiSD M. METCMJ, (J y^. 77^^2^ HISTORY OF INFUSORIA^ rsrcLUDnsTG THE DESMIDIACE^ AND DIATOMACE^, BRITISH AND FOREIGN. BY ANDREW PRITCHARD, Esq., M.R.I., AUTHOR OF TUB 'MICROSCOPIC CABINET,' ETC. FOURTH EDITION. ENLARGED AND REVISED BY J. T. AELIDOE, M.B., B.A. Lond. ; W. AECHEE, Esq. ; J. EALES, M.E.C.S.L. ; W. C. WILLIAMSON, Esq., F.E.S. AND THE AUTHOE. ILLUSTRATED BY FORTY PLATES. LONDON: WHITTAKER AND CO., AVE MARIA LANE. 1861. [ The rig Jit of translation is reserved.'] PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. — v^, {uu LIBRARY j. J PREFACE. Special interest has always been taken by man in the structure and development of the minute forms of life, whether animal or vegetable : in this volume I propose to lay before the reader a resume of the present state of our knowledge of the multitude of K^dng beings called Infusoria. This term_, as employed by Professor Ehrenberg of Berlin^ includes a wide range both of animal and vegetable life; while it is now restricted by other naturalists to the Protozoa^ and, in the works recently commenced by Dr. Stein and MM. Claparede and Lachmann, to the ciliated members of that group. The former editions of this work having included a Histoiy of the Bacillaria, Phytozoa, Protozoa (under the name Polygastrica), and of the Rotatoria, it is incumbent on me to retain these groups, though the researches of late years have so extended our acquaintance with them that much difficulty has been felt in the attempt to comprise the whole in a single volume, so necessary for a practical manual. The successful investigation of this department of Natural History arose mainly from the improvement of the microscope consequent upon the discoveries of "Test Objects'^ and "penetrating power/^ the latter depending upon " angular aperture/^ — discoveries which my colleague the late Dr. Goring and myself had the pleasure of presenting to the public. The microscope, having become thereby a reliable instrument, has revealed to us the true forms and structure of these beings. Part I. is devoted to a General History of the several more or less natural groups of Infusoria: it contains also the observations and opinions of British and Continental naturalists on their nature, structure, functions, and classification. The foreign writings on these subjects are so voluminous that even an abstract of them has increased this part of the work much beyond what it occupied in IV TREFACS. former editions_, wliile the introduction of the Tables from Part II. has further extended it ; but, as I have been anxious to give an impartial account of the researches on this subject, a briefer summary- might have impaired its usefulness and value. To Dr. Arlidge is due the rearrangement and preparation of this part. Part II. contains descriptions of the Families, Genera, and Species of the groups whose general history forms the subject of the preceding part of this volume. The systematic arrangement of Ehrenberg has been retained for the Phytozoa, Protozoa, and Rotatoria, the new genera and species of other naturalists being collated and engrafted thereon. The descriptions of those curious and higlily-organized creatures the Rotatoria have been extended and revised by Professor Williamson of Manchester, whose original researches and observa- tions on this group are greatly appreciated, both in this country and abroad. In consequence of the long illness of Mr. Ralfs, who had under- taken the re\dsion of the Bacillaria, the publication of this edition has been delayed, and that group has been printed last — a deviation from the original design which it is hoped will not inconvenience the reader, while it has allowed opportunity for the insertion of the latest researches. Owing to the circumstance stated above, the revision of the Systematic History of the Family or Subgroup Desmidiacese has been kindly carried out by Mr. William Archer of Dublin, who has added some original views, expressing by symbols the characters of certain genera ; moreover, M. de Brebisson of Falaise has given this edition the benefit of his valuable co-operation, by furnishing descrip- tions of the newly- discovered foreign species. The elegance and variety of the forms, the beauty and elaborate sculpturing of the silicious shells of the Diatomacese, and the general interest now taken in their study, rendered it desirable to bring together in this volume ail the known genera and species, British and foreign. This I have been able to effect by the research of Mr. Ralfs, whose name is so intimately identified with the knowledge of these organisms, and whose present arrangement of their families and genera will no doubt tend to facilitate our better acquaintance with them. Owing to the great dimensions which this treatise has acquired, and the limited space consequently at command, I was under the necessity of con- densing the manuscript of Mr. Ralfs, and of introducing abbrevi- PREFACE. V ations. Still 1 havC;, in accordance with my original design, given every known specific name, wlietlier synonym or variety, whereby observers may avoid confusion in the nomenclature by not employing the same names for newly-discovered forms. The references now introduced are to works published subsequently to the early editions of this book : for their verification I am indebted to Mr. Kitton of Norwich. Twenty-one new Plates have been added to this edition, of which six are engraved by Mr. Tuffen West. In the case of the Diatoms, all the new figures are drawn to one scale, representing a magnifying power of 300 diameters; many of them likewise are drawn from specimens, whilst others are engraved from original drawings kindly lent by Mr. George Norman of Hull, Mr. Eoper of Clapton, and Mr. Brightwell of Normch. It now becomes my pleasing duty to acknowledge the kind assist- ance received from the late Professors Gregory of Edinburgh and BxiiLEY of New York; also to tender to Drs. Donivin, Greville, Francis, Wallich, Strethill Wright, and Mr. Gosse, along with the gentlemen before named, my best thanks for their aid and advice during the progress of this laborious undertaking. In conclusion, should the object proposed in the reissue of this work be attained, viz. to produce in a single volume a compendium of the present state of knowledge, calculated to promote and facilitate the study of the veiy interesting branch of Natural History which forms its subject, and which has occupied much of my leisure time for more than forty years, I shall be fully content. ANDREW PRITCHARD. Canonbury, London, N. .•■-^ To "*•**>. November 15, 1860. /Cm^ ^^A^ ^ ii^/^ ^♦-<*. V\^ 1^\ ^c^^ /^. XUTivJiPT)!^ j^r CONTENTS. Preface Page iii List of works quoted and abbreviations used herein ix PAET I. — A General History op Infusoria, etc. Bacillaria : Desmidiece, their figure, page 1 ; colom*, consistence, envelopes, openings in lorica, 4 ; movements and external cilia, 5 ; contents of fronds, 6 ; circulation of con- tents, 7; reproduction, 11; habitats, distribution, appearance in masses and vital endowments, vegetable natm-e and affinities, mode of collection, 20. — Tediadrece, their figure, composition, and contents of cells, 24 ; number and disposition of the cells in the fronds, 25 ; development and growth, 29 ; systematic position, 30. — Biatomacecs, their general and external characters, 31 ; figiu'e, 32 ; the silicious shell or lorica, its divisions and structm'al composition, markings, striae, canalicidi, puncta, &c., 37; contents of frustides, supposed digestive sacs, reproductive vesicles, &c., 47; move- ments, their character and causes, cilia, circulation of contents, respiration, 50; nutritive functions, supposed stomachs, 56 ; multiplication, reproduction, and develop- ment, 58 ; conjugation, 61 ; habitats, appearance m masses, abundance, 75 ; geogra- pliical distribution, 79 ; geological importance and fossil accumidations, 82 ; aerolitic Diatomete, 85 ; uses of Diatomaceous deposits, 86 ; of the nature of Diatome^e, whether animals or plants, various hypotheses, 87; determination of species and genera, varieties, classification of Kiitzing, Smith, and others, 96 ; on the mode of obtaining, preparing, and preserving specimens, 102. Phytozoa: the beings included imder this name, their general character, division into groups or tribes, their figure, coverings, 111; cell-contents, 113; movements, 117; process of nutrition, 119; multiplication and reproduction, fission, macrogo'nidia^ microgonidia, 120; encysting process, condition of rest, 123; phases of being and' alternation of generation, 124; on their nature, animal and vegetable characters, 128; habitats, occurrence in masses, colour caused by their accimiulation, 129. — Families : Monadina, ISO ; Cryptomo7iadma, 14Q ; Volvocin a, 144:; Vibrionia, 184: ; Astastcea ov Euglencea, 188 ; nature of Astasiaea, 196. Protozoa, 199. — Bhizopoda, 201; movements of contained particles, 210; nucleus, 211- reproduction, 213; of the testaceous shells of Monothalamia, 218; shells of Polytha- lamia or Foraminifera, 222; dimensions and conditions of life, 227; habitats and distribution, 229 ; of their cell-nature and characters as individuals or as colonies of animals, 232 ; on their affinities, 234 ; classification, 237. Actinophri/ina, 243 ; movements, 246; prehension and entrance of food, 247; contractile vesicle, 250; nucleus, 252 ; encysting, fission, gemmation, embryos, 253 ; conjugation, 256 ; loca- lities, affinities, 257. Acinetina, 258 ; origin and development, 261. Gregarinida, 262. Psorospermia, 265. Ciliata, 266. Subgroup A. Astoma: OpalincBa, their general characters and functions, 267 ; nucleus, self-division, supposed embryos, 269 ; habitats, vital endowments, nature, affinities, classification, 270. Peridinicea' 271 • contents, 274 ; reproduction, 275. Subgroup B. Sfomatoda : dimensions, 277 ; figure,' 278 ; consistence, 279 ; integmnent, markings on surface, spines, lorica, 280 ; externai sheaths or cases, 282; ciHa and ciliary action, 285; locomotive and fixed forms varieties of locomotion, transitory power of locomotion among the attached genera,' 288; structure of pedicles, 292; compound special organs of locomotion and pre- hension, the peristom and rotary or ciliated disc, the spirally-coiled head of Spiro- chona, 294. — Ciliated Protozoa, internal organization : subtegumentary layer, chloro- phyll, thi'ead-cells, 297 ; muscles, 300 ; organs of digestion, nutrition, and secretion, 301; the polygastric hypothesis, 303; dental apparatus or teeth, 311; contractile vesicle, 312; nucleus, nucleolus, 326; ovules, 334; spermatozoids, 337; accessory contents, graniUes, molecules, spherical cells, supposed glands, 338; circulation of contents, 339. The encysting process, .341 ; reproduction, fission, gemmation, internal 39723 Vlll CONTENTS. ova producing germs or embryos, impregnation, production of new beings with aiid without metamorphosis, transformation into Acinetre, 345 ; nature of Ciliated Pro- tozoa, their existence as independent organisms, cell-theory applied to tlunn, 368: conditions of life, 370 ; succession of species, 371 ; duration of life, influence of external agents, heat and cold, 373 ; necessity of air, chemical agents, electricity and galvanism, 374; affinities with other animals, geographical distribution, 375 ; classi- fication, 376. Subgroups of Ciliated Protozoa : Icldliyclina, 380; Noctihicida, 382; Dysteria, 387. EoTATORiA or RoTiFERA : general characters, 392 ; appendages, 397 ; the muscular system, 406 ; movements, 409 ; the digestiA^e system, 410 ; reception of food, its deglutition, 420 ; the secreting system, 422 ; the vascular and respiratory systems, 426 ; the nervous system, organs of sense, psychical endowments, 434; reproductive organs, 441 ; formation of ova, 442 ; development of embryo, 445 ; the embryo-metamor- phosis, 447 ; winter ova, 450 ; male Rotatoria, 453 ; duration and conditions of life, habitats and distribution, 463 ; affinities and classification, 468 ; Elirenberg's classifi- cation, 478 ; Dujardin and Ley dig's classifications, 480. Tardigrada : their structure, habitats, and affinities, 482. PAET II. — A Systematic History of Infusoria, with Descriptions op the Families, Gtenera, and Species. Group PiiYTOzoA. Families : Monadina, 485 ; Hydromorina, 503 ; Cryptomonadina, 505 ; Volvocina, 514 ; Vibrionia, 529 ; Astasia^a or Euglenaea, 538 ; Dinobryina, 547. Group Protozoa — Subgroup Ehizojyoda. 547: Amoebsca, 548; Arcellina, 551; Actino- pliryina, 558 ; Acinetina, 564. — Subgroup Ciliata, 568. Astoma : Opalinsea, 569 ; Cyclidina, 571 ; Peridinisea, 574. Stomatoda : Vorticellina, 579 ; Ophrydina, Vaginifera, 598; Enchelia, 605; Colepina, 616: Trachelina, 616; Ophryoc«rcina, 630; Aspidis- cina, 631 ; Kolpodea or Colpodea, 631 ; Oxylrichina, 639; Euplotina, 645. Group Rotatoria. Families : Ichthydina, 660 ; CEcistina, 663 ; Megalotrochasa, 664 ; Floscularia, 665 ; Hydatineea, 677 ; Albertina, 693 ; Euchlanidota, 693 ; Philodineea, 700 ; Brachionsea, 706. Group Tardigrada, 713. Group Bacillaria : Desmidiacete, 715 ; Diatomacese, 756. Index to the Illustrations of the Diatomaceae, 941. Description of the Plates, 949. Index to the Families and Genera, 965. A LIST OF ABBREVIATIONS OF WORKS AND AUTHORS' NAMES REFERRED TO IN THE PRESENT EDITION. Abliandlimgen der Berliner Academie der Wissenscliaften. Abhandlimgen der SenckenlDergisclien Gesellschaft in Frankfiiii; am Main. Ag CD. or AD. Agardli's Conspectus Diatomonim. ANH. Annals and Magazine of Natural History. Anat. d. T\drbellos. Thiere. Siebold, C. Tli. you. Lehrbuch der vergleicheuden Anatomie der wdrbellosen Tliiere. Berlin, 1848. Ar. or Ai'n. Professor G. "Walker- Arnott, LL.D. ASA. or A A. Agardh's Systema Algarum. ASN. or Ann. d. SN. Annales des Sciences Naturelles, Pans. B. or Bai. Professor Bailey of New York. BAJ. Professor Bailev, in American Journal of Science. BC. or BSC. Professo\' Bailey's Contributions to Knowledge, Smithsonian Insti- tution. BMO. Professor Bailey's Microscopic Organisms Boston Journal of Natural History. 1853. Braun, A., Prof. Algarum Unicellularum Genera nova aut minus cognita. 18.55. Breb. M. de Brebisson of Falaise. BD. M. de Brebisson's Diatomaceae of Cherbourg. Bri. T. Brightwell, Esq., Nor\%'ich. Brit. Assoc. ' Transactions of the British Association for the Advancement of Science. British Desmidiese. By John Ralfs. 1848. Brit, and Foreign Med." Rev. British and Foreign Medico-Chirurgical Review. Bulletin de L' Academie de St. Petersbourg, xiii. 1855. Cai*penter, Dr. W. B. The Microscope. Carus. Icones Zootomicse. 1858. Cohn, R. S. Professor Cohn on the Structm'e of Protococcus ijhiriulis. Ray Society, 1853. London. Comptes Rendus de 1' Academie Imperiale des Sciences. D'Orbigny, Alcide, Foraminiferes Fossiles, 1846. Duj. or Du. Dujardin, F., Histoire Naturelle des Zoophytes. — Infusoires. Paris, 1841. E., Eh., or Ehr. Professor Ehrenberg, Berlin. EA. Professor Ehrenberg's Mikroscopischen Lebens in Amerika. Edin. New Phil. Jouni. Edinburgh New Philosophical Journal. Einzell. Alg. Nageli, Prof., Gattunoen einzelliger Algen. Zurich, 1849. EI. or Inf. Professor Ehrenberg's Die Infusionsthierchen. EK. Professor Ehrenberg's Kreidethierchen. EM. Professor Ehrenberg's Mikrogeologie. ERBA. or EB. or ER. Professor Ehrenberg in Reports of Berlin Academy. Ehrenberg, Prof. Passatstaub und Blutregen. X LIST OF ABBEEVIATIONS, ETC. Entw. Colin, Prof. F. Entwickeliings-gescliiclite der mikroskopischen Algen imd Pilze. 1854. Fauna Infusoria, Norfolk. T. Brightwell, Norwich. Gr. Dr. R. K. Greville. GBF. Dr. R. K. Greville's British Flora. GCF. Dr. R. K. Greville's British Cryptogamic Flora. Greg. Dr. Gregory of Edinburgh. GDC or GC. Dr. "Gregory's Diatomacete of the Clyde. HBA. HassaU's British Algse. Jones, T. Rymer, Prof. A General Outline of the Animal Kingdom. London, 1841. K. or Kiitz. Professor Kiitzing. KA. or KSA. Professor Klitzing's Species Algarum. KB. Professor Kiitzino-'s Bacillarien. Kiitzing. Phycologia Germanica. 1845. KL. Die kleinsten Lebensfonnen. KSD. Professor Klitzing's SjTiopsis Diatomeormn. Linnaea, xiv. 1840. Lpio-b. Professor Lpigbye's Tentamen Hydrophytologi?e Danicee. Medical Times. Loudon,* 1856. Professor Huxley's Lectures. Me. or Men. Professor Meneghini. Meneghini, R. S. Professor Meneghini on the Animal Nature of Diatomeae. Ray Society. London, 1853. Mem. de I'Acad. Roy. Belgique. Memoires de I'Academie Royale de Belgique. Micrographic Dictionary, The. By Dr. Grifhth and Prof. Henfrey. Microscopic Illustrations. By C. R. Goring, M.D., and Andrew Pritchard. Mittheilungen der Naturforschenden Gesellschaften in Bern. 1849. MJ. or JMS. Journal of Microscopical Science. Monatsb. Berlin. Acad. Monatsbericht der Berliner Academic. MT. or TM. or TMS. Transactions of Microscopical Society. Miiller's Archiv. Archiv fiir Anatomic und Physiologic. Yon Dr. J. Miiller. Miiller, O. F. Prof. Animalcula Infusoria. Na. or Nag. Professor Niigeli. Nat. Hist. Review. Natural History Review, Dublin. Nov. Act. Acad. Curios. Nova Acta Academiae Naturae Curiosorum. Owen, Richard. Lectures on the InAertebrate Animals. London, 1843. Owen, Richard. On Parthenogenesis. London, 1849. Ph, Professor John Phillips, F.R.S. Phil. Trans. Philosophical Transactions of the Royal Society of London. Perty, Max., Dr. Zur Kenntniss kleinster Lebensformen. 1852. Proceedings of the American Association for the Advancement of Science. Proceedings of the Boston Society of Natural History. Proc. Roy"^ Soc. Proceedings of the Royal Society of London. Proc. Roy. Soc. Edin. Proceedings of the Royal Society of Edinburgh. Proceedings of the Academy of Natural Sciences of Philadelphia. 1853. Rab D. or RD. Dr. Rabenhorst, Die Siisswasser Diatomaceen. Ra. or R. Mr. Ralfs. R.S. Ray Society's publications. R.S. Reports. Ray Society Reports. Rejuv. R.S. Braun, A., Professor, On the Phenomena of Rejuvenescence in Nature. Ray Society. London, 1853. Ro. F. C. S. Roper, Esq. Schleiden, J. M., Prof. Principles of Scientific Botany : translated by Dr. Lan- kester. 1859. Schultze, Dr. Max S. Ueber den Organismus der Polythalamien. Leipzig, 1854, Schneider, Ant. S^anbolae ad Infusoriorum Historiam Naturalem Dissertatio In- auguralis. Berlin, 1854. Sh. or Shadb. G. Shadbolt, Esq. Sill. Joum. Silliman's American Journal of Science and Arts. S. or Sm. Professor Smith. SBD. or SD. Professor Smith's S}Tiopsis of British Diatomaceas. Stein, F., Prof. Die Infusionsthiere, auf ihre Entwickelungsgeschichte. EEEATA, ETC. XI Transactions of the Pliilosopliical Societ}- of Manchester. Transactions of the Medical and Physical Society of Bombay. Untersuchung-en liber die Familien der Conjiigaten. By Professor de Bory. Van der Hoeven. Lehrbiich der Zootomie. 1850 & 1856. Wagner. Zootomie. Wiegmann's Ai'chiv. Archiv fiir Naturgeschichte. Von A. F. A. Wiegmann. Williamson, Prof On the Recent Foraminifera of Great Britain, Ray Society. London, 1857. Zeitschr., or Siebold's Zeitschr. Zeitschrift fiir -mssenschaftliche Zoologie. Von Carl T. yon Siebold iind Albert Kolliker. 1848-59. Note. — The names of Ehrenberg, Dujardin, Perty, and Siebold are frequently mentioned \\dthout particular notice of the work quoted ; but the ti'eatises intended are those in which each of those several authors has given a general history of Infusoria, and which are named in the above list. So, in the account of the Rhizopoda, Schiiltze is often quoted, his special work on their organization being referred to ; and lastly, in the History of the Rotatoria, the opinions of Leydig are all derived from his essays in Siebold's 'Zeitschrift.' For abbreviations employed in Systematic History of Desmidiaceae, see p. 721. Note. — The references to the engravings in this work are printed thus : (xn. 20.) for Plate XH. fig. 20. EEEATA, ETC. Page 10, line 8 from bottom, dele See Appendix at end. — 218, line 7 from top, for Foraminiifera read Foraminifera. — 243, line 7 from bottom, for peuliarity read peculiarity. — 253, line 3 from top, for Actinopln-gs read Actinophrys. — 259, line 4 from bottom, for XVIII. read XXIII. — 316, line 6 from bottom, for Leuckhart read Leuckart. — 324, line 14 from bottom, for Wagener read Wagner. — 470, line 7 from top, for 1855 read 1858. — 535, line 5 from bottom, after figm^ed, inseri subsequently. — 726, col. 2, line 20 from bottom, i7isert segment 3-lobed, before lateral lobes. — 726, col. 2, line 1 1 from bottom, for side read sides. — 729, col. 2, line 25 from bottom, dele comma after surface, a^id insert after middle. — 732, col. 2, line 22 from bottom, for finely read finally. — 735, insert " C. aciculare (West). — Elongated, very slender, straight, except at extre- mities." — 741, col. 2, transpose reference to figm'e from 8. globulatum to S. bacillare. — 744, col. 2, line 34, for paradoxum read tetracerum. — 753, line 18 from top, /or Pediastrium read Pediastrum. — 758, line 5 from bottom, dele Synedrese. {^See p. 940.) — 760, col. 1, line 28, after capitate, insert strias. — 761, col. 1, line 4 from bottom, /or 159 read 156, and insert xr. 1-8. — 764, for E. Terra read E. Serra. — 765, col. 2, line 2 from bottom, for Argus read Arcus. — ■ 768, after Grenus Oncosphenia, insert Genus Podosphenia from p. 769. — 771, col. 1, hne 14, for broadly read loosely. — 772, col. 2, line 5 from bottom, for pear-like read pearl-like. — 773, col. 1, line 10 from bottom, for in. read xiii. — 774, col. 1, Hne 5, insert (iv. 32.) — 775, transpose Odontidium mesodon to end O. hyemale as syn, — 775, for " 0. pinnatum " read pinnulatum. Xll ERE AT A, ETC. Page 777, end of F. virescens, insert (ix. 176.) — 778, line 6, after Ralfs, msert . — — 779, before Genus Nitzseliia, insert Fam. characters of Surirellege from p. 783 ; and see Note, p. 940. — 781, col. 1, Hne 2 from bottom, for 20 read 21. — 783, col. 1, line 12, for 22 read 23. — 784, col. 1, line 5 from bottom, for 2, 3 ; read 24. ~ 784, col. 2, line 22 from bottom, for 19 read 20. — 786, S. pulehella, insert (iv. 28.) — 789, S. fulgens, i72sert (xiii. 20.) — 791, col. 1, line 2, for xviii. read vrii. — 796, S. striatula, insert (ix. 137, 138.) — 798, col. 1. line 24, for diyiduate read dimidiate. — 799, col. 1, line 21 from bottom, for magnificent read marginal. — 802, col. 2, line 14, for xv. read xii. ; line 29, for xv. read xir. ; last figure, for 56 read 50. — 806, Gomphogramma rupestre, insert (iv. 46.) — 806, Tetracyclus lacustris, ijisert (viii. 10.) — 809, Gephyria incxwratsi, insc7't (v. 50.) — 809, Gephyria media, insert (v. 49.) — 809, Eupleuria pulehella, insert (viii. 2.) — 812, for G. undulata read C. midata. — 821, col. 2, line 6, after ochracea, insert (Ralfs) from next line; and after ferruginea insert (Elir.). — 836, col. 2, line 8 from bottom, for x. read xi. — • 844, A. Kittoni, insert (viii. 24.) — 851, col. 1, line 17 from bottom, for nervosa read enervis. — 863, Dicladia Capreolus, insert (vi. 28.) — 875, CymbeUa Arcus, insert (vii. 78.) — 891, col. 1, line 2 from bottom, for xir. read xi. — 893, for "N. dissimUis (Rab.)" read "N. clepsydra (Ralfs)." — 903, for " N. jiroducta " read " N. extensa." — 911, S. Fidmen (Breb.), read "S. Fuhnen (Bri.)," and insert that species after S. con- stricta. — 923, col. 1, last line, for (viii. 43.) read (viir. 48.) — 929, col. 1, top line, for octocarpoides read ectocarpoides. — 938, col. 1, line 9, for " C. radiata'^ read " C. stylorumy — 941, Actinoptychvis Jupiter, now Actinocyclus Ehrenbergii. — 952, in description of Plate VII., insert " 78. CymbeUa Arcus, to right of fig. 42. 79. AmjDhora monilifera, to right of fig. 49." {Note. The engraver has omitted the numbers to these two figures in that Plate.] WORKS BY THE SAME AUTHOE. MICROSCOPIC ILLUSTRATIONS, with Descriptions of the New Microscope?, Rules for constructing them, and Directions for their management, MICROSCOPIC CABINET, with Descriptions of the Jewel and Doublet Micro- scopes, Test Objects, &:c. MICROGRAPHIA, with practical Essays on Eye-pieces, Solar and Gas Micro- scopes, &c. NOTES ON NATURAL HISTORY, selected from the ^Microscopic Cabinet,' with 10 coloured Plates from original Drawings by C. R. Goring, M.D. MICROSCOPIC OBJECTS : Animal, Vegetable, and Mineral. A LIST OF ENGLISH PATENTS for the first Forty-five Years of the present Century. PART I. A GENERAL HISTORY OF INFUSORIA Sect. I.— OF THE BACILLARIA. Under this designation, contrived by Ehrenberg, two families of microscopic unicellular Alga) are comprehended, viz. the Desmidie^. and the Diatome^. The Diatomea) differ from the Desmidieae chiefly by their dense silicious envelope, composed of two opposite portions or valves and of an interposed segment, and by the general absence of the usual green colouring matter of plants — chlorophyll or chromule. The Desmidieae, on the contraiy, have a non-sihcious envelope, separable into two segments, and filled with bright grass-green chromule. In various vital phenomena the two tribes accord ; but whilst the Desmidieoe are all but universally admitted to be plants, the Diatomese are still regarded by many to be of an animal natm-e. With respect to this question, the arguments ^^ro and con. wiU be best understood when •the organization and vital endowments of these beings have been discussed. I.— OF THE FAMILY DESMIDIE^ OR DESMIDIACE^. (Plates I. II. III. and XYI.) The Desmidiese are (pseudo-)uniceUular Algae of a herbaceous green colour, of freshwater habit, and have a membranous lorica composed of two symme- trical segments or valves. In Kiitzing's arrangement {8p. Alg.), the Desmidieae constitute a family of the Chamaephyceae, a suborder of the class Isocarpeae. Ehrenberg treated the genus Closterium as a distinct family, which he placed between the Yibrionia and Astasiaea, with the name Closterina. That the Desmidieae are actually unicellular (in the sense of forming a single enclosed cavity), Mr. Ralfs has, in his most valuable monograph on the family (1848), taken much pains to demonstrate. 0^^dng to the very deep constriction of the fronds of many genera, e. g. of Euastrum and Micrasterias, the appearance of the little organism is that of two cells united by a narrow band (I. 1, 2, 24, 26, 27; II. 18, 28), forming, in Ehrenberg's opinion, a binary cell or frustule. However, between such deeply partite forms, and others in which no constriction is j)erceptible, for instance in Closterium, eveiy intermediate gradation is met with. Other evidence of the unicellular structure is afforded by the phenomena of conjugation and of the formation of sporangia, by the newly-formed segments resulting from self-fission being interposed between the old valves, and by the fact that the entire contents wiU escape through an opening made in either valve. Moreover, in several genera the circulation of portions of the contents throughout the frond, from one segment to the other, clearly demonstrates the continuity of their interior. Figure. — There is great variety in the fig-ure of Desmidieae, and much 2 GENEEAL HISTORY OF THE INFUSOEIA. beauty. This will be best illustrated by reference to the Plates I. and II. ; for description alone would fail to convey even a tolerably accurate conception. In Micrasterlas (I. 18, 20, 21) the frustule has a general circular outhne, but is bipartite and variously cut. In Euastrum (I. 23, 24, 26 ; II. 10) it is bipartite, and each valve deeply sinuated. In many species of Cosmarium (1. 1, 2 ; II. 33) the constriction is much shallower, the valves hemispherical, and their margin entire. In Staurastrum (I. 31-34 ; II. 3, 7) each segment is more or less irregularly produced at the extremities into horn-like pro- cesses. In Penium, Docidium, and Clostermm (II. 1, 2, 9, 14) the frond is elongated and wand-Hke, without constriction, or with only a very faint one, and in many species is, moreover, curved or crescentic. Not a few genera present numerous fronds united together ; the outline of the compound being will consequently vary, both according to the figure of each individual frond, and especially to the mode in which the several fronds are united. Thus in HyaTotluca, Desmidium, and other genera (II. 35, 37, 39), the quadrate fronds are united side by side in single series, so as to foim a chain or filament, in other words are concatenated. The lateral view or cross-section of the fronds furnishes valuable characters, and is largely made use of by Mr. Ralfs with that object, especially to distin- guish between the several filamentaiy species. His figures show that the fronds may be more or less compressed, and consequently offer on a transverse section (end view) an oval and more or less acuminate form (I. 25 ; II. 23, 29), further modified by the elevations and depressions which the surfaces possess (I. 25 ; II. 23). In other cases the section is circular, e. g. in ffya- lotheca and Didymoprium (II. 32, 38), whilst in others, again, three or four sides exist which are commonly concave, as m Desmidmm (II. 40). The end view exhibits the arrangement of the mass of chlorophyll, which in some instances would appear to be pecuhar and determinate of species. The appearance of the Desmidiese is much modified by the sinuosities, eminences, depressions, and processes, as well of the sm-face as of the margin of the fronds, and also by the depth and width of the central constriction. The surface may be dotted over irregularly, or more often regularly : the dots themselves are in most cases elevated points, and in fewer instances depressions. An irregular distribution of minute dots produces a granular-looking surface (I. 24 ; II. 23, 30). Where the spots are larger their elevated character becomes e\ident on the margin, to which they give a finely-toothed or dentate appearance, e. g. in CosmciHum (I. 1, 2, 3). In some elongated fonns, such as Tetmemorus and Penium (II. 15), the puncta are disposed in lines parallel to the length : in Docidium, however, the disposition, so far as regular, is transverse. In several examples the surface is marked by elevated hues or by furrows (II. 6). Such markings seem peculiar to the elongated genera, particularly to Closterium. Many apparent lines are resolvable by higher magnifying powers into rows of puncta. Where the lines are fine, they are said to produce a striation of the surface, as in Closterium attenuatum and C. acerosum ; where they are more distinct they are termed costa?, and the surface they cover is costate or ribbed, as in Closterium costatum and C. angiistatum. In general, in order to discover the striation of the surface, the fronds must be viewed when empty ; sometimes indeed the Hues can be made out at the extremities which are unoccupied by chlorophyll. The strige and costae of Closterium and Penium referred to are disposed longitudinally, but frequently they are intersected at one or more points by a transverse line. In these spindle-shaped genera, where no constriction is found, one such transverse line, usually central, is constant, and indicates OF THE DESMIDIE.E. 3 the point of separation into two valves (II. 1, 2, 9). Each valve again is occasionally subdivided by another line (II. 6, 15). These lines may be single or double, and in the case of the middle suture their number may be more multiplied, as in Closterimn lineatum and C. Rcdfsii. The median sutiu^al line is e\ddent in other genera, e. g. in Hyalotheca, Cosmarhim, and Euastrum (II. 35). In several it takes on a further development, and becomes an elevated ridge or band, appearing, in a front \iew, as a double line, terminating on each margin in a dentation. Instances occur in Docidium and in DidymoiJrmm (II. 9, 39). Such double lines are also sometimes met with on each side the median suture, and at others, among the concatenate forms, at the junction-siu'faces of connected fronds. That the dots or pimcta on the surface of the frustules are commonly small elevations has already been stated; a further development of such into papillae or minute spines crowned by a globular apex is seen in Micrasterias jpapUlifera ; whilst in many Cosmaria and Staurastra, the edge or the entire surface is bedecked by fine hair-like spines or by obtuse ones, looking on the margin like crenations (I. 1, 2, 3). When short and stout, many elevated processes of the surface are called tubercles (II. 16, 17) ; when long and tapering, they constitute spines, and in this form may be either straight or curved : such are especially produced from the angles of the fronds, as in Arthrodesmus (II. 18, 28). Among the Staurastra, illustrations of forked spines (II. 3, 7) are found ; whilst among sporangia of many species, spinous processes, besides tubercles and other appendages, are highly develoi)ed (II. 22, 25, 34) and attain their most complex conditions. The modification of surface in several genera seems due, not to mere simple appendages, but to positive expansions of the limiting membrane itself into thick processes, which in their turn usually end in spines ; instances occur in Xanthidium and Staurastrum (I. 27, 28 ; II. 3, 7, 20, 25). Generally these large productions from the surface occupy constant and definite positions, such as the extremities, the rounded angles of the fronds, or a margin, and are rarely indifferently placed. A general distribution over the surface is rather characteristic of Xanthidimn (I. 27, 28). In Euastrum the surface is thrown into very broad round swellings, hence caUed inflations ; such may be presumed to be constant in number and position (I. 24, II. 30, the empty divided fronds). The margin of the more flattened, and the extremities of the elongated, spe- cies furnish important specific and generic characters. Micrasterias has its margin deeply incised into lobes (1.18, 20, 21, 22), which, with reference to the centre of the frond, have a radiating arrangement, and are themselves incised or inciso- dentate. The fronds of Euastrum are more or less deeply sinuated (I. 23, 24, 26 ; II. 10), and the intermediate lobes produced vary both in dimensions and outline. Where the lobes on the margin of fronds are small and little prominent, they constitute crenations and dentations which may occur singly or in paii'S ; in the latter case, the margin so modified is said to be bidentate or bicrenate (I. 1, 2, 3 ; II. 31, 26, 37). For example, some fronds of Euastrum binatum are bicrenate on the sides, and those of Didy- moprium at the angles of the filaments (II. 39), whilst bidentate frustules are seen in Desmidium (II. 37), and in Hyalotheca mucosa. It has been before remarked that when the surface is covered by tubercular eminences or conical granules, a dentate outline is produced ; instances of this occur in EimMrum verrucosum and in several Cosmaria. Another variety of margin exists, known by the term undulated or wavy, where its elevations and de- pressions are comparatively shallow. Lastly, the , general concavity or the convexity of the margin furnishes other specific characteristics. b2 4 GENERAL HTSTOEY OF THE INFUSORIA. Among the variations in the ends of the fusifonn or elongated genera may be noticed the notched or emarginate apices of Tetmemorus (II. 12); the truncate extremities of Docidium (II. 9, 10), sometimes also, as in D. Ehrenbergii, tnberculate; and the more or less acutely conical apices of Closterimn, prolonged in some species, as in 0. attemiatum, by an abrupt contraction of the frond into a conical process — in others, as in C. setaceum and G. rostratum, by the gradual tapering of the whole frond — into long rostrate or setaceous beaks. Colour. — This is due to the endochrome or internal substance, which is usually of a herbaceous green colour, and often diffused pretty uniformly throughout the fronds, sometimes however leaving intervals at which the enclosing membrane (lorica, Ehr.) becomes visible. This lorica is itself mostly coloiuiess ; yet in several species of Closterium and Penium it has a reddish-brown tint (II. 5, 6, 15). The green colouiing matter of the interior is identical with that of plants, i. e. it is chlorophyll or chromule, and con- sequently undergoes a change of coloui' in autumn, becoming, like the leaves of plants at' that season, a reddish-brown. When this change occiu's, it is equally indicative of the termination of hfe. Consistence. — Envelopes. — The hmiting membrane of Desmidiaceae is firm, though flexible ; it exhibits some elasticity and considerable resistance to pressure, is not brittle, and not readily decomposable. Traces of siHca are found in a few species, but not, says Mr. Ralfs, " in sufficient quantity to interfere with their flexibility." It is lined by a softer flexible membrane ; and besides this, the Desmidieae generally have an external mucous or gela- tinous covering, mostly so transparent and homogeneous as to be overlooked. To bring it into view, it is a common plan to add some colouring matter to the water in which the organism is viewed ; but good manipulation with a high power will frequently succeed without recoiu-se to this expedient to demonstrate it. The particles of colour diffused about the frond, and indeed any external bodies, such as small vegetable cells, are seen, not in contact with the fronds, as they would often be if these were naked, but kept at a distance corresponding with the width of the hyahne envelope (I. 15 ; II. 35). In Didymoprium GrevUlii and Staurastrum tumidum the mucous sheath is distinct and well defined ; " in others (to quote Mr. Ealfs) it is more atte- nuated . . . . , and, in general, its quantity is merely sufficient to hold the fronds together in a kind of fihny cloud which is dispersed by the shghtest touch. AATien they are left exposed by the evaporation of the water, this mucus becomes denser, and is apparently secreted in larger quantities to protect them from the effects of drought." The hning or the primordial membrane of the firm lorica is thin, colourless, and highly elastic, and alters its contour with the varying movements of the endochrome which it immediately invests. It is in contact with the outer case only at some points, mostly about the centre, and being elsewhere free, an intei-val exists between the two envelopes. This elastic lining is acted on by various chemical reagents ; for instance, it is contracted or connigated by iodine and by acids. Openings in Lorica. — Openings have been represented by several writers in the finn envelopes of Desmidieae, and more particularly in those of Clos- terium. Ehrenberg, for instance, stated that apertures existed at the extre- mities, through which soft, veiy short, and conical transparent papiUae shghtly protruded to serve as locomotive organs. Both Mr. Varley and Mr. Daliymple also described tenninal orifices, closed within, however, by a mem- branous envelope ; but neither they nor any other observers have detected the papilla-Hke locomotive organs Ehrenberg represented. '^ In no instance OF THE DESMIDIE^. (Mr. Balfs says) can any portion of the contents of the cell be forced out from the extremities." More recently the belief in terminal apertures has been revived by the published researches of the Kev. Mr. Osborne and others (J. M. S.), who affii-m, that not only the outer hard case, but also the mem- branous lining is penetrated by foramina, through which water enters from without into the ca\-ity of the frond. Another writer in the Mic. Journ., Dr. "Wright, describes, in a specimen of CJosterium didymotieum, certain circular markings, consisting of two concentric ring-s, as apertui^es penetrating " both layei-s of the investing membrane at irregular intervals:" yet neither the character of these circular bodies, as represented by their observer, nor their irregular distribution, countenances such a notion, and the appeal he makes to Mr. Ealfs's figures, instead of aiding his argument, is totally subversive of it ; for although, in the fronds of Closterium didymotieum and of C. Balfsiij some large globules are distinguishable, these are in single linear series in a definite and constant position, except when disturbed from it by the death of the plant, or by its exhaustion by parasitic growths upon it, and clearly are not aperiui'es. Besides, any such globules are sought in vain when the frond is empty, as Mr. Ralfs distinctly shows by his figiures ; whereas if they were openings, they would then be more evident than when the fnistule is filled with its endochrome, Mr. Wenham {J. M. S. 1856, p. 159) has been un- able to confiim the presence of apertiu'es, and writes — " It may be assumed that if such an opening existed it would have something like a structui'al margin of such a size as to allow its position at least to be visible under the microscope, but not the slightest break can be observed in the laminated structui-e that the thickened ends display." MovEME]!f TS AJfD EXTERNAL CiLiA. — By coutiuued observation the Desmidieai are seen to move very slowly onwards, or with an oscillating movement backwards and forwards. This phenomenon is most notable in the long spindle-shaped fronds of the genus Closterium ; in others it is scarcely, in many not at all, cognizable. Ehrenberg having persuaded himself of the existence of pedal organs or papillae at the extremities of the fronds of Clos- terium, found no difficulty in explaining their locomotion; but other observei^, who deny the presence of such organs, have been compelled to seek some other explanation of the subject. Some have referred the locomotion to the influence of the vital acts taking place within the organism, to the extri- cation of gas, &c. ; others again, particularly of late, have attributed it to the presence of cilia covering the suiface. This latter hypothesis is sup- ported chiefly by the Rev. Mr. Osborne and Mr. Jabez Hogg, who represent these organs as covering the fronds of Closteymmi, of Staurastruin, and of other Desmidieae (see page 7, on the Circulation). Mr. Wenham has sought cilia in vain, and attributes the supposition of their existence to an optical illusion. Powerful oblique sunlight, which is found necessary to display the apparent ciliary movement, this obseirver remarks, " causes a refractive atom to appear elongated as a ray or line . . . . , and this line also to appear to extend over the boimdary of a cell- wall or other a^oining body: another cause of deception arises from a large angle of aperture." The pos- sibility of such errors he illustrates by reference to the circulation as seen in Anacharis. In those fronds invested with a mucous sheath, cilia on the surface of the lorica could perform no locomotive function, and therefore can scarcely be supposed present. Likewise in the concatenated species they cannot be looked for, since any movements they possess are of that general sort seen in other filiform Algae, springing from vital action under the influence of light. Apart from this inconsiderable movement, seen under the microscope, the 6 GEIfEEAL HISTORY OF THE INFTJSOEIA. Desmidieae are known to move through considerable spaces. They travel towards the light ; appear on the side of the vessel on which the Hght falls, or rise to the surface and form a peUicle upon it. These, and the analogous fact of their penetrating to the surface of mud in which they have been imbedded, when exposed to light, are phenomena common to the Desmidiea? with other Algae. ''Another proof (writes Mr. Ealfs) of their power of locomotion is afforded by their retiring in some instances beneath the siui'ace when the pools diy up," a phenomenon witnessed also in the case of other plants. Braun {R. S. p. 203) casually refers to this kind of motion, dependent on the resumption of vital action. The Penium curtum {Cosmarium curtum, Ralfs), which grows '' in rain-pools which are altemately quickly filled and dried up in the changes of the weather, ascends from the muddy bottom, when the pools fill, in the form of beautiful bright green clouds, produced by the social growth and the very fluid, widely- extended gelatinous invest- ment of the cells." The movement of this plant, it is added, is more active and more regular than that of other Desmidieae, and "it is a remarkable sight to behold all the individuals in a dish of water in a short time turn their long axes towards the hght, and thus arrange themselves in beautiful streaks in the gelatinous mass. Observation likewise shows that it is the younger haK of the cell, distinguishable as such for a long time after division, which here turns towards the hght." Contents of Feonds. — The contents of the fronds or frustules of Desmidieae are designated generally by the name of Endochrome. This endochrome, we have already remarked, is of a grass-green colour, and contained in a proper sac hning the denser lorica. It is not homogeneous, but presents nmnerous globules, small vesicles, and many refracting coipuscles ; it is commonly not unifonnly diffused, but collected in a definite manner, and it either com- pletely fills its sac or leaves it unoccupied at parts, which not seldom are constant in position and aspect. The appearance of the endochrome is modified by age, by external physical circumstances, and by the process of development. Nageh and Braun describe it as constituting two layers within the primordial utricle, viz. an outer and an inner mucilaginous layer, the latter the thicker of the two. Ehrenberg, influenced by his behef of the animal natiu^e of the Desmidiaceae, and by his pecuhar h}^3othesis of their polygastric organization, represented the larger vesicles or globules to be digestive sacs or stomachs, and the smaller green corpuscles, ova. He even exerted his imagination still fiu-ther, by announcing that in Micrasterias, Arthrodes^nns, and one or two other genera, male reproductive stmctiu^es are visible. These suppositions it is not necessary to disciiss, seeing that they are unsupported by any facts in the stnictiu'e and oeconomy of this family. The globules and corpuscles of the endochrome of Desmidieae seem to differ in no respect from those in other Algae, consisting of chlorophyll, starch, and of oily materials floating in a wateiy medium. In most species of Closterium and of Tetmemorns, some large diaphanous vesicles are con- spicuous, either disposed irregularly, or more frequently in a single longi- tudinal series (II. 1, 12, 13). These have the appearance of being distinct cells ; and Mrs. Thomas has indeed described two such, of large size, in Cosmarium margaritiferum, as '' vesicles filled with mo\dng granules." No doubt many of the apparent vesicles are nothing more than vacuoles which, as in other protoplasmic substances, tend to arise in the ceU-contents, and may assume a fixity in size and in position. The several species of Closterium and of Docidium, and some of Penium^ present also, at each extremity of the endochrome (II. 2, 9, 14), '' a large OF THE DESMIDIE^. 7 hyaline or straw-coloured globule which contains minute granules in con- stant motion." It is seen even in the earhest stage of the frustules, but disappears in dried si)ecimens. In addition to these strictures, distinguishable in certain genera only, Nageli and others state that a central nucleus exists in all the Desmidiese, mostly containing within itself a nucleolus. " In CJosterium (Braun writes) the nucleus with its colourless mucilaginous envelope is maintained in the centre of the spindle-shaped cell by the green lamellae of contents, arranged radiantly around the long axis of the cell, which lameUae are interrupted by it in the middle of the cell. In many cases it seemed to be surrounded as by a band, or by a cavity containing water." Niigeli affirms that " Artlirodesmus possesses a small colourless corpuscle on the wall of the cell, which looks like a nucleolus. Euastrum also exhibits frequently among the green contents two obscure bodies resembling nuclei, always one in each half, when the division through the middle takes place. These are not attached to the ceU-membrane, but lie free in the midst of the cavity : they appear to possess a dark centre (nucleolus) and a clear peri- pheiy (enveloping layer ?).... In CJosterium a nucleus lies in the centre which possesses a thick whitish nucleolus within a clear enveloping layer. It is coloured brown by iodine, and wholly resembles the nucleus in S;pi- rogyra." Probably the vesicles mentioned and fig-ured by Mrs. Thomas are really nuclei (I. 2, 5). There is something special in the disposition of the endochrome in very many of the Desmidieae. On a front view of Desmidium, the endochrome is divided into Hnear portions by a pale transverse line between the angles ; and on a transverse view it is seen to send out as many thick rays as the cell has angles. Again, in Cosmarmm Ealfsii the endochrome is somewhat radiate ; but it is in the elongated genera, in Penium and Closterium, that its disposition is most characteristic. In both these genera the green matter of the endochrome seems condensed, so as to produce broad longitudinal bands (II. 2, 14), technically called fillets, which have their continuity always interrupted at the median transverse suture, and in several examples of the genus Penium by three cross bands. These fillets are more or less strongly marked in different cases, and, it may be, are constant in number in the same species. Mr. Ralfs (p. 159) tells us that Meneghini considers them of too much importance to be omitted in the specific definition. They may occa- sionally be useful in discriminating nearly allied forms ; but as they are fre- quently indistinct, or from various causes not readily counted with certainty, he is unwilling to introduce them into the specific characters, except in the absence of more permanent marks of distinction. Circulation of Contents. — A circulation or rotation of much of the liqiiid contents may frequently be seen in the Desmidieae. The Closteria afibrd the best subjects for witnessing this phenomenon, but careful focusiag and other microscopical adjustments are always needed to display it. Even Mr. Ealfs had failed to observe it until he watched it in conjunction with Mr. Bower- bank, in Closterium Lunula and in Penium Digitus, Since Mr. Ralfs's account was wiitten, much more attention has been bestowed on this phenomenon ; and it has been observed by eveiy micro- scopist who has sought for it. The Eev. Mr. Osborne has particularly studied it, and has come to the conclusion that it is due to ciHary action. " If (he writes, J. M. S. ii. 235) I put a specimen on the stage, cover the stage so as to exclude the hght, use the parabolic illuminator with the direct hght of the sun, in certain focal positions I see what appear to be cilia working evenly and continuously along the whole external margin of the plant. I 8 GEXETIAL HISTORY OF THE INFUSORIA. am inclined to believe that this is not so, that this is some ocular deception, and that these ciha, so seen, are within the outer case. It may be that these cilia are on the external surface of the membranous sac, as well as over the endochrome ; more practised observers with higher powers may yet determine that. Of the existence of the cilia throughout the plant there can be no doubt, and no object I have ever seen will bear comparison with this when beheld under sunhght It is seldom that I can trace a current up one margin, and round the point down the other ; these currents seem to me as the rule to pass from the point, when they reach it, down to the centre of the spot where the cilia are seen terminating the endochrome." In a second part of this communication the writer adds : "I have scarcely failed in one attempt to see the circulation and cihaiy motion in the Clos- terium Lunula. I tried today heating a little water, by putting a small bottle in a cup of warm water ; the eifect seemed to retard the circulation, but to make the globules larger. I have traced it over the whole extent of the en- dochrome, but it is best seen at the convex sid.e a short way from the edge. I am more than ever convinced the cyclosis is the waving of attached tongues of cilia. The specimens are capricious in the results they afford ; they show best when the sun has been on the jar for a time, I have watched the move- ments of the globules in Yallisneria, Nifella, &c., and they are to me altogether of a different natiu'e to that in the Closterium^ &c. To my eye there is no real analogy between this circulation and that in the above plants ; but there is much more with the branchial action in the mussel." Mr. Jabez Hogg's supplementary notes to Mr. Osborne's paper represent the whole frond as *' brilliantly glittering with the moving and active cilia ; whilst in the cyclosis numerous zoospores were most actively moving about hj the same agency. When the sunlight falhng on these httle bodies warmed them into life and motion, the rapid undulations produced hj the action of the cilia illuminated the whole frond with a series of most channing and dehcately- coloured prismatic fringes or Newton's rings. The motion and distribution of the cilia must be seen by the aid of the direct sun-rays and parabola ; for although I tried every other mode of illumination, and with Mr. Brooke used Gillett's condenser, yet neither of us noted satisfactorily their situation and distribution until we resorted to the parabola. At the same time the cir- culation may be most accurately obseiTed to take place over the entire surface of the frond. The stream is best seen to be nmning up the external margin, just internal to a row of cilia, with another taking a contrary direc- tion next to the serrated ciliary edge of the endochi'ome ; the whole being restricted to the space between the mass of endochrome and hyahne integument passing above and around the cyclosis, but not entering into it." Another wiiter (J. M. S. 1855, p. 84), Mr. Western, adduces an observa- tion which he believes to confirm the presence of ciha in Closterium, and even goes so far as to advance the notion that the circulation in the cells of Chara, and, by analogical reasoning, in those also of other water-plants, originates in cihary movements. In Chara, as in Closterium, he tells us, he observed " precisely the same appearances, the same rapid undulations, to- gether with the same brilliant coruscations." Dr. Wright, whose contribu- tion in the same Journal (1855, p. 171) we have previously quoted, admits the presence of cilia, and starts the extraordinaiy supposition that the circu- lation of the contents of Closterium is carried on through canals or vessels, which he describes as marginal, and that it is independent " of a frequent irregular movement of granules of endochrome more resembhng imperfect cyclosis." If our doctrines concerning the physiology of animal and vegetable cells be OF THE DESMIDIE^. 9 at all correct, the statements above quoted respecting the ciliary origin of cyclosis, and more particularly the hypothesis of a vascular system, are scarcely or not in any way admissible. We are disposed to attribute the appearances so intei-preted to misconception. Dr. Wright's notion of canals or vessels is equally extravagant with that once advanced by Schultze, of the network of sap-vessels in and about the cells of plants, and requires no dis- cussion. The opinion of Mr. Osborne that the ciuTcnts in Closteria and other Desmidieae are due to ciha, and are not analogous ^dth the in all respects similar currents in the cells of various aquatic plants, is simply an assump- tion, and one indeed in opposition both to what an unbiassed observation of the phenomenon in the two sets of plants would suggest, and to what com-, parative physiology would teach. Again, the analogy he suggests between his supposed ciliary cyclosis and the ciliaiy action of the branchiae of the mussel will be inconceivable to any one who understands the stnictiu'e of the branchial apparatus of Mollusca, the distribution of the cilia on the external surface of a mucous membrane, and their office there in providing for the active performance of the respiratory function. Analogy would, indeed, in- duce us to beheve, that if cilia are the motory organs of the cyclosis of Desmidieae, they are equally so of that in other unicellular Alga3, as well as of that in the cells composing the tissue of compound forms. If so, we might adopt Mr. Western's belief in the existence of ciha wherever a cii'culation of the contents of cells is visible, did not our opinion of the natm-e of cells and of the histological relations of their parts deter us from accepting the doc- trine at all of the presence of internal cilia within unicellular organisms. Then, again, we cannot see the necessity of a ciliary apparatus to secure the fluctuating, oscillating or irregular and mostly incomplete movements of the corpuscles within the cells of Desmidieae. To us such movements are expli- cable by reference to the changes ensuing in the nutritive processes of the living organism, and to the currents caused by the ever-acting endosmose and exosmose. Moreover, it should be borne in mind how exceedingly minute these molecular movements are ; how very inconsiderable the space passed through is ; how sluggish, compared with those due to undoubted ciliary ac- tivity, the movements themselves are. But in addition to arguments deducible from analogy and general morphology, those put forward by Mr. Wenham, resting on direct observation and experiment, seem to us strongly adverse to Mr. Osborne's hypothesis, and indicate it to be a consequence of optical de- ception. At a preceding page (p. 5) we have quoted Mr. Wenham's remarks on the deceptive effects produced in viewing objects by oblique sunlight, or by any powerful source of illumination, and by the use of a large angle of aperture ; we will here add his comparative obseiTation of the circulation of Anacharis. In viewing this, he tells us {op. cit. p. 159), " with a large aper- ture, the chlorophyU-granules traversing along a straight and thin septum (if the position is favourable) appear to project into the neighbouring cell, seem- ing to pass directly under the line of the ceU-waU. Smaller particles will apparently travel within the substance of the cell-wall ; and in case of a boundary or single cell, or in unicellular plants, if the surrounding water has nearly dj'ied up, the rim or prism remaining round the exterior (by the way, just the conditions under which Mr. Western made his obsel'^^ation) causes irregular refracted images of the particles of protoplasm to appear outside the cell, bearing such a remarkable similarity to external cilia, that the passing shadows may even be mistaken for currents in the water." Besides the incomplete rotation or circulation of the contents just con- sidered, there is an active bustling sort of movement of minute granules within an apparent globular Tesicle situated at each end of the elongated 10 GENEEAL HISTORY OF THE INFUSOEIA. fronds of some Desmidiese, e.g. of DocicUum and of Closterium. The vesicles in question are known as the '' terminal globules," or chambers, and would appear to be actually invested with a membrane, and therefore distinct en- closed sacs. In Closterium rostratum and C. setaceum, the collection of moving granules is at a distance from the extremities, and apparently not contained •within a vesicle. In all species exhibiting terminal globules these structures appear in their earliest stage, but disappear when they are dried. Ehrenberg imagined the supposed retractile locomotive organs to be fixed to these globules, and that the granular movement within them was no other than that of the bases of these organs. Mr. Varley described the chambers as having contractile walls, and the molecules as transparent spheroids mea- suring from l-20,000th to l-40,000th of an inch, sometimes escaping from their chamber and circulating vaguely and irregularly between the periphery of the gelatinous body and the sheU, Mr. EaLfs regarded the terminal glo- bules to be pecuHar to the Closterina ; yet their contained granules seemed to him '^ to differ in no respect, except in position and iminterrupted motion, from other granules in the same frond." He once saw the motion continue after their escape from the cell. Mr. Osborne (oj>. cit. p. 235) behoves the granules to be cihaiy bodies. He writes : "At the extremities of the green matter there are certain bodies acting with a ciharj- movement within what has been called a chamber, lying towards the point of the membranous sac ; certain bodies, apparently of the same kind, separate from the endochrome in a small mass, appearing at the extreme end of this so-called chamber, or at the side close to the end ; these also impart a ciliaiy movement to the water within the sac around them." He adds (p. 239) : " When the endochrome is of a rich dark green, I find the chamber at the extremity very plain and defined, with its cilia veiy active .... As the endochrome gets of a hghter colour. . . .the chamber becomes smaller and the ciha are barely seen." At p. 236, Mr. Osborne fiu'ther states, " The loose bodies seen in the chamber of Closterium Lunula have very generally cilia, and are, I behove, zoospores ; loose pieces of endochi^ome are sometimes brought round in the current, but these are easily distinguished. I have never seen anything like true cyclosis, i. e. molecules in circular movement, within the so-called chamber." Of the purpose of the moving granules vrithin the tenninal globules, the prevaihng notion is that they are zoospores. Meyen hkened them to the " spennatic animalcules of plants ;" and, as above noted, Mr. Ralfs saw them move about as do the zoospores of other Algae when freed from the enclosing capsule and frond. So far as we can gather from his remarks, Mr. Osborne also inclines to this opinion, which is likewise supported by Mrs. Thomas (T. M. S. 1853, p. 37). We are sony that we can present no more definite views concerning the nature, characters, and purpose of the terminal globules than those comprised in the foregoing extracts. We find no similar globules in other Algae, and therefore obtain no guide from analogy ; indeed such structures seem to be peculiar to the elongated Desmidieae — to the genera Closterium, Penium, and Docidium ; we must consequently look to subsequent research to elucidate the question. (See Appendix at end.) Another sort of internal movement, more prevalent among the Desmidieae than that last considered, is " the sivarming motion" so called, seen either at one or two parts of the frond when mature, or other^dse throughout its con- tents. Having once commenced, it never ceases, but extends itself, and induces changes in the nature, appearance, and colour of the endochi'ome ; for this loses its grass-green colour, acquires the autumnal yellowish or reddish-broTNTi tint, and a finely granular aspect. When the granules burst OF THE DESMIDIE^. 11 through the openings of the suture between the valves, they escape to a distance and still keep up their active movement. In the genus Cosmarium this phenomenon is frequently and readily ob- served. Mrs. Thomas, in her interesting obser\-ations on Cosmarium mar- garitiferum (T. M. S. 1855, p. 33), has detailed the following appearances : — " In each half (she wiites) the centre was occupied by a vesicle (as it appeared) filled with moving granules, while smaller vesicles were at the four sides (I. 2). The granules did not appear to circulate through the plant, but kept to their own place, which was either a bag or cavity — I could not decide which." In another example " the granules were swanning over the whole plant." These peculiar movements of the granhles are not restricted to this tribe, but are known to occur in many genera of Algae. Their piu'pose seems con- nected with the reproductive process. Mrs. Thomas {he. cit.) refers to it as in some way related with the formation of sporangia ; whilst Mr. Ralfs, who speaks of the swarming particles as " zoospores," confesses himself perfectly unacquainted with theii' subsequent histoiy, although he coincides with Pro- fessor Harvey in regarding the phenomenon of swarming as a " strictly vege- table pecuharity." Eepeoduction of Desmtdie^. — This function presents itself under two phases, the end of one of which is to multiply or perpetuate the individual plant, whilst that of the other is to reproduce the species. The fonner pur- pose is attained by the process of fission, the latter by that of the development of sporangia, and, it may be, by the swarming of zoospores. The act of self-division is frequently observed, and is in all respects the same process as in the cells of other Algae, or indeed of any plant. Analogy, and not, indeed, dii-ect obsei-vation, suggests as necessary the initiative action of a nucleus to precede the constriction of the soft lining sac of the lorica, i. e. of the primordial membrane, which is next followed by that of the harder external coat. The proceeding is varied, in some non-essential particulars, by the figiu'e of the fronds, and also by the cii'cumstance of its own completeness or incompleteness. !Mr. Ralfs has well described the fission of Euastrmn (op. cit. p. 4). The narrow connecting band between the two segments of the frond lengthens and is " converted into two roundish hyaline lobules ; " these, though at first veiy minute, increase rapidly in size, and exhibit from their origin the deep constriction characteristic of the mature fronds. The advancing growth of the interposed new fonnations necessarily pushes fiu'ther asunder the original segments, which finally become disconnected, " each taking with it a new segment to supply the place of that from which it has separated .... At first the new portions are devoid of colour, and have much the appearance of condensed gelatine ; but as they increase in size the internal fluid acquires a green tint, which is at fii^st very faint, but soon becomes darker ; at length it assumes a granular state. At the same time the new segments increase in size and obtain their noiTaal figui'e ; the covering in some species shows the presence of puncta or granules, and, as in Xanthidium and Staurastrumj the spines and processes lastly make their appearance, beginning as mere tubercles, and then lengthening until they attain their perfect fonn and size. Complete separation, however, often occiu's before all these details of develop- ment are complete (II. 11, 24, 26). This singular process is repeated again and again, so that the older segments are united successively, as it were, with many generations." Illustrations of this act are fiu-nished, in the case of two species of Cosmarium, in the appended jDlates (I. 4 ; II. 26), to which the above account will be found equally well to apply. ^•In Sphcerozosma the same changes take place (I. 11), and are just as 12 GENERAL HISTOEY OF THE INEUSOlilA. evident; but the cells continue linked together, and a filament is formed, which elongates more and more rapidly as the joints increase in mmiber. This continued miiltif)lication by division has its limits ; the segments gradually enlarge whilst they divide, and at length the plant ceases to grow; the division of the cells is no longer repeated ; the internal matter changes its appearance, increases in density and acquires starch-granules, which soon become nume- rous ; the reproductive gi*anules are perfected, and the individual perishes. In a filament the two oldest segments are found at its opposite extremities ; for so long as the joints divide, they are necessarily separated further and further from each other. Whilst tins process is in progress, the filament in Sjohcerozosma consists of segments of all sizes (1. 11) ; but after it has reached matuiity there is httle inequahty between them, except in some of the last- formed segments, which are permanently smaller. The case is the same with those genera in which the separation of the cells is complete .... It is obvious that the new portions must arise from the whole of the junction-margin of the original valves ; consequently when the junction occupies only a part of the breadth, the new portion will be naiTower than the old ; but when the junction of the valves is as broad as the cell, the new poiiion will from the beginning be of the same breadth," and will remain undistinguishable by its size when fission is complete. Mr. Balfs goes on to say that, " when the ceU is oblong, or only rounded at the extremities, the process, though similar, is less evident ; the cell at first seems merely to elongate (II. 11), until it attains nearly twice its ori- ginal length, when the division commences, and the rounding of the new ends becomes apparent. The tapering cells present but little diiference, for the separation takes place before the extremities are fully developed ; sometimes these cells separate obhquely, as in Sjpirotce7iia.'^ The mode of self-division in Closterium has been illustrated by the Rev. Mr. Osborne (J. M. 8. 1854, p. 57), from whose account we abstract the fol- lowing particulars : — '^ I have (he says) watched for hours the process of complete self-division ; one-half of the frond has remained passive, the other has had a motion from side to side, as if moving on an axis at the point of juncture ; the separation has become more and more ardent, the motion more active, until at last, with a jerk, one segment leaves the other," each having one extremity — the one newly formed along the line of junction of the two segments — much more obtuse than the other. '^ The circulation of the con- tained globules for some hours previons to subdivision, and for some few hours afterwards, runs quite round the obtuse end of the endochrome." Previously to complete separation each segment begins to show a central constriction of its endochrome, which in due time extends across the new frond, and constitutes the median clear space or band. A true reproductive act is presented by the act of conjugation, or coupling of two fronds, and by the resultant development of a sporangium (II. 6, 8 ; XYI. 11, 12, 13, 14). This process consists in the apposition and subsequent intercommunication of the cavities and contents of two cells, which may be free, or otherwise, members of a chain or filament. It is an act not peculiar to the Desmidieae, but common to them along with the Diatomeae and Con- jugat£e. " In the family Conjugatae (says Mr. Ralfs) the cells conjugate whilst still forming parts of a fidament ; but in the Desmidiese the filamentous species almost invariably separate into single joints before their conjugation, and in most of the species the valves of the cells become detached after they are emptied of their contents." To bring about the necessary apposition, it is usual for the conjugating cells to expand or bulge out on those sides which are to come into union ; and whilst this is proceeding, the vesicles or globules OF THE DESMIDIEiE. 13 increase much in number, and, together with the granular contents, become aggregated about the conjugating part. When contact is complete, an absorp- tion of the opposed walls of the two cells takes place, or the suture of each opens, the endochrome from both is discharged and intermingled, and an orbicular green granular mass, enveloped in a mucous sheath thrown out around it by the conjugating cells, is produced. When the process has pro- ceeded thus far, the original valves are more or less completely emptied of theii' contents, lose their vitality, and are sooner or later detached, and float away from the sporangium developed. The foi-mation of a sporangium by conjugation occupies no great time. Indeed, in the case of Closterium Ehreyibergii, the Eev. W. Smith tells us that " the discharge of the endochrome and the fomiation of the sporangia are accomplished with much rapidity, and may often be seen taking place in the field of the microscope ; the whole operation not occupying more than a few minutes .... During the formation of the sporangia there appears to be a second development of mucus in the form of rings around the reproduc- tive bodies ; this is probably only the eftect of the pressure produced by the growth of the sporangia on the mass of investing mucus." This act of conjugation admits of slight variations in character, determined by the form of the conjugating cells, and by other circumstances pecuhar to the tribe, family, or genus in which in it occurs. In the filamentous species of Desmidieae, the joints, as before noted, usually become separated before their conjugation ; and in most instances the old valves left empty after the act of conjugation are almost immediately detached from the sporangium ; but in a few species they persist some time afterwards, e. g. in several of Penium. In Didymoprium the separated joints, on conjugating, unite by means of a narrow process pushed out from each, and often of considerable length ; through this the endochrome of one cell is transferred into the other, and thus the spoi-angium is produced within one of the two cells, just as in the Conjugatae. In Staurastrimi and Micrasterias the contents of both fronds are discharged into a delicate intermediate sac or bag, which gradually thickens, produces eminences, and at last forked spines (II. 25). Again, in Tetmemorus, " the process of foiming the sporangium (says Mr. Ealfs) is interesting, as it exhibits a striking similarity to the change during the formation of similar bodies in Stcmrocarpus among the Conjugatae. In Staurocarpus, after conjugation, a subquadrate ceU is formed, within which the endochrome is collected. The latter is at fii'st of the same figure as the ceU, but in at least one species is at length condensed into a compact globular body, and in every species the cell with the contained sporangium finally separates from the filaments with which it is connected. In this separate state I can discover no character by which to distinguish the sporangium of Tetmemorus from one belonging to a species of Staurocarpus.''^ To quote the same authority, — ^^In Penium Jenneri the conjugating fronds do not open and gape at the suture, as is usual in the Desmidieae, but couple by small and distinct cylindrical tubes like many of the Conjugatae In Closterium two fronds unite by means of projections arising at the junction of the two segments, and then the newly-formed portion continues to enlarge until the original segments are separated by a cell of an irregular figure (II. 5, 6). The contents of the fronds being collected in this cell become a dense seed-like mass, which is sometimes globular, resembhng the sporangium of Mougeotia, and sometimes square, like that of Staurospermum. The newly- formed cell is thinner and generally paler than the segments of the fronds ; in some species it looks like a prolongation of the segments, and in others these are so loosely attached that their connexion is scarcely perceptible. 14 GENERAL HISTOEY OF THE INFUSORIA. The coupling of the fronds generally takes place from the convex margin, but may occur on the concave, or even the convex margin of one frond may couple with the concave of the other." The Rev. W. Smith (A. N. H. 1850) represents the conjugation of Closterium Ehrenhergii to be peculiar (XYI. 11, 12, 13, 14). The fii'st phenomenon (he tells us) is an alteration in the granular condition of the endochrome. This, from a light yellowish green, passes to a much darker shade, and the larger granules, or '' diaphanous vesicles " of Ealfs, which were originally few in number, and arranged in a somewhat irregular longi- tudinal series (XVI. 10), become exceedingly numerous and pervade the entire frond. While this change is about taking place, the fronds approach in pairs, approximating by their concave surfaces, and finally coming into such close neighbourhood that their inflated centres are in contact and their extremities slightly overlapped (XYI. 11). In a short time, probably in the course of twenty-four hours, a remarkable change takes place, both in the appearance and condition of the fronds ; a mass of delicate mucus is secreted around the approximated fronds ; these remove to a little distance from each other, undergo " self -division," and present altogether an irregular oval figiire, the outline of which is formed by the periphery of the mucus, the four divi- sions of the fronds being placed in the middle in a somewhat quadi'ilateral manner (XYI. 12). Duiing the progress of cell-division, the internal mem- brane of the cell-wall becomes enlarged at the suture or line of separation, and projects in the form of an irregular cone, with a blunt or rounded apex forming a beak, whose side view presents a triangular outhne. This beak becomes fiUed with endochrome, either by the dilatation or increase of the contents of the half-frond, and the divided frond assimies the appearance of one with two unequal segments (12), being what M. Morren calls '' a Clos- terium of two unequal cones." On these membranous expansions, at the con- cave sui-faces of the fronds, and close to the original sutm-es, there appear, almost simultaneously with the fonuation of the beaks, two cii'cular projec- tions, which, rupturing at their apices, give egress to the delicate sacs which enclose the endochrome, and which, drawing with them their contents, and meeting with the endochrome sacs emitted through similar projections from the other half-fronds, form, by their connexion, irregular masses, which quickly consolidate and assume the appearance of perfectly circular, smooth, dark-coloui'ed baUs, the sporangia of Ralfs and seminules of Morren. Lastly, we may add, that Siebold {J. M. S. 1853, pp. 118, 119) remarks that the conjugation in Closterium Diance, C. lineatum, C. striolatum, C. setaceum, &c., differs from that in C. Lunula, G. rostratum, and other members of the family, by dehiscence at the central transverse suture, and the consequent coalescence of the contents of the two cells into a rounded or angular mass, — an observation which tallies with the account presented us by Mr. Ealfs. Braun (On Rejuvenescence, B. S. p. 286 et seq.), speaking of conjugation generally in simple cells, gives an elaborate view of the Variations the phe- nomenon exhibits, and arranges them under several heads. Thus among the Desmidiese " the conjugating cells unite with participation of the external membrane, [and] the reproductive cell is formed [either] through contraction of the contents clothed by the internal cell-membrane, [or] out of the mere contents as a new cell inside the mother- ceU." But in the majority of the Desmidieae, " the conjugating cells, after dehiscence of the outer membrane, unite through the inner ; the reproductive ceU is formed out of the mere contents as a new cell inside the conjugation-cell." By the first-named mode, " the formation of the reproductive cell is ... . not a direct result of the conjugation, but it is formed subsequently in the interior of the con- OF THE DESMIDIE^. ' 15 jugation-cell, in the strongly expanded isthmus of this. The delicate internal membrane, mth the contents enclosed by it, draT\ang itself out of the extre- mities of the double cell, forms a seed- cell, at first cniciate, four-lobed, then bluntly quadi^angular, and finally globular, clothed by a many-layered thickened membrane "within the persistent four-horned conjugation-cell. From Ralfs's representation, this is most probably the way in which the pro- cess is to be understood in Cylindrocystis (Penium) Brehissonii.''^ The second mode, when the union of the isolated cells is also lateral and parallel, is exemplified in CJosterium Lunula, in which, according to Morren's express statement, thi-ee different membranes take part in ^ the formation of the canal of union, — an inner and an outer cell-membrane, and a membrane (the primordial utricle) immediately enclosing the green mass. The glo- bular reproductive cell formed in the connecting canal is an active gonidium, which begins to revolve even while in the canal, and soon breaks through the gelatinously-swollen membrane of the latter. Very often two approximated individuals divide again and conjugate before they have completely separated, whence result conjugated double pairs. The third scheme of conjugation, the most widely extended, is itself reduced by Braun to two principal secondaiy varieties, and to several sub- sidiary ones. Thus conjugation takes place either in a parallel position or in a crossed (decussate) manner. The former is peculiar to the Closterina ; the latter is met with in Euastrum and allied forms, and also in many genera formerly united with Desmidium. The modifications, in various species, of these plans are well explained in Braun's work, to which we would refer for particulars, as well as for an elucidation of the production of a " really double spore (not two-lobed, as Ealfs terms it) " in Closterium lineatum. The next question which presents itself is, whether the product of con- jugation is to be esteemed a spore or a spore-case, i. e. a sporanyium. That the latter is its natiu-e appears pretty clear, and is assumed as a fact by Mr. Ralfs. This authority observes: "The sporangia I consider capsules, and this view seems to be confirmed by the experience of Mr. Jenner, who states that the coveiing of the sporangium swells, and a mucus is secreted, in which minute fronds ai)pear, and by their increase at length rupture the attenuated covering." In this opinion Siebold coincides ; and the Rev. W, Smith {A. N. H. 1850, p. 4) represents, on the authority of Mr. Jenner, the biu-sting of a sporangium of Closterium acerosum, and the development of young fronds from its contents. Braun, in his philosophical treatise (oj). cit. B. S. p. 133), remarks of the products of conjugation in the Desmidieae, that " they do not pass, Hke the swarming-cells of the PalmeUaceae and the reproductive cells of the Dia- tomaceae, directly and by uninterrupted growth into the primaiy generation of the new vegetative series, but persist for a long time in a condition of rest, during Avhich, excepting as regards imperceptible internal processes, they remain wholly unchanged. To distinguish these from the direct germ- cells (gonidia), I shaU call them seed-cells (spores). The development of these spores has not yet been observed ; but it may be assumed as certain, that they do not pass as such into the primary generation, but produce this at the period of germination, by an internal transformation of their contents, and bring these to light as a new generation with a dehiscence of the old en- velope. Certain early conditions observed in Closterium and Euastrum, namely fanuhes of unusually small individuals, enclosed in transparent colourless vesicles, render it even probable that in certain genera of Desmidie«, a number of individuals are produced from one spore, by a formation of transi- toiy generations occiUTing already within the spore. The enclosing vesicle 16 GENERAL HISTORY OF THE INFUSORIA. is probably the dissolved and swollen-iip internal cell-coat of the spore, which holds the young individuals combined for some time after the outer coat of the spore has been throvrn off." Although Braun has, in the preceding account, made use of the teiTn ''spore'* to express the conjugation-product, yet, in the veiy admission that, in those Desmidieae in which only we have any clue to the subsequent history, it produces, not a single indi\idual, as does a spore commonly so called, but a multitude, he essentially agrees with Mr. Ralfs, who prefers to call the body a capsule. We may quote Mrs. Thomas in support of the same view ; for she considers the s]X)rangium a capsule, or {T. M. S. 1855, pp. 36, 37) " the winter casing of a large nimiber of j^oung plants which escape fi'om it by rapidly knocking against its walls, when these have been loosened by spring- warmth, or which grow up as the waUs gradually decay in the midst of slimy gelatinous masses." In proof of this oj)inion this lady appeals to the immense increase in the number of plants seen in the spring beyond what can be ex- plained as the result of self-fission. In her opinion the sporangium is a capsule (I. 8, 9) filled with zoospores similar to those moving granules, supposed to be such, seen mthin the fuU- grown plant, capable, when their fitting time comes, of filling the waters with their countless progeny. In these accounts there is a pervading harmony ; and the truth seems to be that, by the formation of a sporangium, provision is made for the per- petuation of the species through the "wdnter, when the large majority, at least of adult plants, have ceased to exist. The phenomenon is clearly analogous to that of the foimation of seeds by herbaceous plants, or of ova by insects and other animals, when the cycle of existence of the parent being is complete, or is put an end to by unfavoiu-able external circumstances. Braun has expressed the sequence in the phases of existence in the follow- ing technical language {R.S. p. 133): '' In the Desmidiaceae, the Zygnemaceae, and in Pahnoglcea, the transitional generation is divided into a double one, since the last generation does not pass directly into the fii^st, but the first generation of the succeeding cycle is produced as a new structure in the ger- mination ; so that we have here to distinguish three kinds of generation of cells, — the commencing generation, the concluding generation, and the intermediate vegetative generations." The last-named is represented by the process of self-fission, which takes place in the perfect plant, and is con- tinued through a long series of individuals. Between its firet appearance and its ultimate development, the sporangium of Desmidieae undergoes a progressive series of changes ; at first it is pale and homogeneous, but soon gets granular, acquires a gradually deepening green colour, and presents vesicles and globules in large number. The enve- lope, at first very dehcate, augments in thickness, and becomes lined by others, whilst its surface either remains smooth or becomes granular, tuber- culated, or spinous, and the spines themselves in many instances forked or branched (II. 15, 22, 25, 30, 34). Simultaneously with these changes the integument increases in density, and together with its processes acquires considerable firmness and toughness. Moreover, as it advances in age it usually assumes a reddish-brown colour; when this has happened, the sporangium and contents may be presumed to have reached maturity. Mrs. Thomas (op. cit. p. 35) thinks she encountered a mature sporangium of Cosinarium margaritiferum in the shape of a many- coated ball filled with granules in the same rapid motion as observed in the full-grown Cosmarium (I. 10, 11). " The similarity of the movement (she says) attracted my attention; and I also saw that in one part the enclosing membrane appeared OF THE DESMIDIE^. 17 thinner, as if giving way at that spot. On the third morning the membrane had broken and the granules escaped, leaving the nearly emptied case" (I. 12). Inasmuch as a sporangium may pass successively from a smooth to a spinous condition, it follows that the transitional stages of one species may be mistaken for the final stage of another ; hence a difiiculty in determining to what plant detached scattered sporangia may belong. It is only, indeed, when these seed- capsules occur in company with the fronds producing them that we are enabled to pronounce decisively by what species they are generated. As the foregoing account of conjugation and sporangia passed through the press, we met Tvdth the valuable paper of Dr. Hofmeister on the propagation of the Desmidieee and Diatomeae, translated by Prof. Henfrey from the Report of the Natural History Society of Saxony for 1857. This commu- nication tends to clear up the questions of the nature of the sporangia and of the relation of theii' contents to the propagative process. The conciseness of the description renders abridgment undesirable ; and we accordingly present it (so far as it relates to the points in question) as it stands in the Annals of Natural History (1858, i. p. 2) :— " The conjugated indi\iduals of Cosmariwn tetraojjhthahmm displayed exactly the behavioui* which Kalfs has represented and Braim described of those of Cosmarium margaritiferum. The Cosmrtr/a which had commenced the conjugation process appeared cracked apart at the constricted place in the middle. Into each of the halves of the tuberculated cell- coat of the two mother-indi\'iduals extended a continuation of the membrane of the conju- gation-ceU. This smooth membrane completely lined the interior of the tuberculated half-shells. The contents of the conjugation -cell revealed no definite arrangement ; they were mostly accumulated in the middle into an irregularly-shaped ball ; in other cases separated into several such balls, part of which extended even into the split haK-sheUs of the mother-cell. With these conjugated individuals, in the same fiuid, occuiTed (very sparingly) par- ticular specimens which bore, in the middle space between the two separated half- shells, a broad, delicate- walled utricle, the circumference of which about equalled that of the two half-ceUs taken together. The arrangement of the cell- contents in the primary portions of the cell did not appear essentially altered ; the contents of the intermediate expansion consisted of a thick coat upon the wall of granular protoplasm "svith sparingly-scattered chlorophyll. This condition is probably that which immediately precedes conjugation, originating by excretion of new cellulose at the deepest part of the constric- tion, after the cracking of the membrane and separation of the primary halves of the cell, exactly as in normal cell- division, from which this process can only be distinguished by the omission of the formation of a septum at the narrowest part of the isthmus. Similar phenomena have been observed by Niigeli in Cosmarium crenulatum, and by Mrs. Herbert Thomas in Cosmarium margaritiferum (scarcely specifically distinct from C. tetraophthalmimi), only that here the intermediate piece of the Alga did not conjugate with the similar piece of another individual, but, producing tubercles on its outer surface, continued the vegetative life. " In other conjugation-cells there lay, in the middle part of the conjugation- cell, a globular ceU enveloped in a rather thick membrane, of gelatinous aspect, and smooth on the outside (the spore). No intermediate stages could be found between this and the previously- described condition. Experiments, in which an attempt was made to obtain a completion of- the less-advanced conjugation under the microscope, all failed. Apparently the conjugation- ceU is exceedingly sensitive to any external injury, especially to contact with 18 GENERAL HISTORY OF THE INFUSORIA. foreign bodies. Very probably the contents, in the above-described cases, were ali'eady abnormally altered, and incapable of further development. *' In other conjugation- cells the young spore displayed a still thicker mem- brane, covered on the outside with tiimcate- conical elevations, in which membrane could be detected a composition of two colourless layers. The outer of these layers remained clear and transparent even in the advance to maturity. Its elevations became developed into rather long spines, which forked at the apices into two or four branches. The deeper- seated layer of the spore-membrane meanwhile assumed a dark-brown colour. By rolling under the covering-glass, the tough, colomiess, outer layer may be readily stripped from the inner, more brittle, brown layer ; then the latter appears covered on its outer surface with slight elevations, similar to those which first appeared upon the yoimg spore. The brown layer of the spore-coat encloses a thii'd, delicate, coloiuiess layer (perhaps the primary membrane of the spore) which immediately envelopes the cell-contents. *' At the beginning of July, the green contents of all the spores appeared conglobated into a spherical mass with sharp outlines, which, lying free in the middle part of the cell, nowhere touched its internal Avail. Three weeks later, in many of the spores these contents appeared separated into two flattened ellipsoidal masses; when I cracked the cell by careful pressui^e, I was sometimes successful in diiving out one or both of the masses of contents in an uninjured condition. They could then be recognized beyond aU doubt as primordial cells; bodies destitute of a solid ceU-membrane, having a thin coat of protoplasm which * bubbled ' out in water, to which adhered a thick investment, coloiu-ed bright green by numerous imbedded chlorophyll-granules, sm-rounding a central ca^-ity filled with transparent fluid. The fluid contained in the spore in which the two primordial cells were immersed, was not colouiless, but rendered tui'bid by numerous im- measui-ably smaU granules exhibiting molecular motion. In August each of the ellipsoidal primordial cells had divided into two globular cells, of similar character to the mother-cell. Towards the end of September, some of the spores exhibited another such division, so that they then contaiaed eight, not globular, but strongly flattened primordial cells. Most, however, passed through the winter-rest imchanged, during which the majority died. At the beginning of April of the next year, the spinous, transparent, outermost layer of the coat was more or less completely decayed on all the spores, even on those which were still to be recognized as living by the vivid green colour of the contents. AU the spores still alive contained at least eight, many six- teen daughter-cells, all very strongly flattened, almost discoid. In several spores the outline of the daughter-cells was no longer cu^ular, but displayed two shallow lateral notches. The still -existing, brownish, inner layer of the spore-coat was now seen to be softened ; it no longer exhibited its former brittleness, and it was difficiilt to crack it by pressure. Daughter-cells whose lateral constrictions were most strongly marked, were about half as large again as the circular, whose diameter about equalled that of the isthmus of the former, and they almost entirely filled up the cavity of the spore. When these were pressed out from the crushed spore, their form and size agreed almost exactly with that of Cosmarium Meneghinii. " I saw similar phenomena in the spores of Cosmarmm undulatum (Corda), in which the investigation is rendered very difficult by the minute size, and which, cultivated for some months in my room, entered abundantly into con- jugation. In this, again, I observed the contraction of the green contents of the cell into a globule occupjdng the central part ; the division of this ball into two, foiu', eight, and sixteen spherical masses ; finally, the transition of OF THE DESMIDIE^. 19 these daughter-cells of the last generation from the form of cii^cular lenticular bodies into two-lobed ones like the mother-plant. Here the young Cosmaria, whose diameter amoimted to scarcely ith or ith of that of the mother-plant, were set free by the very gradual solution of the membrane of the spore. A similar process very probably occurred in Cosman'um tetraoplithcdmum, but could not be observed there, from the circumstance that aU the materials had been used up in the investigation. '' These facts place it beyond doubt that the contents of the spores produced by the conjugation of two individuals of Cosmarium, are transformed by repeated binary division into eight or sixteen daughter-ceUs, which assume the form of the mother- cell, and finally become free by the solution of the wall of the spore. Such behaviour of the spores had indeed been rendered pro- bable before, by the discovery of the vesicular structure observed by Focke and Ealfs, which enclosed a nimiber of small Chsteria, for the most part beginning to divide. But the certainty which can only be given by direct observation of the development was altogether wanting. '' The development of four daughter-cells in the interior of spores produced by the conjugation of tvv^o individuals (with participation of the whole of the cell-membrane), has been demonstrated by Alex. iJraun for the Palmellacean Pahnoglcea macrococca, Kiitz. (?)." Sporangia are the only portions of Desmidieae of past eras which have been preserved to us in a truly fossil condition. Ehrenberg discovered certain orbicular and spinous bodies in flint, some of which he referred to the genus Xanihidium among the Desmidiese, and others to Pyxidicula among the Dia- tomese. However, as Mr. Ealfs remarks (p. 13), this association is, no doubt, erroneous, since in tnie Xanthidia the cell is compressed, bipartite and bi- valved, whilst in these fossils it is globose and entire, and there can be no doubt that they are fossil sporangia (XYII. 506 to 515). To quote ]\Ii\ Ralfs's account (p. 13) — " The fossil forms vary like recent sporangia, in being smooth, bristly, or furnished with spines, which in some are simple, and in others branched at the extremity. Sometimes, too, a membrane may be traced even more distinctly than in recent specimens, either covering the spines or entangled with them. Some writers describe the fossil fonns as having been silicious in their living state ; but Mr. Williamson in- forms me that he possesses specimens which exhibit bent sj^ines and torn margins, and thus whoUy contradict the idea that they were silicious before they were imbedded in the flint." Another mode of propagation is presumed to take place by means of the active molecules seen within the fronds of Desmidieae — in other words, by zoospores, as happens in many families of Algae. M. Morren advanced this notion, and imagined the minute particles which he denominated " propa- gules," to be at once transformed into small fronds. Mr. RaKs countenances the opinion so far as to say that the escape of the granular contents of the mature frond is probably one mode of reproduction. He, however, likewise regards (as Prof. W. Smith observes) the swarming of the granules as identical with the movement of the zoospores, and confesses to his ignorance of the history of the motile granules after their escape. But we perfectly coincide with Prof. Smith that the swarming of the granules within a mature frond is in most cases " a disturbance attendant upon the decay of the granular mass," and not a phenomenon connected with reproduction. Still our acquaintance with the swarming granules, particularly after their escape from the frond, is so imperfect that it is useless to speculate on their func- tional purpose. Ehrenberg, to carry out his hypothesis of the animal nature of Desmidieae, c2 20 GENEEAL HISTORY OF THE INFUSORIA. and to assimilate their organization -w^ith that he attributed to other Poly- gastrica, represented the larger oil-vesicles and starch-grains to be either stomach-sacs or ova, — at one time the one, at another the other, in a purely arbitrary fashion. Some again of the more transparent or refracting vesicles were, with no shadow of reason, called fecundating or spermatic glands. An attempt to show the error of such an hypothesis of internal organization would be futile and uncalled for at the present day. Habitats, Distribution, Appearance in Masses, and Vital Endoa\tvients OF Desmidie^. Vegetable Nature and Affinities. Mode of Collection. — The Desmidieae live in fresh water, in ditches and ponds, and rarely in streams, except when these are very sluggish. They will often rapidly aj^pear in a recent collection of water, and are not destroyed when the pool is dried up, as their reappearance immediately after a shower proves ; nevertheless, ponds which do not dry up dui^ing the summer, and pools in boggy ground, are richer in these organisms, provided the water remains sweet. To quote Mr. E-alfs's experience — " The Desmidieae prefer an open country. They abound on moors and in exposed places, but are rarely found in shady woods or in deep ditches. To search for them in turbid water is useless ; such situations are the haunts of animals, not the habitats of the Desmidieae, and the waters in which the latter are present are always clear to the very bottom." They no doubt inhabit the fresh waters in all parts of the globe, for they have been found wherever sought in each hemisphere. Still the several genera and species are not universal, for, as in the case of higher plants, some species are peculiar to one country, others to another ; and in the same country the presence and prevalence of any one species wiU be determined by the physical features of localities, by the nature of the soil, and the like. The distribution, however, of the Desmidieae has not been inquired into so fully as to justify any attempt to lay down special laws. Oftentimes in smaU collections of water, Desmidieae of the same or of various species and genera multiply to such an extent as to colour the water, and in the case of the filamentous species, to appear in filmy masses on the surface or at the bottom of the pool ; still this enormous multiplication, and the coloration of the water thej^ inhabit, are far less frequent in the case of the family in question than with others — for instance, the Eugleneae, or even the Diatomeae. Mrs. Thomas {op. cit. p. 36) has described the green masses formed by Cosmarium, which duiing summer and autumn " would float to the surface, rapidly disengaging oxygen as the sun shone on them, and sinking again to the bottom with the coolness of the evening. Later in the year, masses would adhere to the inner surface of the bottle in the form of a thin pellicle, or collect in slimy masses, which appeared to dissolve with the warmth of the coming spring. The green colour changed to that of a reddish yellow; and it might have been thought that all was dead, did not the microscope show the same beautiful green, both in young and fiill-groAvn plants, together with much bright red and brown, apparently the casings of the sporangia Large Cosmaria still in active motion (the remains of the mature growth of the pre- ceding summer) lay imbedded in the mass, when a small portion was separated for microscopic observation, as well as clusters of young ones (I. 13, 14). When the bottle had remained more than a year untouched, except for change of water, these masses increased in leathery hardness ; green life was not extinct, but became feeble in colour, and too much changed to warrant further observations, while a small portion placed in another bottle, and more freely exposed to the light, multiplied with great rapidity." • Many of the vital endowments of the Desmidieae have already been de- OF THE DESMIDIEiE. 21 scribed: we have noted their process of reproduction and of growth, the molecular and circulatory movements within them, their slight locomotive power ; but besides these, there are others requii'ing to be mentioned : for instance, their powers of secretion are highly pronounced ; — the production of firm envelopes to fronds and sporangia ; the formation of starch-grains, of colouring matter, and of oil-globules within ; the exhalation of oxygen from the surface, — a respii^atory act ; and lastly, their ability to resist decomposition. The Desmidieae serve as food to many sorts of small aquatic animals, to the Rotifera, to various Annelida and small Ciiistacea, and to the fi^eshwater Mollusca. They are supposed also to preserve the freshness of the water, and by the oxygen they exhale, to fiu'nish the vital air necessary to the respii'ation of the aquatic animals found Avith them. They are subject to destraction not only in the way of supplying food to animals, but also by disease. For instance, Cohn has shown (Enhu. d. mih\ Alg.) that the Closteria are attacked by a microscopic unicellular fimgus, called Ohytridiiim, the spores of which affix themselves on the integument, and on germinating, penetrate the cavity of the frond by their delicate fibres, and induce a pro- gressive breaking-up and absorption of the contents, until nothing but the empty hull of the plant remains. Mr. Ralfs has the following remarks (p. 13) : — '^ In all the Desmidieae, but especially in Clostenum and Micrastenas, small, compact, seed-like bodies of a blackish colour are at times met "with. Their situation is uncertain ; and their number varies from one to four. In their immediate neighboui^hood the endochrome is wanting, as if it had been requii^ed to form them, but in the rest of the frond it retains its usual character and appearance. I cannot satisfy myself respecting the nature of these bodies ; but I believe them to arise from an unhealthy condition of the plant, or else to be parasitic." With respect to the views expressed in this extract, we are disposed to think Mr. Ralfs right in his conclusion that the black bodies he met with were parasitic ; and on comparing his account ^yith. the figures and description of the parasitic Chytridium in Cohn's memoii^ (Enhv.), it seems to us highly probable that the globules referred to were no other than the spores of that microscopic fungus. Tor a long time discussion was rife respecting the animal or the vegetable nature of the Desmidieae. That it was the former was the prevailing notion until within the last few years, when the improvements in the microscope, and the more extended and accurate knowledge of the features of vegetable life in its simplest manifestations, rendered this opinion no longer tenable, and at the present day it may be considered exploded. It is un- necessary, therefore, to go minutely into this question ; for it will suffice to indicate the most striking distinctive characters, especially those which rest upon the affinities of the family under consideration. Those readers who would see the point fully discussed will do well to refer to Mr. Ealfs's admi- rable monograph, to which we, and others also, resort as to a mine, for the materials to build up a histoiy of the Desmidieae. An old argument advanced by Ehrenberg for the animality of the Des- midieae, was, that they had a power of voluntary movement like animals. Without staying to consider the loose and unphllosophic use of this term voluntary, as applied to the motion, whether in the Desmidieae or in the simplest animal existences, its occurrence can be no proof of animal life, seeing that it is exhibited by acknowledged plants, and in a still more marked manner by their spores. Moreover, such movements are doubtless effected by cilia, both in the animal and vegetable world alike, and are likewise determined by the vital processes going on within and also mthout these simple organisms, in relation with external media and ^dth surroimding 22 GENEEAL HISTORY OF THE rNTUSOEIA. physical conditions. Siebold, quoting Nageli's opinions, says (J. M. S. i. p. 120) — " The slow turning, and at the same time rare movements of the Closteria (the genus in which motion is more evident), present no character of spontaneity; these motions are merely the consequence of an active endosmosis and exosmosis, by which the water immediately surrounding the Closteria, and consequently themselves, are put into motion." Again, as Mr. Ealfs remarks, the motive power is less in degree than in the Diatomece. Cell-multiphcation by fission or transverse division, enumerated by Ehren- berg as an animal peculiarity, is now so completely established as a vegetable phenomenon, that it can claim no consideration when the question of the actual affinities of a disputed organism is to be solved. And equally unde- serving of critical examination at the present day is the complex animal organization attributed by the Berlin microscopist to the fronds of Desmidieae. Concerning the apparent sac containing the moving particles in the Closteria and in other genera, regarded by Mr. Dahymple as a vegetable peculiarity, Mr. Ralfs observes, " I confess I am unable to refer to any example in other Algae of terminal globules like those present in the Closteria, but neither can one be found amongst animals ; and if in some respects they have an analogy with organs belonging to the latter, in others they agree better mth vegetable life." On another argument raised, the same author remarks, " The eon- traction of the internal membrane of the Closteria, or the expulsion of their contents on the application of iodine or other reagents, cannot be rehed upon as a satisfactory test for determining their nature ; for the blandest fluids will in some cases (both among recognized Algee and the Closteria themselves) occasion \iolent action." On the other side of the question, the act of swarm- ing, the emission of actively motile germs (presumed in this family), the presence of starch and of chlorophyll, the chemical relations between these substances, and also \\'ith the oily matters formed in the fronds, the exhala- tion of oxygen in sunhght, and the absence of azotized material in their chemical constitution furnish reasons for arranging the Desmidieae with plants. Besides these reasons, others are found in the general form and in the modes of propagation being precisely analogous with those in admitted unicellular Algae. Theu- intimate affinities with Alga3 are shown by the fact that Meneghini and Kiitzing placed Metnsmopcedia among the Desmidieae, and that Braun refers the two genera Scenedesmiis and Pediastrum, included by Ehrenberg himself in the family in question, to the Palmellaceae. The process of conjugation, which has been often appealed to as a characteristic of plant-life, would appear, however, to be, in exceptional cases and under peculiar modifications, also an animal phenomenon, and therefore inapplicable as a test. Meneghini, who contends for the animality of the Diatomeae, has pro- nounced {B. S, p. 497, 1853) the opinion that — " The Closteria and Des- midieae in general are plants, and not animals. In the actual state of science we are compelled to admit this proposition. The organic structui'e, the phy- siological phenomena, the history of their development, the chemical materials they contain, manifest in these beings a perfect correspondence with others, which in every point of view correspond with the abstract idea of a plant. But what they present in common with other beings evidently animal, is merely an appearance, or at the most, a resemblance in external form. Ehrenberg was misled by this appearance, and, guided by this fallacious similitude, thought that he discovered in the Desmidieae the same organic pecuHarities which proved the animahty of other beings." Kespecting the affinities of the Desmidieae, Mr. Ralfs states that, " on one side, they are allied to the Conjugatae (Zygnemeae) by similarity of reproduc- OF THE DESillDIE^. 23 tion, and on the other to the Palmelleae, by the usually complete transverse division, and by the presence of a gelatinous investment. Indeed the relation to the latter is so intimate, that it is difficult to say to which family some genera belong. . . . Some species of Scenedesmus may be allowed to have an almost eqnal claim to rank with either." Again, they are related to the Diatomese by similarity in the reproductive process. In Ehrenberg's system of Polygastria, the Closteria were placed together as a distinct family, imder the name of Closterina, whilst aU the other genera of Desmidieae were ranged as a section of the Bacillaria. This separation, based as it was upon presumed sti-uctural peculiarities, is no longer accepted by microscopists, who cojoin Closterium with the several genera included in Ehrenberg's section Desmidiaeea in one group — the Desmidieae. The division of this family proposed by Mr. Ralfs is made according as — 1. The plant forms an elongated jointed filament (by incomplete division of its cells) ; or — 2. The frond is simjile, from complete transverse division, and distinctly constricted at the junction of the segments, which are seldom longer than broad ; sporangia spinous or tuberculated — rarely, if ever, smooth ; or — 3. The fi^ond is simple, as above, generally much elongated, never spinous, frequently not constricted at the centre; sporangia smooth; or — 4. Cells elongated, entire, fasciculated ; or — 5. The fi'ond composed of few cells, de- finite in number, and not forming a filament. This last section is so exceptional in general characters, and especially in the mode of reproduction, that Braun detaches it from the Desmidieae and associates it with the Palmelleae. In this plan we coincide, and have there- fore treated separately this last section of Mr. Kalfe, comprehending Pedias- trmn and Scenedesmus. Kiitzing {Species Algarum) includes the Desmidieae in his subclass Mala- coPHYCE^, suborder Chamaephyceae. Mr. Ealfs enumerated 20 genera ; viz. — In Sect. 1, Hyalotheca, Didymo- jirium, Desmidium, Aptogonium, Splicerozosma. Sect. 2, Micrasterias, Eiuxs- trum, CosmaHum, Xanthidium, Arthrodesmus, Stcmrastrum, Didymocladon. Sect. 3, Tetmemorus, Penium, Docidium, Clostermm, Spirotcenia. Sect. 4, Aiikistrodesmus {Kliaphidiimi). Sect. 5, Pediastrum, Scenedesmus. When compiling his systematic work, Kiitzing appears not to have seen Mr. Ralfs's monograph, but only his detached papers in the Magazines, and consequently was imable to compare the genera established by the English author ^ith those described by himself. The consequence is that Kiitzing describes several genera not admitted by Mr. Ealfs, who has otherwise dis- posed their representative species, disallowing the supposed distinctive generic character. Nevertheless it seems desirable to enumerate the additional genera of Kiitzing, since several are new (unnoticed by our English authority), and derived from the papers of Ehrenberg or of other obsen^ers, or from his own researches. Those instituted by Ehrenberg were introduced in our last edition. The additional genera are: — Trochiscia (K.), Tetraedron (K.), Pifhiscus (K.), Stauroceros (K.), Polysolenia (E.), Microtheca (E.), Polyedrum (jS'ageh), Zygoxantliium (E.), Phycastrum (K.), Asteroxanthium (K.), StepTianoxcni- thium (K.), Grammatonema (Agardh), Bamhushm (K.), Isthmosira (K.), Spondyhsum (Brebisson), Eucampia (E.), Geminella (Turpin), Mo-nactinus (Corda), Staurogonia (K.), Sphoirastrum (Meyen), Sorastrum (K.), Coelas- trmn (Nageli), Bliaplddium (K.), Oocardium (NiigeH). The value of the several genera instituted and their characteristics form the subject of the systematic historj^ of the Desmidieae by Mr. Ralfs in the subsequent portion of this treatise. 24 GENERAL HISTORY OF THE INFUSORIA. SUBFAMILY PEDIASTEE^. (Plate I. 37 to 69. Plate II. 19, 36, 37.) This includes the genera MicrasteHas and Arthrodesmus of Ehrenberg, the Pediastrum and Scenedesmus of Ealfs, Kiitzing, and others ; and, in addition to these two, to foUow NageU's classification, Soi^astrum, Coelastrmn, and probably also Splicerodesmus. At the time Mr. Ealfs wrote, much nncertainty prevailed respecting what shonld be considered characteristics of species, and what were the modes of propagation ; and it is much to be regretted that, although some of the diffi- culties and doubts are removed, oiu- knowledge of these microscopic Algae is far from complete. Ehrenberg, in harmony mth the general views of organization he had adopted, placed Mm^asterias and Arthrodesmus among the Desmidieae, in the class of Polygastric Infusoria, and described the existence in them of ova, stomach-vesicles, and seminal glands. Yet he was unable to point out one single feature reaUy indicative of their animal natm-e, even locomotion being unrecognized. Indeed, among those who might be inclined to foUow the distinguished Berlin naturalist in attributing an animal nature to most of his Polygastria, the generality would hesitate, in face of the many intimate ho- mologies, structui-al and physiological, between the Pediastreae and admitted AlgaB, to predicate it of that group of organisms. EiGTJRE, Composition, and Contents of Cells. — The individual cells among the Pediastreae do not exist isolated and independent, but are united together in a frond, in determinate number and in a definite arrangement for each genus. In all the species they agree in having a membranous wall like the Desmidieae and PalmeUeae. We confine ourselves, it should be imderstood, in noting the figure of the cells, to the mature phase or stage, which, although but one of several known phases, is that most marked, best understood, and most perfect. The cells of Scenedesmus {Arthrodesmus, Ehr.) (I. 37 to 43) are entire, oval, oblong, or fusiform, with their ends either rounded or pointed. Theii' length is from two to four times theii' width or thickness, and they are spherical on a transverse section. They exliibit no constriction or sutui^e at the middle, neither in their waU nor in theii' endochrome, and in these particulars con- sequently differ fr'om the cells of true Desmidieae. The membrane is fr^e- quently drawn out in the form of straight or ciu'ved spines ; this happens usually only with the ceU at each end of the chain (I. 40, 41) ; but in a few cases, other cells nearest to the outer ones become also armed with spines (I. 42). When this extension to the other cells occui^s, Nageli remarks that the spines do not appear on both the superior and inferior extremities of each cell, but only on the upper of the one, two, or three next within the one terminal cell, and on the lower extremity of the same number within the other terminal cell (I. 42). It is rare that the central cells of the chain are armed, and even when this occurs it is only with short spines. In addition to a spine, or, as may happen, a pair of spines from the upper and lower ex- tremity, the end cells at times have a third spine standing at right angles from their sides (I. 41). The cells of Pediastrum are considerably compressed, so that when aggre- gated they form a flattened tabular stmctui-e (I. 44 to 48, 59 to 69). In figui^e, as seen fr'om above, they vary according as they occupy the margin of the collection, i. e. are peripheral, or are central. The latter are polygonal, frequently hexagonal, and no doubt owe this shape to mutual lateral pressure during growth : the marginal cells have fewer sides, and are frequently irre- OF THE PEDIASTEE^. 25 gulaiiy quadiilateral, but their free margin is more or less deeply notched, and therefore bilobed (I. 44, 45, 53, 62). The lobes are usually tapering, and form a tubular process either truncate or acute at the extremity (I. 62). In a few cases the notch is not angular, but cui-ved and crescentic (I. 62) ; in others again it is deep, angular, and gaping (I. 52, II. 27), and gives the cell an irregular figure ; this latter condition is more seen where only a few cells are united together, and where the lobes are not prolonged as pro- cesses. In some species, moreover, the lobes are terminated by short hair- like spines. The notch on one side is not confined to the peripheral ceUs, but extends, in several species, also to the contained cells of the frond (I. 52, 66) ; their lobes, however, are not tapering, but sharply truncate. Nageli instituted a subgenus of Pediastrmn under the name of Anomopedium, the chief charac- teristic of which is the absence of bilobed peripheral ceUs (I. 46, 47, 48). The ceUs of Ccelastmm are hexangular (I. 49, 50, 51), the central ones very regularly so, whilst the peripheral are rounded oif on their free aspect in one species, and in another notched and bilobed (I. 54, 55). Those, lastly, of Sorastrum (I. 56, 57) are wedge-shaped or triangular, with rounded angles ; they cohere by their apices, whilst the base is perij^heral, often rather concave or emarginate, and, as a rule, armed at each angle by a pair of short spines. On a lateral view the cells are oblong (I. 58). There is a pervading uniformity in the contents of the cells of the different genera of Pediastreae, which consist of the usual vegetable protoplasm, and are spoken of collectively as the endochrome. At first the colour is very pale green, but it becomes deeper with advancing age, and in fully matiu'e or decaying cells is seen to change to red or brownish red, just as the leaves of trees change colour on the approach of autumn. At first, the protoplasm is clear and homogeneous, but in course of time granules appear, enlarge in bulk, and multiply in number. Moreover, each cell presents a single ehlo- rophyU-vesicle, which is least discernible in very yoimg and in very old cells (I. 53 to 58). It is ordinarily seen in or about the centre of the cell, but may occur on one side, as in Pediastrum Rotula. Around this vesicle are seen in several species clear cii^cular spaces or globules, recalling those of Closterium, varying in number in difierent cases from two to six (I. 44, 45, 53). In Pediastmm Rotula, Nageli observed two such ; in P. Boryanum and P. Selencea (I. 44, 45), from two to six ; in the species of Scenedesmus and of So7%istrum (I. 57), one hyaline space. This author likewise represents the relative position of the chlorophyU-vesicle and of the translucent space to be constant in similar fronds. In those made up of two cells only, the chloro- phyU-vesicle is placed outside, whilst the clear cavity lies against the parti- tion-wall. In chains of four to eight cells the chlorophyll- vesicle is external relatively to the central cell, and the clear space internal (I. 40, 41), — the position being regulated, not by the partition -wall, as in the Palmelleae in general, but by the centre of the entire frond. Oil-globules are also con- tained in the cells ; their presence is readily demonstrated by the addition of tincture of iodine, for they continue colouiiess when the surrounding mass is coloured brown ; their position often exhibits much regularity. Unless the chlorophyll- vesicle be esteemed nuclear, no nucleus has been cUscemed in the cells of Pediastreae. On one occasion Nageli saw, in Pediastrum Boryanum, the endochr^ome disposed in a radiating manner around the chlorophyll-vesicle, an arrangement which often obtains in Algse, and in many vegetable ceUs where there is a central nucleus. T^UMBER AND DISPOSITION OF THE CeLLS IN THE FllONDS. The CcUs of Pc- diastrese are always united together in compound fronds. The number so 26 GENERAL HISTORY OF THE rNFUSOEIA. united, and their mode of combination, differ in^ the different genera and species. In Scenedesmus the cells are arranged (I. 37 to 43) in single linear series, side by side, united by a mucous hj^aline matrix, which is less abundant than in Pediastrum. Two, mostly four, and less frequently eight cells are concatenated ; and, as a rule, the line of union extends the entire length. Ex- ceptions occur, owing to the junction-surfaces being less extensive, in the form of chains of cells having a zigzag border, every alternate cell being depressed below the normal plane, or in that of an obhque chain, having each member in succession depressed beneath the preceding. Sometimes two rows of eight cells each lie side by side (I. 38), so that the one dovetails into the other by the alternate elevation and depression of their component cells : this may happen in the whole extent of the two coherent chains, or in a portion only of their length at one or other extremity ; or one chain may be broken into two segments, each dovetailed to the other chain at opposite ends so as to leave an unoccupied central space. The alternation of the cells in fronds composed of two rows, is the result, according to Mr. Ealfs, of the obhque manner of division. In the genus Pediastrum the fronds are generally com- posed of a larger number of cells than in Scenedesmus, disposed in the same plane according to a definite and usually concentric arrangement, and foiming compound steUate fronds (I. 52, 53, 62, 66, 67), whence the term Micras- terias (httle star-like beings) invented by Ehrenberg, and also the second half of the generally adopted term {Pedi)-astrum. To distinguish species, Ehrenberg chiefly employed the number of the cells in a frond — both the entire number and that of each concentric circle, together with the number of circles. Succeeding naturahsts, however, have pointed out that the number of cells in the same species is subject to con- siderable variation. TmT^)in detected the true law determining their number, and Nageh fui^ther illustrated and enforced it. The latter wiites that {Einzell Alg. p. 92) '' the cells are united 2, 4, 8, 16, 32, or 64 together in a frond. These numbers are always constant in young fronds without exception. In older specimens one or more cells may be lost, and the frond become therefore apparently irregular. These cells do not spontaneously detach themselves from the rest, but die, and are partially or entirely dissipated, as a consequence of injury from some external cause, probably in most cases by small aquatic animals. They occur in all stages of destruc- tion, and when entirely vanished, the vacant space indicates their fonner position. The cells are aggregated together in a single plane, which possesses mostly a circular or somewhat rounded outline ; but in the disposition of the cells there is considerable variety. In the case of 4 cells they are either all in opposition (II. 27), or only 2 in the centre ; with 8 cells, one usually lies in the middle, and the other 7 surround it in a circular manner (I. 52); less commonly, 2 are central and 6 peripheral (I. 62); rarely, one occupies the centre with 6 around it in a circle, whilst the remaining or eighth cell is placed on the perii^heiy ; and stiU rarer, the disposition is quite irregular. Where 16 cells are combined, the rule is that there is one in the centre surrounded by an inner circle of 5 and an outer circle of 10. At times, 4, 5, or 6 internal cells are encii^cled by 12, 11, or 10 outer ones (I. 53, 66, 67), whereby a double ring is produced: more rarely the arrangement is completely irregular. Again, 32 cells are mostly so placed that one central cell has around it 3 circles, the innermost of 5, the middle of 10, and the outer of 16 cells ; less frequently, the 3 circles are respectively composed of 5, 11, and 15, or of 6, 10, and 16; occasionally 5 internal cells have 2 outer scries, one of 11, the other of 16 OF TUE PEDIASTKE^. 27 cells; or 6 cells are enclosed by 11 and 15, or by 10 and 16 ; or, lastly, the distribution is partly or completely iiTegular. In the case of 64 cells, no regular aggregation frequently is observable : sometimes 2 or 3 external con- centric series are perceptible, where the position of the inner cells follows no rule ; less fi^equently, the concentric arrangement can be followed to the centre ; when this is the case, one central cell may be enclosed by four series respectively of 6, 13, 19, 25, or of 7, 13, 19, 24 cells; or again, 2 middle cells have around them 8, 13, 18, 23, or 7, 12, 19, 24, or 7, 13, 19, 23 ceUs in four rows ; or fui'ther, 3 central ceUs have 8, 13, 18, 22 ceUs around, and so forth. " The form of the genus PecUastrum has in general a decided tendency to a concentiic disposition of the ceUs. Thus 4 cells combine in 1, 8 in 2, 16 in 3, 32 in 4, and 64 in 5 circles. A\Tien this concentric arrangement is distui^bed, it occui's more frequently in larger than in small fi'onds, and more frequently among the central than the peripheral ceUs." Braun {Gen. Nov. p. 71) has entered much in detail respecting the number ajjd disposition of the cells, and arrived at the same general results as Nageli. He observes that " the same numerical law is common to all the species [of PecUastrum'], but the number may vary more or less within the legitimate series, even indeed in one and the same species : the disposition also is liable to variation where there is the like number of cells in the same multifarious species ; and this so much the more the greater the number of cells. . , .The legitimate (normal) series, viz. 1, 2, 4, 8, 16, 32, 64, 128, is explained by the binary division which takes place in the formation of gonidia, and which is quicldy arrested or continued for a longer period. " I have no dii-ect observations to show whether specimens consisting of a single cell are generated singly from the parent cell, or, after being developed in company with others, they have become dispersed by some accident, which is very probable. Such specimens, belonging pretty clearly to PecUastrum Ehrenbergii, occur eveiyw'here in company with the multicellular fi'onds of this species. Unicellular examples of other species are, it would seem, very rare. I have seen one such of P. Motida ; of some which I think should be assigned to P. Boryanum. Bi-cellular specimens I have only observed in the case of P. Ehrenbergii : instances of 128 cells have frequently occurred to me with P. valgum, and twice with P. Boryanum. The other numbers are common, and occur in very many or in all species, or in the majority ; certain of them indeed much more frequently than others. " Numbers divergent fi^om the normal series, whether incomplete or more than complete (supra- complete), are rare, whilst veiy divergent ones are very rare. The former have their origin in the process of fission and the formation of gonidia, when one or other segment in the penultimate division remains undivided, or divides once too often. Thus in P. Boryanum, specimens are occasionally found ha\dng 15 instead of 16, 31 for 32, 63 for 64 cells, or on the contrary, 17 for 16. Examples of 65 in lieu of 64 cells have occuiTed to me in P. asperum. The latter, i. e. those numbers widely divergent, may originate, if in the earlier division of the cytioplasm [protoplasm] some seg- ment is, as it were, passed by, and subsequently enters again in the series of segmentation. In this way the numbers entering into the series 3, 6, 12, 24, 48, examples of which are at hand, may be explained. Three cells have been met mth by me in P. Ehrenbergii, and more frequently 6, both in this species and in P. Rotula ; . . . .24 cells, once, in P. asperum.^' Braun adds that, if any person should doubt that the number of cells differs in the same species, he has only to inspect collections made in the same place and li\ing imder like conditions, and to note the unequal fonns produced 28 GENERAL HISTOEY OF THE INFUSOEIA. from the same parent individual, and lastly, to remark the analogy presented in other allied genera, e. g. Scenedesmus, Sorastrum, and Coelastrum, to con- vince himself of the fact. Moreover, as shown by Nageli, when the number of cells is the same in a frond (coenohium, Braun), their arrangement varies considerably, tending more and more to irregularity as the ceUs are more multiplied. " The normal and most frequent disposition is orbicular, the cells being arranged, according to their number, in one or several concentric circles, around either a single central cell or none at all. Where two cells are placed in the centre, the circles around incline to an elliptic figure; fi^om this a transition to an elongated form still more aberrant from the orbicular type is indicated, in which the elongate -elliptic circles surround several intermediate cells placed in single or double longitudinal series. By the less regular concentric or the entirely confused disposition of the cells, the elliptic form passes at length into others still more abnormal, such as reniform, panduriform, cuneiform, &c., all which agree in ha\ing 64 or 128 ceUs. The regular concentric arrangement is moreover deranged by the occasional intercalation of ceils referable to no one of the circles ; and lastly, owing to an incompleteness of the circles of cells, they become so connected one with another, that a spiral disposition is the result, which, although abnormal in every species, is in some specimens constructed with wonderftd regularity. All these various arrangements arise from the manner in which the motile gonidia are disposed and marshalled in their first stage ; for these are distributed within the parent depressed orbicular cell, according to the laws of juxtaposition, in a plane." Another peculiarity in the disposition of the ceUs in the fronds of Pedias- trwn is, that sometimes, instead of being all in juxtaposition, so as to form an unbroken congeries of cells, or, in the language of Nageli (op. cit. p. 94), instead of being parenchymatic, apertures or interspaces are left between them (I. 53). This is most seen where the inner cells are more or less bi- lobed, so that an opening subsists between the lobes of each ceU ; but similar apertures may likewise occur at the angles where the cells come into contact. "When the position of the cells in the table is regular, that of the foramina is so also. Pediastrwn Selencea with 16 cells has, as a rule, 6 large and 8 small openings ; the large are bounded by 3 cells, the small by 2 ; the small spaces are sometimes absent, when the large become very evident. Pronds of the same species, having 32 cells, display usually 11 larger interspaces lying betwixt 3 cells, and 18 smaller enclosed between 2 cells. Anomopedium, a subgenus of Pediastrum, differs not only in its peripheral cells not being bilobed, but also in having its cells partially disposed in a double plane (I. 46, 47, 48). The ceUs which are in the numerical series of 4, 8, 16, 32, and 64, are subject to manifold arrangements, and frequently aggre- gated quite irregularly. They are mostly so placed, that in one, two, or even three directions, they can be clearly discerned to be in parallel straight rows. A concentric disposition is quite exceptional ; not unfi-equently, instead of aU the cells occupying the same plane, some form a partial second layer upon the other about the middle. In Ccelastrum (I. 50, 51, 52) the hexangular cells are so arranged that they form a hollow, globular, areolar frond. Coel. sphcericum consists of 25 to 40 cells, which compose a lamina perforated by 3, 4, 5, 6, 8 angular meshes (areolae) somewhat larger than the cells themselves, and from 13 to 22 in number. Coel. cuhicmn consists of 8 cells united in a cubical form, hollow inside : on each side are 4 cells enclosing a quadrangular aperture. Lastly, in Sorastrum the wedge-shaped or cordate cells (I. 56, 57) are all OF THE PEDIASTEE^. ^9 in close apposition and form a globular frond. The cells in the typical species, S. echinatiun, are 8 or 16 in number, and so arranged that all their apices converge towards and meet in the centre of the frond. SjyJicerodesmus, which probably is rightly accounted one of the Pediastreae, is named, but not described, by Niigeli ; we are, however, informed by Braun (Gen. Nova, p. 70, in foot-note) that its fronds are composed of 4 spherical cells closely aggregated in a rhomboidal form. Development and Growth. — Seenedesmus multiplies by fission, as Ealfs believed, in an obhque direction, but according to Nageli, parallel to the long diameter of the cells. The former adopted his opinion from the features of biserial chains ; but the latter interprets those appearances by the simulta- neous occurrence of longitudinal and of transverse fission (I. 37, 39). The process of self- division commences generally at the same period in each cell of the frond (family, Niigeh), and proceeds with so great rapidity that its intermediate stages are unobserved. One of the two terminal cells (I. 39), or, in an eight-celled, probably the two, sometimes remain for awhile undivided. The cell separates into two, then each of these again into two others, and at times this act of subdivision is repeated a third time. By a more prolonged act of segmentation of the cell-contents, the result is a number of minute cells which arrange themselves in rows of two, four, or eight, and thus form miniature fronds which ultimately escape the parent-cell by rup- tui'e. Occasionally, adds Niigeli, the young fi'onds are connected together by mucus, formed by dissolution of the parent cell-wall. Development takes place in parallel planes, although by their increase they become mutually compressed and in-egular, and the chains curved j)rior to their discharge. This production of macrogonidia and their cohesion into fronds has not been seen by Braun, and is^ in his experience, an exceptional phenomenon {Gen. Nova, p. 67). When Mr. Ealfs wrote his work on the Desmidieae (in 1848), he had to confess himself altogether ignorant of the modes of reproduction both of Pediastrum and Seenedesmus. He, however, described self-di\ision of the cells in both genera, but rightly regarded this process as one not of develop- ment, but of vegetative increase and repetition. On this subject he remarked {op. cit. p. 182), — " I have not seen the cells duiing the process of division, but I am informed by M. de Brebisson that it takes place at the notch, in the same manner as in other Desmidieae : hence the cells in each cii'cle are connected at their ends, like those of the filamentous genera. I do not, however, understand in what manner the additional circles are formed, nor why the numbers in each circle are so constant." Niigeli, likewise, was equally ignorant of the propagation of Pediastrum, but thought it highly probable it resembled that of Seenedesmus. The num- ber of cells in a table or frond, indicated to his mind its production by a series of fissions in the power of two ; and he presumed that a new frond was gene- rated within a parent cell by division of its protoplasm, just as in Seenedesmus, — a supposition supported by the fact that the entire young fronds are not larger than the single cells of mature specimens, that like these they are composed of the same number of individual cells similarly disposed, and undergo no subsequent segmentation into a larger number. The more recent researches of Braun are confii^matory of the views of Na- geli (Gen. Nova, p. 68). Amid a large number of specimens of Pediastrum Boryanum he detected the escape of, in most instances 32, more seldom of 16, and rarely of 8 gonidia, from a parent cell, — the number gene- rally, but not invariably, corresponding with that of the cells composing the matui-e frond or coenobium. The collection of gonidia was enclosed by a 30 GENEEAL HISTORT OF THE rN'FUSOEIA. common envelope, 'witliin whicli they moved actively about for a quarter of an hour before coming to a state of rest, and arranging themselves regularly in a frond (I. 64). This sac is described in the author's work on Rejuvenes- cence {Bay Soc. p. 184) as the vesicular inner layer of the mother-cell. He witnessed this production of gonidia from many, but not from all the cells of the fronds, for it seems to take place in them in succession, and pro- bably in some definite manner, according to theii' position in the frond. He further describes the development of microgonidia to follow the same plan as that of macrogonidia, but to differ from the latter in nimiber, size and form, and in duration and cessation of motion. Macrogonidia have a subglobose figure, a diameter of y^th of a millimetre ; one side hyaline, and scarcely elongated, the other tui^ned towards the periphery of the frond, green, and by-and-by extended and emarginate : no vibratile ciHa discoverable on them. They never leave the sac in which they are produced ; and the yoimg fi'ond is seen, until the close of the second day, loosely enveloped by a gelatinous layer, which ultimately disappears by deliquescence (I. 64). On the other hand, microgonidia are at fii'st densely aggregated and closely invested by the sac in which they are generated ; like macrogonidia they are subglobose (I. 60, 61, 68, 69). After a while the sac is gradually dilated, and, growing more and more in length, forms an acute hyaline beak {rostrum) as long as the green portion, which constitutes the rest, or the body, of the gonidium. This rostrum, moreover, is furnished either with a pair of cUia, longer than the body, or with a single cilium. The length of these developed microgonidia is nearly y^-o-th millimetre ; the thickness -g-J-o th (I. 61, 68, 69). The movement within the sac is at first slow; but when this is fully expanded, it is very active, and continued for an hour and upwards, until the sac is ruptured, and the Avhole heap of microgonidia escape. The number of microgonidia cannot, by reason of their aggregation and their swarming movement, be easily determined ; at least 64 occur in a sac, and most commonly many more, for instance, 128. Of theii' subsequent history, Braun can give no satisfactory account. A reference to the same able writer's book on Eejuvenescence {R. S.) informs us, at p. 200, that before the formation of the gonidia of Pediastrum, the single starch-grain, the nuclear character of which has been above re- marked, disappears. From the same source we also obtain a series of illus- trations of the development of macrogonidia, of their arrangement in the characteristic stellate frondose form, and of the varieties in the number and arrangement of the component cells, which may be seen in examples of the same species of Pediastrum. The development both of Coelastrum and Sorastrum is unknown. The Pediastrese are of freshwater habit, living in ponds, on which they frequently form, in conjimction with other small plants, a coloured film or scum. They are also common in tm-fy pools on moors, and invest the sui'face of various aquatic plants. Systematic Position op Pediastreje. — Mr. Ealfs followed Ehrenberg, Meneghini, and others in placing the Pediastrese among Desmidiese ; but Corda, Nageli, and Braim have separated the two as distinct tribes. Indeed, Mr. Ralfs has modified his views since the publication of his monograph, and would treat the Pediastreae as a subfamily of Desmidiese. Nageli {Einzell. Alg) arranges them with the PalmeUese as a distinct group, and in this has the support of Braun {Gen. Nova, p. 69). These natui'alists point out that the distinctive features between the Pediastreoe and the Desmidiese, are that the former neither conjugate nor miiltij)ly by continued transverse division of their cells in the same direction, each newly-formed segment acquiring aU the OF THE DIAT0MEJ2. 31 characters of a complete cell ; that, iinlike the Desmidieae, they propagate by gonidia; have but one instead of two or more equally-sized starch-grains and a central nucleus ; and that their fronds are not distinguishable into two symmetrical halves. '' The Desmidiese are e\idently multicellular, or pseudo- unicellular, from separation of their cells, whilst (says Braun) Pediastrum is a true unicellular Alga rendered pseudo-multicellular by the cohesion of the cells. The aggregation of cells in Desmidieae is always uniserial, filiform or concatenate ; the fronds of PediastriLm are grouped on a plane of a disc-form or frondose character." Braim next traces the affinities of Pediastrum, and remarks that, although it resembles Hydrodictyon in the construction of its fronds (coenobia) by the connexion of motile gonidia, yet since in Hydrodictyon the gonidia are simultaneous, and in Pediastrum successional, it is rather an analogy than an affinity which exists between these two genera. However, he admits the correctness of the association of Pediastrum with the genera Nageh indicated, viz. with Sorastnon, Coelastrum, Scenedesmus, and probably Splicer odesmus, and would add to their number the genus Staurogonia (Kiitz.), the Crucigenia of Morren {Ann. des Sciences Nat. 1830, p. 404). All these genera agree ■with Pediastrum in the successional formation of gonidia, yet differ from it in other particulars except in the construction of the frond from motionless gonidia. Among other genera, Polyedrum may be likened to Pediastrum in the form of its cells, but its propagation is unknown ; lastly, Characium and Cystococcus agree with Pediastrum in the successional genesis and activity of their gonidia. To this elucidation of the affinities of Pediastrum we have to add the observation of Cohn (EntwicJc. d. miJcr. Alg.), of the analogy or affinity in general stnictiu-e between this genus and Goyiium. The di-^ision of Pediastrum into tribes or subgenera, as proposed by Braun, and the distinction of species of the Pediastreae in general, will receive due consideration in our systematic account of the family. II.— OF THE FAMILY DIATOMEJE OR DIATOMACEJE. (Plates ly. to XYII.) General and External Charactees of Diatome^. — Testules or Frus^ tides. — Figure : free, concatenated, and fixed Forms. — VaHeties of Filaments and of Pedicels. — Aggregated Frustules. — The Diatomeae, Diatomaeeae, or CymbeUea?, are unicellular organisms composed of two opposite plates or valves, generally convex, and of an interposed connecting thii'd segment, forming together a miniatui^e box of a silicious nature, enclosing a soft organic matter, rarely green, but usually yelloT\ish or orange-brown in colour. They inhabit either fresh, salt, or brackish water. They were reckoned by Ehi'enberg among the BaciUaria, and have in con- sequence been sometimes described as silicious Bacillaria. Each individual Diatom enclosed in its silicious envelope is spoken of as a fi'ustule, testule, frond, or bacillum, and in general phraseology as a cell. The first term is that now most in use, whilst " testule " and " baciUum " are words rarely employed, except in the works of Ehrenberg and of his im- mediate disciples. A rectangular or prismatic figure most widely obtains in this family ; and the angles of jimction of the valves are as a rule acute. Deeply notched fronds, like those in Desmidieae, e. g. Micrasterias and Euastrum, do not occur ; and the production of spines and tubercles on the valves, so common in that family, is rare among the Diatomeae. 32 GENERAL HISTORY OF THE INFUSORIA. EiGURE. — There is an immense diversity of figure among the frustiiles, determined chiefly by that of the opposed valves, but in some degree also by the amount of development of the interposed third segment or eingulum (XYI. 23, 24.) This last Mr. Ralfs considers an essential part of every frustule ; but Prof. Smith states it to be a secondary, non-essential element consequent on the growth of the organism, and specially developed .in rela- tion to the process of self- division. When this eingulum or " connecting membrane " is much enlarged prior to fission, the figui'e as viewed on this side is considerably changed, and the apj)earance of a double frastule often occasioned. Not a few of the Diatomese are much elongated and narrow, and from pre- senting a wand-like figui-e (IX. 148, 166, 174 ; X. 184, 185), suggested to Ehrenberg the term Bacillaria to designate the family. However, some species are trapezoid, or square, or nearly so (X. 47, 21, 22), others round like pill-boxes (IX. 131, 181; X. 200, 204), whilst others again are almost globular or sj)heroid, owing to the great convexity of the valves. Several genera are boat-shaped, scaphoid, or navicular in figui-e (IX. 139, 135 ; XII. 5, 6, 8, 48, 43) ; some are mther oval, egg-shaped, or ovoid ; many resemble thin flattened discs — are discoid (XI. 33, 35, 36, 39); many are wedge-shaped — cuneiform, or cuneate ; a few are triangular (XI. 43, 45) ; lastly, some are curved or twisted on themselves, and others assume in certain directions a sigmoid or an undulated figiu^e (IX. 144, 145 ; XV. 11, 22, 59, 60). Evenly-curved valves are said to be arcuate, such as those of Eunotia (IX. 165; XYI. 10, 18), and of some species of Cymhella and Nitzschia, whilst the peculiarly-twisted valves of Campylodiscus (XVII. 517) are saddle-shaped. In Cymatopleura, again, the surface of the valves is undulated, and when bent rather sharply at an angle on themselves, the valves become geniculate, as in Ach)ianthidium. As a rule the frustules of Diatomeae are sjrmmetrical, and consist of two equal and similar halves ; but exceptions to this are found in the Achnantheae, Cocconeidae, and one or two other families (IX. 159). Another variety of frustules is described as winged or alate, — the ala being a smooth expansion in the form of a margin (XIII. 5, 6, 7). The alae may arise from the margin, and are then said to be marginal, as in Surirella, or otherwise from the disc, as in Tryhlionella, in which they are called submar- ginal. A further modification of the valves afiecting the figure is exemplified in Nitzschia and AmpMprora, which have a longitudinal elevated ridge extending from one extremity to the other ; such ridges are called keels, and the valves keeled or carinated. In the discoid forms two portions are commonly distin- guishable, viz. the disc and margin or rim (XI. 31, 35, 38), the one at times separated by a distinct line, and often presenting different sculpturing from the other. The disc moreover exhibits occasionally at its centre a promi- nence or elevated thickness called an iimho or boss. In Eupodiscus (XI. 41, 42) tubular horns come off from the surface of the valves, and in Triceratium from the angles. The extremities of some species, e. g. in Nitzschia and Pleurosigma, are extremely elongated, forming long, filiform, tubular processes ; and in Den^ ticella, Biddulphia (II. 46, 48, 50), and RMzoselenia (Ehi-.), short tubular processes and spines are produced from the surfaces and margins. These processes are commonly simple, but according to Ehrenberg are branched (ramose) in the genus last cited, and in Dicladia and Syndendrium. More- over, very singular hispid and sometimes bifid processes or styles have been noted on the valves of some species of Goniofhecium (Ehr.), recalling by their figure that of the spines on the sporangia of many Desmidieae. Other OF THE DIATOME^. 33 Diatoms, referred by Mr. Brightwell {J. M. S. 1856, p. 106) to the geniis CJice- toceros, have highly developed spines on the valves, besides the two pairs of very long filiform smooth or spinous horns spiinging from the fi'ustules themselves, or froin the interposed cingulum. Cerataulus is another genus provided with a pair of long horn-like processes. Great variety of outline may prevail in a genus, so considerable indeed that an accurate definition is mth difiiculty laid doT^Ti, the characteristics shading off through several species, untU at length the similarity to an as- sumed typical form is much diminished, whilst on the other hand an ap- proach is made towards the features of another genus. The like latitude of form prevails also with species, and gives rise to very numerous and fre- quently perplexing varieties. On this topic Prof. Smith remarks — '^ While a typical outline of its frustule is the general characteristic of a species, this outline may be modified by the accidental circumstances which smTound the embryo during its growth and the development of its sihcious epiderm ; then, any such aberration of form becomes stereotyped by the process of self-divi- sion of the frustule, generating multitudes of others slightly deviating from the normal form." It must not be forgotten that the figui'e is greatly modified or entu-ely changed by the position of the valves, whether seen in face or on one side ; for each frustule generally presents four planes or sides, and, unless regard be paid to this circumstance, one genus may be mistaken for another, or even each view be presumed a distinct genus. Thus in the genera Navicula, Pinnularia (XII. 5, 6, 15, 18), and in many others, the frustules are on one aspect boat-shaped, but on the other oblong with truncated ends, or prismatic. In the genus Triceratium (XI. 43, 44), the difference of figure is very re- markable according to the side viewed (as presently illustrated). It is there- fore necessary to examine a specimen on eveiy aspect it presents : this can generally be effected by the accidental rolling over of frustules under inspec- tion, or can otherwise be brought about by a very slight sliding movement of the thin glass cover upon the slide under the microscope. Mr. Brightwell thus describes and explains the transitions of form produced by a change in position of the frustules of the genus Triceratiuin (J. M. S. i. 248) : — " The normal view of the frustule may be represented by a vertical section of a triang-ular prism. If the frustule be placed upon one of its flat sides, we look down upon its ridge and obtain a front view of its two other sloping sides. If it be placed upon one of its ridges, we have a front view of one of its flat sides, generally broader than long, and of its smooth or transparent suture or connecting membrane. If the frustule be progressing towards self- division, it is then often considerably longer than broad, and when nearly matured for separation presents the appearance of a double frustule." It would be in vain to attempt to describe all the numerous forms assumed by the members of this extensive family ; the representations in the plates of this volume will convey the clearest notions of their diverse outline and markings (see Plates 4 to 17). Great difference unfortunately has existed re- specting the sides which should be esteemed primary and afford specific cha- racteristics, and those which should be held as only secondary; and the nomenclatui-e of the surfaces has been equally a matter of dispute and imcer- tainty. Ehrenberg employed the terms dorsum, venter, and lateral surfaces or sides, but so loosely that they do not always Indicate homologous portions. Thus he has often called a convex surface the dorsum, simply from its convexity, and a concave one the venter, on account of its concavity. Kutzing attempted a more certain and scientific phraseology by calling those sides which have no central opening (umbilicus), but through which self-di\ision occurs, the primary sides, and the other two the secondary sides, further distinguishing D 34 GENERAL HISTORY OF THE INFUSORIA. the latter into a right and a left with reference to the frustule when lying on a primary side. The left side is often concave, and the right convex ; mostly, however, the two are alike. As a general rule the primary sides correspond with the lateral surfaces, and the secondary with the dorsum and venter in the terminology of Ehi'enberg. Mr. Ralfs, in his papers in the Ann. Nat. Hist., used the simple terms '/>'on< view^ and ^ side vieiu,' corresponding respectively T^ith Kiitzing's names primary and secondary sides. The Rev. W. Smith adopts this nomenclature as the most convenient for the English student, and uses the term 'front vieiu' to denote the aspect of the frustule when the valvular suture (connecting membrane), or the line along which self-division takes place, is turned towards the observer, and the term * side vieiu^ when the centre of one valve is dii-ected to the eye. He adds — " Even these terms will requii'e modification when applied to some of the more complex and irregular forms ; but in general theii' meaning will be sufficiently obvious." It must happen, therefore, from this terminology, that at times a front view cannot be said to exist, viz. when the connecting membrane is obsolete and the opposed valves are closely applied to each other, a suture alone in- dicating the line of junction. In size the Diatomea) vary very greatly ; some individual frustules are cognizable by the naked eye, whilst others require the highest powers of the microscope to display them. Even among specimens of the same species great diversity of size prevails, — a peculiarity much determined by the cii'- cumstances surroimding a frustule at the period of its development, and afterwards perpetuated through a long series of individuals multiplied by self-fission. The Diatomese exist under three chief forms, as — 1. Single isolated free frustules. 2. Frustules attached by a stalk, stij^es, or pedicle. 3. Frustules coherent in chains, or aggregated together in ramose tufts by an interposed gelatinous substance. The third form is the consequence of incomplete fission, or of imperfect separation after fission. Incomplete fission and consequent concatenation are observed in Bacillaria, Meridion, Himantidi^mi, Melosira, Odontidium, Striatella, Fragilaria, &c. (IX. 131, 167, 171, 175, 176, 177) ; and the form of the chain or filament produced -^-ill be determined by the figiu^e of the indi^-idual frustules composing it. For instance, if these be rectangular, then the resulting chain (IX. 171, 172, 176 ; XIV. 2, 4, 6, la) is straight, but if wedge-shaped, it is cun-ed or spiral (IX. 177, 179 ; XII. 21). The extent and degree of attachment of the adjoining frustules difier in difierent genera ; thus, in Bacillaria it is very shght, and readily yields, allowing one segment to glide on another, or to separate from it, except at one point, yet at the same time possessing the power of recovering itself. In Odontidium, Himantidium, Denticida, and Meridion (IX. 177), the mutual adhesion of the several segments is stronger ; and after the opposed sui-faces have been separated, futiu^e adhesion is not effected. In Fragilaria, the ad- herence is more tenacious. In Diatoma, Tahellaria, Ghr(mmatoj)7iora, Am- phitetras, &e. (II. 46 ; XI. 22, 52 ; XIV. 23), the frustules hang together by a sort of hinge inserted between adjoining angles in a zigzag fashion. In IstJimia, this hinge or connecting link attains a greater magnitude, and, in fact, is double. In Podosira (II. 45) and in some species of Melosira a junction-process is developed from the centre of each frustule in the chain. In other Melosirce and in OrtJiosira, the junction-siufaces are toothed (den- tate), and thus hold the adjoining frustules in firm union. In the instance of Biddidpliia (II. 46, 48), the siufaces in union are curiously elongated at the angles into rounded or horn-like processes, whilst theii' convexity is OF THE DIATOME^. 35 crowned bj^ several bristles or setae. Lastly, in Eiicainpia (II. 48) the junction-surfaces are so excavated, that when the frustules are concatenated a filament is formed, perforated by oval foramina. In not a few genera, as above mentioned, the attachment is at opposed angles, and a zigzag chain produced ; but in Istlimia (X. 183) it is peculiar in being indiscriminately made at any part of the adjacent frustule, and thereby produces an iiTcgularly branched filament. The above examples will suffice to illustrate the characters and varieties of concatenation in the form of filaments, whether straight or spiral ; but it is necessary to add that the width of a filament " equals the length of the frustule or valve measured along the suture or junction-line, and that the breadth of the valve denotes the thickness of the filament " (Smith, Synojos. ii. 6). In those instances in which frustules are connected together by a process or small isthmus acting as a sort of hinge, the concatenation cannot be ascribed to incomplete division only, for the existence of such a process is the result of a special formation which essentially coiTesponds with the pedicle or stipes of fixed species. Numerous Diatomese grow attached to foreign bodies by a stalk of variable length, and which, although generally simple, is sometimes comjDound by dividing and subdividing in a ramose manner. Even among the recognized free Diatomeae, such as Navicula, Pinnularia, Nitzscliia, &c., specimens are not unfrequently seen adherent by one extremity, about v>^hich they turn or bend themselves as on a hinge ; however, in these instances such union is but temporary, and no connecting medium exists. In Synedra (X. 184), on the other hand, a bond of union occurs in the form of a little gelatinous conical nodule, resembling very nearly the hinge-like isthmus which binds to- gether the frustules of many genera in a sort of zigzag chain. By the process of self- division it also comes to pass that groups of Synedrce occiu' attached together by the same point, in a fan-like or a stellate form, as in S. radians, S. affinis, &c. In other species detachment after fission is too speedy to allow of this sort of combination, except of some two or four indi\dduals. The fan-like collection of frustules is said to be flabellate, fan-like, or radiating ; and when the component members are curved, they and the bun- dles they form are described as arcuate. The nodule of attachment occurs in various degrees of development, and attains in this same genus Synedra to the dimensions of a pedicle — ex. in Synedra sujperba, and even to branch, as in Synedra fulgens and Synedra pidcJielJa. ^Tien a stipe branches, it does so normally in a dichotomous manner by the very circumstance of the process of self- division, each new individual produced by that act developing its o"v\ti secondary pedicle, or pedicel. This regular dichotomy is instanced in the genera Dorypliora (XIV. 21), Cocconema (XIII. 10), and Gomphonema (XIII. 11). In Licmopliora (XIII. 20), and in one species of Rhiindoijliora, viz. Rh. Dalmatica, an irregular branching — essentially dichotomous, however — is met with, and is thus ex- plained by Prof. Smith : — " In Rhipidophora paradoxa and Rh. elongata, self- division is immediately followed by the separation of the half-new frus- tules and a dichotomy in the filamentous stipes, while in the present genus the frustules remain for a time coherent, and continue dividing and mul- tiplying on the summit of the pedicel, which becomes elongated and incras- sated at each successive repetition of the process .... A branching, or rather longitudinal rupture, of the pedicle takes place at irregular intei^als ; and the entire organism presents us with more or less complete flabeUa (fan-like clusters) on the summit of the branches, and imperfect flabeUa or single frustules irregularly scattered throughout the entire length of the pedicel." B 2 36 GENEKAL HISTORY OF THE INFUSORIA. The same authority has the following remark on the process of ramification : he says (i. 75), " When self-division {i. e. of the frustules) is completed, the extension of the filament below the fnistules is suspended, a joint or arti- culation is formed at the base of the dividing frustule, and each of the half- new frustules begins anew, in its progress towards special self- division, the secretion of a new joint or internode ; and a dichotomy is the result." The occurrence of the double condition of union of frustules in a con- catenate manner and of attachment by a pedicle is illustrated in the genera Achminthes (X. 201, 202), Striatella (X. 203, 204), BhabcJonema (XIII. 27), and Podosira (II. 45). In Melosira also, attached species occur ; and Prof. Smith inclines to the opinion that all filamentous Diatomese are stipitate on their first production. In the second stalked genus cited, viz. Striatella, the stalk attains the highest development, but remains slender and unbranched. Between this most developed foim and the mere nodules of attachment in the genera Achnanthes and Melosira, every intermediate phase is encountered. In any one species, however, there is no positive determinate length of the stipes, for this varies according to the idiosyncrasy, vigour, and external con- ditions affecting the organism; consequently characters derived from the dimensions of the stems can have no specific value. There is a large section of Diatomeae in which the frustules are diffused throughout a mucous or muco- gelatinous mass, rarely confusedly, but mostly in a definite manner, usually in thread- or tuberlike branches, which nor- mally ramify in a dichotomous fashion, and resemble on a minute scale the tufts formed by many large sea-weeds. This peculiar aggregation is the consequence of the large production and subsequent persistence of the mucus which is thro^Ti out when the system of reproduction, whether by sporangia or by fission, takes place. Histologically, therefore, it is homologous with the pedicles and connecting nodules or isthmi thrown out duilng the act of seK-division, as also with the mucous stratum, which still very often persists when that act is complete, around specimens of Cocconeis, Chcetoceros, Melo- sira, Fragilaria, Striatella, &c. The tissue thus composed of mucus and enclosed frustules constitutes what is called (from analogy with the large Algae and other Crj^togamic plants) the frond, and affects various shapes, in some measure characteristic of the genera. Thus, in one of those so-called frondose Diatomeae, viz. DicMeia (XY. 30, 31), it is membranous and leaf-like, and resembles a species of IJlva; in Mastogloia, filiform with nipple-like expansions; in Encyonema (XIV. 22), Homceocladia (XIY. 37, 38, 47, 49), and Sehizonema, filamentous and more or less branched ; in Colletonema suhcohcerens, globose. Again, when filamentous, the ramifications differ much in thickness and in expansion, and in the extent of adhesion between the branches ; where these are long and slender they are called ' capillary,' and where contiguous branches coalesce, they give rise to a submembranous condition. The degree and mode of division, the collection of the branches into bundles (i. e. fasciculi), or, on the contrary, their loose or diffuse arrangement, supply useful characters in the distinction of species. Again, the fronds differ in consistence, being in some genem or species more rigid, setaceous, or robust, in others softer, flaccid, and more delicate : these opposite conditions furnish Prof. Smith with grounds for the division of the genus Sehizonema into two tribes. The disposition of the fi^ustules within the mucous investment supplies other important distinctions. Thus in DicMeia it is irregular ; in Mastogloia each little frustule occupies '' the summit of a little nipple-Hke cushion of gelatine ; " in BerTceleya (XIV. 34, 35) the frustules are densely packed in the filaments ; in Encyonema they occur mostly " in single file, except OF THE DIATOME^. 37 towards the extremities, where they are somewhat crowded" \vithin the distinctly tubular filaments, and enjoy a certain latitude of movement ; and, lastly, in Colletonema and Schizonema (X. 207, 208) they are arranged in one or more files according to the stage of growth, within less per- fect tubes than in the genus last mentioned, and retained in situ by the mucus around. Ehrenberg recognized this tribe of compound Diatomese, and introduced it as one of the sections of his great family Bacillaria, under the name of Lacerifuita, or Naviculce with a double lorica. His acquaintance with the group was, how- ever, very imperfect, and he appears to have comprehended in it organisms quite foreign to it, and to have failed to give that precision to his classifi- cation of the included beings which could alone confer a high scientific value and permanence upon it. Of the Eitvelopes of the Feustules of DiATOiiEJE. — The Silicioiis Shell or Lorica ; its Divisions and Structural Comiwsition, Markings, Strict, Canali- culi, Pumta, ^c. — Sufficient has been said of the mucous coat which at certain times, and always in certain genera, surrounds the frustules of Diatomese. The frustules themselves remain to be described: they are hollow variously-shaped cells having but one cavity — unicellular, and a siUcious outer wall, unafi'ected by a red heat and by strong acids, which would corrode and dissolve every other substance belonging to a living being except silex. This silex is stated not to polarize light, as does the mineral silex not in combination with organic beings ; and the erroneous statement made by some authors, of the polarizing effect of some Diatomaceous shells is due to the circumstance, that they did not take care to thoroughly remove the organic carbonaceous matter with which the silex is in union in the fnistides in question. The silex, besides being united with organic matter, deposited it may be within a cellular tissue, is contaminated by iron, which Professor Frankland of Manchester states {Smith, Synops. p. xxi) *' exists in the state of a silicate or protoxide . . . . " and he attributes to its presence " the brown colour which is assumed upon exposing the Diatoms to the influence of a moderate heat; the protoxide of iron, by the gradual absorption of oxygen, being converted into brown peroxide of iron, which assumes a redder tinge upon being more strongly heated." The relative proportion of silica varies within considerable limits in different genera of Diatomeae. In several genera, perhaps in marine ones exclusively, it is very deficient, and the wall of the frustule is httle more than horny, or it may be even flaccid, as for example in Dichieia and Schizonema. The frustules of Fragilaria, Striatella, and Poclosira are less firmly sihcious than those of many others of the filamentous Diatomese. In some genera (those, viz., which produce tubular processes) silex is deficient or absent from the pro- duced wall ; in Poclosira this deficiency occurs at the apex of the valves, and in Prof. Smith's opinion is probably intended "to allow a free secretion of the mucus which unites the frustules and provides a pedicle for their attach- ment to the plant on which they grow, as it does not occur on the non- attached valve of the fii^st- formed frustule. In the Hving state the absence of silex is not perceived; but when the frustules have been macerated in acid, these portions of the valves appear as perforations, owing to the dis- appearance of the ceU-membrane." The frustules of the Diatomeae are composed, as before stated, of two usually more or less convex valves, enclosing a single cavity, which becomes augmented by the growth of a third segment interposed between them, pro- duced preparatory to the process of self-division. Meneghini asserts that 38 GENEEAL HISTORY OF TfiH INFUSOEIA. the silicioiis sMeld or lorica is four-sided, and composed of four pieces or valves. Although this appears to be the true stnictm-e of some species, omng to the ready separation of the connecting membrane into two portions, yet the majority oifer no countenance to the notion, the connecting membrane forming a continuous oval or circular ring. In Triceratium, however, is an example of an even more pseudo-multiple composition ; for its prismatic tri- angular frustule breaks up into " two triangular plates or walls of silex forming the ends, and into three oblong rectangular pieces or bands forming the three sides, the latter usually dividing themselves into several elongated paralleliform pieces" (Brlghtivell, J. M. S. i. 248). Again, in several genera, doubtfully arranged by Ehrenberg among the siHcious Bacillaria, e. g. Dictyocha (XII. 62, 63) and Mesocena (XII. 71), the individuals are represented as composed of several segments united together. Each valve consists of a sihcious lamina supei-posed on an organic soft lining (or primordial) membrane which immediately encloses the contents of the cell. Nageli speaks of a mucilaginous peUicle on the inside of the organic layer as a sort of third tunic ; and Kiitzing likewise discovers a thin stratum brought into view when recent frustules are dried, and particularly after heating them to redness, in the shape of an opake bro^vnish stain, or of brown hues or points, extending not unfrequently over a considerable portion. To this supposed independent material its observ^er applied the name ' cement/ imagining it to be the connecting matter of the valves and of frustules when in luiion, and attributed its bro^Ti colom^ to the presence of ii'on. This presumed layer of cement we can regard as nothing more than the stain produced by the oxidation of the salts of iron in chemical union ■with the silica, as Prof. Erankland has shown (p. 37). However, Meneghini adopts the notion of this third envelope or cement, inasmuch as he observes it to be constant, without employing the means used by Kiitzing to display it, not merety in the species enumerated by its discoverer, but in many others, and possibly in all (R. S. 1853, p. 361) : — " Por to me (continues the same author) it appears to correspond with that fine membrane of the Ach- nanthidia, which, according to Kiitzing's o^^ti observation, is always \isible whenever the two new individuals (into which every Diatom is resolved in its multiplication by deduplication) begin to separate. The lines and points supposed to belong to the subjacent shield belong very frequently to this kind of covering." The analogy expressed in the quotation just given, between the delicate stratum — the ' cement ' of Kiitzing, and the secretion poured out when self-division is proceeding, we cannot regard as correct ; for this latter is a special and usually not persistent coating, in all j)robability exuded through the fissui^es or pores uncovered by the silieious lamina, by the sub- jacent organic membrane, and is T\dthal destroyed by the heat generally required to brmg the ' cement ' into view, whereas the presumed coat is represented to be constant and also permanent both under the operation of fire and of acids. However, the belief in the existence of a vegetable mem- brane outside the silieious epiderm gains ground ; for Mr. Shadbolt, in his presidential address before the Microscopical Society, 1858 {T. M. S. 1858, p. 72), states it as the result of his researches, that the frustule of Arach- noidiscus and of other forms consists of a silieious frametvorJc, over which is stretched a species of membrane, whether silieious or not he does not presume to decide, but certainly pliant to a considerable extent, capable of being par- tially rolled up by mechanical agency without breaking, and elastic enough to return to its original position when the extraneous force is removed. " The structiu-e noticed by Mr. Eoper in Coscinodiscus Jahyrinthus, and by myself in the more common species C. radiatus and Triceratium favxis, I OF THE DIATOME^. 39 believe to be of precisely the same nature, and I am much mistaken if we do not find it in many other species of the Diatomacea." In the accompanying part of the Jom-nal {J. M. S. 1858, p. 162), Prof. "Walker- Arnott refers with approval to this opinion of Mr. Shadbolt, and appends some most important remarks bearing on the presence or absence of this membrane in the determination of species. He observes that " There can be no doubt that these discs (i. e. of A^mchnoidiscus) have a horny vegetable outer covering, in addition to the siHcious one, and that by too long boiling in acid, as is necessary for guano, the marks are much obli- terated or entirely removed. This, however, is not peculiar to the present genus, but may be observed, more or less, in all Diatoms, although sometimes the vegetable pellicle is very thin and may be removed by a few seconds' immersion in boiling nitric acid. It is this circumstance which gives a quite different appearance to the same species, according as the preparation is made. Thus, in Actinocydus the vegetable epidermis is cellular, while the silicious part is striated like a Pleurosigma ; and when the vegetable part is removed, we often find nodules or knobs along the margin (forming, then, the genus Omj^halojyelta), not previously visible. Those who describe Diatoms from slides are thus liable to commit great errors, and indeed no certainty can be obtained, except by getting the recent or growing Diatom and examining it, 1st, after being immersed for a short time in cold acid, or simply washed in boiling water ; 2ndly, after being boiled in acid for about half a minute, or a whole minute at most ; and Srdly, after being boiled for a considerable time : we shall then see that many of the supposed distinct species of authors are the same, prepared in a different way. Of course, deposits or guanos can yield little or no information, although, when once a species has been determined by the way I have indicated, we may be able to refer forms occurring in guano or deposits to it with tolerable certainty." Mr. Brightwell, speaking of the lorica or silicious epiderm of Triceratmnij states that the valves are resolvable into " several distinct layers of silex, dividing like the thin divisions of talc, and frequently found of such exquisite delicacy as to be difficult of detection" (J. M. S. i. 248). The siHcious lamina is generally looked upon as a production or secretion fi'om the subjacent organic membrane, the true cell-waU. NageU (B. S. Rejports, 1846, p. 220) says, " it lies outside the membrane, and must be regarded, from analogy Avith aU other similar structures, as an extra- ceUular substance excreted from the ceU;" and, as Meneghini {op. cit. p. 360) adds, "in fact, anorganic mem- brane ought to exist, for the silica could not become solid except by crystal- lizing or depositing itself' on some pre-existing substance." Prof. Smith moreover states (A. N. H. 1851) that, apart from analogy, he has direct evi- dence of the independence of the silicious coat, having in his possession numerous specimens of a Stauroneis (probably S. aspera, Kiitz.), in which the valves, after slight maceration of the fnistules in acid, have, in part or wholly, become detached fi'om the ceU- membrane, leaving a scar on its walls bearing the distinct impression of the numerous and prominent valvular markings of this beautiful species. The same observer adds that he has in some cases noticed this organic membrane to contract around the ceU-contents, upon the death of the ceU. Again, the application of hydrofluoric acid, proposed by Prof. Bailey, to recent, and sometimes even to fossil shells, proves the same fact, by leaving a distinct internal flexible ceU-membrane retaining the general form, after the dissolution of the siHca by the acid. Further support, if needed, is furnished by the phenomena of cell-division, in which the lining membrane takes the initiative, and is foUowed by the doubling-in of the external coat upon it. 40 GENEEAL HISTORY OF THE INFUSOEIA. Nevertheless, although a silicioiis layer be artificially separable from the underlying organic coat, the relation and union of the two are indeed very intimate : and in the case of the apparently inorganic external lamina, the silex must be presumed to be deposited in some form of connective tissue, or, in other words, to permeate it. This opinion is advocated by Meneghini, who adduces in its support the circumstance of the sihcious shield of Ach~ nanthidia being covered with "a very delicate dilatable membrane, itself containing silica, as is proved by its sustaining imchanged the action of fire and acids." This author goes on to suggest that "this permeation may occur either in the wall of a simple cell, as is seen in the epidermal cells of many plants, or within minute cells, as in various plants and animals." The surface of Diatomaceous frustules is generally very beautifully sculp- tured, and the markings assume the appearance of dots (pimcta), stripes (striae), ribs (costae), pinnules (pinnae) ; of furrows and fine lines ; of longi- tudinal, transverse and radiating bands ; of canals (canalicuh), and of cells or areolae, whilst each and all these varieties present striking modifications in number, relative distribution, and in degree of development. Again, two or more sorts of markings may occur together in the same individual ; and lastly, the entire frustule may be covered, or certain spots may be left unoccupied by them, in the form of bands, circular spaces, and the like. The preceding accoimt of the coverings of a Diatomaceous frustule make it clear that the apparent superficial markings, although chiefly due to the sculpturing of the silicious epiderm and to its internal involutions, are still in some instances and in a certain degree dependent on the overlying firm vegetable membrane which Mr. Shadbolt and others have shown to exist. But, apart from this, modem research shows that puncta, lines, costae and other markings are not the same in nature in all examples presenting them ; that in one case a circular point is a depression, in another an elevation, and in a third a mere thickening or condensation of silicious material. So of lines or costae: some are markings of the surface, and either furrows, ridges or thickenings, or actual canals, whilst others are the result of invo- lutions or foldings of the internal coat or incomplete septa. Again, the fine lines or striae of many frustules are resolvable into rows of minute dots, as in Navicula and Pleurosigma. When the striae are more distinctly composed of rows of dots or puncta, they are described as monili- form ; examples occur in Gomplionema and Podosphenia. Speaking of striae, lines, and puncta generally. Prof. Smith {op. cit. i. p. xvii) confesses his belief that they are all " modifications in the arrangement of the silex of the valve, arising from the mode of development peculiar in each case to the membrane with which the silex is combined ;" and, referiing to the areolar or cellular-looking valves of Triceratium and of Isthmia especially, and to the recognized growth of organized beings by cells, he arrives at the conviction that " the valvular markings in every case arise from modifications of cellular tissue," which forms, so to sjDeak, the matrix of the silicious epiderm. " No difficulty (he adds) presents itself to the suj^position that the moniliform striae of Epithemia, Navimda, and others, the circular markings of Coschiodiscus eccentricus, and the iiTegular star-like stiTictiu'e of Eupodiscus Argus, are aU modifications of cellular tissue ; and even in the costas of Pin- nularia, and the unresolvable striae of Eupodiscus sculptus and others, it is not difficult to conceive we have confluent cells whose union gives rise to the appearance of lines or bands." Great difi'erence has existed, and even yet exists, in the interpretation of the exact nature of many superficial markings. Some cuTular dots or puncta are held by certain observers to be pits, by others holes, and by others to be OF THE DIATOME^. 41 elevations. So of stripes, costoe, and pinnules : to some, such markings in special instances are ridges ; to others, furrows or fissures ; to others, ele- vations ; and to others again, canals. The ardent microscopical research of this period is daily diminisliing the number of these enigmas, and intro- ducing certainty in place of doubt and vague conjecture. To Ehrenberg's apprehension, many puncta were real pores, and many striae or costse real fissures ; the former of these were supposed to give exit to a few or to multi- tudinous imaginary ' pedal organs ' for locomotion, the latter to serve for the passage of ova, and generally to bring the presumed internal animal organiza- tion into immediate relation with the external medium around it. Perhaps the discussion respecting the nature of apparent pores has been most animated in the case of the genera Navicula and Pinnularia, which present a large rounded spot at each extremity of the frustule and a central space known as the umbilicus*^; with a tubular or canal-like band connecting them together (XII. 15, 21, 46 ; XYI. 1). Prom the umbihcus, Ehrenberg believed a single locomotive organ to proceed — an undivided sole-like foot, similar to the locomotive organ of snails, whilst he represented the terminal jDoints to be orifices for the purposes of nutrition (IX. 134). Although denjdng the offices assigned them by the Berlin micrographer, Kiitzing coin- cided with him in the belief of their being actual pores, and supposed that they give exit to a gelatinous substance, such as is actually found sur- rounding some Navkulce, and becomes a prominent character in the tribe of Diatomeae represented by ScJiizonema. Schleiden (Princijyles of Botany, hy Lanhester, p. 594) speaks of the longitudinal band as a cleft, and of the median and terminal spots as circular enlargements or thickened spots of silicious matter. He moreover appends an enlarged lateral view of a Pin- nularia (XYI. 2, 3, 4, 5), to prove that the seeming central orifice is simply a depression. This explanation of their nature coincides in the main with that given by Prof. Smith, who asserts that these markings are due to a lon- gitudinal band of condensed and more solid silex, widened into small expan- sions at the centre and extremities, or at the extremities only, and probably designed to give firmness to the valve. " That these expansions (he adds) are not perforations in the valve, as alleged by Ehrenberg, and acquiesced in by Kiitzing, might be shown in various ways. The internal contents of the frustule never escape at such points when the frustule is subjected to pressure, but invariably at the suture or the extremities .... nor does the valve when fractured show any disposition to break at the expansions of the central Hne, as would necessarily be the case were such points perforations, and not nodules. Moreover, the central band of silex is itself frequently traversed by a narrow line which arises from the confluence of a series of cells, which thus form a minute tube ; but this tube invariably ends in a rounded extre- mity at the central and terminal nodules, and does not pass into an opening or aperture in the valve The bending down of this tube and the thickening downwards of the silex at the nodules give the semblance of depressions to the siu-face of the valve at such places. But I am disposed to think that this is merely an optical appearance, and at aU events assured that no perforation exists at such points, and that the terms apphed to these nodules by difi'erent authors, implying that they are openings or ostiola, are altogether inadmissible." Examples of nodules at the centre and extremities are found in the ^GneTQ. Ampliiprora, Pinnularia, Navicula (XII. 5, 6), and Gomphonema (XII. 15, 21, 46). In Stauroneis the central nodule is developed transversely, so as to form a smooth transverse band or ^'stauros" free from markings (XII. 7, 8, 18). A median longitudinal ridge or band exists in Navicula, 42 GENEBAL HISTORY OF THE INFUSOEIA. Stauroneisy &c., whilst in Am])M]pleura (XIII. 1, 2) two ridges are noticeable, but whether these are of the same nature structurally is uncertain. In Doryphora, again, there is a median band, but no nodules distinguishable ; and in Eunotia and Himantidium the terminal nodules would seem exceptional in character, being due, as Prof. Smith supposes, *' to an inflection of the valves at the point of junction." The roimded space in the centre of the discoid valves of Actinocyclus (XI. 132) and Arachnoidiscus (XV. 18-21J, which is devoid of areola, is designated by him a pseudo-nodule, in order, we presume, to contrast a mere bare space with the like smooth but condensed and thick- ened spots described as nodules. In this record of opinions, those of Siebold and Niigeli (J. M. S. i. 196) should not be omitted : — " Precisely at the spots (says the former writer) at which Ehrenberg and others suppose they have seen six openings (i. e. three on each valve) in Navicula, the silicious cell-membrane is thickened, and con- sequently forms so many rounded eminences which project internally." These views thus far tally with those of Prof. Smith and others ; however, a few lines further on in his essay, Siebold expresses the belief that the lines running along the middle of the sui-faces from one thickening to another " are to be referred to a suture, fissure, or rather gap, in which no silicious matter is deposited, so that in these places the delicate primordial membrane which lines the silicious shield can be brought into close relation ^ith the external world. I come to this conclusion fi'om the circumstance that it is exactly at these four sutures or fissures that the water surrounding the Navicula is set in motion." (See p. 50.) Upon the whole question of the actual nature of the markings on the surface of the silicious fnistules, we are happy to add a paper published by Prof. Bailey (SiU. Journ. ii. 349), which appears to afford a satisfactory elucidation. We present it entire, with the practical notes on manipulation, so that our readers may imdertake a critical examination for themselves : — " I now offer proof which removes all doubt, and shows that these markings are neither apertures nor depressions, but are in reahty the thickest parts of the shell. If the shells are placed in dilute hydrofluoric acid and watched by the aid of the microscope as they gradually dissolve, the thinnest parts of course dissolve fii'st, and apertures, if any exist, should become enlarged. Now the very parts which have been called orifices by some, and depressions by others, are the last of all to disappear as the shell is dissolved. This mode of observation, besides establishing the fact that these are the thickest parts of the shell, reveal many interesting particulars of structure. Thus, in the large Pinnidarla, it may be seen, with even a low power, that the two parallel bands (separated by a canal) which reach fi'om the central knob to the terminal ones, and which appear smooth before the application of acid, become distinctly striated after their surface is dissolved off, as does also the central spot itself, showing that striae which existed in the young shell are covered up and nearly obhterated^by subsequent deposits. In Staurosira the cross-band and the two longitudinal bands are the last to dissolve, and these last bands, as in most Diatomacea, appear separated by what is either a canal or thin portions of the shell. In Grammatoj>hom the undulating lines are internal plates, which are the last to dissolve. In HeliopeUa, Actinoiytyclms, &c., the polygonal central spot is the last to disappear. In Isthmia, the spots on the surface, which at first appear like granular projections, are in reality thin portions of the shell, and imder the action of the acid they soon become holes. The acid also proves that the larger spots at the transverse bands are a series of large arcuate holes in the silicious shell, and the piers of this series of arches remain some time after the rest of the shell has vanished. OF THE DIATOME^. 43 A few directions on the mode of manipulation may be useful. As the fumes of the hydrofluoric acid, if they reach the lenses, would greatly injure them, it is advisable to protect the front face of the objectives by temporarily con- necting to them a thin plate of mica by Canada balsam, as mica resists the action of hydrofluoric acid much better than glass. I prepare the cell in which the solution is to take place by cementing a plate of mica to a glass slide, and then cover all its surface, except a central small disc, with wax. On this disc, which forms a cell, the shells are put with a dish of water, and after adding a drop or two of acid by means of a dropping-rod of silver or platinum, the cell is covered with another plate of mica, and the slide is then placed imder the microscope." Some markings of the surface, apparent only as striae under inferior magni- fying powers, are in several genera resolvable, as before noticed (p. 40), into rows of rounded dots, e. g. in Pleurosigma ; and in consequence such specimens have been employed to try the relative powers of microscopes, and are spoken of as ' test objects.' But the powers of microscopes have been more severely tested of late years, by the endeavour to ascertain whether such dots are eleva- tions or de]3ressions of the surface, and, as might be expected, the dissension on this matter has equalled that respecting the central band and umbilicus. Dr. J. W. Griffith is in favour of their being depressions {Proc. Roy. Soc. 1855). He argues that, as the markings '^ are evidently depressions in the genera and species with coarsely marked valves (IstJimia, &c.), we should expect from analogy that the same would apply to those with finer markings (those viz. in dispute, Gyrosigma, Pleurosigma, and others). And this view receives further support from the fact that under varied methods of illumina- tion corresponding appearances are presented by the markings when viewed by the microscope — from those which are very large, as in Isthmia, through those of moderate and small size, as in the species of Coscinodiscus, down to those in which they are extremely minute, for instance in Gyrosigma, &c. The angular (triangular or quadrangular) appearance assumed by the markings arises from the light transmitted through the valves being un- equally oblique ; this may be readily shoAvn in the more coarsely marked valves {IstJimia, Coscinodiscus), which present the true structural appearance when the light is reflected by the mirror in its ordinary position, and the spiuious angular appearance when the light is rendered oblique by moving the mirror to one side." Another statement is put forward by the same author in the MicrograpMc Dictionary (Introduction, p. xxxiii) in support of his oj)inion, viz. " that the line of fracture of the broken valves passes through the rows of dots on the dark lines corresponding to them, showing that they are thinner and weaker than the rest of the substance. Had these dots represented elevations, the valves would have been stronger at these points." The more prevalent opinion, however, is, that these delicate dots in rows are elevations of the sm-face. Mr. G. Himt {J. M. S. 1855, pp. 174-175) adduces an observation to demonstrate this fact. He found that on a speci- men of Pleurosigma being moistened, the markings were almost entirely •obscured, but that on the application of a gentle heat " the moisture slowly retreated, lea\ing patches of the shell diy, and with the markings as dis- tinct as before." On observiaig these dry parts of the sheU, they were seen to be uniformly bounded by straight ]hiQB, parallel to the two directions of least distance of the dots. " Now (continues Mr. Hunt), on the supposition of these Httle dots being elevations, the phenomenon appears to me easily ex- plicable on the princijjle of capillaiy attraction. We can readily conceive the moisture clinging from one dot to another ; and it would always have a tendency to arrange itself in lines parallel to the directions of least distance. 44 GENERAL HISTORY OF THE II^FUSOEIA. I am, however, quite at a loss to imagine how the same principle would apply on the hypothesis that the dots are depressions, nor do I see upon what principle the phenomenon is explicable." A (hrect demonstration that the markings in general of the Diatomea3 are elevations is attempted by Mr. Wenham, whose knowledge of optics and prac- tical skill in mechanical manipulation are not exceeded by any microscopist of the present day {J. M. S. 1855, j)p. 244^245). To quote his words— "A careful study of the coarser varieties will distinctly prove that the markings are raised ribs or prominences on the surfaces, in some instances on one side of the shell only, as seen in the Cajnpylodiscus spiralis and others. Though the microscope proves this fact satisfactorily in the large species, it fails to do so in the most difficult specimens, chiefly on account of the above-named deceptive appearances, arising from the irregular refraction and reflection of light. It occurred to me that it might be possible to obtain a perfect cast or impression of the structure ; and by viewing this as an opake object, the error, if arising from refraction, would be avoided, and a discovery might be the reward of the experiment. I have succeeded in effecting this by means of the electrotype process, which for many reasons is to be preferred, as it does not distort the object, and is so minutely faithful that even the mere trace of organic matter, left by a slight finger-mark, is perfectly copied. The method I have adopted is this : — Procure a small plate of metal highly polished (a piece of daguerreo- type plate answers extremely well), and, after gently heating it, rub a piece of bees- wax over the surface ; while this is still melted wipe it nearlj^ all off again with a piece of rag, so as to allow a very thin film to remain ; when the plate is cold, arrange the Diatomacea or other objects, previously moist- ened, upon the waxed surface, heat the plate again to at least 212°, in order to cement the objects on it. The wax serves a twofold purpose : first, its interposition prevents the possibility of a chemical union of the metallic deposit with the plate ; and secondly, the object is secm^ely held thereto by its agency. The objects are now ready to receive a coating of copper. If the battery is in good working order, three or four hours will give a film sufficiently strong to bear removal ; when this is stripped off, if the process has been properly managed, the objects will be seen imbedded in its siu-face ; whether they are silicious or organic, they may be entirely dissolved out by boiling the cast in a test tube Avith a strong solution of caustic potash, and afterwards washing with distilled water ; the copper film may then be mounted in Canada balsam. By these means I have obtained distinct impressions of the markings of some of the more difficult Diatomacea, such as N. (Pleuro- sigma) Balticum, P. Hipjpocam'pus, &c., leaving no doubt of their prominent nature." (See MicroscojJic Cabinet, ed. 1832, chap. xvi. and xviii.) Besides the superficial markings explicable on the supposition of an invest- ing areolar membrane, and the sculptiu^ing of the silicious epiderm, there are others, dependent on structural modifications of the sihcious laminae of the valves, and on inflections of these internally. Among the former are many of the stronger-marked costae and pinnules of Ehrenberg ; and among the latter are to be reckoned the imperfect partitions (^ septa') seen in several genera, and those peculiar processes of the internal surface which Kutzing called ' vittce.' Schleiden described ' pinnules ' to be clefts or fissures. " In these spots (says he), the shield consists of two leaves lying one over the other; these leaves are penetrated by the small clefts, which, when both the lamellae touch each other, are somewhat broader, which explains the varying breadth of the clefts according to the alteration of the foci. Frag- ments in which this structui'e is clearly represented may be frequently obtained by crushing the shield." (XVI. 5, 6.) OF THE DIATOME^. 45 Prof. Smith likewise describes inter-lamellar channels, under the name of * canalicidi/ " hollowed out between the silicious epiderm and internal cell- membrane, and apparently formed by waved flexures of the epidermal enve- lope They are very conspicuous in Epithemia longicornis, and form distinctive characters in the genera Surirella and Campylodiscus.''^ This observer also regards them " as minute canals which convey the nutri- mental fluid to the surface of the internal membrane," this fluid entering them from without through pores or fissures existing along the line of sutiu-e of the valves (p. 50). That these canals are not modifications of the cellular structure of the silicious epiderm is shown by the cii'cumstance of the stri86 passing uninteiTuptedly over the entire surface of the valves in some Epithemice. The costae of Campylodiscus equally appear to be canaliculi, and are dis- posed in a radiate manner. In Surirella and TryhJionella these canals are usually parallel, whilst in Mastogloia they take the form of loculi. Kiitzing assigned a special structure and purpose to the markings he called ' vittce,' and used them in forming a subsection of Diatomeae he called Vittatce. The Kev. Prof. Smith remarks that to him these markings do not seem special organs, but modifications in the outline of the valve, which is inflected. In Grammatoplwra (XI. 48, 49, 52, 53) these inflections con- stitute a leading feature of the genus, and, from their resemblance to written characters, have suggested its name. In this instance they form incomplete septa. The terms striae and costae or pinnules are not synonymous. Striae are the finer lines of slight breadth, which may look like narrow grooves or ridges, whilst costae or pinnules are the wider markings, having an evident double contoiu', and the appearance of fissui^es or canals. The fineness of some striae is such that, as before noted, they may be readily overlooked ; however, their presence, when not positively demonstrable, may be assumed by the coloui's displayed on focusing diied specimens. An analogous fact presents itself in the case of mother-of-pearl, which owes its varying and beautiful colours to the existence of fine lines covering its surface. The colour varies in different species, and is due to the refraction of the rays of light passing through the silicious epiderm ; its shades depend on the direction of the striae and on their distance from each other ; its aid may therefore be advantageously evoked in the determination of species. Striae generally seem to be produced by the confluence of minute rounded points or beads — in other words, are commonly moniliform, and often extend, as products of an investing areolar tissue, over the entire surface of the valves, unlike those costae which originate in structural peculiarities of the silicious plates. Rows of puncta occur in Nitzschia, and moniliform striae in Navicida, Pleiirosigma, Gomphonema, and Podosplienia. To the confluence of the superficial cells, Mr. Smith attributes the production of the costae of Pinnu- laiia, whilst those of Achnanthes he looks upon as thickenings on the under surface of the silicious valves, and generally similar to those of Istlimia, which line the valves and anastomose on their under sui^face ; lastly, the striae of Rhahdonema are constituted of series of oblong cells. The value of the external markings of Diatomeae, in a systematic point of view, has been much discussed. Ehrenberg assumed the number of striae or of costae or pinnules to be constant in the same space in each species, and accordingly gives the number of striae counted within a given fraction of a line. A great multitude of species was the consequence of this plan ; never- theless the mere fact of number of striae within a given space cannot be esteemed a valid specific character by itself ; for it seems quite clear that the relative closeness of striae, their number within the -001 of an inch, varies according 46 GEKEEAL HISTOEY OF THE INFUSORIA. to the age and to the size of the valves, and both size and figure are consi- derably aifected by circumstances of growth, of locality, and the like. A writer in the Microscoj^ical Journal (1855, p. 307) suggests that the number of striae on the entire valve may supply a more stable character ; yet even on this point we are wanting in direct observ'ation to show that this number may not be affected by accidental circumstances. Although " the relative distance of the strise and their greater or less dis- tinctness " be accounted by Prof. Smith of specific importance, yet he is obliged to admit (J. M. S. 1853, p. 133) that it is by no means certain that these features may not to a slight extent be modified by localities and age, and is disposed to believe that they are certain guides only when we have made allowance for these conditions, and that while they are constant in fnistules originally from the same embryo, they may slightly vary in those which owe their birth to difierent embryonic cells. It is also worthy of note that, in certain instances, e. g. in Odontidium hyemalis, Ejnthemia A^xus, &c., the costse are frequently more numerous on one valve than on the other. Other illustrations of the variation in the number and in the distinctness of striae in the same species are to be found in the late lamented Dr. Gregory's valuable papers (T. M. S. 1855, p. 10). The relative position of striae — if parallel or radiate, their monihform or confluent character, their equal and general diffusion over the entire surface, or theii' absence at parts, are other circumstances available for the pmposes of classification. Besides striation, the other descriptions of superficial markings are resorted to for specific and generic characters. Such are the presence or absence of a median band, with central and terminal nodules, the existence of a trans- verse band, the figure, relative position and aggregation of the areolae or cells of the surface. The median and transverse bands have been employed by aU systematists, and would seem well suited to furnish characteristics by their constancy. The same may be said of the pore-like spots or nodules. Kiitzing went so far as to make the presence or absence of a central nodule or um- bihcus the turning-point in his grand division of the Diatomeae into um- bilicated and non-umbilicated. Lastly, speaking generally, the precaution intimated by Prof. Walker- Arnott (p. 39), of having specimens, intended to be compared together for the determi- nation of specific forms, similaiiy prepared, must ever be borne in mind where the superficial markings are referred to for characters; otherwise an excessive and erroneous multiplication of species, and a deplorable confusion will result. We have already seen that the connecting membrane is not an essential segment of a Diatomaceous frustule, but an after- development in connexion with the process of self- division; yet, notwdthstanding, it is so frequently present, and in many examples its dimensions and characters are so marked, that it supplies an important element in specific and generic descriptions. In the circular and discoid Diatomeae, it assumes the form of a continuous ring (XI. 40, 42), but in many oblong and navicular frustules it is itself oblong or navicular, having a figure the reverse of the valves it is placed between (XII. 17, 24, 31 ; XIII. 5, 6, 7). In these latter and in other instances it is frequently separable into two portions, at the opposite extre- mities of the frustules where the silex is absent ; and hence it is that the shells of the Diatomeae have been described by Meneghini and other writers as composed of foiu' segments. In general, the proportion of silex in its constitution is less than that in the valves; and the existence of markings— of areolae, striae, and the like— is also much rarer. Where they do occiu-, they furnish useful particulars in defining species and genera. The small development of the connecting OF THE DIATOMEiE, 47 membrane in Pleurosigmn is a remarkable feature of that genus, whilst in Gomplionema (XII. 28, 53), and other genera with cuneate (wedge-shaped) frustules, the figure is due to the greater development of this segment at one end than at the other. In Amphiprora (XIII. 5, 6), Achnanilies, Himanti- clium (XII. 50, 52), and Melosira, the connecting membrane is striated, and in Biddiilpliia (II. 48), Isthmia (X. 183), and Amphitetras (XI. 21, 22) is cellulate or areolate. In certain genera the connecting membrane takes on an extraordinary development, which greatly modifies the figure of the frustules. Instead of being Hmited to the interspace between the opposed valves, it extends on either side beyond the sutures (XII. 9), presents itself as a band of greater or less width, and acquires an unusual persistence. Under this form it con- stitutes the ' cingulum ' of descriptive wiiters, and is seen in Ampliitetras, Biddulphia, Podosira, and Melosira. In the last two genera. Prof. Smith tells us, the persistence of this cii^cular band is '' eminently conspicuous, retaining the frustules after self- division in a geminate union until the self- dividing process is renewed." Contents of Feustules. — Nucleus, supposed Digestive Sacs, Heproductive Vesicles, ^r. — The organic membrane of the frustules of Diatomeae, strength- ened externally by the silicious plates, encloses within its cell-like cavity a soft mucilaginous substance filled with numerous granules and globules, and usually of a yeUow-brown or orange-brown colour, but at times of a green hue, and technically known as the * endoclirome,^ or in Klitzing's phi'aseology, the ' gonimic substance.^ The granular matter is particu- larly aggregated about the organic waU, leaving the central portion more clear. In this clear central space is a transparent vesicle, representing the nucleus of the cell, having the granules frequently collected around it in an annular form. Nageli states that the nucleus, enclosing a nucleolus, lies sometimes free in the centre of the frustular cavity, but at other times is affixed at one spot to the wall, and therefore ' parietal.' He also describes two sorts of nuclei, viz. primary and secondary, attributing to the former the active part. Schleiden represents the nucleus to be primarily concerned in the original formation of the cell, as well as in its subsequent multiplication by seK- division. Among other elements of the endochrome are more or fewer rather translucent globules, which Prof. Smith believes, like Kiitzing, to be secre- tions of the cell, of a fatty or oily composition, and to be the source of the peculiar odoiu* emitted on burning the Diatomeae. In support of this \'iew Kiitzing states that he has occasionally seen two coalesce, proving the absence of proper walls, and expresses his conviction that these corpuscles are akin to the amylaceous secretions of the Desmidieae and Confeiwae and the starch-granules of the higher vegetables. These globules are smaller than the nuclear space, and occupy a pretty constant and definite position. " The number of these globules is frequently four, often placed near the extremities, or more rarely clustered round the central vesicle." Meneghrni (op. cit. R. S. p. 364), alluding to these vesicles, states them to vary in number, size, and disposition at different stages, and according to various conditions, even under the eye of the observer. These apparent oU-globules were called by Ehrenberg male sexual glands or testes, whilst those other vesicles distributed within the mucilaginous matter, often about the nucleus, were named stomachs. The latter idea he based especially on a series of experiments to introduce colouilng matter into the interior of the frustules, in which he believed he succeeded. The species mentioned are Navicid a gracilis, N. Ampjhishoena, N. viridida, N.fidva, 48 GENERAL HISTORY OF THE INFUSORIA. N. Nitzschii, N. lanceolata, and N. capitata ; also Gomplionema truncatum, Cocconema cistula, Arthrodesmus quadricattclatus, and Clostei^imn acerosum. The two last, however, are Desmidieae. In the seven species of Navicula enumerated, fi'om 4 to 20 little stomach- sacs are said to have become filled with the indigo employed as the colouring matter. *' This effect (as Meneghini remarks) could only be produced by keeping the Diatomeae a long time in water laden ^vith particles of indigo, and often re- newed." Kiitzing deduced an opposite conclusion from these experiments, viz. that they were solid corpuscles which, being seated near an opening, exerted an especial attraction upon the colouring matter. Meyen argued, so long since as 1839 {Jahreshericht d. Akad. Berlin), against the supposed stomach-sacs and the entrance of colouring matter within them. His objections are thus expressed : — " On the one hand, I can see no stomach-sacs in the Naviculce, and never observed in the living and moving Bacillaria the colouring matter received at one extremity and carried towards the centre, where these stomach-sacs should lie, whilst among the ciliated Infusoria such observations are easy ; on the other hand, it is not uncommon, especially in the larger species, to see the molecules of the colouring matter employed, lie upon the middle of the broad ventral surface, looking as if actually within the organism ; but if a glass plate be placed upon the specimen and then carefully removed, the particles of colouring matter are taken away with it." Even Ehrenberg admitted that the presumed stomach-sacs varied in number, were quite irregular in their disposition in the interior, and not unfrequently wanting altogether. This last circumstance, Kiitzing remarks, is opposed to the belief in their digestive functions, since such important organs as stomachs can never be supposed absent. Although the existence of this fanciful polygastric apparatus in the DiatomeaB is scarcely worth controverting, yet we may add to the above objections to it the fact that, in the hands of other experimenters, the attempt to introduce colouring matter by any definite apertures into the frustules of this family has been unsuccessftd. The arrangement of the mucilaginous endochrome, or rather of its pro- minent globules, vesicles, and granules, is sufficiently definite and constant in the same species to afford useful characteristics. At one time these molecules are diffused rather irregularly ; at another they are collected in a rounded heap towards the centre, whilst at another they are disposed in lines radiating from the nucleus, or formed in a layer upon the cell-waU, — ** at all times " (adds Prof. Smith) " having one or several oily globules, which occupy in different species different positions, but are constant in number and position in the same species. The minute granules " (he con- tinues, i. p. 20) " are generally accumulated in thin layers towards the internal cell-waUs : when the frustule is so turned that this layer of endochrome is presented edgeways to the eye, the granules appear to be chiefly aggregated into two plates applied to the opposite sides of the frustule ; and when self- division is in progress and the cell-contents are divided into two portions, such a separation or temporary aggregation must necessarily ensue ; but in the simplest condition of the fi^ustule the contents are diffused over the entire surface of the cell- walls, precisely as may be seen in the cells of many of the larger Algae, or of some water-plants of a higher order, as in the leaves of Hydrocharis Morsus-rcmce and others." Schultze has recently represented (Milll. ArcMv, 1858) a definite peculiar disposition of the endochrome — of its mucilaginous and granular portions and its' coloured corpuscles. In the more or less quadrate frustules of Denticellay and in the circular ones of Coscinodiscus, he describes the existence of a central OF THE DIATOME^. 49 clear vesicle, from which thin, finely granular lines or threads extend and intersect and branch in a reticulate manner, with a more or less distinct radiation, the more fluid contents flowing between them. In the long cylin- drical fnistules of RMzosolenia, on the contrary, these granular mucilaginous threads run longitudinally. Within these threads the colom^ing, yellowish- brown corpuscles, not circular, but, as Schultze says, irregularly multangular, are disposed and retained in their position. Although these researches extend to so few forms, yet we are disposed to believe that this disposition of the elements of the endochrome will be found to be the rule. A regular arrange- ment is figured in many di'a wings of the Diatomeae by various observers ; and where it does not appear it is most probably due to the want of attention to its presence, — or to the excessive multiplication of the coloming corpuscles, causing them to appear spread beneath the envelopes as a pretty uniform layer. A definite disposition of the chlorophyll-granules is common in plants, particularly among the lower Algae, and owes its constancy to the presence of the mucous and less fluid contents, which are condensed from the sur- roimding fluid in the form of filmy threads, and serv^e as a nidus to the colour- ing particles. In this disposition, therefore, of the endochrome and its cor- puscles we perceive a vegetable character, as contrasted with what is seen in animal ceUs, and find in it an additional argument for the vegetable nature of the Diatomeae. Notwithstanding that the endochrome is, by pretty general consent, ho- mologous with that of recognized vegetable Algae, still it would seem to be of a different chemical composition as well as of another coloui\ Kiitzing, indeed, insisted on the fact of the similarity of the endochrome to the gonimic substance of Algae, from the circumstance that, by means of alcohol, he was able to extract a coloimng matter similar to chlorophyll ; yet Eaben- horst and others have remarked a difference in chemical nature. Prof. Smith again, whilst admitting the imperfection of our knowledge on this point, goes on to say that " the tincture of iodine causes the internal membrane to contract upon the cell-contents, and converts these from the golden yellow which they exhibit in some species, into bright green, and that a weak solution of sulphuric acid, while it eff'ects the same contraction in the ceU- waU, gives to the contents, which have been previously treated with iodine, a dark-brown hue : alcohol, on the other hand, as in the case of vegetable ceUs in general, dissolves the utricle and its contained endochrome, or at all events entirely removes their colour, and leaves their silicious epiderm in a state of perfect transparency. It does not, however, dissolve the envelope in which the frustules of the frondose forms are imbedded, nor the filamentous stipes or gelatinous ciLshions to which other species are attached." Meneghini {op. cit. R. S. p. 365) contends that the identity in nature of the endochrome of Diatomeae and of Algae is not proved. " Its colour is dif- ferent ; and it is diiferently coloured by chemical reagents. The resemblance to it in some instances, as in Melosira, in regard to conformation and suc- cessive alterations, is only in appearance. In the endochrome of Algae the monogonimic substance begins by presenting a granular appearance ; then it becomes distinctly granulated and changes into the polygonimic substance, so minutely described by Kiitzing. But these changes do not occur in the coloured substance of Diatomeae. If we insist on a parallel, we can only compare it to the cryptogonimic substance of Byssoidia, CaUithcimnia, Griffiihsia, and Polysi])ho7iia. It divides into two parts which successively undergo ulterior division ; and in regard to these changes we may observe that there is an essential distinction between those that occur during life and those that take place after death, the greater number happening in the latter 50 GENERAL HISTOEY OF THE INFrSORTA. condition The identity of this substance with endoclirome is contradicted by KUtzing's own experiments, ...... which prove it to be very rich in nitrogen : it emits ammonia copiously when decomposed by heat ; and this can only proceed from a substance abounding with it, which such a decom- position compels it to yield up. Nor, on the contrary, do I beheve that there is any weight in the argument from the solubility of its colouring principle in alcohol ; for this is not aproperty pecuhar to chlorophyll, or to any sub- stance of vegetable origin." The contents of the frustules are brought into relation with the surround- ing medium through certain pores or fissures, which have been referred to as existing here and there along the sutures between the opposed valves, or othermse between the valves and the interposed connecting membrane. The existence of such openings in the siHcious envelope, and the consequent exposure of the organic internal or primordial membrane in the situations mentioned, have been demonstrated chiefly by the researches of Prof. Smith, who apphes to them the name of 'foramina.^ Thej^ are thus described {op. cit. i. p. 15) : — " Along the line of suture in discifonn or circular fnistules, but more generally at the extremities of the valves only, when the Diatom is of an oblong, hnear, or elongated form, there exist perforations in the silex which permit the surrounding water to have access to the sm-face of the internal cell-membrane. The fonnation of silex seems occasionally to be arrested in the neighboui-hood of these spots ; and the connecting membrane is in consequence either wholly or partially interrupted at such places. Thus, after the internal cell-membrane has been removed by acid, when it often happens that the valves fall away from the connecting membrane, the latter separates into two parts ; and the fi'ustule has in consequence been described as consisting of foui' plates. The interruptions in the silicious epiderm are usually apparent as shght depressions at the extremities of the frustule ; and the appearances they present have been denominated ' puncta' by Mr. Ralfs. In some species these interruptions are more numerous, being found along the entire line of suture, and are often connected with minute canals hollowed out between the silicious epidenn and the internal ceU-membrane, and ap- parently formed by waved flexui'es of the epidermal envelope." The latter constitute the canalicuh heretofore spoken of (p. 45). Siebold regarded the longitudinal bands having a double outhne, and ex- tending from the apparent dots or pores at either end of Naviculce to near the centre, to be fissures ; but the account previously given proves this able man to have been mistaken on this point. Like Prof. Smith, however, he con- cluded that the internal membrane was imperforate, and that it served as the medium for the exosmosis and endosmosis attending the function of nutrition. Movements of the Diatomeje ; — their character and causes ; — Cilia ; — Circulation of Contents ; — Respiration. — The peculiar movements noticed in many Diatomeae have attracted the observation of all microscopists, and have induced many, especially among the older observers, to receive it as evidence of their animal nature ; but even those who agree on this point are in no better accord among themselves respecting its cause than are those who refer these beings to the vegetable kingdom. The power of movement is not confined to those only which are free, but also to concatenate and to some fixed forms, e. g. Synedra, which move on their fixed extremity. There is considerable diversity both in the manner and extent of movement of different species; but in none is it exhibited in an equal degree to that seen in the spores of Algae. " The motion," says Prof. Smith, " is of a peculiar kind, being generally a series of jerks producing a rectilinear OF THE DIATOME^. 51 moTement in one direction, and a return upon nearly the same path, after a few moments' pause, by another series of isochronal impulsions. The move- ment is evidently of a mechanical natui'e, produced by the operation of a force not depending upon the volition of the living organisms : an obstacle in the path is not avoided, but pushed aside ; or, if it be sufficient to avert the onward course of the fi'ustule, the latter is detained for a time equal to that which it would have occupied in its forward progression, and then retires from the impediment as if it had accomplished its fuH course. There is cer- tainly no character of animality in the movement ; and the observer, familiar "vvith the phenomena of life in the earlier stages of vegetable existence, is constrained to see a coimterpart in the involuntary motions of the filaments of the Oscillatorieae, or of the gemmiparous spores of the Fuci and Con- fervae." This same view was taken by Morren in 1839 {op. cit.), who says — '' The movement of the BaciUaria, however free it may be, is by no means so free and active as that of the spores of Algae, which are plants, or, at least, parts of plants ; and the motion is no positive ground for the belief in their ani- mality." The cause of the motion of the Diatomese has hitherto not been satisfacto- rily determined. To the hypothesis of a snail-like expanding foot projecting fi'om the central pore or umbilicus, advanced by Ehrenberg, we have already alluded (p. 41); and since no one original observer, in spite of the best-dii^ected efforts, has been able to detect the remotest evidence of such an organ, and as all evidence goes to show that no actual perforations exist at the point indicated for its extrusion, it would be useless to raise any argument upon it. This distinguished natui^alist subsequently satisfied himself of the presence of other locomotive organs in a Navicida (Surirelhi gemma, XII. 3, 4), which he has thus described : — " Instead of a snail-like expanding foot, long delicate threads projected, where the ribs or transverse markings of the sheU joined the ribless lateral portions, and which the creatui'e voluntaiily drew in or extended. An animalcule ^th of a line long had 24 for every two plates, or ninety- six in all ; and anteriorly, at its broad frontal portion, foui^ were visible. Whether these organs were supernumerary, and existed along T\dth cirrhi, &c., and with the flat snail-hke foot which the rest of the Naviculce possess, could not be determined. Longitudinal clefts at the broad side of the shell were not present ; but as many as 96 lateral openings for the exit of the ciiThi were perfectly distinct." These ciliary processes were farther stated to be actively vibratile, and to be retracted or extended at short periods. Prof. Smith has remarked on this appearance, that the presence of haii^s apparently on all parts of the frustule may often be detected, and that he has noticed them on nearly every occasion on which he has gathered this species, but in no case has he been able to perceive any motion in such hairs ; and he therefore concludes that they are merely a parasitic growth, such as the mycelium of some Algae. He has also seen similar appendages to other Dia- tomeae, but in every case devoid of motion. The notion of exsertile and retractile feet has been renewed by M. Focke {Comptes Remlm, 1855, p. 167), who attributes the movements of Navicida to such organs of a temporary kind, which he says pass through openiags he has detected on the sides of the lorica. Nageli offered the following, and, to Siebold's mind, satisfactory, explana- tion of the forward and backward movement, as well of many Desmidie* as of Diatomeae {J. M. S. 1853, p. 195). " The cells," he writes, " have no special organs for these movements. But as in consequence of their nutri- tive processes they both take in and give out fluid matters, the cells neces- e2 52 GENERAL HISTORY OF THE INFUSORIA. sarily move when the attraction and the emission of the fluids is unequally distributed on parts of the surface, and is so active as to overcome the resistance of the water. This motion, consequently, is observed more particu- larly in those cells which, in consequence of their taper form, easily pass through the water ; these cells, moreover, move only in the direction of theii' long axis. If one half of a spindle-shaped or ellipsoidal cell chiefly or en- tirely admits material, the other half, on the contrary, giving it out, the cell moves towards the side where the admission takes place. But as in these cells both halves are physiologically and morphologically exactly alike, so it is that it is first the one and then the other half which admits or emits, and consequently the cell moves sometimes in one, at other times in the opposite direction." In our apprehension, this mechanical interpretation of the phenomenon is not sufficient ; the alternate reception and discharge of fluid matters by each opposite half requires an effort of imagination, to conceive, unwarranted by analogy. We shall, however, presently see that Prof. Smith gives the pre- ference to this supposition, amid the many conflicting fancies of authors and the obscurity of the question. Encouraged by apparent success in discovering cilia on the fronds of Des- midieae, Mr. Jabez Hogg searched for them on Diatomeae, and tells us {J. M. S. 1855, p. 235) that he has repeatedly satisfied himseK that their motive power is derived from ciha arranged around openings at either end, — ^in some also around the central openings, which, mth those ciha at the ends, act as paddles or propellers. He, moreover, states his impression that the frustules have a degree of volition sufficient '' to move along and to steer their coiu'se ; for intervals of rest and motion are most clearly to be distinguished." To this behef in cilia on the frustules of Diatoms, Mr. Wenham is as determined an opponent as he is to the Hke hy[Dothesis respecting the Desmidieae (J. M. S. 1856, p. 159), and he offers the folloTving speculations on the cause of the movements : — " If caused by the action of ciha, such extremely rapid impulses would be required to propel the comparatively large body through the water, that surrounding particles would be jerked away far and Tvdde ; a similar effect would be observed if the propulsion were caused by the reaction of a jet of water, which, according to knovni laws of hydrodynamics, must neces- sarily be ejected with a rapidity sufficient to indicate the existence of the current a long distance astern. I consider that there is no ground for assuming the motions of the Diatomaceae to be due to either of these causes. They are ui'ged forward through a mass of sediment without displacing any other particles than those they immediately come in contact with, and quietly thnist aside heavy obstacles directly in their way, with a slow but decided mechanical power, apparently only to be obtained from an abutment against a sohd body. In studying the motions of the Diatomeae, I have frequently seen one get into a position such as to become either supported or jammed endways between two obstacles. In this case, particles in contact with the sides are carried up and down from the extreme ends with a jerking move- ment and a strange tendency to adherence, the Diatom seeming unwilling to part with the captured particle. Under these circumstances I have dis- tinctly perceived the undulating movement of an exterior membrane ; whether this envelopes the whole sui^face of the silicious valves I am not able to determine, nor do I know if the existence of such a membrane has yet been recognized. The movement that I refer to occupied the place at the junction of the two valves, and is caused by the imdulation of what is known as the * connecting membrane.' This will account for the progressive motion of the Diatomeae, which is performed in a manner analogous to that of the OF THE DIATOMEJE. 53 Gasteropoda. The primaiy cause, however, is different, and not due to any property of animal vitality, but arises, in my opinion, merely from the effects of vegetable circulation. I have observed several corpuscles of uniform size travel to and fro apparently vrithin the membrane, which is thus raised in weaves by their passage." Mr. Wenham foUows up this explanation by a conjecture with respect to the rarer movements of the Desmidieae. " As there are in these," he writes, " no indications of either external orifices or cilia, may not their locomotion be effected by the currents of protoplasm forcing their way between the primordial utricle and outer tunic, which will thus be raised in progressive waves if the investment happens to be in a suitably elastic condition." (See p. 5.) The undulating movement of an exterior membrane thus indicated by Mr. Wenham, over the surface of Diatomaceous fnistules, is doubtless identical -with the ciuTcnt demonstrated by Siebold by means of indigo (J. M. S. i. pp. 196, 197). The latter states that the particles of this colouring matter which come in contact with the living NavicuJce are set into a quivering motion, although previously quite motionless ; but this happens only along the lines of the foiu" sutures, the particles adherent to other parts of the shield remaining motionless. " The indigo particles, which are propelled from the terminal towards the two central eminences, are never observed to pass beyond the latter : at this point there is always a quiet space, fi'om which the particles of indigo are again repelled in an inverse direction towards the extremities. This proves that the linear sutures, as may in fact be seen, do not extend over the central eminences of the shield. The current at these clefts is occasionally so strong, that proportionally large bodies are set in motion by it." The sutures and clefts alluded to by Siebold, it should be imderstood, are not the sutures between the valves and connecting membrane, but the evident lines extending between the apparent pores on the valves, and w^hich, to his apprehension, are actual fissm^es in the silicious envelope, by which " the delicate primordial membrane which lines the sihcious shield can be brought into close relation with the external world." This belief in the presence of such fissm^es on the valves we have previously examined and shown to be unfounded. (See p. 41.) Prof. Smith has the following remarks on this debateable point of the cause of the motions of Diatomeae {op. cit. vol. i. p. xxiii) : — " Of the cause of these movements, I fear I can give but a very imperfect account. It appears certain that they do not arise from any external organs of motion. The more accui'ate instruments now in the hands of the observer have enabled him confidently to affirm that all statements resting upon the revelations of more imperfect object-glasses, which have assigned motile cilia, or feet, to the Diatomaceous fi'ustule, have been founded upon illusion and mistake. Among the hundreds of species which I have examined in every stage of growth and phase of movement, aided by glasses which have never been surpassed for clearness and definition, I have never been able to detect any semblance of a motile organ ; nor have I, by colouring the fluid with carmine or indigo, been able to detect, in the coloured particles surrounding the Diatom, those rotatory movements which indicate, in the various species of true infusorial animalcules, the presence of cilia. I am constrained to believe that the movements of the Diatomaceae are owing to forces operating within the frustule, and are probably connected with the endosmotic and exosmotic action of the cell. The fluids which are concerned in these actions must enter and be emitted through the minute foramina at the extremities of the silicious valves ; and it may easily be conceived that an exceedingly small quantity of water expelled through these minute aper- 54 GENERAL HISTOEY OF THE INFrSOEIA. tures would be sufficient to produce moYements in bodies of so little specific gravity. " If the motion be produced by the exosmose taking place alternately at one and the other extremity, while endosmose is proceeding at the other, an alternating movement would be the result in fnistules of a linear form, — while in others of an elliptical or orbicular outline, in which foramina exist along the entire line of suture, the movements, if any, must be irregular, or slowly lateral. " Such is precisely the case. The backward and forward movements of the Naviculece have been already described ; in Sninrella and Campylodiscus the motion never proceeds farther than a languid roll from one side to the other ; and in Gomphonema, in which a foramen, fulfilling the nutritive office, is foimd at the larger extremity only, the movement is a hardly perceptible advance in intermitted jerks in the dii-ection of the narrow end. The subject is, however, one involved in much obscurity, and is probably destined to remain, for some time to come, among the mysteries of Nature, which baffie while they excite inquiry." The last clause of this quotation expresses the unsatisfactoiy state of the question; yet the foregoing examination will, we think, leave only three hypotheses desei'ving further inquiiy : viz., 1. the existence of cilia, or, 2. of an undulating membrane ; and 3. the operation of endosmose and exosmose, as a mechanical cause. To our apprehension, the presence of cilia, perhaps ranged only along the sutural lines, has not been completely disproved ; and, on the other hand, considered as locomotive organs, cilia have the great advantage of analogy over the presumed undulatory membrane. Do not, indeed, the experiments with indigo, recoimted by Siebold, suggest cilia to be the active agents of the movements recorded ? The rate of motion of the Diatomeae is exceedingly languid and slow; sometimes it amounts to no more than an oscillating movement, with Httle or no change of place ; and at anothei*, the backward and forward movements are so nearly equal, that the fnistule makes no appreciable advance. Prof. Smith has measured the rate of motion of some species, and remarks that, however vivacious and rapid they may at first sight seem, yet, when con- sidered vdth reference to the high magnifying powers employed, and the consequent amplification of their movements, they are very slow. " I have noted the movements of several species with the aid of an eye-piece micro- meter and a seconds watch, and found that one of the most rapid, viz. Bacil- laria paradoxa, moved over g- ott^^ ^^ ^^ ^^^^ ^^ ^ second ; Pinnularia radiosa, one of the slowest, over ., .^....th of an inch in the same time ; and that the same period was occupied by Pinmdaria ohlonga m traversing -ginroth of an inch, Nitzschia linearis y-V^th of an inch, and Pleurosigma strigosum ytwo^^ of an inch. Or, expressing the spaces and times by other units, we find that the most active required somewhat more than three minutes to accomplish movements whose sum would make one inch, and the slowest nearly an hour to perform the same feat." Before quitting the subject of the movements of the Diatomeae, we would briefly advert to the peculiar motion of some species, especially of BaciUaria paradoxa. The movements of this organism, as the specific name implies, are paradoxical, or very strange in character. Mr. Thwaites essayed to describe what indeed can be rightly apprehended only by personal ob- servation, in the following words (Proc. of Linn. Soc. i. p. 311): — "When the filaments have been detached from the plants to which they adhere, a remarkable motion is seen to commence in them. The first indication of this consists in a shght movement of a terminal fnistule, which begins to slide OF THE DIATOME.E. OO length^\dse over its contiguous fmstule ; the second acts simultaneously in a similar manner mth regard to the third, and so on throughout the whole filament, — the same action having been going on at the same time at both ends of the filament, but in opposite directions. The central frustule thus appears to remain stationary, or nearly so, — while each of the others has moved with a rapidity increasing with its distance from the centre, its OAvn rate of movement ha\ing been increased by the addition of that of the inde- pendent movement of each fmstule between it and the central one. This lateral elongation of the filament continues imtil the point of contact between the contiguous frustules is reduced to a veiy small portion of theii' length, when the filament is again contracted by the fnistules shding back again as it were over each other ; and this changed direction of movement proceeding, the filament is again di'awn out until the frustules are again only shghtly in contact. The direction of the movement is then again reversed, and con- tinues to alternate in opposite dii'ections, the time occupied in passing from the elongation in one direction to the o^^posite being generally about 45 seconds. If a filament while in motion be forcibly divided, the iminjured frustules of each portion continue to move as before, proving that the filament is a compoimd structure, notwithstanding that its frustules move in unison. When the filament is elongated to its utmost extent, it is extremely rigid, and requires some comparatively considerable force to bend it, the whole filament moving out of the way of any obstacle rather than bending or separating at the joints. A higher temperatiu'e increases the rapidity of the movement." To this account Prof. Smith appends these observations : — " The motion here so accurately described is not essentially diff'erent from that noticeable in many of the free species of Diatomeae, the pecuHarity being that it is here exhibited in numerous united frustules ; when observed in a band of one hundred or more frustules, the singular appearances assumed by the filament under the action of so many individuals moving at one time in apparent concert, and another in opposition, never fail to excite astonish- ment." Mr. Thwaites's account conveys the impression that the movements are always regular : but this is not the case ; for Mr. Ealfs tells us, by letter, that both Dr. Bailey and himself have convinced themselves that they are at many times irregular. Dr. Donkin, in his description of a new species of Bacillaria he names B. cursoria (J. M. S. 1858, p. 27), has the following account of its singular move- ments : — " When the filament is in a quiescent state, the frustules are all dra^Ti up side by side, their extremities being all in a line, thus forming a group. When a filament previously at rest resumes its activity, the movement] is commenced by the second or inner fmstule at one end of the filament gliding forward along the contiguous surface of t\iQ first or outer frustule until their opposite extremities overlap each other. This is soon followed by a similar movement of the third, fom^h, and fifth, &c., all moving forward in the same direction, and each fmstule gliding along the suiface of the one preceding it, imtil they have extended themselves into a lengthened filament or chain. In the course of two or thi'ee seconds after this has been accomplished, a retrograde movement, exactly of the same character, begins to take jDlace, and continues until the filament has retraced its course, and stretched itself out in a direction exactly opposite to the position it had previously occupied. This phenomenon is repeated again and again ; and in this manner the whole group is kept in a state of activity for an indefinite period of time ; and all the while, if no impediment produces irregularity, the outer or terminal frustide, next to which the movement commenced, maintains a stationary atul fixed position. 56 GENEEAL HISTOHY OF THE INFTJSOEIA. " The rapidity with which each individual frustiile moves is in direct rati to its distance from the terminal stationary frustnle, being most rapid at the opposite or moving extremity of the filament. On this account, most of the friistules, while the filament is moving to and fro, cross a line drawn at right angles to the middle of the long axis of the stationary frustule, at the same instant of time, afterwards shooting past each other like horses on a race- course. " The force with which the filament moves is very great, so much so that I have observed it upset and shove aside a large fnistule of A. arenaria, n. sp., at least six times its own bulk, obstructing its path. This force is, in a great measiu-e, due to the rapidity with which the frustules move, — the time which a filament, even of considerable length, occupies in crossing the field of the microscope being only a few seconds. " Light appears to be a necessary stimulus for the maintenance of this motion. When a filament in active motion is placed in the dark for a short period, and then examined, the movement is seen to have ceased, but again commences when the filament is exposed to the light for a short time. Is not this singular movement, Tvith which the present species is endowed, a vital phenomenon, and independent of physical causes for its existence ? '^ When the moving extremity becomes entangled in any kind of substance intercepting its coui'se, the opposite or stationary extremity commences to move, and continues to do so until the entangled extremity is set free ; sometimes, in such instances, a frustule in the centre remains fixed, a move- ment of each half of the filament in opposite directions, on either side of it, taking place. But all these irregularities cease as soon as the impediment has been got rid of. " These facts lead to the conclusion that the present species is a true Bacil- laria, although aiDparently somewhat anomalous in the structure of its frustule. The gliding movement of one fi'ustule over the contiguous one is the same as is observed in B. paradoxa ; but it difi'ers from this latter species in this essential particular, that the wlioU of its filament moves on one side of a terminal frustule which is stationary, — while, in B. paradoxa, each half of the filament moves in opposite directions on either side of a central stationary frustule." The movement of one segTaent upon another is witnessed in other con- catenate species, but in a less degree, where the medium of attachment is limited to a small space, as in those several genera having the alternate or opposite angles of their frustules connected by a link-like isthmus, e. g. Diatoma, Fragilaria, Grammatophora, &c. Nutritive Fitnctions; — Supposed Stomachs; — Circulation of Contents; — Kespiration. — The nutrition of Diatomeas is provided for primarily by the endosmotic and exosmotic action going on through the ' foramina ' in the silicious epiderm, whereby fluid material laden with the matters necassary to build up the various elements of the endochrome is introduced into the organisms. On the first appearance of a frustule, the endochrome is homogeneous and granular ; but as time advances, granules are seen to congregate in certain parts, and globules or vesicles of various size speedily develope themselves, and either take up definite positions or are irregularly diffused. During these changes in the contents — during, indeed, the entire life of _ the cell, under the influence of light, oxygen is given off, and the gases -with which it was united in various chemical compounds are appropriated to the purposes of the economy. The veiT fact of the existence of the silicious epiderm, thrown off, it would OF THE DIATOME^. 57 seem, as an excretion from the organic membrane of the frustiiles, indicates the activity and energy of the nutritive fimctions, — a fact further demonstrated by the production of the ' connecting membrane/ and, in short, by the whole process of reproduction, whether by self-di^dsion or by sporangia. The silica present in the lorica must be taken up by the organism in a state of solu- tion ; and although the quantity of silica dissolved in water is inconceivably small, it is nevertheless sufficient to supply the material for the construction of millions of Diatomaceous shells, even in a short time, as the phenomena of reproduction and the rapid appearance of these structures as an appre- ciable powder, or as a coloui'ing matter in water, prove. " It is probable," says Dr. Gregory {J. M. S. 1855, p. 2), " that as fast as the silex is extracted from the water hj them, it is dissolved from the rocks or earths in contact mth the water, so that the supply never fails ;" and we may add, so that the quantity never accimiulates beyond the very minute fi^actional portion chemists can detect. Ehrenberg's untenable hypothesis of the presence of stomach-sacs and of an alimentary canal opening externally has received sufficient attention in the history ah^eady given (pp. 47, 48), of the natiu^e of the contents of the Diatomeae and of their investing lorica. "Were other considerations needed, the absence at times of any such vesicles as Ehrenberg conceived to be gastric cells, their occasional coalescence, and the phenomenon of cyclosis or the circulation of the contents, each and all subjects of direct obsei^ation, might be appealed to as proofs of the errors that great naturalist fell into respecting the internal organization of the Diatomeae. The phenomenon of cyclosis has been observed by Niigeli in a species of Navicida, and in one of GallioneUa {Melosira) (XY. 27), and by Prof. Smith in other Diatoms. This writer says {op. cit. i. p. xxi) — " In SurireUa biseriata this motion has been more especially apparent ; but I have also observed it take place in Nitzsclda scalaris and Camj)i/lodiscus scalaris. This cii^culation has not, however, the regularity of movement so conspicuous in the Des- midieee, and is of too ambiguous a character to fuiTiish data for any veiy certain conclusions, save one, viz. that the Diatom must be a single cell, and cannot contain a number of separate organs, such as have been alleged to occupy its interior, — since the endochrome moves fi^eely from one portion of the frustule to the other, approaching and receding from the central nucleus unimpeded by any intervening obstacle." Schultze, in his contribution on the movements within the frustules of Diatomeae {Midi. Arcliiv, 1858), represents them to occur in and along the finely granular threads into which the less fluid mucilaginous portion of the endochrome is di^awn out. He compares the movements in character to those of the ' variable processes ' or pseudopoda of Ehizopodes, and thereby assimilates the mucilaginous films of Diatomaceous fnistules with the soft sarcode of those simplest animalcules, — a similarity countenanced by the now weU-known fact of an Amoebiform phase in the cycle of development of some of the lower Algae {vide section on Phytozoa). The cyclosis in plant-ceUs is no doubt rightly attributed to the operation of the vital processes of nutrition and of the so-called respiration, and primarily to the chemico-vital action proceeding by the medium of the chlorophyU-globules ; and it seems most con- sonant with the teachings of science to assign the less active and less complete and regular internal movements of the Diatomeae also to the similar vital forces, — the coloured corpuscles, it may be, acting here likewise as the prime mover. We are aware that the nucleus has been represented to be the first source of the movements in plant- cells, since the current seems to flow from and to return to it in many cases ; but this phenomenon is explicable in 58 GENEEAL HISTORY OP THE INFUSOllIA. another way, by admitting the disposition of the mucous threads as displayed by Schultze, extending as they do from the nucleus on all sides, and serving at the same time to limit and to direct the movements taking place within and by them. We have not adverted to ciliary action as the cause, for ; so far as we can gather, Mr. Osborne and Mr. Jabez Hogg have failed to impress many naturalists with the fact of its existence and operation in Diatoms. Lastly, Schultze remarks that, to see the mucilaginous threads and the internal movements, living and fi^esh specimens are needed ; for they are soon arrested when the frustules are removed from their natui-al habitats, and are quite lost to vision when they become diy. Hence it is, no doubt, that no previous observer has detected and rightly apprehended the facts enunciated by Schultze. The so-called function of respiration is evinced in the fixing of the carbon of the carbonic acid and in the disengagement of oxygen gas ; but this is rather an act of nutrition, and resembles that silent and invisible disengage- ment of certain particles, and the rearrangement of others, which proceed in the formation and in the removal of worn-out tissues in higher animals. MuLTiPLiCATiois", REPRonrcTio:?^, AifD Developmej^t of DiATOMEiE. — Among the modes of reproduction of the Diatomeee, self- division has usually been accoimted one, but erroneously so, since this process is no more than a mul- tiplication of an individual cell, and completely homologous with the process of cell-fission exhibited in the construction of animal and vegetable tissues in general. The peculiarity in the self-division of the Diatomeae, i e. among the free simple beings, is, that the division is followed by separation ; for each cell, instead of imiting Avith its neighbours in the formation of a tissue, commences an independent existence. Self-division in one direction, not followed by separation, produces the filamentary or concatenated Diatomeae, whilst the abundant excretion of a mucus around the dividing frustules, and its persistence, give rise to the frondose genera, which make an approach towards the character of vegetable cellular tissue, — each ceU, however, retain- ing an independent vitality greatly more pronounced than in the latter. The process of self-fission or deduplication in this family resembles in all essential particulars that in other vegetable cells (XY. 28, a, h, c). Preparatory to its visible occurrence, or rather simultaneously Tvith certain changes in the interior, the valves separate by the progressive gro^i;h of the connecting membrane. The nucleus within is observed to divide into two portions, each of which eventually becomes detached from the other, and, in Prof. Owen's language, serves as a centre of spermatic force, and induces an aggregation of the granules of the endochrome about it. Whilst this separation of the nucleus and of the general contents is going forward, the lining or primordial membrane of the cell becomes doubled inwards in the entire cii'cumference along the line of division, and advances gradually until it at length forms a complete septum, cutting the original single cell into two. This septum is actually double ; and in each lamina a deposit of silicious material speedily proceeds, so as to produce two new valves, each opposed to, and immediately continuous around its circumference with, one of the two original valves. Thus, on the completion of this process of deduplication, two finistules result, awaiting only the final act of separation to enter on an independent exist- ence and to repeat the like series of phenomena, and so on through a seemingly almost endless chain, to perj)etuate the existence of the particular species or individual. (See Meneghini's account of the process and peculiari- ties of self-di\dsion in this class, in the examination of the argimients for the animality of the Diatomaceae, in a subsequent page.) The true nature, there- fore, of this process of self-di\-ision being an extension, not a renewal, of OF THE DIAT03IEJE. 59 individual life, has been justly represented by Mr. Thwaites as an act of gemmation, not of reproduction. In the coiu\se of self- division, in some instances at least, a mucous or muco-gelatinous matter is thrown out around the fiiistules engaged. This cii'cumstance did not escape the notice of Nageli ; and Prof. Smith (Si/nopsiSj i. p. 62) has, after noting it in previous pages as'a common phenomenon in the family, thus referred to it in the genus Pleiovsigma : — " While self-division is actively going forward, the mucus generated by the dividing fi^ustules is often so considerable as to produce the appearance and effect of a distinct frond, which assumes the form of a thin pellicle of some little tenacity. At other times, when the mucous secretion does not assume the continuity of a pellicle, it invests the individual frustule with a transparent envelope, which has the appearance of an exterior membrane, and has been sometimes mis- taken for such. On one occasion I also met with the fnistules of P. Hippo- campus enclosed in mucous or gelatinoiLS tubes, precisely like those of a Colletonema ; but these conditions must be regarded, for the present at least, as temporary or accidental, and cannot be admitted into the specific or generic descriptions." The process of self- division is affected in some unimportant particulars by the figure and habits of certain genera. Thus in one section of the MelosireWy the fnistules of which have convex ends, Mr. Ealfs points out (A. iV. H. xii. p. 347) that the central line is more strongly marked, and seems to divide the frustule into two equal portions. It becomes broader, and at length double, and ultimately an intermediate growth separates the two halves of the fnistule, which, during this process, do not increase in size ; but when the intermediate space is equal to the diameter of the original frustule, two new frustules are formed, by the addition of two hemispheres on the inner sides of the separated portions. The outer silicious covering still remaining, the fnistules are connected in pairs, and appear like two globules within a joint, as they are characterized by Harvey in Melosira nummuloides, and by Carmichael in M. glohifera. The above description belongs more particularly to M. nmnmulokles ; but the process in the other species of this section is the same : a series of changes, nearly similar, occurs in Isthmia. " In this genus," the author quoted says, "■ the mode of growth is very curious. As in most of the Diatomeae, the plant increases by a division of the fnistules ; but in this genus, as also in Biddiilphm and Amphitetras (and in the Achnanthece), two new fi^ustules are formed within the old one, and as they enlarge, ruptui^e it, when it falls off. In these the front portion is at first very narrow, and merely a broad line, but it increases greatly in breadth until the new frustules are fiilly formed." In this description and explanation the widening band or fi'ont portion mentioned is in fact the * connecting membrane ' of Prof. Smith, which, in the genera named, has an extra development, " an extension beyond the sutures of the valves," and also an unusual persistence, retaining the two frustules together after self- division, in such a manner that they seem to be enclosed Avithin an original single frustule, just as Mr. Ealfs describes. This longer persistence of the connecting membrane has been noted by Prof. Smith {A. N. H. 1851, p. 4), who writes—'' In some cases, by the new, or rather semi-new frustules proceeding immediately to repeat the process [of self-division], the connecting membrane is thi^own off and disap- pears ; in others it remains for some time, linking the fi'ustules in paii's, as in Melosira and OdonteUa.'" Another peculiarity, again, not unfi-equently obtains in this process of self- fission, viz. a departure from the prevailing law of similarity which exists 60 GENERAL HISTORY OF THE rNFTJSORIA. between the new valve and the parent one with which it is united in the newly-created frustule. The newly- developed segment occasionally acquires slightly greater dimensions, — a fact best exhibited in the filamentous genera, since in them it gives rise to an evident irregularity in the chain, affecting its width. Yet, as Prof. Smith remarks (i. p. xxvi), " This increase is so small, that in a filament of many hundred frustules, the enlargement is scarcely appreciable. The rapid attenuation represented by some authors in the filaments of the FragilaricB must therefore be attributed to the deceptive appearance presented by a compressed band when slightly twisted, the sem- blance of attenuation being thus given to the portions which are presented in an oblique direction to the eye of the observer .... Starting from a single frustule, it will be at once apparent, that if its valves remain unaltered in size, while the cell-membrane experiences repeated self-di\ision, we shall have two frustules constantly retaining theii' original dimensions, four slightly increased, eight somewhat larger, and so on in a geometrical ratio, which will soon present us with an innumerable multitude containing individuals in every stage, but in which the larger sizes preponderate over the smaller ; and such are the circumstances ordinarily found to attend the presence of large numbers of these organisms." Mr. Balfs has favoured us ^ith the follomng remarks on this subject in letters. He writes (March 1856) — *' In a recent number of the Ann. Nat. Hist, Mr. Carter expresses his belief that the fnistules of Diatomaceae gra- dually become smaller by division, and that it requires the sporangial frustule from time to time to keep them the proper size. This I cannot admit ; for any person who will take the trouble to watch a species of Gomphonema from its fii'st appearance in spring, as a scarcely \isible fringe to aquatic plants, will observe not only increase of mass, but also enlargement of the frustules. If Mr. Carter is right, the filament in Fragilaria would be veiy unequal : for instance, as the first-formed frustule could not decrease, and as its segments after division would always form the two ends of the filament, they should be the largest, then the adjacent valves of the two central frustules of the filament the next largest, and so on." In a subsequent letter the same distinguished authority writes : — '' I see that Prof. Smith, in his Synopsis, p. xxvi, takes the contrary view to Mr. Carter, and considers that the frustules do not grow after they are fully formed, but that, in dividing, the new frustules may slightly increase in size. It is thus that he accounts " for the varying breadth of the bands in the filamentous species, and the diversity of size in the frustules of the free forms." If he is correct, his opinion is still more adverse to Mr. Carter's views respecting the frustules formed after self- division. But I doubt also the correctness of Mr. Smith's views. He himself states that " the enlargement is scarcelj^ appreciable ;" and yet we find a vast difference of size in the frustules of the same gather- ing. The filaments are so fragile in Fragilaria, and even in Himantidium, that it is very difficult to determine whether the frustules in the same fila- ment do diff'er much ia size, and whether, if they do, the variations are alter- nating or irregular, as would be the case if either Prof. Smith or Mr. Carter be correct. The rate of production of specimens of Diatomeae, even by this one pro- cess of simple self-division, is something really extraordinary. So soon as a frustule is divided into two, each of the latter at once proceeds with the act of self- division ; so that, to use Prof. Smith's approximative cal- culation of the possible rapidity of multiplication, supposing the process to occupy, in any single instance, twenty-four hours, " we should have, as the progeny of a single frustule, the amazing number of one thousand OF THE DIATOME-E. 61 millions in a single month, — a circumstance which will in some degree explain the sudden, or at least rapid appearance of vast numbers of these organisms in localities where they were, but a short time previously, either unrecognized or only sparingly diffused." This multiplication by self- division now described, is generally supposed, after a time, so to speak, to exhaust itself, and thereby to render necessary other plans of propagating species. That some other modes do really exist is suggested by the fact of the considerable variations of size of frustules of the same species obtained at one time from the same locality, and moreover by diversities in the relative distance and in the delicacy of the strise of the surface. One such mode of propagation Mr. Thwaites has demonstrated to consist in the production of sporangial frustules by a process of conjugation analogous to that in the Desmidiese and many other Algae. Con jroATio^r. — The method of conjugation, although essentially alike in all cases, exhibits several important modifications in the genera of this family. These were more or less clearly perceived by Mr. Thwaites, who spoke of them as exceptional varieties ; but to Mr. Smith belongs the credit of reducing all of them under four principal forms: viz., 1. That in which two parent frustules produce two sporangia by conjugation, as mEpitliemia,Cocconema,Gomjphonema, Encyonema, and Colletonema. 2. Two parent frustules generate a single spo- rangium, e. g. in Himantidium. 3. '' The valves (vol. ii. p. xii) of a single frustule separate, the contents set free rapidly increase in bulk, and finally become condensed into a single sporangium. This may be seen in Cocconeis, CijcIoteUa, Melosira, Orthosira, and Schizonema. " In Melosira nummuloides, M. Borrerii, and M. subflexilis, the second valve of the conjugating frustule is rarely found united to the mucus surrounding the sporangium, the conjugation taking place only in the last frustule of the filament ; but in Melosira varians and Orthosira orichalcea, conjugation taking place throughout the entire filament, both valves are usually found adherent to the sporangium or its surrounding mucus. " From a single frustule, as in the last method, two sporangia are produced in the process of conjugation : this takes place in Achnanthes and Bhahdonema.^' In describing the process as generally as possible, we cannot do better than follow Mr. Thwaites's account, although it is illustrated by an example taken from the fii^st categorj" of variations. " For the most part," he tells us, *' conjugation in the Diatomeee, as in the Desmidieae, consists in the union of the endochi'ome of two approximated fronds, — this mixed endochrome developing around itself a proper membrane, and thus becoming converted into the sporangium. In a veiy early stage of the process, the conjugated fnistules, as in Eunotia turgida, have their concave surfaces in nearly close apposition (XI. 1), and from each of these surfaces two protuberances arise, which meet two similar ones in the opposite frustule (XI. 3) ; these protu- berances indicate the future channels of communication by which the endo- chrome of the two fnistules becomes united, as well as the spot where is subsequently developed the double sporangium, or rather the two sporangia. A front view of two frustules at the same period shows each of them to have divided longitudinally into two halves (XI. 4), which, though some distance apart, are stiU held together by a very delicate membrane : this, however, soon disappears. '' The mixed endochrome occurs, at first, as two irregular masses between the connected frustules ; but these masses shortly become covered, each with a smooth cyUndiical membrane, — the young sporangia, which gradually increase in length (XI. 5, 6), retaining nearly a cjdindi'ical fonn (XI. 7), until they far exceed in dimension the parent frustules, and at length, when 62 GENERAL HISTORY OF THE INFUSORIA. matm-e, become, like them, transversely striated upon the surface (XI. 8). Around the whole structure a considerable quantity of mucus has, during this time, been developed, by which the empty frastiiles are held attached to the sporangia (XI. 5-8).'* The variations in the process are aUuded to in the follo^'ing extracts from the same eminent observer's papers : — " In different genera, slight variations are met with in the method of conjugation : thus, in some species of Gom- phonema the sporangia lie in a direction parallel to the empty frustules, instead of across them, as described in Eunotia turgida. Again, there are examples (in Gomjphonema minutissimmn and Fragilaria pectinalis) where, instead of the conjugated frustules separating into two halves, only a slit appears at one end, to serve for the escape of the endochrome. Instead also of the pail' of conjugated frastules producing between them two sporangia, they may develope but a single one, as happens in Fmgilaria pectinalis. In this species, too, the sporangium, at first cylindrical, soon assumes a flattened, somewhat quadrangular form, and in many cases undergoes fissiparous divi- sion before it has put on the exact appearance of the frustule of a Fragilaria. "The Melosirece (GaUionellce, Ehr.) and the Biddulphice,^^ Mr. Thwaites remarks, " would seem, in their development of sporangia, to offer an excep- tion to most Diatomeae ; for in those genera no evident conjugation has been seen. However, something analogous to it must take place ; for, excepting the mixture of endochromes of two cells, the phenomena are of precisely similar character. Thus, instead of the conjugation of two fi-ustules (XV. 29, a, h, c, d, 32, 33), a change takes place in the endochrome of a single frustule, — that is, a disturbance of its pre\ious arrangement, a moving towards the centre of the frustule, and a rapid increase in its quantity: subsequently to this it becomes a sporangium ; and out of this are developed sporangial frustules, as in the other Diatomeae. In a single cell, therefore, a process physiologically precisely similar to that occurring between two conjugating cells takes place ; and it is not difficult to believe, taking into view the secondary character of ceU-membrane, that the two kinds of endo- chrome may be developed at the opposite ends of one frustule, as easily as in two contiguous frustules, and give rise to the same phenomena as ordinary conjugation." Fui*ther, in his notes on Schizonema suhcohcerens, Mr. Thwaites writes, — " The sporangia of this species are produced by the conjugation of a pair of frustules outside the filaments ; but sporangial frustules are frequently found in a filament intermixed with ordinaiy frustules, from which they differ only in size." - Dr. Giiffith and !Mr. Carter, moreover, have portrayed peculiarities in the conjugating process, which Prof. Smith can neither explain nor confii'm, and is equally unable to reduce under either of the leading variations he has defined. The first-named natui-alist stated that in the conjugation of a species of Navicula (amphirhynchus ?) a silicious sheath enveloped the spo- rangial frustule, indestructible by heat and nitric acid. " It is," he writes, " colourless, elongate, rounded at the ends, and furnished with coarse trans- vei-se striae or depressions, through which the line of fracture runs when the object is crushed." This account seems to Prof. Smith erroneous ; and he suggests that this sheath " may probably have been an appearance resulting from the condensation and corrugation of the mucus developed around the reproductive body." This conclusion Dr. Griffiths declares untenable, since no kind of mucus wiU resist the action of a red heat and nitric acid. The specimen examined was, besides, not an isolated one, but hundreds such were present" (A. N. H. xvi. 92). OF THE DIATOME.E. 63 Prof. Smith thus alludes to Mr. Carter's \-iews : — '' The cii'cumstance dwelt upon by Mr. Carter as having an important bearing upon the rationale of the process, viz. that one of the conjugating finistules is invariablj^ smaller than the other, is altogether at variance -^^ith my experience, and is totally irreconcilable with the process as it occurs in the genera mentioned under the third and foui'th classes. 1 am therefore disposed to believe that the difference in size noticed by Mr. Carter was a mere accidental diversity, and of no essential signification." The four typical modes of conjugation established by Prof. Smith have their occuiTence thus explained (>Sywops. ii. p. xiii) : — " The functions of life and growth are not suspended dimng the act of conjugation ; and in consequence self-division may take place at any stage of the process which accompanies the formation of the reproductive body, or the latter process may intnide upon, or arrest any step in the progress of self-divi- sion. *' In the fii'st mode of conjugation, as occurring in Epithemia, &c., self- division may be regarded as in the earliest stage of its progress, which merely involves the separation of the endochrome of the parent frustules into two portions, but does not include such a differentiation of these portions as renders them capable of the conjugative act : the endochrome capable of conjugating with these segregated portions must be sought for in other frustules ; hence the process in these genera involves the presence of two parent frustules, and results in the production of two sporangia. " In the second mode, met with in Himantidium, the progress of separa- tion is arrested at a still earlier stage ; no differentiation has taken place, and conjugation intervening, necessitates the union of the entire contents of two parent frustules to form a single sporangium. " In the third mode, the progress of the separation of the endochrome in the parent frustule must be considered as so far advanced that complete differentiation has taken place. In eveiy respect but the formation of new valves, self- division has been completed ; the incomplete fnistules are there- fore prepared for conjugation, which, intervening at this stage, leads the observer to believe that but one fi-ustule has been concerned in the produc- tion of the single sporangium. This we see in Melosira and the other genera mentioned under this class. "And lastly, self-division occurring during the progress of conjugation, the endochrome becomes segregated in the veiy act of intermingling, and a single frustule, whose contents have been abeady differentiated, gives rise to two sporangia, as in Achnaiithes and Rhahdonema . " Nor is the self-dividing disposition in aU eases permanently arrested by the complete formation of the sporangium. Having assumed the form of the parent frustules, with a great increase in size (the enlargement in dimen- sions being in some cases due to the accumulation of the contents of the two conjugating frustules, and in others to a rapid assimilation of nutritive material from the surrounding medium), the sporangial frustule immediately submits to self- division, and by the repetition of this act developes a series of fnistules equal in size to the original product of the conjugating process. This is notably the case in the filamentous species, as may be easily seen in Melosira, in Orthosira, and in Himantidium. How far this self-division may be carried in the sporangial frustules is at present unknown ; it is pro- bably of short duration, as we rarely meet with any considerable number of frustules characterized by the enlarged size of the sporangial form. In most cases an arrest of growth, and consequently of self- division, seems imme- diately to follow the complete formation of the sporangia, and the reproduc- B4 GENERAL HISTOEY OF THE INFT7S0EIA. tive body assumes the quiescent character wliich belongs to the seed of the higher plant, its Yital function remaining dormant until circumstances favour its furthei; development and the production of the young frustules of which it is the destined parent. '^ In the gathering of Cocconema Cistula made in April 1852, which con- tained numerous instances of the conjugating process, I observed the frequent occurrence of cysts enclosing minute bodies, variable in their number and size, and many of which had the outline and markings of the surrounding forms, and were obviously young frustules of the Cocconema. It would appear from the figui^es [appended to this account], that the production of the j^oung frustules is preceded by the separation and throwing off of the silicious valves of the sporangium, and the constriction or enlargement of its primordial utricle, according to the number of young frustules originating in its pro- toplasmic contents. In this gathering, forms of every size intermediate between the minutest frustule in the cyst and the ordinary frustules engaged in the conjugating process were easily to be detected ; and the conclusion was inevitable, that the cysts and their contents were sporangia of the species with which they were associated, and indicated the several stages of the re- productive process." Since the preceding account of conjugation was written, a valuable, although not a very lucid, contribution on the subject has appeared by Dr. Hofmeister, in the Reports of the Saxony Natural Histor}^ Society for 1857, and has been translated by Prof. Henfrey in the A. N. H. for January 1858. Prom this we extract the following as supplementary to the previously-written history of the conjugation-process and of self-fission, as well of the Desmidieae (p. 11) as of the Diatomeae : — '' Conjugation is far more rarely met with in the Diatomeae than in the Desmidieae. It appears that this process occurs here only at particular epochs, differing according to the seasons, happening simultaneously in all individuals, and quickly completed. Frequently as indications of conjugation having taken place have been met with (the occuiTence of individuals of the same species, of remarkable diversity of size, side by side, in free Diatomeae, e. g. Pinnularia virklis, Surirella hifrons, Staurosigma lacustre, all the year round, besides the occurrence of shorter or longer rows of cells of about double the diameter, in the bands, of the forms remaining connected by the lateral surfaces, e. g. Mehsira, Poclosira), yet it has seldom happened that they have been met with in the moment of conjugation. " Since the classic researches of Thwaites upon this subject, the knowledge of it has on the whole been but little advanced by the observations of Focke (conjugation of Surirella)^ Griffith (conjugation of Navkida), W. Smith and Carter (conjugation of Cocconeis, Cijmhella, Amphora). The following cases have been observed : — " Formation of a single conjugation-ceU, dividing very soon after its origin : in Himantidium pectorale, Cymhella Kiitzingiana, Cocco- neis Pediculus, Cocconeis Placentida, Oomplionema lanceolatum, Schizonema GreviUii, Orthosira oricJialcea, 0. DicTciei, remarkable from the repeated throw- ing-off of the coats of the conjugation-ceU, the cracked halves of which clothed the conical ends of the conjugation -cell in shape of funnels ; Orthosii^a va- rians, Surirella hifrons, and a Navicida not specifically determined. Here belongs also the only conjugation of a Diatomacean that I have seen, that of Cyclotella operculata, conjugation- cells of which, with adherent empty coats of the mother-ceUs, I found abundantly in ditches of a marshy meadow not far from Leipsic, in October 1852. They were not distinguishable in any essential respect fi^om the Cyclotella Kiitzingiana figured by Thwaites. " Next to these cases of the formation in the first place of only one conju- OF THE DIATOilE^. 65 gation-cell, come a series of observations in which two new cells were seen between the empty conjugated mother- cells, without any convincing evidence being offered of a division of the mother-cells having occurred just before conjugation, as in the cases hereafter to be mentioned, — where, rather, the position of the empty cells in relation to the conjugation- cells, and the affinity of the forms in question to some in which the entire development has been obsei^ed, render it probable that the unicellular condition of the conjugation- cell has hitherto escaped obsei'vation. In tliis group are to be counted Coc- conema lanceolatum, C. Cistula, GompJionema dichotomum, G. lanceolatum, G. marinum, AchnantJies longipes, Rhahdonema arcuatum, ColUtonema suhcohcerens, " In a smaller number of DiatomefB, species of the genera so nearly allied together, Epithemia, Ci/mbeUa, and Amj^hora, the conjugation is immediately preceded by a division of the mother-cells into two, analogous to the division of the ceUs of CJosterium rostmtum when about to conjugate. This division is longitudinal, taking place exactly as in the vegetative division in Cymhella Pedicidus, Ampliora ovalis, arid Epithemia Sore.v, but transverse and in a direction crossing that of the vegetative division in Epithemia turyida, E. gihha, and E. verrucosa. " Eecent obsei^ations show distinctly that the conjugation of the Diatomese agrees in all essential points with that of the Desmidieae. ^yhen a cell is about to conjugate, there is produced in it a coat round the entire contents, accm-ately liiiing the old membrane, but not adhering to it. . The growth of this coat cracks the old cell-membrane exactly in the same way as occurs in vegetative division. From the fissure the young, smooth coat emerges, in the form of a vesicle, and unites with the similar structiu"e produced by a neigh- boiuing cell. Al. Braun thought it must be assumed, from Thwaites's obser- vations, that the primordial utricles of the two conjugating Diatomean cells imited ; but that this is not the case, and that a soft and flexible cell-mem- brane, protnided from the cracked, rigid, old shell, encloses the contents destined to be blended with those of the neighbouiing cell, is distinctly shown by Smith's figure of Rhahdonema arcuatum, and Carter's of Cocconeis Pedi- cidus and Amphora ovalis. The introductory part of the conjugation is dis- tinguished in no respect from the vegetative cell-division in Epithemia Sorecc, Amphora ovalis and Cymhella Pediculus, and, further, in CJosterium rostratum ; in Epithemia turgida, gihha, and verrucosa, only by a different position of the wall dividing the mother-cell ; in the rest of the Diatomese and Desmidieae, by omission of the formation of septa, — frequently, also, by one-sided dehiscence of the cracked mother-cell, whose shells remain still connected at one side. " Thwaites's observations estabhshed that the ceU produced from the conju- gation of two cells of a Diatomacean, very soon after its origin, assumed the form of the mother- cell, becoming distinguishable from it almost solely by being twice as large. Smith has endeavoured to render it probable that the colonies of young individuals, enclosed in a cyst, of Coccoyieis Cistida, Gom^ phonemci dichotomum, and Synedra radians, some of which he found associated with conjugated, fiill-grown individuals, must have originated from the divi- sion of the spores (sporanges of Enghsh authors). This hypothesis has much in its favoiu% but, in the present condition of our knowledge, it is inexplicable where the sihcious shells of the spore-cells remain. However this may be, there is no doubt of the occurrence of cysts of this kind. In the same pools of a marshy meadow which repeatedly furnished me with conjugated indivi- duals of Cyclotella late in autumn, I found, in early spring of two successive years, globular cells, each of which enclosed a great number (32 to 40) of small individuals of the same species. The walls of these cells appeared shai^ply defined internally and externally ; the contents of a thin, fluid nature. 66 GENERAL HISTORY OF THE INFIJSOEIA. Structures similar to those represented by Smith, of Synedra radians, oecui-red in extreme abundance in the end of the autumn of 1854, in company with Synedra Ulna, Here the cells, which, like those observed by Smith in the allied species, had a diseased aspect and an abnormal arrangement of the coloured contents, were imbedded in a granular jelly, of a reddish colour by transmitted light. I very much doubt whether these last were in a condition capable of further development ; while in reference to the cysts of CydoteUa ojyerctdata, I share Smith's opinion. " The estabhshment of the assertion that the commencement of conjugation in the Desmidieae and Diatomeae is but little distinguished from the com- mencement of vegetative cell-division, renders some discussion of the latter requisite. Pringsheim has already dii^ected attention to the resemblance of this process in the Desmidieae to the vegetative cell-multiplication of the joints of (Edogonium. In fact, it is an absolutely general phenomenon in the true Desmidieae, so far as observation reaches, that the older parts of the membrane of a cell about to divide, do not, as in other cases (for example, in Zygnemeae), regularly increase in size with the parent-cell by growth in all directions ; but the older, outer layers of the integument spht open with an annular crack at the equator of the cell, shortly after (or during ?) the division. They still remain sticking on, covering the ends of the cell with a thick envelope, but become removed gradually fiu'ther apart by the interpo- sition of new cellulose between their fractured edges. The interposed new coat is the dii'ect continuation of that which hues the internal surface of the cracked halves of the old shell. It is the margins of the half-sheUs which constitute the rings, parallel to the end-surfaces, upon the cyhndrical lateral surfaces of the cells of Hyahtheca dissdiens and H. mucosa, the wrinkled pro- jections of the membrane in the middle of the deep constriction of the cell of Micrasterias and the large Euastra, of the flat constriction of the cell of Docid'mm, as also the ring at the equator of the external surface of Closte- rium : in CJosterium and in Docidmm, frequently as many as six may be counted, — a phenomenon which, in Docidium truncatum and the large Clos- teria, may be recognized at fii^st sight as dependent upon a number of halves of cracked cells regularly encasing their successors. " The dehiscence of the coat of the dividing cell is, in all obsei^ved cases, preceded by the formation of the septum dividing the cell into two halves \Cosmar'mm margaritiferum). The gradual development of this from the margin of the cell- wall inwards, as a gradually- widening annular fold of the innermost layer of the integument, has not yet been observed, and, from analogy with the processes in (Edogonium, is scarcely probable. But, as in (Edogonium, the contents of the cell may be contracted, before the fonnation of the septum, into two masses, in contact, but separated by a sharp hne of demarcation (two contracted daughter- cells imperfectly cut off from one another, still adhering together at the place of constriction). " From the half-shells of cells of the same Docidium which dehisced under the eye of the observer, emerged, within half-an-hom% to the extent of 4th or ^th of the length of the half- shells, the daughter- cells, still intimately con- nected at the point of contact. They could henceforth be perceived to be enclosed by a cellulose coat, fii^m although dehcate. Treated with reagents strongly extracting water, such as glycerine, one or both of the extruded pieces frequently di-ew back into the halves of the shells of the mother- cell, the projecting pieces of membrane becoming doubled inwards. The just- emerged coats of the daughter- cells of Docidium did not take a blue colour when treated with iodized chloride of zinc, while the old halves of the mem- brane of the divided cell assumed the blue colour immediately. OF THE DIATOME.E. 67 " In Cosmarium margaritifermn and Staurastrum dejectum, it may be easily obseiTed that a slight elongation of the isthmus, and the fonnation of a septum passing across the middle of this, precede the aj^pearanee of new half-cells in the deep constriction. It is after the appearance of the septum that the old waU of the mother- cell breaks by an annular fissure exactly at the place where that septum is formed. The two halves of the old cell-coat are then separated by the bulging- out of the younger, inner layers of membrane, not fii^mly adherent to the old portions. The new halves are at first lined only by protnided portions of the peUicle of theii' contents (outermost layer of the parietal coats of protoplasm) belonging to the older half-ceUs ; from the moment only of the dehiscence of the old cell- coat, does a portion of the granular contents of the older cell-halves make its way into the new emerging halves. " In like manner, doubtless, occurs the cell- division of Micrasterias, of the large foiTas of Euastrum, Cosmarium, Staurastrum, and other Desmidieae, only that they have not been observed completely, because these larger Des- midieae very seldom multiply by division out of their natural stations. The ceU-di\dsion of the Diatomeae that have hitherto been observed in vegetative multipKcation, differs in essential points from that just described. '' When a cell of Navicula {Pimiularia) viridis is about to divide, there appears upon one of the secondary sides (front view of English authors), parallel to the primaiy sides (the furrowed faces of the cell having an elon- gated elliptical outline), an annular rim, which, growing gradually inwards, constricts the contents of the cell by an annular fiuTow, in a manner exactly similar to that of the commencement of cross -division in a cell of CJadopliora. AMien a cell in this state is treated with substances producing slight endos- mosis (for instance, a weak solution of carbonate of ammonia), the contents retract on both sides from the annular rim, and constitute two completely separate cell-Hke stnictiuTS (halves of a primordial utricle), each of a very long ellipsoidal form, and each lying close agaiust one of the primaiy sides {faces of halves) of the cell. I^Tien the annular rim has grown inwards to about the sixth part of the shortest diameter of the cell, its development is arrested. In natural conditions, this stage is succeeded by the retraction of the primordial utricle from it. Each of these halves of the cell-contents becomes clothed, on the side turned away from the primary side of the cell, with a new membrane, which soon exhibits the fii\st indications of the pecu- liar thickening ribs and nodules of one of the primaiy sides of our Pinnularia. The cell has now completed its division. Seen from one of the secondary sides, it contains two new individuals, equal to the mother-cell in length and breadth, but only possessing one-third of its thickness. The externaUy- situated primaiy side of each of them is the old piimaiy side of the mother- cell, to which we must imagine the newly-formed membrane of the daughter- cell closely adherent at all points. Perhaps the narrow secondary sides of the new cells may be in the same condition. But the contiguous primary sides of the daughter- cells are totally new structures, which, developed rapidly, in a short time become similar to the old primaiy sides in every part. The two daughter- cells are at first held together by the broad middle piece of the secondary sides of the mother- cell, bearing the above-mentioned annular rim inside. The contents of the intermediate space consist of a transparent fluid destitute of any solid structures, doubtless pure water. The two daughter- cells are finally set free by the gradual ' weathering ' of the zone-membrane which holds them together. The division of Surirella hifrons takes place exactly in the same way. An essentially similar kind of vegetative multipli- cation is widely diffused, if not general, in the Diatomese. The well-known f2 68 GENERAL niSTORY OF THE INFUSORIA. phenomenon of the formation of a tubular membrane, often impregnated with silex, and elegantly dotted or areolated, connecting the two segments of Isthmia, Melosira, &c., depends upon the same process. " An analogous case is met with in the formation of the spores of Pellia epipliylla. The mother- cell here produces six ridges of cellulose projecting inward from the internal wall, intersecting at an angle of 60° ; these ridges grow in toward the middle point of the cell, like the annular ridge of Cla- dojpJiora at the commencement of cell-division. A\Tien these projecting ridges have attained the breadth of a fourth part of the transverse cHameter of the mother- cell, the cell- contents divide into four parts, which, retracting from one another and from those ridges, occupy the four chambers of the cell, each of which is vaulted externally and bounded laterally by three of the ridges, — here becoming coated with a membrane and developed into a spore, while the tetrahedi'al space in the middle of the cell, bounded by the six ridges, remains filled only with watery fluid. The spores become free by the solution of the enveloping part of the membrane of the mother- cell. The resemblance of this process to the vegetative multiplication of Navicula consists in the inter- ruption of the division of the cell by the formation of septa, and the subse- quent completion of the daughter- cells by secretion of membrane on the external surface of contracted portions of the contents of the mother- cell. A deviation occurs in the circumstance that in Pellia the segment of the coat of the mother- cell which is in contact with the external smface of the daughter- cell becomes dissolved, while in Navicula it persists and remains most inti- mately connected with the daughter- cell. " The newly-formed parts of the cell-coat facing together in the division are, in the Diatomeae, and still more clearly in the Desmidiea), perfectly smooth and even for some time after theii' production ; it is subsequently that they obtain the often veiy considerable tubercles and spines, consisting principally of cellulose. The same applies to the processes upon the outer integument of the spores of Euastra, Cosmaria and Staurastra produced in the conjugation. These phenomena, as also the autumnal secretion of jelly by many of the Desmidiese, deserve more notice than they have hitherto attracted in connexion with the theory of the life of the vegetable cell. Still more remarkable behaviour is displayed by the cell-coat of an organism which I refer only doubtfully to the DesmidieEe. In many pools about Leipsic, in which Desmidiese abounded, occuiTcd large, accurately si^herical, tliick- walled cells, some as much as -05 miUim. in diameter, rich in chlorophyll, which not only lined the internal wall as a connected granular layer, but — as in many Desmidieae — formed groups, distributed, in the interior of the cell, in a system of radially-arranged plates, which presented a stellate appearance when seen from the side. It would be no great stretch of imagination to regard these cells as the conjugation- spores of a large Desmidiean. But these spores are all spiny, with the single exception of those of Xanthidium armatum. This very striking form occurs but rarely with us, having hitherto been found only in a single locahty, while these globules are as common as they are abundant, and are often found in great numbers in forest pools, wliich harbour, in addition to them, only very small Desmidieae. But such a supposition is still more decidedly negatived by the circumstance that the cells in question are sometimes found dividing into two. This renders it in the highest degree probable that they are inde- pendent organisms — Desmidieae without a central constriction, which may form the commencement of a series of forms terminating in Micrasterias. " These cells frequently appear surrounded by a wider coat, inside which the cell then floats freely, enclosed by its own closely-investing coat. Several such empty coats are often met 'vvith, even as many as six sticking one inside I OF THE DIATOilEJE. bM another. Close investigation shows that the broader empty coats have an orifice, towards the border of which the membrane grows gradually thinner. These holes have not the aspect of perforations of the outer walls through external injiuy ; they rather resemble the orifices of the walls of CJadoj^hora, thi'ough which the swarming-spores escape. It might be conjectured that the plant multiplied by swarming-spores, and that solitaiy ones becoming developed inside the empty coat of the mother- cell gave rise to that appear- ance ; but this is contradicted by the great frequency of their occurrence, as also by the circumstance that we never find a number of green cells inside one cell- coat. It is more probable that the contents of the cell contract, and become coated with a new membrane, when the old one is perforated, — by unknown causes, which perhaps lie in the course of development of the species. " If we seek to bring the phenomena introductory to vegetative cell-mul- tiplication under one point of view mth the preparations for conjugation, we find that, in the Desmicheae, in both cases a new membrane is formed aroimd the total contents of the ceU, wliich indeed lies close upon the old coat at all points, but by no means adheres to it, as we are accustomed to conceive of the so-called layers of thickening of the cell-wall. The growth of the young membrane cracks the stronger old one — in vegetative cell-multiplication always in an annular fonn, in conjugation, mostly in a one-sided manner, with a valve-hke slit (Hi/ahtheca dissiliens ; Closterhim). At this stage first occurs a distinction between the two processes of development, — the foimation of a sej)tLun taking place in cell-division, while in conjugation the protniding part of the young membrane continues to enlarge outwards, without, in many cases, any separation of the contents into two halves taldng place. The younger, innermost layer of membrane remains with that portion lining the old cell-coat, sticking wholly in this in Hyalotheea, Bambimna, Cosmarium. But even in individuals of species of the last genus it sometimes occurs, in Tetmemorus and Closterium (e. g. C. acutum) as a rule (although by no means without exception), that the ends of the connected inner coats of the conjugating cells draw themselves out of the cast-off" shells of the mother- ceUs, in extreme cases entirely ; so that the cell originating by the blending of the internal coats of two individuals (inside which the spore is fonned) becomes capable of being rounded off" into a sphere. " Both the ceU- division and the preparation for conjugation of Zygnemese are distinguished from the processes in Desmidiea? by the circumstance that in the former the wall of the oldest cells grows in its entire mass, and does not allow the younger layers of membrane to protnide through fissures or slits. " In the Diatomece, lastly, the division into two, like the conjugation, takes place, seemingly, in all cases, through and after a preparatory contraction of the contents or separate portions of the contents of the cells ; and in not a few cases the conjugation takes place during, and is accompanied by, di\-ision of the contracted contents into two portions. A\Tiat import for the life of the species has the conjugation of the Zygnemeae, Desmidieae, Palmelle£e (Pal- mofjloea), and Desmidie^ ? Our knowledge of the race of Algae, so import- antly advanced by the labours of Pringsheim and Cohn, should allow a more positive answer to this question than that inquirer, to whom the study owes most brilliant acquisitions, is inclined to give. The idea of sexuality of the lower Algae depends principally upon the perfectly justifiable, but still only analogical conclusions which, starting from the observations made diuing a centurj^ on the Phanerogamia, have advanced, through the intermediation of those, less numerous, on the Vascular Ci-jiitogamia and Muscineae, and the 70 GENEEAL HISTOEY OF THE INFUSOEIA. facts established in Fitcus by experiment of artificial separation or union of the sexes, to the (Edogoma, Vaucheria, Sjphceroplea and Volvox. Pringsheim's declaration, that physiological questions of such a kind as the necessity of the action of the fecundating matter in generation can only be certainly decided by the observation of morphological processes, will not be adopted. Expe- riment has long ago proved the existence of sexes in the Phanerogamia, before the penetration of the pollen-tube into the ovule, and its relation to the germinal vesicle, had been made out, — obseiTations which that theory really no longer required for the establishment of its main question. And if, among so many confirmatory experiments, a few negative results present themselves, in what branch of human knowledge do we not meet with similar phenomena ? The general niles of evidence hold good in such cases. " The same analogies, then, which lead ils to recognize a fecundation in the penetration of the spermatic body of (Edogonium into the mother- cell of the spore, in the mixtm^e of that body with the contracted contents of the mother-cell of the spore (with Pringsheim's ' fecundation-globule '), must necessarily lead us to regard conjugation as a fecundation. It is distinguished from the process in (Edogonium only by the fact that the portions of cell- contents which become blended into one cell are of equal size, and that there is not one of them provided with apparatus by means of which, like the spermatic body of (Edogonium by its cilia, it is moved onward until it reaches the cell to be fecundated, — both points, evidently, of no essential importance. " The sporangial frustules difi'er in general from the parent forms not merely in size, but also in the number of striae or of other markings, and to some slight degree in outline. Such variation, M. Thuret contends, proves the phe- nomenon of conjugation to be, not a true mode of reproduction, but only ' a second mode of multiplication of frustules, very curious and very abnormal.' *' In the immature condition, we are infoiTaed by Mr. Thwaites, it happens that the sporangia in many species resemble in general characters the mature frustules of another species or even of an allied genus. Thus the sporangia of Gomj)lionema mimttissimum (XI. 17) and of G. dichotomum have a close resemblance to the frustules of Cocconema. On the other hand, in some genera, as in Cocconema, the sporangia take on at once the exact characters of the ordinary frustules, from which they differ only in their exceeding that of the majority of the latter in dimensions. ^' When a sporangium in a transitional condition is like the frustule of another genus, we are assisted in distinguishing its true natiure and affinity, oftentimes, by the" persistence of the mucus diffused around it ; or by continued observa- tion we may witness its assumption ultimately of its true specific characters, including the development of its pedicle or stalk, where the possession of such an organ is a characteristic (as in Gomjyhonema).^' The above fact suggests it as very probable that transitional forms have been described as particular species, or located in wrong genera. Thus Mr. Thwaites thinks that Xiitzing's Epithemia vertagus is no other than the sporangium of Eunotia turgid a, and also that the enlarged frustules of the Melosirece, which that same writer had conjectiu-ally regarded as reproductive bodies, are in. fact the sporangial product of conjugation, and give rise to a chain of frustules larger than those from which they had themselves originated. The subsequent history of' the sporangial frustules on being matured is not satisfactorily made out. Prof. Smith has the following on the question (J". M. S. 1855, p. 131) : — " The ordinary Diatomaceous fmstule seems to owe its production to the protoplasmic contents of the sporangial frustule formed by the process of conjugation. These sporangia, like the seeds of higher OF THE DlAT031EiE. 71 plants, often remain for a long period dormant, and are borne about by cur- rents or become imbedded in the mud of the waters in which they have been produced, until the circimistances necessary to their development concur to call them into activity. At such times theii' sihcious epiderms open to per- mit the escape of the contained endochrome, which is resolved into a myriad of embryonic fnistules ; these either remain free or surround themselves Tvdth mucus, fonning a pellicle or stratum, and in a definite but unascertained period reach the mature form of the ordinary frustule," when their fiu'ther growth appears almost entii^ely arrested by the production of the sihcious coat, and when multiphcation by self-division provides for the continuation of individual life. To continue the quotation, '' The size of the mature frustule before self- division commences is, however, dependent upon the idiosjTicrasy of the embryo, or upon the cii'cumstances in which its embryonic growth takes place ; consequently a very conspicuous diversity in their relative magnitudes may be usually noticed in any large aggregation of individuals, or in the same species collected in different locahties." The behef that the contents of the sporangial frustules resolve themselves into a ' brood' of Diatoms, having the same form and specific characters as the original parent-cells. Prof. Smith establishes by the following observations made by himself (Si/no2:)sis, vol. ii. p. xv) : — " In the gathering of Cocconenia Cistula made in April 1852, which contained numerous instances of the con- jugating process, I observed the frequent occiuTence of cysts enclosing minute bodies variable in their number and size, and many of which had the outhne and markings of the siUTounding forms and were obviously young frustules of the Cocconema. It would appear that the production of the young frustules is preceded by the separation and throwing off of the sihcious valves of the sporangium and the constriction or enlargement of its primordial utricle, according to the number of young frustules originating in its protoplasmic contents. In this gathering, forms of eveiy size, intermediate between the minutest fiiistule in the cyst and the ordinary frustules engaged in the conjugating process, were easily to be detected ; and the conclusion was inevitable, that the cysts and their contents were sporangia of the species with which they were associated, and indicated the several stages of the reproductive process." Again, in a gathering of Synedra radians, although not found at the time in a congregating state, yet the appearance of the cysts and of their contents was equally characteristic of the reproductive process. That such a " cystoid condition is one stage in the normal development of its reproduc- tion," a subsequent examination in a distant locahty satisfied him. The prosecution of this inquiiy into the final changes of the sporangial fnistules is seriously impeded by the dissolution of the investing mucus and the consequent dispersion of the reproductive bodies. Thirty-two species of the Diatomeae have been observed in the act of con- jugation, belonging to the genera Epitliemia, Cocconeis, Cocconema, CymbeUa, Cyclotella, GompTionema, Himantidium, Achnantlies, Rhahdonema, Melosira, Navicida, Surirella, Amphora, Orthosira, Encyonema, Colletonema, and Schizo- nema. On this paucity compared with the number of known genera. Prof. Smith has the following explanatory remarks {Synops. ii. p. xi) : — "One reason for the paucity of observations on this process in the Diatomeae is no doubt to be foimd in the changes which usually take place in the condition of these organisms at this period of their existence. During conjugation the progress of self-division is arrested, the general mucous envelope or stratum produced during seK-division is dissolved, and the conjugating pairs of frustules become detached from the original mass ; they are thus more readily borne away and .72 GENEKAL HISTOEY OF THE INFUSOBIA. dispersed by the surroimding currents or the movements of worms and in- sects, and their detection becomes in consequence more casual and difficult. By far the greater number of the species I have mentioned belong to those genera whose frustules are adherent, or attached by stipes to foreign bodies, or which form continuous filaments or aggregated frondose expansions. ISTot more than four, viz. CycloteUa Kutzingiana, Navicula firma, Amphora ovalis, and Cymhella Pediculus, are to be regarded as free forms : the reason I have just given will account for this cii'cumstance ; and the larger proportion of adherent or frondose species detected in conjugation may doubtless be ascribed to the firmer position conferred upon such forms by the presence of these accessory methods of attachment and adhesion, while the filamentous species, being usually aggregated in considerable masses or entangled amidst the branches of the larger Algae, are also less liable to dispersion." Another mode of development, first pointed out by Mr. Ralfs in his early contributions to the history of the Diatomese {A. N. H. 1843), by an internal gemmation or production of cells approaching in physiological features to self- division, appears to prevail in at least some instances. It is alluded to by Prof. Smith, when speaking of the Meridion circidare {op. cit. 7). He met with a variety of frustules, which upon a close examination, especially in a li\'ing state, led him to the conviction '' that the appearance of a double wall of silex is owing to the formation ^\4thin the original frustule of a second perfect cell, instead of the usual mode of division by which the original fnistule is divided into two half-new cells .... In the present case, the central vescicle or cyto- blast becomes enlarged without division, and secretes on its extension two new valves, which are pushed outwards until they lie in close apj)roximation with the original valves. This process is not always repeated ; the usual mode of seK-division again recul^s, and two valves are formed in the interior of this new cell according to the nonnal method. . . .This unusual method of development is not, however, sufficiently constant to warrant the separation of such frastules from the species in which it occm^s, perhaps hardly sufficient to constitute a variety, as frustules in both the ordinary' and abnormal states may be met with in the same gathering and even in the same filament." Himantidimn Soleirolii is another species producing internal cells, which Prof. Smith quoted, remarkmg that he had no doubt it is merely an accidental modification of cell-growth, since, in the same filament, cells thus formed may be frequently found along -vsdth others following the normal mode of self- divi- sion. In Odontidium anomalum, this variety is in fact the usual condition of the frustules, and the ordinary mode of self-di\dsion is but rarely to be met with. A remarkable instance of this abnormal development presented itself to Prof. Smith in Achnanthes subsessiUs, in which '-' the formation of a cell interior to the original one had proceeded through several successive stages, and the result is a compound fnistule, consisting of the mother-ceU and a number of included cells, each successive development being embraced by the others pre\iously formed." Mr. Ealfs has recently {J. M. S. 1857, p. 14) recurred to the subject of this plan of reproduction, and has found himself obHged to differ from Prof. Smith in some particulars. He writes : " Although it is true that ' we frequently find in the same filament cells thus formed, and others following the normal mode of growth,' as I foimerly showed, yet I cannot agree to Prof. Smith's statement under Bimantidium Soleirolii, that ' there is no doubt of its being merely an accidental modification of cell-growth.' On the contrary, I beheve it to be a reproductive state of the species, and consequently to have a definite and important part in their economy. '' Por several years I have attentively watched the circumstances connected I OF THE DIATOME^. 73 -^-ith the fonnation of these inner cells in HimanticUum undaJaium, by gatheiing specimens at short intei-vals. Dming great, part of the T\inter, the filaments increase in bulk, by repeated division of the frustules, until they form large masses, filling the ditches ; at length the inner cells make their appearance, at first spaiingiy ; but as spring advances, it is difficult, in many situations, to obtain a filament without them. I have found that when these become abundant, the filaments cease to grow, and the entire mass soon breaks up and disappears. The same thing happens in the other species of Himan- tidium, and in Meridion. '' I do not find that the inner cell commences in the centre and pushes its valves outwards, as stated by Prof. Smith. Were this the case, the internal matter also would necessarily be pushed outwards by the advancing valves, and thus condensed between them and the walls of the frustule. On the contraiy, in the Himcuit'idium the internal matter, before nearly fluid, collects within the new cell, becomes dense and more granular, and the new walls are formed round it in the situation they are to occupy, leaving an empty space between them and the walls of the frustule. *' The alteration and condensation of the colouring matter, and the ap- pearance, or at least great increase of vesicles, have a strong resemblance to what takes place previous to the formation of sporangia, the completion of which, as in this case, usually preludes the death and disappearance of the mass. " As in most acknowledged sporangia, the ceil thus formed always tends to assume an oval or orbicular form. It, however, is very frequently, and perhaps generally, divided in halves, as in the fission of the frustules, so that the oval seems made up of two neighboimng frustules ; but this is not the case, as may readily be ascertained by noticing the marginal puncta of the original fnistule. " Do these newly- constituted cells ever continue to divide, as Prof. Smith supposes ? I beheve not ; at least I have never seen a specimen in which the semi-elliptic portions were separated by the interposition of other valves resembhng either themselves or those of the ordinary fnistule. For my own part, I have been unable to trace the species after the formation of these cells, owing to the quickly succeeding disappearance of the mass. If, indeed, this renewed division does occur, the resemblance to what takes place in the sporangia of some species of Melosira would be increased. " Prof. Smith, in his most interesting and valuable account of the ' Eepro- duction in the Diatomacese,' enimierates four modes in which sporangia are formed. The third is thus defijied : — " ' The valves of a single fnLstule separate ; the contents, set free, rapidly increase in bulk, and finally become condensed into a single sporangiimi.' " As far as regards the Melosira varians, the only one in this group which I have had an opportunity of noticing, I beheve the process is essentially the same as in the examples already described. The only difi'erence is, that the new-formed cell being inflated, and much larger than the original fnistule, the valves of the fnistule must necessarily be either ruptured or iDushed apart by the increasing growth of the sporangium, and the latter alternative happens. " I have seen no specimen of Mr. Brightwell's Chcetoceros Wighamii, but from his figures I beheve the goniothecia-hke bodies constitute another example of the formation of internal cells. " I have said that I consider these interaal cells sporangia, and essentially of the same nature as the inflated ones of Melosira varians. At the same time we should not forget that Mr. Thwaites discovered the Himantidium pectinale in a truly conjugated state, and that it is contrary to our experience / 4 GEXEEAL HISTOEY OF THE IXFrSOKIA. of the economy of nature that the same result should be obtained in the same species in two different ways." M. Focke has satisfied himself of the reproduction of some species of Navi- culce (A. iV. H. 1855, 237) by a strange complication of the phenomena of ^' alternation of generation " and conjugation. Navicula hifroiis, for example, forms, he says, by the spontaneous fission of its internal substance, spherical bodies which, hke gemmules, give rise to Surirella microcora. These by. conjugation produce N. sphndida, which gives rise to iV^. hifrons by the same process. This last act of gemmation has been obsei^ed by the author in all its phases. He saw two specimens of N. spJendida, enveloped in a sort of mucosity, open and evacuate the whole of their contents, which serv^ed to form a N. hifrons. The production of the reproductive bodies by the latter was also observed; but their development into Surirella microcora, and the pro- duction of N. splendida by conjugation, rest solely on the inductions of the author. These facts require revision and confirmation, but they are, nevertheless, worthy of the attention of observers, and appear to point to phenomena quite as singular as those which have been revealed to us within the last few years by the study of the reproduction of so many of the lower animals. They, in fact, present in a manner the converse of the phenomena exhibited in the ordinary alternation of generation, as several germs or eggs are necessary for the production of the last individual of the cycle. Kiitzing has sunnised the existence of another mode of development, viz. by germs or sj^ores prepared from the gonimic contents of the fmstules. This method of j^ropagation was indeed comprehended in Ehrenberg' s doctrine that much of the granular contents were ova ; an hj^iDothesis started rather to bring the stnicture of the Diatomeae in accordance ^ith the generally assumed poiy- gastric organization, than to explain any observed j^henomena, complicated as it also was with other suppositions of fecundating male glands or seminal vesicles and a sexual discharging orifice. Eabenhorst {S'lissw a sser- Diatom, p. 3) has followed up Kiitzing's suggestion, and affinns that the frastules of Diatomeae swell up in a vesicular manner and become filled with a greater or less number of cells, which at first have an irregular figiu-e, but subsequently assume a regiilar oval shape. This having happened, the cells move in a current from right to left within the cavity of the parent-ceU, which by-and-by sphts open and emits its progeny, each of which has, at an anterior clear space, two long projecting cilia. Por a very short time these germs enjoy a swarming movement, and afterwards, on becoming stationary, attain with extreme rapidity, or even sui-pass, the size of the parent-cell, which is itself destroyed in the act. This plan of reproduc- tion by the development of a brood of young organisms ^vithin a parent -cell, or, in more technical terms, this formation of active gonidia (microgonidia), prevails in many of the lower ^Ugae, and consequently has no a-priori argu- ment against it. However, as Prof. Smith remarks, " Its occurrence in the Diatomeae cannot be received as estabhshed without fm^ther observation and a more careful record of the phenomena attending its progress " {op. cit. vol. ii. p. x^ii). Eabenhorst has illustrated this mode of development in only one species of Melosira, although he puts it foi-ward in a general manner as if tnie of aU the Diatomeae. Indeed it occau\s to us that it is not a special and otherwise unobseiwed process of reproduction, but merely that variety of the act of con- jugation described by Mr. Thwaites in the genus Melosira, in which a change in the endochrome of a single frustule, attended by an increase of contents and a consequent enlargement — such as is intimated in Rabenhorst's account — OF THE DIATOME^. 75 converts it into a sporangium. Beyond this stage, Mr. Thwaites does not appear to have followed the sporangial fnistiile so generated ; but, assuming the correctness of Prof. Smith's hypothesis of the generation and subsequent evolution of numerous minute frustules mthin it, do we not find a precisely analogous phenomenon with that which Eabenhorst represents as an addi- tional mode of propagation, or with what Focke (see preceding page) describes as the formation of gemmules out of the internal substance, and their sub- sequent discharge? The supplementaiy phenomenon of alternation with change of specific form, included in the statement of the latter observer, even if confirmed, will not afi'ect the general analogy presumed. Habitats. — Appearance in masses, abundance, geographical distribution. — Fossil Diatomece. — Existence in the atmosphere. — Practical uses and appli- cations of the Diatomece. — The habitats and the distribution of the Diatomeae, both in time and space, are the most extensive, various, and wide, of all organic beings. In fresh, in salt, and in brackish waters they are ahke foimd ; they exist abundantly in a h^ing state about the roots of plants and diffased in moist earth ; they are also to be met ^vith in the dust of the atmosphere and in meteoric products. They are, in fine, inhabitants of earth, air, and water. When no longer ahve, their silicious skeletons preserve their form and constant characters, iminjiu'ed by most of the causes which obhterate the remains of other Hving beings. They are so. preserved in most of the rocks above the oldest primaiy — in all, indeed, in which intense heat has not operated to fuse sihca into a molten mass. At the present day they are ejected from the bowels of the earth in the lava, cinders, and ashes of vol- canos, and are borne about by the winds from one continent to another in showers of dust. In respect of habitat, the Diatomeae are divisible into marine and fresh- water species ; some indeed are common to both fresh and salt water, or exist in brackish water. The following accoimt of the habitats of Diatomeae, illustrated by reference to particular examples, is from the experienced pen of Mr. Ralfs, who has supplied us with it : — " The Diatomeae may be obtained at all seasons of the year, but are most plentiful in spring and summer, many of them indeed being hmited to that period ; thus the species of Micromega and Schizonema are, with few excep- tions, in perfection only in May and June, when they are met with in shel- tered situations, forming wide patches on the ground and on the flat surfaces of rocks exposed at ebb-tide. About the end of May the Enteromorpha compressa, so common on our shores, often seems as if faded at the end ; this appearance is frequently accompanied by the presence of Grammonema Jur- gensii, which is easily recognized by its slippery feel, when from its pale colour it would otherwise escape detection. '' At all seasons of the year, the smaller and more slender Algae, marine and. freshwater, as soon as they attain maturity, become almost invariably covered ^vith parasitic Diatomeae, which impart to them a brownish colour. In this way we obtain species of Cocconeis, Achnanthes, Striatella, Tahellaria, Grammatophora, Isthmia, Gornphonema, Podosphenia, Rhipidophora , and Si/nedra. On the contrary, Amphitetras and Biddulphia prefer the muddy cre\ices in the sheltered sides of pei-pendicular rocks. *' In salt marshes we may expect to find the Achnanthes subsessilis on the slender filaments of Etiteromorpha, but so sparingly as hardly to discolour them. The species of Epithemia are parasitic on Claclophora, both in brackish and in freshwater pools. The Melosirce are common in marshes, especially at the mouths of large rivers, where they form Conferva-hke brownish masses. " Many of the unattached Diatomeae are produced in dark brown patches 76 GENEEAL HISTOEY OF THE OFUSOEIA, at the bottom of pools, or on the surface of mud ; the freshwater species often by the road-side ; the marine forms usually near high-water mark. Am- pMpleura injiexa and A. scalaris congregate, in large brown stains or spots, on the muddy sides of rocks, whilst other species, for instance CampijlodiscuSj and Coscinodiscus concinnus, form similar collections, but prefer more shady situations. '' The sides of ditches in brackish marshes are very prolific, especially after spring-tides, and in situations not again covered until the next high-tides. We may expect to gather in such places species of Smnrella, Navicida, Pleu- 7'osigma, Ceratoneis, Amphiprora, Amphora, &c. The soil about the roots of rushes and of other plants inhabiting salt marshes often aiford interesting forms, but seldom in abundance. We find there species of Coscinodiscus and of Zygoceros ; but such are obtained more abundantly from the mud or from the washings of bivalve shells brought uj) from deep w^ater or collected at the mouths of rivers. Oyster-beds are in general productive. The Bac'illaria paradoxa inhabits ditches in w^hich the water is nearly fresh, and is frequently obtainable from the scum diiven from the siuface to the banks. " Pew Diatomeae are peculiarly autumnal ; we have, however, gathered Homoeocladia Martiana, Berheleya fragilis, DicTcieia pinnata, and Striatella umpmictata, chiefly at that season. . " On warm siunmer days, Diatomeae, with various microscopic Algae and Fungi, rise to the siu-face of water by the disengaged oxygen gas still ad- hering to them and buojing them up, and there form a dehcate film or a scum, and at times even a layer of considerable thickness. Such collections are rich in species of Navicida, CgmheUa, Surirella, and Si/nedra. When an entangled larger mass is formed, there is usually one prevailing species. Specimens of Fragilaria are generally found on decapng wood or leaves, or amongst Confervae diffused in the water. From the drainings of Sphagnum may often be obtained Synedra biceps and various species of Himantidium. Boggy soil, especially when situated on a slope, affords various species of Epi- themia and Navicula ; so hkemse does the soft matter on rocks on which water constantly trickles. Washings from oysters and the refuse raised by trawlers are usually rich in spheres of Coscinodiscus, Actinoptychiis, Pleurosigma, Di- pJoneis, Navicida, Dictyocha, &c. The same kind of washings from sheltered harbours give Surirella fastuosa, Auliscus scidptus, together with species of Campylodiscus, Triceratimn, &c. Washings of corallines are like^vise some- times productive." Mr. Norman supplies us with the following hints : — " The most interesting forms occur in salt water, especially in shallow lagoons, saltwater marshes, estuaries of rivers, pools left by the tide, &c. Their presence in any abun- dance is shown by the colour they impart to the aquatic plants they are attached to ; or when found on mud, by the yellowish-brown film they form on the surface, and which, if removed with a spoon mthout disturbing the mud, will be found a very pure deposit. " Such collections are best put at once in bottles, or even partially dried and wrapped in pieces of paper or tin-foil. When placed in bottles, a few drops of spirit are advantageously added. In all cases it is essential that the locahty whence obtained should be plainly written on each package. Capital gatherings are obtainable by carefully scraping the brownish -coloured layer from mooring-posts, or the piles of wharfs or jetties. "" In clear running ditches, the plants and stones have often long streamers of yellowish-brown slimy matters adhering to them, generally composed almost wholly of filamentaiy species. The layers of Diatomaceous fronds on the surface of mud are often covered with bead-hke bubbles of oxygen, which OP THE diatohe-t:. 77 from time to time rises to the sm-face of the water and carries up with it some of the deposit in the form of a scum, Avhich gets blown to leeward, and may be readily collected from the edge of the pond quite free from particles of mud and other impurities. " Good and rare specimens have been obtained from the stomachs of Ho- lothuridae and other Mollusca which inhabit deep water, and are often thrown on shore after severe gales of v^dnd. These animals may be merely dried and preserved just as found, and the contents of the stomach obtained afterwards by dissection. Shells and stones, covered with seaweed, &c., from deep water, also afford most interesting and little-known forms. The rougher these are, the better (they ought by no means to be cleaned). Deep-sea soundings (especially those from great depths) should be presei-ved ; for they are often exclusively DiatomaceoiLS. " Yerv rare species have often been fonned in immense quantities in the arctic and antarctic regions by melting the ' pancake ice,' rendered brownish by these microscopic shells. The sea is also often observed discoloiu^ed with brownish patches, which should be collected, and the water filtered through blotting-paper or cotton wool : the residuum will frequently turn out to be composed of Diatomeae. It is also highly interesting to collect and examine the impalpable dust which occasionally falls into the folds of the sails of ships at sea." Scallops and other MolliLSca often contain rich and rare collections in their stomachs. In Ascidia (e. g. Phallusia sulcata^ Ascidia mentula) Mr. ISTorman and the Rev. E. CressweU found an abundant source. Mr. J^orman adds, in a further note kindly sent us — " The Ascidians, whose stomachs are almost always so loaded with Diatomaceous frustules, are to be found abundantly on the shells of oysters dredged in deep water, and readily procurable from the trawlers. " The Salpce (found so abundantly floating on the surface of the sea in warm latitudes) aflbrd very pure gatherings. The roots of the various species of mangrove, growing in the dense swamps of rivers and estuaries in the tropical regions of Africa, Australia, and the Eastern Archipelago, are said to be fre- quently covered with a brownish mucous shme very rich in Diatomese. I liave also obtained very pure gatherings from the roots of the Dutch rushes, as imported, and from the Zostera marina from the Baltic, used for stuffing beds, &c., by upholsterers. Stones, moreover, brought as ballast from abroad, will amply pay the diligent collector by yielding foreign and perhaps rare species. The roots of aquatic plants from tropical countries, stored in her- baria, would, if properly examined, peld many interesting forms of Diatoms." Indeed we may add, generally, that the roots of land plants, particularly of mosses, hchens, &c., growing around trees on the ground, or upon them, are fniitful in Diatomese, and, in fact, of some of the rarer fonns. In the ■N^umber of the Microscoincal Transactions just published (July 1858, p. 79), Col. Baddeley notes the occurrence of Diatoms in considerable numbers in the Koctiluca miliaris. They are the chief constituents of a mass of dark matter near the nucleus, and lie in the so-called vacuoles, into which they enter from the mouth. This occurrence suggests an easy method of obtaining different marine species of Diatomese in their natural state, often alive, and with their endochrome perfect. The Colonel discovered in this way several rarer species, and gives a list of nearly 50 which he identified, besides not a few forms of whose true name he was uncertain. To extract the Diatoma- ceous mass from the interior of the Noctilucce, Col. Baddeley recommends that the seawater and its h\'ing freight be poured, on arriving home, in a white hand-basin, and be let stand for an hour or two. " This rough treat- iO GENERAL HISTORY OF THE INFUSOEIA. ment causes these creatures to disgorge their food ; and if, after an interval, the water be carefully poured off, a sediment will be found at the bottom, which will consist of Diatoms mixed with some refuse." Dr. Donkin lately (T. M. S. 1858, p. 11) called attention to the occiuTence of that rare form, Syndendrimn diadema, in the stomach of the lobster, and in a subsequent paper {op. cit. p. 14) alludes to the abundant deposit of Uving Diatoms upon the sands at the sea-side, in the follomng paragraph : — " Professor Smith states that ' the shallow pools left by the retiring tide at the mouths of our larger rivers ' are the favourite habitat of marine species. But such localities I have found not to be half so prolific in species as the smids of stdl bays, or the sJiore, where they are exposed hy the reflux of the tide, at a distance corresponding ivith the half-tide margin. In these places, where the sands are sloping towards the sea, and grooved out into small fuiTows, filled -with salt water oozing out from behind, the abundance of Diatoms aggregated into a living mass imparts to the surface of the sand difi'erent hues of chestnut and oHve, the difterence of colom- being due to the natiu'e of the species present. These coloured patches, it is interesting to observe, are, during the sunshine, studded with numerous minute air- bubbles, undoubtedly given off by the Diatoms themselves. ^' To separate the Diatoms thus detected, from the surface of the sand, I found to be impossible. I therefore seized hold of the nearest bivalve shell which happened to lie in the way, and with this I carefuUy scooped up the surface of the coloured sand. This I emptied into a wide-mouthed, stoppered bottle, capable of holding eight ounces, until half full ; the other half of the bottle I filled up with salt water. I then shook the whole briskly and allowed the bottle to stand for a short period. The sand, being composed entirely of fine round grains of quartz and the minute fragments of shells, settled at the bottom in a few seconds, leaving the Diatoms all suspended in the water above, and forming by their abundance a chestnut-coloured cloud, but not more than 1 part in 1000 of the whole sand collected. The coloured water was then poured into another bottle, and formed the gathering, while the sand was thrown away. The Diatoms, in theii' tiu^n, were separated from the superfiuous water by subsidence, and brought home in l|-oz. bottles. In this manner I soon found that any quantity could be collected in a pure and un- mixed condition, affording an excellent opportunity of examining their living forms, and one of which I availed myself on Qxevj occasion. *' After carefully exaroining materials collected in this way from various parts of the beach, I -detected not less than about 100 species, all these strictly marine, and, with a few exceptions, each species in considerable abundance." The fact of Diatomeae rendeiing themselves perceptible to common vision by their excessive accumulation and the coloiu" they impart to water, is illus- trated by the phenomenon of coloration of the sea recorded by Dr. Hooker, also by the Melosira ochracea, which occui's in many, perhaps in all, cha- lybeate waters, and also in peat water containing a small proportion of iron. It is of the colour of ii^on rust, and in mineral springs, in which it abounds, is often taken for precipitated oxide of iron. It covers everything under water, but forms so delicate and floccose a mass that the least motion dissi- pates it. In the spring of the year this mass is composed of very delicate, pale-yellow globules, which can be easily separated from each other. They unite together in rows like short chains, and produce an irregular gelatinous felt or floccose substance. About summer, or in autumn, they become de- veloped into more evidently articulated and stiff threads of a somewhat larger diameter, but still form a complicated mass or web, and, either from adhering OF THE DIATOME.E. '9 to each other or to delicate Confei-vae, appear branched. In the young con- dition, when examined under shallow magnifiers, they resemble gelatine ; but with a power of 300 diameters the flexible granules are discoverable, and, with dextrous management, the little chains forming the felt or fioceose web can be made out. In summer, on the other hand, its structiu^e can be observed much more easily and distinctly. Early in spring the coloiu' is that of a pale yellow ochre, but in summer that of an intense rusty red. Other examples occur where a single species becomes tangible to the unaided senses ; such are met with in the brown specks mentioned in the preceding account of habitats formed by particular species upon the larger Algse and Confervse. So the GompJionema geminatum forms on rocks tufts of a spongy texture and brownish coloiu' when young, but white aftei^wards. The St/nedra Uhm often produces a white incrustation on stones in rivers in summer ; and Fragilaria and Odontidium are seen outstretched as dehcate brown filaments, several feet in length, like many filiform Algce, from which, however, they differ by breaking up so very readily, on the least disturbing force, into their separate joints. ^' Large numbers of Rhizoselenia'' (writes Mr. Brightwell, J. M.S. 1858, p. 95) "have been detected in the stomachs of Salj^ce, and they have also been observed floating free in the ocean in vrarm latitudes, their appearance being that of httle confervoid flakes of exquisite dehcacy, but of a sufiicient aggregation of filaments to be seen by the naked eye. The mass appeared (probably from the endochrome) of a faint, evanescent, ochraceous colour." Moreover, the frondose species generally attain an appreciable magTiitude. Thus Encyonema prostratum forms a tuft-like stratum, — when recent, dark brown, but when dried, of a dull green colour. Schlzonema suhcohcerens grows into tufts from a quarter to half an inch or more high ; and S. vidgare con- stitutes a dark bro^Ti gelatinous stratiun on stones in shallow water, fila- ments simple or nearly so in deep still water, and much branched filaments in deep rapid streams. Mr. I^orman, of Hull, has most kindly furnished us with the following original observation on the growth of one species, the Campylodiscus cos- tatus : — " In the early part of the spring of 1856," he "«T:ites, " I made a gathering of freshwater Diatomere from the ' Spring Ditch,' Hull. Although I met Tvith a few odd finistules of the species named, I did not consider it of sufiicient interest to boil in acid for moimting, and the phial containing them was left in the window of my laboratory during the ensuing summer. Some time in the autumn I had occasion to make use of this bottle, and was on the point of thro^ving away the contents, when I noticed the sui'face of the de- posit and the sides of the bottle to be covered A\'ith a dense brown growth of Diatoms. On further exarmination I found an immense colony of Campylo- discus, which gave by preparation some beautifully pui'e slides of thi§ species. In removing the upper layer I purposely left a few of the frustules in the bottle, which was again placed in the window. These have again increased to a great extent, and now (December 1857) they appear to thrive in perfect health. Does not this occiUTence suggest an easy plan of prociu^ing in a pure state such forms as are rarely found together in any abundance ? " Geogeaphical Distribution. — Species of Diatomeae are for the most part distributed over a very wide geographical area. Some, indeed, would seem cosmopolitan, whilst others are limited to certain regions. For instance, the Terpsinoe has not been discovered in Eiu'ope ; and Synedra Entomon is reckoned by Ehrenberg as peculiarly a South American production. This author has given full force to this seeming fact, and employed it in the en- deavour to discover the origin and course of meteoric dust, and also to arrive at certain geological deductions. For example, he says {Monatsh. Berlin, 80 GENEKAL HISTORY OF THE IXEUSOHIA. Akad. 1849), " The chain of rocky mountains traversing the continent of North America, forms, Avith reference to the distribution of Infusoria, a stronger barrier between California and Oregon, and the rest of the continent, than does the Pacific Ocean, with Chraa, between the western plains of North America and the region of Siberia. Thus, the United States, with Mexico, never present any of the forms characteristic of Oregon and Cali- fornia, whilst, on the other hand, the peculiar forms of these latter countries are met mth in Siberia. All this is remarkably confii^med in this, that the gold region of the Sacramento, in the extent and abundance of its Infusorial products, finds its parallel only in Siberia." This presumed fact of limited geographical distribution is thus applied by Ehrenberg m another paper (Monatsh. 18-16) : — " The atmospheric dust which, since 1830, has fallen in the Atlantic Ocean as far as 800 miles west from Africa, on the Cape de Yerde Islands, and even in Malta and Genoa, has been all of an ochre-yellow colour, never grey like the dnst seen in the north of Africa, and consists of from -i-th to k'd of organic particles referable to 90 species, the greater number of which are of freshwater habit, and found equally in the most "widely separated regions named. This dust, even in Genoa, whence it is carried by the Sirocco wind, contains no characteristic African forms, but, on the contrary, presents the Si/nedra Entomon, a deci- dedly characteristic species of South America." From his observations on this meteoric dust, Ehrenberg concludes that there is a current of aii' imiting Africa and America in the region of the trade winds, and occasionally dii'ected towards Eui^ope. On the other hand, their wide diffusion is exemplified in Dr. Hooker's Report on the Diatomaceous vegetation of the Antarctic sea {Brit, Assoc. 1847) : — " The genera and species of Diatomaceoe collected within the Antarctic sea are not at all peculiar to those latitudes ; on the contrary, some occur in every country between Spitzbergen and Victoria Land. Others, and even some of these, have been recognized by Ehi-enberg as occurring fossil in both Americas, in the south of Europe and north of Africa, in Tripoli stone and in volcanic ashes ejected both from active and extinct volcanos, whilst others again exist in the atmosphere overhanging the tropical At- lantic." Prof. Smith has the foUo^ving remarks on cosmopolitan or very widely- difiused species (Sr/nops. ii. p. xxvii) : — " Of freshwater species frequent in the British Islands, the following seem almost cosmopolitan, viz. Si/nedra radians, Pinnularia vir^idis, Pinnidaria horealis, and Cocconema lanceolatwn. Gatherings from many locaHties in Europe, from Smyi-na and Ceylon, from the Sandmch Islands, New Zealand, and New York, from the loftiest accessible points of the Himalaya in Asia, and the Andes in America, have supplied specimens of these forms. *' Navicula seriam abound in all our mountain bogs, and is equally common in the marshes of Lapland and America. " Epitheinia gihha is an inhabitant of the Geysers of Iceland and the lakes of Switzerland. *'The South Sea Islands supply Stauroneis acuta, and Ceylon Synedra Ulna, while Stauroneis Phoenicenteron is equally abundant in Britain, Sicily, and Nova Scotia. ''These notes of localities will give some idea of the wide distribution of our fluviatile Diatomaceae : more numerous gatherings would, no doubt, greatly extend the list ; and the following circumstance \vi\l show how gene- rally our commoner British forms are diffused throughout European localities that have been carefully examined. During a tour in Languedoc and the Auvergne in the spring of 1854, I made upwards of forty gatherings from OF THE DIATOME^. 81 the rivers, streams, and lakes of the district I traversed. In these I detected 130 sjDecies, and but one form not yet determined as indigenous to Britain. If this be the case with a district much of whose Phanerogamous flora is so different from our own, it bears out the \iew I have taken, that these or- ganisms enjoy a range of distribution far more general than the higher orders of plant -life. '' Nor is the distribution of marine species less notable for its extent and uniformity. Coscinodiscus eccentrkus and C. 7'adiatus range from the shores of Eritain to those of South Africa. Gmmmatopliora marina and G. macilcnta are found in almost every marine gatheiing from the Arctic Ocean to the Mauri- tius. Stauroneis pidchella, Cocconeis SciiteUiim, and Bkldulj[>hia pulcliella are equally abundant on the Eiu'opean, the American, and the African coasts, while lihabdonema Adriaticum belies its name by its occurrence in the Indian, Atlantic, and Pacific Oceans. During the researches already mentioned, in the South of France, I made several prolific gatherings on the shores of the Gulf of Lyons; but, of 33 fonns occurring in these, HyaJosira deUcatida, Kiitz., was the only one not famihar to me as a British species." The supposition that many species of Diatomeae occupy a very limited geo- graphical area, and that considerable numbers have, in course of ages, disap- peared or become extinct, as many animal and vegetable organisms have done, was thus ably examined by the lamented Dr. Gregory in a communication to the Royal Society of Edinburgh, made in 1856 (Proc. Boy. Soc. Edin. 1856- 57, p. 442). The subject of discussion is introduced in his notice of Ma- vicida prcetexta, a form previously considered only fossil. " I have," he says, *' selected this form because the bed in wliich it occurs fossil is the oldest in which Ehrenberg has found any Diatoms. He has indeed found microscopic organisms in the chalk, and even in older rocks, among which he mentions the mountain Hme^tone and the Silurian greensand. But the forms in the two latter rocks are not numerous, and, as well as those Avhich abound in the chalk, belong to the Foraminifera or to the Polycystina, not to the Diato- macea .... In short, I have no hesitation in saying, that I believe all the forms in the ^gina clay-marl, which is the -oldest Diatomaceous deposit yet de- scribed, will be found living on our coast." The stratum at -^gina belongs either to the chalk formation, or to the oldest tertiary or Eocene beds. Dr. Gregory continues, " It may also be observed that, of all the forms figured by Ehrenberg from more recent strata, whether mioeene, like the bed on which the town of Richmond (Virginia) is built, and several kinds of Bcrg- mehl — or phocene, like other Berg-mehls or pohshing- slates, &c. — or stiU more recent, the great majority are perfectly identical wdth existing Diatoms. Indeed, although many forms are stated in Ehrenberg's earhest writings to be fossil only, and have been supposed to be extinct, the progress of obser- vation is continually adding to the number of species which are found also in the recent state. Thus, for example, the whole group of dentate Eunotke, which abound in the Lapland and Finland Berg-mehls, were long thought to be only fossil ; but they have been nearly aU found in America, and I have myself seen several of them recent in this countiy. Eunotia triodon, long supposed to be extinct, occurred scattered in many of the Scottish freshwater gatherings. " Taking these facts into consideration, I am led to beheve that we have no evidence that any species of Diatom has become extinct, as so many species, and even genera and tribes, of more highlj' organized beings have done. I obser\^e that Mr. Brightwell expresses a similar opinion in his valuable paper on Chcetoceros (J. M. S. iv. p. 105)." Wherefore Dr. Gregory comes to the conclusion, that '' the whole of the G 82 _ GENERAL HISTORY OF THE INFUSORIA. speciea wJiicli occur fossil will, ere long, be detected in the recent state. It is at all events certain that a very large proportion of the Diatoms found in the fossil state also occur in the living state, and that every day adds to their number. There is at present no good evidence of the existence of Diatoms earlier than the chalk, if so early. But we must not forget that the shells of Diatoms appear to be altered by long contact with carbonate of lime, so that they may have existed at one time in the chalk. We find them, how- ever, in spite of the action of calcareous matter, in the recent chalk-marls of Meudon and of Caltanisetta, which are rather more recent than the chalk, and probably of about the age of the clay-marl of ^gina. If, as I believe, no Diatoms have become extinct, this may perhaps depend on their minute size and extreme simplicity of structure, which probably render them more indiiferent to climatic changes than more highly organized and larger beings. We have evidence, to a certain extent, that this is the case ; for by Ehren- berg's figures it appears that, in gatherings of recent Diatoms from all parts of the world, in every possible variety of climate, the majority of species are identical with om- own. *' Diatoms, therefore, are not materially affected by existing differences of climate, and have probably been as little affected by the geological changes which have occurred, at all events, since the period of the Eocene deposits." Geological Importance of Diatome^. — Fossil Accumulations. — Although so exceedingly minute and apparently insignificant in comparison with the animals and plants usually claiming our notice, yet, by their excessive multi- plication and accumulation, they assume even a greater importance, in the physical history of the earth, than the largest trees or animals mth which we are acquainted. This lesson is taught us by hving examples of these microscopic beings constituting appreciable masses, and by innumerable in- stances where only the silicious skeletons remain, in a fossil or semi-fossil condition. Ehrenberg thus illustrates their rapidity of production and accumulation. " Silicious Infusoria," he says, "form, in stagnant waters during hot weather, a porous layer of the thickness of the Jiand. Although more than 100,000,000 weigh harcfly a grain, one may in the coui'se of half-an-hour collect a pound weight of them ; hence it will no longer seem impossible that they may build up rocks. However, one of the most striking examples of the operation of Diatomese as a physical agency on a large scale, is afforded by Dr. Hooker's observations addressed to the British Association {Ueport, 1847). He saj^s — " The waters, and especially the newly-formed ice of the whole Antarctic Ocean, between the parallels of 60° and 80° south, abound in Diatomaceae, — so numerous as to stain the sea everywhere of a pale ochreous bro^vn, the surface having that colour as far as the eye can reach from the ship. Though pecu- liarly abundant in the ley Sea, these plants are probably uniformly dispersed over the whole ocean, but, being invisible from their minuteness, can only be recognized when washed together in masses, and contrasted with some opake substance. They were invariably found in the stomachs of Salpoe and of other sea animals, in all latitudes between that of the tropic and the highest parallel attained in the Antarctic expedition. Their death and decomposition produce a submarine deposit or bank of vast dimensions, consisting mainly of their silicious shields, intermixed with Infusoria and inorganic matter. Its position is from the 76th to the 78th degree of south latitude, and occupies an area 400 miles long by 120 wide. The lead sometimes sank two feet in this pasty deposit, and on examination showed the bottom made up in great measure of the species now living on the surface. This deposit may be considered as resting upon the shores of Victoria Land and of the Barriers, and hence on the OF TUE DIATOME.E. ^ 83 submarine flanks of Mount Erebus, an active volcano 12,000 feet high. From the fact that Diatomete and other organisms enter into the formation of pumice and ashes of other volcunos, it is perhaps not unreasonable to con- jecture that the subterranean and subaqueous forces, which keep Mount Erebus in activity, may open a direct communication between this Diato- maceous deposit and its volcanic fires. Moreover, this bank flanks the whole length of Victoria Barrier, a glacier of ice 400 miles long, whose seaward edge floats in the ocean, whilst its landward extends in one continuous sweep from the crater of Mount Erebus and other mountains of Victoria Land to the sea. The progressive motion of such a glacier, and accumulation of snow on its surface, must result in its interference mth the deposit in question, which, if ever raised above the surface of the ocean, would present a stratified bed of rock which had been subjected to the most violent disturbances." But instances of the abundance of silicious organisms in sea- or river- bottoms are to be met with nearer home. Mr. Boper has explored the mud of the Thames {J. M. S, 1854, p. 68) ; and he tells us that, excluding the coarse sand, nearly one-fourth of the finer part of the residuum is entirely composed of the silicious valves of difierent species of Diatomeae, — '' marine forms prevailing." This writer also quotes the experience of Ehrenberg, who, Avith respect to the mud of the Elbe, has established the remarkable fact that at Gluckstadt, a distance of 40 miles, and even above Hambiu'g, upwards of 80 miles above the mouth of the river, marine silicious- shelled Infusoria were found alive, and theii' skeletons deposited in it in such abun- dance, that at the former locality they form from one-quarter to one-third of the entire mass, and that the proportion is stiU about one-half that amount at Hamburg, as far as the flood-tide extends. All his observations gave a great predominance of marine over freshwater species, even when the salt taste of the water was no longer perceptible. His examination of the mud of the Scheldt and Ems fiu-nished similar results, as did that of the marine deposit in various littoral regions of the North Sea and Baltic. Reverting to the Thames deposit, Mr. Roper expresses his beUef that the silicious shells " have a perceptible influence in the formation of shoals and mud-banks in the bed of the river. , . . And the great abundance and general chstribution of species serve to illustrate the occurrence of similar dejiosits in a fossil state at localities now far removed, by alterations in the earth's surface, from the streams or harbours in which they were originally de- posited. " Another point worthy of attention is the influence of these organisms in the formation of deltas at the mouths of large and slowly- flomng rivers — such, for instance, as the Mississippi, in which the mean velocity of the current at N'ew Orleans is only about one mile and a half per hour for the whole body of water. Sir Charles Lyell, from experiments on the pro- portion of sediment carried down by the river, has calculated that, taking the area of the delta at 13,600 square miles, and the quantity of solid matter brought down annually at 3,702,758,400 cubic feet, it must have taken 67,000 years for the whole delta. Now, as the silicious frustules of the Diatomea) are secreted from the water alone, and would most probably be extremely abundant in so sluggish a stream (especially as Prof. Bailey has found both marine and freshwater species abundant in the rice-grounds), there can be little doubt that, without taking the larger proportion noticed by Ehrenberg in the Elbe, even if it were considerably less, it would reduce the above period by several thousand years ; and the same cause would probably apply wnth equal force to the Ganges and Nile. Ehrenberg considered that, at Pillau. there are annually deposited from the water from 7200 to 14,000 G 2 84 GEXEEAL HISTORY OF THE LNFUSOEIA. cubic metres of fine microscopic organisms, which, in the course of a century, would give a deposit of from 720,000 to 1,400,000 cubic metres of infusory rock or Tripoli stone." Another fact exemphfying the widely pervading presence of silicious In- fusoria was revealed by the experiments of Ehrenberg, viz. their existence in a h^ing state in moist earth beneath the surface, the only ^ital condition necessary being a small quantity of moistiu^e. The presence of their remains at considerable depths in mud also is well exemplified by the experimental borings made by Mr. Okeden {J. M. S. 1854, p. 26) at Neyland, a creek of IMilford Haven, where deposits rich in Diatomaceous remains of marine or brackish and freshwater character occurred at the depth of 20, 30, and 40 feet. The preceding illustrations wiU suffice to show the active share taken by the Diatomeae at the present day in the ever-occiu-ring changes of the earth's siuface ; others must now be adduced to exemplify their influence in the past physical changes of the globe. These examples are so numerous, and, relative to other phenomena, so important, that it is embarrassing to make a selection. Ehi-enberg is the most assiduous cultivator of this department of knowledge. He has personally examined deposits collected from almost every countiy of the world, and described, with illustrative plates, the genera and species he has encountered in them, in his recent large work the Mihrogeologie, 1855. One of the most striking and, to his mind, unique instances of a Diatoma- ceous deposit, formed at a remote or geological period, he has shoAvn to exist in North America, on the banks of the Colimibia Eiver. The river of Columbia, in its course at Place-du-Camp, rims between two precipices 700 to 800 feet high, composed of porcelain- clay 500 feet thick, covered over by a layer of compact basalt 100 feet thick, on which, again, some volcanic deposits exist. The clay strata are of very fine grain, and vary in coloiu' ; some are as white as chalk. Dr. Bailey has shown, from some por- tions submitted to him by Col. Fremont, that this apparently argillaceous layer is entirely composed of freshwater Infusoria. Its perfect purity from sand shows that it is not a drift, but has been formed on the spot. By its immense thickness of 500 feet, this layer of biohthic Tripoli far surpasses any similar layers elsewhere, which attain ordinaiily only one or two feet thickness, although those of Limebiu'g and Bilin have a depth of 40 feet. Some beds we also know elsewhere ha\ing 70 feet ; yet such are not pure, but inter- sected by strata of tufa or of other material. A very pm^e Diatomaceous deposit has been met with by Dr. Gregory in the island of Mull, which when diy is almost white, and much resembles chalk, being light, pliable, and adherent to the fingers {T. M. S. 1853, p. 93), and in composition hardly contains anything besides silicious organic remains '' for the most part entii^e, but with some fragments ; other portions which are denser contain also many fi'agments of quartz of various sizes, and vast numbers of comminuted fragments of loric?e." Prof. Smith {Sijnops. vol. i. p. xii) says — "Districts recovered from the sea, in the present or other periods of the earth's histoiy, frequently contain myriads of such exuviae forming strata of considerable thickness." Examples of this nature in our own coimtiy are met with in " the ancient site of a mountain lake in the neighbourhood of Dolgelly, locahties of a similar kind near Lough Island- Reavey in Down, and Lough Moume in Antrim." Mr. Okeden concludes, from facts collected by borings in the mud of some creeks and rivers of South Wales, " that not the smface merely, but the whole mass of these tidal deposits is penetrated by these minute and wondrous organisms, while, from the fact of their being foimd at Neyland at a depth of 40 feet below the OF THE DIATOME-E. 85 present surface, and close upon the rock which forms the original bed of this estuaiy, the mind is irresistibly led to the conclusion that they have existed there from the time when the waters fii'st rolled over the spot." Berg-mehl, Tripoli, and other polishing-powders, the stratified deposits at Bilin in Bohemia and in ^gina, and numerous others examined and reported on by various microscopists might like"\vise be adduced to demonstrate the important part played by these individually in\-isible beings, when accumu- lated in countless mpiads, in the construction of the earth's cnist. The Oolitic, and even some earlier metamorphic rocks, poq^hpitic rocks, &c., are not wanting, according to Ehrenberg, in species of Diatomeae ; but in the Pliocene, Miocene, Eocene, and in chalk and flint, and still more in the tertiary deposits, the abundance and variety of forms are greater. Diato- maceous shells are cuiiously preserved to us in large abundance and perfec- tion in guano, in which they have doubtless entered as a component in the way of mixture Tvith food taken by the bii'ds which have deposited that manui'e. The foregoing facts teach us that probably, in the present condition of our planet, no portion of its siuface is destitute of Infusorial life ; and now, from the prosecution of microscojDic research in connexion with geological facts, it would appeal' that, under this simplest and primary form, organic Hfe made its fii'st appearance on the globe, and has, during the many epochs of this world's histoiy, and notwithstanding the mightiest changes its suiface has undergone, been sustained imtil the present moment ; and, what is more, so extraordinaiy is the capability of the silicious Diatomeae to preserv^e life, and so astonishing theii' powers of multipHcation, that species which are now found li\ing have their generic and even their specific types at the very da^vn of creation. Prof. Ehrenberg has advanced this same statement in his recent work (Mikrogeologie), saying that the oldest sihcious Infusoria, whe- ther Carboniferous or Silurian, belong to the same genera, and often to the same species. Aeeolitic Diatome^. — Ehrenberg was the first to demonstrate the fre- quent existence of Diatomeae along with other microscopic beings and or- ganic particles in the atmosphere, principally in those showers of dust which fall from time to time in various parts of the world, and in those other mete- oric products known by the name of ' meteoric paper ' and ' blood-rain.' In such atmospheric productions, the Berlin natui^alist has detected above a hun- di^ed species ; these, accompanied by descriptions and figm^es, and prefaced by an account of aU such atmospheric phenomena on record, were pubhshed by Ehrenberg in a large brochure entitled " Passatstaub unci Blutregen/' consisting of 192 foho pages. An extract from this book wiU convey the best attainable notion of the physical importance of these aerial dust-showers. The quantity of actual solid matter that has fallen from the atmosphere by showers is far more considerable than supposed ; for, though it falls in a diffused dust-like form, the extent of surface covered at any one time is veiy considerable. Comparing it vdth. meteorolites, Ehrenberg obsei-ves that the total quantity of these stones which fell between 1790 and 1819 weighed 600 cwt., while in a single dust-shower at Lyons, in 1846, the soHd matter weighed fuUy 7200 cwt. Other dust-stoims in Italy, at Cape de Yerd, and in other localities have exceeded even that at Lyons, in the quantity of matter precipitated to the earth ; and Ehrenberg suggests to the imagination the millions of tons that must have fallen since the time of Homer. Lastly, he entertains the ciuioiLs opinion, that this meteoric dust does not necessarily derive its existence from the earth's surface, and from the force of atmospheric currents, but from some general law of the atmosphere, according to which 86 GENEEAL HISTORY OF THE INFUSOKIA. the living organisms mainly composing it may have the power of self- development in the aii\ Uses of Diatomaceous Deposits. — The utility and possible and probable piu-poses of these minute organisms to mankind have not yet met with due consideration. Their relation to the soil, in which they are so abundant, and their influence on its fniitfulness are matters only incidentally reflected on by authors. " Sufficient attention," remarks Prof. Gregory (J. M. S. 1855, p. 2), '' has not yet been paid to the fact of the invariable presence of Diatomea) in all earths in which plants are found. Ehrenberg, in his Ml- Jcrogeohgie, has established the fact as a universal one, and pointed out the important bearing it has on the growth of the soil. Indeed, it is difficult to imagine a more effectual agent in the transference of silica from the waters to the solid earth than the growth of Diatomeae, the shells of which are as indestructible as their multiplication is rapid. Ehrenberg is of opinion that they live in the soil as well as in water ; and the constant presence of moisture in the soil renders this conceivable, ^ilthough tlie proportion of silicious matter dissolved in ordinaiy water is but small, it is e\idently sufficient to supply the shells of millions of Diatoms in a veiy short time ; and it is therefore probable that, as fast as it is extracted from the water by them, it is dissolved from the rocks or earths in contact with the water, so that the supply never fails." Mr. Roper has also suggested, from the consideration that the best samples of guano contain the greatest number of these sUicious skeletons, which doubtless serve to replace the large amount of silica abstracted from the soil by the cereal crops, that it is probable that the deposits of many of our rivers would have a beneficial efl'ect if applied to the land ; and it rests vdth the microscopist to point out the most favourable localities for obtaining them. Ehrenberg notices an instance where this has been done in Jutland, where a blue sand abounding in calcareous and sihcious shells is collected, and greatly increases the fertility of the arable soil to which it is aj^plied ; and Prof. Bailey also states that the mud of Newhaven harbour is used as a fertilizer, and is found to contain 58*63 per cent, of silica. The author last-named has moreover adduced instances to prove that the great fertility of the rice-fields of South Carolina is mainly due to their richness in Diato- maceous remains. This notion is strengthened by the examinations of Ehrenberg, and by the commonly observed fact of the occurrence of Diatomeas about the roots of plants, especially of the cereals, which demand a large supply of silicious material to construct their stems. Dr. Hooker {ojy. cit.) contends that the abundant Diatomaceous deposits of the South Pole supply ultimately the means of existence to many of the smaller denizens of the ocean, and that they keep up that balance between the animal and the vegetable kingdom which prevails through all other lati- tudes. He adds that they probably piuify the vitiated atmosphere, just as plants do in a more temperate region. In the arts, the remains of Diatomaceous shells, as the chief ingredients in certain deposits, are brought into use as polishing-powder under the name of Tripoli, and also, as an extremely fine and pure silicious sand, in the manu- facture of porcelain. The powder called Tripoli has various origins, and differs in the microscopic organisms it contains. Species of Melosira especially abound — for instance, of Melosira varians. Ehrenberg informs us that the Tripoli of Jastraba in Hungary and that from Cassel resemble each other in their component species. A very remarkable application of a deposit of Diatomeae is its use as an article of food, imder the pressure of want, by the wretched inhabitants of OF THE DIATOME^. 87 some inhospitable and barren districts of Europe — for instance, in some localities of Lapland and of Himgaiy, and in other parts of the world. Ehrenberg mentions a sort of earth under the name of " Tanah/' eaten in Samarang and Java, which overlays some moimtains of Java at several places at a height of 4000 feet. It is generally solid, plastic, and sticky; it is rolled and diied in the shape of small sticks over a charcoal fire, and is eaten as a delicacy. An examination of this earth disclosed 3 or 4 species of Polygastrica and 13 of PhytoKtharia. It has been attempted to make the specific characters of Diatomaceous de- posits of critical value in deciding on the date and superposition of rocks. However, the geographical distribution of these beings is as yet insufficiently knoTVTi ; and eveiy day reveals the fact that species deemed peculiai* to some one locality are to be foimd in others, and to have at least a very wide range. We have already quoted some examples of apparent limited diffusion in our remarks on geographical distribution ; it is therefore not necessary to illustrate the subject fui^ther in this place. The circumstance that some one or two species seem at times peculiar to a neighboui'hood, has encoiu'aged antiquarians to seize on it with the hope of determining the locahty whence the clay was procui^ed from which ancient specimens of pottery or porcelain were manufactured. Another practical pm^pose to which the shells of Diatomece have been put is as test-objects for microscopes, the penetrating and defining powers of which are measured by their abihty to detect and demonstrate the existence and natiu"e of certain markings on the siu'facc of the silicious epiderm — such, for example, as the stria3 of PUurosigma. Ox TUE NATUEE OF DiATOMEiE, AYHETHEK AnIMALS OE PlAISTS VAEIOUS HYPOTHESES. — The natiu-e of the Diatomese is still a much-vexed question, although the opinion of those natui^alists who hold them to be plants — mem- bers of the great family of Algte — preponderates. Ehrenberg assumed their animal natiu^e, and persuaded himself of the existence of a complicated organi- zation, such as neither the researches of others can confii*m nor analogy sup- port. In his latest papers on Organization, he has insisted most strongly on the -apparent successful feeding of these organisms \vith particles of coloiu' which entered A\ithin their interior. These experiments are not satisfactory, and have failed in the hands of others ; it is besides quite clear, that the umbilicus, at which he represented the coloiu'-granides to enter, is no real opening in the lorica, but a tliickening of its epiderm. Prof. Meneghiui, now many years ago, penned a learned treatise to prove the animality of the Diatomese ; but although he offered many ingenious argu- ments to support his opinion, he did not succeed in establisliing it. Many de- tails of structiu'e and organization and micro-chemical characters, ui^gedby him in favour of their animal nature, have been considerably modified or entirely set aside by subsequent researches ; and the general argument, that the varia- tion fi'om recognized plants is in many particulars very marked, has only a comparative or relative force, according to the extent of differential stmcture of animals which may, on the other hypothesis, be set forth and proved. The distinguished Itahan naturalist indeed limits his design in the treatise before us (On the Animal nature of the Diatomeoe, R. S. 1853) to disputing Kiitzing's arguments for their vegetable nature, saying (p. 365), " Whilst unable to confirm or refute the opinions of Ehrenberg, we seem to have observed facts sufficient to disprove those of Kiitzing." On this same side are ranged Eocke, Eckhardt (a pupil of Ehrenberg), and Prof. Bailey, who express thou- inabihty to reconcile some of the structural details and physiological phenomena with vegetable organization. Schlcidcn 88 GENERAL niSTORY OF THE INPUSORIA. perliaps should also be reckoned of the number, since he remarks, in his de- scription of the shield of a Navlcula, that "such an artificial and complicated structure amongst plants has no explanation, and is entirely without signifi- cation. In all actual plants we find the silica present in quite a difi'erent form, as little separate scales or drops, and distributed through the substance of the cell-wall." In favour of the vegetable nature of the Diatomeae, on the other hand, the majority of the original observers in this countrj^ unite mth many of the most distinguished natui-alists of the Continent, such as Kiitzing, Siebold, Nageli, Rabenhorst, Braun, Cohn, Meyen, &c. The last inquirer, so long ago as 1839, urged various objections against the presumed animality of the Desmidieas and Diatomeae, and more particularly against Ehrenberg's views. Respecting the animality of the Diatomeae (Naviculacea), he remarks generally — " The reasons adduced for such belief are so weak, that the conclusions deduced from them are yet for the most part very doubtful." A small nimiber of natiu\alists have expressed the notion that the Diatomeae belong equally to the animal and to the vegetable kingdom. M. Thuret may be named as one of these, since he has stated that there is no more reason in favour of the one afiinity than of the other. Such an idea is certainly unphilo- sophical; for it would cut the knot instead of loosening it, by the assumption of an order of organic beings intermediate between the animal and the vege- table kingdom, and undeterminable to which they belong. We will now proceed to state the leading arguments for the animality of the Diatomeae, indicating the name of the writer suggesting each, so far as practicable : — 1. The Diatomeae — many species at least — exhibit a peculiar spontaneous movement; which is produced by certain locomotive organs. — Ehrenherg. 2. The greater part have in the middle of the lateral surface an opening, about which certain roimd corpuscles are situate, which become coloured blue when placed in water containing indigo, like the ' stbmach-ceUs' of many In- fusoria, and consequently may equally be regarded as stomachs. — Ehrenherg. 3. The shells of many Diatomaceae resemble in structiu-e and conformation the calcareous shells of Gasteropoda and similar Mollusca. — Ehrenherg. 4. The method of multiplication by self- division. — EJirenhei^gandMeneghini. 5. The complicated structure of the waU of the frustules, and the characters of the silicious deposit. — Schleiden, Bailey, and Meneghini. 6. The greater affinity in chemical composition of the contents (the endo- chrome) with animal than with vegetable products. — Meneghini. Each of these arguments requires examination in detail, and its value tested. To begin therefore with the first — the occuiTence of locomotion and the organs by which it is effected, as e^ddences of animal constitution. Morren, in the paper quoted {Jahreshericht Akad. Berlin, 1839), pointed out that motion is not confined to animals, but exhibited also by the spores of Algae and by sperm- atic particles. To these examples may be added the Oscillatoriae, Proto- coccus in its various phases, Vaucheria clavata, Ulothrix zonata, and other Algae, among which are the now admitted genera of Yolvocineae. In many of these, the movements are much more active and lively, and present more seeming spontaneity than those of any of the Diatoms. The employment of the word spontaneous to signify the sort of movement of these organisms is certainly unjustifiable, if understood at all in its usual signification, of an act originating in the moving body directed to a special purpose ; for no more spontaneity is manifested in the motions of these siKcious organisms than in those of the leaves of the Dionc^a ^niiscijnda when any particle impinges on their sensitive hairs. Meneghini, in examining this point, is compelled to OF THE DIATOME.E. oYf admit that no absolute proof is deducible from the movements of the fmstules, in support of their animal nature ; and the only difficulty to him against admitting that they may be vegetable in character, is, that they are so dif- ferent from those of Oscillatoriae, Desmidiese, and Protocoecoidese, — a worth- less objection, to be sufficiently answered by asking whether that motion does not diifer as widely from that of any -animals, and whether the movements of the Desmidieee are not equally unlike those of the OscillatoriaB as those of the Protococciis. The locomotive organs insisted on — consisting, according to Ehrenberg, of a retractile foot and of retractile ciliary processes — have not been sufficiently demonstrated to use as an argument. Ehrenberg, Corda, and more lately Focke, are the only observers who pretend to have seen such organs, although the organisms said to possess them are subjects of daily minute research by hundreds of wonder-finding microscopists. The mucous film which invests many Diatomaceous fmstules may, indeed, have been seen and misinterpreted. Meneghini calls attention to a kind of sparkling or agitation — actually a rapid and indeterminate change in the refraction of light at their extremities, which he seems disposed to believe shadows forth the presence there of some sort of ciliaiy locomotive organs. Granting, however, that cilia were ascertained to be the cause of the movements perceived, the doctrine of animality would in no way be advantaged, since cilia are not peculiarly animal structures. According to Nageli, one sort of vegetable movements originates in the act of growth. Of such a kind are probably the \ibrations of the Oscillatoriae ; and possibly the motions of the Diatoms are in some degree reducible to the same category. And it is to be remarked that these motions are not equally apparent and active under all circumstances, even among specimens of the same species, but are most so when the vital phenomena of the organisms are most aroused — when the most rapid interchange of material is going on between the external medium and the internal cavity. 2. The second argument rests entirely upon hj^^othetical grounds, derived from Ehrenberg's observations, and is valueless so long as those observations are imconfirmed. It seems quite clear that the central opening or umbilicus spoken of has no real existence ; and if this be so, then the apparent entrance of coloming matter within a set of corpuscles situated around it must be an error of obsei-vation, unless the unproved and improbable assumption be made that the coloui'-particles enter at foramina placed elsewhere (as at the extre- mities), and become transmitted to these centrally placed sacs or so-called stomachs. Kiitzing declares that the seeming entrance of colour-granules is the result of mechanical causes, and adds the more important statement that the central collection of vesicles is often wanting. 3. The third argument, that a resemblance obtains between the shells of Bacillaria and those of some Molluscous animals, is, to say the least, fanciful, and in a scientific inquiry can be admitted to prove nothing. If external similarity proved anything, it might as weU be adduced to demonstrate the affinity of a lead-tree with the higher plants, whilst, again, the error to which this sort of proof wiU lead is well exemplified in the case of the Eoraminifera, which from mere outward resemblance were for years accounted members of the Cephalopodous family. In the latter instance, indeed, the similarity in external form was very striking — far exceeding that of any Diatom with any testaceous animal. Kiitzing, in his review of this assigned reason for their animality, meets it in another way, by observing that, among the cells of higher plants, examples are to be found which in configui^ation and other particulars agree mth Dia- toms— for instance, the numerous forms of pollen with their angles, spines. 90 GENERAL HISTORY OF THE INFUSORIA. &c. But, as Menegllim remarks, '' he might have added the more appropriate instance of the Desmidieae, which would be very closely allied to the Diatomege, if the latter, like the former, could bo referred to the vegetable kingdom. If not equal in constancy and regularity, the Desmidieae display a greater degree of complication: and we must remember the different nature of their substance; for in the vegetable cell, when lime or silica predominates, the wall becomes imiform and regular." 4. Multiplication by self-division was at one time cited by Ehrenberg as peculiarly an animal phenomenon, — a notion at variance Avith the observations of every naturalist, and now requiring no refutation. However, Meneghini has more recently advanced the statement that an essential difference in the process of fission prevails between the Diatomeae on the one hand and the Desmidieae and Algae in general on the other, applying to the former modifi- cation (in accordance "with Brebisson's views) the term deduplication, to the latter reduplication. To extract his remarks {op. cit. 368) — " Division is always longitudinal, and takes place underneath a fine external sihcious membrane, by the formation of contiguous diaphragm walls which divide the internal ca\T.ty. Thus the contents are longitudinally divided ; and this divi- sion is complete if the two new individuals detach themselves and so acquii^e individual liberty. It is imperfect if the fine silicious persistent membrane and the secreted gelatinous substance retain them connected together. This mode of reproduction (which Brebisson distinguished by the name of dupli- cation and deduplication, from the reduplication of Desmidieae) deserves the most attentive observation. The foregoing exposition presents the fact in its most rude and superficial general appearance, and makes us feel acutely the want of a more ciix'iunstantial description peculiar to various forms. It is only after having established facts relative at least to the principal generic tj-pes, that we can establish, on a scientific basis, the general idea of multi- plication by duphcation. A few observations suffice, however, to prove that this does not occur in so simple a manner as we are taught to believe, by compaiing it with that in vegetable cells. In the Achnanthidia, for example, it is described and figured that the principal surfaces, which occupy the inter- mediate space between the two superior and the inferior valves, commence by presenting fine transverse lines, and next a strong longitudinal line along the middle ; then there appear two new intermediate valves contiguous to each other — the superior valve (?) of the new inferior individual, and the inferior one of the superior. My observations convince me that the affair does not proceed vsith so much simpUcity. I have often seen the two lateral valves separated, and the intermediate space thus largely amplified. In other cases there appeared only a new inferior valve complementary to the superior, the inferior individual thus remaining incomplete. Finally, in others, between the complete superior individual and the incomplete inferior valve, there appeared a new individual with both its valves, but nearer together, smaller, finer, with lines much less distinct." In short, " in this phenomenon there is more complication than that of a simple cellular deduplication." 5. In a previous page (p. 88) we have quoted Schleiden's notice of a dif- ficulty in the way of recognizing Diatoms to be plants. It is one likewise which has presented itself to others, for instance, to Prof. Bailey and Mene- ghini. ^' If we suppose them to be plants," says the latter writer, " we must admit every frustule, every Navicida, to be a cell. We must suppose this cell with walls penetrated by silica dev'eloped within another ceU of a different nature, at least in every case where there is a distinct pedicle or investing tube. In this silicious waU we must recognize a complication certainly im- equalled in the vegetable kingdom." (op., cit. p. 372.) OF THE DIATOMEiE. ~ 91 This critique of Meneghini loses much of its force when it is noticed that the existence of a pedicle, or isthmus, or of a muco-gelatinous sheath envelop- ing the frustules, is assumed by him, quite h}^:)othetically, to indicate their formation within a cell-wall represented by the soft investment, — an idea originated by him because he could not admit of an extra-cellular formation. The present state of knowledge, however, clearly recognizes the not infi-equent formation of extra- cellular matters about cells, and consequently this portion of the difficidty in question will cease to have importance. On the other hand, no animals can be pointed out having a similar complex silicious stmetiu'e, whilst an analogy may be, to a certain extent, foimd with the Desmidiea), some of which have a small deposit of silica in their envelopes, which again in some Diatomaceous frustules is very deficient (see p. 37). Indeed, the affinity between the Dcsmidiese and the Diatomea) is manifested by the diffferential characters vrhich naturalists feel themselves called upon to indicate (see p. 95). The composite structure of the fnistules is principally the residt of the per- meation of the external timic with silex. The little box or capsule, when first produced, represents a simple enclosed cell, imbued with more silica than a Desmidiaceous frond, but otherwise not histologically unlike. When the Httle being prepares for self-di\'ision, the opposite valves separate, much as the opposed halves of a frond of one of the Desmidiea?, and the intermediate production, according to the habit of the class, becomes penetrated by silica (to a less extent, however, than the original valves), and assumes so much of a permanent character that it is very frequently considered an independent tliii'd segment. So again, the cellular, or areolate, or otherwise figured and involuted sui-face of the frustules, cited by Meneghini as dissimilar to any plant- structure, would also ajjpear to be a consequence of this permeation of the organic membrane with silica, and of various modifications consequent thereon. To show that analogies are not wanting in the vegetable kingdom of ciuiously modified and figured cell-waUs, we may mention as examples, besides poUen-grains, in- stanced by Kiitzing, the sporangia of Desmidiea? and of various Algae. More- over, the capability of the simplest enclosing membrane to develope a very complex superficial structm^e is illustrated in the case of the Rhizopodes, among which are many examples of striated, areolated, and other-wise modified shells, which, in the eyes of many, range "with imiceUular organisms. We must not forget to state that Meneghini himself seems to have appreciated the eff'ect of the permeation of silica upon the characters of the ceU-wall ; for he says, in liis supplementary annotations {op. cit. p. 511), " the part which sHex takes in the formation of the cell- wall is undeniable," as in the epi- dermis of Gramineae, Palms, and Equiseta. " The stomatic cells of Equiseta merit particular attention, both fi'om the silex they contain, and the transverse striae they present on the internal surface. This resemblance to the shield af Diatomeae might lead us to believe that we ought to regard it as an argument for maintaining the vegetability of the latter: but I do not think that I ought to dwell upon such an objection ; I only notice it because I would not appear to be, or pretend to be, unacquainted with it. Yet it seems to mo important in another point of view — the apparent complication that the simple cell may assume when penetrated by silica." We cannot do better than close this part of the argument by Prof. Smith's review of the subject (Si/noj^s. ii. p. xix) : — '' In every case this membrane [of the frustule] is more or less penetrated or imbued with silex; and the presence of this substance appears to have modified the intimate structiu^e of the membrane, and induced great variety in the mode and character of its 92 GENEKAL HISTORY OF THE INFUSOEIA. formation in different genera, accompanied by great regularity in the indi- vidual species. " These variations exhibit themselves in the different modifications of structure which constitute the markings of the valves, aj^pearing imder the form of ribs and nodules, costae, striae, or cellules of an elliptical, circular, or hexagonal outline. A wide comparison of specimens seems to me to prove that these various markings originate in the tendency impressed upon all organized structm-e to develope itself upon the type of the cell, and that the presence of the silicious constituent in the cell-membrane of the Diatom gives a fixedness to this tendency, which, in ordinary cases, is either not discern- ible in the structure of the membrane, or whose effect is obliterated by the coalescence of the softer material which constitutes its substance. However this may be, it ajipears to me certain that the structure of the silicious valve in the Diatomaceae is invariably cellulate, the cellules being more or less modified according to the peculiar requirements of each species, and that no other explanation of their characteristic markings seems consistent with the facts which are established by a carefiil examination and comprehensive know- ledge of Diatomaceous structure. That this explanation does not involve con- siderations at variance wdth the conditions of unicellular vegetable life, will be ob\ious to any one familiar with the stnicture of the sihcious epiderm in the Equisetaceae and Graminaceae, and the distinctly cellulate structui'e of many pollen-grains, while this very presence of silex as a constituent of the cell-wall in the Diatomaceae appears to be wholly unaccoimtable except on the supposition of the vegetable nature of these organisms. In no instance do we find a parallel condition in the animal kingdom (for the secretion of silicious spicula, as an mtemal skeleton, in some of the Spongideae, cannot be regarded as an analogous phenomenon), whereas the vegetable kingdom furnishes us with cases, not merely of the secretion of silex as a vegetable product in the Bamboo, but with frequent instances of its intimate union with cellulose in the membrane which forms the epiderm of the cell, as in the Natural Orders abeady mentioned, in the Palmaceae and others." On the nature and mode of deposition of the silex. Dr. Bailey has ad- vanced the statement that the silica in Phytolitharia, as well as in Diatomeae, Polycystineae, and Spongilithes, is not doubly refi'active and polarizing, as Ehrenberg described, and that even the adniitted exception of AracJinoi- discus is not such. The error in supposing it so has originated from the im- perfect removal of the dense carbonaceous tissues which are deposited beneath the silica. 6. The final argument we have to consider for the animality of the Diatomeae is, that the greater affinity in the chemical composition of the contents, i. e. of the endochrome or gonimic substance, is with j)lants, and not with animals. This argument is certainly based on a nice and very drfiicult- tb-be-determined fact. Meneghini insists on it as important. His remarks have already been given in om- notice of the contents of the frustules, to which we must refer (p. 47), adding here only some supplementaiy obser- vations to fully convey his opinions. '' Finally," he Avrites {op. cit. p. 366), for this is not a property peculiar to chloroj)hyll, " I may add that, if a portion of chlorophyll could be demonstrated in the interior of Diatomeae, this would by no means mvalidate their animal nature ; we might still suppose they had swallowed it for food. As to the oil-globules " w^hich Kiitzing represents, Meneghini considers they may be no more than particles of sarcode, which have an oily appearance ; and he would observe '' that the number and volume of these globides increase considerably after death, and that during life they are situated upon a longitudinal line extending from one extremity to the OF THE DIATOME.E. &3 other. And," he continues, '' I rely upon the observation that there is some motion and successive alteration in them, as if these minute globules mixed with larger ones, and separated again from them." For, to the mind of the Italian naturalist, the hypothesis of stomachs is admissible, although the fact that a polygastric structure (affirmed by Ehrenberg) has not been shown in the ciliated Protozoa is in itself an a priori argument that such an organization is not to be found in the Diatomeae, among which animal cha- racteristics are so much more deficient and indeterminate. Although, to our apprehension, this argument, based on the diiferential chemical composition, to the extent it is developed by Meneghini, is incom- plete and inconclusive, yet it was a duty to present it, in order that some of the many ardent English microscopists may be induced to attempt the solution of this micro-chemical question. Rabenhorst, we should not omit to state, describes the colouring matter of Diatomca? as quite different from the chlorophyll of plants. For instance, he states that the chlorophyll of plants is taken up by alcohol, dissolves with a yellowdsh-green colour in alkalies, and with muriatic acid acquii'es an emerald- green colour, whereas the coloming material of Diatomece is insoluble in alcohol (although after a time its coloiu" fades), remains unchanged by alkalies, and acquires a pale-green colour mth muriatic acid. It still remains to point out the facts which speak in favom' of the vegetable nature of the Diatomacese. The following summary was offered by Kiitzing : — " 1. The great resemblance of compound forms to xilgse, and their develop- ment by fission. There are, indeed, compound Infusoria, as Monad-masses and Polypes : but the former are very questionable animals ; and the latter have this essential distinction, that the individual animal lives without (external to) its habitation, and moves freely, whereas such Naviculce as Encyonema, Scliizonema, and Micromega, and similar genera, grow within the enclosing substance, building themselves up like the cells in the stem of a plant — so vegetating here only as cells. In like manner, the individuals of Fragilaria, Melosira, Himantidium, &c., are steadily fixed, and unable to exhibit animal motion. "2. The inner soft organic parts, which I have designated gonimic sub- stance, possess, as well in their chemical nature as in theii' development, peculiarities akin to those met T\dth in the ceU- contents of confervoid Alg^e. *' This relation is most clearly seen in the genus Melosira and its allied forms, which, not only in form, but also in the chemical components of their con- tained matter (since the presence of chlorophyll is common to all Diatomea?), are closely allied to the confervoid Algae. " 3. The development of seeds, or young [as Kiitzing represents it], occurs here as in undoubted Algae, but never as in true animals. " 4. The Diatomeae, and especially the free moving Naviculce, develope, in the sun's rays, an appreciable quantity of oxygen, like all admitted plants. " The evolution of oxygen, indeed, occurs in green Monads and Euglence ; but this affords no argument for the animality of the Diatomeae, but renders the animal nature of those Infasoria themselves veiy doubtfirl, and the more so as recent observations confirm the idea of the origin of the lower plants themselves from Monads and Euglence. AVherefore all these comparisons serve to favour the belief in the vegetable nature of Diatomeae." To these arguments has been added another, resting on the assumption of conjugation being peculiar to plants ; and Mr. Blackwell chscovers further evidence of plant-life in the variations of form of the fmstules of the same species (J. M. S. 1853, i. p. 247). It is necessary to inquire, seriatim, into the real value of the arguments 94 GENERAL HISTORY OF THE INFUSORIA. on this, as has been clone with those on the other side of the question . Meneghini enters the lists with Kiitzing, and disputes the conclusions arrived at by him, rather than the facts on which they rest. The first argument, founded on external resemblance, has little value, and offers no certain indications of affinities. However, taking Kiitzing' s state- ments in his own words, modem research has added to its weight ; for it has proved, what was before only a probability, that the so-called Monad- masses are only of a vegetable nature. The second reason advanced has been already discussed, whilst the thii'd rests as yet on incomplete observations, and in Meneghini' s opinion has an equally strong analogy in animals, for example, " in the ovaries of PoIj^dcs and other inferior animals, as in many 0\ipara of superior classes. And, in fact, the bag of a spider, with the thousands of small eggs that it contains, seems to me quite as like, as the spore of an Alga, to the organ of propaga- tion of a Scliizonema or a Micromccja.''^ These analogies cannot be allowed much weight, whilst it is, on the contrary, pretty clearly ascertained that the sporangia of Diatomeae produce a brood of young forms within them, — a phenomenon according in all particulars with the mode of reproduction in numerous Algae and Fungi. The foui^th argument for their vegetable nature must be admitted to possess great importance. Since Kiitzing enunciated it, the apparent objections against the vital phenomena in question being restricted to plants, have been removed by subsequent inquiry. The green Monads and Euglence, cited by Kiitzing, are now recognized to be vegetable, and can no longer east doubt, by reason of an assumed animal nature, on the fact of the evolution of oxygen being a characteristic of vegetable life. The evolution of oxygen, as Prof. Smith, like every other careful observer, tells us, " may be noticed in any mass of Diatomacea3 during the warmer months of the year, or in gatherings freely exposed to the sun, in the elevated temperature of a confined apartment, during the winter or spring. Under these conditions the water in the vessel becomes covered with mmute bubbles of oxygen, and portions of the Diato- maceous stratum are floated up by the buoyancy of the globules of this gas adhering to their frustules. Such phenomena can only be accounted for by supposing that the Diatomaceae are plants, and that they exhale, like all plants in a state of active vegetation, oxygen from their tissues ; but this pro- cess is iiTeconcilablc with the hypothesis of their animal nature." (Si/noj)s. vol. ii. p. XX.) Prof. Carpenter insists {Microscope, p. 469), that the most positive and easily defined distinction between Protophyta and Protozoa "lies in the nature of the aliment, and in the method of its introduction," in each case. " For whilst the Protophyte obtains the materials of its nutrition from the air and moisture that surround it, and possesses the power of detaching oxj'gen, hydrogen, carbon, and nitrogen from their previous binary combina- tions, and of uniting them into ternary and quaternary organic compounds (chlorophyll, starch, albumen, hcera ; for Cohn writes (A. N. H. 1852, x. p. 326), " This is not only made evident by the multifold changes of form which they undergo in the coui^se of vegetation, and by the fihform prolongations and ramifications which are produced directly from theii' sub- stance (XIX. 38, 39-53), but is clearly shown by the transformations which the primordial cells pass through in consequence of external influences. Under certain circumstances namely, the filiform processes may be retracted, being torn away from the envelope -ceU and taken up into the substance of the primordial cells ; the produced ends of the primordial cells also disappear, the latter becoming rounded off into theii' original spherical or short cyhndiical form. Such a change would be impossible if the primordial cells were sur- rounded by a rigid membrane, such as that of the envelope-cell for example." i2 116 GEIS^ERAL HISTORY OF THE INFUSORIA. According to Prof. Henfrey, the primordial cells or gonidia of Pandoinna (XIX. 59-63), and also, in the opinion of many, the Euglence (XVIII. 45-48), are similarly undefended. The internal globular coloured body of the motile form of Protococcus is in the same state. Thus Cohn {R. S. p. 531) points out that although this body has a sharply defined outline, yet, " either by mechanical means, or by chemical reagents, the internal globular mass may suddenly be made to lose its contour, and to sjjread so as entirely to fill the ca\ity of the colourless envelope. From which it would appear that the internal globular body is not surrounded by any special cellulose membrane, but only by one readily destroyed by chemical or physical agency — probably nothing more than a dense layer of protoplasm." In the case of Volvox the cells originate without an enclosing membrane ; but after the appearance of the red spot, a dehcate one shows itself, and extends at difierent points into the connecting thread-like processes (XX. 37, 39, 41). So in Gon'ium we may presimie the jDrimordial cells to be originally naked, although Cohn has not remarked this fact, but confined himself to describing the matui^e ceUs (XIX. 32, 34), which have an enclosing wall of cellulose (Enhv. pp. 175, 1 76). Lastly, in the ' still' form of Protococcus a special membrane invests the protoplasmic gonidium. In Goniiini (XIX. 34), and in Volvox (XX. 37, 39, 40), filiform prolongations extend between the several cells in the compound organism ; in Stephanospluera similar processes are given ofi" at the opposite poles of the cells, and are consequently not inter- current (XIX. 39). Prof. Williamson has in the case of Volvox offered the best explanation of these threads, wliich have by some been supposed inter- communicating canals. He first makes good his opinion that the green cell- Kke organism represents the nucleus of a cell, the wall of which is separated from it by a greater or less space ; and then he compares the processes in question with the fihform extensions fi'om the nucleus which are met with in many vegetable cells, suspending that organ in the centre. In the early stage of the cell, the protoplasmic substance fills up more or less completely the cell- wall (XX. 42, 44) : by-and-by the latter becomes outstretched from it by a sort of di'opsical efiusion within it (XX. 37) ; but as the protoplasmic nucleus has contracted adhesions at difii'erent parts, it becomes di'awn out from the adherent points into thi^ead-hke processes (XX. 39, 40, 45), which grow more and more filiform in proportion as the cell- wall expands. This expla- nation (agreeing in every particular with the observed phenomena of cell- growth) being accepted, it follows that these elongations are bounded by the particular cell- wall to which they belong, and are not continuous with those of adjoining cells. The processes of Volvox are therefore ofi'-shoots of the protoplasm of which each cell or gonidium consists ; they are given ofi" before any enclosing wall or peUicle appears, and wliilst that substance is still duc- tile, and they disappear on the commencement of the process of development, whether of macrogonidia or of microgonidia, and whether mth or without the process of encysting. In the case of Gonium, Cohn gives {Entw. p. 176) a different account of the connecting bands. It will be remembered that in this genus that ob- server indicates an enclosing cellulose membrane to each cell or gonidimn. Now this cell does not closely invest the protoplasmic substance at all points, but is so separated as to produce a hexagonal cell-wall aroimd it, from each angle of wliich the membrane is produced in a tubular form, and joins mth a similar process coming from the angle of an adjoining cell (XIX. 32, 34). Hence each process of the membrane has a double outline, and is in fact a tube, only that its interior must be presumed to be shut-off from that vdi\\ OF THE PHYTOZOA. 117 which it joins, by a septum representing the divisional membrane of each of the contiguous cells. The state of things here is therefore quite different from that in Volvox : for in the latter the cell-membrane is widely detached from the protoplasmic nucleus, but the adjoining cells are adherent at all points ; the intercurrent thi^eads are therefore v\dthin the cells, and uphold an attachment between the nucleus and the cell- wall, — whilst in Gonium the contrary obtains : the cells themselves are not in apposition, but held together by a tubular extension from each angle ; and the nuclear protoplasm within nearly fills the cell-cavdt}', and has no bands uniting it v\dth the waU — in fine, the intercurrent processes of Gonium and of Volvox are not homologous. Besides the wall and processes just described, calculated to give strength and resistance to the organisms, there are also the long cilia or filiform ap- pendages known as filaments, flabella, or flageUa, seen at one extremity of most Phytozoa, derived from the protoplasmic mass. To these are entirely or chiefly due the locomotive powers of these beings ; they also act the part of rudders in turning them on themselves, and in directing them hither and thither. They do not belong to the class of vibratile cilia, but are larger, filiform or whip-like, and have an undulating lashing movement. In some cases they are many times longer than the organism to which they are attached (XVIII. 15, 21, 22) ; and when two, as more frequently happens, are pre- sent, they wiU often cross and intertwine. At times, in elongated forms, they appear to be the mere terminations of the tapering-Hke extremity or neck ; but the rule is, they do not proceed from the apex itself, but from one side of it. Whei'e the species is encased in a fii^m integument, separated by an interval from the central protoplasm, the filaments actually extend from the latter and perforate the enclosed case ; in which, particularly when these processes are fallen away, their points of issue are occasionally to be detected b}^ depressions or by pores. Duiing frequent rapid movements these fila- ments are not to be seen ; but when the motion is more gentle, or they are at rest, or otherwise when colouiing matter is mixed mth the water, they generally become visible. Even when their existence has not been noticed duiing life, it may be sometimes demonstrated after the diying up of the being, by the streak left upon the glass where it rested. Where more than one or two filaments are present, their whirling, and the consequent agitation of the fluid about them, makes their existence apparent. The number of filaments in Phytozoa varies. Two is the prevailing number, which may or may not be of equal length ; but in not a few genera only one is found, e. g. in Euglena, Monas, and Chilomonas, — whilst in others more than two may be counted, situated together anteriorly, or some in front and others behind. Where two are present anteriorly, it is not an uncommon arrange- ment for one to extend in the direction of the long axis of the body, whilst the other trails behind (XYIII. 12, 22, 23). MovEiiEXTs OF Phytozoa. — The motion of many Phytozoa is but slow, and rarely intermitted ; in others it is more rapid and varied. It wiU be modified by the figui-e of the organism and by the degree of firmness of its waUs, with which it stands in inverse proportion. In Euglena the move- ments are extremely varied and lively : the being is unrestricted in its movements by an integument, and the contractile protoplasm has full scope ; it is, in fact, in the condition of swarming gonidia, unenclosed by a wall of cellulose. In many species of Monas and Bodo (Cercomonas), the motion is irregular and peculiar ; it may be oscillating or rolling, at times leaping, at others backward. Among the Vibrionia (XYIII. 57-69), an oscillating spiral movement is a common characteristic, and either end may be advanced. The revohing rolling motion of Volvocinece has for many years attracted 118 GENEKAL HISTORY OF THE KfFUSORIA. attention, and for a long time was deemed sufficient proof of the animality of the beings exhibiting it. It is the consequence of the play of the ciliary filaments of each of the component cells of the aggregate organism, which project beyond the common envelope : it consists in a revolution on the axis, and a simultaneous onward movement — not, however, in a straight course, but in an iiTcgular one, representing a spiral or series of curves. " The collective idea of such motions," says Cohn (A. N. H. 1852, x. p. 328), "is best represented by the coiu'se described by a top, which rims through the most varied curves, while at the same time constantly revohing on its axis." jS'ageh. (as quoted in J. M. S. i. p. 198) remarks of swarm-cells (zoospores), which many Monads imdoubtedly are, that " under the microscope the motion appears very rapid, somewhat of an infusorial character, consisting in a con- tinual progression, in which the hyahne narrower extremity is usually in front, and the cell is continually turning on its long axis. Although the swarming bears a resemblance to the motion of Lifusoria (i. e. of Ciliated Protozoa), it clearly wants the s23ontaneity of the latter. The Infusoria advance, spring back, turn round, retui-n, all spontaneously ; the swarm- spores piu'sue a imiform and, for the most part, pretty straight com^se, de- \iating from it, or turning round only upon meeting an obstacle, impinging upon which they are diverted into another direction." To this account Siebold {Joe. cit. p. 201) adds that the spores do not retreat, as if frightened, like the Infusoria, when they strike against an object, but " remain close to it, and continue their motions according to the number and arrangement of their ciliary apparatus, in a rotatory or \4bratory way for a little time longer, as if they aimed at overcoming the obstacle by force, until at last, probably in consequence of the death of the cilia, they become still.and germination goes on. ... The movements of the swarm- spores in general have only a short diu'ation. After the spores have come to a state of rest, they usually become attached by the hyaline ciliated extremity, and the locomotive faculty is for ever lost." In the aggregated families the process of reproduction is ever going on in some members of the colony, and the movements are kept up much longer. Braim {Bejuv., R. S. p. 212) represents Chlamydococcus as enjoying a longer duration of motion than is iLsual with the swarming gonidia of Algee, whilst Protococcus viridis forms an intermediate link in this respect between it and the Volvodnece. The kind of movement, he adds, is essentially the same in these organisms as in all active gonidia, namely an uninternipted revolution round the long axis, combined with an advance towards the side of the ciliated point. It is, indeed, in the swarming movement of gonidia and spermatozoida that the phenomena of motion are most striking, "that is, in cells which are either yet without their cclbilose coating, or which never acquii'e one." Cohn {B. S. p. 558) states generally that, " leaving out of the question the more highly organized Infusoria furnished with a manifest mouth and a^sophagus, the motion of a large part of the Anentera (Ehr.), the Astoma (Sie- bold), is not essentially different from that of the zoospores of certain Algae." Likewise, in his description of Gonium (Entiu. p. 180), he observes that the movements of this organism resemble in every particular those of Stephano- sjjlicera, Chlamydococcus, and other swarming- cells, " which certainly do not bear at all the character of pui^posing, conscious volition, but appear as an acti\T.ty determined not by any external causes, but by internal causes in the organization and vital processes." {A. N. H. 1852, x. p. 328.) The character of the locomotion of Phytozoa may be described in brief as ' automatic ;' accepting that term as physiologists now agree to do, to distin- guish such motion from the voluntary movements of animals. It cannot be OF THE PHYTOZOA. 119 voluntary, or the result of volition, any more than the marvellous motion of the leaves of Dioncea rnuscipula. Peocess of Nutrition-. — The process of nutrition of Phytozoa is of the most simple kind ; and no valid evidence can be adduced in proof of the com- plex polygastric organization represented by Ehrenberg. In fact, an apparatus of stomach-sacs could not, by any analogy, be presumed in a set of beings destitute of mouths ; and Ehi^enberg was unable to demonstrate, even to his own satisfaction, an oral aperture, except in a very doubtful manner and in a very few instances. What he took to be gastric cells are no other than vacuoles and clear vesicles — sometimes the chlorophyll-cells ; the last, how- ever, were more commonly assumed to be ' testes.' To support his behef in the presence of stomachs, and also of a mouth at the anterior clear space, particularly Avhere there is a j^rojection of the protoplasmic mass, the Berlin natm'alist appealed T\ith most confidence to his experiments in feeding with coloured substances. By this means he believed he demonstrated such organs in some Monadina, — but so rarely, amid a large number submitted to experiment, and moreover in so few species, that much weight could not be attached to the result, especially when it is considered how many difficulties and doubts must arise where such very minute beings are concerned. Allow- ing that particles of colour actually entered within the interior, and Avere not merely adherent (a question which the magnifying powers of the instrument Ehrenberg used could scarcely determine), it is even then much more rational to suppose that their entrance was by mere mechanical causes (by pressure or the like), than by the medium of a mouth. This interpretation is adopted both by Perty and Leuckart, who describe the introduction of such particles as possible, although, indeed, exceedingly rare in the more clearly vegetable structui'es, the Diatomeae. The former mentions {op. cit. p. 61) three in- stances in which he encountered foreign particles Avithin the substance of Phytozoa ; but these would, instead of supporting, be really opposed to the polygastric hypothesis. For instance, he discovered in a Peronema a species of Bacillaria as large as itself, and consequently not containable within one of the supposed gastric cells. In the case of the soft, illoricated minute Monadina, into which fine particles have found their way, it is to be remembered that they are mere masses of yielding protoplasm unprotected by a cuticle ; and further, we may, along Avith Perty, reasonably presume that, in some examples of the entrance of external matters, it has been effected much in the same way as mth the Amoebce, by the soft substance overlying and then surroimding them. If a mouth and stomachs have no existence, it follows that nutrition must be effected by imbibition — by endosmotic and exosmotic action — just as in any simple vegetable or animal cells. Perty (op), cit. p. 62) adduces an experiment showing that, to some Phytozoa at least, water rich in nutritive organic material is necessary to their complete and healthy development ; for when taken fi'om such water and placed in other quite pure, they dwindled in size, although, curiously enough, they at the same time became more active. To complete what we have to say of their vital endowments (irrespective, that is, of the reproductive functions), the Phytozoa seek the light ; and aU their nutritive acts are carried on more actively under its influence. The only exception is when, in the process of propagation, they are about to pass into the ' stiU ' condition and to become encysted ; then they eschew the light, sink out of sight, and recede to the bottom, or under cover of aquatic plants or of theii' debris. Under the influence of light they exhale oxygen gas, and the green colour is especially developed, — whilst when kept in the dark they lose colour, become pale, and present few chlorophyll-particles. The 120 GENEEAL HISTORY OF THE INFUSOEIA. intensity of Kght may be too great, and destroy life ; and a great elevation of temperature is less favom^able to vital activity than a moderate one. Cold retards vital action, and if considerable, arrests it, except in the case of the encysted beings, which are so modified by natiii'e as to resist its injmioiis influence; these consequently persist through the winter when the motile forms are cut off, and in the coming spiing bm\st forth into life. The same provision which imparts to the encysted organisms a tolerance of cold, enables them also to withstand the effects of evaporation, which to the unprotected motile varieties is speedily destructive, unless, indeed, so gradual as to allow them time to pass into the ' still ' form. Starch or cellulose may be detected chemically in the great majority of the Phytozoa; and even where iodine fails to produce the characteiistic blue colour during Hfe, it will at times act strongly when a breaking-up of the contents follows evaporation or some other injmious influence. The efficiency of nutrition is manifested by the decided changes, chemical and vital, which are seen in constant operation within the beings — such as, among others, the transformation of clilorophyll into starch, and of one or both these into an oily matter. When in the ' stiU ' encysted condition (XIX. 4-1-69), aU nutritive changes are at a standstill, and the organism may exist ^Aeeks, months, and even years unchanged, until external conditions are sui3plied to awaken its latent energies and to renew the cycle of Hfe. In this torpid form the spores are carried about with the dust, or remain buried in the earth, or are elsewhere hidden or stored up against the day of revival. The passage into the ' stiU ' condition by the throwing-out of an external denser envelope and by the loss of ciHa, is governed, it would seem, in some measure by external circumstances. Motile forms are replaced by the ^ stiU ' in whole or in part, and with greater or less rapidity, by poimng the water containing them into a larger and shallower vessel, and by gradual evaporation. The protoplasm of Phytozoa being homologous in all perceptible particulars \\\th. the '■ sarcode ' of Protozoa, suffers, like it, the destructive process of ' diffluence ' or ' deliquescence ' when evaporation reduces the quantity of water around the improtected motile forms below the quantity necessary to \'ital action. The first noticeable result of evaporation is, according to Cohn, at least in the instance of Protococcus (op. cit. p. 538), a more rapid change of figure and appearance, followed, if the evaporation continue, by diffluence, in which he distinguishes two stages or phases : — '' In the fu'st, the outlines appear less sharply defined, because the coloured substance is somewhat retracted from the border of the piimordial cell ; the cells become flattened, and at the same time ^^ider : the contents are also now altered ; previously more homogeneous and transparent, they now become thi^oughout granular, and the red substance runs together in large drops. At this time the forma- tion of vacuoles commences ; and their number continues to increase. In this way the interior of the primordial cell again becomes colourless, clear as water, and the granular coloui-ed contents pressed against the walls. . . .The figiu-e of the cell in the warm time is so much expanded, that it comes to be apphed upon the wall of the enveloping cell, alternately filhng it altogether, so that the entire zoospore appears to consist of only a single coloiu'cd gra- nular vesicular disc, corresponding in size with the original enveloping cell." Multiplication and Reproduction of Phytozoa. Fission : Macrogonidia ; MicROGONiDiA : Encysting process : Phases of existence. — The multiplica- tion of the individuals of the species of Phytozoa is provided for by the process of self- division, deduplication, or fission. This takes place according to the plan obtaining in vegetable and animal cells in general. OF THE PHYTOZOA. 121 The cell-contents divide into two or more segments, each of which can further develope around itself a gelatinous investment, and enter on an inde- pendent existence. In Euglena, self-division occurs longitudinally into two portions ; and the newly- developing half is of smaller size than the other, but becomes complete in all its parts before its severance is effected. The motile cells of Cldamydococcus undergo fission into two or four seg- ments (XIX. 23-26) : this takes place in the protoplasmic or primordial cell contained within the hyaline spherical enveJope-ce]l ; when division is com- plete, the latter is ruptured, the sections escape as independent beings, each throws out around itself its envelope- cell, and in aU points goes through the same cycle of development as the parent-cell. Many Monads also divide into two beings, whilst others separate into foiu\ In the above-cited ex- amples the fission is complete, and each segment, on detaching itself from the other, becomes an independent, free being. But this same act of fission may proceed under different circumstances ; and instead of a single organism, a colony may be formed, consisting of several individual cells united together, either permanently or only for a time, within a common envelope. These aggregate Phytozoa are especially represented in the family Volvocinece. In this second mode of fission the process is repeated a greater number of times — for instance, some 3, 4, or 5 times — the result being a higher midtiple of 2, the product of the first act of scission. Each repetition of the process of fission, from the commencement until its completion, constitutes, in Xiigeli's language, a transitional generation, whilst the final repetition produces the permanent generation. For example, in Stephanos]jha;ra two segments are produced by the act of fission, which re- present the first generation (XIX. 45) ; then each of these subdivides, and so developes four portions (XIX. 40, 46) — the second generation ; and, lastly, each of the foiu' separates into two, and in that way produces eight segments — the third, and in this organism the final or permanent generation (XIX. 41, 42, bQ). Unlike the segments resulting from a single act of division, or, as may happen, from this act once repeated, each newly-formed i^rimordial cell does not commonly siUTound itself with an envelope and enter on an isolated existence, but the whole eight or more continue to live within a common tunic, which presently expands by endosmotic action and acquires a more or less spherical figure (XIX. bQ, 57, 58). Simultaneously with this expansion, the previously contiguous particles are drawn away more and more from each other, and chsposed within the common envelope, after a more or less regular fashion, characteristic of the species to which they belong (XIX. 42, 58). In general, the separation of the primordial cells is not complete; bonds of union between them in their early state, when closely approximated, become cbawn out, and ultimately present themselves as interciuTcnt thj-eads. When this series of changes is terminated, we have before us a reproduction of the aggregate organism of which the dividing primordial cell was but an individual member. Braiin has styled this variety of reproduction by fission, development by ' Diacrogonidia.^ It is well illustrated in Steplianosphcera, above cited, in Volvox (XX.), in Goniiim and Pandorina (XIX. 35, 36, 37, and 62-66), and also in undoubted Algae, the Hydrodictyon or Water-net for example. But the segmentation of the cells of Phytozoa occurs in yet another form ; i.e. the fission, instead of stopping at the third or foiuih generation, pro- ceeds still further, until 32 or 64, a hundi'ed, a thousand and upwards of minute cell- structures are produced, technically called ' micror/onidia,' in- 122 GENERAL HISTOEY OF THE INFUSORIA. tended to perpetuate the species by their ulterior development. Although, like the ' macrogonidia,' they are formed within a common envelope, yet each cell among them does not, as in those products, enclose itself with its own tunic, and fix itself permanently within the general investment — in other words, assume at once the ' still ' condition ; but the whole, after entire separation from one another, become endued with vital acti^dty, and are sub- sequently set free, by the dissolution or ruptm^e of the surrounding parent-ceU, as so many moving zoospores (XIX. 51). The motion of these Httle bodies "within the original cell is of a hurrying to-and-fro or up-and-down cha- racter, and has been styled ' swarming.' On emerging from the ruptui^ed ceU, each little body is seen to have a spindle-shaped figiu-e, terminated at its anterior clear and usually elongated extremity by two or fom- cilia (XIX. 52). In eveiy essential particular these microgonidia are homologous with the motile gonidia, swarming- cells, or spores of the common Algae, such as Bry- opsis, Codium, Achlya, Chcetophora , VlothrLv, Hydrodictyon, &c. Cohn's re- marks on the formation of microgonidia in Stephanosphoira {A. N. H. 1852, x. p. 346) may elucidate this subject stiU fiu'ther. He says, " While, in the formation of macrogonidia, the secondary cells become surroimded by a common envelope and are not free (as an entii-e connected family of ceUs arranged according to a definite law), in the mode of propagation of micro- gonidia the little secondary ceUs finally become totally separated from one another without secreting an envelope-cell; and in this way each of the eight primordial cells of the perfect Steplianosplicera is broken up into 32 to 64 independent, green, elliptical or spindle-shaped corpuscles, which then separate from one another, commence an independent and active motion, and fill up, in great numbers (as many as 256-512), the common parent envelope- cell (XIX. 51). . . . The crowding-in among each other of the microgonidia of SteplianosphQ), which invests them like an integument, first Ipng close upon them, but afterwards, through the imbibition of water, raised from them all round, assuming a globular fonn ; but so that the primordial cells occupy the periphery at the equator of the globe like a ring or zone (XIX, 57, 58), having their eight pairs of filaments protruded through the openings in the common envelope (XIX. 38). ChJamydococcus and Chlamydomonas stand in the same relation to Stephanosphcera that Pleurococcus does to Pal- mell-a, Phycastnim to Desmidium, Navicula to Schizonema, VorticeVa to Epi- stylis, or as Hydra to Campanularia. But, further, a second mode of development, \^z. by microgonidia, prevails 146 GENERAL HISTORY OF THE INFUSORIA. alike in the three genera in question, the bisection of the contents of the cell proceeding so far that they are eventually resolved into numberless small, mostly spindle-shaped corpuscles (XIX. 51), which at first oscillate by the aid of two or four \ibratile filaments mthin the common envelope-cell, but subsequently escape singly from it, (XIX. 52), and, after enjoying for a con- siderable time very energetic infusorial movements, finally pass into a state of rest, preparatory to some futui'e development. " The larger undivided macrogonidia, after swarming often the whole day, are also seen to enter (as ^vitnessed in Chlami/dococcus and Steplianosphcera) into the condition of rest, when each primordial cell contained within the delicate envelope-cell secretes about itself a second more compact cellulose membrane which closely invests it, and is not perforated by the ciliary fila- ments (XIX. 20, 21). It is, in fact, the countei^part of the membrane which, in common plant-cells, overhes the primordial layer. In tliis distinctly plant-like or protococcoid condition the cells remain without motion, and may endure, even when dried, for a whole year, and then, on the addition of water, undergo segmentation into two, foui', or eight gonidia, which, imme- diately after developing their filaments and envelope-cells, break through the walls of the parent -cell and crowd the surrounding fluid." The facts relating to the structure and functions of the genera above adduced, apply in the main to all the Volvocinece ; for the diff'erences between the several genera, although demanding special consideration, are not essen- tial. Thus, for example, in Gonium (XIX. 32) the figiu'e is a flattened sphe- roid, and the green primordial cells, \iewed collectively fi'om above, resemble a four- sided disc or plate, having each angle truncated. Moreover, the trans- parent coloiu'less envelope does not acquire the character and appearance of a firm membrane, but presents itself as a mucous or gelatinous, not cellulose, sheath. Chlamydomonas. — The first of the genera included by Ehrenberg in his family Vohocina, of which we shaU attempt a description, is Chlamidomonas or Chlamydomonas (XIX. 16). It recommends itseK to our attention because of its simplicity and its existence in an isolated state. This last fact seemed to Dujardin a sufiicient reason for remo^dng it from the Volvocina to the Thecamonadina, and for renaming it Disehnis, on accoimt of its having two filaments ; for he would admit into the former family only aggregate organ- isms " enclosed within a common envelope, or ha\'ing special envelopes mutually adherent." On this same ground he also advocated the transposi- tion of Gyges from the Volvo.v family to that of the Thecamonadina, a genus which we shall presently have to note under the name of Chlamydococcus or Profococcus pluviaVis. To this arrangement Cohn objects {A. N. H. 1852, X. p. 334) ; for, says he, '' a more profound investigation, not only of the structure, but also of the history of development, teaches us that Chlamydo- monas (Disehnis, Duj.) possesses only external analogies with Trachelomonas, while this form, as Ehrenberg abeady discovered, exhibits the closest alhance to Gonium and Pandorina. The relation of the colourless envelope to the enclosed green globes, the position of the two ciha, which arise from the latter and pass out through the former, and lastly, the laws of division of the green cells inside the envelope, in powers of two, display themselves in exactly the same way in Chlamydococcus as in the rest of the Volvocinece ; and the only distinction between them consists in the circumstance that in Chlamydomonas (and Chlamydococcus) the individuals produced by the di\-ision of the green globes separate after the absorption of the parent envelope, and live on as individuals, while in the other Volvocineoi the daughter- cells produced by the division of one green primordial cell remain connected by the persistent OF THE PHTTOZOA. 147 parent- cell as by a common envelope, and move about as a well-defined body composed of many cells." The best accounts of the structm^e of Chlamydomonas we have at hand are those by Perty (op. cit. p. 85), by Eraim (Eejiiv., li. S. p. 214), and by Thuret (Sw les Zoospores, Ann. Sc. Nat. xiv. 1850). Unfortunately, each of these writers describes a different species, which renders our attempt at a general history the more difficult. The figure varies between ovoid and globular ; and the cell is not prolonged at the point from which the pair of vibratile filaments proceed, although a colourless space exists there. The organism consists of a green mass — the primordial cell — surrounded by a dia- phanous delicate envelope, wliich, unlike that of Chlamydococciis, is closely applied to it, so that it leaves no clear interspace between the two. The contents are green globules and larger vesicles, ^ith a single large chlorophyll- utricle in the centre — the nucleus (XIX. 16) — very like in appearance to the starch-globule so frequent in the cells of green Algae. In addition, there is a red stigma, and in some rare instances two such ; in other examples, again, it is altogether wanting. Motion is effected by the ciliaiy filaments, which penetrate the external envelope from the enclosed globule; the envelope resembles that of zoospores in general ; and, like those structures, these uni- cellular beings seek the light and exhale oxygen. Perty describes colourless germs from which new specimens originate, — a statement no doubt equivalent to saying that these beings reproduce them- selves by microgonidia, as Cohn represents. Fission into macrogonidia is binaiy or quaternary, as in Tetnispora, and gives rise to two, fom% eight, and even, at times, sixteen or thirty- two individuals. Generally whilst this act proceeds the cells are quiescent, ceasing from their usual movements. This process of multiplication is not influenced by the size of the Chlamydomonads, for it occurs in specimens varying between -j^ to -^-j'". Amid the film-like collections of Chlamydomonas, groups of individuals may be encoimtered in various stages of change and of breaking up : some have entirely or partially lost their green contents ; others have acquired a yel- lo'\\'ish-brown, or, more seldom, a red colour ; others are much contracted as small globules within the clear gelatinous cases, whilst others, lastly, acquire a proboscis-like process, or, by pressiu'e, an angular outline. The variety and transition of colour just remarked depend upon the phase of existence and the entrance on the resting or quiescent condition. The ceUs of Cldamydomonas ohtusa, Braun teUs us, when swarming are of a dark green coloui', truncate at both ends, and, after multiplying for some time, produce here and there veiy minute paler and more bro^vnish-yeUow micro- gonidia. " In the course of a few weeks no more active cells could be found in the water, the full-gro^Ti swarms having all gradually come to rest and sunk to the bottom. The original longish shape of the cells had changed into a perfect sphere with the transition to rest ; the colour of these resting- cells, origmally green, gradually passed into a light yellowish brown ; at the same time a number of small, sharply- defined, brilliant globules were formed in the interior, ha\TLig quite the appearance of drops of oil. In this altered condition the Chlamydomonads remained, exhibiting neither growth nor increase." It is added, in a note, that these resting (seed) cells are about ■^"' in diameter, have a tough, colourless, and transparent membrane, and finally assume a flesh-red coloiu-. On awakening from this ' resting '-stage, segmentation of the contents re^ives, with the disappearance of the red and oil-like elements. The resting-stage of the microgonidia has not been suffi- ciently investigated, Chlamydomonas Pidvisadus. in the opinion of Cohn and most others, is l2 148 GE^^ERAL mSTOEY OF THE IXFrSORIA. undistiiigiiishable from Pohjtoma UvelJa in every material i3oint, — the absence of colour, and its habitat in decomposing infusion alone offering themselves as distinctive of the latter. Nay, what is more, he discovers the intimate resemblance of Ghlamydomonas to the resting- stage of a Volvooc which he discovered in decomposing infusions, and named V. liyalma. From these considerations he concludes that Clilamydomonas and Polytoma must be ranked with Volvox in the vegetable kingdom. But ChJamydomonas is made to appear a metamorphic condition of yet other organisms. For instance, Itzigsohn states that, after the joints of the filaments of Oscillaria tenuis are separated, they produce motile gonidia " Avhich present in all respects the aspect of Chlamydomonads, but which, after passing through many intermediate forms, grow into perfect Euglence. " (J. M. S. 1854, p. 189). Likewise Hartig, in his account of the transforma- tions of the Phytozoa of Antheridia (J. M. S. 1855, p. 54), makes one phase to resemble Chlamydomonas destruens of Ehrenberg. Lastly, Cohn confesses {On Protococmis, R. S. p. 555) that the motile or swarming form oi Protococcus is scarcely distinguishable from Chlamydomonas, except that the latter has not been observed by him in the ' still'' condition. But this presumed point of divergence itself vanishes since Braun's observations have made us ac- quainted with the quiescent phase of that organism (p. 147). The relation of Cldamydomonas to Stephanosphcera, and, in general, its alliance with the Volvocina as a plant, have been re\dewed in the preceding remarks on the family (p. 145). Chlamydococcus (XIX. 20-31), another unicellular, isolated organism of the family Volvocina, has arrested much attention, and been described at large by Flotow, Braun, Cohn, Perty, and others under the additional names of Protococcus, Ha^matococms, and Hysginum. Ehrenberg has no genus similarly named; but modern researches show that Gyges is in part its equivalent, although but one phase of its existence. Ehrenberg's account of Gyyes is very meagre. He characterizes it as wanting both filaments, eye, and tail, and as completely encased within its lorica (an urceolus). He could discern no traces of a nutritive system, and, except a very slight movement rendered e\ddent by colouring the fluid, could detect no indication of animality. On the other hand, Mr. Shuttle- worth examined G. sayiguineus, and stated it to have a lively motion (Edinb. Phil. Journ. v. p. 29). In our preliminary notes on the Volvocinece in general, a vegetable nature is assigned to the Chlamydococcns ; and its relation to other Volvocinece is thus laid down by Cohn (A.N.H. 1852, x. p. 335) :^ " Chlamydococcus is a unicellular Alga in the strictest sense of the word, never composed of more than one cell at any period of its growth, and each division forms the commencement of a new individual, whilst the remainder of the Volvocinece [i.e. excepting Chlamydomonas'] present themselves as families of cells, in which a definite number of equivalent ceUs are combined, in some measure, into an individual of a higher order. " The researches of Alex. Braun, like my own," he continues, '' have proved most distinctly that Chlamydococcus can only be placed with pro- priety among the Alga). It is distinguished, indeed, from the moving germ- ceUs by which far the greater part of the species of Algse are propagated, both by a somewhat more complex structui'e and by the circumstance that the motion lasts for a very long time, and, finally, by the power of the moving cells to propagate as such Avithout entering into the state of rest (germina- tion) otherwise than as quite a temporary condition. But these objections touch only, to some extent, the specific character of Chlamydococcus and the OF THE PHYTOZOA. 149 Volvociticce generally as unicellular plants; and they do not stand there among the Algae altogether without intermediate conditions, as Alex. Braiin has proved, especially from the long movement of the Volvocinece. " On the other hand, the external form, like the chemical and morphological organization of the contents, the laws of motion, and the general physiological phenomena, especially however the behaviour in the transition into the con- dition of rest, in Chlamydococcus, agree so perfectly mtli the moving spores, the transformation of which into undoubted plants has been demonstrated with scientific clearness, that no unprejudiced observer can discover an essential distinction. I have mentioned in my essay that Ehrenberg himself, although he claims the moving condition of the forms allied to Chlamydo- coccus as Infusoria, has declared the resting-stage of this, or a most closely allied genus, to be an undoubted Alya ; and yet the mo\'ing Infusoria are only a propagative form of the motionless Alga. Finally, I have succeeded in demonstrating the membrane of the cells of Chlamydococcus, both in the resting and ixirticularly in the moving stage, to consist of cellulose, and thus in establishing the most important criterion of a vegetable cell we are at present acquainted with — the ternary composition of the cell-membrane — in the Infusorioid condition of Chlamydococcus. In fact, all the more recent observers of Chlamydococcus, the number of whom is not inconsiderable, have, almost without exception, agreed in recognizing in all coyiditions of the development of this form, only a plant and nothing hut a plant. ^^ Besides the valuable sketch referred to, of the relations of Chlamydococcus, Cohn has presented an elaborate memoir on this organism under the name of Protococcus, in a paper translated for the Ray Society (Botanical and Physio- logical Memoirs, 1853), and has subsequently extended his \iews of it and its aiSnities in his essay on the development of microscopical Algce (EntwicJc. d. mihr. Algen, 1854). Of these most important j)apers we shall make free use in sketching the history of this genus. " The moving cell of Chlamydococcus is composed of two principal parts, a hyaline spherical envelope, which is formed of a delicate structureless mem- brane consisting of cellulose, and immediately surrounds colourless contents, perhaps consisting of pure water. In the centre of the envelope occurs a coloured globule, composed of the universal nitrogenous p>7'otoplasm or mucus of vegetable cells, coloiu-ed red or green by chlorophyll or a carmine-red oil, and containing imbedded in it numerous gramdes of protoplasm, as well as one or more large chlorophyll- vesicles. This coloiu^ed globule is attenuated at the upper end into a colomdess point ; from this go out two cilia, which protrude into the water through two orifices in the membrane of the enve- lope, and produce the movements of the whole. The inner coloured globule is not bounded by any rigid membrane, but merely by a thickened layer of protoplasm ; hence its contour is very changeable and passes through mani- fold transformations in the course of its development. In particular it fre- quently becomes elongated in all directions into colourless radiating filaments, which keep the internal coloured globule suspended freely in the envelope, and are afterwards retracted in the course of the development. '' The motionless cells of Chlamydococcus are of much simpler structure, and, like all forms of Protococcus, consist simply of a tough spherical ceUiilose membrane and green or red contents organized as primordial utricle. The history of development shows that under certain conditions the contents of the motionless cells become divided into a number of portions, which always correspond to two, or a power of two, in their number, that these portions become organized into special primordial utricles, and as such break through the parent-cell, each developing two cilia, and by the aid of these rotating 150 GENERAL HISTORY OF THE INFrSORIA. actively in the water. During their motion they excrete a delicate cellular membrane o\X'r their entire surface, which is gradually removed farther and farther from the primordial utricle by endosmose of water, imtil at length it becomes the vnde envelope of the mo^dng form described above. From this it follows that the latter forms do indeed possess on the whole the character of simple cells, but display some peculiarities in theii' stractm^e and develop- ment, since the internal coloured globule corresponds originally to the pri- mordial utricle of other vegetable cells, yet is not surroimded by a membrane, as usual, but suspended free in it like a ceU-nucleus, while watery, unazotized contents appear between the membrane and the primordial utricle. For this reason I have called the enclosed coloured globule, which is formed first, and originally moves about without a special membrane in the manner of a cell, and corresponds to the primordial utricle of vegetable cells in general, the j^rimordial cell, and the enclosing membrane "^ith its watery contents the envelope-cell. The moving Chlamiidococcus-QOTidiitioii is capable of propagating as such, by the enclosed primordial cell dividing anew, the individual portions slipping out of their envelope-ceU and running through the cycle of develop- ment of their parent-cells. In passing into the state of rest, the enclosed primordial cell secretes over its surface, inside its. envelope, like every pri- mordial utricle, a new tough cellulose membrane, and through this metamor- phosis assumes the form of an ordinary Protococcus-cell, while the envelope- ceU is dissolved. ^ But only such primordial cells behave in this way as are produced by the division of a Chlannjclococcus-glohule in a lower power of two : the primordial cells originating from a 16-64-fold division move far more actively and do not secrete an envelope-cell ; they are incapable of any propagation, and pass immediately into the condition of rest. Alex. Braun has called these forms of Chlami/clococcus, which develope an envclo23e-cell, macrof/onidia, and distinguished the smaller ones originating from multifold di\asion, as microgonkUa.^' The division of the spore- or red resting- cells of ChJamydococcus into two, and then into foui' segments, each producing a new generation of resting- cells, has of late been questioned by Cohn and Wichura ; but Mr. Ciu'rey believes he can confirm this occurrence, since he has " distinctly observed the process of self- division in some red resting- cells, which were probably those of Cldamydococcus. I say," he writes, ^^ prohahly, because the red resting-cells of Cldamydococcus are quite undistinguishable from those of another of the Volvocinece, viz. SteplianospTia?ra pluvialis, so that without following out the development it is impossible to predicate whether such red cells belong to one or the other." (J. M. S. 1858, p. 209.) A further refer- ence to this topic will be found in the account of Stephanosph(xra. On reviewing his history of Cldamydococcus (Protococcus) pluvicdis, Cohn attributes to this plant an ' alternation of generations,' and points out the periodicity observed in the appearance in a collection of water of the several phases, the one replacing the other {On Protococcus, R. S. 1853, pp. 549, 550). Subsequently he details the number of very various and changing forms of develojmient it passes through, '^ which have been either erroneously arranged as distinct genera or at least as remaining stationary in those genera, although in fact only transitional stages " (p. 559). " Thus," he continues, " the ' stiU ' Protococcus-ee]l (XIX. 20) corresponds to the common Protococcus coccoma (Kg.) ; when the border becomes gelatinous it resembles P. pidcJier, and the small cells P. minor. The encysted motile zoospores are the genus Gyges granulum among the Infusoria, resembling also on the other side P. turgidus (Kg.), and perhaps P. versatUis (Braun). The zoospores divided into two must be regarded as a form of Gi/ges hipartitus, or of P. dimidiatus. In the quadri- OP THE PHYTOZOA. 151 partite zoospores with the secondary cells arranged in one plane, vre have a Gonium. That with eight segments corresponds to Pandorina Monim, and that with sixteen to Botnjocijstis Volvox. When the zoospore is divided into thirty- two segments, it is a Uvella or Sijncrypta (XIX. 27). When this form enters the ' still ' stage, it may be regarded as a form analogous to Microhcdoa protogenita ; this Algal genus is probably, speaking generally, only the product of the ?7i'e??« -division in the Eughnce or other green forms. The naked zoospores (XIX. 28), finally, would represent the form of a Monad or of an Astasia (XIX. 29) ; the caudate variety approaches that of a BodoJ' Perty has devoted several pages to recount his own obsei-vations and ex- periments on the genus CJdamydococcus, or, as he prefers to call it, Hysgi- num. He institutes two species, which he states to be equivalent to Proto- coceus ]yluvialis and P. nivalis of other authors, and insists on their specific distinctness. Probably, he adds, other varieties of Protococcus coloiu'ed red are also referable to this genus, at least such of them as present an animal phase of existence. To his mind, the vital phenomena of such organisms are best explicable on the supposition of an animal nature ; for, says he, cells which move altogether like Infusoria, and exhibit sensation in their yoimg conchtion, so long as they j)resent such phenomena, are not vegetable cells. Moreover, he thinks it established concerning the Phytozoa in general, that in certain stages of their life they sometimes belong to one, and in others to another kingdom of nature, or are so nearly allied to both that a separation is impossible. After the space akeady devoted to the structure of Chlamydomonas and Chlamydococcus, an abstract of Perty's long contribution on the subject can- not be introduced ; and indeed, apart from his diiferent interpretation of their vital phenomena, little could be produced not included in Cohn's com- plete examination. There is, however, a paragraph in Mr. Carter's just published valuable contribution on Eudoyina, referring to Chlamydococcus, which must not be omitted. He writes {A. N. H. 1858, ii. 244) : " Chlamy- dococcus undergoes the same kind of changes in development as Eudorina, from which it only differs in structiu-e in being smaller and globular instead of ovoid, in the absence of an external envelope, and in the ciha of the daughter- cells being included within the parent-cell ; hence it also difi'ers in being motionless, though the compartments of the daughter- cells are suffi- ciently large for them to tiu-n round and move their cilia freely therein, which they are continually doing. The primary cell of Chlamydococcus, like that of Eudorina, divides up into two, four, eight, or sixteen cells, and those of the eight- and sixteen-di\-isions again into groups of sixteen or thirty-two each, so as to resemble the thii^d stage of Eudorhia. Hence we may perhaps infer that its fecundating process is similar to that of Eudorina ; but this remains to be discovered. Chlamydococcus has also a great tendency to stop at the two- and four-division, from which it may pass into the ' stilL ' or Protococcus-f orm., and, floating on the water in a kind of crust, present ceUs of all kinds of sizes undergoing ' still' division. "In aU its multiplications, partial and entire, however, it generally maintains its primary or spherical foiTu, and does not become ovoid or oblong like the groups of Eudorina, — the only exceptions being in the two- and four-division, where the green cells are sometimes ovate (probably from want of room in the parent capsule), as represented by Ehrenberg in C. Pulvisculus, to which I should refer it, had he not also given an ovate form to the type-cell of this species : nor can I refer it to C. pluvialis ; for in all the changes I have yet seen it undergo, the red colour has not increased beyond the minute eye-spot, while this also dis- 152 ge:neeal history of the ineusokia. appears, and the cilia too, when this species passes into the ' still ' form. Here it undergoes the same kind of division that it does in the active state ; but the parent-cell, instead of becoming distended by imbibition, remains closely attached to the daughter- cells, so as to give the group a mulberry shape. How long it remains in the ' still ' form I am ignorant ; but having only seen it in the active state during the months of May, June, and August, and throughout the rest of the year in the ' still ' one, I am in- clined to think that it only comes into the active state during the summer months, and then for the purpose of fecimdation. " In several instances, also, where I have found this Chlamydococcus with Eudorina, they have been accompanied by long Closteriform cells. It was the case in that above mentioned, where the latter was imdergoing impreg- nation. Some of these have an eye-spot, which, with the natui'e, arrange- ment, and general aspect of theii* internal contents, shows that they belong to the class of organisms with which they are associated. Theii' cell-wall also is more or less plastic, or was so when they were assuming this spicular form ; for many have one or more diverticula extending from them, some are bifid, and a few irregularly stellate. AMiat they are, I know not ; but Dr. Cohn has figured the same kind of cells, in company with Splicei-o_pha annu- lina, under impregnation." Mr. Currey {op. cit. p. 216) has noticed and figured what he conceives to be a generative variety of Chlamydococcus (XX. 24). " This," he says, " I take to be a state of Chlamydococcus. The outer membrane was colourless, and the two internal globular cells of a clear, bright ruby crimson. The pecu- liarity of the plant consisted in the fact of the cell being filled with minute staff"- like subcylindrical bodies in active motion, precisely similar to the spermatozoa of Vaucheria. I watched these bodies at inten^als for about twenty-four hours ; and the motion was incessant. At the end of that time the cell slipped amongst some other AlgsG on the same shde and was lost. Whether these little active organisms wxre reaUy spermatozoa, or whether they belonged to the mysterious bodies w^hich, in some way or another, are supposed to find their Avay from without into the cells of Algae, it is im- possible to say." The next figm-e (XX. 25) is also copied from Mr. Currey, and, as he re- marks, evidently " represents the final stage of some Yolvocineceva. which the gonidia have become encysted." We allude to it here, although it does not belong to Chlamydococcus. Mr. Currey observes further, " I notice it be- cause the encysted cells were of a pale yeUowish-brown colour, and covered with minute pits or depressions, and were altogether different from those of any other Alga with which I am acquainted. In Pandorina and Stephano- Sjphcera the resting- spores are red, in Volvox bright orange; and in neither case are there any such marldngs as those in the membrane of the cells showTi in the figure referred to." GoNiUM (XIX. 32-37). — This genus received considerable attention from MuUer and Ehrenberg. The latter described it as composed of sixteen Monads, resembling Chlamydomonas in all points except in the absence of an ej^e-speck, collected together in a quadrangular tablet, with fi'om three to six intercommimicating tubes or cords. Each Monad was said to be enclosed in a hyaline lorica, called here a mantle (lacenia), which it could at times quit ; also to have two filaments (proboscides) extended from the mouth, re- presented by a clear spot at their base ; several clear stomach- sacs, a con- tractile vesicle, two round sexual glands, and numerous green ova. Detached individuals, he added, swam like Monads, in the direction of the longitu- dinal axis of their bodies, with tlic mouth in advance ; but when in tablet- OF THE PHYTOZOA. 153 like colonies sometimes moved horizontally, at others vertically, or rolled on their edges like wheels by the aid of the pair of vibratile filaments of each member projecting fi-om the siuface. The animal organization here represented is now-a-days generally ignored, and Goaium takes up its position among plants. Prof. Cohn (to whom we are so much indebted for oiu' knowledge both of Protozoa and Protophyta) has contributed a valuable paper (Entw. d. mihr. Algen u. PUze) on this in- teresting being, of which we shall present an abstract. The entii'e organism is invested by a colourless transparent muco-gela- tinous envelope without any cellulose limit-membrane, whence it is that this common envelope has frequently passed imobsen'ed unless some colouiing matter, such as Indian ink, has been added to the water. The figiu'e varies according as the plant is viewed from above (on its polar aspect) or from its side (on its equatorial aspect), being in the former point of view a quadiilateral tablet with tnmcated angles and rounded cor- nel's (XIX. 32), and in the latter a flattened spheroid. The simple or primordial cells (XIX. 33) enclosed in this mucous sheath are sixteen in number, disposed in a imiform manner, so that fom- cells, leaving a square interval in the centre, are bounded externally by twelve others, three of which form one of the four sides of the organism (XIX. 32). The central ceU of the three is, moreover, not in a line with the other two on the same side, but set nearer to the centre ; hence each side of the tablet is hollowed out in the middle. Closer research also shows that each of the cells is not spherical, but polygonal, the four internal being six-sided (hex- agonal), the twelve peripheral five-sided (pentagonal) ; the consequence is, angular intercellular spaces are left, the central of aU being quacbangular, and all the rest triangular. This arrangement of the primordial cells is normally so regular, that Cohn represents it by a geometrical chagram ; still, in aU tablets of Gonium this is not the case, and particularly in very young specimens. The regular polygonal contoiu^ of the cells indicates that they are not mere masses of soft variable protoplasm, hke those of Stephanospliha^ra-g\obo still rolls through the water according to the known laws, even when most of its primordial cells have abeady become more or less com- pletely divided into four or eight secondary cells. Only shortly before the completion of the division do the cilia of the parent- cell lose their motion and disappear, it may be by being retracted or by being thrown off"; but the OF THE PHYTOZOA. 173 orifices through which the cilia previously passed out into the water may now be observed in the common envelope-cell, as minute points surrounded by a thickened border. " Immediately, after that, it is seen that the newly-formed secondary cells have developed their ovvn cilia; for the yoimg generations formed in the interior of the parent- envelope now begin to move and to roll over like a wheel, so far as the confined space allows of this. In consequence of this movement of the eight small wheels rotating in the interior of the common envelope- cell, which constitutes a very pretty object, the parent-cell soon becomes enlarged and attenuated at certain points ; the cellulose of which it is composed appears to be transformed into soluble jeUy, and soon afterwards one after the other breaks through out of the common envelope and revolves fi'eely and independently in the water, according to the same laws as the old spheres, but more actively and energetically. The young Sfej)hanoSjphcera exactly resembles a green wi-eath composed of eight small cylinders, upon which by itself no envelope and cilia can be detected (XIX. 42, 48, 49) ; but if killed with iodine, the eight primordial cells are seen to be siuTounded by a common envelope-cell in the form of an exceedingly delicate membrane, — only this lies in all parts almost immediately upon the green globes, so that it follows the waved outline they produce, and in its total form resembles a flat spheroid mth eight notches on its border ; it is perforated by the cHia, which go off in pairs from each of the primordial cells ; and two chlorophyll-utricles are already distinguishable in the latter. By degrees the envelope-cell is hfted up by the endosmotic absorption of water ; its surface becomes smoothed out, and it appears cii'cular in the polar view ; on the other hand, it retains for a longer time the form of an almost tabular spheroid, and hence presents an ellipse in the equatorial view (XIX. 58) ; finally it expands uniformly in aU directions and thus acquii-es its normal spherical form, while at the same time it becomes considerably thickened. This whole process of propagation is completed duilng the night ; and on bright days Stephanosphcercn are rarely seen in coiu^se of division at sunrise ; on dull days they may be observed in this condition in the first part of the morning. " The primordial cells, however, not unfrequently come to a standstill in the stage of division of the second generation, so that they only separate into four secondary cells ; these at once develope clLia and an envelope-cell, with- out dividing a third time, and make their exit from the parent-envelope in this condition. Here therefore only the first generation of each primordial cell is a transitional generation, the second already a permanent generation. Hence arises the circumstance that we often find, among other eightfold Ste- phanosphcera-glohes, some in which the envelope-cell encloses only four pri- mordial cells standing at equal distances, which in other respects behave in the ordinary manner. "It is still more frequently observed, when the primordial cells have already become constricted into four secondary cells and are beginning to divide again iuto eight, that this j)rocess of division is not perfectly completed in aU foui' portions, but that the young Stephanosphcera abeady becomes free and developes the envelope-cell, although one or other of the four quadratic segments of the sphere has become constricted but not parted off. Hence origi- nate monstrous forms, since the general envelope-cell then encloses only seven primordial cells ; but in these cases it is always observed that one of them is distinguished by most curious prolongations or mucous filaments, that it appears twice as large as the rest, that it contains four chlorophyll-utricles instead of two as is usual, and that it is also more or less constricted in the middle. AU this furnishes proof that here one secondary cell of the second 174 GENERAL HISTOEY OF TKE I]!^FUSORIA. generation has not been divided the third time like the rest, but occupies by itself the space which is ordinarily filled by two. Very often only six, or even no more than five primordial cells are found in one envelope-cell ; but then two or three of these are twice as large as elsewhere. In like manner Alex. Braun figures a Pediastrum composed of fifteen instead of sixteen cells, wherein one, hoAvever, is twice as large as the rest. "- On the whole, it is ob\ious that the mode of propagation o{ StejyJianosjyhcera already examined corresponds completely to that we are akeady acquainted with as formation of macroc/onidia in Chlamydococcus. It both cases it de- pends upon the envelope-cell remaining unaltered, while the primordial cells become divided, first into two secondary cells, and then so on in a lower power of two, each of the secondary cells immediately developing two cilia, and secreting over its whole surface, as do all primordial utricles of vegetable cells, a delicate cellulose membrane, which, however, becomes gradually re- moved further from the secreting primordial cell through absorption of water. The only distinction between Chlamydococcus and Steplianosphcera arises from the formation of a special envelope-cell to each individual secondary cell in Chlamydococcus, while in Stephanos2yhcera all the generations produced by division form one primordial cell, become enclosed by a common envelope, and move away as famUies of cells. On the contrary, the developmental history of Gonium, Pandorina, and Volvox agrees in all essential particulars with the laws of propagation which I have just described in Steiyhanosphcera, as will be shown elsewhere. We may call the mode of multiplication of the Volvocinece by the general name oi propagation hy macrogonidia. " Another process is met with in Stephanosphcera, besides the above, and which I have observed more rarely, viz. propagation hy microgonidia. In this mode of multiplication the introductory processes are exactly like those of the formation of macrogonidia ; in particular each primordial cell is at first divided into two, then into foui% and lastly into eight secondary cells. But instead of this third generation being permanent and becoming free, as is usual, it not unfrequently happens that the process of division is not arrested with the separation into eight — that the original primordial cell becomes parted off a fourth, fifth, and even a sixth time, in the same manner, and at length is broken up into a large number of cells (16, 32, 64), which naturally are so much the smaller the greater nimiber of times the subdivision into two has taken place (XIX. 43, 51). These little secondary cells finally become totally separated from one another, Tvithout secreting an envelope-cell. These little cellules — 1 shall follow the example of Alex. Braun and call them microgonidia — exhibit a very active and energetic motion inside the envelojDe- ceU, huiTj-ing very rapidly up and down in all directions in its cavity, pro- ducing by their great number that ciu'ious swarming which Alex. Braun has very aptly compared with the interminghng of a crowd of people in a confined area, where every one is constantly changing his place, while the whole together constantly occupy the same space. Sometimes the cellules are scattered in a few large masses ; then they unite again into a knot in the middle ; every moment the general aspect varies. At length the common envelope is ruptured where the microgonidia emerge one after another or in large masses, but free and singly, into the water. Their true form may be then readily detected by killing them with iodine ; they are spindle-shaped and acuminated at both ends, bright green in the middle, and run out into a colourless beak at each end, on the whole not imlike young Eugleyice, without a trace of an envelope-cell ; the extremity which goes first in their swimming bears delicate ciha ; the number of the cilia is four (XIX. 52). "WTien the microgonidia reach the water they move most actively in all directions, and OF THE PHYTOZOA. 175 in a short time all the corpuscles emitted from an envelope-cell are scattered and disappear in the wide surface of the drop of water. ''I have not been able to make out what becomes of the microgonidia subsequently, since they are ordinarily decomposed on the object-holder after a brief swarming ; but it may be conjectiu^ed that they also serve for propa- gation, and probably pass into a condition of rest. At least the latter has been observed in the microgonidia of Chlamydococcus pluvialis by Alex. Braun and myself: the history of the development of the latter agrees wholly with those of the Stephano splicer a ; they originate also by the di\'ision of the pri- mordial cell in a higher power, are distinguished by their minute size and more active, peculiarly Infusorioid movement, and never develope an envelope- ceU duiing their movement. The microgonidia of both therefore are true primordial cells ; that is, primordial utricles resembling cells, organized ex- clusively of coloured protoplasm, without any cellular membrane. The only distinction between them is, that the microgonidia of Chlamydococcus, like their macrogonidia, possess two cHia, while in those of StephanospJicera I observed four. That the microgonidia of Stephanosphcera correspond per- fectly in moi'phological respects to the macrogonidia, and only depend upon a higher power of division, is proved by a case in which seven out of the eight primordial cells in one envelope-cell were broken up into microgonidia, while one divided merely into eiglit secondary cells ; the latter were developed as macrogonidia, and formed a connected wreath suiTounded by an envelope-cell, which rolled slowly about in the parent- envelope, suzTOunded by the swarm of fi'ee, rapidly moving microgonidia. " Abstracting the differences which may be shown always between two genera, we detect the same law of development in Hydrodictyon as m Stepha- nosphcera, — viz. the bicHiated less numerous macrogonidia arrange them- selves into a family of cells abeady "within the parent-cell, according to the character of the given conditions of the two genera, the cell-family being active in the Volvocineoe and immoveable in the Protococcacece, while the more numerous more actively moving microgonidia with foui' cHia leave the parent-cell and enter upon a metamorphosis, the retrogradation from which to the normal type of the genus has not been observed yet here, or indeed in the microgonidia of any of the Algae. Such an mideniable agreement of the law of development of Stephanosphct^ra with an undoubted plant like Hydro- dictyon, which testifies to a near relationship, would be inconceivable if the former were to be regarded as of essentially different organization — as belong- ing to quite another kingdom of nature. Thus the developmental history of Stephanosphcera also fiu'nishcs the most convincing proof of the vegetable nature of this genus, and consequently of the Volvocineoe generally. " That the formation of macro- and microgonidia does not exhaust the whole series of forms which Steplianosphcera may pass through, is proved by the following observation, which unfortunately I have not yet been able to complete. Having cultivated some Stephanospliaerce for a long time in a little glass cup, in the way described in my essay on Loxodes bursaria (7. c), all the primordial cells at length exhibited dark, thick, greenish brown contents, so densely filled with numerous granules that the two chlorophyll-vesicles could no longer be detected ; their form was more or less globular, and the mucous radiating processes were entirely absent ; their outlines were remark- ably sharply defined, as if they had become suiTounded by a rigid membrane. At the same time I remarked that the primordial cells were no longer fixed immoveably at the periphery of the envelope cell, never changing their relative positions, but jerked backwards and forwards, finally tore themselves away from the envelope -cell, and then began to rotate slowly and lazily in the interior. 176 GENERAL HISTORY OP THE INFIISOEIA. Soon after, I saw the envelope-cell also burst at some spot and collapse ; and the eight primordial cells gradually emerged, one after another, as inde- pendent globes : they were now seen to be enclosed in a pretty closely applied envelope, through which penetrated two cilia ; and hence they presented the utmost resemblance to Chlcnnydomonas Pidviscidus. They moved about for some time in the water and at length came to rest, losing their cilia and accu- midating like Utile green Protococcus-glohides at the bottom of the glass. We therefore have here a motionless, perfectly plant-like stage of Stephanosphcera , such as we are acquainted -^ith in Chlamydococcus and Chlamydomonas ; the remainder of the Volvocinece undoubtedly pass into a similar condition of rest, which is the means of their preservation when the Avater of ditches is diied up in summer. The emergence of single globes from the common enve- lope, in a form resembling Chlamydomonas, may also be readily observed in Goniimi. '' I conjecture that the motionless Protococcoid ceUs of Stephanospho'.ra are the means of the presei^ation of the species when the water, as is always the case in the shallow hollows in stones, their natural station, is diied up for a long time and all the living inhabitants are precipitated on the stone. The observations of Major von Flotow have already demonstrated that the dried-up muddy sediment always reproduces StephanosphcBrcE when water is again poured on to it. This capahility of reviving from the dried condition is shared hj Stephanospha^ra Avith Chlamydococcus pliivialis,Yn. which likewise the motionless cells remain living after being diied up for years, and are capa- ble of giving birth to moving forms, while the swarming- cells themselves are destroyed for ever by rapid desiccation. Herr von Flotow has sent earth with dried htephanospha'rce to Dr. Rabenhorst in Dresden, who, in like manner, succeeded in reviving them by moistening. " Since the moving Stephanosj^hcera? are destroyed, just like the swarming- cells of Chlamydococcus, by rapid desiccation, I believe that the motionless Protococcoid globes, the development of which I have just described, are the fonns which do not lose their vitality by diying, but are capable, when wetted again with water, of going through a cycle of development, by which they return to the normal mo\T.ng form of Step>hanosphcera, Yet I must remark that I have not hitherto obtained sufficient material to observe the resting Stephanosphcera, and to trace the processes which occm^ in the revivification. *' Respecting their vital manifestations, repeated experiments showed that the moving spheres of Stephanosphaera seeh the darlcer part of the vessel, avoid- ing however a total absence of light, and assembling in preference in a moderated light or half-shadoiv. Since other Algse and Infusoria exhibit a different beha\doui' towards the light, we thus possess a means of sorting, to a cer- tain extent, the microscopic inhabitants of a specimen of water, as I did the shade-loving Stephanosphcerce from Chlamydococcus, which ordinarily seek the brightest light." An important appendix to this histoiy of Stephanosphcera has quite recently appeared from the joint labours of Professor Cohn and Wichura {Nov. Act. Acad. Curios. Natures, 1857, Part I.), and has been translated into English by Mr. Currey {J.M.S. 1858, p. 131). The resting- stage above spoken of is again referred to concisely and clearly in this paragraph : — " Under ceriain circumstances each of the eight cells secretes a cellular covering, and swims about in the interior of the globe in the form of free Chi amijdomonas -like cells (XIX. 44) ; eventually they escape, either by fissm'e of the globe, or by its gradual dissolution, lose their cilia, form a thicker membrane, become motionless, and accumulate at the bottom of the vessel. If the vessel be then permitted to become thoroughly diy, and OF THE PHYTOZOA. afterwards be again filled with water, motile Stej>hanos^hcerce reappear, from which it seems probable that the green globes are the resting-spores of the plant." These, it may be added, are with difficulty, if at all, distinguishable from those of Chlamydococcus pluviaVis : they vary very much in size, and apparently grow after entering on the state of rest. Their coloiu' is deep green (occasionally yellowish or ohve) ; and they have a nucleus, and fre- quently a nucleolus. We cannot do better than copy Mr. Currey's abridged translation, in endeavouiing to convey the results arrived at by Cohn and Wichura : — '' When the water is permitted to evaporate graxlually, the resting- cells become yellow, and afterwards orange or red, and their contents have a more oily appearance. The authors found that if the water was not permitted to evaporate, the resting-spores, although continuing to live, did not become developed into Steijlianosphcerce ; but when fresh water was poiu-ed upon de- siccated resting-spores, twenty-four hours sufficed for the production of motile Steplia nosjyhcf^i'ce. ''The following is the process of transformation from the state of rest into 'the motile form. " The dried resting-spores take up the water, and their contents (hitherto somewhat misshapen) gradually fill up the cavity of the containing mem- brane, and become cloudy and granular ; the border becomes yellowish, and the red coloimng matter is concentrated in the centre. The cells then begin to divide ; and the successive forms assumed in this process will be better imderstood by reference to XIX. 44-47, than by description. In pass- ing from the state shown in fig. 45 to that shown in fig. 46, the outer mem- brane has gradually become invisible. Up to fig. 47 the process has occupied about two hoiu-s. The four daughter-ceUs (fig. 47) begin to quiver, and to endeavour to separate from one another. Two cilia are now perceptible at the pointed extremity of each of the four ceUs, by the action of which the group begins to move as a whole, and in a laboui'ed manner, in the water ; ultimately, however, all trace of the enveloping membrane and of the gluti- nous connecting substance disappears, and one by one the daughter- ceUs escape and become free. Pigs. 48 and 49 exhibit different forms of these free daughter-cells, which contain two, three, or several granules (amylon ?) and sometimes also vacuoles. The sharp end is often prolonged into a coloui^- less beak. At this period there is no proper cellulose membrane. At the moment of escaping, their diameter never exceeds O'OIO mm. ; but they soon enlarge and attain a diameter of 0-013 to 0-015 mm. " Their form and the length of the beak are variable, the latter being some- times altogether wanting. In form and motion they resemble exactly the naked primordial-cells, which are produced by division from the resting-cells of Chlamydococcus lyiuvicdis. The authors have never seen the resting-cells of SteplianospJiceroi di\ide into more than four parts, but think it not improbable that division into a greater number (eight or possibly sixteen) sometimes OCCUl'S. '' The length of time which elapsed between the immersion of the diied resting-spores and the fii^st appearance of the motile ceUs varied from nine to twenty-four houi^s. It was noticed that those resting-spores which did not produce zoospores within six days never did so afterwards, although they continued to live and were perfectly healthy. '' Zoospores, produced in the month of November, did not advance beyond the fii'st stage (fig. 49). Others, however, produced in March, remained only a few houi\s in that condition, after which time a delicate membrane was formed round the body of the piimordial cell (XIX. 50 ); this membrane was 178 GENERAL HISTORY OF THE INFUSORIA. at first closely attached to the primordial-cell, but became gradually enlarged by absorption of water into a colouiiess enveloping vesicle (figs. 50, 54), usually globular but sometimes oval, having two openings, thi'ough which the ciha penetrate. In this condition they attain a diameter of 0-017-0-022'", and are not distinguishable from encysted forms of Chlamydococcus plu- vialis. Other zoospores, produced on the 1st of April, 1857, attained a larger size ; and the protoplasm of the primordial cell, instead of retaining its con- tinuous outline, became elongated here and there into simple or forked muci- laginous rays, which were either colourless or green from the presence of chlorophyll (fig. 53). These rays are probably produced by the protoplasm adhering at certain points to the surrounding membrane, and being carried outwards by its growth. The Chlamydococcus-]ike form only lasted a few hours : towards the even- ing the zoospores mostly began to divide. In the first place, the protoplasmic rays are di^awn in, and the primordial cell becomes roimd ; it then elongates itself in the direction of an axis passing through the point of origin of the ciha, and by the process of division assumes the forms shown in figs. 54 and 55. This state is usually attained by about nine o'clock in the evening ; and about eleven o'clock a constriction commences in a plane at right angles to the former plane of division ; and eventually the primordial cell is divided into quadi\ints, each containing a nucleus and a portion of the red substance. The two cilia, which have retained their activity, originate in the interspace be- tween two quadi^ants. About midnight usually, but sometimes earlier, con- striction recommences, and the form in fig. 56 is attained. This constriction proceeds towards the middle point of the spheroid, by which the quadrants are bisected, and ultimately divided into eight wedge-shaped portions, whose con- tour-hnes, like the spokes of a wheel, meet in the middle. " And now commences a further process of development, which forms the ground of the generic distinction between Stephanosplicera and Chlamydo- coccus. For, whilst in Chlamydococcus the indi\4dual portions of a piimor- dial cell separate entirely from one another, each developing its own enveloping membrane, and ultimately escaping as a unicellular individual, in Stephano- sphceyxt, on the other hand, the eight portions remain united as a family. The coloured contents of the individual portions become drawn back towards the periphery in a centrifugal direction, a colourless plasma remaining about the central point ; this disappears at first in the centre ; a cavity is formed in the middle of the disk ; and as this enlarges, the eight portions assume the foim of a wreath, consisting of eight globular or ellipsoidal bodies in close contact (fig. 57), and usually not exactly in one plane, owing to the outer membrane not having expanded in proportion to the enlargement of the plasma. The original cilia continue active, causing the motion of the whole organism, until the eight portions are completely individualized ; and then their motion ceases : but at this period each of the eight parts may be seen to be provided with two ciha, which are in motion so far as their limited space allows. The separate parts of the plasma now form eight independent but closely- packed membraneless primordial ceUs. Shortly afterwards it is seen that a delicate membrane, common to them all, has been secreted beneath the mo- ther-cell membrane, round the disk formed by the primordial cells ; this membrane at first lies in close contact with the latter cells, foUovving the constrictions of the disk, but afterwards becomes further and further re- moved as it swells and tends to assume a globidar form (fig. 58), By the motion of the cilia the mother- cell membrane is gradually thrown ofif, and the young family escapes into the water. Its eight green primordial cells still enclose the last traces of the red substance, which gradually disappears, and OF THE PHYTOZOA. 179 instead of which are seen two granules; the primordial ceUs are in im- mediate contact at the sides, and are of an oval or globular shape ; their common enyeloping membrane is at first constricted at the border following the outHne of the primordial cells ; it eventually becomes globular, although continiung for a long time much flattened at the poles, in the form of a disk- shaped spheroid. When the Chlamydococcus-like unicellular Sfej^hanosjyJicera has commenced its division early in the evening, the di\'ision into eight is perfected during the night, and early in the morning the young family quits its cast-off mother-cell membrane. " In the course of the day the individual primordial cells, and their common enveloping membrane, grow until the latter attains a diameter of 0-040- 0-048'". Dming this growth the shape of the primordial cells is changed by the formation of various prolongations in the manner above described : but in the coiu'se of the afternoon the primorchal cells again become round ; and during the evening, division commences in them precisely similar to the process in the imicellular Stephanosphceixi : on the follo^dng morning we find eight young families, with the common enveloping membrane, which soon escape and go through the same process. It is calculated that in eight days, imder favoiu^able circumstances, 16,777,216 families may be formed from one resting-ceU of StepTianospli(xra. It is remarkable that the division of the primordial ceUs in Steplianospluera is confined to a certain time of day : it begins towards evening, and is completed the following morning. In the observations made in Laj)land, at a time when the daylight there lasted diuing the whole night, the beginning and end of the division were observed to take place at almost the same hours as in the observations made at Breslau m the spring, when the day and night were almost of equal length. Sometimes the division ceases after the formation of only four primordial cells. On one occasion the authors observed a family with only three cells, one only of the two halves first formed having undergone a second division. In Lap- land a family with sixteen cells was once observed. '' The authors then proceed to discuss the natiu-e of the resting-cells in Stephanosjjhcera and CliJamydococcus, and come to the conclusion that they are not spores ; i. e. that they are not of the same nature as the red cells of (Edogonium, BulhocJicete, Draparnaldia, CJicetopJiora , Sphceroplea , Volvocc, &c. " They come to this conclusion upon two grounds : 1st, that the resting- ceUs in question continue to grow after becoming quiescent ; and secondly, that it is probable (although not yet proved) that the resting-ceUs increase by self-division, thus producing new generations of resting- cells. These two characteristics the authors consider inconsistent with the idea of a spore. '' In conclusion, the authors notice the formation of microgonidia in Steplia- nosplicera, which takes place by the division of the primordial cells into num- berless small portions. Fig. 5 shows a Stephanosphcera, in which seven of the eight primordial cells have formed microgonidia ; the individual microgonidia (fig. 52 a, h, c) become free by the disintegration of these eight groups into their constituent portions. The authors think it not improbable that the microgonidia exercise an impregnative influence in spore -formation, but admit that there is no evidence to prove it." Mr. Currey (J. M. S. 1858, p. 209) reopens the question concerning the natui^e of the red resting-cells of StephanospJicera, and argues against the conclusion drawn by Cohn and Wichura. He says those observers have noticed '' that these cells in Step}ianosp}ission of various primordial cells ; hence, as a rule, a brood of young globes is to be seen revolving ^^ithin the parent sphere (XX. 33), from which ere long it is released by its rupture. The condition of the individual cells of a young Volvox has akeady been mentioned, — viz. their close apposition at first, their gradual separation by an interval, the appearance of radiating processes from the protoplasm, and their progressive attenuation. To this account we may add that contiguous inter- current processes, in their earher stages, appear to coalesce, — a circumstance which indicates that the protoplasm is then unenclosed by a pellicle or envelope. Again, the protoplasm gradually contracts itself into its flask-shape, the retrac- tion and coalescence of its processes being a simultaneous phenomenon ; indeed contraction of the protoplasmic globules advances continuously until, as in old specimens, only a small rounded mass appears in the centre of a large clear space. Lastly, the coloured stigma is an after- production ; and its advent would seem to indicate the maturity of the cell. Analogy with other Volvocinece would lead us to look for a quiescent or ^' still " stage of the cells of Volvo.v, and the formation of microgonidia, in addition to the process described, viz. multiplication by self-division with the production of macrogonidia. That a '' still " form actually occurs is pretty clearly shown by Mr. Busk's observations of Volvox aureus, from which this presumed species appears to be nothing more than Volvox glo- hator, having a vaiying number of its cells encysted to form the winter or '■resting" spores. The primordial cells which are to undergo this change are at first indistinguishable fi^om the ordinary ones, except in having a deeper green colour {Bv£c, op. cit. p. 38). Afterwards, however, they ac- quii^e a thick wall, change to a yellow colour (hence the appellation aureus, golden or yellow), without material alteration of size, and produce a second equally fiim and distinct envelope ; or rather, it may be, the original cells contract somewhat, and then form a second coat around themselves. Even- tually a considerable space exists between these two coats, occupied by a clear and apparently aqueous fluid ; but upon the addition of a solution of iodine, a granular cloudiness is produced in it. The contents of the inner cell consist chiefly of amylaceous grains, mixed with a greenish material in the one case, and with a bright yellow, apparently oily fluid in the other. The amylaceous particles are of an irregular botryoidal form, and far from uniform in size. Mr. Currey, in a recent interesting communication on fresh-water AlgSB (J. M. S. 1858, p. 208), states that he has seen " one of the large, orange- coloured spores of the so-called V. aureus, which is only the resting form of F. glohator, where the contents divided into five globular colourless cells, which floated in a mass of reddish plasma, being apparently the remains of so much of the original contents of the cell as had not been absorbed in the formation of the secondary cells." Of the Volvox steUatus, Mr. Busk adds that it seems to him merely a modi- fication of V. aureus, and appears to follow the same course of change, and doubtless of future development. With these conclusions Prof. Williamson coincides, and remarks (oj). cit. p. 56) that " the ordinary power of gemma- tion in V. steUatus appears to have worn itself out, since, though the gemmae often exist with the spores (?), they are small, coloiuiess, and abortive." It must also be mentioned that Perty suggests an analogous interpretation of the nature of Volvox aureus, and doubts hkewise the specific importance of V. SteUatus. 8ince the above remarks were penned, Cohn's researches on Volvox glohator 184 GENEEAL HISTOHY OF THE liS^FUSORIA. have determined the reality of another mode of reproduction besides fission, as surmised (Ann. Sc. Nat. and Comptes Rendus, 1856). The abstract of this most interesting paper is translated in the J. M. S. 1857, p. 149 : — " The second mode of reproduction of Volvox requii'es a sexual conjunction, and is not observed indifferently in all indi^dduals. The sj)herules endowed with the sexual fimction are distinguished by their volimie and the more consi- derable number of their component utiicles : they are generally monoecious ; that is to say, they enclose at the same time male and female cells, although the majority of their contents are neuter. The female cells soon exceed their neighboui's in size, assume a deeper green colom-, and become elongated like a matrass towards the centre of the Volvox. The endochrome of these ceUs does not undergo fission. In other cells, on the contrary, which acquire the size and form of the female ceUs, the green plasma may be seen to divide symmetrically into an infinity of very minute particles, or linear corpuscles, associated into discoid bundles. These are fiu'iiished with ^ibratile cilia, and oscillate at fii^st slowly in their prism ; but the movement soon becomes more active, and the bundles speedily break up into theu^ constituent elements. The fi'ee corpuscles are very agile, and it is impossible to regard them as any- thing but true spermatozoids ; they arc linear and thickened at the posterior extremity ; two long ciha are placed behind theii^ middle, and the rostrum, which is curved like the neck of a swan, possesses sufficient contractility to execute the most varied movements. These spermatozoids, so soon as they are they are able to disperse themselves in the cavity of the Volvox, quickly crowd aroimd the female cells, into which they eventually penetrate ; arrived there, they attach themselves by the beak to the plastic globule, destined in each ceU to form a spore, and with which they are gradually incoi-porated. Fecundation having been thus effected, the reproductive globule becomes enve- loped successively by an integument exhibiting conical pointed eminences, and by an interior smooth membrane ; the chlorophyll which it contained is now replaced by starch grains, and a red or orange-coloiu-ed oil. This is the con- dition of the spore at matmity ; and occasionally forty of these bodies may be counted in a single globe of Volvox. The germination of these reproductive bodies has not yet been observed, so that their history cannot be regarded as complete ; but from analogy it may in the meanwhile be assumed that they germinate in the same way as do the spores of (Edogonmm, Splueroplea, and other Algae belonging to the same order. It may be maintained, moreover, as certain that the Splicerosira volvox, Ehr.,is nothing else than a monoecious Volvox glohator ; that his Volvox stellatm is also V. glohator, obseiwed at the time when it is filled with stellate spores ; and lastly, that his V. aureus differs from the other forms of the same species, simply in the smooth [and coloured] condition of the spores;" FAMILY lY.— YIBRIONIA. (Plate XYIII. 57 to 69.) This family foUows, in Ehrenbei'g's system, the VolvocinecB ; yet, by reason of the extreme simplicity of stmcture of the beings composing it, it should, in any attempted natiu'al system, be placed even below the Monadina. The distinguished author of the Infuslonstluerclien attributed an animal nature to the Vihrionia,Q.Tidi although obliged to confess his inability to detect any internal organization, nevertheless argued, from analogy, that a polygas- tric structui-e was to be presumed, and that their movements were voluntary, and of themselves sufficient proof of animaHty. In Bacterium triloculare, indeed, Ehrenberg believed he saw an internal granidar ova-mass, a vibratile OF THE PHYTOZOA. 185 filament, and spontaneous fission. Of the Vihrionia generally, he stated that they were unable to change the form of their body, although without lorica, and that by imperfect self-division they formed chains or concatenated fila- ments, which in S_pirillum, from the obhquity of the junction-siufaces of the component Vibrios, assume a spiral form. Yarious later writers, among whom are Leuckhart, Cohn, and Burnett, would transfer the Vihrionia to the vegetable kingdom. The last-named author contributed a valuable paper to the American Association in 1850 ; but the most recent examination of the nature and structure of the beings in question is from the able pen of Dr. Cohn (Entw.). "We must also mention that Perty has given considerable attention to the Vihrionia, and contributed some original observations. It is to Cohn's account, however, that we shall chiefly resort in oiu' attempt to describe the minute and ciuious members of this family, which, if not rich in genera, is unsurpassed by any in the abun- dance and diffiision of its members. Some natiu'alists have considered the Vihrionia to be the active agents in producing putrefaction, since they are invariably found in decomposing fluids, just as the yeast-plant (Torida) always occurs in fermenting saccharine mat- tei*s and appears to excite the process of fermentation. The Vihrionia are for the most part colourless ; imder certain conditions, however, they assume a yellow, red, or a blue tint, but never a green colour'. Their movements, says Perty, are rapid and energetic, so much so that the corpuscles of Hysginum nivale, although at least one thousand times larger, are thinst aside by Bacterium Termo when in motion. They can advance with either end forward with equal facihty, and mostly seem, after proceed- ing a certain distance, to retrace their course to the point they started from. The extreme minuteness of some Vihrionia may be conceived from the statement of Perty, that, according to his calculation, four thousand millions occupy no more space than one cubic line. Dujardin, who retains the Vihrionia among animalcules, makes the follow- ing remarks : — " The Vihrionia are the first Infusoria which present them- selves in aU infusions, and which from their extreme smallness, and the im- perfection of our means of observation, must be considered the most simple ; for it is only their more or less active movements which lead to their being regarded as animals at all. I have been sometimes induced to beheve that there is a flageUiform filament, analogous to that of monads, or rather perhaps a spiral undulating one, which produces the peculiar mode of loco- motion. Is the Bacterium triloculare, described by Ehrenberg as having a proboscis, a true Vihno ? " AU that can be with certainty predicated respecting their organization is •that they are contractile, and propagate by spontaneous fission, often imper- fect in character, and hence give rise to chains of greater or less length." Cohn modestly premises {Entw. p. 118) that his researches have been di- rected chiefly to one species ; yet, from scattered observations, and fi^om pre- sumptive evidence, he would assign a vegetable nature to aU the species. In decomposing infusions, often after a few hours, extremely minute corpuscles may be seen in countless number, having the figm^e of a dot or comma, or of very delicate hues with the ends somewhat thickened. Their motion is tolerably active, darting hither and thither, contorting themselves at the same time by a rotating movement upon their long axis, and, when in masses, produce the appearance of a ceaseless swarming, in which the indi- vidual specks are easily overlooked on account of their smallness. They, however, differ in size among themselves, varying from 1-2000 to 1-700'" in length. Ehrenberg attributed to this world-wide form the name of Vibrio 186 GENERAL HISTOtlY OF THE INFUSORIA. lineola, whilst Dujardin more correctly separated it from the Vibrios under the name of Bacterium Teryno. Under this latter appellation Perty has also described it. Now when we come to examine an infusion rich in these organisms, nu- merous jelly-like colourless masses of different size and figure (XVIII. 69) may be met with on the waUs of the vessel, and on the surface of the fluid. These when young resemble small balls, fi^om 1-100'" and less in diameter; but as they continue constantly to enlarge, they acquii-e a clustered outline, and exhibit themselves as colourless masses and films of very considerable superficial dimensions and thickness, resembling soft Palmellse in consistence. Like these they are composed of a transparent mucus, in which numberless punctate or linear corpuscles are imbedded. These last are identical with the isolated particles known as Bacterium Termo. That these corpuscles are held together by the common mucus, is evident to the eye ; even the largest films are also composed of globular clusters agglomerated together, the out- line of the gelatinous mass appearing sharply defined in the water. More- over, the linear corpuscles appear more thickly congregated at the periphery than in the centre of the spherical collections ; but this is an optical delusion. Again, when coloiu'ing matter is added to the water, the Bacterium-TmiQ.ws> is not tinged by it ; and when any passing Infusorium impinges against it, its surface is pressed in ; and lastly, the absence of an independent and inherent molecular motion among the particles show them to be enclosed within a re- sistant medium. Frequently, whilst under observation, single corpuscles may be seen to detach themselves and swim away in the characteristic manner. The definite outline and figure of the mucilaginous globules, and of their clusters, refute the notion that such are merely collections of dead Bacterium- corpuscles. The indication is rather that the Pahnella-V^^e masses represent the young condition of Bacterium; indeed, the same cycle of development proceeds as in PahneUa, Tetraspora, and allied forms .... The only difference betwixt the J5ac^^rn«)i-heaps and Palmella- or Tetraspora-va^^^Q^ is, that in the first the individual corpuscles are so minute that the characters of simple cells cannot confidently be assigned them, and that, instead of being yellow or light green, they are quite coloui4ess. Nevertheless, in Kiitzing's Palmella Brehissonii and P. hyalhia, the cells are only 1-3000 to 1-1000'" in length, whilst their figure and distribution are indistinguishable from Bacterium. The absence of colour is a feature of the Pungi connected with their occiuTence in decomposing infusions ; yet Palmella hyalina has only a pale ochreous hue, and Cohn seems to satisfactorily establish that the mere presence or absence of coloiu' cannot constitute that decisive character which the separation of the microscopic Fungi from the Alg^e implies. From the above it appears evident that the corpuscles known as Bacterium Termo are the swarm-cells (zoospores) of a plant aUied to Palmella and Te- traspora, but referable, by reason of the want of coloui% to the microscopical aquatic Fungi. When these Vibrios pass into a state of rest, they accumu- late on the sm^ace of the water in the form of films, &c., as do the resting- spores of Tetraspora, Stigeoclinium, Conferva, and other Algse, but, unHke these, are connected together by an intercellular substance, within which their growth proceeds, and leads frequently, as Perty has illustrated, to theu' disposal in linear branching series. From the analogy mth Tetraspora and the other swarm-cells of Algee and Fungi, it must be assumed that the Bacterium-corpuscles move by means of a vibratile fibre ; indeed Ehrenberg intimates having seen a filament in Bacterium triloculare, and Dujardin considered some such mechanism pro- bable. OF THE PHYTOZOA. 187 The growth of the mucous balls is the consequence of the constantly re- peated transverse fission of the Bacterium-hodies, and is exceedingly raj)id. Yon Flotow seems to have detected the compoimd masses, and named one such Microhaloa teres ; but Cohn finds it necessary to create a new genus, which he has named Zooglma. Of the remaining Vibrios, Cohn has not as yet complete researches ; yet he finds sufficient support from analogy to warrant him in assuming a like history for them as for ZooyJoea. The larger forms of Vibrio have (he says) a striking affinity with the OsciUarice, whilst the longer, slowly-moving species have a very great likeness to the shorter fibres of Hyyrocrocis, from which, some have stated, Vibrios derived their origin. The affinity of Vihyno with the colour- less OsciUarice — mth the genus Beggiatoa, in which also very delicate forms occiu' — may be especially pointed out ; but this affinity is yet more striking with SpiriUmn and Spirocliceta, the other two genera of Vibrioma. Fiu-ther, in Oscillarieae we meet with straight species, e. g. OsciUaria, and spirally convoluted forms, e. g. Spirulina, just as we have straight forms in Vibrio, and spirally-tmsted ones in Spirillum and Sjnrochceta. Likewise, on com- paring the movements of Spirochceta w^th those of Spirulina, we find no dis- tinction between them except in energy and livehness. The results of his examination of Vibrionia are thus summarily stated by Cohn (p. 130) :— "1. The Vibrionia apparently all belong to the vegetable kingdom ; for they •exhibit an intimate affinity with undoubted Algae. " 2. By reason of their want of colour, and their occiu-rence in decomposing infusions, the Vibrionia belong to the group of aquatic fungi {MijcopJiycece)^ Cohn, however, shows good reason for not admitting this as a natiu'al group distinct from Algge. " 3. Bacterium Termo is the motile swarming-phase of a genus, Zooglcea, allied with Palmella and Tetraspora. " 4. Spirochceta plicatilis belongs to the genus Spirulina, of which it must be at once admitted as a species (^Spirulina plicatilis). "5. The long Vibrios which do not coil (Vibrio Bacillus) arrange them- selves Avith the more delicate forms of Beggiatoa (OsciUaria). ^' 6. The shorter Vibrios and SpiriUce resemble indeed, in form and charac- ter of motion, the OsciUarice and Spiruliyice ; nevertheless I cannot positively decide on their true natui'e." To this abstract of Cohn's paper on Vibrionia we must add a notice of Dr. Burnett's essay, which is equally in favour of their plant-Hke natui'e. The chief observations and opinions of Dr. Burnett are — that a branching of the chains, similar to that of the ordinary forms of Algae, is observable in Vibrionia, particularly in Spirillum; that, on watching their gradual growth, the smaller seem no other than the younger forms of larger species (for in- stance, that Vibrio is the first condition under which Bacterium and Sp>i- rillmn appear) ; thaf besides self-di\ision, propagation is effected by budding, a fact fu]-ther exemplified by the occuiTcnce of ramifications ; and that in yoimg forms a nucleus is absent, although one becomes apparent in advanced stages. Again, as to the movements of Vibrionia, Dr. Biu-nett can see no fiu'ther indication of movement in them than in spermatozoa and in vegetable cells, like which they are imaffected by electrical shocks, which are fatal to the lower forms of animal life. '' Their cell- structure and their vital (not voluntary) motion would then lead us to infer that the Vibrionia are Algous plants, and not animals. This throws light on several common phenomena. One in particular is, that the Vibrionia should almost invariably be found in infusions and liquids that 188 GENEEAL HISTORY OF THE INTUSOEIA. contain other Algae, and especially the common Torula; for I do not re- member to have seen the Torula without Vibrionia.^' Perty moreover testifies to Vibrio Bacillus assuming a still condition, and, by its branching concatenation, a plant-like form, out of which are constructed masses and films in the infusion and upon its surface, resembling Hygro- crocis and other Algae and aquatic Fungi. Dr. Ayres {J. M. S. i. p. 301) contributes the following obsei^vations on the self-division of the Vib/ioma : — " A\Tiile," he writes, " the shortest of the Vibriones were in active motion, the longer ones were comparatively quies- cent ; and these exhibited, according to their length, from one to six trans- verse lines, indicating the points of separation in the reproductive process. Those of moderate length, presenting only one or two transverse hnes, were rather active, and often bent at an angle at the transverse lines, which pre- sented the appearance of separation into two distinct indi\iduals ; and the character of the movements appeared such as to favour the separation. Those with fi'om three to six transverse lines were, for the most part, quiescent. I imagined, although from their excessive minuteness and transparency this was not plainly and unequivocally discernible, that there were indentations of the extremities of the transverse Hnes, by which constrictions were pro- duced, which, by their increase, would finally efi'ect a complete transverse division of the animals." The occurrence of Vibrios, or at least of Vibrio-]jke forms, as one of the metamorphic phases of the Pliytozoa of the antheridia of Characece, e.g. Marchantia, has been mentioned in a foregoing page (126), to which we must refer our readers. FAMILY v.— ASTASI^A OE EUGLEN^A. (Plate XYIII. 36—50, 62, 53, 55, m.) Dujardin very properly prefers to caU this group Euglencea {Eugleniens), on account of the resemblance in sound of the fii^st name with that of Astacicea (Astaciens) used to designate a family of the higher Crustacea. In Ehrenberg's system it constituted a family of the Polygastrica, and was characterized by wanting a tnie alimentary canal, a lorica and appendages, and by having a mouth sm^mounted by one or two proboscides, and in most species by a changeable form. Internally, digestive sacs, ova, a seminal gland, and contractile vesicle, and in most genera one or more red specks or eyes, were represented as present. The genera included were — Astasia, Ambly- oj)his, Euglena, Chlorogonium, Colacium, and Distigma. The value of these genera has been called in question by various wiiters. Dujardin makes the variability of form — in other words, a contractile integument — a leading fea- ture, and rejects the eye-speck as neither distinctive nor constant ; conse- quently he excludes from the family the EugUnce with rigid integument, and transplants them to the Thecamonadina, and rearranges the remaining species according to the number, disposition, and character of theii' locomo- tive filaments. Likewise Schneider (A. iV. H. 1854, xiv. p. 327) separates Chlorogonium from the Astasia^a because of its unchangeable figure ; and Mr. Carter {A. N. H. 1856, xviii. p. 116) would also detach Astasia from Eu- glena, from the conviction that the former has an animal organization, and that the latter is referable to plants. In the follo^ving general history of the Astasicea, our descnption will chiefly apply to the two genera Astasia and Euglena, respecting which we have very copious details in the papers by Mr. Carter, (A. N. H. 1856, xviii.). OF THE PnXTOZOA. 189 Of the remaining genera, some comparative observations \\dll be made in pass- ing, and particular researches respecting them added from Perty and other inquirers. EufjJence and Astasice are mostly spindle-shaped (fusifomi), and give off from theii' anterior extremity one or two delicate filaments, and posteriorly a usually short blunt tail. Excluding the doubtful Euglenece, which, on account of their rigid integument, we think, mth Dujardin, should be transferred to another family, the remaining species of the two genera in question are, from their inherent contractility, capable of varying their form to a remarkable extent; i.e., to use a technical word, they are " meta- holicJ^ This property is, nevertheless, much more restricted than in the Amcebce ; for the Astasicea can send off no oifshoots or variable processes like those animalcules, but in all their manifold contortions, elongations, and contractions do not completely lose theii' primitive figure. In general, the recurrence of the changes of figure is quite arbitrary and without regu- larity. In Eutre])tia viridis and Astasia margaritifera, however, Perty represents an alternate or peristaltic expansion and contraction of the or- ganism, so that first the anterior and then the posterior extremity expands. He adds, besides, that in this Astasia the contained clear globules are not transferred backwards and forwards, but only a fluid matter which runs in channels between them. The Astasicea are covered by a distinct flexible and elastic envelope, which ]\Ii\ Carter calls the " pellicle," and states that it resembles the cover- ing of Amcehce, is stnictiu'eless, and hardens after secretion. Stein also afRi-ms that in Euglena it is similar to the enclosing membrane of Grvegarina, and, like it, a shut sac without mouth or other aperture. On the contrary, the translator of Kolliker's paper on Actinophrys (J. M. S. i. p. 100, note) denies the existence of a distinct envelope to this genus. Beneath the peUicle, adds Mr. Carter, is a transparent moving substance, with an inhe- rent property of contractility and polymor})hism, which proves itself inde- pendent of the superposed pelhcle when, in the process of encysting, the two become separated : this substance is the " diaplianey Enclosed within these laminae are the contents, consisting of a proto- plasmic matter with suspended particles and certain definite structures, viz. a nucleus and contractile vesicle (XYIII. 46 «, c). The protoplasm is the same matter Dujardin names the " sarcode," and is occupied with a varying quantity of corpuscles, diff'ering among themselves in size, and imparting the colour peculiar to the species. " In Euglena,^^ writes Mr. Carter {op. cit. p. 119), " the sarcode is separated from the diaphane by a layer of pointed sigmoid fibres, arranged parallel to each other, so as to fonn in Cnimemda texta (Duj.) a conical cell, which, so soon as the ovules have become developed, and the diaphane and other con- tents of the sarcode have died off, becomes transparent, although it still retains its conical form until the resiliency of the fibres, now unrestrained by the diaphane and other soft parts, causes dehiscence, and sets the ovules at Uberty." These fibres are therefore the cause of the spiral markings of several Emjhnce, as well as of Phacus and Chonemonas ; they are strongly marked in Euglena spirogijra. " In another specimen of Euglena,^' says Perty (p. 57), " of fully a sixth of a line in length, and of a grass-green coloiu% some thirty dehcate longitudinal lines were perceptible, which, when the body turned on itself, looked as if spii-ally disposed. Moreover, on examining Lepocinclis- globules wheu partially diied, the spiral lines appear composed of rows of closely aiTanged dots " — a phenomenon probably explicable on the supposi- 190 GENERAL HISTORY OF THE INFUSORIA. tion that the fibres, as a consequence of evaporation, have been broken up into particles by the act of diffluence. Mr. Carter distinguishes certain minute colouiiess granules diffused in the general protoplasm of the interior, which he specially designates " mole- cules." These, says this obseiTer, are the first to appear in the homogeneous sarcode, but afterwards become intermixed ^vith larger corpuscles — " gra- nules"— and with " ovules ;" and by the time the o\Tiles have become fully formed, the sarcode and its molecules have dried off or disappeared, " More- over, in Astasia, digestive globules also appear ; but here the food is taken in through a distinct mouth, while in Euglena the absence of such vesicles would appear to indicate that its suj^port is of a different kind, if not intro- duced in a different way." Ehrenberg noted the existence of a contractile vesicle at the anterior ex- tremity of Euglena ; the like is also seen in Astasia ; but in neither instance have its pulsations been directly obsei^ed. A nucleus is also present of a discoid shape, and siuToimded, according to Mr. Carter, by a transparent capsule, which appears like a narrow pellucid ring aroimd it, owing to its greater size. In Chlorogonium and Amhhiopliis, Ehrenberg encoimtered what he called a seminal gland, i.e. a nucleus, and, in the latter genus, men- tions the presence of two wand-hke bodies in front and three behind it. Thirteen such peculiar structiu'es were also seen by Perty in a large specimen of Euglena sjyirogyra, which he concluded had originated from a peculiar disposition of the internal substance. The same ambiguous structures are doubtless referred to in the following paragi^aph by Mr. Carter, although, indeed, structm-al pecuharities are detailed which would render Perty's ex- planation inadmissible unless qualified in some measure {A. N. H. 1856, xviii. p. 241): — ''With reference to the single, glaiiy, capsuled body which exists in the centre of Phacus and in the large lip of Crumemda texta, also dually in Euglena geniculata, Duj. {Spirogyra, Ehr.), on each side the nu- cleus, I can state nothing further than that in the two first it consists of a discoid transparent capsule, which at an early stage appears to be filled with a refractive, oily-looking matter ; that it is fixed in a particular posi- tion, and remains there apparently imaltered, with the exception of becoming nucleated, until every part of the animalcule has perished, and nothing is left but the spiral-fibre coat, and perhaps a few o^iiles. In Euglena geniculata it is bacilliform, and contains a correspondingly-shaped nucleus; and al- though I can state nothing respecting its uses, I cannot fail to see that it has an interesting analogy, particularly in the latter instance, T\dth two similar organs which are commonly seen in the Navicula, and which in N. fulva, e.g., are situated in a variable position between the nucleus and the extremities on either side." The numerous globules diffused thi^oughout the body, which, in addition to the foregoing, make up the contents of the Astasicea, and according to Ehrenberg are to be considered ova, have, after being denied that nature by Dujardin and others, been again brought to notice under the name of ovules or germ-cells by Perty and Carter. They are, in the words of the latter observer (p. 223), nucleated cells, which, at an early stage, " consist of a transparent capsule lined with a faint yellow film of semi-ti'ansparent matter, which subsequently becoming more opaque and yellowish, also be- comes more marginated and distinct, and assumes a nucleolar form.". . . . " In the discoid cells of Astasia I have seldom been able to distinguish the capsule from the internal contents, on account of their smallness and the incessant motion of the animalcule. In Euglena, however, they are veiy evident ; and it is worthy of remark, that each partakes of the form of the OF THE PHYTOZOA. 191 Euglena to which it belongs. Thus, in E. acus it is long and cylindrical ; in E. viridis, oblong and compressed ; and in Crumenula texta and Phacus, cir- cular and compressed. There is yet another set of structures pointed out by Mr. Carter, deve- loped from the nucleus, to which he assigns the nature of spermatozoids, or male reproductive particles. " In Astasia/' he writes (p. 227), " irregular botryoidal masses, dividing up into spherical cells, colourless and translu- cent, or of a faint opaque yellow tint, present themselves so frequently (and generally inversely developed with the o\ailes, as in the Rhizopoda), that I cannot help tliinking that they are also developments from the nucleus ; but, from not having seen them present that evident granular aspect which characterizes this development in the Rliizojipoda, I have not been able to determine satisfactorily whether they are parts of the latter, or that kind of division of the sarcode into green spherical cells which sometimes takes place in Efglena. " In Euglena, also, I have described a development of the nucleus partly imder the idea that it might be a parasitic Ehizopodous develojmient ; but now it appears to me a simple enlargement, granulation, and segmental de- velopment of this body into polymorphic, reptant, mucous cells filled with spermatozoid granules, as in EMzojJods I have never been able to see the nucleus and its capsule in their original form when the spermatozoid mass has been present, though I have occasionally in Amoeba, and almost always in Euglypha, seen the empty globular capsule in connexion vrith the latter." The contents of Astasicm, even of the same individual, are subject to great variations in colour, distribution, and other characters, induced by age, the action of the reproductive processes, and the influence of external conditions. Thus, Perty tells us (p. 57) Phacus pUuronectes is at times filled with a homogeneous green mass, at others has a large, round, central spot (vacuole or nucleus ?), at others a large, clear space in the middle, having a central dark nucleus ; and at others, again, the contained endochrome forms three or four segments, each exhibiting many dark green nuclei. In Euglena vhndis and E. Acus the contents become resolved into a formless mass, or into a heap of nearly equal-sized germ-cells, and frequently the colour is changed from green to red, or the whole organism is rendered hyaline by the escape of the coloiuing matter. The colom-ed speck in Euglena, AmhlyopMs, and other Astasioia, reckoned as an eye by Ehrenberg, has in fact no pretensions to that character. We have pointed out that similar specks occur in Volvox and other generally recognized plants, in all probabihty precisely similar to and stnicturally the same as those of Astasicm. Sometimes in Euglena the red is diifased over the entire body, as Cohn represents to occur in Sj^hceroplea annulina {A.N.H. 1856, xviii. p. 83), in small globules, which have the physical and chemical relations of oil. In other instances, and occasionally in very young forms, the red stigma is altogether absent. In Phacus pleuronectes, Perty states, one speck is placed close behind another with an intermediate band uniting them. Often in Euglence, instead of one stigma, two or more red granules occiu', whilst in Euglena cleses the pigment-mass is quite irregular. In Cru- menula the red spot is comparatively Yery large, and rests in the form of a small obtuse cone upon the contractile vesicle. '' The eye-speck oi Euglena viridis,''^ says Perty (p. 117), " is round or oval, and exhibits an elliptic or spherical vesicle, within which the colouring matter is contained, smTounded by a more or less comi)lete brownish-black ring : at a subsequent period the colouring matter is diffused in a most irregular manner 192 GENERAL HISTORY OF THE INFUSORIA. beyond the ring." In AmhlyopMs viridis the red jDigment may either entirely or only partially fiU the dark areola. Perty very sensibly remarks, " All these red stigmata are deficient of all the requisites of an eye — they have no refracting medium ; and the presence of an eye is inconceivable among beings which have neither nervous centres nor communicating nerves. They are probably nothing more than drops of red-oil, like those which are produced among the chlorophyll in imicellidar Algae " (p. 118). Another fact, bearing on the character of a red pigment- speck in Euglence, is the change of colour these beings at times undergo fi'om green to red, just as Chlamydococcus and various unicellular Algae do when they enter on the " resting " stage. JReprodudion of Asfasicea. — In Ehrenberg's opinion, the members of this family are reproduced both by self- division and by ova : he speaks of having witnessed the former process in the genus Euglena, but only as a rare occurrence. In other genera he failed to discover it. A\Tien fission takes place it docs so in the usual manner, longitudinally, and produces two equal and similar organisms ; rarely, the new beings are of unequal size. More- over, in the encysted condition, which was mistaken by Ehrenberg for the death of the Euglena, or confounded ^Adth other structures, fission is a con- stant phenomenon. "WTien the motile Euglena becomes "still," or enters into a state of rest, it contracts itself into a ball, and, while retaining its red stigma, loses its fila- ment. A gelatinous layer is thi'own out around it, which gradually hardens into a rigid colourless cyst : this at first lies close upon the mass of the Euglena, but ultimately is removed from it all round by an interval ; and when quite matiu'e, it frequently acquii'es a brownish colour and opacity. In the encysted condition, Euglena closely resembles the "stiU" cells of Protococmis ; hence the term " Protococcoid/' to express this condition. When Euglence have undergone this transformation, they cohere together by a mucilaginous ex- cretion, so as to form expansions or films resembling in appearance those produced by many Palmellew. This close resemblance subsisting between encysted Euglence and the rest- ing-spores of numerous Algae, e. g. of (Edogonium, explains many of the wonderful transformations recounted, such as the germinating of encysted Euglena-ceWs into branching filiform Algae. Again, the filmy masses pro- duced by Euglenm have been described as independent genera and species of Algae, — as, for instance, those formed by E. viridis, as Microcystis olivacea, and those by E. sanguinea, as Microcystis Noltii. That the contained green Euglena is not dead within its case, is proved by its sometimes being seen to revolve within it, and also by the circumstance that, in the early period of encysting, on rupturing the cyst, the contained being escapes and resumes the appearance and movements of its free brethi^en. It would seem, indeed, that Euglena: are in the habit of temporarily encysting themselves as a means of protection against injurious external causes, such as evaporation, and that, when a normal condition is restored, they throw off their protecting envelope and reassume their active contractile character and movements. The empty cases are often to be met with floating on the sur- face of water, united with others and with encysted Euglenoi in a common membranous mass. The vitality of the enclosed being is further displayed by the process of fission, which advances in the power of two until very small segments are produced, which soon develope severally a red speck and fila- ment, and, on the dissolution or rupture of the common cell-wall of the parent, escape as small free-moving corpuscles rather resembhng Monads than Eu- glence by their minuteness. The encysting act maj^ transpire in very small as well as in large Euglence, or THE PHTTOZOA. 193 and the subsequent fission may be arrested at any point, so that either a few sections which, in the phi'aseology of botanists, may be called macrogonidia, or other^vise very numerous small ones, or microgonidia, may be developed. As the simply encysted Euglence have been represented as independent genera of plants, so the same thing has occurred when their contents have been seen in the process of self- division ; thus, for instance, Perty thinks it probable that Protococcits turgidus and P. clialyheus (Kiitz) are no other than two such transitional conditions. Another circumstance attending encysted Euglena', is the forming an attach-^ ment to other bodies by a sort of pedicle, which extrudes from what has been the anterior extremity of the being. "When viewing large collections of Eu- glence, specimens may occur of two or several united together by the head or tail, sometimes with the tail of one to the head of another. Examples of two partially united have been explained by supposing the act of fission of a parent-animal to be nearly accomplished ; but other observers have seen in such united beings an instance of conjugation, i. e. of an act, to some degree, of impregnation. The union, however, of several by the tail, sometimes seen, is an argument against this supposition, and is rather suggestive that such combinations are the remnants of primitive adhesions betwei3n gonidia within the parent-cell or between germs before a pellicle has formed around them, or, agaiuj that a mucoid matter thrown out from the surface, as happens in many Phytozoa, may constitute the band of union, when incomplete fission or persistent primitive adhesions cannot be considered its origin. There is cer- tainly no a priori argument against the occurrence of conjugation in this family, and some naturalists would, from analogy with related beings, look for it ; but at present it has not, we think, been proved. Ovules or germs. — That Euglence reproduce by internal germs is an opinion now advocated by several naturalists. To oiu^ minds this mode of propagation is really homologous with the formation of gonidia in admitted plants. Kol- liker vmiea (J. M. S. i. p. 34) — " Multiplication by means of germs generated in the interior indubitably occurs in certain Infusoria : in Euglena four to six embryos are seen in one individual, entirely filling it, which at length, fur- nished with their red speck and filament, break through their parent, leaving it as an empty case." Mr. Carter {op. cit.) has entered very largely into an account of the ovules of Infusoria and of their development. " In Euglena viridis/^ he writes, " the ovules are of an oblong shape : they are found, like those oi Spongilla, scattered over the sides of the vessel, and evidently have in Kke manner the power of locomotion in addition to that of turning upon their long axis when otherwise stationary .... The pellucid central area in them corresponds with the oblong shape of the capsule ; but beyond this and the central granule I have not been able to follow their development out of the parent, though, from the number of young E. virklis present, it may be reasonably inferred that they came from the ovules. The young Euglence, however, being so rapid in their movements when once the cilium is formed, it can hardly be expected that, except imdcr a state of incarceration, their development can be followed so satisfactorily as that of the slow-moving Rhizopocl. Instances do occui', how- ever, where the ovules gain the cilium within the cell, and there bound about when fully developed like the zoospores of Algae ^^-itliin theii' spore- capsules. In this way I have seen them moving rapidly within the effete transparent capsuled body of E. viridis and in Crumenula texta, where the spiral-fibre layer is so strongly developed as to retain the form of the Euglena for a long time after all the soft parts have perished. On these occasions the embryos are perfectly colourless, with the exception of a central point which reflects a 194 GENERAL HISTOEY OF THE INFrSOEIA. red tint ; and on one occasion, while watching a litter in rapid motion within the encysted body of E. viridis, the capsule gave way, and they came out one after another just as zoospores escape from the spore-capsule ; but, from their incessant and vigorous movement, I was imable to follow them long enough to make out anything more about them." This same observer, moreover, refers to a rhizopodous development of the nucleus of Euglena, whereby the form of an " actinophorous Rluzopocl " is assumed, from which, in his opinion, young Euglence are probably developed. Perty, again, records some original observations on the development of Euglence from ovules or, as he terms them, germs (Keime). At p. 79 he states that, among numerous veiy minute resting germs, intermingled with larger indi\-iduals, some were seen to acquire the faculty of motion, to stretch themselves out, and to assume the form of Cereomonas. Between such and completely-formed Euglence every intermediate size occurred. The motionless spheroidal germs set free by the dissolution of the parent-cell soon develope a tapering extremity, terminated by a locomotive filament, at the base of which is a hyaline space, and in and near to this a dark speck which subse- quently changes to red. The differentiation of the homogeneous contents of the granules, out of which the germs are to be developed, takes place at a very early period, but not in the same way or time in all specimens ; neither do aU. the young of a brood attain the same dimensions and figure ; indeed but few attain a considerable size, and many acquire an abnormal figiu^e. For example, Perty regards AmhJgoplils viridis as only an accidental variety of Euglena, of large size and trimcate at one end ; for he has remarked nimierous small indi\iduals, derived from a Euglence, also with a truncated extremity. Further, he reports the multiplied varieties in form, in colour, and in arrange- ment of contents, &c., which occur in collections of the same species of Euglena, and adds that the great differences exhibited by E. viridis, when in a dying condition, are most varied and inexjilicable. In illustration of this opinion, he remarks that the utmost variety of fonn oeciu's ; or all the vesicles and granules change to a red colour or become transparent ; or the vesicles vanish and the green mass contracts itself into a small ball, or otherwise dis- appears, leaving only an empty shell. In the last-named state the stigma often retains a black coloiu\ The empty envelopes frequently accumulate so as to form masses resembling a vegetable cellular tissue, and in one instance approached, bj^ mutual pressiu^e, a regular hexagonal figure. Some such acci- dental groupings of \\dthered Euglena-eells have been, as Perty believes, described under the name of Pcdmella botri/oides by Kiitzing ; and Cereomonas vhmlis, and also probably Bodo viridis, are merely phases of development of Euglena viridis. There is a distinct concordance between Carter's and Forty's account of the development of the contents of Euglena' into minute germinal bodies, or, as we may legitimately call them, microgonidia ; and, on the other hand, the formation of two- and four-fission products (in other words, the formation of macrogonidia from these beings in their still-condition) has been a matter of direct observation. Consequently the developmental history of Euglena is so far complete ; and it only remains for naturalists to witness the actual relation, the contact and incorporation of the micro- with the macrogonidia, to bring this genus within the same pale as Volvox, in reference to its sexuality. Mr. Carter has reverted to his notes on the ovules or germs of Euglena, in his just-published paper on Eudorina {A. N. H. 1858, ii. p. 245), in the following remarks : — " There is no doubt that E. viridis becomes chstended with the cells which T have heretofore described, and thouo'ht to be ovules OF THE PHTTOZOA. 195 or embryonic cells, and that during this time the chlorophyll passes into red grains, and subsequently disappears, while the organism is secreting a capsule around itself, and its original cell-wall passes into a tough spherical ovisac, so to speak. But what becomes of this, if it be the result of impregnation, or what the process of impregnation is like, or when it takes place, is for future discovery to determine." ChJoroc/onium eiichlorum (PI. XX. 15-21) was the subject of an interest- ing observation by Weisse (Wiegmann's Archiv, 1848), who thought he had demonstrated in this species propagation by ova or germs, and, in fact, elu- cidated in it the development of microgonidia, by repeated acts of self-fission of the contents, just as in the spores of Algae. For instance, he described the contained green matter of the fusiform being fii'st to contract in some mea- sure upon itself (XX. 16), then to exhibit a constriction followed by a line of division into two portions, which, by subsequent redivisions, resolved the whole into a nodular mass resembKng a bunch of grapes (XX. 17-18). This grapebunch-like mass possessed a certain mobility within the enclosing integument; and as the process of development proceeded further, its se- veral particles or segments displayed a movement among themselves, which in- creased in extent and vigour until the external envelope gave way before it, and permitted their escape in the form of so many distinct particles or beings (gonidia) endowed with ciliary filaments, whereby they kept up an active movement in the surroimding water (XX. 21). The young forms produced exhibited active movements within the parent- cell, and at one stage prior to theii' discharge, when connected together in heaps, resembled Uvella Bodo. On the ruptui^e of the cyst they escaped freely into the water with the fig-ure of Chlorogoniwn. Schneider has also some remarks on this genus {A. N, H. xiv. p. 326). He could discover no decided red speck, although as many as twelve reddish spots were distributed over the surface of the green mass ; a contractile vesi- cle, moreover, eluded his search. Of the mode of propagation he reports that '' division takes place in the interior of the investing membrane, in exactly the same manner as in Polytoma. The number of individuals produced is never less than four, but often as many as thirty- two ; in the latter case they are very small, but always resemble the parent in other respects. A spheri- cal state of rest also occui'S. It appears that, when the requisite conditions are present, the young proceeding from the division of the parent pass into this state immediately after they are set free, — their soft investing mem- brane probably rendering them fitter for this purpose. The contractions which then take place are probably the same that were observed by Ehi^en- berg. In other respects I have found the form unchangeable ; and Clilo- rogonium must consequently be separated from the Astasicm, amongst which it has hitherto been arranged. On the addition of iodine, only a few blue granules are to be seen in the fusiform individuals ; the green spheres, on the contrary, which are completely filled with green granules, acquire a deej^ blue colour with this reagent : if the colouiing-matter be destroyed by means of concentrated sulphimc acid, the granuifes are dissolved, and on the addition of iodine, a beautiful blue colour is produced. By long keeping, the green of the cyst passes to red. The cysts are not to be roused from their toi^oid condi- tion by the production of fermentation. I have, however, observed their re- vivification under other circumstances ; but my materials are insufficient to enable me to describe the mode of reproduction of the investing membrane and filaments, which would certainly be interesting. The conditions required for the existence of Chlorogonium are apparently quite different from those of Polytoma : the former did not multiply abundantly in infusions imtil the fa 196 GENERAL HISTOEY OF THE INFrSORIA. latter had passed to the state of repose." This view of the affinity of Chlo- rogonium accords with that which Weisse indicates in the statement that this genus and Glenomorur,i tingens (species of Ehrenberg's family Monadind) are but two phases of the same being. Weisse has appended some remarks to the preceding account by Schneider Midi. Archil', 1856, p. 160). He says that he mtnessed the revivification of encysted Cldorogonia (a phaenomenon unnoticed by Schneider) on placing some cysts, collected the preceding year, in water. The reddish and pre- viously spherical cysts were seen to gradually lose their regular outhne by the elongation of one end, and thereby to acquire an ovate form. After a short time the naiTower end of the cyst ruptured, and a very thin-walled vesicle protruded through the rent : whilst this took place, a movement of the contents of the cyst became evident ; and after a while several constric- tions appeared, which extended deeper until they di\ided the whole into four portions. For a time the protniding sac elongated itself more and more, but ultimately, owing to the pressure within it of the moving particles, gave way and allowed their exit. The escaped sections were, as a rule, of pretty uniform sizes, but had not the remotest resemblance to the mature Chlorogonium, and indeed might have readily been assigned to another group of beings. Their figure was elongated, irregular, and often triangular, on fii^st escaping from the cyst ; they were also flexible in every direction, and of a dusky brown colour. After dispersion, on reaching the margin of the drop of water, they re- sumed a globular shape, changed to a rusty red colour, and after a few hoiu's assumed the appearance of clear-green spindle or bodo-shapcd organisms. Between their evolution from the cysts and their development into the form of ChJor^ogonium, two hours, less or more, intervened. This di^^sion into four segments, representing four new beings of Chlorogonium progressively evolved, apparently without actual metamorphosis, may be rightly esteemed an act of reproduction by macrogonidia, whilst the breaking up of the organism into a multitude of zoospores, as previously described by Weisse, is a process of re- production by microgonidia. Kature of Astasi^a. — It is with certain members of this family that Thuret pointed out (Ann. iSc. Nat. 1850, xiv.) the close resemblance to the zoospores of Algae, amoiinting, as far as outward appearances indicate, to actual identity. "This affinity," he says, ''is exhibited in the colour, form, in the number and character of the ciliary filaments, in the contents, not excepting the coloui-ed eye-speck, in the mode of self-fission, and also in the power of locomotion. What is still more, both zoospores and Astasicca tend to the light, disengage a gas, most probably oxygen, and emit a peculiar spermatic odour. However, by continued watching the zoospores are seen to affix themselves to some body, surrender their seeming animal life, and proceed to germinate, developing a tissue similar to that of the plant which gave them birth. On the other hand, the true Astasicva, if they attach themselves, it is but for a time, and no ap- pearance of germination ensues. The closest similarity exists in the case of the Chlamydomonas pidvisculus (Diselmis viridis, Duj.), and in a less degree in the Euglence, .... In the form of the body, in that of the flabelliform ciha, and in the disposition of those cilia, as also in the contents of the body, the resemblance is complete. The movements of Diselmis are like those of zoospores ; and, like them, they tend to the Hght. In one distinct species, or rather, in a particular state of the same species, a very clear red spot is dis- cernible, and a central globule, very hke in appearance to the amylaceous granules so frequent in the cells of green Algae. These Infusoria appear to act on the atmospheric air like Algae and the green parts of other plants, dis- OF THE PHYTOZOA. 197 engaging a gas (oxygen ?) under the influence of light. They exhale an evi- dent spermatic odour. Their reproduction occurs by spontaneous division, 2-4 young ones being formed within the common integument. I have ob- served the same mode of reproduction in the Euglem^, which act on the air and tui^n to the light like DiseJmis, but have an extremely contractile body changing its figure every moment, which will not admit of their being con- founded with zoospores, and leaves no doubt of their animality. This binary or quaternary division is met with also in the various species of TetmsporcBy which, though arranged mth the Algae, appear to me of very doubtful vege- table nature. In Tdraspora gelatinosa I have recognized green globules, dis- posed in foiu's, and each furnished with two cilia of extreme length, which are lost in the gelatinous mucus of which the frond of this supposed plant is constituted. All these productions, as well as Gonium, Pandorina, Volvo.v, Protococcus nivalis, &c., present, in my opinion, characters of animality too decided and too permanent for it to be possible to refer them to the vegetable kingdom ; and I think it would prove more convenient to unite them, with aU the other Infusoria (Poh/gastrica) coloured green, in one and the same group, which might be called CJilorozoidece. We have before noticed the sweeping statement of M. Agassiz, that all the mouth- less Infusoria are nothing but various forms and phases of development of Algte." Although many natm-alists stoutly claim the Astasicea, and the genus Eu- glena especially, as plants, yet others, and among them some of the most able, particularly in Germany, stiLL pronounce them animals. But, as we have before noticed, there are undoubted Euglena-iorms which are actually phases of existence of known plants, and which, if watched, may be followed in their development until by germination they assume all the special fea- tures of those plants ; and, on the other hand, there are EuglencB which at no period of their existence can be seen to germinate, although they may exhibit a plant-like condition when encysted and motionless, like Protococcus resting- cells. As an example of the former set of transitional beings, we may aj)peal to the observations of Itzigsohn already recorded (p. 125), showing that, in the development of Oscillatorice, minute Chlamydomonads are transformed into Eagleme, that these in their turn generate microgonidia, which, after some in- termediate transformations, eventually produce the ' Leptothrix,'' and lastly the perfect OsciUatoria. Another illustration might be adduced from Cohn's essay on Protococcus pluvialis, in which he points out both an Astasia- and a Euglena-\SkQ phase of that unicellular plant. Let it, however, be noted that whilst Cohn records a Ejiglena-yihdL^e in Protococcus, he nevertheless admits the existence of animal Euglence, distinguished by their extraordinary con- tractihty (Entiu. p. 208). Withal, this distinguished observer's discovery of the mutual sexual relation of micro- and of macrogonidia constitutes (sup- posing these reproductive products, as seems to be actually the case, to be generated in EiiglencB) an additional argument for theii' vegetable natui^e, by bringing them Tvithin the same category of organized beings as Volvox and PaiKlorina. If Mr. Carter be correct in his account of Astasia, this genus can no longer remain in the category of doubtful organisms, but must forthwith be trans- ferred to the animal kingdom ;' for he asserts the existence of a mouth with a complicated buccal apparatus for biting off and taking in food, of a strong prehensile organ, and stomach-sacs. Besides, he speaks of its near affinity mth Amoeba, and refers it to the Rhizopoda. In Euglena, on the contrary, no mouth- or stomach-vesicles are discoverable, and the filament is comparatively li 198 GENEKAL HISTORY OF THE INFUSOEIA. imperfectly developed ; hence Mr. Carter allies this genus rather with the zoospores or gonidia of Algae, and assumes that it must, like other mouthless organisms, derive its nutrition through endosmosis. Cohn, on the other hand, although cognizant of many plant-like features in Euglena, cannot ac- quiesce in detaching it from animalcules, because of its great contractihty and of the fact that there are undoubted animals, such as Opalina, Rhizojwda, Gregarina, Trematoda, &c., which want the special animal characteristic of a mouth. Mr. Carter would, it seems, recognize both Euglena and Astasia as close alhcs with Amoeba, — an affinity remarked by Ehrenberg, who placed the family As- tasioia between Chsterina and Amoeba^a, treating the variability of the form of the body as a leachng characteristic. Indeed, the first-named observer alludes to an actual transition of Astasice into Amcebce, in the following paragraph {A. N. H. xvii. 1856, p. 115): — '' Young Astasice are developed within the cells of Spirogyra to a great extent ; and although they at first have almost as much polymorphism as an Amoeba, still they retain their cilium, and after a while assimie the form and movements pecuhar to Astasia. I might here mention that on one occasion I saw" a lay^ge Amoeba with a long cilium at one time assuming the foim of Astasia, and at another that of Amoeba, which thus gives us the link between these two Infusoria. The cilium, however, had not the power of the filament of Astasia, though it occasionally became terminal." At a previous page, a rhizopodous development of the contents of Euglena; into granuliferous Amoeba; of a pinkish colour has been adduced as a fact noticed by the same observer. We need not stay to examine the vital endowments and habitats of the Astasice ; for, except the facts occuiTing in the preceding history of the family, and in the general account of Phytozoa, there is nothing important to adduce. OF THE PROTOZOA. 199 Sect. III.— OF THE PROTOZOA. (Plates XXI.-XXXI.) The term Protozoa, borrowed from two Greek words, protos, first or primi- tive, and zoon, an animal, has of late been very generally adopted to signify the simplest forms of animal life. Upon a review of these rudimentary animals, it is at once perceived that they differ among themselves in organiza- tion— that whilst some are amorphous and almost homogeneous, others exhibit a degree of differentiation of parts, and the fii'st vestiges of internal organs to carry on the processes of hfe ; again, it is seen that some have a distinct orifice for the admission of food, or a mouth, which in others is absent, and, lastly, that some with a definite figm^e are moved by vibratile cilia, whilst others slowly progress by the alternate protrusion and retraction of ever- changing and changeable processes derived from the general mass of their body. From a consideration of these structiural differences, one division of the Protozoa is suggested into those moved by cilia, and those moved by variable processes or ^ pseudopodes ' ; and a second, into those furnished with a mouth, and those which are mouthless. We have accordingly constituted two pri- mary divisions, viz., 1. Ciliata, Protozoa moved by cilia ; and 2. KJiizopoda, moved by variable processes. The Rliizopoda (XXI.) are all mouthless, or ^ astomatous,' whilst the Ciliata (XXIV.-XXX.) have a mouth, and are styled by Siebold ' Stojnatoda,^ with the exception of a small family, the Opalincea (XXII. 46, 47), and perhaps also of that of the Peridinicea (XXXI. 16-23). However, besides the beings usually included among the Ciliata andi^A/zo- poda, there are several subordinate Protozoic groups, some of which either stand as it were midway between them, or represent a development of the amoi-phous and mouthless Rhizopoda in a different direction ; such are the Gregarinida (XXII. 28-36), with the associated Psorospermia (XXII. 37- 41), the Spongiada, Thalassicollida, and Polycystina, all which must rightly also be numbered with the Protozoa. Of the Ciliata themselves, there is a fiu-ther and higher development of their type in the subordinate groups of Ichthydina (XXII. 46-47) and Noc- tilucida (XXXL), and, on the other hand, a degradation of it, as ah-eady noted, in the case of the Opalincea and Peridinicea. Here we would remark that the term ' Infusoria ' has been employed by several writers, in hen of that of Ciliata, which we adopt ; still it is, to oui' mind, both less appropriate, and also open to objection, not only on account of its meaning being quite indefinite, but also by its having everywhere acquii'ed a very much wider signification, in consequence of which it will always be open to misconception when apphed to a comparatively very small class instead of, as heretofore, to a very various and ^vide collection of microscopic organisms. Another word invented is ' Stomatoda,' which is precisely equivalent in the extent of its signification with the term Ciliata, the mouthless families only being excluded. Excepting their subordinate groups, the organisms comprehended among the Ciliata and Rhizopoda formed, in conjunction with the Desmidiece, Dia- tomece, and the families we have brought together imder the appellation Phytozoa, the great class Polygastrica in the system of Ehrenberg. Little reflection is necessary to convince ourselves of the very heterogeneous nature 200 GEA'EEAL HISTORY OF THE INFUSORIA. of the collection of li^-ing objects assembled in that class ; and even Ehrenberg himself would never have suggested such a grouping, had he not imbibed the hypothesis of a pervading uniformity of organization possessed by the simplest animated beings in common mth animals considerably advanced in the scale, and under its influence, aided by his imagination, found in all these various organisms, a polygastric structure, viz. an apparatus of numerous stomach- sacs, communicating dii^ectly or indirectly with the mouth. Notwithstanding the many prominent errors in Ehrenberg's classification, he rightly recognized in framing it the value of the external means of locomotion, and distinguished a group of PoJygastrica under the name of Pseudopoda. Siebold, who proposed the term Protozoa, limited it to two classes, distin- guished as the ' Infusoria ' and the ' Rhizopoda ', omitting the supplementary groups above mentioned. The Infusoria he di\ided into two orders, the * Astoma ' and ' Stomatoda,' the latter of which, together with two of the three families of Astoma, is e(]uivalent to our class Ciliata, its remaining family Astasuea being a member of oiu' group of Phytozoa. The Protozoa, as understood by us, may be thus exhibited at one view. Ciliata. Eiiizopoda. f. . r Opalingea a. Amoebsea a. s oma | Peridinigea (?) b. Monothalamia or Monosomatia b. Stomatoda c. Polythalamia, Polysomatia, or Foraminiiera. Gregarinida Psorospermia N^JUill Suppleruentar, groups. ' Polycystina ThalassicoUida Spongiada In treating of these several classes and groups we shall commence with the Phkopoda, omitting, however, lest our subject-matter be too much ex- tended, the Polycystina, ThalassicoUida, and Sjjongiada ; we shall next pro- ceed with a brief description of the Greyarinida, and its subordinate family Psorospermia, and then after considering the Opalinoea and Peridinicea as intermediate groups, proceed to detail the history of the perfect Ciliata — the Stomatoda, — finishing our account Avith the Ichthydina and Noctilucida as the highest developments of Protozoic life. As a result of our inquiry, we shall see, on the one hand, in the true Ciliata, sim^^le animal organized matter, with a very sKght amount of differ- entiation, attain its acme of development in the Vorticellina, and in these animalcules exhibit a superiority in organization above the lowest links of groups relatively higher in the chain of animal life ; and, on the other hand, in the Rhizopoda, of still simpler organization, the same organic living material developed in a totally different dii'ection to a maximum in the most beautiful and complex- shelled Foraminifera, which in outward form, although in no real homology, emulate the highest class of Invertebrata, viz. the Cephalopoda Another lesson may also be derived from the objects of our present study, viz. the fact of the marvellous variations which can be made out of one or, it may be, two elementary stnictm^es. Thus the simple contractile substance which can live independently in the Amoeba condition (XXI. 1-4 ; XXII. 1-23) encases itself in a one-chambered shell in the Monothalamia (XXI. 6-19), and into a many- chambered one in the Polythalamia (XXI. 20-36), and again lives partly within and partly without the curious silicious skeleton of Poly- OF THE PROTOZOA. EHIZOPODA. 201 cysthia, and in singular relation with a spiciila skeleton in Sjpongiada and TJialasskoUlda. So, if we look to the Ciliata, we find that the hardening of the superficial lamina of their substance into a sort of integament gives rise to numerous modifications in external form and fimctions, according to the degree of induration, and the processes sent out. The flexible-skinned Colpodea (XXIX. 25-50) depend for their movements upon their garnitiu-e of \-ibratile cilia, and are merely swimmers, whilst the hard-coated Euplota (XXV. 350- 353) produce short moveable processes which act as legs, upon which they can rapidly creep. Lastly, the selfsame primitive contractile substance is formed into a stem in the Vorticella, which supports the animalcule at its apex, and exhibits helicoid contractions, astonishing both by their rapidity and completeness. SUBSECTION I.— EHIZOPODA. (Plates XXI. XXII.) The true Wiizopoda constitute a large class of microscopic animated beings of the most simple character. They may be defined as non-ciliated Protozoa moving by variable expansions. Their organic animal substance presents no distinction of tissues or of organs, but is homogeneous, contractile, and trans- lucent, resembling a tenacious mucus or soft tremulous jelly, and is perpetually changing its form by expanding itself at one or several points into processes of ever-vaiying dimensions, arrangement, and number, and called in conse- quence "" variable processes." Inasmuch, moreover, as these shifting offshoots are their only means of locomotion, they have frequently been called " feet," and, as they are also characteristic of the class, have given origin to the terms *^ Pseudopoda " (with false feet) and " EMzopoda " (root-like feet) to desig- nate it. Again, the lining mass is, in numerous instances, capable of enclos- ing itself by a sheU of various figaire, consistence, and complexity ; and such variations serve to separate the Ehizopoda into famihes and genera. In the simplest shell-less beings (XXI. 3, 4), vitality is exhibited by the slow protnLsion and retraction of the variable processes, by the change of form, their onward movement, and the introduction of nutritive substances, and by the gradual changes of the introduced matters indicating a digestive act. They therefore manifest vital contractility, a power of locomotion, a degree of sensibility, and a digestive process. Eepeated observation likewise reveals the fact of progressive growth, and the faculty of reproduction. The testaceous forms exhibit their \itality after the same manner, and surpass the naked Ehizopoda only in the mar- vellous power of secretion displayed in the production of their shells (XXI. 6-3G). Although in organization the Ehizopoda stand even below the ciliated Protozoa, yet an animal natui'e must be allowed them ; indeed the simplest forms are the rudest specimens of animal existence. Under the term RJiizo- ptoda are comprised three well-marked families, viz. the Amcehina or Amoehcea, which are without, and the Monothalamia and the Foraminifera, with shells. The Monothalamia have one large opening to their monolocular (one-celled) shells (XXI. 6-17) — hence the name, — whilst the Forambiifera owe theii^ de- signation to the existence of numberless small orifices, generally distributed over a multilocular (many-celled or chambered) testa (XXI. 20-36). We have frequently^ in the following pages, used the term ArceUina as sjTionymous with Monothalamia ; for although the family known to Ehrenberg under that name comprehended only a portion of the genera that Schultze 202 GENERAL HISTOKY OF THE INFUSOKIA. arranges in his group of single -chambered or nionolocular shells, yet its meaning may be equally extended. It would probably have been correct to have placed the Acmetina (XXIII.) among the Rhizopoda, as another family closely allied to the Amoehina ; but the detail of their peculiarities would have too much embarrassed the general description of structure which we have endeavoiu'ed to give of all the usually acknowledged or true Rhizopoda ; we have therefore preferred to describe them as a subclass in the follo^ving chapter. The examination of the Ehizopoda requires to be conducted with great care and skill, — a requirement sufficiently illustrated by reference to the erroneous notions and descriptions of the older observers. They must be viewed in aU positions under different degrees and modes of illumination, by reflected as well as by transmitted light, and, especially in the ease of the testaceous varieties, after submitting them to pressiu^e and to the action of various chemical agents, or, when sufficiently large, after making sections of them in different dii^ections. The organic Kving mass of all Ehizopoda is alike, and corresponds with the " Sarcode " of ciliated Protozoa and with the amorphous contractile substance of Hydra and of other low organisms. It appears in the present class a con- tractile, highly elastic, colomiess, almost fluid mucus, hyaline or diaphanous, homogeneous, and in refracting power cliffeiing little from water. Xo di- stiQction into an enclosing fii-mer membrane or integument and contents is discoverable ; and cilia are never found. These characters exist in entirety only in very yoimg animals ; for at a veiy early period molecules, granules, and globules or vesicles, and various foreign particles, make theii^ appear- ance, diminish the transparency, and often impart colour. A new species of Amceba, figiu'ed by Schultze, the A. ghhularis, is repre- sented as ha\ing a thin, transparent, colourless lamina of contractile substance, from which the processes are given off, and which surrounds a globular, co- loured, and granular chief or nuclear mass (XXI. 1,2). A similar distribution of the substance of an Amceha into a hyaline colourless cortical, and a granu- lar coloiu'ed medullary portion, is represented by the same author in another species ; and it is moreover a structiu^e homologous vdth that in the allied genus Actinoijlirys (XXIII. 28, 29). As to the assigned character, of the animal sarcode being destitute of a distinct investing membrane or integu- ment, the shell produced by the testaceous forms might be considered equiva- lent to one ; and if some observations hereafter alluded to be correct, a re- sistant integument among the Ehizopoda must be admitted as an estabhshed fact. It is possible that in some instances the organic substance has a coloiu' of its own ; for instance, Ehrenberg describes Amoeba pynnceps as having a yellow colom\ However, in general the occiuTence of coloiu- is consequent on that of granules, and on the introduction of food ; and obsen-ation proves that the depth of coloui^ augments ^^ith age, and is otherwise in direct relation with the abimdance of food. The coloui' is usually pretty uniformly diffused. Schultze shows this, and also its relation with the thickly- distributed minute granules, in many Miliolidce, Rotalidce, and Gromice. In larger species (he adds), such as PoJystomella strigilata and Gromia oviformis (XXI. 16), the colour occiu's in scattered and much larger particles or vesicles ; yet under what form soever foimd, it is, in the case of the many-celled or chambered Foraminifera, deepest in the oldest cells, and progressively fades on aj^proach- ing those most recently formed, the last being commonly quite colourless (XXI. 28, 33, 36). Experiment also showed that, by depriving the animals of food wliich could convey colour, other chambers than the last lost their OF THE PROTOZOA. EHIZOPODA, 203 tint, and, vice versa, that by feeding- tlicm abundantly vnth such food, even the animal substance of the ultimate cell acquii'ed coloiu*. Irregular accu- mulations of colouring particles in the ultimate chamber are of rare occur- rence. Ehrenberg has iigiu^ed such in Nonionhia germanica. The colomiess, or almost colourless Ehizopods, principally Amcehce, are, owing to their transparency, visible with difficulty, and require nice adjust- ment of the microscope and of the light to demonstrate their vitality and movements. Concerning the chemical relations of the organic substance, it is stained yellow or yellowish-brown by solution of iodine, like other proteine matters, and, according to Schultze, is unaltered by diluted acetic acid, is slightly hardened by a dilute solution of the alkahes, and more so by one of the car- bonates. Moreover, its resistance to chemical action would seem to differ in different species ; for the Gromia Dujardinii was the least affected of se- veral animals experimented on. ''The colouring-material," to quote the same writer, *' assumes by the action of sulphiuic and of hydrochloric acids an intense verdigris green, and by that of nitric acid, first a green and then a yellow tint. Concentrated sul- phuric acid destroys the colouied substance, but when combined -svith sugar, renders it green. By concentrated solutions of potash and soda, the coloui'ed granules are dissipated without change ; and in ether and alcohol they are readily and completely dissolved. In these reactions the coloming-matter agrees with Diatomece, from which, no doubt, it is derived in the form of food." jS'o definite figure can be said to belong to the animal portion of the Rhi- zopoda, owing to its capability of thro'wdng out processes in every direction, of various dimensions and in different numbers, changing them almost every moment. Auerbach, however, asserts of the Amcehce that they have normally a spherical figiu^e. Dr. Bailey has pointed out the influence of pressure from within, due to the various articles swallowed, in modifying the figure. The Amoebce, being untrammelled by a shell, exhibit the Protean changes of form in the highest degree, whilst the completely enclosed Foraminifera present them in the lowest. In the latter the organic mass must follow the windings of the canity of the shell (XXI. 24), and can escape only from the foramina (holes) as thread-hke filaments, in the form, extension, and subdivisions of which great latitude prevails. We have said that the sarcode of FoJythala- mia follows the windings or adapts itself to the figure of each segment of the shell, and has actually no figure of its own. However, when separated from its calcareous investment by means of an acid, it retains the outline originally imposed on it. ThiLS (XXI. 24) Schultze exliibits the sarcode substance of a Miliola so separated, which shows a constriction at each half turn of the spii^al and the deheate membrane which invests it or lines the shell. So, again. Dr. Carpenter, in his description of Orhitolites, states that the soft sarcode body is made up of a number of segments equal and similar to each other, and arranged in concentric zones around a central nucleus. Among the Amcehce the varia- ble processes may either be protruded at one time from eveiy portion of the little mucous mass, so that, as Ehrenberg remarks of the Amoeba rcaJiosa, it may, when fully outspread, be likened to a miniatm-e porcupine ; or, othei-wise, they may be produced chiefly or entirely from one side ; or, as when the ani- mal is moving, they are thrown forward in the direction it is progressing, and retracted on the opposite side. Among many Monothalamia the bulk of the Hying mass issues through the one large orifice, and can spread out in a similar manner to the free Amoehhia, — the shell, according to the direction of the pseudopodes, resting in the centre of the mesh or on one side. The Forami- nifera have a like capacity of extruding their processes in one direction rather 204 GENEEAL HISTORY OF THE INFUSORIA. than in another, or in all directions together ; and acciiraulations of their mucous substance, or fusions, may take jjlace on any one side. In this family the fiHform fibres are, as a rule, not seen protruded at any one time through all the pores perforating the shells. Many genera have, besides the generally- distributed small foramina, a larger orifice in the ultimate chamber ; such is seen in Botalia and Textilaria. In these, says Schultze, it may be remarked that the jDi'ocesses fii'st throAvn out come principally from the large openings, and frequently a considerable time elapses before the numerous fine pores give exit to fibres. Often, again, the filaments are extended only from the two or three last-formed cells. Yet after long lying imdistiu-bed, fibres may be seen proceeding from eveiy part of the surface of the finely porous shells. Still the question requires further examination, to decide whether the processes can be extruded through all the foramina or only thi'ough some of them in certain places. However, as Schultze remarks, the universal porosity would seem without a purpose if it does not give vent to the contained substance at all points. The processes of PoJytliaJamia attain the greatest length and fineness, and often constitute a network of several hues in diameter, — the shell of the ani- mal occupying the centre, like a sj^ider lodged in the middle of its web. The length of such fibres not imcommonly exceeds twelve times the diameter of the shell. The processes of most Monotludamia are not so numerous, and do not equal on an average those of the Pol y thai cmiia, whilst those of the Amoebce are mostly shorter and broader. The length, number, and fineness of the processes, together with theii' mode of termination, supply, under considera- ble hmitations, characters for distinguishing species chiefly of the Amcebina, and, in a less degree, of the single- chambered testaceous Rhizopoda. The ever-fluctuating form of the animal mass and of its processes is ex- pressed by the term "■ ijolymorphism,'''' It is, as before noticed, a well-marked character of Bhizoj^oda, although not restricted to them ; for the like is exhi- bited by the yolk-cells of Planaria, and by detached fragments of the substance of Hydra ; in fact, illustrations are not wanting in the vegetable kingdom. The phoenomenon of polymorphism would seem to discountenance the hy- pothesis of the presence of a limiting membrane or skin. Ehrenberg described a resistant, very elastic, and contractile integument, and, to explain the vaii- abihty of figure and the extension of the pseudopodes, supposed a relaxation or suspension of the natm^al contractility of the integ-ument at the extending point, and a consequent passive yielding before a pressure from within exerted by the contained substance. This explanation he endeavoured to illustrate by comparing the process with the formation of a hernia or rupture, — a com- parison, by the way, involving an effort of imagination to discover any simi- larity between the two occurrences. Thus he remarks of Aiyioeha princeps that " its normal shape, if such it can be said to possess, is globular ; but it can relax any portion of its body, and contract the rest, so as to force the in- ternal substance do'wn into this relaxed portion, which thus becomes, as it were, a hernial tumour." This notion is opposed by the results of observa- tion. The very characters of the processes, their great length and frequent tenuity, their branching, adhesion, and coalescence contradict the assimip- tion ; and the fact of their not uncommon extensoin from all sides of an ani- mal involves, as a consequence of Ehrenberg' s hypothesis, a behef in the exertion of internal pressure in opposite dii-ections at the same time. Other evidence of the error of this h5q)othesis is found in the following facts, ^dz. the adhesion and entrance of foreign bodies at any part of the sarcode sub- stance, the cohesion of two individuals, and that, as pointed out by Dujardin, when the gelatinous mass of an Amoeba is torn or cut across, no escape OF THE PROTOZOA.-— EHIZOPOD A. 205 of a contained softer matter or of grannies takes place, but each segment con- tracts on itself and continues to live, and, again, that when a Rhizopod is shaken about, its processes become flexuous, and float loosely instead of being vvithdi'avvn within the general mass, as should happen if a general contractile integument enveloped it. Among the Amabel generally, a distinct hyaline cortical substance is found enveloping the interior more fluid matters, and restraining their escape. (See afterwards, on shells of MonotliaJamia, excep- tional forms noticed by Dujardin and Bailey, and the researches of Auerbach.) Although an integument be, therefore, no part of the structui^e of Rhizopoda, yet their soft substance is capable, as is shown best in the Amoeb'ina, of resist- ing internal pressure, such as that from silicious shells of DiatomecB and other hard substances, which oftentimes cause irregular and sharp projections during the movements of the animals, but yet very rarely perforate them. On the other hand, Rhizopoda become sometimes impaled upon the rigid fibres of plants or other substances, and, though thus transfixed, will move fi'om one extremity to the other, without any apparent inconvenience or injury. This cii'cumstance has been long noticed in the case of the Amoehce ; and Schultze has figured a specimen of a testaceous Rliizopod — the Gromia Dujcuxlinii — penetrated by a large curved hair. Dr. Auerbach, in a recent Essay on the AmoehaKi {Zeitsclir. 1855, pp. 365- 430), has advanced the statement, from observation, that all the Amcebce are enclosed by an adhesive, elastic and structureless membrane or integument. This fact has, he says, been so universally overlooked by reason of the diffi- culty in determining it, and, where caught sight of, has been misinter- preted, as, for instance, by Schneider {Midler's Arcliiv, 1854, p. 201), who represents Amoeba enclosed by a membrane as being in a state of " rest," or encysted. Auerbach makes particular reference to two new species discovered by him, as illustrative of the presence of an integument, ^dz. A. bilimbosa (XXII. 7- 11), and A. act'mojyliora (XXII. 13), in both of which he detected a double peripheral line. But besides this e\idence he appeals to the eff'ects of reagents, of acetic or of diluted sulphuric acid and alkahne solutions, both on the species just cited and on others well known — for instance, A. iirinceps — in demon- strating the membranous investment. And what seems at least very strange, we might say quite inexplicable, he asserts that upon all the processes, how- ever branched, anastomotic, or fine, this membrane is extended to their very extremities ; for on adding a dilute alkaline solution to Amoeba radiosa, the granidar and molecular contained mass became shrunken, and retreated to- wards the centre, leaving the figm^e of the animalcule with all its processes as before the addition, the latter appearing as tubules mth closed ends, which ruptured by over- extension. This same author accoimts for the entrance of solid particles from without by imagining the integument to rupture to receive them, and then to close on them so as to leave no trace of the proceeding. Fui^ther, the membrane is not soluble, at the ordinary temperature, in acetic nor in mineral acids, nor in dilute alkaline solutions, and therein agrees with the tissue noticed by Cohn in Paramecium and other Ciliata {vide chap, on Ciliata), and with the cell-membrane of animal cells. These observations of Dr. Auerbach are well deserving attention, although we are indisposed to accept them in their entirety. The wonderful poly- morphism, the coalescence of processes, and the particulars alluded to above (p. 204) as inconsistent with the presence of an integument need not be again adduced in argument. What is desirable is, that observations should be multiplied on this subject, which is one that strongly commends itself to 206 GENEEAL HISTORY OF THE INFUSOEIA. the notice of microscopists on account of its bearing on the question of cell- constitution. The variable processes serve the Rhizopoda for locomotive organs. An ex- pansion is thro^vn out in advance, into which a constant influx of the sarcode substance sets, — whilst in the opj^osite direction a counter- current occurs, effecting the retraction of the posterior processes. This onward flow of the substance of the body proceeds until at length the whole is transferred into the advanced process, mo^dng from its base to its termination. In this manner the animal progresses, the space passed over equalling the length of the ex- pansion it protrudes. This method of locomotion may be designated creep- ing or crawling, and is the only one with which this class of animals is en- dowed. The consequence is that they are, as a rule, to be only foimd adherent to solid bodies, and cannot move by swimming. However, they can move as passive particles of matter, be rolled along by currents upon any substance they are in contact with, or, from being (as in the case of Amoeba) of almost the same specific gra\'ity with the water in which they hve, may float, or be suspended in it for a long time. Theii^ motion by creeping is exceedingly slow, and oftentimes is appreciable only by attentive watching. The graphic description of Schultze, of the expansion of processes in a naked Amoeba and in a testaceous species, viz. the Gromia oviformis, will make the phaenomenon more distinct. The former is a new species discovered and named by himself the Amoeba porrecta (XXI. 3). It is distinguished from other species in the genus by the great extension it is capable of, and by the lively motile energy of its contractile substance. " It sends out from its colourless body, on all sides, numerous fibrous processes, short and broad on theii' fii\st extrusion, but which gradually elongate until they exceed the diameter of the body eight or ten times, and taper to such fine extremities that a mag- nifying power of 400 diametei^ is needed to distinguish them. The figui'e and extension of the body change every moment, according to the side in which the ramifications are extended. If two or more of the filiform pro- cesses touch, a coalescence takes place, and broader plates or net-like inter- lacements are produced, which, in the continual changes of figm^e, are either taken up again into the general mass, or otherwise are fui'ther increased by a fresh influx of matter, until finally the entire body is transposed to their place." In the testaceous Gromia ovifornnis (XXI. 16), after a state of rest of some dm^ation, fine fibrous processes are seen to be extended from the single large opening of the shell, which, on their first extrusion, move about in a groping manner until they lay hold of some solid body (such as the siuface of the glass slide) on which they may stretch themselves out, receiving in the meanwhile new matter from within the shell. The first fibres are extremely fine ; but pre- sently they grow wider, and proceed to elongate themselves, pm^suing a straight course, ramifj-ing in their own way and coalescing with adjoining processes, until, becoming progressively finer and finer, they attain a length exceeding that of the body six or eight times. The fibres having now outstretched themselves in eveiy dii^ection, and absorbed the greater part of the finely- granular contractile substance, their further extension in length ceases. However, the reticulations go on miiltiplying ; numerous bridges (inoscula- tions) are estabhshed between them ; and by the continued changes of position a constantly shifting protean web is produced, where a greater number of fibres come together at the periphery of the sarcode-net as we may term it, broader plates (lanunae) of the perpetually-flowing substance are formed, from which again new filaments are pushed out in new directions, as if it were a separate Amoeba. In the PoJi/stomelhe, the long fibres are seen to converge to form a pyramidal i)undlc, and to coalesce into wide laminte at its apex. OF THE PROTOZOA. EHIZOrODA. 207 Dujardin made some precise observations respecting the characters of the locomotive variable processes and the rate of movement. In Gromia oviformis, he describes a filament to begin as a very fine simple and imiform offshoot, which elongates and directs itself in different directions, in order to seek a point of attachment ; sometimes it oscillates, at others it exhibits a tolerably rapid nndiilatory movement, or, otherwise, it rolls itself up in a spiral manner, when the several coils coalesce, and a mass is formed capable of throwing out afresh other processes. Proportionately to the extension of the filament, its substance is added to by an afliux of new substance from the chief mass, evi- denced by the movement of irregular granules, which give the fibres an un- equal and nodose appearance. Moreover, the fibre gives off branches here and there at a more or less acute angle, which, in theii' tui-n, ramify after the same fashion, and establish communications or anastomoses with one another. Often also films or laminte of the gelatinous substance form at the extremities of contiguous fibres, which extend themselves variously. The filaments retreat by an inverse movement ; and this is occasionally so sudden that the end as- sumes a button-like termination from the fusion of the mass of matter engaged in its formation. The expansions of M'dlola, he fiu'ther tells us, are six times finer than those of Gromia, and the movement of the animal more rapid ; for during summer it moves from about -^^ih to ^th of an inch in an hoiu-. CristeUaria moves -J-th of an inch, and Vorticicdis from -^th to -^rd of an inch in a like period. The variable processes also constitute the prehensile organs of the Rhizo- poda. Any small objects serviceable for nutrition, with which they come into contact, are laid hold of by them apparently by means of their viscid surface ; and, except they are animalcules of considerable size and power, they are un- able to escape. When a filament or, as we may call it ^vith reference to this function, a tentacle has so seized its prey, adjoining fibres aggregate about it and coalesce, a current of the viscous substance sets in towards the spot, and very soon envelopes the object by a fJm. The prey being thus secured, the processes shorten themselves and di^aw it towards the chief mass or body of the animal, or, otherwise, the object seized continues in the same i>lace, and the whole organic substance moves towards it, — the result being in either case that it is engulfed. In the Amoehina this prehensile act proceeds as just stated; in the Monothalamia and in those Foraminifera having a large opening in the last chamber, the body seized is directed to the large orifice of the shell ; but in those having no other than fine pores or minute fissures, it would not seem to reach the general mass, but to be used up for the jDur- poses of nutrition externally to the shell, by a digestive action inherent in the fibres themselves. The mode of entrance, therefore, of food within the Aiscid organic matter, is not so simple and mechanical an act as Dujardin re- presented it, but has much mxore of a vital character. This observer's state- ment was, that the mere pressure of the body of the animal on the smface it moved over caused the penetration of foreign matters, which, by subsequent extensions and contractions of different parts of the substance, became at length completely involved in it. It would seem that animalcules may swim about unharmed within the meshes of the sarcode-web, but that so soon as they touch one of its fibres, they are as it were paralysed and incapable of further motion, and are consequently dra^^m deeper into the net without any opposition. Sehultze, who has noticed this circumstance, believes it to be quite exphcable as a simple mechanical act, and no proof of a special be- numbing property resident in the soft substance as Ehrenberg was inclined to suppose. Food, or indeed any extraneous matters, may enter the soft bodies of Rhizopoda at any point of their surface ; ?. e. in other words, those 208 GENERAL HISTORY OF THE INFUSORIA, animals have no definite aperture for food — no mouth. This absence of a mouth, on anatomical grounds alone, involves that of an alimentaiy canal, or of a polygastric structure such as Ehrcnberg imagined. The digestive cells, so called, of Arcellina are nothing more than hollow spaces or vacuoles (XXII. 7, 8, 9), which spontaneously and irregularly develope themselves in the mu- cous sarcode substance. They especially make their appearance after the in- troduction of food, the particles of which generally appear enclosed within them, and to be surrounded by a fluid. In the allied organisms represented by Actinophrys, M. Claparede states that the particle of food always hes in a cavity filled with fluid — a vacuole, — and that the fluid is of a pale reddish colour, with difterent refractive powers to those of water, and is in all proba- bility a solvent or digestive fluid. This pale-red or reddish-yeUow tint of the vacuoles is remarked also in Amoehoi ; and the observed dissolution and eventual disappearance of organic matters absorbed is a sufficient proof of the presence of a digestive secretion. In an Arcella vulgaris, Perty witnessed the successive appearance of four vacuoles, each in its tiu^n enlarging from a small roimd to a large reniform space, and thereby expanding the dimensions of the animal itself. He believed them to be filled with air, and, like the air-bladders of fish, to serve to float and tm^n the animals in the water, when free and without solid objects to crawl upon. Ehrenberg states that in some Arcellina, where " digestive sacs " were otherwise invisible, they were brought into view by feeding the animals with coloured substances. He thus presumed on the prior existence of these cells, supposing the colouring particles to be merely the means of bringing them into view. The true explanation, however, is, no doubt, that the con- struction of vacuoles is consequent on the introduction of food, and de- pendent on the manner in which the animal substance enfolds the solid par- ticles which it has seized. Obsei-vation, indeed, proves that the vacuoles have no constant and definite existence and position ; for they coUapse and disappear when the contents are removed or are reduced to a few fine granules dispersable in the common mass. They also constantly shift their position, and not unfrequently make their way to the siuface, at which they bluest and disappear. As Dujardin also remarks, they sometimes form at or near the surface, and may even serve as a medium for introducing foreign matters into the body. Dr. Bailey, in his description of a new species which he names pampTiagus, represents it as having (although a shell-less Rhizopod) a mouth from which alone pseudopodes protrude, and a single stomach ; hence, he adds, it cannot be considered po7^(7asfr?c. However, no evidence is adduced to support this notion of a gastric cavity ; on the contrary, indeed, the details given stand opposed to such an hypothesis, — for instance, to quote only one, that of their being frequently seen transfixed by dehcate fibres of foreign matters, and moving unharmed up and down them. Schultze states that in Foraminifera veiy clear vesicles are uniformly diffused throughout the body, some entirely homogeneous, others finely granular, or filled mth corpuscles. However, nuclear corpuscles, which can be regarded as cells in the ordinary signification, are never found. This naturalist, moreover, indicates the existence of a larger species of vesicles in Gromia oviformis (XXI. 16), containing other clear corpuscles, sometimes to the number of eighteen, but never strung together ; he believes Kkewise that similar vesicles exist among other Fora^nimfera, and seems disposed to attri- bute to them a nuclear character. Ehrenberg professed to discover in the Polytlialamia, in each chamber, saving the last, an alimentary tube, having a greyish-green colour and very OF THE PEOTOZOA. RHIZOPODA. 209 thick. This intestinal cavity, he affirmed, communicated with the cell in front, and the one next behind it by a narrower canal — the siphon, — and that in this manner a sort of continuous moniliform intestine was produced, extending from the primary to the penultimate cell. He adds that, after the solution of the shell of Nonionina Germanica by dilute acid, various sihcious Infusorial shells could be seen within this digestive tube, as far back in the animal as the fii^st chamber. Moreover, he was fortunate enough to be able, after the dissolution of the shell of Rotalia by acid, and by proceeding very gradually, to set fi'ee an internal, spiral, jointed body, the segments of which were strung together in Nonionina by one, and in Geojoonus by fi^om 18 to 20 tubes (siphons) ; strong acids destroyed the shell so rapidly that the con- tained delicate body became broken up into many insignificant fragments. In none did he succeed in introducing coloured food. This digestive apparatus others have sought in vain in the Foyximinifera. The spiral articulate body extracted by the Berlin naturalist from the shell, was undoubtedly nothing- more than the soft animal contents, somewhat acted on by the acid, such as Schultze has pictured from the cavity of a Miliola (XXI. 24). Eespecting the penetration of food to the primordial chamber, which Ehren- berg imagined he had seen in Nonionina, Schultze observes that, among the many beings he has examined, he has not detected nutritive matters fiu'ther back than the second or third cell. The substances received from without, after ha\dng served their purpose within the gelatinous body of Ehizopoda, make their way outwards and escape from any part of the siu-face, — an anus being, like the mouth, pro- duced temporarily, at any point whatever, where matters present themselves for discharge. The materials taken within the body of Rhizopods are most heterogeneous ; no selecting power being displayed by the animals, various Ciliated Protozoa, fragments of the filaments and spores of Algae, frustules of Diatomece and Desmidiece, even Rotatoria, fall a prey : but along with these, from which nutriment may be extracted, are other substances which can be supposed to serve no useful purpose ; such are particles of sand, morsels of woollen and of cotton tissues, and the like. The introduction of particles indiscriminately is explicable from the mode in which they are eaptm^ed by the filamentary arms, which seem to act in a prehensile manner, on feeling the contact of any foreign object, be that what it may. Dujardm threw doubts upon the nutritive purpose of the solid objects swallowed, and supposed the act of nutrition consisted in the simple imbibition or endosmosis of fluid from without. " It is," he writes, ^' difiicult of belief that these included particles, by reason of their consistence and the unalter- abihty of many of them, can serve to nourish the Amoebce ; yet, whilst admit- ting that they are nourished by absorption, I would not deny that they may find means of stiU more readily appropriating nutritive materials, by swallow- ing various foreign bodies, and by so increasing their absorbent surface." The evidence of direct observation, hov\^ever, is in favour of the conclusion that the substances received within the simple animal mass actually afford ma- terials for its nutrition. The contents are ever changing and making their exit from it ; and an act of digestion or of solution is perceptible — slow, indeed, even when soft Ciliated Protozoa are the subjects. Thus animalcules, when within the sarcode mass, are first compressed into small balls ; the distinct- ness of their parts then fades, and they are presently converted into small gelatinous globules, which in due course disappear, from amalgamation with the enclosing substance. Where the included body consists partially of insoluble material, this remains behind in the form of fine granules, or, in p 210 GENERAL HISTORY OF THE INFUSORIA. the case of the silicious- enveloped Diatomece, the dense skeleton, emptied of its organic contents, continues visible for a longer or shorter time. The robbing of the frustules of Bacillaria, and the appropriation of their coloured endochrome, has been referred to in the foregoing remarks on the colouring of Rhizopoda (p. 203) by the green colouring-matter of plants. The Rhizopods Bailey describes were met with in a vivarium, into which " bits of boiled beans and potatoes had occasionally been introduced as food for other animalcules ; .... on the application of tincture of iodine to these animals, a distinct blue colour was often seen diifused over the whole surface of many of the grains of sand in their stomach." The above facts — to which we may add another, viz. that the abimdance of granules in the interior is in direct proportion with that of food — furnish sufficient proof of the occurrence of a digestive faculty, and of a power of assimilation among the Ehizopods. This imphes the existence both of a digestive fluid, and of a secretory fimction ; the latter, too, is further ex- emplified by the production of shells in the majority of the class. Auerbach (op. cit. p. 422) distinguishes two leading varieties of granules in Amoehce : — one of a pale colour and finely di^dded, and either soluble in alkalies and acids, and tui'ned brown by iodine, or, more rarely, insoluble in alkalies ; the other, dark in hue, strongly refracting, and usually corre- spondent in number and relative size with the animalcules to which they appertain. These latter have the aspect of fat-molecules ; are spherical or elliptic, or at times crystallized in a rhombic form ; and they are easily soluble in cold alkaline solutions, and more slowly so in concentrated acetic and sul- phuric acids. In one species, A. bilimhosa, he met with starch globules ; but these were probably of extraneous origin. Movements of contained particles. — Every movement of the mucous sub- stance of Khizopoda is accompanied by one of the granules, and of the small vesicles or globules contained within it. This motion of the contents follows a certain course, and is especially observable in the outstretched variable pro- cesses. Schultze thus describes it in the large Amoehctpor recta : — '' A continued current of the granules, imbedded in the contractile substance, accompanies all these phenomena {yiz. of polymorphism) ; and, in the processes, this cuiTcnt follows two directions ; thus the globules may be seen advancing on one side, towards the end of the process, when they turn round to the other, and are carried Tvith a comparatively more rapid motion back towards the base of the filament, where they are lost in the substance of the body, unless they happen to meet another stronger stream by which they are reconveyed through the same circuit." A precisely similar phenomenon is witnessed in the testaceous E-hizopods. Thus in Gromia oviformis, Schultze says, the granules are seen to depart from the substance within the shell to the end of the filaments, and thence to retui^n again to the point from which they set out. This circula- tion goes on in every process ; but it is in the broader filaments, containing numerous granules, that the double stream is chiefly visible : for in the finer ones, whose diameter is often less than that of some of the corpuscles, it is more rarely seen ; in fact, in the latter the granules seem not to be included within the substance, but to be transported on the surface. Oftentimes a corpuscle, on arriving at a point where a fibre bifiii'catcs, is arrested for a time, until di^awn into one or other current, — whilst at the bridge-like con- nexions between adjoining filaments, where the granules pass across from one to the other, it not unfrequently happens that they are transferred from a centrifugal to a centripetal stream, and are consequently turned back again towards the body. Moreover, in the broader processes, granules are observed to come to a stand, to oscillate for a time, and at length to take a retrograde OF THE PROTOZOA. RHIZOPODA. 211 coui'se. Since there is no appreciable distinction of tissues, not even of integument and contents, the existence of vessels to account for these cui^- rents cannot be presumed. A cimous exception appears to exist in Gromia Dujardhiii, the filaments of which exhibit no granules, but are perfectly hyaline, and moreover show no circulation. In their transparency, Sohultze remarks, they resemble the processes of Arcella and Diiffiugia, and so also in the matter of breadth, but differ by their greater length, their finely-pointed extremities, and by their frequent ramifications. This species has also in its principal mass pecuKar coipuscles, roimd, oval, or iiTegular in figure, with a sharp outline, and of a bro"svn coloiu-, differing fi^om all other known elementary particles in chemical reaction, in resistance to alkaline solutions, and to mineral acids, even to sulphuiic. Amid the many shifting corpuscles and small globules is a large vesicle, constant in position, alternately collapsing and dilating, and hence called the contractile vesicle (XXII. 4, 5, 6). This organ, which is homologous with the pulsating sacs of Ciliated Protozoa, has not been remarked by every observer, nor in many of the Rhizopoda ; nevertheless we presume it to be an essential organ, and its existence general in the class. Li Arcella a con- tractile vesicle has been seen by many ; in Actinoj)hrys Sol, Claparede has satisfactorily proved it a true sac, ha\ing a resistant membranous wall, and has counted as many as ten such vesicles in Arcella vulgaris ; Auerbach treats of the vesicle as general among Amoehcea ; on the other hand, Schultze was imable to discover such an organ among the many Foraminifera he examined. I^iJCLEUs. — Another definite body is mostly chscoverable in Ehizopods, viz. a nucleus in the form of a more or less rounded or oval body, more opaque than the rest of the contents, and consequently more solid in appearance (XXII. 4, 5, 9, 16, 20). In Amoeba and Arcella, Ehrenberg and Siebold admitted the existence of a nucleus ; Schneider says that Amoeha cliffluens and A. racliosa possess one, that a round reddish nucleus having a white nucleolus is present in Difflugia at its hinder end (XXI. 19 a, b,f), and that probably aU the Rhizopoda have such an organ. Kolliker, to whose hypothesis of the ceU-natiu-e of Rhizopods the recognition of a nucleus was of much importance, remarks, " with respect to the nucleus, it really appears to be present in some of them (see Ehrenberg' s figures) ; and where it is want- ing, as in Actinophrys, a true nucleus may have existed at an early period, and be absent only in the full-grown animal, or, again, it may be entirely wanting, and still the animal be regarded as a cell." Claparede, on the contrary, denies a nucleus to the naked Rhizopoda, at least to Amceha dijfluens ; and hkewise to the testaceous species, such as Arcella. However, he admits that the usual opacity of the shell is an obstacle to an accurate determination of the question, and remarks, concern- ing the foregoing supposition of Kolliker, that there is no evidence of its truth, and no foundation in fact. Schultze has encountered an undoubted nucleus in nine different species of Amoeba, in Diffliigia proteiformis, D. acuminata, and D. Helicc, in Arcella vulgaris and several species of Euglypha. In Ch^omia oviformis a round, clear, delicate body fiUed with very transparent small vesicles may always be found. In old full-grown individuals not one but several such bodies are seen at the posterior part of the animal, all of equal size and of similar struc- ture (XXI. 12, 13, 14). In one specimen as many as eighteen of these nuclei were counted. In young small Gromicf only one nucleus is seen; in a solitary instance two were found. p2 212 GENERAL HISTORY OF THE INFUSORIA. In Difflugia ^roteiformis usually several (8 to 12) nuclei are perceptible, as in Gromia oviformis, in the j)osterior portion of the shell. The nuclei of freshwater Ehizopocls either appear to be homogeneous deli- cate elastic globules, here and there finely granular, or they resemble the nuclear body of Grojnia oviformis, and consist of a group of small vesicles or globules enclosed by a common membrane (XXI. 14). The single nucleus of young beings, Schultze supposes to be derived from the parent animal ; and he fiu-ther presumes that, in the coiu'se of age and growth, this organ is capable of multiplying itself, and may, moreover, serve as a centre aroimd which the fine graniiles of the li^-ing contents aggregate, and that, after the formation of an enclosing membrane, an embrj'o is generated from it. On the other hand, this careful obsei'ver was not able to discover a nucleus in Foramimfera, and admits that the above suppositions are highly doubtful. In a large specimen of Gromia Dujardinii, Schultze met with certain en- closed bodies, having a firm shell and granular contents, and only wanting a mouth to complete their resemblance to the parent animal (XXI. 18 a, b). He also cites, as still more questionable examples of a nucleus, a clear spot in the fii'st chamber of Rotalia veneta, and in Textilaria picta, a finely-granular, sohd, and nucleariform body in each of the two last cells (XXI. 32). On this point, the presence of a nucleus in Foraminifera, we have the state- ment of Ehrenberg, that in each cell, except the last, there is a coarsely granular yellowish brown mass, which represents an ovary in structiu^e and function. Unfortunately, however, the Berlin microscopist stands alone, both in this observation and in its pendent corollary. Dr. Carpenter uses the word nucleus to signify the primordial mass of sarcode seen in the fii'st cell, of which all the subsequent chambers and their contents may be deemed the ofishoots. Scattered among the amorphous granules of the sarcode are, for the most part, numerous refracting coipuscles of less size than vacuoles, which are soluble in ether, and therefore concluded to be fat-globules (XXI. 14-16). There are also other molecules dissolved by caustic potash. It is these various globules and granules that some observers have esteemed to be ova, without, however, any countenance from facts for the supposition. To recui' to the naked Ehizopoda, Auerbach, in the essay before quoted, attributes a nucleus to the Amoebcva in general. He remarks that the sohd-looking organ, of a dull aspect and commonly spherical figui'e, noted by certain authors in some Amcebce, is rather the nucleolus than the nucleus, and that the latter is perceptible in the form of a hollow space, oftentimes having a ghstening rosy hue, which surrounds the other like a sac (XXII. 4, 5, 9, 10, 11). This sac is sometimes visible as a dark areola, but at others requires the operation of chemical reagents to reveal it, or will manifest itself in dead specimens when all the ordinary vacuoles have disapj)eared. At times, both it and its nucleolus have a dumb-bell figure, and thereby indicate the occurrence of the process of self-division. A similar nuclear sac is men- tioned by Schneider. As to its chemical relations, Auerbach found that both nucleus and nucleolus were readily soluble in alkalies, and that they became darker in dilute acetic or sulphuric acid, which also caused the precipitation of a finely-granular matter in the vesicular or saccular nucleus. In concentrated acids they fii^st expanded, and were subsequently dissolved. The generally- assigned character of the nucleus, viz. that it becomes darker on the addition of acetic acid, is true only when dilute acid is used. Auerbach discovers a nucleus and nucleolus in Arcella, similar to those OF THE PROTOZOA. RHIZOPODA. 213 of Amoebce, often displayed when, by a fracture of the shell, the animal con- tents escape. The nucleus has the form of a thick-walled sac, and encloses a large nucleolus. But it is remarkable that, whilst one or at most two nuclei only are discoYerable in Amoebce, several such organs are frequently present in ArceUce, theu^ number being in direct proportion with the magnitude of the animals. In large specimens, of i'" in diameter, above 40 such nuclei have been encountered. Reproduction of Rhizopoda. — This function is not satisfactorily made out, especially in the case of the Foraminifera ; what is known will best be de- tailed of each family separately. Among the Amoebina self-division has been noticed by Ehrenberg to occur in t\iQ Amceba prince])s; and Dujardin remarks that '^ they may doubtless multiply by spontaneous fission, or by the thi'o^ving off a lobe which imme- diately commences an independent existence." This separation of a portion of their substance is not unusual, as, when a large variable process has been shot out far from the chief mass and become enlarged at the extremity, the expanded end retains its position, whilst the portion connecting it vdth the body becomes finer and finer by being withdrawn into the parent mass, until it at last breaks across, lea\'ing a detached piece, which immediately on its own account shoots out processes, and manifests an independent existence. This phenomenon is therefore one of simple detachment, and cannot rightly be called a process of fission. Schneider terms it '' propagation by gemma- tion," and supposes it attended by a division of the nucleus, of which every such offset, in his opinion, includes a portion. This same observer fiu-ther states that Amoeba has actually a " state of rest " {i. e. an encysted condition). He observed it fii^st to become round, and then to form a fii^m membrane on one side, whilst the other portion continued its peculiar character and move- ments. By degrees the membrane extended itself over the whole body, the moveable portion constantly becoming smaller, until at last a completely- closed cyst was produced, in the clear interior of which a round nucleus, vdih. a reddish halo, exactly like that of Polytoma and other Monaclina, might be distinctly observed. He adds — " In the nucleus of Amoeba I have often noticed on the outer surface of the reddish halo, granulations which united to form a closed membrane, whilst at other times the nucleus exactly resembled that of Polytoma " (^. e. was without an enclosing membrane). What is the next phase of development following this encysted stage, Schneider has nothing to show. If Lieberkuhn's obseiwation be correct, a most extraordinary relation sub- sists between Amoebce and Oregarince, involving the existence of the former as a distinct class of animated beings. This observer saw the production of Amoebce from Navicellce, the origin of which from Gregarince is as good as proved ; and also met with such Amoebce in eveiy transition to perfect Gre- garince. This fact is alluded to in a paper by Kolliker (J. M. S. i. p. 212), who behoves the AnguiUula-like animal noticed by Henle, and termed by Bract Filar ia, to be an Infusorium aUied to Opalina Proteus, and goes on to say that the transition of this presumed F'daria into a Gregarina- and finally into a iV«y^ERAL HISTORY OF THE INFUSORIA. lleproduction by positive complete fission is opposed by the existence of the shell, which is a product from the siuface of the animals adapted to their outline, and increasing only in proportion with the augmentation of the animal substance. The cohesion of two or even more ArcelUna by means of their gelatinous substance, and often with the near approximation of the orifices or mouths of their shells, has been remarked by many observers, who for the most part have pronoimced it a sort of " conjugation," a true rejH'oductive act. Oohn has indeed designated it " copulation," and states it to be a general phe- nomenon among Ehizopods. He afih^ms that he has many times seen two Difflugice with the mouths of their shells so firmly connected, that strong shaking of the water about them failed to detach them ; and that likewise one shell was often empty, and the contents of the two aggregated into a globular mass in the other. Leclere, the fii'st describer of Difflugice, in 1815, noticed a like cohesion between two individuals of Difflugia HeJiv ; and Cohn, moreover, is able to confirm the fact represented by Perty of the cohesion of a brown and of a pale shell together. Schneider has likewise noticed this adhesion of two animals, and thus speaks of it : — " Tnie double animals of Diffiugia Enchelys are frequently met with (XXI. 19/), two bodies with membranous cases and nuclei being attached to a common foot. The foot veiy often consists only of a thin thread, but in other cases it exhibits all the forms which have been described as belonging to the foot of the simple animal. Both bodies are well filled vdih. food. Three, four, or five bodies are frequently seen hanging together in the same manner ; these, however, are by no means in the same plane, but stand out from the foot in various directions. If these animals are ob- tained in considerable numbers, the formation of these colonies by gemmation may easily be observed. The foot is seen gradually to increase in size, and acquire an oval form. A new investing membrane and nucleus are then formed. The offset is always equal to the parent-animal in size. Like the foot of a single animal, the common foot of two or more is, as might be suj)posed, still in a condition to form offsets." This adhesion Schneider prefers to consider an act of gemmation rather than of copulation, and sup- poses its occiuTence among other Ehizopoda. He adds, '' with Perty and Cohn I have also seen a pair of the Arcella vulgaris attached to one another by their openings, of which one (as was obsei'ved by those naturalists) was provided with a white, the other with a yellow shell. The white shell is probably newly formed, and therefore indicates the young specimen produced by gemmation from its companion." An aggregation of the animal contents of a Monothalamous shell, such as Cohn noticed in one of the two coherent Difflugice and attributed to an act of conjugation, Schultze has seen in Phizopods, quite independently of that phenomenon. In Lagynis Bcdtica, he states he has frequently seen the con- tents collected into a ball, having a clear speck in the centre, and situated at the posterior end of the shell, without trace of extended fibres ; and he adds, " the origin of this globular mass may be followed in a great number of individuals. The posterior portion of the transparent body of the actively- moving animal gradually becomes darker, owing to the advaneuig develop- ment of numerous molecular and strongly refracting particles. In the midst of this dark portion a clearer spot is always visible, although it cannot be isolated or more intimately examined. By degrees the dark portion en- croaches upon the entire substance of the body, and at last fills up the whole posterior portion of the shell, the body of the animal thus seeming to shrivel up into the ball-like mass described." This process, observed in numerous OF THE PROTOZOA. RHIZOPODA. 215 individuals in different stages, Schnltze never saw accompanied by a con- nexion between two animals ; and he was not able to discover what subsequent changes awaited the spherical body produced. The phenomenon just considered appears to us to be analogous to the encysting process recounted by Schneider in the case of Amceba, and by Stein in so many Cihated Protozoa. Two other probable modes of reproduction are briefly noticed by Schneider, but requii'e to have theii^ existence confirmed by fiu'ther observations. " I have observed," he says, " another mode of propagation in our Difflugice ; and although my obseiwations have certainly not been frequent, they have been sufficiently satisfactory. After I had kept a great number of these creatui'es for some weeks in a clayey sediment, the substance of the body in all the individuals contracted into a ball. All foreign substances had previously disappeared. The ball, which had a fatty outline, then divided into two and four parts ; but the nucleus could not be traced dming this pro- cess (XXI. 19 d, e). This investing membrane fell to pieces, and the little spheres Avhich may perhaps be regarded as four quiescent spores, were no more to be seen. " Whether another circumstance observed by me has any connexion ^\dth the reproduction of Difflugia must be ascertained hereafter. In all the indi\iduals of Difflugia contained in one vessel, the substance of the body became converted into granules closely packed together, the form and the investing membrane being retained (XXI. 19 c). I often saw these granules in quick molecular movement in the interior of a sac, which appeared to be formed from the outermost layer of the body, but I watched in vain for any issue to this ; after moving about for about half an houi% the granules always became quiescent again." A note by Perty must not be omitted, although no considerable importance can be assigned to a solitary and ambiguous observation. That naturalist tells us he " once saw two round motionless animals within an Arcella vul- garis, each having a much greater diameter than the mouth of the sheU con- taining them. Were these," he asks, " young beings to be set free on the death of the parent and the breaking up of the shell ? " A somewhat similar fact is recounted by Schultze of Gromia Dujardinii, in one large specimen of which he found several oval bodies enclosed possessing a firm envelope and granular contents, and representing in every respect young Gromia, except in ha^-ing no evident opening in their shell, which, however, may possibly be formed when set free from the parent (XXI. 18). That the piu-pose of the nuclear bodies in Gromia oviformis (see p. 211) is not connected with the function, Schultze feels compelled to assume, princi- pally from the absence of such nuclei in Ehizopoda generally, and from his having failed to observe their undergoing those changes known to occur in true nuclei when the generation of new individuals is in progress. Yoimg Arcellina, when first recognizable as such, have the general form of older individuals ; but theii' shells and tissues are much more transparent, and at first colomless and without granules. But it is very probable that the young of many Arcellina, when fii^st thrown off from the parent, are naked — destitute of shell, — a \iew supported by an observation of Cohn, who records having seen, amid the sUmy matter about living Difflugice, a large number of pecuHar animalcules consisting of a contractile greyish or bro^vn finely- granular substance, about J-th of a line in diameter and upwards, of a roimd, ovoid, or angular outline, and having a muco-gelatinous envelope, through, but chiefly at one end of which several fibres were extended. At a stiU earlier period these young beings may therefore be presumed to have been mere 216 GENERAL HISTORY OF THE INFUSORIA. sarcode-like particles or minute Amcehce. If this be so, some ground may be said to exist for the hyi^othesis of certain naturalists, who esteem the ArceUina, and even the Foraminifera, to be a more advanced stage of existence of the simple naked Amoehina. Schneider hints at the possibility of a still greater transformation in the case of his Diffiugia Enchelys. He writes — " A Ehizopod occurred in com- pany with Polytoma (see p. 136), the description of which Avill show how very readily it might be supposed to be produced by a metamorphosis of the latter animal. Unfortunately I cannot confirm tliis supposition, and must confine myself to recording the fact." Foraminifera. — It is veiy questionable whether the Many- chambered Rhi- zopods can reproduce themselves by off'shoots after the manner of Amoehina, and MonoiJialamia ; and, in short, nothing certain is known as yet of the modes of propagation of this family. A group of figiu'es occurs in Schultze's illustrations of Polystomella (XXI. 39) which bear on this point of the possible production of new beings by de- tachment of sarcode matter. The description of the figures informs us that some of the sarcode-globules, separated from the chief mass by pressure, have the tendency and power to thi^ow out from themselves contractile variable processes. They exhibit a finely-granular deHcate semifluid tissue, contain- ing many flat globules and large colom^ed vesicles. Other portions, pressed from the general mass, are almost exclusively composed of colouring-particles, derived from the inmost part of the shell ; such become entirely free, or othermse continue attached by a sort of pedicle. In the following examination into the modes of development of Polytlialamia we are greatly indebted to Schultze's valuable monograph. Dujardin men- tions seeing in some TrvMcatulinoi the grouping of the contents of the cham- bers into spherical masses, comparable to the green bodies in Zygnema. Schultze, moreover, encountered, in a deposit of living Foraminifera, along ^¥ith numerous empty shells of Rotalidce, several whoUy or partly filled with black globules, the appearance of which suggested their connexion with the reproductive process. Eepeated observation showed that these globules differed in size, but mostly had the diameter of the siphon intervening be- tween the several chambers, or of that of the opening of the last cell. They occupied either eveiy segment of the shell, when those of the innermost were smaller than those of the outer compartments, or otherwise they occiuTcd in only one or two of the ultimate chambers. Every intermediate condition was met with between these two extremes. The globules were composed of a collection of dark molecular corpuscles not enclosed by a membrane, but proved by pressure to be an aggregation, held together by some sort of delicate tissue. They were unacted on by sulphuric, nitric, and by hydro- chloric acid, and by boiling alkalies. The ordinary animal substance coexisted in some of the chambers of an animal when others were occupied by these black balls ; but in such instances no outstretched fibres were seen. These structures must be derived either from without as foreign matters, or otherwise be the result of a metamorphosis of the sarcode matter. The former supposition is discountenanced by their appearance, by their resistance to reagents, and their presence even in the inmost chambers. On the latter supposition they are either the result of decomposition of the substance, or they are physiological products, probably of the transformation of the entire body into germinal masses. The former origin is opposed by the direct observation that such bodies have never been en- countered among Foraminifera in coiu'so of breaking up or of decomposition. As to 'the second mode of origin, they bear an analogy to the germinal OF THE PROTOZOA. EHTZOPODA. 217 elements of Gregarince, viz. to the Navicelke developed from the contents of those animals, and to the brood of germs developed out of the contents of an encysted Vorticella : and it may so happen with the Foraminifera, that their entire substance is resolved into germs ; indeed, a progressive formation of such germs is intimated by the circumstance of the ultimate chamber being the last to become completely emptied. Although, therefore, the figure and size, the peculiar and successive empty- ing and distribution, the evident periodical appearance in the spring, and the analogy of other Protozoa speak for the hyjDothesis of these globules being reproductive germs, it must, on the other hand, not be concealed that their peculiar composition out of granules imperfectly bound together and enclosed by a membrane, and their remarkable resistance to the strongest acids and alkalies, are facts opposed to this supposition. Hoping to elucidate theii- purpose, Schultze, in some few cases, isolated those shells filled ^dth these black balls, but, after keeping them several weeks, could discover no change in them. Ehi-enberg siu-mised that the Polytlicdamia propagated by ova, and thought he perceived in them a sexual apparatus. On the surface of the shells of some samples of Geojoonus {Polystomellci) and Nonionina, from Cuxhaven and Christiania, he discovered stalked, yeUow, membranous sacs, which he repre- sented to be ova-sacs. When first thrown out they were soft and small, but soon swelled up and hardened in the water. Schultze also met with many specimens of Geoponus, at Cuxhaven, having Cothurnice afiixed to their shells, and of a yellow colour, which he believes Ehrenberg mistook for ova- cases. Being so unsuccessful by direct observation in his attempts to detect the method of reproduction among Foraminifera, Schultze endeavoured by an ex- amination of these beings in their earliest recognized form to gather some knowledge of it. The smallest and youngest beings he met with belonged to the families Rotalid(B and Miliolida}. Those of the latter family have a non- porous shell, and a spherical figure exhibiting the commencement of the spii^al winding which eventually extends to several turns (XXI. 20 a, h). The sheU- contents are quite coloiu'less, and present few granules. As the spiral winding advances, the contents of the first-formed orbicular cell acquire a darker colour from the appearance of fat-drops and sharply- defined proteine corpuscles ; and the sheU simultaneously assumes the characteristic yellow colour. The differ- ence in size of the primary cell in different species is remarkable. Still younger forms of Eotalidce occurred to him, 0*01 of a line in diameter, spherical, and colouiiess, with a delicate glass-Eke calcareous sheU, through the fine open- ings of which fibres protruded. Others also, entii^ely colourless, had a second chamber superposed on the first, or even three or four ; but in the latter instances the characteristic yellow hue made its appearance, and raj^dly in- creased on fiu-ther growth (XXI. 31). A striking variety was, moreover, remarked in the size of the first chamber, even in the same species ; the dimensions of the second and third cells were determined by those of the first. This great variation in size considerably lessens the possibility of the certain specific detennination of young specimens. From these researches it follows, that in MilioUdce and Eotalidce, and pro- bably in all other Pohjtlialamia, the first appearance of the animal is in the form of a colourless spherical mass, invested by a delicate calcareous waU, — the mass consisting of a homogeneous, sparingly-granular Amoeha-hodcy . This first-formed cell has the faculty of producing others like itself from those portions of its sarcode substance. Of the manner in which successive chambers are formed, we learn from Dr. Carpenter that the addition of new zones (in the Pohjtlialamia) probably 218 GENERAL HISTORY OF THE INFUSORIA. takes place by the extrusion of the sarcode through the marginal pores, so as to form a complete annulus, thickened at intervals into segments, and nar- rowed between these into connecting stolons, the shell being probably pro- duced by the calcification of theii' outer portions. Since the above account was ^viitten, Schultze has produced a supple- mentaiy sheet detailing further observations on the development of Forami- niffera {Bericht der Naturforschenden GeseUschaft in Hcdle, 11th August, 1855). Having met mth some large specimens of TrUocidina ^"' in diameter and without a tooth in the oral aperture, he kept them for a length of time under observation. Those which remained adherent to the sides of the glass vessel for eight to foui^teen days mostly became invested with a brownish slimy matter, which more or less completely obscui-ed the view of the external characters of the shell. After some more days had elapsed, the lens brought into view a num- ber of small, round, sharply- defined coi'puscles, which loosened themselves from the soft enveloping mass, and gradually diverged fi^om one another imtil some forty were visible. On removing these, and placing them imder the microscope, they proved to be young Mdiolidce, with their process outstretched. Inter- nally, neither vacuoles, cells, nor contractile vesicle, nor a nucleus could be detected. The brief abstract of Dr. Carpenter's elaborate essay (read before the Royal Society, 1855) furnishes us also with the following memorandum of hisAiews regarding the reproduction of Foraminifera, "svith especial reference to Orbi- tolites. " He is only able to suggest that certain minute spherical masses of sarcode with which some of the cells are filled may be gemmides, and that other bodies enclosed in firm envelopes which he has more rarely met with, but which seem to break their way out of the superficial ceUsj may be ova." Mr. Jeffrey's views {Proceedings of JRoyal Society, 1855) do not quite coincide. Dr. Carpenter's '' idea of their reproduction by gemmation," he says, " is also probably correct, although I cannot agree with him in considering the granules which are occasionally found in the ceUs as ova. These bodies I have fre- quently noticed, especially in the Lagence ; but they appeared to constitute the entire mass, and not merely a part, of the animal. I am inclined to think they are only desiccated portions of the animal separated from each other in consequence of the absence of any muscular or nervous structui'e. It may also be questionable if the term ' ova ' is rightly applicable to any animal which has no distinct organs of any kind. Possibly the fry may pass through a metamorphosis, as in the case of the Medusce.^' Of the many Amcehce seen in company with Foraminifera, the A. por recta is particularly remarkable, and might easily pass for one of the latter when young and destitute of its shell ; for its processes resemble those of Mdiolidce and Rotcdidce in delicacy and extensibility and in the cmTent of granules which passes through them. This circumstance suggests the possible deriva- tion of testaceous Rhizopoda from the naked forms ; and if we recall to mind the black globules sui-mised to be germs, their j^rimary transformation into Amoehce is imaginable, and the whole cycle of development of Foraminifera becomes thereupon explicable. *' However, I must," says Schultze, " confess that this change of the black spheres into AmoebcB is a further argument against their nature as germs, since between these granular bodies, so imaffected by che- mical agents, and Kmoehce no intermediate link is discoverable. Of the Shells of Testaceous Rhizopoda. a. Shells of Monothalamia. — The family ArcelUna (Ehr.) corresponds in most points with the section Mono- thalamia of Schultze. The Berlin Professor, however, believed that his family Areellina and the Polythalamia belonged to entirely different classes of ani- or THE PROTOZOA. RHIZOPODA. 219 mals, because, as he supposed, the Polyihalamia are aggregated animals with calcareous shells, and the ArcelUna solitaiy animals with a silicious testa. Subsequent researches prove, on the contrary', that all these difiPerential cha- racters are wanting. Each foraminiferous shell contains a solitary inmate ; and although, as a rule, of a calcareous composition, yet a genus, Polymor- phina, is pointed out by Schultze, which, as in the instance of Difflugia, has its testa made up of coherent silicious particles (XXI. 38). Besides all this, the shells of ArcelUna are not silicious, but of a chitinous nature, and the basement membrane in which the earthy matter is deposited in Foraminifera is the same. These circumstances, together with the homology in the animal contents both of MonothaJamia and of Polythalamia, the absence of the h^-po- thetical polygastric organization in the former, and of the imaginary internal structures in the latter, render Ehrenberg's distinction of the two families as separate classes imtenable. The ArcelUna of Ehrenberg, and the MonothaJamia of Schultze, do not en- tirely accord in respect to the genera grouped under them. Ehrenberg in- cluded in his family the genera Difflugia, Arcella, Cgphidium, and SpinlUna, The last-named genus departed much from the others by ha\'ing a marine habitat and a convoluted, sjnral, porous shell, — its only real relationship, it would seem, being comprehended in the one assigned feature, its sihcious lorica. On the other hand, Schultze (see tabular ^-iew of his system, p. 241), by not emplopng the chemical constitution of the shells as a distinctive cha- racter, includes among his MonotJialamia calcareous, membranous (chitinous), and such silicious shells as are exemplified by Dijflugia. The essential cha- racter employed is that of the imilocular chamber ; for the other nearly general feature, ^iz. the presence of one considerable orifice, is departed from in the instance of the porous shell of OrhuUna. The sheUs of Monothalarnia are of a more or less spherical figure ; some- times they are ovoid (XXI. 11, 12, 16) or pjTiform (17), at others compressed in one or other direction (XXI. 8), and even at times in opposite directions, so that .-everal faces are produced. Thus in the genus Difflugia the spherical out- line prevails (XXI. 10) : the sheUs are globose, or subglobose, or elongated in a pear-shape (XXI. 17), or in a club-Hke (clavate) manner ; in Arcella they are fi'equently compressed, and assume a more or less discoid figure, mostly convex above and flat beneath (7, 8, 9). In G-romia, again, the ovoid or glo- bular shape is diversified by the elongation of the portion about the mouth of the shell into a sort of neck (16). In Lagijnis (Schultze) this tapering of the oral end developes a retort-shaped sheU. In Squamulina (Schultze), again, the testa resembles a plano-convex lens. An exceptional form is described by Ehrenberg, under the name of Arcella disphcera, as oblong, almost divided into two by a central constriction. The first impression would be that the supposed species was no other than two animals coherent by the mouth of the shell ; that such, however, is not the ease is indicated by the next clause of the description — that one segment is nearly occupied by the large foramen. Another example of a remarkably-formed shell is afforded by Cii2:)hidium (XXII. 24-27), which Ehrenberg states to be cubical, with large protuber- ances, giving it in some positions a four-sided or an irregular figure. Again, in the genus Spirillina (Ehr.) (XL 37) and Cornuspira (Schultze) (XXI. 2b), we have examples of spii-aUy-roUed equilateral shells, like those of Planorhis. In consistence the shells of most ArcelUna are firm, mth a degree of flexibility and elasticity, and are composed of a dense membrane proved by its chemical properties to be of a chitinous nature. This shell not only resists the action of boiling solutions of the caustic alkalies and of vinegar, but also concen- trated nitric and chloric acids, and a mixture of the two, also chromic acid. 220 GENEEAL HISTOKY OF THE INFrSOEIA. in the solution of which chitine itself is dissolved. Further the shell is dis- solved in sulphuric acid, and, unlike cellulose, is not coloured blue by this acid. Such are the chemical relations of the testa of Gromia according to Schultze ; and such we may presume with him are those of the freshwater genera ArceUa, Eugli/jpha, and Trinema. The shells of Difflugia are peculiar by being composed in many species of a softer substance, to which various foreign particles, shells oiDiatomece, grains of sand and the like, adhere and thereby furnish an accidental or supple- mentary shield to the animals (XXI. 17). The substance on which those accidental matters are affixed we may presume to be chitinous, but not con- densed or hardened as in the tnie testaceous forms. Schultze is disposed to think that, besides merely agglutinated sihcious particles accidentally, as it were, appropriated, the investing tunic has actually the power of secreting sihcious molecules, represented by the smallest and most intimately adherent granules of the testa. He would also extend this hy[3othesis to the sihcious polythalamous shells, illustrated by Polymorpliina silicea (XXI. 38) and another newly- discovered species. Cohn apparently saw young Difflugice in the act of building their sheUs. These yoimg beings consisted of a mass of sarcode siuTounded by a muco- gelatinous envelope, through which fibres were protruded in different dii*ec- tions. These processes, by retraction, brought to the surface of the animal various foreign particles, which had become affixed to them, and were then imbedded in the mucous involucre. At length all other pseudopodes, save those from one extremity, were permanently withdrawn, and the exterior of the animal was clothed with a layer of silicious particles, grains of sand, shells of Cyclotella, and of other Diatomece, many of them of a blackish or brown colour'. Dr. Bailey indicates an exceptional tunic in a Rhizopod, having much of an AmoehaA^kQ character, which he names Pamphagus. It would seem to be enveloped by an integument, which, although resistant, admits of an immense modification of figure, both from external and internal pressure, and ofi'ers no impediment to the animal transfixing itself, just as if it were a completely homogeneous jelly. ''These creatures," says their discoverer, " connect the genus Amceba with Diffugia, agreeing with the first in the soft body without shell, but difi'ering in having true feelers or rhizopods confined to the interior part of the body." Just as in Difflugia, they are limited to the region of the mouth. From this last-named genus, " and from the whole family of Arcellina, these forms are distinguishable by having no lorica or shell." A very similar tunicated amoebiform animal is described by Dujardin under the name Corycia {A. S. N. 1852), which, although clothed by a membranous envelope, can be twisted and folded in every direction by the movements and contractions of the animal, and permits the extrusion of processes from any part of its surface. In this respect it differs from the Parnpliagus of Bailey, and certainly exemplifies a pecuhar phenomenon, which, in the case of the usual variable processes mth circulating contents, would not be conceivable, but become so upon the explanation of Dujardin, that they do not contract on adhesion to the surface on which the animal moves, nor ghde along it in the ordinary manner, but remain free, and, as we are told, seem only to serve to change the centre of gravity of the animal. ^' It must, therefore," says its describer, " form a new genus of Amoehina/^ intermediate between the naked Amcebce and the Arcellina ; and in another direction indicating an aUiance Avith the Noctilucida. With reference to these pecuhar beings, it is worth while to bear in mind the account given by Cohn of the development of young Difflugice and the OF THE PKOTOZOA. RHIZOPODA. 221 progressive formation of the shell. To recall the particular points of interest, in the primary stage the Difflugia was seen covered by an integument, but having processes extruded from various parts of its surface, so far resembling the Corycia of Dujardin, — whilst in a later stage all processes were withdi-awn, except Ithose at the one end where the single large orifice or mouth is placed, and thus came to resemble the Pami:>liagus of Bailey. Calcareous-shelled Monothalamia are represented by the genera Squamu- lina, Orhulina, and Cornusjmri. Such shells are brittle, and in all essential featiu^es resemble those of the next-considered family, the Fo7rim{nifera. The shells of Monothalamia are generally coloui'ed. When seen, as they often may be, empty, they have an orange-yellow, a bro^^m, or brownish-black tint. This coloiu' is acquii^ed by age ; the younger the being the less is it, ccetens parihus, colonized. In the youngest, as before noticed, the whole sub- stance and its commencing envelope are quite colourless. Most shells are also translucent or. diaphanous when empty ; but in others the colour is so deep, that, when filled, scarcely anything of the contained substance is dis- cernible through them. The testae of Difflugice are mostly opaque. The sur- face of the shells is subject to numerous modifications. Occasionally it is uniformly smooth ; but many, which so seem when occupied by the animal, are found when empty to be really finely sculptured (XXI. 11-15). Arcella liyalina is represented by Ehrenberg to have a smooth and coloui^- less testa ; A. vulgaris and A. dentata, one superficially divided into facettes ; A. aculeata, A. spinosa, and A. caudicola, a delicately hispid shell. Where the intersecting lines or ridges are not sufficiently developed to produce fa- cettes, they give rise to areolae and an areolated or reticulated surface. The surface is beset with rounded tubercles or eminences in Euglypha tuherculata, and by spirally-disposed polygonal depressions (alveola) in Euglypha alveo- lata (XXI. 11). In Difflugia acanthophora (Ehr.) (XII. 64), the surface looks as if covered by scales laid on in an imbricated manner and in. a spiral direction. The same species and Euglypha alveolata (XXI. 11) afford instances of testae armed with large and strong spines. This same Difflugia presents likewise an example of the mouth of the shell being strongly serrated. Several Arcellina have small depressions or pits on their sui'face, which at fii^st sight resemble pores, e. g. Arcella Ohenii ; and both this species and A. vulgaris, according to Perty, present very numerous striae diverging from the centre of the closed end, and concentric ciixles, the outermost of which in Arcella Okenii are dentated, and follow the stellate expansions of the shell (XXI. 15). Among Difflugice the shell is more often rough from the adhesion of parti- cles of sand and of other extraneous substances (e. g. in D. iwoteiformis, J). gigantea, D. acuminata), but in others consists of a smooth membrane, as in D. Enchelys, D. ohlonga, and D. glohidosa. Moreover, Ehrenberg enumerated D. ciliata, D. acanthophora, and other species as having an areolated surface, D. ampulla as punctated, D. dryas and D. reticulata as cellular, D. Bructerii as rugose, and D. striolata as striated. He further states that D. ciliata has a bristle or cii'nis in the centre of each posterior areola. Where spines or other elevations of the smface — or, in fact, markings in general, exist — they may not be imiformly disposed, but be produced in larger number or of larger dimensions in some parts than in others. Thus Ekrenberg signalizes an irregular disposition of the spines in Arcella aculeata ; and not uncommonly such processes are produced only from the vicinity of the mouth. These examples will sufficiently illustrate the diversity of sm^face jDreva- lent among monolocular shells ; but these shells moreover differ as remark- ably among themselves in size, figure, and character of the margin, and likewise in the relative position of their mouth, foramen, or orifice. These 222 GENEEAL HISTORY OF THE INFUSORIA. differences supply specific and generic characters of much vahie by reason of their constancy. Where the mouth has an even uninterrupted margin, it is said to be " entire." Its normal figure may be considered circular (XXI. 9). However, in many instances it is irregular (XXI. 15), or a projecting portion encroaches on it (XXI. 6). In Dijflugia depressa and I), gigantea it is uneven ; in Arcella lunata, semilunar ; in Difiugia ampulla, ovate ; in Splienoderia, so contracted as to be linear. Still more frequently the margin of the aperture is dentated or spinous : examples occiu' in Difflugia denticulata, D. Jmvigata, D. oligodon, D, acantlwpliora (XII. 64), and D. ciliata, in Arcella dentata and in EughjpJia. The symmetrical position of the mouth is wanting in several species ; and Schlumberger elevated this variation to the importance of a ge- neric distinction. The obliquity of the aperture — its position out of the median line — is noticed in Arcella Americana, A, constricta, A. ecornis, and in A. lu- nata, also in the genus Trhiema (Duj.) and in Cijplioderia (Schlumberger). WTien the mouth appears formed by the mere incompleteness of the outline of the shell, and is without a neck or deep margin, it is often said to be trimcate — in fact, the oral end of the shell is truncated or abruptly cut ofi" by the orifice. The shells of A^xellina may be fractured by pressure when the contained sarcode matter escapes through the fissures, extending itself in lobe-like pro- longations, which take on the characters of ordinaiy expansions (XXI. 7). Since the opacity of the shell is generally an impediment to the observation of the contained matter, its ruptui-e by pressiu'e, or its partial solution by some reagent, as sulphui'ic acid, which acts upon the chitinous basis, must be resorted to in order to discover the nature of the animal mass within. With or without such preparation, it is not unfrequently seen that the living mass is not uniformly adherent to the inner surface of the shell, but is, on the contrary, detached at different parts, leaving interspaces between it and the testa, varying in size and number. These vacuities may possibly arise from the detachment of the soft matter by reason of the quantity poinded out fi'om the mouth of the shell, or other^vise from the formation of vacuoles at those points, just as often happens on the surface of an Amceha. h. Shells of Polythalamia or Foraminifera. — These have a great diver- sity in figure and size, and are often veiy beautifully coloured and sculptm^ed. From the resemblance of many to the shells of Cephalopoda, especially to those of Nautili (XXI. 28), they were for a long time ranged along -^ith those highly- developed Mollusca. The shells of Polythalamia consist of a greater or less number, according to age and species, of communicating chambers or cells, aggregated together or superposed on one another in different ways, the mode of disposition, however, varying within certain limits even in the same species. Thus Dr. Carpenter, speaking of Orhitolites, says {Proceedings Royal Society, 1855), — " Starting from the central nucleus, w^hich consists of a pear-shaped mass of sarcode nearly surrounded by a larger mass connected with it by a peduncle, the development may take place either on a simple or upon a complex type. In the former (which is indicated by the circular or oval fonns of the cells, which show themselves at the sui-face of the disk, and by the singleness of the row of marginal pores), each zone consists of but a single layer of segments, connected together by a single annular stolon of sarcode, and the nucleus is connected with the first zone, and each with that which siuTounds it, by radiating peduncles proceeding from this annulus, which, when issuing from the peripheral zone, will pass outwards through the marginal pores, probably in the form of pseudopodes. In the complex type, on the other hand (which is indicated by the narrow and straight- sided form of the supei-ficial cells and by the multiplication of the horizontal rows of OF THE PROTOZOA. KHIZOPOBA. 223 marginal pores), the segments of the concentric zones are elongated into vertical columns, with imperfect constrictions at inter^-als ; instead of a single annular stolon, there are two, one at either end of these columns, between which, moreover, there are usually other lateral communications, whilst the radiating peduncles, which connect one zone with another, are also multiplied, so as to lie in several planes. Moreover, between each annular stolon and the neighbouiing surface of the disk, there is a layer of superficial segments distinct from the vertical columns, but connected ^ith the annular stolons ; these occupy the narrow elongated cells just mentioned, which constitute two superficial layers in the disks of this type, between which is the inter- mediate layer occupied by the columnar segments. '' These two types seem to be so completely dissimilar, that they could scarcely have been supposed to belong to the same species ; but the examina- tion of a large number of specimens shows that, although one is often developed to a considerable size upon the simple type, whilst another com- mences even from the centre upon the complex type yet many individuals, which begin life and form an indefinite number of annuli upon the simple type, then take on the more complex mode of development." Each cell is occupied by the animal sarcode substance — sometimes not completely, so that intervals exist at points between the contained matter and the enclosing calcareous wall, just as in Monothalamia. The first cell pro- duced, about which all others are arranged and may be considered ofi'shoots or dependencies, is called the primary or primordial cell ; and in it is con- tained the mass of condensed sarcode which Dr. Carpenter calls the nucleus. The link-like portions connecting one chamber with another are called by Schultze bridges (Briicken) or isthmi, by Ehrenberg siphons, and by Car- penter ' stolons.' In chemical composition the shells of Poh/thalamia are calcareous, with the exception of those of Polymorphina silicea, which, like those of many Diffiugice, are composed of small granules and tablets of silex. Schultze observes that, in addition to this species, Spiridina agglutinans and Bignerhia aggJutmans have their surface covered by adherent grains of sand, to give it the fii'mness and resistance provided for in other forms by theii' shells. The consequence of their calcareous composition is, that the shells are hard, brittle, and opaque, and their contents only visible so far as protruded in the form of processes. To examine, therefore, the animal matter, it is necessary to crush the shells, or, better, to carefully remove some portions and so expose the subjacent tissue to view ; or they may be acted on by dilute acid, which dissolves out the earthy matter, leaving the transparent organic basis of the testa. Dujardin employed dilute acid mixed -^ith alcohol, which contracted and rendered the sarcode substance harder, and gave it the appearance, in the many- chambered cells, of laminated or lobulated masses connected together by thinner portions. When the calcareous earthy matter is dissolved out of the shells oiForami- nifera, the organic matrix or basis is left as a transparent membrane, retaining the precise form and markings of the complete shell, and perforated by the characteristic pores. Its chemical relations are those of the membranous testa of Gromia. In thin shells the organic matter is in relatively greater abund- ance than in the thick ones. Acids produce an active effeiTescence, and so prove the presence of carbonate of lime as the principal mineral constituent. Schultze has also detected the presence of phosphate of lime, at least in some shells, viz. in those of Orbiculina adunca and PohjstomeUa strigilata. The shells of Polythalamia are commonly white, when viewed by reflected light, and when emptied of their organic contents. \\Tien the latter remain 224 GENERAL HISTORY OF THE INFUSORIA. a reddish- or yellow-brown colour is ^jrodiiced. Sufficiently transparent specimens and opaque fragments, \iewed by transmitted light, exliibit either a glass-like (vitreous) colourless appearance, or have a brown hue. Examples of the latter condition are afforded by all solid and not finely porous shells, by MiUolidce, Ovulince, and others. Moreover, the youngest, thinnest, and most transparent shells are rendered visible by their apparent intense brown colour. Amongst porous species are some, such as Orbiculina and Sorites, which have the brown colour only in stripes. Lastly, Schultze has never met with the peculiar yellow, red, and violet tints mentioned by D'Orbigny in some RotaUnce, Roscdince, and PlanorhuUnce. The figure assumed by various PoJytJudamia is extremely varied, but is nevertheless reducible to certain types. We will restrict ourselves to a brief description of the primary forms established by Schultze ; these are three in number: — 1. In which the chambers or cells are superposed on one another in a straight series. 2. In which they are disposed in a spiral manner ; and, 3. in an iiTegular fashion. The Nodosaridoi, which have their cells placed one on another in a simple row, are examples of the fii^st ty^Q ; the Sjnrocidince of the second ; and the Acervulince of the third (XXI. 34). In spiral shells the chambers may be rolled in one plane, so as to form a spnmetrical shell with opposite sides alike, e. g. in Cristellcma, or, otherwise, in an asjTnmetrical mode, so as to produce a sheU. like that of the common snail {Helix), e.g. Eotcdia and Bosalina (XXI. 25-28). This latter variety may be so modified by the great elongation of the spiral, as to produce an elongated conical outline, as in Uvigerina and Bidimina, when the chambers above and below each other may present an alternate arrangement. Other varieties of the spiral are exemplified in Orbicidina, Alveolina, and Nonionina. In many instances a simple or regular spiral disposition is commenced in young animals, which is departed from variously as they attain the adult condition and characters. Thus in Planorhidina the regular s]3ii^al is transformed eventually into a completely irregular form. Lastly, the Acervulince con- sist of spherical or spheroidal cells aggregated into formless colonies. With reference to the minute structm-e of the shell. Prof. Williamson {Report of British Associcition, 1855, p. 105) recognizes three principal types: viz. — " 1. The hyaline, generally consisting of a transparent vitreous carbonate of lime, with, usually, numerous foramina. 2. PorceUanous, white, opaque, and rarely foraminated. 3. The arenaceous, mainly consisting of agglomerated grains of sand." Schultze makes two tj^es : in the one, the shell is perforated by numerous fine pores or canals; in the other, it is homogeneous and solid. The contents of the second series are brought into relation with the external world by means of one large opening, or by many smaller ones collected in one group. This division corresponds, in the main, with that of Prof. Williamson, except that the German naturalist has omitted to notice, as a thii^d series, those shells constituted of a membrane covered by extraneous particles of sand and the Hke. The size and distribution of the foramina, along with other stnictiu'al pecu- liarities, afford the best specific characters. To examine these details the shells must be view^ed by transmitted light, and by high powers. The thick- waUed opaque Foraminifera are best explored, as Ehrenberg first pointed out, after being soaked in some strongly refracting varnish, either entire or when cut into thin sections. The dimensions of the canals vary in different species from -0003 of a line (a scarcely measurable size) to -005 of a line. They are of extraordinary fineness in Polystomella strigilata, in P. gihha. and P. venusta, whilst in Orhulina OF THE PROTOZOA. RHIZOPODA. 225 universa and in Acei'vuUna globosa (XXI. 35-37) they obtain their greatest diameter. In the latter, and in Glohiger'ina, the canals dilate towards the sui'face, and are consequently fimnel-shaijed (infimdibidiform). In a few instances two different sorts of pores exist, as in Orbulhm universa and Eosalina varicnis, the finer kind being more abundant. A peculiar sort of slits is characteristic of the genus Pohjstomella ; that they completely perforate the shell is shown by sections. They are largest in P. strigilaUi, and in P. gihha apj^ear to be only shallow excavations. Besides the openings named, the surface of the shells often presents regularly- disposed eminences or elevated lines. In Pohjstomella strigilata and P. venusta (XXI. 28-30) there are hemispherical or conical eminences, perforated severally by a fine opening. In Textilaria picta elevated lines are arranged around the widely-separated pores, so as to produce an elegant design (XXI. 2b). Lastly, many shells have a spinous or stellate appearance, from the prolongation of some canals into long and fine projecting tubes, or from that of the whole of them into thick processes. Illustrations are afibrded by Rosaluia Imperatoi^ia, Cal- carina, and particularly by Siderolina calcitrapoides. Carter has described a greenish, perishable, organic membrane as investing the entii^e suiface of the shells ^\dth all their irregularities ; and d'Ai-chiac has assumed this to be the secreting membrane of the calcareous matter. Schultze, however, has failed to detect such a structure in every specimen he has examined, whether in a Hving or in a dried condition ; and he observes that, even if this membrane does exist in certain cases, there are abundant facts to prove that it is not the seeretiug organ of the sheU. The foramina are, as a i-ule, uniformly distributed over the shells, those parts only being free which are placed immediately above the partitions between adjoining cells. Exceptions, however, occur. Thus, in the iuequi- lateral Rotalidce (XXI. 33) and their allies, the under or umbilical side has fewer pores than the upper. Also, iu some of the thick-shelled species the position of the subjacent septa are not indicated by the absence of pores. The long winding canals pass in difterent directions, unite, and appear on the surface in groups, producing a complex wavy pattern on the surface, as in many Calcariiue. The partitions between the several cells are perforated by oiifices, which differ in size, number, and distribution in the several species. They occur in the septa as fine pores similar to those of the surface, but in less number. Again, in species having a single large opening in their terminal chamber, there is a similar one in each partition, as in Nodosarida, Miliolkla (XXI. 21, 22), Textilaria (XXI. 36), Rotalida, and in Nonionina, Rotidina, Cristellaria, &c. Among this group the Comdina form an exception, in having numerous foramina in the last cell and in the septa between the others. In Acervulina, again, the several cells communicate by a single opening. In Peneroplis, Cosciiiospira, and in Pohjstomella the septa have numerous pores ; and the foramina proportionally increase in number mth the increasing size of the septa, i. e. from the fii\st- to the last-formed chamber (XXI. 28-30). In Orhicidina the thick septa are penetrated by canals. Ehrenberg pointed out the presence, in several species, of numerous per- pendicidar calcareous columns interposed between the septa, which he sup- posed to be hollow tubes, opening up a communication between the whole series of chambers and the exterior. Both their fimction and their tubular natui-e Schultze disbeheved, and asserted that Lunulites (Etw.) is not one of the Polythalamia, but actually a colony of Bryozoa. Mr. Carter {A. N. H. 1852, x, p. 170), on the contrary, asserts the ex- istence of such tubes in the septa, in the following passage : — Q 226 GEKEKAL HISTOET OF THE IN^FUSOEIA. " The septa occupy (in OjperciiVina Arahica), transversely, about -^th of the breadth of the chambers ; and each septum encloses within its walls two calcareous tubes or vessels, one on each side, some little distance below the contiguous sui'face of the shell (fig. 7 a, a); these we shall call inter septal vessels. They are irregular both in their size and coiu'se, though generally about -j-J^th of an inch in diameter, in the last-formed septa of a shell having the dimensions of the one described, and diminish in calibre back- wards or towards the fii'st-foiTned whorls. Each vessel commences in the centre of an intricate network of smaller ones, spread over its own side of the margin of the preceding whorl, and under the layers of the shell ; these networks, which are joined together, we shall call the marginal plexus. In its course each interseptal vessel gives off two sets of ramusculi, and the marginal plexus one set. Of those coming from the interseptal vessel, one set terminates on the siuface of the shell, particularly about the borders of the septum ; the other goes into the walls of the shell, and through the septum, to open probably on the inner surface of the chamber, while the set from the marginal plexus opens on the margin. As this vascular system appears to extend throughout every part of the shell, and must be for the circulation of some fluids we will call it the interseptal circulation.''^ Prof. Wilhamson has likemse described a series of intraseptal canals in Faujasina, and illustrated their arrangement by engravings. We have not space to give the details, but can quote only the general results : — " The intra- sejDtal spaces are vertical, and give off true divergent cylindrical canals from their external margins, penetrating the thick parietes of the shell. These spaces extend from the top to the bottom of each septum, and only assume the form of canals when they approach the peripheral shell-walls. The con- necting branches which unite the S2)aces of different convolutions are also tubular. In no instance do these spaces or their divergent canals commimi- cate with the interior of the segments (chambers) ; for the only dii^ect com- mimications between the two parts of the organism are thi'ough the pseudo- podian foramina, many of which open into the tubular portions of these passages ; but never, so far as I have observed, into the intraseptal spaces." Again, " the caidties in the translucent shell are thickly lined mth a dark ohve-brown substance, which, if it be the desiccated soft animal, proves that in this species the gelatinous tissue has not only filled the true chambers, but has also occupied the intraseptal canals and passages. If this be so, it is curious that the only medium of commimication betA^'ecn the soft tissues in- habiting the spiral segments of the shell and those occupying the intraseptal and central passages, should be the minute pseudopodian foramina .... It is, however, ob\'ious that this organism supports the conclusion at which I arrived in a previous memoir, viz. that the soft animal had the power of extending itself externally far beyond the limits of any individual segment, and would thus be able to secrete calcareous matter in other situations than the mere parietes of its o^tl segment. It is only in this way that we can explain the production of the dome-like covering which encloses the central umbihcal cavities and their ramifying canals. But if it should be ultimately proved that the soft tissues have occupied all these irregular cavities, we shall then have a form of organization which, from its great variability of contour, ^vill approach much more closely to the calcareous sponges than any hitherto de- scribed." Schultze says that the species referred to by the two observers just quoted have not come in his way, but that in none of the genera he has examined has he met with a similar structure. He has been equally unsuccessful in finding the interseptal spaces noticed by Carpenter in Nummulites ; and in OF THE PROTOZOA. EHIZOPODA. 227 no genus he has examined, has he been able to discover its shell to be com- posed of calcareous spicula, such as Carter represents in OpercuUna Arahicay and refers to as indicative of the intimate affijiity between Foraminife^xi and sponges, in the ensuing j^aragraph {A. N. H. x. 1852, p. 173) : — '' It must be now generally allowed that the Rhizopodous nature of Foraminifera is identical with that of the Amoeba or Proteus, and through the latter with the Sponge-cell ; and in addition to this, we have the former, at least the genus Operculina, stiU more nearly aUjing Foraminifera to the Sponges, by possess- ing a spicula structui^e, if not a circulating system also, like that of SjDonges." The calcareous sheU of Rhizopoda is lined (XXI. 16) within by a delicate organic homogeneous membrane, with a sharp outline, and of a more or less deep-broAvn colour. It is in immediate contact with the animal, and closely apphed to the shell, and has the same perforations (XXI. 24). It penetrates from one chamber to the next through the intermediate pores and canals. Duiing life it is, in the last-formed chambers, colourless. It is not equally visible in all species. By the addition of dilute acid to Botalia, Rosalina, and Textilaria, it is readily brought into \dew ; but in Miliolida this is difficult, o^ving to its dehcacy and want of colour. In the first-formed (primordial) chamber, occupied by colourless substance, it would seem to be absent. In its chemical relations it resembles the chitinous shell of Gromia, and is so very slowly destroyed by decomposition, that it may be demonstrated in empty shells found amidst the sand at the sea- side, and, according to d'Archiac and Jules Haime, even in fossil specimens. Dimensions and Conditions of Life of Rhizopoda. — The size of the Rhi- zopoda is very varied, even among members of the same genus. Ehi-enberg describes Amoehoi fi'om ^ l^^th and i^J-jjth to y^th of an inch ; Difflugice from g-JfTo-tli? and YY,Vuth to T^th, and ArceUce from yy-o-th to ^xo^^ ^^ ^^ inch. Between individuals even of the same species, he represents a diversity of size of nearly equal extent. Schultze states the diameter of the shells of Gromia oviformis, and of G. Diijardinii, to be -gyth of an inch, whilst that of Lagynis is only tt-J ,jth in length. Dujardin remarks that the largest fresh- water Rhizopoda attain a diameter of -^2^(^, whilst the marine Foraminifera are for the most part visible to the naked eye, and have a length of from ^^^th to -i-th of an inch. The Xautiloid shells of PolystomeUa have a diameter of gL-th to 2yth of an inch, and the ii'regularly- chambered AcervuUnce a length of fi'om Jjtt^ to -1th of an inch. Among fossil Foraminifera larger sizes prevail : thus. Sir E. Belcher brought one species from Borneo measuring more than 2 inches in diameter ; and many Nummulites are found an inch and upwards in diameter. Mr. Jeffreys gives the following account of the habits of Foraminifera (Proc. Roijal Soc. 1855) : — "■ Most are free, or only adhere by theii' pseudo- podes to foreign substances. Such are the Lagena of Walker, Nodosaria, Vor- ticiaJis, and Textidaria, and the Miliola of Lamarc. The last genus has some, although a very limited, power of locomotion, which is effected by exserting its pseudopodes to their fiiU length, attaching itself by them to a piece of seaweed, and then contracting them like india-rubber, so as to draw the shell along with them. Some of the acephalous mollusks do the same by means of theii' bj^ssus. This mode of progression is, however, exceedingly slow ; and I have never seen, in the course of 24 hoiu-s, a longer joui^ney than a quarter of an inch accomplished by a Miliola. . . . Some are fixed or sessile, but not cemented at their base like the testaceous Annelids. The only mode of attachment appears to be a thin film of sarcode. The Lohatida of Fleming, and the Rosalia and Planorhidina (D'Orb.) belong to this division. Dr. Cai^Denter considers the q2 228 GENERAL HISTOEY OF THE rNTFSOIlIA. Foraminifera to be phytophagous, in consequence of his having detected in some specimens fragments of Diatomaceae, and other simple forms of vegetable life. But as I have di^edged them ahve at a depth of 108 fathoms (which is far beyond the Laminarian zone), and they are extremely abundant at from 40 to 70 fathoms, ten miles fi^om land and beyond the range of any seaweed, it may be assumed, T^dthout much difficulty, that many, if not most of them, are zooj)hagous, and prey on microscopic animals perhaps of even simpler form and structure than themselves. They are in their turn the food of Mollusca, and appear to be especially relished by Dentalium entale.^' The assumption that, because the Laminarian zone ceases at a much less depth than that at which Foraminifera occur, therefore no Diatomeae are found, is quite gra- tuitous, and opposed to observation. The notion also that animal life fur- nishes nutriment to Foraminifera at depths where vegetable existence, and where the doubtful Diatomeae cannot be sustained, is opposed to all proba- bihty. Of the rate of growth and of the duration of Ehizopoda we have few re- corded observations : we must, however, suppose them regulated by external cii'cumstances, such as abundance of food, moderate temperature, and the like. Schultze observed of 'Foraminifera living in a small quantity of sea- water, so to speak, in captivity, that they grew exceedingly slowly. In only one Po- ly stomeila out of many, kept under observation for several months, did he ob- serve the production of a new chamber. Rotalice, however, were more fre- quently seen in process of growth, the walls of the new-formed segments being extremely dehcate and deficient of calcareous matter. Some very young specimens of MiJiola ohesa were found to produce two new chambers, after the completion of the primary one, in the com^se of four weeks. From this fact of their very gradual growth, says Schultze, we may con- clude that a year or more may elapse before the construction of a many- chambered shell is completed. This natui'alist has, indeed, kept the same specimens of PohjstomeUa and of Rotalida in capti\dty for nine months ; and theii' persistence for a much longer period is highly probable. If, he adds, the production of germs put a termination to life, then this phenomenon entails a fixed limit to its duration. Dujardin, again, found Arcellce alive after two years, in a vessel in which he had preserved them. The testaceous Ehizopoda possess the power of repaii'ing the efi'ects of me- chanical injimes to their shells. This has been proved by Schultze in the case of the Polythalamia ; and we may conclude the same faculty is possessed by the Monotlialamia. He has seen almost one-half of the shell of Pohjsto- mella strir/ilata, which had been broken away, repaired by a new calcareous wall resembling the normal one both in its pores, eminences, and markings. He also frequently noticed in this same species irregularities in the conforma- tion of the shell, which he attributed to damages previously inflicted ; and experiment showed him that, even on the same day that a considerable portion was removed, the animal set vigorously to work to rei)lace the lost sheU, and protruded its processes just as before. Occasionally the destruction of a portion of the shell gives rise to monstrous (abnormal) forms. Thus Schultze noticed a double PolystomeUa strigilata, and Eeuss a monstrous Nodosaria anmdata, which he called N. dichotoma ; and Dr. Carpenter has foimd several " monstrosities of Orhitolites resulting from an unusual outgrowth of the central nucleus." The Ehizopoda can, doubtless, maintain life under very prejudicial condi- tions. The power possessed by the sarcode substance, of sustaining existence when even the greater part is torn away, and the capability of repair mani- fested by the testaceous species, are facts indicative of their tenacity of fife. OF THE PEOTOZOA. EHIZOPODA. Another proof is found in the capacity of Foraminifera to exist for weeks and months in the same water. Schiiltze states that he has found them lying motionless, with retracted processes, at the bottom of a vessel of putrid water, in which they had been kept a long time, and that when this water has been changed, or its foul odour removed by an acid, they have recommenced to move about, and to thrust out their fibres. In a small glass containing mud from the lagoons of Yenice, and in which life appeared extinct, he found Ro- talidte and Miliolidce creeping on the sides, and in great numbers in the sedi- ment at the bottom. Some still more recent experiments have convinced this eminent naturalist that fresh water is not very detrimental to them, but that, on the contraiy, they may be kept ahve in it for a considerable time. He found at the same time that some dried Polytlialamia from mud obtained at Muggia, and let dry for five weeks, continued motionless after six weeks' immersion in sea- water. Haeitats and Distribution of Ehizopoda. — Fossil Poe:ms. — The Amoehce are met mth particularly in water containing much organic debris, provided that decomposition is not proceeding. They are common inhabitants of infu- sions, and of stagnant water, and are foimd adherent to foreign bodies, to plants, Confei^'ae, and the like. Although unable to s^Wm, they are fi^equently floated to the surface on the matters to which they stick, such as dead leaves. Algae, or stalks of plants. They occur both in fresh- and in sea-water, but are much more commonly seen in the fonner. The Moaothalamia, with reference to their habitats, form two groups,— one marine, the other freshwater. Arcella, Diffiugia, and Euglypha are essential freshwater genera, whilst Spirillina (Ehr.), Gromia, Lagynis (Sch.), and SquameUa (Sch.) are marine. They are not met with in infusions arti- ficially prepared although common in stagnant water holding organic matters in suspension, and found crawling on these or on the sides of the vessel containing the water. PoJythalamia are all marine. Their abimdance and extent of distribution are surprising ; this is true of them both in the living and in the dead or fossil condition. Schultze states that on the northern level shore of the har- bour' of Ancona, the shells of the Foraminifera cover the suiface here and there Kke a fine sand, and are discovered in many places in smaller numbei^ at a depth of 20 feet. When this sand was placed in water in a glass jar, no specimens were found to crawl up the sides ; and observation showed that few among them retained any organic contents. Prom a small rocky islet in the harboui' he scraped into a fine net the slimy mud, and then separated the lighter suspended particles from the mixture of animal and vegetable matter, and placed them in another glass. On examining, a few hours later, the fine sand so separated, he found it almost entirely composed of Polytlialamia, filled with theii' organic substance and alive, many of them having crawled up the sides of the vessel. His experiments at Yenice were entirely correspondent ; no living beings were found in the sand from the shore, but countless specimens in the debris about the Alga3 in the lagoons. Once, however, at Cuxhaven, on the Elbe, he met with living Foraminiftra in the sand. Dujardin also says of the Polytlialamia, that, from being imable to SAvim, they are only to be found attached to the surface of bodies on which they crawl, such as aquatic plants, or, otherwise, lying amidst the debris covering the base of such plants, or in the hollows between the asperities of the shells of marine Mollusca. Sponges, again, form a convenient habitat for li^dng Polytlialamia, ha\ing theii' pores at times pretty well filled with them ; in the same way Corals and Corallines are fix-quently beset with them. This necessity of attachment cannot universally prevail, since the Foraminifera are 230 GENERAL HISTOEY OF THE INFUSOEIA. SO often found scattered over the bed of the ocean, as well in the li\dng as in the dead state, without any Algae near, whereto they can adhere. The extraordinary abundance of Foraminifcrous shells in the sand of some sea-shores has been long observed. Plancus, in 1739, counted, with the aid of a low magnifying power, 6000 individuals in an ounce of sand from Eimini, on the Adriatic; and D'Orbigny states that 3,840,000 exist in an equal quantity of sand from the Antilles. Schultze also counted 500 shells of lihi- zopoda in ^th of a grain of sand collected from the Mole of Gaeta, which had pre\'iously been passed through a sieve and separated fi'om all particles above yi^th of an inch in size. Ehrenberg describes finding Pohjthdlamia both on the surface of the sea and also at the bottom, even at a depth of 12,000 feet. From these great depths they are procured by soundings ; the lead, after being coated mth grease at the bottom, brings up attached to it the small particles of sand and other matters mth which it comes into contact at the sea-bottom. Numerous such soimdings were taken by Sir J. Iloss in his Antarctic expedition, and have been practised by others in different regions. Dr. Bailey records the results of a series of deep soimdings made in the Atlantic, over a considerable geograjihical area, from latitude 42° 4' to lat. 54° 1 7', and depths varying from 1080 to 2000 fathoms. " None of the soundings," ho states, " contain a particle of gravel, sand, or other recognized unorganized mineral matter. They all agree in being almost entii'ely made up of the shells of Foraminifera. .... But neither the smface-water nor that of any depth . . . collected close to the places where the soundings were made, contained a trace of any hard- shelled animalcules." Schultze is unable to receive Ehrenberg's statement of finding shells floating on the sm^face of the sea, seeing that they naturally sink in water. Still he admits that in shallow water they may be suspended by the tossing of the waves, and that they may float on the surface attached to sea- weed torn from the bottom, or to other floating substances. He likewise, and, we think (judging from the laws of distribution of organic life at different depths as pointed out by the late Prof. Edward Forbes), very justly, demurs to Ehrenberg's conclusion, that the Polythalamian shells fished up fi'om the great depths cited, and others approaching them, lived at those depths, and had become empty by speedy decomposition of their animal contents. At depths far less considerable, we believe all organic life ceases, and should consider the Foraminifcrous shells there found to have been drifted from other less profound places by currents in the ocean. Prof. Bailey also started the question, whether the Foraminifera found at the bottom of the sea actually lived there, or were borne there by submarine currents, but admitted that these and other like questions could not be at j^resent decided. What, however, is veiy remarkable, is that the species " whose shells now compose the bottom of the Atlantic Ocean have not been found li^dng in the surface waters, nor in shallow waters along the shore. It is but fair, also, to state that Mr. Jeftreys has dredged living Polytlialamia from a dei)th of 108 fathoms (648 feet). So far as Schultze' s researches go, they prove a very Hmited geographical distribution of some species of PolythaJamia. Thus, he has never foimd the Rotalia Veneta elsewhere than at Venice and Muggia, near Trieste, whilst the Polystomella strigilata, of Ancona, is altogether absent at Venice and Trieste. Nodosaridoi, which are common enough at Rimini, are sought in vain at Ancona, close by, whilst Rotalia Beccarii occurs at both those places. So Peneroplis ])lanata is found in the sand on the Istrian coast, from Citta Nuova to Pola, but is absent at Trieste, Venice, and Ancona. Similar illus- trations might, says Schultze, be multiplied, to show the considerable diversity of local fauna. OF THE PROTOZOA. RHIZOPODA. 231 A limited distribution, both in reference to place and to the conditions of existence, has been determined by Ehrenberg and other observers of the Poly- thalamia, and also employed by geologists in fixing the period of the deposi- tion of certain strata, and the circumstances under which it has occurred. Thus Bailey records of the Atlantic soundings, that they " contain no species belonging to the group AgatMstegia (D'Orbigny), a group wliich appears to be confined to shallow waters, and which in the fossil state first appears in the tertiary, where it abounds." Again, they " agree with the deep soundings off the coast of the United States, in the presence and predominance of species of the genus Glohigerina, and in the presence of the cosmopolite species Orbu- lina universa (D'Orb.) ; but they contain no traces of the Margimdina Bachii, Textilaria Atlantlca, and other sj)ecies characteristic of the soundings of the Western Atlantic. In the vast amount of pelagic Foraminifera, and in the entire absence of sand, these soundings strikingly resemble the chalk of England, as well as the calcareous marls of the Upper Missoiui ; and this would seem to indicate that these also were deep-sea deposits. The cretaceous deposits of New Jersey present no resemblance to these soundings, and are doubtless littoral, as stated by Prof. H. D. Rogers." A fijj:ed geographical distribution is also implied by the division made by D'Orbigny of the sj^ecies he observed, — viz. into 575 peculiar to the torrid zone, 350 to the temperate, and 75 species to the frigid zone. Moreover, Dr. Carpenter stated (in the Annual Addi'ess at the Microscop. Soc. 1855) that he and Prof. Williamson find " that there are certain species whose range of distribution is limited, and whose form is remarkably constant, but that, in by far the greater number of cases, the species of Foraminifera are distributed over very wide geographical areas, and have also an extensive geological range." Mr. Jeffreys remarks that, in his opinion, <' the geographical range, or distribution of species, is regulated by the same laws as in the Mollusks and other marine animals. I have found in the gulf of Genoa species identical with those of our Hebridean coast, and vice versd.^^ Fossil Foraminifera. — In a fossil form the PolytJialamia are very common, and enter largely into the formation of several rocks, chiefly calcareous or of the tertiary series, m every part of the world. Ehrenberg, in his microscopic examination of the chalk formation, represents these shells as the most im- portant constituent ; and Dr. Bailey speaks of them as largely concerned in the formation of the tertiary rocks of South Carohna, and adds, they '*are still at work in countless thousands on her coast, filling up harboui^s, forming shoals, and depositing their shells to record the present state of the sea- shore, as theii^ predecessors, now entombed beneath Charleston, have done with regard to ancient oceans. For the city just named is built on a marl 236 feet thick. The marls from the depth of 110 to 193 feet are tertiary, as also, in aU likelihood, are those beneath, extending from 193 to 309 feet, and also of the Eocene epoch. The lithological characters of the marls from 236 to 309 feet differ from those above them, although many of the same species are stiU to be detected " {A. N. H. 1845, vol. xv.). The most abimdant Foraminifera of the chalk belong to Eotalia, Spirulina, and Textilaria : the fossil genus Nummulina abounds in tertiar}^ strata ; and their shells constitute the chief ingredient in the composition of many lime- stone rocks used in building, such as those in Egypt, from which the huge stones of the Pyramids are quarried. In America this genus is largely re- placed, as a component of limestone, by the genus Orhitoides. Species of Textilaria are the most abundant in Oolitic formations. In the cretaceous earths, says D'Orbigny, genera and species augment in rapid progression from the lower to the higher formations. On arriving at the tertiary rocks, Fora- 232 GENERAL HISTOEY OF THE INFUSOEIA. minifera become still more multiplied, and many previously unobserved genera make their appearance. In the Silurian and Devonian rocks of the palaeozoic series, Foraminifera appear to be absent. In the carboniferous deposits D'Orbigny found one species, but detected none in the Permian, Triassic, or Jui'assic strata. Mr. King has, however, discovered shells in the Permian rocks. Many genera have hitherto been found only in the fossil state : some such we may suppose to have become extinct ; but others will probably be discovered when the search after hving specimens is further prosecuted. It may be generally stated that the relative number of identical fossil and recent species is much greater in this family of Foraminifera than in any other known ; and specific forms have continued from the Mesozoic era until the present day, so connecting, as by an imbroken chain, the fauna of our own time and that of almost countless ages past. QuESTION^ OF THE CeLL-NATUEE OP EhIZOPODA, AND OF THE ChAEACTER OF Foraminifera as Individuals, or as Colonies of Aniiials. — The prevailing theory of the cellular composition of all animal and vegetable tissues induced several distinguished naturalists to represent the Rhizopoda as ceUs. KoUiker ingeniously argued (J. M. S. 1853, i. p. 101) in favour of this view, and for a time succeeded in persuading most scientific men of its truth. It had the character of a grand generalization, and recommended itself by its simphcity. Yarious structural peculiarities and general considerations are, however, opposed to this theory: these we will adduce after KoUiker's arguments have been stated. He first assumes that the Rhizopoda and Ciliated Pro- tozoa are comprehended in a single class of simple animals, which, like the Gregarince, are unicellular ; and he foi^ther groups the Actinophryina with Rhizopoda. The absence of an integument to represent the cell-wall, and in most of them of a recognized nucleus, are difficulties he would explain away. Pirst, he supposes that, where a nucleus is not seen, it " may have existed at an earlier period, and be absent only in the full-gro^vn animal, or, again, that it may be entirely wanting, and stiU the animal be regarded as a cell." Secondly, " with respect to the membrane, it may be regarded as certain that there are cells mth a membrane of such extreme tenuity as to be hardly distinguishable from the contents," and others in which at a later period all difference between the membrane and contents disappears, — for instance, the elements of the smooth muscles of the higher animals." AATiich of these two possible conditions obtaias in the Rhizopods, he cannot undertake to say, but would remark '' that their other relations are not opposed to the notion that they may be simple cells, — such as their stnictureless homogeneous contents, their contractihty, and the vacuoles which occur in them, resembling in all respects the contents of the body of unicellular Infusoria. So, likewise, the simplicity of their form and mode of taking food, so closely resembhng the way in which Infusoria introduce a morsel into their parenchyma. Certainly the presence of a ceU-membrane is scarcely reconcHeable vrith the circumstance that the body is capable of admitting a morsel of food at any part of the sur- face ; but in one point of view it is not indispensably necessary to assume that such exists in the fully-developed Actinoplirys, and in another it is by no means wonderful that a membrane, in consistence almost the same as the rest of the parenchyma, should be capable of being torn and of reuniting." It is therefore, he concludes, best to consider the Rhizopoda simple, although modified, cells, especially since there is little else to be made of them. " It cannot be admitted that they consist of a whole aggregation of cells ; and as little is it to be supposed that they are simply a mass of animal matter with- out further distinction — as it were, independent hving ceU-contents. And the less can this opinion be entertained, because " cells are the elementary OF THE PEOTOZOA. EHIZOPODA. 233 parts of the higher animals and plants, and the unicellular condition the simplest form in the animal kingdom." The existence of an investing mem- brane in the Rhizopoda he finally considers probable. The arguments here quoted from Kolliker's paper on Actinophrys, have been examined by several later writers, and have had their defects pointed out. Perty declares himself opposed to the cell-theory since Ehizopocla are want- ing the essentials of the cell-nucleus and cell-wall ; and the hypothesis cannot be applied to animals composed not of cells, but of an amorphous primitive substance. M. Claparede attacks Kolliker's arguments in detail. The question raised, whether the nucleus and membrane may not disappear in the course of growth, he answers by another queiy — " \Ye may conceive the possibility of this ; but where do we find any proof of it ? " — and proceeds to remark his own failure, and that of Ehrenberg and of most others, to discover a nucleus, even in very small animals, and after treating them with dilute acetic acid. " The supposition, that Actinoplirys and other Ehizopoda pass through a previous cellular condition, has consequently no foundation in fact." He cannot agree with Kolliker, that of the three parts of a cell — the nucleus, membrane, and contents — two " may be deficient, — that for example, we may attribute the signification of a cell to the contents remaining alone and contained in nothing .... If, therefore, with Kolliker, we regard the Ehizopoda as a class of unicellular animals, the organisms which it includes will be principally distinguished by their having nothing to do with cells, as they consist of a shapeless mass of a stinictureless homogeneous substance." M. Claparede next subjects to examination the argument for the cell-nature of Ehizopoda deduced fi^om analogy with Ciliated Protozoa, which Kolliker takes for granted to be unicellular organisms. This assumption, and conse- quently the analogy dependent on it, are shown to be erroneous ; and then the wiiter goes on to say that, ''.even if we admitted that Actlnophrys was the equivalent of a cell, it would still not be unicellular, inasmuch as an endogenous cell-production has taken place in it. The contractile vesicle is nothing but a cell" invested by a membrane ; and this being the case, the existence of such a membrane in other Ciliated Protozoa becomes all the more probable. " Kolliker himself supposes that the contractile vesicle, when pre- sent, is the equivalent of a cell-membrane ; and with the proof of the exist- ence of such (an endogenous) formation in Actinophrys, his hy^Dothesis of the unicellular constitution of the animal consequently falls to the ground." Leuckart has also briefly argued against the cell-theory of Ehizopoda ; but as no novel views are taken of the question, we shall not quote his remarks. Our own opinion is, that to insist upon the unicellular nature of Ehizopoda and of other Infusoria is to limit the operations of natiu^e, in the manifesta- tion of animal life, to one sort of mechanism, as though life could not be exhibited except by an organic substance enveloped by a membrane and enclosing a nucleus. Eeasoning by analogy should teach us differently ; for everywhere in the animal series do we see ty^Dcs or grades of organization progressively developed from theii^ simplest to a more or less complicated degree, as if nature would show us by how many different plans she can attain similar and equally beneficial results. And are not the Ehizopoda an illustration of this fact, an example of the establishment of independent animality in primordial animal matter, and, as in the case of the multilocular Polythalamia, of the possible extent of development tliis simple type may undergo without the separation or addition of any other definite structural element ? If Schneider's researches be confirmed, we must admit several Ehizopoda 234 GENERAL HISTORY OF THE INFUSORIA. to be possessed of a nucleus. On the other hand, a large number of species are able to produce new individuals by the mere detachment of a portion of theu' sarcode substance, — an act in which no nucleus is concerned, whereas in cell-propagation by fission a preparatory section of the nucleus appears a necessary process. In the Ehizopoda, therefore, we may conclude that, in the language of Professor Owen, " the spermatic force " is diffused through- out their entire substance, and not, as it were, concentrated in a particular organ or nucleus. The question respecting the nature of the many-chambered Foramin'ifera, whether thej" are to be considered single individuals or colonies of animals, is elaborately examined by Schultze, who comes to the conclusion that the inhabitant of each shell is a single animal. Ehrenberg is the supporter of the opposite view ; but Schultze shows that several structural details given by him, upon which the colony-theoiy is partly established, are erroneous, and that it is one common connected substance which occupies each and every chamber. Prof. Williamson {T. M. S. 1851) has the following pertinent observation on this colony-theory. Speaking of the Orbiculhia adunca, he says — '' The attempt to isolate the various portions, and to raise each portion to the rank of an individual animal, even in the limited sense in which we should admit such a distinction in the polypes of a Sertidaria or of a Gorgonia, appears to me wholly inadmissible." Moreover, the soft-structiu'es being devoid of visible organization, " the whole animal wiU be very httle raised above the Polypifera, only possessing a symmetrical calcareous skeleton, which is at once both external and internal " (/. e. the Porifera). Of THE Affinities of Ehizopoda. — That the Ehizopoda constitute a class of animalcules distinct from every other is evidenced by their characteristic \T.tal structure and phenomena, their power of producing their like, their growth, theii' faculty of digesting and appropriating nutrient matters, and by the ascending stages of development seen among them, advancing fi'om the simple Amoeba to the compound testaceous Cristellaria and Polystomella. In the natiu'e of their animal portion they resemble Cihated Protozoa ; it con- tains similar vacuolae and graniiles, and also a contractile vesicle. On the other hand, they differ from them in having no definite outline to the animal tissue boimded by a hmiting membrane or integument, and particularly in possess- ing no cilia, which, as locomotive organs, are replaced by the pecuHar and characteristic pseudopodes. In variabHity of outline an approach is made to Ehizopoda by some genera of the heterogeneous family, Enchelia of Ehi'enberg ; but they never exhibit any such changeable character as the siu'face of the former, never protrude similar variable processes, nor present a circulation of granules. The Dinohryina might perhaps be cited as affording an example of a considerable variability of form ; but our knowledge of this family is too incomplete to render analogies based on it of value. The affinity between Ehizopoda and Phytozoa is no closer. Some of the latter can greatly modify their form in mo\dng ; but in none does this partake of the character and extent of the variability exhibited by Ehizopods. More- over in none are variable processes found, but in general one or more elon- gated cilia or filaments, which, by their imdulation, serve as the principal organs of locomotion. Between the Testaceous Ehizopoda and CHiated Protozoa the alhance is even less evident ; for in none of the latter do we meet "\;\ith shells like those of the former, and in none is the relation between a lorica and its contents corre- spondent to that of the shell and sarcode substance of Ehizopoda. It has already been noted that the distinction between the two classes of Protozoa founded on the silicious character of the shells or lorica) of the Ciliated, and OF THE PEOTOZOA. EHIZOPODA. 235 the calcareous natiu'e of those of the Pseudopodoiis class, is not in accordance with fact ; for although all, or almost all, Polythalamla have calcareous shells, yet the flexible loricse of many Monothalamia are chitinous, just as those of loricated Ciliata. In the presumed fact of the shells of Arcellina being silicious, Ehrenberg discovered a relation betTs^een that family and the Bacillaria. This affinity he traced still further ; for, when describing the genus CyphkUum, he remarked — '^ It forms a connectmg group between ArceUa and Bacillaria, by reason of the simple locomotive organ (like a snail's foot), and approaches very closely to the group Desmidieoi" However, even if he be right as to the single un- divided process of Cyphidium, the presence of any extended foot or pedal organ from the silicious fronds of EaciUaria, whether Diatomew or Desmidiece, is not now admitted by any natui^alist. If Stein's observations and opinions be correct, an indirect relationship actually exists between Ciliated Protozoa and Rhizopoda; for that pains- taking observer has con\inccd himself that the VorticeUina, by ulterior de- velopment, become transfoiTaed into Aciiieta-]ike or Actinophryean organisms, of the intimate affinity of which no doubt can be raised. The questions raised by this apparent transformation do not require discussion here, since they are fiilly entered upon in the history of the Ciliata, and in that of the Acinetina, considered as a subclass of Rhizopoda. Another alhance was formerly assigned to the Multilocular Rhizopoda, \-iz. mth the Cephalapoda, of which they were treated as a subdi\'ision. This association was suggested, by the ]Sfaidilus-]ike form of some genera, to the earliest observers of the Foraminifera — Beccarius in 1731, and Plancus in 1739 ; and the error was perpetuated by D'Orbigny in 1826. Dujardin has the great merit of first combating this mistaken opinion, and of pointing out the extremely simple nature of their contents, and their true affinity with the simple Amcebce. Several natui'alists, and among them M. de Quatrefages, have classed the comparatively large Noctilucce with the Rhizopoda. But direct observation seems to show that, although in a few particulars a likeness obtains, yet the sum of the differences greatly surpasses that of the resemblances. The Noctilucoi show a more complex organization ; they have an integument com- posed of two layers, an evident mouth and gastric cavity with aj^pendages, and motile filaments, but no variable processes. A striking general resemblance subsists between the ^N'aked Rhizopoda — Amcebce — and the like isolated individuals and the germs of freshwater Sponges or Spongilke, which Mr. Carter has named Proteans (XXI. 5 a, h, c). The resemblances are well conveyed in the following quotation from Mr. Carter's paper : — " A ragged portion torn off with a needle, will be seen gradually to assume a spheroidal form ; and if there be a spiculum, it wiU embrace it within its substance, it may even be seen to approach it, and it may bear away the spiculum, having, as it were, spit itself upon it. On its circumference ^vill be obsei-ved little papiUse, which gradually vary theii- form, extending and retract- ing themselves, imtil one of them may be seen to detach itself from the parent mass and go off to another object. This little animal, one of the group which it has left, may remain stationary' on the second object, or descend to the watch-glass, assuming in its progress aU forms that can be imagined, sphe- roidal or polygonal, whilst every point of its body appears capable of ex- tending itself into a tubular attenuated prolongation .... These transparent little sacs (the gemmules of Grant and Hogg) are sometimes filled with green matter. They appear to be able to adapt themselves to any form that may be convenient for them to assume ; and when forcibly separated from each 236 GElfEEAL HISTOET OF THE IK^FUSOEIA. other (by tearing to pieces a minute portion of the sponge under water in a watch-glass), the isolated individuals may be seen to approach each other, and apply themselves together in twos and threes, &c. and so on, until, from a particle only discernible by the microscope, they assume the form of an aggregate mass visible to the naked eye ; and such a portion, growing and multiplying, might ultimately reach the size of the largest masses adhering to the sides of the tanks at Bombay. They appear to belong to the genus Am(eba of Ehrenberg." These changeable globules Mr. Carter, in the subsequent part of his paper, designates Proteans, and states that they commonly resemble the Pro- teus difflaens (Miiller). (" Notes of the species, &c. of the Fresh-water Sponges of Bombay," Trans. Med. and Phys. Society, Bombay, 1847. Appendix.) In his more recent contribution on the freshwater Sponges, Mr. Carter describes ceUs, capable of greatly and rapidly changing their form, endowed \^ith considerable motile powers, and furnished each ^^dth an imdulating locomotive filament (XXI. 5). These organisms he considers to be zoospcrms, or the speimatozoa of Sponyilla. Speaking of one, he says — *' When its power of progression and motion (of a serpentine creeping character) beguis to fail, and if separated fi'om other fragments, it soon becomes stationary, and, after a httle polymorphism, assumes its natural passive form, which is that of a spherical ceU. Diu'ing this time the motions of the tail become more and more languid, and at length cease altogether." On the other hand, it may attach itself to some fragment, or to another cell, and " become indistinguish- able fi^om the common mass ; and the tail, floatrag and undulating outwards, is all that remains ^'isible." In these structures there is, therefore, polymor- phism as in Rhizopoda, but no actual extrusion of pseudojjodes ; and the points of agreement, after all, are realty accidental, and not demonstrative of a structiu^al affinity. In them we have reproductive germs, which coalesce and disappear as independent existences, whilst in the case of Amoeba each speci- men is an independent individual, and is never seen to coalesce with others mto a common or sponge -hke mass. Dujardin devoted a couple of pages to speak of this affinity between ^?>zo?6ce and Sponges ; and Perty even goes so far as to make the latter a third class of the Ehizopoda, intermediate between Arcellina and Amoebina, on account of the calcareous, silicious, or homy spicula which occur in their compound mass, and constitute a sort of skeleton. The affinity ^vith Sponges is traceable even in the case of the testaceous Polytlialamia, as Prof. AVilliamson pointed out in 1848, and in a subsequent memoir in 1851 {Trans. Mic. Soc.) thus enters on the question : — " Looking at the structiu-e of the shell of the Orbicidina adunca, and esj)ecially at the large orifices which communicate between its various cavities, we cannot fail to observe that it is a reticulated calcareous skeleton, whose proportionate rela- tion to the size of the soft animal has diff'cred but Kttle from that of the sihceo-keratose network of many Sponges to the slimy substance "with which they are invested." So Dr. Carpenter (Proc.Roy. Soc. 18.55), in his critical examination of Orbito- lites, " places that genus among the lowest forms of Foramrnifera, and con- siders that it approximates closely to Sponges, some of which have skeletons not very unlike the calcareous network which intervenes between its fleshy segments." AYith respect to this idea of Dr. Cai^penter, that they are allied to Sponges, Mr. Jeifi'eys (same journal) would remark " that Polystomella crispa has its peripheiy set roimd at each segment with sihcious spicula, like the rowels of a spiu\ But as there is only one terminal cell, which is con- nected A\ith all the others in the mterior by one or more openings for the OF THE PEOTOZOA. HHTZOPODA. 237 pseudopodes, the analogy is not complete, this being a solitary, and the Sponge a compound or aggregate, animal." In a previous pag-e the theoiy of Ehi-en- berg, that the Fomminifera are compound or aggregate animals, has been referred to. It was on this hypothesis that he assumed theii* affinity with Polypes — with Flustrae and Bryozoa, at the head of which he arranged them. This association, like the hypothesis it rests upon, is untenable. In his work on the Foraminifera of the Vienna basin, M. D'Orbigny assigned a position to these animals as an independent class between Echinodeims and Polypes, which, from the present knowledge of the structui^e and reproduc- tion of those classes, we cannot suppose he would seek to maintain. CLASSiFiCATioif OF Ehizopoda. — The fii'st division of Rhizopoda that suggests itself is into naked and testaceous forms, or, as Ehrenberg would say, into illoricated and loricated. The naked forms constitute the family Amoehma, represented by the single genus Amoeba. The determination of specific characters in this family is attended by almost insurmountable difficulties, and can only be imsatisfactoiy, by reason of the absence of any definite figiu^e, and of determinate organs or parts. More- over the semiiluid body of any one presumed species must be much influenced by external causes, and in some measui-e by the matters which may have entered into its substance ; and the like causes will doubtless operate by modifjing the outline, dimensions, and number of the processes. Among such causes the density of the liquid in which they live, and the quantity of organic matter contained in it, may be particularly mentioned. Claparede remarks — " It appears almost absurd to attempt the distinction of species amongst the Amoehce until we know something more of their intimate organization. Thus Ehrenberg' s A. radiosai^ characterized by the regularity of its processes, and its generally stellate form when at rest ; but when the creature creeps, it slowly expands and the peculiar outline disappears; it flows along like a cloudy veil or di-op of oil, and A. radiosa has become converted into A. diffluens.^^ Yet, this author afterwards goes on to say — "even the changeable Amoebce have their ty[ncal forms, such as the stellate and globu- lar." Other grounds of specific distinction (of no very certain value, indeed) are foimd in the shape, length, and mode of termination of the variable pro- cesses, and in the size, colour, transparency, activity, and habitats of these bemgs. The Testaceous Ehizopoda natiu-ally fall into two groups, — one distinguished by having a unilocular, the other a multilocular, shell — the former called, by Sehultze, Monotlialamia, the latter, Polythalamia or Foraminifera. These grand di\isions have been recognized by every natiu^alist ; but some have been led, from giving importance to other particulars, to arrange difierently cer- tain genera, or, otherwise, to detach some as additional families. Thus Ehrenberg, swayed by his polygastric hypothesis, and satisfied in his own mind that the ArceUce, Difflugice, and one or two other monolocular genera possessed a series of stomachs and other organs like other Polygastria, imited those genera into a family which he caUed Arcellina. This detachment of one group of pseudopodous beings from the rest, he further justified, as heretofore stated, by representing it to have sihcious instead of calcareous shells. In this dislocation of evidently- aUied forms he finds no imitators, and is unsup- ported by facts. D'Orbigny distinguished the one-chambered, sac-like, shelled Ehizopoda as one of the six orders into which he separated the Foraminifera, and named it Monostegia. This order is nearly equivalent to that framed by Ehrenberg, under the title of Monosomatia, to comprehend the genera Gromia, Orhidina, and Ovidina, — a term subsequently borrowed by Siebold, but extended by him 238 GENEEAL HISTOEY OF THE INFUSORIA. SO as to include not only the particular genera enumerated, but also the' families Anuiehce and AreeUma of that naturalist. The term Monothalamia contrasts \Yell mth that of Poh/thalamia, expresses the fact, and involves no hyi)othesis as do Ehrenberg's words Monosomatia and Pol y so mat i a, which are foimded on his belief in the colony-like aggrega- tion of several individuals ^vithin a Poraminiferous shell. The Monothalamia of Schultze (as before remarked) do not precisely cor- respond with the one-celled group of either of the other authors named ; for, besides the Monostec/ia of D'Orbigny, it comprehends the Arcellina of Ehren- berg and a few other new genera. The groupings and relations of the several species are represented in the appended table exhibiting Schultze's system. In the classification of the Monothalamia certain and constant characters are deducible from the shells, whilst those ch'a^Mi from the soft parts, from the length or tenuity or mode of termination of the pseudopodes, are of compara- tively secondary importance, and not to be relied on alone. Definite charac- ters are deiivable from the figm^e, size, composition, sculptimng or appendages, and colour of the entii^e shell, from the presence of a single large aperture or of many small pores, and from the form of the apertiu'e and of its margin ; consequently it is in the shells of the Polythalamia that we must seek generic and specific distinctions. As animals, they have all alike the same sarcode sub- stance, which extrudes similar variable fibres : hence any diversities observed in its colour or transparency, in its contents, or in the maimer in which the processes are extruded or other^^ise comport themselves, serve but a sub- ordinate purpose in the scheme of classification. On the contrary, the cha- racters of the shells are, Avithin certain limits, determinate and fixed. They are derivable from the figure, size, coloiu% and consistence of the shell ; from the markings, processes, pores, and slits occupying its surface; from the relative position and figiu'e of the several chambers; from the mode and degree of their connexion ; and from the presence or absence of large apertm^es in company Avith the usual foramina ; and last, not least, from the intimate structiu'e of the shell. Dujardin recognized the value of the shells to supply the basis of a classification of the Rhizopoda ; but he had recoui'se to the form of the variable expansions to make his primary di\-ision, " although," as he remarks, *' it has no absolute value." He arranged all the Rhizopoda, with the exception of the Amcehce (which he treats as a distinct family), into two sections, — one having a single unilocular shell mth a single large apertui-e ; the other a foraminiferous compound shell, or one having several aggregated chambers, each ^^ith a simple orifice, as represented by the tribe Miliola. It is in the subdivision of these sections that he employs characters derived from the variable processes. Thus he separates the first into — 1. those animals pro- vided with short and thick processes rounded at the extremities, viz. Difflugia and ArceIJa ; and 2. into those having filiform expansions, acutely drawm out at the ends. The latter di\ision is more largely represented ; and he separates its numerous species into three tribes, viz. Trinema, with a lateral orifice ; Euglypha, with a tuberculated or areolated shell and few sim2:)le exj^ansions ; and Gromia, with a membranous spheroidal shell and expansions, thick at the base, but very long and branching. He has not attempted the classifica- tion of the whole of the Foraminifera, but restricted his accoimt to some few genera which he has foimd in a living condition. D'Orbigny instituted five orders of the PolijtliaJamia, viz. — 1. Stichostegia, having the ceUs arranged one above another in a straight or shghtly-curved line ; 2. Helicostegia, ^ith cells disposed spirally around an axis ; 3. Ento- mostegia, having the chambers alternating and coiled spii\ally ; 4. EnalJo- stegia, with alternating but not spirally-disposed chambers ; 5. Agathistegia, OF THE PROTOZOA . RKTZOPODA. 239 ha\ing the cells spirally arranged, but each one occupying only one-half the circuit. The three sections proposed by Schultze are — 1. shells disposed in recti- linear series or in a slightly- curved line, Bliahdoidea ; 2. those coiled in a spii'al, HeUcoidea ; 3. those irregularly aggregated, Soroidea. The first of these corresponds to the SticJiostegia of D'Orbigny ; the second includes all the remaining orders of that wiiter ; whilst the third section is represented by a small number of species, previously itn mentioned, vrhich Schultze unites in the genus Acervulina. ^\Tiat structural peculiarities should be employed to determine species, is a question now much mooted \\dth respect to the Foraminlfem. In reference to this subject, Dr. Carpenter (in the annual address at the Microscopic So- ciety, Feb. 1855) obsei-ved " that a large proportion of the species, and even of the genera, which have been distinguished by systematists, and especially by M. D'Orbigny, have no real existence, being nothing else than individual varieties." This error is at once accoimted for by M. D'Orbigny's mode of proceeding (as stated) : "for that, in examining any new collection, he set an assistant to pick out the most divei^gent forms, and then described all that might prove new to him as distinct species, mthout troubling himself in the least about those connecting links, the existence of which should have at once convinced him that he was following an altogether wrong method. Through- out the whole of his labom\s on the group, in fact, I find the influence of the erroneous ideas which he originally entertained ^^ith regard to the natiu-e of the animal of the Fomminifem ; for in the formation of his orders, as well as of his genera and species, he has proceeded as if the characters of the tes- taceous skeleton were of the same distinctive value when its construction is due merely to the solidification of the siuface of a minute fragment of animal jelly, which is subject to an almost indefinite variation both in size and in shape, as when it belongs to a moUusk of high organization, the plan of whose conformation is definitely fixed .... When a collection is brought to- gether containing large numbers of individuals of one generic type, which appear, however, to belong to several distinct species, it very commonly hap- pens that, although it would be easy to make 6, 8, 12, or 20 species by selecting the most divergent forms, yet, when the attempt is made to sort the entire collection under these tj^pes, only a part of it can be unhesitatingly arranged aroimd them as centres, the remainder being transitional or inter- mediate forms, for which another set of species must be made, if the principle of separation be once adopted. In fact, to such an extent does individual variation often go, that (as in the case of the human race) no two specimens are precisely alike, and there is no satisfactory medium between grouping them all as varieties of one species, and making every individual a species, which is manifestly absurd." The error of D'Orbigny has not escaped Schultze's notice ; for in his chapter on classification he has repeatedly pointed out the insufiiciency of the charac- tei-s on which that observer relied in framing his species, genera, and families. For instance (p. 52), he points out the erroneous separation of the Stichoster/ia (D'Orb. j into two families, according to the equilateral or inequilateral con- dition of the shell. And further on, he remarks that the variations elevated by D'Orbigny to the rank of specific distinctions are merely accidental diver- sities in growth, connected together by every intermediate variety. Hence, for example, he combines the genera Trilocidina and Quinquelocidina (D'Orb.) into one genus MilioJa, and the Orhitoides and Orbitulina (D'Orb.) into a single genus Orhitolites. Various other illustrations might be adduced, for instance, the family Nautiloidce ; but it is unnecessaiy to muluply them. It 240 GENEE,AL KISTORT OF THE INFUSORIA. is only fair, however, to state that D'Orbigny is not alone guilty of unduly manufacturing species, but that Ehrenberg, Reuss, and others are equally involved in the fault, which, by the way, is one almost inseparable, and therefore very excusable, in the case of the first observers and systematists of any newly-discovered group of organic beings. Mr. Jeffreys {Proc. Roy. Soc. 1855) deplores the multiplication of species and genera in the present day, and observes that " the Foraminifera exhibit a great tendency to variation of form, some of the combinations (especially in the case oi Margiyiulina) being as comphcated and various as a Chinese puzzle. It is, I beheve, undeniable, that the variability of form is in an inverse ratio to the development of animals in the scale of Nature I am induced to suggest the following arrangement : — "1. Lagena and Entosolenia. " 2. Nodosaria and Marginulina, &c. " 3. Vorticialis, JRotcdia, Lobatida, and GlohigeriTia, &c. " 4. Teoctularia, Uvigerina, &c. " 5. Miliola, Bdocidina, &c. *' This division must, however, be modified by a more extended and cosmo- pohtan view of the subject, as I only profess to treat of British species. To illustrate McLeay's theory of a quinary and cii'cular arrangement, the case may be put thus : — " The first family is connected by the typical genus Lagena mth the second, and by the Entosolenia Avith the fifth ; the second is united with the third through Marginulina ; the third with the foiu'th through Glohigerina ; and the fourth with the last through Uvigerina J' "VYe append a tabular view of the groupings into families and genera, as proposed by Prof. Schultze, since it presents the most complete system yet pro- duced, and advances much nearer a true arrangement of the Foraminifera than that made by M. D'Orbigny. OF THE PROTOZOA. RHIZOPODA. 241 RHIZOPODA. A. NUDA. G-en. Amoeba (Noctiluca?). B. TESTACEA. I. MONOTHA LAMIA. Testa or shell one-chambered ; animal imdivided, having the same conformation as the shell. Fam. 1. Lagvnida. — A sacciform, calcareous or membranous, non-porous testa, with a large opening. Gen. Arcella, Difflugia, Trinema, Euglypha, Gromia, Lagynis, Ovulina, Fis- sm'ina, Squamulina. Fam. 2. Orbulinida. — A globose, calcareous testa, finely porous throughout, without a large opening. Gen. Orbulina. Fam. 3. Cornuspirida. — A calcareous shell, convoluted like that of a Planorbis, with a large opening. Gen. Cornuspira. II. POLYTHALAMIA. Shell polythalamous ; the animal composed of segments, connected by commissural bands. 1. G-roup Helicoidea. The chambers disposed in a spiral. Fam. 4. Miljolida. — Each chamber occupies a half-spiral, which is developed either in one plane or in various planes. The shell has only one large opening at the extremity of the last spiral, and no pores. G-en. Uniloculina, Biloculina, Miliola, Spiroloculina, Articulina, Sphee- roidina, Adelosina, Fabularia. Fam. 5. Turbinoida. — The chambers so disposed spirally as to resemble the shell of Helix or Tm-bo. The spiral is only visible on one side of the shell. Some are so much elongated that the chambers are, as it were, disposed alternately in two contiguous rows. The shell has a large opening in the last chamber, and its sm'face is almost always finely perforated. Subfam. 1 . Rotalida. — Shell flattened or conical ; chambers do not encircle each other ; shell glass-like, transparent ; finely perforated. Gen. Rotalia, Rosalina, Trmicatulina, Anomalina, Planorbulina, Asterigerina, Calcarina, Siphonina, Planulina, Colpopleura, Porospira, Aspidospira. Subfam. 2. Uvellida. — Shell in the form of a longer or shorter cluster like a bunch of grapes. The chambers frequently appear to ahnost completely embrace one another. Shell usually thick and coarsely perforate, or solid. G-eh. Globigerina, Bulimina, Uvigerina, G-uttulina, Candeina, Globulina, Chrysalidina, Pyrulina, Clavulina, Polymorphina, Dimorphina, Ver- neuillina, Chilostomella, Allomorphina, Ehynchospira, Strophoconus, G-rammobotrys. Subfam. 3. Textilarida. — Spire so much produced that the chambers form a double row and alternate. G-en. Gaudryna, Textilaria, Virgulina, Vulvulina, Sagrina, Bigenerina, Bo- livina, Gemmulina, Cmaeolina, Clidostomum, Proroporus. Subfam. 4. Cassidulinida. — Textilaridas curved once in a direction perpendicular to the original spiral. Gen. Ehrenbergina, Cassidulina. Fam. 6. Nautiloida. — The chambers so disposed spirally that the shell has a general resemblance to that of an Ammonite or Nautilus. The spire is either visible or, otherwise, concealed on both sides of the shell. The anterior wall of the last chamber is furnished with one larger or several smaller openings ; the other portion of the shell is usually finely perforated. Subfam. 1. CristeUarida.—^\\e\\ thick, finely perforate, colourless, transparent; chambers encircling, -with a large opening at the upper angle of the anterior wall of the last chamber, which corresponds in position with the communicating openings between the sevei-al chambers. Gen. Cristellaria, Robulina, Marginulina, Flabelliaa. Subfam. 2. Nonionida. — Shell thick or tliin, colourless, transparent, finely perforate ; chambers either encircling (imbricate) or not. The opening is in the 242 GENEKAL HISTOEY OF THE INFUSORIA. anterior wall of the first chamber on the under side looking towards the penultimate spiral ; the communicating openings of the several chambers have a similar position. Gen. Nonionina, Hauerina, Orbignyna, Fusulina, Nummulina, Assilina, Siderolina, Amphistegina. Operculina and Heterostegina should pro- bably be formed into a special subfamily of Nonionida. Subfam. 3. Peneroplida. — Shells usually thin, always brown, and transparent with or without fine pores ; the chambers very narrow, either imbricate or not. Numerous openings, scattered over the whole of the anterior wall of the last chamber ; or, instead of these, a lai'ge opening produced by the coalescence of ntmierous smaller ones. Gen. Peneroplis, Dendritina, Vertebralina, Coscinospira, Spii'olina, Lituola. Appended genus, Orbiculina. Subfam. 4. Polystomellida. — Shell tolerably thick, colourless, transparent, finely por- ous ; chambers imbricated ; the anterior wall of the last chamber has, besides the fine pores, either no larger opening at all, or a few very small irregular scattered fissures, on the contrary side to the penultimate whorl. The same applies to the septa. On the surface of all the chambers, rows of fissure-like, often perforating, depressions are placed at right angles to the direction of the septum. Gen. Polystomella. Fam. 7. Alveolinida. — Globose, ovoid, or barley-shaped shells, composed of spiral tubes, each resembling a cornuspira, and fm*nished with a special opening at the end of the turn or spiral. The tubes all commimicate by con- necting openings, and, besides this, are all subdivided by incomplete dissepiments (partitions), in the same manner as species of Nonionina. The situation of these septa, which are but few in number, and of the coimecting openings, is indicated by lines, which traverse the shell in the direction of meridional lines. Gen. Alveolina. Fam. 8, Soritida. — Discoid, multicellular shells, exhibiting an indication of a helicoid spiral only in the centre ; elsewhere cycloid, that is, growing uniformly at the whole border of the disk. The brown, transparent, finely porous shell is formed of minute chambers, connected together in the direc- tion of straight or curved radii, and each presenting a large opening at the border of the disk. Gen. Sorites, Amphisorus, Orbitulites. Appended genus, Cyclolina (cham- bers perfectly annular, with numerous openings on the border of the disk). 2. Group Ehabdoidea. The chambers piled one on another, in a straight or slightly curved line, in a single row. Fam, 9. Nodosarida. — Eod-shaped shells, whose chambers are superimposed one upon another in a row, and communicate with each other by a large opening; a similar opening in the last chamber (except in the genus ConuUna, which has numerous openings instead of the single one). The shell visually thick, probably always perforated by fine pore-canals. Gen. Glandulina, Nodosaria, Orthocerina, Dentalina, Frondicularia, Lin- gulina, Rimulina, Vaginulina, Webbina, Conulina. 3. Group SOROIDEA. Chambers grouped in irregvdar masses. Fam. 10. AcERVULiNiDA. — Chambers usually globose, disposed very irregularly, and of pretty uniform dimensions ; shell finely perforate, with a few larger openings at. indeterminate places. Gen. Acervulina. The preceding account of the Ehizopoda we believe to be ample to lead the student forward in the study of that peculiar class of animals. Yet, with re- spect to the division Foraminifera it may be considered less complete : for, from the close attention given of late to those beings, every monthly and quarterly periodical of natural science teems with fresh facts and opinions concerning them ; and, above all, we have had placed in our hands, since the foregoing history was written, the very elaborate and critical researches of OF THE PROTOZOA. ACTINOPHRYINA. 243 Prof. Williamson and Dr. Carpenter, to which we would particularly refer the inquirer intent on following out his knowledge of the Foraminifera, but which both the dimensions and the character of the present work forbid the attempt to condense or analyse in its pages. Prof. "Williamson's work, ' On the Recent Foraminifera of Great Britain/ forms the volume for 1857, published by the Ray Society. Dr. Carpenter's learned essays on the structure of shells, on the value of form and other external characters in generic and spe- cific groupings, and on the structural and physiological relations of several genera, are to be found in the ' Transactions ' and in the ' Proceedings ' of the Royal Society. Additional facts concerning both the structure and relations of the several groups of Rhizopoda will be found in our Systematic History of them in Part II. SUBFAMILY OF RHIZOPODA, ACTINOPHRYINA. (Plate XXIII. 24-37.) This is a remarkable group of Protozoa, which can take its place neither with Ciliata nor strictly with Rhizopoda, although its affinities with the latter are very close. Ehrenberg attached the several forms of this family with which he was acquainted to his heterogeneous collection — the famil^^ Enchelia, and referred them to five genera, viz. Actinophrys, TricJiodiseus, Podophrya, Dendrosoma, and Acineta. Moreover, according to liis fundamental hypothesis, he represented them to have a mouth and an anus, an alimentary canal with ofi'shoots in the shape of stomach-vesicles, a sexual gland, and ova. Since the Berlin professor's investigation of these animalcules was made, several distinguished natm^alists have most carefully studied them, and particularly the Actinophrys Sol. In oui' last edition we named a genus Alderia, in honour of Prof. Alder, to distinguish certain organisms described by him in the Annals of Natural His- tory (1851, vii. p. 427). Subsequently, however, that eminent natui^alist wrote us to state that the name proposed had been abeady applied to a genus in an- other class of animals ; and on fiu-ther consideration and reference to Stein's researches, we were inclined to renounce their claim to a generic independ- ence, and to consider them three forms of Podophrya. Dr. S. Wright has, however, apparently observed the same beings very lately, and instituted a new genus, EpJielota, to receive them {Edinb. New Phil. Journ. 1858, p. 6). Notwithstanding the very close affinities of Actinophryma and Acinetina, there are sufficient differences between the two, and so many peculiar forms of the latter that they deserve a particular consideration. The history of the first family is very fairly represented by that of Actino- phrys Sol, or of Act. Eichornii, both of which have been very completely studied by Siebold, KoUiker, Claparede, Stein, and Weston. Some diversity prevails among these several observers respecting a few points in their organ- ization, which it wiU be incumbent on us to notice in the proper place. The species of Actinophrys have a circular figure, and are either spherical or so compressed as to have a discoid form (XXIII. 28, 29). The distinctive peuliarity of their figure is, however, due to the filaments or tentacles, which radiate from aU parts of their surface and give the beings (to employ a familiar and not inapt illustration) the appearance of a ball of cotton stuck thickly over with pins ; for the filaments have nodular extremities, or, in technical phrase, are capitate. The figure is determinate, and in this respect contrasts with the protean changes of form exhibited by Rhizopoda. Not that the figure is completely unalterable ; for slight variations are possible. r2 244 GENERAL HISTORY OF THE INFUSORIA. although slower than even those of Amoeba. Stein represents the usual orbi- cular figiu'e to be frequently exchanged for a pear-shaped, an oblong, or a partially angular and lobed one, — varieties dependent, according to his state- ments, upon inherent changes taking place in connexion with progressive de- velopmental phenomena. The aspect of the entire organism is, moreover, modified from time to time, by the altered length, direction, and disappear- ance of a portion of the filaments, chiefly consequent on the act of prehension in which they are engaged. Stein, indeed, represents still more considerable modifications, involving the complete disappearance of tentacles from various portions of the surface, and the aggregation of the rest upon angular emi- nences in a penicillate manner, — an occurrence which would assimilate still more closely the Actiiiojyhryina and the Ac'inetina. Lastly, the figure is varied durmg the acts of self-division and of conjugation, as will be presently noticed at large. In coloiu' the Actinopliryina are commonly of a milky-yellow or greyish hue, the intensity of which is determined by the number of contained granules, or, in other vvords, by the supply of nutriment. Acetic acid and cold solution of potash remove colour ; the latter fluid, when heated rapidly, dissolves the entire mass, and indicates its nitrogenous natiu^e. Observers are not agreed on the point of the existence of an integment. Dujardin, Xolliker, and Cla- parede deny it, whilst Stein, Perty, and Mr. Weston {J. M. S. 1856) affirm its presence. Among the latter, one speaks of it as a hyaloid membrane ; another declares it to be double, consisting of a delicate elastic membrane immediately investing the contractile substance of the animalcules, covered by an outer fii^mer timic. This statement is especially made by Stein of Podophrya, which is, in his opinion, a merely stalked variety oi Actino_phrys, and indistinguishable from it even as a species (XXIII. 1, 3, 4, 5). On the contrary, Cienkowsky (J. M. S. 1857, p. 98) remarks that he could discover no membrane surroimd- ing the body of that animalcule. To account for this diversity in descriptive details, we must suppose that the different authors have not had the same animalcule under observation ; indeed Stein asserts that Kolliker did not examine Actinophrys Sol, as he supposed, but Act. Eichornii. Lieberkuhn likewise suggests that Claparede and Kolliker have written upon difi'erent species under the same name ; and Stein must, we beheve, have committed a similar mistake ; for the Actinophrys and Podophrya described by him difter in so many important particulars from beings bearing the same name in the writings of others, that it seems impossible they can be identical with them. The fact seems to be that certain Acinetoi have in external characters so close resemblance to Act inophryma, thai they may be mistaken for them. Be this how it may, if we take into consideration the pecuhar relation of the tentacles with the body, their movements, and especially the mode of introducing food into the interior, it seems quite improbable that there should be a firm investing membrane. These remarks, indeed, apply only to the usual forms or phases of these beings ; for when an encysting process proceeds, then, certainly, an external envelope mil manifest itself, yet not without the sacrifice of the tentacula and of the ordinary phenomena of vital activity, the ingestion of food and the like. " It is impossible," to quote Claparede {A. N. H. 1855, xv. p. 286), " to admit the existence of a general integument, as Actinophrys can push out the mucous or gelatinous matter of which its body is composed, take in nourishment, or evacuate the residue of digestion, from any point of its surface at pleasure." In this same observer's opinion, Perty's notice and figures of a capsule are evidently erroneous, the consequence of optical illu- sion. Mr. Carter adopts an intermediate opinion, by admitting the existence of an enveloping pellicula, like that in Amoeba, which, although not a separable OF THE PROTOZOA. ACTINOPHRYINA. 245 layer or skin, is a somewhat iirmer or more condensed tissue than that sub- jacent. The Actinophryina are composed of a homogeneous elastic sarcode, occupied by granules in varying number, and by vacuolae. The granules are especially accumulated in the centre, to wliich they consequently impart a greater opacity and deeper colour. Hence several authors have spoken of a central medullary mass surroimded by a clearer cortical lamina (XXIII. 28, 29). Still there is no natural separability into two such portions ; for their relative size varies according to the supply of food received. Dr. Strethill Wright (in a letter) proposes to apply the unexceptionable terms " endosarc " and " ectosarc " to the medullary and cortical portions respectively. The contained granules are rounded, opaque, and, for the most part, of a fatty character. The granules are less abundant in the ectosarc ; but those of a finer sort are seen in smaller numbers even in the lower end of the filaments, and Lachmann (A. N. H. 1857, xix. p. 223) asserts that he has seen their motion there, as well as in the general substance of the body. Mr. Weston also remarks {op. cit. p. 122), *' With a -i-th objective I can distinctly see granules in constant motion in the body of the ActinopJirys, similar to those always found in the points of Clos- terium Lunula.'''' The vacuoles occur both in the cortical and medullary portions, but are smaller in the latter, and they never penetrate into the substance of the filaments. At first sight, as Kolhker notices, the tissue appears delicately ceUular : a closer inspection, however, shows that this is not the case ; for on pressure being made, a coalescence into larger, or, otherwise, a subdivision into smaller, areolae is the consequence (XXIII. 28, 29, 30). The tentacles or filaments give to the Actinophryina their most distinctive features. They are usually pretty regularly and uniformly distributed over the entire surface, and in figure taper from the base to the apex, which is sui^mounted by a rounded knob. Unlike other observers, Cienkowsky {J. M. S. 1857, p. 101) represents the capitate form to be exceptional, and that the rule is for the filaments to taper like setae. Dujardin, by the way, appears to have thought the capitate extremities accidental ; for he describes the filaments as often becoming globular in the act of contraction. In smaller specimens the filaments exceed the diameter of the body in the length, but in larger ones are not more than equal to, or are even less than, it. In the same species their number and position are tolerably constant. In composition, the tentacula are processes given off from the sarcode mass, and are destitute of an integument, as proved by their power of coalescence when approximated. They are retractile, and can be withdi^awn into the common mass ; they can also be dii-ected towards dififerent sides, and curved upon themselves. Perty states that they can assume so rigid a condition that other animalcules some- times impale themselves upon them ; this statement is nevertheless uncon- firmed, and, indeed, seems scarcely probable. KoUiker (op. cit. p. 31) speaks of the filaments as undergoing various changes of form, '" such as elongation, shortening, local sweUing, bending, &c It is especially interesting to observe that the filaments, singly or together, frequently disappear entirely, entering at last, as it were, by continued retraction, into the substance of the body, leaving no trace of their former existence .... whether the filaments which disappear are always reproduced in the same spot is not determined ; i-n some instances this did not appear to be the case, although in every instance the number and position of the filaments is pretty constant " — unlike the variable processes of Amoeba. Ehrenberg assigned to the tentacles, among other purposes, that of organs of progression ; direct observations are, however, wanting to prove this purpose, and both KoUiker and Stein are 246 GENEEAL HISTORY OF THE INFrSOEIA. quite unable to admit it as even probable. They have been supposed by- several authors to have a benumbing effect upon the prey they may seize ; but this view is merely hypothetical. '' It is nevertheless," says Claparede {ojp. cit. p. 287), " quite certain that small animalcules and plants remain adherent to them ; for these rays are true tentacles. Indeed, their contact must have something very unpleasant about it ; for larger Infusoria, even such as Paramecium Aurelia, on coming accidentally within their reach, start back with the greatest rapidity, sometimes even dragging the Actinophrys a considerable distance with them." So, again, Weston states — '' on the instant of contact with these tentacles, the victim appears paralysed." Yet, withal, it seems clear that, unless actual contact ensue, no harm attends proximity to the formidable prehensile organs ; for animalcules may frequently be seen swimming about unharmed among them. Kolliker rejected the supposition of an intrinsic fatal influence existing in the filaments, wliich appeared to him to serve only for retaining the prey by their adhesive surface, and pro- bably to involve it with their extremely fine extremities, until they di-ew it by their progressive contraction to the surface. Even after being seized upon, an animalcule may escape, both by great exertions in tearing itself away, and sometimes, as Mr. Weston remarks, by the act of the ActhiopTirys, when, as it Avould seem, its appetite was " sated, or the prisoner was not approved ; for after remaining stunned sometimes for a few seconds, four or five, some- times much longer, ciliary motion (of a Vorticella, for instance) is feebly com- menced, not ^^ith sufiicient energy to produce motion, but as if a return to vitality were being effected by struggles ; shortly it is seen to glide off the tentacle (as if this appendage possessed the power both of appropriation and rejection), and, frequently with but little sign of recovered life, it slowly floats out of the field." One function distinctly possessed by these tentacula is that of sensibility. KoUiker has thus well conveyed this fact {op. cit. p. 33) : — "Actinoj)h'i/s perceives mechanical influences, and reacts upon them by movements. This is proved by what takes place when animalcules, &c. remain aflixed to its tentacles, and moreover by the circumstance that, when the water in which it is contained is carelessly agitated, every ActinopJirys contracts its tentacles and even makes them disappear altogether (and, indeed, with greater speed than is otherwise perceived in these creatures), and when all is quiet they are again protruded. These filaments, conse- quently, may just as well be called tactile as prehensile ; or it may more generally be said, that the substance of the body is both contractile and sensitive." Movements. — There is not much to be said respecting the movements of the Actinophryina ; for these beings are even more sluggish than the Amcebcea, and appear to change place rather as mere passive particles of matter than as living animals. They may float hither and thither in the fluid surrounding them, or rise to the sm-face ; but how this latter movement is effected we have no data to show. On this subject KoUiker has the following paragraph : — " Its power of moving from place to place is indubitable ; for it was found, for instance, that when a vessel, with several individuals of Actinophrys, was emptied into a flat glass capsule, they were all at flrst scattered about at the bottom, but subsequently, after from 12 to 24 hoiu's, were all floating at the surface, and, indeed, at the side of the capsule. Ehrenberg and Eichhom assert that the ascension of Actinophrys in the water is effected by the taking in, and the descent by the gi\ing out, of air. But this is certainly not the case ; for whence could they obtain this air ? Can it be said they secrete it within themselves like fishes ? In that case it must be visible. It appears to the author more natural that the rising and sinking should be effected by OF THE PROTOZOA. ACTINOPHRYINA. 247 alternate eontractions and expansions of the whole body. Other motions can affect both the filaments and the body, but in any case only through the slowest possible contractions." Besides these ill-understood translations from place to place, and those movements chiefly affecting the tentacles in the act of taking in food, to be presently noticed, there also occur, according to Kolliker, ^' faint indications of contraction, such as slight undulations of the border, and inconsiderable quivering motions here and there. The creature also seems to be capable of altering its entire form to a certain extent, and to be able to expand and to contract itself in toto^ Stein contradicts these statements, affirming that he could neither observe any movement in the organic mass, nor any change of position, whilst Claj)arede, on the other hand, writes, '^ nevertheless the animal, in its ordinary sun-like form, is able to move slowly in a given direction ; but during this movement no contraction of the body or bending of the tentacles is to be observed." A singular obser- vation is recorded by Mr. Boswell {T. M. S. 1854, p. 25), which needs con- firmation before it can be accepted, viz. that the Actinophryina can suddenly change their place by a leap. This phenomenon, he tells us, he witnessed twice among a number of the animalcules found floating on the suiface of the water. Usually the Actinophrys is found attached to some object, and that so firmly that large animalcules may strike against it, or strong succussions of the water take place without loosening it from its hold. Podoplwya and Demh'osoma are exceptional Actinopliryina, by possessing a pedicle. In the former this stem is commonly short and always simple, whilst in the latter and hitherio little-known genus it is branched. As elsewhere noticed, Stein will not admit the pedicle of Podophrya to be a generic, indeed not even a specific, distinction, and therefore treats Actinophrys and Podophrya as identical. In connexion with his belief in the presence of an enclosing integument, he describes the wall of the hoUow pedicle of Podophrya to be continuous upwards with the external envelope of the body (XXIII. 3, 4). It is proper, however, to remember that Stein wanted both to establish his hypothesis of the conversion of Vorticella into an Actinophrys and Podophrya, as a consequence of the act of encysting, and preparatory to embryonic repro- duction, and, further, to assimilate those genera with various Acinetce, which, in his opinion, were derivable from other members of VortlceTlina. This detracts from the value of his details of the structure and functions of Actino- phrys ; and, as expressed above, a great doubt suggests itself whether he has always examined the selfsame animalcules, and whether what he has de- scribed applies to the Actinophrys investigated by Kolliker and Claparede. Cienkowsky, who has latterly tested Stein's hypothesis, asserts, respecting the question of the structure of the stem of Podophrya, that the pedicle is an appendage to the body, which has no integument. " I am unable " (op. cit. p. 100), he writes, " to adopt Stein's view that the Podophrya are enclosed in a membrane, of which the slender pedicle is simply a tubular protrusion. This is true only with respect to the short peduncle of the encysted Podophrya " (XXIII. 36, 37). Prehension and Entrance of Food. — The movements of the tentacula of Actinophryina are chiefly directed to the prehension of prey for food. This they eff'ect primarily by seizing it by means of their apparently sticky surface, and then, by shortening themselves, drag it to the surface of the animalcule. If the prey has been caught by one tentacle, the neighbouring ones conspire to clutch it more firmly, and (to use Kolliker's words) " apply themselves upon it, bending their points together, so that the captive becomes gradually en- closed on aU sides." This concui'rence and crossing of the tentacles is men- tioned also by Stein ; but Mr. Weston states that he has never witnessed it. 248 GENEKAL HISTORY OF THE INFUSORIA. Concerning the mode of entrance of the nutritive matter when di'awn to the surface, some difference of opinion prevails among the several writers who have treated of it. Ehrenberg, true to his hypothesis, attributed to Actino- phri/ina a mouth sui^mounted by a proboscis, and an anus at the opposite side Avith an intercommunicating intestine and numerous stomach-sacs opening into it. In short, they were, according to his scheme of organization, Enantiotreta, of the class Enterodela. Dujardin rejected this account, and supposed them to be nomished by absorption, carried on by the general siuface, or by means of thick expansions from it. At the present time all observers unite in denying a mouth, anus, and alimentary canal to Actino- phryina, and in admitting that food may be introduced, and its debris dis- charged, at any part of the smf ace, — a fact patent to direct observation, which shows the seizing and the entrance of prey going on, occasionally, at more than one point at a time (XXIII. 29-32). We have followed the captured morsel until it apjDroaches the sui'face, and when the force of the tentacles behind it still tends to press it onwards into the body. The following pro- ceeding, according to Kolliker {op. cit. p. 28), now takes place : — " The spot of the sui'face, upon which the captured animalcule is lying, slowly retracts and forms at first a shallow depression, gradually becoming deeper and deeper, in which the prey, apparently adherent to the surface and following it in its retraction, is finally lodged (XXIII. 29 m). The depression, by the continued retraction of the substance, now becomes deeper ; the imprisoned animalcule, which up to this time had projected from the surface of the ActinophrySy disappears entirely Avithin it ; and at the same time the tentacles, which had remained with their extremities applied to each other, again erect themselves and stretch out as before. Finally, the depression acquii'es a flask-like form, by the di^awing in of its margin, the edges of which coalesce ; and thus a cavity closed on all sides is formed, in which the prey is lodged. In this situation it remains for a longer or shorter time, gradually, however, ap- proaching the central or nuclear portion, and at last passing entirely into it in order to await its final destination. In the meanwhile the external por- tion of the Actinophrys regains in all respects its pristine condition. The engulfed portion is gradually digested and dissolved." Whilst admitting the general correctness of this account by Kolliker of the act of inglutition, Stein asserts that, prior to the appearance of the prey in a depression of the body, a large vacuole, rising above the smface, comes into contact with it, and then, by its collapse, drags it downwards into the substance of the animalcule. This stage he supposed KoUiker to have overlooked. However, Claparede denies that the reception of food is ever effected by means of the expansion and contraction of a vesicle, or that, as Kollilier believed, the food penetrates the substance of the body by the force exercised upon it behind by the tentacula : it is rather, he says, the substance of the body which approaches and embraces the food ; for before the latter has touched the surface of the body, it is seen to be envelojDed in a kind of mucus. -' This mucus is com- pletely undistinguishable from the parenchyma of the Actinoplirys ; it appears as though the substance of which it is composed had suddenly drawn itself over the captured object. The elevation thus produced then slowly flattens; and by this means the food is gradually di^awn into the body. Astasice, which I frequently saw sucked in by Actinophrys in this way, continued to move for a Httle time, endeavouring to break thi-ough the substance that enveloped them ; their movements, however, soon ceased ; they became converted into a globular mass, which circulated very slowly through the parenchyma with the so-called vacuola." . . . . " At fii'st I thought the substance, which so suddenly enveloped the object to be swallowed, was produced by the mere OF THE PROTOZOA. ACTINOPHRYINA. 249 bending, expansion, and fission of the tentacles. I could not, however, retain this opinion: an extension of a mucons substance, apparently the parench}Tna, really takes place from the side of the Act'mo]phrys ; and this is afterwards drawn in with the prey. This expansion sometimes takes place very slowly ; a thick, regularly lobed mass is seen to embrace the object ; and I have once observed this extension Avithout the presence of any prey. I can only compare this process with what takes place in Amoeba ^ Dr. Strethill AYright (in lit.) expresses the same fact in a condensed form, thus : — " In Actinophrys the tentacles bring the food to the sui-face of the ectosarc, which closes over it and cames it to the endosarc." Mr. Weston's observations tend to a similar interpretation of the mode of introduction of food. " From the margin of the body of the Actinophrys,^^ says this gentle- man, " a thin pellucid membrane is projected up the side of the creatui'e destined for food (XXIII. 24-32), which proceeds rapidly, but almost imperceptibly, to siuTound one side of it ; a similar membrane sj)rings sometimes also from the Actinojplirys, but more frequently from the tentacle on its other side ; these amalgamate on the outer surface of the prisoner, which is thus enclosed in a sac composed of what I take to be the extended outer vesicle of the Actinopjhrys. This vesicle gradually contracts, or, rather, seems to retiu-n by elasticity to its original position ; and the food thus be- comes pressed within the body, there to become digested." The conclusion to be drawn is, that, after the act of prehension by the tentacles is complete, the retraction of those processes is succeeded by the protrusion of a sort of variable i^rocess, similar to those of Amoeba in character, and also in its mode of enveloping and engulfing the morsel. After its admission into the soft substance of the interior, the nutrient matter undergoes a process of digestion, by which, if soft, it suffers complete dissolution and absorption ; but if it contain insoluble matter, this remains behind, after the disappearance of the rest, as a residue to be sooner or later cast out through an apertiu-e temporarily formed at the point of the surface it comes into contact with, and of which aE. trace is lost so soon as the act of extrusion is accomphshed. The molecular and granular matters derived fi^om food coUect especially in the central or nuclear portion of the body, the depth of coloiu', opacity, and strength of which are directly proportionate to the supply of food. The particle of food (the animalcule or other substance), when in the interior, is surrounded by or suspended in a drop of fluid, or, in Dujardin's phi^aseology, occupies a vacuole. This fluid is either di-awn in by the act of inglutition, or is a secretion pom-ed out around the food for the pm-pose of digestion. Claparede takes the latter view, and states that the fluid always exhibits the same pale-reddish colour as the contents of the contractile vesicle, and indicates different refractive powers from those of water. This observation accords with one made by Sclmeider, of the digestive vacuoles of Amoeba. The process of digestion is slow. Claparede observed the changes of a Chlamydomonas, and states that three hours scarcely sufficed for its conver- sion into an unrecognizable gelatinous mass. KoUiker represents the time to vaiy from two to six hom^s ; but this must differ jDerpetuaUy according to the nature of the food, the \itality of the animal, &c. '' The number, as well as the size," writes Kolliker, " of the morsels taken at one time by the Actinojyhrys is very various. Yeiy frequently there may be 2, 4, or 6 at the same time, frequently also more than 10 or 12. Ehrenberg counted as many as 16 stomachs, i. e. in other words, so many separate morsels. He also noticed the ingestion of indigo, which could not have gained admission in any other way than that by which the Infusoria and other ahmcnts enter. The largest morsels 250 GENERAL HISTORY OF THE INFUSORIA. noticed consisted of a Lynceus and a young Cyclops. Eichhorn, indeed, mentions a water-flea {Daplinia ?), about the size of which, however, no re- mark is made." Indeed, the Actinophryina are rapacious animals, and will appropriate to themselves any organisms, vegetable or animal, which fall in their way. Thus, besides those beings alluded to already, Eotifera, various minute Crustacea, Cihated Protozoa, Phytozoa of all sorts, Desmidieae, Dia- tomeae, minute Algae, and their spores ahke fall a prey to these remarkable animalcules. The excrementitious particles of food, as already stated, pass out at any spot where circumstances may dii-ect them ; and no definite anal aperture, such as Ehrenberg imagined, has an existence. The expulsion of re- sidual matters, Mr. "Weston {J. M. S. 1856, p. 121) states he has " fi'equently seen, — in one specimen twice in less than half an hour, at diiferent spots. In watching the digestion of a Rotifer, it occurred to me to see a dark body, composed apparently of the case, remain for some hours in the same spot, and then gradually approach the side, as if for expulsion ; but while waiting for this to take place, an opening in another part occuiTed, and excrement was voided in quantity : this voided matter lies amongst the bases of the tentacles, while the opening through which it has passed closes ; and then, with the same stealthy motion I have before described, it is apparently diiven along the tentacles (as if by repulsion) beyond their extremities, finally dis- appearing in the surrounding medium." Contractile vesicle. — The rule is, that only one contractile vesicle belongs to each animalcule (XXIII. 36, 37). If more appear, it usually indicates either the approach of fission, or the conjugation of two or more individuals (XXIII. 33-35). Kolliker failed to recognize this organ in Actinophrys, and concluded that Siebold had described as such the mere changeable vacuola. However, Stein, Claparede, Cienkowsky, and others concur in representing a contractile vesicle as normally present ; the fii'st-named writer, indeed, de- scribes in a few instances two such, as Siebold has done before him. Stein exhibits, in Actinophrys Sol, the vesicle as central (XXIII. 1) ; but other naturahsts concur in representing it as supei-ficial, — so much so, according to Siebold, that it will frequently dming its expansion project above the general surface, and thereby prove itself to have a distinct wall (XXIII. 29 m) ; for if composed of only the gelatinous parenchyma of the body, it would burst at the moment of greatest expansion. It is, therefore, a closed sac or cell. Claparede has never found more than one vesicle, and thinks both Siebold and Stein in error in describing two. " Several vesicular elevations," he writes, " often occur on the margin ; but only one of these is contractile. I have, however, observed two contractile vesicles in several individuals ; but in these cases the form always gives rise to a suspicion of fission, or of an amalgamation of two individuals (Act. clifformis, Ehr.). The presence of a single contractile vesicle does not, however, appear to be imiversal among the Rhizopoda ; I have observed two in Arcella vulgaris .... It is surprising that Kolliker, who was acquainted with Siebold's observations, should have cha- racterized them as inexact, and as arising fi'om an illusion. According to him, Siebold had mistaken accidental expansions and contractions of the sub- stance enclosing the vacuoles, in which the latter were persistent, for phe- nomena indicating the existence of contractile reservoirs. This, however, is not the case ; the size, the unchanging position, and the regular expansion and contraction of this organ will prevent its being confounded with a vacuole. That KoUiker should have overlooked it is particularly iminteUigi- ble, as the phenomenon is immediately presented by nine out of ten specimens of Actinophrys.''^ Carter {A. N. H. xviii. p. 129) makes the curious assertion, that the '^Actino- OF THE PROTOZOA. ACTINOPHHYINA. ' 251 ■phrys Sol, Ehr., is siuTounded by a perii^heral layer of vesicles " (he is speaking of contractile vesicles), " which, when fully dilated, appear to be all of the same size, to have the power of communicating with each other, and each, individually, to contract and discharge its contents externally, as occasion may require, though generally only one appears, and disappears, in the same place." Stein describes and figures a row of vesicles immediately beneath the surface of a new species he calls Actinojphrys oculata (XXIII. 24, 25), but does not, hke Carter, treat them as so many contractile sacs, an interpre- tation which cannot be received without much more extended inquiiy and confii-mation. Notwithstanding this assertion, Mr. Carter, in his outline of facts relevant to contractile vesicles in general, has the following clause, ap- plying specially to the animalcules under consideration, and giving a most apt illustration of the phenomena witnessed : — " In Actinophrys Sol, and other Amcehce, diuing the act of dilatation, the vesicula projects far above the level of the pellicula, even so much so as occasionally to form an elongated, transparent, mammilliform eminence, which, at the moment of contraction, subsides precisely like a blister of some soft tenacious substance that has just been pricked with a pin." At another part, this same author says, generally (op. cit. p. 128), and in some measure contradictoiily to the first statement quoted from him, that "in Amceha and Actinoplirys the vesicula is generally single ; sometimes there are two, and not unfrequently in larger Amoebcea a greater number." It should be mentioned that Stein found in the animal- cule, which he took to be Act. Eiclioy^nii, a superficial group of vacuola, ren- dering the outline irregiilar, — a phenomenon no doubt the same as that intended by Carter. Stein, moreover, described in the same animalcule two contractile spaces, one at each pole, immediately beneath the surface, but capable of alternately elevating themselves above, and depressing themselves within it, and of thereby aiding to introduce food. Podophi^ya has, according to Stein and Cienkowsky (XXIII. 34, 35, 36, 37), a single circular contractile vesicle. Stein, indeed, figures two in one specimen. So far as appears, the vesicle is not placed so close to the surface as in Actinophrys. Among other structui'es mentioned by Ehrenberg, was a contractile proboscis, by means of which the animalcule was supposed to re- ceive food ; but other observ^ers have looked in vain for any process to which such an appellation could with justice be apphed. The structure intended by Ehi'enberg is, in Claparede's opinion, no other than the contractile vesicle, — an opinion in which Mr. Weston seems to agree (see below), although he attributes to it a structure and action without parallel in other Infusoria. A glance at the quotation above made from Mr. Carter's paper will show also that the contractile sac was intended. The following are the observations of Claparede, referring to the matter in question: — *Trom time to time a globular prominence rises slowly and gradually from a particular point on the surface of the animal ; this increases more or less in difi'erent cases, sometimes, espe- cially in small individuals, attaining nearly a thii^l of the size of the entire body, but generally reaching only -i-th or ^ij-th of that size. The margin of this projection is always well defined, much more so than the other parts of the body, especially when it has attained its greatest evolution. At this moment it contracts suddenly and disappears entirely, so that a flattening of the outline is often to be observed at the point previously occupied by this remarkable elevation : the margin soon becomes rounded again ; the globular projection gradually rises, attains its previous highest development, and then suddenly disappears again." The following paragraph from Mr. Weston's paper {J, M. S. 1856, p. 116) refers, doubtless, to the selfsame expanding and contracting process distinguished by Claparede : but the fimction of respiration 252 GENERAL HISTORY OF THE INFUSORIA. and a valvular structure of a very extraordinary natui'e are attributed to it. We suspect, indeed, that Mr. Weston has been led into error by appearances, — a supposition he will pardon us for making, since, as he himself tells us, his microscopic experience is less than two years old. His account runs thus : — " There appears to be no doubt about the existence of a valvular opening : I have had some thousands of these animalcules under my observation, and have never met mth a specimen where the valve was absent. It is best distinguished when about the edge of the seeming disc, and, so far as my observations go, is never still night nor day, — being slowly, but without cessa- tion, as it were, protruded, occupying from 10 to 70 or 80 seconds in its development, and then, like the bursting of a vesicle, rapidly and totally subsiding ; for an instant it has utterly disappeared, only to be again as gradually and as certainly reproduced. Should that side of the creature, where the valve is placed, be tiu-ned from the observer, the effects of the contraction are distinctly seen, although the valve itself is not ; for at the instant of its bursting and closure, some half-a-dozen or more of the tenta- cles, situated on or about it, which have been gradually thrust from their normal position by the act of its protrusion, now rapidly approach each other with a jerk-Hke motion, caused by the sudden biinging together of their bases. " With -i-th of an inch objective, I have been led to imagine the valve to be formed of a double layer of the external hyaloid membrane, the edges of which appear to adhere to each other tenaciously, notwithstanding the growing distension from within, until the force becomes so great that the lips, as they may be called, suddenly separate, apparently to give vent to some gaseous product ; and at this moment there is, as I have stated, enough seen to induce the belief in the existence of a double lip -like valve, perhaps the organ of respiratioyi.''^ He afterwards adds (p. 118) — " In many instances I have seen half-a- dozen or more prisoners attracted to the tentacles of an individual, each gra- dually absorbed ; and although thus busily occupied, no cessation of the action of the valve takes place." Stein imagined the movements of the contractile sac to be subservient to the reception of food ; but this supposition, as men- tioned already (p. 248), is opposed to analogy, and is wanting in direct obser- vation to establish it. Among the general contents of the body of Actinophrys, Kolliker (pp. cit. p. 27) mentions some separable nuclear cells as detached by crushing from the innermost portions of the animal. When isolated by pressure, they be- have themselves as cells, with nucleus and nucleolus, sometimes as free nuclei. " The author is, in fact, inchned to regard them as cells and nuclei, Ipng in some of the interior vacuoles ; for such, and such only, are the vesi- cular spaces in which they are enclosed." (XXIII. 29.) NucLErs. — Kolliker applied the term nucleus, very improperly, to the more granular and darker central or medullary portion of the body (XXIII. 29 h), and overlooked the presence of the real nucleus. However, Stein, Carter, Cienkowsky, and others have determined the existence of this organ in the genera Actinophrys and Podophrya. Unfortunately, some difference prevails in the descriptions of this organ by the several observers, which it is most desirable to have removed. Carter {A. N. H. 1856, x\iii. p. 221) represents it to be a cloudy body, " discoid in shape, of a faint yellow colour, and fixed to one side of a transparent capsule, which, being generally more or less larger than the nucleus itself, causes the latter to appear as if suiTounded by a narrow pel- lucid ring." Stein describes it in Actinophrys Sol as finely granular, band- shaped, and curved, or reniform, or rounded oblong (XXIII. 1 b). Cien- OF THE PROTOZOA. ACTINOPHRYINA. 253 kowsky says that the nucleus of PodopTirya is ^' transverse and frequently curved," and thereby implies that it is an elongated body. The nucleus of Actinojphrgs oculata (says Stein, p. 159) may be brought into view either by crushing the animalcule, or, much more satisfactorily, by adding dilute acetic acid (XXIII. 24 h, 25 g). On viemng it from above, it appears like a round hyaline cell, containing a granular nuclear mass in its centre, and suiTounded by a rather condensed layer of the medullary matter. On its entire detachment, by means of the acid, it is seen to possess a distinct wall, ha^i^ng a double out- line ; its nucleolus, on the contrary, seems undefined and irregular in shape, composed of a mere heap of fine granules. The relative size of the nucleus to the whole animal is veiy considerable. Thus, whilst the majority of spe- cimens had a diameter of 1-38 to 1-35'", the nucleus measured 1-125'", and its nucleolus 1-250'". From his account of Act. EicJiomii, Stein would appear to have seen a similar nucleus in that species ; for he states that the round nucleus appeared hke a nucleus-holding cell, having a double contoui' and clearly-defined waU, and containing a large, finely-granular nucleolus. Encysting and Repeoductive Processes of Actinophryina : — Encysting — • Fission — Gemmation — Embryos — Conjugation. — Stein represents his Acti- nophrys Sol and Podophrya fixa as having a double integument (XXIII. 1, 3), through which the tentacles penetrate, — whilst, as we have seen, other ob- servers insist upon the naked state of the muco-gelatinous body of those as well as of the other species of Actinophryina. The questions therefore arise, whether the being so named and described by Stein is identical with that in- tended by other naturalists, and, if so, whether it is not, in the so-called encysted condition, at least in its earlier stage. For Stein subsequently describes and figures truly encysted examples, in which the cyst appears like a plicated loose sac around the contracted body, and the tentacles in part or wholly gone (XYIII. 3). Cienkowski afiirms (0^3. cit. p. 101) that the being described as Actinophrys by Ehrenberg is really a non-pedunculate Acineta ; and he further remarks that, although numerous points of relation exist between certain ^cme^a -forms and Poclophrya flxa,h.e is unable to determine whether they should be regarded as identical, or as the extreme links in the morphological cycle of one and the same species. The same critical observer details the process of encysting of PoclopJirya, — a process, by the way, which he has not met with in ^t-me^^-form organisms having a general resemblance with it. To quote his account {op. cit. p. 99), " If PodoplirycB are allowed to remain several days upon the object-glass, and care is taken not to let the water diy up, eveiy stage towards the quiescent condition — that is to say, towards the ' encysting ' — may be followed (XXIII. 34, 36, 37). *' In Podophi^y a ihi^ process takes place in the following manner: — On the surface of the body a gelatinous mucous layer appears to be secreted, through which the tentacles pass. The tentacles disappear in the neighbourhood of the peduncle ; and the gelatinous layer in this situation hardens into a loose transversely-plicated membrane, whilst at the upper end it is still soft, and the^ tentacles clearly visible. Ultimately these also are retracted, and the entire body of the Podophrya is enveloped in a wide loose membrane ; the plications are caused by parallel annular constrictions, placed at equal di- stances apart, and separated 'by circular, angular, or rounded ridges ; these pli- cations are in a plane perpendicular to the peduncle. At the summit of the Podophrya, and often also at the base, the membrane presents deep depres- sions ; the inclosed body of the Podophrya acquires on its surface a sharply- defined smooth membrane, whilst the contents of the body become somewhat opaque, enclosing a round clear space. The Podophrya-ajst thus formed is supported by a peduncle, which is widened at the base. In many instances 254 GENERAL HISTORY OF THE INFUSORIA. in which the membrane was not plicated, but loosely enclosed the Podophrya like a sac, I noticed that the peduncle of the cyst was continued uninterrupt- edly into the membrane, of which consequently it must be regarded as a pro- trusion, and that it had no connexion whatever with the original slender pe- duncle of the Podophrya itself. In fact, I noticed cysts in which this original slender peduncle was appended to the saccular envelope. I am unable, there- fore, to adopt Stein's view that the Podophryce are enclosed in a membrane, of which the slender peduncle is simply a tubular protrusion. This is true only with respect to the short peduncle of the encysted Podopliryce. " What afterwards becomes of the cysts I have been unable, in spite of ob- servations continued for months, to determine." Multiplication by Spontaneous Division seems now to be sufficiently de- monstrated. Ehrenberg and other earlier writers, indeed, mentioned the occurrence of self-fission ; but their accounts were too uncertain and inde- finite, and strong doubts prevailed whether they had actually witnessed that process, or the act of conjugation, to be presently noticed. Mr. Brightwell appears {Fauna Infusoria of Norfolk) to have confounded the two processes ; for he says — " They multiply by division, so that two and sometimes three individuals are seen adhering together by theii' outer edge — the middle one, the parent, being the largest," — an explanation inconsistent with the process of fission as generally understood. Claparede states distinctly that he has seen the act of fission ; "Weston describes it in Actinoplirys, and Cienkowsky in Podophrya. " With regard to the reproduction of Actinophrys Sol/' writes Mr. Watson (op. cit. p. 119), " I can positively affirm that self-division is one mode ; for I may say I have witnessed it a hundred times and shown it to others .... First was noticed a deep depression above and below, not far from the centre of the body ; this, as it increased, threw the tentacles across each other, in a manner similar to that described by Kolliker, when in the act of inclosing an object of prey. This crossing, however, in the act of self- division would appear to be only the necessaiy consequence of the depressions alluded to, and the position into which the outer membrane (in which the tentacles are inserted) is drawn. As division proceeded (XXIII. 31), the two animalcules steadily, but rather quickly, increased the distance between them, until the connecting medium was apparently a long membranous neck, which, to my unpractised eye, appeared composed first of four, then of three, then two irregular lines of cells (possessing no nuclei), which ultimately di- minished into a single cord composed of three simple cells elongated like the links of a chain, this becoming gradually more attenuated, imtil the exact moment of its division could not be seen. All this latter portion of the pro- cess was rather rapidly performed, — that is, from the first formation of the rows of cells to the time of what I supposed to be the final separation, occupied only about a quarter of an hour .... During the whole of the process, the valve (^. e. the expanding and contracting superficial vacuole) of each segment, situ- ated at nearly opposite extremes, was in constant action, and each creatui-e Avas busily employed seizing its food." On following one segment after its separation, " a floating faint line, the broken thread " (of connexion), extended from it; and two of the cells, formerly contained within this bond, were attached to its side, but were in a few minutes drawn into the body of the Actinophrys, which there assumed a perfectly normal character. In Podophrya the process of fission is similar (XXIII. 34) ; at first an annular constriction displays it- self, and so rapidly deepens, that in an about half- an -hour complete trans- verse fission is effected. The history of the segments is thus portrayed by Cienkowsky (ojd. cit. p. 98), about ten minutes after the commencement of the act of division: — "The upper segment had assumed an elongated form, was more OF THE PROTOZOA. ACTINOPIIRYmA. 255 cylindiical, a little indented in the middle, and I'oimded at each end ; and at the extremities, slight oscillations to the right and left could be perceived. A transverse, and frequently curved, nucleus was visible in the fluid contents ; and a lateral contractile space could be clearly distinguished in the upper parts. The vibrations increased in frequency and force until the segment became whoUy detached and escaped. During the process of division both segments were furnished with tentacles ; but when the oscillations of the cylindrical portion commenced, very fine and short cilia might be seen, though with difficulty, vibrating on the free end, — the tentacles at the same time being retracted, and remaining visible only on the posterior segment. I now followed uninterruptedly the movements of the liberated segments. They moved for the most part in curved Hues, in the course of which the motile segment appeared to seek the illuminated side of the drop of water. Cilia could not be perceived over the whole sm-face. The contractile space during the movements was al- ways in front. The motions were rapid, but still such as to allow of their being followed with a magnifying power of 370 diam. After waiting patiently for twenty minutes, I saw the motion cease ; and at the same time short tentacles made their appearance, which were protruded more and more ; and in a few minutes afterwards the segment regained the spherical form : thus, after moving about freely for a time, it was again transformed into a Todoplirya. " This process of division was witnessed by other observers. It takes place more especially when sufficient nutriment is supplied by numerous Stylony- cMce to the PodopTiryce. The Podoi^hrya does not always divide into two equal halves ; the segments are more frequently unequal. After repeated division, the specimens always become more transparent." This temporary production of vibratile cilia from the surface of one of the Actinopliryina, in connexion with the process of fission, is a phenomenon so opposed to received notions, that it will necessarily be admitted with great reserve until confirmed by repeated observation. The process of Gemmation is recorded by Lachmann to occur in Dendrosoma radians, a being of which we know too httle to pronounce with certainty if it be one of the Actinophryina or of the Acinetina. He says (op. cit. p. 231) — " In Dendrosoma radians, Ehr., a branch of the nucleus grows mto the bud whilst it still remains united to the parent animal." Reproduction by Embryos or Germs has been presumed by several autho- rities. Stein, in pursuing the history of the organisms he identified with ActinopJirys Sol and PodopTirya fixa, satisfied himself of the successive development in their interior of a ciliated germ, which he compared to the gemma of a Vorticella, into which, indeed, he supposed it subsequently to ftdly unfold itself (XXIII. 2, 4, 5). However, as before noted, Cienkowsky rejects the beings observed by Stein from Actinophryina, and treats them as Acinetina ; yet he, at the same time, confirms the production of ciHated motile embryos within Acineta, but declares them reconverted into similar Podophryce to those that give birth to them. Apart from the researches of Stein, which have invoked so much attention to the development of Protozoa generally, and particularly to that of Actinophryina and Acinetina, the idea that the members of the former family probably reproduce themselves by germs has been suggested by the occurrence of very minute individuals, either alone or in clusters. Thus KoUiker remarks (op. cit. p. 34) that the smallest individuals of Actinophrys Sol measured only 0-01"' to 0-02'", and presented very inconspicuous and few granules, and that the granular and vesicular corpuscles within the nuclear portion of the body may be germs just beginning to be evolved. Mr. Weston is also led to believe in the internal generation of minute germs ; but the obseiTation he records, as 256 GENERAL HISTORY OF THE INFUSORIA. possibly an instance of such a process, entirely fails, in om^ opinion, to sus- tain the supposition. The occurrence alluded to was that of a thin, pellicular, irregularly-shaped sac — sometimes of two or three such, — which elevated itself above the surface of the ActinojDlirys, and presently burst, emitting some fluid and fine granular matter, and then contracted. " Does this emitted fluid," he asks, " contain the germ of future generations?" We think not ; for, to our mind, the phenomenon mtnessed was nothing more than the bursting of superficial vacuola, j^robably acting as excrementory media ; and if this view be not correct, Mr. Weston's is improbable, inasmuch as such a discharge of germs from superficial sacs is without parallel in the history of Protozoa. Conjugation. — The remarkable act of conjugation, also known as Zygosis, has attracted very much attention in the class of animalcules under consi- deration, among which it is of very frequent occurrence. Much discussion has taken place concerning the purpose of this process. Most of its early observers considered it a reproductive act, a sort of copulation between two individuals ; but the tendency of opinion at the present day is to deny it this natui^e, and to treat it as little more than an accidental phenomenon, without apparent object or aim. Nevertheless its occurrence is so fi-equent, and the process of so complete a character, that it is hard to believe it to be in vain and to no purpose in the economy of the Actitiojpliryina. A difi'erence of opinion likewise prevails as to the nature of the process, one set of authors maintaining that there is an actual fusion and intermingling of substance between the conjugating animals, whilst another party asserts that there is no fusion, but merely a temporary adhesion or accretion between their bodies. The determination of this question is very necessary before we can speculate fairly respecting the pui'pose of the act. Kolliker, who was among the first to carefully explore this phenomenon, described it as a process of complete fusion, and surmised it to be of a reproductive character. Stein speaks at one place of conjugation {op. cit. p. 148) in Act'moplirys and Fodophrya as consisting in a fusion ( Verschmehung) of the animalcule. At another (p. 160) he describes it as an organic union of two or more individuals into a group, involving no fusion of their contents, but only a cohesion by their suii'aces ; and goes on to say (p. 161) that the coming together of two Actinoplirides is due to external forces, and that the first thing observed is an entangHng together of their tentacles, which act precisely in the same manner as when a foreign body is seized upon, and by their contraction bring the bodies into apposition. At the same time they fuse together and form a sort of commis- sure, which is sometimes areolated, owing to interruptions to its continuity by the incomplete confluence of the tentacles. In the case of Act. oculata, several — as many as seven — individuals were seen by Stein connected toge- ther, in a line, by this intermediate commissural matter, which he calls a common mantle, — but all of them preserving their individuality, just as in the instance of other species. This mode of connexion, by means of an interposed matter derived fi'om the tentacula of the conjoined siu-faces, explains what Stein means by conjugation being a fasion of the animalcules concerned — not a fusion or commingling of their substance in general, as some have thought it. Cohn, in his account of the conjugation of Actinoplwys {Zeitschr. Band iii. p. QQ), noticed the connecting band or commissure to sometimes contain, besides granules, particles of food, and vacuola, a vesicular body which he presumed to be nuclear, or a germ, developed as a consequence of the zygosis in operation. Stein encountered once or oftener a similar body, but concluded that it was accidental, probably of vegetable origin, and not in any degree embryonic; and (p. 164) he expresses himself satisfied that this act of con- OF THE PROTOZOA. — ACTINOPHRYIIfA. 257 jugation is not associated with the reproductive faculty. In fact, he has never met with the development of an embrj'o in conjugated individuals of his (Acinetiform) Actinophrys and Podophrya. Claparede questions {op. cit. p. 286) whether the compound forms noted by Stein and Perty were, as they supposed, all derived from conjugation ; and he proceeds to say that, if it be proved that more than two individuals may thus be fused together, the connexion of conjugation with reproduction will become exceedingly doubtful, and that the term had better be di'opped, and either Stein's phrase " process of fusion," or Ehrenberg's word " zygosis," adopted in its room. Whatever value attaches to Claparede's deduction from the circumstance of more than two being fused together, there can be no doubt that this may, and indeed does frequently, happen. Lieberkiihn, one of the most recent investigators of this group of beings (Zeitschr. 1856, 308), recognizes the occurrence, and observes that the number united may be estimated by that of the contractile vesicles. The process, he further asserts, is not one of genuine conjugation, but merely a temporaiy cohesion ; for, after watching a group for six hours, he saw the separation of the several component individuals, preceded by a narrowing of the connecting bands or commissures. Such is an outline of the opinions and statements of some leading naturalists respecting the nature and design of this so-called act of conjugation. The balance of authority and evidence is against the supposition of its reproductive purpose ; but when this view is rejected, we have no other to replace it, and are sensible of the want of sufficient data from dii'ect observation before a hopeful attempt can be made. Ehrenberg, it should not be omitted to state {Monatsb. Berl. Akad. April 1854), started the notion that conjugation is intended as a means of invigo- rating the species : " a curious idea," says Claparede {op. cit. p. 286), " and not Y&vy reconcileable with the ordinary laws of nature." Kolliier {op. cit. p. 100) canvassed the question, if Actinophrjdna, along with Rhizopoda, are to be considered cells, and, after an elaborate examina- tion of the point, concluded that they must be regarded as peculiarly modified simple cells. Claparede, after weighing Kolliker's arguments and reviewing the stnictiu'al peculiarities of these animalcules, comes to the opposite conclu- sion, viz. that, '' as regards ActinopTirys Sol in particular, we must either drop the class of unicellular animals altogether, or refer this animal to some other place." We do not deem it at all necessary here to enter upon this con- troversy ; it has already engaged our attention in other places, and has of late lost much of its interest by the extended modifications introduced latterly in that particular hypothesis of ceU-natui^e, which, at the date of Kolliker's paper in 1849, exerted so powerful an influence over the histological specu- lations of all the writers of that period. Localities. — Actinophryina are inhabitants both of fresh and salt water. They occur often as parasites upon the larger Protozoa, such as Stylonychia, and on various small animals of other classes, and seem to draw nourishment from them. They are also common among the filaments of Conferva and the stalks of Lemna, where other animalcules congregate. Another locality is amid the vegetable debris and minute animals which often float together, as a dust-like film, on the surface of ponds. Affinities of Actinopheyina. — All recent writers refer this group of beings to the Ehizopoda, except Siebold, who curiously enough retains Actinophrys in the family Enchelia, along with Leucophrys and Prorodon, two genera of Cihata of quite a difi'erent type of organization. Although the preceding sketch of the history of Actinophryitui will afford ample evidence of many homologies with the Rhizopoda, yet it will equally display not a few differ- ential characters, sufficient, we believe, to separate them at least as a subclass. 258 GENERAL HISTOEY OF THE INFUSORIA. The most striking points of divergence are the more definite and constant figure of Act'inopliryina, their peculiarly formed tentacula in lieu of ordinary- variable processes, and, of minor moment, their greater immobility, and the operation of the tentacles in the introduction of food. Acineta was placed by Ehrenberg with Actinophrys in a family or order Acinetina ; and most writers treat them as if the relation between these two families were actually so near. A closer attention will, however, prove that something more than a generic diiference subsists, and that Acineta had better stand as the representative of another group, well named Acinetina, although more limited in its significa- tion than that so termed by Ehrenberg. The most tangible diff'erences between Actinophryina and Acinetina are, that no food enters the substance of the body in the latter group, and that the body is covered with an integu- ment. The history of this division, as far as at present known, reveals yet other distinctions ; for self- division has never been observed, whilst the pro- duction of motile ciliated embryos from the interior has been seen over and over again, without, as far as is known, an antecedent act of conjugation. It must likewise not be forgotten, that it is the Acinetina which, according to Stein's hypothesis, constitute an intermediate phase of existence in the de- velopment of many Vorticellina. Indeed, could this naturahst's supposition be proved, the existence of Acinetina as a class of independent beings would at once be sacrificed. Another afiinity is discoverable with the Polycystina, both in the natiu-e of the soft, muco- gelatinous mass, in the long, tentacular filaments, and in the ciuTcnts of granules detected in the processes. This relation is best seen with some Acanthometra {vide Midler's paper, Monats- hericlit, Berlin, April 1855). The Actinophryina are related to the Ciliata also by their sarcode, by the structiu'e and action of the contractile vesicle, b}" the formation of alimentaiy vacuoles, and by the nature and composition of their granules. But, over and above these general resemblances, a more special afiinity is manifested if Cienkowsky's statement, that the fission produced is clothed with vibratile cilia, be correct. This degree of affinity must be ad- mitted in the case of the Acinetina which appear, as a rule, to generate cihated embryos. Since the above history was written. Dr. StrethiU Wright, of Edinburgh, has most kindly furnished us with notes on several Infusoria, among others of two new forms of Actinophryina, presenting great peculiarities in struc- tui^e. The accoimt of these novel genera wiU be found in the second part of this work, in the Systematic History of the ActinopJiryina. SUBFAMILY ACINETINA. (Plates XXIII. 1-23; XXYI. 3, 4; XXX. 3, 4, 7, 8, 21-26.) The reasons for separating Acinetina from Actinophryina, with which they have generally been united, have been stated in the last chapter, where likewise the difierential characters of the two groups, and the supposed part they play in the cycle of development of Vorticellina, have been examined. There remains therefore, to fill up the history of the Acinetina, nothing more than some further remarks on the various forms they assume, and on certain peculiarities in their structiu-e. The form of Acinetoi is subject to great variety. Ppiform and ovoid shapes are the most prevalent ; but some are almost spherical, and others, again, nearly triangular (XXIII. 6, 7, 8, 15, 17, 22, 23). A lobulated anterior end is common ; and then the tentacles are usually restricted to the lobules (6, 17, 18). These lobed forms have no such firm integument or capsule at aU as OF THE PEOTOZOA. ACINETINA. 259 that seen in others ; or the anterior lobed part is undefended by such a cover- ing, except of a very delicate and yielding structure. Cienkowsky speaks of the Acineta he examined as naked without limitary membrane (XXIII. 40). Very frequently, on the other hand, the Acineta is entii^ely enclosed within a stout capsule. This capsule is readily discerned when, as frequently happens, the internal animal mass of the Acineta does not fill it ; or it may be brought into view by the application of diluted acetic acid or alcohol, either of which causes the shrinking of the contained body. In general the capsule appears to be a very thin, coloiuiess, hyaline membrane ; but after the action of acetic acid. Stein represents it to be, in the supposed Acineta of Ojyercularia Lichtensteinii, of considerable thickness (XXIII. 22, 23). This thickening is doubtless due to the action of the acid in causing the membrane to swell out. With the exception of the so-called Actinojplirys Sol of Stein, and the Dendrocometes, the Acinetina are attached by a stalk of varying length, more commonly very short, to the body on which they live (XXIII. 17, 18, 22 ; XXYI. 3, 4). This stalk or pedicle is a tubular prolongation backwards of the capsule itself, like which, it is hyaline and transparent. It is not articulated with the body of the Acineta, but expands more or less abruptly into the capsule, and has a proportionately greater or less infimdibuliform figure. Occasionally the stem at the upper part has trans- verse rugae, and in a few instances exhibits a sort of longitudinal striae, par- ticularly near its junction with the body (XXIII. 3, 4). Stein describes the stem of the supposed Acineta of Ejnstylis, to be solid like that of an Ejpistylis itself. Frequently the capsule is thrown into transverse folds, at times, of considerable depth. There is no aperture in it ; but it is penetrated by the tentacles which rise from the contained organic being. The capsule, if in some specimens of considerable firmness, would seem to be in others, even when thick, very yielding, — so much so as to allow great variety in figure by the contractions of the contained body, as instanced by Stein in the Acineta attributed to Opercidaria Lichtensteinii. The tentacles of Acinetina have not the imiformity of stnicture seen in those of Actinoi^liryina. In some Acinetce they closely resemble those of ActinopJirys, are long, gently tapering, and capitate ; in others they form parallel tubular processes, dilated a Httle, or not at all, at the extremity, and either straight or slightly curved or undu- lated ; in others, again, they rather resemble bristles, appear stiff, and taper to a sharp point. In the remarkable Acineta called Dendrocometes, the tentacular character is entii^ely lost, and a few most bizarre branched tubular processes spring from one to six points of the surface (XXX. 22, 23). Per- haps these processes are homologous Avith tentacles ; yet, imlike them, they seem to be formed from the capsule of the animal, into which the granular contents of the interior penetrate, as into hollow tubules prolonged from the surface of the organism. In certain Acinetina that approach Actinophrys in external characters, the tentacles are equally difiused over the body. In the large ppifonn Acineta, assigned by Steia to Opercularia articulata, the short slender tubular pro- cesses appear chiefly marginal (XXX. 3, 4). The digitate Acineta is covered by long tapering and thick processes on its dorsal convex suiface (XXIII. 21) ; and the Diademiform Acineta has its long setiform tentacles in twos and threes at considerable inteiwals, chiefly on the margin (XXIII. 15, 16). The Actinophryean Acineta of Epistylis plicatilis bears a bundle of long finely capitate tentacula on each of its four lobes (XYIII. 2) ; that of Vorticella nehulifera has two such bundles, — whilst the triangular Acineta, with its tongue-Hke process (XXIII. 17, 18, 19), carries a large expanding pencil of shorter obtuse tentacles upon each angle at its base. s2 260 GENERAL HISTOEY OF THE INFUSORIA. The tentacula are moveable and retractile, the divergent bundles may be collected into parallel groups, and di-awn inwards, with the protruding sup- porting lobes, to a greater or less extent. Stein aifirms that, in the first stage of development, Acinetce have no tentacula. The body of an Acineta, within the capsule or external integument, con- sists of soft colourless sarcode, rich in granules, fat- corpuscles, and minute globules. It is enveloped by an elastic yielding membrane, which becomes most distinct when the body shrivels mthin the capacious cavity of the capsule (XXIII. 3, 6, 8). The body appears in some Acinetce capable of extending itself above the capsule, which must therefore be fissured in front, in the form of a tongue-hke process (XXIII. 17, 18, 19). A finely granular and opaque nucleus is always distinguishable in the interior, usually near the centre. Its shape is very varied, and may be oval, ovoid, clavate, reniform, band-like, vermiform, or horse-shoe shaped (XXIII. 1, 6, 17, 22). In a few examples, e. g. of the supposed Acineta of Opercularia, it is much and irregularly branched (XXX. 3, 4). The addition of dilute acetic acid is a ready and efifectual means of bringing the nucleus to hght, and of demon- strating its enclosing sac ; and as it is more solid and compact than the contents around it, it may now and then be separated by crusliing the Acineta. The nucleus is enveloped by its peculiar membrane ; a fact which becomes e\'ident in sevei^al cases by the apparent double line surrounding its gra- nular mass (XXIII. 6-22). In a few instances, moreover. Stein has de- scribed a contractile space witliin the nucleus, e. g. in that of Opeixularia berberina. Xot unfrequently the nucleus looks as if double, or as sending ofi* a process from itself; a critical examination of such specimens has convinced Stein that the ofi'shoot is the commencing development of the germ or embiyo of the Acineta (XXIII. 7, 8, 19). This he has proved by watching the nucleus through all its intermediate stages, from a simple ovoid or elongated figure until the embiyo has gro^Ti and separated itself from it prior to its escape from the Acineta. The nuclear appendix, when separated, is found to have an enclosing membrane, which ultimately surrounds the embiyo like a sac, and admits of a certain degree of movement within it (XXIII. 4, 5). Another distinct organ of Acinetina is the contractile vesicle. Usually one only is present ; but in some instances two, and more rarely three or more, make their appearance (XXIII. 1, 5, 21). Xear the external margin a series of clear vesicular or vacuolar spaces presents itself, as in the Diademiform Acineta (XXIII. 15, 16) ; such, however, present no rhythmical contractions, and cannot be regarded as true contractile sacs. The embryos developed from Acinetw are likewise furnished with one, and occasionally mth two, of those organs (XXIII. 2, 4, 5, 15, 27). Excepting the embryos or germs, no other special structures are seen amid the granular contents of Acinetina. Alimentary vacuoles and particles of food or other matters derived from with- out never make their appearance ; for the body, even if not entii'ely enclosed within the shut sac or capsule, is covered with an integument, and has no sign of a mouth for the admission of food. Yet Acineta; generally have the power of nourishing themselves, by the medium of their tentacula, which appear to act as suckers, di'awing in by endosmosis the nutrient juices from the animalcules which get entangled by them. If Stein's details be correct, some Acinetiform beings would appear to have no power of self-nutrition ; for their substance is described as gradually used up in the formation of germs, and this decrease to be followed by a shrinking or collapse of the capsule, but at a comparatively slower rate. Tliis phe- nomenon is illustrated by Stein in the Acineta ascribed to Vaginicola OF THE PROTOZOA. ACINETINA. 261 aystalUna, and in the so-called Acimta with the tongue-like process (XXIII. 17, 20). If this account be admitted, that certain Acinetce display no power of self- nutrition, and seem destined only to subserve, as mere media, the purposes of reproduction, an independent nature could scarcely be attributed to such beings, and their history would be entirely comprehended in that of the beings in whose cycle of development they might enter as one link. Lach- mann (A. N. H. 1857, xix. p. 222) has the follomng account of the mode in which Acinetina nourish themselves : — "Each ray" (tentacle) "is a sucking proboscis, and we soon see that a cuiTent of chjTue-particles runs from the alimentarj' cavit}' of the captured Infusorium into the body of the Acinetaj through the axis of the rays, which, after seizing the prey, have become shortened and thickened. In the body of the Acineta the chyme-particles still run at first in a slender row, but afterwards they coUect in a di'op, which although drops are also formed in the chjTne of the Acineta by other suckers, soon becomes amalgamated with these. AMien a considerable quantity of the chyme of the captured animal has passed over into the body of the Acineta^ a remarkable change gradually takes place in its appearance: if it was pre\dously pale, nearly transparent, and only very finely granulated, larger dark globules, resembKng fat-di'ops, now make their appearance here and there ; and these soon increase so that the body (which at the same time, of coui^se, increases in thickness) acquires a coarsely-granular aspect, and becomes opaque. The globules or drops which make their appearance can only be formed in the body of the Acineta, as they are far larger than the chyme-particles which are seen flowing through the sucker. The animal whose contents are thus sucked out, gradually coUapses and dies ; many become liquefied when only a little of the chyme is extracted from them, others still live for a long time ; in large animals, such as Stylonychia Mytilus, Paramecium Aurelia, &c., the sucking often continues for several hours." Origin' and Development of Ace^etina. — In our history of the development of Vorticellina, Stein's hypothesis of the transformation of those highly-de- veloped Ciliata into Acinetiform beings as a stage of existence necessary to their development by embryos, and of the reconversion of the embryos into Ciliata of the primitive type, is sufficiently enlarged upon. In the same chapter, moreover, Cienkowsky's contradictory statement and observation are detailed, viz. that, though Acinetce develope ciliated embiyos, yet these embryos give origin to beings like those they issue from, and are not trans- formed into Vorticellhia. According to this opinion, the Acinetina take a position as independent beings in the animal series. Stein determined, to his own satisfaction, an Acinetiform phase in the following Vorticellina and Ophrydina : — Cothurnia maritima. SpirocJiona gemmipara. Epistylis branchiophila. Vaginicola crystallina. Opercularia articulata. VorticeUa microstoma, Opercularia berberina. VorticeUa nebulifera. Opercularia Lichtensteinii . ZootJiamnium affine, Ophrydium versatile. CarcTiesium pygmceum ? The description of the Acinetiform beings assigned to the species enume- rated is given in the Systematic History of the Acinetina, which wiU likewise afford a more complete idea of the structure and forms of this peculiar class of beings than the above general history itself. 262 GENERAL HISTORY OF THE INFUSORIA. SUPPLEMEl^TARY FAMILIES OF PROTOZOA. A. — Gregarinida. Their General Characters, Structure, and Affini- ties.— The Gregar'inida constitute one of the three groups into which several eminent naturalists subdivide the Protozoa ; they therefore claim from us a brief description. They are of the most simple structure ; indeed, some writers place them below the Rhizopods in the animal series, because, unlike these, their simple type undergoes no further elaboration or developmental complication. They are parasites, living in the visceral cavities of other animals, and in their simple structure are comparable to a cell, or to the o^iim of higher animals. Thus they consist of a homogeneous albuminous -like matter, -with numerous granules of coarser and finer character and fat-like globules, enclosed within a membrane of more or less perfect structure, which in all essential points I'epresents a cell-wall; besides, they have always one distinct central vesicular body or space containing one or more granules, and evidently of the nature of a nucleus. Of these parts, the general mass may be taken to resemble the yelk-matter, and the nucleus the germinal vesicle of an ovum. The enclosing membrane is very yielding, and admits of great and constantly fluctuating alterations of figure by the varying contractions and extensions of the internal contractile mass ; but there is no such thing as the formation of pseudopodes, as happens among Ehizopoda. It is entire, without orifice either in the shape of a mouth or anus ; consequently no foreign particles are ever seen in the interior. Moreover, the Grer/arinida contain no contractile vesicle, and have never been found to undergo either fission or gemmation. Their vital endowments are so shght, that their animahty is at fii'st sight doubtful ; but, imlike vegetable organisms, their envelope contains no cellulose. The above brief account comprehends all that can be stated generally of the organization of these simple creatures, which, if above the Amoebcea in the possession of a more or less definite membrane, yet sink beneath them in not possessing a contractile vesicle. Notwithstanding their simplicity of structure, they yet are truly animal organisms, enjoying an independent existence, manifesting the phenomena of motion, growth, nutrition, and reproduction, in the last of which they exhibit a peculiar cycle of changes. Moreover, there are various notable difierences between the various Grega- rinida known, with respect to size, figure, to the activity of their functions, and to some minuter points of structm^e. Hence theii- division into genera and species. In size they vary from foiu' or five lines (as in the genus Didymojplirys) to a few thousandths of an inch. Of their figure, some are simply rounded or oval sacs, as in Monocystis ; others constricted around the middle, e. g. Grega- rinida. Again, the majority have a smooth, naked membrane, whilst others are armed with a ring of uncini at one extremity, like many Hehninthidce. When two nuclei occur in a single animal, it probably betokens an act of reproduction. The encysting process is exhibited among the Gregarinida, in connexion, however, onl}^ with their reproductive processes, and has this pe- culiarity, that it does not occur to a single individual, but to two together, which become enclosed within the common cyst or capsule. In their progress to this union the two Gregarince are seen first to approach, and then by mu- tual pressiu^e to flatten, the opposed surfaces, so that the binate being acquires a globular form. The substance to form the cyst is in the meantime thrown out, of a soft gelatinous consistence, but gradually becomes condensed and contracted into a membranous -looking capsule. OF THE PROTOZOA. GEEGAEINIDA. Stein stated that, on the completion of the act of apposition, an actual fusion of the contents of the two animals transpired, the opposed walls being previously removed by absorption. Other observers state, however, that there is no such removal of the external membranes, and that the reproductive processes in the interior of each being proceed without any real commingling of their contents, which is a subsequent and probably not a necessary event. This act, which, fi'om its general resemblance to the zygosis of plants, is spoken of as one of conjugation, appears immediately concerned in the de- velopment of a multitude of germs "svithin each Gregcunna, by the general breaking up of the granular contents. Still, if Lieberkiihn's account be ad- mitted, this process of conjugation is not a necessary prelude to the develop- ment of the internal germs ; for, according to it, this result may accrue in individuals which have never conjugated. The germs assume a rod- or spindle-shaped figure, which, from its re- semblance to the prevailing form of the Naviculce, has suggested for them the name of " J^avicellce " or " pseudo-Navicellce.^^ They consist of an external comparatively firm wall, enclosing a finely-granular gelatinous substance. When the *' Navicellce " are sufficiently matui^e, the cyst of the Gregarince biu'sts and sets them at large. Their future history, according to Lieberkiihn's researches, is, that the case of each jpseiido-Navicella ruptures and gives exit to the soft contained matter, which at fii'st much resembles a minute Amoeba, but gradually assumes, by progressive growth and the formation of a pellicle around it, the characters of a Gregarina. Between this mode of development of Gregarinida and that of the Ciliated Protozoa, Leuckart draws this distinction, that in the former it consists in the production of granular germs, in the latter of living embryos. But it may be questioned whether there is a positive difference in kind between these two results of the reproductive process, and whether, on the contrary, the Navicellce of the Gregarinida may not be considered as merely encysted em- bryos, homologous with those of Colpoda Cucidliis among the CiLiata. The act of conjugation in the Gregarinida is not precisely like that occui'- ring among the lower Algae, the leading difference being that in the former there is no commixture of the two approximated beings. In all essentials, indeed, conjugation in this family resembles that believed to happen in the Actinophryina. There has been much dispute whether the Gregarinida are to be held in- dependent animals, or merely embryonic phases of others ; the balance of authority is in favour of the former view. Kolliker and Leydig advocated the opinion that they are metamorphic stages of Anguillulce or Filarice, or a link in the series of development of the Helminthidce. The arguments adduced by Leydig are thus briefly stated (J. M. S. i. p. 208, and Miiller's Archiv, 1851) : — " In the intestine of a large species of TereheUa he was enabled to observe the most distinct transition between Filaria-like Nematoid wonns and Gregarince. The forms of the latter, which he observed not once only, but many times, were — 1. A Gregarina of from 0-02'" to 0'04'" long, which had the form of an elongated sac, rounded at one extremity, and sharp at the other. The contents were those usual in the Gregarince — a consistent fluid with a corpuscular substance, which did not occupy the pointed end, and im- bedded in this a clear vesicle -^ith a nucleus. 2. A Gregaiiniform creature, of a spindle-shaped figure, closely resembling Gregarina Terehellce, Kohh 3. A Gregarina, generally resembling the preceding, differing only in two particulars : the internal substance is arranged in longitudinal streaks ^ and the body, instead of being straight, is more or less curved at each end. 264 GENEKAL HISTORY OF THE INFUSOEIA. 4. The same form, but with the body more elongated, vermiform, and for the first time exhibiting motion. 5. A very pretty Nematoid worm, about 0*10'" long, blunt at one end, sharp at the other; the contents in longitudinal streaks, as in the two preceding forms, but with the spaces between them wider. Its motions are very active." This view of a metamorphosis being admitted, the question arises, do the Gregarince become changed into Filarice ? or is it that the Filaria-like worms are transformed into Gregarince ? Although at first inclined to consider the former as the true state of the case, Leydig is now disposed to follow Heule and Bruch, and adopt the latter view ; otherwise it would seem impossible to account for the formation of the pseudo-Navicellce and " Psorospermia " within the " Gregarince.^' KolHker has the following remarks on this subject (J. M. S. i. p. 212) : — " Although the change of a FUciria into a Gregarina is not an impossible cir- cumstance, before we admit such a thing it is first necessary to inquire whe- ther the facts stated may not be otherwise explained. It is by no means proved that the Anguillula-^e animal noticed by Henle, and termed by Bruch Filaria, is really a Nematoid worm." Kolliker is more inclined to regard it as an Infusorium allied to Oj^cdina, Proteus, &c. If this be the case, there is nothing extraordinary in its transformation into a Gregarina, and finally into a Navicella-rece^iOiQle. " For many reasons," says Stein (Zeitschr. iii. 1852), " the endeavour to show the Gregarince to be larvae of higher animals, and especially to connect them with encysted Nematoid worms, appears to be a vain attempt. Thus, I am acquainted with Gregarince of such peculiar fonns that one requires a very strong imagination to deduce them from Nematoiclea, or to suppose they can pass into these. The encysted Nematoiclea are always found in the cavity of the body of insects, never in their intestinal canal, where alone encysted Gregarince are to be found." Again, the cysts of the Nematoidea of insects are made up of nucleated cells, and are plainly a product of the vital activity of the insects, not the exudation of the enclosed worm, while the cysts of Gre- garince are produced as an amorphous secretion from the animals themselves. *' If, therefore, encysted Nematoiclea change into Gregarince, or vice versa, their cyst must undergo a metamorphosis which, perhaps, no one will assume, and of which no observer has seen anything." Lieberkiihn's observations have gone far in shomng that, under usual con- ditions at least, the Gregarinida are not converted into Filarice or any other form of Vermes, but that their germs, after a short-lived Amoebiform period, not amounting, however, to a true metamorphic stage, assume the characters of their parent. Thus the cycle of development of these beings appears com- plete ; the saccular animal constructs, by a process of segmentation of its in- ternal substance, a host of germs, which, after breaking loose from their parent and involving its destruction, emerge from their cases in a soft Amoe- biform condition, and soon acquire the matui'e Gregariniform condition. The Gregarinida exhibit a marked affinity with other Entozoa, particularly with the Trematoda and Opcdincea ; and, as before remarked, they are allied with the Amcehcea in the extreme simplicity of their stnicture. By the possession of a limiting membrane (not independent or separable, indeed), they stand between the mucilaginous fluctuating Amoehcea and the Ciliated Protozoa. Unlike the Amoehcea, they do not receive into their substance solid particles, — a circumstance explicable by their being covered by a somewhat resistant, hardened lamina or tegument, which necessarily impedes that peculiar intus- susception of solid matters witnessed in that familj^ As to habitat, the Gregarinida are parasites in the intestines of various In- OF THE PROTOZOA. PSOROSPERMIA. 265 vertebrate animals — worms, moUusks, and insects, — but have not been found in Vertebrata. B. — PsoROSPERMiA (Plate XXII. 37-41). — This is a small group of para- sitic animals, first observed by John Miiller in 1841, closely related to the Gregarinida, of which, indeed, they might be included as members. Unlike the Oregarince, they live upon vertebrate animals, viz. upon many species of fish, about their skin, giUs, and internal organs, several together enclosed within sacs. Leydig has more recently applied himself to the study of these minute parasites, and has given the results of his observations in Miiller's Archiv for 1851, of which an abstract appeared in the Journ. of Mic. Science, i. p. 206, which we shall here take the liberty of using, as sufficient for our pui'- pose : — '^ The Psorospermia are microscopical corpuscles of a peculiar kind, which may be generally characterized, in the full-gro^Ti condition, as rounded organisms, having a sharply- defined outline, with or without a tail-like ap- pendage. They are flattened and lenticular in figure, and one pole is usually acuminate ; and towards this pole several internal vesicles converge in a symmetrical manner. These creatures were discovered by John Miiller in 1841 (Miill. Archiv, 1841, p. 477). He found in a j^oung pike minute round cysts in the cellular tissue of the muscles of the eye, in the substance of the sclerotica, and between this and the chloroid coat. The contents of the cysts was a whitish substance, which, when examined microscopically, Avas found to consist of peculiar elements — the ' Psorospermia.^ [A detailed notice of these observations is given in the Microscop. Journal, vol. ii. p. 123, and in the Brit, and Foreign Med. Rev., January, 1842.] In the following year the same observer (Miiller's Archiv, 1842, p. 193) discovered parasitic corpuscles in the swimming-bladder of a Gadus CaUarias, which, although specifically distinct from the Psorospermia, approached very near to the latter in their organization. They resembled in general a smooth ventricose Navicula, and consisted of two elongated cases apphed to each other at the cavity, and with an elliptical outline and convex outer surface. They were in part free, in part enclosed in masses within a tunic. Similar cysts, containing Psorosper- mia, have been found by Leydig in several species of fish, and in aU parts nearly of their bodies, and even in the blood contained in the heart and in the peritoneal cavity. " Some facts, however, observed by him, connected with this subject, which came under his notice in 1850, during some researches on the cartilaginous fishes, served to throw a more general light upon these mysterious forms. " In the gaU-bladder of a Squatina Angelas there occiuTed in the bile, and in large quantity, peculiar forms of various organization, but which were manifestly developmental forms : — 1. Rounded vesicles, consisting of a delicate membrane and a consistent fluid ; the latter was of a yellow colour, and con- tained a multitude of also yellow granules. 2. Other vesicles presented, be- sides these, other elements of a new kind : in the middle of the granular contents were several perfectly transparent cellules ; smaU vesicles had only one of these cellules, larger ones as many as six. 3. Other parent vesicles, again, exhibited, besides their membrane, a granular contents and secondary vesicles, containing Psorospermia, always one in each secondary vesicle. 4. In the latter form, finally, the secondaiy vesicle had attained a large size, and the Psorosperm floated in a spacious clear chamber, which occupied nearly the whole of the parent cyst. Besides these motionless cysts, there were nu- merous free Psorospermia in the bile. " He found, upon examination, very similar things in other fishes of the 266 GENERAL HISTORY OF THE INFUSORIA. same class, — as in Spmax vulgaris, ScylUum Canicula, Torpedo Narhe, and Baja Batis, in which the Psorospermia differed from the more usual form, in being grooved or ribbed. " It was very remarkable that the above- described organisms were never met vrith in any other part or tissue of the body than the gall-bladder or biliary duct. " With respect to the nature of these bodies, Ley dig is inclined to tliink that the cyst should be regarded as belonging to the family of the Gregarince, and that the Psorospermia must be looked upon as generically analogous to the pseudo-Navicellai which have been observed to be generated within the Gre- gariiice. *' The question next arises, as to the existence of similar Gregariniform or- ganisms producing Psorospermia in fresh-water fishes. Leydig thinks there is reason to suppose that the animalcule discovered by Yalentin in the blood of Salmo Fario is a Gregarina. Moreover, John Mliller and Leydig have ob- served two or three ecaudate Psorospermia in Leuciscus Dohulst enclosed in a cyst, — whence it might be supposed that secondary cells may be developed within one of Valentin's Haematozoa after it has been conveyed in the coui^se of the circulation to one organ or another, in which cells Psorospermia may originate. With the growth of the latter, the granular contents of the Gre- garinoi gradually disappear, which are thus transformed into cysts filled with Psorospermia. Such a cyst would then be equivalent to a Navicella-recei^- tacle." Prof. Huxley, in his Lectures on Natural History (Medical Times, 1856, xxxiii. p. 508) has the follomng account : — " The Psorospermia are pyriform sacs, frequently provided with an elon- gated, filiform, motionless appendage, and containing two or foui' clear rounded bodies, attached side by side, within their smaller ends, and besides these, as Lieberkiihn has lately pointed out, a rounded mass of plasma. Under fitting conditions, the Psorospermia burst, and the plasmatic mass emerges as an Amoebiform creature. The sacs in which the Psorospermice are developed, on the other hand, can be traced back to Amoebiform masses full of granules ; and it seems a legitimate conclusion, that the Psorospermia are the pseudo- Navicellce of an Amoebiform Gregarina or Gregarinoid AmoebaJ' SUBSECTION II.— CILIATA. (Plates XXIY.-XXXL) According to the arrangement we have adopted (p. 200), the Ciliata, as a subsection of Protozoa, are divisible into two groups : — 1. Of such as are mouthless ; 2. Of those possessing a mouth. The former group constitute the Astoma, the latter the Stomatoda. In Ehrenberg's system the Astoma were not recognized ; for where he did not find a mouth in any ciliated Polygasirica, he nevertheless assumed its existence, supposing that from its minuteness, or some other cause, it merely escaped observation. This procedm^e was, indeed, rendered necessary by the hypothesis with which he set out, of their polygastric organization. It must be admitted, to Ehrenberg's credit, that recent researches have proved him right in assigning a mouth, in by very far the largest number of Ciliated Protozoa, contrary to the assertions and opinions broached by many of the most eminent microscopists a few years since. Yet there is a limited number of mouthless Ciliata, independently of the peculiar family repre- sented by the genus Actinophrys, placed very erroneously in the family or THE PROTOZOA. CILIATA. 267 Enchelia by Ehrenberg, which must be separated not only from Stomatoda, but also from the Ciliata. This separation we have carried out, in consti- tuting the two groups Actinophryina and Acinetina, intermediate between Ehizopoda and Ciliata. Excluding these veiy remarkable creatures, the Ehrenbergian families comprehended in our history of Ciliata are the Peri- dinicea, Dinohryina, Vorticellina, Ophrydina, Enchelia, Colepina, Trachelina, Ophryocercina, Aspidiscina, Kolpodea, Oxytrichina, and Euplota. Among the Traclielina were enumerated those very simple parasitic beings which late observations have proved to be moutliless, and are referred chiefly to a genus Opalhia. These we therefore abstract, and, treating Opalina as the type, have constituted a new family, Opalincea, a member of the group Astoma. In connexion with this we have placed the very imperfectly known Peridinicea, although some recent writers seem disposed to attribute to them the posses- sion of a mouth and digestive apparatus. The organization of the Dinohryina is, if possible, still less understood ; and since we have no other descriptions of it than those supplied by Ehrenberg, we shall allow it to be mustered with the other ciliated families named in the large group of Stomatoda. GeOIJP a. AsTOMA, ASTOMATOUS OH MoUTHLESS CiLIATA. FAMILY I.— OPALIN^A. (Plate XXII. 46, 47.) Geneeal Characters and Functiois^s. — This family, represented by the genus Opalina, consists of minute miscroscopical animalcules, moved by vibra- tile ciha distributed generally over the body, without mouth, of an oval or oblong compressed figure, living parasitic in the interior of larger animals, upon whose juices they nourish themselves. Their contents consist of a finely-granular substance, hoUowed out into a small number of vesicular spaces, mth no contractile poAver ; extending through the centre is an elon- gated band-like (Hgulate) nucleus, enclosed by a definite but delicate mem- brane, and composed of a homogeneous finely- granular substance. In two species, 0. Planariarum and 0. uncinata (XXII. 46, 47), a large pulsating vascular canal is found ; the latter species is also fm-nished mth strong hooks, whereby it efi'ects its attachment to the intestinal surface, from which it draws its nutriment. Propagation takes place by transverse self- division, and also, in the opinion of a few observers, by germs or embryos. The OpaUna3 are com- posed of sarcode enveloped by an integument, and rapidly imdergo difliuence. In several species the existence of a mouth has been surmised, — for instance, by Ehrenberg in Bursaria {Opalina) JRanarum, and by Dujardin in Opalina Lumhrici. All doubt on this point may be always removed, Stein tells us {op. cit. p. 181), by using chemical reagents, such as alcohol, acetic acid, or weak solution of iodine, which destroy the fold, and prove no real opening to exist. If further proof were wanted, the constant absence of foreign particles in the interior might be adduced. This absence of a mouth afi'ords evidence of the merely transitional nature of Opalincea ; for the same featiu'e prevails in the case of embryos produced from the Acinetina, &c. The vesicles or, as Dujardin calls them, " vacuoles," seen in greater or less number in all the Opalincea, are irregularly disposed in the interior, and, according to this author and Stein, have no limiting membrane. However this may be, they remain clear and transparent when the rest of the contents are coloured by the bile of the animals the Opcdina3 inhabit. This fact, moreover, attests another, Aiz. that they cannot owe theii' formation to fluids received from without, but that it must depend on the pecuhar properties of the contents themselves. The formation of vacuoles in Opcdina? was adduced 268 GENERAL HISTOKY OF THE INFTJSOfilA. to disprove the origin of the alimentary globules in the Ciliata generally by the introduction of liquid from without ; but it is to be remembered that in these two groups of organisms we have very different structural conditions, and that in the CiKata the entrance of water mostly holding solid particles in suspension, through the oesophagus, and the moulding of it into a more or less spherical outline, are matters sufficiently proved by direct observation. We have stated above, that the vesicles are not contractile ; Dujardin has, however, described those of Leucophrys striata as irregularly so. The cilia are disposed in longitudinal lines, and in some instances, where there are ridges or margins, present a greater length and thickness, as, for instance, upon the edges of the ciu'ved surface by which the 0. Planariai'um adheres. The suiface can throw itself into plaits or folds, — an occurrence, however, probably limited to animals in a diseased or dying state, as Perty remarks in speaking of Opal'ina Eanarum (op. cit. p. 156). The Opalincea are not very active ; they swim onwards, moving at the same time in an oscillating manner. The above account comprises all that can be stated of the Opalincea gene- rally, since the differences in internal structure among the several reputed species are so great, that it constitutes, as Stein points out {op. cit. p. 182), a strong argument against the existence of the family as a group of inde- pendent beings. However, from the study of the peculiarities of the several members of the admitted genus Opalina, this author reduces them to three types, viz. : — 1. The most common form of Opalina, represented by the Leucophrijs striata of Dujardin, has an oblong body, marked by some 35 longi- tudinal granular striae, and contains a number of vacuoles var}ing according to external conditions, and a central band-Hke nucleus. This animalcule occurs in the interior of the common earth-worm (Lmnbriciis). Stein found them of different lengths from 1-60'" to 1-14'", and in all stages of the process of transverse fission. "WTien placed in water, they become more active. 2. The second form differs from the preceding by the in-egular distension of the body when placed in water : a strong endosmotic cuiTents sets in through the enclosing waU and raises it from its contents, so that these at length pro- duce the appearance of a smaller Opalina enclosed within a large one. Du- jardin has described this variety under the name of LeucopTirys nodulata. This Stein would imite with the first named, under the term of Opalina Lum- brici, which, indeed, Schultze applied to the same animalcule. 3. The third modification of Opalina might be treated as an independent species ; for, notwithstanding a general resemblance, it has a striking pecuharity of its own, visible under a strong magnifying power (such as 100 diameters), in the shape of a single, strong, homy apparatus, placed near the anterior end on the flat abdominal surface of the animal (XXII. 47). From a short common base situated to the right of the median line, slightly cui^ed, uncinate, pointed processes are given off, of which one is much longer and stronger than the other. To the left of this organ a fold or furrow occurs in the surface, which might be mistaken for the entrance to a mouth. The deve- lopment of this organ may be readily followed during self- division. It appears first as a homy protuberance close to the line of section (XXII. 47), which extends backwards into the base of the process, and forwards or up- wards into the two hooks. It is also worthy of notice, that generally a greater or less number of solid oval nucleoli and short rod-like bodies make theii' appearance within the homogeneous substance of the nucleus. The Opalina Lumhrici of Dujardin is no other than the animalcule described, although its characters are incoiTectly represented by that author, who, from his figure, OF THE PROTOZOA.— opalin.5:a. 269 has evidently seen a specimen which has very recently completed the act of self-fission and not yet reacquired its rounded posterior extremity. The dark stiipe shown at the fore part, and supposed to indicate a mouth, repre- sents the uncinate apparatus above described. Stein would call this form of Opalina the 0, armata, and regard it as a further stage of development of his so-called 0. Lumhrici. This view is supported by the fact that he has never met with j^oung individuals of 0. armata ; for all the specimens he encountered were of a nearly equal size, and larger than the largest of 0. Lumhrici, in company with which young beings are very common. Thus 0. armata attains a length of 1-12'" to 1-9'", and 0. Lumhrici of not more than 1-14"' ; even the products of fission of the former are from 1-16"' to 1-14'". ** If now it be considered that, excepting the horny process, not the least difference in structure exists between 0. Lumhrici and 0. armata, it is ren- dered very probable that the latter is merely a fui'ther stage of development of the former. If this be the case, a subsequent more considerable meta- morphosis of 0. armata may be presumed, when it becomes transferred to a more favourable habitat, as happens when the worm it inhabits becomes the food of some other animal. I have not actually seen Opalina armata adhering to the surface of the intestine, for I have always found it amidst the undi- gested mineral and organic fragments which fill the alimentaiy canal of the earth-worm. Hence it is more likely that the adhesive organ is destined to subsequently fix the Opalina in a more permanent manner." The long pulsating vessel seen in Opalina Planariarum and in 0. uncinata deserves particular notice, by reason of its peculiaiity. Stein has described it in the first-named species, where it extends the entire length of the ani- malcule, as bounded by a definite, delicate, structiu'eless membrane, and to be without the outlets Schultze imagined. It contains a clear liquid like water, which, by its rhythmical movements, it forces to and fro -within it. On killing the animal with alcohol, the walls of the vessel are rendered very evident. It becomes divided through the centre in the act of self- fission, and is, in Stein's opinion, not homologous with the contractile vesicles of the Ciliata. Ntjclfxs. Self-divtsiox. Supposed Embryo. — The nucleus is a very evident organ in all the Opalincea, with the single exception of 0. Ranarum, in which Stein has sought for it in vain among multitudes of specimens and by the aid of various reagents. In this same exceptional species it is also to be noted that he never vidtnessed the act of fission, yet Siebold (" Ueher Monostomum,'' Wiegmann's Arcliiv, 1835) described, in an Opalina living as a parasite in the intestines of a frog, the existence of a number of smaU embryos within a ca\'ity of the posterior extremity of the body : whether this animalcule, however, was the Opalina Ranarum does not appear ; for the peculiar habitat does not by any means prove such to be the case. A contrast occurs in the Opalina Branchiarum, where the nucleus which lies in the axis of the body has the same figure as the entire being, and one- half its dimensions. Even among examples of the same species the position of the nucleus varies exceedingly. Simultaneously with the appearance of a constriction in the general figure, the nucleus shows signs of approaching fission ; but ere this is manifested it assumes a central position (whatever may have been its previous one), so that each of the two future segments may acquire an equal section of it. Moreover, it would appear, in some cases at least, that the constriction and scission of the body advance more rapidly on one side than on the other of the animal. According to Stein, the production recorded by Schultze (Beifrdge zur Natur- 270 GENERAL HISTOET OF THE INFT7S0EIA. gescMchte cler Turhellarien, 1851, p. 67), of a granular germ-mass in Ojmlina Planariarum, at the posterior extremity of the animalcule, was nothing more than the act of fission misconceived. The granular contents of the nucleus (says Stein) are finer or coarser in the animals iiTespective of their size ; and the supposed germinal masses, as the figiu^e given shows, were merely the segments of the nucleus in process of di\ision, and not illustrations of the ulterior development of that organ into other beings. Schultze witnessed this process but once, in a specimen he named Opalina polymorplia, but which was the same as the 0. Flanariarum of Siebold and Stein. Habitats, Vital Endowments, &c. — As stated before, the Opalincea are pa- rasites of various animals, the most common of which are frogs, newts, and other Batrachia, earth-worms {Lumhrici), some shell-fish, as the Anodon and the common muscle {Mytilus eduUs), and of Planarke and several Entozoa. They are found in the intestines in the earth-worm, in the rectum and bladder in the frog, among the ciha of the tongue of that reptile, or among those of the gills in the shell-fish, &c. As a memorandum touching the vital properties of Opalincea, we may quote here an experiment made by Kolliker on the vitality and development of the spermatic filaments {J. M. S. 1855, p. 298) : — '' The OpcdiiKB move in a solu- tion of common salt of 1 per cent., and of phosphate of soda of the strength of from 5 to 10 per cent. In a solution of salt of 5 per cent., and of sugar of from 10 to 15 per cent., they shrink up and become quiescent, though re\'iving upon the addition of water. I have even succeeded in reviving the Ojpalince after they had been treated vnXh. a solution of common salt in the proportion of one-tenth." Nature of Opalin-f:a. — The observations of microscopists in general concui' to prove that these simple beings are not independent, but the mere embry- onic or transitional phases of other animals. This opinion was put forward by Schultze, and has been seconded by Agassiz, Stein, and others. Agassiz asserts (Silliman's American Journal, 1853) that the deficient Hnk in Steenstrup's history of the succession of alternate generations of Cercaria, and its metamorphosis into Distoma, is supplied by his discovery that a ge- nuine Opal'um is hatched from the eggs of Distoma. Stein coincides also in considering them metamorphosed into Vermes, and states that Steenstrup has watched the transformation of Leuwjyhrj/s anodonta (Ehr.) into an intestinal worm. He saw first that the cilia vanished, that they fixed themselves, and became by-and-by changed into oval motionless bodies, which continued to grow, and formed an internal space, within which a germinal mass was de- veloped, out of which Cercaria originated. Affinities and Classification of Opaline: a. — Upon this head the first point is to settle what genera and species are to be numbered with the Opali- ncea. For our part we are chsposed to place in this family all Cihata which are mouthless, andAvhich lead a parasitic life. As already noted, the absence of a mouth is indicative of an embiyonic character, an indication strengthened, if not confirmed, by observation ; consequently this group of beings is at best but provisional, serving only the purposes of definition and nomenclature, until science shaU be enabled to indicate the particular animals into whose cycle of life they severally enter. Furthermore, we have seen that some reputed species are, in all probability, only drfferent stages of existence of the same Opalina, — for instance, the 0. armcita a more adult state of 0. Lumhrici. And, again, the stnictural differ- ences between 0. iincinata and 0. Planariarum (consisting in the possession of a singular pulsating vessel) and the rest of the group are so stiiking, that they can scarcely be rightly included in one genus. OF THE PROTOZOA. OPALIN.EA. 271 On turning to the systematic descriptions of various writers, we find much discrepancy in detail, and much difference in opinion, respecting both the species to be counted among Opalincea and their generic distribution. The family ' Leucophryens ' of Dujardin, and the CobaUna of Perty, severally include most of the species which we would reckon as Opalincea. These, in Ehrenberg's system, were scattered through several genera, — the majority, however, being comprised in his genus Bursaria. Stein points out three prin- cipal modifications of form, but is not prepared to constitute them into genera. In the classification adopted by the three first-named writers, the Opalincea were accounted ordinary Ciliated Protozoa. Perty and Dujardin so far re- cognized their peculiarities as to erect them into a distinct family. Siebold went ftiriher, and, on account of the absence of a mouth, placed them, with Astasia^a and Peridinicea, among the Astoma. We coincide with Siebold in thus more completely separating them from the stomatodous Ciliata than the other authors named, but at the same time look upon them as more nearly allied ^vith Ciliata than with either Peridinicea or Astasicea, and consequently prefer to treat the Opcdinoia as a subgroup of those Protozoa. Neither the intimate stnicture, nor the developmental histoiy of the Opa- lincea, is sufficiently well understood for them to be arranged in well-defmed genera ; nevertheless, as both Dujardin and Perty have each essayed a sy- stematic distribution, it behoves us to set their schemes before the reader. Dujardin divides the Leucophryens into three genera, viz. Spathidium, Leucophrys, and Opcdina. Besides these, he has other mouthless genera in his family Ploesconiens, viz. Diophrys and Coccudina, maiine but not parasitic animalcules ; also a genus Trochilia without distinct mouth, also marine in habit, located in the family Erviliens ; and last, the genua Plagiotoma, among the Bursariens, parasitic in habit, and supposed to have a mouth situated at the bottom of a fossa, but which contained no foreign matters, and could not be fed artificially with colouring matter. Of these genera Coccudina, Dio- phrys, and Trochilia are imperfectly kno^vn, particularly the two last, and the absence of a mouth cannot be predicated of them with any certainty, — whilst of the last named {Plagiotoma) the balance of evidence is against the existence of a mouth, and, as we shall see, this genus is a member of Perty's family Cohcdina, and has, moreover, in Stein's opinion, no claim to rank as a distinct genus. The parasitic family Cohcdina, Perty, comprises the genera Alastor, Plagio- toma, Leucophrys, and Opcdina. The characters of these several genera, placed by observers among the Opcdincea, or some parallel group, together with their mutual relations and differences, will be fuUy treated of in the systematic section of this work. FAMILY II.— PERIDINI^A. (Plate X. 224-226; XXXI. 16-23.) This family, in Ehrenberg's classification, comprehended four genera, viz. ChcetotypJda, Chcetoglena, Peridinium, and Glenodinium ; but, as Dujardin rightly judged, the two first genera belong rather to the Cryptomonadina, by being destitute of the ciliary furrow, the leading characteristic of the Peri- dinicea. Our description ^viU therefore particularly apply to the two other genera, Peridinium and Glenodinium. The beings imder consideration have received little attention from natu- rahsts, and are stiU imperfectly imderstood. Indeed, we feel that no sufficient data are at hand whereon to ground an opinion relative to their true position, nature, and affinities. We place them here as a supplementary group of 272 GENERAL HISTORY OF THE INFUSORIA. Ciliated Protozoa, fii'st, because of their wreath or general clothing of cilia — a phenomenon seen among none of the Phytozoa or Plagellata, which have never more than one or two, or, rarely, four filaments or flabella ; and secondly, be- cause every author who has described them treats them as animalcules. Perty, although recognizing them as animals, nevertheless groups them with his Phytozoidia, probably omng to their bizarre form and to the characteristic internal organization of CiHata not being perceptible. Siebold, on the con- trary, places them, together with Euglenwa and Opalincea, among the asto- matous or mouthless Protozoa. Ehrenberg's description of the Peridinicea is as follows : — The animalcules of this family are polygastric, but have no alimentary canal ; the mouth is usually found in a depression near the middle, and from its vicinity a delicate filament (proboscis) is given ofi' in three of the genera. They are clothed with a shell or lorica, having a transverse furrow or zone occupied with a row of vibratile ciha ; and besides this wreath, several species have also fine setae or cilia scattered over them. In Peridinium acuminatum, P. fulvum, and P. ( Ceratium) cornutum the digestive sacs are visible without recourse to artificial means ; but in P. Pulvisculus and P. cinctum those organs can be demonstrated only by the use of coloui-ed food, chiefly because they are hidden by the clusters of ova, to which the colour of the animalcules is due. This is com- monly red, yellow, or brown, and rarely green. In Peridinium Tripos and P. Fusus a seminal gland (nucleus) is visilDle, and in Chcetoglena and Glenodinium a red eye-speck. Longitudinal self-division has been observed in P. Pulvisculus and P. Fusus. Dujardin, unable to accept these views of their organization, described the ' Peridiniens ' as " animals without known internal organs, enveloped by a definite resistant membranous lorica, which sends ofi' a flagelliform filament, and has, in addition, one or more furrows beset with vibratile cilia. The lorica would appear to have no orifice, since foreign particles and colouring matters cannot enter it ... . The members of this family are distinguished from Thecamonadina by the ciliated furrow or furrows." Further, Dujardin ignored the red stigma as a generic distinction, and in this is followed by Perty. Ehrenberg created a subgenus of Peridinium for those species which have the lorica prolonged into hom-like processes, under the name of Ceratium. Both Dujardin and Perty retain this appellation, but would elevate the group comprehended under it to the rank of a genus. Let us now proceed with a resume of the facts at present received respect- ing the organization and habits of the Peridinio'.a. The lorica is double, consisting of an outer, more or less firm, non-contrac- tile layer, and an inner, homogeneous, hyaline membrane : usually a space occurs between the two coats ; but in Glenodinium they are in close apposi- tion— a double contour, however, being perceptible. The inner layer may be taken to represent the primordial utricle ; it immediately envelopes the contents, which consist of a homogeneous protoplasm, enclosing within itself numerous globules, granules, and vesicles. In the case of the smallest Peri- dinicea, such as P. Pulvisculus, P. monadicum, and P. Corpusculum, the di- stinctness of envelope from contents ceases, and when in a dying condition the whole figure undergoes a great variety of changes — a fact indicating a less perfect development of the lorica — and there is a rapid breaking up of the contents. In the larger species the outer tunic is more elaborated, and either displays a minute cellular or reticulate structure, or appears quite smooth and structureless, although firm and resistant (as in Glenodinium cinctum). A cellular lorica occurs in Ceratium, and also in various Peridinia, which Perty separates from the rest, under the name of Glenodinium, by reason of this OF THE PROTOZOA. PERIDINI.EA. 273 structure. This external tunic is decomposable, although it resists destruc- tion much longer than tlie contained matters ; and it is esi3ecially after a certain amount of change has proceeded, that its delicate retiform structure is more distinctly exhibited. The figiu'e of Peridinicea is very various and bizarre : the simplest is that of a spheroid divided into two segments, equal or unequal in size, by a trans- verse ciliated fiuTOW or zone. In some instances one side is flatter and concave, and, according to Perty, presents a wide opening, or elongated fissure (XXXI. 16), from which the filament may sometimes be seen to proceed. Moreover, besides the transverse furrow, a second is seen in some species to proceed from it at right angles, as far as the vertex of the anterior half, — as, for example, in Dr. Allman's species Peridinium uberrimimi (XXXI. 16, 18), and in P. fuscum and P. ocidatum {Glenodhiium cinctum, Ehr.). Indeed, in Glenodinium apicu- latum Ehrenberg describes several subsidiary, shalloAver, hispid furrows branch- ing over the surface (X. 224-226), and in G. tahidatum a series of non-hispid lines or ridges. These last two forms recall in general features the pollen-cells or grains of the higher plants, and may, indeed, from the deficiency of a loco- motive filament, and from other exceptional characters, be considered doubtful members of the family Peridinicm. An inequality of the two segments, as separated by the ciliary zone, is seen in Peridinium Corpuscidum and P. mo- nadicum, and in a less degree in P. ocidatum {Glenodinium cinctum). The figure, however, is very curiously and materially altered by the production of tapering or horn-like processes, of a large diameter and great length relatively to the principal portion or body of the organism. These processes difter in number in diiferent species, and give rise to very bizarre forms, dej^arting widely from those of any Phytozoa or from any other ciliated Protozoa. The number of horns in Ceratium Fusus is two, and, being in the same line, produce the spindle-shaped figure of the entii^e being (X. 222, 223). In C. furca two occur in front and one of larger dimensions beliind ; the same is seen in P. Tripos (X. 219, 220), in which, however, the two anterior processes are curved, — whilst P. cornutum {Ceratium HirundineUa) has from two to three posteriorly, and one, usually curved, anteriorly. In Ceratium Micliaelis (X. 221), again, we see three short processes project from the posterior half ; and, lastly, in C. macroceras (Perty) three are represented behind, of which the central is much the longest and straightest, and in front one still longer but rather curved. The length of the horns compared with the body of the Ce- ratia affords, however, no specific character, inasmuch as it varies according to age and probably also other conditions. The vibratile cilia are usually con- fined to the groove surrounding the lorica, and to the direct continuations from it. Nevertheless Dr. AUman discovers in P. uberrimum the whole sur- face sparsely covered with them ; and Ehrenberg mentions the supplementaiy farrows of Glenodinium apiculatum as occupied with hispid hairs (X. 224- 226). The locomotive filament, which Ehrenberg failed in seeing in all even of his genus Peridinium, is usually of great length and tenuity, and, accord- ing to the great Berlin micrographer, proceeds from the neigh boiu-hood of the mouth which he believed he detected in Peridinium Fusus in a hollow near the middle of the animalcule. Allman more definitely points out its situation as being near the junction of the transverse and vertical furrows in the species he has described (XXXI. 16). Lastly, Perty states that Ceratium HirundineUa {C. cornutum, Ehr.), when swimming, stretches out the filament as if stifi", and that, although 2^ times longer than the body, it may be easily overlooked, on account of its active swinging movement. It is apparently a production of the protoplasm, protmded externally through an apertiu'e in the investing tunics. Opinion is divided respecting the existence of a mouth. Ehi-enberg repre- 274 GENERAL HISTOEY OF THi; IIM L.-SOlcIA. sented one, and also the possible admission of coloured food, but was contra- dicted by Dujardin, who denied both. Siebold reckons Peiidinicea among mouthless Infusoria {Astoma). Perty mentions the fossa in the shell, but no aperture ; and Allman remains silent on the matter. On the other hand, Lach- mann admits its presence, and thus discusses the mode of reception of food (J..iV^.ir.l857, vol. xix. p. 220) :— "Prom the point of insertion of the flagel- lum, on one side the large notch, in the upper part of the row of cilia, a clear canal passes into the body of the animal, and dilates at the extremity to form a cavity of variable diameter. The flagellum is often seen to contract rapidly into a spiral form, and apparently disappear ; and not unfrequently we may then succeed in perceiving that it is jerked back into the above-mentioned cavity, from which it soon retui^ns into its previous position. Now it cer- tainly appears worth while to see whether small particles of food are not carried into the cavity by this jerking in of the flagellum." Contents. — These may be divided, as in the Euglence, into minute shapeless molecules, and globular corpuscles and vesicles with red stigma and nucleus. Sometimes the corpuscles are green, and resemble chlorophyll, but more fre- quently they are red, yellow, or brown, or intermixtui'es of those colours. In the earliest stages, indeed, colour is absent, and, just as in Euglencea, only minute moleculse are found interspersed in the colourless protoplasm. More- over, when a colour appears, it may not simply become more intense or darker by age, but change to another tint belonging to the same series of colours. In younger specimens again, the contents more completely occupy the entire being, whilst frequently in old, and more especially in specimens withering or dying, they become contracted into a ball, placed either in the centre or more or less to one side (excentric). A swelling out of the external tunic, the disappearance of the red stigma, the vibratile cilia, and the filament accompany this shrinking of the cell- contents. The retrograde change in the contents is further manifested by the appearance of a large vesicle about the centre, or of several dispersed smaller ones at that or in other parts. Some at least of these vesicles are merely oil- drops, which, as Braun shows in his essay on Rejuvenescence, are the usual concomitants of a process of destructive assimilation. After the destruction of the cell- contents, the firm lorica remains hke an empty shell, boldly displaying its sculpturing, and in many instances also a curved, apparently internal, stripe about the middle or to the right of it, which Perty presumes to be either the Line of attachment of the contents or a fold. Among more constant structures. Dr. Allman describes a central nucleus — the organ probably alluded to by Ehrenberg under the name of an oval semi- nal gland, in Peridinium Trij>os and P. Fusus. AUman describes the nucleus to be of an irregular oval form, quite colomiess, and marked on the surface with curved striee (XXXI. 20) ; under pressure the envelope gives way, and the nucleus escapes with the other contents. A contractile vesicle has not hitherto been discovered. One or more large clear vacuoles may originate in the internal substance ; but such have not the pulsating power of definite vesicles. The red speck or stigma (XXXI. 16, 17) has no pretensions to the nature of a visual organ. It is not always present even in examples of the same species ; or it is multiplied ; and it is known also to disappear v^ith advancing age. Again, Perty recounts the fact of the diflPiision of the red colour of the speck throughout the whole contents, at times leaving a narrow ex- ternal ring w^hich retains its green colour. This phenomenon was witnessed in a specimen of Olenodinium cinctum. In young individuals of Peridinium tahidatum, which are of a light-green colour and translucent, there is no trace of a red speck ; yet Perty met with a collection of these beings of apparently OF THE PROTOZOA. PEEIDINI^A. 275 smaller size than usual, yellow in colour, and not, like older animalcules, greenish-brown or brown, which had from 10 to 12 red vesicles or globules about the middle of the anterior segment. Still the general rule is that in very young indi\iduals no stigma is present. The inconstancy of the presence of the red speck, even in matiu-e specimens, its absence in very young, its dis- appearance in old ones, and the many irregularities, not only in its occurrence but also in size and number, are facts which sufficiently prove its worthless- ness as a generic or even as a specific distinction, and which declare against its assumed function of a visual organ in this as in other families of Protozoa. REPEonrcTioN. — Longitudinal fission has been seen to take place in several species. Self-di\T.sion, says Perty, presents many peculiarities among the Pendinicea. In Ceratium HirimdineUa, fission is longitudinal ; it commences anteriorly close to and on the left side of the great horn (as the animalcule is viewed from above), and advances towards the posterior extremity. The pro- cess is not confined to the large specimens, but is equally enjoyed by the small. During the act of fission in Peridinium Pidviscidus, Perty noticed that before its completion the newly-formed segment continued to augment in size until it surpassed the original being, which underwent no enlargement. Dr. Allman noticed, in the species he examined (J. M. S. 1854, p. 25), that spontaneous division took place " parallel to the annular furrow " (XXXI. 18), i. e. therefore transversely, "■ and in the unfurrowed hemisphere." He also remarked the important fact, that this process appears to be invariably preceded by a di\T.sion of the nucleus ; and he had succeeded in isolating nuclei presenting almost eveiy stage of transverse fission. But besides their reproduc- tion by fission, Perty adopts Ehrenberg's \dews and insists on their development from ova or ovules, which present themselves in the form of brown or green corj3uscles in the interior. Peridinium tahulatum is often seen to be full of such, elHptic in figure, and as much as 1-150'" in length, and which can be expelled by pressure from the animalcule. In P. Pidviscuhs Perty met with specimens from 1-400'" which were aggregated together in masses, and moved together. In P. Oorpiiscidum, he asserts, development from ovules may be directly observed ; and he gives figures of ovules set free, and of the young generated from them, which would seem the same structures with the addition of a cell- wall. The ovules, too, are large and very e\ddent in Ceratium cornutum ; and he regards the small brown organisms which may be found in company with mature individuals at various times of the year, as the primitive stage of ge- neration of those ova before acquiring the perfect figure of Ceratium. In some specimens, indeed, he remarked the long filament peculiar to the species, and a red stigma in the posterior segment. The smallest examples measured 1-200'", and were at first elliptic ; from this they changed to reniform, and became distinguished into an anterior and a posterior half. Their movement was ro- tatoiy or spiral, and quicker than in old individuals. On one occasion he saw small examples of Ceratium Hirundinella only 1-25'", of the same figure as the large specimens, but completely colourless ; at another time he encountered pale brownish-green individuals, with a beautiful red stigma, and the poste- rior lateral horns scarcely developed, — whilst in one instance the anterior cornu was completely formed, and the posterior extremity rounded. These examples, he observes, appear to be different structural phases through which the products generated from the ovules have to pass. The reproduction by ovules or internal germs has its parallel in Euglencea ; and, like as in this group, so in the family Peridinicea a quiescent, resting, or " still '* stage appears to occur. Dr. Allman has put forward this fact most clearly. He writes (,/. M. S. 1854, p. 24) — " Before death, and also when passing from a motile to a quiescent state, most likely preparatory to under- T 2 276 GENERAL HISTORY OF THE IXFL'SORIA. going some important developmental change, the contents contract towards the centre ; and then an external transparent and perfectly colomiess vesicle becomes visible, while the flagellum and cilia disappear. The contracted contents present a very definite and general spherical boundary, and are evi- dently included in a distinct cell " — the primordial utricle. On a subsequent examination of the pond in which the species examined occurred in prodi- gious quantity, he found " immense masses " of the Peridinimn " towards the bottom, where they appeared quite healthy, though presenting the condi- tion described above as characterizing the quiescent state of the animalcule." Our imperfect information respecting the organization of the Peridinicea renders any argimients concerning their nature unsatisfactory and inconclu- sive. Perty, to whom we owe most of our knowledge respecting these crea- tures, agrees mth Ehrenberg in assigning them an animal nature ; and we gather from the few remarks Dr. Allman has made, that this opinion has also the advantage of his support. Dujardin, we may add, treated the Peridinicea as animalcules. Of the opposite opinion, viz. that they are members of the vegetable kingdom, we know of no advocates, although some facts, such as the apparent absence of the known internal stnictui'e of the Cihated Protozoa, the non-contractility of their bodies, the character, colour, and changes of their contents, might be adduced in its favour. However, the force of those presumed facts will be much lessened by the consideration that the internal organization of the Cihata may yet be discovered in these organisms when they receive their due share of attention from microscopists, that even the ab- sence of a mouth and rudimentaiy digestive tube would not absolutely exclude them from the animal kingdom ; and that in the form and character of their ciliary armature they present an animal much more than a vegetable type. Of their Vital Endowments, we may state that some swim mth consi- derable activity by means of their flagellimi, aided, no doubt, by their ciliary wreath, which probably gives the oscillating and rolling character to their movements. They are inhabitants both of salt and of still fresh water, among aquatic plants, but not of infusions ; and they disappear from water when long kept. Most of the genus Peridinimn are marine. They may occur in such enormous multitudes as to colour the pond or other collection of water in which they have accumulated. Of this phenomenon Dr. Allman mentions an example in which his Peridinimn uberrimum was so abundant in the ponds of Phoenix Park, Dublin, as to colour' the water brown : — " This colour was sometimes uniformly diffused through the water ; at other times it appeared as dense clouds varying from a few square yards to upwards of a hundred in extent." This was in Jime ; in July " the coloration of the ponds had much increased in intensity .... The colour in some parts was of so deep a bro^svn, that a white disk half an inch in diameter became invisible when plunged to a depth of 3 to 6 inches, while a copious exit stream, which constantly flowed away from one of the ponds, presented the same deep-brown tint." The most remarkable vital phenomenon presented by the Peridinicea, and which is particularly common in them as a family, is that of phosphorescence, which is possessed in a high degree by several of the marine species, having a yellow or yellow-brown colour. In nine phosphorescent drops of sea- water from near Kiel, taken up one after another by Ehrenberg, nothing save a single individual of Pendinium (Ceratiu7n) Tripos was discoverable. Besides this species, the following other Ceratia are phosphorescent, viz. Ceratiuni Fusus, C. acuminatum, C. Michaelis, and C. Furca. Ehrenberg has reported the occiuTence of fossil Peridinicea ; but the or- ganisms so considered are peculiar in having a silicious shell, which renders OF THE PROTOZOA. 277 their alliance to this family somewhat doubtful. They are met with in chalk, the only secondary stratum, and here in the substance of flints ; but they also occur in strata of later formation. Their presence in flints renders it, indeed, sujDposable that their silicious constitution is an ulterior result of the infiltration of silex in a state of solution into the texture of theii' previously membranous envelope. They are found in company with fossil Fyxidicula and Xanthidia. Ehrenberg described two fossil species under the name of Ceratium pyro^horum and C. Delitiense. CILIATA. Grotjp B. — Stomatoda. (Illustrated by Plates XXIY.-XXXI.) The animalcules whose general history we have noAv to write are, as before mentioned, comprehended for the most part in the families Dinohryina, Vort'wellina, Ophrydina, EncJielia, Colejmia, Trachelina, Opliryocercina, Aspi- discina, Koljjodea, OxytricJiina, and Euplota, as instituted by Ehrenberg, with the removal of the OpaUncea from the Trachelina, and of the Acinetina and Actinopliryina from the Enclielia. The descriptions of the beings composing these several families, as furnished by Ehrenberg, are so tinged by his peculiar views of organization as to mar their utility ; and therefore, for precision and accuracy of detail, we have to rely in great measure on the observations made within the last few years, chiefly by German naturalists. Notwithstanding the jDersevering industry •vvith which these scientific men have piu'sued their inquiries, many genera yet remain almost imknown, or little understood, in respect to their structm-e, whether internal or external. The Ciliated Stomatoda, or as we shall more briefly style them the Cihata, are microscopical animals having a defijiite limiting membrane or external tunic covered more or less completely with vibratile cilia, by which they swim ; and when it is indurated, as not unfrequently happens, it is further furnished with bristles or other tegiunentary appendages, by which they are capable of crawling or leaping. They aU possess a more or less di- stinct mouth, which opens into an oesophagus or gullet, continued to a vari- able extent into the interior as a digestive or alimentary tube, but ending abruptly by an open extremity. In many genera a discharging orifice or anus is perceptible ; and in all there are a nucleus and one or more contractile vesicles. They propagate by self-di\^sion, by gemmation, and by internal germs or embryos, with a greater or less degree of metamorphosis, and they undergo the encysting process : the act of gemmation appears limited to a few genera ; but self- fission and embryonic development may be predicated as general phenomena. Dimensions. — In dimensions aU the Cihata are microscopical ; for if some, such as Spirostomum, Stentor, Opercidaria, Zoothamnium, Vayinicola, and other genera of Volvocina and Ophrydina are visible to the naked eye as minute specks or globules, they are far beyond its ken for any purposes of investigation, and are therefore essentially objects for the microscope. Yet amid these hosts of equally microscopic beings, the range in point of size is actually as great as that between the dog and the elephant among animals cogv nizantto our ordinaiy observation. Even among members of the same genus, and, indeed, of the same species, their dimensions may vaiy within limits extremely wide. To quote a few examples : Spirostomion ambigimm (Ehr.) has a length of ^th of an inch ; the branching polyparies in EpistyUs and Opercidaria reach ith in height, those of Zoothamnium 1th, whilst many 278 GENERAL HISTOKY OE THE INEUSOBIA. stalked VorticelUe extend themselves to y^th in length. Paramecia are men- tioned by Ehi'enberg from ^th to ^ ^\. ^th in length ; and specimens of the same species of VorticeUa, viz. F. microstoma, are described to vary in size between 2-gVo^^ ^^^ yio^^* Stein has also noticed examples of Chilodon CucuUulus from 2^0^^ ^^ TTUU^^- ^ ^^®^ surprising magnitude is attained by the polypoid masses of Oplirydium versatile, which range between mere microscopic globules and aggregated masses the size of the fist or even of the head of a man. FiGUEE. — In figure the Ciliata exhibit an immense variety, but have a rounded outline in all instances. The prevailing figure is oval or oblong ; but some taper much at one or both ends, and acquire a spindle-, or a flask-, or a club-shaped aspect, whilst others, as the VorticelUna (XXVII. 1, 2, 4, 16; XXX. 1, 9, 11), present a bell-shaped or campanulate outline, and others again, as Spirostommn (XXIV. 298), an elongate ribbon- or band-like one. However, the best idea of the manifold forms can be gathered by inspecting the subjoined plates of the Ciliated Protozoa, which render verbal description imnecessary. The figure is determinate and constant under like phases of existence for each species, although liable in the majority to very great changes by the contraction and movements of the animalcules, by their contact with more solid bodies, and by the introduction of food. These changes are proportionate to the elasticity of the integument and to the contractile power of the contents ; and hence, in several with firm integument, they are veiy limited, or not possible. The figui^e is also much modified by the processes of multiplication and of reproduction. The act of fission materially modifies it ; gemmation does so to a less extent ; but the most remarkable change is caused by the encysting- process, which is generally a prelude to the peculiar set of phenomena attend- ing the reproduction by germs or embryos, and, according to Stein's views, would seem to temdnate in actual metamorphosis or transformation of the beings concerned. Indeed the Ciliata in general appear to pass thi'ough a cycle of changes, each of these entaihng a distinct figure ; in other words, in the historj^ of each ciliated Infusorium, there are several phases of ex- istence, difi'ering from one another in form and other particulars. The history of an animalcule, therefore, is comprehended in that of no one form or phase, but in that of every one it normally assumes ; nevertheless it is necessary to fix upon one phase, either as the most important or the most perfect, and to characterize and name it, just as is done in the case of insects, which are described in their most developed or " imago " condition. Another point to be remembered is, that the figiu'e of a specimen appears diff'erent in most cases, according to the aspect in which it is viewed ; and, again, there is often much diversity in shape between young beings and those arrived at maturity. Perty has applied the term ' metahoUa ' to express the changes of figure animalcules may assume. The figure is extremely varied in Lacrymaria by its movements, and chiefiy by the lengthening or shorten- ing of its elongated anterior portion or neck. This variability of form struck Baker and other old observers so forcibly, that they applied the term Proteus to designate the animalcule (XXIV. 274, 275). Trachelocerca (XXIV. 317- 319) and PMalina have a similar power of varying their outline ; and all three genera are further remarkable by the manner in which their surface can be thrown into transverse or even intersecting folds or plaits. The influence of food when swallowed in modifying the figure, Ehrenberg particularly illustrated in his Enchehjs Farcimen (XXVIII. group 64). This animalcule devours others nearly as large as itself, and, to efiect this, Avidcly dilates its mouth, and so becomes shorter and broader ; and as during the OF THE PKOTOZOA. CILIATA. 279 operation it continues to swim about, its appearance with the hall- swallowed being is very curious. Again, when engulfed the anterior portion contracts, whilst the posterior becomes dilated, gi^^ng the Enchelys a flask-shaped outline. In descriptions of the Ciliata, authors have used various terms, applied to the segments or members of higher animals, to designate varieties in the form and in the mutual relation and position of their parts. The application of many of these terms to the Protozoa is indeed very arbitrary and fanciful ; and it is only from the absence of better that we continue to emj)loy them. The end of the body which advances foremost in swimming, and at which or near to which the mouth is ordinarily placed, is called the head, and often has an additional claim to the appellation by its construction as a segment distin- guished by some points of structure from the rest of the body. The opposite portion of the animal constitutes, when tapering or provided with some sort of process, the tail, but is more generally spoken of, especially when not distinguishable as a segment, as the posterior or caudal extremity. A ' dorsum ' or back, and a ' venter ' or abdominal surface, are usually de- scribed, but are not readily determinable in aU genera, as, for instance, in the VorticeUina and OpTirydina. To distinguish the one surface from the other, regard must be had to the position of the mouth (which indicates the abdo- minal surface), to that of the locomotive cilia and other processes, and to the mode of progression. But, after all, the distinction will oftentimes be arbi- traiy, and in consequence the description of a right and a left side frequently so too. It is a general character of the Ciliata, that they are asymmetrical, i. e. not formed of two equal and similar halves. An exception to this rule exists in Coleps (XXIY. 284) and in the IchtJujdina (XXXI. 28-30), which in Ehrenberg's system were included with the Rotatoria. Where, although symmetry is not visible, a right and a left side are distingiushable, such Infu- soria are called ' bilateral,' — e. g. the O.vytrlcMna (XXYIII. 10), Paramecimn (XXIX. 25-30), CMlodon (XXIX. 48). Of minuter modifications in the figure of Protozoa, a large number have found names which t\tl11 be best understood in the special structiu*al details of particular animalcules. However, to mention some here used by Ehrenberg, we may cite the frontal region or forehead — the obtuse or truncate part of the head above the mouth ; the lips — projections above and below the mouth, when this aperture is situated in a fissiu-e ; the tongue or palate, usually a process in the oral fissure ; the rotary or ciliary disk, seen as a ciliated pro- jectile process above the margin of the anterior extremity of the VorticeUina (XXX. 1, 2, 9, 11, 14). In several genera the anterior portion of the body is much produced, and looks like a long tubular neck or a tnmk, and hence is called frequently by Ehrenberg proboscis, — e. g. in the genera Lacrymaria (XXIV. 274, 275), Trachelius (XXIV. 287-289), Amphileptus, and Trache- locerea (XXIV. 317-320). This term proboscis we have already seen used to designate the long locomotive filaments or flabella of Phytozoa, totally different processes from those called by the same name in the CiUata just enumerated. Its use for one or the other should be set aside ; and although at the best it conveys a very erroneous impression — for no such thing as a proboscis or trunk, in the proper meaning of the word, has an existence in any of the Protozoa — its application to these is less objectionable than to the Phytozoa. In Uroleptus (XXY. 333) the posterior extremity is abniptly elongated, and forms, according to the description of the same distinguished naturalist, a tail. Consistence. — The Ciliata are composed principally of a very soft, almost mucilaginous matter, which has been well named ' sarcode,'' since, like the flesh or muscular tissue of higher animals, it seems to present an inherent 280 GENERAL HISTORY OF THE INFUSORIA. contractility and elasticity, and is the active agent in the movements of their bodies. It is hyaline, transparent, and colomiess ; but its refractive power is not much greater than water, which is essential to the exhibition and continuance of its properties, for when this fails the homogeneous mass of sarcode breaks up into minute globular portions, which disperse themselves on every side. This disruptive process has received the appropriate name, from Dujardin, of ' diffluence.' Ecker states this self-same sarcode to be the common contractile element of all the lowest forms of animal life — for instance, of the Polypes. The par- ticles set free by ' diffluence/ he also represents to be contractile, and to assume Amceba-like movements ; but this, according to Gohn and Stein, is an error, inasmuch as they are simply elastic. Cohn also adds that the vaiiable movements of the sarcode-particles of Hydra are merely a physical phenomenon due to endosmosis. The process of diffluence, whether fi'om external injiuious conditions or damage, or from noxious matters received ^vithin, varies so much in rapidity, that Cohn (Zeitschr. 1851, iii. p. 267) con- eludes that it must indicate some variations in its composition and stnicture in different animalcules. For instance, he says, Steator ccertdeus bursts ; and its contents break down by diffluence as rapidly as sugar in water, streaming- out from the rest until the fimnel-like pharynx only is left behind. On the contrary, in other animalcules, e. g. Paramecium Aurelia, the sarcode exudes through the surface at all points, and s^dms away, lea\ing a vacuolated or areolated interior. Again, Loxodes breaks up into fragments of a considerable size, which escape through lacerations of the sui'fiice. Integument. Markings on the Surface. Condensed Integument or LoRiCA. Appendages of Integument. Cilia. Spines. External Sheaths. -— Ehrenberg described his Polygastrica as in all cases defended, and their figure defined, by an integument or skin, — a statement as g-eneraUy contra- dicted by Dujardin, though now confirmed (in the case of all the true Ciliated Protozoa) by the researches of numerous later naturalists. The means resorted to for its demonstration, where not otherwise e\ddent, consist in the application of chemical agents — for example, of acetic acid, of tincture of iodine, and of diluted alcohol, aU which operate in a different maimer upon the integument and on the contents of the body, most frequently causing a separation of the two by corrugating the latter, and, it may be, coloimng it at the same time. Perty could not convince himself of the existence of an epidermis, although he believed the external surface to be modified so far as to render it more resistant, or in fact to form what Mr. Carter calls a pelKcle ; at the same time he attributed marks or lines visible on the surface to fat- or other corpuscles subjacent to it. '^The pellicula," Mr. Carter says, '^is a structureless pro- duct, which hardens after secretion ; and the inference is that there is a layer below specially organized for its formation," and that it is not secreted by the lamina known as the " cortical layer " or the '' diaphane." On the other hand Meyen, Siebold, Kolliker, Erey, and Leuckart conciu- in describing a distinct enveloping delicate membrane, which Erey thought evidenced both by the manner in which an animalcule ruptures under pressure and gives vent to the soft contents, and by the appearance of little shreds he noticed on the torn edges of a Stentor. A more direct demonstration was afforded by Cohn, who resorted to chemical reagents for the purpose. This excellent observer experimented with several of the larger Ciliata, but for illustration referred chiefly to Lo.vodes (Paramecium) Bursar ia. Stein argues that the animalcule so described by Cohn was not a Loxodes, but a Paramecium, .since aU its cilia were of equal length, a feature pecidiar to this genus (Stein, op. cit. p. 239). On adding a little alcohol to a drop of water containing OF THE PKOTOZOA. CILIATA. 281 specimens of this animalcule, death ensued ; but before this happened, a deli- cate membrane was seen to elevate itself at parts of the surface, producing a vesicular appearance, and accompanied by a shrinking of the contained matters ; while these changes proceeded, several contiguous vesicles would run into one, and thus strip more or less completely the subjacent tissue, until, by the pro- longed action of the alcohol, a central shrunken mass appeared, surrounded by a loose membrane, adherent to it only at the spot where the mouth was con- tinued inwards as a pharynx. This membrane, so demonstrated, is homoge- neous and transparent, but not entirely structui^eless ; for close observation reveals, over its entire surface, two series of spirally-disposed, delicate, and closely-approximated lines, which so intersect one another as to produce a miniature diamond pattern (XXIX. 26). Further, the notched or serrated appearance of the periphery (XXIX. 28, 29, 30) shows that these lines are actually folds or fiuTOWs, and that each little chamond may be represented as a minute four- sided pyramid bearing a cihum at its summit. By piu'suing a similar plan of investigation, a separable integument has been demonstrated in many Ciliata. For instance, Stein described such a covering in the several genera he subjected to observation, and proves its ex- istence also after the process of encysting has taken place. On adding dilute acetic acid to the VorticelUna — for example, to specimens of Epistylis or Oper- culcuia — the contents shrink into a denser mass, and in so doing detach them- selves from the integument, which is then rendered evident as a transparent, structureless, homogeneous, and smooth membrane, having a clear, shai-p out- line. When tincture of iodine is applied, the integument remains uncoloiu-ed, whilst the contents acquire a golden-yellow tint. A solution of sugar, and afterwards a drop of concentrated sulphuiic acid, being used, causes the con- tents to swell up and to assume a rose-red colour, the external wall continuing uncoloiu^ed. Eespecting the chemical constitution of the membrane of Loxodes, Cohn informs us it is soluble neither in sulphimc acid nor in potassa, whilst the con- tents are dissolved and dispersed by the latter. From this reaction he con- cludes that the cuticle is not a proteine compound, hke animal membrane in general, but the substance called chitine, and therefore in this respect similar to the cuticle orplants. In Parmnecmm, he adds, an integument having the same sort of markings and a similar chemical reaction exists, and that, with- out doubt, aU the species described by Dujardin as having a reticulated envelope, in his families ^ Bui'sariens ' and ' Parameciens,' have a hke structure. Moreover, this sldn has its special characters in different genera, as is illus- trated in the above accoimt of Paramecium Bursaria, and may be exemplified in other cases. Thus in Coleps and Stentor polymorphus, the cuticle is so intersected by lines as to leave intermediate four-sided prisms, each of which bears a cihum at its apex, whilst at the intersection of the lines, single long hairs are also seen, similar, says Lachmann {A. N. H. 1857, xix. p. 1 2b, in foot- note), to the hairs of many TnrheUaria. Again, Ophrydium versatile has its integument thrown into fine, closely-aggregated, annular folds, and into three longitudinal rugae on one side (XXX. 5), which disappear when the animal shortens itself by contraction (XXX. 6). Spirochona (XXX. 17), says Stein (p. 208), has a hyaline, firm, inflexible parchment-Hke sldn, with a distinct double outline, but mthout any inherent contractility. It is most like the integument of Euplotes, but differs apparently in not being capable of falhng into folds around the body. It resists the action of acetic acid, which dis- solves out the whole of the Hving contents, and leaves it in an isolated state. Whilst representing all animalcules to be covered with an integument, Ehrenberg distinguished those enclosed by a firm, more or less unyielding, 282 GENERAL HISTORY OF THE INFUSORIA. envelope or sheath, as ' loricated,' in opposition to the rest, which he called * illoricated.' These terms he has, however, employed in so loose a manner, that they really possess no definite and constant meaning. For example, the sheaths of encased animalcules represented by the Opliy^ydina are designated loric£e, the enclosed animal, although possessing a distinct integument, being considered naked, — while, again, the indm^ated closely-fitting integiiment of Eivplotes and Coleps is equally styled a lorica, although so different in cha- racter and relations. The term lorica could only, indeed, be legitimately employed either to designate the sheaths of such animalcules as the Opliry- clina, or the indiu-ated integument of others, as Coleps, — to one or the other, but not to both ; to the former it is unnecessaiy, to the latter it is admissible. The integument of the Ciliata has generally been regarded to be in itself contractile ; but it seems that this is an error, and that, in fact, it is simply elastic. As such, its action must be counter to that of the subjacent con- tractile layer, and be therefore the chief agent in restoring the figure when the contractile force is relaxed ; at the same time its elasticity will allow of considerable alterations in form, from contact and pressure of external more rigid objects. To this an exception occiu^s in the case of those Ciliated Pro- tozoa in which the integument is much hardened, and forms a lorica or shield. This induration may be more or less extensive, so as either to cover the dorsum Avith a shield-like plate (scutellum), as in Chlamidodon, or to entirely sur- round the animalcule, as in Coleps, when it constitutes an " urceolus," open at the ends. The external envelope, when thus hardened, has developed from it various processes, of a more or less rigid character, which look hke spines (setae) (XXiy. 284, 285), or hooks (uncini) (XXV. 344, 347), or are elongated as styles (XXXYIII. 10 ; XXV. 350, 351), all which are oftentimes made sub- servient to the act of locomotion, and less frequently to that of prehension also. It must, however, be admitted that such processes are not confined to genera in which the integument is veiy appreciably indurated, but occur where it is of softer consistency — for instance, in Stylonychia (XXV. 343, 344). The integument is combustible and also diffluent, even when indurated, just as are the softer contents, although more slowly. External Sheaths or Cases. — Before quitting the accounf of the common integument or cuticle immediately investing the body of the Ciliated Protozoa, a description of an homologous membrane, in fact, of a prolongation, dedu- plication, or process of it, in the form of an external sheath or case about certain fixed species, becomes necessary. The species so encased are either sessile or have only a short stalk attach- ing them to the bottom of the case ; thus Vaginicola (XXVII. 10, 11) is stalkless or nearly so, whilst Tintinnus has a more appreciable pedicle : on the other hand the case itself may be stalked, as in Cothurnia (XXX. 12-16) ; where this happens, the stem does not equal the length of the sheath, but is short, solid, and thick, expanding upwards to its attachment with the base of the latter, and frequently thrown into transverse folds and curved (XXX. 12, 15). It is homologous with the rigid stem of Epistylis, which it resem- bles also in chemical characters. A very remarkable exception to the general rule of the attachment of tunicated VorticelUna to the bottom of their case, occurs in the new genus Lacjenophrys, in which the animalcule is suspended from the narrow aperture of the sheath, so as to leave a more or less considerable space aroimd it (XXX. 29-34). The margin of the head of the animal, i. e. the peristom, is beneath the opening of the sheath, which has the further pecuHarity of being very narrow and two-lipped (XXX. 29, 32, 34). In one species {L, nassa) a OF THE PROTOZOA. CILIATA. 283 cylindrical short tube, with a serrate edge and longitudinally striated, is re- presented by Stein to project from the opening of the sheath. It is, he adds, separable above into two lips, which close when the animal retracts itself. It is not very unusual to meet with sheaths occupied by two animalcules, — a cii'cumstance due to the act of self- division (XXVII. 10 ; XXVIII. 19). In a few instances also, one, two, or more small young individuals lie free within the sheath of the parent, e. g. Lagenophrys (XXX. 29, 34). The sheath is always a product secreted from the animalcule, and first makes its appearance around its base as a soft, homogeneous, colourless, jelly-like matter. Diuing the process of its formation, the animal preserves a contracted state, which diminishes, however, as the excreted layer advances, and ceases on its completion ; and since each genus has a characteristic outline, as well in the contracted as in the expanded condition, the sheath acquires also its special character only. More or less of the posterior extremity is concerned in ex- creting the formative matter ; but this having adhered to the anterior part whilst in a contracted state, becomes di'awn forward by the progressive elongation of the entire body, until at length, on full expansion taking place, the connexion is broken and the sheath acquires a free edge. So soon as excreted, the gelatinous layer proceeds to solidify, and simultaneously to contract itself in thickness, so as to form a membrane, which, on its subse- quent detachment from the fore part of the animal, forms a loosely-investing case aroimd it. This description of the construction of the sheath applies to all those genera where the animal is fixed at the bottom ; but in the instance of Lagenophrys, where it is suspended from the constricted orifice of the case by its peristom, some other plan of formation must be presumed, concerning which, however, we have as yet, unfortunately, no direct observation to teach us. In several species, as Goihurnia imberbis, the sheath not merely acquires a parchment-Kke firmness, but also a decided colour — mostly yellow at first, afterwards a rusty red. Dr. StrethiU Wright, of Edinburgh, has kindly sent us some notes on the intimate structure of the sheath of Lagotia ; and doubtless they hold good to a greater or less extent, so far as they represent general facts, in the case of sheaths of other Oplirydina. He wiites — " The tube consists of yellowish chitine, lined with a layer of dark-green sarcode of varying thickness (which, I believe, secretes the chitine), and covered externally by a much thinner layer of matter, which appears to be equivalent to the ^ coUetoderm ' of the Hydroidce:' This structure is illustrated by figs. 12 and 13, PI. XXXI. The following accoimt applies specially to the sheath of Lagotia (XXXI. 7, 8, 12, 13), which presents a series of rings, apparently spiral, but, in our opinion, not so. '^ The Hnes," says Dr. Wright, " are seen to consist of the remains of the tmmpet-shaped mouth, which is partially absorbed as the tube increases its length, but stiU remains as a slightly-overlapping ridge over the new part of the tube growing within it. The groove thus formed is filled up with the * coUetoderm.' The spiral character seems to be in some way connected with this mode of growth ; but I have not satisfied myself in what way." In a subsequent letter he writes — ^' The chitinous matter of each successive ring is not continuous with that of the lings above and below it ; it is only at- tached to it by the inner lining of sarcode and by its outer covering (XXXI. 12, 13). We have by this condition a provision for the growth of the tube, both in width, length, and thickness, similar to that which occurs in the shell of Echinus, Growth in length may be eff'ected by deposition of chitine on the upper and lower edge of each ring, growth in breadth by the gradual unrolling of the spiral, while a continuous deposition of hard matter from the inner lining of sarcode thickens and strengthens the whole tube." 284 GENERAL HISTORY OF THE INFUSORIA. In spealdng of the attachmeut of the sheath, we have mentioned only that by the base, with or without a stalk. But there are a few fonns which affix themselves to foreign bodies by one side of their sheath, e. g. Vaginicola decumhens (Ehr.) and the genus Lagenophrys. In such cases the attached side is flattened, so as to increase the sui^face in contact. But, apart from the mode of attachment, the sheaths of different genera vary in figm^e ; and as to size, there is no constant relation between that of the ease and that of the enclosed being. The figure of the sheath, even in one and the same species, is subject to modification fi'om age and from suri'ounding circumstances. Thus, in Vaginicola crystallina it is usually cylindrical and truncate (XXYII. 11), but at times it may be bellied posteriorly (XXYII. 10), or, otherwise, have its anterior border expanded and curved outwards, or be narrowed in front, or comj)ressed in one direction. Nevertheless there is usually a general resemblance in figui-e among individuals of the same species or genus, sufficient to furnish descriptive characters. For example, Cothurnia imberbis has commonly a cylindiical sheath, bellied posteriorly and shghtly contracted anteiioiiy (XXX. 15), whilst C. Sieboldii is campanulate, and has its anterior half compressed in one direction, and its angles in front prolonged and tapering (XXX. 13, 14). In the genus Lagenophrys, when adherent by its flattened side, the sheath appears ovoid or shaped like a bellied oil -jar, ^ith a contracted truncate mouth (XXX. 29, 30). A peculiar form of sheath is presented to us in the genus Lagotia (XXYIII. 21, 23), which may be de- scribed as retort- shaped, the relative diameter and length of the body and neck differing in different specimens or species. In one species, at least, the neck has the further peculiarity of being throT^^l into spiral or, otherwise, annular folds or rings (XXXI. 7, 8), the presiuned form and origin of which have just been described. We are fiu'ther indebted to the discoverer of Lagotia for the recognition of a remarkable valvular structure within the tubular sheath of a species of Va- ginicola, which he in consequence names Vag. valvata (XXYIII. 18, 19). Dr. Wright states (Edin. New Phil. Joiirn. April, 1858) — " On examining the valve in situ, I found it to consist of a rigid plate imbedded in a thick layer of transparent sarcode (XXYIII. 18 b), which latter was continuous at the lower end of the valve with a thin layer of the same substance, lining the whole of the interior, and coating the upper part of the exterior of the tube. The valve was closed by a contractile process passing from its under- surface to the wall of the tube .... I am disposed to consider the whole ap- paratus to consist of an oval plate of soft sarcode, supported by an included bar or narrow plate of horn or chitine .... In some specimens the tube was marked w^ith close transverse or cii'cular striae." In Stentor Mi'dleri (XXYIII. 16, 17), we have the curious instance of an animal living indifferentl}^ with or without a sheath, and enjoying fi^eedom of movement. Amidst numerous specimens of this species, not a few (says Cohn) may be seen swimming freely about, or, otherwise, attached, enclosed within a roomy ovate sheath, composed of a soft gelatinous substance, and open at one end (XXYIII. 17). The animalcule is fixed by its posterior extremity (apparently converted for the time mto a suctorial disk) to the closed end of the sheath ; but it is still able to evert its spiral ciliary wreath, and to extend itself beyond the open mouth, or to retract itself in a contracted condition witliin its interior. Ehrenberg remarked the exudation of a mucous sheath around this animal- cule when kept confined for some time for observation within small glass tubes, but mistook it for a sort of morbid act preparatory to death. Cohn, on the contrary, has shown {Zeitschr. 1853, iv. p. 263) that it is in no way con- nected with disease or "v^dth approaching death, but happens with individuals OF THE PROTOZOA. CILIATA. 285 in fiill ^'ital activity and surroimded by favourable external conditions, and adds that gemmation frequently proceeds in these encased beings, and that, ■when from evaporation of the surrounding fluid or other prejudicial cause the animals are threatened with injury, they quit their sheaths and swim away, the pre^'iously suctorial extremity resohdng itself into a pencil of bristles. The result of these observations of Cohn is to disassociate this phenomenon of sheath-formation in Stentor from that of the encysting process, to which Ehrenberg's account of it would have led it to be referred. Dr. Strethill Wright coincides "\^'ith Cohn in denying the relation between the presence of the sheath of Stentor Mulleri and the diseased or dying state of the animalcule. Indeed he speaks of the presence of a gelatinous case as the rule, and adds that '' as the zooids (animalcules) di\dde they form a gelatinous mass, which is attached to weeds and often to the siuface of the water, from which I have seen some 10 or 15 combined Stentors hanging with their heads downwards." Cilia ais^d Ciliaey Action. — The most common, and at the same time the characteristic external appendages of the Ciliated Protozoa are the cilia, Avhich constitute their most active and powerful locomotive organs. Cilia are, moreover, not wanting internally, but are there comparatively few, since they are appendages only of free surfaces. They are met with lining the oesophagus, where they, no doubt, seiwe to facilitate the ingestion of food and of the water taken in for the purposes of aeration. The nature and cause of ciliary movement have been much debated. To account for the energetic and peculiar movements of cilia, Ehrenberg imagined the existence of a muscular aj)paratus at their globular roots, consisting of four muscles, each pulling in an opposite dii'ection, but, by acting in succession, causing the apparent rotation of the axis around the fixed base. This bold idea has met with no favour among physiologists, who condemn it as purely imaginary and as opposed to the simplicity of natiu-e, to all analogy, and to aU the admitted facts and principles of liistology. Most inquirers despair of attaining a satisfactory explanation, of ciliary action, and treat it as an ulti- mate fact. However, Cohn, looking to the peculiar structure of the integu- ment of Paramecium {Loxodes) Bursaria (XXIX. 26), fancied that ciliary motion admitted of explanation, since, on the supposition of an inherent contractility in that membrane, each Kttle pyramid might be imagined to contract its sides in turn, and make the cilium surrounding it revolve in the figure of an inverted cone. But granting the possibility of this explanation in the case of the animalcule cited, it could in no wise be applied generally to cihary motion ; for a similar structiu-e is found in comparatively few other examples, and the innate contractility of the supporting membrane, assumed in the instance in question, has certainly no existence in many ciliated sur- faces, and involves nearly an equal stretch of imagination to conceive as Ehrenberg's muscles. Returning from this digression on the nature and cause of ciliary action, let us briefly review the mode of distribution of cilia in the Protozoa. In. many genera they are chstributed universally over the surface (XXIX. 20, 28, 48 ; XXYIII. 1, 8, 31), not at random, however, but in definite parallel lines, more or less approximated, usually traversing the length of the body. A distribution in parallel lines is also not unfrequently obsei-ved across or around the body. Even where generally difi'used over the body, they are commonly more developed at certain parts, as about the mouth, the head, and tail, as well as on any processes or in any depressions of the body, e. g. in Chihdon (XXIX. 48), Bursaria, Leucophrys, Stentor, &c. Stein represents it as a generic character, that in Paramecium (XXIX. 28) all the cilia are 286 GENERAL HISTORY OF THE INFUSORIA. of uniform length. In Coleps (XXIV. 284), the lorica is divided into a mul- titude of minute facettes bj intercurrent lines or sulci, and the cilia are placed at the points of their intersection. In Colpoda Cucidlulus (XXIX. 35, 36, 37), the cilia are much longer at the anterior prolonged extremit}^, the lip, just as in Chilodon ; but there is besides, in the deep sulcus where the mouth is found, a dense pencil of long and strong cilia (XXIX. 37), which Ehrenberg mistook for a solid process of the body, and called the " tongue." From this fasciculus or bundle, a row of long cilia is, moreover, seen to extend backwards to the posterior extremity (XXIX. 37). Other groups of Ciliated Protozoa have the cilia confined, more or less strictly, to one part or organ of the body, — a circumstance exemplified in the Vortl- cellina and Ophrydina (XXX. 1, 2, 5, 9 ; XXIX. 1, 3, 4, 5). This Hmita- tion, as contrasted with the general diffasion of cilia, imphes an advance in the scheme of organization, and is attended by the constniction of a special apparatus about the head of the animalcules. Thus, in the families named, the rule is that the anterior extremity is bounded by an evident, mostly thick- ened margin, either curved or straight — the "peristom " — crowned with vibra- tile cilia and complicated by an internal, usually extensile, ciliated disk or rotary organ (XXX. 1, 2, 9 a, 29 «), the whole apparatus recalling the stnic- ture of the rotary organ of the Rotatoria. The cilia appertaining to the pe- ristom and disk are highly developed and strong, although, instead of ser\dng for locomotion, they only subserve the processes of nutrition and aeration or respiration, by reason of the fixed condition of the animalcules possessing them. Another peculiarity of the ciliar}- apparatus of the Vorticellina and Opliry- dina is that it is retractile (XXX. 6 a), or can be involuted and withdi-awn into the interior of the animal (XXX. 13), and the peristom closed completely, and contracted sometimes so far as to di-aw in a part of the wall around it, and not leave a single ciKum visible externally (XXX. 11b, 31, 33). When thus retracted, the ciHated organ appears like an internal, irregular-sigmoid, contracted cavity or fissure, with the cilia closely packed together and scarcely distinguishable (XXVII. 5 a, b ; XXX. 11 b). The retraction of the ciliary wreaths, which takes place very rapidly, is caused by the presence of sur- rounding objects in the immediate vicinity of the animal, by their contact with it, by any shocks it may feel, and by the presence of noxious matters in the water. On the removal of such and similar causes of annoyance, the ex- tension of the delicate apparatus follows ; this act, however, is less rapid than that of retraction, and may be arrested at any point. A more permanent withdrawal of the rotary apparatus, in the families named, occurs when the process of self- division is about to proceed (XXVII. 3 ; XXVIII. 18), and also when the animalcule prepares to enter into the en- cysted condition (XXVII. 5, 7). The disappearance of ciHa is witnessed not only in Vorticellina and Ophry- dina when the process of encysting takes place, but is a general phenomenon among ciliated organisms under the same circumstances ; yet it would appear that in some cases, even when an animalcule has surrounded itself with a cyst, its cilia are not actually lost, but only withdrawn from view, — a fact adverted to by Stein in his account of Chilodon Cucidlulus, which at times, after encysting itself and developing one or more Hving germs within the cyst, has been seen to renew its original appearance, to regain its cilia upon its surface, and, after rotating for a while within the sac, to burst at length through it and escape (XXIX. 55, 58). Moreover many observers have asserted the fact that an animalcule may, soon after encysting itself, be set free by rupturing the cyst by pressure, and then reassume its previous ciliated and active condition. Nevertheless the act of encvsting, when advanced to OF THE PROTOZOA. CILIATA. 287 a certain point, or when the reproductive process consequent upon it differs from that seen in Chilodon, appears to involve the final disappearance both of generally diffused cilia and of specially organized ciliary wreaths. The an-est of the motion, and the ultimate disappearance of cilia, are phe- nomena attendant also on the death, or on the approaching diffluence, of ani- malcules— when the surrounding w^ater dries up, or when their vitality is injiu'ed by chemical agents or by physical forces, such as electricity and heat. Stein, however, states that, although the animalcule, e. g. a Paramecium, is killed by the addition of very dilute acetic acid, yet its cilia continue visible and of their normal length. Cohn behoved the cilia to be very much longer than Ehrenberg represented ; but, as Stein affirms, this notion originated from an unnatural appearance consequent on the dying state of the animalcule, from evaporation of the surrounding water ; and he adds that a similar elongation of cilia appears immediately at the point where strong acetic acid comes into contact with the suiface. But this explanation has since been set aside by Prof. Allman's discovery of the existence of trichocysts, or thread-cells, within the subtegumentary layer of the body (XXXI. 1-4), to which he at- tributes the phenomena observed and discussed by Cohn and Stein. An instance of a temporary formation of cilia is seen in the VorticeUina and OpTirydina when the offspiing, formed by fission or by gemmation, is pre- pared to detach itself from the parent being. Under such circumstances, and prior to the development of the interior retractile ciliary organ, a wreath of ciha makes its appearance (XXVII. 4, 11) near the posterior extremity — but which, indeed, for the time, advances first in swimming, and continues to do so until the animalcule has attached itself and proceeds to unfold the ciliated apparatus at its head. In the above account, reference has been chiefly made to vibratile cilia, but, as before noticed, there are tegumentary processes of larger size, coarser and stiffer, and withal not vibratile, although moveable. Such serve frequently as special organs of locomotion, or of prehension, or of both, and may also be occasionally considered weapons of offence and defence. Accordiag to their form they are named setS^. Icmceolata, in various VorticeUce, in Bursaria trunca- tella, B. Jateritia, Poclo^hrya jixa, Loxodes CucuUulus fDuj.), Leucophrys Spathula, AmphUejotus margaritifer, Ilolojohrya brunnea, and less completely in Amphileptus Anas, Stylonychia Mytilus, Paramecium chrysalis, Spirosiomum ambiguum, Stentor po(ymorj)hus, St. Millleri, Paramecium AureJia, and Loxodes Bursaria. In Loxodes Cvcidhdus (Duj.) and Stylonychia pmstidata he saw the dis- charge of the whole of the contents of the cyst in the form of encvsted Infu- soria. The embiyo born from the cysts of Stylonychia pustulata resembles closely the Triclioda Lynceus, and can multiply itself by self-fission just in the same manner as mature and independent beings. In cyst- development, he observes, the whole of the contents are, as Jules Haime stated, not metamorphosed into the resultant embryo, but one or more portions escape in the form of globules, apparently ciliated, and move off with a rotating motion. PEPEonrcTiox of the Ciliated Protozoa: — Fission, modes of; Gemmation- INTERNAL Ova producing Ghrms or Embryos ; Impregnation ; Production of new Beings a^ith and without Metamorphosis ; Transformation into Acinet^, and Development of Embryos. — Until lately, naturahsts in general did not acknowledge other methods of reproduction than by fission, or, as 346 GENEEAL HISTORY OF THE INFrSOEIA. some would call it, fissation, and by gemmatioii or budding, which, from not being true generative acts, have been called ' vegetative ' modes of propagation or multiplication. Kecently, however, the Ciliata have had attributed to them true generative processes, resulting in the development of embryos either with or without intercurrent metamorphoses. The simpler processes of fission and gemmation are, in Stein's opinion, modes of propagation pecuhar to immatiu-e beings, and are replaced in mature animalcules by the agency of germs or embiyos. Fissiojsr. — This duplicative subdivision may be longitudinal, transverse, or obhque ; and whilst some species divide in only one dii'ection, others are capable of so doing in two, for instance, in the longitudinal and transverse, but not simidtaneously. Among the VortkelUna longitudinal fission alone occurs ; Paramecium (XXIX. 27), Chilodon, and others divide both longi- tudinally and transversely; Lacjenophrys obliquely only. Fission has not been mtnessed in SjiirocJiona nor in Trichodina, nor in Coljjoda when in a free state and not encysted. Ehrenberg came to the conclusion that multiplication by spontaneous divi- sion is the character which separates animals from j)lants. It is true (he argued) that gemmation in plants, especially in veiy simple cells, is at times very similar to the division in animals ; but this relates to the form, not the formation. A vegetable cell, apparently capable of self-division, produces one, or contemporaneously many exterior buds (gemma;), vrithout any change in its interior. An animal which is capable of di\ision, first doubles the inner organs, and subsequently decreases exteriorly in size. Self-division proceeds from the interior towards the exterior, from the centre to the periphery' ; gemmation, which also occurs in animals, proceeds from the exterior towards the interior, and forms first a wart, which then gradually becomes organized. This supposed distinction between fission in vegetable cells and that in simple animals like Infusoria is set aside by modern researches, which show that, when a plant- cell is about to divide, the mucilaginous layer of the wall (L e. the primordial utricle) manifests a constriction, which presently involves the waU itself, and, gradually deepening, at length cuts the ceU into two. The observations on this subject in the chapters on Desmidie^ and Diatome^ will more completely elucidate it. Considered with respect to the condition of the animalcule, fission occurs in the active and unchanged state, as in Paramecium ; or In a contracted state, as in Vorticellina ; or only when encysted, as in the case of Colpoda. Hence it follows, that it presents several slight modifications in its course. One general fact is, that whilst fission proceeds, the rotation of the contents of the animalcule is at a stand- still. In its simplest variety, the dividing being first presents a constriction at each pole or side of the body, which gradually ex- tends until it completely cuts it into two equal or unequal parts. Simulta- neously Avith the fh'st indication of an act of fission, and in some cases before a sign of it is to be detected in the peripheiy of the animal, it has been generally taught that the nucleus, after elongating and usually disposing itself across the direction of the line of scission, takes the initiative in the act, by commencing a fission of its own substance (XXIX. 27), which sub- sequently proceeds step by step with that of the entire body, until complete. This statement is, according to Lachmann {A. N. H. 1857, xix. p. 230), a mistake when made respecting the Protozoa generally ; for in some cases the division of the nucleus is consecutive to that of the body, and " in others, again, the actual fissation of the nucleus does not lead to that of the body, but embryos are developed in it ; " on the other hand, ^' fissation is generally commenced rather bv a new formation of contractile vesicles." OF THE PROTOZOA. CILIATA. 347 In some species where fission proceeds on its simple type, food may con- tinue to be received for a short period by the di\'iding animal. The small share the abdominal contents within the cortical lamina have in the \'ital processes, is shown by Lachmann's observation of a Stylonychia, " which, although a considerable part of its chyme had been sucked out of it by an Acineta, still imderwent division, so that one of the gemmules of division swam away from it briskly, and only the other half of the old animal was destroyed." The direction of the line of section is perhaps, when longitudinal, usually from before backwards, the constriction appearing fii'st and advancing more rapidly at the head ; but the contrary, according to Stein, prevails in Chilodon Cucidhdus, where the constriction makes its way solely from the posterior pole. When fission is transverse or oblique it necessarily involves the reproduc- tion, in the posterior half, of the organs existing in the anterior, viz. the ciliary apparatus of the head, the oral aperture, the tube prolonged from it, and the contractile vesicle. So far, therefore, it approaches nearer the act of gemma- tion than does longitudinal fission, wherein segments of the already existing organs are separated for the piu-poses of the new individual, and are not actually reproduced or created anew. " In those Infusoria," says Lachmann (A. JSf. H. he. cit.), '' in which a peculiar series of stronger cilia leads to the mouth (such as Oxytrkliince and Eiq)htece), the furrow in which this series of cilia is situated is seen, subsequently to or simultaneously with the division of the contractile vesicle, to become produced backwards over the mouth ; in this prolongation cilia are produced, and its posterior extremity becomes deepened into a mouth and oesophagus, which then opens towards the ali- mentary cavity of the animal ; then, simultaneously with the external con- striction of the body, the new fuiTow is separated from the old one. (In Stentor the new fi^ontal series of cilia first makes its appearance on the old animal as a lateral straight series — the crista lateralis of Ehrenberg). In animals which also possess peculiar processes of the body as organs of motion (hooks, styles, &c.), the fissation usually takes place in such a manner, that each of the newly-formed animals acquires a portion of these from the old animal, whilst the other part is of new formation." The manner in which self-division proceeds in Protozoa with a firm, and seemingly almost brittle integument, is exemplified in Goleps (XXTV. 284, 285). Along the line of section a new secretion of chitinous substance takes place, soft in consistence and transparent, which by its increasing width separates the two portions of the original lorica ; in this interposed new tissue a constriction presently manifests itself, and advancing in depth, the two segments are finally simdered. It thus comes to pass that each product of fission is one half covered with a dense shield, and the other half with a soft, yielding integument. After a while, more molecules make their appear- ance in the latter, which gradually assumes a firmness equal to that of the old lorica. The Vorticellina, including the Ophrydina, do not divide until they have assumed a sort of semiquiescent condition, by the complete withdi-awal of their ciliary apparatus and the contraction of the body generally into a more or less rounded or oval shape, — in short, until they have advanced one step towards encysting themselves. Ehrcnberg portrayed their fission as a simple constriction advancing from before backwards to separation of the body ; but Stein pointed out the actual antecedents of the process. According to the latter writer, the head-portion and its appendages withdraw ; the rotary organ is absorbed, and also the oesophagus ; at the same time the contractile space vanishes ; the body ex- pands in width, the nucleus outstretches itself across it, a constriction appears 348 GENERAL HISTORY OF THE INFUSORIA. on its anterior border, and, extending constantly in depth, at length effects its complete division. When the section has reached the third of the body, a conical space displays itself towards the anterior portion of each half (XXYII. 3), lined by a special membrane, covered by cilia on its posterior side or base, which are seen to vibrate within the cavity. This formation is the rudiment of the futiu^e rotary organ. The apex of the conical hollow is prolonged by a canal which eventually opens on the sui-face, and thus establishes a con- tinuity between the lining membrane and the external integument. At the same time the internal angle at the base of the cone is j)roduced inwards so as to form the ahmentaiy tube. When these changes are accompHshed, the body is half cut through, and the appearance is rather that of two indi\-idual animalcules united posteriorly, having their ciliary apparatus retracted, and the peristom contracted in a splinter-like manner over it. Lastly, the advancing act of scission divides the nucleus ; and the whole body becomes resolved into two individuals seated upon the same stalk. From this account it follows, that, of the original organs of the animalcule, the nucleus is the only one divided between the two resultant beings by the process of fission ; all the rest are formed anew out of the homogeneous substance of the body, viz. the peristom, the rotary organ, the alimentary tube, and the contractile vesicle. This absorption and renewal of parts during fissation is denied by Lachmann, who affirms that the movement of the cilia upon the ciliary apparatus, and in the vestibulum and oesophagus, which are closed up by the peristom, may be observed during the whole process. We have no means of deciding which of these two statements is correct : yet we rather incline to Stein's account ; for when we admit that in fission there is a separation of all the organs and appendages of the body into two portions, one to each resultant being, an act of stnictural development becomes necessary to reproduce the remaining por- tion, so as to perfect each new animal and to assimilate it in characters to the parent. This being the case, the method of development stated by Stein is more consonant Avith oiu' ^dews of histogeny than that of Lachmann. The oblique fission of Lagenophrys vaginicola (XXX. 32, 35, 36) presents several peculiarities. The line of section commences below the peristom on one side, and proceeds diagonally across to the opposite, and thus gives rise to an anterior lateral segment retaining all the special organs, and a posterior lateral possessing nothing save its half of the elongated divided nucleus. Diuing the process, the anterior half continues in the enjoyment of all its functions and activity (XXX. 32), whirls its ciliary organ, and takes in food by the mouth : the food, however, does not reach to the segment behind ; and whatever alimentary particles might be present in this vanish, and its whole contained substance becomes homogeneous and granular, the half of the curved band-like nucleus extending into it. WTien the line of section is fully formed. Stein remarks that the posterior lateral segment rather resembles a gemma than the result of self-division, and j)roves how closely united are the two processes of gemmation and of fission. WTien the scission is nearly complete, a contractile space appears, and, either before or behind this, a curved elongated cavity, ciliated on one side and produced upwards as a tube from one angle, is formed (XXX. 35), out of which the rotary organ and peristom are developed. As there is no room for movement, the new being lies motionless close against the old one : how- ever, its contractile space acts energetically ; and the alimentary tube, filled with fluid, moves upwards and downwards, and from side to side within it. At length a row of cilia appear around the circumference of the body ; and now two beings occupy one case, the anterior adhering by its peristom to the narrow OF THE PEOTOZOA. CILIATA. 349 orifice of the sheath, whilst the posterior lies immediately behind it, fixed from want of space, and unable to free itself (XXX. 36). The question that now presents itself is, how is the newly-formed animal to escape its prison and to exercise its vital endowments ? This, Stein has been able to solve by ob- servation of another species of Lagenoplirys, viz. L. Amjpidla. The upper seg- ment ceases to put forth its ciliary organs and to take in food, and shortly contracts itself and detaches its hold from the opening of the external sheath, developing simultaneously a row of cilia around its margin (XXX. 35). It also not unfrequently happens that the body is divided from the peiistom, leaving this portion adherent in its natural position to the orifice of the sheath, and possessed of such remarkable vitality, that it continues to con- tract and dilate, and to implicate the orifice of the sheath itself in its move- ments (XXX. 35). AVhen the peristom, with a portion of contractile sarcode (35 I) enclosing at times a contractile space within it, thus plugs the only outlet from the cyst, the two products of fission cannot gain their liberty, and only enjoy the limited degree of locomotion allowed within theii- narrow prison-house. But where, as is more common, the orifice is opened, they sooner or later make their way out, experiencing, nevertheless, some difficulty in passing through the narrow outlet. A curious circumstance pertains to these fission-products of Lagenophrys, and indeed to those of all the OpTirydlna and Vorticellina, viz. they are not precisely like the parent. Thus, the young of Lagenoplirys, produced as above described, exhibit the rotary organ and peristom in a contracted con- dition, whilst a row of ciHa surrounds the body in a ring-Hke groove on the abdominal siuface, and serves the purpose of a locomotive organ (XXX. 35, 36). On the ventral aspect, adds Stein, the figui'e of the animalcule recalls that of Stylonychia, between w^hich and the normal form of Vorticellina it may be considered a transitional type. Turning now to the other members of the Vorticellina and Ophrydina, we see that the history of the fission-products differs according to their habits and structural peculiarities. In the branching forms many of the newly - formed beings proceed each to secrete from its base a pedicle, and so continue the dichotomy of the little arborescent colony they belong to. Others, on the contrary, detach themselves from the parent-stem and enter on a free and independent existence. In this case one of the two segments consequent on self-division, in order to enter on its new mode of Hfe, undergoes certain modifications in structure, viz. it continues in a completely contracted state, and a furrow appears about the posterior third of the body, within which a ciliary circlet develops as the locomotive organ of the animal (XXVII. 11). This occurrence is general among Vorticellce and Ophrydina ; for among the former the pedicle never ramifies, and in the latter one fission -product must quit the capsule, which serves as the nidus of only one being at a time. The after-history of these locomotive segments is widely different in dif- ferent specimens. Some, after swimming about for a time, come to a state of rest, affix themselves by theii' posterior extremity, and produce, according to their natural habit, either a stalk or a sheath, and resume aU the charac- teristics of the parent-stock. Others, again, become quiescent, but instead of se- creting a pedicle or sheath, proceed to encyst themselves, either for their own preservation or preparatory to the fulfilment of an act of reproduction. In- deed, the process of encysting may overtake the animals whilst still seated on their stalk or within their case, and thus anticipate the formation of the posterior ciliary wi-eath. Lastly, in a few genera, fission seems only, or at least mostly, to occur after the animalcules are encysted. Stein represents this to be the case ge- 350 GENERAL HISTORY OF THE INFUSORIA. nerally in Colpoda CucuUulus, which he never found in process of fission (XXIX. 38-47). Indeed, Ehrenberg himself never saw self-division of this animalcule, although he has, on the authority and ambiguous observa- tions of some of the old observers, described its occuiTence. According to Stein's researches, encysting would not appear absolutely necessary ; for he witnessed self-division in some specimens only contracted in a spherical form : however, in others, the more numerous, a cyst was thrown around the body before that process ensued. According to the general plan, the Ciliated Protozoa di\ide into two ; yet there are some — and Colpoda is one of such — in which the act of fission is repeated, and 4, 8, and even 16 segments and upwards result. The products of fission have a certain latitude of motion within their cysts, and ultimately escape by rupture. Another peculiarity about Colpoda is, that the segments resulting from fission secrete individually a capsule around themselves, and thus we have encysted beings enclosed within a general cyst. Lastly, each young cyst has its own nucleus and contractile vesicle (XXIX. 43). The fission of the animal when encysted appears to be the rule in Glau- coma ; for example, in G. scintillans ; and Stein surmises that it is this occurrence which Cohn witnessed in Chilodon uncinatus, and thought to be two animalcules enclosed within a common cyst, as happens with Gregarhiw. The importance of fission as a means of multiplying individuals among the CiHata admits of numerous striking illustrations. We may quote one given by Ehrenberg, by no means an extraordinary instance. He made out that a single individual of Stylonycliia Mytilus lived nine days : during the first 24 hours it divided into 3 ; and duiing the next space of 24 hours each of these three had subdivided into two beings ; so that by self- division alone this animalcule can multiply itself three or fourfold in foiu' and twenty hours, and in the space of ten days be represented by a million derived beings or offshoots. Another instance may be adduced from the same distinguished micrographer. On the 14th of November, he divided a Paramecium Aiirelia, yL-th of a line in length, into four parts, each of which he placed in a sepa- rate glass. On the 17th, the glasses numbered 1 and 4 each contained an iso- lated Paramecium swimming actively about. The pieces in Nos. 3 and 2 had disappeared. On the 18th, there was no change. On the 19th, each animal- cule presented a constriction across the middle of the body. On the 20th, No. 1 had propagated 5 individuals by transverse fission, and No. 4 eight such. On the 21st, no change had taken place. On the 22nd, No. 1 contained 6, and No. 4, 18 specimens. On the 23rd, the beings produced were too nu- merous to be counted. From these notes Ehrenberg calculated, if this process continued in activity for a month, 268 millions might be produced. Apart, however, from these, which we may term speculative considerations, we have in Ophrydium the clearest and most direct evidence of the extent to which fission is carried out. On the completion of self-di\T.sion in this animal, the products remain together, connected by a common gelatinous mass at their base exerted by themselves. By the repetition of the process again and again, through a long series, the Opliryd'ia accumulate in large greenish masses, or poljT^aries, at times of the size of the fist or even of the head of a man. Now, by comparing the size of the individual Ophrydia (about y^th of an inch in length) with that of the masses they form, "some estimate," says Dr. Car- penter {The Microscope, p. 487), " may be formed of the number included in the latter ; for a cubic inch would contain nearly e'lgJit millions of them, if they were closely packed ; and many times that number must exist in the larger masses, even making allowance for the fact that the bodies of the animalcules are separated from each other by their gelatinous cushion, and that the masses OF THE PROTOZOA. CILIATA. 351 have their central portions occupied only by water. Hence we have in such clusters a distinct proof of the extraordinary extent to which multiplication by duplicative subdivision may proceed without the intei-position of any other process. These animalcules, however, free themselves at times from theii- gelatinous bed, and have been observed to undergo an ' encysting process ' corresponding with that of the VorticelUna. It is much to be desii^ed that mi- croscopic observers should devote themselves systematically to the continuous study of even the commonest and best-known forms of these animalcules, since there is not a single one whose entire life-history, from one generative act to another, is kno^vn to us ; and since it cannot be even guessed at, with- out such knowledge, what, among the many dissimilar forms that have been described by Prof. Ehrenberg and others, are to be accounted as tnily di- stinct species, and what are mere phases in the existence of others that are perhaps very dissimilar to them in aspect, it is obvious that no credit is really to be gained by the discovery of any number of apparently new species, which shall be at all comparable with that to be acquii^ed by the complete and satisfactoiy elucidation of the Kfe-history of any one." Gemmation (iUustrated by XXYII. 1-4 ; XXX. 17, 27, 29, 31, 33, 34).— This is the next process of multiplication to be considered. It has much analogy with fission, but is not nearly so widely diffused, being restricted apparently to the families VorticeUina and OpTirydina, that is, to attached species of Ciliata ; yet even among these it would seem not to be general ; for Stein has failed to observe it in the genus Ojyercularia. In it a promi- nence forms upon the surface, mostly near the posterior extremity, and of the same granular homogeneous substance as the rest of the animal : a line of constriction soon displays itself, and gradually deepens, whilst the budding process increases in size and developes internal organs and external ap- pendages, until, being sufficiently perfected for an isolated existence, it severs itself from the parent stock. The gemma3 or buds thus produced are much smaller than the parent, and, even when they have acquired theii' largest di- mensions before separation, are less than the new beings originating from self-division. In everj^ instance of fission the nucleus becomes di\ided be- tween the two segments ; and some authors, as we have seen, hold the ojdI- nion that these share between them a portion of other pre-existent organs of the dividing animal ; on the other hand, in gemmation the bud is a mere offshoot of the general substance, containing no portion of any pre-existing organ — not even, so far as can be seen, of the nucleus ; and consequently all the specially- organized parts are developed in it de novo. If the doctrine of internal germs be admitted, then it may be imagined that each gemma origi- nates from one of these, which takes on this external direction of development. On the completion of the gemma, we find that it resembles (except in Spi- rocliona and Lagenophrys) a completely- contracted specimen of the parent animalcule, and possesses, in lieu of the usual ciliated whorl on the head, a posterior ciliary wreath, whereby, when detached, it swims freely away, 'wdth the posterior extremity, however, in advance. It resembles, therefore, in all respects the product of fission when separated from its fellow, and, like it, may either presently attach itself, losing its posterior circlet of cilia, and acquire aU the characters of its parent — as well as, in process of time, its dimensions, — or advance to a completely encysted state, prepara- tory to a process of development, or simply for the object of preservation from untoward external conditions. The act of gemmation goes on alike in small and in large specimens. Stein notes its occuiTcnce in Vorticelke of only ^"' in length. A few illustrations may render the above account of gemmation more clear. 352 GENERAL HISTORY OF THE INFUSORIA. Speaking of this process in Vorticellce, Stein (ojy. clt. p. 28) says, the interior of the knob-like process is quite homogeneous at first (XXVII. 1) ; but when it has attained a hemispherical shape, a crescentic cavity forms at its anterior part, from which the peristom, rotary organ, and alimentary tube are even- tually developed (XXX. 17, 27), just as happens in the result of fission. Whilst this proceeds, the swelling acquii^es an oval or globose figure, and the width of its attached base d^vindIes to a constricted neck or isthmus. The addition of acetic acid proves that no portion of the nucleus extends into it, but that this organ retains its normal cui'\'ed reniform figure. Stein here adds the remark, that no sharp Kne of distinction exists between self-fission and gemmation — that the latter may be looked upon as an act of unequal division, in which the whole organization has to be created, and not, as in fission, simply perpetuated ; or fission may be described as a variety of gemmation, one segment being regarded as a bud ; at least this view holds good in the case of transverse fission. Longitudinal fission consists in the formation of two gemmae, which subsequently involve the entire being. So also in one sense gemmation does not always end in the production of a single bud ; for VorticeUce with two are common, and occasionally with three, one of which is ready for detachment, whilst the other or others are very incomplete. In Sp'irochona (XXX. 17, 27), which does not multiply by fission, gem- mation is very frequent ; and often two buds are produced, one immediately behind the other, the hindmost being first in development. Where two exist, the first-fonned usually appears on the side of the body at its widest part ; and the second forms subsequently in front of it, nearer the neck. Re- latively to the size of the parent, the bud is usually of greater dimensions than in VorticeUa, and may, by thrusting aside the head of the Sj;>irochona, place itself in the longitudinal axis of the body. \\Tien the gemma com- mences to contract its base and to acquii^e the form of an independent being, an opaque, sharply-defined, homogeneous speck makes its appearance about its middle, or, rather, in front of it, which, by further development, becomes the nucleus (XXX. 17), wliilst a shallow groove displays itself at its anterior tiTincate end, and somewhat later is transformed into a curved and rather angular ciliated fissui'e extending some way down one side of the body. In this so-formed gemma of Spirochona there is, therefore, a wide depar- ture from the rule observed in any of the VorticeUina and Ophrydina. No posterior ciliary wreath is fonned ; and the anterior ciliary apparatus, together with the head itself, is at first developed in a temporary and rudimentary manner. After moving about for some time by means of the ciliary antero- lateral chaimel, the free gemma fixes itself by its posterior extremity, by an adhesive substance, or occasionally by a short stem ; and then the opposite sides of the ciliated furrow approximate, and coalesce behind, whilst in front one edge rises above the other (XXX. 19), and soon forms a spirally-con- voluted membrane, which becomes clothed with cilia replacing those of the old furrow, which are absorbed and disappear (XXX. 20). This growth into perfect Spirochonce does not happen with all gemmae ; for some assume a quiescent condition, become encysted, and, if Stein be right, are ultimately converted into very peculiar Acinetiform beings — the Dench-ocometes para- doxus (XXX. 23). Before encysting, the cilia cease to play, and disappear ; and very soon the furrow itself closes up. When enclosed within the trans- parent but firm capsule, nothing but a finely-granular homogeneous substance appears, containing the peculiar nucleus, which, however, requires the action of acetic acid to display it (XXX. 21). The process of gemmation presents several peculiarities in the genus La- genophrys, due mostly to the peculiar connexion between the enclosed ani- OF THE PROTOZOA. CILIATA. 353 lualeule and its sheath. Tlie rule seems to be that two or four gemmae are produced within the sheath at the same time (XXX. 29, 34) ; but since Stein had never encountered four, and very rarely three, gemmae upon any animalcule, the idea crossed his mind that these small buds of Lagenophrys might perhaps be embryos developed within the interior, and subsequently discharged. Another- explanation was possible, viz. that they were animal- cules which had found their way into the sheath, and were quite foreign to it. However, both these hypotheses are set aside by the history of deve- lopment and by the characters of the beings produced. The process consists in the enlargement of the posterior extremity (XXX. 33), or of a part of the side of the Lagenophrys, and the progressive detachment of the enlargement as a segment or bud, and simultaneously the production of a band-like nu- cleus and contractile vesicle T\ithin it. Tlus stage being so far complete, the gemma does not proceed to develope into the fonn of the parent animal, but self-fission takes place, and two similar ovoid bodies, each with its contractile vesicle, is tlie result (XXX. 29). ^^Tien the constriction of the single gemma announces approaching fi^ssion, a circlet of cilia ajipears on each side of it (XXX. 34) ; and on the completion of the process, each segment has a conical head surrounded with a wreath of cilia. From this mode of production in pairs, the number of gemmae wdthin the sheath of Lagenophrys should always be two or a multiple of two ; hence, when three are seen, it is to be i^resumed that one has previously made its escape. From the peculiar way in which the body of the Lagenophrys is sus- pended by its attached peristom to the orifice of the sheath, it is clearly im- possible that anything can dii-ectly either make its entrance into or its escape from the animal, without rupture, of which we have no inchcation. The way in which this impediment is sm-mounted is, on Stein's authority, by the sudden contraction of the body of the Lagenophrys rupturing the adhesion of the peristom to the orifice of the sheath, and by its subsequent retraction within it (XXX. 31). In this manner a free exit is aflforded to any contained gemmae ; and after a certain time allowed for their passage, the anterior part of the body again enlarges itself, and reassumes its adhesion to the sheath. After their exit. Stein has no observations to show what becomes of them ; but his idea seems to be that they do not produce a sheath until nearly arrived at maturity, since they are so much smaller than the least of the sheathed examples to be met with. If this account be correct, the gemmation of Lagenophrys is actually a compound process of budding and fission, wliilst the resultant beings differ ^ddely from those of other Vortlcellhia in all details, and are so veiy abeiTant in form from the parent, that they require to undergo a metamoi^Dhosis before they gain it. Development from Ova. Ixteexal Geems and Embetos. — Although the reproduction of the Ciliated Protozoa is so largely provided for by the two processes of fission and gemmation as just described, it is even more marvellously so by their possession of true generative functions — a fact clearly established by the latest obsen'ers, although denied by Siebold, Kolliker, and others some years since, when the unicellular hypothesis of Protozoic life militated against the notion of the existence of internal ova or germs. Even now, indeed, Avhen we look to the researches disclosing to iLS the development and discharge of germs and of living embryos, we find diverse and contradictoiy statements concerning both the antecedent or pre- paratory acts, and the final results. AVe cannot attempt to reconcile these discrepancies, but wiU record the principal opinions of naturalists and the observations on which they are based. 2 a 354 GENEEAL HISTORY OF THE INFUSORIA. In a previous page we have stated the views of Carter and Perty, relative to the existence of ova or germs in the inteiior of CiUated Protozoa, and have rejected them as unsatisfactory. Further, when we come to inquire the process of development of the presumed OM.iles, their mode of exclusion, and other particulars necessary to complete their history and even theii' identification, we find that those naturalists have no direct observations to adduce, but can appeal only to analogy and to some casual and unconfiimed observations of others. For instance, Mr. Carter, when treating of the develop- ment of ovules, appeals to the process in Spongilla and Eiiglyplia, and endea- vours to make out that,Tvdth some modifications, the ovules oiEuglence, and pro- bably those of all the Rhizopods and Astasice, have a similar mode of generation. Perty, likewise, unable to advance any direct proof of the existence of ovules and of their discharge, appeals to Eckhard's observations on Stentor cceruleus, which Oscar Schmidt repeated and generally confirmed. In the recorded observation of Eckhard {A. N. H. xviii. 1846), three or four globules, in dififerent stages of development occurred in the interior of the Stentor in a row (XXIX. 8-13) : — " In the fii^st stage, the contents of the globules, consisting of minute granules, exist most imperfectly developed ; but few granules at present occur, and the globule, when it lies in the body, is not very distinct, on accoimt of the granular parenchyma of the lat- ter. In the second stage of development (fig. 9) the granules appear more numerous, the contents are therefore more concentrated, and the globules can then be very distinctly observed in the body. Fig. 11 shows the third stage ; granules commence arranging themselves in a row Or, as some- times happens, they appear grouped in the same manner at two spots. The gTanules thus arranged and closely pressed together, blend into a glandular but clear organ (fig. 12), in which the granular structure cannot be any longer detected ; frequently it is also divided in two parts. Lastly, in the situation of the transparent glandular organ a row of cilia appears, evidently the mouth (fig. 13). Whether this organ is formed immediately from the former, I have not been able to ascertain with certainty ; yet that it is so, is extremely probable, since on the one hand the row of cilia occurs in the situation of the bright gland, whilst, on the other hand, in all the germs which exhibit this, the former organ is absent. Simultaneously \\dth the development of the mouth there appear one or two clear vesicles (fig. 13). On the 18tli of May I observed in the interior of St. cceruleus a germ as in fig. 12 ; I saw the cilia very distinctly in motion ; the vesicles were, however, still absent, and they did not escape on this occasion. On the 21 st, I saw the perfect form (fig. 13), which issued out, whilst the parent animal swam away. I now attentively observed the young one to follow up its fiu'ther changes, perhaps the bursting of the carapace ; but I was obhged to leave ofi* watching it in half an hour, as I could not vouch for the accuracy of further observa- tion on account of the strain upon my eyes. On the 4th of June I saw a germ escape, as in fig. 13: it differed from that observed on the 21st of May ; for, being at first roimd, it at once exhibited an incurvation at its lower extremity — an appearance frequently observed in young Stentors, sometimes in old ones, when they contract fi'om the elongated form to one more or less rounded. I have subsequently once seen the escape of a similar germ ; and it appears to me that the true point of maturity is that at which vesicles begin to be visible. In Stentor polymorplms I have observed two such globules, but I have not succeeded in seeing any perfectly formed escape. In autumn I have often sought for the reciUTcnce of this phenomenon, but have never been able to observe it so perfectly as in the spring, although similar globules are not rare in the later parts of the year." or THE PROTOZOA. CILIATA. 355 From the poriisal of this account, the thought arises, whether, instead of proving- the existence and progressive development of internal ovules or germs in the sense Perty adopts, it is not another illustration of embryo-de- velopment by a sort of gemmation or breaking up of the nucleus, such as the researches of Cohn, Stein, Lachmann and others have made known to us, and concerning which we have now to speak {see Balbiani's researches, p. 329). The development of the nucleus into embryos takes place under different circumstances and in a varied manner in different genera of Ciliated Protozoa. It may occui' either without the previous encysting of the animalcule, or after this process is completed. Again, in the latter condition, and without ulterior change or metamori)hosis, either a few active embryos, or some encysted germs, may be the result, or the whole nucleus may resolve itself into a brood of monadiform beings, or, lastly, according to the views of Stein, the encysted animal" may be metamorphosed into an Acinetiform being, out of which embiyos are developed diverging in character more or less com- pletely from the original ciliated Protozoon, to which, however, they eventually recur. The development of embryos without the previous encysting of the animalcule has been followed out by Focke, Cohn, and Stein in Nassida and in Pammecium (Loxodes, Cohn) Bursaria (XXTIII. 10-14, XXIX. 28 to 34). A portion of the nucleus is separated by fission or by an act of gemmation, and constitutes a more or less orbicular body, in which a nucleus (XXIX. 34), and then a contractile vesicle, shortly declare themselves (XXIX. 29). Focke surmised that the so-called nucleolus originated this germ, which then foimd, as it were, a lodgment and nutrition in the nucleus as in a uterus {see Balbiani, p. 329) ; but Stein affirms that this body has nothing to do with the origin of the germ, and is frequently to be seen separated and removed to some distance from the nucleus (XXIX. 29). In appearance the disk-like germ is finely granular, paler than the nucleus, and not surrounded, like the latter, with a special membrane. Cohn represents it as existing in a distinctly Hmited cavity, prolonged to the external surface as a tube or oviduct, and terminated by a two-lipped orifice, through wliich the embryo makes its exit (XXYIII. 11, 12). According to Stein, however, no such duct and external orifice have an existence, except temporarily, dming the passage of the germ, or germs when two or more follow in succession. This assertion of Stein is supported by Cohn's o^vn observation, that the point of extrusion varied in different indi^-iduals in its position, being at one time at the middle, at another above it, at a thu'd below it, and, as the inile, on the left side, although as an exception on the right side or even towards the anterior margin. The act of birth occupies about twenty minutes ; and when the embryo is about to escape, it exhibits a vibration on its surface, which causes a motion in the surrounding water and hastens its detachment. This motion, after continuing a short time, ceases, and the little being attaches itself to the exterior of the parent (XXIX. 30). The chasm produced in the parent during the extrusion soon closes up, and leaves no trace, except, it may be, a slight hollow in the sm-face. The embryo has an elongated fissure, is rounded at each end (XXIX. 30), and frequently rather contracted at its middle ; internally it is finely granular and colomiess — not greenish, as Focke asserted — and contains, besides a darker nucleus, one or two contractile spaces (XXYIII. 14). Cohn could discover no mouth ; but Stein displays in his figure an oblique fold or groove (XXIX. 30), which may possibly rei)resent the oblique funnel-like vestibule of the mature Paramecium. The vibratile movement visible about the surface indicates ciliary action ; and if the embiyo be killed ■with iodine, the presence of long cilia is demonstrated. StiU the most peculiar feature in the new-bom animalcule is the possession of several soft 2 a2 356 GENERAL HISTORY OF THE INFFSORIA. tentacular processes at each end, siuTounded by small knobs, recalling in figure the knobbed tentacles of some Acinetina (XXYIII. 14, XXIX. 30) ; by means of these the embryo secures its hold to its parent. Such pro- cesses are not present in all specimens, and are therefore non-essential ; or it may be they have disappeared by withdi^awal into the general substance of the body. The embryo once freed from its parent, commences an independent existence, moving freely about in the water — much more similar in figure and structure, however, to some of Ehrenberg's Ci/clidina or to Dujardin's Enchelyens than to Parameciwn . Cohn notes its affinity with the Cyclidium margaritacenmy or to the Pantotriclmm Enchelys (Ehr.), and also with several species of Dujardin's genus Enchelys (Cyclidmm Ehr.). Cohn adds that, in his opinion, several embryos are developed simultaneously, and that, where only one or two are found, others have already escaped. In some instances he has noticed as many as six or eight in process of develop- ment, and, it would seem, in almost precisely the same stage, although their birth is successive. Fiu-ther, besides these normal embryos, he has fre- quently witnessed the escape of others having a globular figure, clothed with cilia and fm^nished with tentacular processes and a contractile vesicle. During the act of birth, the pulsations of the contractile space of the parent are uninterrupted, and the rotation of the contents is arrested until every germ has escaped. Another ciuious fact is, that the birth of embryos may proceed as usual even whilst the act of fission is taking place in the parent animal. The further history of the free embryo is not known ; yet, in aU pro- bability, it is ultimately transformed into a perfect Paramecium, — an event which, from its figui'e and stnicture, ensues readily and perhaps without more than one intermediate phase. Judging from the above details, it is probable, as before remarked, that the development of embryos in Stentor cceruleus (XXIX. 8) recorded by Eckhard {supra, p. 354) was a precisely similar phenomenon to that just described in Paramecium ; and it is clear that the like obtains in Stentor polymorjjhus, in an Opalina or Bursaria noticed by Siebold (probably the Bursaria Entozoon Ehr., parasitic in a frog), in Urostyla grandis, as mentioned by Cohn, and in the animalcule which we conceived to be Trichodina pedicuJus {A. N. H. 1849, iii. p. 269). Since this was written, the indefatigable labours of Cohn have added, another instance of this endogenous mode of development, in Nassula elegans {Zeitschr. 1857, p. 143; XXYIII. 11-14). This animalcule possesses an elliptic nucleus, having its nucleolus lodged in a fossa near one end, and surrounded by a vesicle, just as in the Paramecium Bursaria. Among many specimens, Cohn found several having a large, elliptic, hollow space, evidently limited by a membranous wall. Where this space approached nearest the external surface of the animalcule, this was depressed in a cup- like foiTQ, and from its centre a canal or fissure (XXYIII. 11 /) penetrated the interior of the space, where were two, never more, large globules, pj-jj'" in diameter (XXYIII. 11 d). After a longer or shorter delay, these globules escaped and appeared motionless, without coloui', but granular, and having a central nucleus and an excentric contractile vesicle. As in the instance of the germs of Paramecium Bursaria, no cilia, but a few short, knobbed, radiating, tentacular-looking processes (XXYIII. 14), were visible on the siuface. Lastly, Cohn noticed the formation of these germs in animalcules recently produced by self-fission, and which had attained only one-half their normal dimensions. The development of an embryo within an encysted animalcule is illustrated OF THE PROTOZOA. CILIATA. 357 in Stem's history of ChUodon CucuUulus (op. cit. p. 134). At a preceding page (p. 342) we have given an abstract of the mode of encysting of this animal, and have stated that the capsule remains gelatinous and soft. Inside the cyst, Stein discovered an actively- moving embryo contained within a special cavity (XXIX. 54-56), occupying precisely the spot where in other encysted Chilo- clons the nucleus is found, -viz. in the chagonal line connecting the two oppo- site contractile spaces. The embryo had an oval or ovate compressed figure, with one side straight or gently curved, and the anterior extremity notched. Its entire surface was covered with longitudinal, widely-separated rows of unusually long cilia, in incessant motion, which tiu^ned it in a spii'al or vermi- cular manner. Pressiu-e on the cyst caused its expulsion (XXIX. 59), either alone or together with the substance of the parent- cyst, to which it always remained adherent. This embryo. Stein concludes, is derived from the nucleus. Many cysts may be met with in which the nucleus is replaced by a much larger body, having a different consistence, opaque and motionless, and possessing in all respects the outhne of a germ. On pressing it out of its place, its siu'face is seen to be not quite naked, but to have short, stiff, and imperfectly-developed cilia at one end or entirely around its margin. Since the embryo occupies the site of the nucleus, it might at first sight be supposed that the latter was wholly transformed into it; but analogy leads us to the contrary inference, that the nucleus, although obscm^ed from view by the internal germ, is nevertheless present ; and this conclusion is fuiiher supported by the fact, that a successive development of embi^os goes on until the entire contents of the cyst are used up in their formation, an event that does not occur without the influence of a nucleus. Stein declares the embiyo (XXIX. 59) to be precisely similar to Cydidimn Glaucoma, both in figure and movements. Its size varies with that of the animalcule producing it ; and individuals of aU sizes may imdergo the encysting process. The smallest cysts met with were ^"' in length, and their embryo not more than ^hs'" > ^^® largest y^-'", and their embryo from ■^'" to ^■" (XXIX. 56). A remarkable circumstance happens in the case of some encysted Chilodons, even after they have given birth to one or more embryos, — viz. that they seem to emerge from their quiescent state and resume their active form. For instance. Stein met with cysts containing a freely-moving Cliilodon, together with an active embryo, both which ultimately escaped by an aperture in their walls (XXIX. 58). This revi\'ification of the ciliated Chilodon as above referred to, is urged by Stein as an argument to prove that the cilia are not lost or destroyed when encysting takes place, but probably merely closely compressed against the surface. Another variety of development of germs within an encysted animalcule is seen in Colpoda Cuctdlus (XXIX. 35-47), which we have described under the head of '' Fission," since the formation of the germs is the consequence of self-divison of the whole animal either into two or, as a rule, into four segments, which themselves become individually encysted, and present their own nucleus and contractile space. This plan of development explains the occurrence of very small encysted Colpodm. It was in this genus that Ehi'enberg conceived he had made out very clearly the hermaphroditism and cyclical development of " Polygastrica." A third way in which the encysting of an animalcule is made to serve the process of development is by the resolution of the nucleus into a multitude of minute segments, each eventually assuming an independent animal ex- istence. This formation of what may be caUed brood-cysts, occurs, as shown by Stein's later researches, in Vorticella microstoma (XXIII. 10-14), 358 GENEKAL HiSTOKY OF THE INEUSOKIA. Among cysts of the usual form and dimensions, are some in which a sac, not uniformly adherent to the inner surface of the capsule, contains from two to eight, or, more generally, from four to six, oval or reniform secondary sacs, irregular both in position and size (XXIII. 10, 11), and containing a dull and fine or coarse granular matter, wdthin which, again, is a clear (contractile ?) space, but no nucleus is discoverable even when acetic acid is added. Pre- sently these vesicles elongate, and, becoming flask-shaped, protrude their necks through the enclosing sac and the cyst-waU (XXIII. 12, 13), and proceed to discharge their contents (XXIII. 14) through their open extremi- ties ; after which, they corrugate and wither. The discharged matter is composed of a mass of monadiform corpuscles united together in a globose gelatinous mass, the whole of the organic matter filling the cyst being used up. A precisely similar act of propagation Stein also witnessed in an encysted Vorticella nehulifera. Cienkowsky (ZeitscJir. Band vi. p. 381) also reports its occurrence in Nassula vindis, Duj. (XXYIII. 65-71); according to this author's researches, the contents of the cysts of Nassula vindis break up into a number of globular cells (XXYIII. 68-70), which soon partake of a certain degree of rotating movement among themselves, develope in their interior a multitude of wdiat he terms swarm-spores, and at a certain period, when mature, severally produce, in turn, a tapering neck-like tubular process (XXYIII. 68, 69), which perforates the softened cyst-waU and gives exit to the spores or germs (XXYIII. 71). This account taUies with that given by Stein of certain Vorticella-cysts. Lachmann has the foUo\\dng remarks on this topic (A. N. H. 1857, xix. p. 238): — " It was only in his most recent observations on Vorticella microstoma, that Stein saw the production of larger globules, ' daughter- vesicles' {Tochterblasen), in the interior of the mother- vesicle ; but pre\iously he had seen nothing of the kind : it must remain uncertain whether he had overlooked them, w^hether, instead of several globules, only one very large one, entirely fiUing the mother-vesicle, had been produced, or whether two different modes of development actually occur in this case. This is the only mode of reproduction of the Infusoria w^hich has hitherto been observed in encysted animals alone ; but some ob- servations made by E. Claparede and myself upon an undescribed vagini- colous Infusorium, indicate that encystation is not a necessary condition even for this mode of propagation." The last plan of generative development to be considered is that wherein, according to Stein's hypothesis, the encysted animalcule undergoes an actual metamorphosis, and subsequently, as a rule, produces an embryo wliich, although very dissimilar to the original ciliated animalcule, is nevertheless presumed to be convertible into it after passing through one or more trans- itory phases of existence. This cycle of life, or, according to Steenstrup's hypothesis, this " alterna- tion of generation," in the generative acts of ciliated Protozoa, Stein has most diligently sought to establish as a fact, but, in the opinion of most of the best naturalists, has failed so to do. Still the hypothesis is too curious and interesting to be omitted from our description, and, what is more, has been adopted as true by several observers. It will therefore be best, fii'st to set forth Stein's own account, and then to add the remarks and objections of others. On some of the branching stems of Epistylis plicatUis, and of E. nutans, Stein encountered not only the ordinary animalcule in full activity and in a contracted state, but also some pear-shaped bodies, presenting merely the ordinary nucleus and a contractile space, without mouth or any remnants of the alimentary tube or of food. On other branches, again, were other 0¥ TUE PEOTOZOA. CILIATA. 359 bodies having the figiu'e of Acinetce, furnished with tentacles slightly move- able and more or less retractile (XXYII. 17, 18, 19, 20). These Acineti- form beings were noticed and figui'ed by our countryman Baker a century ago ; they, moreover, did not escape the observation of Ehi'enberg, in the alHed genus Oj)e7'cidaria, hut were regarded by him as parasitic animalcules. On another occasion, Stein met with a stem of Epistylis plicatilis bearing some thirty Acinetce, diffeiing among themselves very much, both in size and in their stage of development. Each was supported on a branch presenting the characteristics of this species, but smaller in dimensions, and tapering from the base of the Acinetiform body (where it had the usual thickness of an Epistylis-stalk) to its jimction Tvdth the stem below. The length of the branches also varied greatly, being in some instances not quite so much as that of the body they supported, in others twice as long ; however, there was no proportion between the length of the stem and the size of the body. Most of the Acinetoi had a smooth siuface and no tentacula ; they were of a pyri- form compressed figure, and contained a coarsely granular and homogeneous substance, two or three irregularly-placed contractile spaces, and a central nucleus ha\TJig either the normal horse-shoe- or an elongated oval shape. Where the Acinetce had tentacles, these processes were few and small, and the surface of the body thro^Ti into irregularities by its contractions ; their nuclei were either round or oval. These Acinetce exhibited no movements, except some slight ones affecting the tentacula. Were their anterior extremity un- folded and theii- tentacles outspread, they would assume the figure presented by those described in the first observations on this species, whilst the closed pyi'iform bodies were precisely ahke. The further developmental history of this particular E_pistylis could not be followed out, and to arrive at the purpose of its ^cnieto-metamorphosis, the research was extended to other species. A particular form of Acineta occurs in company with Episti/lis digitalis, which Stein concluded to be derived from it by a similar process to that presumed in E. j^Hcatilis, although the Acinetce were isolated and seated on short pedicles. At the anterior part of each Acineta, amid the large granules crowding the homogeneous contents, were a contractile space and, in many specimens, a mo\'ing embiyo having a cylin- drical figui'e, rounded at each end and narrower in the middle, where several zones of long cilia, in apparent folds of the smface, surrounded it. In ge- neral characters it would, as an independent organism, be referable to the genus Trichoclina, and is probably no other than the T. vonuv or T. gran- clineUa, Ehi'enberg. The embryo escaped through a temporary opening, which closed very speedily afterwards, leaving the animal apparently unin- jiu'ed ; moreover the tentacles, which are retracted during the birth, were again outstretched. The conclusion arrived at is, that the Acineta -condition is specially provided to cany out embryonic development, and that in so doing the Acineta gradually exhausts itself. Stein's fii'st impression was, that the embryo resulted from the develop- ment of the entire nucleus, and that this organ was formed anew from the general contents of the Acineta ; however, later researches lead him to be- heve that only a portion of the nucleus is concerned in building up the em- bryo. No particular season seems devoted to this Acineta -formation, since Stein has observed it from the middle of March through the whole sum- mer, and in fewer instances imtil December ; moreover, embryonic gene- ration is not restricted to any particular size of Acineta, but occurs in all except the very smallest ; nevertheless the embryo is smaller proportionably to the decreasing size. Active embryos were seen in Acinetce of onlj^ ^"', the germ itself being only Yko'"' 360 GENERAL HISTORY OF THE INFrSOElA. Besides the cysts and Acinetce supported on branching E2jistt/lis-iitem^, Stein found others attached separately by very short stalks, or nearly sessile ; these, his observations go to show, are probably derivable from the beings produced by fission or gemmation, which have detached themselves from the parent-stem in the strongly- contracted or partially-encysted condition, and, on afterwards fixing themselves, proceeded either to complete their encysted state or to assume the Acinetiform condition. Another set of beings Stein is disposed to introduce in the developmental history of Episfiflis digitalis, in the shape of miniature branching Vorticellina. The branches are dichotomously disposed, veiy slender, short, and rigid. Seated at the extremity of each is a small campanulate being, with a stiff bristle proceeding from each angle of the base (XXYII. 22, 23). Internally they are finely granular. They exhibit slight changes of outline and jerking movements upon their stalks ; they, moreover, can detach themselves and swim freely away like a detached Epistylis digitalis, and may sometimes be seen to affix themselves again by their base and produce a pedicle. These beings, whether derived from E. digitalis or from Carchesium pygmcPAiin — for they occur in company with both these animalcules, — their discoverer would regard as their earliest phase of development, and believes that not improbably similar miniature beings belong to all the pedicellate Vorticellina. This notion involves no great stretch of the imagination ; for there is no extra- ordinary metamorphosis necessary, and we may throw out the suggestion that such minute Vorticellina are developed from the monadiform contents of the brood-cysts. To take another illustration of Stein's hypothesis from the allied genus Ojjer- cularia — the 0. herherina. Direct observation is wanting to identify the Aci- neta as belonging to this Ojjercularia, except so far as contiguity on the same filament of a plant or on the same member of a marine animal, and their frequent occurrence, be allowed to have weight. Stein argues that the conversion of an encysted Opercidaria into an Acineta is readily conceivable, by reason of their congmity of form and the existence of intermediate phases, whilst, on the con- trary, the transformation of the ciliated embryo into an Acineta, without first passing through the intervening stage of an Opercidaria (a change easily imagined), is a circumstance scarcely probable : on similar grounds he would associate the pear-shaped Acineta, ha\ing a ramified nucleus (XXX. 3, 4), with Opercularia articidata (XXX. 1), as a phase of existence interposed between it and its embrj'onic stage of a free ciliated animalcule ; but his developmental history of Vorticella microstoma is by far the most elaborate, although much too long to present here except in abstract. His first step in the investigation of this species was the illustration of the act of encysting (XXYII. 5 a-d) in its widest range, and the next, to identify certain globular cysts, found in company with the Vorticellce, Tvith the cysts of those animals. These cysts were about 4^'" in diameter ; they had a clear double outhne, and contained a homogeneous, transparent, coloui'- less and granular substance. In most, the characteristic band-like nucleus and contractile space were ^dsible, together with, in many specimens, the in- voluted cihary apparatus and oral ca\T^ty, looking, as a whole, hke a fissiu'e at the anterior part of the cyst (XXYII. 7, 9). In other cysts, again, nought could be discerned save the nucleus and the contractile space, sometimes di- vided (XXYII. 1,8); and lastly, in others, all distinction of organs was lost, the nucleus being the last to disappear (XXYII. 9). Stein considered, at first, those peculiar capsules to be connected with the process of reproduction, and, from meeting with torn empty sacs, supposed that the interior was broken up into germs which made their escape through OF THE PROTOZOA. CILIATA. 361 the walls. With this interpretation, however, he was not satisfied ; and at the same time his attention was aroused to the circumstance of Vorticellce occurring so frequently in company with Actinophrys and Podophrya, and to that of the increase in the number of the one as that of the other decreased. He therefore applied himself to watch the changes going on in the cysts de- scribed, and at length satisfied himself of the intermediate changes in their transition into Actinoplirys or Podojphrya — two varieties of the same animal- cide, in his opinion, and not two genera, as usually represented. Stein was brought to the conclusion that this transition takes place, by comparing Podo- phryie at an early stage of development with metamorphosed Vorticella-ejsts. AmoTigPodophryce of the common form, examples occurred ha\dng their usually wide rounded capsule produced into a hollow funnel-shaped pedicle, and thrown into annular folds, alternating with acute, parallel, angular ridges (XXIII. 3). Most of these indi\iduals were unarmed ; but some had numerous capi- tate tentacles. On the other hand, old Vorticella-cysts were found in which the enclosed animal had detached itself from the cyst-wall, and become thrown into sinuosities and elevations, the latter of which pressed against the wall, threat- ening to rupture it. These and the above-described Podophryce Stein supposed to merge into one another. The leading changes noticed in the encysted Vorticellce consisted in the disappearance of the nucleus, in the multiplication of the contractile spaces, and in the detachment of the contents from the walls of the cyst (which they.no longer completely fiUed), and their disposi- tion into irregular and changing lobes. Thus far, in detecting such Vortlcella- cysts. Stein proceeds by direct observation ; but his next step is simply h}"po- thesis, viz. suj)posing their contents to shoot out tentacula through the dense capsule, and assume the figm-e of Actinophrys or of Podophrya (XXIII. 1, 2, 4, 18, 19). That the metamorphosis should at one time be into the one ge- neric fornix at another into the other, he endeavours to explain by assuming that where no resistance is offered on any side to the developing Actino- phrj^an, it assumes the form of an Actinophrys, but where resistance occurs at one point, it there developes a stem and becomes a Podophrya. To coun- tenance his hypothesis further, he appeals to the great similarity between the Acifieke met with in company with Vorticella nehidlfera on duck-weed, and Podophi-yce — so great, he says, that when the former are detached, it is difficult to know them from Podophryce. Granting that the history of metamorphosis is thus far complete and satisfactory, it remains to show what becomes of the Actinophryans thus transformed from the cysts of Vorticellce, and to reply to the question whe- ther they originate a generative act, At the outset of this inquiry Stein finds himself at variance mth KoUiker and others respecting the structure and vital endowments of Actinophrys. The writers referred to state Acti- twphrys to receive food within its interior, to excrete undigested matters, and to exhibit certain powers of locomotion ; these peculiarities Stein ignores,. and insists on identifjdng the Acinetiform beings he has encountered with Actino- phrys Sol and Podophryafixa, which, he affirms, give birth to a ciliated embryo. This embryo, he asserts, is produced within a defined cavity, so far larger than itself that it can move mthin it (XXIII. 2, 4, 5). Its figure is pear- shaped mth a central constriction, and several folds occupied by cilia ; and it ajDpears composed of a finely-punctate sarcode, containing, in the axis of its posterior and larger segment, an oval or band-like nucleus, and near to this a circular actively-pulsating space, and occasionally, on the other side of the nucleus, a second smaller one. No mouth could be detected. The being, as a whole, very closely resembles a detached gemma of Vorticella microstoma, into which it can be very easily conceived to be changed, on fix- 362 GENEKAL HlSTOKY OE THE INFUSORIA. ing itself by its anterior end and then developing, in its larger and hitherto posterior segment, a mouth and ciliary 's\Teath. After Hvely rotary movements -within what might be called its uterine cavity, the embiyo escapes with a sudden bound, and gains a fi'ee, active existence. The passage by which it has made its way thi^ough the substance of the parent Actinophrys continues for some time open, but is gradually closed up from behind. The size of the embryo is proportioned to that of the parent, and varies between jj-^'" and -^"'. The diameter of the smallest parent being in which a matiu^e germ presented itself, scarcely exceeded -J3-". One other instance "will suffice to illustrate Stein's hypothesis of Acineti- form transformation. The one we select is the Vaginicola cri/staUina, which that author attempts to show becomes, by a metamorphosis, Acineta mystacina (XXYII. 10-15). Out of a large number of specimens contained in a vessel of water, few could be found at the end of foiu'teen days, the place of the great majority ha\dng been assimied by Acinetina. This occurred even when great pains were taken to isolate a certain number of Conferva - filaments richly covered ^vith Vaglnicolce, and to place them in pui'e spring- water, so as to avoid the introduction of other colonists. That the Aciiietce were derived from the Vaglnicolce, a comparison of the structure of the two will indicate. The contracted body of the Vaginicola may be recognized in the Acineta detached from the bottom of its sheath and raised to the upper pari, which it completely fills, — the mouth of the sheath having previously been bent inwards over it as a cover, and a layer of gelatinous matter poured out to bind the two together. The outermost parts of the roof-like cover project freely above tliis layer, and are traversed by several radiating folds or fissures. The clearest notion of the transformation efi'ected is obtained when we can look down upon the top suriace of the capsule, by getting the axis perpendicular to the eye. The contained body is closed in on all sides ; and its contents are substan- tially the same as those of the body of the Vaginicola (XXYII. 12), with numberless fine granules, and sometimes with a preponderating number of large granules scattered through them, rendering the body opaque and of a greyish-yellow coloiu-. There is likewise a similar roimd contractile space ; but instead of a band-Hke nucleus, there is a rounded one. This diff'erence in respect of the nucleus is not important, inasmuch as its length varies greatly in Vaginicola according as the animal is extended or in a contracted state, — being in the latter much shortened or merely elongated- oval, whilst in the former its length exceeds two or three times its width. Hence it is m no way remarkable that, in the very contracted condition of the encysted and Acinetiform state, the nucleus should be veiy much shortened and rounded, — a change which analogy, indeed, -with various encysted animals would lead us to anticipate. From the upper surface of the encysted body Yeiy many bristle-Hke tentacles with knobbed ends are given off, which penetrate the gelatinous layer through the fissures in the cover of the sheath, and outspread them- selves in a radiating manner. These tentacles are for the most part straight, and slowly extend and retract themselves in length. Pressure causes theii- contraction, and huddles them together ; but they are not entirely withdi-awm. Some smooth Acinetiform specimens are met with, which may be considered to be in an earlier stage, and similar to the incomplete Acineta of Epistylis plicatilis. The origin of the Acinetce from Vaginicola is further substantiated by the relative dimensions of the two. Thus Vaginicolce were foimd on Conferva; 0¥ THE PROTOZOA. CILIATA. 363 having sheaths betwixt ■^"' and -^"' in length ; those most common were from ^ij'" to ^"' in length and J-g-'" in width. The height of the cap- sule of the Acineta was from -^"' to -^"', and its width not much less. Moreover, intennediate phases between Vaginicola and Acinetina were met with, — as, for instance, capsules occupied anteriorly by the contracted body, which still exhibited, upon being moved up from the bottom of the case, the posterior annular furrow and traces of the ciliary wreath previously existing, and had its anterior half enveloped in a gelatinous lamina, uniting it to the inner surface of the sheath, which was at one time more, at another less, incui'ved upon the animal, but had as yet not been converted into the peculiar pent-house-like cover. The metamorphosis, therefore, of a Vaginicola into an Acineta may be thus explained. The animacule is in the fii'st place contracted in the ordi- nary manner ; it then developes its posterior fiuTow and ciliaiy wreath (XXYII. 11), and, detaching itself from the bottom of its sheath, rises to the upper part, which it entii^ely fills and closes up. From this time the rotary apparatus and digestive tube dLsappear by absorption ; the excretion of the gelatinous matter from the fore part ensues, and fixes the animal in its posi- tion, while its tendency to fall to the bottom of the case, and to contract, draws inwards the mouth of the case, and completes its enclosure within a shut sac or capsule (XXYII. 12). The contractile tendency of the body still continuing to operate, brings about a narro^^ing of the anterior part, and with this a consequent elongation of the sheath ; in this way an ex- planation may be given of the veiy long specimens frequently encomitered. The extrusion of the tentacles is an after-occiu-rence (XXYII. 13). The complete Acineta can entangle smaU Infusoria with its tentacula, which, by their crossing and retraction, draw the captured particles to the siuface, where probably their nutritive matters are absorbed through it; at aU events, no food or foreign particles are seen in the interior. Stein next attempts the identification of this Acineta of Vaginicola crystal- Una with the Acineta mystacina of Ehrenberg, and in a subsequent paj)er proceeds to show that it developes within itself a ciliated embryo. Amid many Acinetce, he discovered some bearing a clear oval or roimded cyst, or, less commonly, several such, upon the surface of the enclosing Hd ; where there Avas a plm-ality, they were evidently in difi'erent stages of development. The cyst contained a sharply-defined Infusorial being, of a homogeneous finely- granular substance, and having an actively-pulsating sac. At first Stein imagined these might be animalcules casually afiixed to the Acineta? ; but fur- ther obsei-vation proved their organic connexion with, and derivation from it. The cyst-walls were internally soft and gelatinous, and their substance continuous, through the fissm-es of the cover, with the gelatinous layer of the Acineta, of w^hich they might be more correctly represented pouches or diverticula. The appended animalcule is not a bud produced from the Acineta-hodj ; for it is never found in organic connexion with it, but un- doubtedly has its origin as a germ within it, and makes its way outwards. In fact, it is developed from the rounded nucleus by its elongation and sub- sequent transverse fission. The yoimgest cysts are round or shortly oval, and have no other indication of life and movement than that exhibited by the contractile space. In the next stage they are sHghtly emarginate at one end and stiU motionless, whilst in the oldest the fissure or emargination extends deeply into the interior in a curved manner, and veiy clearly exhibits a number of vibratile cilia. In this mature state they enjoy considerable locomotive powers within their capsule, and recall in their form that of con- tracted Vorticelliaa. Thus, at their fore part they present a rounded ciliated 364 GENEEAL HISTORY OF THE INFIJSOEIA. lobe, resembling somewhat a retracted rotary organ, Avhilst the fissure ex- tending inwards indicates the alimentary tube. There is yet another apparent mode of embryonic development in the Acinetce of VorticelUna described by Stein, which occuiTed in some specimens not provided with tentacles. In place of these, one or two short closed tubular processes extended from the fore part of the animalcule; of the usual granular contents scarcely a trace remained ; and the nucleus and contractile space had entirely vanished. The membrane of the enclosed body, thus deprived of its ordiuary constituents, contained, in their room, six elongated- oval cell-like bodies, J^'" long, w^hich seemed to have been developed at the cost of the contents of the original Acineta. These structures had a sharp outline, and contained a coarse granular substance and a contractile sac. They seem to develope into embryos ; for in one case a ciliated furrow was observed, assimilating the being to the more usual embryos of the Acinetce. Probably the ^cmefa- condition of the Vag'inkola is terminated in this manner, after developing for a period embryos according to the plan above mentioned, by the final breaking up of the nucleus into several large germs. In addition to the species described. Stein believed he made out the Acineta-^i?iiQ of several other species of Vorticella, of EpistiiVis, and Oj^ercu- laria (XXX. 1-4), as well as of ZootJiamnmm, Ophrydimn (XXX. 5-8), and Sph'ocliona (XXX. 18-26). However, sufficient details have been given to illustrate the presumed fact in the developmental histoiy of the Ciliated Pro- tozoa ; and we must refer those of our readers desii'ous of more fully testing the views of that most excellent observer, to his often- cited work, ' Die Infusionsthiere auf ihre Entwdckelungsgeschicte,' Leipzig, 1854. More- over, the several new forms of Acinetina he has pointed out A\all be found referred to in the general histoiy as well as in the systematic views of that group. It is now incumbent on us to review the opinions of other naturalists upon this remarkable and interesting hypothesis. A few have accepted it, among whom are Mr. Busk (as we gathered from his lectures at the College of Sui'geons in 1857) and Mr. Carter. The latter has the following remarks on the subject {A. N. H. 1856, xviii. p. 237) : — "I could not discover an elongated nucleus, as Steiu has figiured, in the Amoehce and Acinetce, which I saw developing young VorticeUce, the fonner in plurality (one to three) and the latter singly : if present in the Amoebous form, it was circular, and if in the Acinetce, undistinguishable from the general ' granulation.' Again," he goes on to say, " where are these transformations to end ? Into what kind of Rhizopods do the sheathed VorticeUce pass ? How many of the fresh- water Bhizopocla are alternating forms of VorticeUce ?" At the time of his writing the above, Mr. Carter had not seen Stein's latest work, which would have resolved some of the doubts and queries expressed. Thus, the Gennan naturalist finds the nucleus, if elongated and band-Like in the encysted being, to become orbicular or oval when in an ^mie^a-state, and points out that acetic acid wiU reveal this organ when obscui-ed by the granules of the interior. Moreover, his later researches have been extended to sheathed VorticelUna or Ophryclina — for instance, to Vaginicola, of which we have given the par- ticulars. However, it is very important to obtain Mr. Carter's statement that he has seen young VorticeUce developed from Acinetce and Amoehce, — in- tending by the latter, we apprehend, Acinetce without tentacles and capsule, and not the simple Amoehce commonly understood by that term. The objectors to the hypothesis are by far the more numerous. The emi- nent physiologist .Johannes Midler, to whom Stein showed ActinopTirys and OF THE PKOTOZOA. CILIATA. 365 Podoplirya developing embryos, could not agree with the conclusion the latter arrived at (viz. that they became VorticeUce), but was more disposed to believe that they relapsed into Acinet