’ ‘ ‘ . BE a Ta aw a Sees 3 eS eset ste%, m ch ' Ka-gn's Hit g & tye s : aoe <> CORNELL UNIVERSITY. THE Roswell P. Flower Library 7 THE GIFT OF ROSWELL P. FLOWER FOR THE USE OF * THEN. Y. STATE VETERINARY COLLEGE 1897 2787 ‘ornell Universit: The Protozoa, Date Due This boo’, ce , 7 he kept = —— 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/cu31924001026727 THE PROTOZOA Columbia Gniversity Biological Series. EDITED BY HENRY FAIRFIELD OSBORN AND EDMUND B. WILSON. 1, FROM THE GREEKS TO DARWIN. By Henry Fairfield Osborn, Sc.D. Princeton. 2. AMPHIOXUS AND THE ANCESTRY OF THE VERTEBRATES. By Arthur Willey, B.Sc. Lond. Univ. 3. FISHES, LIVING AND FOSSIL. An Introductory Study. By Bashford Dean Ph.D. Columbia. 4. THE CELL IN DEVELOPMENT AND INHERITANCE. By Edmund B. Wilson, Ph.D. J.H.U. 5. THE FOUNDATIONS OF ZOOLOGY. By William Keith Brooks, Ph.D. Harv., LL.D. Williams. 6. THE PROTOZOA. By Gary N. Calkins, Ph.D. Columbia. COLUMBIA UNIVERSITY BIOLOGICAL SERIES. VI. THE PROTOZOA BY GARY N. CALKINS, Pu.D. INSTRUCTOR IN ZOOLOGY, COLUMBIA UNIVERSITY “Lies dieses Buch, und lern dabey, Wie gros Gott auch im Kleinem sey.” D, G. L. Huth: Résel von Rosenhof. e ¢ unne~ Netw Work THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., LTD. ~ IQgOI ed All rights reserved No. VAI COPYRIGHT, I90I, By THE MACMILLAN COMPANY. Ee ls Abb C15 6 yqot (1) Nortwoot ¥ress J. 8. Cushing & Co. — Berwick & Smith Norwood Mass. U.S.A Ts EDMUND B. WILSON IN GRATEFUL RECOGNITION OF HIS VALUABLE ADVICE AND FRIENDLY INTEREST PREFACE THE Protozoa not only claim the interest of the professional naturalist, but also that of a wider circle of nature students who, with the aid of the microscope, have always found here a fascinating field for observation and research. In writing the present volume, embodying a summary of the more recent discoveries concerning these minute animals, I have aimed to keep in mind the needs of the latter class of naturalists, as well as those who search more deeply in the unicellular organisms for the solution of many morpho- logical problems which remain unsolved in the higher animals, or for vital processes which afford a transition from the manifestations of life in its simplest expression to life as seen in the lower forms of invertebrates. The subject-matter of the volume is treated from three points of view: (1) The historical, to which the first chapter is devoted. (2) The comparative, to which five chapters are given: one to the group of Protozoa as a whole, the other four to the main classes. (3) The general, to which three chapters are devoted. One of these is given to the phenomena of old age or senile degeneration in Protozoa and renewal of youth through the union of two individuals, and to the bearing of these phenomena upon sexual reproduction in general. Another is given to the special structures of nuclei and centrosomes of the Protozoa; this, the most technical chapter in the book, is introduced because of the growing importance which the Protozoa have in the problems of cellular biology, especially with those dealing with the origin of the division-centre and its accom- panying structures in the cells of the Metazoa. The last chapter is devoted to a consideration of the physiology of the Protozoa, with especial reference to the Protozoa as organisms endowed with the powers of codrdination and of adaptation, which up to the present time have eluded physical and chemical analysis. Every one who works with the Protozoa is mindful of the debt we owe to Professor Otto Biitschli, whose indefatigable labors of vil LIST OF FIGURES INTRODUCTION AND CHAPTER I FIG. PAGE 1. Types of Protozoa . . . : ‘ . - : ° , 5 : : 3 2. Actinophrys sol Ebr. . : : : 3 ; : 7 : . . 16 3. Aradiolarian, Actissa princeps Heals z : 2 5 é . : « 47 4. Types of Flagellidia ¢ - 3 3 . : 5 7 t : » 19 5. Dinoflagellidia . : E 7 ¢ : . . : 7 : - 20 6. Coccidiida in epithelial cells . ; A a : 6 . F ‘ 5 - 20 7. Leptotheca agilis, a Myxospore 3 ‘ ‘ 5 ‘ , : ‘ 7 . 21 8. Plasmodium malarie inhuman blood . : - » . 5 : + 22 g. A spheroidal colony, Uroglena americana . A , : . : : » 25 CHAPTER II 10. Protoplasmic structure in different Protozoa . é . ‘ : - 36 11. Flagellates with stigmata : : A ‘ bo Z . . ‘ 2 Bz. 12. Ectoplasmic modifications. : : ; z , . . é é - 39 13. Shells andtests . . : : : : : : . : : i . 4! 14. Types of nuclei. 5 F : F 5 7 ‘ . 2 eS » 42 15. Types of pseudopodia . ‘ ‘ : A ‘ : 3 : : : - 44 16. Cilia and myonemes of Infusoria . 5 . : : 5 . ‘ ‘ » 45 17. Types of cysts 2 : : 3 : . : Z . . . : - 47 18. Food-taking . g ‘ 7 : 4 ‘ . F ‘ P . 49 19. Actinobolus radians F . . i a : : ‘ : ‘ - 51 20. Tentacles of Suctoria . . . 2 : : ‘ : ; : ‘ - 52 21. Frontonia leucas . zg 4 . . 3 : . - : 3 3 » 53 22. Division of Euplotes. i A : c : é 7 : ‘ : - 54 23. Budding of Zuglypha alveolata . ‘ a 4 : 3 é : : » 55 24. Microgromta socialis, a gregaloid colony. : . . : . . - 56 25. Uroglena americana . 5 Fi ‘ is : 3 F ‘ - 56 26. Codosiga cymosa, an aibeatid ddloay . : ‘ : 2 ‘ : S - 57 27. Elermocystis polymorpha, a catenoid colony . F : . . z z w 58 28. Exogenous budding in Ephelota biitschliana . ‘ ‘ - 2 ‘ , - 58 29. Degeneration in Onychodromus grandis ‘ - : . , 3 : - 59 30. Conjugation of Onychodromus grandis . : F : : : . . . 60 31. Internal parasites . . F . : : : ‘ . ‘ : : » 63 CHAPTER III 32. Actinophrys sol. ‘ ; ‘ j 3 ‘ ‘ . . 68 33. The protoplasmic regions of a \eatlioledlan ‘ 7 s 3 ‘ ‘ é . 69 34. Central capsules of Radiolaria : . : . . . . : ~ go xiil xiv LIST OF FIGURES FIG, PAGE 35. Types of marine rhizopod shells. : : F c : ‘ r F “9 36. Polythalamous shell types schematized . , : ‘ E ‘ 7 . : 92 37. A complex polythalamous shell. : : * 2 : . : . 2 Y3 38. Megalospheric and microspheric shells . ‘ ‘ 3 5 : 3 7 - 74 39. Clathrulina elegans 2 2 5 . 4 . . i : a : « 95 40. Types of spicules in Heliozoa , ‘ é ‘ ‘ < 3 . ‘ . 76 41. Skeleton formation : ‘ : p . . 7 - : : , 2. BF 42. Lichnaspis giltochit : 5 ‘ - : e . . 3 7 : . 78 43. Plagiocarpa procortina . 5 . : Z z : | F : ‘ - 79 44. Types of pseudopodia . 2 is : : a ‘ 3 5 : : . 8 45. Camplonema nutans. ‘i : * - . E : : . 81 46. Ciliophrys, pseudopodia and asia aicibs , . 5 : P : . a. 82 47. Ameba proteus pseudopodium, diagram : ‘ : ; . : é . 85 48. Ameba verrucosa, ectoplasm and vacuoles. F 3 Pi r é ‘ 3 85 49. Contractile vacuole of Ameba proteus . : : ‘ F , . 89 50. Gromia oviformis . : : : : 2 oF os 4 s : : - 91 51. AMicrogromia socialis in division . ‘ ‘ ‘ F 4 2 z i « OF 52. Paramaba etlhardi “ ‘ ‘ ‘ ‘i a ‘ 3 F F . - 94 53- Spore-formation in Heliozoa . . ‘ é A 5 Fi ‘ 5 ‘i - 96 54. Conjugation of Actinophrys sol. : ; ‘ - ‘ : ‘ ‘ . 98 55. Dimorpha nutans . : ‘ , ‘3 é : . ‘ : , 2 . 100 56. Nuclearia delicatula . ; : E 4 7 F ‘ a . 102 57. Protozoa with pseudopodia and flagélts , - ‘ 7 2 j : » 103 58. Membrane in Actinospherium eichhornit . c : ° . . . » 104 CHAPTER IV 59. Proterospongia haeckelt . és 2 : - ‘ a : - 7 F » 113. 60. Codonaca costata . , ‘ Z - é Z : ‘ z : : . 11g 61. Dinobryon sertularia . 5 7 é é A : . . . . » IIs 62. Phacotus lenticularis . : < ‘ A F : - a ‘ . 116 63. Distephanus speculum . . 3 é ‘ : 3 ‘ ‘ . ~ FD 64. Gymnodinium ovum and Peridinium dusdmmens ‘ c . e : ‘ » 118 65. Synura uvella . : : : : r : 5 . F i » 11g 66. Primitive forms of Dinoflagellidia : : 2 : ‘ : . A : - 125 67. Phalansterium digitatum . : . . . : . . : - 122 68. Types of collars in Chomeilagclias ‘ 3 : . : . : ‘ - 123 69. A Choanoflagellate type F : ‘ : ss : : : : ‘ ¢ (128 70. Nuclear division in Moctiluca miliaris . : : 3 < as : ‘ « T24s 71. Megastoma entericum . - : : ‘ ; é : ‘ . : 2 126: 72. Gonium pectorale . : 7 : ‘ ‘ 4 ; ‘ : : : . 128 73. Gonium pectorale in division : : 5 : F : - ‘ : » 129 74. Budding in Noctiluca miliaris. is - : : « F382, 75. Cercomonas crassicauda, division and spore- femation : : ‘i 3 : - 133. 76. Pandorina morum, conjugation . : ‘ . . : . zi : « 134 CHAPTER V 97. Life history of a gregarine; schematic . . ; ; ; : : . - 141 78. Pfeifferia tritonis in Triton cells . ‘ ‘ ‘ ‘ ‘ : A ‘ . 142 79. Leptotheca agilis,a Myxospore . ‘ : , : - . é : » 143. LIST OF FIGURES XV FIG. PAGE 80. Clepsidrina munieri, myonemes . é , F . < 5 ‘ . . 145 81. Lymphosporidium Trutte . - : : - : : . 5 . . 147 82. Movement of a gregarine . z : j . ‘3 ‘ : 7 A . 148 83. Types of spores . i : ‘ . a Zi é F : ‘ : . 150 84. Sporulation in a gregarine, schematic . : . . - 7 z 2 . 152 85. Gamocystis tenax, sporoducts. 5 x ‘i ‘ : , : - 153 86. ALyxobolus, capsule formation . : 3 . 3 : i . : - 155 87. Aonocystis ascidie, conjugation . . 5 - , : A ‘ : « IS7 88. Life history of a Coccidium . é g ’ ‘ é ‘ : 2 : . 160 89. Klossia helicina, conjugation ‘ , ‘ e : : : : : . I61 go. Life history of Plasmodium malaria . , ‘ ‘i ; F ‘ és . 163, CHAPTER VI gt. Types of Ciliata . : : B 2 F : - . . : z = 172: 92. Dileptus anser . : z . eS ce fs : 5 - : - 173 93. Coleps hirtus : ; : - : 2 7 : : F - é - 176 94. Lacrymaria coronata . 3 : ‘ a ‘ ‘ ‘ i « 077 95. Supposed shifting of the mouth ae Ciliata : - : Fi 7 F j . 178 96. Zoothamnium arbuscula, myonemes . 3 ‘ 5 : : F . - 179 97. Myonemes and cilia. : ‘ 7 ‘ ‘ : é ‘ a . . 180 98. Schematic hypotrichous ciliate. : x ‘ é F . : : . 182 99. Urocentrum turbo F . : a é 5 : : 5 ‘ ‘ . 183 100, Actinobolus radians. é k ‘ % . é j é ‘ . . 184 tor. Buccal apparatus of ciliates . 4 - Z Z ; F . : ‘ . 186 102. Anterior end of Ophrydium eichhornti a F a F . ; i . 187 103. Types of macronuclei . F 5 F ‘ 5 ¢ ‘ $ 3 = . 189 104. Loxophyllum meleagris, nucleus . 3 f . : - : a é - 190 105. Spirochona and Parameciunt, mitosis . : : : : . : . - 191 106, . Stentor reseliz, division . . : : : 5 ‘ : . A - 193 107. L£pzstylis umbellaria, conjugation c : ‘ é : : a : - 194 108. .Tentacles of Suctoria . . ‘ 2 ‘ F ‘ ‘ . . ; . 196 109. Dendrosoma radians . . : 3 5 : : # a - 197 110. Lphelota biitschliana, exogenous padding : ‘ A . ‘ ‘ , . 198 111. Endogenous budding in Suctoria é 4 z 3 : : . é . 199 112. Multicilia lacustris. : ‘ . . : . . 200 113. Illustrating Biitschli’s origin ‘of Hiypoteiohida ‘ ‘i B , 5 F . 201 114. Illustrating Biitschli’s origin of the Vorticellide . * ‘ . ‘ ‘ + 202 115. Ciliates with tentacles . : . ‘ : . ‘i : . . . » 205 CHAPTER VII 116. Conjugation in Cercomonas . F : é 3 - ‘ ‘ . , » 285 117. Conjugation in Zetramitus rostratus . 3 ; ‘ F A : - 216 118. Conjugation in Rhizopoda . : : ‘ i : . 7 . F . 217 119. Conjugation in 4rcella vulgaris . 7 : ‘ . 7 : z ‘ . 218 120, Conjugation in Polyloma uvella . : : ZA : r : ~ a 2 222 121. Conjugation in Lagenophrys ampulla . . 7 : 2 7 - . 35223 122. Conjugation in Afistylis umbellaria . : 5 ‘ 3 . i : - 224 123. Conjugation in Chlorogonium euchlorum . : . : : : . - 225 Xvi LIST OF FIGURES FIG, PAGE 124. Conjugation of Monocystis ascidie ; ee th ee . » 220 125. Division of Gontum pectorale ‘ c ‘ 7 P ‘ ‘ 9 ¥ . 227 126. Conjugation of Pandorina morum . 7 ; is ‘ 3 . 228 127. Formation of microgametes in Alossia . 7 : . . z ‘ . 230 128. Life history of a Coccidium . . : . - ‘ P ‘ 2 - . 231 129. Conjugation of Zuglypha alveolata . ® $ _ ‘ : F i . 235 130. Conjugation of Actinophrys sol. ‘ ‘ i ; 2 7 5 : . 236 131. Conjugation of Paramecium caudatum ‘ r 5 ‘ ‘ . . . 239 132. Onychodromus grandis, degeneration . s : zi - é 5 ‘ . 241 CHAPTER VIII 133. Diagram of a cell - : : Z ee F ‘5 ‘i 2 a - 247 134. Types of protozoan nuclei . : ‘. : : . . z : . . 251 135. Nucleus and karyosome in AVossia_. . i F . : 5 2 + 255 136. Mitosis in Euglena. . . 3 . ss F F ‘ é 3 - 260 137. Division in Ameba crystalligera . F . 3 : : 7 : ‘ . 261 138. Various nuclei in division . < F $ c . 7 . : 5 . 262 139. Mitotic division in the Infusoria . 5 . 5 P 3 . P 3 » 263 140. Nuclear division in Actinospherium . . é é ‘ c a . 264 141. Mitosis in Moctiluca miliaris : . . . E . . 267 142. Parameba eilhardi, sporulation and division a 3 3 ‘ ; . . 269 143. Mitosis in Ze¢ramitus chilomonas i . ni . . 2 . + 270 144. Nuclear division and spore-formation in Helioti . . . . . 2° 271 CHAPTER IX 145. Starch grains in Ciliata after partial digestion . ps Fs 5 3 - . 282 146. Digestion in Reticulariida . ‘ : é 2 F 5 7 c é . 284 147. Digestion in Carchesium . F : . : . a . . . . 285 148. Excretory granules in Paramecium . 2 g : . F 5 : . 287 149. Shell-formation in Gromia fluviatilis . 2 7 . : . : . - 293 150. Phosphorescence in Woctiluca miliaris . ‘ é . . s - 294 151. Motor response in Paramecium . . . : : 5 S31 aie : + 299 152. Isolated nucleus of 7’%alassicolla nucleata . . : . : ‘ : » 303 153. Reactions of Ameba verrucosa and of fluids : : . : . 2 + 307 THE PROTOZOA THE PROTOZOA INTRODUCTION “In the clearest waters and in muddy pools, in acid as well as alkaline waters, in brooks, lakes, rivers and seas, often, also, in the interior fluids of living plants and animals, abun- dantly in living men, and periodically borne on the dusts and vapors of our atmosphere, there exists a world unknown to the ordinary senses of man, of minute, peculiar forms of life.” —C, G. EHRENBERG, 1838. Beyonp the ordinary range of unaided vision there exists a world of minute animal organisms, technically known as the Protozoa. They abound in the dust of the air, in the sea, in freshet and ditch, in brackish and potable waters — wherever, in short, there is air and moisture, while even air is apparently superfluous for the vast majority of parasitic forms which make their homes in the living bodies of higher plants and animals. Their beauty, their varied modes of life, the suddenness of their appearance and disappearance, the simplicity of their structure, and modes of reproduction, combine to make them, even to the superficial observer, a fascinating group. Apart from their superficial attraction, however, the Protozoa have a deeper sig- nificance to the student of zodlogy. As the name Protozoa indicates, they are primitive animals, and in the scale of living things they are not far removed from the colorless bacteria on the one hand, and the primitive green plants on the other. Their chief significance, how- ever, and the main feature which distinguishes them from the higher animals or Afetazoa, centres in the fact that they consist of but a sin- gle cell within the confines of which are carried on all of the essential vital functions which characterize the highest many-celled animals. In their main characteristics these cells do not differ from those which make up the tissues and the body of higher animals. Like a tissue-cell the protozoén consists of protoplasm differentiated into nucleus and cell-body or cytoplasm, both parts being variously modi- fied in the several types (Fig. 1). Unlike tissue-cells, however, the Protozoa are not specialized for the performance of any one function. They invite attention, therefore, from both the morphological or structural and the physiological or functional points of view. Mor- phologically they are equivalent to the isolated epithelial, muscle- or nerve-cell; physiologically, they are equivalent not merely to the muscle- or nerve-cell, but to the entire group of cells which collec- 1 The term Protozoa was first used in its modern sense by von Siebold (45). B I 2 THE PROTOZOA tively constitute a higher animal. The Protozoa are, in short, com- plete, but unicellular organisms, and are to be regarded as the most generalized of single cells. Considered as a complete animal, the protozoon cell at once arouses the inquiry as to the nature of the organs by means of which the vital functions are carried on. Lending themselves readily to the experi- mental method of investigation, the Protozoa have already contributed not a little to knowledge of the localization of function in the cell. . The importance of the nucleus in the economy of cell-life, which Barry and Goodsir early pointed out in animal tissues, has been fully confirmed by the researches of Gruber, Balbiani, Hofer, Verworn, and others upon the Protozoa. From the structural point of view, the protozo6n nucleus with its accompanying structures must ultimately throw considerable light on the vexed questions connected with the finer structures of metazoan cells. As the sequel will show, consider- able advance has already been made in this direction through the efforts of Biitschli, Schaudinn, Balbiani, R. Hertwig, and many others. Here, the generalized structures, especially those elements concerned in cell-division, although difficult of analysis, must, when more thoroughly studied, aid the interpretation of the more specialized structures in Metazoa which are now involved in some of the most deeply-lying problems of biology. Physiology likewise has been and is still to be greatly enriched by the study of unicellular animals. Bichat’s theory of tissues, pro- pounded at the very outset of the last century (1801), formed the basis of Virchow’s development of the cell-theory along physiological lines (758). It was Virchow who put on a working basis Schwann’s conception that the vital activities of an animal are the sum of all of its parts, and that each part, a cell, or, as Briicke suggested, an “elementary organism,” performs all of the characteristic activities of life. Thus while the older physiologists were satisfied with the knowledge that the function of the kidney is to secrete urine containing the waste matters of living activity, the modern problems, as Virchow intimated, centre more especially in the inquiry as to the activity of the kidney cells as such. Again, the modern physiological problem of contractility or of nervous action is concerned with the muscle- and ganglion-cell, and is therefore a cell-problem. For investigations upon cellular physiology there are obvious advantages in studying the unicellular organisms, which, says Verworn, “seem to have been created by nature for the physiologists, for, besides their great capacity for resistance, of all living things they have the invalu- able advantage of standing nearest to the first and the simplest forms of life.”? 1 Lee (’98), p. 50. Fig. 1.— Types of Protozoa. A. Ameba proteus, a rthizopod. B. Peranema trichophorum, a flagellate. [BUTSCHLI.] C. Stylonychia mytilus, a ciliate. [BUTSCHLI.] D. Pyxinia sp. a sporozoén, [WASIELEWSKY.] £. Tokophrya quadripartita, a suctorian. [BUTSCHLI.] c. contractile vacuole; ¢. epithelial host- cell; 2. nucleus; v. food or gastric vacuole. 4 THE PROTOZOA Although, as Virchow pointed out, each cell of a tissue is a complete organism performing all of the functions of living matter, some one of these functions predominates over the others and gives to the cell and to the tissues of which it forms a part its special character- istics. In these specialized cells the secondary functions, z.e. those acting only for the good of the cell itself, fall into the background and are not readily investigated. In the Protozoa, on the other hand, no one function predominates, and despite their primitive nature, the protoplasm of which they are composed appears quite similar to that of the most highly specialized tissue-cell. In it, however, lies the secret of digestion and assimilation, of the kidney’s secretion, and of muscular contraction. The Protozoa invite attention from still another point of view. As the lowest animals they show the beginnings of sex differentiation, of maturation, or the changes which the germ-cells undergo before fer- tilization, and of fertilization, while their union into cell-aggregates or colonies with incipient division of labor among the constituent cells, - points the way toward the Metazoa, and makes them significant in the light of evolution. As complete primitive organisms, therefore, the Protozoa are impor- tant from many points of view: structurally, they contain in simple form the elements which in higher tissue-cells are moulded into more complicated organs of the cell; functionally, they epitomize the life activities of even the highest many-celled animals, but their vital pro- cesses are more easily observed and correlated ; theoretically, they occupy a prominent place in questions of phylogeny, of sex, and of reproduction, and finally, placed as they are at the lowest limit of animal life, they must ever be closely connected with problems con- cerning its origin. With this conception of the Protozoa in mind the present volume has been written. The work makes no pretence of a comprehensive description of the Protozoa or of any one group, but aims rather to give an intelligible idea of the main types, to point out the problems of biology with which the Protozoa are most closely connected, and, so far as possible in a limited space, to survey the work already accomplished. In the present introductory chapter there is a brief historical review of the stages by which the Protozoa have come to be regarded as single cells, and at the same time as complete animal organisms. Here, too, is a short account of the interesting position which the Protozoa have held in the time-honored dispute over the limitations of the anima] and plant kingdoms, and in theories of spontaneous generation. The second chapter deals with the general structures and functions of the Protozoa as a group, and introduces the four following chapters, which INTRODUCTION 5 are devoted to the structural and functional adaptations of the organ- isms in each class. The last three chapters, finally, deal with the rela- tions of the Protozoa to more general problems. A. HISTORICAL REVIEW The Dutch microscopist, Anton von Leeuwenhoek (1632-1723), using crude lenses of his own make, was one of the first to apply the microscope to scientific investigation. His contributions to micro- scopic anatomy and to physiology, inaugurating as they did the invaluable services of the microscope in biological research, marked an epoch in the history of science. An ardent follower of Harvey, he was one of the first to offer experimental evidence against the current belief that many of the lower organisms arise by spontaneous generation, and on every occasion he sought to establish the truth of Harvey’s dictum ex ovo omnia. In 1675, while searching for evi- dence of spontaneous generation, Leeuwenhoek discovered “ living creatures in Rain water, which had stood but four days in a new earthen pot, glased blew within.” “This invited me,” he continues, “to view this water with great attention, espe- cially those little animals appearing to me ten thousand times less than those repre- sented by Mons. Swamerdam, and by him called Water-fleas or Water-lice, which may be perceived in the water with the naked eye. The first sort by me discover’d in the said water, I. divers times observed to consist of 5, 6, 7, or 8 clear globuls, without being able to discern any film that held them together, or contained them. When these azzmalcula or living Atoms did move, they put forth two little horns, continually moving themselves. The place between these two horns was flat, though the rest of the body was roundish, sharp’ning a little towards the end, where they had a tayl, near four times the length of the whole body, of the thickness (by my Microscope) of a Spider’s-web ; at the end of which appear’d a globul, of the bigness of one of those which made up the body; which tayl I could not perceive, even in very clear water, to be mov'd by them. These little creatures, if they chanced to light upon the least filament or string, or other such particle, of which there are many in water, especially after it hath stood some days, they stook entangled therein, extending their body in a long round, and striving to dis-intangle their tay]; whereby it came to pass, that their whole body lept back towards the globul of the tayl, which then rolled together Serpent-like, and after the manner of Copper or Iron-wire that having been wound about a stick, and unwound again, retains those windings and turnings. This motion of extension and contraction continued awhile; and I have seen several hundreds of these poor little creatures, within the space of a grain of gross sand, lye cluster’d together in a few filaments.” + This is the first description of a protozoon; and although the descrip- tion is incomplete, it undoubtedly refers to a species of Vorticclla. Leeuwenhoek observed several other forms at the same time, but for the most part their identity is uncertain. 1 See Phil. Trans., London, Vol. XII., 1677, p. 821. 6 THE PROTOZOA At this period, although the term ce// had already been used by Robert Hooke (1665), the idea of simplicity of organization, apart from minuteness of the organs, was unknown, and until the cell- theory was established in 1838, the Protozoa were regarded as com- plex animals having all of the parts and organs, although of micro- scopic size, found in Metazoa. Leeuwenhoek allowed his imagination to see what his eyes could not. “ When we see,” said he, ‘“ the sper- matic animalcula [spermatozoa] moving by vibrations of their tails, we naturally conclude that these tails are provided with tendons, muscles, and articulations, no less than the tails of a dormouse or rat, and no one will doubt that these other animalcula which swim in stagnant waters [Protozoa], and which are no longer than the tails of the sper- matic animalcula, are provided with organs similar to those of the highest animals. How marvellous must be the visceral apparatus shut up in such animalcula!”?! The minute size of the Protozoa made it impossible for the early investigators with their crude instruments, to follow out any life-cycle, and the prodigious numbers and the sudden appearance of certain forms in stagnating waters led to the belief already current in respect to other forms, that they arose de novo. Two misconceptions thus sprang up almost at the beginning of our knowledge of the Protozoa: one, that Protozoa are provided with organs like higher animals; and, two, that they arise by spontaneous generation; and one of the main tasks of research on the Protozoa down to our own times has been the correction of these early errors. It is not strange that Leeuwenhoek and his immediate followers considered Protozoa as complicated organisms. Organisms without organs were as novel to them as animals without cells would be to us, and they described only what experience had taught them to expect. With increasing knowledge of many forms and with con- stantly improving microscopes, the conception of simplicity of organ- ization gradually gained ground until Dujardin, about 1840, defined the Protozoa as simple, slightly differentiated structures composed of a fundamental living substance to which he gave the name of savcode. Despite the crudity of their instruments, the early microscopists obtained wonderful results. Leeuwenhoek himself, although study- ing these low forms only incidentally, gave recognizable descriptions of twenty-eight species, and in addition, noted the rapid increase of some of the larger forms, saw conjugation or the temporary union of two individuals, and discovered so-called embryos. The early litera- ture soon became crowded with notices of new and interesting forms, found in all sorts of hitherto unthought-of localities. Forms with 1 Quoted from Dujardin (’41), pp. 21, 22. INTRODUCTION 7 whip-like appendages, or flagella ; with cz/ia, or motile appendages, similar in general form to eyelashes; with changeable processes, or pseudopodia ; or with no motile apparatus whatsoever; forms of the most diverse size and shape, including many higher Metazoa, such as worms, rotifers, ctenophores, crinoids, and crustacean larvz, as well as many plants, were all described as “ animalcula.’’ Descriptions of internal organs soon began to accompany the descriptions of types. The contractile vacuole, a characteristic pulsating vesicle of the Pro- tozoa, was discovered by Joblot (1754~'55), who also showed that cilia on Infusoria have a definite arrangement in different species, and that many forms are provided with cuticular stripings. All of these forms, sometimes called insects and sometimes fish, were still generally supposed to be microscopic reproductions of higher animals. Dujardin’s criticism of Joblot’s work might well be applied to that of many others of this early period: “ Several of the figures which he gives,” says Dujardin, “bear the impression of a too lively imagination for scientific purposes, and are frequently so bizarre and fantastic as to discredit the use of the microscope.”! It is easy to understand this criticism when we think of Joblot’s picture of the worm Anguzl/ula with a serpent’s head, or the flagellated pro- tozoon Luglena with a broad mouth, flagellum, and well-developed mammalian eyes. ‘For his picture of the ciliate Paramecium aure- fia,’ says Dujardin, ‘he apparently used his own slipper as a model.” The life history of a protozodn was first made out by Trembley (1744-47), who saw the microgonidia or young spore-forms of cer- tain Vorticellidz leave the parent-colony and begin the formation of new colonies by longitudinal division. The discoveries made by means of the microscope were regarded with complete scepticism by Linnzeus in his earlier scientific works, and the very existence of Leeuwenhoek's animalcula was at first denied by him, but in the later editions of his Systema Nature they were grudgingly admitted under the significant generic name of Chaos [Chaos proteus (Ameba), Chaos redivivum, etc.]. The organ- ized nature of Volvox globator, a form which had been discovered and fairly well described by Leeuwenhoek, was admitted at this time, and finally, in the twelfth edition (1767), the animal nature of a Vorticella. Many of the early investigators studied the Animalcula from the physiological standpoint, and attempted to ascertain the functions of many of the so-called organs. Theire efforts were often strikingly successful and have been confirmed by later observations. Corti (1774), Spallanzani (1776), and Gleichen (1778) are the most familiar names in this line of research. Corti and Gleichen compared the 1 Dujardin (’41), p. 7. 8 THE PROTOZOA contractile vacuole of Vorticella, with its regular pulsations, to a beating heart, while Spallanzani, distinguishing the vacuole from its canals, assigned to it the function of respiration. The mouth was found in a number of forms, by Gleichen, who first used the now common experiment of feeding the Protozoa with minute particles of colored substances, such as carmine, indigo, etc. A considerable knowledge of reproduction was also obtained. Longitudinal division, discovered by, Trembley (1744), was confirmed by Spallanzani, who, in addition, observed transverse division in no less than fourteen species, while his friend Saussure followed out for the first time the division of an encysted Col/goda; an observation confirmed by Corti and Gleichen as well as by Spallanzani himself, who saw a Colpoda slip out of its cyst, which he not unnaturally mistook for an egg-case. These early discoveries were, in most cases, so bound up with fan- tastic speculations that their zodlogical value was greatly impaired. Many of these early inaccuracies were, however, weeded out by Otto Friedrich Miiller (1786), to whom we are also indebted for the scientific naming of the Animalcula, which up to his time had been called by long descriptive names given according to the fancy of each observer, and often based on far-fetched resemblances. Miller, adopting the Linnzean binomial nomenclature, described and named some 378 species, of which about 150 are retained to-day as Protozoa. His classification was the first successful attempt to bring order out of the heterogeneous collection of forms included under the name Animalcula. He used Ledenmiiller’s (1760-63) term /xzfusorza, for the name of the entire group, which he placed as a class of the worms.! While he eliminated the inaccuracies, he confirmed the substantial observations of the earlier observers, extending many of them to all groups of the Protozoa. He ascertained the presence of an anus, showed that many Infusoria are carnivorous, and observed the process of conjugation, his description of the latter being more accurate than that of any of his predecessors or followers until the time of Balbiani in 1858-59. Like his predecessors, Miller included among the Protozoa many other organisms; placing here diatoms, nematode worms, Déstomum larvee, and larval forms of ccelenterates and molluscs, as well as the rotifers. The majority of these miscellaneous forms were, however, properly classified before 1840. The larvz of molluscs and ccelente- rates, and the worms were the first to be removed from the “animalcula,” while finally spermatozoa (discovered by Ludwig Hamm, who is said to have been a pupil of Leeuwenhoek), which had been universally regarded as Protozoa inhabiting the seminal fluid, were withdrawn during the present century. 1 Cf. Biitschli (’83), p. 1129. INTRODUCTION 9 Unlike his predecessors, Miiller did not regard the Protozoa as complicated animals, but considered them as the simplest of all living things, composed of a homogeneous gelatinous substance, a view in which he was followed by a majority of the ‘ Nature-philosophers ” (Lamarck, Schweigger, Treviranus, Oken), most of whom gave little or no study to the Protozoa, but, accepting Miiller’s work as final, based many of their speculations upon it. It is difficult to understand why, after Miiller’s work, the next great authority, C. G. Ehrenberg (1795-1876), the renowned Berlin micro- scopist, using much finer achromatic lenses, should have returned to the crude view of Leeuwenhoek, assigning to the Protozoa a system of minute but complete organs. His conclusions on Protozoa were brought together in one great work, the title of which alone shows his point of view: “The Infusoria as Complete Organisms” (Die /nfu- stonsthierchen als vollkommene Organismen). He was primarily a student of their finer structure, and the details of organization, although erroneously interpreted, were clearly described. In working out the internal structures he made use of Gleichen’s experiments in feeding. The animals were seen to ingest the powdered carmine, so that the boundaries of the internal gastric vacuoles were clearly marked. He followed these particles as they passed from the mouth into the cesoph- agus and thence into one of the many digestive or gastric vacuoles found in the inner plasm of nearly all Protozoa. He saw that the particles followed clearly defined paths which might be straight or curvilinear, or otherwise varied in different forms, but which always ended in a more or less clearly marked anal opening. He saw also that the parts of the supposed tract nearest the mouth fill first; that they become globular, and that successive reservoirs become filled, down to the posterior end of the body. He inferred from this the existence of a digestive tract, concluding that the parts thus filled were stomachs. As soon as the first was filled, the overflow of food passed on into another stomach. From the supposed possession of many stomachs Ehrenberg gave to this group the name Polygastrica or Magenthicre, making it a sharply defined class in the animal kingdom. To all forms in which he could find no stomachs, but in which he supposed that mouth and anus were the same opening, he gave the name of Anentcra (gutless), while to forms with many stomachs he gave the name Exterodela (gut-bearing). The red pigment spots of many forms were interpreted as true eyes, but as eyes could not be conceived without an accompanying nervous system, he sought for nerve-ganglia in different organisms, and supposed he found what he was looking for in a species of Asvasza. He described the eye in this form, as seated upon a “spherical glandular mass,” which he considered equivalent to the supra-pharyn- 1ce) : THE PROTOZOA geal ganglion of the rotifers (cf. Fig. 11). He discovered the myonemes or muscular elements in the stalks of Vorticella, in Stentor, and in certain other Ciliata, and interpreted them as muscles. He discovered that the flagellum of the flagellates is the motile organ, but explained its vibrations as due to the action of exquisitely fine muscle-fibres. Pigment spheres and protoplasmic granules were de- scribed as ovaries, the nucleus as a testis, while the contractile vacuole was at first regarded as a respiratory organ. With this latter conclusion he could not harmonize his subsequent observations, and finally decided that the vacuoles have the same functions as in the rotifers. Ehrenberg’s strong position as an investigator of Protozoa is due to his remarkable powers of observation, especially of the finer structure of flagellates and ciliates, which in many cases he described and accurately figured, and these justify the tribute which Bitschli pays him: — . “The great service which Ehrenberg did in furthering the knowledge of these forms cannot be clearly enough recognized. After a naturally somewhat difficult comparison, I find among the species described in 1838 a few more than 100 Infusoria (in the present sense), of which five are Suctoria. Also his system of classification” was much more natural than that of any of his forerunners, and formed the basis of all subsequent efforts. Many of his genera had correct limitations which hold even to-day, although many indeed cannot be sustained. . . . With astonishing assiduity he sought to collect, study, and systematically interpret everything that had been done upon the Infusoria.” (°83, p. 1145.) Ehrenberg’s interpretations, however, were not as successful as his collection of data, and it is to be regretted that throughout his life he obstinately clung to his view of the Poluasaiica, even after the period of the complete establishment of their unicellular nature. It was surely the irony of fate which led to the publication of his immense work on the Polygastrica the same year (38) that the Dutch botanist Schleiden made the greatest advance in the conception of the cell as the unit of structure. A formidable opponent of Ehrenberg soon appeared in France, — Felix Dujardin, — who, influenced by long study of the RAzzopoda,(or Protozoa with changeable processes), came to the conclusion, in 1835, that the marine forms (Foraminifera), which, up to that time, had been classed with cephalopod molluscs, are in reality the simplest of organisms, composed of a simple, homogeneous substance which he called sarcode. He showed that the many stomachs, which, according to Ehrenberg, constituted the digestive tract, were mere vacuoles without definite walls, which become filled with water taken in from the outside with the food. He denied Ehrenberg’s assertion that an anus terminates the digestive tract, although in some cases his gener- INTRODUCTION II alization was made without adequate observation, for at first he denied the presence of a mouth as well as anus. Dujardin further showed that the motile organs of the Protozoa, whether cilia, flagella, or pseudopodia, are mainly the prolongations of the outer coatings of the organism, and are in no sense similar to the hairs of higher animals, and he even suggested the transition, which has since been shown to occur, between the simplest of pseu- dopodia and the more complex flagella. He contradicted Ehrenberg’s theory as to the function of the contractile vacuole, reverting to the interpretation given by Spallanzani. He also denied the complexity of the reproductive organs, as described by Ehrenberg, but made a singular mistake in regarding the granules inside of the body as germs. Many besides Dujardin had begun to criticise Ehrenberg’s theory. Carus (’32) insisted, on purely theoretical grounds, that animals must exist whose structure is as simple as that of an egg, since all animals begin with the simple egg structure. Two years later, he criticised Ehrenberg’s theory, on the ground that inner circulation of the plasm in Paramecium (discovered by Gruithuisen, ’12), which resembles the circulation in the plant Chara, does not accord with Ehrenberg’s description of the digestive apparatus. A similar objection was raised by Focke (36), based on observations upon the streaming plasm in Vaginicola and Paramecium. The first suggestion that Protozoa might be single cells was made by Meyen (’39), who compared the entire infusorian body to a single plant-cell. The cell-theory, according to Biitschli, however, was first applied directly to the Protozoa by Barry (’43), who asserted that Monas and its allies among the Flagellidia are single cells, and that the nucleus found within them is the equivalent of the cell-nucleus of higher animal forms. At the same time Barry expressed the view that cells increase only by division, and he compared the processes of multiplication in Volvor and Chlamydomonas with the cleavage of eggs which he, with Schwann, regarded as single cells. Barry’s view was accepted in part by Owen, who thought, however, that the Infusoria could not be included with the Flagellidia as single cells, because of their higher differentiation. It was von Siebold (’48), however, who finally asserted the unicellular nature of all Protozoa. Ehrenberg’s theory was not given up without a struggle, and, among others, we find Schmidt (’49) coming to his support with the fact that the zvzchocysts, or stinging threads of the Infusoria, found by Ellis (1769), and by Spallanzani (1776), and the contractile vacuoles 1Cf. Biitschli (’83), p. 1153. 12 THE PROTOZOA with their canals, show the strongest similarity to the corresponding structures in flatworms. The trichocysts were particularly difficult for the opponents of Ehrenberg to explain. Stein (’56) regarded them as ‘“‘taste-bodies” (7astkirperchen), and we find even Leydig (57) regarding them, together with the microsomes in the stalks of Vorticella, as the nuclei of very minute cells. Kolliker ('48, ’49), following von Siebold, but at first almost alone, strenuously maintained that all Protozoa are single-celled animals, in spite of severe criticism, especially by the ardent and brilliant young naturalists, Claparéde and Lachmann, who, not able to make out the cellmembranes and nuclei in many cases, placed the Protozoa with the Hydroida, making them a subdivision of the Ccelenterata. It should be noted, in justice to Claparéde, that later he admitted his. error. The opponents of Kolliker were, however, gradually convinced. Max Schultze (’63) showed the identity of Dujardin’s sarcode with protoplasm; Stein (’67) vigorously assailed the objections of Leydig and Haeckel, while the latter (’73) brought back his Infusoria from the Articulata, to which he had consigned them in 1866, and became an ardent advocate of Kolliker’s theory. The next few years saw the remarkable researches of Biitschli, Engelmann, and Hertwig, upon the physiology and finer organization of the Protozoa, and their work, with that of the hosts of others since them, aided by modern tech- nique, has fully demonstrated the unicellular nature of all Protozoa.? The theory of alternation of generations (the alternation of a sexual with an asexual method of reproduction) also became curiously in- volved in the foregoing controversy. Steenstrup (’42) applied his discovery of alternation of generations to the Protozoa, regarding the parasitic Infusoria which he found in certain molluscs, as the larval form of the liver-fluke, Dzstomum. The same view was found in various forms in the works of Claparéde and Lachmann, Perty, and Kolliker, and finally as the “ Acineta-theory” in the works of Fr. Stein. This theory was based upon the supposed metamorphosis of one form of Protozoa into another. The first suggestion of such a metamorphosis seems to have been given by Pineau (’45), who ob- 1L. Agassiz (’57), adopting a point of view which has appeared sporadically since von Siebold announced that the Protozoa are single-celled animals, advocated the abandonment of the Protozoa as a group, placing some divisions with the’ lower plants, others with the larvee of worms, and still others with the Bryozoa. His most curious error was in placing Trichodina pediculata, one of the higher forms of Protozoa, as the medusa-generation of the fresh-water polyp //ydra. “TI have seen for instance,” says Agassiz, “a Planaria lay eggs, out of which Paramecium were born, which underwent all of the changes these animals. are known to undergo up to the time of their contraction into a chrysalis state; while the Opatina is hatched from Distomum-eggs” (’57, p. 182). Similar views were held by Alder (’51), Burnett (754), and even recently by Lameere (’91), and by Villot (’91). INTRODUCTION 13 served that decaying flesh apparently breaks into minute granules (bacteria). Influenced no doubt by the teachings of the nature-phi- losophers, Buffon and Oken, he further thought that he had observed the formation of larger forms of life from these minute granules, and among them, some Podophryas, which changed into Vorticellas, and these again into Oxytrichinas. Stein’s famous Acineta-theory was first brought out in his work of 1849, in which he described the many division phases of Vorticella, and gave a very good account of the process of encystment. The encysted animal, he thought, breaks down into a great number of minute particles, having at first the form of certain flagellates, which develop into young Vorticellas. Later he adopted a second hypothe- sis, equally untenable, vzz. that Aczueta is derived from the cysts of Vortecella. This conclusion was based upon the fact that he had seen the preparatory stages of encystment of the Suctorian Podophrya, which he thought were transition phases from the encysted condition to the adult free Podophrya, while the cysts from which he supposed they had come he thought were formed by Vorteced/as. Generalizing from this supposed fact, and seeing supposed confirmation in many different directions, he finally regarded the entire division of the Suc- toria as merely reproductive phases of the genus Vordice/la. An apparent support for his theory was found in 1854, when he discov- ered the ciliated embryos in Suctoria, which closely resemble the Vorticellidae. Not once did he follow out the development of these embryos by actual observation; it was purely hypothetical, and the discovery of Aczzeta embryos, since found to be parasites’ in various other ciliates, only strengthened him in this point of view. Stein’s theory soon found opponents. Perty (’52) feebly opposed it, while Johannes Miiller and his pupils, Claparéde and Lachmann, and Cienkowsky (’55) traced the development of the supposed young Vorticellas to the adult forms of Suctoria. The theory was finally completely overturned by Lachmann (’56) and Balbiani (’60), the former showing by actual observation that neither does Vortdcella develop into Acznefa, nor do embryos of the latter develop into Vor ticella, while the latter discovered that the supposed embryos are in reality parasitic Suctoria, a view in which he was ably supported by Metchnikoff (54) and Kolliker (’64). Balbiani’s researches in the life history of the Protozoa at first led him into a curious error, a reminiscence apparently of Ehrenberg’s and the older point of view. O. F. Miiller had observed and cor- rectly interpreted conjugation in different forms, but his successors down to Balbiani regarded this interpretation as incorrect, maintain- ing that he had seen only stages in simple division. Balbiani (’61) returned to Miiller’s view, and clearly stated that, in addition to 14 THE PROTOZOA simple division, another and a sexual method of reproduction occurs. His interpretation of the sexual organs of the Protozoa was given in 1858, when he maintained that the larger of the two kinds of nuclei of Infusoria, the macronucleus, is the ovary, and the smaller one, or micronucleus, the testis. He saw and pictured the striped appear- ance of the micronucleus prior to division, and interpreted the stripes as spermatozoa. The eggs were said to be formed in the macronu- cleus, to be fertilized and then deposited on the outside, where they develop into new ciliates. Stein at first opposed this assumption, but in the second volume of his work on the-Infusoria, misled by his Acineta-theory, he practically adopted it, maintaining, however, that the embryos develop in the nucleus first, and only later leave the mother organism. Biitschli (73) was apparently the first to point out Balbiani’s error, and in his epoch-making work of 1876, after demonstrating the ‘‘striped” appearance of many egg-cells during division (mztotic figure), he concluded that the stripings which Bal- biani held to be spermatozoa were no other than this striated con- dition of the nucleus during division. He held, therefore, that in addition to the macronucleus there is a second and a smaller nucleus in Infusoria, and to this he gave the name Wedenkern or micronucleus ('76). Biitschli further showed at the same time that during conjuga- tion the macronucleus or larger nucleus disintegrates, and that the parts which Balbiani regarded as eggs are eliminated, to be replaced by one of the subdivisions of the Mebenkern (micronucleus). His interpretation of the process was equally happy. After observing that a continued asexual division of certain forms resulted in decreased size and a general “ lowering of the life energy,’’ he concluded that the function of conjugation is to bring about a re/uvenescence.( Ver- Jjungung) of the participants. He called attention to the similarity between conjugation and fertilization of the egg in animals and plants, and, at the same time, made the classic comparison between the body of the metazoon and the chain of individuals which arise from one individual protozoén subsequent to conjugation. In the same year Engelmann (’76) obtained very similar results. Quite independently of Biitschli he also proved the error of Balbiani’s view, and came _to a conclusion not far different from Biitschli’s. “The conjugation of the Infusoria,” he said, “does not lead to repro- duction through ‘eggs, ‘embryonic spheres,’ or any other kind of germ, but to a peculiar developmental process of the conjugating individual, which may be designated as reorganization.” (Reorganization.)} Neither observer noted the conditions which induce conjugation or the mutual interchange of parts of the micronuclei, although both, indeed, suspected that the latter might take place. The actual inter- 1 Engelmann (’76), p. 628. INTRODUCTION 15 change was first made out by Balbiani (’82), by Jickeli (’84), by Gruber (86, ’871*), and by Hertwig (’89), and in great detail by Maupas (88, ’89), by whom the conditions leading to conjugation were for the first time made known. B. MODERN CLASSIFICATION OF THE PROTOZOA Although the Protozoa are the simplest forms of animal life and the most generalized of cells, it does not follow that they are simply organized and devoid of complicated structures. On the contrary, in many cases they are highly differentiated, and in the Infusoria, the highest group of the Protozoa, they become so complex, that Stein, who was never an ardent advocate of the simplicity of Protozoa, re- marked: ‘“ The adult Infusoria must ever be considered doubtful single-celled organisms, for they are not simply cells which have undergone further development, but the original cell-structure has given place to an essentially different organization entirely foreign to typical cells.”+ On the other hand, there are simpler forms of Protozoa in which the undifferentiated protoplasm falls within the description of sarcode, as given by Dujardin in 1835. Between the two extremes of structure lie the vast majority of Protozoa, showing among them all gradations from extremely simple to extremely com- plex forms. A partial explanation of their frequent complexity of structure lies in the fact that, unlike tissue-cells, they live free and usually motile lives, and, like other independent organisms, are subject to changes of form and to intracellular modifications in response to their mode of life. Notwithstanding the innumerable forms and the various intracellular modifications, differentiation, as a rule, has followed comparatively few general lines (Fig. 1). It thus becomes possible to arrange the Protozoa in groups or classes, with numerous divisions and sub- divisions. The four classes which are now generally recognized are the Sarcodina, the Mastigophora, the Sporozoa, and the /nfusoria. The first attempt to classify the Protozoa was made by O. F. Miiller in 1786. Rude and simple, and based upon the presence of visible motile organs (Bullaria), or upon their absence (Infusoria _ s. str.), this nevertheless was retained as the chief system of classifica- tion until the time of Ehrenberg, who made use of it in his own system, based upon the presence or absence of “stomachs.” Despite the progress made by Dujardin, his classification, in its main divisions, based upon unnatural differences of symmetry was equally imperfect. His two divisions were very unequal, the “asym- 1 Stein, Organismus, etc., II. (67), p. 22. 16 THE PROTOZOA metrical’’ Infusoria including all but one or two known forms. The subdivisions were, however, remarkably happy, and were based upon natural lines which have never been displaced. While Ehrenberg’s subdivisions were based upon gross external characters, such as the presence of hairs, the position of the mouth, etc., Dujardin’s were based upon the means of locomotion, and in this early grouping we see the first use of our modern terms “ rhzzopod,” “ flagellate,” and “ciliate.” “Von Siebold (’45) was the first to divide all Protozoa into Fig. 2. — Actinophrys sol Ehrenberg, a heliozoén, [After GRENACHER from BUTSCHLI.] An individual with a large gastric vacuole (g), contractile vacuole (c), and axial filaments (2) in the ray-like pseudopodia. two classes, Rhizopoda and Jnfusoria, a system which formed the basis of our modern classification; the Mastigophora or flagellates, regarded by von Siebold as plants, found no place in his zoology. Three of the four great classes recognized to-day were thus out- lined by Dujardin in 1841. The modern Rhizopoda (Sarcodina) were characterized as “animals provided with variable processes”; the Mastigophora as “animals provided with one or several flagelliform filaments, serving as motile organs” ; and the Ciliata as “ciliated animals” (Fig. 1). The further subdivisions, which, little by little, have been developed along the lines laid down by Dujardin, have brought order out of this heterogeneous group of organisms, which at the present time includes nearly sixteen hundred genera and many thousands of species. As the name of a class, the term Rhizopoda, INTRODUCTION 17 as used by von Siebold, may be replaced by the more comprehensive term Sarcodina, given by Biitschli (’83), while the term Rhizopoda may be applied to one group (subclass), characterized by an amceboid or changeable adult condition, and with lobose or reticulate motile processes or psewdopodia.1 Two other subclasses are now universally included in the Sarcodina, the He/zocoa (Haeckel), or “sun animal- Ratmemedeagne 5 An enemy Pa NeN ashi Fig. 3. —A radiolarian, 4e¢issa princeps Haeck. [HAECKEL.] The central capsule (c) separates the inner protoplasm (v) containing the nucleus (z) with its nucleolus (2), from the outer protoplasm which gives rise to the pseudopodia (/). cula”’ (Fig. 2), characterized by fine ray-like pseudopodia, which often contain a central axial thread of stiffened protoplasm, and the Radiolaria (Haeckel), characterized, in addition to the ray-like pseudopodia, by the possession of a central portion of protoplasm, which is surrounded bya perforated membrane, the “ central capsule” (Fig. 3). | | Before the modern system of classification was established, many of 1 The term “ pseudopodia” was given by von Siebold to replace Dujardin’s more descriptive phrase “ changeable processes” (expansions variables). c 18 THE PROTOZOA the forms which are now recognized as Heliozoa or Radiolaria, were variously interpreted. Ehrenberg did great service in describing the skeletons of many Radiolaria, especially of the fossil forms, but he had no conception of their organization, and placed them with the Bryozoa, Rotifera and Echinodermata as a special class ( 7dz/ata). Under the name, Actinophryens, Dujardin grouped the Heliozoa, together with a modern subdivision of the Infusoria (Swctorza), as “forms with slowly contractile appendages.” The structure of the Radiolaria was first made out by Huxley (’51), who recognized them as Protozoa, and correctly compared 7halassicolla with the heliozoon Actinospherium. The pseudopodia, however, were not recognized, and he was inclined to regard these forms as higher in organization than a single cell, and placed them between the Protozoa and the Sponges. Johannes Miiller(’55—’58) first saw the resemblance between the fine ray-like pseudopodia of the Radiolaria and of the Heliozoa, and his pupils, Claparéde and Lachmann (’58), discovered the same granule-streaming in their pseudopodia that Schultze had observed in some of the Rhizopoda. With these data, Miller included the Radiolaria and the Heliozoa in the class Rhizopoda of von Siebold, under the name Rfzsopoda radiaria, which was modified into its modern form, Radiolaria, by another of his pupils, Ernst Haeckel (62). Four years later Haeckel (’66) separated the Radiolaria from the similar fresh-water forms, to which he gave the name Heliozoa. The further subdivisions of the subclass Rhizopoda have been made upon two bases having almost equal value. In one system they are divided according to the nature of the pseudopodia into the orders Lobosa (Amebea of Ehrenberg) and the Reticularitda (Rett- cularta of Carpenter, 62). In the other they are subdivided accord- ing to the absence or presence of a shell, into the orders Amwbida (Ehbg.) and TZestacea (M. Schultze, ’54).1- The former system is adopted by Delage and Hérouard, by Lankester and the English zoodlogists generally ; the latter by Biitschli. A third order under the name Mycetozoida, is usually included with the Amcebida and the Reticulariida. Although generally recognized in part at least, by zodlogists as Protozoa, the taxonomic position of the organisms included in this order is in dispute. Under the name MJyromycetes they are included with the fungi by most botanists, while by the zodl- ogists they are usually placed as a class of the Rhizopoda under the name MMycetozoa (de Bary, ’59). The relation to the fungi is claimed on account of their saprophytic mode of life (terrestrial forms), and their mode of spore-formation in sporangia which are often compli- cated by the presence of stalks, columelle, and other plant-like 1 Thalamophora, R. Wertwig (74); Foraminifera, VOrbigny (’26). INTRODUCTION i9 structures such as elastic capillitia for dispersion of the spores. The relation to the Protozoa, on the other hand, is claimed on account of the unicellular nature, development of the swarm-spores, and occa- sional holozoic mode of nutrition. The spores leave the sporan- gium as amoeboid or flagellated organisms and may increase by ~ simple division during the swarming stage. If flagellated, the spore after a time loses the flagellum and becomes amceboid, in which con- dition division may again occur; finally numerous amceboid indi- c Fig. 4.—Flagellidia. [STEIN.] A. Chrysomonas (Chromulina) flavicans, Ehy. with chromatophores and an engulfed diatom (2d). &. The same encysted. C. Phacus longicaudus Duj. viduals group themselves together, forming a colony or plasmodium. In some cases the fusion is complete, in others the outlines of the individual Amcebe persist. In view of the questionable position which these forms occupy, there is some danger of their being neglected altogether, the botan- ists refusing them because of their animal characteristics, the zodlo- gists because of their plant-like features. No harm can be done by including them in both kingdoms, for on purely @ prior? grounds it is to be expected that some organisms should be on the boundary line between artificial groups such as the unicellular animals and plants. The present group and the Phytoflagellida among the Mastigophora appear to occupy such a position, and it is advisable to include them as provisional groups of the organisms with which they show the greatest number of common points. With our present knowledge, 20 THE PROTOZOA the majority of Mycetozoa undoubtedly resemble fungi more than they do Protozoa, and will not be further considered in the present work ; the Phytoflagellina have, on the other hand, so many obvious connec- tions with the animal flagellates that they cannot well be omitted. Fig. 5.— Dinoflagellidia. [ScHUTT.] A. Gymnodinium ovum, Schiitt. B. Peridinium divergens Ehy. f, the transverse furrow. The flagellated organisms now included under Diesing’s name, Mastigophora, fall naturally into three subclasses: (1) the Flage/lidia (Fig. 4) (flagellates in a strict sense), recognized by Dujardin and 0, aad, ONS Res uy os £ a8 Jez! Hes Fig. 6.— Coccidiida in epithelial cells. [LABBE.] The coccidium, a species of the genus AZyxinia, is supposed to have divided in one case (to the right). c¢, the sporozoén; , the nucleus of an epithelial cell. named by Cohn (’53); (2) Dinoflagellidia (Biitschli) (Fig. 5), which were first seen by O. F. Miiller (1773) and later fairly well described INTRODUCTION 21 by Ehrenberg, but curiously misinterpreted as ciliated forms (a mis- take rectified only during the last twenty years), which led: Clapa- réde and Lachmann (’58), R. S. Bergh (84), and Saville Kent (’81) to regard these organisms, under the name Ci/io-flagellata, as inter- mediate forms between the Ciliata and the Mastigophora; (3) Cysto- Jlagellidia (Haeckel), including two genera, Noctiluca and Leptodiscus, the former observed during the eighteenth century, the latter dis- covered by R. Hertwig (’77). yaar o es Fe BiB oe Eig TElR EO eer fl Get ae Fig. 7. — Two forms assumed by Leffotheca agilis, a myxospore. [DOFLEIN.] The history of the Sporozoa as a class dates from Kolliker’s (’45- 48) and Stein’s (’48) works, although the name Grvegarine now used as the title of an order (Gregarinida) goes back to Leon Dufour (728), and the first observation to Rediin the seventeenth century.! The different kinds of Sporozoa were first grouped together by Leuckart (’79) under the present name, and he subdivided the group into the Gregarinida (Fig. 1, D) and the Cocctdiida (Fig. 6), the former dwelling in cavities of various invertebrate hosts, the latter inside epithelial cells in, chiefly, vertebrate hosts. Under the term psorosperms (Joh. Miiller, ’41), a number of fish parasites belong- ing to the Sporozoa were known early in the century, and these were grouped together by Biitschli under the term J7/yxospo- 1 Cf. Diesing, p. 183. 22 THE PROTOZOA vidia (Fig. 7), and in the present classification form a fourth order of the Sporozoa. A third order under the name Hemosporidii 7a (Labbe, 94), includes the sporozoan parasites dwelling in blood-cells and plasm of different vertebrates (Fig. 8). The Infusoria finally have been variously classified since von Siebold restricted the term as given by Ledenmiller (1760-63) to its modern significance. Until their unicellular structure was defi- nitely established, the various types were placed among the higher animals, sometimes with the worms, sometimes with the Coelenterata. Even Perty (’52), who was the first to bring the ciliated forms together under their present name Ciliata, believed them to be combinations of Fig. 8.— A blood parasite or Heemospore, Plasmodium malarig. Amceboid, spore-forming and sexual phases are shown. [WASIELEWSKY.] cells. He included the Suctoria and the Ciliata as subdivisions of the Infusoria. Stein (’§7), who put the classification of the Ciliata upon its final modern basis, had previously confused the relations of Suctoria and Ciliata in his Acineta-theory. Claparéde and Lachmann (58-61), after showing that Stein’s interpretation was incorrect, raised those Infusoria which are provided with suctorial tentacles and are ciliated only during the embryonic phases, to the grade of a separate subclass to which they gave the modern name Swetoria (Fig. 1, CG £)A Since Stein’s work there have been but few important changes in the classification of the Infusoria. Biitschli (83-88) divided the Ciliata into two unequal groups distinguished by the nature of the mouth parts, the Gymnostomata and the Trichostomata. Stein’s sub- divisions based upon the arrangement of the cilia are more simple, however, and the advantage of Biitschli’s division is somewhat ques- tionable. C. ANIMALS AND PLANTS In determining the boundaries of the subkingdom Protozoa, two very interesting controversies have arisen, one relating to the boun- dary between animals and plants, the other to the relations of Protozoa to Metazoa. The modern attitude toward the first of these problems is well expressed by Delage (’96), who says: “The question is not so important as it appears. From one point of view, and on purely 1Cf. Stein, II (67), p. 142. INTRODUCTION 23 theoretical grounds, it does not exist, while from another standpoint itisinsoluble. If one be asked to divide living things into two distinct groups of which the one contains only animals, the other only plants, the question is meaningless, for plants and animals are concepts which have no objective reality, and in nature there are only indi- viduals. If, in considering those forms which we regard as true animals and plants, we look for their phylogenetic history, and decide to place all of their allies in one or the other group, we are sure to reach no result; such attempts have always been fruitless.” ? No one at the present time denies the extremely close relation which Huxley (’76) has so clearly pointed out between the lower algze and some of the flagellates, and it is the general opinion that no one feature separates the lowest plants from the lowest animals, and the difficulty —in many cases the impossibility — of distinguishing between them is clearly recognized. Curiously enough, this modern idea was early expressed by Buffon at the time when Aristotle’s view of the plant-like nature of some animals (Zodphyta) was still accepted in regard to the Ccelenterata. Buffon wrote as follows in 1749: “From this investigation we are led to conclude that there is no absolute and essential distinction between the animal and vegetable kingdoms; but that Nature proceeds from the most perfect to the most imperfect animal, and from that to the vegetable.” This state- ment might have been written in 1899, but Buffon unfortunately goes onto say: “Hence the fresh-water polypus (/Zydra) may be regarded as the last of animals and the first of plants.” ? Ehrenberg included a large number of plant forms among his Infusoria, most of which Dujardin threw out, restricting the group, practically, to the Protozoa as known to-day. But the discovery of flagellated swarm-spores of algee cast doubt on the animal nature of the organisms which Dujardin had described as flagellates. Von Siebold (’45) was thus led to retain only the families Astasiidee and the Peridinidze in his zodlogy, removing the Mastigophora, as a group, to the botanical side. In this he was followed by Bergmann and Leuckart (’56), while Cienkowsky (65) placed them as an intermediate group between animals and plants. Others went to the opposite extreme and actually excluded the algal swarm-spores from the plants, on the ground that they were merely flagellated parasites living on the plant-cells (Diesing, 65). Still others, noting that some of the flagel- lates are animal and some vegetable in their nature, undertook the impossible task of finding a single distinguishing character. The presence of green coloring matter or chlorophy/, upheld by Cohn (’7€) and others as a characteristic vegetable feature, seemed to be a good 1(’96), p. 518. 2 Edition 1812, p. 357. 24 THE PROTOZOA test; Oersted (’73), however, showed that in the lower plants there are forms differing only in the presence or absence of chlorophyl. These forms may be arranged in a series as follows :1— With chlorophyl Without chlorophyl With chlorophyl Without chlorophyl Oscillaria. Beggiatoa. Spirulina. Spirocheta. Leptothrix. Leptomitus. Palmellacee. Chroccoccacez. Chlamydomonas. Chlamydomonas hyalina. Synedra. Synedra putrida. A similar series can be arranged among the Protozoa, including forms which cannot be genetically separated, though some contain chlorophyl, and some are colorless. In the first of these, nutrition is holophytic or of the green plant type, in the second saprophytic or of the fungus type. The chlorophyl differential, if used here, would separate closely allied and in other respects identical forms, always to be found among the Mastigophora, and would lead to confusion. Furthermore, the chlorophyl differential would cause confusion in the classification of the fungi, where colorless representatives of several families of the Phycomycetes reproduce by colorless swarm-spores. Again, some of the Mastigophora with chlorophyl are not dependent upon this substance for their nutriment, but may combine t =< plant type with the animal type of food-getting (e.g. Chromulina and some Dinoflagellidia, Fig. 4). Stein sought a differential in the presence of contractile vacuoles and of nuclei, which, he maintained, are not found in vegetable swarm- spores, but are characteristic of all animal cells. This view has not been supported by later discoveries, for not only have vegetable spores been found to possess nuclei, but many of them are also provided with contractile vacuoles. Haeckel bases the classification of animals and plants upon nutri- tion, which differs but little from the earlier chlorophyl differential. All forms with the power of absorbing carbon dioxide, water, and nitrogen compounds, and of combining them into proteids, he calls plants, those without this power, animals, but he considers that this division, though logical, is at best only artificial, and gives no clue to the actual phylogenetic relations of Protozoa and Protophyta. Asa single differential, however, the method of nutrition is probably as satisfac- tory as any, for there are only a few forms which combine the two modes of food-getting. If rigorously applied, however, it cannot fail to shock the prejudices of both botanists and zodlogists in claiming for the animal kingdom forms which have usually been identified with the vegetable kingdom, and wee versa. Although Haeckel states that the dividing line is purely arbitrary and does not represent genetic affinity 1See Entz (’S8). INTRODUCTION 25 in the least, animal forms being derived from plants in a polyphyletic series, he does not hesitate to rank certain of the fungi, together with the Sporozoa and bacteria, as animal forms; the majority of chlorophyl-bearing Protozoa, on the other hand, are placed with the plants. Another differential, which, perhaps, has been the most widely accepted, is the power of spontaneous motion. It is supported to-day Fig. 9.— A spheroidal colony, Uroglena americana Calkins, consisting of monads embed- ded in a gelatinous matrix. as the most universal of the arbitrary differentials by Biitschli, Bergh, and Delage. Briefly stated, all forms, which are freely-motile in their adult life, are animals, while stationary forms are plants. This distinction is applied only to the lower forms, and not to the higher groups, but even as thus limited, this differential would neces- sitate some striking changes in existing schemes of classification. The freely-moving diatoms, which, since the time of Nitsch (’38) have been classed with the unicellular plants, would be included among the Protozoa, while the majority of Sporozoa, which are almost devoid of motion, would be excluded. The point of view which demands the strict separation of animals and plants has, however, little utility save perhaps to determine the limits of a text-book or monograph. Many observers, recognizing this truth, have included all forms in which the transition from plants to animals is shown, in a special group of the Protozoa, and usually with some heading which gives a clue to their position. This is first seen in Aristotle’s Zodphyta (Coelenterata); again in a more modern form in Perty’s Phytomastigoda, and in the Phytoflagellida of Delage. Haeckel (’66) made a group of equivocal forms large enough to include all of the Protozoa, and, under the name Pvof7sta, vainly attempted to establish a third kingdom between the animal and the plant. 26 THE PROTOZOA The arbitrary dividing line between the Metazoa and the Protozoa can be much more sharply drawn than that between animals and plants. The Protozoa are usually defined as single-celled animals, the Metazoa as many-celled; but this definition is not strictly accurate, for many forms of Protozoa live in aggregates, or colonies in which specialization and division of labor have progressed to a considerable degree ( Volvox, Uroglena, Magosphera, etc.; Fig. 9). As a rule, however, colonies do not form a distinct tissue of cells as in the blas- tula stage of Metazoa, while a still stronger point is that they never form a diblastic embryo.! D. GENERATION DE NOVO Leeuwenhoek’s discovery of the Protozoa had a marked effect upon current thought, some speculative writers seeing in these minute organisms the hypothetical units of organic structure, which, from the time of Democritus to that of Descartes, had been a subject of philosophical discussion. The rapid and incomprehensible increase of Protozoa in standing water could apparently best be explained by a theory of spontaneous generation; Leeuwenhoek, nevertheless, was convinced that their origin would be found in minute eggs or germs which are carried through the air as dust, or brought from place to place by birds, etc., thus showing his firm belief in Harvey's axiom, ex ovo omnia. He was supported in this view by Joblot (1718), whose experiments led him to the conclusion that the lower stratum of the air is filled with the germs of various kinds of animalcula, while Réaumur (1738) asserted that the dust of the air also contains dis- ease germs, which are the cause of epidemics. These men were, however, in the minority, and until the last fifty years only an occa- sional observer opposed the theory of spontaneous generation, as applied to these minute organisms. Even in Leeuwenhoek’s time it was well known that dead organic matter of any kind, when left exposed in water, gradually decom- poses, while the water, at first clear, becomes murky, and minute organisms of various kinds develop in it. Adopting the view that higher organisms are composed of organic units, speculative writers inferred that the small animals discovered by Leeuwenhoek were the units which had again become freed from the aggregated condi- tion. This is the key-note of Buffon's (1749) famous theory of gen- eration, which, in one form or other, persisted well into the 19th century. Briefly stated, Buffon believed that all organisms are composed of an infinite number of organic particles. The In- 1See Saville-Kent (’81) for the obsolete theory that Sponges are colonial Protozoa. INTRODUCTION 27 fusoria he believed to be nothing but these particles become free. ‘The destruction of organized bodies is only a separation of the organic particles of which they are composed. These particles continue separate till they be again united by some active power. When, however, a man’s body has nearly attained its full size, he does not require the same quantity of organic particles; the surplus is, therefore, sent from all parts into reservoirs destined for their recep- tion. These reservoirs are the testes and seminal reservoirs” (page 397). ‘The different parts of the body are, however, built up of dif- ferent kinds of organic units, so that upon disintegration there are different forms of animalcula, which are in no respect different from the spermatozoa of the same animal. The freed units are therefore neither animals nor plants, but the formative elements of both. Arising as the disintegrated parts of dead organisms, or rather as elements which never die, they are organisms which pass from one living state into another.” This view was carried further by Need- ham (1748), and as the Buffon-Needham hypothesis, was generally accepted. Thus the early advocates of the theory of spontaneous gen- eration did not maintain that living things arise from not-living sub- stances, but that all organisms are derived from parts of those living before, —a sort of transmigration. Spallanzani, however, to whom so much credit is due for our early knowledge of the Protozoa, adhered to the view of Leeuwenhoek that the Infusoria are not the units which constitute higher organisms, but distinct forms of life which, like other organisms, are derived from definite germs. Furthermore, he vigor- ously upheld their animal nature against Buffon and his school, basing his arguments upon their voluntary movements, changes of direction when moving, food taking, and upon their relations to moisture and dryness, warmth and cold, to which they reacted like higher animals. He found that Infusoria do not develop in a vacuum, and must, therefore, come from germs contained in the air. Seeing a Colpoda emerge from its cyst, he concluded that the cysts were eggs, mistaking the cyst-case for the egg-membrane. He separated the large from the small forms of Infusoria, a separation which was the first attempt to distinguish the Protozoa from bacteria, and which was destined to have great effect upon the theory of spontaneous generation, for it is a significant fact that the forms which have been supposed to arise by spontaneous generation have always been those approaching the limits of vision. 1 Spallanzani’s work has hardly been sufficiently recognized by later writers. Never car- ried away by enthusiasm, but describing only what he saw, he placed himself outside the current of popular favor by opposing the tempting hypothesis of the nature-philosophers. He seems to have combined his power of observation with a remarkable breadth of view, which in some cases gave rise to daring conceptions. Thus, in 1776, he wrote: “ Pour des 28 THE PROTOZOA The distinction which Spallanzani drew between large and small forms was also adopted by O. F. Miiller in his classification of the Protozoa. The latter maintained, however, that the lower of his two groups (Infusoria) were formed according to Buffon’s view, from the disintegrated parts of higher organisms. These parts, after the disintegration, collect, forming a slimy scum on the surface of the in- fusion (Zodglwa), which formed a most important adjunct in all subsequent theories of spontaneous generation. Minute vesicles arise later from this scum, and these remain as living organisms in the form of “Infusoria,” which included bacteria, spermatozoa, and the smallest forms of flagellates. This mode of origin he limited to those Protozoa which have no visible organs or means of locomotion. The other group (Bullaria), which included the larger of the animalcula (worms, ciliated Protozoa, rotifers, etc.), he maintained were formed, as in the higher animals, fromeggs. Miiller also held that these units mix with the inorganic particles to form the solid and fluid portions of the body of higher forms, while alone, and without contact with foreign matter, they form the nerves and “soul.” Oken (1805), another advocate of the theory of spontaneous gen- eration, held that all Protozoa arose in a similar manner. Since all plants and animals were built up of these Infusoria, he named the latter Urthzere, although, like Buffon, he held that they were neither plants nor animals. Infusions demonstrated to him that all plants and animals could disintegrate into Infusoria. Small Infusoria at first joined together to form larger ones, and out of their union arose the polyps and higher forms. While the outline of Oken’s view would seem to indicate a prophecy of the cell-theory, it is quite evident from his book on creation that he had little real conception of what we now regard as the essence of that theory. The majority of contemporary naturalists followed Buffon and Oken, either absolutely or with slight modifications. Among these Treviranus (703), Goldfuss (’20), and Carus (’23) accepted Oken’s views, while Lamarck (’15), Blainville (’22), and Bory de St. Vin- cent (’24) followed Miiller in restricting spontaneous generation to the simpler and smaller forms. Dallinger and Drysdale (’73—75), taking turns over the microscope by day and night, followed out the life-histories of many of these simpler forms through the process of division and spore-formation, thus showing that the monads arise, as do the higher Protozoa, from animaux inférieurs, le changement de demeure, de climat, de nourriture, doit produire pet a@ peu dans les individus, et ensuite duns Véspece, des modifications tres considérables qui deguisent a nos yeux les formes primitives” (cited by Dujardin (’41) from Spallanzani). 1The name “ Protozoa,” given by Goldfuss (’20), meant the same as Oken’s “ Urthiere.” It did not acquire its present significance until 1845, when von Siebold gave it a new meaning. INTRODUCTION 29 ancestors similar to themselves. They found that the spores which burst from the encysted forms were at first far beyond the limits of vision even with the high powers of the microscope at their command, but remained together in the form of a “glairy’”’ mass in which minute specks soon appeared, and these specks were watched until they had become full-grown monads similar to the original form. In later years the theory of spontaneous generation has been limited almost exclusively to the bacteria, but even here it has been energeti- cally and successfully opposed by Pasteur, Tyndall, Milne-Edwards, Claude-Bernard, Quatrefages, and others, against a constantly de- creasing number of advocates. No one is in a position to assert, however, that it does not take place in some organisms, although such a view is highly improbable; nor can it be maintained that it never has taken place in the past. Many theories of “archigony” (Haeckel), or the first origin of life by spontaneous generation, have been held by modern naturalists ; but all such theories are of a purely inferential character and lack substantial foundation. Without attempting to discuss these! it may be pointed out that the eminent botanist Nageli has advocated an hypothesis which suggests that of Buffon. Assum- ing that protoplasm consists of minute structural units or “ micelle,” he suggests that such micelle were first formed from not-living matter and secondarily united into organisms. Nageli does not hesitate to say that the evolution of the simplest protozoén from inorganic compounds involved a far greater step than from the first organism to man, and in accordance with this idea Haeckel places the beginning of life in the oldest known geologic age and in the oldest period of that age, the Laurentian. This, again, is entirely specula- tive; for if we except the questionable form /ozodx, the rocks of the Laurentian contain no recognizable records of past life.? The rocks of the period after the Laurentian, however, the Cam- brian, possess a great number of well-marked types, families, and genera, thus indicating, even at this time, a considerable antiquity. Haeckel and Nageli argue with Huxley, and the argument is of great 1For a discussion of this topic the reader is referred to the essays of Huxley, Tyndall, and Haeckel, and to Verworn’s Allgemeine Physiologie, pp. 298-319. Lee’s translation, pp. 297-319. 2The supposed genus Zozedz (“dawn of life’?) was discovered by Logan, of the Geologic Survey of Canada in 1865, and the name was given by Dawson in the same year.. There has been a lengthy dispute, however, in regard to this supposed fossil, some asserting that it is the earliest known foraminiferon, others that it is entirely inorganic. The former Opinion was held by Carpenter (’65, 66, etc.) and Dawson (’65, 75, etc.), the latter by the majority of geologists and petrologists, beginning with King and Rowney (’66) and followed by Mobius and others. Biitschli, while admitting that Dawson and Carpenter had a certain amount of evidence, inclines to the opposite view, while petrologists maintain that the same structure as that of Eozoén has been frequently observed in minerals forming parts of rocks. of undoubted igneous origin. 30 THE PROTOZOA weight, that since organized living bodies are composed of the same materials as unorganized or lifeless bodies, and after death are again resolved into those same lifeless materials, it may be logically assumed that in the beginning and under certain conditions, simple materials were combined into new compounds having the properties which we know to-day as life. Haeckel at first held that these complex com- pounds were primitive organisms which he called A/onera or organisms consisting of homogeneous plasm without differentiations of any kind, since differentiation follows the localization of function and can originate only as a result of living activity. In his later work, how- ever, Haeckel (’96) follows Nageli in postulating simple structural units as the primitive forms of life instead of the homogeneous and formless lumps of proteid. Nageli maintained that two stages must be distinguished between inorganic matter and the lowest organisms known to us. The first consisted of the synthesis of the albumin compounds and the organi- zation of these into micellaz which constitute primordial plasm. The second stage was the transformation of the primordial plasm into the simplest of living organisms. Haeckel’s hypothetical A/onera, if they existed, would approach most closely to these primordial forms of living matter, being described as “organisms without organs.” They could be called structureless, however, only from the anatomical standpoint. Physically, the earliest organisms must have been already complex, for, chemically considered, an albumin mole- cule is an extremely complex substance, and every unit of plasm which Nageli calls a micella must have had, and now has, that same complex composition. Somewhere in the obscurity of this early period came the change from the plant to the animal mode of nutrition. The latter must have begun at an early time, although the possibility of change at any time from plant to animal nutrition is not excluded, as shown by the numerous instances among the higher plants of adaptation to a parasitic or a saprophytic mode of life. So too, among the Protozoa, the acquisition of a cannibalistic mode of life, or, as Haeckel calls it, metasitism, may have required, and probably did require, a long period, and there Is little reason to doubt Haeckel’s view that the Pro- tozoa are polyphyletic in their origin. We possess no positive data for the conclusion as to which of the Protozoa were the most primi- tive. In considering this question, it must not be overlooked that, during the eras that have passed, the Protozoa may have been adapted and re-adapted many times over to changing conditions of environment, and living species have, in all probability, not come unchanged from that remote past.! 1See Lankester (’91), Klebs (’92), and én/ra, p. 99. INTRODUCTION 31 SPECIAL BIBLIOGRAPHY I Biitschli, O0.—Protozoa. In Bronn’s Klassen und Ordnungen des Thierreichs.: Leipzig, 1883-1888. Dujardin, F. — Les Infusoires. Parzs, 1841. Entz, Geza — Protistenstudien. Ludapesth, 1888. Huxley, T. H.—On the Border Territory between the Animal and the Vegetable Kingdoms. Collected Essays, D. Appleton & Co. Vol. 8, Edition 1896. Kent, W. Saville. — A Manual of the Infusoria. London, 1881. Stein, Fr.— Organismus der Infusionsthiere. Lecpzgg. Abth. I., 1861; II., 1867; Ill., 1878. CHAPTER II GENERAL SKETCH It is a widely accepted opinion among men of science that life originated in the sea, and here to-day are found the great majority of species of Protozoa. In the littoral regions, particularly in the super- ficial slime and upon submerged water-plants, are found a profusion of Rhizopoda. Farther out, Radiolaria and shelled Rhizopoda belong- ing to the order Reticulariida float upon the surface or at varying depths below it, while their empty shells, settling slowly to the bottom, have added little by little to the accumulations of the past, until to-day,. under the names Radiolarian ooze and Globigerina ooze, they form vast areas, miles in extent, and often attaining a depth of many feet. By the agency of earthquakes or slow upheavals, these beds have beconie exposed from time to time, and we recognize the Barbadoes as composed in large part of the skeletons of Radiolaria, or the chalk cliffs of England as built up of the lime shells of reticulate Rhizopoda. Apart from the Sarcodina, the majority of Protozoa leave no memo- rial in stone of their past existence. Pelagic forms such as Dinofla- gellidia and Cystoflagellidia, living near the shores, and often drawn together into great aggregates by currents, winds, etc., become the food of whales, fishes, and other marine animals. Many Rhizopoda, Ciliata, and Suctoria are attached by mineral secretions, or by stalks, to rocks, submarine plants, etc. Others are parasites upon the out- sides of fish and other animals, while still others are parasites within. The fresh-water Protozoa, while less rich in species, are much better known than the marine forms, for their modes of life, habitats, and life histories are more easily observed and controlled. Many kinds of Rhizopoda, Heliozoa, and Ciliata are found both in fresh water and in salt; and numerous experiments by Verworn, Gruber, and others have shown that some forms can live either in salt water or in fresh; the change from one to the other usually results, how- ever, in modifications of structure. In general, the Protozoa abound in fresh water which contains enough food material for their growth and reproduction, but the widespread belief that each drop of drink- ing water contains countless myriads of microscopic forms has absolutely no foundation. Protozoa cannot live in chemically pure water, and on the other hand, many of them cannot live in foul wateis.. 32 GENERAL SKETCH 33 Thus, in sewage, one finds occasional ciliates and flagellates, but no such numbers as are sometimes found even in good drinking waters, where, obtaining their food as do the green plants through the agency of their green or yellow coloring matter (chlorophyl), the Protozoa sometimes become a source of annoyance. They thrive in standing waters where the accumulation of bacteria gives food for numerous ciliates and rhizopods; the decomposing organic matter dissolved in the water is taken in by saprophytic forms of flagellates, which multiply to prodigious numbers, and these in turn may form the food- supply for predaceous Infusoria and Sarcodina. Rotifers, Crustacea, - molluscs, and worms prey upon all forms, and when the cycle is passed, the water becomes cleared of animal life. In nature, the pools rarely if ever become thus cleared, because new food is con- stantly brought in from fresh sources, and the cycle becomes continu- ous. In such places the superficial slime upon the bottom contains naked and shelled rhizopods, although the latter are more often found alive upon the leaves and stems of water-plants; here, too, are colo- nial Infusoria or single forms attached by their stalks. Suspended in the water are to be found the majority of species of Flagellidia, a few Dinoflagellidia, the majority of Heliozoa, many predatory ciliates, and a few rhizopods, especially certain shelled forms which secrete a ~ bubble of gas to buoy them up. Many forms of Protozoa are capable of sustaining life either as terrestrial or as parasitic organisms. The former, allied to the Myceto- zoa, grow over damp wood, while a number of rhizopods are almost able to withstand dryness, for as Dujardin, Ehrenberg, Greeff, and others early pointed out, they live in damp moss and leaves of the woods. Forms which have become adapted to a parasitic mode of life may be found in all classes. Among the Rhizopoda, various species of intestinal A@be may be found in all sorts of vertebrate and invertebrate hosts; about twenty species of Flagellidia and many more of Ciliata live as parasites, some in the blood, some in the intes- tinal fluids, and others in the cavities of various organs in man and other hosts. These forms, however, are only occasional parasites, and are more like commensals than parasites, having little signifi- cance when compared with the Sporozoa, a ‘class of Protozoa which, without any exceptions, are parasitic. These infest all animal forms from Protozoa to man: one group lives in the digestive tract and the cavities of the body (Gregarinida); another in the cells of the digestive organs (Coccidiida); another in the muscle-cells and lymph surrounding them (Myxosporidiida, Sarcosporidiida); and still another in the blood-corpuscles and in the blood-plasm (Hzemosporidiida). Of all Protozoa these are the only forms which are known to menace the life of man. D 34 THE PROTOZOA A. GENERAL MORPHOLOGY As might be expected from the wide distribution of the Protozoa and their varied modes of life, each of the several classes contains organisms of varying forms and grades of complexity. In fact, no one form is characteristic of any group, but in all cases where the body is plastic and subjected to an even pressure the form is spher- ical (homaxonic), readily changing, however, into an elongate or monaxonic condition. In the higher types, especially those which are inclosed in a firm membrane, the form is usually asymmetrical, and cannot be interpreted. as the direct result of mechanical condi- tions. The homaxonic type prevails among Heliozoa, Radiolaria, and intra-cellular Sporozoa (Coccidiida), and occurs in the simpler types of all classes. The monaxonic form prevails among the Mastigophora and the lumen-dwelling Sporozoa (Gregarinida), while asymmetrical forms are dominant among the Infusoria. In all classes, when for any reason the surroundings become unsuitable, or at times as a pre- liminary to some methods of reproduction, the organisms secrete a thick and resistant protective coating or cyst which is usually homaxonic. The various adaptations found in the Protozoa are confined almost entirely to the outer protoplasm or ectof/asm, the inner portion or endoplasm remaining approximately similar in structure throughout the group. The ectoplasm, being in direct contact with the sur- rounding medium, becomes hardened into ectoplasmic coatings of various kinds, serving as protective coverings for the inner endo- plasm. It also becomes differentiated into various external organs of locomotion, of food-getting, of defence and offence, and, in the higher types, into organs of sensation. 1. Lhe Endoplasm. Examined under the low powers of the microscope, the body of a protozodn appears to be made up of a gelatinous, diaphanous sub- stance which, under certain conditions, breaks out of the confines of the cell-membrane, forming irregular globular masses in the water. This phenomenon was early recognized, and under the term “ difflu- ence’ was regarded by Dujardin as a special property of sarcode.} Examined under higher powers of the microscope (c.g. with a one- 1 «Sarcode. Je propose de nommer ainsi ce que d’autres observateurs ont appelé une gelce vivante, cette substance glutineuse diaphane; insoluble dans eau, se contractant en masses globuleuses, s’attachant aux aiguilles de dissection et se laissant étirer comme du mucus, enfin se trouvant dans tous les animaux inférieurs interposée aux autres élémens de structure.” — DUJARDIN, 735, p. 367. GENERAL SKETCH 35 twelfth inch objective), the mass of endoplasm is seen to consist of a more or less definite matrix, and if the cells be properly fixed and stained, a distinct structure is visible. This appears to be little more than a definite meshwork, the meshes of which are sometimes minute, compressed, and narrow, sometimes large and open. The substance of the mesh proper appears to differ noticeably from that within its spaces. The latter is fluid-like, and not infrequently contains gran- ules of larger or smaller size; the former, also a fluid, appears more dense, and is made up of exceedingly minute granules (microsomes). Differential stains show that the various granules differ not only in size, but in chemical composition, and it has been determined that some are food particles in process of assimilation, and that others are waste matters. This protoplasmic structure, which Biitschli (92) compares with a foam structure (Schaumplasma), is described by him as consisting of small drops of a liquid a/veolar substance inclosed within the meshes of a continuous zyter-alveolar substance, also liquid, but of a different composition. Each alveolus may be compared to a bubble in a foam structure; the air of the bubble corresponding to the alveolar substance, the walls to the inter- alveolar substance. : While the endoplasm of all Protozoa is alveolar in structure, there is considerable variation in density due to the relative sizes of the alveoli and to the nature of the granules contained within them (Fig. 10, A-D). They vary in size from minute vesicles in Sporozoa (C) to large vacuoles in many Heliozoa, Radiolaria, and Infusoria. In some cases, ¢.g. in the heliozoon Actinospharium (D), or the cystoflagellate Noctiluca, the vacuoles are so large that the protoplasmic structure appears parenchymatous like a plant-cell. The granules in the walls of the alveoli are equally variable in size. In some cases they are exceedingly minute, and correspond apparently to the fine elementary granules which Altmann (’94) regarded as the basis of all protoplasm (e.g. Ameba, A); in others they are coarse and obviously of different kinds (Pelomyxa). The various granules within the alveoli are sometimes inert and functionless and often crystalline in form.! In other cases they may have some function to play in the economy of the cell. Thus car- bohydrates in the form of starch, sugar, or cellulose are generally present and serve as a reserve store of food, or of building material for the outer covering. Other granules which are invariably present may be food particles in various stages of digestion, assimilation, and excretion, or oil particles of various forms and sizes. With the exception of the Sporozoa, every class of Protozoa includes 1Cf. Chap. IX., p. 286. SEARED a +S va Bc Fig. 10. — Protoplasmic structure in different Protozoa. [From preparations.] A, Ameba proteus pseudopodium. The endoplasm has broken through the ectoplasm, and is now in advance. 2. Chilomonas paramecium Ehv. a flagellate. C. Lymphosporidium trutte Calkins, a sporozoén. D. Actinospherium EHichhornii, endoplasm and one nucleus. a, alveoli. Same magnification throughout. GENERAL SKETCH 37 some species in which colored masses of protoplasm — chromatophores —are present, either as living parts of the cell (Mastigophora) or as commensals or symzbzonts, the protozodn and the plant living together for mutual benefit (Infusoria, Sarcodina). The chromatophores are colored by different substances, usually green by chlorophyl (Chloro- monadina, some Infusoria), or brown by diatomin (Chrysomonadidz and Dinoflagellidia), and have a definite shape and size for each species. Brilliantly colored patches of pigment, the so-called eye- spots or stigmata, are frequently seen, chiefly among the Mastigoph- Fig. 11.— Flagellates with stigmata. [FRANCE.] A, Euglena Ehrenbergii, Klebs. The color-mass (5) contains several concrements (lenses ?). B, Pandorina morum, Ehr. The color-mass (5) is attached to a single spherical lens. ora, where they are situated near the base of the flagellum. These spots are supposed to have some special relation to light,’ an unproved, though probable, view which is based chiefly upon the fact that in many of them there is a distinct lens-like body, and other structures which usually accompany eyes of primitive form in other types of invertebrates? (Fig. 11). Among other inclusions occasionally found within the endoplasm are the peculiar trichocysts found in the holotrichous ciliates (Para- mecium and its allies). These are minute defensive or possibly offensive weapons analogous to the stinging threads of the Celen- terata. Nematocysts containing a spirally wound thread, as in the Ccelenterata, are also found in two forms, one a dinoflagellate (Poly- krikos), the other a ciliate (Epistylis wmbellaria),. while analogous thread-bearing structures are found in the spores of all Myxospo- ridiida among the Sporozoa (Fig. 12, C, D). 1Cf. Pouchet, ’86. 2 Engelmann’s (’82) experiments, on the other hand, tend to show that it is not the colored body, but the colorless protoplasmic mass in front of the stigma which is particularly sensitive to light. 38 | THE PROTOZOA 2. The Ectoplasm. In many Protozoa, especially among the Rhizopoda, there may be no distinction between ectoplasm and endoplasm. These cases, how- ever, are exceptions, for in the majority of forms a well-marked ecto- plasm can be distinguished. In many cases the difference appears to be only in the presence or absence of granules, and their distribu- tion depends upon the density of the fluid plasm. No great mor- phological importance can be attached to this regional difference, for it appears to be only an index of the physical conditions of the protoplasm. The body of the common rhizopod Amwéa, for example, consists of a more or less fluid mass in which lie suspended the various granules, vacuoles, nuclei, crystals, and food particles, and, as Griiber (’84) pointed out, if the plasm is thin, z.¢. more fluid, the contents can spread easily through the whole mass, while if the plasm is dense and viscous, they will be held back by the resistance, and a relatively broad ectoplasm may result. The more fluid condi- tion is seen in rhizopods like Protomyxa and Pelomyxa, the denser in Ameba proteus, and the majority of fresh-water shell-bearing forms. In some of the latter and in a few Infusoria the distribution according to density is so marked that several regions can be made out. Thus Pénard (’90) described no less than four zones in the shelled rhizopod, Luglypha, while in many Infusoria and in some Sporozoa a mem- brane, ectoplasm, cortical plasm, and endoplasm, differing from one another in density, can be distinguished. It is an interesting fact that in the artificial mixtures which Biitschli has so successfully made to imitate protoplasm, a similar regional differentiation, at least as far as ectoplasm and endoplasm are concerned, may be seen. It is perhaps to a tendency of protoplasm to stiffen while in con- tact with water that we can turn for an explanation, first pointed out by Griiber (81), of the outer condensation of protoplasm resulting in the numerous membranes and tests of the Rhizopoda, and of the outer coverings of Protozoa in general. The simplest form of mem- brane is an almost invisible cuticle of extreme delicacy (pe//écula of R. S. Bergh) as in the rhizopod Ameba proteus (Griiber, 81). In other forms of the same genus, however, the outer zone becomes greatly thickened (A. ¢entaculata, A. actinophora, Fig. 12, A), and a more or less lifeless membrane results. In these thick-skinned forms the membrane is often perforated by the pseudopodia, which form long finger-like processes, and when retracted leave minute holes in the membrane. In these cases there is usually a sharp distinction between the inner plasm and the cortical part, but in many Infusoria and Sporozoa there is a gradual increase in density from within outward, and the outside is covered by living membranes which may become complicated by the addition of muscular fibrils (azyonemes), of GENERAL SKETCH 39 sensory and tactile organs (czrrz), or protective structures like hooks, spines, and tentacles (Fig. 12, B-G; see also Fig. 16). Like many of the cells which constitute the tissues of higher ani- 1b caer ae <= ea - are a 4. Fig. 12. — Ectoplasmic modifications. A. Ameba tentaculata, [GRUBER] B. Clepsidrina munieri, [SCHEWIAKOFF.] C. Tri- chocysts. [SCHEWIAKOFF.] 2, Nematocysts from the sporozoén A/yxobolus. [BALBIANL.] £, F, G, attaching hooks and spines from different Gregarinida. [WASIELEWSKY.] mals, the protozoan body has the power of forming by chemical pro- cesses over and above those which relate merely to nutrition, various products which are secreted just within the peripheral plasm, where they usually form a protective armor in the shape of shells, tests, or “houses.” The materials thus formed within the cell-body may be chitin (composed of C, H, N, and O, and supposed to be a deriva- tive from carbohydrates, but the exact formula is in dispute), ced/zlose 40 THE PROTOZOA (CgH,)0;), calcium carbonate (CaCO), and silica. The secretions may take the form of plates, of continuous deposits, or of regular skeletons which are often extremely complex (Fig. 13, D). In the majority of cases, the secretions are made in the ectoplasm, although in one well-authenticated case at least (Euglypha alveolata, Fig. 13, A), the plates destined to form the shell are formed in the endoplasm and in the immediate vicinity of the nucleus! In other shell-bearing forms of Rhizopoda, there is usually a basis of chitin, upon which the various shell-substances are deposited, or the shell may consist of the chitin alone. In some cases it is no more than a cap covering a small portion of the body, and into which the entire protoplasmic mass could not possibly be withdrawn (Pseudochlamys, Fig. 13, C). Here the chitin which forms the shell is perfectly smooth; but in other forms it may be ornamented in various ways by pits or pro- tuberances. Again, in many fresh-water Rhizopoda the shell-material is not secreted, but the test is composed of foreign particles, such as diatom shells, sand crystals, mud, or detritus of any kind, fused together and to a chitinous substratum by means of mucilaginous cement secreted by the organism. 3. Nuclet. Haeckel’s claim (’68) that there are organisms without nuclei (Monera), although it rests upon negative evidence, cannot be rejected until all of the forms considered have been shown to possess them. On purely @ priort grounds, it is possible to conceive such organisms, although the numerous experiments which have been performed dur- ing the last decade upon nucleated and non-nucleated parts of Pro- tozoa, show, in these cases at least, the absolute necessity of the nucleus for the life of the organism. These experiments make it probable that the so-called Monera have in reality some structure or structures which perform the functions of the nucleus, although a well-defined nucleus with membrane and other characteristic parts may be absent. In the majority of Protozoa there is but one nucleus (many Sar- codina, Mastigophora, Sporozoa), while in some forms two nuclei are the rule (some Khizopoda). In others, again, there may be a great number of nuclei, the number varying with the age of the organism (examples occur in all groups of the Protozoa). In many of the Pro- tozoa, although not in all, the nucleus is provided with a membrane and contains two substances; chromatin, staining with certain basic dyes and consisting largely of nucleinic acid, and achromatin, a sub- stance which is not stained by the chromatin dyes, in the form of a 1Cf. Schewiakoff (’88). Fig. 13. — Shells and tests. [4, SCHEWIAKOFF; B, ORIGINAL; C, BUTSCHLI; D, STEIN.] A, Euglypha alveolata Duj. The shell consists of oval siliceous plates glued together by a sili- ceous (?) cement. B. Cochliopodium digitatum, n.sp. The test is membranous and perforated for pseudopodia. C. Pseudochlamys patella Clp.and Lach, The test is membranous and shield- like. D. Ceratium tripos Nitsch. The shell consists of cellulose plates of diverse size and shape. 42 THE PROTOZOA network, or of a homogeneous body of considerable size (Karyo- somes). Several different types of nuclei may be distinguished ; some of the most important being: (1) The distributed nucleus, Fig. 14. — Types of nuclei. [4. Calcituba polymorpha Roboz, from SCHAUDINN; &. Colpidium colpoda, from a preparation; C. Euglena viridis Ehv. from a preparation; D. Tetramitus chilomo- mas, n.sp.; 4. Noctiluca miliaris Sur., from a preparation.] A single karyosome (.1) becomes vesicular, and ultimately gives rise to several daughter-karyo- somes (so-called ‘fragmentation’ Schaudinn). Several karyosomes in Actiluca (E) hold the chromatin, the rest of the nucleus is filled with “achromatic” granules. In Tetramitus chilomonas (P) the chromatin is scattered throughout the cell; the lighter-colored body in the centre of the cell is the homologue of the deeply stained central body in Euglena (C). GENERAL SKETCH 43 consisting of innumerable chromatin granules distributed throughout the cell (7rachelocerca, Chenia tercs, Holosticha flava, HI. scutellum, Tetramitus). (2) The homogencous nucleus consisting of a single mass of chromatin with a homogeneous structure throughout all stages, and with no trace of reticular substance (many Phytoflagel- lates). (3) Dimorphic nuclei, consisting of a large nucleus called the macronucleus, and a small one, the micronucleus, in the same individual. The former is generally regarded as functional chiefly in vegetation, the latter in conjugation. With the exception of Polykrikos among the Mastigophora, dimorphic nuclei are found only in the Infusoria (Fig. 14). The typical form of the nucleus is spherical, although it may be discoid or ellipsoid, or, in the case of the macronucleus, drawn out into various fantastic shapes, of which the horseshoe (Vorticellidae), the beaded (Stentor and Spirostomum, etc.), or branched (Aciveta, Dendrosoma) are examples} 4. Organs of Locomotion. With very few exceptions, the Protozoa have the power of moving from place to place. The exceptions are found among the para- sitic Sporozoa, although even here there is, in some cases, a peculiar gliding motion. In no adult sporozodn is there a special organ of locomotion, yet the Gregarinida and Heemosporidiida actually move from place to place, although very slowly. In some cases, the motion is due to peculiar peristaltic waves of contraction; in other cases to the contraction of muscle-like fibrils, the myonemes. An analogous movement is also known in certain flagellates (Euglenide) and ciliates (Heterotrichida). In the majority of Protozoa, however, movement is accomplished by the activity of special motor organs, which may be either changeable processes (pseudopodia) or permanent vibratile appendages (flagella and cilia). The changeable processes or pseudopodia, found chiefly in the Sar- codina, are sometimes numerous, sometimes few; when few in number they are usually short, finger-formed, and quick to change in form and appearance by the flowing protoplasmic substance of which they are composed (Fig. 1, A, and Fig. 15, 4, 2); when numerous, they are fine-pointed, and often sticky, so that when two or more come in contact, they fuse or anastomose (Reticulariida, Fig. 15, ©). Again, the pseudopodia may be fine and pointed, but rigid in structure and unchanging in form, a condition brought about by the presence of an ‘axial filament of stiffened protoplasm, which runs down the centre of each pseudopodium (Heliozoa, Radiolaria, Fig. 15, D). Unlike pseu- 1Cf. Chapter VII. for further details concerning nuclei. 44 THE PROTOZOA dopodia, the protoplasmic filaments, known as flagella and cilia, are derived solely from the ectoplasm and are constant in their position, and, save for the occasional absorption within the body, for some rea- son or other, they are unchangeable. Flagella-motion, characterized by energetic contractions or undulations, or by rotary motions, differs MAS gant este 7 nt CN Rye eg Fre a RL IE Fig. 15.— Types of pseudopodia. A. AmebalimicolaRhmb, [RHUMBLER.] &. Amoeba dlatte Biitsch, [BUTSCHLI.] C. Lieber- Riihnia sp. (VERWORN.] D. Actinospherium Eich, Ebr, [ORIGINAL.] , the axial filament. entirely from the slow flowing movement of pseudopodia; yet, as Dujardin first observed, in some forms pseudopodia change into flagella, and flagella into pseudopodia. — In structure, flagella are long, thin, usually pointed threads of protoplasm, which, as a rule, are longer than the cell itself; they are typically single, but there may be two, three, or many. Cilia, on the contrary, are always multiple, and are never interchangeable with pseudopodia (Fig. 16). Although GENERAL SKETCH 45 characteristic of various epithelial tissues in Metazoa, they are found only in a single specialized group of the Protozoa, the Infusoria. In form, they are similar to flagella, but as a rule they are shorter, never pointed, and more numerous, many of them acting in unison, with a quick regular motion like a set of oars. In some groups, the cell is completely clothed with these motile elements (Holotrichida), in others only a portion is covered either in one or more rings about the body (Peritrichida), or upon one surface only (Hypotrichida). The cilia may also become variously modified by fusion with one another, REE E oe ; is Fig. 16.— Cilia and myonemes of Infusoria. [a, 6, and c, JOHNSON; ¢, d, f, g, BUTSCHLI.] The surface view of Stentor ceruleus (c, e) shows rows of cilia inserted on the borders of canal- like markings, each of which contains a myoneme (d). These are more clearly shown in the optical section (f). In AHolophrya discolor (g) the canals and myonemes are inserted deeper in the cortical plasm. a@, the membrane of Stentor cwruleus under pressure. giving rise to motile organs of a more complex structure, such as the membranes, membranelles, and cirri found in different groups of the ciliated Infusoria. In many Protozoa the adult forms have no distinct motile organs, although they may pass through embryonic stages in which such structures are present. The Suctoria, for example, are, for the most part, entirely devoid of cilia in the adult stages, although the embryos possess them. Again, many of the Rhizopoda pass through flagellated stages before assuming the amceboid condition, and certain Mastigophora pass through amoeboid swarm-spore stages. Some Heliozoa and Radiolaria similarly pass through both flagellated and amceboid stages before assuming their own adult forms. Normal movement on the part of Protozoa provided with pseudo- 46 THE PROTOZOA podia consists in the simple protrusion and retraction of the change- able processes. It becomes much more definite in forms provided with flagella, where, in many cases, a steady progression with the flagellum in advance is the characteristic motion. In one group of the Mastigophora, however, the Choanoflagellida, the flagellum, like the tail of a spermatozoon, is directed backward during motion. Among the Ciliata, complex movements accompany the high organiza- tion of the cell, and the change from one form to another, apparently at the will of the organism, is extremely suggestive of conscious action. Here, in addition to the normal and constant motion of the cilia, are various forms of contractile movement varying from the simple sarcode streaming, which is characteristic of the Suctoria, to the . definite contraction of distinct muscular elements in the myonemes of Heterotrichida and Peritrichida. B. GENERAL PHYSIOLOGY In all Protozoa, as in higher animals, the functions of nutrition, respiration, excretion, reproduction, and irritability the analogue of nerve-response, are indispensable for the life of the organism. When compared with the vital functions of the higher animals, all of these processes appear simple; yet the difference is one of degree only, and among the unicellular animals, as among the multicellular, the func- tions become more complicated and difficult to analyze as the cell- structures become more complex. In the simpler forms, the naked unmodified protoplasm contains the beginnings of the most compli- cated functions, none of which can be regarded as having a par- ticular time and place of birth in the series of animal forms; all are characteristic of the cell, and beyond that, of living protoplasm, of which they are the distinguishing properties. The most primitive Protozoa, entirely destitute of organs, feed without mouth or digestive tract, move without appendages, react to external stimuli, excrete, and reproduce. In the higher types the cell-organism becomes dif- ferentiated into special parts for the performance of these various functions, and the relative position of the organism in the scale of Protozoa depends upon the degree of this differentiation. Inno class of animals is the connection between division of physiological labor and regional \ differentiation so clearly marked as here. This is especially noteworthy in the outer plasm, which, directly correlated with the action of the’ environment, has apparently become progres- sively modified into external coverings, into motile organs, and into organs of sensation, while the endoplasm retains the same character throughout the group. One function, that of excystment, is limited almost exclusively to GENERAL SKETCH 47 the Protozoa, although occasionally seen in some Metazoa (e.g. Macrobiotus, or the “water bear,” and some rotifers). This is a special adaptive process by which the organisms are enabled to survive when the environment is unsuitable. If a pool dries up, becomes too dense, or too foul from putrefaction or other causes, Fig. 17. — Types of cysts. A, Ameba proteus. [SCHEEL.] B. Stylonychia mytilus Ebr. [BUTSCHLI.] C. Pleurotricha grandis St. (BUTSCHLL.] D. Euglpha alveolata Duj. [LEIDY.] £. Actimospherium Lich. Ebr. (BuTSCHLI.] /. Colpoda Steinu. [MAUPAS.] a, gelatinous matrix; 4, outer cyst wall; c, middle cyst wall; @, inner cyst wall. the cell draws in its appendages, rounds out into a sphere and secretes a resisting membrane, within which it can exist for a long period. When first formed, this membrane is a delicate gelatinous substance, which soon hardens and gradually acquires the peculiar characters of chitin. With the exception of the contractile vacuole, which continues to contract rhythmically for some time, all of the organs of the body are quiet at this period. The water, expelled by the vacuole, collects between the cyst and the spherical wall of the animal, the latter 48 THE PROTOZOA becoming smaller and smaller as more and mort water is expelled. The nucleus appears unaltered, except for a very slight reduction in size (Fig. 17). In this condition the animal can withstand a long period of desiccation, or even extreme heat and cold, and, owing to its minute size, it may be blown hither and thither until it reaches some favorable spot where it may recommence active life. Water is then absorbed, the cyst is ruptured, and the former active life begins anew. Encystment may occur in some cases after a particularly heavy meal, or more frequently, before reproduction by spore-formation or simple division. 1. Nutrition. The processes of nutrition, as in the higher animals, may be divided _ into three stages: I, the capture and ingestion of food; 2, the digestion of the ingested parts; and 3, the ejection or defecation of the undigested remains. Many of the Protozoa have no special apparatus for seizing and ingesting food, but absorb it directly from the surrounding medium. Thus many Mastigophora live, like the fungi, by absorption, through the body walls, of fluids which hold in solution the products of decom- position of other animal and plant forms. Others, as the Sporozoa and some Ciliata, live like a tapeworm and other intestinal parasites, upon the digested foods of the alimentary tract, or in nutritive fluids in other cavities of different hosts. The Phytoflagellida, also, do not ingest solid food, but, by the aid of chromatophores, they have the power of manufacturing their food in the same manner as do the green plants. The majority of Protozoa, however, take in solid food through more or less definite regions of the body. In some of the phytoflagellates there is a distinct mouth-opening, in addition to the chromatophores, and such forms may combine both animal and plant modes of nutrition. Food-taking has been carefully examined in connection with the Ciliata, where many species living upon certain specific organisms apparently select their food. Thus Maupas (’88) distinguishes forms that are herbivorous, others that are carnivorous, and still others that are omnivorous. The food that may be thus selected consists of all sorts of lower plants, such as desmids, diatoms, zodspores, bacteria, filamentous algze, etc., while among the animals the Mastigophora and smaller ciliates are the most frequent victims, although rotifers and small worms are often eagerly seized. Maupas believes that the cause of these various adaptations in feeding should be sought in the modifications of the mouth. ‘The mouth is, in short,” he says, “the dominating organ par crcellence in the morphology and the physiology of the Ciliata. Nutrition in its manifold phases in these GENERAL SKETCH 49 minute beings absorbs and completes their entire existence. This function assumes with them an intensity which, I believe, is equalled nowhere else in the animal kingdom. They are gluttons par excel- fence, absorbing and digesting night and day without repose. It results that the apparatus charged with the performance of such an intense function becomes modified, diversified, and developed to an astonishing degree, especially striking when it is remembered that these are unicellular organisms.” + The capture and ingestion of food, in its simplest form, occurs in Fig. 18.—Food-taking. [.4, PENARD; Z and C, BUTSCHLI.] A. Raphidiophrys elegans Hert. and Lesser. B. Oikomonas termo Ehr. C. Didinum nasutum, O.F.M. ¥ food particles. the group of Rhizopoda, where, as in Amaba proteus, any part of the body can act as a mouth. In this form pseudopodia are pushed out toward the victim (a flagellate, ciliate, minute plant form of any kind, or even a higher animal, such as a rotifer or worm) and entirely surround it, together with a certain amount of water, thus forming a gastric vacuole, or an improvised “stomach.” When the rhizopod is provided with a shell, the food-taking area is limited to a mouth-open- ing in the shell, while in many of the shelled Heliozoa the taking of food is complicated by the presence of an unbroken coating, and a special opening must be made for each ingestion (Fig. 18). In the Reticulariida, the gastric vacuoles are on the outside of the shell, and are formed in the network produced by the anastomosis of the pseu- E 1 (88), p. 185. 50 THE PROTOZOA dopodia. Here the prey is digested, and the products of digestion find their way by protoplasmic streaming to all parts of the animal. In many Mastigophora and Ciliata, the motile organs create a vor- tex current in the region of a well-defined mouth, which usually leads into a distinct pharynx. In some flagellates, the base of the flagel- lum is an area of soft plasm, through which the food particles can be readily engulfed as they strike against it, but in others there is a dis- tinct opening which leads into the endoplasm. In other flagellates (Noctiluca and the Choanoflagellida), a peculiar protoplasmic funnel- shaped collar surrounds the region which answers the same purpose. In most of the Ciliata, the buccal region is surrounded by strong cilia, which are frequently fused to form membranes or membra- nelles; these send a powerful current of water, containing innutri- tious as well as nutritious particles, toward the mouth, which receives all without discrimination. In some cases, as in certain of the holo- trichous Ciliata, there is a true swallowing or deglutition, by which solid food is gulped into a capacious pharynx and thence into gastric vacuoles. Many of the latter forms have offensive trichocysts, resem- bling the rhabdites of Turbellaria. One of these, upon the approach of its prey (usually a small ciliate or flagellate), launches its darts, which penetrate the cuticle and paralyze the prey. The victim is then swallowed, the mouth of the carnivore enlarging to accommodate it (Fig. 18, C). This process is strikingly illustrated by the ciliate Actinobolus radians, which combines the selection of food with the offensive use of trichocysts. This remarkable organism possesses a coating of cilia and protractile tentacles, which may be elongated to a length equal to three times the body-diameter, or withdrawn completely into the body. The ends of the tentacles are loaded with trichocysts (Entz, 83). When at rest (Fig. 19), the mouth is directed downward, and the tentacles are stretched out in all directions, forming a minute forest of plasmic processes, amongst which smaller . ciliates, such as Uvocentrum, Gastrostyla, etc., or flagellates of all kinds, may become entangled without injury to themselves and without disturbing the Actzobolus or drawing out the fatal darts. When, however, an Halteria grandinella, with its quick and jerky movements, approaches the spot, the carnivore is not so peaceful. The trichocysts are discharged with unerring aim, and the Helteria whirls around in a vigorous, but vain, effort to escape, then becomes - quiet, with cilia outstretched, perfectly paralyzed. The tentacle, with its prey fast attached, is then slowly contracted until the victim is brought to the body, where, by action of the cilia, it is gradually worked around to the mouth and swallowed with one gulp. Within the short time of twenty minutes, I have seen an Actinobolus thus capture and swallow no less than ten Hadterias. CENERAL SKETCH ; SI Still another mode of food-taking is found among the Suctoria. Here there is no mouth and no motile organ to create currents, but the body is provided with distinct tentacle-like processes, through the Z Fig. 19. — Actinobolus radians St. The organism is represented at rest, with the mouth turned downward, and with the tentacles widely outstretched. At the base of each tentacle is a brush of 8 to 12 cilia which vibrate like flagella instead of striking like cilia. Within the body are represented the nucleus, contractile vacuole, and one Hadlteria. ends of which the food substances are absorbed into the body. These tentacles are of various kinds, some sharp-pointed for piercing, others cup-shaped for attachment by suction, while others are pointed and spirally wound (Fig. 20). The cuticle of the prey is pierced by the . 52 ; THE PROTOZOA sharper tentacles, and its fluid endoplasm passes in a current down the cavity of the tentacle and into the endoplasm of the suctorian. In other cases, the endoplasm of the tentacle passes into the body of the prey and there digests the internal substance zw sztu, the digested parts flowing back into the body of the minute carnivore. A similar mode of food-taking occurs in some Heliozoa (Vampyrella), where the parasite penetrates the cells of algae and there digests the proto- plasm. In all Protozoa, digestion is accomplished within the endoplasm. The ingested proteid is contained within a gastric vacuole filled primarily with water, which is taken in with the food. The water, however, gradually changes by osmosis with the fluids of the plasm, Fig. 20. — Tentacles of Suctoria. [HERTWIG.] A. Seizing tentacles of Ephelota. B. Veeding and seizing tentacles of Ephelota. among these is a digestive, acid fluid, which reduces the digestible portions of the food probably to some form of peptone. Then, again by osmosis, the digested portions are assimilated in all parts of the endoplasm. The indigestible remains of the food are excreted in various ways. Sometimes, as in the Rhizopoda, they are voided from any portion of the body, usually, however, from that part which at the time is posterior. The gastric vacuole, after the contained food has been digested as far as possible, frequently becomes a defecatory vacuole, and its contents are expelled to the outside at the posterior end of the individual. Finally, a distinct and permanent anal opening is found in the more complex ciliates. 2. Excretion. Like all other animals, the protozoén uses a certain amount of pro- toplasm in the performance of its vital activities. Ina large number GENERAL SKETCH : 53 of Protozoa there is no known organ by which the waste products are removed. In such forms excretion probably takes place by osmosis through the walls of the body, in the same way possibly that sapro- phytic forms take food. This must be the case in the Sporozoa and many marine forms as well as in certain flagellates, in which there is no specialized excretory organ. In the majority of the Protozoa, however, there are specialized structures which regularly throw to the outside of the organism a certain amount of fluid substance. These structures are the contractile vacuoles, which, with the ex- ceptions of the Sporozoa and the marine forms, are found in every class of the Protozoa. In the living animal the vacu- ole is a clear spherical area in the endoplasm. It is formed by the slow addition of water from the endoplasm, and grows until a maximum size is reached, when it suddenly disappears, the contained water being driven to the outside. Vacu- oles are frequently variable in position (Sarcodina), while the number is, to a certain extent, dependent upon the condition of the protoplasm, several ob- servers having shown that, as the individuals lose their vital- ity, the protoplasm becomes more and more vacuolated. In Fig. 21.— 7) ontonia leucas Ehr. [SCHEWIAKOFF.] many Cases the vacuole moves ¢, canal; v, vacuole with external pore; A’, macro- about with the endoplasmic nucleus; x, micronucleus. , flow until, becoming heavier than the protoplasm, it remains stationary, while the rest of the endoplasm moves forward with the organism (many Rhizopoda). In this manner the vacuole, as it attains its full size, is gradually left at the posterior end of the moving organism, where it finally bursts. Again, as in some Mastigophora and Ciliata, the contractile vacuole is a stationary organ connected with the out- side by a definite pore. Here, too, are numerous accessory structures in the form of canals and reservoirs, the former apparently collecting the water and waste matters from all parts of the cell, and conducting them to the contractile vesicle, the latter receiving the fluid after con- traction of the vacuole, and conveying it to the outside, with which 54 ; THE PROTOZOA they are in open connection. The canal system, which some observers (e.g. Fabre Dumergue, ’90) consider widely spread throughout the Ciliata, is often strikingly developed, as in /vontonza, where there is a complicated network traversing the entire cell (Fig. 21). . While the excretory function of the contractile vacuole is generally accepted, there have been only a few satisfactory experiments to demonstrate it, and the possibility of other functions is not excluded. At the present time the balance of evidence is in favor of the view that the contractile vacuole has both excretory and respiratory func- tions, inasmuch as it regularly empties a fluid to the outside, which carries with it the products of destructive metabolism in the form of wrea, and probably carbon dioxid, although the respiratory function has never been demonstrated.1 Whatever may be the function of the contractile vacuole, it does not appear to be universally necessary for the life of the organism, for it is lacking in the Sporozoa and the majority of the Sarcodina (Reticulariida and Radiolaria). Furthermore, whatever the use of the vacuole, it is independent of the nucleus, non-nucleated fragments form- ing new vacuoles which pulsate rhyth- mically for some time. Hofer (’89) found that vacuoles in non-nucleated bits of Ameba proteus would contract for ‘fourteen days. He also noted that whereas the regular period of pulsation was seven minutes, the periods became longer and longer, until at the end of the fourth day there was but one pulsation every two hours, and even then the con- tents were not completely expelled, a reaction which Pénard (’90) formulated later by the statement that the activity of the contractile vacuole is directly proportional to that of the entire indi- vidual. 3. Reproduction. Fig. 22.— Division ot Euplotes. [FROM . . ‘ A PREPARATION.] With the exception of the Sporozoa, The danghter-cells are almost ready simple division, or splitting into two to separate; the daughter-micronuclei : eee ge cian ees a macronuclens Parts, is the characteristic mode of re- (m) is not quite divided; the gastric production in all Protozoa. In the vaguoles (7) are equaily aisitibuleds. Srorezed, aud at times in niost of the the two daughter-cells, one of which has nee! ; generated the adoral zone (az). other Protozoa, division is replaced by 1Cf. Chapter IX, p. 283. GENERAL SKETCH 55 spore-formation or the breaking up of the body into many small particles, each the germ of a new organism. While the major- ity of the Protozoa reproduce asexually in these ways, reproduc- tion in some is bound up with complete sexual differentiation, and a series of forms may be selected which indicate the probable develop- ment of the sexual from the more primitive methods. In numerous cases the sexual phenomena include many of the preliminary matura- tion stages shown by the Metazoa, in the formation of polar bodies and reduction of the quantity of chromatin, etc. Simple division, the most common method of reproduction, is usually a separation of the body into two equal parts either longitu- Fig. 23. — Division (budding) of Euglypha alveolata Duj. [SCHEWIAKOFF.] The shell-plates which were stored in the endoplasm about the nucleus pass out with the stream- ing protoplasm (4) to form the shell of the daughter-cell. The nucleus is shown in differem stages of mitosis. - dinally (Flagellidia) or transversely (Ciliata). It is invariably preceded by division of the nucleus, and is often accompanied by the equal division of certain of the internal structures of the cell, such as the chromatophores, pyrenoids, etc. It may take place either during active life or under the protection of a cyst. Ciliata in the process of division may be frequently seen swimming about actively, the con- necting-strand becoming narrower and narrower, until finally only a delicate strand of protoplasm separates the daughter-cells, ard this, after a few energetic contortions, gives way and the young cells are 56 THE PROTOZOA free (Fig. 22). The presence of a firm shell or coating complicates the process, especially if the shell is a secretion (Fig. 23). In many Fig. 24. — Microgromia socialis Hert., a gregaloid colony. [HERTWIG.] cases the new shell-parts are secreted before the act of division be- gins, and when the protoplasm buds out of the original shell-mouth, they are carried with it, and the bud is covered with the newly formed Fig. 25.— Uroglena americana Calkins, a spheeroid colony. pieces, which are glued together by means of a chitinous or silicious secretion. GENERAL SKETCH 57 Simple division frequently leads to colony-formation through incom- plete separation of the daughter-individuals. Four general types of these colonies are met with among the Protozoa. Adopting Haeckel’s terms, they may be designated according to their general structure as (1) gregaloid, (2) spheroid, (3) arboroid, and (4) catenoid. A gregaloid colony is an aggregate of Protozoa having a round, ellipsoidal, or indefinite shape, and usually with a gelatinous basis in which the single individuals are variously distributed. The colonies may be formed by incomplete division of the individuals or by partial union of two or more adults (Fig. 24). A spheroid colony is a globu- Fig. 26. — Codosiga cymosa Sav. K., an arboroid colony of Choanoflagellida. [KENT.] lar, ellipsoidal, or cylindrical aggregate in which the individual cells form a superficial layer in a common gelatinous matrix. When these superficial cells are closely packed together into an almost continuous layer as in Volvox, Magosphera, or Uroglena, they are extremely sug- gestive of certain stages in developing Metazoa (Fig. 25). An ardo- void colony is a tree- or bush-like aggregate arising by the dendritic or dichotomous branching of a primary stalk or a gelatinous matrix. Such colonies are usually attached by the base to some foreign object and often resemble hydroids or Bryozoa (Fig. 26). They may, how- ever, as in Dznobryon, be free-swimming. ’ = OG —— 3 ? ’ / ” 7 7’ $ May . My. x a: J 1 Cf. Chapter VI, p. 220. GENERAL SKETCH 61 indefinitely, but that periods of division recur at intervals. This sug- gestion was confirmed by Biitschli (’76) and by Engelmann (’76), who demonstrated in connection with a number of Ciliata that after a certain number ot divisions the resulting individuals become reduced in size and show other evidences of degeneration. Biitschli regarded this as evidence of old age, and he observed that the normal size and the general vitality of the reduced organisms are restored by conju- gation; and he was one of the first to demonstrate that the function of conjugation is not for purposes of reproduction, but for the renewal of vitality as expressed in his term Verjungung (rejuvenation). Maupas ('88), finally, has confirmed the latter conception of conjuga- tion, and in a series of brilliantly planned and carefully executed experiments has shown that Protozoa, contrary to Weismann’s a priori assumption, may die of old age unless they be reinvigorated by conjugation. ‘Senescence,’ says Maupas, “appears to be a very general phenomenon, at least in the animal kingdom. ... It is inherent in the organism and comes from internal causes which act independently of the surrounding conditions... . Its deleterious action is offset and annulled by sexual rejuvenescence or conjugation.” ! 4. Lrritability. Unlike the Metazoa, where the phenomena which are characterized as manifestations of consciousness are expressed through special or- gans of the nervous system, the Protozoa in the simplest forms have nothing, so far as we know at present, but the undifferentiated proto- plasm which at the same time must be the seat of all functions. The sensory phenomena are, however, very little known. All Pro- tozoa are irritable, reacting in certain definite ways, although in dif- ferent degrees, toward various external stimuli. All are sensitive to. electrical, mechanical, thermal, and chemical irritations, and many to light, while few or none are affected by acoustic vibrations. The reactions to these stimuli are usually expressed in motion of some sort, which may be either indefinite or definite, —in the latter case, as a tule, either positive, z.¢. toward the source of irritation, or nega- tive, ze. away from it. In many Protozoa, particularly in the lower forms, there seems to be no portion of the cell more sensitive than others; in the higher forms, however, there is a greater or less degree of sensory localization. Here, as a rule, the ectoplasm reacts ener- getically, and, like the cuticle of Metazoa, becomes a general sensory organ. The appendages frequently serve as special sensory organs. of touch, as in the aboral cirri of the hypotrichous ciliates, while spe- cial organoids are frequently present in the form of “ eye-spots,”’ etc. 1°88), p. 272. 62 THE PROTOZOA a C. SOME ECONOMIC ASPECTS OF THE PROTOZOA The Protozoa are frequently objectionable because of the appear- ances, odors, and tastes which they may impart to water. In the sea great areas may be colored orange, red, etc., by incalculable numbers of Noctiluca or Dinoflagellidia (Prorocentrum, Glenodinium), while at night their presence is indicated by brilliant phosphorescence, the light being due to the rapid oxidization of a substance created by the organisms and thrown out by them upon irritation. In Puget Sound and in Alaska I have seen hundreds of acres of the sea surface colored orange by Woctiluca miliaris, although the single individuals are less than one-fiftieth part of an inch in diameter, and Haeckel (90) graphically compares such masses to “tomato soup”! When Protozoa occur in great numbers in fresh water, and especially in drinking water, they may cause considerable annoyance; for by the color, odor, and taste which they impart they render the water unfit to drink. The colors are due in the main to the Phytoflagellida, and only those forms which are capable of making their own food are able to live in pure drinking waters. The most frequent causes of trouble in this respect are Uroglena, Peridinium, or its allies, Euglena and other Euglenoids, and Syzzra, all of which are flagellates. The odors and tastes, however, are more offensive than the colors, and as they are frequently misunderstood and regarded as evidence of pollu- tion, an explanation may not be out of place. Ehrenberg noticed that certain flagellates (Chlamydomonas pulvisculus and Chlorogonium) impart a certain oily odor. Dunal (’38) and Joly (’40) described an odor like that of violets from the masses of Hematococcus which gave to a portion of the Mediterranean a distinct red color. The Massa- - chusetts State Board of Health, dealing with this problem of the drinking waters, have obtained important results in this direction. They have shown that certain of these organisms may have definite and specific odors which, like the odors of flowers, can be recognized. An “oily odor” was traced to Syaura and Uroglena, an “Iceland moss” odor to Perzdinium, a ‘violet odor” to certain Euglenoids, etc.1 The cause of these odors has been the subject of a number of investigations, and it has been found that they are “living odors” due to disintegration of the cells rather than to their decomposition, a view first advanced, I believe, by Biitschli ('84), who described a highly characteristic “fishy odor” from Euglena saneuinea, while the cells were found to be disintegrated, although not decomposed. The matter was considered more extensively by the writer (92), who found that in waters infested with colonies of (roglena americana the odor was not developed until the organisms had passed through the water 1See S. B. IT. (’92). GENERAL SKETCH 63 pipes, but after such passage the odor was extremely strong and repulsive, while no colonies could be found. It was suggested at this time that the odor was one of disintegration, and due to the libera- tion of minute drops of oil-like substance which become disseminated through the water, giving it the characteristic Uroglena smell. It was also suggested that these drops of oil are analogous to the perfume oils of the fragrant plants, like them having a certain individual odor often strong enough and characteristic enough to identify the organ- ism. Similar oil-like inclusions are found in the protoplasm of all Protozoa, but to be detected through the sense of smell, they must be present in great numbers. Far more serious noxious effects of the Protozoa are produced through their frequently parasitic mode of life. In all classes there Fig. 31.— Internal parasites. [4,B, LEUCKART; C, GRASSI; D, BUTSCHLI.] A. Ameba coli Lésch, a supposed cause of dysentery. B. Monocystis agilis Leuck., a grega- rine. C, Megastoma entericum Grassi, a flagellate. D. Balantidium entozoin Ehbr., a ciliate. are certain forms which live as parasites (Fig. 31), and which for con- venience may be separated into two groups, the intercellular and the intracellular forms. So far as known these parasites, with few excep- tions, do not produce noxious products like bacterial ptomaines, but whatever damage they may cause is due to the mechanical disturb- ances set up by their presence. The intercellular parasites infest the body cavities of various hosts, the cavities of blood-vessels, and ducts of various glands, or penetrate the spaces between muscle-fibres, while the intracellular parasites (which belong almost exclusively to the Sporozoa) bore into cells of epithelia (Gregarines, Coccidia), or the corpuscles of the blood (Hemosporidiida). From the wide distribu- tion of the intercellular parasites, it is quite possible that no animal is entirely free from Protozoa of some kind. Without entering upon a 64 THE PROTOZOA discussion of these forms, it may be stated that Rhizopoda, Flagellidia, Ciliata, and Sporozoa may be found in the various cavities and canals in man and the other vertebrates, where they usually give little or no trouble. One form, however, Amba coli (Fig. 31, 4), has been long in dispute as the reputed cause of dysentery. If it is the specific cause of this disease, the animal occupies an interesting position amongst the intercellular parasites ; for, so far as known, none other of this kind of protozoan parasites exerts a deleterious effect upon the intestinal epithelia. Nor is it proven that Awa coli does this in the case of dysentery, although a belief to that effect is widespread. Briefly reviewing the history of this belief, it appears that Lambl (’60)1 was the first to observe 47z@ba in the human intestine, although Lésch (75), who named it, was the first to consider it in connection with dysentery. Many subsequent observers (Kartulis, Mannaberg, Cohn, etc.) found Ameba coli in the feces of dysentery patients, Kartulis (89) amongst others stating that he found them in no less than five hundred cases. The belief received a setback, however, by the observations of Cunningham (°81), Grassi (82), and Calendruccio (’90), who found Asmeba colz in the intestine of sound and healthy men as well as in dysenteric patients, while still other observers maintained the entire absence of such an enteric organism. Councilman (91), in a work which is certainly as reliable as any that has been undertaken upon this subject, partially harmonized these views by showing that there are at least three forms of dysentery, of which one, at least, is characterized by certain definite symptoms and by the presence of Amba coli, although it was not demonstrated that the rhizopod was the cause. The entire matter received impartial and critical treatment by Laveran (’93) in France and by Schuberg (’93) in Germany, and both came to the conclusion that the cause of dysentery was not yet known, the former basing his opinion largely upon the absence of Aveda in all but one of ten cases, the latter upon numerous experiments and observations upon normal and diseased individuals. Schuberg not only found that Ameéa colz is present in normal men, but also found that there is no specific difference in the various intestinal Awzewbe which have been described by various observers as living freely in the intestine in the same way as the commensal ciliates and flagellates also found there and generally believed to be harmless. He pertinently says: “If the flagellates are harmless, it is certainly not impossible that Ameba is also. The increased number of Ameéde in dysenteric patients is not necessarily evidence that they are the cause of this disease.”2_ Both he and Laveran expressed the view that all experiments which had been made up to that time had not excluded the possibility of other causes, ¢.g. bacteria. That dysentery is due to some specific cause had been early demonstrated by experiment, but in none of these experiments had it been possible to isolate the Protozoa from bacteria which invyari- ably accompany them. The reverse experiment is, however, possible, and it is singular that it has not been made more frequently. Among the first to exclude the Protozoa were Celli and Fiocca (’95), who obtained cases of dysentéry by inject- ing cats with material from faeces in which the Protozoa had been killed by heat; the same result was also obtained by injecting material in which both Aveda and bacteria were absent, the cause evidently being in the poison of the sterilized matter and not in -d#eba colz. They concluded that the poison is the product of bacteria (Bacillus coli communis, together with typhus-like bacteria and a streptococcus, were suggested as possible causes). This view was supported by a number of observers, amongst whom may be mentioned Gasser (’95), Cassagrandi and Bar- bagello (’95), and Petridis (98). The latter especially has shown that dysentery as observed in Egypt is due to a bacillus and not to Protozoa. He found that S¢ep- 1Cf. Leuckart (79). 2 Page 701. GENERAL SKETCH 65 tococcus is the most numerous of the micro-organisms and the probable cause of the disease, for he was able to isolate the bacillus and to produce dysentery in cats by injecting them with the culture obtained from it. Thus, as the matter stands, Petridis’s results, the most positive that have yet appeared, together with growing evidence from the bacteriological side, make it exceedingly probable, although not definitely established as yet, that bacilli and not Amada coli are the cause of this disease. While the majority of intercellular parasites are harmless, it is quite different with the intracellular forms. These, by making their way into the interior of the cell and growing at the expense of the cell-contents, gradually cause degeneration of the tissues which may end in death of the host. These parasites belong almost exclusively to the class Sporozoa of which the Coccidiida and Hemosporidiida are found in vertebrates, while the Gregarinida are confined to the inverte- brates, where they are widely distributed. The Coccidiida are found in nearly all of the tissues of the lower vertebrates although rarely in man, unless indeed, as many observ- ers believe, they are the cause of various tumors and cancers. That there is some reason for this belief is shown by the fact that in the lower vertebrates, especially in fishes, the presence of Sporozoa leads to ulcers and tumors and to the ultimate death of the fish. The sub- ject, however, as far as man is concerned, is in a very unsatisfactory state, and opinions differ widely as to the nature of certain elements found in cancerous growths. By some observers these are regarded as parasites, by others as disintegrated or pathological cells. Up to the present time no satisfactory evidence has appeared to prove the former view, and until such evidence is forthcoming the entire matter must rest in abeyance. From the pathogenic point of view, the most important protozoén is the malaria germ (Plasmodium malari@), a form belonging to the Hemosporidiida. These organisms, in the young stages, move about by amceboid motion in the blood-vessels of men and birds. They penetrate the red blood corpuscles, which slowly hypertrophy, until in one type of the disease, at least, they attain a size three to four times that of the normal corpuscle, the parasite in the meantime growing at the expense of the haemoglobin and finally reproducing by spore- formation. In this form alone there appears to be a poisonous sub- stance analogous to bacterial ptomaines, which is produced by the organism and periodically discharged (at spore-formation) into the blood, thus causing the pyrexial attacks so characteristic of malaria. The recent successful results obtained by Ross, Manson, Koch, Grassi, and others, in locating the seat of the malaria germ when outside the human body, leads to the hope that some successful means of guard- ing against this disease may soon follow.! 1 Vide infra, pp. 160-165, F 66 THE PROTOZOA SPECIAL BIBLIOGRAPHY II Biitschli, 0.— Protozoa. In Broun’s Klassen und Ordnungen des Thierreichs. Leipzig, 1883-1888. Delage et Hérouard. — La cellule et les Infusoires. In Zrasté de Zovlogie concréte. farts, 1896. Ehrenberg, C. G.— Die Infusionsthierchen als vollkommene Organismen. Le7fzzg, 1838. Entz, G. — Protistenstudien. Ludapesth, 1888. Lankester, E.R.— Protozoa. In Zodlogical Articles from the Encyclopedia Britan- nica. 1891. : Stein, Fr. — Der Organismus der Infusionsthiere. Lezpzzg, 1861, 1867, and 1878. CHAPTER III THE SARCODINA THE term Sarcodina, introduced by Biitschli (’83) as the class name of the most primitive of the Protozoa, includes all forms which, like the common fresh-water type Ama@ba proteus, move by the pro- trusion of protoplasm in the form of broad and finger-like, or sharp and ray-like, processes called pseudopodia. These forms fall naturally into three groups readily distinguished by clearly marked differences in structure, — the Rhizopoda, Heliozoa, and Radiolaria. Among the Rhizopoda are included forms of Sarcodina with blunt, finger-form or lobose pseudopodia (Ameézda) or with branching and anastomosing pseudopodia (Reticularizda). They may be naked (Gymnamebina), or shelled (Thecamebina or Foraminifera). The pseudopodia may arise from all parts of the body or they may be limited to special regions; in shelled forms they may pass through one common opening (Reticulartida imnperforina), or through many finer openings (Reticularitda perforina). The body form is typically globular, but may be variable in consequence of amoeboid changes, or drawn out into a monaxonic form. The material of the shell may be chitin, silica, foreign particles, or calcium carbonate. The Heliozoa are naked or shelled forms of Sarcodina; they are usually globular with fine ray-like pseudopodia arising from all parts of the body. The rays are, as a rule, stiffened by an axial filament formed of modified protoplasm which may be readily dissolved by the organism. The shells are less compact than those of the Rhizopoda, and are usually formed of more or less loosely joined silicious spicules. The Radiolaria are similar in form to the Heliozoa. As in the latter, the pseudopodia arise from all parts of the body and occasion- ally anastomose. The endoplasm is separated from the outer plasm by a firm, chitinous, perforated membrane, the central capsule. A test or skeleton, often of exquisite beauty, is usually present, consist- ing of isolated spicules of silica, or of a compact skeleton of acanthin or silica. One or more nuclei are invariably present within the central capsule. The finer structure of the rhizopod protoplasm has already been mentioned. In many cases, especially in the monothalamous forms, the plasm is divided into a number of clearly marked zones. Schewi- 67 68 THE PROTOZOA akoff (’88) describes three, Pénard (’90) no less than four in Euglypha, and Rhumbler (’98) the latter number in Cyphoderta. Schewiakoff (88), apparently on very good grounds, maintained that certain spe- cific functions characterize each of these zones, indicating, in a general way, a regional differentiation and division of physiologicallabor. To the outer zone, which corresponds to the ectoplasm of Ama@ba, he ascribed a locomotor function, this being the seat of pseudopodia for- mation ; to the second zone, which contains the nucleus, the function of assimilation, and to the third zone a reproductive function. Pénard and Rhumbler separate Schewiakoff’s second zone into two on account of certain structural differences. According to these observers the Fig. 32. — Actinophrys sol Ehr. [BUTSCHLI after GRENACHER.] The axial filaments (a) extend through the endoplasm to the membrane of the nucleus; ¢,a contractile vacuole in the ectoplasm; g, an ingested food particle in a gastric vacuole. outermost zone is distinctly vacuolated, the second contains food-par- ticles in the process of digestion, the third, granules which represent waste matter not determined, and the fourth, excretory granules. The appearance of the protoplasm in Heliozoa or Radiolaria is quite different from that of the Rhizopoda. Ectoplasm and endoplasm can be distinguished, but unlike the hyaline ectoplasm of Amedéa, the outer plasm of Heliozoa is made up of vacuoles much larger than those of the endoplasm, the walls of these vacuoles being distinctly granular (Fig. 32). The extremely vacuolated appearance, however, seems to be largely dependent upon the medium in which the animal. THE SARCODINA 69 lives. Griiber found that an Actinophrys when transferred from fresh into sea water soon loses its vacuoles; and, vice versa, when trans- ferred back to fresh water, again acquires its vesicular appearance. In general appearance a radiolarian resembles a heliozoon, but there is a considerable difference in the corresponding regions. A typical radiolarian can be conceived if we imagine a thick perforated chitinous membrane between the ectoplasm and endoplasm of aheliozoon. The intra-capsular plasm (Fig. 33, ¢) contains nuclei, fat particles, and plastids of one form or another, and is in communication with the extracapsular plasm through the pores in the membrane, although, as shown by Verworn’s experiments upon the isolated central capsule, it can live for a time independently. The outer or extra-capsular plasm is composed, according to Haeckel, of four parts. The outermost (¢) is a zone of pseudopodia ; the latter, however, originate in the deeper fourth zone, forming a network through the other extra-capsular parts. The second zone is of net- like (alveolar?) protoplasm, the sarcodictyum. A third zone, the calymma, is of jelly-like consistency and forms the bulk of the ecto- plasm. The fourth and most im- portant zone, the sarcomatrtx, lies close against the central capsule, Fig. 33.—The protoplasmic regions of a and is the go-between for the intra- ‘adiolarian ( Thalassicolla maculata) Haeck. ‘ [HAECKEL.] and extra-capsular portions. The. a, large alveoli forming part of the calymma sarcomatrix is also the seat of di- in which foreign bodies (4) are enclosed, and gestion and assimilation, the food whicl is penetrated by meshes constituting the ij sacrodictyum; ¢, the central capsule and intra- coming to it through the pseudo- capsular plasm; f retracted pseudopodia. The podia and the network. As the nucleus () contains a distinct nucleolus (2); . om the sarcomatrix is darkened by pigment means of communication between passes (), the central protoplasm and the sar- comatrix is of vital importance to the organism, the arrangement of the apertures in the central capsule offers a good character for the classifi- cation of the Radiolaria. Hertwig(’79), who first used this character, divided the group into four legions, as follows: (1) the Peripylea, in 7O THE PROTOZOA which the membrane of the central capsule is perforated by pores arranged regularly about the entire surface (Fig. 34, A); (2) the Acztz- pylea, in which the pores are arranged in groups over the surface (B); (3) the M@onopylea, in which there is but one such group of pores in the membrane. In these forms the perforated disk is con- nected with the centre of the central capsule by a conical mass of endoplasm, the podoconus (DP), rich in food particles and gran- Fig. 34. — Central capsules of Radiolaria. [HAECKEL.] A. Thalassolampe maxima Haeck., one of the Peripylea. B. Acanthometron dolichoscion Haeck., one of the Actipylea. C. Aulographis candelabrum Haeck., one of the Monopylea, D. Zriptero- calpis ogneoptera Haeck., one of the Cannopylea. c, central capsules; 7, nuclei. ules ; (4) the Caznopylea, in which the membrane around the pores is drawn out into funnel-like projections termed astropyles (C). The central capsule is double in these forms. Haeckel has found that certain skeletal forms accompany the structure of the membranes, and he names the above legions respectively as follows: —(1) Spaumel- laria; (2) Acantharia; (3) Nasselaria, and (4) Pheodaria. In each of the orders of the Sarcodina, and especially in the Radiolaria, there are some forms with symbiotic plant-cells. The THE SARCODINA 71 relationship between the symbionts was worked out by Cienkowsky, Brandt, Haeckel, and Entz, the latter noting that the plant-cells are invariably found just outside of the endoplasm, where they do not “come in contact with endoplasm and its digestive fluids. According to the more recent observations of Le Dantec (’92), however, the digestive fluid of these animals is unable to dissolve the cellulose membranes of the plant-cells, and they remain uninjured in the endo- plasm, dividing there when the conditions are favorable. A. SHELLS AND TESTS The ectoplasm of naked protoplasm shows a tendency to condense or stiffen when in contact with water, and a cuticle or membrane is the result. Amwda proteus, with its differentiation into endoplasm and ectoplasm, shows a primitive stage in the development of such mem- branes. Here the ectoplasm remains plastic enough to yield to the inner pressure of the organ- R ism and to form the first part of every pseudopodium, it is rapidly pushed aside, however, and the endoplasm becomes the advancing part. In Amba tentaculata the outer layer has become more firm and the pressure from within expends itself upon pseudopodia which are pro- truded through permanent : holes (Fig. 12, A). The # membrane may become still Fig. 35.—Types of marine rhizopod shells (Retccudu- riida. [CARPENTER.] more firm through the A, Lateral. &. Ventral view of a monothalamous deposition of chitin, until, shell (Cornuspira foliacea Phillips). C. A simple poly- as in the radiolarian central thalamous shell (Nodosaria hispida D'Orb.). D. Verte- A bralina sp., a fossil form, capsule, it is an efficient means of protection. In addition to the chitin, certain Sarcodina secrete a silicious mucilaginous material, which, like the chiti- nous cement, is frequently the means of gluing together not only regular plates or disks which the organism also secretes, but foreign particles of various kinds. The tests thus made may be entirely of lime, as in the Reticulariida, or of silica, as in the Radiolaria and many of the Heliozoa, or of sand crystals, diatom-shells, or detritus of various kinds. In the lime-shells (Reticulariida or Foraminifera) the secretion of calcium carbonate, except for the invariable presence of a mouth- « . 7 72 THE PROTOZOA opening, forms an almost complete investment like a cyst. In many cases this opening is the only means of communication with the sur- rounding medium (Imperforina), but in other cases the entire shell is punctured by minute openings through which pseudopodia pass to the outside (Perforina). These two types of shell are further distin- guished by their appearance; the Imperforina when seen by reflected light are opaque and like porcelain, while the shells of the Perforina are almost transparent (vitreous). Monothalamous or single-shelled Foraminifera may be either im- perforate (2g. Sguamulina, Pilulina, or Saccammina) or perforate (Lagena). In each group a graded series of shells can be arranged, varying in complexity from the simple monothalamous to the compli- Fig. 36. — Polythalamous shell types schematized. [CARPENTER.] A. Linear Nodosaria type. B. Frondicularia form of the Nodosaria type. C. Spiral form of the Modosaria type. ‘ cated polythalamous forms (Polystomella, Calcarina). One of the simplest of these shells is that of Cornuspira, where the plasm, as it slowly grows, constantly secretes new shell material and is capable of unlimited extension (Fig. 35, A). It is never divided by septa into separate chambers as in the polythalamous shells. A further step, the simplest of the polythalamous types, is found in shells where the separate chambers adhere end to end as in Modosaria (C). Here there may be only a slight septum between adjacent chambers, but enough to indicate that growth is periodic, and not constant as in Cornuspira. In these chamber-dwelling animals the plasm, as it grows, extends out of the primary shell-opening and reaches to a certain distance down the outside; new shell material is then secreted, and the process is repeated until a chain of chambers is the result (Fig. 36, 4). If THE SARCODINA 73 the plasm extends entirely around the shell, the new chamber almost incloses the older ones as in Modosarina (B). In other cases the plasm may extend over one side only of the old shell, and a curvi- linear axis of growth is the result (Fig. 35, A, B, and 36, C). The spiral thus formed may be flat or coiled around a longitudinal axis as in the mollusc Z7ochus, giving an involute shell. This type, the most highly differentiated of all of the rhizopod shells, exhibits all grades of complexity (Fig. 37). In the highest forms each new chamber has a complete wall, so that the septa between the adjacent chambers consist of two lamella, while between the lamellae there is fre- Fig. 3'7.— A complex polythalamous shell (schematic) of Operculina. [CARPENTER.] The shell is represented as cut in different planes to show the distribution of the canals (a’,a"’, a’); c,¢, €, the outer chambers with double walls (d, d,@), one of which is shown in sec- tion (.g). The chambers communicate by apertures at the inner ends of the septa (e), and by minute pores (/). The outside (4) of the shell is marked by the radial septa. quently a space filled with a calcareous deposit or what Carpenter (62) calls the “intermediate skeleton.” This inter-lamellar deposit is traversed by a complicated system of canals, and the deposit itself is frequently carried out into external processes and knobs (Cadécarina). In the annular or discoid types a process of budding takes place around the entire circumference instead of at a localized area, and concentric circles of chambers are thus formed (O7ztolites). The character of the mouth-openings between adjacent chambers depends upon the nature of the outer coating. If the lime casing is perforated by numerous pores through which pseudopodia can be thrust to collect food, then each chamber is sufficient for itself, and the so-called mouth-opening is small; but if the perforations are absent, the mouth-openings are large and allow a free communication 74 THE PROTOZOA‘ between the youngest or external chambers and the oldest or internal. Hence there are morphological and physiological grounds for sepa- rating the Reticulariida into Perforina and Imperforina. It frequently happens that the central or original chamber varies in size in the same species, being large (megalospheric) in some individuals, and small (szcrospheric) in others (Fig. 38). While the relations of these two forms have been much discussed, no satisfactory conclusion has yet been reached. Lister (’95) regards the case as one of alternation of generations in which spores from individuals A conjugate and form individuals of the type &, while the latter develops spores which grow into the form A again. The conjugation of swarmers in these dimor- phic types is a matter of inference rather than of observation, for the process has never been seen. [SCHLUMBERGER.] The dimorphism is shown by the central chamber c. Among the Heliozoa and Radiolaria, shell formation is of a somewhat different type, consisting of the deposition of spicules and rays rather than a continuous layer of material forming a compact coating. Even naked forms of Heliozoa, such as Actino- spherium, secrete these spicules at certain times for the purpose of encystment, while others have them in greater or less numbers throughout life. Isolated spicules are usually retained by a gelat- inous mantle, which covers the entire animal (Mwclearia, evidence which is strengthened Be A = = by the position of the cirri : aN nY along the lines of the cilia- 6 Y aN Ss markings. “Crp, The membranelles are flat plates of striated appearance usually in the form of tri- a Sy Aipy GZ ~ = cok IH angles, squares, or parallelo- grams. Each membranelle is. Fig. 98.— Schematic hypotrichous ciliate. inserted in a furrow below az, adoral zone; ¢, ventral cirri; e, endoral mem- which is a_ basal stripe of brane; eo, endoral cilia; pv, praeoral membrane; Zo, thickened protoplasm continu- paroral cilia; foc, preoral cilia, ous with the longitudinal cil- iary markings (Heterotrichida). Like the cirri, they can be readily reduced to component fila- ments resembling cilia, and there is, therefore, every reason to suppose that the membranelles which form such a characteristic differential for all orders save the Holotrichida, are merely the differ- entiated portions of the ciliary rows! The basal stripes of the membranelles, which are spirally arranged upon the peristome, are in turn inserted, in some cases at least, in a thick fibrous strand which 1Johnson (’93) alone regards the membranelles in Sven¢or as endoplasmic in origin. THE INFUSORIA 183. runs around the peristome connecting the series, and possibly form- ing a nervous organ (Delage, ’96; Moore, ’93). The undulating membranes, finally, which are almost always con- fined to the oral region, and like the membranelles chiefly concerned with food-taking, have probably a similar origin, although the con- nection with the cilia is less apparent. They are frequently, as in the Hypotrichida, placed deep in the vestibule, but in many forms they are confined to the pharynx itself, as in many of the Holo- trichida. In addition to cilia, membranelles, and membranes, the ectoplasm. has other modifications, such as pseudopodia (¢.g. Stentor) and tenta- cles. The pseudopodia are used for anchoring the animal, and are produced at the posterior end by the so-called foot-disk (Johnson, ’93). The cortical plasm gives rise to these processes, and also to the peculiar tentacle-like appendages found in some forms. In Ac#tinobo- lus (Fig. 100) these pseudopodial tentacles are particularly well known through the complete study made by Entz (’82). Here the threads pass out between the cilia and not infrequently reach a length of twice or even three times the body diameter. The threads are of nearly uni- form thickness, with blunt or slightly knobbed ends (Entz). These tentacles, while occasion. . ally stiff and unyielding, can be shortened or lengthened, or drawn into the body in a manner surprisingly suggestive of pseudo- See yee podia, while the protective and offensive func- O. F.M, [BUTSCHLL] tion is shown by the presence of trichocysts at their extremities. Similar tentacles are found in Mesodznitum and Sleonema (see Fig. 115). While the ectoplasm is devoted to the functions of motion and irri- tability, the endoplasm is charged with digestion and reproduction. Thus the membranelles and membranes are important in creating the current which brings the food particles; the trichocysts are occasion- ally developed as food-killing organs, and these, with the mouth, vestibule, and pharynx, are ectoplasmic in origin. While all these special modifications are developed for the pur- pose of food-getting, the endoplasm, with its digestive processes, shows but little advance, so far as can be made out, over the already complicated endoplasm in the less highly organized forms. Simi- lar food substances are treated in similar gastric vacuoles, and the products of assimilation are carried about in the plasm by similar cyclosis, while indigestible remains are excreted in the same way. The Protozoa thus offer in the most striking manner an example of 184 THE PROTOZOA how species may have originated through structural adaptations of the parts (ectoplasm) that are in direct contact with the environment. The mouth parts, which are functionally the beginnings of the diges- tive system, are formed by the invagination of a limited portion of ‘ \ | \ " % \ | XQ . \ he | \ . \ ws) REF j Vy) Ly f 3 ~ (\Qw NI " a NS AA \ “ . \\ = Ww ess a SN Fig. 100. —-fc/inobolus radians St. the ectoplasm in a manner analogous to the formation of the stomo- deum of Metazoa. The peristome is the beginning of the mouth depression, becoming more and more deeply depressed as the mouth region is reached. It is not present in all forms, the mouth in its original position probably being anterior and terminal in the monaxonic THE INFUSORIA 185 body, and leading by a mere passage into the endoplasm below. Mouthless forms are known, but these have degenerated through parasitism and are not primitive (Opalinide). In the majority of forms the mouth is displaced from the original terminal position and has become ventral and central. Biitschli maintains that this change in the position of the mouth is brought about by the gradual shifting from the anterior end, as shown by the meeting point of the lines of ciliary markings. As previously indicated, the original course of these lines is from the anterior to the posterior end, but in numerous transitional forms in which the mouth has a more or less ventral position, the markings become curved to agree with the changed position, while the course which the mouth is supposed to have taken is shown by the converging lines (Fig. 95). In almost all cases the mouth is not in direct communication with the endoplasm, but is separated from the latter by a longer or shorter pharynx, cesophagus, or gullet, which frequently bears cilia, mem- branes, or membranelles. The cesophagus is likewise an ectoplasmic invagination, as is also a second cesophageal apparatus, found in some forms (Vorticellidz), where the mouth leads into a comparatively large ciliated or membraned space, known as the vestibule ( Fig. 101, C, PD), and this leads into the cesophagus or gullet proper, which, in turn, communicates with the endoplasm. This space begins as a wide tube and gradually narrows down to a more or less narrow aperture or constriction at the cesophagus. The anus and the contractile vacuole, in some forms, open to the exterior through the vestibule. In some of the Holotrichida, the region about the pharynx is strengthened by accessory apparatus developed in the cortical layer, which in this region is greatly thickened and which in some cases contains secretions in the form of bars arranged in a peculiar basket structure (4, B). The membranelles which surround the mouth are usually in motion, as are the membranes and cilia which extend into the vestibule or cesophagus. Even while the animal is lying quiet, the membra- nelles continue their active vibrations, keeping a constant current of water toward the mouth. This current brings a supply of bacteria, diatoms, algz of various kinds, rotifers of small size, or parts of animals undergoing disintegration, flagellates, etc. A distinction can be made here between herbivorous and carnivorous forms, although the differences can hardly extend to structural adaptations, unless it be, perhaps, in some carnivorous forms, where special weapons of offence (the trichocysts) are found. Probably all forms are more or less omnivorous and make little or no selection of food. The food particles are thrown by the current of the membranelles into the peristomial depression and thence into the vestibule or 186 THE PROTOZOA cesophagus, until they come in contact with the endoplasm at the base of the latter. Here they are readily absorbed by the endoplasm, in which, together with a small amount of water, they are confined in a small gastric vacuole. The vacuole enlarges by the constant addition of new material, until it is caught up in the current of the endoplasm and dragged away. In this improvised ‘‘ stomach” it is slowly digested, a new drop being formed in the meantime at the mouth opening. If food is abundant, the animal may become filled with these gastric vacuoles. The liquid of the vacuole is, at first, simply water, like the surrounding medium, but gradually becomes acid through osmosis in the plasm, and the digestible substances are Fig. 101.— Buccal apparatus. [BUTSCHLI.] A,B. Nassula aurea Ehr. A, From the ventral side. &. The buccal apparatus strongly magnified. C. Urostyla grandis Ehr. D. Vorticella nebulifera O. F. M. slowly dissolved, the residue being cast to the exterior through the anus. Unlike the mouth, the anus, as a rule, is a simple opening in the outer wall (Maupas, ’83; Biitschli, ’88), although Stein (67) described an anal tube in certain forms (Myctotherus). In the Heterotrichida it is sub-terminal in position. In the Hypotrichida it is never ter- minal, but usually dorsal, and toward the left edge. In the Peritri- chida, especially in the Vorticellidz, the anus opens into the vestibule. B. CONTRACTILE VACUOLES A certain amount of water is taken in with the food through the mouth, and at the same time (as in those cases where the mouth is THE INFUSORIA 187 absent) by absorption through the body wall, and it is the function of the contractile vacuole to get rid of the surplus. This organ is variously complicated by the development of a more or less extensive series of canals, which empty in a common excretory vacuole. Always situated in the cortical plasm, the con- tractile vacuoles are fixed in position and com- aa municate with the exterior at systole by a we permanent aperture, which, however, becomes (vy \ WA B| covered internally during filling or diastole. 5 4 They vary in number from one to a hundred, or even more, and are absent, apparently, in only one form (Opaéina), although Vejdovsky (92) describes contractile vacuoles in a closely allied form, Monodontophrya longissima, while even in Ofalina the reminiscence of the vacu- ole is seen in the remnants of the feeding canals (Delage, 96). In its simplest form the vacuole is single and terminal, a condition C----> which may be found in each of the four orders. When there are more than one, they are grouped around the original vacuole in a ter- minal position, or arranged along one or more lines upon the dorsal side. In Descophrya and Hoplitophrya (Holotrichida) there is no regular vesicle, but a long contracting canal which runs the length of the body. Spzrostomum (Heterotrichida) has a terminal vesicle, with one long feeding canal, and from this the canal system is developed in a variety of ways. Thus there is a vesicle with two feeding canals in Climacostomum (Fig. 91, 8), one terminal vesicle and four feeding canals in Urocentrum. Fig. 102. — Anterior end of In Stentor there is a single vesicle near the career erent tg a peristome, with two feeding canals, one of © ¢, the reservoir of the vacu- which runs to the end of the body, while the ole (¥) emptymg through a < long canal into the vestibule; other runs around the peristome edge. Fabre- 4 the cesophagus; 2, the nu- Dumergue (’89) holds that canals, for the most cleus. part invisible, are present in all ciliates. This is certainly true in /7ox¢onta, where there are one or two vesicles on one side and an immense number of feeding canals, which anasto- mose and branch to form a complicated network, involving the entire body. In some forms the vesicle communicates with the exterior directly, but it may be complicated by the formation of ducts or reservoirs. In the holotrichous form, Lembadion, the vesicle lies 188 _ THE PROTOZOA dorsally in the middle of the body, but is connected with the terminal aperture by a long canal. In the Peritrichida there are one or two vesicles, which empty by contraction into special reservoirs, and these, in turn, empty into the cesophagus (Fig. 102). According to Delage (’96) the contraction of the vesicle is brought about by the contractility of the surrounding cortical plasm. Rhum- bler (’98) has shown, however, that the contained water may so affect the plasm that it becomes differentiated like ectoplasm, and this gives some substantial basis for the view that a special membrane surrounds the vacuole. There is no evidence, however, to show that this modi- fied protoplasm acts like a sphincter. Biitschli holds that the vesicle contracts through a mechanical force exerted upon the thin plasmic layer between the vesicle and the opening of the excretory pore by the pressure of the filling vacuole and the turgor of the cell. At the completion of the diastole the pressure becomes too great for the lamella, and the latter is ruptured, allowing the contained fluid to pass to the exterior. , C. THe Nuc.Leus The nuclei of the Infusoria show some of the most striking structural characteristics connected with the Protozoa. Here there is a differentiation of the nuclear material into two forms, a larger macronucleus, and a very much smaller szzcronucleus. With the single exception of Polykrtkos (Dinoflagellidia), this differentiation of the nuclei is found nowhere outside of the present group. The functions of the two kinds of nuclei are supposed to be respectively vegetative and reproductive (Biitschli), but this distinction is, perhaps, too sweeping. Julin (’93) held that the macronucleus stands not only for nutrition, movement, sensation, and regeneration, but for asexual division as well, in fact is a “‘ somatic nucleus,”’ while the micronucleus functions only as a sexual nucleus. There may be one or many of each kind in each cell. The macronucleus, which is invariably present, recalls the nucleus of tissue cells. It is usually single, and, lying in the endoplasm, it may be carried about with the flowing granules, or maintained in a permanent position in the cortical plasm, or by processes from this plasm (e.g. /sotricha). Its form is quite variable and has little significance for systematic work, for in the same species under certain conditions it may even become amceboid (Loeb & Hardesty, 95). The usual form is spherical, but it may be elongated into an oval, or into a flattened rod which may be curved or straight, or it may be divided into small pieces resembling a string of beads, connected by a membrane (Fig. 103). It is always provided with a membrane (Maupas), but the chromatin contained within it is vari- THE INFUSORIA _ 189 ously distributed. The vesicular structure, in which the nuclear substance is so distributed as to leave more or less space filled with “nuclear sap,” is almost never seen, the macronucleus appearing solid and completely filled with chromatin. Biitschli described the finer structure as almost invariably alveolar, the meshes correspond- ing to those of the surrounding plasm. The entire network stains deeply with the nuclear dyes, but at certain stages, especially during division, distinct fine lines can be made out connecting the Fig. 103.— Types of macronuclei. [SAVILLE KENT.] A. Macro- and micronucleus of Loxodes rostrum O. F. M. 8. Of Nyctotherus cordiformis Leidy. C. Macronucleus of Plagiotoma lumbrici Duj. D,. Dendrosoma radians S. K., a young nucleus, £. Dendrosoma radians 8. K. F. Stentor polymorphus Ehr. G. Stylonychia mytilus O. F.M. A. The same in division. J, the macronucleus; x, the micronucleus. chromatin granules, and corresponding to the linin reticulum of most nucleii In some cases (e.g. Loxrophyllum) a permanent spireme is present, as in the nucleus of cells from the salivary gland of Chironomus larvee, and is transversely striated, indicating disks which Balbiani (90) thought are alternately chromatin and linin (Fig. 104). In many cases there are internal modifications of the nuclear material forming so-called “nucleoli,” although there is a possibility that these structures are similar to the intranuclear bodies found in Mastigophora. In many macronuclei a peculiar division of the organ is made by a Igo THE PROTOZOA split, which the Germans call a Kernspalt and the French a fete. While this peculiar feature of the nucleus has not been explained, what may be an important light has been thrown upon it by Bal- biani ('95), who described the appearance as due to the presence of Fig. 104. — Loxophyllum meleagris O. F. M. [BALBIANI.] A, Vegetative nuclei with chromatin in the form of a permanent spireme. 2, CD. The same in division. two materials within the nuclei, one of which is chromatin, the other, achromatic material or archoplasm. This interpretation, however, cannot be accepted as final. While the macronuclei are, as a rule, single in number, the micro- nuclei are often multiple. Probably all Ciliata have at least one micro- nucleus, although the small size and the extreme difficulty in staining sometimes render it hard to find. In one case at least (Opalina rana- vum) there is only one kind of nu- cleus. The number of micronuclei is usually greater where the macro- nucleus is elongate, and especially where it is beaded (Stentor, Spiro- stomum, etc.). Asarule the micro- nuclei are closely attached to the membrane of the macronucleus, occupying a minute indentation in the latter, but in some cases they are well separated. In form they are round, ellipsoidal, or spindle- shaped, but the form varies with the nuclear activity, and does not mean much in itself. Their longest axis measures from I » to 10 pw, and like the macronuclei, they are covered with a distinct membrane, while the chromatin is usually massed at some part of the nucleus. In cer- tain cases the appearance is like that of the macronucleus with the chromatin in the form of a densely packed reticulum, giving to it a mas- sive appearance. Here two distinct portions, the chromatin and achromatin, can be made out (Fig. 105). Division of the nuclei takes place by mitosis in the micronuclei, and, THE INFUSORIA IQI as a rule, by amitosis in the macronuclei. The latter is the simpler; in many spherical or elliptical nuclei the structure merely draws out and segments into two equal parts. It is more or less complicated, however, in different macronuclei, until well-developed mitosis replaces simple division (¢.g. Spzrochona). There is reason to regard the sim- ple division of the larger nuclei as the mere degeneration of mitosis, by a process in which the various stages have gradually disappeared until only the preliminary stages of such division are to be found. These preliminary stages are seen in the transformation of the reticu- lum of chromatin into thread-like masses, which recall the spireme of Fig. 105. — Mitotic division of the nuclei of Spirochona and Paramecium. [R. HERTWIG.] A-C. Macronucleus of Sf:rochona with well-developed pole plates. D-H. Different stages in division of the micronucleus of Paramecium. ’ higher cells; the threads are then divided across into equal parts. In Spirochona, however, the process of division is strikingly similar to mitosis in Metazoa (Fig. 105, B, C). Division of the micronuclei is accompanied by the formation of polar attraction-spheres, and by the rearrangement of chromatin into chromosomes. Before division, the micronucleus swells to nearly twice its size during resting stages (Hertwig, 77), while the granu- lar chromatin begins to collect in lines—at first equally thick, but later concentrated in the equatorial region (Fig. 105, D-H). Divi- sion then takes place through the centre. 192 THE PROTOZOA D. ENcySTMENT The phenomenon of encystment may be seen in the Ciliata as in all other groups of the Protozoa. It occurs when the animal is in danger of drying, in some cases before division, in others, for the purpose of digesting a full meal. The cilia are drawn in, the mouth and peri- stome disappear, the contained body-granules are voided, and a gelati- nous secretion is poured out from the ectoplasm. The secretion soon hardens, becoming chitinous. The vacuole continues to pulsate for some time, and the secretion forms a liquid layer about the animal under the cyst. The cysts are variously diversified with spines and processes of different kinds, and are occasionally multiple, the spaces between the cysts being filled with water (Fig. 17, B, C, F, p. 47). E. REPRODUCTION Reproduction among the Ciliata takes place almost exclusively by simple division or fission. It is practically the same for all forms, the variations being of minor importance. The nuclei first divide, new mouth parts are developed in the posterior half, and then the cell divides. The first indication of division in Stentor, for example, is a rift in one side of the animal below the adoral zone. This rift rapidly develops motile organs (membranelles), and acquires the full length of the lower daughter-individual. The nuclei in the meantime divide, and the original animal draws out, leaving a slender foot for the upper or anterior cell,and a swollen portion for the pharyngeal region of the second individual. The new adoral zone is completely formed before actual division; the steps in the process are shown in the accompany- ing diagram from Johnson (’93) (Fig. 106). The new contractile vacu- ole, according to him, arises de novo in S. ceruleus, and by a dilatation of the longitudinal canal in S. rese/zz. The new vacuole thus formed remains in connéction with the longitudinal canal, the upper part of which becomes drawn out with the torsion of the adoral zone to form the much-discussed ring-canal discovered by Lachmann. In some forms, as in Sfzrochona, division simulates budding, un- equal division giving rise to mother- and daughter-cells. When division takes place within the cyst, the various mouth parts may or may not first be absorbed, but in all cases the vacuole still continues to pulsate. Here, as a rule, division is double, resulting in broods of four which escape as embryos, and gradually grow into the parent form. This condition closely simulates spore-formation, which results when, as in Ofadina, the number of divisions within the cyst reaches three, four, five, or six. Nowhere among the Protozoa has the process of conjugation been so thoroughly studied in connection with the life-history of the organ- THE INFUSORIA 193 ism as in the Ciliata. Worked out first by Biitschli and Engelmann in 1876, it has since been carefully studied by numerous observers, and the conditions preliminary to conjugation, during, and subsequent to it have been made known in a great variety of forms representing all divisions of the class. Biitschli and Engelmann early recognized that conjugation is necessary for continued life activity of the organ- ism, and came to the conclusion, which has been fully confirmed by subsequent observers, that conjugation is a process of rejuvenation or a renewal of vitality, the need of which is shown by the reduced size Fig. 106. — Diagrams to illustrate the division of Stentor raselit, [JOHNSON.] V, the vacuole; A, the ring canal. and general degenerate condition of the organism prior to conjuga- tion. Maupas (’89), in his classical work on conjugation among Infu- _soria, found that the number of generations which may be formed from one conjugating period to the next varies with the species, but is usually between three hundred and four hundred and fifty. He found, furthermore, that certain conditions are necessary for conjugation. These conditions are: (1) maturity of the organisms, z.e. forms which have just conjugated will not again conjugate until after a certain number of generations; (2) partial lack of food, 2.2. if plenty of food is present, conjugation will not take place even though the individuals are well along in degeneration ; (3) diverse ancestry, z.e. the conju- gants must come from different ancestral conjugants. oO 194 THE PROTOZOA The two conjugants fuse either temporarily or permanently, and the external structures, such as the membranelles, are absorbed. ‘If the fusion is temporary, as in the majority of forms, the two ecto- plasms fuse at or near the mouth parts, and a protoplasmic bridge is formed between the two organisms. The two organisms then become sluggish, and rest for a considerable time upon the bottom without movement of any kind. They ultimately separate and begin to divide. The micronuclei play the most important part in conjugation. Each divides two or more times to form four or more daughter-nuclei, some of which de- generate, while one divides again, one half to fuse with a similarly derived nu- cleus of the other organism, while the other half remains as the receptive nu- cleus, or the female pronucleus. The two conjugating nu- clei cannot be distin- guished from those which degenerate, but are apparently only those which lie nearest the bridge - joining the two organisms. Mean- Fig. 107. — Conjugation in Zpistlis umbellaria while the macro- Greeff. (GREEFF.] M, macrogamete ; my, microgametes, nucleus undergoes complete degenera- tion, breaking up into a number of pieces, which are gradually absorbed by the proto- plasm. The new macronucleus is formed by the enlargement of a daughter-micronucleus derived from the fusion nucleus. Hoyer (99), however, asserts that in Co/pzdium colpoda it forms by the union of two daughter-nuclei. When there are two or more micronuclei in each conjugant, the process is repeated for each of them, although it is not known whether this holds when, as in Stentor, the number reaches sixty or seventy. In a few cases (Vorticellidze) the conjugants are of diverse size. THE INFUSORIA 195 The larger form or macrogamete is usually a normal-sized individual, although in some cases it is somewhat larger than the ordinary cells (Zoothamnium). The microgametes, on the other hand, are con- siderably smaller, and from four to eight are formed by each cell. These never develop a stalk, but leave the parent colony, and swim about by means of the ring of cilia around the lower pole. They finally come in contact with the macrogamete and fuse with it, the union taking place at the lower end of the attached organism, and near the insertion point of the stalk (Fig. 107). Il. THE SUCTORIA The Suctoria differ decidedly from the Ciliata, from which they have undoubtedly sprung. With the exception of Hypfocoma (Fig. 115, C ), which remains ciliated throughout life, the Suctoria possess cilia only during the embryonic stages. They are, for the most part, sedentary forms, and grow upon a chitinous peduncle, which is at- tached at the lower end to some foreign object. The upper end of the peduncle is hollowed out into a bowl, within which the animal lies. Owing to its attached mode of life, and to the equal pressure on all sides, the general form of the animal is spherical or radially symmetrical. In some cases there is a well-defined membrane, but the various students of the group are not agreed as to its structure. It is never striated, as in the Ciliata, and there is no cortical plasm. The endoplasm shows no differentiations other than the usual food granules or assimilation products common to all Protozoa. An essential point of difference from the ciliate structure is the presence of ¢ezzacles, which, in the majority of Suctoria, are the only motile appendages of the adult. In many respects they are similar to the tentacles of Actznobolus, [leonema, and Mesodinium (Fig. 115), but differ in the very important fact that they are hollow, while the extremities bear the mouth openings. There are two general types of tentacles: one, according to Biit- schli, captures prey, while the other devours it. Of the latter forms, there are also two types. One is long and broad, and, like a thorn, pointed at the extremity; the other is nearly uniform in diameter and flattened at the top, or hollowed out into a cup-like sucking organ (Fig. 108). These are distinguished as the sty/zform and capitate tentacles (Delage). Both sets of tentacles are hollow, and their lumena open at the ends. There is a difference of opinion, however, in regard to their inner structure and function. Biitschli holds that some of them are solid, and others hollow. He maintains that, in the solid forms, the internal portion is formed of endoplasm, which is continuous with the inner plasm of the cell. Delage claims that they 196 THE PROTOZOA are allhollow. The function of the endoplasm, according to Biitschli, differs in the styliform and the capitate tentacles. In the latter, the prey is retained by the sucking disk at the extremity while the endo- plasm within the tube meantime works up and down like a pump- piston, and a vacuum being thus formed, the cuticle of the prey is burst, and the fluid endoplasm flows down the tentacle canal to the endoplasm of the captor, where it is digested. Such an explanation of the action of these tentacles is regarded by most observers as extremely doubtful. Delage finds no motion in the endoplasm during feeding, save in the rhythmic pulsations of the contractile vacuole, an organoid which Eismond (‘90) believed is the cause of the suction. The excretion of water from the vacuole, he argued, creates a semi-vacuum in the protoplasm, and the pressure Fig. 108. — Tentacles of Suctoria. [R. HERTWIG.] A. Different types of styliform or piercing tentacles. JS. Capitate and piercing tentacles. from without forces food or loose particles, etc., through the tentacle openings to the endoplasm. This explanation, although somewhat fanciful, is certainly as plausible as the principle of the pump, but the matter must remain for the present as one of the many unsolved problems connected with this group. In some cases (7richophrya angulata) the tentacles are apparently unnecessary for food-taking, as Dangeard (’90) found that particles are occasionally engulfed, as in the Rhizopoda, at any point of the naked body. In the styliform tentacles, on the other hand, the sharp points pierce the membrane of the prey, while the endoplasm contained within the tentacle possibly flows into the prey, whose endoplasm is digested 7 sztz. In some cases they appear to have a paralyzing effect upon other forms, and ciliates coming in contact with them have been seen to stop their movements as though stunned. THE INFUSORIA 197 In all cases the tentacles are remarkably like pseudopodia, and may change their form and their position, and may even be entirely with- drawn into the body, to reappear, possibly, at some other place. Some forms have the power of withdrawing their tentacles and developing cilia, which may be retained for a longer or shorter , x a ay /a Fig. 109. — Dendrosoma radians Ehr. [SAVILLE KENT.]} z, nucleus. period. In some cases the tentacles distinctly originate in the endo- plasm, and penetrate the membrane (Hertwig, ’76; Ishikawa, ’96). The nuclei, like those of the Ciliata, are of two kinds, macro- and micronuclei. The former are little different from the macronuclei of the more generalized Ciliata, while very little is known about the latter. In the colony-form Dendrosoma, where the many branches suggest a hydroid colony, the macronucleus extends through all the 198 “THE PROTOZOA branches and trunks, penetrating the entire system, like the ccenosarc of a hydroid (Fig. 109). The contractile vacuole never becomes so complicated as in some Ciliata, but consists, usually, of a single vesicle, which may be surrounded by a circle of small vacuoles emptying into it. In some cases there is a short excretory duct leading from the vesicle to the excretory pore in the membrane, which, as ‘in the Ciliata, is a per- manent opening. These animals en- cyst only for protec- tion, never, apparently, for reproduction. As in the Ciliata, the pro- cess consists of the secretion of a chitinous mantle about the cell, the tentacles being withdrawn into the body. Reproduction is almost invariably by simple division, which may be either equal or partial (budding). In the simplest. cases the upper portion of the cell is constricted off, and moves away from the lower portion, which remains upon its stalk (Podophrya, Spir- ophiya, Urunula, etc.). Fig. 110. — Exogenous budding in Ephelota Butschliana Ishi, The detached part de- XN, nucleus. velops cilia and, after a longer or shorter free- swimming period, settles down, loses its cilia, and secretes a stalk. Partial division, or budding, may be either exdogenous or exogenous. The latter is the simpler; an individual prepares as for division, but instead of dividing into two equal portions, a number of papillae appear at the outer surface, each becomes a bud, receiving a portion of the nucleus (Fig. 110). Endogenous division arises by the invagi- nation of such a budding area, while the walls surrounding it grow THE INFUSORIA 199 together above the developing buds, which, when ripe, break through the birth-opening left in the covering membrane (Fig. 111). In some cases the buds are multiple, again single, and a number may develop at the same time within the brood-sac (Aczneta, Ophryodendron). The embryos thus formed are variously ciliated in the different genera. In some they are holotrichous, in others hypotrichous, and in others peritrichous (c, @). Fig. 111. — Endogenous budding in Suctoria. [BUTSCHLI.] A-B, Two stages in the formation of the bud in Tokophrya guadripartita Cl. and Lach. c. The swarm-spore liberated. C. Buds in Acineta tuberosa Ehr. ad. A swarm-spore liberated. Conjugation occurs here as in the Ciliata, but the process rests upon the single observations of Maupas, who shows, however, that it differs in no essential features from that already described. III. INTER-RELATIONS OF THE INFUSORIA In searching for the origin of the Ciliata, the naturalists of thirty years ago had an apparent advantage, in that the supposed ciliated girdle of the Dinoflagellidia offered a direct transition to the peritrichous Ciliata, which, accordingly, were regarded as coming from the flagellate stem at a comparatively late date. Unfortunately for the theory, however, it was ascertained by Biitschli (85) and others that the girdle of cilia is only a vibrating flagellum in the transverse groove. In other directions the search for the origin of these forms has been almost equally vain. The singularly con- servative structure which the ciliate body presents leaves but little clue to their ancestry. The universal presence of macro- and micro- nuclei is paralleled by only one other known case, the almost universal reproduction by transverse division is met with elsewhere but rarely. The sole possibility which presents itself is that the 200 THE PROTOZOA infusorian stem was derived from the flagellate at a very early period, and that the side branch became progressively differentiated until the well-marked characteristics of to-day distinguish the Infusoria as an entirely independent group. The first forms to diverge from the flagellate stem may have been like the type described by Cienkowsky, under the generic name of Mudtictlia (Fig. 112, A), a form with a number of long flagella. It is thought by Biitschli that the Ciliata might have been derived from such generalized forms by progressive increase, with shortening of the motile elements, until cilia were the \ A Pa Fig. 112. — 4. Multicilia lacustris Lauterb, [LAUTERBORN.] B. Fyrsonympha vertens Leidy. [PORTER] x, the vibrating band in the inner plasm. outcome. There is no close connection, however, between cilia and flagella, such as exists between the flagella and the pseudopodia. Other forms, more or less similar to Multicilia, have been described by various observers, so that the hypothesis of Biitschli is not without warrant. Among these forms are Grassia, Trichonympha, Leidyonella, Lophomonas, Pyrsonympha, etc., which are placed by some among the Flagellidia (Delage), by others among the Ciliata (Biitschli). Another point of view has been based upon the relations of the Ciliata to the Suctoria, and through them to the Sarcodina THE INFUSORIA ; 201 (Entz, Maupas). This view will be more appropriately examined in connection with the Suctoria. The Holotrichida appear to be the most generalized of the entire group of Infusoria, but a few forms among them have a slight regional differentiation of cilia suggesting the characteristics of the Heterotri- chida(Lembus, Pleuronema, Ophryoglena, etc.). In fact, there appears to be no sharp line between the two divisions, although the presence of an adoral band of cilia in the Heterotrichida is a sufficient differen- N) i a: » ww. <<: ine fo . a: ’ Ss ie . ss \a Fame a = Z z Py aS Nel SEZZZO ae oe 8 = os “Tag tr Fig. 113. — Illustrating Biitschli’s hypothesis of the origin of the Hypotrichida. [BUTSCHLI.] A, Stephanopoyon colpoda Entz. B. Peritromus emm@ St. C. Onychodromus grandis St. rope tial. In some forms the uniform coating of cilia is broken in certain regions, giving characteristic girdled forms, which are included as a separate order apart from the Holotrichida by some writers (Haeckel). In the Holotrichida, also, there are a few forms which show a distinct tendency toward bilateral symmetry, due primarily to a bending of the body, and followed by a reduction of the cilia upon the arched side (Stephanopogon, Fig. 113, A). Biitschli derives the Hypotri- chida from the Heterotrichida by the supposition of the loss of cilia upon the arched dorsal side and incomplete closure of the adoral ring 202 THE PROTOZOA of cilia, which are here fused to form the characteristic membranelles; the mouth, as in Heterotrichida, remaining on the ventral side. Inthe most generalized forms, such as Perttromus or Oxytricha (B), the cilia are well distributed over the ventral surface, but in most of the other Hypotrichida they are reduced, and many are obliterated or fused into character- istic cirri. The cirri in the Oxytrichine are primitively ar- ranged in six rows, but in the various genera the number becomes reduced, and frequently only iso- lated cirri mark the original position of the row (C). The Peritrichida, finally, show the most far-reaching _—_ devia- tions from the holo- trichous type, from which they are prob- ably derived through the Heterotrichida and the Hypotrichida. In all members of this group the adoral zone is continued into D E a spiral, which may Fig. 114. — eee ne Biitschli's view of the origin of the Vor- have as many as five ticellidze, [BUYSCHLI.] The Trichodina form C is supposed to have arisen from the complete turns (Cam- Lichnophora-like form A by the outgrowth of the lower ciliated panclla). The chief area, first forming an intermediate stage B. This ring of cilia interest concerning becomes lost in the Vorticellidae, appearing only when the indi- : viduals are free-swimming. D, £. Side and front of Lichnophora this adoral zone is eee Slay that in some forms the spiral is turned to the left, similar to that of all of the other groups of Ciliata, while in other forms, belonging to the great family of the Vorticel- lide, the spiral is turned to the right. The sinistral type of the Peritrichida originates, according to Biitschli, from an hypotrichous. form, becoming attached at the posterior half of the ventral surface, SS SNANN EA s THE INFUSORIA 203 with loss of the posterior girdle of cilia, and elevation of the anterior region bearing the adoral zone, which, as in the other groups of Ciliata, is turned toward the left. The key to the other group of Peritrichida is seen, Biitschli maintains, in the family Lichnophoride, where the individuals closely resemble hypotrichous forms (Fig. 114), being oval, flattened ventrally, and arched dorsally. The cilia, as in the Hypotrichida, are limited to the ventral surface, and an adoral zone is present, which runs from the mouth near the middle of the left body edge, entirely around the anterior region of the body, to form an incomplete arc which terminates in the line of the mouth, but on the right side. Another closed ring of cilia is present in the pos- terior half of the ventral surface. The anterior and posterior rings of cilia are separated in Lichnophora by a stretch of plasm in such a way as quite to divide that surface into a posterior and an anterior division (£). The posterior part becomes modified to form an attaching organ upon which the animal creeps about upon its host; the anterior region at the same time is elevated, and held in a posi- tion at right angles to the plane of attachment, the apparent stalk which supports it being in reality the intermediate plasm between the posterior and the anterior regions of the ventral surface (J). Thus the curious anomaly arises of an animal whose anterior and posterior ends represent parts of the same ventral surface. Biitschli derives the entire family of the Vorticellidze from this primitive type, through forms like the Urceolarine, where the attaching disk, primarily, is not so far removed from the peristome, nor so stalk-like, as it is in the present-day Lichnophoride (DL, £). He argues that the Vortice//a-type is derived from the Urceolaria- type by the attaching part of the ventral surface, 7.e. the pos- terior part being carried outward from the remainder of the ventral surface, and thus borne upon a platform so that the two portions of the same surface are no longer in the same plane (4). The anterior ring of cilia is then supposed to have grown around the base of the elevated portion until the original adoral zone of cilia now forms a ring about the entire ventral surface. The new arm of this line of cilia grows on past the mouth-opening and forms a spiral, which, looked at from the ventral side, turns to the left, as in all other Ciliata seen from the same surface. Looked at from the other side, however, z.¢. dorsally, the spiral turns to the right (C). This condition is practi- cally represented by the genus 77ichodina, which moves about on the skin of various Invertebrata by means of the ciliated or attach- ment disk, in reality the posterior part of the original primitive ventral surface; while the other portion is now carried dorsally and parallel to the attachment disk, the mouth being on the left side of this anterior part. In the Vorticellidee this posterior or attaching 204 THE PROTOZOA part becomes drawn out into the long contractile stalk, while the ciliated condition, as represented by 7richodina, is again brought about in Vorticella, when the latter breaks away from its stalk, develops a ciliated band in the posterior region, and swims freely about. The ciliated band is homologous with the posterior ring of Lichnophora and the attaching disk of Y7ichodina, while the adoral zone of cilia conforms to the typical left-handed spiral of the remain- ing ciliates, when looked at from the same morphological point of view., In Gerda, the peristomial region has degenerated, while the ciliated disk remains as the organ of locomotion. Returning now to the origin of the Ciliata as a group, quite another view has been maintained by a number of observers, the essential point of which is that the Ciliata are connected with the Sarcodina through the Suctoria, the tentacles in the latter being regarded as modified pseudopodia. This view was apparently first suggested by Stein (’54) when he included the Heliozoa and the simpler forms of Suctoria in the genus Actinophrys. The assumption was taken up seriously by Maupas (’81), who held that through the Suctoria, the Ciliata were derived from the Sarcodina, and Pénard ('90) accepted the same view in regarding Actinolophus capitatus as a connecting link between the two groups. Claparéde and Lachmann were the first to deny the connection of Ciliata and Rhizopoda, but made the even more improbable assertion that the Suctoria are derived from the Flagellidia through forms like Syucrypta volvox. The close rela- | tion of the Suctoria and the Ciliata was brought into prominence through Stein’s famous, though erroneous, Acineta-theory, in which the Suctoria were supposed to be young forms of Ciliata. The con- nection between the two was, however, first put on a substantial basis by the discovery of the ciliated embryos of the Suctoria, a connection which was early accepted by students of the Protozoa, and which was greatly emphasized by the discovery that, like the Ciliata, the Suctoria have macro- and micronuclei. At the present time it is almost universally held that the Suctoria are offshoots of the Ciliata, although the opposite view is maintained by some observers, who, with Entz (’79, ’82), consider the Ciliata as permanent forms of the ciliated embryos of Suctoria. Entz himself regards the matter as insoluble, and believes that the evidence is about equally balanced. A number of cases certainly gives strength to Entz’s position, for many of the Enchelinide, in addition to their cilia, have distinct tentacular processes (//conema, Mcsodintuim, Actinobolus, etc., Fig. 115). Actinobolus, discovered by Stein, and more recently examined by Entz, has long tentacle-like threads evenly distributed about and between the cilia (Fig. 100). They can be lengthened or shortened THE INFUSORKIA 205 or entirely drawn in by the animal. In Mesodinium, there are only four of these tentacles, which are arranged about the mouth (Fig. 115, B). Leonema has only one (A). These processes were considered so important from the phylogenetic standpoint that Mereschowsky (’82) formed a special group, the Szctociliata, for their reception. Neither Entz, nor Stein, nor Mereschowsky, however, regarded the tentacles as food-taking organs like the tentacles of the Suctoria; the former, at best, could assign to them no other function than that of assisting in the capture of aliments. Maupas regarded them simply as pseudo- podia, and upon them as a basis formulated his view connecting the Ciliata with the Sarcodina. Biitschli strongly opposed Entz’s view as to the origin of Suctoria and Ciliata, and believed that there is no A B Cc Fig. 115. — Ciliata with tentacles. © A. Leonema dispar Stokes. [STOKES] 2B. AMesodinium pulex Clap. and Lach. [ENTz.] C. Hypocoma parasitica Grub. [ENGELMANN.] 4, tentacles. _ direct connection between the tentacles of the two groups, but regarded them as independent adaptations. The hypothesis advanced by Biitschli is that primitive forms of Suctoria (such as Hypocoma (C), which has but one suctorial tentacle, and which retains its cilia throughout life, the cilia being upon the ventral side only, as in hypotrichous forms of Ciliata) were derived from hypotrichous ciliates by the mouth portion becoming progressively drawn out into a tentacle. Haeckel (’96), adopting Biitschli’s view, compared the simple, single, and terminal mouth-tube of a primitive suctorian with the long, proboscis-like oral region of certain holotrichous ciliates, such as Lacrymarta olar or L. phenicopterus. In the closely allied forms, Didinium and Mesodinium, the oral tube is not ciliated and is contractile, so that when food is taken in, the tube widens into more or less of a disk similar to many suctorian tentacles. In Alesodindum, 206 THE PROTOZOA this tube is not only retractile, but is also surrounded by four tentacle- like processes which simulate some kinds of tentacles in the Suctoria. As the majority of the larvae of the Suctoria are ciliated in girdles, Haeckel holds that this division of the Holotrichida represents the nearest allies of the Suctoria, and that the loss of cilia in the adult is already foreshadowed by the regional loss of cilia in these girdled forms. The entire matter, finally, of the origin of Infusoria from more generalized forms of Protozoa remains unsolved; the various hypotheses are interesting possibilities, but no more can be said for them. This problem, like that of the origin of the Protozoa, may never come nearer settlement ; for, without the assistance of palzonto- logical and embryological evidence, which in other great groups of the animal kingdom are of inestimable value in tracing ancestors, the possibility of tracing their origin is reduced to a minimum. CLASSIFICATION Cuass V. INFUSORIA. Protozoa in which the motor apparatus is in the form of cilia, either simple or united into membranes, membranelles, or cirri. The cilia may be permanent or limited to the embryonic stages. With two kinds of nuclei, macronucleus and micronucleus. Reproduction is effected by simple transverse division or by budding. Nutrition 1s holozoic or parasitic. Subclass I. CILIATA. Infusoria provided with cilia during adult as well as embryonic life. Reproduction is brought about typically by simple transverse division. Mouth and anus are usually present. The contractile vacuole is often connected with a complicated canal system. Order 1. HOLOTRICHIDA. Ciliata in which the cilia are similar and distributed all over the body, with, however, a tendency to lengthen in the vicinity of the mouth. Trichocysts are always present, either distributed about the body or limited to a special region. Suborder 1. GYMNOSTOMINA. Holotrichida without an undulating membrane about the mouth, which remains closed except during food-taking intervals. Family 1. Enchelinida. The mouth is always terminal or sub-terminal, and is usually round or oval in outline. Food-taking is usually a process of swal- lowing. Genera: Holophrya Ehr. (31); Urotricha Clap. & Lach. (°58) ; Enchelys Hill (1752), Ehr. (38) ; Spathidium Duj. (41) 3 Chenza Quennerstadt (68) ; Prorodon Ehr. (°33); Dinophrya Biitschli (88); Lacrymaria Ehr. (’30); Trachelocerca Ebr. (33); Actinobolus Stein ('67); Heonema Stokes (84); Plagiopogon Stein (59); Coleps Nitsch ('27); Zvarina Bergh ('79); Stepha- nopogon Entz (84); Dzdinzum Stein (59); Afesodinium Stein (62); Biitschlia Schuberg (°86). Family 2. Trachelinidea. The body is distinctly bilateral or asymmetrical, with one side, the dorsal, slightly arched. The mouth may be terminal-or sub- terminal, or the entire mouth-region may be drawn out into a long proboscis. An cesophagus or gullet may or may not be present; when present, it is usually supported by a specialized framework. Genera: —— clusions of others, he obtained the following results: (1) the crys- tals are insoluble, in the ordinary sense, in water; (2) slightly soluble in concentrated acetic acid and in dilute ammonia ; (3) more soluble in solutions of different salts, weak acetic acid, and ammonia; (4) easily soluble in mineral acids and alkalies ; (5) insoluble in alcohol, ether, and carbon bisulphate ; (6) negative results with staining agents showed that they can be neither albuminate nor carbohydrate in na- ture; (7) reactions to osmic acid, alcohol, and ether excluded the possibility of fats; (8) delicate tests showed that the crystals were composed of an unorganized substance; (9) final tests showed this 1 Protozoa, p. 103. 2 Loc. cit., p. 1484 (788). 288 THE PROTOZOA to be a calcium salt, which was determined as calcium orthophos- phate (Ca,H,(PO4),).? While there are many chances for error in Schewiakoff’s work, it is probable that he has come very near to the correct interpretation of these bodies. Their origin, however, as well as their significance, remains in doubt. Their disposal also has not been satisfactorily ac- counted for. Stein reported their defecation with the undigested remains through the anus, but Entz, Maupas, and Schewiakoff believe, apparently on justifiable grounds, that they are dissolved and pass to the outside through the contractile vacuole. B. RESPIRATION The assumption that Protozoa take in oxygen and liberate carbon dioxid rests almost entirely upon indirect evidence, which, however, is so strong as to leave little reason to doubt the validity of the assump- tion. An infusorian, for example, moving rapidly day and night during its entire life, and eating constantly throughout this period, must undergo continual waste in the liberation of energy by com- bustion. A constant supply of oxygen and a constant excretion of the waste products of combustion appear to be equally necessary for the continuance of this activity. With remarkable intuition, Spallan- zani (1776) suggested the contractile vacuole as the organ of respira- tion by means of which the waste matters are thrown out, and later observers have offered no evidence of value to disprove the suggestion. In a ciliate, for example, the volume of a contractile vacuole at com- plete diastole is about one-tenth of the volume of the animal itself, and, contracting every two or three minutes, the vacuole must in half an hour expel to the outside a volume of water equal to that of the entire animal. The oxygen-laden water which is thus expelled must have entered the body through the mouth opening or by osmosis through the body walls. The important réle which respiration plays in the physiology of the Protozoa, and the agency of the contractile vacuole in this process, was first clearly recognized by Schwalbe ('66) and Zenker ('66), then by Wrzesniowski (’69), and later by Ross- bach (72), Biitschli (’77), Limbach (’80), Maupas (’83), and Fiszer (85). Before the period of Schwalbe and Zenker, the contractile vacuole had been interpreted as a heart and the centre of a circu- latory system (Corti, 1774; Gleichen, 1778; Wiegmann, ’35 ; Siebold, ’48), etc., and Pouchet (’64) went so far as to describe colored blood pumped by the vacuole throughout the body. This view, which now 1“ Calcium is by far the most abundant metallic element in the body. ... It is found in all the cells and fluids of the body, probably loosely combined with proteid.” — Howell, doc. cit. p. 967. SOME PROBLEMS IN THE PHYSIOLOGY OF THE PROTOZOA 28G has but an historic interest, has recently been rather feebly advocated by Greeff (’91) and Pénard (’90), who adopted it without the supposed justification which the older naturalists had in comparing the contractile vacuole of Protozoa with the water vascular system of the flatworms. Until Leydig (’57) demonstrated the excretory function of the water vascular system, it was supposed that the flatworms obtained oxygen from a stream of water taken in by the vascular system from the out- side, in a manner analogous to the air supply from the trachea of insects, and Schmidt (’67), following Dujardin, and followed by Bal- biani (’60, ’61) and Maupas (’79), attempted to explain respiration in Protozoa in the same manner. At the present time, while the prob- ability is very strong that the contractile vacuole expels water in which the oxygen has been replaced by carbon dioxid, there have been singu- larly few actual observations to confirm it. Certes’s (’85) experiments show that some alteration takes place in the water after its entrance into the protoplasm. This was demonstrated by placing Infusoria in water colored by dissolved aniline dyes; the water of. the contractile vacuole remained clear and colorless, although the surrounding medium was intensely colored. The only direct observations of the presence of carbon dioxid was made by Brandt (’81) upon Amedéa. Placing these organisms in a medium colored by dilute haematoxylin, he found that the water of the vacuole became yellow and then red, thus showing the characteristic reaction of hamatoxylin in the presence of an acid. The observation is not conclusive, however, for the presence of uric acid might also give this reaction. Numerous attempts have been made to describe the series of events which lead up to, and cause, the contraction of the vacuole. Being entirely hypothetical, they may be dismissed with a brief mention. Schwalbe, Rossbach, Engelmann, Maupas, and many others explained the bursting as due to the contractility of the protoplasm. Schwalbe attempted to trace the impulse or stimulus of contraction to the products of destructive metabolism, which become stored up in the vacuole so that the latter, when full, presses upon the pro- toplasm and causes it to contract. Rossbach (’72) more obscurely attempted to trace the stimulus to the chemical change which takes place at the moment of oxidation. Each oxidation forms an oxidation product which, as soon as formed, incites the stimulus. Zenker (’66) was more clear in describing the process as due to the attraction of protoplasm for oxygen-holding water, and repulsion for water without oxygen, the result being that when the oxygen is re- moved from the imbibed water, the latter is expelled from the body. Rhumbler (’98) gave a similar interpretation and adduced experi- ments with inorganic fluids simulating the contractile vacuole. Biitschli (’83) regarded the systole as due to a simple physical - 290 THE PROTOZOA force, —surface tension. The liquid of the vacuole mixes quickly with the surrounding water, as a small drop fuses with a larger mass, as soon as the intervening layer of protoplasm gives way before the pressure of the growing vacuole. Delage and Hérouard (’96), on the other hand, held that contractility of the protoplasm brings about the contraction just as it causes the expulsion of undigested food matters. When present, carbon dioxid is probably dissolved in the water of the contractile vacuole, although, in some cases, especially among the Sarcodina, gas vacuoles containing, probably, carbon dioxid have been repeatedly observed, first by Perty (’49) in Avce//a, and subsequently by Biitschli (’74), Engelmann (’78), Entz (’78), and others, not only in Avcella, but in other rhizopods as well. According to Engelmann, the gas is secreted very rapidly, but at irregular intervals, and he, with other modern observers, accepted and confirmed the suggestion made by Perty, that the gas vacuoles serve as an hydrostatic apparatus, by means of which the organisms can raise and lower themselves in the water. Although the contractile vacuole appears to play an important réle in respiration, it is not absolutely necessary for the performance of this function, for a great many forms have no such organ. The ma- rine rhizopods and Radiolaria, and some of the fresh-water forms of Rhizopoda (¢.g. Pelomyxa), have no contractile vacuoles. Respira- tion in such cases must take place by osmosis. An interesting series of forms are the Opalinidz, parasitic ciliates of which some genera have a contractile vacuole with numerous feeding canals (Azoplophrya, Hloplitophrya), while others have no contractile vacuole, although the canals are present (Ofalina, according to Fabre-Dumergue). In none of these forms is there a mouth, and respiration must take place by osmosis. There is, on the whole, very little direct evidence to support the conclusion which on @ przore grounds appears indisputable, that, like other organisms, the Protozoa take in oxygen and give off carbon dioxid. The fragmentary evidence which we have tends to the con- clusion that, when present, the contractile vacuole, probably in addi- tion to other excretory functions, is the active agent in the disposal of carbon dioxid, while the income of oxygen-holding water takes place by osmosis through the body walls, by ingulfing through the mouth, or by both methods. C. SECRETION AND EXCRETION Carbon dioxid is but one of the waste matters formed by the decom- position of proteids in vital activities. In the higher animals the final SOME PROBLEMS IN THE PHYSIOLOGY OF THE PROTOZOA 291 products are carbon dioxid and urea (CO(NH,),), and it has long been assumed upon @ priovz grounds that a similar result follows combus- tion in Protozoa. Again, there have been but few observations to confirm this supposition. The contractile vacuole was regarded as an excretory vesicle (Urizdlase) by Boeck ('47), Rood (’53), Stein (56), Leydig (57), Kolliker (64), and more recently as an excretory organ by Maupas (’83), Rhumbler (’88), Griffiths (89), Schewiakoff (’94), Delage and Hérouard (’96), besides many others. Biitschli! believed that it is a pure hypothesis to assume that the vacuole has an excre- tory function other than that of respiration, but Maupas (’83) insisted upon the physiological necessity of such an excretory organ, and cited as an argument the presence of contractile vacuoles in vegetable zoéspores, which, having chlorophyl, can presumably make use of all the carbon dioxid formed, and which, therefore, probably make use of the vacuole for secretion. Maupas’s argument is offset by the fact of numerous Protozoa which have no contractile vacuoles, and it follows that if these can get rid of their waste organic matters by osmosis, it is quite possible that forms with vacuoles candothe same. Entz(’88) held that the crystals occasionally found in the vacuoles and reser- voirs of different forms are uric acid (arnconcremente), a supposition which was supported with direct evidence by Griffiths (89). The lat- ter determined the presence of uric acid in several different types of Protozoa, including the rhizopod Amada and the ciliates Paramecium and Vorticella. A number of animals were placed on a slide under a cover-glass, and killed with alcohol followed by nitric acid. The slide was then gently warmed, and ammonia was introduced. When the experiments were successful, a number of purple prismatic crys- tals of murexide appeared in the contractile vacuoles, showing that uric acid had been present. These results were repeatedly obtained, although the experiments were not always successful, showing, Grif- fiths says, that the vacuole may have some other functions besides secretion. Until this interesting series of experiments is confirmed, however, Griffiths’s results must be inconclusive. If they are confirmed, on the other hand, the following reflection is warranted, and has a sin- gular interest in the present-day problems of biology: “ Through all the multitudinous changes,” says Griffiths, “that have taken place dur- ing the lapse of ages in the development of the mammalian kidney, we find that the physiological functions are the same as occur in its origi- nal or primitive form, as represented in the Protozoa.” ? The secretion from the protoplasmic body of definite particles of matter, which may or may not have been at some time a part of the animal protoplasm, and which play some further part in the life activi- 1°88), p. 1452. 2 Loc, cil. p. 135+ 292 THE PROTOZOA ties, is definitely established in a number of cases. The materials thus secreted vary in nature from purely inorganic solids, like calcium carbonate, silica, etc., to chitin, cellulose, fats, and jelly-like protoplas- mic products. The simplest cases of secretion are seen in those Mastigophora and Sarcodina where the outer protoplasm becomes gelatinous, to form the jelly-like mantles of different types (many Flagellidia, Heliozoa, Radiolaria). In Ameéa there is a secretion of such a substance which aids the animal in securing food by sticking it to larger objects, as well as by ensnaring the prey (Rhumbler, Ver- worn, Hofer). In Luglena, according to Klebs (’86), the protoplasm throws out a slimy mantle when the surrounding conditions are un- suitable. This mantle at first is not homogeneous, but is in the form of minute gelatinous threads which arise beneath the cuticle from the outer protoplasmic layer of the body. A network is then formed be- tween the threads, which finally unite to form a homogeneous man- tle about the animal. An identical process has been described by Schewiakoff (’94) and by Siedlecki (’99), in the movements of certain gregarines,! where a gelatinous layer beneath the membrane secretes filaments of slime-like material which harden outside the body. In other instances the secreted material is in the form of granules which unite outside the body to form stalks or houses, or even shells. In many such cases the granules have not been a part of the body protoplasm, although they may have been created there. Such, for _ example, are the lime shells of the’ Reticulariida, or the silicious and acanthin skeletons of the Radiolaria. In other cases they appear to be a growth product of the organism, as in the branched stalks of many Flagellidia, although even here foreign particles may be used for this end. Thus, in freshly formed Azthophysa stalks, Kent and Biitschli observed that the excreted material was granular, and Ehrenberg had already noticed that, if Azthophysa colonies are fed with indigo, the colored particles collect at the base of the animal, while Kent (’81), repeating the experiment, observed that the gran- ules were actually deposited to form a part of the new stalk material. The materials for the shells of Rhizopoda may be foreign particles analogous to the indigo granules, or they may be the result of chem- ical activity of the protoplasm. The various shells of Diflugia, Cen- tropyxts, Cyphoderia, Lithicolla, etc., are examples of the first type, while Euglypha, Quadrula, most Heliozoa, Reticulariida, and Radio- laria are examples of the second. In the Sarcodina, where the shells, as in Reticulariida, are formed by deposition of calcium carbonate, it has been shown by Carpenter, Kolliker, Wallich, and especially by Dreyer (’92), that the material 1Cf p. 149. SOME PROBLEMS IN THE PHYSIOLOGY OF THE PROTOZOA 293 is deposited from a well-defined portion of ‘the protoplasm (chz/osare, Wallich), and not upon the outside of the body, but between two chitinous lamellze situated in the ectoplasm (Fig. 149). The manufac- ture of the shell material of the Mollusca was explained by Stein- mann as a purely chemical phenome- non, and not as an expression of vital activity. The early experiments of Harting (’73) in allowing carbonic acid alkalies to act upon albumin or other nitrogenous substances, there- by obtaining a precipitate of calcium carbonate in the form of granules similar to Coccoliths, gave Steinmann the clue to his theory that calcium chloride and other salts acting upon albumin in animal protoplasm give a similar precipitate. Applying this theory to the marine rhizopods, Dreyer argued that the protoplasmic body is saturated with dissolved cal- cium salts, and that albuminoid stuffs secreted by the living animal undergo fermentation through the agency of bacteria, and ammonium carbonate is formed, wha acting i eage Epe eal Fig. 149. — Shell formation in Gromia cium salts, results in the formation fluviatilis Daj. [DREYER,] of calcium carbonate! ada @NOESVNuoBNORS ZARA y Ee NAYQANS BROT SAR OR N AGARDG, ’28. Icones Algar. Europ. — Agassiz, L., 57. 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