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STATE VETERINARY COLLEGE. 1897 oo University Library QL 50.T A text-book of agricultural zoo il CTT Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu381924001035330 A TEXT BOOK AGRICULTURAL ZOOLOGY ge IK Se A TEXT-BOOK AGRICULTURAL ZOO KOGY% FRED. V. THEOBALD, M.A. (Cantas.), F.ES. Foreign Member of the Association of Official Economic Entomologists, U.S.A. ; Zoologist to the S, E, Agricultural College, Wye; Author of ‘An Account of British Flies,’ ‘Insect Life,’ ‘The Parasitic Diseases of Poultry,’ &c. WILLIAM BLACKWOOD AND SONS EDINBURGH AND LONDON MDCCCXCIX '¥ } | $9 + bs PREFACE. TuE subject treated in the following chapters, Agricultural Zoology, has perhaps been more neglected in England than any other branch of science applied to agriculture: even the name itself is hardly at present understood. It is true, indeed, that the labours of Curtis, and in later years of Miss Ormerod, have developed one branch of economic zoology—namely, the part played by insects in causing disease amongst animals and plants ; it is true also that some of our veterinary surgeons have done excellent work on the other parasitic diseases of animals; but there remains a vast portion of the subject that has neither gained the attention of English scientific men nor been sum- marised in an English text-book. Agricultural Zoology treats of the life-histories, the habits, the peculiarities of all the animals which affect for good or for evil our stock and crops, whether on the farm or in the garden, and the structure and development of domestic animals. Parasitism plays an im- portant part in this subject, especially in the worms; but the economic effects of parasites are not confined to worms—the parasitic insects, the minute protozoa, equally take their annual and preventable tol! of our flocks and herds. Nor, again, is parasitism always an injurious phenomenon: its beneficial effects are equally marked and equally under control, given only the vi PREFACE. requisite knowledge. In either case, the necessary thing is an acquaintance with the complex structure and the life-history of both the higher animals we meet upon the farm, which may serve as host, and also of the smaller organisms met along with them, whether injurious or beneficial, parasitic or leading an independent existence. With an injurious insect, for example, there is some period when it is open to attack : our observation should enable us to discover this period, and our science to suggest an appropriate weapon. In the same way our domestic animals are weak at certain points and at certain times: only an intimate knowledge of their organisation and their habits will enable us to apply the corresponding safeguards. In the following text-book the writer has endeavoured to summarise the habits, characters, and development of the animals that may be met with in farm and garden. Groups pos- sessing little or no economic importance have been but briefly referred to, such as the Ceelenterates, Sponges, and Echino- derms. On the other hand, the structure of one domestic animal, the horse, has been treated at some length. It is hoped that the book may be of service to the farmer ; but it is primarily written for the rapidly increasing class of students in our Agricultural Colleges, &c. In their hands lies the future of scientific agriculture, in the development of which economic zoology must play not perhaps the least part. My thanks must here be expressed to Sir George Brown, K.C.B., for kindly revising the chapter on the Anatomy of the Horse, and for other help generally ; to Dr Hans Gadow for the great trouble he has taken in examining the proof-sheets of chapters xiv., xv., and xvi., and for his valuable advice in other matters. The chapters on Mites and Insects have been read over by Mr Charles Whitehead; and to him I tender my grateful thanks, not only for his help in examining the proofs, but also for allowing me the use of some of his excellent figures from the publications of the Board of Agriculture. In connection with the latter, I must here acknowledge the courteous per- PREFACE, vil mission of the Controller of Her Majesty’s Stationery Office to use the electros, several of which were supplied gratuitously. To Dr George Fleming, C.B., I am indebted most of all: thanks to his generosity, many of the excellent electros of worms, mites, &c., from his translation of Neumann’s ‘Parasitic Diseases of Animals,’ have been lent me for this book, and others he has allowed me to reproduce; but it is especially for the trouble he has taken in revising the chapters on Worms, Embryology, and the parts concerning domestic animals, that I owe him so many thanks. His publishers, Messrs Baillitre, Tindall, & Cox, also readily gave their consent to the free use of his figures, and I cannot let this opportunity pass without expressing my thanks for their great courtesy in this matter. Professor Nicholson has very kindly contributed a number of figures from his well- known ‘Manual of Zoology,’ which greatly add to the value of the work. JI must also acknowledge Miss Ormerod’s kindness in allowing me the use of fig. 94, and for other advice always so readily given. I must also express my thanks to Sir William Flower, K.C.B., the Trustees of the British Museum, Professor Ritsema Bos, Professor A. D. Hall, and Professor Adam Sedgwick, for either allowing their figures or those of institutions they represent to be reproduced, or for lending the blocks. Mr H. Cousins has kindly revised the part of Appendix IT. dealing with insecticides. Not only in England but also from abroad, especially from America, have I received much courteous and valuable aid, and to one and all I tender my many thanks. FRED. V. THEOBALD. Wre, December 1898. Note.—The figures so kindly lent, and those purchased from other works, are here gratefully acknowledged, with sufficient clearness, I trust, for every one’s satisfaction :— From Her Majesty’s Stationery Office, by permission of the Con- troller, figs. 44, 59, 60, 71, 86, 87, 89, 99, 108, 111, 112, 114, 122, viil PREFACE. and 125—some purchased and some lent with Mr Whitehead’s permission. From Dr Fleming’s translation of Neumann’s ‘ Para- sitic Diseases of Domestic Animals,’ figs. 4, 5, 13, 15, 16, 21, 28, 29, 30, 43, 45, 46, 115, 127, and 131 have been kindly lent by translator and publishers. Figs. 1, 6, 39, 49, 50, 85, 128, 129, 134, 138, 139, 144, 145, 146, 165, 166, 167, 168, 169, 172, 188, 190, 209, 219, 224, are from Dr Nicholson’s ‘Manual of Zoology’; figs. 17, 20, 22, 23, 24, 47, 72, 73, 74, 78, 79, 80, 81, 82, 88, 119, 120, 126 are original drawings by the author, the blocks being lent by the §.-E. Agricultural College, from the College J ournal. From Messrs Churchill the following figures from Chauveau’s ‘Comparative Anatomy of Domesticated Animals’ have been purchased—viz., figs. 148, 149, 150, 151, 155, 156, 158, 160, 161, 163, 175, 180, 204, 206, 207, 210, 211, 212, 213, 215, 216, 217, and 218. Fig. 159 has been reproduced from the same work, with the publishers’ permission. From Curtis’s ‘Farm Insects’ the following have been purchased, figs. 55, 56, 65, 67, 77, 83, 84, 100, 103, 109, 113, 118, and 130. Fig. 153 is reproduced from one of Sir William Flower’s drawings in his ‘Osteology of the Mammalia.’ The figures of Eelworms, figs. 18 and 26, are reproduced with the permission of Professor Ritsema Bos; and fig. 94 is a reproduction from Miss Ormerod’s ‘Manual of Injurious Insects. The Department of Agriculture, U.S.A, kindly allowed me to reproduce Dr Howard’s figures of the San José Scale, figs. 123 and 124 (part). Figs. 137, 170, 228 are from the British Museum Guides. From Foster and Balfour's ‘Embry- ology’ figs. 197, 199, 200, 201, 202, 203, 205 are reproduced, with the permission of Professor Adam Sedgwick. Fig. 48 is reproduced from several figures in Neumann’s ‘ Para- sitic Diseases of Domestic Animals,’ and also part of fig. 3. Figs. 121 and 135 are from ‘Insect Life’ (original), with the permission of Messrs Methuen & Co. To all who have helped me in this work, by lending their blocks, or allowing their figures to be reproduced, or by lending specimens, I offer my thanks. BF. OV. Ts CHAP, I. II. VI. VII. VIII. CONTENTS. PART I. THE CELL AND SIMPLE ANIMAL TISSUES. THE CLASSI- FICATION OF ANIMALS . PROTOZOA, OR SINGLE-CELLED ANIMALS . MESOZOA, SPONGES, CHALENTERATES, AND ECHINODERMS . WORMS (VERMES). PLATYHELMINTHES OR FLAT-WORMS . WORMS (VERMES)—Continued. NEMATHELMINTHES OR ROUND-WORMS . WORMS (VERMES)—Continued. ANNELIDA OR SEGMENTED WORMS ARTHROPODA OR JOINTED-LIMBED ANIMALS. (CRUSTACEA, MYRIAPODA, AND ARACHNOIDEA) . INSECTA OR HEXAPODA. (COLEOPTERA, HYMENOPTERA, LEPIDOPTERA, DIPTERA, THYSANOPTERA, HEMIPTERA, ORTHOPTERA, NEUROPTERA, APTERA) MOLLUSCA . PAGE 56 86 x CONTENTS. PART II. X. CHORDATA, (TUNICATES OR SEA-SQUIRTS AND AMPHI- OXUS = ACRANIA) 277 XI. CHORDATA—Continued. THE CHARACTERS OF CRANIOTE OR VERTEBRATE ANIMALS 281 XII. THE STRUCTURE OF THE HORSE 285 XIII, CLASSIFICATION OF THE CRANIOTA. A. THE ICHTHYOP- SIDA. (FISH AND AMPHIBIA) 321 XIV. B, SAUROPSIDA, (I. REPTILES) 330 XV. B, SAUROPSIDA—Continued. (II. AVES) . 335 XVI BRITISH BIRDS 3 353 XVII EMBRYOLOGY OF THE CHICK (THE EGG OF THE FOWL) 407 XVII MAMMALIA (DEVELOPMENT AND FETAL MEMBRANES) 424 XIX. MAMMALIA—Continued. CLASSIFICATION OF MAMMALS. BRITISH MAMMALS (DOMESTIC AND WILD) 436 APPENDIX, I. THE PREVENTION AND TREATMENT OF VERMICEOUS PESTS 481 II. THE PREVENTION AND DESTRUCTION OF INSECT PESTS. 486 INDEX 497 ILLUSTRATIONS. . Blood Corpuscles of Vertebrata . Amoeba c ‘ ‘ : . Infusoria and Foraminifera (Euglena, Cercomonas, Polytoma, Textularia, and Globigerina) . Ciliate Protozoon (Balantidum colt) . Coccidium oviforme of Rabbit’s Liver The Common Starfish (Uraster rubens) . Liver-fluke (Distomum hepaticum) . Life-history of Distomum hepaticum . Diagram showing Life-history of Liver-fluke . Scolex of Tenia solium and Proglottis of Tapeworm . Two forms of Cysts of Cestodes (Cysticercus and Cenurus) . Sturdy in Sheep (Cenurus cerebrulis and Tenia cenurus) . Fragment of Measly Pork . Tenia echinococcus . Diagram showing formation of Proligerous and Secondary Ves- icles in Echinococcus . Tenia serrata. . Embryo and Ova of Sclerostomum rubrum . Anguillulide (Eelworms) . . The Lung Worm (£ustrongylus filaria) . Armed Palisade-worm of Horse (Sclerostomum armatum) . Vermiceous Aneuriem of Great Mesenteric Artery . Sclerostomum tetracanthum xii 23. 24. 25. 26. 27. 28, 29, 30. 81. 32, 33. 34, 35, 36. 37. 38. 39. 40. 41. 42. 43. 44, 45. 46. 47. 48. 49. 50. 51. 52. 53. 54, 55. 56. 57. 58. ILLUSTRATIONS. Small Red Sclerostome (S. rubrum) from Horse Gape Worm (Syngamus trachealis) Trichina spiralis Eelworms (Anguillulide) Ascaridze Oxyures of Horse (Curvula) Oxyures of Horse (MJastigodcs) The Horse-Leech (Heemopis sanguisuga) Structure of an Arthropod (Periplaneta americana) Head and Lower Lip of Cockroach Structure of Insect Leg Digestive Organs of the Cockroach Trachea and side-view of part of Abdomen Nervous System Wood-lice (Armadillo vulgaris, Porcellio scaber, and antenna of Oniseus, &c.) Millipedes (Julus pulchellus and I, Londinensis) . House Spider (Tegenaria civilis) Orb-weaving Spider, &c. Harvest Bug (Trombidium holosericeum) . Red Spider (Tetranychus telarius) Harvest Bug (Leptus autumnalis) Red Hen Mite (Dermanyssus avium) and egg Red Mange. Demodectic Scabies (section of skin) Beetle Mite (Oribata orbicularis) . Linguatulide A Hexapod (Tipula oleracea) Mouth parts of Insects Larve of Insects . Pupe of Insects . Pupa of Tipula oleracea Alimentary Canal of Larva (Tipula paludosa) Lady-birds (Coccinellide) Mustard-beetle (Phadon betule) Apple-Blossom Weevil (Anthonomus pomorum) Apple- Blossoms damaged by Apple Weevil (Anthonomus pomorum) 100 102 ILLUSTRATIONS. . Pea Weevil (Sitones lineatus) - Bean Beetle (Bruchus rufimanus) . Red-legged Weevil (Otiorhynchus tenebricosus) . Striped Click-beetle (Agriotes lineatus) . Rose Beetle (Cetonia aurata) . Cockchafer (Melolontha vulgaris) . . Beet Carrion-beetle (Silpha opaca) . Ground-beetle (Carabus violaceus) . Corn Ground-beetle (Zabrus gibbus) . Pupa of a Sawfly . Honey-Bees . Mouth and Sting of Bee, dissected . Gooseberry Sawfly (Nematus ribesit) . Slug-worm of Pear (Eriocampa limacina) . Pear Sawfly (Zriocampa limacina), and cocoon . Leaf of Cherry eaten by Slug-worms . Cynipide . . Larva of the Large White (Pieris brassicc) 77. Green-veined White (Pieris napt) . Currant Clearwing (geria tipuliformis) . Larva and pupa of Currant Clearwing (diyerta tipuliformis) . Black Currant Stems damaged by Larvee of Currant Clearwing. . Garden Swift-moth (Hepialus lupulinus) 7 . Cordyceps entomorhiza (a fungus on Hepialus larve) . Heart-and-Dart Moth (Agrotis exclamationis) . Silvery Y-Moth (Plusia gamma) : . Life-history of Currant or Magpie Moth (Abraxas grossulariata) . Codlin Moth (Carpocapsa pomonella) . Diamond-back Moth (Plutella cruciferarum) . Cherry-tree Case-bearer (Coleophora anatapenella) . Raspberry Shoot-borer (Lampronia rubiella) . Haltere of Fly . A Gnat (Culex annulatus) and Head of Gnat . Plumed Gnat (Chironomus plumosus) . Larva and Pupa of Flies . Anchor Processes . . Wing of Cecidomyia . Wing of Diplosis . xiv 117. 118. 119, 120. 121. 122. 123. 124, 125. 126. 127. 128. 129, 130. 131. 182. 133. 184, ILLUSTRATIONS. . Bibionidee . . A Sand-fly (Simulium reptuns) . Crane-fly (Tipula oleracea) . Winter Gnats (Trichocera) . Head and Proboscis of Tabanus autumnalis . Ox Gad-fly (Tabanus bovinus) Hover-flies (Syrphide) . Ox-warble (Hypoderma bovis) Ox-bot . . Horse-bot Fly (Gustrophilus equ) Larva of Horse-bot Fly - . Onion Fly (Phorbia cepetorum) . Root-eating Flies . Wheat-bulb Fly . 5 . Mangold Fly (Chortophila bete) . Gout Fly (Chlorops teniopus) . Carrot Fly (Psila rose) . Celery Fly (Tephritis onopordinis) . Head of Stomoxys . Sheep-tick (Mclophagus ovinus) . Larva and Pupa of Hen-flea (Pulex avium) Thrips Proboscis of a Hemipteron Hop damaged by Hemiptera-heteroptera Cherry Aphis (Myzus cerasi) Plum Aphis (Aphis pruni) Female San José scale Male San José and Mussel scale . Apple-sucker (Psylla mali) Needle-nosed Hop-bug (Calocoris fulvomuculatus) Louse of the Ox (Hematopinus eurystcrnus) Migratory Locust (#dipoda migratoria) Female and Male common Cockroach (Blatta orientalis) Mole Cricket (Gryllotalpa vulgaris) Trichodectes spharocephalus of Sheep Mallophaga or Bird-lice . Lace-wing Fly Dragon-flies (schna grandis) . to or = On oer wo rw nw ty to or or i) oO ot on 155. Pelvic Arch 156. General View of the Intestines of the Horse ‘ 157, Diagram of Alimentary Canal . 158. Theoretical, Longitudinal, and Median Section of Abdominal ILLUSTRATIONS. . Silver Fish (Lepisma saccharinu) . Edible Snail (Helix pomatia) ? . Two transverse series of teeth from radula of Limpet . Shells of Lamellibranchs 9. Common Calamary (Loligo vulgaris) . Water-snails (Limneide) . Grey Field-slug (Limax agrestis) . Testacella (7. haliotidea) . Garden Snail (Helix aspersa) . Structure of a Tunicate. . Development of a Tunicate . The Lancelet (Amphioxus lanceolata) . Diagrammatic Sections of an Invertebrate and Vertebrate . Skeleton of Horse . Lumbar Vertebra . Axis . Atlas . Skull of the Horse . Diagram of the Relations of the » Balneipal Bones of the Mam- malian Skull ‘ 54. Fore and Hind Leg of Horse Cavity, to show Peritoneum . Median Longitudinal Section of Head and Upper Part of Neck of Horse Uro-Genital Apparatus of Male, ak Aeteuios . Generative Organs of the Mare . . Diagram of the Circulation of the Blood . Brain of Horse (dorsal view) . Brain of Horse (ventral view) 5. The Perch (Perca fluviatilis) . Diagram of the Circulation in Fishes . Development of the Frog . Male Crested Newt (Triton cristatus) . Diagram of the Circulation in Reptiles xvi 170. 171. 172. 173. 174. 175. 176. 177. 178. 179. 180. 181. 182. 183. 184. 185, 186. 187, 188. 189. 190. 191. 192. 193. 194. 195. 196. 197. 198. 199. 200. 201. 202. 203, 204, 205. ILLUSTRATIONS, Pleurodont and acrodont dentition Head of Reptiles Blind-worm (Anguis fragilis) Feather of Bird . Wing of Bird Skeleton of Fowl ; Skull of Fowl es Pectoral Arch of Fowl Pelvis of Fowl (lateral view) Alimentary Canal of Fowl Ovary of Bird . Types of Birds’ Skulls. Types of Birds’ Skulls . Sternum of Fowl (front view) Split-Swimming Foot of Grebe (Podiceps fluviatilis) Foot of Raptorial Bird ° Head of White-tailed Eagle (Haliaétus albicilla) Skull of Duck . . . Head of Grey Lag Goose and Foot of Domestic Goose Foot of Gallinaceous Bird Scolopacidee Head of Barn-Owl (Strix fammea) Head of Nightjar (Caprimulgus ewropeus) Scansorial Foot, as seen in Woodpeckers and Parrots Foot of Passerine Bird (Wagtail) Head of Finch Head of Shrike Ovum and Structure of a Fowl’s Egg Section through part of Blastoderm (first day of incubation) Transverse Section of Blastoderm, incubated for eighteen hours Transverse Section through Posterior Part of the Head of an Embryo Chick of Thirty Hours Head of Embryo Chick of the Fourth Day Ovum of Rabbit. Diagram of Foetal Membranes of a Mammal Vertical Section of Injected Placenta of a Mare Diagrammatic Section of Pregnant Human Uterus with con- tained Foetus 348 wow w am Ov or On oN FO oo for) w 206. 207. 208. 209. 210. 211. 212. 213. 214. 215. 216. 217. 218. 219, 220. 221. 222. 228. 224, 225. ILLUSTRATIONS, Foetus of Sheep . . Diagram of Parts of Foetal Horse Feet of Ungulata Skeleton of Foot in various forms of Equidz Section of Horse’s Incisor Tooth Transverse Section of Horse’s Upper Molar Teeth of Pig . Skeleton of Pig 5 Stomach of Ruminant Skull of Ram Skeleton of Sheep Median Section of Ox’s Head Skeleton of Cow Feet of Carnivora Teeth of Dog, and Jaws. Bones of Toe of Cat Head of Rodent . Skull and Shoulder Girdle of Mole Skull of Hedgehog (Erinaceus europaeus) Long-eared Bat (Plecotus auritus) XVii 433 434 439 442 443 444 447 448 450 454 455 456 457 460 464 466 467 474 476 477 PART LI ACHORDATA (INVERTEBRATA) CHAPTER J. THE CELL AND SIMPLE ANIMAL TISSUES. THE CLASSIFICATION OF ANIMALS. THe foundation of all livine bodies is the cell. The cell is more or less the unit of life, and may even of itself constitute a definite organism. Most organisms are nevertheless built up of numbers of these cell units, numbers reaching into incaleul- able figures. In animals the cells lose their original form, whereas in plants their true symmetry is more or less retained. All the tissues, then, of the animal (and plant) are composed of cells collected and joined together in masses, forming the various groups or tissues that constitute the bodies of animals. Tue CELL-STRUCTURE. The essential part of the cell is the protoplasm. This proto- plasm is a clear gelatinous substance which is found in all cells, both animal and vegetal. It has been described by Huxley as the “physical basis of life.” Generally protoplasm is par- tially enclosed in the cell itself by means of a constricting membrane, the cell-wall. The protoplasm of each cell is con- nected with that of the surrounding cells by minute strands passing through pores in the cell-walla This living matter may also be observed in a naked or free state. 4 THE CELL AND SIMPLE ANIMAL TISSUES. Masses of a slimy substance—prohbably protoplasmic —in nature, named Bathybius by Huxley, are said to be found on the floor of the Atlantic. Sir Wyville Thomson, who at one time believed in the protozoon nature of this Bathylius, later asserted that it is in reality a gelatinous precipitate of calctum sulphate thrown down by the action of alcohol upon sea-water, —the dredgings in which the slime was detected having been preserved in spirit. Protoplasm is certainly found unprotected by any surrounding membrane in some of the simplest Protozoa This all-important living substance is endowed with the powers of contractility and movement, and is subject to such external influences as light, heat, and electricity. Movement takes place by the protrusion of any part of its surface, the protruded parts being known as “pseudopodia,” the rest of the protoplasm flowing in a wave-like manner after these processes. Inside the protoplasm of a cell is a body called the nucleus, which may be either a solid mass of protoplasm or a more fluid mass enclosed in a membrane, and containing one or more solid particles called nucleoli. The nucleus is composed of a more liquid part, the “nuclear fluid,” and a more solid part, the “nuclear protoplasm.” The nucleus varies in form: sometimes it is round, at others oval, or again it may be elongated and twisted. Protoplasm and nucleus are surrounded, as a rule, by a cell- wall, a definite bounding membrane, which more or less retains the contractile protoplasm. The essential part of the cell is the protoplasm, which has the power of independent movement, of metabolism, and of reproduction. Most organisms that we shall deal with, excepting the simple Protozoa, will be seen to be made up of numbers of these cells, which become united in various ways, and so form the animal tissues. We now know that a cell always originates from a pre-existing cell, The formation of one cell from another takes place chiefly by a process known as kuryokinesis or “ cell-division.” When a cell has received its full share of nourishment—that FREE CELLS AND EPITHELIUM. 5 is, when it has reached maturity—its protoplasm commences to separate into two equal halves. This division is preceded by a corresponding separation of the nucleus, and then the whole cell splits into two cells. During this process of cell-division certain definite changes take place in the nucleus. This body at first is spindle-shaped ; its contents are drawn out into longitudinal striae, when the centre of these striz becomes thickened and forms an equatorial zone or “nuclear plate.” This “ plate” divides, and each half travels to the poles of the spindle, which assumes a dumb-bell shape, then elongates, and the two nuclear masses, the remains of the equatorial plate, become surrounded by a clear fluid mass. These form the two nuclei at the poles of the spindle. As soon as this has taken place the whole protoplasm constricts in the middle, and the cell divides into two. There are two other ways in which cells reproduce—namely, by “budding” and by “endogenous cell-formation.” “ Bud- ding” is when one of the produced cells is smaller than the parent cell. In “ endogenous cell-formation” we get the proto- plasm and nucleus of the parent cell, splitting up internally into a number of small bodies, known as “spores.” These are seen only in the lowest forms of life. The separation of groups of various cells leads to the forma- tion of the different tissues. Of tissues we make out two chief kinds—namely, vegetative tissues and animal-life tissues. The former carry out the nourishment and maintenance of the body ; the latter are those tissues which are characteristic of animals, and whose functions are for movement and sensation. Of vegetative cell-tissues there are two divisions—(1) epi- thelium and free cells, and (2) connective tissue substances. The tissues of animal-life are (3) muscular tissue and (4) nervous tissue. 1. Free Cells and Epithelium. (a) Free or wanderiny cells are those that are found floating 6 EPITHELIAL TISSUES. in some fluid medium. The corpuscles of the blood, chyle, and lymph are excellent examples of free cells. In the invertebrate blood, which is normally colourless, will be found numbers of pale ameboid bodies. In vertebrate blood these amoeboid cor- puscles are augmented with red blood corpuscles (fig. 1), round cell-dises which contain the colouring matter of blood—namely, hemoylobin—a substance which, as we shall see later, plays such an important part in respiration. Besides blood and lymph corpuscles we find other isolated cells in the body, the ova and spermatozoa, which become detached as single cells 0. V6 Fic. 1.—BLoop CorPposcLes oF VERTEBRATA. u, Of man; b, of goose ; c, of crocodile; d, of frog; e, of skate. (Nicholson.) from the epithelial walls of the male and female organs, the testes and ovaries. The form, especially of the spermatozoa, varies greatly: in most cases the spermatozoa have a long thread-like tail attached to the nucleated cell. ()) Epithelial tissues consist of groups of cells, which in simple layers line the exterior and interior of the body surface. The internal lining is known as “endothelium.” There are four chief types of epithelium, each distinguished hy the form of the cells—namely (1) cylindrical, (2) ciliated, (3) pavement, and (4) glandular epithelium. The lower cells of these cell-masses retain their natural form ; but the upper ones may become hardened. Thick stratified layers of such cells occasionally become fused, and produce horns, nails, claws, hoofs, &c. Sometimes the outer walls of the epithelial cells are thickened, forming a “cuticle.” These cuticular membranes are perforated by small pores and also by larger passages: in these cuticular pores are placed the hairs and feathers, The cuticular secretions may form v hard shell CONNECTIVE TISSUES. 7 or ease for the organism, an exoskeleton, as seen in the Crustacea and insects. Glandular epithelium is that epithelium in which some cells secrete not a solid but a liquid substance. Jn the most rudi- mentary cases the gland is formed by a single epithelial cell, the secretion passing out by either a special opening or through the superficial membrane. Several of these cells may arrange themselves around a central space and pour their secretion into it; the gland then forms a blind invaginated sac opening to the exterior or interior by the neck of the whole glandular mass. From this simple gland a compound gland is built up by re- peated regular or irregular outgrowths. The terminal portion of each gland is converted into a duct in most glands, for the carrying away of the fluid secreted. Some glands, however, are ductless or blind (spleen, &c.) 2. Connective Tissues are those which connect and surround other tissues, and act as supporting and skeletal structures. The presence of intercellular substance distinguishes this group. This intercellular matter is secreted by the whole of the cells which it surrounds, and is very variable both in consistency and in structure. One variety is known as _jilrillar-connective tisswe, in which elongated cells are embedded in a solid inter- cellular substance broken up into bundles of fibres. In liga- ments and tendons the fibres have a wavy outline, and are parallel in arrangement. When the fibrille are treated with acids, they swell up, and a second form, which resists these reagents, appears. These threads are elastic jilres, and may predominate so as to form elastic tissue, which branches and forms a ‘network, sometimes of great strength, such as the lzga- mentum nuche of the neck—the ligament by which the head of quadrupeds is held up in a horizontal posture: at other times they spread out, forming the so-called “ fenestrated membranes ” of Henle in the arteries. The two most important skeletal tissues are cartilage and bone. Cartilage is also a true connective tissue, and may be told by 8 MUSCULAR TISSUE. its spherical cells and gristly intercellular substance in which the cells are embedded. We can recognise three distinct kinds of this cartilage — hyaline, fibrous, and elastic. The cells of cartilage are placed in clear round spaces. Its varieties will be pointed out when we come to more special parts. Suffice now to say that it is found in both of the great divisions of the animal kingdom, and may even constitute the entire skeleton of some of the fish (Zlasmobranchii). Osseous tissue, or bone, is hard and possesses a high degree of rigidity, by the intercellular substance being hardened by the deposition of carbonate and phosphate of lime, these salts constituting about two-thirds of the weight of bone. The cells (the bone-corpuscles) occupy spaces in this intercellular matter. Numerous canals (Haversian canals) run through the bone, con- taining blood-vessels and nerves. The calcareous matter is arranged in concentric rings round these canals, which begin in that highly vascular periosteal layer that circumscribes the whole bone and open into long spaces, the marrow canals, in the axes of the long bones. In all cases bony tissue is preceded by either cartilage or other connective tissue. The two animal-life tissues are muscle and nerve. These can be detected in all animals save the very lowest forms, which are apparently nothing but undifferentiated protoplasm. 3. Muscular Tissue is contractile : this power of contraction is due, as has been pointed out, to the protoplasm itself. By differentiation of the protoplasm of certain cells and groups of cells the power of contractility is brought to a higher state of efficiency, and a tissue, the so-called muscular tissue, is formed solely for movement. Muscle-cells during move- ment contract and expand. In some of the lower animals we see cells in which only part of the cell is differentiated into a muscle fibre. A stage further, and we find the whole cell becoming elongated and converted into a definite muscle fibril. Of muscle there are two kinds, the striated and the unstriated, NERVOUS TISSUE. 9 The unstriated muscle is composed of flat, elongate, spindle- shaped bodies, which contract slowly and remain in a con- tracted state for some time. They seldom are more than gdg of an inch in length. They form muscles over which we have no control, and are thus called involuntary muscles. This variety is prevalent in the lower animals, but is also found in all high forms of life. Each smooth muscle-cell has one distinct nucleus. Striated or voluntary muscle consists of multinucleated masses called primitive bundles. It is composed of long cylindrical fibres, about 335 of an inch in diameter in mammalian muscle. Most or all of the cell protoplasm is converted into a cross- striped substance, due to the alternate double and single re- fractive powers. This striped or voluntary muscle is under the control of the animal will, and can contract with great energy. Almost the entire protoplasmic contents of the cells are con- cerned in the production of this voluntary muscular tissue. The cells become elongated into long fibres, the primitive bundles; and the nucleus divides and forms numbers of nuclei, each fibre being surrounded by a membrane, the so-called “ sarco- lemma.” The sarcolemma is an elastic sheath. The primitive bundles also arise by the fusion of several cells. Muscular tissue, then, is also cell-tissue modified for a certain definite object—namely, movement. There is certain striated muscular tissue called cardiac muscle, which forms the walls of the heart, and is involuntary in action. Cardiac muscle is cubical in form, and has a little side projection from each cell. 4, Nervous Tissue is found generally with muscular tissue. It forms the seat of will and sensation, and is the means by which stimuli are carried to the muscles to cause their move- ment. The nervous tissue is supposed to have originated from the ectodermal sense-cells found in the skin, and that, still re- maining united to the same, they have grown inwards, and have thus only in a secondary way become united to the muscle-cell, which is prima facie contractile. In nervous tissue there 10 THE DIFFERENCES BETWEEN ANIMALS AND PLANTS. are two distinct elements — namely, nerve-cells and nerve- jilaments—which have separate structural differences. Nerve-cells are found in the brain, in the spinal cord, in the so-called ganglia of the lower animals, &c. ; they are really central areas for the nervous stimuli, Each nerve-cell or gang- lion cell possesses a very distinct nucleus and nucleolus, and one, two, or more processes, when they are known as uni, bi-, or multipolar ganglion cells. One root is always that of a nerve-filament. Nerve-fibres are of two kinds: one variety carries impulses —sensations—from the central organ (cells) to the peripheral organs,—these are called motor or secretory fibres; the other carries iinpulses from the periphery to the central organs, and are known as sensory fibres. In most cases the sensory nerves are united at their peripheral end with the so-called ‘“end- organs” in the skin, &c., these end-organs being derived from the modified epithelial cells. Such are some of the modifications that are assumed by cells in the animal kingdom. The lowest animals, we shall see, possess neither tissues nor organs composed of cells, and yet each organism, although only a single cell, is complete in itself and reproduces a similar species. Tue DirrerReNces BETWEEN ANIMALS AND Puants. Living bodies are divided into two groups called “king- doms,” the one the Animal Kingdom, the other the Vegetable Kingdom. Although there are apparently great differences between the two, yet when we come to examine the lowest animal forms and compare them with the lowest vegetal forms we shall observe so great a similarity that it is impossible to say to which kingdom they belong. In fact, there is no hard-and-fast line to be drawn between these two organic groups. Such lowly creatures as Volewe are treated by THE DIFFERENCES BETWEEN ANIMALS AND PLANTS. 11 botanists as plants, whilst the zoologist includes them in the Protozoa. It may be said, speaking generally, that animals are capable of free movement and that plants are fixed ; but when we examine some of the simplest forms of life this distinction will be found untenable. .Animals are endowed with sensation, plants are not, as a rule; but such plants as Drosera, Venus’s fly-trup, &c., surely have this phenomenon developed. Animals have their organs internal, their absorbent surface inside ; plants have external organs, and the absorbent surface also external. Think for a moment of the Tapeworms (Cestoda), which obtain their nourishment by osmosis through the skin, and we shall at once see that this again will not hold good. When we compare the tissues of an animal with the tissues of a plant, then we observe greater differences. The cells of the animal are altered in form, whilst those of the plant retain more or less their original appearance. The cell-wall, too, of the animal is nitrogenous, that of the plant is non- nitrogenous. But all this only applies to the higher plants and animals : if cannot apply to those unicellular forms, where, as we see in Amceba, there is vo cell-wall at all. It is often thought that we can tell a plant by its green colouring matter, chlorophyll, but not all plants have this chromatic substance in their tissues ; whilst, on the other hand, some animals—such as Hydra, Bonellia (one of the Worms), and some sea-anemones (Actinuzoa)—owe their green colour to the presence of this sub- stance. Cellulose is the substance that forms the cell-wall of plants, and is characteristic of the vegetable kingdom ; but we also find it in the “tests” or cases of those curious marine animals, the sea-squirts or Axc/diuns. In the higher animals a substance known as cholesterin is found: this was at one time considered a purely animal component, but we now know that it is also found in at least one family of plants, the Leguminosee: or Pea and Dean family. Generally speaking, animals are nitro- genous, plants carbonaceous; but, as in the prior instances, this also will not invariably apply. There are no definite distine- He2) THE CLASSIFICATION OF ANIMALS. tions, then, between the animals and plants in regard to their chemical constituents. Perhaps the greatest differences are to be found in the metabolism of organisms. We cannot feed an animal on purely inorganic food, whilst, on the other hand, we can so feed a plant. Both must have salts and water; but whilst plants can be nourished with the addition of carbon dioxide and nitrates of ammonia, an animal must have nitrogen- ous and carbonaceous matter in some organic form and not in a mineral form. An animal absorbs oxygen and gives out CQ, ; a plant exhales oxygen which is derived from the absorbed CO,. Thus we see that there are differences between the plant and the animal, but that many of them do not invariably hold good. There are forms of life which we may fairly say bridge over the great hiatus that separates the horse from the grass upon which it feeds: such intermediate species, interesting as they are, we must only briefly refer to in this manual. THE CLASSIFICATION OF ANIMALS. The old method of classifying animals was to divide them into two sub-kingdoms, known as the Invertebrata and the Vertebrata, —the absence or presence, respectively, of an internal skeleton being the character upon which this division was based. Invertebrates are those animals which have no internal skel- eton; but, of greater importance still, they possess no structure known as the notochord. The notochord is a primitive axial skeletal rod, found on the dorsal surface. In all invertebrate animals the nervous system is ventral—that is, it is always present on the lower surface of the animal; whilst, on the other hand, the hemal or blood system is dorsal, the ali- mentary canal or gut being situated between. Invertebrates may possess a skeleton, but it is always external (exoskeleton). Vertebrates, on the other hand, always possess a notochord, and nearly always an internal skeleton, composed of an axial rod, the vertebral column, besides the cranium, and an appendicular THE CLASSIFICATION OF ANIMALS. 13 skeleton—the limbs. The vertebral column—the backbone— and the cranium enclose the central nervous system, which is always dorsal, whilst the nervous system in invertebrates is ventral. The hemal system—the heart—is placed ventrally,— that is, in the reverse position to that in which it is found in the former group. Just as there are intermediate forms between the animals and plants, so are there connecting links between these two primary groups of animals. A small fish, known as the lancelet (Amphioxus lanceolatus), found in the sands of the Mediter- ranean, has no proper internal skeleton at all, yet it has a noto- chord and dorsal nervous system. The groups of Asczdians, or sea-squirts, are in their young stages distinctly vertebrates ; for the young so-called Appendicularia larva has a distinct dorsal nervous system and an axial rod, but the adult Tunicate, as it is also called, is distinctly an invertebrate animal with no noto- chord and a ventral nervous system. How, then, can we distinguish these from true vertebrates? At no time do they possess a brain or cranium as we see in the higher animals. They are called, therefore, Acrundu, to dis- tinguish them from all the other vertebrates, which are knotvn as the Craniotu. This was the most generally adopted primary grouping of animals, into Invertebrata and Vertebrata ; but for many reasons a more recent classification has many advantages over it. This latter is based on the cell-structure of the animal. By it the whole animal kingdom is divided into three primary groups, known as the Protozoa, Mesozoa, and Metazoa. The Protozoa are those animals of extremely simple organisa- tion, and whose bodies are composed of a single cell. The Mesozoa are a small group of parasitic animals whose bodies are composed of a few cells only, the cells retaining more or less their original form. These constitute a connecting link between the single-celled Protozoa and the third group, the Metazoa. 14 THE CLASSIFICATION OF ANIMALS. The Metazoa constitute a group that includes the majority of animals, These are built up, not of one cell or a few cells, but of countless numbers of cells, which form the complicated animal tissues—muscular, nervous, connective, &c. This divi- sion will be found to contain both invertebrates and vertebrates. The Protozoa form the first group of animals, the lowest organisms, single-celled creatures, which are, nevertheless, im- portant to us agriculturally, as many of them produce diseases, such as diphtheritic roup in fowls, liver-rot in rabbits, malarial fever in man, psorospermosis of the skin, &c., in man and many domestic animals. The Mesozoa consist of one division only. They are small parasitic germs, such as the Dieyema, which are found in invertebrate animals. They are extremely rare, and as they are of no agricultural importance whatever, can at once be dis- missed with a word of remembrance that they constitute one of those stepping-stones that fill up the great gap between the Protozoa and the Metazoa. The multicellular animals, or Metazoa, are divided into the following groups, called classes :— 1. Coelenterata, or Jellyfish, Polyps, Sea-anemones, Corals, &c. 2. Echinodermata, or Starfish, Sea-urchins, and the nearly extinct Sea-lilies. 3. Vermes, or Worms. . Mollusca, or Shells. 5. Arthropoda, or the Jointed-limbed animals, as Insects, Spiders, Scorpions, and Crabs, &c. The above are all Invertebrate Metazoa. The Spongide, or Sponges, may belong to this division : but whether they are to be looked upon as colonies of Protozoa, or Metazoa, there is some diversity of opinion. They scem to present most atinities to the Metazoa, and should doubtless be included in the Iny tebrate division of that group. 6. The sixth class of Metazoa include the Ascidians, Tunt- cates or Sea-squirts, the Amphioxus or Lancelet, and the worm. i er- THE CLASSIFICATION OF ANIMALS. 15 like Balanoglossus These form the connecting group between the Invertebrate and Vertebrate Metazoa. The Vertebrate Metazoa are contained in five classes, namely— 7. Pisces, or Fish. 8. Reptilia, or Snakes, Crocodiles, and Lizards. 9. Amphibia, or Toads, Frogs, and Salamanders. 10. Aves, or Birds. 11. Mammalia, or Quadrupeds and Man. The above eleven classes of Metazoa may be grouped in two divisions, according to the absence or presence of a notochord. Those without a notochord are called Achordata, those with a notochord Chordata. The latter, again, are divided into Acrania and Craniota. The Acrania include, besides the Tunicates, the worm-like creature called Balanoglossus and the quaint little fish-like Amphioxus. These always have at some period of their life a dorsal nervous system and a notochordal rod which extends nearly the whole length of the body ; but the nervous system, which develops as an open canal (another character common to vertebrate animals), never expands anteriorly into a brain. In fact, in general appearance Tunicates and Balanoglossus are in- vertebrates, while Amphioxus forms another stage higher, con- necting the lower animals with the Fish. Amphioxus has been described by Couch and others as a fish. The Craniota, on the other hand, have the anterior end of the nervous cord enlarged into a brain placed in a cartilaginous or bony box, the cranium, and are supplied with an internal skeleton. The groups of animals, then, may be tabulated as follows :— CLASSIFICATION OF PROTOZOA Lee MESOZOA . ACHORDATA = Invertebrata METAZOA CHORDATA = Vertebrata. [A more re- cent classifica- tion of Verte- brates has just. appeared, by Dr Hans Ga- dow, and will be referred to later.] ANIMALS. Rhizopoda. ( Ciliata. * | Flagellata. Foraminifera. Sporozoa. Dicyemidz. Spongide Hydrozoa. Coelenterata .+ Actinozoa. l Ctenophora. Echinuride. Echinodermata, Asteride. \ Bolothuride. Trematoda. Platyhelminthes { Cestoas. Nemertini. Vermes : Nemathelminthes { pe ane { Chetopoda. Annelida -, Gephyrea. Hirudinea. Peripatus. rai i ulide, Myriopods * { Scolopendride. 5 { Malacostraca. Cmstacea: *'( Entomostraca. ( Scorpionide. Arachnoidea 7 Araneide. Acarina. Arthropoda Coleoptera. Hymenoptera. Lepidoptera. Insecta . .) Diptera. (Hexapoda)! ‘\ Hemiptera. Neuroptera. Orthoptera. Aptera. ( Lamellibranchiata. Mollusea . ) Gastropoda. (Proper) Pteropoda. Molitsee ( Cephalopoda. Molluscoidea { Sess gag ACRANIA CRANIOTA Urochordata (Ascidians). Cephalochordata (Amphioxus). ( Marsipobranchii. Elasmobranchii. . i Ganoidei. { Urochanta ( (Balanoglossus). Pisces Dipnoi. Teleostei. “Ophiomorpha. - Anoura. \ Urodela. [ Chelonia. Ophidia. * |) Lacertilia. Crocodilia. f Hauke : ‘arinate. Ornithodelphia is Monotremata. Didelphia = Marsupialia. Edentata. Sirenia. Cetacea. Ungulata. Proboscidea. arnivora, potentia. usectivora. Cheiroptera, Primates, Ichthyopsida Amphibia Reptilia Sauropsida . Aves Mammalia . Monodelphia . 1 Thrips (Thysanoptera) are now placed in a separate order, 17 CHAPTER IL PROTOZOA, OR SINGLE-CELLED ANIMALS. Tue Protozoa are the simplest forms of animal life: they are all of small size, of extremely simple constitution, and invariably unicellular. In no case do we find sexual reproduction or sexual differences of any kind. They are animals that have remained as simple cells, to all intents and purposes like the cell described in chap. i. Some forms of protozoa are simple drops of sarcode—protoplasm ; others have not only a definite cell- wall, but possess the power of secreting calcareous and siliceous shells. These shell-bearing species, or Foraminifera (tig. 3, iv. and v.), are present in myriads in the waters of the ocean, their “tests” or shells falling to the floor of the sea as the animals die. Many of these tests are dissolved before they reach the bottom, if the depth of water be very great; yet millions of others arrive safely upon the bed of the sea, and there by slow degrees they form a layer of a white or creamy colour. Of such formation is the globigerine ooze on the floor of the Atlantic and also the radiolarian ooze,—protozoa of the genera Globigerina (fig. 3, v.) and Radiolaria taking the chief part in the formation of these two oozes respectively. Of ancient rocks we know that much of the Chalk has been formed in a similar way, by the slow accumulation on the sea-bed of these and other falling tests. Not only do we find that the Chalk in many instances is built up of these minute organisms, but also that their tiny shells represent genera existing at the present day. What countless B 18 AMCEBA. myriads of these microscopic organisms must be present in the chalk rocks of our North and South Downs alone, when we consider that thousands go to the square inch! The Protozoa that have a Gefinite cell-wall are sometimes called Infusoria (fig 3, i., ii, iii): these and the shell-bearing Foraminifera (fig. 3, iv. and v.) are of definite form. The In- fusoria are quite unable to alter their shape, but some of the Foraminifera have the power of throwing out long thread-like processes or pseudopodia through minute perforations in the shell. One of the simplest Protozoa is known as the Proteus- Animalcule or Amba (fig. 2). Ameba is a simple, unprotected mass of protoplasm or sar- code, which may be found in damp earth and in water. In appearance it resembles a small speck of white, transparent, structureless jelly. If this speck is observed under strong magnifying power, it will be seen to move by throwing out little finger-shaped processes, the pseudopodia (Psu). This simple organism is apparently composed of two layers, a granular Jayer inside and a clear transparent layer on the outside: the former is known as the endosare and the latter as the ectosarc. These two layers must not be mistaken for two distinct membranes, for they are continuous, only certain granules collect towards the interior. When the pseudo- podia (Psu) are thrown out we shall see, if we watch care- fully, that the granules flow up the centre of the process as it elongates. Three other bodies are to be noticed in this minute creature : first, a small dark oval spot, with a clear border and permanent in shape, situated in the endosarc ; this is the nucleus (z), and it will be found to stain dark-red with picro-carmine. There will also be seen contracting and expanding a clear space; this is the so-called “pulsating vacuole ” (cv), of which there are two in some forms of Protozoa (Paramavium). The pulsating vacuole is said to be an excretory organ ; uric acid has been extracted from these minute cavities. Lastly, there are present a number of so-called “food vacuoles” (/'v), spaces surround: AMCEBA. 19 ing the particles of food ingested by the ameeba. This pro- teus-animalcule is neither provided with mouth nor anus. The food can be taken in and expelled at any part of the body. This process can easily be watched if particles of indigo are placed in the water surrounding an amceba: a speck of indigo will be found to be drawn to the protozoon by the pseudo- podium, and then it can be watched gradually sinking into the protoplasm until it reaches the endosarc, where it remains whilst the substance (if an organism) is digested, the waste part being expelled through any part of the animal. The food con- ee A x : --@ Fic. 2.—Ama@pa (greatly magnified). i. Large specimen, showing structure. ii. A smaller specimen in process of division. iii. Later stage of ii, @ and n, nucleus; ) and cv, contractile vacuoles; Fv, food vacuoles; Psu, psendopodia. sists of organisms still smaller than the amcebe are themselves. Amceba reproduces by the primitive method of “fission” or division. The nucleus of the amcba divides into two (fig. 2, ii. and iii., a), and one of these nuclei, surrounded by part of the original protoplasm, breaks off and floats away ; thus one ameeba becomes two. This division may go on until one amcba has given rise to hundreds. But by degrees each amcba becomes smaller and smaller, and they would eventually die out. To counteract this, what is known as “ rejuvenescence ” takes place. Rejuvenescence is the union or conjugation of two amcebe, 20 INFUSORIA. whose protoplasm unites together, together with the nuclei, forming one larger individual, which is again in a fit state to undergo once more rapid division. This conjugation is really a kind of primitive sexual reproduction, although there is, as far as we can see, no difference between the conjugating individuals, Infusoria (fig. 3, i., i., and iii.) are those protozoa which, unlike Ameeba, have a definite form, with an external membrane, which bears either cilia or flagella. Cilia are fine, short, hair-like threads of protoplasm ; flagella are long whip-like processes that pene- ’ trate the membrane of the animalcules. The Infusoria were Fic. 3.—INFUSORIA AND FORAMINIFERA. L Euglena. ii. Cercomonas intestinalis. iii, Polytoma, free and encysted. iv. Textularia. yv. Globigerina. discovered at the end of the seventeenth century. The outer mem- brane is in the form of a cuticle, showing a double contour, These protozoa are usually to be found in liquid media, such as putrid water and other fluids ; whilst many are found living in the ali- mentary contents of man and other animals, as also in other parts of the body. Sometimes they are so far parasitic as to cause seri- ous disorders, and even death. According as to whether there are numbers of cilia surrounding the infusorian or only one, two, or more whip-like flagella, these protozoa are placed in two divi- sions, known respectively as the Ciliata and the Flagellata, FLAGELLATA. 21 The Flagellata are allied to certain fungi. They are animals, because the body and the flagella are contractile ; they are cap- able of voluntary movement; they possess excretory organs in the form of contractile vacuoles ; and, moreover, they are pro- vided, unlike Amceba, with a more or less definite space for a mouth. One family of them, the Monadine, are found in putre- fying infusions, and are exactly like fungoid monads. Two genera, Trichomonas and Cercomonas (fig. 3, ii.), which are pro- vided with whip-like flagella, may be found in abundance in the intestines of vertebrates. Reproduction takes place by transverse fission, the flagella being first withdrawn within the membrane prior to the nucleus dividing. When that stage is completed, the protoplasm divides, and then the whole organism splits transversely across, forming two flagellata, which soon protrude their flagella and become active (iii.) Reproduction in the Flagellata also takes place by spore formation ; the protozoon draws in its flagella and becomes encysted: when in the en- closed stage, the protoplasm, following the rapid division of the nucleus, forms around each new nucleus a round mass, which develops a hard shell or coat, and so produces a spore. Hun- dreds of these spores may be formed from one individual. This spore formation is always preceded by the conjugation of two individuals, similar to what we observed in Amceba. The Flagellata are divided into four sub-classes, as follows :— i. Lissoflagellata.—With no collar - like outgrowth around the oral pole. ii. Choanoflagellata.—Flagella provided with a collar sur- rounding the anterior pole of the cell. iii, Dinoflagellata.—Provided with a longitudinal groove and a flagellum projecting from it, and also a transverse groove in which lies a second flagellum. iv. Rhynchoflagellata.—Provided with reticulate protoplasm (marine). Trichomonas and Cercomonas both belong to sub-class i One species of Cercomonas—viz., gallime—is often found in 22 CILIATA. abundance in the diphtheritic growths in fowls, but the exact part it plays in the disease is not known. Another species is found in the liver of pigeons. The Ciliata have a more complicated body than the forms we have been considering. They may have a definite mouth and anus, and have not only a nucleus but a distinct para- nucleus. Some forms, such as Vortzcella, the bell-animalcule, are stalked. They are all more or less covered with fine vibratile cilia. Reproduction takes place by a process of budding or “gemmation.” This gemmation is when one of the divided parts of the ciliate is smaller than the other: the smaller part—the bud—breaks off, then floats away and forms a fresh specimen. Reproduction also takes place by direct fission, whilst conjugation is of common occurrence, the conjugating individuals usually being of different sizes. The Ciliata are divided into four groups, as follows :— All the cilia alike and A, Cilia cover the whole short (i) Holotriche. surface of the body. |A row of long cilia around the mouth (ii) Heterotriche. 8. Cilia on ventral surface . (iii) Hypotriche. Cc. Cilia arranged in a crown around the puieh, and often in the form of a girdle (iv) Peritriche. The Holo-, Hetero-, and Peritriche are all found in domestic animals. Two holotriche, known as Isotricha prostoma and I. intestinalis, are abundant in the rumen of ruminants. They are not there as parasites but as commensals. Commensalism is when an animal lives upon another animal, ovcasioning not only no harm but actually benefiting its host. On the other hand, a species called Globidium Leuckartt causes serious inflammation of the mucous membrane of the horse’s intestine. A very deadly disease in horses and mules in India, called swrra, is due to one of these infusoria, 7 upano- soma Evansi, which takes up its abode in the blood, producing a pernicious anemia. Whilst the infusoria increase there is also SPOROZOA. 23 noticed an increase of the white blood-corpuscles and a similar decrease of the red, death possibly resulting in from twenty to sixty days. As much as fifty per cent of the cavalry horses in India have been in some cases destroyed by it, and at Tonquin the French army horses also suf- fered similarly. The Tsetse disease in 8. Africa is likewise due to a Try- panosoma in the blood, the Tsctse- fly merely acting as a carrier. Balantidum coli (fig. 4) is one of the Heterotriche. It is found in the rectum of animals and man. These white ciliata are found free- swimming in the rectal matter. They encyst and pass out in the dung: when the food becomes soiled by the excrement they are again taken into the body in the Fic. 4.—CILiaTE Prorozoon (Balantidum colt). case of pigs, in which large num- bers are to be found. No harm is portrasile vacuoles ; B peristome done apparently to the pig by their Nanna) pict presence. In man a related form often produces serious disturbances in Russia, Sweden, and other parts, but I know of no record in Great Britain. These are only a few cases of the many Ciliata that are found in various parts of animals. Sporozoa.—Another very important group of protozoa para- sitic in both vertebrate and invertebrate animals is the group of Gregarines or Sporozoa (fig. 5). These protozoa are capable of producing serious pathological disturbances, often leading to death. Sporozoa are typically elongate in form, as seen in the family Gregarinide, the anterior part becoming apparently con- stricted off: this division is not a true one, however, for, as in all Protozoa, these parasites are unicellular. In the most typical cases there is hatched from a spore, called a chlamydospore, 24 DISEASE-PRODUCING SPOROZOA. one or more flagellule or falciform young, which become con- verted into creatures similar to Euglena (fig. 3, i.), the so-called “Euglenoid phase.” These conjugate and encyst, and their contents split up into spores. The reproduction of sporozoa is chiefly by spore formation, the spores being of a peculiar lemon shape in many cases, and are known as “ pseudo-navicelle ” (fig. 5, m). Each of these spores contains one or more bodies, the falciform bodies, 0, each falciform body giving rise to a small flagelloid creature. To these Sporozoa are no doubt closely related the curious bodies called Psorosperms found in the liver, muscles, and intestinal slime of animals and man, greatly resembling in appearance pseudo-navicelle. The family Gregarini?de are only parasitic in invertebrate animals, and need no further notice. Another family of Sporozoa are called Coceidia, which trans- form themselves into egg-shaped zoosperms by the formation of a capsule and the production of several large spores from their granular contents. Disease-producing Sporozoa.—Three well-known maladies are produced in birds, animals, and man by these low forms of life —namely, coccidiosis, or “liver-rot,” in the rabbit; psorosper- mosis of the skin in many animals, and especially birds—the so-called canker” of pigeons; and an often fatal malady, diphtheritic roup, in poultry—which the writer has in many instances demonstrated to be due to protozoon parasites of this group.! Coccidiosis, which we may here take as typical of these diseases, is a common complaint affecting the liver especially of the rabbit, and is produced by the species known as Coreidium oviforme (fig. 5). This sporozoon is ovoid when adult, and enclosed in a double-contoured shell from 304 to 50m long and from 20 to 284 broad. These extremely minute bodies become encysted, when we observe that their protoplasmic contents 1 The Parasitic Diseases of Poultry, p. 4. Gurney & Jackson, 1897 COCCIDIOSIS. 25 separate away from the cell-wall and form a central round or oval mass (7). Both adult and encysted stages may be freely detected in the liver, in the white and yellow patches which are characteristic of the disease. Now if we collect numbers of these encysted forms and place them on damp sand in a warm temperature, we shall soon observe by microscopic examination that the central protoplasmic ball splits into two and then four (g and h). This is a kind of segmentation or division, the round bodies being known as “sporoblasts.” These sporoblasts Fic. 5,—CoccIDIUM OVIFORME OF Rassit's Liver. After Balbiani. a, b, e, Young Coccidia in epithelium of liver; d, e, f, encysted adult Coccidia; g-l, development of sporoblasts; m, mature sporoblast, showing the two falciform hodies ; x, the two spores separate; o, a falciform spore—y, its nucleus. (From Par. Dis. Ani., Neumann.) elongate, expand at each end, and are seen to be surrounded by a thin membrane, within which is also seen a granular lump. Each of these “sporoblasts’ really contains two spores, the falciform spores (0), described in a typical sporozoon—in fact, the so-called sporoblast is a pseudo-navicella. Just as in the type referred to on the preceding page, so here, each falciform body gives rise to a little flagelloid creature. This form migrates from cell to cell of the animal’s liver, encysting and produc- 26 COCCIDIOSIS. ing more spores, and so rapidly increasing the area of the disease. It is supposed that these sporiferous cysts are carried with dust, &c., and hence get taken into the mouth with food, eventually reaching the liver. The sporocyst ruptures in some region near the liver and the sporoblasts appear ; these latter burst and discharge the spores or falciform bodies, which become active, and are said to ascend by the ductus chole- dochus to the epithelium of the liver and bile-duct. Here the germs, having entered some of the hepatic cells, cause these cells to rupture, and they may even destroy the walls of the bile-duct itself. They finally encyst, pass out into the intestine, freed by the breaking up of the tissues in which they are embedded, and so out to ground by the anus of the diseased animal. Their presence causes the liver to swell, They are detected by the creamy cystic areas, varying in size from a millet-seed to that of a pea. They are often so abundant that the cells of the liver atrophy, and cheesy-like masses appear not only in the liver substance but in the bile. These prurigerous masses on microscopic examination are found to contain numbers of coc- cidia. The disease may affect man as well as the rabbit, and I have found it in the liver of fowls. It may possibly be taken for tuberculosis unless carefully examined. The walls of the intestine may be invaded as well as the liver. To suchlike forms is the “ diphtheritic roup” of poultry due, the “canker” of pigeons, turkeys, and fowls, and other minor complaints ; whilst in man that terrible scourge malaria is also caused by some ameehoid form in the blood, the germs being transmitted to him by mosquitoes, as has been recently demon- strated by Golgi. Enough has been said of this group of simple animals, the most rudimentary forms of animal life that exist, to show that they are of some considerable importance, not only to the farmer and poultryman but to man in general, and that a slight knowledge of their habits and life-histories is not only of interest but of economic value to us. 27 CHAPTER IIL MESOZOA, SPONGES, CCRLENTERATES, AND ECHINODERMS. Mezsozoa. Tue Jfesozoa are a small group of invertebrate animals living as parasites in frogs, earthworms, &c. Although they are of much scientific interest, they are of none to the agriculturist. Their chief importance to us is from their being intermediate between the two great divisions of the animal kingdom. The principal genus is a small parasite known as Dicyema. SPONGIDE OR PoRIFERA. A sponge is a compound structure of true animal nature. It is composed of contractile tissue, which is supported by a skele- ton of hard spicules or fibres. In past ages sponges were thought to be plants, but their true animal nature has long since been demonstrated. The simplest form of sponge is represented by a fixed cylindrical tube, with an exhalant opening, called the osculum, at the free end. The contractile wall of the cylinder is supported by rayed spicules, which may be calcareous or siliceous and of very variable form: it is perforated by small pores, known as inhalant pores, which lead into ciliated internal chambers. In these ciliated chambers are found cells lining the cavities peculiar to the Sponge. Such cells are called “collar cells,” each being provided with a long cilium and a distinct nucleus in the lower part of the cell. The reproduction of sponges 28 CCELENTERATES. is much more advanced than in the Protozoa. True ova are found in the layer of tissue known as the mesoderm, or middle layer. These ova go through a process of cell-division known as segmentation, a process henceforth to be observed in all the following groups of animals. The single cell, the ovum, at first divides into two, but, unlike the protozoon, it does not separate ; then by further division four cells are produced, then eight, then sixteen, then thirty-two! Eventually there is formed a free- swimming body, a larva, which is composed of a number of cells ciliated on the exterior. This larva is called an amphi- blastula, which, after leading a free aquatic life, eventually settles down, and, fixing on to a stone on the floor of the sea, becomes gradually metamorphosed into a sponge. Most sponges are marine; a few, however, are fresh-water — one common form, Spongilla fluviatilis, being often abundant in our streams. CG@LENTERATES. Ceelenterates include the Jellyfish, Sea-anemones, and Corals. These marine animals have regular consistent tissues. The cells of which they are built up have lost their original form, and have become sorted out into different eroups, each with their special functions, the various groups forming the tissues of which the animals are built up. In the outer layer of cells (the skin or epithelium) there are found in all Ccelenterates, more or less highly developed, certain cells that are known as “ thread- cells ”—-cells that are modified as weapons of offence and defence, being endowed with stinging propensities. Each of these cells, or “cnidoblasts,” is provided with an internal barbed thread. When the cell is touched, this thread, like a flagellum of one of the Protozoa, is darted out and enters the skin of the prey or enemy, carrying with it a certain amount of poison, which produces the curious stinging and even paralysing sensation we experience when a jellyfish settles upon us when we are swim: ming in the sea. The amoeboid cell-unit here loses its individ- CCELENTERATES. 29 uality. Amongst these Coelenterates we find two chief types, the so-called Medusa or Jellyfish and the Polyp. These two totally different animals are one and the same, the medusa being asexual form of the asexual polyp. There is thus produced a most remarkable phenomenon, known as the alternation of generations—that is, the alternation of a sexual and an asexual form of the same creature. The class Coelenterata contains the Corals (Actinozoa), Dead- men’s Fingers (Octactinia), Sea-anemones (Hexactinia), the polypoid and medusoid Hydrozoa, and the Ctenophora,