i p- i a O; s a a a m a V A STUDENT'S TEXT-BOOK OF ZOOLOGY. * CORRIGENDA. Page 82. In the description of Fig. 71 omit ''(triods)." ,. 177. Lilies 12 to 16. Professor Hickson has pointed out to nvi that in some genera the siphonozooids have generative org.-ms. ", 17S. 22nd line from the top. For "Stereosoma Hickson, with" read "Stereosoma Hickson, without." 1SS. For "Section 2. Paractinia " irad "Section 2. Paractiniae." ,, 2S7. Line 2. For "sarcolemina" read "sarcoleniina." 300. Line S from bottom. ) For "Bdclloidea read "Bdelloida. 306. Line 4 from top. 323. Line 2 from bottom. For "Pectinobranchiata" read "Pectinibranchiata." 375. Line 4 from bottom. For "AspiJobranchia" read " Aspidobranchiatu." 411. For "Section 1. Tritonioidea " read "Tribe 1. Tritonioidru." 413. In description of Fig. 329 for "Eolis" read "Aeolis." A STUDENT'S TEXT-BOOK OF ZOOLOGY. BY ADAM SEDGWICK, M.A.. F.R.S., FELLOW AND TUTOR OK TRINITY COLLEGE, CAMBRIDGE ; AND READER OF ANIMAL MORPHOLOGY IN THE UNIVERSITY. VOL. I. LONDON: SWAN SONNENSCHEIN AND CO., LTD., NEW YORK: THE MACMILLAN CO. 1898. V PREFACE. IN preparing the present work I have heen actuated mainly by the desire to place before English students of Zoology a treatise in which the subject was dealt with on the lines followed with so much advantage by Glaus and his predecessors in their works on Zoology. My original intention was to bring out a new edition of Glaus' Lchrbuch, revised and brought up to date, and a trace of this intention may be seen in a few pages of the present volume. But this plan was, for various reasons, soon given up, and the present treatise is, with the exception of about twenty pages, an entirely new work. For a successful study of Zoology it is necessary that the student should begin by making a thorough examination of individual animals, of their structure, of the functions of their parts, of their relation to the external world and to each other. This method of study by types, which was largely introduced into this country by Huxley, and is admirably exemplified by that author's book on the Crayfish, is absolutely necessary as a preliminary to any thorough study of Zoology. I'.y pursuing it the student acquires, if the animals are properly selected, a knowledge of the principal forms of animal life, and a basis from which more extended studies can be made. It is to assist these more extended studies that the present work is designed. At the same time it is hoped that the book will be of value to all interested in Natural History, whether professedly students of Zoology or jjot, if in no other way than as a handy book of reference in which, by means of the index, information may be gained of A 2 VI PREFACE. the general nature and habits of a large number of animals, and of the more important and striking of the phenomena of animal life. To assist in giving the book utility in this direction, I have endeavoured, in the index, to refer the reader to the page on which technical terms are used for the first time and explained. At one time I thought of adding to each chapter a detailed account of some easily accessible species belonging to the group with which it dealt, but on reflection it appeared to me that such accounts were not required ; for we possess them in an excellent form in many useful and well-known books, which are accessible to everyone. Moreover, to have done so would have either unduly increased the size of the book or rendered necessary the omission of much interesting matter concerning the infinite variation of animal structure and habits not found in works easily accessible to students. Small print has been used for those parts of the work which deal with disputed matters, or with subjects of a more recondite character. It has also been employed for the accounts of the families and genera which will be used mainly for reference. By this means I have been able to give far more information than would otherwise have been possible. To further the same object I have used, in the small print dealing with families and genera, not only abbreviations, but also what has been called by a friendly critic the style of the note-book. I very carefully considered my critic's objection to this "note-book style," but I decided that so long as I did not become unintelligible, the employ- ment of it was justified by the object in view. Moreover, I have been careful to limit its use to those parts of the work which were apart from the main narrative, and would be almost entirely used for purposes of reference. Most of the abbreviations are explained in the index, and it is hoped that no inconvenience will arise on account of their use. Authors' names for genera are given throughout. It has been pointed out to me, too late however for alteration, that the customary abbreviations for those names are not always used, and that my abbreviations have varied even on the same page. I am PREFACE. Vll afraid that this charge is true. I can only hope that my carelessness in this respect will not cause my readers serious annoyance. To make the book more complete as a work of reference, I have endeavoured to mention and give an account of as many families as possible. For the same reason I have named a large number of genera without giving any account of them. It may appear to some absurd to name without describing so many genera. My object in doing it has been to make the book more useful in enabling students to track as many unknown names as possible to their place in the system. I must ask the indulgence of my readers towards the many imperfections of this work. It is impossible to have a specialist's knowledge of every group, and in a book of this size, dealing with an enormous number of facts and names, it is beyond human capacity to avoid mistakes. Every care has been taken, and it is hoped that they will be found to be neither numerous nor important. The errors would undoubtedly have been much more numerous had it not been for the kind assistance given me by my friends. To Mr. J. J. Lister I am especially indebted. He has looked through all the proof sheets, and has brought to bear a critical power and discrimination which have been invalu- able. I cannot be sufficiently grateful for his assistance. Mr. Lister has also contributed the account of Coral Reefs, and of the reproduction of the Foraminifera. My thanks are also owing to Mr. Heape and Mr. Graham Kerr. who looked through the greater part of the proofs, and to Mr. Shipley, Dr. Benham, Professor Haddon, and Dr. Harmer, who looked over the proofs of portions of the book, and gave me the benefit of their special knowledge. I have thus often been saved from errors into which I should other- wise have fallen. My principal sources of information are acknowledged in the foot-notes ; but I must not omit to make mention here of works from which I have obtained special help ; these are Blitschli's Protozoa in Bronn's Thierreich, Chun's introductory account of the Codentcrata also in Bronn, Vlll PREFACE. Wasiliewski's Sporozoa, Pelseneer's Mollusca, and Benham's Pulychaeta in the Cambridge Natural History. Of the illustrations about fifty are new, of the remainder the majority are from Glaus' Leln^buch ; but some, which I have been permitted to make use of by the courtesy of the author and publishers, are from Bronn's Thierreich, Terrier's Zoologie, Korschelt and Heider's Embryology, and Lang's Text- book of Comparative Anatomy. In the classification the principal departures from precedent concern the group of Ampkineura, which has been given up, and the Gephyrea, which has been broken up into four inde- pendent phyla. The reasons for these innovations are given in the body of the work. The work will be issued in two volumes. The present volume deals with the whole of the animal kingdom except the Arthropoda, the Echinodermata, and the Chordata. The treatment of these will be included in the second volume, in the production of which I have been fortunate enough to gain the co-operation of Mr. Lister. The second volume is in preparation, and will, we hope, appear without any great delay. It will, if possible, contain a part dealing generally with the facts and principles of Zoology, but it may be necessary, from considerations of size, to reserve this for a third volume. TABLE OF CONTENTS. CHAPTER I. PHYLUM PROTOZOA . Class I. GYMNOMYXA (SARCODINA) Sub-class 1. RHIZOPOPA Order 1. Amoeboidea . ,, 2. Testacea Sub-class 2. MYCETOZOA ., 3. HELIOZOA . ,, 4. RADIOLAKIA Class II. INFUSORIA . Sub-class 1. MASTIGOPHOKA . Order 1. Flagellata Sub-order 1. Monadina ,, '2. Euglenoidea . PAOE 1 3 6 11 11 15 18 20 24 27 27 30 30 ,, 3. Hcteromastigoda 31 ,, 4. Isomastigoda . 31 ,, 5. Pliytomastigodu 32 Order 2. Choanoflagellata . 32 ,, 3. Dinoflagellata . 33 ,, 4. Silicoflagellata . 35 ,, 5. Cystoflagellata . 35 Sub-class 2. CILIATA . . 37 Order 1. Gymnostomata . 45 ,, 2. Trichostomata . 46 Sub-order 1. Aspirotricha . 46 ,, 2. Spirotricha . 48 ". Heterotricha . 48 '). Oligotricha . 4t c. Hypotricha . 4!> (7. Peritricha . 60 Sub-class 3. ACINETARIA . 51 Class III. SPOROZOA . . 54 Order 1. Gregarinida . . f,6 ('HAFTER I. PROTOZOA contd. PAGK Sub-order 1. Monocystidca . 59 ,, 2. Polycystidca . 59 Order 2. Coccidiidea . . 59 ,, 3. Haemosporidia . 61 Sub-order 1. Drepanidiidia 61 ,, 2. Acystosporidia 62 Order 4. Myxosporidia. . 64 . , 5. Sarcosporidia . . 68 CHAPTER II. THE METAZOA . . 70 CHAPTER III. PHYLUM POEIFERA . . 72 Class I. CALCAREA . . s;i Order 1. Calcarea . . 89 Sub-order 1. Homococla . 89 ,, 2. Heterococla . 90 Class II. TRIAXONIA . . 90 Order 1. Hexactinellida . 90 Sub-order 1. Lyssacinci . 92 ,, 2. Dictijoiiimt . 93 Order 2. Hexaceratina. . 93 Class III. DEMOSPONGIAE . 93 Order 1. Tetractinellida . 93 Sub-order 1. Choristida . 93 ,, 2. Lithial/tlti . 94 Order 2. Carnosa . . 95 ,, 3. Monaxonida . . 95 Sub-order 1. Halichondrina 95 ,, 2. Spinfharophora 97 Order 4. Ceratina 97 63274 X TABLE OF CONTENTS. CHAPTER IV. PAGE PHYLUM COELENTERATA . 99 SUB-PHYLUM I. CNIDARIA . 123 Class I. HYDRO-MEDUSAE (CRASPEDOTA) 123 Order 1. Hydrida . .127 ,, 2. Hydrocorallinae . 127 ,, 3. Tubulariae . . 129 Antliomedusae . 130 ,, 4. Campanulariae . 132 Leptomedusae . 133 ,, 5. Trachomedusae . 135 ,, 6. Narcomedusae . 136 ,, 7. Sipb.onopb.ora. . 137 Sub-order 1. Disconrmthac . 141 Section 1. Disconectae (Velellidae) 141 Sub-order 2. SipJionanthac , 144 Section 1. Calyconectae (Calycophoridae) 144 ,, 2. Physonectae iPhysophoridae) 150 ,, 3. Auronectae . 153 ,, 4. Cystonectae (Physalidae) 154 Class II. ACALEPHAE (ACRASPEDA) 156 Order 1. Scyphomedusae . 162 Sub-order 1. Xfiti/rii<:dusae 163 ,, 2. Pcromcdusae . 165 3. CltlniitrtftiSflC . 166 Order 2. Ephyroninae . .166 Sub-order 1. Cannostoume . 167 ,, 2. Sc/Hostomac . 167 ,, 3. Ehvzostomae . 167 Class III. ACTINOZOA (ANTHOZOA) 168 Order 1. Rugosa . . .175 ,, 2. Alcyonaria (Octactinia) 175 Sub-order 1. Frotoalcyonaria 178 ,, 2. Stolonifera . 178 ,, 3. Alcyonacca, '. 178 ,, 4. rciiinitnlucca . 179 Section 1. Penn;itnlr,-i . 180 2. iSpicata . .181 ,, 3. Renillea . . 181 ,, 4. Veretillea . . 181 Sub-order 5. Gorgonacca . 181 Section 1. Scleraxonia . 182 ,, 2. Holaxonia . 182 IV. COELENTERATA -o,it. Mytilacca . 349 Order 3. Pseudolamelli- branchiata 346 ,, 4. Eulamellibranchiata 347 Sub-order 1. Submytilacca . 347 ,, 2. Tellinacea . 347 ,, 3. Veneracea . 348 ,, 4. Cardiacea . 348 ,, 5. Myacea . 348 ,, 6. Plwladacea . 348 ,, 7. Anatinacea . 349 Order 5. Septibranchiata . 349 Class II. SCAPHOPODA . 349 III. SOLEXOGASTRES . 352 PAGE 356 387 392 392 CHAPTER X. MOLLUSCA coittil. Class IV. GASTROPODA Sub-class 1. ISOPLEUKA . ,, 2. ANISOFLETKA Order 1. Streptoneura . Sub-order 1. Aspido- branchiata 393 Tribe 1. Docoglossa . 394 ,, 2. Rhipidoglnssa . . 394 A. Zygobninchiata . 394 B. Azygobranchiata . 395 Sub-order 2. Pec/ in i- bm iicliiata 395 Tribe 1. Ptenoglossa . 3!6 ,, 1. Kacliiglossa . . 396 3. Toxoglos^a . . 397 ,, 4. Taenioglossa . . 397 A. Platypoda . . 397 li. Heteropoda . 400 ,, 5. Gyiniiii.nlossa . . 402 Order 2. Euthyneura . . 402 Sub-order 1. Opistho- branchiata 403 Tribe 1. Tectibraucliiata (includes Pteropoda) 403 Section 1. Bulloidea . . 405 ,, 2. Aplysinhli ;i . 407 ,, 3. Pleurobranchioidea 408 'J'ribe 2. Xudibranchiata . 409 Tribe 1. Tritonioidea . 411 ,, 2. Doridioidea . 41i! ,, 3. Aeolidioidea . 412 4. Elysioidea . . 413 Sub-order 2. Pulmonata . 414 Tribe 1. Basommatophora . 415 ,, 2. Sty lorn matophora . 416 Class V. CEPHALOPODA . 417 Order 1. Tetrabrancbiata . 443 ,, 2. Dibranchiata . . 444 Sub-order 1. Decapu,>]] ;/',>r,i/in . 490 ,, 2. //' fun Hii'tiruiiii 491 ,, ,, Myzostomida Order 2. Oligochaeta . Sub-order 1. Z/////<-i>/"< 2. 492 493 508 509 Class III. HIRUDINEA . 512 ,, IV. ECHIUROIDEA (KEPHYREA ARMATA) 527 CHAPTER XII. PHYLUM SIPUNCULOIDEA (GEPHYREA ACHAETA) 534 CHAPTER XIII. PHYLUM PRIAPULOIDEA . CHAPTER XIV. PHYLUM PHORONIDEA . CHAPTER XV. PHYLUM POLYZOA . Class I. ECTOPROCTA . II. EXTOPROCTA . CHAPTER XVI. PHYLUM BRACHIOPODA . Order 1. Ecardines ,, 2. Testicardines . 4 CHAPTER XVII. PHYLUM CHAETOGNATHA PAGE . 540 . 542 . f.49 . 564 . 568 . f.73 . 585 . 585 . 586 CHAPTER I. PROTOZOA.* Animals in which there is one nucleus, or, if more than one nucleus, in which the nuclei are disposed apparently irregularly and without relation to the functional tissues of the animal. Conjugating cells of the form of ova and spermatozoa are never formed. Structurally the Protozoa are so simple that the reproduction of the species is effected either by division of the body into two or more parts, or by a separation oft' of a small portion, which so nearly resembles the parent in structure that the phenomenon of embryonic development is almost, if not completely, absent from the life-history. The body is always composed of a contractile granular substance, filled with vacuoles ; it may also contain a pulsating vacuole, and present the phenomenon of granule currents. The pulsating vacuole consists of a space without differentiated Avails filled with a clear fluid. This space apparently diminishes and disappears through the contraction of the surrounding plasma, and then reappears. There are, however, differentiations, both in the interior of the body and in its external boundary, on which a classification may be founded. In the simplest cases, the entire body consists of a small lump of protoplasm (or sarcode, as it was at first called), the contractility of which is confined by no firm external membrane. This lump of protoplasm is sometimes semi-fluid, and protrudes and retracts processes. It is sometimes of tougher consistence in parts, and protrudes thread-like rays (Rhizopodci). Nutrition takes place through the intussusception of extraneous bodies, which can be surrounded and enclosed by the protoplasmic substance at any portion whatsoever of the periphery of the body. In other cases the body which sends out slender processes (pseudopodia) secretes silicious or calcareous needles, lattice-work shells, or shells perforated by holes, to shelter and protect the body (Foraminifera, Radiolaria). * 0. Biitschli, "Protozoa" in Bronn's Thierreich, 1880-2. B PROTOZOA. In the Infusoria the body is bounded by an external membrane, and is capable of quick and varied locomotion by means of the movements of the cilia, hairs, bristles, etc., which it possesses. The nourishing matter may be solid, in which case it is taken in through a mouth, and the remainder after digestion cast out through an anal aperture (Iwlozok- nutrition), or it may lie in a fluid form as a putrescent solution, in which case the name Infusoria is well applied, and be taken in by simple osmosis through the walls of the body (saprophytic nutrition). The conjugation, or fusion, of two or more individuals has been observed at some period or another of the life-history in most of the groups of Protozoa ; and in most groups the power of with- drawing the pseudopodia or cilia and of forming stout membranes round the body (encystment) to protect the organism against adverse external influences is generally present. The Protozoa fall into three main classes. Of these the first (Gijiiinoiiiij.i'd) possess the power of thrusting out processes of their body as pseudopodia ; the second (Infusoria) are, for the most part, without pseudopodia, but bear cilia, or flagella ; while the third (Sporozoa) possess neither pseudopodia nor cilia, and are parasitic in habit. Table .showing the classification of the Protozoa. CLASS I. GYMNOMYXA (SARCODINA). Sub-class 1. RHIZOPODA. Order 1. Amceboidea. , , 2. Testacea. Sub-class 2. MYCETOZOA. ,, 3. HELIOZOA. ,, 4. RADIOLARIA. CLASS II. INFUSORIA. Sub-class 1. MASTIGOPHOUA. Order 1. Flagellata. Sub-order 1. Monadina. ,, 2. Euglcnoidea. ,, 3. Hetcromastigoda. ,, 4. Isomastigoda. ,, 5. Phytomastiyoda. Order 2. Choanoflagellata. ,, 3. Dinoflagellata. ,, 4. SilicoHagellata. ,, 5. Cystorlagellata. CLASS If. INFUSORIA Continvnl. Sub-class 2. CILIATA. Order 1. Gymnostomata. ,, 2. Trichostomata. Sub-order 1. Aspirotricha. ,, 2. Spirotricha. a. Heterotricha. b. Oligotricha. '. Hypotricha. d. Peritricha. Sub-class 3. ACINETAKIA. CLASS III. SPOROZOA. Order 1. Gregarinida. Sub-order 1. Polycystidca. ,, 2. Moiiocystidca. Order 2. Coccidiidea. ,, 3. Haemosporidia. Sub-order 1. Drepanidiidea. ,, 2. Acystosporidea. Order 4. Myxosporidia. ,, 5. Sarcosporidia. GYMNOMYXA. 6 Class 1. GYMNOMYXA (SARCODINA).* Protozoa possessing the power of thrusting out pseudopodia. An investing membrane is absent, or, if present, is incomplete, and leaves a considerable portion of the protoplasm exposed. A calcareous shell, or silicious skeleton, is very usually secreted. The body-substance, which is richly granulated, and may contain pigment, contracts slowly, and sends out at the same time the processes called pseudopodia; and these serve not only as a means of movement, but also for the reception of nourishment. The pseudopodia may be broad, lobed, or finger-like processes (Fig. 2), by means of which a quick and flowing motion can be imparted to the body mass ; or they may be filiform radiating processes (Fig. 1 ) ; or, lastly, they may anastomose with one another, and form networks. A tougher, clear homogeneous external layer (exoplasm) is usually to be distinguished as the peripheral boundary from a more fluid and more granular internal mass (endoplasiu ). During motion the former is , FIG. 1. Optical section through portion of the body of ActinosylMerium projected in Eichhomii (after Hertwig and Lesser). N nuclei in the endoplasm, processes into from which the vacuolated ectoplasm is clearly distinguishable. In the centre of the pseudopodia the axial thread is visible. which the gran- ules of the latter stream more or less quickly. In the stiffer pseudo- podia streams of granules are observable, slow but regular, passing from the base to the extremity and vice versa. The explanation of * Dujardin, " Observations sur les Rhizopodes." Cmnptes reiidus, 1835. Ehrenberg, "Uber noch jetzt zahlreich lebende Thierarten der Kreidebildung und den Organismus der Polythalamien." Abhandlung der Akad. zu Berlin, 1839. Max Sigm. Schnltze, "Uber den Organismus der Polythalamien." Leipzig, 1854. Job. Mliller, "Uber die Thalassicolen, Polycystinen und Acan- thometren." 1858. E. Haeckel, "Die Radiolarien." Erne Monographic. Berlin, 1862. PROTOZOA. these movements is to be sought in the contractility of the surround- ing portions of protoplasm (Fig. 1). A pulsating space, the contractile vacuole, is not unfrequently to be found in the protoplasm, e.g., Difflugia, Actinophrys, Arcella (Fig. 2). Nuclei are usually to be made out, but there are forms in Avhich no trace of a nucleus has yet been found. In such cases either our methods of observation are faulty, or the protoplasm of the nucleus is not yet differentiated as a separate structure (the Monera of E. Haeckel), or we have to do with a transient, non- nucleated stage in the life-history. The protoplasm usually secretes silicious or calcareous structures, either as fine spicula and hollow spines, which are directed from the centre to the periphery in regular order and number, or as lattice- work chambers (Radiolaria), which often bear points and spines, or finally as single and many-chambered shells with, in some cases, finely perforated walls (Foraminifera) and larger opening. Through this last (Fig. 4), as well as through the countless pores of the small shells (Fig. 3), the slender threads of sarcode pass out to the exterior as pseudopodia, changing without intermission in form, size, and number, and often joining themselves together in delicate networks. (Figs. 3, 4.) The pseudopodia, by their slow contraction, afford a means of locomotion, while they also serve for the taking up of nourishment by surrounding and transporting into the interior of the body small vegetable organisms as Bacillaria. Among the shell-bearing forms, the reception and digestion of food takes place outside the shell in the peripheral threads and networks of sarcode ; for each spot on the surface can for the time being assume the functions of mouth, and also of anus, by rejecting the undigested remnants. While the power of emitting pseudopodia is characteristic of the form in which the Gymnomyxa are usually met with, it is usual to find a stage in their life-history in which locomotion is effected by means of flagella. To such flagellated forms the term mastigopod has been applied, pulsating vacuole. GYMNOMYXA. 5 as opposed to myxopoil, a word indicating a form with the power of emitting pseudopodia. Reproduction is commonly effected by simple division, but in some cases encystment occurs, and the protoplasm breaks up into a number of minute portions called spores. The spores may be either naked or provided with a wall, forming the spore-case. FIG. 3. Rotalia veneta (after M. Schultze), with a Diatom taken in the network of pseudopodia. The marine shell-bearing forms contribute by the accumulation of their shells to the formation of the sea sand, and even to the deposition of thick strata. An innumerable quantity of fossil forms from various and very ancient formations are known. D PROTOZOA. SUB-CLASS I. KHIZOPODA.* Gymnomyxa, either naked or with a shell, the shell generally calcareous and often pierced with fine pores for the e.rit of the pseudopodia. Only in rare cases is the shell substance of a silicious nature ; in all other forms it is membranous, with or without adhering sand particles, or consists of a calcareous deposit in a basis of organic \ FIG. 4. MlUola ienera, with network Oi pseudopodia (after M. Schultze). matter. The shell is either a simple chamber, usually provided with a large opening, or is many -chambered, that is, is composed of numerous chambers arranged upon one another in a definite order * Besides D'Orbigny, Max Schultze, 1. c., compare W. C. "Williamson, "On the recent Foraminifera of Great Britain," London, 1858. Carpenter, " Intro- duction to the Study of the Foraminifera," London, 1862. Reuss, "Entwurf einer system. Zusammenstellung der Foraminiferen," Wien, 1861. H. B. Brady, "Report on the Foraminifera," Challenger Reports, 1884. J. J. Lister, " Contributions to the Life-History of the Foraminifera," Phil. Trans., 186, 1895. RHIZOPODA. 7 according to definite laws. The spaces of these chambers com- municate by means of narrow passages and large openings in the partition walls. In like manner those portions of the protoplasm which are enclosed in the individual chambers are in direct commu- nication with one another by means of processes which pass through the passages and openings in the septa, and connect one portion with another. In the perforated forms there may be an additional complication owing to the formation of a secondary shell by the protoplasm. This secondary shell is placed outside the primary, and is traversed by canals containing the protoplasm. The multinucleate condition is very generally found, and probably constitutes a phase in the life-history. For instance, in Groin in and Diffliu/ia specimens have been found with a large number of nuclei, though the usual condition appears to be with one nucleus. The quality of the body-substance, the mode of movement and nourishment, agree closely with those which have been depicted as characteristic of the class. Our knowledge of the mode of repro- duction is imperfect. Amongst the forms without a shell, fission has been observed. In Haliphysema one of the nuclei with a small portion of protoplasm is said to become marked off from the rest and to form a small body not unlike an ovum imbedded in the protoplasm. This may be called internal budding. In several of the families of our order (Miliolidce, Layenitlie, RotalidcB, and NummulinidoB) we meet with, the phenomenon of dimorphism, that is to say, the species is made of two distinct kinds of individuals, which appear to alternate with one another in the life-history. (Fig. 5.) The one of these forms the microspheric is distinguished by the small size of the initial chamber and by the possession of a large number of small nuclei ; while the other the megalospheric has a large initial chamber and one large nucleus. In the microspheric form, reproduction is effected by the simple emergence of the protoplasm from the shell and its division into a number of spherical bodies ; each of these secretes a shell which constitutes the first chamber of a megalospheric form. In the megalospheric form, on the other hand, the protoplasm in the shell breaks up into a number of small masses, each of which issues as a flagellated zoospore. The further history of these is not known, but they probably give rise to the microspheric form. In Polystomella crispa L., one of the Nummulinidce, whose life-history is better known than that of other Foraniinifera, the initial chamber, or microsphcre, occupying the centre of the shells of the microspheric form, has a diameter 8 PROTOZOA. of about 10 /a. It is succeeded by a series of chambers of gradually increasing size, which are added one after another in a spiral manner. Numbers of small nuclei which increase in number by simple division, are scattered apparently irregularly through the protoplasm. The existence of the microspheric form, as an individual, is terminated in the following manner. The animal becomes firmly attached to some object by its psexidopodia, and the protoplasm emerges from the shell. After involved streaming movements which continue for some hours, the protoplasm divides simultaneously into a number of spherical masses, having generally a diameter of about 70 /t., which, after secreting a shell, rapidly draw apart from one another, and each sets up an independent existence. These form the initial chambers of the 'megalospheric form of the species. The FIG. 5. mioculina depressa il'Orb. Sections of the shell : A, of the megalospheric form (megalosphere 200-400 /*) longitudinal. li, of the microspheric form (microsphere 20 M-) transverse. The two terminal chambers are omitted in II (from Lister, after Schlumberger). whole of the protoplasm of the parent is thus divided up to form the brood of young, its empty shell falling to the bottom. The second chamber of the megalospheric form of Polystomella has a peculiar shape, and the other chambers added in succession build up the spiral shell. In this form a single large nucleus is present, whose size increases witli the growth of the protoplasm. Prior to the reproduction of the megalospheric form the large nucleus disappears, and in place of it, though the way in which they are produced lias not been followed, great numbers of minute nuclei are found scattered through the protoplasm. After a preliminary division of these nuclei by karyokinesis, the protoplasm breaks up into flagellated zoospores having a RHIZOPODA. 9 diameter of 5 /j.. The intervening stages between the zoospore, produced by the megalospheric form, and the microsphere in which the microspheric form takes its origin, have not been followed ; but there is some, though at present incon- clusive evidence, in favour of the supposition that the microsphere results from the conjugation of two zoospores. The relative sizes of the microsphere and zoospore 10 /*. and 5 /j.., agrees fairly well with this view. One of the earliest observations relating to the dimorphism of the Foraminifera was of the well-established fact that the microspheric form is much less abundant than the megalospheric, and this admits of easy explanation on the supposition that the union of two separate organisms is required for its production. Finally, Schaudinn's observation of the conjugation of the zoospores of Hyalopus, which is, however, a form not known to be dimorphic, supports the hypothesis. From the foregoing account of the life-history of Polystomella it appears that the dimorphism of the Foraminifera is due to the occurrence of alternating or recurring generations, and there is some, though at present inconclusive evidence in support of the view that the megalospheric generation arises asexually, and the microspheric generation as the result of conjugation. In the genus Orbitolites (Miliolidce), while the megalospheric form has been found to be produced from a microspheric form as in Polystomella, it has also been seen to arise from a megalospheric parent. In this case, then, it must be supposed that the generations do not regularly alternate, but that the megalo- spheric form may be repeated before the brood of zoospores is produced. Besides the difference in the size of the initial chambers, the shells of the two forms present in some cases marked differences in the mode of growth. Thus in the genus Biloculina,* (Miliolida;), while the mode of growth of the megalospheric form is, as shown by Schlumberger, on the biloculine plan from the first (Fig. 5), that of the microspheric form is at first on the quinqueloculine plan, and it is not until many chambers have been formed that the biloculine plan, characteristic of the genus, is assumed. The application of the term dimorphism to the phenomenon above described is in accordance with its general use in zoology and botany. It has, however, been used, together with the terms trimorpliism and polymorphism, in another and quite different sense, namely to indicate the occurrence of two (three, or more) different modes of growth in the building up of the shell of a single individual. Thus, in the shell of the genus Peneroplis, the chambers * The mode of growth of the shells of the genera Biloculina, Triloculina, and Quinqucloculina is a modification of the spiral. The chambers are elongated and increase in size as they succeed one another, each occupying half a turn of the spiral. The result is that the mouths of the chambers are directed succes- sively in opposite directions, and a long axis of the shell is thus established. In the genus Biloculina (Fig. 5) the chambers lie in the same plane, and each overlaps its predecessors at the sides. Hence only two chambers are exposed in the outer contour of the shell. In the other genera the chambers are narrower and do not lie in the same plane, the median plane of each being directed at a definite angle, which is constant for the genus, to that of its predecessor. The result is that in one case three, and in the other five chambers are exposed in the contour of the shell, and the triloculine and quinqueloculine forms of shell are respectively produced. The genera Triloculina and Quinqucloculina (d'O.) were by Williamson included in the genus Miliolina. 1 PROTOZOA. are at first arranged spirally, Imt in the later stages of growth in a rectilinear series. Such forms are called dimorphous. Conjugation has been observed to take place in a few cases (Arcella, Diffluyia, Euglypha, etc.), but details concerning it are unknown. In the Polythalamous forms, it is possible, as hinted above, that conjugation takes place between the free-swimming zoospores. The Foraminifera present four main varieties of shell: (1), the chitinous, e.g., Gromia, imperforate ; (2), the porcellaneous, e.g., Miliola, imperforate, and characterised by their opaque white colour and abundant organic basis ; (3), the hyaline, e.g., Glolir/enna, perforate, and with but little organic basis ; and (4), the arenaceous, perforate, as in Psammosphcera, Imt generally imperforate. The last are formed of small foreign particles united by a cementing substance. It is the fact that perforate and imperforate arenaceous forms are found within the limits of the same family, which has ren- dered necessary the abandonment i >f the old division of the order into Perforata and Imperforata. Specimens of Biloculina ringenx living in the red clay at 3000 fathoms, a depth at which calca- FIG. e. Nummuiitic Limestone, with reous organisms are generally absent, horizontal section of N. ilixtvna (after , ,, were found by Brady to have a shell composed of silica. Analysis of the calcareous shells shows that the mineral con- stituents consist of carbonate of lime and carbonate of magnesia, the latter varying from five to ten per cent. There is besides a trace (generally under 0-5 per cent.) of silica. In spite of their small size, the shells of our simple organisms may lay claim to no small consequence, since they not only accumulate in enormous quantity in the sea sand (M. Schultze calculated their number for an ounce of sea sand from Molo di Gaeta at about one and a half millions), but are also found as fossils in different formations (the cretaceous and tertiary), and have yielded an essential material to the construction of rocks. Silicious nodules of Poli/thal ami awe even found in Silurian deposits. The most remarkable, on account of their considerable size, are the X// annuities (Fig. 6) in the thick formation of the so-called ISTum- mulite limestone (Pyrenees and elsewhere). A coarse chalk of the BHIZOPODA. 1 1 Paris basin, which makes an excellent building stone, contains the Triloculina trigonula (Miliolite chalk). The greater number of Fora in in if era are marine, and move by creeping on the bottom of the sea, but some of them are pelagic and Gloliiyerina and Orlulina live at the surface. Some of the genera are found in the brackish water of estuaries, and they may even extend into fresh water. The bottom of the sea at very consider- able depths is also covered with a rich abundance of forms, especially with Globig&rina, the remains of the shells of which give rise to an enduring deposit. Order I. Amceboidea. Naked Amoeba-like Rhizopoda, with lobose or reticulate pseudo- podia, usually with nucleus and contractile vacuole. Amoeba, nucleated forms, with contractile vacuole and lobose pseudopodia. Protamoebn Haeckel, small forms, with lobose pseudopodia ; nucleus and con- tractile vacuole not observed. Hyalodiscus Hertwig and Lesser, disc-shaped, nucleated forms, without pseudopodia ; locomotion by a flowing movement without change of form. Protomyxa Haeckel, Myxodictyum Haeckel, Protogcncs Haeckel, are forms with anastomosing pseudopodia, and without observed nucleus. PelomyseaGreef, large amoeba-like forms, containing many nuclei, retractile bodies, and cylindrical crystals. Other genera are Gloidium Sorokin, Chwtoproteus Stein, Plakopus F. E. Schulze, Dactylosphcera Hertw. and Lesser, Podostoma Clap, and Lachm., Amphizonclla Greef, Gymnophrys Cienk. Bathybius Huxley, found in the deep sea mud of the Atlantic, if it is indeed a living organism (and not simply a deposit of gypsum). Coccolitlts, C'occospheres, and Rhabdosphcres are found in the gelatinous mud of the bottom of the Atlantic, and were supposed by Huxley* to be portions of the body of Bathybius. Similar bodies have been found in the chalk. They are in reality small marine vegetable organisms, with calcareous walls, and are oceanic in habit. They form with Diatoms and pelagic Oscillatoricc, a large part of the vegetable food of marine animals, f Order II. Testacea (Foraminifera). Principally marine Rhizopods, with a shell which is either membranous, calcareous, or rarely silicious, and may be single- chambered (Monothalamia) or many-chambered (PolythdLamia), usually with more than one nucleus. In this order the pseudopodia are generally slender and anastomosing, but in the fresh water Arcella and Difflugia (Fig. 8) they are lobed. The protoplasm has the power of exuding through the openings in the shell and of forming a layer which may be much vacuolated on the outside of the shell (Fig. 10). In such cases the shell may be regarded as an internal structure, and appropriately Q.J.M.S., vol. 8. t Vide Nature, 1897, p. 510. * 12 PROTOZOA. compared with the internal capsule of the Radiolaria. The shell also often possesses long, delicate, spiny processes, which are broken off unless the animal be very carefully handled (Fig. 10). The Foraminifera are mainly bottom organisms, but a few genera of the hyaline forms are pelagic. The pelagic genera are important because of their extraordinary abundance. Whether these pelagic forms have the power of supporting life on the surface of the bottom- ooze is unknown. The definition of species and genera in this order is rendered difficult by the large number of intermediate varieties, which, indeed, often constitute a complete series. Carpenter* on this subject writes as follows: "The ordinary notion of species as assemblages of individuals marked out from each other by definite FIG. 7. EuglypJia glnliosn- (after Hertwig and Lesser). FIG. 8. Difflvgia oblonga (after Stein). characters that have been genetically transmitted from original prototypes similarly distinguished, is quite inapplicable to this group ; since, even if the limits of such assemblages were extended so as to include what would elsewhere be accounted genera, they would still be found so intimately connected by gradational links, that definite lines of demarcation could not be drawn between them." Fain. 1. Arcellina. Shell watch-glass shape, membranous ; with more than one nucleus ; with contractile vacuoles ; gas vacuoles with a hydrostatic function may be secreted by the protoplasm. Fresh water. Cocliliopod ium Hertw. and Lesser, Pyxidicula Ehrbg., Arcclla Ehrbg., Hyalosphenia Stein, Quadrula F. E. Schulze, Difflurjia Leclerc, shell incrusted by foreign particles, usually pyriform in shape (fig. 8). * W. R. Carpenter, " Introduction to the Study of the Foraminifera," preface, p. x. RHIZOPODA. 13 Fam. 2. Euglyphina. Shell chitinous or silicious, composed of hexagonal or roundish plates ; pseudopodia pointed, branched. Fresh water. Euylypha Duj. (Fig. 7), Trinema Duj. Fam. 3. Gromidae. Test chitinous, smooth or incrusted with foreign bodies, imperforate, with a pseudopodial aperture at one or both extremities ; pseudo- podia long, branching, reticulated. Fresh water and marine. Gromia Duj., Lieberkuhnia C. and L., Mikrogromia R. Hertwig, Diaphoropodon Archer, Shepherdella Siddal. Fam. 4. Miliolidae. Test imperforate, mono- or polythalamic ; normally calcareous and porcellaneous, sometimes incrusted with sand ; under starved conditions (e.g. in brackish water) becoming chitinous or chitino-arenaceous ; at abyssal depths occasionally consisting of a thin homogeneous, imperforate silicious film. Marine. Squamulina Schultze, Nubecularia Defrance, Bilo- culina d'Orb. , Fabularia Defrauce, Spiroloculinad'Orb., Miliolina Williamson, Hauerina d'Orb., Vertcbmlina d'Orb., Orbiculina Lamarck, Orbitolites Lamarck. Fam. 5. Astrorhizidae. Test invariably composite, usually of large size and monothalamic ; often branched or radiate, sometimes segmented by constriction of the walls, but seldom or never truly septate ; polythalamic forms never symmetrical. Sub-fam. 1. Astrorhizince. Walls thick, composed of loose sand or mud very slightly cemented. Astrorhiza Sandahl, PcJosina Brady, Syringammina Brady. Sub-fam. 2. Pilulince. Test monothalamic ; walls thick, composed chiefly of felted sponge-spicules and fine sand, without calcareous or other cement. Pilulina Carpenter. Sub-fam. 3. Saccamminincc. Chambers nearly spherical ; walls thin, composed of firmly cemented sand grains. Saccammina M. Sars, Psam- mosphccra Sch., Sorosphccm Brady. Sub-fam. 4. Rhabdamminina-. Test composed of firmly cemented sand grains, often with sponge-spicules intermixed ; tubiilar, straight, radiate, branched, or irregular ; free or adherent ; with one or more apertures ; rarely segmented. Rhabdammina M. Sars, Rhizaminina Brady, Sagenella Brady, Botellina Carp., Haliphysema Bowerbank. Fam. 6. Lituolidae. Test arenaceous, usually regular in contour ; septation of the polythalamic forms often imperfect, chambers frequently labyrinthic. Comprises sandy isomorphs of the simple porcellaneous and hyaline types (Cornuspira, Miliolina, Lagena, Globigerina, Rotalia, etc.), together with some adherent species. Lituola Lamarck, Thurammina Brady, Ammodiscus Reuss, Trochammina Parker and Jones, JVebbina d'Orb., Cyclammina Brady. Fam. 7. Textularidae. Test of the larger species arenaceous, either with or without a perforate calcareous basis ; smaller forms hyaline and conspicuously perforated. Chambers arranged in two or more alternating series, or spiral, or confused; often dimorphous. Textularia Defrance, Cuneolina d'Orb., Verneuilina d'Orb., Tritaxia Reuss, Pavonina d'Orb., Valvulina d'Orb., Clavulina d'Orb., Bulimina d'Orb., Virgulina d'Orb.", Bolivina d'Orb., Pleurostomclla Reuss. Fam. 8. Chilostomellidae. Test calcareous, finely perforate, polythalamous. Segments following each other from the same end of the long axis, or alternately at the two ends, or in cycles of three ; more or less embracing. Aperture, a curved slit at the end or margin of the final segment. Ellipsoidina Seguenza, Chilostomellct Reuss, Allomorphina Reuss. 14 PROTOZOA. FIG. 9. Planorbulina (Acervu- l ! it a) ylvbosa (after M. Schultze). Fam. 9. Lagenidae. Test calcareous, very finely perforated ; either mouo- thalamous, or consisting of a number of chambers joined in a straight, curved, spiral, alternating or (rarely) branching series. Aperture simple or radiate, terminal. No inter- septal skeleton nor canal system. Layena Walker and Boys, monothalamous ; Nodosaria Lamarck, chambers in linear series ; Linyulina d'Orb., Frondicularia Defrance, Rhabdogonium Reuss, Marginulina d'Orb., Vaginulina d'Orb., Rimu- lina d'Orb., Cristcllaria Lam., chambers in spiral series ; A mphicorync Schlumberger, Lingulinopsis Reuss, Flabellina d'Orb., Polymorphina d'Orb., Dimorphina d'Orb., Uvigerina d'Orb. Fam. 10. Globigerinidse. Test free, calcareous perforate ; chambers few, inflated, arranged spi- rally ; aperture single or multiple, conspicuous. No supplementary skeleton nor canal system. All the larger species pelagic in habit. Globiycrina d'Orb. when taken in a spoon shows very long fine calcareous spines projecting from the shell (Fig. 10). These are not found in forms taken in the tow-net or in ooze. Dimorphism has not been observed in this genus. Orbulina d'Orb., spherical shell, often double, containing Globigerina-like shell ; it is formed by the external protoplasm as a kind of large last chamber. Hasti- gerina Wy. Thomson, Pul- Ui>in P. and J., Sphceroidina d'Orb., Candcina d'Orb. Fam. 11. Rotalidae. Test calcareous perforate ; free or adherent. Typically spiral and " Rotaliform," i.e., coiled in such a man- ner that the whole of the segments are visible on the superior surface, those of the last convolution only on the inferior or apertural side, sometimes one face being more convex, sometimes the other. Aberrant forms evo- lute, outspread, acervuline, or irregular. Some of the Fig. 10.HustigeriitH ((Hobigcrina) Murroyi W. Thomson, higher modifications with bubbly vacuolated protoplasm, enclosing 6, the per- double chamber walls, sup- forated Globigeriua.like shell. IFrom the peripheral p ] ementa l. skeleton, and a protoplasm project not) only fine pseudopodia, but , , . .,, . hollow calcareous spines, which are set on the shell system of canals. Spinlhna (from Murrayj . Ehrbg., Cymbalopora Hage- uow, Discorbina P. and J., Planorbulina d'O. (Fig. 9), Truncatulina d'O., Anomalina P. and J., Carpcn- tcria Gray, Pulvinulina P. and J., liotalia Lam., Calcarina d'O., Tinoporus Carpenter, Gypsina Carter, Thalamopora Roemer, Polytrema Risso, Patellina. MYCETOZOA. 15 Fam. 12. Nummulinidae. Test calcarecms and finely tubulated ; typically free, polythalamous, and symmetrically spiral. The higher modifications all possessing a supplemental skeleton and ,a canal system of greater or less complexity. Fusulina Fischer and Sclnvagcrina Moller extinct, palaeozoic, Nonionina d'O. , Polystomella Lam., Archccdiscus Brady, carboniferous, Amphistegina d'O., Operculina d'O., Heterosteyina d'O., Nummulites Lam. mostly extinct (Carboniferous and Eocene), CydocJypeus Carp., Orbitoides d'O., Eozoon (?) Dawson. TestamcEbiformia (Carter. An. and Mag. 1880). Adherent testaceous Rhizopoda with the general form of Amoeba. Systematic position doubtful. Holodadina test calcareous and branched with pustuliferous surface, Cystcodictijina test calcareous, sessile, unbranched, uniformly punctate surface, Ceratcstina test chitinous and polythalamous. SUB-CLASS II. MYCETOZOA.* G-ymnomyxa of large size, formed by the fusion of many small amoeba-like forms. Fruit-like cysts or sporophore, ami coated spores are always formed. The Mycetozoa were formerly regarded as Plants, and under the name Myxomycetes placed amongst the Fungi. After the discovery that the spores do not produce a mycelium, but hatch out as swarm cells, de Bary introduced the name Mycetozoa. They have the form of large masses of a .granular protoplasm bounded by a clear proto- plasm the ectoplasm without granules. These masses, which are called plasmodia and may attain a surface extension of several square inches, infest the damp surface and interstices of vegetable substances, such as dead leaves, rotten wood, or even sound wood. They spread out into a network on their substratum, over which they advance with a creeping movement due partly to the formation of pseudopodia at the advancing margin and partly to the flow of the dark granular endoplasm. The flow of this latter is a rhythmic one, being reversed at nearly regular intervals. The endoplasm contains numerous nuclei and vacuoles, and sometimes granules of calcium carbonate. The vacuoles often contract and expel their contents which is either watery or of refuse matter. Occasionally the streaming ceases, the plasmodium breaks up into masses containing ten to twenty nuclei, a superficial membrane is formed round each of these masses, and they enter a resting state : this is the stage of the Sclerotium. The sclerotium can be made to reassume the active condition by the addition of moisture. * De Bary, "Die Mycetozoen." 1864. A. Lister, "A Monograph of the Mycetozoa."" London, 1894. W. Zopf, "Die Pilzthiere oder Schleimpilze." Encyklopcedie der Naturwisscnschuften, 1885. 16 PROTOZOA. The reproduction is always effected by spore-formation. The spores are either contained within fruit-like cysts the Sporangia (Endosporece), which are either simple (spore fruits) (Fig. 11) or combined into an cethaliuni (fruit-cake) of a cushion-like shape consisting of numerous convoluted sporangia (Fig. 12); or they are not contained in a cyst, but are produced upon the surface of upgrowths of the plasmodium the sporophore (ISxosporece). In the latter case the spores divide, after issuing as amoeboid organisms, by three successive bipartitions into eight cells, which soon obtain flagella and separate ; they are comparable to the just-hatched spores of the Endosporeas. The spores are always enclosed in a coat of a cellulose-like material and possess a single nucleus. They are contained as a rule in the meshes of a network of supporting fibres the capillitium which is formed within the FIG. 11. Physartvm nutans (from Lister), a, two sporangia magnified nine times ; '', capillitium threads, with lime-knots attached to a fragment of the sporangium- wall, x 110. FIG. l2.Fidigo septica, a, Aethalium, one third natural size ; b, capillitium threads with lime-knots and two spores, x 120. sporangia! cyst by the spore-protoplasm. The division into spores is in the Emlosporece preceded by a single division of the nuclei of the sporeplasni by karyokinesis. * On the germination of the spore the spore coat bursts and the contents issues as an amoeboid organism which soon protrudes one flagellum. (Fig. 13.) The swarm-cells so formed swim by their flagellum, ingest solid food by their pseudopodia (at the non-flagellate end) and undergo frequent bipartition. They may also withdraw the flagellum and encyst (ntio-ocysts), but this is only temporary : they emerge and re-assume the swarm-cell form. After a time the flagellum is withdrawn and they creep about in an amoeboid manner, and ultimately several of them fuse together to form the multinucleated plasmodium. (Fig. 14.) * The nuclei of the plasmodium sometimes multiply simultaneously by karyokinesis, though it is highly probable that simple division occurs as well. MYCETOZOA. 17 Order 1. Exosporeae. Spores produced on the sporophores and not enclosed in a cyst. Ceratiomyxa Schroeter, plasmodium in rotten wood fruiting on the outside. Order 2. Endosporeae. Spores produced in a sporangium. Badhamia Berkeley, Physarum Persoon, Fuligo Haller, sporangia combined into an rethalium. F. septica Gmelin, flowers of tan. Cienkowskia Rostafinski, Physarella Peck, Craterium Trentepohl, Leocarpus Link, Chondrioderma Rost., Trichamphora Junghuhn, Diachaxt Fries, Didymium Schrader, Lepidoderma de Bary, Stemonitis Gleditsch, Comatricha Preuss, Enerthcnema Bowman, Lnmprodcrma Rost., Clastoderma Blytt, Amaurochcete Rost., Brefeldia Rost., Lindbladia Fries, Cribraria Pers., Dictydium Schrad., Licea Schrad., Orcadclla Wingate, Tubulina Pers., Siphoptycliium Rost., Alwisia Berkeley and Broom e, DictydioBthalium Rost., Enteridium Ehrenb. , Rcticularia Bull, Trichia Haller, Oligoncma Rost., Cornuvia Rost., Arcyria. Hill, Lachnobolus Fries, Perichccna Fries. Margarita Lister, Dianema Rex, Prototrickia Rost., Lycocjnla Michel i. n O 7 iG. 13. Didymium di/orme (after Lister), a, spore ; b, swarm-cell escaping from the spore-case ; e, newly hatched swarm-cell with nucleus anil three vacuoles ; d, flagel- lated swarm-cell ; t-, swarm-cell with two vacuoles containing bacteria, and produced at the posterior end into pseudopodia ; /, amoeboid swarm-cell, x 720. FIG. 14. Didymium di/orme (after Lister), young plasmodiuni with attendant amoe- boid swarm-cells, some of which have turned into microcysts (m) ; one micro- cyst being digested in a vacuole (v). An empty spore-shell at s. x 470. In the neighbourhood of Mycetozoa may be placed provisionally the peculiar marine form Labyrintliula, described by Cienkowsky (Arch. f. M. Anat., III.), from the harbour of Odessa. This animal consists of aggregations of roundish to spindle-shaped cells placed in a finely granular substance. From this mass, hyaline or finely fibrous processes are given off. These processes branch and anastomose so as to form a labyrinthic network along which the cells glide. Clilamydomyxa Archer (Q.J.M.S., XIX.), seems to be a fresh-water organism of the same nature. The Sorophora which are classed by some authors with the Mycetozoa, appear to be more nearly allied to Labyrinthula. In the vegetative phase they live on the dung of various animals, and are formed by the coming together of numbers of amcebulfe produced from spores. The amcebulse, however, retain their distinctness, and do not fuse to form a homogeneous plasmodium as in the Mycetozoa, nor are there streaming movements throughout the mass. The mode C 18 PROTOZOA. of increase of the amosbulse in this stage has not been followed. In the spore formation of Dictyostelium the mass rises up into club-shaped prominences, in the axis of which a septate stalk is formed, and the amoebulse become gradually aggregated at the summit of the stalk, where they encyst. The amcebulae which escape from the spores divide by fission, but they do not pass through a flagellate stage. Genera. Copromyxa Zopf., Cynthulina Cienk., Dictyostelium Brefeld, Acrasis Van Tieghem, PolyspondyJ ium Brefeld. SUB-CLASS III. HELIOZOA* For^ the most part fresh-water Gymnomyxa with stiff radiatin/j pseudopodia, and one or more nuclei ; usually with contractile racuole. A radial silicious skeleton sometimes present. The characteristic pseudo- / podia give the name to the group. (Fig. 15.) "When a skeleton is secreted, it consists either of radially arranged silicious spines (A caii- thoaystis) or of latticed sili- cious shells (Clathi'uUna), and so closely resembles the skele- ton of the Radiolaria that the _^_ Heliozoa have been actually described as, fresh-water Radio- laria. They differ from the Radio- laria in the absence of the complicated differentiations of the protoplasm, particularly of FIG. lu. Young Actinosphccrium, still with a single nucleus (after F. E. Schulze). N nucleus. the central capsule. One or more nuclei may be present in the central mass. An important distinguishing mark is afforded by the presence of the pulsating vacuoles, which have not been observed in any marine Radiolarian. Reproduction is effected by fission. Encystment and subsequent f L. Cienkowski, " Ueber Clathrutina." Arcliiv. fur mikrosk. Anatomic, Tom III., 1867. R. Greeff, "Ueber Radiolarien und radiolarienahnliche Rhizo- poden des siissen Wassers." Ibid. Tom V. & XL R. Hertwig und Lesser, "Ueber Rhizopoden und denselben nahe stehende Organismen." IbiJ. Suppl. Tom X., 1874. Also Archer and F. E. Schuke, etc. HELIOZOA. 1 ( J spore-formation sometimes takes place. This has been observed in ActinospTicerium, in which form the spores acquire a silicious coat. In some genera, e., Trichomonas vuginalis (after Leuckart). FIG. 22. Trichomonas IKI truclior urn (after Stein). Us undu- lating membrane. FIG. 23. Oikomonas termo (after Biitschli). n nu- cleus ; Cv contractile vacuole ; Ni> vacuole which takes up the food (oral vacuole). that special conjugating cells of the nature of ova and spermatozoa are not formed. Maupas especially, by follow- ing the history of the individual result- ing from conjugation, has definitely established the fundamental distinction between conjugation and reproduction, and has thrown a flood of light upon the meaning of the whole phenomenon of conjugation. The outer boundary of the body is usually formed by a cuticle a delicate transparent membrane, the surface of which is beset with vibratile and moving appendages of various kinds. In the smallest Infusoria the Mastii/vj/hora, we find only one or two long whip-like cilia ; while . the more highly differentiated Giliata are usually richly provided with cilia. Finally, in the Ai-ineiaria the young forms have cilia, and the adults a number of delicate tentacle-like processes, which either end in suctorial discs or are pointed. Fio. 24. Ooninm pectorale (after Stein). The colony a from above, li from the side. INFUSORIA. 27 SUB-CLASS I. MASTIGOPHORA. Infusoria generally of small size provided with flaydla. This sub-class includes forms Avhich live in putrefying infusions, parasitic forms, and forms which live freely. They all have con- tractile vacuoles, and some of them have an opening at the base of the fiagellum for the reception of solid substance (holozoic nutrition). Encystment and spore formation are very commonly found ; and it has been shown by Dallinger and Drysdale* that the spores are capable of resisting a temperature above boiling point. Dallinger has also shown, in the case of some of the infusion forms, that it is possible by very gradually raising the temperature in which the animals are living during a number of successive generations to produce a race for which the optimum temperature is considerably above the normal killing temperature for the species. Conjugation is known to occur very generally, and in some cases the conjugating individuals (or gametes) \ are especially differen- tiated. This is notably the case in Volvox, in which the gametes are of two kinds, and recall the spermatozoa and ova of the higher animals. Many members of our sub-class are difficult to distinguish from the swarm-spores of certain Rhizopoda and of the Myeetozoa, and even from the zoospores of unicellular AJijw. It is necessary, therefore, to point out that in the Mastigophora the flagellated stage covers the main, if not the entire, period of the life of the organism. The nucleus is almost invariably single. Order 1. FLAGELLATA. : Mastigophora withflagella, without collar or cilia. This order includes holozoic, holophytic, and saprophytic forms. Many of them are parasitic and many live in infusions. It is not infrequent to find an amoeboid condition of the body combined with the possession of the fiagellum (Mastigamceba), or to find these two conditions alternating in the life -history. Many of them form colonies, and an outer cuticular skeleton in the form of a cup or investing membrane may be present ; and in some forms a gelatinous layer is secreted. In the holozoic forms food may be taken up by * "Researches on the Life-history of the Monads." Monthly Hie. Journal. 10-13. t An organism which conjugates, whether specially differentiated or not, is called a gamete, and the product of the conjugation is a zygote. t G. Klebs, " Flagellatenstudien." Z. f. w. Z., 55, 1892. 28 PROTOZOA. means of pseudopodia in an amoeboid fashion, or there is a definite spot at the base of the main flagellum Avhere the food enters : this spot is either marked by a mouth-vacuole (Fig. 23 2Y>) into which the food slips, or by the presence of a mouth-opening with or without a pharyngeal continuation. The expulsion of undigested remains of food appears to be localised and often to take place by the bursting of a vacuole ; but the position of the temporary anus, which seems to be variable in the different forms, has only been determined in a few cases. Contractile vacuoles close to the body- surface seem to be always present, and in the Ewjlenina they appeal' to open into a receptacle which is in communication with the hind end of the pharynx. Chromatophores of the same character and function as those of plants are present in the holophytic forms, and vary in colour from a light green to a brown (Chlorophyll and Diatomin). They contain amylum bodies, which consist of a central mass of a highly stainable plasma the pyrenoid and of an outer zone of amylum. The pyrenoids may increase by division. Amylum bodies are also found in colourless saprophytic forms. Paramylum, a substance more nearly allied to cellulose, is sometimes present in the protoplasm. Chromatophores may be present or absent in closely allied forms, and even in the same form at different times ; their presence is of no systematic importance. The nucleus is always single except in Ti-fpomonas, which some- times has two. Stigmata as red pigment spots are often present in the protoplasm, usually at the base of the flagellum. Reproduction takes place by fission, which is usually, if not always, longitudinal, in both the active and resting state, and some- times by continued fission (spore formation) in the resting state. In the first case the fission may be into two, or by successive binary fissions into four, eight, sixteen, or even thirty-two before the young- separate. When the fission is into two, the flagella become doubled in number before the body divides. The manner in which this doubling occurs is disputed: very likely a new set of flagella and of the other organs of the body is formed before the division occurs. When the first binary fission is succeeded by others, the successive fissions take place within the cuticle, while the animal continues to move by the two original flagella which remain attached to one of the products of fission. Finally reproduction may take place by continued fission (spore formation), during the resting state (Bo. ; Oxyrrhis Duj. 32 PROTOZOA. The following three families of the Isomastiyoda are separated as a sub-order named Phytomastigoda on account of their plant-like features. Sub-order 5. PHYTOMASTIGODA. Holophytic, vegetable-like Isomastigoda with chlorophyll, without mouth. Fam. 17. Chrysomonadina. Solitary or colonial ; rarely with test ; with two, rarely one, brown to greenish-brown chromatophore ; usually with eye-spot at the base of flagella ; colonies free-swimming, with spherical grouping of individuals. Styfochrysalis Stein ; Chrysopyxis Stein ; Ncphrosclmis Stein ; Synura Ehrb., colonial, with cuticle often growing out into fine spines ; Syncrypta Ehrb. Fam. 18. Chlamydomonadina. Almost always green on account of considerable, usually single, chromatophore ; usually delicate membranous shell without large opening ; one to two contractile vacuoles at base of flagella ; usually one eye-spot (stigma). Reproduce by continued division within the shell-membrane ; usually forming macro- and niicrogonidia ; mostly solitary. Hymcnomonas Stein: Glilorangium Stein; Chlorogonium Ehrb.; Polyto-ma Ehrb., saprophytic, without chromato- phores, with amylum bodies ; Chlamydomanas Ehrb. ; Hcematococcus Agardh. ; Spondyl&morum Ehrb., colonial; Coccomonas Stein; Phacotus Perty. Fam. 19. Volvocina. Billagellate colonial Phytomastigoda, intermediate in structure between Ghlamydomonas and Hcematococcus. Reproduction by continued division of all, or of certain, indi- viduals of the colony (parthenogonidia] to form daughter colonies. In some, probably in all, con- jugation occurs between definite individuals of the colony, with or without differentiation of the colonies and gametes into male and female. The result of conjugation is a resting zygote, which develops later into one or into several new colo- nies. Gonium 0. F. Miiller (Fig. 24), colonies of o, colony, l, one f our or sixteen individuals united to a quadran- A- collar; * mi- ,. ., late . like gro up ; reproduction by simul- cleus ; Cv contractile vacuole ; f , , . , . . , , * ,. Xv oral vacuole taneous division ol all the individuals to form daughter colonies ; Stcphanosphcern Colin ; Pan- dor ina Bory de Vincent; Eudorina, Ehrb.; Volvov L., spherical colonies with numerous individuals, which are placed at equal distances within the common thick colonial membrane, and lie in special membranes which stand off from the cells and are compressed against one another into the form of hexagons. Cv I ni. 20. Codosiyc. Mrytiit (after Butschli). inclividual. Order 2. CHOANOFLAGELLATA. iijojjliora irith a collar-lilo' process <>f protoplasm rouno<1ai-ia). Their soft parts were imperfectly known, owing to the fact that they are small, exceedingly sensitive to adverse influences, and consequently very difficult to get under observation in the living state. The body lies within the skeleton, and contains some small brownish-yellow spherical bodies. There is a nucleus in the centre of the protoplasm, bounded by a membrane, and con- taining a nucleolus; it has been called the central body. There is one long vibratile flagellum. The body is without a bounding membrane, and there are no pseudopodia. The reproductive processes are unknown. The skeleton consists of hollow silicious rods, and has the form of two circles united by rods ; it invests the body in a cap-like manner. Fani. Dictyochidae, with the characters of the order. Mesocena Ehrb. ; Didyocha Ehrb. ; Distephanus H. ; Cannopilus H. Order 5. CYSTOFLAGELLATA (RHYNCHOFLAGELLATA). Mastigoph&ra of large size with a single nucleus, reticular proto- frfasni, and a stout membrane. Noctiluca is a nearly spherical form of large size (1 mm. in diameter), and has on its ventral side a groove, called the peristome, at the base of which is the elongated slit-like mouth. From the anterior end of the peristome projects a large transversely striated flagellum, sometimes called the tentacle, and a little further back on the right side are two organs, the tooth and the lip. The flagellum is a contractile organ and varies in form : it moves slowly from side to side. The tooth is a protoplasmic projection, and is probably actively movable. From the lip there projects forward a smaller and vibratile flagellum. The greater part of the protoplasm with the nucleus is aggregated on the ventral side at the base of * A. Borgert. " Ueber die Dictyochiden," etc. Z. f. w. Z., 51, 1891, p. 629. 36 PROTOZOA. the peristomial groove, and from it there radiate in all directions to the periphery branching strands of protoplasm. At the periphery there is a thin layer of reticulated phosphorescent protoplasm immediately underlying the stout cuticle which bounds the body. The nutrition is holozoic, and food vacuoles are formed. Leptodiscus has the form of a flattened disc, concave on one side and convex on the other. On the convex side is the mouth somewhat eccentrically placed, and from the same side there is a tubular depression from which projects a flagellum. The protoplasm is much vacuolated as in Nodihiea, and the principal part of it is aggregated at the centre of the concave or aboral side of the disc. l-'ic. 29. Noctilura minm-is partly after Cienkowski. N nucleus ; a, single animal ; 1>, conjugation of two individuals ; c ami il, swarm spores. Noctiluca occasionally draws in its flagella and loses its peristome and enters the resting state, but has not been observed to encyst. It reproduces in two ways : by binary fission and by the formation of small swarmers. If by fission, the division of the nucleus and central plasma is soon followed by that of the whole body. Before the latter is completed the development of the peristome and its organs in the new individuals begins. Individuals with two central masses and two nuclei are occasionally found. The formation of spores takes place during the resting state. The central plasma projects slightly on the surface, and divides by a superficial con- striction into two prominences. The nucleus karyokinetically participates in this and future divisions. These two again divide CILIATA. 37 into four, and so on, until a large number of small prominences are formed ; these eventually become free, and constitute the spores. The latter are provided with a flagellum, a pointed process the so-called spine and a nucleus. Their later history has not been followed, and it is not known whether they conjugate. The process of division by which these spores arise is incomplete, and resembles the cleavage of a meroblastic egg. While it is taking place a part of the protoplasm of the rest of the body seems to pass into the dividing disc, but the superficial layer beneath the cuticle always remains. The fate of the maternal body after the separation of the spores is not known. Conjugation takes place between two individuals, and results in complete fusion ; but the fate of the zygote has not been traced. Noctiluca owes its name to its phospho- rescent power. The light is emitted from numerous points in the surface protoplasm, and principally when the animal is disturbed. It sometimes appears in enormous numbers on the sea surface. It is cosmopolitan, and is principally confined to the coasts, but it has been taken in the open ocean. There are two genera both marine. Noctilucn Suriray, with very slight power of change of form ; cosmopolitan. Leptodiscus R. Hertwig, body con- tractile and movements energetic ; Mediterranean. SUB-CLASS II. CILIATA.* Infusoria provided irith cilia : mouth and anus, mtcJeiis and paranucleus are generally present. This group contains the most highly FlG> 30 ._ Sfy , onychia organised of the Protozoa. The locomotive ( ilfter stein )> seen from ven - appendages are cilia, which are modified in diverse ways, as will be explained below ; and immovable hairs and stiff bristles, which may even have the form of bent hooks and be employed in loco- motion and attachment, are often present. The power of forming * 0. Btitschli, loc. cit. W. Saville Kent, A Manual of the Infusoria. London, 1880-82. E. Maupas, " Sur la multiplication des Infusoires Cilies." Arch. Zool cxp. et gin. (2), Vol. VI.; and "La Rajeunissement Karyogaimque chez les Cilies. Ibid., Vol. VII. tral side. ll~z adoral zone of cilia; C contractile vacuole ; N nucleus ; N 1 paranucleus ; A anus. 38 PROTOZOA. pseudopodia is almost always absent, and the body is generally bounded by a thin pellicle or cuticle. Certain fixed Ciliata, as Stentor (Fig. 31) and Cotliurnia, secrete external coverings or shells into which they can be retracted. Nourishment is in a few cases taken in by endosmosis through the whole surface of the body; but as a general rule there is an oral aperture usually near the anterior pole of the body, through which solid food is introduced. A second aperture, which acts as anus, and which can be seen as a slit during the exit of the excreta, is often present at a definite part of the body. The pellicle seems to be part of the living tissue, and frequently has an alveolated struc- ture, in which case it forms the alveolar layer. Beneath it there is generally a layer of cortical plasma the ectoplasm which has a firmer consistence than the more fluid endo- plasm. The pharynx, or oesophagus, projects into the endoplasm as a tubular prolongation of the ectoplasm and pellicle. Through this the food-stuff passes into the endoplasm, in which, it gives rise to food-balls. The latter undergo a slow rotating movement round the body in the endoplasm, during which the food is digested ; and finally the solid useless remain- der is ejected through the anal aperture. A digestive canal, bounded by distinct Avails, exists . no more than do the numerous stomachs which FIG. 8I.Stentor rceselii Bhrb., after stein, o Ehreuberg, who was deceived by the food vacu- oral ap^ure^gul- ^ ^^ ^ } ^ Infugoria po l ygast rica. In vacuoie ; N nucleus. some cases there is a tube leading in from the anus towards the oesophagus (Nyctofkerus), but it ends in the digestive endoplasm, and does not join the oesophagus. In some cases (the Endielina and Chlamydodonta, Fig. 32), the oesophagus is surrounded by a layer of stiff rods forming the so- called rod-apparatus of the oesophagus. The firmer, more viscid ectoplasm is to be regarded pre-eminently as the motor and sensory layer of the body. In it we may find fibrillse resembling muscular fibres (Stentor, stalk of Vorticella). These fibrillse are differentiations of the alveolar layer and are sometimes varicose. When they shift into the cortical layer (ectoplasm), they form the so-called myopliane layer. Small rod-shaped bodies the CILIATA. 39 trichocysts are sometimes present in the cortical plasma. It appears that on suitable stimulation they have the power of everting needle-shaped structures which probably have a stunning action upon other organisms. In one form, Epistylis untlellaria, definite nematocysts, like those of the Ccelenterata, are present in the ectoplasm. The contractile vacuoles are fixed in position and contained in the ectoplasm, generally near the surface of the body. When more than one is present they increase in number with the size of the individual. They open outward through pores in the pellicle, or in some cases (Vorticellines) into a reservoir, or there may be a long excretory canal as in Lemladion. The contractile vacuoles are re-formed by the fusion of formative vacuoles which appear in the neighbouring plasma during the diastole of the preceding vacuole, or there may be canals leading even from distant parts of the body, which collect the fluid for the formation of the new vacuole (Paramiecidiu). The walls of these canals are, in some cases at any rate, contractile. These vacuoles and canal -systems are probably excretory in function, collecting waste matters in solution from the body gener- ally and discharging it externally. They have been compared, probably with some justice, to the excretory organs of Platyhelminthes and Rot if era. The vibratile appendages of the body are of n i . -. , , lour kinds, and they all seem to be processes of the cuticle or alveolar layer. . (1) Ihe fine cilia which serve for swimming. (2) The Cirri : stouter vibratile processes which taper towards their free ends. They are placed on the ventral surface of the body, and serve for locomotion in a pediform manner (hence called leys or styles], or for attachment. (3) Membranellse : short flattened cilia which, when ending in a point, are not clearly distinguishable from cirri ; they form the adored zone of the peristome of the Spirotricha, in which they create the whirlpools by which the food is brought to the mouth. (4) Undulating membranes placed in the neighbourhood of the mouth, and assisting in the prehension of food. The fibre which can often be made out running from the base of the cilium, apparently to the myophane layer, is continuous with the FlG - w.- his, after Stein ; with rod -apparatus round the oesophagus. nucleus; excreta are passing out per anum. 40 PROTOZOA. cuticle as well as with the cilium. In a few forms (Actinobolus) retractile tentacular processes are present. In the simplest forms the mouth is at the anterior end of the body, the ciliary covering is uniform, and the cilia are nearly all the same size (JEnchelina). An advance upon this is presented by those forms in which the mouth is on the ventral surface, and in which there is a triangular area the peristome leading back from the front end of the body to the mouth (Paranicecium). There may be a special row of strong cilia, cirri, or membranellae the ml oral row, or zone- running along the left side of the peristome (Hypotricha, Fig. 30). The peristome, when ventral, is very commonly asymmetrical. In some cases the adoral row has the form of a spiral round the mouth region, and the peristome may be placed at the front end of the body (Stentor, VorticeUa). In the Hypo- triclia the following regions may be distinguished on the ventral surface of the body : a pre-oral and a post-oral region. The pre-oral region consists of the peristome on the left side, and the frontal area on the right (Fig. 41.) The majority of the Ciliata are multinuclear, and the nuclei are almost, if not quite, always differ- entiated into two kinds. One of these the macro- nucleus is larger than the other, the micro-nucleus. The macronucleus, which lies in the endoplasm, is generally single, and presents considerable variation of form; it may be spheroidal, band-shaped, moniliform, or even branched. In some cases the macronucleus is represented by a great number of small nuclei. It is probable that these small nuclei are all parts of one nucleus, and connected with one another by fine fibres ; so that the condition is really that of a much-branched nucleus. Fragmentation of the macronucleus into fine pieces has been observed, and is probably a stage in its final disappearance ; but the real significance of the phenomenon is unknown. The micronucleus is often multiple ; it varies in position, form, and number, in different species. It is always smaller than the macro- nucleus, and usually lies close to the latter. It appears only to be absent in certain Opalime and in some of the so-called multinuclear Ciliata just referred to. In the normal reproduction of the animal it appears that, while the micronucleus divides by karyokinesis, the macronucleus divides directly. FIG. 33 Opctli-na rananim (after W. Engelmanu). CILIATA. 41 AT' The most usual method of reproduction is by fission. When the forms reproduced remain connected together, a colony is formed, e.i/., the colonies of Epistylis and Ca/rJiemini. Fission usually takes place by a transverse division (at right angles to the long axis), and the products may be equal or unequal. In cases of inequality we have transitions to budding, which is really only a modified fission. Less frequently (Vorticella) the fission takes place through the long axis (Fig. 36), and still more rarely in a diagonal direction. The onset of fission does not appear to depend upon the size of the indi- vidual, for it may take place in large or in small specimens. The nuclei always participate in the division, but do not always lead the way ; for in many cases un- doubted new formations appear in the protoplasm n , (rudiments of new cili- ary structures, of a mouth and contractile vacuole), before any changes are observed in the macro- and micro- nuclei. As to the Other FlG - Ss. l-aramceciwn avrelia in division, organs they do not par- after R. Hertwig. N titipate in the division "wcronucleus ; nmicro- , nucleus - o. mouth of division, from Stein. C con- (unless they extend the the anterior portion; tractile vacuole ; N macro- whole length of the **'' n '' ' the same f nucleus ; n micronuclei. the hinder portion. body), but one of the fission products develops them afresh, generally before the fission is completed. In the Hypotricha the ciliary structures of both the products of fission appear to be new formations. In Opalina the nucleus divides many times, so that a multinucleate condition is produced (Fig. 33). The gradual division of the whole animal by a series of binary fissions into a number of small pieces which encyst, takes place subsequently. From the cyst a small uninucleate form eventually emerges. Reproduction is often preceded by encystment, which appears to be of great importance for the preservation of the body from desiccation. FIG. 34. Stylonychia mytilus in 42 PROTOZOA. The animal retracts its cilia, contracts its body to a globular mass, and then secretes a transparent cyst which hardens and protects it and enables it to survive in damp air. In water the contents of the cyst divide into a number of parts, which attain freedom by the bursting of the cyst, each one becoming a young animal. The rapidity of fission depends upon the temperature and upon the food, and seems to be fairly constant for each species. Thus an individual of Stylonychia pust.ulata, if well supplied with food, will divide once in twenty-four hours in a temperature of 5 to 10 C., and once in twelve hours if the tempera- ture be from 10 to 15 C. Although the rapidity of fission is less in senile individ- uals, there does not appear to be any special increase in it after con- jugation. The Conjugation of the Ciliata is generally of a temporary nature. Two individuals (rarely more) apply themselves together and acquire protoplasmic continu- ity. After a few hours FIG. 36. Vorticclla microstoma, after Stein, a, in process of , ill fission ; N nucleus, the mouth apparatus in each portion is tliey separate and lead formed afresh ; 6, fission is completed, one product of it their ordinary life. Ill is set free after the formation of a posterior circlet of cilia ; wadoral zone of cilia; cc oesophagus ; c, Vorticella in process tne V Orticellines tlie of bud-like conjugation ; k the bud-like individuals (micro- conjugation ^ Complete gametes) attached. and permanent. As a general rule conjugation takes place between two ordinary individuals of the species, but in some cases the conjugating individuals, i.e., the gametes, are specially produced by division from the ordinary individuals. Thus Leucoplirys patvla divides rapidly several times, and produces dwarfed forms uniformly ciliated and incapable of taking nourishment. These small forms are the gametes. In the Vorticellince the gametes differ ; one of the conjugating individuals is the ordinary fixed form, and is called the megagamete, while the other is a small free-swimming form, produced by two or three CILIATA. 43 successive fissions (or in some species by budding) of a fixed form into four or eight. These are the microgametes ; they become free-swimming and conjugate with a fixed form (Fig. 36). In Zoothamniuiu the megagamete is also modified, being larger than the ordinary individual. The results of conjugation may be considered under two heads the physiological and the morphological. The physiological results of, and the conditions favourable to conjugation, have been mainly elucidated by Maupas. He found that it actually effected, as had long been suspected, a rejuvenescence of the conjugating individuals ; that without it senile degeneration, followed by death, ensued, and that to be effective it must take place at a particular stage in the life- history. His course of procedure was as follows : he isolated an exconjugate, i.e., an individual which had just been released from conjugation, and he kept it and the products of its bipartition under continuous observation. He found that after a certain number of bipartitions the vigour and size of the descendants or products of his initial exconjugate diminished, and that their nuclear and ciliary apparatus became imperfect ; and that these changes, to which he applies the term senile, eventually led to the death of the whole stock. He further found that it was not possible to induce conjugation during the period of the earlier bipartitions ; this is the period of immaturity ; but that after a certain number of bipartitions puberty is attained and conjugation can be induced ; this is the period of eugamy. This stage merges into the last, the period of senescence, during which the individuals become gradually reduced in size, the ciliary apparatus more and more imperfect, the micronuclei absorbed, and conjugation ineffective. The period of senescence ends in death. In St ylony chia pustulata puberty occurred at the 130th bipartition, and senile degeneration began at about the 170th, and death took place at about the 316th. Conjugation in the period of euganiy con- ferred the power of again beginning the cycle; but the conjugation of the period of senescence had no result in retarding the degenerative changes or in averting death. Maupas further asserts that fertile conjugation between descendants of the same exconjugate cannot be effected in the period of eugamy ; but this statement requires confirmation. These facts explain why it is that when conjugating individuals are met with they generally occur in large numbers (epidemics of conjugation), for the inclination to conjugation comes only at a particular stage in the life of the stock ; and the divisions 44 PROTOZOA. being rapid, there will always be a considerable number of descendants of the same exconjugate in juxtaposition. Maupas also found that exhaustion of the food supply, which usually determines encystment, causes conjugation among individuals of mixed origin and of suitable age. The morphological changes, our knowledge of which we owe mainly to Balbiani, Biitschli, and particularly Maupas, appear to consist of the breaking-lip and disappearance of the macronucleus, the particles of which in some cases, at any rate are excreted FIG. 37. Conjugation of I'aramcecii.ini m taint inn after R. Hertwig. A" macronucleus ; n micro- nucleus ; o mouth. In a the micronucleus is forming a spindle ; b illustrates the second division of the micronucleus, resulting in the formation of four micronuclei in each animal ; of these, those marked 2, 3, 4, 6, 7, S will atrophy, while 1 and 5 will persist and divide ; c, the micronuclei 2, 3, 4, 6, 7, 8 are disappearing, while 1 and 5 are dividing into two, one of which, 1m and 5;/(, migrate respectively through the protoplasmic connection into the other conjugating individual, while the other, lw and 5w, remains in its own individual. through the anus ; and in the increase by successive bipartitions of the micronucleus. Of the micronuclei so produced, all abort except two, one of which is migratory and the other stationary ; the migratory nucleus passes into the other gamete, and fuses with its stationary nucleus to form the zyyote-nuclens. The two gametes, eacli with a zygote-nucleus, now separate, and the zygote-nucleus gives rise by successive bipartitions to the nuclear apparatus of the exconjugate. The details differ in different species. As an example of the process we may take the simple case of Colpidium colpoila, which possesses one macro- and one micronucleus. Soon after the onset of conjugation, which lasts some hours, the micronucleus of each gamete undergoes two successive bipartitions, and so gives rise CILIATA. 45 to four micronuclei ; of these three abort, and one divides again to form the two pronuclei, as we may call them. One of these migrates into the other gamete, and fuses with its stationary pro- nucleus to form the zygote-nucleus. This undergoes two bipartitions, during which the gametes separate and the old macronucleus dis- appears. The exconjugates now possess four nuclei, all derived from the zygote-nucleus. Of these, two become micronuclei and two macronuclei of the first bipartition, which takes place at from four to nine days after the separation. So that the exconjugate has for some time double the ordinary nuclear apparatus, and the first bipartition takes place quite independently of the nuclear division. For some days after conjugation the exconjugates take no food, and appear to be without a mouth and gullet. They acquire the latter and begin to feed about twenty-four hours before the first bipartition. The mode of life of the Ciliata is very various. Most of them lead an independent life ; some are carnivorous and others herbivorous. The former are very rapacious, and may take up even RoHfera. Some, as AmpMleptus, select fixed Infusorians, as Carchesium and Epistylis, for their prey, and swallow them down as far as the origin of their stalk. They then, while fixed on the stalk, secrete a capsule, and divide into two or more individuals. Some, as the mouthless Opalina and many Bursaridic, are parasitic in the intestines and bladder of Vertebrata. To these belong the Balantidium coli, from the large intestine of man. (Fig. 40.) Order 1. GYMNOSTOMATA. The mouth is usually closed except during inception of food, and is without undulating membranes. The pharynx when distinctly developed is without ciliary structures, but is usually provided with a rod -apparatus or a modification of one. The food is always swallowed, never taken in by a whirlpool. Ciliation usually holotrichous, but often more or less reduced. Fam. 1. Enchelina. The mouth is terminal or sub-terminal, is usually round, rarely slit-like. Anus usually terminal. Conjugation terminal. Sub-fam. 1. Holophryina. Without tentacular structures. Holophrya Ehrb., m. and f.w.*; Urotricha Clap, and L. with caudal bristle, f.w. ; EnchcJys Hill, m. and f.w.; Spathidium Duj., f.w. ; Cliccnia Quennerstedt, m. ; Prorodon Ehrb.; Dinophryu Btitschli, f.w.; Lacrymaria Ehrb. Sub-fam. 2. Actinobolina. With retractile tentacular organs and cilia. Actinobolus Stein, f.w. * in., f.w., and infus. are abbreviations for marine, fresh-water, and infusions. 46 PROTOZOA. Sub-fain. 3. Colepina. Mouth terminal, surrounded by a circle of cirri. Body sometimes surrounded by armour composed of pieces of the pellicle arranged in an annular manner. Plagiopogon Stein, f.w. ; Coleps Nitzsch. f.w. ; Tiarina Berg, m. ; Stephanopogon Entz, m. Sub-fam. 4. Cyclodinina. Cilia confined to one or several rings. Mouth on a papilliform projection. Didinium Stein, f.w.; Mcsodinium Stein, a large oral papilla with one or more cirri arising from its base, m. and f.w. Sub-fam. 5. Prorotrichina. Bluntly truncated oral end ; ciliation confined to front end, or there are in addition incomplete rings of cilia. Butscldia Schuberg, rumen of Ruminants. Fain. 2. Trachelina. Mouth is either a long slit which extends from the front end along the ventral surface backwards, or its hinder part is alone developed as a short slit-like or roundish opening. The oral end of the body usually tapers in a proboscis-like manner. Pharynx short or absent. Sub-fam. 1. Amphileptinse. Mouth on the convex ventral edge of the dorsalwards-bent proboscis, sometimes as long slit, sometimes as round opening. Ampldleptus Ehrb., m. and f.w.; Ziono^fsWrzesniowski, mouth along whole ventral edge of long proboscis, f.w. and m. ; Loxophylluin, Duj., f.w. and m. ; Trachelius Schrank, mouth as round opening at base of proboscis, endoplasm vacuolated, f.w.; Dilcptus Duj., f.w. and m. Sub-fam. 2. Loxodina. Proboscis bent ventrally, and mouth on its concave edge. Ciliation confined to the right side. Loxodcs Ehrb., large size, endoplasm vacuolated, on dorsal side a row of excretion vacuoles, each with a dark body, f.w. Fam. 3. Chlamydodonta. Body never elongated ; mouth always at a distance from the front end. Pharynx always with well-developed rod-apparatus, or a smooth, sometimes peculiarly-formed oesophageal tube. Sub-fam. 1. Nassulina. Ciliation complete; Nassula Ehrb., m. and f.w. Sub-fam. 2. CMlodontina. Ciliation confined to, or stronger on the ventral surface than on the back. Orthodon Gruber, m. ; Chilodon Ehrb. (Fig. 32), f.w. and infus., m. ; Chlamydodon Ehrb., m. ; Ojnsthodon Stein, mouth far back, f.w.; Phascolodon Stein ; Scaphidiodon Stein, m. Sub-fam. 3. Erviliina. Ciliation confined to ventral surface, or a small field of it. Caudal end with a well-developed movable style usually arising a little ventrally of hind end. Acgyria Clap, and L., m. ; Onycho- dactylus Eutz, m. ; Trocliilia Stein, f.w. and m. ; Dystcria Huxley, f.w. and m. Order 2. TRICHOSTOMATA. Mouth as a rule always open, rarely closed when not in use ; pharynx always tubular and open ; edges of mouth provided witli undulating membranes which are continued into the pharynx, or the latter is provided with cilia. Food rarely swallowed, usually brought by a whirlpool or by special ciliary structures. Sub-order 1. ASPIROTBICHA. The mouth in the most primitive forms extends as a slit from the front end along the ventral surface ; but is usually removed from the front end as a reniform or crescent-shaped opening. Pharynx, when present, without rod- apparatus. At the edges of the mouth or in the pharynx are one or two undxilating membranes. CILIATA. n Fam. 1. CMlifera. Mouth in the anterior half of the body, or close behind the middle. Pharynx either scarcely developed or short. The undulating membranes stand either at the edges of the mouth or in the pharynx. A so-called peristomial field leading to the mouth absent or little developed. Lcucophrys Ehrb., f.w.; Glaucoma Ehrb., f.w. and infus.; Dallasia Stokes, f.w.; Frontonia Clap, and L., f.w. and m. ; Ophryoglcna Ehrb. , f.w.; Colpidium Stein, f.w.. infus., m. ; Chasmatostoma Engelmann, f.w.; Uroncnia Dnj., f.w., m., par. on skin of star-fishes; Urozona Schewiakoff, f.w.; Lo.wccphalus Kent, f.w. and infus.; Colpoda Miiller, f.w. and infus. (hay). Fam. 2. Microthoracina. Asymmetrical ; mouth in hinder part of body, placed somewhat laterally at the anterior end of a peristomial furrow, which begins behind ; ciliation sometimes complete, sometimes confined to ventral surface, always sparse. Cinetochilum Perty, f.w., m.; Microthorax Engelmann, f.w.; Ptychostumum Stein, paras, in intestine of Oligochretes ; Ancistrum Manpas, in mantle cavity of Mytilus, Venus, and probably Ostrea; Drepanomonas Fresenius, f.w. Fam. 3. Paramaecina. Month sometimes &V*Z\ jjm*'^ ''' in the anterior, sometimes in the hinder half Pf-^fSHSj ,? a '4t*''tl 'fjf% of the body, with considerable triangular shallow peristomial pit passing to it from the left side of the body. Pharynx tubular, with long undulating membranes or row of cilia. Ciliation close and uniform. Paramceeixm. Hill (Fig. 37-39), f.w. and m. Fam. 4. TJrocentrina. Mouth in middle of ventral surface with long tubular pharynx, like that of Paramcedna. Ciliation reduced to two broad annular zones, one in front and one behind. Uroccntrum Nitzsch, f.w. and m. Fam. 5. Pleuronemina. Ciliation complete and usually considerable ; mouth at the end of a peristome placed at varying distances from the front end on the ventral surface. The left edge of the peristome with con- siderable undulating membrane ; the right edge with a weaker membrane, or with a row of closely- placed cilia. Pharynx slightly developed or absent. Leinbadion Perty, f.w.; Pleuronema Dnj., f.w. and m.; Calyptotricha Phillips ; Lcmbus Colin, f.w., infus., m. Fam. 6. Isotrichina. Pellicle thick ; ciliation total and close. Mouth posterior. Parasitic in rumen of Ruminants. Isotricha Stein ; Dasytricha Schuberg. Fam. 7. Opalinina. Ciliation complete and almost always uniform ; mouth and pharynx absent. Anoplophrya intest. of Oligochretes, Polychsetes, Clepsiue, Paludina ; Hoplitophrya Stein, with two hook-like structures, Oligochfetes and Planarians ; Discophrya Stein, with anterior sucker, Planarians and Annra ; Opalinopsis Foettinger, macronucleus in young forms elongated and twisted, later aii t irregular, even branched and anastomosing mass breaking up into pieces ; venous appendages of Sepia, Octyws, or in liver of Scpiola and Octopus ; FIG. 38. Paramcecium bursaria about one hour after conjugation (after Biitschli). n inicronucleus ; A" macronucleus ; PV contractile vacuole. 48 PROTOZOA. Opalina Park, and Val. (Fig. 33), in young state a roundish nucleus. Micro- nucleus not observed ; no contractile vacuole ; rectum of Anura. Sub-order 2. SPIROTRICHA. Always with distinct adoral zone, which usually consists of membranellse, and has a more or less spiral course round a peristomial area. The latter is distinguished by other peculiarities from the rest of the body-surface. Section 1. Heterotricha. With well-developed adoral zone or spiral, and a complete ciliary covering (except Gyrocorys). Fam. 1. Plagiotomina. Peristome as a narrow furrow, which usually begins close to the front end and passes along the ventral surface to the mouth, which is either at the middle of the body or at the hind end. The adoral zone stretches from the mouth along the left side of the peristome, and is usually straight. Pharynx tubular. Conchopthirus Stein, ma.n.* single or multiple, f.w. , ectopar. in slime of different laud and f.w. molluscs, in gastral cavity of Actinire ; Placjiotomn Duj., paras.; Nydotherus Leidy, with anal tube, paras, in intestine of Anura, Insects, and Myriapods ; Blepharisina Perty, f.w.; Metopus Clap, and L., f.w. and m.; Spirost.omum Ehrb. , ma.n. single, mi. n. numerous, f.w. and m. Fam. 2. Bursarina. Peristome as a more or less triangular (apex oralwards) field, and not a furrow, as in Plagioto- mina. Pharynx absent or but slightly developed. The adoral row extends along the left peristome-edge only, or crosses over in front as far as the right anterior angle of the peristome. Balantidium Cl. and L., paras, rectum of man, pig, Amphibia, body cavity of Polychretes-; Balantidiopsis Biitschli, intestine of Rana ; Condylostoma Duj., mi. n. numerous, f.w. and m. ; Bursaria, 0. F. Miiller, large size, ma. n. long, mi. n. numerous, f.w. Fam. 3. Stentorina. Body elongated. Peristome short and at front end. Its two edges sometimes prolonged into wings. The adoral spiral passes either across the front end of the peristome to the right corner of the same, or completely surrounds the peristomial area. Undulating membrane absent. The peristomial surface is ciliated and spirally striped. Pharynx tubular. Climacostomum Stein, f.w.; Stcntor Oken (Fig. 31), ma.n. long, mi.n. numerous, sometimes fixed and with gelatinous tube, f.w.; Folliculina Lam. with peris- tomial wings, usually inhabits chitinous tubes, f.w. and m. Fam. 4. Gyrocoryna. Bell-shaped, anterior end rounded, posterior end as caudal appendage projecting from the bell ; a ventral furrow with cilia, a row of * ma.n., mi.n. are abbreviations of macro- and micronucleus respectively; f.w. and m. similarly standing for fresh-water and marine. FIG. 39. Paramce- ciumaurelia, after Ehrenberg. M month ; Cv con- tractile vacuoles with canals. FIG. 40. Balantidium coli, with two con- tractile vacuoles after Stein. Near the nucleus lies a starch grain which has been eaten ; a ball of excrement is passing out per anura at the hind end. CILIATA. 49 cilia at edge of bell leading to mouth at base of appendage. CeenomorpJia Perty, f.w. and in. Section 2. Oligotricha. Never elongated, usually spherical or conical. Peristomial field at front end and at right angles to the long axis. Adoral row nearly or completely a closed circle. Ciliation of body partly well developed, partly much reduced. Fam. 1. Lieberkuhnina, possibly a young form of Stentor. Fam. 2. Halterina. Peristomial surface without cilia. Body with few scattered or no cilia : sometimes with scattered immovable setaj. No shell. Strombidium Cl. and L., f.w. and m. ; Haltcria Duj., f.w. Fam. 3. Tintinnoina. Provided with a tubular shell, to the base of which the body is fastened by a stalk. Adoral row as a circle of large membranellae, inside which is a row of fine cilia (paroral). Tintinnidium Kent, f.w. and m.; Tintinnus Schrank, m. ; Tinlinnopsis Stein, m. ; Codonella Hack., f.w. and m. ; Dictyocysta Ehrb., m. Fam. 4. Ophryoscolecina, with thick pellicle, hinder end often with spine- like processes, deep funnel-shaped peristomial region. Anus terminal, usually with anal tube. Parasitic in rumen of Ruminants. Entodinium Stein ; Diplodinium Schuberg ; Ophryoscolex Stein. Section 3. Hypotricha. Body dorso-ventrally flattened, ventral surface usually flat, dorsal convex ; peristomial field usually triangular and in same plane as rest of ventral surface. Dorsal surface without cilia, but with stiff bristles. The ventral cilia uniform or in various ways reduced and differentiated. Pharynx little developed or absent. Fam. 1. Peritromina. Peristome but little marked off from frontal area. Ciliation of ventral surface close and uniform without differentiation of stronger cilia or cirri. Peritromus Stein, m. and f.w. Fam. 2. Oxytrichina. Peristome distinctly marked off from frontal area. Ventral ciliation in the most primitive forms uniform in oblique longitudinal rows ; but some stronger cilia are almost always present on the frontal area (frontal cirri) and at the hind end (anal cirri). Usually the ventral cilia are cirri. A right and left row are distinguished as marginal cirri from the imperfect median rows which are called ventral cirri (Fig. 41). These rows of cirri must not be confused with the adoral row of membranellse (a.) on the left side of the peristome. There is an undulating membrane on the right side of the peristomial area (the preoral membrane, Fig. 41 TO.), and in many forms a row of cilia on the right side of the adoral row (the paroral row, Fig. 41 b) ; both these structures are, like the adoral row, continued into the pharynx. Trichogaster Sterki, f.w.; Urostyla Ehrb., f.w. and m. ; Kerona Ehrb., com- mensal on Hydra; Epiclintes Stein, m. ; Stichotricha Perty, f.w. and m. ; Strongylidium Sterki, f.w.; Holosticha Wrzesn., m. ; AmpMsia Sterki, f.w. and m. ; Uroleptus Ehrb., f.w. and m. ; Onychodromus Stein (Fig. 41), f.w.; Pleuro- triclia Stein, f.w.; Gastrostyla Engelm., f.w.; Gonostomum Sterki, f.w. and m.; Urosoma Kowalewsky, f.w.; Oxytricha Ehrb., f.w. and m. : Stylonychia Ehrb. (Fig. 30), f.w. and m. ; Actinotricha Cohn, m.; Balladina Kow., f.w.; Psilotricha Stein, f.w. Fam. 3. Euplotina. Ciliation much reduced ; the anal cirri are always present, but the marginal frontal and ventral cirri may be absent ; encuirassed. J-htplotes Ehrb., f.w. and m. ; Diophrys Duj., m. ; Uronychia Stein, m. ; Aspidisca Elirb. (Fig. 42), f.w. and m. E 50 PROTOZOA. Section 4. Peritricha. Cilia confined to an adoral spiral and a posterior circlet which is not always present. The adoral spiral with the peristoniial area is placed at the front end of the body (except in one family). The mouth, amis, and reservoir of the contractile vacuole all open into a depression of the peristome called the vestibule. The peristome and adoral cilia are generally surrounded by a projecting lip-like ridge. Fam. 1. Spirochonina. With a peculiar peristomial funnel rolled into a spiral at the front end. Reproduction by budding near the peristome. Attached by an adhesive disc at the hind end. Total conjugation between small animals with undeveloped peristome. No posterior circlet of cilia. Parasitic on the legs of Gummarus, Limnoria, Nebalia. SpirocJwna Stein. FIG. 41. Ciliary apparatus of a Hypotrich Onycho- dromus gmndis (from Perrier after Maupas). a adoral membranellse ; b paroral cilia ; c mar- ginal cirri ; d frontal cirri ; c ventral cirri ; / anal cirri ; m preoral undulating membrane ; n nucleus ; v contractile vacuole. FIG. 42. a, Aspidisca lyncaster, and b, Aspidisca polt/styla dur- ing fission (after Stein). Fam. 2. Lichnophorina. Peris- tome and adoral spiral ventral. Hind end as a sucker for attach- ment, and surrounded by the pos- terior circlet. Ectoparasitic on the skin of Medusfe, Opisthobranchs, worms, and Asteroids. Liclmo- plwra Clap. Fam. 3. TJrceolarina. Free-swimming, with posterior circlet of cilia, which encloses an adhesive disc; without peristomial lip. Trichodina Elirb., ecto- parasitic on the skin of fresh-water and marine animals, e.g. , Hydra, Planarians, etc. also endoparasitic in bladder of fishes and Amphibia. Cyclochceta Jackson, on the surface of sponges, gills of Scorpccna and Trigla, etc. ; Trichodinopsis Clap, and L. , in gut and mantle cavity of Cyclostoma. Fam. 4. Vorticellina. For the most part attached ; without permanent posterior circlet ; with peristomial lip, which can be closed over the peristome in a sphincter-like fashion ; a large undulating membrane continued into the vestibule. In addition to the adoral zone there is an inner circle of cilia cor- responding to the paroral row of other types ; it extends into the vestibule. ACINETARIA. 51 Scypliidia Laclimann, ectopar. ; Gerda Clap, and L., f.\v. ; Astylozoon Engelmann, f.w. ; Vorticella L., with long contractile fibre for attachment, f.w. and m. ; Garchcsium Ehrb. , colonial, f.w.; Zoothamnium Ehrb. , colonial, f.w. and m. ; Glossatella Blitschli, attached, but without stalk ; Epistylis Ehrb., colonial, and Rhabdostyla Kent, solitary, stalk without contractile fibre ; Opcrcularia Goldf. ; Ophrydium Bory ; Cothurnia Ehrb. ; Vaginicola Lam. ; Lagenophrys Stein, with lorica. Forms of uncertain position : Multicilia Cienk., covered by long flagella-like cilia, m. and f.w.; Grassia Fisch, covered with long cilia, parasitic in stomach of frog and in blood of Hyla viridis ; Mugosplucra Haeckel, free-swimming ciliated forms occurring in spherical colonies. SUB-CLASS III. ACIXETARIA. Infusoria with knobbed tentacle-like processes which serve as sucking tubes. Ciliated in the young state. These animals are always sedentary in habit, and either free or attached ; when the latter they may be sessile or stalked. They the living tissues of other organisms means of prey upon u ^ "-0 their tentacles. The latter are processes of the cor- tical protoplasm, and are of two main kinds, con- necting which there are intermediate forms : ( 1 ) the so-called prehensile tenta- cles which taper distally, although they do not end in a sharp point, and (2) the suctorial, which are cylindrical in shape and rounded at the end, which may even be swollen into a distinct knob. The tentacles of both kinds appear to contain a canal which opens distally to the exterior, and leads at the other end into the central protoplasm of the body. The fluid or semi-fluid contents of their prey pass down these canals in a current, the cause of which is not quite understood. Maupas has suggested that the transparent ecto- plasm of the Acinetan first passes in an invisible current by the tentacle into the body of the prey, there absorbs the protoplasm, and then returns with its burden to its own body in a current which can be traced by the granule contents of the protoplasm. All tentacles G- ^' Acineta ferrwmeguinum Ehrb., sucking the body of a small infusorian (Enclidys), after Lachmann. T suctorial tentacle ; V vacuole ; N nucleus. 52 PROTOZOA. are retractile, and tlie prehensile do not seem to differ materially in function from the suctorial.* In their retraction they often become marked by a peculiar spiral wrinkling of their surfaces possibly due to torsion. Mouth (other than the tentacular pores) and anus are not present. Contractile vacuoles are present and vary in number. The macro- nucleus may be elongated or branched, attaining a great extension and complexity in such a form as Demlrosorna, which looks like a colony of Acinetans attached to a creeping stolon. A micronucleus is certainly present in some forms, and probably in all. The body 1ms a pellicle which is in some cases thickened to form a shell or theca. The stalk of attachment, when present, is not contractile. N FIG. H.Epliclota (fodophrya) geMniijiru-n, after R. Hertwig. a, with extended tentacles (both prehensile and suctorial) and two contractile vacuoles; /', the same, with ripe buds into which processes of the branched nucleus N enter ; c, free young form. Reproduction takes place in one of three ways : 1. Equal transverse fission; as a result of thife the organism divides into two equal pieces, one of which the distal retracts its tentacles, acquires cilia, and swims away, while the other, or basal piece, keeps the old attachment and condition. Such reproduction, in which the products are more or less equal in size, is found in Hypocoma, Splicer opliry a, Poiloplirya, Urnula, etc. 2. Simple to multiple budding ; this is characteristic of the genus Eplielota (Fig. 44). One or more buds, each containing a process of '' The prehensile tentacles when present first seize the prey, bring it within reach of the knobbed tentacles ; but it is by no means clear that they do not share in the suction act. ACINETARIA. 53 the nucleus, are formed, and eventually nipped off as free-swimming ciliated forms. 3. Internal budding is the most common method of increase. It takes place in Tdkophrya quadripartita as follows : a funnel-shaped invagination of the apical surface is formed, the opening of which narrows to a pore. The bud arises from the base of the pit or brood-pouch so formed, as a projection containing a part of the nucleus. Eventually the bud becomes constricted off so as to lie freely in the brood-pouch, accpuires some cilia, and escapes through the opening as the free-swimming young form. In Dendrocometes the bud is evaginated through the pore before separation, so that it forms a projection of the body of the mother. The young are always ciliated, and the ciliation may be holotrichous, hypotrichous, or peritrichous. It occasionally happens (PoJoplinja fixa, etc.) that a whole individual retracts its tentacles, acquires cilia, and breaks away as a free-swimming swarmer. Conjugation of the temporary kind has been observed, and is probably a general phenomenon in the group. The changes of the macro- and micronucleus accompanying it seem to be of the same nature as in the Ciliata. Encystment is of common occurrence, but its relation to other vital phenomena is not known. The cyst wall often possesses annular thickenings. Fam. 1. Hypocomina. Freely movable, not attached ; with permanently ciliated ventral surface and one suctorial tentacle. Hypocoma Gruber, m., ectopar. on Zoothamnium. Fam. 2. Urnulina. AVith one or two (rarely more) tentacles not distinctly knobbed, llhynchcta Zenker, freely motile, without theca, on ventral side of Cyclops ; Urnula Clap, and L., attached and with theca, on stalk of Epistylis. Fain. 3. Metacinetina. With stalked funnel-shaped theca, the walls of which are perforated by slits for the exit of the knobbed tentacles. Metacinetu Butschli, f.w. Fam. 4. Podophryina. Tentacles numerous and usually considerable, on the whole surface or only apical, either all distinctly knobbed, or some of them without knobs serving as prehensile tentacles. Spwrophrya Clap, and L., without stalk, endoparasitic in Ciliata; Endosphxra Engelm., Podophrya Ehrb , stalked, with knobbed similar tentacles from all parts of body ; Ephelota Wright (Fig. 44), tentacles both knobbed and pointed, chiefly from free end, m., on Hydroids, Polyzoa, and Crustacea; Podocyathus Kent, like the last, but with theca. Fam. 5. Acinetina. Stalked, or with stalked or unstalked theca with simple opening. Tentacles numerous, all alike, and usually distinctly knobbed. Tokophrya Butschli ; Acineta Ehrb. (Fig. 43). stalk continued as theca ; Soleno- phrya Clap, and L., theca sessile. Fam. 6. Dendrosomina. Without stalk or theca. Tentacles numerous, all 54 PROTOZOA. alike and knobbed, arranged in tufts, which may be numerous and placed at the ends of branch-like lobes. Trichophrya Clap, and L., Dendrosoma Ehrb. , large animal resembling a colony, with branched niacronucleus extending throughout the body. Fam. 7. Dendrocometina. Sessile, with numerous knobbed tentacles on branched arms or over the whole free surface. Attached by the whole basal surface or by a part of it. Dendrocomeles Stein, gills of Gammarus pulex ; Stylocometes Stein, on gill-plates of Asellus aquaticus. Fam. 8. Ophryodendrina. With short or long stalk, tentacles rarely distinctly knobbed, and borne by one to several proboscis -like processes of the body. Ojihryodendron Clap, and L. Class III. SPOKOZOA.* Parasitic Protozoa H-liirh reproduce by spore- formation. Nutriment is talci'n up in the liquid tfate. In most, jirobably in all, the young stages at least are intracellular in habit. The Sporozoa are found in all the great groups of animals except the Proto- zoa and Coelenterata. In the young state at least they live embedded in the protoplasm of their host, into which they make their way when hatched out from the minute spores. They are there- fore described as intra- cellular parasites. In some forms they remain within the cell throughout life, but more often they outgrow the cell and come to lie free in the tissues or spaces of the body. They live entirely on the nutritive juices of their host, and their power of movement is limited. Some have little or no power of * Balbiani, Lecons sur les Sporozoaires, Paris, 1884. Biitschli, "Sporozoa," in Bronn's Klassen u. Ord. d. Thierreichcs, 1880-82. L. Pfeiffer, Die Protozoen als Krcmkhcitserrcger, ed. 2, Jena, 1891, and Nachtrdgc, Jena, 1895. Idem, Die Zellerkrankungcn etc. durch Sporozoen, Jena, 1893. V. Wasielewski, Sporozoenkunde, Jena, 1896. FIG. 45. Gregarines (after Stein and Kolliker). a, Stylorhynchvs oligacanthits from the intestine of Calopteryx; 6, Gregarina (Clepsidrina) polymorphic, from the intestine of the meal-beetle, two forms in "association"; c, two forms of the same in conju- gation ; d, encystment completed ; e, sporulation ; /, cyst with completely formed spores (pseudo- navicellse). SPOROZOA. 55 changing their form, while others are amoeboid. They vary much in size, some not exceeding ten micromillim.etres in length, while others may attain a length of sixteen mm. The protoplasm usually exhibits a differentiation into ectoplasm and endoplasm, and the endoplasm is often highly granular a feature which becomes more marked with the age of the individual. Conjugation occurs in some groups (Gregarinida, Drepanidiidia, etc.), but has not been observed in all. Reproduction is effected by the division of the protoplasm into spores, which may be coated or naked. In most cases encystment precedes speculation, but in some of them the spores are produced gradually during the ordinary life of the individual. In the Gregarinida and CoccidUdea the spore-protoplasm divides to form the young forms. In others the whole spore becomes the young form. There is often a little residual protoplasm generally non- nucleated left over after the sporulation. The young which issue from the spores are either falciform or amoeboid. In Gregarinida and CoccidUdea the sporulation usually takes place after the cyst has left the host (exogeny), but in the other forms it is effected within the host (endogemj). A process which may or may not be analogous to the formation of polar bodies of the metazoan ovum (or speaking more generally, to the reduction- divisions of the progametes) has been observed by "VVolters in Gregarines (Arch. Mic. Anat. Bd. 37) and by Labbe (loc. cit.) in Coccidia. The nucleus divides ; one half remains in the animal, while the other passes to the surface and disappears. This phenomenon precedes the fusion of the nuclei in the con- jugating gregarine, and sporulation in the Coccidia. In Gregarinida and CoccidUdea the cysts pass out with the faeces and enter another host in its food. In the other orders the method of transference from host to host is not certainly known, but probably in some cases the spores are not able to leave the host until its death, after which they may enter a new host in the food ; while in other cases it is possible that the infection is transmitted by blood-sucking insects, or through the lungs in dust. It is possible that there may be in the exogenous forms at least some other mode of reproduction besides that of spore-formation. Very little is known on this head ; but unless there is some other reproductive process, it is difficult to see how in exogenous forms, such as Coccidium oviforme of the rabbit, the enormous number of individuals which characterise acute coccidiosis is produced. It is also probable that in some cases, e.g., the forms which live in 56 PROTOZOA. blood, there is an intermediate host, or that the spores have the power of developing and living outside the body. As a general rule they do not inflict serious damage on their hosts ; but in some cases they are very injurious, and may cause, death. This is sometimes due to the destruction of large tracts of cells or of great numbers of blood corpuscles. Whether in such cases the injury is due to any other cause than merely eating out the cell, such as the production of an injurious substance as the result of their vital activity, is not known. In some endogenous forms, e.g., Myxosporidia, in which the spores cannot escape from the host, extensive tumours may be formed. In the classification of the class adopted in this work, the blood-parasites have been united in the order Hccmosporidia, and the Coccidiidea have been separated from the Gregarinida. It is very probable that these three orders, which are more closely allied to each other than to the other two orders, should be united in one group. Order 1. GREGARINIDA.* Parasitic Protozoa which are embedded during the whole or a part of their lives in the protoplasm of their hosts. They are without mouth or amis, and they usually reproduce by coated spores. Cilia and pseudopodia are absent. The Gregarinida live as parasites in the alimentary canal, and in the tissues of most animals. They are not found in Protozoa, Coalenterates, or Yertebrata. In the young state they lie entirely within the protoplasm of a cell of their host, usually an epithelial cell of the intestine ; but as they grow older and increase in size they project from the cell, to which they remain attached for a time. Eventually they become free, and lie in the cavity of the intestine or other organ of their host. The body is generally elongated in a vermiform manner, and consists of a granular semi- fluid endoplasm containing a nucleus, a thin external layer of clear ectoplasm, and a thick external cuticle. Hooks for attachment, and hair-like processes may be present as modifications of the cuticle. The structure of the body may be complicated by the presence of a partition wall dividing the endoplasm into an anterior portion called the protonierite, and a posterior the deutomerite. The partition consists of a prolongation of the ectoplasm, and the * Aime Schneider, " Contributions a 1'histoire des Gregarines des Invertebres , showing the parasite broken up into spores (after Labbe). ff Fir;. 52. Hamamceba laverani, variety quaterna, from the blood of a man with malaria (after Labbe). a, newly-infected blood-corpuscles ; ft, c, d, successive stages in the growth of the parasite in the corpuscle ; c, beginning of sporulation ; /, rosette-shaped group of spores round a central residual body ; a, spores (young forms) set free in the blood by the breaking up of the corpuscle. a b c d e FIG. 53. Hcemamcsba larerani, variety tertiana, from the blood of a man with malaria. , young parasites in a corpuscle ; ft, amoeboid form ; c, rounded form ; d, sporulation ; c, free spores (after Labbe). have attained some notoriety from the fact that the organism (Glugea bombycis), which causes the Pe&rw-disease of silk- worms, belongs to the order. They include tAvo principal varieties, viz., those which lead a free life, creeping about on the surface of the gall-bladder, urinary bladder, and kidney tubes (Fig. 54), and those which are embedded * R. R. Gurley, "The Myxosporidia, or Psorosperms of fishes and the epidemics produced by them." Hull. U.S. Fish Commission, Part 18, 1894. P. Thelohan, "Recherches sur les Myxosporidies." Bull. Sci. de In France et Bclgiquc, 26, 1895. MYXOSPORIDIA. 65 iii the tissues. The tissue-forms occur either in cysts, which are often visible to the naked eye, or in an infiltrated form, and they may infest almost any tissue (bone, cartilage excepted). It is not quite clear to what extent they are cell- parasites. Many of them are certainly intracellular in the young state, and it is possible that all may be so ; but the youngest stages have not been studied in all forms. Sporulation in the intracellular forms may begin in the quite young forms, even before they have outgrown their cell- host. The Myxosporidia differ from other Sporozoa in their tendency to cause tumours in their host. They may cause serious diseases : the silk - worm disease has been referred to, and they have been known to cause serious mortality among fishes. Those which lead a free life are amoeboid and vary much in shape (Fig. 54). The shape of the cysts and of the infiltration -forms depends upon the physical condition of the tissues. The Myxosporidia, though amoeboid, do not take up solid food, but resemble other Sporozoa in absorbing the nutritive juices of their hosts. The body shows a division into ecto- and endoplasm. The nuclei are numerous and lie in the endoplasm, which contains granules and fat-drops. Reproduction takes place by spore-formation. They differ, however, from other Sporozoa in the fact that the whole body does not break up into spores at one time, but the spores are formed gradually in the endoplasm while the parent F FIG. 54. Leptothcca agilis as a type 01 free-living Myxo sporidia, from the gall-bladder of Trygon vidgaris- ps pseudopodia ; g fat-drops ; ; refractile granules ; sp spores (after Thelohan). 66 PROTOZOA. still continues to grow and to move. When a spore is about to lie formed, a small spherical mass of endoplasm containing one nucleus is marked off from the rest by a delicate membrane ; it thus constitutes an ovum-like body lying in the endoplasm. It is called a primitive, sphere (Fig. 55) ; its nucleus gradually divides, karyokinetically, into ten nuclei, and it then itself divides into two parts, each of which contains three of Ihe ten nuclei of the primitive sphere ; the four remaining nuclei together with a portion of protoplasm forms a small residual body, which soon disappears (cf. the residual bodies of other Sporozoa). The two trinucleated bodies thus formed are the sporoblasts ; they are enclosed in the membrane of the original primitive sphere, which soon thickens into a resistent spore-case. Each sporoblast divides into three cells (Fig. 55e), of which one gives rise to one spore, and the other two to the two polar-capsules (Fig. 55/). The polar-capsules are formed in and at the expense of the protoplasm of the polar-capsule cells, which wholly disappear in the process. The polar- capsules are ovoid bodies containing a long spirally-coiled thread (Fig. 56), which is everted with considerable force when the spore is acted upon by the digestive a d FIG. 55. Spore-formation of Myxdbolus (after Thelohan). a, primitive sphere with nucleus, a little endoplasm of the parent is shown ; 6, stage with six nuclei, and c, with ten nuclei. d, division of primitive sphere into two sporoblasts a and b, each with three nuclei, and a residual body with four nuclei n ; e, division of one of the sporoblasts into two smaller capsule-forming cells cp, each with a vacuole, and a larger cell (the spore) g. f, formation of polar-capsules. juices of the animal which swallows it. It is probably everted with such force that it pierces the wall of the alimentary canal, and thus effects the attachment of the spore to its new host (Fig. 56). The spore-case bursts in the course of twenty-four hours after this attachment, and the contained germ makes its way as an amoeboid form through the intestinal wall and migrates to the tissue in which it is to live. In the case just described, which is that of the genus Myxobolus, each primitive sphere gives rise to two spores ; but in some cases only one spore results, and in others three or more are formed. In the tissue-forms a considerable number of spores proceed from each primitive sphere. The species are distributed by the spores, which are carried to the exterior, or when this is impossible, as in the case of the tissue-forms, are set free on the death of their host. MYXOSPORIDIA. 67 Fam. 1. Myxididae. Spores variously formed with two polar-capsules; includes the forms least degenerated by parasitic life. Principally in gall- bladder and kidney tubes of fishes and amphibia. Leptothcca Thi-lohan (Fig. 54), gall-bladder or kidney of various fishes and amphibia; Ccratomyxa Thel., gall-bladder of fishes; Sphcerospora Thel., kidney-tubes of fishes, S. elegans Thel., kidney- tubes and ovary of stickleback ; Myxidium Biitschli, M. liebcrkuhni Butschli, urinary bladder of pike ; Sphceromyxa Thel. ; Myxosoma Thel. abed FIG. 50. Polar-capsules of Myxobolus ellipsoidcs. a, polar- capsule with spirally-coiled thread ; 6, c, d, eversion of the fibre (after Balbiani). Fio. 57. Spores of Myxoholus ellipsoides (after Balbiani), showing polar-cap- sules in 6 the threads are everted. Fio. 58.Glitgea lombycis (after Balbiani). a, ripe "spore; b, c, hatching o. amoeboid young; d, e, growth stages ; /, g, h, sporulation ; i, testis-follicle of silk-worm caterpillar, strongly infested with Glugea ; k, I, two infected stomach-epithelial cells of the caterpillar of Attacus (Saturnia) pernyi Tc, beginning of infection ; I, the cell is completely filled with spores. 68 PROTOZOA. Fain. 2. Chloromyxidae. Spores with four polar-capsules. Chloromyxum Mingazzini : C. incisum Gurley, gall-bladder Raja batis. Fam. 3. Myxobolidse. Almost all tissue-parasites, principally gills, spleen, etc., of fishes ; one or two polar-capsules. Myxobolus Biitschli (Figs. 55-57) ; M. piriformis Thel., gills, spleen, kidney of the tench (Tinea vulgar is] ; M. dispar Thel., gills of Carp (Cyprinus rutilus) ; Henncguya Thel. ; H. psoros- permica Thel., gills, eye-muscles, ovary of pike; H. media Thel., kidney and ovary of stickleback. Fain. 4. Glugeidae. With very small oviform spores, having at the broad end a non-colourable vacuole, at the narrow end a polar-capsule usually invisible. Glugea Thel., mainly tissue -parasites ; GL bombycis Thel. (Micro- sporidium bombycis Balb.), in all tissues of Bombyx mori, is the cause of the Pebrine disease of silk-worms (Fig. 58), which between the years 1854-67 caused the loss of one milliard francs to the French silk-worm industry ; combated by microscopical examination of eggs and rejection of those infected (Pasteur and Balbiani) ; Gl. bryozoidcs Korot- neff, sexual organs and body-cavity of Alcyonella fungosa; Pleistophora Gur- ley; Thelohania Henneguy, muscles of Palfemon, Crangon, Astacus; Th. contcgeani Hen., muscles of Astacus fluviatilis. Order 5. SARCOSPORIDIA.* Cylindrical intracellular para- sites infest i-Jif/ the striped mus- cular fibres of certain vertebrates. These are the so-called Mi- sclier's tubes, the contents of which are known as Rainey's Corpuscles (Fig. 59). They con- tain a number of more or less spherical bodies, which divide up into still smaller bodies the enns. These latter become o sickle-shaped and appear to con- stitute the young. Very little FIG. 59. Rainey's Corpuscles from the flesh of a pig. c, an animal inside a muscle-fibre ; b, posterior end of same strongly magnified ; C cuticle ; B spores. is known about this group. We are ignorant of the manner in which the transference from host to iiost is effected, and of the young stages of infection. * Bertram, "Beitrage z. Kennt. d. Sarcosporidien. " Zool. Jahrb. Abth. f. Anat., 5. Ai. Schneider, " Ophryocystis biitschlii." Arch. Zool. Exp. (2), 2, 1884. SARCOSPORIDIA. C9 Sarcocystis Lankester, in the muscles of pig, sheep, gecko. Sarcosporidia have been described in man, cat, dog, mouse, rat, hare, rabbit, ox, deer, horse, etc. The Amcebosporidia and Serosporidia may be taken here. The Amcebosporidia arc multinucleated amoeboid forms, which conjugate, encyst, and produce one coated spore. The spore divides into eight falciform young ; they may also increase by dividing directly ; they live in the Malpighian tubules of some beetles. Opliryocystis A. Schn. in Blaps, and Akis. The Serosporidia are long oval parasites which infest the body-cavity of some Crustacea. They increase by direct division, and by encysting without conjugation and subsequent I'.reaking up into numerous amceboid young. Serosporidium L. Pfeiffer, in Cypris, Daplmia, and Gammarus. CHAPTEE II. THE METAZOA. ALL animals above the Protozoa have been classed together as Metazoa, and possess the following characters in common : There is always more than one nucleus, and the nuclei are for the most part arranged with a definite relation to the functional tissues. Conjugation always takes place, but the structure is so complex that conjugation between the ordinary individuals of the species is impossible. Consequently special individuals the gametes are produced for the purpose of conjugating. These individuals, which have a very similar form throughout the group, are simple in structure and unicellular in character ; there are always two kinds of them in every species, called respectively ova and spermatozoa. They arise by a process of unequal fission from their parent, and may both be produced by one individual or by different individuals. When they are both produced by the same individual, that indi- vidual is said to be hermaphrodite. When they are produced by different individuals, that parent which produces the ova is called the female, while that which produces the spermatozoa is called the male ; and the individuals are said to be unisexual and the species dioecious. The conjugating individuals, or gametes, produced by the male never have the power of assuming the ordinary form of the species, and though they have, as a rule, the poAver of inde- pendent locomotion, soon die unless placed in the most favourable circumstances. The gametes produced by the female, on the other hand, Avhile they are Avithout the power of locomotion and have a rather greater power of independent life, are in rare cases capable of becoming more complex in structure, and of assuming the form of the adult. To females Avhich produce such ova the term partlieno- yenetic is applied. In the vast majority of cases, however, the ovum has not the poAver of changing its form and of developing into METAZOA. 71 the ordinary form of the species unless it first conjugates Avith the spermatozoon. The zygote so produced is uninuclear, and has the property of developing into the ordinary form of the species. This method of reproduction, in which a new individual arises from the combination of two independent individualities in the zygote, is called the sexual method of re-production, as opposed to the asexual method, in which a multinucleated mass is separated off from the parent with the power of assuming more or less directly the ordinary form of the species. The asexual method, though common in the vegetable kingdom, is comparatively rarely found amongst animals (Coelenterata, Polyzoa, Tunicata, Annelida, etc.). It thus appears that the Metazoa may be defined as Animals in which the ordinary (so-called adult) form of the species has always more than one nucleus, ami in which the nuclei are for the most part arranged regidarly and with a definite relation to the functional tissues of the animal (so-called cellular arrangement). Special conjugating individuals of the form of ova and spermatozoa are always formed. CHAPTEE III. PORIFERA.* THE Porifera present a great variety of external form. They may be cup-shaped, saucer-shaped, tubular, rod-shaped, foliaceous, trumpet -shaped, fan-shaped, mushroom -shaped, lobed, digitate, branched, or irregular, etc. (Figs. 60-62.) As a general rule, the form is extremely variable even in the same species, and is therefore of little use in identification. They are almost, if not quite, always attached to foreign objects ; this may be effected by a broad basal surface, or they may be stalked. In some cases they are rooted in sand or in mud by basal processes or by special rooting spicules. With the exception of the fresh-water Spongillidce, they are marine, and are found at all depths. One family the Clionidce bore into shells and stones. As the name implies, the surface of the body presents a large number of pores, which are minute in size and inhalent in function. These pores lead into a system of channels which, after permeating almost the whole body, open to the exterior by one or more but always a few larger exhalent openings called oscula. This system of spaces connecting the inhalent pores with the exhalent oscula is the canal system. Through it there passes maintained, as we shall see, by ciliary action a continual stream of water, which enters by the inhalent pores and passes out through the oscula. The sponge is covered by an epithelial layer which we may call ectoderm; the canal system is lined by an epithelium, which as we shall see is usually partly ectoderm and partly endoderm ; but the main mass of the body is formed of a soft tissue which we shall call mesodenn. The mesoderm consists of a gelatinous basis (though no gelatine has been detected in it), containing a protoplasmic network holding * For principal literature see classes and orders. E. Hanitsch, " Revision of the generic nomenclature and classification in Bowerbank's 'British Spongiadae.'" Proceedings and Transactions of the Liverpool Biol. Soc., vol. 8, 1893, p. 173. PORIPERA. 73 nuclei, and presenting differentiations of various kinds so-called muscle cells, amoeboid cells, generative cells, scleroblasts (spicule- forming cells). The mesodermal network is continuous both with the ectoderm and with the endoderm ; indeed, these layers may fairly be regarded as superficial bounding expansions of the meso- dermal mass. Skeletal structures, the main function of which is FIG. 61. Euspongia qffiehinlis adrintiea, with a number of oscula, (after P. B. Schulze). Fics. 60. Axindla polypoides (after O. Schmidt). FIG. 62. A branched Ascon-colony (after Haeckel). to support the sponge-body, are contained in the mesoderm. These may be calcareous or silicious, in which case Ave get the so-called sponge-spicules ; or they may consist of a horny material called spongin (common bath sponge, Fig. 63) ; or finally, spongin fibres and silicious spicules may co-exist. The generative cells are budded off from the mesodermal network, and are eventually dehisced into PORIFERA. some part of the canal system, whence they are carried to the exterior. It is probable that all the protoplasmic tissues of the sponge are contractile, i.e., both the epithelial layers and the mesodermal net- work ; but special structures in the course of the inhalent and exhalent parts of the canal system have been described as muscular sphincters. Ectodermal cells carrying hair-like sensory projections have been described ; these, like other epithelial structures, are connected below with the mesodermal network, parts of which have therefore been interpreted as nerve-fibres and nerve-cells ; but Fio. 63. Piece of network of horny fibres from Euspongia equina. Mes FIG. 64. Section through a calcareous sponge (Sycon mphamts), after F. E. Sch. Ect ectoderm; En endoderm of a flagellated chamber ; Mes meso- derm ; N calcareous spicule in the mesoderm ; Eiz ovum. there is no reason why one part of the network should be considered as more especially adapted for nervous conduction and reflection than another. The ectodermal epithelium consists of flat cells; the endoderm is partly formed of flat cells and partly of somewhat cylindrical cells, each with a flagellum and collar. These are the choanocytes (Fig. 64). They are perhaps the most characteristic constituents of the sponge-body ; the collar is a membranous pro- longation of the cell at its free end round the base of the flagellum ; and the whole cell resembles an individual of the Choanoflasjellata. It contains one or more contractile vacuoles, and its base is prolonged PORIFERA. 75 into processes which join similar processes of neighbouring cells and the mesodermal network. The collared cells are, as a rule, confined to special parts of the canal system called the flagellated or ciliated chambers. Their main function is, no doubt, to cause the current of water which is continually flowing through the sponge. Ciliated epithelium is not found in the Porifera, though in some sponges (Oscarella lobularis, Plaldna monolopha, etc.) the ectoderm cells carry flagella. "We may now proceed to describe in greater detail the various parts of the sponge-body. The simplest form of sponge we do not say the most primitive, though it may be so is presented by the Ascon type of the order Calcarea. The Ascon-person, which is characteristic of the genus Leucosolenia,* consists of a cup- or vase-shaped animal attached by one end, and presenting at the other an opening the oscu- lum. The walls are thin, and consist of ectoderm outside, flagellated endoderm inside, lining the cavity of the cup, and thin mesoderrn, containing triradiate calcareous spicules, between the two. They are further pierced by numerous pores, the prosopyles. In the Si/con-person (Fig. 65), which is FIG. 05. Longitudinal characteristic of the Heterocala, there is a tube oi' cup open by the osculum at one end and attached at the other. This tube is lined by flat cells, and gives off all around and through- out its length numerous short diverticula lined by flagellated cells. These are the radial flagellated chambers: they possess, in addition to the one main opening into the cavity of the central tube, Avhich we may call the gastric cavity, numerous minute pores the prosopyles through which water passes from the exterior into the flagellated chambers. These radial tubes, in short, resemble an Ascon in structure, except for the absence of an osculum at their free end. In the simplest Heteroc -11 \ U.1U1U.O. (111U. an Antliozoan polyp, passing through an enteric pouch on the left side and through a mesentery possess a more Complicated on the right, r perforation in mesentery ; ek ecto- O . nc ,trovh onoglyplies). They remain open when the walls of the rest of the oesophagus are ap- plied to one another (Figs. 88 and 89). The tentacles are hollow, and may be smooth (Zoanfharia, groove long grooves FIG. 87. Longitudinal section through a Hexactinian (Phellia limicola), from Chun, after Andres, a acoutia ; c, c' septal ostia ; g gonad ; m.f mesenterial filament; m.l longitudinal muscles ; o mouth ; o' internal opening of oesophageal tube ; oes oesophageal tube : s primary mesentery ; s' secondary mesentery; s" tertiary mesentery; t tentacle. Fig. 86) or pinnate (Alcyonaria, Fig. 85), and are placed in one or in several rows. Pores may be present at the tips of the hollow tentacles, and on the side walls of the body, in which case they are called cinclides (Fig. 84). In the genus Ceriantlms and its allies there is a large aboral pore. The mesenterial thickenings or filaments are specially characteristic of the Antliozoa. They consist of thick- enings of the endoderm containing gland -cells and thread -cells. COBLENTERATA. 105 Iii some sea-anemones contractile fibres the acontia arise from the edges of the lower ends of the mesenteries : they are closely set with thread -cells and can be protruded from the lateral pores (cinclides) in the contraction of the polyp and serve as weapons of defence (Fig. 87). The muscular system is much more complicated than in Hydroids. The muscles are both ectodermal and endodermal. The ectodermal muscles of the body- wall (longitudinal) are generally feebly developed, while those of the peristomial disc (radial) and of the tentacles (longitudinal) are powerfully developed. The endodermal circular muscles of the pedal disc, the side body-wall, and of the oesophageal Fio. 88. Transverse section through an Alcyonarian (after R. Hertwig). 11 gonidial groove ; 1, 2, 3, 4 the four pairs of mesenteries with their muscles. FIG. 89. Section through an Actinian (Adamsia), after R. Hertwig. Hf the unpaired (dorsal and ventral) chambers ; R, It gonidial grooves. tube are well developed. To this system there is added a character- istic and well-developed set of endodermal muscles on the mesenteries. Each septum is provided on one face Avitli transverse (radial) fibres, and on the other with longitudinal (Fig. 90). The lowest section of the transverse muscles are often independent of the rest, and pass from the side body-wall to the pedal disc (m.fy. The longitudinal muscles are well developed and cause a projection on the face of the mesentery (Figs. 88, 89). While a nucleus is generally associated with each of the ectodermal muscular fibres, the endodermal muscles are in close connection with the base of a cylindrical epithelial cell. In correspondence with the powerful formation of the musculature, the nervous system reaches a considerable development. It has the 106 COELENTERATA. form of a diffuse plexus of much-branched glanglion cells, which are contained in both ectoderm and endoderm between the lower ends of the epithelial cells, and are especially developed in the peristome, tentacles, and oesophagus. The Antlwzoa are almost always dioecious, rarely her- maphrodite (CeriantJius). Ova and spermatozoa arise from the endodermal cells of the mesenteries, and lie in follicles in the jelly of the same struc- tures. They cause swellings on the faces of the mesenteries, a short distance from their free ends (Fig. 91). Asexual reproduction by budding and fission is very generally present, and often leads to the forma- tion of colonies. The Antho- zoan polyps are much inclined to the formation of skeletal structures, which consist of slimy (Ceriantlius), horny, or calcareous substances. The symmetry of the Antho- zoan polyps is almost always radial. The Od actinia (Alcyonarid) indicate their 8-radiate structure by their eight feathered tentacles, CLCr- FIG. 90. Primary mesentery of a Hexactinian (Sagartia parasitica), and the parts of the body to which it is attached, ac Acontia ; c Septal ostium ; / pedal disc ; m.l longitudinal mus- cular fibres; m.t transverse muscular fibres; m.p parietal muscles ; p peristome, t tentacle. FIG. 91. Section through the mesentery of an Actinian (Edwardsia tubcrcvlata), after O. and R. Hertwig. el: ectoderm ; en endoderm ; m./mesenterial filament; m.l section of the pro- jection caused by the folding of the muscular lamella of the longitudinal muscles, the fibres appear as dots ; ov ovary. ov. COELBNTERATA. 107 FIG. 92. Eight-armed Scyphistoma-polyp with wide mouth. M longitudinal muscles of the gastral ridges; Csk chitinous tube. a strictly radiate and a bilateral structure. The tentacles rarely show a tendency to the bilateral arrange- ment, but the mesen- teries, as shown by the arrange- ment of the lon- gitudinal muscu- lar bands, are generally grouped in a bilateral manner (Figs. 88 and 89). The Scypho- polyp or Scy- phistoma is a transitional form between the Hydro- and An- thozoan- polyp. It resembles the hydroid in the and the horny corals (Anti- pafharia) their 6-racliate sym- metry by their six tentacles ; multiradiate usually in a mul- tiple of six are the Actiniaria and stone-corals. Nevertheless, hardly a single anthozoan-polyp can be found in which all the organs are strictly arranged according to one and the same number. The fact that the mouth-opening is not usually round, but slit-like, indicates an inclination to a biradiate or bilateral symmetry, and there are transitional forms between FIG. 03. Sixteen-armed Scy- phistoma (slightly [magni- fied). G'wTgastrar^ridges. 108 COELENTERATA. absence of the oesopliageal tube* and mesenteries, but it recalls the Anthozoan-polyp in the fact that the structureless lamella is developed into a gelatinous layer, and in the presence of gastral ridges (taenioles) or folds of endoderm resembling rudimentary mesenteries, into which the jelly is continued. It is somewhat cup-shaped (Fig. 92), and is attached by the aboral end which is elongated and narrow, and often secretes a chitinous tube for fixation. There are eight or sixteen tentacles (Fig. 93) round the mouth supported by a central axis of stiff endoderm cells. There are four gastral ridges or taenioles (Fig. 94), each of which is accompanied by a longitudinal muscle derived from the endoderm. The Medusa is a free-swimming animal, and consists of a flattened disc or arched bell of gelatinous consistence, from the under or sub- umLreUa surface ~ek of which hangs a central stalk ii&) ^^^jA* r ^^~ ^- f+3 ^f^S * ^jjmi ft* ii ^*tr " f~*^t Hie // / 1 Lit (,(,'('/ itl'ii(~ m.l.-- -en. bearing at its free FIG. 94. Transverse section through the middle part of a Scy- phistoma. ek ectoderm ; en endoderm ; s jelly (structureless lamella) ; ml longitudinal muscle ; gw gastral ridge; gv enteron (from Chun, after Glaus). end the mouth. The greater part of the umbrella consists of the jelly or enlarged structureless la- mella ; this is often traversed by protoplasmic strands which may contain nuclei. In the normal position the medusa swims by the contraction of the bell with its convex or e.c-uin!>rella surface upwards. The manubrium is frequently prolonged in the region of the mouth into lobes and tentacle-like structures, while the edge of the umbrella is beset with a variable number of true tentacles. In a few cases the medusae are attached by the ex-umbrella surface ; in the Luccrnaridac (Fig. 134) by a styliform prolongation of the aboral pole ; in some Ehizostomus by a sucker-like plate of the ex-umbrella. Some of them can creep * Gotte asserts that there is an oesopliageal depression of ectoderm in the Scyphopolyp. COELENTERATA. 109 eac.ii s.u. -t. by means of small suckers on their tentacles (Clavatella prolifera, Pectanthns astcroidcs), or can adhere by the suctorial action of their mouth openings (Pclagia), and even in rare cases are able to lead a parasitic life (Mnestra //arasitica on a pelagic snail Phyllirhoe bucephala). The contraction of the bell is effected by the circular muscles of the sub-umbrella surface. The ejection of water caused by this contraction drives the medusa along. The velum is a mus- cular membrane at the edge of the bell. It consists of a fold of ectoderm, and assists in the move- ment of the medusa by elongating the umbrella cavity and narrowing its aper- ture. When the velum is absent the margin of the bell is lobed (Acraspe- dote Medusae, as opposed to Craspe- dote Medusae in which a velum is present). The marginal ten- tacles are rarely absent (Rhizostoma) ; occasion- ally there is only one (Ktcenstrupia) or two (Aeginopsis, Gcmclla- ria) ; more frequently there are four or some multiple of four. Occa- sionally there are six or a multiple of six (Carmarina, Fig. 101); or the tentacles may be numerous, in which case they are either uniformly distributed round the edge of the bell ( Tiaropsis, Aurelia, Fig. 100), or grouped in bundles (four bundles in Bougainvillea, eight in Lucernarulac, Fig. 134, and in Cyaneci). Occasionally the tentacles are removed from the edge of the umbrella, and inserted either on the ex-umbrella (Narco- medusac, Fig. 96), or on the sub-umbrella (Cyaneidae). The tentacles are FIG. 95. Sarsia mirnbilis (from Chun, after Agassiz). A cras- pedote ocellate medusa budded from Coryne mirabilis. c.r radial canal; c.c circular canal; ex.u- ex-umbrella; g manu- brium containing the elongated stomach and surrounded by the gonads (manubrial gonads) ; o mouth ; t tentacles ; v velum ; s.u sub-umbrella. 110 COELEXTERATA. n.r -c.p. FIG. 96. Portion of the edge of the umbrella of a Narcomedusan (funiiKi lutii-cntrls) from Chun, after O. and R. Hertwig. )' velum ; t tentacles with stiff endodermal axes ; t.b roots of tentacles ; n.r nerve ring ; n.s radial nerve which passes to the base "of the tentacles; ot marginal bodies; x otoporpa ; g.t gastral pouches ; c.p, c.p the two peronial vessels ; they form originally a part of the circular canal, which in the shifting of the tentacles dorsalwards on to the ex-umbrella is festooned and opens into the gastral pouches (after Hertwig, from Chun). usually hollow and unbrancbed, more rarely they have a solid endodermal axis (Narcomcdusae, Fig. 96, Tesseridac, Ephy- ridae), or are dicho- tomously branched (Cladoncmidae). Be- sides the larger main tentacles there are often smaller inter- mediate tentacles at the umbrella edge (Tessera, Fig. 133). Occasionally the ac- cessory tentacles are confined to the young stages and drop off in later life, or they may become trans- formed into the mar- ginal bodies. In the gastrovascular apparatus a central stomach for digestion, and a carrying or circulating sj'stem of peripheral canals and pouches FIG. 97. Diagrammatic longitudinal section through a Rhizostoma. U umbrella ; M gastric cavity ; S sub-umbrella ; gonad ; Sh sub-genital pit ; F gastral filament ; S?I muscular system of the sub-umbrella; erisark}. In one order, however, the secretion is calcareous (Hijdrocorattinae). The colonies very often present, in a well-marked manner, the phenomenon of polymorphism, and in describing the various - en/ ch FIG. 109. Development of hydroid polyps (from Chun, I and II after Metsclmikoff, III after Allnian). I. Young larva of (.'bjtla flat'idiila six hours after attachment, ek ectoderm ; en radially pouched endoderm (rudiment of hydrorhiza); g enteric space; liy cylindrical projection which constitutes the hydrocaulus. II. Larva of Clytia one day after fixation; the hydrorhiza forms a chambered disc from which the cylindrical hydrocaulus pro- jects ; nematocysts are present in the ectoderm. III. Older larva of Eudendri-um mmosum ; the hydrocaulus invested by the chitinous perisark (o/i) projects from the discoidal hydrorhiza; a hydrocephalis with a tentacular circlet (t) has been developed at the free end of the hydrocaulus ; the mouth is not yet formed. modifications which may be present it will be convenient to explain some of the more common terms which are iised in the cumbrous and complicated nomenclature of the group. The fertilized ovum very generally gives rise to an oviform free-swimming larva the planula (Dalyell*), consisting of an outer layer of ciliated .ectoderm and an inner hollow mass of endoderm. After a short time it loses its cilia and secretes a thin cuticular covering the perisark and becomes attached by one end (Fig. 109). The free end elongates and develops a terminal mouth and 1847. Sir J. Graham Dalyell, Rare and Remarkable Animals of Scotland, London, HYDROMEDUSAE. 125 tentacles, while the attached end often spreads itself into a discoidal root (Fig. 109), the hydrorliiza* This is the first polyp. The free upstanding portion is correctly termed the hy- dranth, though the word polyp is some- times loosely ap- plied to it. The hydranth elongates and begins to bud, and two parts be- come distinguish- able in it a ter- minal part called the polyp-head or hydrocephalis with the mouth and ten- tacles, and a lower part with the buds, the stem or coeno- sark. The buds lengthen, remain attached to the parent, and themselves become differ- entiated into hydrocephalis and coenosark. The whole colony of hydranths thus formed is called the hydrosoma. The term hydrophyton seems to be applied to the coenosark plus hydrorhixa, while hydrocauhis^ appears to be synonymous with coenosark. In some forms the perisark does not extend on to the polyp-head but stops short at its base ; in others it is con- tinued round the polyp -head as a cup the hydrotheca (Fig. 114), which, however, stands off from the polyp, being only connected with it by psendo- podial prolongations of the ectoderm. The polyp-head can shrink into the hydrotheca for protection. Some of the buds formed by the colony develop in-ecf bl FIG. 110. Gonangium with hedrioblasts of Gono- tlujmta loi-cni (from Chun, after Allman). 1)1 blastostyle ; gth gonangium (gonotheca) ; c oper- culum of gonangium ; jro 1 " 3 budding gonophores (hedrioblasts); mec 1 hedrioblast with planulae pi; mec' 2 hedrioblast with ova in manubrium. * The hydrorliiza has some- times the form of a branching and anastomosing tube, from which the hydranths arise by budding. t The coenosark or hydrocaulus is said to be fascicled or polysiphonic when it is composed of several adherent tubes, monosiphonic when consisting of a single tube. 126 COELENTERATA. into medusae which become free-swimming, or medusoids which are imperfectly developed medusae and do not become free. These medusae and medusoids are called^ the 'yono2)liores because the gonads are contained in them. A phancro- codonic gonophore is a free - swimming medusa, and is sometimes termed a planoblast. ; an addocodonic gonophore is a medusoid, and is sometimes called a liedriollast. Sometimes the gonophores are budded only from special hydranths, which are then modified by the absence or diminution of size of the tentacles and mouth. Such a proliferous hydranth is a blastostyle. In the forms with hydrothecae, the hydrotheca of the blastostyle forms a chitinous capsule enclosing the blastostyle and gonophores ; it is called the gonangium or gonotheca (Figs. 110, 114). Colonies with gonangia are called calyptoblastic ; those without f/ymnoblastic. The word zooid or ^?ersy lud/Ung from an original, probably medusoid, individual. Gonads in yonophores which, as a rule, are not set free. The colonies of the Siphonophora are characterised by the extreme specialization of the individuals composing them. So great indeed is this specialization that some zoologists (Eschscholtz, Huxley, Metscknikoff) have held the view that their component parts are really organs of a single niedusoid individual, which is distinguished from an ordinary medusa by the fact that its various parts rnanu- brium, tentacles, umbrella have multiplied independently of one another, and have become differentiated and in part dislocated from their primitive positions ; in short, that a siphonophore, in possessing in a marked degree the power of vegetative increase of its parts, resembles a plant more than an animal. This multiplication of the parts of an organism, often independently of one another, is not however by any means exclusively a vegetable characteristic. It must have happened largely in the animal kingdom, and have been a potent factor in determining the forms of animal life. Another view, and the one more generally held, is that they are free-swimming polymorphic colonies of highly specialized polyps, with the power of producing medusae (Vogt, Leuckart, Gegenbaur, Glaus, Chun). According to it, all the parts of a siphonophore are either modified polyps or medusae, and the primitive zooid of the colony is of the polyp type. Just as the first theory errs too much in denying the colonial origin of our group, so the second theory probably goes too far in affirming it. It is probable that the truth lies between the two views. We hold, with Haeckel and Balfour, that the colonial theory is the true one, but that the primitive zooid of the colony was probably a medusa which has produced other medusae by budding, and that the parts of these medusae possess the power of becoming discrete and removed from the bud to which they belong, and of becoming in some cases secondarily multiplied. So * R. T. Giinther, Quart. J. Mic. Sci., vol. 36, p. 284. t E. Haeckel, "Report on the Siphonophorae," Challenger Eeports, vol. 28, 1888. C. Chun, "Die Canarischen Siphonophoren," I. and II., Abhandlungen d. Senckenbcrgischen naturf. Gesellsch. 1891-2. 138 COELENTERATA. that many organs of the colony which on the old colonial theory are modified polyps are on this view nothing more than parts of medusiform indi- viduals which have shifted their attachment, and are therefore really" organs. For in- stance, the struc- tures called pal- pons (hydrocysts, dactylozooids) are to be looked upon as mouthless ma- nubria of medu- soids, the um- brellas of which have become modi- fied as bracts, or are entirely degen- erate. The siplwns (trumpet - shaped polyps, nutritive polyps) are the manubria of medu- soids, of which the umbrella is a bract, or a nectocalyx or degenerate. The tentacle, on the other hand, is to be looked upon only sur- marginal tentacle of the medusoid of the siphon, which has shifted so as to be attached to the base of its manubrium. This theory then agrees with the second theory in asserting the colonial nature of the Siph.onoph.ora, but admits that there has been that vegetative as the Fio. 116. Diagram of a colony of Siphonantliae. St coenosome or stem ; Ek ectoderm ; En endoderm ; Pn pneumatophore ; Sk budding nectocalyx; ,S' nectocalyx; Tpalpon (hydrocyst, dacty- lozooid); ,S/ tentacle and palpacle ; P siphon (polyp); mouth of siphon ; Nk battery of nematocysts ; D hydrophyllium ; G gonophore. viving .SIPHONOPHORA. 139 repetition and specialization of certain organs which is demanded by the first view. The diagram (Fig. 116) shows nearly all the possible parts found in colonies of SipJionanthae, the largest of the two sub-orders of the Siphonophora. We may briefly enumerate these and consider their relation to the colony on this " medusome" theory of Haeckel. The stem (St) or trunk is the coenosark or coenosome of the colony ; it is the elongated manubrium of the original larval medusoid, and produces by budding all the parts of the colony. Two parts may be distinguished in it an upper part, the nectosome, to which the swimming organs (nectocalyces and pneumatophores) are attached, and a lower part, the siphosome, bearing the nutritive and repro- ductive organs (siphons, palpons, gonophores). All parts are budded off from the same surface of the stem (the so-called ventral median line), their apparent radial disposition in some forms being due to a spiral twisting of the stem.* The swimming organs. The nectocalyx (S') is a medusa with canal system and velum but without a manubrium. The pneumato- phore (Pn) is more difficult of interpretation ; it may either be regarded as a medusa, in which the umbrella cavity is the air- chamber or pneumatocyst, or it may be simply regarded and this is Haeckel's view as a part of the ex-umbrella region of the original medusoid larva, the ectoderm of which has become invaginated upon the contained enteric system to form the pneumatocyst (Haeckel distinguishes the ectodermal invagination as the pneumatosac, the secreted chitinous lining as the pneumatocyst). The space round the pneumatocyst lined by endoderm is the pericystic space. The siphons (P) may be regarded as polyps, or as the manubria of medusoids. The palpons (tasters, hydrocysts, dactylozooids) are mouthless manubria. The tentacles (Sf) are organs of the siphons (see above). The palpacles (Sf) are similar organs of the palpons found in one order. The hydrophyllia (bracts) are the umbrellas of medusae which are cleft on one side, or which have simply lost their umbrella cavity and of which the manubria are either degenerate or slightly shifted as siphons and palpons. In many forms bracts have undergone a large secondary increase. Gonophores (G) are either budded from the stem or from processes of the latter called gonostyles, which may, or may not be, mouthless polyps. * The twisting when present takes place in opposite directions in the necto- some and siphosome. 1 40 COELENTERATA. The zooids are generally attached to the stein in groups called cormidia (Fig. 119). The points of attachment of the cormidia are called nodes, the part of the stem between being internodes ; in such cases the cormidia are said to be onlinate. Sometimes this regular grouping does not occur, and the various zooids bud off separately from the stem ; the cormidia are then said to be irregular or dissolved. The nectocalyces by their contractions move the colony through the water ; they have a deeply concave muscular sub-umbrella sur- face. The pn.eumatoph.ore is a hydrostatic apparatus, and, in those forms which have a long spiral stem, serves to keep the body in an upright condition. The gaseous contents is secreted by some of the cells lining the pneumatocyst and can, in some cases, be expelled freely by contraction of the Avails of the pneumatophore through one or more openings the stigmata. The enteric or gastro vascular system is continuous throughout the colony. The gastral zooids are without oral tentacles, but possess a tentacle arising at their base. This tentacle can be extended to a considerable length and be retracted into a spiral coil. It rarely has a simple form, but, as a rule, it bears a number of unbranched lateral twigs the tentilla, which are also very contractile. These tentacles are invariably beset with a great number of nematocysts, which in many places are closely packed and have a regular arrange- ment. These aggregations of thread-cells are especially found upon the tentilla, where they give rise to large brightly-coloured swellings, the cnidosacs or batteries. The gonophores have a velum, a complete gastrovascular system, and a manubrium ; but the mouth is nearly always absent. The generative cells are ectodermal, and arise in the manubrium ; they are without radial divisions (as in the Codonidae of the Antliomedusae). The colonies are generally hermaphrodite, but the gonophores are male and female. The sexual medusoids frequently become separate from the colony when ripe, but are only rarely liberated as small medusae ( Velellidae), which produce the generative cells during their free life. The hydrophyllia are leaf-shaped, and composed of a stiff gelatinous substance ; they are protective in function. All the appendages are developed as buds formed of ectoderm and endoderm, and containing an encloderm-lined cavity which communicates Avith the cavity of the stem. The Siphonophora are extremely beautiful transparent, marine DISCOXANTHAE. 141 organisms, with here and there spots of colour (the hepatic cells of the siphon the apex of the pneumatophore, the cnidosacs of the tentacles, etc.). They are mostly pelagic in habit, but some come from the deep sea. The ova are large, generally without vitelline membrane, and undergo a complete and regular segmentation. A free-swimming, solid planula is formed. There are two main sub-orders* the Disconanthae, in which the primary form is an 8-radiate medusa, the Disconula, which produces biids on the ventral side of its umbrella ; and the Siphonanthac, in which the promorph is a bilateral medusa which produces buds on the ventral side of the base of its manubrium. Sub-order 1. Disconanthae. The body (coenosome) formal Inj the umbrella of the original octo- radial medusa, which includes a potythalamous pneumatocyst ; the huds arise in concentric rings from the sub-umbrella. Larva octoradial (Disconula). This sub-class includes one order. Section 1. DISCONECTAE. YELELLIDAE. Siphonophora with a permanent primary umbrella, without necto- calyces and bracts. The Disconectae are medusae with a large manubrium (Fig. 117, ms), hollow marginal tentacles, and radial canals opening into a circular canal. There is no velum, and the ex-umbrella surface is pitted inwards in the centre to form an ectodermal sac, the pneumato- cyst (Ik}. From the under side there hangs downwards a number of accessory manubria (gni) which bud the gonophores and are called f/onostyles (f/w). The gonostyles open into the radial canals at their basal ends, while distally they may be closed or open. Beneath the pneumatocyst there is a large cellular mass, the centradenia (cd\ or so-called liver. The pneumatocyst opens on the upper surface by * Chun, who objects to Haeckel's separation of the Disconanthae from the rest of the class, arranges the Siphonophora as follows : Order 1. CALYCOPHOEIDAE. With nectocalyces without pneumatophore. Order 2. PHYSOPHORIDAE. With pneumatophore. Sub-order 1. Haplophysae. Physophoridac with unchambercd pneumato- cyst, which is partly lined by gas-secreting ectoderm and is without tracheae. Tribe 1. Physonectae. "With pneumatophore and nectocalyces. Tribe 2. Pneumatophoridae (Physalidae). Without nectocalyces. Sub-order 2. Tracheophysae (Haeckel's Disconectae). With chambered, chitin-lined pneumatocyst, which gives off tracheae to the polyps. Gono- phores set free as mediisae (Chrysomitra). 142 COELEXTERATA. small apertures the stigmata and communicates with the centra- denia and adjacent tissues by a number of fine tubes the tracheae which project from its base. The tracheae are lined by a prolongation of the chitinous lining of the pneumatocyst. The centradenia is separated from the dorsal endoderm of the stomach by a gelatinous plate the t/astrobasal plate (sp) which is pierced by the gastral ostia (primitively 8) for the passage dorsalwards of the radial canals (/7r), which arise from the fundus of the stomach. It is a composite organ, partly consisting of a dense network of endodermal gastral canals, and partly of a parenchyma of ectoderm cells Avith many cnidoblasts. The function of the former is probably partly digestive and partly renal, of the latter gas-producing. In the simpler Dis- conectae, i.e., in the Disealidae the cen- tradenia is composed solely of a compact mass of ectoderm cells and cnidoblasts without canals. The only canals of the centradenia of such forms are eight sim- ple radial canals which arise from the eight ostia of the stomach and run on its upper face between it and the pneumatosac uniting in its centre to form a typical octoradial liver star. They are to be looked upon as ascending branches of the eight primary radial canals of -the sub- umbrella. The canals which perforate the centradenia of the more complex forms are branches of these (Fig. 117). The canal system is primitively octoradiate ; it consists of the radial canals above mentioned, which branch as they pass outwards to be united at the margin of the umbrella by a circular canal (not marked in the figure). This system gives off, in addition to the FIG. 117. Forpcili.a prunella (after Haeckel from Lang), cd centradenia (central gland) ; Ik pneumatocyst ; q> central stigma of pneumatocyst ; rk radial canal ; sj> gastrobasal plate; eu ex-umbrella; su sub - umbrella ; t tentacles; g gonophores ; o mouth ; IHS chief siphon ; ijm accessory siphons, in this case gonostyles. DISCONECTAE. 143 centradenial canals, a set of canals the pallial canals on the ex- umbrella or upper surface of the pneumatocyst, which unite over the centre of the pneumatophore (round <-p). This pallial system is the result of the invagination of ectoderm to form the pneumatophore. The constitution and function of the centradenia, tracheae, and pneumatocyst of the Disconectac is disputed. Haeckel's account has been followed in the text. He regards the supposed ectodermal portion of the centradenia or liver as gas- secreting in function, and corresponding to the gas-secreting portion of the pneumatocyst of the Siphonanthae (see below), the tracheae being for the purpose of carrying the gas, so secreted, into the pneumatocyst, which is entirely hydro- static. Chun, on the other hand, holds that in the Disconanthae, which habitually float on the surface, the pneumatocyst has no gas-gland, and that the cell mass of the centradenia, which Haeckel calls ectoderm, is endoderm with a rich development of thread cells ; further, that the tracheae often end in places where this tissue is absent. He considers that these tubes are really tracheae for the conveyance of oxygen to the thick glandular endoderm, and that, the pneumatocyst in this group is a breathing organ. In confirmation of this view he states that the living Vclella does periodically contract its body as though it were expelling air from the air-sac. The elastic chitinous lining receives its explanation also on this view, as it would by its elasticity tend, in regaining its original form, to suck air in through the stigmata. The gas-secreting ectoderm of the pneumatocyst is present in the young forms, which apparently live below the surface, and probably in the deep sea forms ; and no doubt the function of the air-sac is, in these cases, purely hydrostatic, as in other Siphonophora in which there is a gas-gland and no tracheae. Chun G.,JSericht iib. eine nach d. Canarischcn Inseln ausgef. Eeisc. Sitzb. Acad. Wiss. Berlin, 1888. The gonophores which are produced on the gonostyles are small 4-radiate medusae, which do not produce sexual cells until after detachment, when they are known as Chrysomitra. It is probable that the young of the Disconectae pass through a larval stage resembling in structure Discalia. This would be the so-called Disconula, a form actually met with in Discalia and presenting an 8-radiate medusiform structure with eight radial canals, eight marginal tentacles, and a dorsal 8-radiate in- vagination of ectoderm the pneumatocyst. Fam. 1. Discalidae. From the deep sea. Ex-umbrella without crest, gonostyles without mouth, pneumatocyst divided into a central chamber sur- rounded by 8 radial chambers, to which may be added a still more circumferential arrangement of 5 to 10 concentric ring-chambers. These chambers communicate with each other by the apertures called pncumothyrae, and some of them with the exterior by stigmata. The tentacles have terminal cnidospheres. f Discalia H. ; Disconalia H. Fam. 2. Porpitidae. Circular umbrella without crest ; pneumatocyst divided into an octoradiate central part and numerous concentric rings. The gonostyles have mouths. Pneumothyrae* are present. With many stalked cnidospheres t on the tentacles. f Pneumothyrae are communications between the concentric chambers of the pneumatocyst. f Cnidospheres are spherical knobs composed of cnidoblasts. 144 COELENTERATA. Sub-fam. 1. Porpalidae. Umbrella highly vaulted. Pneumatocyst campanulate, with a radially lobate margin. PorpaUa H. (Fig. 117) ; Porpema H. Sub-fam. 2. Porpitellidae. Umbrella flat, slightly vaulted. Pneu- matocyst discoidal, without prominent radial marginal lobes. Porpitella H. ; Porpita Lamarck. Fam. 3. Velellidae. With an elliptical, often nearly quadrangular, umbrella including a polythalamous pneumatocyst of the same form, composed of numerous concentric rings, and usually bearing in its diagonal a vertical crest. Marginal tentacles simple, without cnidospheres ; gonostyles with mouths. A chitinous prolongation of the pneumatocyst -lining into the crest is generally present. The 8-radiate character of the canal system exists but is much hidden and has become in part bilateral. The pneumatocyst consists of a central chamber sometimes markedly 8-radiate and of many concentric elliptical rings, with stigmata and pneumothyrae. Eataria Esch., pneumatocyst without crest. Vclclla Lamarck ; Armenista H. Sub-order 2. Siphonanthae. Stem (coenosome} formed l>y the manubrium of the original bilateral medusa. The buds arise in the ventral line of this manubrium. Larva bilateral (Siphonula). Section 1. CALYCOXECTAE. CALYCOPHORIDAE. Siphonanfhae with one or more nedocalyces, without pneumatocyst and palpons. Cor in id ia ordinate. A typical member of this group such as Diphyes (Fig. 118) consists of a long con- tractile hollow stem bearing at its upper end two opposed nectocalyces or swimming bells without manubria, but with four radial canals, a circular canal, and velum ; and at regular intervals along its course groups of indi- viduals called cormidia (Figs. 119, 120). At the point where the Fio.ns. Di'phyesacumi- stem joins the nectocalyx nata magnified about 8 times, sb somatocyst. (Fig. 121), or between the FIG. 119. Three cor- midia attached to the stem (coenosome) of a Diphyid (after Leuck- art). D hydrophyl- lium ; OS gonophore ; P polyp (siphon), with tentacle. The cormidia separate from the stem to form eudoxids. CALYCONECTAE. 145 br- nectocalyces if two are present (Fig. 118), there is a deep groove or pit in the jelly called the hydroecium, into which the contractile stem with its cormidia can be retracted. In the jelly of the upper- most nectocalyx is a space lined by large vacuolated cells, and sometimes containing an oil-drop. This is a dilatation of the upper end of the central canal of the stem and is called the somato- cyst. Each cormidium consists of two medu- soid individuals the one of these is a sterile and the other a fertile medusoid. The sterile medusoid consists of a bract or liydropliyllium, a' siphon (trumpet- shaped polyp), and a tentacle, while the fertile one is a gono- phore. The hydro- phyllium is the bell of the sterile medu- soid; it possesses rudiments of the radial canals which radiate from an api- cal dilatation the pJiyllocyst (Fig. 120) which corresponds to the somatocyst of the nectocalyx and is connected with the central canal of the stem. The siphon is the manubrium of the sterile medusoid, which is displaced from its umbrella and has a trumpet-shaped mouth at its free end. The L FIG. 120. Endoxia Esclischoltziia. female eudoxid of giaca Kochii (after Chun), with helmet-shaped hydrophyl- lium, br containing phyllocyst, siphon p, tentacle t, and three gonophores of different ages, go 1 , go 3 , go 3 , with eggs in the manubrium. 146 COELENTERATA. col tentacle is the single marginal tentacle of the medusoid Avhich has shifted on to the base of the manubrium. In some forms the gono- phores become sexually mature while still attached to the stem, but in the greater number the cormidia are detached before maturity and become free-swimming. Such free-swimming groups are called Eudoxia (Fig. 120), and are distinguished as monogastric forms (there being only one mouth and stomach) from the pi ilygastric colonies from which they arise, and when found free are classified separately from the poly gastric forms, just as the medusae of the Anthomedusae are classi- fied separately from the polyp colonies. The nutritive canals of all the parts of a cormidium unite in the bract (Fig. 120), from which point a bracteal canal passes to join the canal of the stem. The phyllocyst (Fig. 120), which corre- sponds to the somatocyst (Fig. 122), arises from the same point. The tentacle is tubular and is beset with a series of lateral tent ilia, also tubu- FIG. 121. SpMeronectes gracilis (from Chun), seen from lar. Each teiltilllim is the side, ny hydroecium : c.oZ somatocyst ; c.v ventral i f f i , radial canal, c.d dorsal radial canal, c.c circular canal of nectocalyx ; tr coenosome with cormidia. (1) a thill pedicle or proximal part, (2) a dilated middle part the miiloxac, and (3) a slender terminal filament. The swelling of the cnidosac is due to a rich development of nemato- cysts of various kinds, forming the battery. The gonophore has a 4-radiate canal system and a velum, but is without tentacles or mouth (Fig. 120). The sexual cells originate in the ectoderm of its manubrium. It forms the swimming organ of the cormidium. In some forms it becomes detached, and then a secondary gonophore is formed. In some species (of Alujla] a cluster of small gonophores is developed in a single cormidium, CALYCONECTAB. 147 in which case a special nectocalyx is developed as a swimming organ. The gonophores are of separate sexes, but the same stem is usually hermaphrodite, bear- ing male and female cormidia. The variations in structure of the order depend principally upon the number of the nectocalyces. In the Monopliyidae there is one necto- calyx, in the Diphyi- dae two, and in the Polypli yi< hie several pairs of nectocalyces. The first formed mouthless siphon is supposed by Haeckel to elongate and form the stem of the future colony. The oldest cormidium is that which is placed furthest from the necto- calyces (Fig. 122). Chun states that the first nec- tocalyx (cap-shaped) is retained only in Mono- phyes and Sphacroncctcs (Fig. 121) ; in the other Calyconectac it is thrown off and replaced by a differently shaped (pyra- midal) secondary necto- calyx (Fig. 122), to which more secondary nectocalyces are added later. All Calyconectae pass therefore through a monophyid stage. As stated above the buds of the cormidia are always formed at the upper end of the stem, so that the oldest cor- A -c.oL -sn tr FIG. 122. Young colony of Muggiaea Tcochii with the primary cap -shaped nectocalyx (A) which is soon cast oft', and the secondary pyramidal nectocalyx (B). c.ol somatocyst with oil-drop; hy hydroecium ; tr coenosome (stem) with two cormidia, the upper one being the younger ; Br bud of hydrophyllium ; go bud of gonopliore ; p siphon ; t tentacle, su sub-umbrella. midium is the lowest (Fig. 122). The law as to the formation of the necto- calyces is not clear in the Calyconectac, but in the Pkysonectae the pneumatophore 148 COELEXTERATA. is at the top of the stem, the youngest nectocalyx bud next to it, while the oldest nectocalyx is at the lowest end of the siphosome, i.e., next the youngest connidium bud. The development of the egg leads to the formation of a variety of the Siphonula larva (Fig. 123). It is a medusoid composed of a nectocalyx (A) the umbrella, of a cylindrical mouthless process the manubrium, and of a tentacle. The mouthless process is attached to the ex-umbrella surface of the nectocalyx (to what is called in Siphonophorau parlance its ventral side), and is regarded by Haeckel as the original siphon. It is supposed to have protruded through a fissure in the ventral wall of the nec- tocalyx. This disloca- tion* of the siphon (if it really exists) from its proper position in the nectocalyx is an example of a widespread phenom- enon in the Siphono- phora, which accounts for a good many of the peculiar features of the group. The alternation of generations in this order is between the polygastric colony and the monogastric cormi- dium, produced by bud- ding from the former and when detached known as a eudoxid. f The gouophore of the eudoxid after shedding its genital cells is cast off and a new gonophore is formed. Fain. 1. Eudoxidae. Monogastric, connidium composed of two rnedu- soids, a sterile and a en- s.u. - -p. "I\\\\W" FIG. 123. Developing Siphonula larva of Mmjijhirn Kocli.ii with buds on the ventral surface. A, rudiment of primary neetocalyx, with somatocyst of, and commencing jelly ga between ectoderm el' and endoderm en,; su sub-umbrella; t budding tentacle; p siphon; en' yolky endoderm cells which are absorbed later (after Chun). * This attachment of the primary siphon to the ex-umbrella surface of the primary nectocalyx is a serious difficulty to the medusome theory. The difficulty may be got over by supposing that the primary siphon is the manubrium of an umbrella which has disappeared, and that the primary nectocalyx is the first bud from the persistent manubrium. t In some forms the primary gonophore loses its sexual manubrium, and is developed into a special nectocalyx, and a secondary gonophore is formed. In this case the cormidium is composed of three medusoids, and is called an Ersaeid. CALYCONECTAE. 149 fertile ; without special nectocalyx. Diplophysa Gegenbaur ; Eudoxella, H. ; Cucubalus Q. and G. ; Cucullus Q. and G. ; Cuboidcs Q. and G. ; Amphiron Blainville ; Sphenoides Huxley ; Acjlaisma Esch. Fain. 2. Ersaeidae. Monogastric, cormidiuni composed of three medusoids, a sterile, a fertile, and a special nectocalyx. Ersaea Esch. ; Lilaea H. Fain. 3. Monophyidae. Calyconcctae Polygastricae with a single nectophore at the apex of the long tubular stem. Cormidia eucloxiform, separated by equal free internodes ; each siphon with a bract. Monophycs* Glaus ; Sphacroncctcs* Huxley (Fig. 121) ; Mitropliyes H. ; Cymboncctes^ H.; Muggiaea\ Busch. (Fig. 122); Cymba Esch. ; Doramasia^ Chun ; Halopyramis^ Chun. Fam. 4. Diphyidae.J Poly- gastric Calyconcctae with two nectocalyces at the apex of the long tubular trunk. Cormidia eudoxiform separated by free equal internodes ; each siphon with a bract. Praya Blainville ; Galeolaria (confounded with Epibidia a Cystonect) Lesueur ; Dipliyes Cuvier (Fig. 118) ; Diphyopsis H.; Abyla Q. and G. ; Bassia Q. and G. ; C'alpe Q. and G. Fam. 5. Stephanophyidae. Polygastric, with several apical nectocalyces and a special necto- calyx on each cormidium. With small palpons with long tentacles on the internodes. Cormidia not set free as ersaeids. Stcphano- pliyes Chun. Fam. 6. Desmophyidae. Poly- gastric Calyconectae with four or more nectocalyces, opposite, i7i pairs. Cormidia eudoxiform or ersaeiform, separated by equal internodes ; each siphon with a bract. Dcsmalia H.; Desmophyes H.; umbrella edge of special nectocalyx with 8 ocelli and 8 short tentacles. Fam. 7. Polyphyidae. Poly- gastric Calyconectae with four or FIG. 124. An advanced Siphonula larva of Epi- bulia aurantiaca with one large nectocalyx (after Metschnikoff, from Balfour) . So somatocyst ; nc second imperfectly developed nectocalyx ; hph hydrophyllium ; po siphon ; t tentacle. * According to Chun the primary nectocalyx of the larva persists in these genera, and there are no secondary or replacement nectocalyces. t Chun states that in these genera the primary cap-like nectocalyx is thrown off and replaced by a pyramidal secondary nectocalyx. J In this family the primary nectocalyx is replaced by two secondary bells, which are themselves replaced by a succession of similar bells formed from similar buds. 150 COELENTERATA. more nectocalyces opposite in pairs. Cormidia without bracts. Gonophores reach maturity while attached to the stem ; no free eudoxids or ersaeids. Hiylpopodius Q. and G.; Polijphyes H. ; Vogtia Kolliker. Section 2. PHYSONECTAE. PHYSOPHORA. -Pa 1 Siplionanthae /rifh a pneumatocyst and several nectocalyces (or bracts instead), and pal- pom. Cormidia oi-ilinatt' or irregular. The Physonectae include monogastric and polygastric forms. The stem carrying the cormidia is either short, sometimes spread out in the form of a sac (Fig. 125), or elongated and spirally twisted (Fig. 126). The small, often brightly coloured apical pneurnato- phore is without a terminal opening of the pneumato- cyst, though sometimes an opening near its base may be made out. The endo- dermal space of the pneu- matophore itself is usually divided by a number of radial septa into pouches, while the invaginated pneu- ruatocyst is divided into two communicating parts h /^ J k \ an iipper part with a J \\^ 4 J ( chitinous lining, and a lower part with a thick glandular lining. The latter is called the air funnel. It is the gas gland and its lining secretes the gas of the pneumatocyst. The nec- tocalyces (except when replaced by paddling bracts with rudimentary FIG. 125. Physophom Jiydrostatita. Pn pneumato- phore ; S nectocalyces arranged in a double row on the stem ; T palpon ; P siphon with tentacles Sf; Nl; groups of nematocysts (cnidosacs) ; G clusters of gonophores. PHYSONECTAE. nectocalyces at their ends) are usually numerous. They have four radial canals, a circular canal, a velum, and sometimes ocelli. The cormidia are rarely dissolved : i.e., the parts are rarely scattered along the stem, but gener- ally ordinate, i.e., in groups (Fig. 126). Each cormi- dium consists of one siphon (sometimes two or four) with tentacle ; several pal- pons each with a tentacle called a palpacle ; several bracts which may even in the forms with ordinate cormidia occur in the in- ternodes of the stem (Fig. 126); two gonostyles, one bearing male gonophores and the other female, and very often a cyston. A cyston is a structure like a palpon but Avith a ter- minal opening : it acts as an anus to the colony, ex- pelling fluid and crystalline excretions through its aper- ture. The batteries of the tentilla of the tentacles are enveloped in an invo- lucruni or fold of ectoderm arising at their proximal end. The female gono- phore produces only one egg- Pn FIG. 126. Halistemma tergestinum. Pn pneumatophore ; S nectocalyx ; P siphon ; D hydrophyllium ; A r fc group of nematocysts on tentacles. 152 COELENTERATA. The planula develops at one pole a pneumatocyst as a thickening and involu- tion of ectoderm (like the entocodon of a medusa bud), and at the other a siphon (Fig. 127 d). The pneumatocyst is supposed by Chun to lie homologous with the primary nectocalyx of the Calyconectae. In some forms the upper part of the body gives rise to a cap-shaped hydrophyllium as well as to a pneumatophore (Fig. 127). The crown of hydrophyllia which is sometimes formed persists only in Athorybia, where nectocalyces are not formed. In Agcdmopsis and Physo- plwra the primary hydrophyllia of the larva (Fig. 128) fall off as the stem becomes larger, and are replaced by nectocalyces. d FIG. 127. Development of Agalmopsis Sarsii (after Metschnikoff ). n, planula ; ft, stage with developing hydrophyllium D; c, stage with cap-shaped hydrophyllium (Z))and developing pneumatocyst Lf; d, stage with three hydrophyllia (D, D', D"), siphon P and tentacle; Lf pneumatocyst. Fam. 1. Circalidae. Monogastric Physoncctae with a corona of nectocalyces, without bracts. Circalia H. Fani. 2. Athoridae. Monogastric Physonectac with a corona of bracts, without nectocalyces. Atlwria H. ; Athoralia H. Fam. 3. Apolemidae. Polygastric Physoncctae with a long tubular stem bearing numerous siphons, palpons, and bracts ; each siphon with unbranched tentacle. Nectocalyces biserial ; either two opposite nectocalyces, or two alter- nate series of opposite nectocalyces. Pneumatophore without radial pouches. Nectocalyces with tentacles arising from the stem. Sub-fam. 1. Dicymbidae. Two opposite nectocalyces only. Cormidia monogastric ; each with a single cyston. Dicymba H. Sub-fam. 2. Apolemopsidae. Two opposite rows of nectocalyces. Cor- midia polygastric ; each with several cystons. Apolemia Esch. ; Apolemopsis Brandt. AURONECTAE. 153 Fam. 4. Agalmidae. Polygastric Physonectac with a long tubular stem, bearing numerous siphons, palpons, and bracts. Nectocalyces numerous, biserial. Pneumatopliore with radial pouches. All the genera except four, viz., Stephanomia Per. and Les., Crystallodes H., Anthenwdes H., Cuneoluria Eysenhardt, have dissolved cormidia. Phyllophysa L. Ag. ; Agalma Esch. : ffalistemma Huxley (Fig. 126) ; Cupulita Q. and G. ; Agalmopsis Sars (Fig. 128) ; Lychnagalma H. Fam. 5. Forskalidae. Polygastric, with a long tubular stem bearing numerous siphons, palpons, bracts ; each siphon with a- branched ten- tacle. Nectocalyces numerous ; multiserial, strobilifonn in several spiral rows. Pneumatopliore with radial pouches. The largest and most splendid of all Physomctae. Cormidia dissolved in all except Strobalia H. Forskaliopsis H. has palpacles among the nematocalyces. Forskalia KiJlliker ; Bathyphysa Studer. Fam. 6. Nectalidae. Polygas- tric, with a short vesicular stem, bearing numerous siphons, palpons, and bracts ; tentacles branched. 2 or 4 rows of nectocalyces. Pneu- matopliore with radial pouches. Nectalia H. ; Sphyrophysa L. Ag. Fam. 7. Discolabidae. Like the preceding but with a corona of palpons instead of bracts ; with- out bracts. Physophora Forskal, biserial nectocalyces (Fig. 125) ; Discolabe Esch., quadriserial necto- calyces ; Stephanospira Gegenbaur, multiserial nectocalyces. Fam. 8. Anthophysidae. Poly- gastric, with short vesicular stem bearing numerous siphons and pal- pons ; each siphon with a branched tentacle. Nectocalyces replaced by corona of bracts (as in Fig. 128). Pneumatopliore with radial pouches. Rhodophysa Blaiuville ; Melophysa, H. Ploeophysa Fewkes. NK FIG. 128. Small larval colony of Agalmop&is after the type of Alhorybia. Lf pneumatophore ; D the crown of hydrophyllia ; Xk groups of nema- tocysts ; P siphon. ; Athorybia Esch.; Anthophysa Mertens ; Section 3. AURONECTAE. Siplionantliae idth a, large pneumatoplwre, a corona of nectocalyces, a peculiar auropJwre, and a network of canals in the jelly of the thickened trunk. Siplwsome spheroidal, ovate, or turnip-shaped. Deep sea forms. The aurophore (Fig. 129) is an appendage of 154 COELENTERATA. the pneumatocyst, and contains a central tube putting the cavity of the pneumatocyst in communication with the exterior. It is placed on one side of the pneumatophore, and its central tube (pistillum) is surrounded by a number of radial chambers, which are separated by septa and communicate with the pericystic (endo- dermal) space of the pneumatophore. Very possibly the aurophore is a gas-secreting gland. Fain. 1. Stephalidae. Stcplialia H. ; Stcplionalia H. Fam. 2. Rhodalidae. Auralia H. ; Rhodalia H. a A-ph Fir;. 120. Stephalia corona (after Haeckel). a, side view ; b, section. Aph Aurophore ; Sg corona of nectocalyces ; P siphons with their tentacles ; CP the large central siphon, the enteron of which forms the central tube of the siphosome (coenosome or stem). Section 4. CYSTONECTAE. PHYSALIDAE. Siphonantliae with a large apical pneumatophore without necto- calyces and without bracts. Pneumatocyst with an apical stiijma. This order includes Physalia, the well-known Portuguese Man of War, which we may take as type. Physalia possesses a large pneumatophore lying nearly horizontally and bearing posteriorly and ventrally the numerous siphons, palpons, and branched gonostyles. The stigma is at the front end of the pneumatophore, and leads into a large pneumatocyst. The pericystic cavity is simple and not divided. The air-secreting cells or pneu- CYSTONECTAB. 155 iiiaouches. Umbrella highly vaulted. The Scyphomedusae are best considered in their relation to the Scyphistoma. They may be looked upon as Scyphistomas deprived of their tentacles, which indeed are only transi- tory structures, and elongated so as to assume the form of a cup, and changed in several par- ticulars which are characteristic The four septa (Fig. 98) arise by the fusion of the four gastric folds with the wide oral disc, which becomes drawn in and concave like a sub-umbrella. These four septa separate the same number of gastrovascular pouches ; while the margin of the cup may be drawn out into eight arm-like processes from which groups of short, knobbed tentacles arise (Fig. 134). The genital organs extend on the oral Avail of the umbrella into the arms as eight band-shaped, plicated ridges (Fig. 134, /.). They run along in pairs at the lower part of each septum in the gastric FIG. F132. g, fully formed strobila with sepa- rating ephyrae; h, free ephyra (1-5 to 2 mm. in diameter). of the medusa stage. STAUROMEDUSAE. 163 cavity (Fig. 98). The ovum, according to Fol, undergoes a complete segmentation, which results in a single-layered blastosphere. This becomes an oval, two-layered larva, which becomes ciliated, swims freely about, and finally attaches itself. The further development probably takes place directly without alternation of generations. The Scypliomeclusae, are without exception marine animals, and are remarkable for their great reproductive power. According to A. Meyer, if the stalk of Lucernaria be cut off, the cup reproduces a new one, and injured individuals, and even excised pieces, can become perfect animals. Gf SK FIG. 133. Tessera princcps (after Haeckel). a, external view magnified about 20 times ; 6, longitudinal section through two perradii ; c, view of sub-umbrella. Gf gastral filaments ; G gonads ; Km circular muscle ; Sk septal unions. Sub-order 1. STAUROMEDUSAE. Without rhopalia, but in their place 8 simple principal tentacles (Fig. 133) or marginal anchors (Fig. 134). Stomach with 4 wide perradial pouches con- nected peripherally by a ring-canal. Gonads as 4 interradial horse-shoe shaped thickenings (Fig. 133), or 4 pairs of adradial ridges in the ventral walls of the gastric pouches (Fig. 134). 164 COELENTBRATA. Fani. 1. Tesseridae. Umbrella edge without lobes ; 8 principal tentacles (4 perradial and 4 interradial) ; marginal anchors absent. Apex of the ex- umbrella surface prolonged into a hollow process or stalk for attachment. Tessera H. (Fig. 133) and Tcsserantha H., with hollow, ex-umbrella process not used for attachment; Depastrella H., Depastrum H., with ex-umbrella stalk for attachment. Fio. ISi.Halidystus auricula (from Chun, after Clark). I. From the side. II. From the oral face. III. From the side with evaginated umbrella and protruded mouth. IV. Marginal anchor from the axial side, p stalk ; SH sub-unibrella ; t one of the eight tufts of knobbed tentacles on the eight hollow triangular marginal lobes ; ra one of the eight marginal anchors; t ' anchor tentacle ; W collar of adhesive glandular ectoderm ; oc eye-spot; en vessel of marginal anchor; o mouth; sc interradial septal ridge passing into the taenioles (/() of the stalk ; gen one of the eight adradial gonads on the sub-unibrella wall of the four radial gastric pouches, representing four iuterradial horse-shoe gonads connected at the oral end of the septal ridge. Fam. 2. Lucernaridae. With 8 adradial umbrella lobes, and tufts of short knobbed tentacles at end of each lobe. With 8 principal tentacles (4 per- and 4 interradial) as marginal anchors (Fig. 134), or absent. An ex-umbrella stalk for attachment. Haliclystus Clark, Halicyathus Clark, with marginal anchors ; Lucernaria 0. F. Mtiller, Cratcroloplms Clark, without marginal anchors. PEROMEDUSAE. 165 Sub-order 2. PEROMEDUSAE. With 4 interradial rliopalia (with otoliths and eyes) ; with 4 perradial tentacles, or with 12 tentacles (4 per* and 8 adradial, Fig. 135); with 8 or 16 marginal lobes. The 4 radial gastral pouches are separated from one another by very short septal-unions or septa, so that the stomach may be said to be surrounded by a wide circular sinus, communicating with it by 4 ostia (Fig. 99). The circular sinus gives off towards the periphery of the umbrella 8 or 16 flat pockets, eacli of which gives off two lobe -pockets, and between these one pocket to a tentacle or sense - body. 4 horse - shoe shaped gonads in the ventral wall of the circular sinus. Pio. ISB.Periphylla hyadnthina (after Haeckel). Rf annular groove dividing the umbrella into a proximal conical part, and a ventral lobed region. FIG. 130. Charybdea marmpialis, natural size. T tentacles ; Rk marginal bodies > Ov gonads. Fam. 3. Pericolpidae. With 4 perradial tentacles, 4 interradial rhopalia, and 8 adradial marginal lobes. Pericolpa H. ; Pcricrypta H. Fain. 4. Periphyllidae. 12 tentacles, 4 rhopalia, 16 marginal lobes. Pcripalma H.; Periphylla H. (Fig. 135). 166 COELEXTERATA. Sub-order 3. CUBOMEDUSAE (Marsupialida}. FIG. 137. The apical half of aCharybdea divided transversely, seen from the sub-umbrella side. The four oral arms are visible. Oe ovaries on the four septa ; Ost ostia of the gastric pouches ; Gf gastric filaments ; S septa. With quadrangular umbrella (Fig. 136), 4 perradial rhopalia (with otoliths and eyes), 4 interradial marginal tentacles, 4 perradial gastric pouches, separated by long and narrow interradial septa. Gonada as 4 pairs of broad plates fastened by one edge to the radial septa (Fig. 137), and projecting into the pouches. With a smooth - edged velarium containing pro- longations of the gastrovascular system. With a nerve ring on the sub -umbrella side of the edge of the bell, having a zig- zag course. Fam. 5. Charybdeidae. Procharagma H.; Procharybdis H. ; Charybdca Per. and Les. ; Tamoya F. Miiller. Fam. 6. Chirodropidae. C'hiropsalmus L. Ag. ; Chirodropus H. Order 2. EPHYRONINAE. OCTOMERALIA. DISCOMEDUSAE. Acalephae with 8 or more rhopalia (sense tentacles) (4 per- and 4 interradial, and often several accessory}. Stomach with 8, 16, 32, or more radial pockets or canals. Gonads sub-gastral (in ventral wall of central stomach). Umbrella flat, generally discoidal. Larval form Ephyra. The Ephyroninae can at once be distinguished from the Scypho- medusae by the discoidal lobed umbrella, and usually by the large size of the oral tentacles. The lobes of the umbrella, however much they may differ in detail, can always be reduced to the eight pairs of lobes of the Ephyra (Fig. 131), which, as the promorph of the Ephyroninae, presents most clearly the 8-rayed symmetry character- istic of the group. The gonads have the form of horse-shoe shaped frills (Fig. 130), and project into the widely open subgenital pits. The germinal epithelium, which is always embedded in the gelatinous substance of the umbrella, is covered with an endodermal layer. Development takes place by alternation of generations. In rare cases (Pelagia) the development is simplified, and the larva passes directly into the Ephyra, missing out the attached Scyphistoma and Strobila stage. The gastrovascular system may be pouch-like or canalicular. In Aurelia (Fig. 130), in which it is canalicular, the eight primary radial canals (i.e., the four perradial and four interradial) are branched, while CANNOSTOMAE SEMOSTOMAE RHIZOSTOMAE. 167 the eight secondary radial canals (adradial) are unbranched. The parts of the stomach from which the eight adradial and the four interradial canals arise are pouched outwards. Sub-order 1. CANNOSTOMAE. With simple quadrangular manubrium without oral arms ; with short solid marginal tentacles. Fam. 7. Ephyridae. Usually 16 wide gastric pouches, rarely 32-64, without terminal branches ; usually 8 rhopalia, rarely 16-32 ; usually 16, rarely 32-64 marginal lobes. This family may be described as consisting of sexually mature Ephyrae. Ephyra, Per. and Les. ; Palcphyra H. ; Zoncphyra H.; Nausicaa H. ; Nausithoe Kolliker ; Nauplianta H. ; Atolla H. ; C'ollnsjris H. Fam. 8. Linergidae. With wide radial gastric pouches, and branched, blind lobe-canals ; without circular canal. Linantha H. ; Linerges H. ; Liniscus H. ; Linuche Esch. Sub-order 2. SEMOSTOMAE. With 4 large perradial oral arms, and with long hollow tentacles. Fam. 9. Pelagidae. Scmostomae with 16 simple wide gastric pouches, without branched distal canals, without circular canal. Pelagia Per. and Les., with 8 adradial tentacles, 8 rhopalia, and 16 marginal lobes ; Chrysaora Per. and Les., with 24 tentacles (and 8 rhopalia), and 32 marginal lobes; Dncty- lomctra L. Ag. Fam. 10. Cyaneidae. Scmostomae with 16 or 32 wide gastral pouches, and branched, blind lobe-canals, without circular canal. 16-32 or more marginal lobes ; 8 or 16 rhopalia (4 per-, 4 inter-, and 8 adradial) ; 8 or more long hollow tentacles. Procyanea H.; Medora Couthouy ; Stenoptycha L. Ag. ; Desmonema L. Ag. ; C'yanea Per. and Les. ; Patera Lesson ; Melusina H. Fam. 11. Flosculidae. Semostomac with 16 or more simple unbranched narrow radial canals and with a circular canal. 8 rhopalia ; 8-24 or more long hollow tentacles. Flosculct H.; Floresca H. Fam. 12. Ulmaridae. Scmostomae with 16 or more narrow radial canals, which branch and often anastomose, and are connected by a circular canal. 8 or 16 rhopalia; 8-24 or more hollow tentacles. Ulmaris H.; Umbrosa H. ; Undosa H. ; Sthcnonia Esch. ; Phacellophora Brandt ; Aurelia Per. and Les. ; Aurosa H. Sub-order 3. RHIZOSTOMAE.* With 8 large adradial, root-like, simple or branched, oral arms, with numerous suctorial mouths, without central mouth opening, and without marginal tentacles. Fam. 13. Toreumidae. Rhizostomae with 4 separated subgenital pits, and with ventral suctorial frills on the 8 oral arms (no dorsal frills). 8, 12, or 16 rhopalia ; 8-16 or more narrow radial canals, branched and anastomosing. Archirhiza H. ; Torcuma H. ; Polydonia L. Ag. ; Cassiopea Per. and Les.; Cephea Per. and Les. ; Polyrhiza L. Ag. Fam. 14. Pilemidae. Rhizostomae with 4 separated subgenital pits, and with dorsal as well as ventral sucking frills on the 8 oral arms. 8 rhopalia ; 8-16 or more branched and anastomosing radial canals, with circular canal. * The forms commonly called by the generic name Rhizostoma belong to the genus Pilema. The term Rhizostomae is kept for the sub-order. 168 COELEXTERATA. Toxochjtus L. Ag. ; Lyclmorliiza H. ; Phyllorhiza L. Ag. ; Eupilcma H. ; Pilema H. ; Rhopilema H. ; Brachiolophus H. ; Stomolophus L. Ag. Fam. 15. Versuridae. Rhizostomae with a single central subgenital portions (i.e., subgenital pits united), with ventral suctorial oral frills only. 8 rhopalia; 8-16 or more narrow, branched, anastomosing, radial canals. Haplorliiza H. ; Cannorhiza H. ; Versura H. ; Crossostoma L. Ag.; Cotylorhiza L. Ag. ; Stylo- rhiza H. Fam. 16. Crambessidae. Rhizostomae with a single central subgenital portions, oral arms with dorsal and ventral frills. 8 rhopalia ; 8-16 or more anastomosing radial canals ; usually a circular canal. G'rambessa H. ; Mastigias L. Ag.; Eucrambessa H. ; Thysanostoma, L. Ag. ; Himantostoma L. Ag. ; Lcpto- brach-ia Brandt ; Leonura H. Class III. ACTINOZOA* (ANTHOZOA). Polyps colonial or solitary, -iritJi oesopliageal tube, mesenteric folds, and endodermal yonads. A medu- soid sexual generation is unknown. The polyp of the Adinozoa has already been described (p. 102). It differs from that of the Hydro- medusae in being larger, in having a greater muscular development, a better developed structureless la- mella or jelly which often contains muscular and skeletal elements. The development of this jelly, which has a tough, dense character, is, in the colonial forms, greater in the lower parts of the polyps than in the upper, the result of which is the formation of the branched or massive coenenchyme (Fig. 138), from the surface of Avhich the free ends of the polyps project. A calcareous skeleton is very generally present, but its form and method <>f formation vary in the different groups. The mesenteries and tentacles vary much in number. In the Alcyonaria there are always eight; in the Zoantharia, in which there are primary and secondary mesenteries, the number is sometimes six * Ehrenberg, " Beitriige zur physiologischen Kenntniss der Korallenthiere im Allgemeinen u. besonders des rotten Meeres, etc," Abhand. d. Berliner Akad., 1832. Ch. Darwin, The Structure and Distribution of Coral Reefs, London, 1842. J. D. Dana, United States Expl. Expedition, Zoophytes, Philadelphia, 1846. M. Edwards and J. Haime, Histoirc Naturelle des Coraillaires, 3 vols. , Paris, 1857-60. Lacaze Duthiers, Histoire Naturelle du Corail, Paris, 1864. FIG. 138. Branch of a polyparium of Coralliam rubrum (after Lacaze Du- thiers). P polyp. ACTINOZOA. 169 or some multiple of six ; but it may be different : indeed, the greatest variety is found in this character in the order Zoantharia. The gonads are produced on the mesenteries (Fig. 91), and the embryos sometimes undergo the early stages of development within the parent. Asexual reproduction by budding and fission is of great importance. Buds can be formed in various positions, even at the oral end, in which case a strobila-like form appears. In Blastotroclms the buds appear at right angles to the axis of the parent (Fig. 139). In Gonadinia prolifera the polyp divides transversely, a new set of tentacles arising on the lower half (Fig. 139). In some cases a portion of the basal expansion is separated off by contraction of the body, and develops into a new polyp. This is called laceration. FIG. \39.-Blastotroclius nutrix (after C. Sem- per). LK lateral bud. Pro. 139a. Two stages of transverse fission of Gonactinia in-nlifera, Sars (after Blochman and Hilger). If the individuals so produced remain connected with one another, a polyp-colony is formed, which may attain very various forms and great size. As a rule the individuals are embedded in a common body mass, the coenenchyme* and their gastric cavities communicate more or less directly, so that the juices acquired by the individual polyps penetrate through the whole stock. This stock affords us an excellent example of an animal community built up out of similar members. The formation of the generative products alone is some- times confined to special polyps, which, however, discharge all other functions of polyp life. The skeletal formations of the polyps are specially noteworthy. In almost every case, with the exception of Actinia, there is a deposit of solid calcareous matter, and according to the density of this deposit, there is produced a leathery, chalky, or even stony framework. * This word is used in a different sense in the Madreporaria, which see. 170 COELENTERATA. If the skeleton has the form of isolated needles or toothed rods (Fig. 140) of calcareous substance deposited in the jelly of the coenenchyma (or polyp), the polyp-stock has a fleshy, leathery nature (Alcyonarid) ; but if, on the contrary, the calcareous structures are fused or cemented together, a solid, more or less firm, calcareous skeleton is de- veloped (Corallium, Tubipora)'. Finally, the skeleton may be of a stony character and secreted by the ectoderm of the lower part of the polyp (Madre- poraria). The important diversities of form in the polyp-stocks are not only occasioned by the differences of structure of the skeleton of the polyp, but are also the resultant of varying Fio. 140. -Calcareous bodies (Sclerodermites) of methods of growth by gem- AJcyonaria (after Kolliker). a, of Plexaurella ; ma ti ll and imperfect fission. 6, of Gorgonia ; c, of Alcyoniitm. According to the method, nu- merous modifications of branched stocks are distinguished, e.g., Madrepores (Fig. 141), Ocu- linidae (Fig. 142), and the lamellar and massive stocks as Astraea (Fig. 143) and the Maeandri- nidae (Fig. 144). The Antliozoa are all inhabitants of the sea, and live mostly in the warmer zones, but certain types of the fleshy Octactinia and Actinia are distributed in all latitudes. Some genera of the Madreporaria are FlG.Ul.-Madreporaverru- found ill the deep Sea, where they may form accu- mulations of considerable extent, but the polyps which take the Ed. H.). ACTINOZOA. 171 principal share in the formation of coral reefs live near the surface, being rarely found alive at a greater depth than 40 fathoms. They are confined to a zone extending about 28 degrees on either side of the equator, and only here and there extend beyond these bounds. Their calcareous skeletons, together with those of mille- Fio. 143. Astraea (Goniastmca) pcctinatn Ehrbg. (after Klunzinger). Fio. 144. Macant.li-iii/>lit/- ton ; it is absent in the autozooids of Pennatulacea, Heteroxenia, and Para- (/orf/ia, but present in the siphono- zooids, in which it is always specially developed. The Pennatulacea are phosphorescent. The enteric cavities of the polyps are connected with the fine canal- system of the coenenchyma, when such exists, and are continued as main canals for a longer or shorter distance towards the base of the colony. In the Stolonifera they all, of course, open into the basal stolon. Development. The ova develop inside (as far as the planula) and outside the parent. They have yolk, and the segmentation is on the centro-lecithal type, and is often delayed until the nucleus has under- gone many divisions. There is usually a free-swimming planula-larva. Extinct forms.f The genera Heliolites (palaeozoic) and Poly- tremacis (chalk, greensand, eocene) were probably Helioporidae, and * This is a special use of the term ventral, and does not imply any homology with the ventral surface of bilateral animals. t K. A. Zittel, Handbuch der Palacontologie, Bd. 1, p. 208. Munich and Leipzig, 1876-80. N FIG. 146. Transverse section through Alcyonium (after Hertwig). R goni- dial groove ; 1, 2, 3, U, the four pairs of septa with their muscles. 178 COELENTERATA. Heliopora itself is found in the cretaceous formation. Syringopora (Silurian, Devonian, Carboniferous) was probably allied to Tubijiom. The Favositidae were probably Alcyonarian. Sub-order 1. PROTOALCYONARIA. Polyps solitary ; with or without spicules. Fam. 1. Haimeidae. Haiinca M. Edw. ; Hartea P. Wright ; Monoxenia H. Sub-order 2. STOLONIFERA. Colonial Alcyonaria with a membranous or ribbon-like stolon. Jelly poorly developed. Polyps either entirely free from one another except at their bases, or connected by horizontal platforms (Tubipora) or connecting tubes (Clavularia viridis}. Skeleton absent, or composed of calcareous spicules which may be joined together or be isolated. In some cases the body-wall is supported by a horny secretion. Fam. 2. Cornularidae. Polyps are not united in bundles, but either spring from a plate-like expansion or a creeping stolon ; or are branched and bear lateral buds. Cornularia Lam., no spicules, horny secretion on polyp-walls and stolon ; Wiizoxenia Ehrb. ; Clavularia Q. and G. ; Sarcodictyon Forbes ; Anthelia Savigny ; Gymnosarca S. Kent ; Cornulariclla Verrill ; Telesto Lamouroux, polyps rise from a flat base, or from stolons, and bear buds ; Coelogorgia M. Edwards, colony arborescent, an axial polyp with buds ; CyatTiopodium Verrill, stolons calcined connecting the short cup-shaped polyps ; Sclcranthelia Studer ; Anthopodium Verrill ; Sympoclium Ehrb. ; Stereosoma Hickson, with spicules, with non-contractile polyps and tentacles, with a horny layer between the ectoderm and supporting lamella ; Erythropodium Roll.; Callipodium Verr. ; Pseudogorgia Koll., axial polyp with lateral polyps budded from the upper part. Fam. 3. Tubiporidae. Colonies consist of tubular polyps parallel to one another, and united by horizontal platforms containing endodermal canals (Fig. 145, 6'). The platforms are formed as outgrowths of the lips of the polyps, into which prolongations of the enteric cavity pass to form the endodermal canals ; they are at first without or with only a few spicnles. The platforms and the greater part of the walls of the polyp-tubes contain a skeleton formed of coalesced spicules, so that the dry corallum has the form of parallel tabes united by lamellae. The first layer of platforms constitutes the plate-like stolon of origin. The tubes are divided at intervals by partitions called tabulae which may be funnel-shaped. Tubipora L., the organ-pipe coral. Sub-order 3. ALCYONACEA. Colonial Alcyonaria with a well-developed canaliferous coenenchyma and loose Kpicules. Without axial skeletal rod. The buds are formed from the coenenchymal canals (Fig. 145, Z>). Fam. 4. Xeniidae. Colonies of long polyps, united in their lower portion by a canal system, ramifying in a connecting coenenchyma with feebly calcareous spicules. Xenia (Heteroxenia Koll.) Savigny. Fain. 5. Organidae. Elongated polyps united together so as to form a short upright stem. Polyps and tentacles provided with spicules. Organidus Danielssen. Fam. Q. Alcyonidae. Massive coenenchyma containing the polyp tubes, which are united by endodermal canals from which the buds are formed. Isolated spicules in the jelly of the coenenchyma. Cry stall ophancs Dan.; PENNATULACEA. 179 Bellonclla Gray ; Nidalia Gray ; Paralcyonium M. Ed\v. ; Sarakka Dan. ; Alcyonium L., A. diyitatum, dead men's fingers; Lobularia Savigny ; Sarco- phyton Lesson, with dimorphic polyps ; Lobophytum Marenzeller, with dimorphic polyps ; Anthomastus Verr., dimor- phic polyps ; Nannodendron Dan., dimorphic polyps. Fam. 7. Nephthyidae. A branched coenenchyma with sterile Lase and terminal polyps. The latter do not exhibit separate calycine and ten- tacular regions, and there is no in- vagination of the latter ; when at rest tentacles folded over oral disc. Buds arise from fine endodermal canals between the polyps. Vocrin- cjin Dan.; Fulla Dan.; Barathrobius Dan. ; Gersemia Marenzeller ; Ger- semiopsis Dan.; Drifa Dan.; Duva Ivor, and Dan.; Euncphthya Verr.; Ammothea Sav. ; Ncphthya Sav. ; Spongodes Lesson ; Paranephfhya Wright and Studer ; Sderoncphthya "Wi. and St. ; Chironephthya AVr. and St.; Siphonogorgia Ki.il 1. Fam. 8. Helioporidae.* Compact corallum formed in the jelly of the coenenchyma. The corallum is tra- versed by tubes closed above, called coenenchymal tubes (possibly modi- fied siphonozooids), and by tubes continued from the polyp calycles. Both systems of tubes are divided by tabulae and are united by endo- dermal canals in the superficial coenenchyma. False septa formed by denticulations of the margins of the calycles. Heliopora, Blainville. Sub-order 4. PENNATULACEA.f Unattached polyp colonies with a stalk embedded in mud or sand, and a r/tchis bearing polyps. The stalk generally has an axial rod. The stalk is without polyps and is embedded in mud or sand. The rachis is a continuation of the stalk and carries the polyps, which are arranged FIG. 147. Kophdbelemnon Lc-uclMrtii. * H. N. Moseley, "The Structure and Relations of the Alcyonarian Heliopora Coerulea," Phil. Trans., 1876. t A. Kolliker, Anat.-syst. Bcschrcib. d. Alcyonaricn Alt. 1. Die Pennatuliden, Frankfurt-a-M., 1872. A. Kolliker, "Report on the Pennatulidae," Challenger Reports, 1880. 180 COBLENTERATA. upon it in different ways. In Vcrctillum they are distributed all round the rachis ; in Kophobelemnon (Fig. 147) they are absent on a streak of one side the so-called ventral side ; in most genera they are arranged bilaterally, there being a dorsal as well as a ventral streak free from them. Further, in some genera they are sessile on the rachis, but in the Pcnnatulca, or Sea-Feathers proper, the polyps are borne only on lateral processes of the coenenchyma, called the pinnules. The pinnules are broad triangular leaf-shaped structures attached by their base to the rachis and carrying the polyps on their dorsal edges (Fig. 148). The polyp-tubes project in some cases to form the so-called cells; the cells may have spines or tufts of spicules. The polyps are dimorphic ; the autozooids have tentacles and generative organs, and are without a gonidial groove ; the siphonozooids possess a gonidial groove but are without tentacles and gonads, also they have filaments on the two dorsal mesenteries only. The siphono- zooids are distributed over the whole rachis in Rcnilla and Vere- tillum ; and in the Pennatulea they are on the rachis or on the pinnules. The stalk generally contains an axial calcareous or horny rod sur- rounded by a sheath of epithelial cells ; and the coenenchyma and bodies of the polyps may contain isolated spicules. The polyps are continued into tubes which join the canal system of the coenen- chyma. This canal-system con- sists of large canals continued down from the polyps and open- ing after a longer or shorter course into a few "main canals," which run in the stalk. There are generally four of the latter (two in Rcnilla), of which two are lateral, one dorsal, and one ventral. At the lower end of the stalk the lateral canals cease, leaving only the dorsal and ventral. They fuse at the end of the stalk and are said to open there. In addition to the large canals there are minute canals uniting them. Some of the polyps are closed below, and open at their base by narrow openings into the general canal system of the colony. The Pennatulacea are not distributed uniformly over all seas. They are mainly littoral, but deep water forms are known, and these, it is important to notice, belong principally to the simpler families, e.g., the Protoptilidac and UmbcHulidae. They appear to be absent, or nearly so, in the deeper parts of the Pacific and Atlantic Oceans and the South Polar Sea at a certain distance from the shore. Section 1. Pennatulea. The Sea- feathers. With pinnules ; rachis with a bilateral arrangement of the polyps, elongated, cylindrical. B FIG. 148.Pennatida Sulcata Roll, (after Kolliker). A, from the dorsal ; B, from the ventral side. GORGONACBA. 181 Fain. 1. Pteroeididae. Pinnules well developed, with siphonozooids on the pinnules. Plcroeitfi'H Herklot ; Godcfroyia Koll. ; Sarcophyllum Koll. Fam. 2. Pennatulidae. Pinnules well developed ; siphonozooida on the ventral and lateral sides of the rachis. Pennatula Lam. ; Lcioptihim Verr. : Ptilosarcns Gray ; HaHsceptrum Herklot. Fain. 3. Virgularidae. Pinnules small, without a calcareous plate. Virgu- laricv Lam. ; Scytalium Herkl. ; Pavonaria Koll. Fam. 4. Stylatulidae. Pinnules small, with a calcareous plate. Styhitn/" Yerr. ; Dubcnia Kor. and Dan. ; Acomthoptilum Koll. Section 2. Spicata. Rachis elongated, cylindrical, with a bilateral arrangement of the polyps ; without pinnules ; polyps sessile. Fam. 5. Funiculinidae. Polyps on both sides of the rachis in distinct rows, with cells ; ventral siphonozooids absent. Funiculina Lamarck ; Halipteris Koll. Fam. 6. Stachyptilidae. Polyps (with cells) on both sides of the rachis in distinct rows. Ventral siphonozooids present. Stachyptilum Kiill. Fam. 7. Anthoptilidae. Polyps on both sides of the rachis in distinct rows, without cells. Anthoptilum Koll. Fam. 8. Kophobelemnonidae (Fig. 147). Polyps on both sides of the rachis in a single series, or in indistinct rows, large and without cells ; rachis elongated, cylindrical ; ventral streak of rachis without polyps. Kophobelemnon Asbjornsen, SclcrobelcmnoH Koll.; Batliyptilum Kiill. Fam. 9. TJmbellulidae. Polyps on both sides of the rachis in a single series, or in indistinct rows, large and without cells ; rachis short (i.e., the polyps are placed at the end of the central stem). Umbellula Lam. Fam. 10. Protocaulidae. Polyps on both sides of the rachis in a single series, or in indistinct rows, small and without cells. Protocaulon Koll ; Cladiscus Kor. and Dan. Fam. 11. Protoptilidae. Polyps on both sides of the rachis in a single series or in indistinct rows, with cells. Protoptilum Koll. ; I/ygomorpha Kor. and Dan.; Microptilum Koll.; Leptoptilum Koll.; Trichoptilum Koll.; Scleroptilum Koll. Section 3. Eenillea. Rachis expanded in the form of a leaf, with bilateral arrangement of the polyps on one side of the expansion ; without pinnules. A single large siphono- zooid (exhalent zooid) terminates the end of the central stem. Fam. 12. Eenillidae. Renilla Lam. Section 4. Veretillea. Club-shaped colonies, without pinnules. Polyps arranged all round the rachis. Fam. 13. Cavernularidae. Spicules long. Cavernularia Valenciennes ; StyTobclcmnon Koll. Fam. 14. Lituaridae. Spicules short. Lituaria Val. ; Verctillum Cuv.; Policclla Gray ; ClaveUa Gray. Sub-order 5. GORGONACEA. Fixed colonial Alcyonaria with a horny or calcareous axial rod, wliicli is covered by a coenenchyma from ivldcli the polyps arise. 182 COELENTERATA. Section 1. Scleraxonia (Pseudaxonia). Fixed upright branched colonies. The coenenchyma consists of a caualiferons cortical layer (with spicules) in which the polyps are placed, and of a medullary substance. The latter contains spicules (different in form from the cortical spicules) which are generally tightly packed, and sometimes fastened together by a horny substance, or cemented into a strong axis by calcareous matter. Without epithelial layer round the central rod. Fam. 1. Briareidae. Coeneuchyma consists of a polyp-bearing cortex and a medullary substance of closely packed spicules. These are either developed on the surface of an upright shrubby colony, or the medullary substance is relegated to the interior of a cylindrical stem, over which is spread the cortex. In tin- latter case there is a more or less well-defined axis, which may be permeated by nutritive canals. LeucocJJa (tray ; Solenocaulon Gray ; Semperina Kiill. ; Sul< ria Studer ; AnthothelaVerr.; Paragorgia M. -Edw. ; Briareum Blainville ; Tituni- deum Ag. ; Iciligorgia Ridley ; Spongioderma Ko'll. Fam. 2. Sclerogorgidae. An axis consisting of closely intercalated elongated spicules with dense horny sheaths. The axis is surrounded by longitudinal canals, into which there open the reticulated coenenchymatous canals, uniting the polyps. Suberogorgia Gray ; Keroeidcs Wr. and St. Fam. 3. Melitodidae. Axis jointed, consisting of alternate portions of cal- careous and soft horny substance. Melitodes Yerr. ; Mopsella Gray ; Acabaria Gray; Psilricubariu Ridley; Wriyhtdla Gray; Clittlirnria Gray; Parisis Verr. Fam. 4. Corallidae. Axis of a dense calcareous mass of fused spicules ; polyps dimorphic ; the siphonozooids are said to grow into autozooids. Corallium Lam.; 0. rubrum, the red coral (Fig. 138) ; Pleurocorallium Gray. Section 2. Holaxonia (Axifera) Coenenchyma branched or simple, with cortical canaliferous layer and axial rod, which is either horny, or of calcified horn, or of alternating joints of calcareous matter and horn. Axial rod derived from a layer of ectoderm cells invaginated at the base of the colony, and surrounding it as an epithelium (Fig. 145). Fam. 5. Dasygorgidae. Simple or branched, coenenchyma thin, polyps large ; both polyps and coenenchyma contain spicules. When at rest the tentacles are folded over the oral disc. Strophogorgia Wright ; Chrysogorgia Duch. and Mich. ; Heropliila Steenstrup ; Da-sygorgia Verr. ; Iridogorgia Verr. Fam. 6. Isidae. Axis consists of alternating horny and calcareous portions. Bathygorgia Wright ; Oeratoisis Wright ; CaJlisis Verr. ; AcaneUa Gray ; IsidcUn Gray ; Selcrisis Studer ; Primnoisis Wr. and St. ; Mojtsca Lamouroux ; Acan- thoisis Wr. and St. ; Is is L. Fam. 7. Primnoidae. Axis calcareous and horny, basal attachment calcareous. Polyps with club-shaped calycine portion. Operculum calycine formed by some of the scale-like spicules of the calycine region, which shut over the tentacular region. Callo~ostrun Wright ; Cctlyptrophora Gray ; Primnoa Lamouroux ; Stachyodes Wr. and St. ; Calypterinus Wr. and St. ; Stenclla Gray ; Thouarella Gray ; . / mphif aphis Wr. and St.; Plumarella Gray; Primnoella Gray; Caligorgia Gray. Fam. 8. Muriceidae. Axis horny ; spicules project beyond the surface of coenenchyma ; operculum tentacular, formed by the spicules at the base of the tentacles which close over the calyx when the oral region is retracted. Acan- thogorgia Gray ; Paramuricea Ko'll. ; Hypnogorgia Duch. and Mich. : Muriccidcs Wr. and St.; Clcmatissn Wr. and St. ; ViUogorgia Duch. and Mich.; Anthogorgin ZOANTHARIA. 183 Verr. ; Menella Gray ; Ads Duch. and Mich.; Thesca Duch. and Mich.; Bebryce Philippi. Fain. 9. Plexauridae. Colony branched, axis horny : polyps occur all over the thick coenenchyina : spicules large ; cortical club-shaped and deeper spindle- shaped spicules. Eunicea Lamouroux ; Plcxaura Lamouroux ; Psammogorgia Verr. ; Platygorgia Studer. Fam. 10. Gorgonidae. Colonies upright and branched iisually in one plane ; axis horny, rarely horny and calcareous ; polyps arise from stem and twigs in a bilateral and biradiate manner. Coenenchyma smooth, spicules small. P/nf.//- caulos Wr. and St.; Lophogorgia M.-Edw. ; Lcptogorgici. M.-Edw. ; Stenogorgia Verr.; Callistcphanus Wr. and St.; Swiftia Duch. and Mich.; Gorgonia L. ; Eugorgia Verr. Fam. 11. Gorgonellidae. Order 3. ZOANTHARIA = HEXACTINIA. Polyps ami polyp-colonies, usually iritli simple imlirandu-il 1i'iif< teles. There are usually incomplete as well as complete mesenteries, awl the tentacles usual/// 'i-n, stage of Aulactinia stelloidi's with twelve primary mesenteries (after McMurrich). The mesenteries are numbered in the order of their appearance, ec ectoderm ; en endoderm ; s supporting lamella ; /mesenterial filaments. Sub-tribe 1. STICHODACTYLINAE. Tentacles arranged radially, some or all of the intramesenterial chambers communicating with more than one tentacle. Fani. 1. Corallimorphidae. With a double or multiple corona of tentacles (marginal, principal, and intermediate accessory), more than one tentacle com- municating with each intramesenterial chamber. Tentacles various ; pedal disc present ; gonads on all the septa ; muscular system weak ; sphincter muscle various ; acontia absent. CorallimorpJi/us Moseley, from the deep-sea ; Corynactis Airman ; Capnca Forbes; Discosoma Leuck. ; Aureliana Gosse ; Rhodadis * Recent researches render it probable that in these cases the tentacles have dropped off. t There is, however, variation in this character, even within the section Hexactiniae. ACTINIARIA. 187 M.-Ed. and H. ; Phymanthus M.-Ed. and H.; Crarnbactis Haeckel ; Cryptodeit- drum Klunzinger ; Adinotlirix D. and M. ; Heterodadyla Ehr. Fam. 2. Minyadidae. Pedal disc transformed into an apparatus for floating. Tentacles in sonic as in the Corallimorphidae. Minyas Guv. ; Dadylominyas And.; Acerominyas And. ; Phy Hominy as And. Sub-tribe 2. ACTININAE. Tentacles arranged in cycles, only a single tentacle communicating with each intramesenterial chamber. Fam. 3. Antheomorphidae. Tentacles digitate ; pedal disc present ; accessory tentacles absent ; gonads on all the mesenteries ; numerous complete mesenteries ; muscular system weak ; without sphincter muscle or acontia. Antheomorplie R. Hertwig, deep-sea form. Fam. 4. Actiniidae. Tentacles digitate, in a single corona ; pedal disc present ; acontia absent, sphincter muscle endodermal, weak ; with numerous mesenteries. Actinia Browne ; Anemonia Risso ; Condytactis D. and M. ; Adinioides Hadd. and Shack. ; Bolocera Gosse. Fam. 5. Aliciidae. With large flat base. Lateral body-wall with simple or compound hollow processes or vesicles, mostly in vertical rows. No cinclides. Sphincter variable, diffuse, endodermal. Acontia absent. Alicia Johnson ; Cysti- actis M.-Edw. ; Thaumactis Fowler ; Bunodeopsis And. ; Phyllactis M.-Ed. and H. Fam. 6. Bunodidae. Tentacles digitate ; pedal disc present ; acontia absent ; sphincter well developed, circumscribed, endodermal ; with numerous perfect mesenteries. Tallin- Gosse ; Lciotealia R. Hertwig.; Bunoiks Gosse ; Phymactis M.-Edw. and H.; AulactiniaVem:; Anthopleura Duch. ; EvactisVevr.; Tlicladis Kluuzinger ; Cercactis Andres. Fam. 7. Paractidae. Tentacles digitate ; pedal disc present ; acontia absent ; sphincter strong, mesodermal ; with numerous perfect mesenteries. Paractis M.-Edw.; Dysadis M.-Edw.; Teaf till inn Hertwig : Antholoba Hertwig; Ophiodiscus Hertwig; Parantlms Andres; Paractinia And.; Actinerus Verr. ; Adinostola Verr. ; Pycnanthus McM. ; Cymbactis McM. ; Xtomphm Gosse. Fam. 8. Amphianthidae. Tentacles digitate ; pedal disc present ; acontia absent ; mesodermal sphincter present ; transverse axis of body and mouth elongated, so that the two gonidial grooves almost touch ; principal mesenteries sterile ; secondary mesenteries incomplete. Attached to the axial skeletons of Gorgonidae. Stcphanadis Hertw. ; Amphianthus Hertw. Fam. 9. Sagartidae. With mesodermal sphincter muscle, usually with only a few complete mesenteries, with acontia. Sub-fam. 1. Sagartinae. With naked ectoderm, the acontia emitted through the mouth and through cinclides. The mesenteries of the second and subsequent cycles may, in a more irregular manner, reach the oeso- phagus. Sayartia Gosse ; Cereus Oken ; Adinoldba Blainv. ; Adamsia Forbes, sessile upon Gastropod shells containing a Hermit crab; Cylista Gosse; Mitadis Haddon and Duerden ; Aiptasia Gosse; Gephyra V. Koch (Morph. Jahrb. 4) solitary or colonial, sessile on zoophytes, to which it is glued by a cuticular matter secreted by the ectoderm, with more than 24 tentacles. Sub-fam. 2. Chondractininae. With thick body-wall, upper portion different in character from the lower, which is provided with a cuticle. The 12 primary mesenteries alone are complete and without gonads. Acontia emitted by the mouth, cinclides absent. Actinauge Verrill ; Chitonanthus McM. ; Hormathia Gosse ; Chitonadis Fischer ; Chondradinia Liitken ; Paraphellia Haddon. 188 COELENTBRATA. Sub-fam. 3. Phellinae. Sagartidae with a cuticular covering ; primary mesenteries alone fertile. Phcllia Gosse ; Octophellia And. ; Ilyactis And. ; Ammonactis Verr. Fam. 10. Heteractidae. Tentacles clavate, knobbed. Eloactis And. ; Rhopo- lactis And.; Ragadis And.; Heteractis M.-Edw. and H. ; Stauractis And. Fam. 11. Sideractidae. With sixteen pairs of perfect mesenteries, and three series of non-retractile tentacles, of which the innermost contains eight. Sidcractis Dan. Fam. 12. Madoniactidae. With a few principal mesenteries, acoutia, and a prominent endodermal circular muscular system. Intermediate between Bunodidae and Sagartidae. Madoniactis Dan. Fam. 13. Andvakiadae. Elongated, without any real pedal disc, seated loose in the sand, the greater part of the body encrusted. The uppermost bare part of the body, the oral disc, and the tentacles completely retractile. Few mesenteries. Endodermal circular muscular system. Near Sagartidae. Fam. 14. Liponemidae.* Tentacles reduced to short tubes or stomidia : with numerous perfect mesenteries. Deep-sea forms. Polysiphonia R. Hert. , tentacles short tubes with large terminal opening, allied to Paractidae ; Poly- stomidium R. Hert., with stomidia, allied to Actinidae ; Liponema R. Hertwig, stomidia very numerous ; Aulorchis R. Hert., with gonads modified into a tube opening through the mouth. Fam. 15. Sarcophianthidae. Sarcophianthus Lesson. Fam. 16. Thalassianthidae. Tentacles replaced by bushy excrescences of the disc. Thalassianthus Leuck. ; Actineria Blain.; Megalactis Ehrb. ; Actinodendron Blain. Fam. 17. Ilyanthidae. With single corona of tentacles ; pedal disc absent, gonidial grooves and sphincter obscure. Ilijanthus Forbes ; Mesacmaca And. ; Halcampa Gosse ; Halcampella And. Fam. 18. Siphonactinidae. Like the last, but with a gonidial groove, the lips of which project beyond the mouth (conckula). Peachia Gosse ; Siphon- actinia K. and D. ; Philomedusa Mull or ; Actinopsis K. and D. Danielssen's genera Aeyir and Fctija^ do not exist. They were founded upon mutilated specimens. Section 2. Paractinia. With paired mesenteries. There are two pairs of directives, and the longi- tudinal muscles are arranged as in Uexactinia. Number of mesenteries has no relation to the number 6. With two gonidia] grooves and two oesophageal lappets. Fam. 1. Sicyonidae. Sessile, with tetramerous arrangement of the mesenteries, sphincter muscle mesodermul, tentacles as short knob-like stumps. Possibly related to the Tctracorallia. Sicyonis R. Hert. Deep-sea form. Fam. 2. Polyopidae. Without pedal disc, tentacles transformed into stomidia. + Polyopis R. Hert. Deep-sea form, probably tetramerous. ' Vide note on p. 186. t D. E. Danielssen, "Actinida," The Norwegian North Atlantic Expedition 1876-8. 1890. I See note on p. 186. ACTINIARIA. 189 Section 3. Protactiniae (Protantheae). With 12 primary and 1 or 2 pairs of secondary mesenteries, which are dorsal rather than ventral. Body-wall and oesophagus with ectodermal ganglionic and muscular layers. Fain. Gonactinidae. Scyto2)horus R. H. ; Gonadinm Sars, with the power of transverse fission ; Oractis McM. ; Protanthea Calg. Section 4. Edwardsiae. Without pedal disc, with 8 mesenteries, including two pairs of directive mesenteries and 4 unpaired mesenteries (Fig. 150). All mesenteries with gonads. Tentacles usually more numerous than the mesenteries. The muscular (longi- tudinal) faces of the 4 unpaired mesenteries are all turned the same way. Live in sand. Edwardaia Quatrefages. FIG. 150. Diagram of the arrangement of the muscles and mesenteries of Edu'ardsia (from Chun after Boveri). S, S sagittal plane; a, a gonidial grooves. FIG. 151. Diagram of a transverse section through a young Zoanthus. The section is a little oblique. D dorsal, V ventral side ; x gonidial groove ; c mesenteric filaments ; s 1 macro-, s 2 micro-mesenteries (from Perrier). Section 5. Zoantheae. With numerous mesenteries of two kinds, (a) imperfect sterile micro-mesenteries, (b) larger perfect macro-mesenteries with gonads and filaments : the two kinds (Fig. 151) usually placed alternately, so that each pair is composed of a larger and a smaller mesentery ; two pairs of directive mesenteries, one pair consisting of macro-, the other pair (dorsal) of micro-mesenteries ; one gonidial groove ventral (near large directives). Usually colonial ; wall of body usually traversed by ectodermal canals, and encrusted with foreign bodies which may even be embedded in the wall. The longitudinal muscular faces of the mesenteries of each pair are arranged as in Hexactiniae. New mesenteries are formed in the inter-mesenterial space on either side of the ventral directives. The colonial forms arise either from a branched stolon, or from a broad basal plate containing anastomosing endodermal canals. Fam. Zoanthidae. Zoanthus Cuvier ; Gemmaria D. and M.; Isaurus Gray; Palythoa Lamx.; Sphenopus Stenstr. , with rounded aboral end, embedded in sand ; Epizoanthus Gray, often on hermit-crab gastropod shells ; Parazoanthus Haddon and Shack. 190 COELENTERATA. Section 6. Ceriantheae. With numerous unpaired mesenteries (Fig. 152), and a single gonidial groove (ventral). The two mesenteries attached to the gonidial groove (directive) are very small ; the mesentery on either side of these is laige, and reaches to the aboral end ; the remaining mesen- teries diminish in size towards the dorsal region where new mesenteries are added (not ventrally as in Zoantlicae). Fam. Cerianthidae. With a double corona of tentacles, marginal principal and circumoral accessory ; aboral end rounded ; without sphincter. With an aboral pore and a sheath of mud, sand grains, and nematocysts, in which the aboral end of the body lies as in a case. Cerianthus D. Chiaje ; Batliyan- thus Moseley ; Arachnactis Sars, pelagic (possibly a larval form). "-a, FIG. 152. Diagram of the arrangement of the mesenteries of Cerianthus. a goni- dial groove. Sub-order 2. ANTIPATHARIA.* Colonial Zoantharia with a tendency to hexamery ; with a usually branched, axial, hollow, horny skeletal rod contained in an epithelial sheath. The coenenchyma consists of the fused bases of the polyps ; it is always thin and without spicules. Except in one genus there is a central horny rod, round which the coenenchyma is disposed. The origin of the epithelial sheath which surrounds the rod is unknown. The polyps have generally six tentacles and six primary mesenteries, four of which are directives, and the other two transverse. The transverse mesenteries bear the gonads. The 4 or 6 secondary mesenteries fade away in the lower part of the polyp. The polyps are always much elongated in the transverse axis (i.e. at right angles to the elongation of the mouth), and in the Schizopathinae the body is actually constricted into three divisions, two lateral containing the gonads and one central with the mouth. Each division has two of the tentacles. To this phenomenon the name pseudo-dimorphism rather than dimorphism (gonozooids and gastrozooids) should lie applied. Fam. 1. Savagliidae. With 24 mesenteries and tentacles. The colonies are without an axial rod, but form a sheath round Gorgonid skeletons. Polyps with typical Actinian structure. Probably Actiniarians. Savaglia Nardo (Gerardia L. Duth.). Fam. 2. Antipathidae. With 6 tentacles, 6 primary mesenteries, and with or without 4 or 6 secondary mesenteries. The two lateral primary mesenteries bear the gonads. The axial skeleton is spiny and has a central canal. Sub-fam. 1. Antipathinae. Polyps not pseudo- dimorphic, each with 6 tentacles ; transverse axis of the polyp more elongated than the axis (sagittal) which is marked by the long axis of the mouth. Cirripathes Blainv. ; Stichopathes Brook; Leioputhcs Gray; Antipathes Pall.; Anti- pathella Brook; Aphanipathes Brook; Tylopathes Brook; Pteropathes Brook ; Parantipathes Brook. * G. Brook, "Report on Antipatharia," Challenger Eeports, Pt. 80, 1889. MADREPORARIA. 191 Suh-fam. 2. Schizopathinae. Polyps exhibit pseudo-dimorphism ; each with two tentacles (i.e. 6 to each polyp). Schizopathes Brook ; Eathypathes Brook ; Taxipathes Brook ; Cladopathes Brook. Fain. 3. Dendrobrachiidae. With branched retractile tentacles. Axial rod without central canal. Anatomy not known, possibly Alcyonarian. Dendro- brachia Brook. Sub-order 3. MADREPORARIA.* Colonial, rarely solitary, soantharian polyps, which secrete by the ectoderm a continuous and complicated calcareous corallum. This old and apparently well-established division of the Zoantharia is still, from a structural point of view, very imperfectly known. The less important features of structure, viz. the arrangement of the hard parts the corallum has been minutely examined, but the soft parts have been neglected, and had it not been for the investigations of the Oxford School, and of v. Koch, we should still know very little more about them than we do of the soft parts of extinct forms. These investigations which will, we may hope, soon lead to the possibility of a satisfactory classification of the sub-order, have established the following im- portant points: (1) the complete disestablishment of the Tabulate division, which, on examination of the soft parts, has been found to comprise forms belonging to Hydromedusae, Ahyonaria, as well as to Madreporaria ; (2) that the corallum is entirely a product of the epithelial ectoderm, and lies wholly outside the animal ; (3) that the structure of the polyps varies in the different groups, though the Hexactinian type seems on the whole to prevail. The most important deviations from that type, so far known, are presented by those forms, in which the directive mesenteries (if indeed they can be called so) present the same arrangement of their muscles as do the other pairs (Lophohelia, Mussa, EupJtyllia, Hetcropsammia), and the number of mesenteries and tentacles is not a multiple of six. Acontia appear to be absent ; but peristomial cinclides are said to be present, allowing of the emission of the much convoluted mcsenteric filaments. The colonies are generally dioecious ; and the gonads are borne upon all or certain of the mesenteries. Pores at the apex of the tentacles seem to be absent. Asexual reproduction by budding, or by fission, is always present. In Fungia and its allies there is formed from the egg a fixed nurse-stock, which has the property of nipping off its disc-shaped apical portion, and of forming in its place a new disc. The fixed nurse-stock is a typical polyp with theca and septa, and at first it does not terminate in an expanded disc. When the walls of the theca, which are at first vertical, have widened out into a disc, the lower part of it forms a stalk. It is this stalk which is left after the fission, and which produces a new disc. The new disc is not a bud, but is a product of the growth of the structures already existing in the base of its predecessor (Lister, Q. J. M. S., 29). It is not certain whether the Fungia stock increases by budding. * Martin Duncan, "A Revision of the Families and Genera of the Sclero- dermic Zoantharia," Journal of the Linnean Society, vol. 18, 1885. H. N. Moseley, "Report on the Corals," Challenger Reports, 7, 1881. G. C. Bourne, "Anatomy of Mussa and Euphyllia," etc., Q. J. M. S., 27, 1887, p. 21. G. H. Fowler, "Anatomy of the Madreporaria," I.-V., Q. J. M. S., vol. 25 to vol. 28. V. Koch, " Ub. d. Verhaltniss v. Skelet u. Weichtheile b. d. Madreporen," Morph. Jahrb., 12, 1886. M. M. Ogilvie, "Microscopic and systematic study of Madreporarian types of Corals," Phil. Trans., 187, 1896. 192 COELENTERATA. Ill the colonial forms, fission by division of the polyps into two may occur (Oculinae, Astraea), or the division may be confined to the oral disc, so that a complex polyp is formed, with several mouths and oesophagnses opening into a common coelenteron (Macandrina, Fig. 144). In many cases, perhaps the majority, the colony is increased by budding from the extra-thecal coenosark. The hard structures or corallum follows more or less closely the shape of the polyp, and were at one time thought to be actually contained in the tissue of the polyp. They consist of a cup or theca, from which the polyp projects and into which it can shrink, and in some forms of a connecting substance, which may or may not be porous, connecting the cups this is the coenenchyma. The cup has, projecting inwards from its walls, a number of radiately and vertically arranged calcareous plates, which suggest calcified mesenteries. These are the septa; they are not mesenteries, but occur between mesenteries. The cup presents a basal plate below, from which rise the walls. -eaf. PIG. 153. Basal plate of a larva of Astroiiles mlyeularis, soon after at- tachment. With 12 radial ridges (after Lacaze Duthiers, from Bal- four). FIG. 154. Diagram to exhibit the relations of the polyp to the corallum. T tentacles ; ec ectoderm ; ed endoderm ; st oesophagus ; m/ mesenterial filaments ;'r extra-thecal coelen- teron; TO mesentery; m' extra-thecal portion of mesentery ; ]lp basal plate ; ep epitheca ; Th theca ; cy calicoblasts (after G. C. Bourne). The hard structures or corallum are secreted by, and on the outer side of, the ectoderm. The first part of the skeleton to appear (Astroides calycularis) is an annular basal plate (Fig. 153), incomplete at first in its central part, between the basal ectoderm and the surface to which the young polyp is attached. Next twelve radially arranged folds of the basal body-wall rise up and project into the enteron. The ectoderm of these folds secrete calcareous deposits, which constitute the first trace of the septa (Fig. 153). The folds of the septa differ from those of the mesenteries (between which they are placed) in being folds of the whole body-wall, and not of the endoderm alone. The septa, therefore, arise as rod-shaped structures in continuity with the basal plate. They increase in thickness and height as the polyp grows, and their outer ends, which do not reach to the body-wall of the polyp, become MADREPORARIA. 193 forked. The theca is formed by the junction (complete in the Aporosa, incom- plete in the Porosa) of these forked extremities of the septa. From this account it is obvious that the theca must not only project into the cavity of the polyp in exactly the same way as do the septa, and divide it into an extra- and intra-thecal portion (Fig. 154), but also must divide the mesenteries in a similar manner. This is actually found to occur in adult polyps, in which the body- wall projects over the lip of the calycle and lies on the outer side of the theca (Fig. 154, r). It appears that when the polyps of a colony are connected by soft tissues (coenosark), the connection is effected by this extra-thecal portion of the polyp, and that the so-called coenenchyme or hard matter filling up the valleys between adjacent polyps is secreted by the ectoderm on the lower side of this connecting coenosark. The coenosark is generally broken up into canals which, in the Porosa, communicate with the coel- enteron of the polyps by apertures left in the theca, and may in some cases, at any rate, be embedded in the superficial layer of the hard coenenchyma. The extra - thecal coelenteron is confined to the upper part of the thecae, and the coenosarkal continuation of it over the coenenchyme (when present) may or may not be broken up by con- tinuations of the mesen- teries. When there is no coenenchyme, and the thecae are isolated from one another except at their base, the living tissues appear to have died away round the basal parts of the thecae. As may be gathered from the last statement, the polyps ascend as the thecae grow and forsake the lower older parts of the cup. In their ascent the ectoderm of their basal walls secretes calcareous laminae, which may either completely occlude the cup as the tabulae of Serialopom and PociUopora, or merely stretch as imperfect plates between the septa as the so-called dissepiments. Synapticula are more rod-like calcareous structures passing from septum to septum through the mesenteries. The columella (Fig. 155) is a central calcareous projection into the theca rising up from the basal plate, and pali (Fig. 156) are accessory columellae arranged in a circle round the central columella, and sometimes joined to the edges of the septa : they are sometimes looked upon as FIG. 155. Vertical section through a polyp of Astroides calycularis (after Lacaze-Duthiers). The mouth-opening, oesophageal tube and mesenteries are seen ; also the calcareous septa between the mesenteries, and the columella Sk (the line from Sk should be produced to the middle of the cup). O 194 COELBNTERATA. Fio. 156. Vertical section through the cup of Cyathina cyatlnis E. and H. = Caryo- phytlia eyathus Lamk. (after M. Edwards). S septa ; P pali ; C columella. Fain. 1. Turbinolidae. projections of the septa. The cosine are vertical ridges along the outside of the theca : they are extra-thecal projections of the septa. The septa may be confined to the intramesenterial spaces, or they may occur in the intermesenterial as well. They are generally present in cycles of different sizes like the mesenteries, but the number is not always a multiple of six. The epitlicca when present is outside the theca : it is attached to the edge of the basal plate (Fig. 154). Section 1. Aporosa, Solitary or colonial forms. Hard parts usually solid and imperforate. Theca or wall solid, may be epithecate. Septa solid near the wall, and usually, hut not invariably, solid at the further part. Interseptal loculi (i.e., the chambers between the septa) open throughout, or closed more or less by endotheca in the form of dissepiments and tabulae. One or more rows of tentacles in relation to the septa and interseptal loculi. The disc with one or more mouths ; a mesentery usually in each inter- septal loculus. Mesenteries usually in multiples of six. Corallum simple (solitary), or in colonies. Gemma- tion from the wall or from an expansion of the basal structures. Wall solid. Septal loculi open to the base. Endotheca rarely present. (a) Corallum simple, rarely producing deciduous buds. Smilotroclms Ed. and H. ; Onchotroehus Duncan; Dc&mophyllum Ehrb. ; Schizocyathus Pourtales ; Flabellum Lesson ; Rhizotrochus Ed. and H. ; Thysanus Dune. ; Placotroclms Ed. and H. ; Sphcnotrochus Ed. and H. ; Nototroekus Dune.; Placocyathus Ed. and H. ; Platytrochus Ed. and H. ; Turbinolia Ed. and H. ; Stylocyathus d'Orb. ; ConocyatJius d'Orb. ; Bistylia T. Woods ; Treinatotrochus T. Woods : Trocho- cyatlms Ed. and H. ; Ddtocyatlius Ed. and H. ; Odontocyathus Moseley ; C'aryophyllia Lmk. (Fig. 156); Ccratotrochus Ed. and H. ; Discocyathus Ed. and H. ; Brachytroclius Duncan ; Sabinotrochus Dune.; Stcphanotrochus Moseley: Anthem ipliyllia Pourt. : Fungiacyathus Sars ; Guynia Dune.; Duncania Pourt. ; Haplopliyllia Pourt. (b) Colonial ; buds free above their origin ; no exotheca uniting the corallites. Coenocyathus Ed. and H. ; Gemmulatrochus Dune. (c) Colony growing from basal expansions ; exotheca absent. Polycyathus Dune. Fam. 2. Oculinidae, Colonial, in the form of branches, espaliers, irregular ramifications on a thick stem ; or massive, or incrusting. Interseptal loculi usually open to the base, but dissepiments or tabulae sometimes occur. Walls of corallites often increasing in thickness exogenously with age, and becoming a solid mass by union with others. Solid intercalicular coenenchyma usualh" present. Polyps when expanded rising above the wall, or long and exsert, the mouth protruding ; the tentacles 10 to 48 or more, elongated, tips usually swollen or capitate. (a) Massive or incrusting colonies. Columella and pali absent, or a false MADREPORARIA. 195 edlumella may be present. Coenenchyma well developed between the calices. Baryliclia, Ed. and H. ; Ncolielia Moseley ; Diblasus Lonsdale. (b) Dendroid or bunch-shaped colonies. Corallites often coalescing ; gemma- tion alternate. Columella absent or rudimentary. Tabulae or dissepiments present or not. Lophohelia Ed. and H.; AmpMheUa Ed. and H.; AcroJielia Ed. and H. (?) Arborescent or tufted colonies. Gemmation rarely from one side only. Columella various. Oculina Ed. and H. ; Cyatholielia Ed. and H.; Trymohelia Ed. and H. ; Sclerolielia Ed. and H. ; Bathclia Moseley. (d) Branched espalier-like colonies. Corallites projecting or twisted. Colu- mella styliform. No pali. Coenenchyma well developed. Prolielia E. de Fro. Jurassic and cretaceous. (c) Arborescent, palmate, or incrusting colonies. Septa few, unequal. Colu- mella styliform. Costae short or absent. Stylophora Ed. and H. ; Madracis From. Fam. 3. Pocilloporidae. Colonial, with tabulae; septa small; Columella well or ill developed. Inter-corallite structure coenenchymal and solid. Polyps with disc, tentacles, and one pair of long mesenterial filaments. Pocillopora Lamarck ; Scriatopora Lamk. Fam. 4. Astraeidae. Solitary or colonial, rarely reproducing by deciduous buds. Colonies increase by gemmation and fissiparous division. Interseptal loculi with dissepimental endotheca, rarely tabulae. Soft parts resembling those of Turbinolidae ; the long serial calices have several mouths in the limited disc which is surrounded by tentacles. Corallites may unite by their walls, but true intermural solid Coenenchyma is rarely seen. Includes the so-called brain corals. Sub-fain. 1. Astraeidae simplices. Simple solitary forms. Propagation rarely by deciduous buds. Pali present or absent. Eudotheca always present, but variable in amount. Lopliosmilia Ed. and H. ; Spheno- pliyllia Moseley; Parasmilia Ed. and H.; Dasmosmilia P.; LitfiqphylUa Ed. and H.; Asterosmilia Duncan. Sub-fam. 2. Astraeidae reptantes. Colonies composed of short coral- lites, which arise by gemmation from stolons or basal expansions. Cylicia Ed. and H. ; Antrangia Ed. and H. ; Ulangia Ed. and H. ; Colangia Pourt. Sub-fam. 3. Astraeidae gemmantes. Colonies increasing by gemmation from the wall below the calicular margin. Endotheca dissepimental. Cladocora Ed. and H. ; Pourtalosmilia Duncan. Sub-fam. 4. Astraeidae caespitosae. Corallites isolated terminally, being free at their sides, springing from a common parent ; increasing by fissiparity, separation occurring rapidly or serial growth persisting. Gemmation rare. Eusmilia Ed. and H. ; Solcnosmilia, Dune. ; Dasyphyllia Ed. and H. ; Dendrocora Dune ; Trachypliyllia Ed. and H. ; Mussa Oken. Sub-fam. 5. Astraeidae confluentes. Increase by fissiparity, with excess of serial growth. Gemmation may occur. Corallites united by their walls, costae, or by intermediate tissue, or free. Euphyllia Ed. and H. ; Dendrogyra Elirbg. ; Pectinia Oken ; Diploria Ed. and H. ; Manicina Ehrb. ; Maeandrina Ed. and H. ; Coeloria Ed. and H. ; Leptoria Ed. and H. ; Symphyllia Ed. and H. ; Mycetophyllia Ed. and H. ; Ulophyllia Ed. and H. ; Tridacophyllia Blainv. ; Colpophyllia Ed. and H. ; Scapo- phyllia Ed. and H. ; Plerogyra Ed. and H. ; Physogyra Quelch ; Hydnophora Ed. and H. 196 COELENTERATA. Sub-fani. 6. Astraeidae agglomeratae fissiparantes. Colonies massive or incrusting. Corallites increasing by fissiparity, and sometimes also by gemmation ; united by costae or coenenchynia ; not forming long series. Dichocoenia Ed. and H.; Favia Oken ; Gonmstraea Ed. and H. Sub-fam. 7. Astraeidae agglomeratae gemmantes. Massive and foliaceous colonies. Colonies increasing by gemmation from the wall from within the calice, or from intercorallite tissue. Corallites joined by costae, exotheca, or peritheca, or fused by their walls. Endotheca vesicular, rarely tabulate. Hcliastraca Ed. and H. ; Phymastraea Ed. and H. ; Solcnastraca Ed. and H.; Plesiastraca Ed. and H.: Ecliinopora, Dana; Galaxm Oken; Accoi- tkopora Verrill ; Leptastraea Ed. and H. ; Acanthastraea Ed. and H. ; Astrocoenia Ed. and H. ; Prionastraea Ed. and H. ; Mcrulina Ehrbg. ; Moselcya Quelch. Section 2. Fungida. Solitary or colonial forms. Septa and septo-costae with synapticula, which cross the interseptal and intercostal loculi. An endotheca is present or absent. Basal structures perforate or imperforate. Soft structures with short, lobe-like, scattered, sometimes obsolete tentacles, not covered when contracted ; discs not circumscribed, and in colonial forms confluent. Fain. 1. Plesiofungidae. Transitional between the Aporosa and Fungida. Simple or colonial, with synapticula in the interseptal loculi, besides endothecal dissepiments. Septa solid and imperforate, occasionally perforate and trabeculate. Epistreptophyllum Milaschewitsch ; Siderastraea Blainv. ; Poly,raca Fritsch. Fam. 2. Fungidae. Simple or colonial, usually depressed ; septa solid or porous. With synapticula, without dissepimental endotheca ; tentacles short ; scattered, sometimes absent. Wall perforated and echinulate. Fii/nyia Dana ; Diafungia Duncan, both solitary. The following are colonial : Halomitra Dana ; Sandiilolitha Quelch; Cryptabacia Ed. and H. ; Herpolitha Esch. ; PolyphyUia Q. and G. ; Lithactinia Lesson ; Zoopilus Dana. Fam. 3. Lophoseridae. Wall neither perforated nor echinulated. Simple forms. Trochoseris Ed. and H. ; ( 'ycloscris Ed. and H. ; Diaseris Ed. and H. ; Bathyactis Moseley ; Psammoseris Ed. and H. ; Sleplianoscris Ed. and H. Colonial forms : Cyathoseris Ed. and H. ; Loplioseris Ed. and H. ; Haloseris Ed. and H.; Tichoseris Quelch ; Myccdium Oken.; Phyllastraca Dana ; Trachy- pora Yerrill ; Leptosens Ed. and H. ; Stephanaria Verrill ; Agaricia Lamck. ; Plesioscris Duncan; Psammocorn Dana; Pacliyseris Ed. and H.; Coscinaraea Ed. and H. Fam. 4. Anabaciadae. Simple or colonial, septa trabeculate and fenestrated. Synapticula small. Dissepiments absent. Wall indistinct. Anabacia d'Orb. Fam. 5. Plesioporitidae. Transitional group with regularly perforate septa. Meandroseris Eouss. Section 3. Perforata. Corallum entirely or almost entirely composed of porous or reticulate coenen- chynia. Dissepiments and tabulae may be present or absent. Septa solid or much perforated , or represented by trabeculae only. Fam. 1. Eupsammidae. Simple or colonial. Walls with costae and apertures in the intercostal spaces. Calices well developed. Increase by gemmation and fission. StepJinnophylKa Michelin. ; Leptopcnus Moseley, deep-water, southern hemisphere; Balanopliyllia S. Wood; Thccopsammia Pourt. ; Eupsammia Ed. and H. ; Heteropsammia'EA. and H.; Dendrophyllia Ed. and H.; Pachypsammia CTEXOPHORA. 197 Yen-ill ; Leptopsammia Ed. and H. ; Endopsammia Ed. and H. ; Astroides Blainv. (Fig. 155) ; Lobopsammia Ed. and H. ; Rhodopsammia Semper ; Mhizopsammia Verr. Fam. 2. Madreporidae. Colonial, arising by gemmation from the sides of the parent polyp : coenenchyma more or less abundant, spongy and reticulate, slightly or not distinct from the porous corallite-walls. Madrepora L. ; Turbi- nitrict Oken ; Astraeopora Blainv. ; Montipora, Q. and G. ; Anacropora Ridley. Fam. 3. Poritidae. Sclerenchyma reticulate and perforate. Septa never completely lamellary. Walls very porose. Corallites increasing by gemmation, and united directly or by intervening porous sclerenchyma. Forties Ed. and H. ; Synaraea Verr.; Napopora Quelch ; Rliodaraca Ed. and H. ; Alveopora Q. and G. ; Diclioraea T. Woods. Sub-phylum II. CTENOPHORA.* Free-sicimminij, tranxfiarent /'/a(jie coelen- terata, irith ei/jht meridional rotes of vibratile plates formed of fused cilia. They possess an oesopliaijeal tul>e called the stomach lined by ectoderm, and a gastrovaseular canal system. Xematocyats are almost ah rays absent. The fundamental form of the Ctenophora is a gelatinous, spherical, or ovoid body, which swims in the sea by the activity of its ciliated plates. It has two poles the oral pole marked by the mouth, and the aboral pole marked by the sense organ. The line connecting these two poles is the main axis, and in describing the structure of the body it is important to recognise two planes which pass through this axis at right angles to one another. The mouth leads into a tube called the stomach (sometimes called oesophagus or stomodaeum, because it is lined by ectoderm), and the stomach opens into the central part of the gastro- vaseular apparatus called the funnel (infun- dibulum). The stomach is furnished with two hepatic bands. Both stomach and funnel are flattened sacs, and both lie in the main axis the funnel of course above the stomach but with their long diameters FIG. 157. Hormiphora (Cy- dippe) plumosa (after Chun). mouth. * C. Chun, "Die Ctenophoren des Golfes von Neapel," Fauna und Flora des Golfes von Neapel. 1880. 198 COELEXTERATA. in different planes. The long diameter of the stomach lies in one of the two planes mentioned above, while that of the funnel lies in the other plane, which is at right angles to the first. These two planes are called the stomach-plane* (Fig. 158, M, M.) and funnel-plane (T, T.) respectively. The stomach-plane divides the body into a right and left half ; but it is impossible to speak of the two parts of the body marked off by the funnel-plane as dorsal and ventral, or as anterior and posterior, as is done by some authors, because these two parts are identical and c.adr. FIG. 158. Diagram of a Cydippe seen from the aboral pole (after Chun). M-M stomach (sagittal) plane ; T-T funnel (transverse) plane ; /-I to j-8 the eight rows of vibratile plates ; p polar plates ; ?ti to w s the eight ciliated grooves ; t.b base of tentacle ; t.st stalk of tentacle ; tt branch of tentacle ; sch sheath of tentacle ; seh.o opening of tentacle-sheath ; <\pr per- radial vessel ; c.ir interradial vessel ; c.adr adradial vessel ; sp l to sp s the sperm producing, ori to ov$ the ova-producing sides of the eight meridional vessels; t.g tentacle vessel; ex 1 and ex 2 the two aboral openings of the gastrovascular system. not distinguishable from one another by any differential character. The tentacles when present are two in number : they arise from the sides of the body in the funnel-plane (Fig. 158, T, T). Further, we may speak of two transverse axes a stomachal axis passing through the long diameter of the stomach, and a funnel axis passing through the long diameter of the funnel. The body (Fig. 157) carries eight meridional rows of vibratile * The plane of the stomach is sometimes called the sagittal plane, and that of the funnel the transverse plane. CTBNOPHORA. 199 plates the ribs. These rows begin close to the aboral pole, and pass in the meridians of the animal towards the oral pole. Four of these rows lie in one half of the body, and four in the other. Further it is to be noted, that of these eight rows we may distinguish those which lie on each side of the tentacle (or funnel-plane) these are the sub-tentacular rows* and those which lie on each side of the stomach-plane, which Ave may call the sub-stomachal f rows (Fig. 158). There are therefore four sub-tentacular rows and four sub-stomachal rows of meridional plates. The central nervous system and sense organ are placed at the aboral pole (Fig. 159). It has the form of a flat depression formed of ciliated sensory ectoderm, and covered over by a bell-shaped structure (the bell) formed of fused cilia (gl). Some of the cilia of the sensory area are very long and fused together to form four large triangular plates. These are the springs (/). Their tips are attached to, and carry a small mass of otoliths (of), which is placed over the centre of the sensory area. The sensory plate is drawn out in the stomach plane into two lobes the polar plates (Fig. 158, p}. Beginning at the base of each of the four springs, or otolith-bearers, is a ciliated groove (pi), which, passing outward through a hole in the bell-like cover, divides into two grooves (w 1 ' 8 ). These are continuous with the aboral ends of two rows of vibratile plates, and are sometimes called nerves because they seem to transmit any movement of the otolith- bearer to the row of vibratile plates, and so set the latter in motion. The movement of the vibratile plates begins at the aboral pole and passes oralwards, each plate successively bending energetically towards the aboral pole, and then slowly regaining its original posi- tion. The movement of the animal is thus with the oral end forwards. The vibratile plates have the appearance of consisting of long cilia fused together at their bases. They arise from specially long ectoderm cells. The gastro vascular apparatus (Fig. 158) consists of a central space, the funnel, which gives off two vessels the perradial vessels (c.pr}; these pass outwards in the funnel-plane in opposite directions and divide dichotomously into the inter radial vessels (tv/r), of which there are four. These again divide, and give rise to eight admdial vessels (c.adr\ which enter the meridional vessels. The meridional vessels underlie the rows of vibratile plates and end blindly above * Sometimes called sub -transversal. t Sometimes called sub-sagittal aud sub- ventral. 200 COELENTERATA. ex ot< PIG. 159. Sense organs and adjacent organs, I of Cestus veneris in side view (from the stomach plane) x 100, II of Encharis 'iiivlticarnis from above x 120 (after Chun), a sense organ ; 6 , r 7 ) extend close together along the whole length of each side of the aboral surface of the body. The perradial vessels are absent, as the four interradial vessels arise directly from the funnel (in correspondence with the compression of the body). The sub-stomachal meridional vessels run horizontally beneath the long ribs to the ends of the body, while the sub-tentacular (