Property of GORHELL UiIVERSITY. Cornell University Library Ithaca, New York COMSTOCK MEMORIAL LIBRARY ENTOMOLOGY Z BOUGHT WITH THE INCOME OF A FUND GIVEN BY THE STUDENTS OF JOHN HENRY COMSTOCK PROFESSOR OF ENTOMOLOGY 1915 ‘ornell University Libra TA Aquatic Microscopy FOR BEGINNERS | OR Common Objects from the Ponds and Ditches BY Dr. ALFRED C. STOKES — — Author of ‘“‘A Contribution toward a Natural History of the Fresh- water Infusoria of the United States;” ‘‘ Analytical Keys to . the Genera and Species of the Fresh-water Algz and the Desmidiee of the United States;” ‘‘ Micro- scopical Praxis,” etc. THIRD EDITION ILLUSTRATED ‘“* The microscope is not a mere extension of a faculty, it is a new sense.” et ‘* The microscope, frequently and intelligently used, makes Nature pellucid,” “PORTLAND, CONN.: EDWARD F. BIGELOW 1896 Ent, | “| Progarty of cunticLh umivcnalTE, CopyRIGHT, 1896, BY EDWARD F. BIGELOW. Preface to the Third Edition. The author has taken advantage of a change of pub- ' lisher to revise and enlarge this, the third edition of his ‘‘Microscopy for Beginners,” and to make a slight alteration in the title, whereby it becomes more nearly descriptive of the character and scope of the book. The opportunity has likewise been taken to add considerable new matter to the text and several new illustrations. Trenton, N. J., 1895. By Alfred C. Stokes. F. AQUATIC MICROSCOPY FOR BEGINNERS. Price, postpaid, $1.50. II. FRESH-WATER ALGZ AND THE DES- MIDIEA, Price, Postpaid, $1.25, III. MICROSCOPICAL PRAXIS. Price, Postpaid, $1.50. Address E. F. Bigelow, Portland, Conn. CONTENTS. PAGE INTRODUCTION, - - xi CHAPTER I. THE Microscope AND ITs Parts, - I CHAPTER II. Common AQuaATIC PLANTS USEFUL TO THE MICROS- COPIST, - 45 CHAPTER III. Desmips, DIATOMS, AND FRESH-WATER ALGA&, 61 CHAPTER IV. RHIZOPODS, - - IIo CHAPTER V. . INFUSORIA, - - - 132 CHAPTER VI. Hynpras, - - - 165 vi Some Aquatic Worms, CHZTONOTUS AND CHI- CONTENTS. CHAPTER VII. RONOMUS LARVA, ROvIFERS, CHAPTER VIII. CHAPTER IX. FResSH-WaTER Poiyzoa, CHAPTER X. ENTOMOSTRACA AND PHYLLOPODA, WATER-MITES AND THE WATER-BEAR, | Some Common Opjects WorTH EXAMINING, GLOSSARY, INDEX, CHAPTER XI. CHAPTER XII. PAGE 173 213 237 257 279 292 3°09 315 FIG. bw Io. II: 12, 13. 14. 15. 16, 17. 18, 19g. . Leaf of ILLUSTRATIONS, ILLUSTRATIONS. . A Growing-slide....... . Air-bubbles........... . Reflector for Drawing the Magnified Object Ranunculus aquatilis............ . Peduntle of Nymphza odorata; transverse sec- . . Whorl of Myriophyllum Leaves......... . A Leaf of Utricularia. . Quadrifid Process from Inner Surface of Utri- cle of Utricularia. .... Whorl of Leaves of Cer- atophyllum........... Lemna polyrrhiza..... Lemna Minor......... Anacharis Canadensis. . Portion of Leaf of Sphagnum.......... Riccia fluitans........ Didymoprium Grevillii. Spherozosma pulchrum Hyalotheca dissiliens. . 40 47 48 49 51 53 54 55 55 56 58 60 72 72 73 . Bambusina Brebissonii. . Desmidium Swartzii.... . Closterium lineatum... . Closterium juncidum. . . . Closterium acerosum. . . . Closterium Lunula. . . Clostérium Ehrenbergii . Closterium acuminatum . Closterium Diane... .. . Closterium Venus..... . Closterium rostratum.. . . Closterium setaceum... . Micrasterias radiosa.... . Micrasterias rotata..... . Micrasterias truncata... . Micrasterias arcuata... . Micrasterias dichotoma: . Micrasterias Kitchelii. . : Micrasterias oscitans.. . . Micrasterias laticeps. .. . Euastrum crassum..... . Euastrum didélta...... . Euastrum ansatum..... . Tetmemorus granulatus . Tetmemorus Brebissonii . Docidium Baculum.... . Docidium crenulatum. . . Cosmarium Ralfsii..... . Cosmarium pyramidatum 81 vii PAGE 73 “73 74 75 75 75 75 75 76 76 76 76 77 78 58 78 78 79 79 80 80 80 80 80 8r 81 81 PAGE vill ILLUSTRATIONS, FIG, PAGE FIG. 49. Cosmarium margariti- 81. Hydrodictyon utricula- fermi ss4 ities eenee 81 CUM eeton reread go. Cosmarium Brebissonii 81 82. Batrachospermum mon- 51. Staurastrum punctula- iliforme............ PUM see cote Fesscnitealt 82 83. Anabena............ 52. Staurastrum furcigerum 82 84. Oscillasia ee (fer cores At aye 53. Staurastrum gracile.... 83 85. Spirogyra pee mae 54. Staurastrum macrocerum § 83 oe Spieyis teen ee se 55. Xanthidium armatum.. 83 ton; wich SPOTS? eG 56. Xanthidiumantilopeum 83 87. Ayenens IDSIE MEO ane Athcodesnis tails, 0. Bs 88. Vaucheria........... eh: Reghraddenis conver 89. Chztophem elegans... ee eae te 84 go. Draparnaldia glomer- 59. Spiroteniacondensata.. 84) gr, Bulbochaste.. 60. T mploceten vesuctiataiy 84 g2. Ameeba proteus...... 61. Pentium Brebissonii. wen Oe 93. Vampyrellalateritia.-. . 62. Meridion circulare..... gi g4. Acanthocystis chzeto- 63. Diatoma vulgare...... gI phora. ........2... 64. Bacillaria ia demagee i sepia 92 gs. Actinophrys GLE 65. Bragiates capucina: fun 02 g6. Actinospherium Eich- 66. Himantidium pectinale 93 otic. cute ocanc ses Bi HCyonema “paradoxte “93 97. Difflugia pyriformis. .. 68, Cocconema lanceolatum 93 98. Difflugia corona...... fo: Gomphonema acum: gg. Centropyxis aculeata. . MUMbpe SF S88 2 Gata 94 | 100. Arcella vulgaris...... 70. Epithemia turgida..... 94 | tox. Arcella dentata....... 71. Cocconeis pediculus... 94 | 102. Trinema enchelys.... 72, Eunotia tetraodon..... 94 | 103. Euglypha alveolata... 73. Pleurosigma angulatum 95 | 104. Cyphoderia ampulla... 74. Surirella splendida..... 95 | 105, Clathrulina elegans... 75. Navicula cuspidata. . 96 | 106. Dendromonas........ 76. Pinnularia major...... 96 | 107. Carchesium.......... 77. Pinnularia viridis...... 96 | 108. Epistylis............ 78. Stauroneis phcenocente- 10g. Vorticella............ TON... eee eee eee ee :++ 97] x10, Dinobryon..........- 79. Scenedesmus caudatus. 98 | 111. Vaginicola........... 80. Pediastrum Boryanum.. 98 | 112. Platycola............ IOL 103 103 104 Lo5 105 106 106: 107 108 10g 116 II7 118 IIg FIG, 113. 114. IIs. 116, Ir7. 118. I1g. 120, 121. 122. 123. 124. 125. 126, 127. 128, 129. 130. 131, 132. 133. 134. 135. 136. 137. 138. 139. 140. 141, 142. 143. 144. ILLUSTRATIONS, ix PAGE FIG, PAGE Cothurnia..... - r..e--. 155 | 145. Turbellarian worms... 193 Stentor polymorphus.. 156 | 146. Anguillula fluviatilis... 197 Stentor Barretti...... 157 | 147. Snout of a Pristina.... 202 Stentor igneus....... 158 | 148. Posterior extremity of Astasia.. 6... 0.0... 158 a Pristina.......... 202 Euglena............. 159 ; T4g. Posterior extremity ‘of Chilomonas.......... 159 a Pristina wits vicina a 202 Phacus pleuronectes.. 159 | 150. Posterior extremity of Phacus longicaudus... 159 A DER. ci nce wes 205 HUN ELE sao ccth sanctenincet 160 | 151. Posterior extremity of — Trachelocerca......... 160 an Aulophorus...... 206 Amphileptus...,... 161 | 152. Podal spines and _ bris- Paramecium......... 162 tles of Strephuris.... 207 Euplotes.......... .. 162 | 153. Nais...........0000, 212 Stylonychia.......... 163 | 154. Podal Spine of Nais... 212 Chilodon............ 163 | 155. Stephanoceros........ 223 Loxodes............. 163 | 156. Floscularia ornata.... 224 Hydras adherent to 157. Ghcistesixacs o25 sages 225 Lemna rootlets...... 166 | 158. Melicertaringens..... 226 Hydra sting......... 168 | 159. Limnias ceratophylli.. 228 Trichodina pediculus— 160, Megalotrocha........ 229 Parasite of Hydra...-170 | 161. Conochilus.......... 229 Chironomus larva..... 177 | 162. Philodina............ 230 Chetonotus larus..... 178 | 163. Rotifer.............. 231 Head of Chetonotus, 164. Stephanops.......... 233 ventral aspect....... 178 | 165. Pterodina............ 234 Dasydytes saltitans.... 183 | 166. Scaridium.......... *. 234 Chezetonotus loricatus. 186 | 167. Polyarthra........... 235 Chetonotusacanthodes 188 | 168. Brachionus.......... 236 Cheetonotus _ spinifer; 169. Pectinatella magnifica. 245 spines and scales.... 189 | 170. Plumatella........... 248 Chzetonotus acantho- 171. Paludicella...7...... 249 phorus............. 18g | 172. Urnatella............ 251 Chzetonotus enormis.. Igo | 173. Fredericella statoblast. 253 Cheetonotus spinosulus 1g0 | 174. Plumatella statoblast.. 253 Chzetonotus longispin- 175. Lophopus statoblast.. 253 OSUSs 4 i Seki Re sietvedd 190 | 176. Pectinatella statoblast. 254 Lepidoderma........ 192 | 177. Cristatella statoblast.. 254 FIG. 178. 179. 180. 181, 182, 183. 184. 185. 186. 187. 188, 189. 190. ILLUSTRATIONS. PAGE Daphnia. ........... 266 Bosmina .. ........ 267 GY PMS) 2825.2 2.0 eatseaanats 268 Camptocercus........ 269 Chydorus... ........ 269 Alonopsis............ 270 Diaptomus......... a 274 Canthocamptus....... 271 Cyclopsiisincy cic aces 273 Limnetis............ 273 Artemia (a female).... 275. Chirocephalus........ 276 Branchipus (a male)... 277 FIG, 1gr. 192. 193. Ig4. 195. : 196. Ig7. 198. A Water-mite........ The Water-bear (Ma- crobiotus).......... Coxze of Hydrachna. . Coxe of Eylais....... Coxe of Arrenurus (female)............ Coxe of Arrenurus (male). csaacnnesca Coxe of Atax... Leann Eye-plate of Limno- 286 288 288 288 288 290 xi INTRODUCTION. To the beginner in the use of the microscope, in- deed to the beginner in the study of any department of natural history, the name of the specimens found is of the first importance. It is the key that opens the door to further knowledge, and until it is obtained the beginner is helpless; the books are closed to him, all conference with others in reference to the object or specimen is impossible, and, in many, a budding in- terest that might otherwise bloom and bear fruit is crushed ard destroyed. The first question asked is always, ‘‘What is it?” and unless the questioner has a kind and experienced friend to whom he can take the: specimen, or a book of common objects from which the names of ordinary natural history materials can be ascertained, the question is too often unanswered, and the beginner soon loses his relish for the unknown in Nature, because to him it always remains the unknow- able. In England innumerable little hand-books in all de- partments of natural science are within the reach of every reader, even the least wealthy. They are writ- ten in an attractive style, they are usually accurate as far as they. go, and they aim to describe the common objects to be found in the green lanes and in the xii INTRODUCTION. woods, in the waters of the ponds and streams, and of the shallow bays and ihlets of the sea, so that any one with the least inclination toward the study of the teeming world of animal and vegetable life can, at slight expenditure of time, labor and money, learn the names and some of the structure of the common things surrounding him. Such books, if correct and helpful, are worthy of all praise. That there is a desire for such, even in this fair land of ours, is evident by their importation, and their appearance on the counters of the booksell- ers and on the shelves of the public libraries, But they are seldom adapted to our needs. Their de- scriptions are commonly too general and diffuse; their writers pay more attention to literary style than to the imparting of definite information, and the text too often bears internal evidence of having been made to. Suit Certain pictures owned and necessary to be uti- | lized by the publisher. That similar and better books on the life in American fields and-streams, and on American sea-shores, are so few is much to be regret- ted. There should be small and untechnical -hand- books adapted to ‘‘all ‘capacities, even the meaneSt,”’ as our forefathers used to put it, and in all depart- ments of animal and vegetable life; books in which the beginner could learn the names of things. “IT do beseech you, what is your name ?”’ is the oft repeated question, not only by the beginner in the use ‘of the microscope, but by the more advanced student in other departments of science. ‘‘Naming things,”’ says. Henry Van Dyke, ‘‘is one of the oldest and simplest of human pastimes. Children play at it with their dol!s and toy animals. In fact, it was the first INTRODUCTION. xiii game ever played on earth, for the Creator who planted the garden eastward in Eden knew well what would please the childish heart of man when He brought all the new-made creatures to Adam ‘to see what he would call them.’” Emerton’s ‘‘Life on the Sea-shore,” and _ his “Structure and Habits of Spiders; ’Hervey’s charming “‘Sea-mosses,” Gray’s ‘‘How Plants. Grow,” Romyn Hitchcock’s ‘‘Synopsis of the Fresh-water Rhizo- pods,” Jordan’s ‘‘Manual of the Vertebrates,” Apgar’s “Trees of the Northern United States,” are delight- ful books that approach the ideal nearer than any others published in this country. But there is so much for our learned scientists to do in this compara- tively unexplored land of ours, that they may have no time to stoop and lend a hand to those who would like to enter a little way into the attractive world of science, from which faint. but pleasant rumors occasionally come. These learned men are all courteous and com- municative when personally approached, but what boy or other young person with an inclination towards “bugs and things” would be willing, or, indeed, would know how to seek aid from these celebrated investiga- tors? And if the student is alone in a country place where Nature smiles her sweetest but where there are no libraries, and no human being to consult, except perhaps ‘‘the minister,’” how then shall he learn the name of the flower, the stone, or the bird that attracts his attention? ‘‘The minister” is usually poor autho- rity on such subjects, and the boy, after wondering and investigating in an awkward and boyish fashion, soon'gives it up, when he might have become a lover of Nature, and perhaps a lover of something even bet- ter than Nature. XIV INTRODUCTION, The microscope is every day becoming a more fami- liar instrument to the young. There is a growing in- terest among the boys and the girls, even among those of larger growth, in the little things of the world, and the number of so-called microscopists is rapidly in- creasing. But the possessor of an instrument looks at the two or three mounted objects supplied by the dealer, and then wonders if they are all, arid if they are the only foundation for the charming stories he has heard of the charming things to be seen with the mi- croscope. ‘“Will you tell me where I can finda book that will -help me to know a microscopic plant from a micro- scopic animal, and teach me how I can best. collect them,’’ is a question that has often, in some shape, been asked the writer, and has as often remained un- answered, for there is no book on common American microscopic objects. It is only possible to direct the questioner to the ditches and the ponds, and to wish him a success that is almost hopeless. In any event, the beginner naturally, and almost instinctively, goes first to the water for his microscopic objects, probably because he has heard so much about the ‘‘animalcules” there. His first examination bewilders him; there is so much life and motion and color; there are so many strange forms; but where shall he turn for help? Since our illustrious scientists have not offered to help him, the writer, who is only, a beginner himself, and who makes not the slightest pretensions, has sym- pathized with the inquirers whom he has been com- pelled to turn away unsatisfied when they have come for printed help in their microscopical work, and this little book is the result. It claims no literary merit; it makes no scientific pretensions. Its only aim is to INTRODUCTION. XV help the beginner to ascertain the names and a little of the structure of a few of the common microscopic creatures, both animal and vegetable, with which the ‘fresh waters of the land are filled, ‘and it tries to do so in the simplest and most direct way, leaping scientific hedges and trampling on scientific classification in a manner that will dismay the learned botanist and zo- ologist. But the botanist and zoologist have weighty books that delight their souls, so why should not the beginner with a microscope have a book to help him if to nothing more than to the names of the commonest aquatic objects, and, it is hoped, delight him by smoothing the path that leads to them? The writer will not be greatly troubled if the learned botanist and zoologist do not like this little book, provided the be- ginner in the use of the microscope approve it and find it helpful, It relates almost exclusively to aquatic objects. One reason for this has already been mentioned: An- other and more potent one is, that even the beginner knows, in a general way, what he is looking at when he magnifies the common objects of the land, but the microscopic creatures from the water are so truly mi- croscopic, the observer must so often go fishing on faith, and only know the contents of his net by faith and imagination until he can examine his collection drop by drop with the microscope, that he is lost at the start unless he has a book to help him, which this one hopes to do. But is it necessary to say that the following pages do not contain notices of everything to be found in the ponds and ditches? The beginner will capture many objects which he will not find described here. xvi INTRODUCTION. It is not possible that this should be otherwise. The waters are crowded with life, and it is only the com- morest objects and those most frequently found, that a little book of this kind can attempt to include. The descriptions of those few have been made as plain as possible. The writer has seldom allowed himself to ‘‘fall into poetry,” although often sorely tempted. The keys, or analytical tables, so freely - scattered through the pages have been purposely made as artificial as they could be. They use the most con- spicuous external characters with little regard to scientific classification, and with regard to but one re- sult only—to help the beginner find the name, at least the generic name, of his specimen. If this is accom- plished the book will have attained its purpose. The method of using the keys is explained on page 67. Finally, to the beginners in the use of the micro- , scope, for whom the book has beén prepared, the writer would say, as has so often been already said: There is no royal road. The mother-bird finds and brings the food, but even the youngest nestling opens its own mouth. Aguatic Microscopy for Beginners, CHAPTER I. THE MICROSCOPE AND ITS PARTS. Simple and Compound Microscopes.—Pocket-lens.—‘‘Craig Micro- scope.’’—‘‘Excelsior Microscope.’’—Watchmaker’s Glass. —Cod- ding Lens.—How to Focus a Simple Lens.—Parts of the Com- pound Microscope.—Draw-tube.—Eye-pieces.—Society-screw.— French Triplets.—Objectives.—Selecting Objectives for the Be- ginner.—Coarse Adjustment.—Focusing.—Fine Adjustment.— The Stage.—Diaphragm.—Mirror and Bull’s-Eye Condensing- lens. —Preparing the Object.—-Thin Cover-Glass.—Cells.—Cement. —Dry Mounting.—Needles.—Dipping-tube.—Bunsen Burner.— Evaporation from beneath the Cover.—Life-slide.—Growing-cell. Air-bubbles.—Drawing.—Camera Lucida and Glass Reflector.— Micrometer.—Measuring the Object.—To ascertain the Magnify- ing Power.—Collecting-bottles.—Books and Magazines for Refer- » ence. Microscopes are compound or simple: compound -when they consist of two or more glasses, one or more being near the object to be examined, and one or more ‘near the eye of the observer; simple when they con- sist of but one double-convex lens to be held near the object, or of two or more lenses which can be -used ‘singly or all at the same time. When thus used in ‘combination, the two or three simple: lenses are not only placed close to each other, but close to the ob- ject, the combination acting as if it were a single lens, the magnifying power being much greater than that. of 2 2 AQUATIC MICROSCOPY FOR BEGINNERS. but one glass, and the distance from the object much shorter when in fucus. In the compound microscope the lenses near the eye magnify the image formed by the lower lenses, and that image is inverted and tran- sposed, the upper side of the object then appearing to be the lower, the right-hand side the left, and the left- hand the right. Inthe simple microscope, however, these changes do not take place; and in those forms where two or three lenses are combined, the effect is the same as though one glass of great magnifying power were used. But separate the lenses so that the upper shall magnify the image produced by the lower, and you will have a simple form of compound micro- scope. With the simple microscope we see the object itself; in the compound we see the enlarged image of the object. As a simple microscope does not seem to invert and reverse the object, and because the distance between the two is long when the low-power glass is in focus— that is, when the lens is in such a position that the magnified object looks clear and distinct to the eye— it is always used for the examination of a flower, the surface of a piece of bark, a stone, an insect, or any other specimen of considerable size, or one that is vis- ible to the naked eye, more.extended study being re- served for the compound instrument at home. A sim- ple microscope, a ‘‘pocket-lens” as it is often and pref- erably called (/#g. 1), is'indispensable to every one that has a taste for nature studies, and a desire ‘to know somewhat of the beauties hidden from our un- aided vision; for the simplest glass shows the student unimagined charm ‘in the petal of a flower, in the ‘sand we: walk.on, and in the green scum that floats upon ‘ , ies oH . « 1 THE MICROSCOPE AND ITS PARTS. 3 every summer pool and disgusts him until his little lens reveals its purity and its grace. The pocket-lens is always ready for the exam- ination of anything picked up in the fields or woods, it is small, and is easily carried in the pocket. It can be obtained in a great variety of shapes, so far as the frame that holds the lens is concerned; it can be had with but one glass, or with two or three of various powers, to be used alone or combined; it can be bought with a large lens of low power in one end of the frame, and a smaller glass of higher power in the other. But whatever form the beginner may select he should remember that the larger the simple lens the lower, as a rule, will be the magnifying power, and the longer the working-distance; or the space between the glass and the object when in focus; and the smaller the lens the more convex it will be, the greater the power it will have, the shorter will be the working-distance, and the less of the object it can show at oné view, and consequently the more troublesome will be its use. The beginner is advised to purchase a good pocket-lens with a working-dis- tance, or ‘‘focal-length” as it is sometimes rather in- correctly termed, of-one or of ome and one-half inches. This is all thatis really needed for the examination of botanical specimens and of the thousand and one ob- jects that attract the attention on every summer ram- ble. . The writer personally dislikes the combination pock- et-lens formed of two or three separable glasses. If but one lens of ‘the combination is wanted for immédiate use, the entire numbér must be pushed out of-the thick Fig. 1.—A Pocket-lens. 4 AQUATIC MICROSCOPY FOR BEGINNERS. and awkward case, one must be selected and sep- arated, for the perverse thing usually comes out of the pocket upside down, andit is of course desirable that the highest-power glass shall be next to and nearest the object, while those not needed are turned to one side, making a series of operations that take time, both hands, and considerable patience if you are anxious to examine the specimen. Your companion will have finished the work with the single glass, and will be telling you how the object looks, before your compli- cated affair is ready to begin, provided you are not wise enough to have avoided the combination pocket- lens. Andif the whole number of lenses is used at once, the working-distance is usually so short that the observer’s head or hat-brim shuts off most of the light, so that very little of the object can be seen, and that little with difficulty. To see at one view so small a portion as these higher-power combinations always show, and to be compelled to pass the lens over so many small portions before an idea of the whole sur- face can be obtained, is, to say the least, not satis- factory; unless the observer is familiar with the entire object, and with the relation and arrangement of all the parts, a low-power pocket-lens is the most useful, and the one to be commended. The reader perceives that this matter of short focus is an important one; indeed the usefulness of the pock- et-lens to a great extent depends upon it. Reject without hesitation the simple lens whose focus is so short that it must be held almost in contact with the object. . Some time ago a rather expensive instrument called the ‘‘Craig Microscope”. was extensively advertised, THE MICROSCOPE AND ITS PARTS. 5 and sold as a remarkable thing. The lens was a small globule of glass fastened to a glass plate, to give it a flat under-surface, and mounted in a brass ring, the whole being supported on an upright brass tube with a plane mirror at the lower end. It was not a com- pound microscope, but a simple lens with mirror at- tachment. The object to be examined was suspended from the flat surface of the glass in a drop of water, the focus being so short that it was at the front of the lens, so that nothing could be looked at unless it was actually adherent to the glass. No mounted object could be satisfactorily studied; to examine the parts of a flower was impossible, and even when a drop of water was suspended from the lens its trembling was exasperating, and its contents were distorted almost beyond recognition. All similar instruments should be avoided. The ‘‘Excelsior Microscope’ makes no false pre- tences. It consists of a small box, which acts as a re- ceptacle for all the parts when notin use, and asa support when a steel rod is elevated to receive the combination pocket-lens and the stage on which the object is to be placed, a small mirror in the front of the box reflecting light to the object from below. A great fault is the absence of weight in the instrument. At the least touch it moves, the light reflected from the mirror is lost, and the object is consequently left in semi-obscurity. It is.intended chiefly for the dis- section of flowers, grasses or large insects, and fairly answers the purpose if the observer desires to have both hands free, and cares to screw the box to the table. But it is no better than a good pocket-lens, which, with very little trouble, can be attached to an 6 AQUATIC MICROSCOPY FOR BEGINNERS. uptight rod and be used for dissections; in some re- spects it is much less valuable. The three lenses sup- plied can be used asa single one or combined. The former is good, the combination of two is not seriously objectionable, but the focus of the united three is, to the writer’s eye, only five-sixteenths of an inch, a dis- tance, aside from the small field of view, that effectu- ally prevents its use as adissecting-microscope. With the lowest-power lens six letters of the type used in this book can be seen, the focal distance being one and one-fourth inches; with two lenses combined, four letters, with a focal length of about one-quarter of an inch; and with the three glasses only one lettey is visi- ble, the focal distance being five-sixteenths of an inch, when tested by the writer’s myopic vision. A ‘‘watchmaker’s glass,” which is sometimes seen on the microscopist’s table, is a simple lens mounted in a short tube of horn or of rubber, so arranged that it can be held to the eye by the contraction of the muscles of the cheek and brow, while both hands are used for the manipulating of the object. It can be ob- tained of various powers and focal lengths, but it is scarcely desirable. The prolonged contraction of the facial muscles necessary to keep. it in place is very fatiguing, and the vapor continually evaporating from the front of the eye, being confined within the tube, is sure to condense on the lens and obscure the object. Everything a watchmaker’s glass will do, a good pocket-lens will do better. A ‘Coddington lens” is admirable in many respects. Its magnifying power is usually great, the image it forms is excellent and the field of view good, but the focus is, as a rule, unpleasantly short. This, apart THE MICROSCOPE AND ITS PARTS. 7 from its cost, is its only objectionable feature. It is named after the gentleman who first brought it to the notice of the opticians, and not as it should have been, after Sir David Brewster, its inventor. It con- sists of a sphere of glass with a deep groove cut around its equatorial center, and filled with a black cement, which acts asa diaphragm to arrest certain rays of light whose presence and action would be undesirable, as they would interfere with the formation of a clear and sharply outlined image. The reader may be surprised to learn that there are people who do not know how to focus a lens. I have seen such persons take the instrument as if they were afraid of it. They extend it toward the object ina hesitating way, move it about irregularly for a few moments, throw back the head, look cross-eyed, and say, ‘‘Oh yes; I see. How beautiful! And how very queer it looks!’ I once offered a lady an opera-glass, which she put to her eyes and never touched the ad- justment-wheel that alters the length of the tubes and focuses the lenses on the actors. When she returned it she said, ‘‘Thank you. I don’t like it much; I can see a good deal better without it.” To ‘‘get the focus” it is not really necessary to close one eye, although that is usually done. If both eyes are open, the one looking through the lens becomes so interested that the other sees nothing; or, if pre- ferred, we may say that the brain becomes so inter- ested in contemplating the image formed:on the retina of the eye examining the magnified object, that it fails to note the retinal impressions of the other. But if one eye must be closed, it can be done, after very little practice, without clapping your hand over it. This 8 AQUATIC MICROSCOPY FOR BEGINNERS. applies equally well to the use of the compound micro- scope. To focus a pocket-lens, hold the object to be ex- amined in the left hand, and, while looking through the lens, raise and lower the glass with the right hand until the magnified object appears clear and distinct, the outlines sharp, and without a fringe of color, and the surface rough or smooth, rounded or concave, as it indistinctly appears to the unaided eye. The focus cannot be obtained withdut this experimenting every time the glass is used. A good plan is to place the lens nearer the object than is known to be necessary, but always without allowing two to cume in contact, and then to raise the glass slowly until the image is distinct, when it will be focused. Keep it steadilyin that position and study the object, The compound microscope (/7g. 2) consists of the stand, the eye-piece, and the objective, although the word, as commonly-used, refers to the entire combi- nation of brass, with or without the magnifying glasses. But without the objective the microscope is only ‘the “stand,” and is practically useless. The stand alone generally includes the tube or microscope-body, the eye-piece (formed of two lenses at the opposite ends of a short tube inserted into the upper end of the body), the arm supporting the body, the stage on which the object is placed to be examined, the mirror to light the object, a movable circular plate, the diaphragm, immediately beneath the stage, and the foot that supports the whole. The addition of the objective, or magnifying glass, at the lower end of the body, makes the stand a compound microscope of the simplest form. The objective is so named because it / THE MICROSCOPE AND ITS PARTS, 9 Fig. 2.—A Compound Microscope is near the object to be examined when the microscope is in use, and the eye-piece is so called because it is then near to the observer’s eye. Without both of these sets of lenses the instrument is useless. 10 AQUATIC MICROSCOPY FOR BEGINNERS. The arm and the foot may be made of either brass or iron, but there should always be a joint between them so that the upper part of the instrument may be inclined. The cheapest stands are made without this arrangement, and they must therefore always be used in a vertical position, the observer being compelled to hold his head and body in a way that soon becomes exceedingly wearisome. An iron arm and foot are quite as useful as if made of brass, but no stand should be selected without the joint for inclination. Brass looks better, and is more expensive than neatly japanned iron, but is practically no more useful. The microscope-body should be about ten inches long. Inthe less expensive stands it is often made in two parts, the upper tube sliding within the other, so that when drawn ont to its full extent the entire body will be of the proper length to obtain the best results from the objectives. In such a stand, when the inner tube, or ‘‘draw-tube” is pushed down, the microscope will have the lowest magnifying power obtainable with the eye-piece and the objective then in use; when fully extended, the power of the objective will be greatly increased, so that by varying the length of the body by the use of the ‘‘draw-tube,” many different magnifying powers may be obtained from the same low-power objective. Insome cases this arrangement may be useful; itis at least not entirely objectionable, neither is it entirely convenient. Stands with an undivided body ten inches long—the standard length—also often have 4 secondary draw- tube by means of which the body can be enormously lengthened, and the magnifying power enormously increased, but usually with a loss of some good THE MICROSCOPE AND ITS PARTS. Ir qualities in the image. This addition is occasionally useful, but it is not necessary. If the reader should select an instrument with a body of the standard length, and find that it is without a draw-tube, he need not be troubled. The stand will be as valuable without as with this secondary part. The eye-piece consists of two lenses at the opposite ends of a short brass tube divided internally by a diaphragm. The lens nearest the observer’s eye when the instrument is in use is the ‘‘eye-glass,”’ the one at the opposite extremity the ‘‘field-glass.”” The price of the stand usually includes one or more eye pieces. If but one is supplied, it will generally be the lowest power, the two-inch or ‘‘A;” if two, the one-and-one-half or the one-inch, often also called ““B” or ‘‘C’”’, will be added. Opticians also make 3, 4, 4, and even +, inch eye-pieces, most of which are for special kinds of microscopical work, their magnifying power being enormous and the result almost worthless; indeed, these very high-power eye-pieces are usually to be avoided. On no account should they be selected by the beginner in microscopy. Every purchaser of a stand should insist upon having the two-inch, if he can have but one, as it is always useful, and is the only one that he will need for a long time, or until he desires to use an eye-piece micrometer for’ the measure- ment of microscopic objects, when he can add the one-inch, or ‘‘B” ocular to his stand. The lower ‘opening in the body always carries a screw to receive the screw on the upper end of the objective. Several years ago the size of these screws varied widely in stands and objectives of different makers, so that if the student desired an objective of 12 AQUATIC MICROSCOPY FOR BEGINNERS. different make from those accompanying his instru- ment,, he was forced to buy a little piece of apparatus called an adapter, one end of which was made to screw into the microscope body, the other to receive the objective. At the suggestion, however, of the Royal Microscopical Society of London, all objectives and stands now have screws of the size recommended by that society, and therefore called the ‘‘society- screw.” Only the very cheapest stands of the present day, or those having the least value as instruments for serious investigation, are without this screw, and they are usually supplied with what are termed French triplets. These are miserable lenses that should always be shunned, as they will do the observer more injury than much time can remedy. It is true that before the optician, especially before the American optician, began to make really good ob- jectives at moderate cost, these French triplets were extensively used, and are said to have done some good work. But at what expense? Not at the expense of any great amount of knowledge or skill displayed in their manufacture, for the lenses were ground, mounted singly, and then combined in an experimental way, two or three, it is said, being selected at random from a basketful, screwed together, and examined ona microscope. ‘If the result was considered satisfac- tory, all was well; if not, one or more of the lenses was replaced by others also selected at random, and the ex- periments were continued until the objective was con- sidered passable and salable. Such, at least, is the credible story. Theirexpense, therefore, was not in the making; it was in the imperfect image, in the great loss of light, in the injury of the eye due to the THE MICROSCOPE AND ITS PARTS. 13 strain caused by an absence of that sharpness and brilliancy characteristic of the image formed by even low-priced American objectives, and in the time . wasted while unconsciouly forming erroneous conclu- sions from objects so imperfectly seen. The writer may be somewhat emphatic on this point, but he knows whereof he speaks, for he began the use of the microscope with French triplets, and em- ployed them for years, because he Was ignorant and had no teacher. What the cost was to him he knows only too well. To the young student who longs for a microscope, I am almost tempted to say, if you cannot afford the cheapest suitable low-power American ob- jective, if you must have the ordinary French triplet or none, take none. It isa hard fate, but is not life itself hard ? Fortunately, however, these inferior com- mercial lenses are not extensively in the market at the present day. Yet the purchaser of a microscope al- ready fitted out with objectives, should inquire if he is buying French triplets. If so, then as his experi- ence, knowledge, and skill increase, so will his dissatis- -faction increase. An intelligent boy had been using these poor lenses for some time, and doing work that, under the circumstances, was commendable, when he for the first time, looked through a good low-power (one-inch) objective. After a momentary examina- tion, he glanced at me in a wondering way as he said: . “How beautifully bright and clear it looks! My mi- croscope is different, I think it needs cleaning !” Modern objectives are the result of the most consum- mate skill of the accomplished optician. There is no chance work in his methods. Every curve is mathe- matically exact, and is calculated and positively known 14 AQUATIC MICROSCOPY FOR BEGINNERS. before the glass comes to the grinding-tool. Objec- tives are usually a combination of several lenses, but the union is not accidentally perfected. The maker’s knowledge of abstruse optical laws tells him the pre- cise result to expect from the combination of lenses of certain forms made from glass of a certain chemical composition. Heis the master; his objective is a masterpiece. The owner of a good objective must not treat it carelessly. He should treasure it, for it is not a common thing. When not on the stand in use, it should be kept in the brass box supplied for that purpose, and it should never be left on the stand when not in actual employment. The part of the brass mounting of the objective which bears the screw is the back; the opposite end which shows a small flat surface of glass is the front, or, as itis often styled, the front lens. The glass of this part is soft and easily scratched; therefore, take care not to let it touch anything hard; especially avoid any gritty substance, or a dirty rag that may hold a minute particle of sand or of hard dust. And never touch it with the fingers, as the oily exudation from the skin will soil it and interfere with the clear- ness and the beauty of the image. I the front lens becomes accidentally stained, or is soiled by long use, the objective should be sent to its- maker, who. can clean it without the great risk that its owner would ex- pose it to if an attempt should be made. to wipe the glass. If fine dust adheres too closely to be dislodged by the breath, ravel out the edge of.a piece .of: very clean old linen or muslin, and with the fringe thus obr. tained gently sweep theisurface. , » If the front lens must be wiped.by the aipandoiee. THE MICROSCOPE AND ITS PARTS. I5 he should use what is called in the trade, Japanese filter-paper, a soft, light, vegetable product from Japan, much employed by dentists, in some of their work, and almost as extensively by advanced micros- copists for drying the fronts of immersion-lenses, or those objectives which are used with a drop of water, of oil, or of some chemical solution between them and the cover-glass over the object. The paper can be bought from the dealers in microscopical supplies. A piece once used should be thrown away. When the objective is to to be taken from its box, unscrew the cover and tip the lens into the ‘palm of the left-hand, supporting it with the fingers; pick it up with the thumb and finger of the right-hand against the sides of the tube or brass mounting, and it will be ready, when reversed, to be screwed to the stand. If it is not to be returned to the box immediately after use, as will often happen if the student has more than one, and he desires to examine the object with an- other power, stand it on its screw-end on the table, and to protect it from dust invert its boxoverit. The latter can be lifted off in a moment, and the objective will then be ready to be picked up as before. What objectives should the beginner select? If possible,.he should have. two, ‘a. low-power and a moderately high magnifying power. If unable to pur- chase both at once, let him by all means first take what is called the one-inch objective; if he,can also buy a high-power, the } or 4 will be the proper glass. But for this he can wait. There is so much to be ex- amined with the one-inch objective, or even by the two- inch, that, for a.long time, he will scarcely feel the need of others. The one-inch, if properly selected, 16 AQUATIC MICROSCOPY FOR BEGINNERS. need not be expensive, but it should be a good and satisfactory glass, not only at the outset, but when the student becomes an expert microscopist; it will thenal- ways be useful. Such objectives are made by several American opticians, and included in what they call their ‘‘Students’ Series.” When in focus, the distance between the front lens and the surface of the object— the ‘‘working-distance’-—is large, and there will therefore be no trouble in using it; and with the two- inch, or the ‘‘A,” eye-piece, the magnifying power will be about forty-five diameters, or a little more than two thousand times. After the student has been using the one-inch ob- jective for some time, and his eye has become edu- cated, he will begin to catch glimpses of minute ob- jects beyond the ability of the low-power glass to ex- hibit properly. Then he will wish for something more, so that he can look deeper into the little things of Nature. What shall it be? The opticians make 4, ~,, and even #,-inch objec- tives, which magnify enormously, cost frightfully, and can be successfully used only by accomplished micros- copists on large and first-class stands. To the be- ginner, even after considerable experience with the low-power lens, any objective higher than the } or 4 will be useless. With either of these glasses he will be well equipped for quite extensive microscopical * study, until he is ready to undertake original work in some unexplored department of science, or in some partly neglected corner, of which there are many in every scientific field, however well cultivated. Like the one-inch, the 4 or the ; will always be useful. As the observer’s eye becomes better educated, THE MICROSCOPE AND ITS PARTS. 17 when it learns, as it will, to see minute parts of deli- cate objects which at the start were entirely over- looked, the high-power objective will not be thrown aside, the student will not become disgusted with it as he would become with a high-power French triplet,. but his quickened sight will again catch glimpses of beauty to be examined, and mystery to be unravelled, which are still beyond the power of his best objective, and he will almost unconsciously have advanced an- other step. Personally the writer prefers the 4-inch objective to the 4, and sucha lens need not be expensive to be good (several opticians’ ‘‘Students’ Series” include them), the working distance is not too short, or need not be, and with the two-inch eye-piece it will give a magnifying power of about two hundred and fifty di- ameters. “The coarse adjustment” is the expression usually applied to the rapid movement of the body produced by turning the large milled-heads, one of which is on each side of the instrument. It is used in focusing, that is, in obtaining a distinct image of the object when seen through the eye-piece and objective. The image then appears surrounded by a disc of light called the ‘Held of view,” or simply ‘‘the field.” Very few, ex- cept the small, vertical ‘‘boys’-microscopes,” and some’ of the cheapest and least desirable Americanor English stands, are without the coarse adjustment. Occasion- ally a stand will be seen in which this part is replaced by a broad, cloth-lined, or tightly-fitting collar, through which the body slides, the movement being made by hand. This is very unsatisfactory, and such stands should be avoided, if possible; as, sooner or later, the 3 18 AQUATIC MICROSCOPY FOR BEGINNERS, body is sure to be suddenly pushed too far down, the objective then coming in contact with the object: an accident to be always guarded against with the great- est care, as the objective, or the object, or both, may be injured. If the object is destroyed it may possibly be replaced, but a scratched or broken objective can beremedied only by buying a new one. Of course, the microscope-body may, by a careless student, be forced against the object by the use of the milled heads, and equally, of course, a man may fill his stomach with gravel-stones or powdered glass; but no sane man will so maltreat that organ, and no sane microscopist will so maltreat his objective as to drive it against the ob- ject on the stage, when the risk is so great. The only proper way to use the coarse adjustment is always to focus upward, When the object to be exam- ined has been placed on the stage, and the light from the mirror is properly arranged, the microscope-body, with the eye-piece and objective, is racked downward by means of the milled heads until the front of the ob- jective almost touches the object, the observer care- fully watching that they do not come in contact. Then place the eye at the eye-piece, and nothing will be visible except the brightly illuminated field of view; “but, while looking into the microscope, slowly raise the body until the image appears sharp and clear, in other words, until the objectis focused. It makes no differ- ence whether the distance between the object and the front lens, when focused, is two inches or the one- hundredth part of one inch, always rack the objective down while you are looking afit, and focus. upward while you are looking ¢hrough it. This is the single rule that must never be forgotten. It has been said THE MICROSCOPE AND ITS PARTS. 19g in a joking way, ‘‘that nothing will throw a microsco= pist into a chill more quickly than to see a friend look into his microscope and focus down with the coarse ad- justment.”” Yet men who should know better have been seen to do this reprehensible thing. In the older instruments a single small milled-head will be found on the front of the body near the lower end, just above the society-screw. In more recent stands it will be on the arm at the back of the instru- ment. This is the ‘‘fine-adjustment screw;’’ and al- though it adds somewhat to the cost, it should always. be on the stand if the purchaser desires to use even moderately high-power objectives. For low-powers it. is not necessary. The fine-adjustment screw is so made that by turning its milled-head the objective, if the adjustment is at the front, or the entire body, if it: is at the back, is slowly raised or lowered. When the high-power objective has been imperfectly focused by racking the body upward, it seldom happens that the image is as distinct as desirable; therefore the microsco- pist, by a few gentle turns of the fine-adjustment screw, raises or lowers the objective, until the magnified image has its outlines as sharply defined as the figures in the best steel engravings. With the one-inch objective, or with others still lower (two, three, or even four- inch) the focus can be accurately obtained by the coarse adjustment alone; but with the 4 or the 4 the fine.adjustment must always be used. A mistake often made by some who should know better, is to try to examine an object not dis- tinctly in focus. In such cases the strain on the eye is severe and injurious, while the pleasure of observing the preparation is much lessened. The changes 20 AQUATIC MICROSCOPY FOR BEGINNERS, made for the better by a few delicate touches of the fine adjustment can be appreciated only when seen. Always try to have the image as distinct as possible. If in doubt as to the focus, after obtaining what seems to be a moderately good appearance, give the fine adjustment a turn or two one way or the other, noticing whether the image become sharper in outline and clearer in its general aspect, or whether it grows cloudy and indistinct. If the'last, the focus has not been improved, and was probably correct at first. A little experience will make the beginner an expert in this important matter. The stage, on all but the largest and most expensive instriiments,. is a square or a circular piece of thin metal, with a large central circular opening for the passage of the light from the mirror. Sometimes the metal stage has a glass plate made to slide over it easily. This is a convenience and a desirable luxury, but it is by no means necessary. The strip of glass that bears the object to be examined can just as -readily be slipped about under the objective by the fingers directly, as it can be if supported on this movable glass stage. These finger movements require a little practice, but the student will so soon become accustomed to them that he will change the position of the object without consciously thinking of the act, and his touch will become so delicate that he . will be able, with the slightest pressure, to move the object for a distance so small that it would be invisible to the naked eye. All this is rather awkward at first, because the object must be moved while the eye is looking through the microscope; and, in addition, if it is to be pushed to what appears to be the left-hand THE MICROSCOPE AND ITS PARTS. 21 side of the field of view, it must actually be pulled towards the observer’s right-hand; and if the image is to travel up the field, that is, away from the observer as he sits at the microscope, the object must be really slipped towards him, because the lenses reverse the image. This seems a very complicated proceeding, but it soon becomes the easiest thing imaginable. At the first trial the object will be sure to leap entirely out of the field, because it will be too rapidly moved, and the motion is magnified as well as the object; but the student will become so expert that before long he will be able to make with fine needles, on the stage of his microscope, complicated dissections of the internal organs of the house-fly, or of some other equally small insect. The stage will probably have two springs on the upper surface, one on each side. ‘These’ ‘‘spring clips” are to keep in position the glass slide holding the object, unless intentionally moved. ‘The slide is put under the clips, and the object, provided it is itself stationary, will remain in the field, where it can be examined quietly and comfortably. The diaphragm should always be present. It will be pierced, near the edge, with a serious of openings of various sizes, to modify the amount of light thrown on the object, the largest opening admitting the greatest amount. The beginner will at first be disposed to use too much light; indeed this is a fault of many older microscopists. More can be seen with a moderately lighted field than when the eye is dazzled and half blinded by a fierce glare. Such a blaze is objection- able, not only because it tends to obscure the finer parts of the object, but it may lead the student or his 22 AQUATIC MICROSCOPY FOR BEGINNERS. friends to condemn the microscope as injurious to the sight—an unjust accusation more than once made... If too much light is undesirable, do not go to the opposite extreme and strain the eye by forcing it to work in semi-darkness. Keep the field sufficiently lighted to be pleasant to the sight. Turn the diaphragm until the opening giving the most agreeable effect, and illuminating the object enough to show the parts clearly, is under the center of the stage open- ing. If the object is very thick or opaque, more light will be needed than if it were perfectly transparent; in such cases use a larger diaphragm opening. The mirror is one of the most important parts of the stand. It should have botha concave and a plane surface, and ought not to be less than two inches in diameter, so that it may reflect enough light and be easily handled. In the newest styles of stands the mirror is arranged to swing from side to side, so as to effect oblique illumination of the object, as well as to rise above the stage, so that light may be reflected down upon an opaque specimen, since it is used below the stage for the illumination of transparent sub- stances only. This swinging arrangement is con- venient, and should be had if possible. It is, how- ever, not absolutely necessary, as similar illumination of opaque bodies can be obtained by the ‘‘bull’s-eye condensing lens,” a rather expensive piece of appara- tus, and somewhat difficult to manipulate successfully. But as the newest and best stands ‘have the swinging mirror, the condensing lens need not be described, especially since the beginner will not care to examine many opaque objects that will demand stronger illumination than that of ordinary diffused daylight or common lamplight. THE MICROSCOPE AND ITS PARTS. 23 When ready to examine an object, the stand is placed near the window, or, if at night, the lighted lamp is stood near the instrument on the left-hand side and one or two inches in front of the mirror, and the objective is screwed on. The microscope is inclined at a convenient angle; the mirror is moved in various directions, until the light is reflected from a white cloud, if possible, or from the lamp, to the front of the objective, where it can be easily seen. The eye is then placed at the eye-piece, and if the field is imperfectly lighted, as it probably will be, perhaps one-half of it being in shadow, or only a faint trace of light visible at one side, the mirror is slowly moved until the field is brightly and evenly illuminated, when every part of the circular bright space within the instument is as well lighted as every other part. The position of the diaphragm is then changed, to be further altered, if necessary, after the object has been placed on the stage. This even illumination may at first be a little troublesome to obtain, but as in so many other actions in connection with the microscope, a very little practice will overcome every difficulty. The fingers are soon taught; they speedily do their work without their owner’s conscious bidding. The specimen to be studied may be permanently preserved, or ‘‘mounted,” ona slip of glass, under a thin cover and surrounded by Canada balsam, glycer- ine, or some other preservative, thus forming prepara- tions called ‘‘slides,” or ‘‘mounted slides,” the plain piece of glass without the object being a ‘‘slip.” The addition of the object therefore changes the slip intoa slide. It is well to remember this distinction in talk- ing with the dealers or in sending orders by mail. 24 AQUATIC MICROSCOPY FOR BEGINNERS. Slides can be made by the student, although to do the work neatly and well demands some skill, and con- siderable preliminary study of the object before it can be prepared for the mounting processes; or the slides may be purchased. Itis much better and, in the end, more satisfactory to the owner of the slides to prepare them himself. Certain rare objects, if desired, must be bought already mounted, but any small object natur- ally dry can be so easily preserved by placing it ina drop of Canada balsam from the druggist’s, and cover- ing it by a circle or a square of thin glass from the op- tician’s, that for the beginner to spend his money for “the foot of a fly,” ‘‘dust from a butterfly’s wing,” “the sting of a bee,” or similar slides crowding the dealers’ lists and drawers, is nonsense, unless he lives alone in the wilderness, and is ignorant of the appear- ance of a slide; in such a case, to buy the mounted foot of a fly may be useful to show what is to be aimed at in the preparation of ordinary objects. A few properly mounted slides, however, usually accompany the stand as specimens, or the dealer will supply them if asked. It is better todo than to buy, and so much has been written on the subject of microscopic mount- ing, and indeed all advanced workers with the micro- scope are such ‘‘good fellows,” and are always so generous in giving away for the asking information that has cost much time and labor to obtain, that the young student need never despair, nor be at a loss as to where to go for help, if he possess the name and the address of some microscopist, and a postage-stamp or two. Cheap little hand-books on the subject are accessible, microscopists are numerous and willing, so why should the beginner ever be discouraged? and why should he buy what he can make? THE MICROSCOPE AND ITS PARTS. 25 It always adds a zest to this work if the worker can make his own tools, and especially if he can prepare his own objects. Almost every tool needed at the be- ginning can be made at home. Slides must be made at home if one desires to examine any of the endless variety of invisible animal and vegetable life with which the great world teems. All the objects referred to in this book can be studied when only temporarily mounted; indeed, no method of preserving some of them has yet been discovered or invented. They must, therefore, be studied alive or not at all. And for the beginner this is not only the easiest, but it is the most instructive and inspiring way. Some things can be examined when dry. Such an object is simply laid on a slip, placed under the spring clips, and the low-power objective used. The ripe seeds of wild plants are easily studied in this way, and some of them are marvellously beautiful. Small insects can also be looked at when dry, but the result ’ is not always entirely satisfactory unless they are viewed as opaque objects. Usually most objects appear better and show more of their structure, if ex- amined under a disk of thin glass and surrounded by water. But seeds, scales from butterfly’s wings, and many other things, can be viewed and preserved in a dry state by enclosing them in a cell with a thin- glass cover fastened above. This ‘‘cell” and ‘‘cover”’ and fastening process will be described presently. All plants and animals living in water must be examined in water. To dry them and expect to learn anything about them, or even to obtain a correct idea of their true appearance, is a waste of time, and worse. When your wet specimens get dry on the slide, and 26 AQUATIC MICROSCOPY FOR BEGINNERS, you think you are seeing some wonderful things, add a drop of water and save yourself a probable blunder. Certain objects, naturally dry, will look better and will reveal their secrets sooner if examined wet. This is due to optical reasons not necessary to explain here. The observer, if he is seeking information, and not merely pretty things to please the eye and the esthetic fancy, will do well if he examine naturally dry objects both in and out of water; but things naturally wet must never be seriously studied in a dry condition. The most convenient size for glass slips is three inches in length by onein width. Some microscopists use and recommend them two and one-half inches long by one-half an inch wide, and this will probably be the size of the slides accompanying the student's stand. They are however, much too small; it will be better for the beginner at once to select. the standard size, three inches by one inch. These can be bought, and the writer would advise that they should be, as the edges will then be ground smooth and perhaps polished, although the polish is not necessary. Slips can be cheaply cut by any glass-dealer who has a dia- mond or a glass-cutting wheel, and if thus made, the best, whitest, smoothest, and thinnest glass should be selected. The rough edges of these home-made slips, however, are not pleasant to handle, the student who uses them taking the risk of cut fingers. Otherwise, unless they have a green color, they are as useful as the more expensive ones sold by the dealers. A drop of water on a slip of smooth glass is not easily kept in position. When the slide is placed on the stage, and the microscope is inclined for use, as it always should be, the water will surely run away, and THE MICROSCOPE AND ITS PARTS. 27 probably carry the object with it. If the microscope is not inclined, the convex surface of the drop, and its tremulous movements, will so affect the light that the image will be distorted, and the observer will obtain erroneous impressions. A piece of glass placed over the water will flatten the surface, the distortion of the image will be partly counteracted, and capillary attraction will keep the liquid from entirely running away. But ordinary glass is too thick for this purpose; consequently thin glass prepared for microscopical use must be purchased. This varies from No.1, measur- ing about ;4, to gf, inch in thickness, or thinner; No. 2, about ;4,; and No. 3, from #5 to; inch. No. 2 glass will be:the proper thickness. It can be obtained either in circles of various sizes or in squares. For permanent mounts the circles are usually employed. For temporary purposes, for the examination of an ob- ject not to be preserved for future use, or when many examinations of separated parts of the same large specimen are to be made, the writer much prefers thin squares, andalwaysusesthem. They are pleasanter to handle, they are more easily wiped dry and with less liability to breakage, and their cost is somewhat less than circles of the same thickness. The matter of cleaning this thin glass is an import- ant one, and unless the ‘‘knack” is soon learned, the beginner will be surprised at the rapidity with which his covers will disappear. This skill, however, is readily attained. The writer has had the same thin square of No. 1 glass in use for three months contin- uously, frequently removing and reapplying it during the five or six hours of daily evening work in which it did important service, and in the end he became quite 28 AQUATIC MICROSCOPY FOR BEGINNERS. attached to it as to a good friend. But a hasty move while cleaning it, or a little undue pressure, finally sent iton the way that thin covers often travel. To clean such glass without much risk of breaking, take the square with two opposite edges, that is, with the edges where the glass was cut, between the thumb and finger of the left-hand, and with a piece of soft, old muslin held smoothly over the thumb and fore- finger of the right-hand, gently wipe both surfaces at once, rotating the square when necessary. The se- cret of success is care, gentleness, and no wrinkles, It was probably a wrinkle in the muslin that ruined my three months’ old pet cover. But a punishment is a good thing sometimes; the microscopist who should begin to think that he was skillful enough to avoid breakage of covers for more than three months, might become insufferably conceited anda nuisance to his friends. But a glass square, however thin, dropped on a deli- cate animal or plant is likely to crush it, and to de- stroy all resemblance to anything that ever lived. Some means must be devised for supporting it at a short distance above the slip, so that the living creatures may have room to move about, and the plants may not be too much flattened. This is done by making a ring of cement on the slip, and thus en- closing a circular space called a ced/, which ‘can be made of any depth by applying more cement after the first application has dried, or by freely using a thick cement. The opticians offer several preparations of the kind for sale, all of which are useful for special purposes; but the one that seems most convenient, the one that THE MICROSCOPE AND ITS PARTS, 29 can be easily prepared by the novice, is simply shellac dissolved in alcohol. The solution can be made as thick as is desired by allowing some of the alcohol to evaporate, or it can be thinned by the addition of more. It should be thick enough to flow freely from a small camel’s-hair brush, but not so thin as to spread in an irregular film over the glass. As shellac dis- solves slowly in alcohol, it is better to add more of the latter than will be needed, and to thicken the solution by evaporation. It will keep for any length of time in a tightly closed bottle. A ring can be built up with a camel’s-hair brush, and this cement, either by the hand alone, or by a little machine called a ‘‘turn-table,” manufactured for the purpose. ‘These turn-tables are as nice and neat and beautiful as can be imagined, and they cost—the cheapest that I can find in the catalogues costs $2.50. They spin perfect circles exactly in the center of the slip, and the result is pretty and desirable if the be- ginner can afford one, but he can get along right well without. If you have none, draw in the center of a strip of white pasteboard the size of a slip, a circle in black ink, and use it as a guideto the brush with which you make the ring after the slip is laid on the pasteboard. Of course, the hand cannot be so steady asa flat disk rapidly rotating on central pivot, and the circles will not be so perfect, but they will be practically as useful. To get the inked circle in the center of the paper, draw a lead-pencil line diagonally across the parallel- ogram, from each upper corner to the opposite lower one, and use the point at which the two lines intersect as the center of the circle. The glass slip can be kept 30 AQUATIC MICROSCOPY FOR BEGINNERS. in better position, and the whole can be turned about, if the pasteboard is fastened to a strip of wood, anda small pin is driven into each corner. When the ring ismade, put the slip ina warm place until the cement is hard, or hold it over the lamp-flame for a few mo- ments at a time, taking care not to allow the shellac to boil, or the bubbles will never disappear and the ring will be weakened. These lamp-dried rings are hard as soon as cold, and they adhere so firmly that they can only be scraped off with a knife and hard work. They have the further advantage of being rapidly made. A deeper and perhaps a somewhat neater cell can be formed from paper. Cut a circular disk, of the di- ameter of the ring required, from porous paper as thick as the depth of the desired cell, and from the center cut out a smaller disk, thus leaving a narrow ring. Soak this ring in thin shellac cement untilits pores are filled with the liquid, and hang it ona pin in a warm place to dry. Several can be prepared at once, and of different size and thickness. They are to be fastened to the slip by touching one side with alittle shellac and pressing the glass on it and allowing it to dry; or by gently heating the slip and the ring together over the lamp. It is well to prepare several slips at one time, so as to have them ready for an emergency, as, for in- stance, after an excellent gathering of microscopical material has been made, and the student is so anxious to see what he has that he cannot take time to clean the slide and cover after a hasty glance for rarities, but must have another ready at a moment’s notice. To mount dry objects, permanently, such as pollen, seeds, scales from insect-wings, and other things suita- THE MICROSCOPE AND ITS PARTS. 31 ble for this method of preservation, arrange the speci- men in the cell, place the cover over it—(preferably a circle in this case), the diameter of the cell being alit- tle greater than that of the cover, so that the cement may project a short distance beyond the edges of the thin glass, and with a camel’s-hair brush paint a thin layer of shellac over the place where the cover and ring meet. There should be but little cement on the brush for the first coat, because if too much is used, or if too thin, it will probably run into the cell by capil- lary attraction and spoil the object. This is the one great trouble in all microscopical mounting. But after the first coat is dry another is to be added, and re- peated until the cover is firmly fastened to the ring. ‘‘Brown’s Rubber Cement,” for sale by the dealers, is useful for this purpose, as it is very fluid, dries with great rapidity, and has little tendency to ‘‘run under.” The cell having been made, the object is to be placed within it in a drop of water, the thin cover dropped over it, and the preparation will then be ready for examination. But how is this minute, gen- erally invisible object to be got into the cell? A glass tube about one-tenth inch in inside diameter, and as long as may be convenient, several needles in wooden ’ handles, and a camel’s-hair brush with a small smooth stick thrust into the quill, will be needed. The needles are used for spreading any small mass evenly over the cell, and in disentangling and arrang- ing the parts of any comparatively large object, as well as for lifting the thin cover from the cell so that it can be easily seized by the fingers, or for tilting it up in the box, where the thin squares should always be kept. Fresh-water Alge (Chapter III.), for instance, 32 AQUATIC MICROSCOPY FOR BEGINNERS. found so abundantly in almost all still water, where they often form delicate green clouds, or thread-like streamers adhering to other plants, dead leaves, or waterlogged sticks, are almost sure to be transferred to the slip in a heaped and tangled mass, which only two needles with gently persuasive movements can straighten out for microscopic study. If an attempt is made to examine such a confused heap, the thin cover cannot be forced to lie flat without crushing the delicate specimen, and if the cover is tilted the objective cannot be properly focused. To make these useful tools, with pliers thrust fine needles head first into parlor-matches, after the phos- phorous ends have been cut off. These round sticks make handles convenient in length and pleasant to use. It is well to have half a dozen or more of these needle- bearing matches lying where they can be picked up whenever wanted. If the student desires to dissect insects, nothing can beso useful for cutting and tear- ing minute parts, and for separating delicate tissues or organs as fine needles. No knives have been made to equal them for this purpose. The glass tube is the ‘‘dipping-tube.” It is really one of the most important little pieces of apparatus that the microscopist can have on his table, if he in- tends to study aquatic life. With it he can pick up any small object that may be visible in the water, transfer any selected matters to the slip, or make the dip that is made by faith, with the assurance that al- though the tube may seem to be filled with water only, it will be pretty sure to have captured something in- teresting, novel, or beautiful. He can. fill the tube with water and allow it to escape in a miniature tor- THE MICROSCOPE AND ITS PARTS. 33 rent, or drop by drop; and he can allow a drop to en- ter or a drop to flow slowly out at his will. Some workers prefer a tube witha hollow rubber-bulb at- tached, by which the water and contained objects are drawn up by the expanding ball, and forced out by its compression. The writer is prepossessed in favor of the simple tube, as it is less complicated, more easily cleaned, and its-contents are more completely under control. To use it, place the tip of the forefinger firmly over upper end, and dip the lower into the water above and near the object desired: lift the finger, and the water will rush in until it is level with that on the outside; close the upper end again, remove the tube, and the water will remain in place as long as the finger stops the upper opening; remove the finger and the water will at once flow out. By the proper regulation of the pressure and of the finger movements, the water can be made to escape drop by drop, or in a sudden rush. In this way any small aquatic object can be easily transferred to the slip, and as readily washed off by a ‘sudden outward flow from a full tube. If the object descends too slowly, rotating the tube will hasten it. Until recently I supposed this little affair was com- mon property, and that the principle on which it acts was understood by everybody. But when I called on a gentleman, a member of a scientific society, to ob- tain some water in which certain plants were growing, he’ expressed surprise at the performance, and called his wife to witness a new and curious method of taking up water with nothing but a glass tube and one finger. His astonishment was amusing; but how much more so was that of a druggist who had a teaspoonful of de- 4 34 AQUATIC MICROSCOPY FOR BEGINNERS. posit at the bottom of a conical glass vessel with a quart of water above it, and who, after running about for bottles and jars to hold this water, which he thought - must be poured off, returned to find the deposit re- moved, and in a small phial in my pocket, the quart of water remaining undisturbed, ‘‘Why,” he said, ‘‘that is strange. I never saw the like. How did you do it?” It is often convenient to have several dipping-tubes, some straight, others drawn out to a point, and some curved so as to be readily directed -into a narrow cor- ner. A glass tube is easily pulled out toa fine ex- tremity or variously curved, when softened in an alco- hol flame. Buta spirit-lamp may not always be with- in reach, and is not necessary, for the student can make a Bunsen burner almost without cost, and use it successfully if his home is supplied with illuminating gas. Prof. Austin C. Apgar, in Science News and Bos- ton Journal of Chemistry, has, under the title ‘‘A Bun- sen burner for two cents,” recently described a simple piece of apparatus that is a boon to any one desiring to doa little amateur glass-blowing. A strip of tin about six inches long and two wide is rolled, without solder or fastening of any kind, into a tube about half an inch in diameter, after two holes, each about one- fourth inch in diameter, have been punched so that they shall be on opposite sides of the tube, and high enough to be ashort distance above the tip of the gas- burner. This simple arrangement is forced over the ordinary burner, so that the holes are just above the tip, the elasticity of the tube holding it in place; the gas is lighted at the upper end, where it burns without smoke and gives a strong heat, the flame being easily THE MICROSCOPE AND ITS PARTS. 35 regulated, and, with ordinary care, not flashing into the tube. It is entirely successful. Evaporation of the water will take place from be- neath the thin cover, sometimes rapidly, and the ob- server will at first be surprised at the way in which his objects will be swept out of the field before an advanc- ing wave that leaves the glass nearly dry behind it. The water in the cell is drying up, and a fresh supply must be added if the objects are not to be entirely lost. Here is another advantage in using square covers on circular cells. The four corners project beyond the cement ring, and by applying the camel’s-hair brush, wet with water, to the slide beneath any one of these projections, the drop will run in and fill the cell by capillary attraction. This supply is much more easily added than if circular covers are used, and aftera little experience the fresh drops can be applied while the eye is at the eye-piece, the hand alone guiding the wet pencil, and the eye taking note of the rush of the incoming wave and of the effect. The student will soon become such an adept that he will be able to add so small a supply at each touch of the wet brush that the movement of the capillary wave will not be strong enough to float the object out of the field. But it often happens that a certain specimen is to be studied for a long time, a whole evening, for instance; but to be continually supplying the water lost by evap- oration is not convenient—the student often becoming so absorbed that he forgets this one of Nature’s laws until he suffers the penalty, and probably loses his object. At such a time an arrangement is wanted for supplying fresh water continuously and without de- manding much attention, and such a contrivance is 36 AQUATIC MICROSCOPY FOR BEGINNERS, easily made. With a triangular file cut one of the smallest homeopathic phials in two, throw away the Le] Fig. 3.—A Growing-slide. upper half, and cement the lower to a little oblong or square piece of ordinary glass or to a broken slip. At- tach this to the slide by a drop of glycerine, taking care not to use too much or the square will glide out of place when inclined. Fill the bottle with water, coil into it one end of a doubled, loosely twisted thread of sewing-cotton, and place the other end in contact with one side of the cover, as shown in zg. 3. The water will pass down the thread to one edge of the cell, where it will flow under as it evaporates from the other three sides. This usually works well, the secret of success being to have the reservoir not more than three-quarters of an inch from the cell, to keep it al- ways full of water, and to have the doubled thread ap- plied closely against the edge of the cover. If the water-supply is too great, and the cell is therefore dis- posed to overflow, shorten the end of the thread against the cover; if not enough, lengthen the thread, and do not allow it to touch the slide in its course from the reservoir to the cell. Again, the observer will frequently want to make a growing-cell of the slide on which he may accidentally have placed a desirable or a beautiful object; that is, he desires to preserve the specimen for several days in THE MICROSCOPE AND ITS PARTS. 37 the cell without disturbing it, and so taking the risk of losing the invisible thing. He may also wish to watch its growth and development. A reservoir for a water- supply is necessary; an ‘‘individual”’ butter-dish makes a good one. Place the slide across the dish, apply a doubled thread of sewing-cotton along one side of the square cover, so that each end shall hang down into the dish, and fill the latter with water, which will then pass up along the thread, and keep the cell full for as long as may be desired. The only objection to this little affair is that, after a few days’ use, the salts in the water will crystallize on the cover, and so pre- vent the absorption of oxygen from the air. But no growing-cell is free from some objectionable features; none can quite imitate natural conditions, and the animal or plant dies before long, either falling to pieces, or becoming buried beneath a mass of fungi. This form will supply an abundance of water, if the water in the dish is always kept in contact with the lower surface of the slide. This, and the absolute con- tact of the thread with the edge of the cover, are the only things whose absence will result in defeat. As the reader already understands, the object must never be examined in water without being covered by either a thin-glass circle or square; the importance of this little piece of crystal must not be forgotten. But often, in lowering it over the wet specimen, small bubbles of air will be caught and not noticed until magnified, when, if seen for the first time, they appear wonderful, if not startling. Some strange statements have been made and discoveries announced whose only foundation has been minute air-bubbles which the ob- server did not recognize. A man once described a 38 AQUATIC MICROSCOPY FOR BEGINNERS, marvellous something that he had found ina cancer, which turned out to be a magnified air-bubble. These little air-drops often play an amusing part at the beginning of the micros- copist’s career. In /¥e. 4 are shown several of different sizes. Let the student examine a drop of saliva or of soapsuds, and he will in future be able to recognize the troublesome things. Pictures or words cannot convey so true an idea of their appearance as a single sight of the bubbles them- selves, At times they become entangled in the parts of an object in such numbers as to interfere with its examination. In these cases nothing can be done ex- cept to lift the cover on the point of the needle, and slowly lower it, or remove it entirely, add more water, and reapply it carefully. In appearance the bubbles are usually circular, with a broad black border which varies in width and depth of color as the objective is raised or lowered. Near the margin is a bright ring, and in the center a bright spot. They often float about, and this movement adds much to the wonder with which the novice usually regards them. Tf the student will have a note-book in which to jot down his observations, or to keep a list of the objects examined, it will not only aid him in forming habits of accurate observation, but will be of great interest when he has become an accomplished microscopist. The entry may be simple, and may be made to serve as a memorandum of items to refesh the memory. Here is an example from a boy’s note-book: ‘‘June 15, 1884—Came across a pool .near the toll-gate with the Fig. 4.—Air-bubbles, ‘THE MICROSCOPE AND ITS PARTS. 39 water colored green, and found the color was caused by a great quantity of Volvox—small green globes rolling about in the water. Volvox is said to be a plant. Wonder if itis? What are the darker balls inside of some of them?” He answered all these queries later in his experience. If you can draw the microscopic objects that interest you most, although the sketches may not be artistic they will help you to remember, and a collec- tion of such drawings will be as interesting and valuable as a note-book. In talking to friends about microscopic matters, a,single rough sketch will do more to help them understand than many words. And if you can look at the object and make the sketch, you will like it better and do yourself more good than if you bought and used the drawing apparatus called a camera lucida, for sale by the dealers. This camera lucida is a glass prism, so arranged that when it is put over the eye-piece, and the microscope is placed in a -horizontal or inclined position, the magnified image seems to be projected on a sheet of paper spread on the table just under the camera, but of course with a space of several inches between them. By placing the eye in the proper position, and looking down towards the table through the edge of the prism, the image and the pencil-point can both be seen at once and the outlines traced. It is a rather expensive apparatus, and difficult to use without a good deal of practice, but if the reader wants a simple arrangement that can be made by him- self let him try the one shown in Fig. 5. From a piece of thin sheet-brass or tin, cut with scissors a strip half an inch wide and long enough for 40 AQUATIC MICROSCOPY FOR BEGINNERS. one end to pass ardund the upper part of the eye-piece, and the other to be bent into a handle like a small , hollow square. Cut another strip about one inch long and one- fourth inch wide, and double it (| a length-wise so that it will still be- an inch long, but only one-eighth SA of an inch broad. Take one of eS the small brass hinges to be a had for a cent,-solder one end Drawing the Magni to the hollow handle and the eee other to the narrow doubled strip; into this narrow piece place a thin-glass square, the thinner the better, and the instrument is done. To use it, turn the microscope horizontal, have a faint light on the object and a strong one on the paper, bend the strip of brass around the upper part of the eye-piece so it will not slip, the hollow handle and hinge being directed toward the table, and move the hinge until the thin cover is placed obliquely in front of the eye-glass of the eye-piece. .Look down through the glass square toward the paper on the table, and the image of the object on the stage will seem to be thrown on the white surface, where it can be traced with a pencil. The image is really reflected from the surface of the thin square, and the pencil is seen through it, but the eye unconsciously combines the two so that both are seen together. The secret of success here is a faint light on the object, a strong one on the paper, and a ¢im glass square. A long sharp pencil-point is also an advantage. . A micrometer is for measuring objects under the microscope. It is made by ruling a number of short THE MICROSCOPE AND ITS PARTS. 41 lines on glass, the spaces between the lines varying from 45 to zg@yy inch or less. Micrometers are said to have been ruled with one million lines to the inch, but the human eye using the best and highest-power objectives has never seen them and never will. All micrometers are prepared by a ruling machine made for the purpose. They are of two kinds, the stage- - micrometer and the eye-piece micrometer. The beginner will not need a micrometer of either kind, but he may desire to know how to use them, Place the stage-micrometer on the stage, turn the micro- scope horizontal, with the reflector referred to above fitted to the eye-piece. With the low-power objective focus the lines that are 4, inchapart, and draw them on the paper. Do the same with every objective, draw- ing the 5,455 inch spaces with the 4 or the 4 inch lenses. These drawings will form the scale for measuring the drawings of the magnified objects. Thus, if the magnified object, when drawn, occupies two spaces of your paper scale made from the 74, inch micrometer spaces, the object will measure 72,5, or 5 inch in length; if five spaces of your scale, then it will measure ;5,, or s', inch long; if only one-half a space of your scale, then it will measure one-half of =}; of an inch; if one-fourth of your scale space, then its actual length will be ;4, inch. If the 4 or the 4 inch objective is used in making your scale from the 7, inch micrometer spaces, then each division on the paper will represent 5,45 inch, and if the drawing of the object measures two of these spaces on your scale, the real length of the object will be zy, inch, or sty. It is perceived that the stage micrometer cannot be used for measuring objects 42 AQUATIC MICROSCOPY FOR BEGINNERS. directly, but only by applying the drawing of the magnified micrometer spaces to the drawing of the magnified object. The eye-piece micrometer is a glass disk of such a size as to slip into the eye-piece mounting and rest on the diaphragm always found there. The glass is ruled in groups of parallel lines, the value of whose spaces must be ascertained by the use of the stage-microme- ter. . : With the latter on_the stage and focused, place the eye-piece, carrying its micrometer, in the body-tube and rotate it until the lines on both micrometers are parallel. Count the number of spaces on the eye- piece micrometer needed to fill exactly a single space on the stage micrometer, and divide the known value of that space by the number of spaces in the eye-piéce micrometer needed to fill it, and the quotient will be the value of a single spacé of the eye-piece microme- ter. Thus, if three spaces of the ocular micrometer fill one of the ;74 inch spaces of the stage-microme- ter, then each space on the former represents soor inch. This process must be repeated with every ob- jective, and the ocular micrometer must always be used in the same eye-piece. With this, the object may be measured directly, by counting the number of spaces it occupies in the ocu- lar micrometer, and multiplying the ascertained value of each space by that number. Thus an object just filling three of the sg45 inch spaces of the eye-piece micrometer would be 3,34 or zq4pq inch in length. The stage-micrometer can also be used to ascertain the power of the microscope. If eachof the 74, inch spaces measures, when drawn on the paper, +5 inch, THE MICROSCOPE AND ITS PARTS. 43 that combination of eye-piece and objective will have a magnifying power of ten diameters; if each ;4, inch micrometer-space measures ;4, inch, the power will be forty diameters; each, therefore, corresponds to ten times. Ifthe =)45 inch micrometer-spaces measure, when drawn,.74 inch, then each tenth corresponds to a power of one hundred times; therefore, if the 4, inch spaces, when magnified, measure ten-tenths, the power of that eye-piece and objective is of course one thousand diameters, or ten times one hundred; if five- tenths, then five times one hundred. The owner of a microscope should never take a walk in the country without one or two wide-mouthed bot- tles in his pocket. Empty morphia bottles, to be had of any druggist, are convenient for small collections; for greater quantities an empty quinine bottle, and for still larger gatherings of aquatic plants the ordinary glass fruit-jar is admirable if a string is added fora handle. No bottle should be entirely filled and corked, or all animal life will be animal death before the microscope is reached. Leave a large space for air between the cork and the water. . Those desiring information as to the optical construc- tion of the compound microscope, the uses of the numer- ous pieces of apparatus often seen for advanced work, and about the methods of permanently mounting mi- croscopic objects, may advantageously consult the fol- lowing publications: ‘‘How to Use the Microscope,” by John Phin; 16mo., New York.—‘‘How to See with the Microscope,” by Dr. J. E. Smith; r2mo., Chicago,— ‘How to Work with the Microscope,” by Dr. Lionel 5S. Beale; 8vo., London.—Carpenter’s ‘‘The Microscope and its Revelations,” edited by Dallinger; 9th edition, 44 AQUATIC MICROSCOPY FOR BEGINNERS. 8vo., London.—Griffith and Henfrey’s ‘‘Micrographic Dictionary,” 4th edition, 8vo., London. — ‘‘Micro- scopical Praxis, or Simple Methods of Ascertaining the Properties of Various Microscopical Accessories,”’ by Dr. Alfred C. Stokes; rzmo., Portland, Conn.— “‘Manipulation of the Microscope,” by Edward Bausch; 2nd edition, 1r6mo., Rochester, N. Y.—‘‘ The History of a Slide,” by Dr. F. L. James; 8vo., St. Louis, Mo. —‘‘Le Microscope,” by Dr. Henri Van Heurck; 4th edition, 8vo., Antwerp. (An English translation is published in London.)—‘‘Vhe Observer,” an. illustra- ted monthly magazine; Portland, Conn.——‘‘The Mi- croscopical Bulletin,’ a bi-monthly illustrated maga- zine; Philadelphia.-—‘‘Journal of the New-York Micro- scopical Society;” quarterly, New York. AQUATIC PLANTS USEFUL TO THE MICROSCOPIS‘’. 45 CHAPTER II. COMMON AQUATIC PLANTS USEFUL TO THE MICROS- COPIST, Ranunculus. —Nymphza. —Myriophyllum. —Utricularia. —Cerato- phyllum.—Lémna, —Anacharis.—Vallisnéria. —Sphagnum,—Ric- cia, There are several common plants floating freely in the water, or more or less firmly rooted in the mud at the bottom of shallow ponds and of slowly flowing streams, that are important to the student of micro- scopic aquatic life. This may be either through their own interesting or peculiar structure, or on account of the minute plants and animals living among their tan- gled leaves or attached to the stem and other parts, these entangled objects being, therefore, more easily and surely captured by transferring the larger visible growths to a small vessel of water than in any other way. Most of these aquatic plants have their leaves divided into fine, thread-like leaflets. They have “‘dissected leaves,’’ as the botanist names them, and these filamentous leaflets become favorite resorts for invisible animals which attach themselves to the nar- row divisions, and feed on the free-swimming kinds that likewise find the same places attractive. So, if the student desires to gather microscopic material, let him find any of the following plants and he will be pretty sure to get what he wants. 46 AQUATIC MICROSCOPY FOR BEGINNERS, But he should remember that by lifting them out of the water many of the slightly adherent creatures which he most: desires, will be washed away. The plants should be slowly and carefully drawn to the shore, and lifted out in a tin dipper and poured into a wide-mouthed bottle. The small tin dipper will prove a convenient implement for all kinds of microscopical collecting, as a handle of any length can be made by © thrusting a stick into the hollow handle of the vessel. If the latter, however, is not accessible, the plants may be gently pushed into the bottle, after it has been partly submerged so thatit lies parallel-with the sur- face of the water. , Many of our. most abundant aquatic plants have no common English names, probably because most of them bear the smallest and least showy flowers of all blooming plants, and for that reason fail to attract the attention of the ordinary observer. In referring to them, the beginner must use the scientific names, or learn the meaning of the Latin words and use the translation, usually with awkward results. It sounds better and is quite as easy to speak of Myriophyllum as of the ‘‘thousand-leaved plant,” which the word means. Many plants might be styled thousand-leaved, another common aquatic one, for instance, which often grows in the same pond with Myriophyllum, the Ceratophyllum, called ‘‘hornwort” because the leaves are rather stiff and horny; and Zémua, as a word, is prettier and more appropriate than ‘‘duckweed,” an ugly term and mean- ingless, because ducks have nothing to do with the plant. If the reader is not already familiar with the appear- ance of the following forms, he need have no trouble AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 47 in recognizing them, nor in learning their names, al- though he may never have studied botany; he has only to compare the leaves with the figures in this chapter. It is, of course, understood that there are many aquatic plants not here referred to, only those being included in this list which afford the most certain sup- ply of microscopic life. The leaves of many water- plants fall against the stem and cling together when lifted into the air; but if the student will place a small part of the plant in a saucer (‘‘individual butter” dishes are good for this purpose), he can float them out against the white surface and so compare them with the figures. RANUNCULUS AQUATILIS (Fig. 6). A part of the stem and a single leaf of this plant are shown about natural size in the figure (Fig. 6). It is not uncommon in ponds and slowly flowing streams. The leaves are dissected into fine, rather stiff and hair-like parts, to which Z many minute animals, FF é suchas Rotifers (Chapter VIII.), Vorticellas (Chap- ter V.), and Stentors (Chapter V.) are fond of attaching themselves. The leaves are placed above each other on opposite sides of the long and rather brittle Fig. 6.—Leaf of Rantinculus aquatilis. stem, and usually rather s wide apart. The whole plant is under water ex- cept at flowering time, when it raises a delicate stalk 48 AQUATIC, MICROSCOPY FOR BEGINNERS. above the surface, and blooms with a single white flower closely resembling the common yellow ‘‘butter- cup” of the fields. NYMPHAA ODORATA (WHITE WaTER-LILY, Fig. 7). Every one is familiar with this beautiful flower, that “marvel of bloom and grace,” and with its large, al- most circular, floating leaves. It is to the under-sur- face of these leaves that the microscopist often goes for several forms of case-building Rotifers, with the certainty of always finding them, together with many and various kinds of minute animal life. Its likewise an excellent place to search for aquatic worms. You will usually capture these creatures if the lower surface ‘is gently scraped and the dark mass obtained examined in water. But if the scented blossom is beautiful to the ordi- nary observer, the interior of the flower-stems and leaf-stalks has charms known only to the microscopist. Cut a thin slice from either of those parts and examine it. The sides of the wide openings made by cutting across the internal tubes are studded with crystalline stars (Fig. 7). Three- pointed, four and _five- pointed, they sparkle there Fig. 7:=Feduncle-of Nymphaea like diamonds, yet they odorata; transverse section. Be oa : were formed in darkness, and in darkness act their part in the life of the plant. What that part is we can only guess. Botanists call them internal hairs; but they are hard, AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 49 sharp, and brittle. They are hollow, too, and their surface is roughened by minute elevations, as though fairy fingers had sprinkled them with crystal grains. I never see a white water-lily without in imagination seeing those long stalks rising out of the black mud up through the dark water, with their entire length il- lumined by the sparkling of these internal star-like gems. The whole plant contains them, even the root. The common ‘‘spatter-dock’’—hideous name!—the Niiphar, also conceals similar stellate hairs within its stems, but they are there larger and coarser, as be- comes a coarser plant. The leaves of the Nuphar, however, are not a good microscopical hunting-ground as they usually stand high above the water. MYRIOPHYLLUM (Fig. 8). This is not rare in shallow ponds and slow streams; it even occurs in running water, but there it is not worth gathering, so faras any adherent microscop- ical life is concerned. Indeed, no running water is a good locality for free-swimming creatures, because ‘the current sweeps them away, and so scatters them that it is not possible to make a collection. But where Myriophyllum grows it Fig. 8.—Whorl of Myriophyllum Leaves. usually ‘grows abundant- ly. It forms long green streamers, cylindrical and thick, sometimes more than an inch in diameter and several 5 5° AQUATIC MICROSCOPY FOR BEGINNERS. feet long, yet it always looks soft and feathery. The leaves are numerous, and ‘each set is arranged ina circle around the stem; they are in ‘‘whorls,”’ as the botanist calls the arrangement. One such whorl is shown in Fig. 8. ¥ive dissected leaves are there drawn, but whorls sometimes occur with three or four, the number helping to distinguish: the species, of which there are several, all of them closely resembling one another when in the water. The parts of the leaf are fine, soft, and hair-like, those nearest the stem of the plant being the longest. They are numerous and close together, thus giving the floating streamers their peculiar thick and soft appearance. and making them an excellent place for the microscopist to explore. To compare with Fig. 8a feathery plant which the collector does not know, select a circle of leaves, cut the stem close above and below it, and after floating the separated whorl in a saucer as already directed, or’ spreading it out on white paper, compare its leaves with those figured. They vary in size in different parts of the plant, the uppermost being smallest and youngest, the lower the oldest and largest. There is another rather common aquatic plant called Proserpindca, or ‘‘mermaid-weed,”’ which so closely re- sembles Myriophyllum when inthe water that it has often been mistaken for it. To make such an error is of no great consequence, unless it should lead the ob- server to imagine, as it once did the writer, that he has found a rare species of Myriophyllum. Yet it is always pleasant, if nothing else, to feel sure, and it is more than pleasant to have a reputation for accurate observation. Proserpinaca, however, is as useful a trap as Myriophyllum from which it can be easily distin- AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 51 guished because the dissected leaves are not in an exact circle around the stem: one is on one side, the next a little further round anda little higher up, another still further round and nearer the first, but still higher, the whole forming a spiral arrangement which the bot- anist calls alternate. Either of these plants is a specially good place for attached diatoms (Chapter III). UTRICULARIA (Figs. 9 and 10). Of all our water-plants with finely divided leaves, Utricularia is probably the most interesting in itself and one that can always be rec- ognized at a glance. It is found in long, somewhat branching streamers, floating freely below the surface or very slightly rooted. A leaf of Utriculéria vulgdris, 4 common species, is shown somewhat enlarged in Fig. 9, with the peculiar hollow bladders, or ‘‘utricles,” that dis- ‘tinguish it from all other plants, and give it one of its scientific 5, jon A Lea? of Uittllirin names. é These utricles are almost always conspicuous when the plant is taken from the water, as small, green, semi-transparent particles attached to the leaves. They are not unlike small pieces of jelly in appear- ance, until examined with the microscope, when their remarkable structure becomes apparent. Until within a few years they were supposed to act as air-sacs to keep the plant afloat. It was even said that they be- 52 AQUATIC MICROSCOPY fOR BEGINNERS. came filled with air or gas at flowering-time, and so lifted the flower-stalk and the blossoms above the water. This was interesting, but the truth. is more interesting and startling. The plant actually feeds on animals. These bladder-like bodies are the food-traps, they are the mouths and the stomachs of Utricularia. Under the microscope the utricles are seen to be hol- low, ovoid bodies, with a narrow, almost straight an- ‘terior end, and with’several long bristles projecting forward or away from the body of the utricle, these bristles probably servingas a guide to an opening at their base. A little animal swims against a bristle, and naturally moves down it towards the opéning at the mouth of the utricle, which it finds closed by a transparent colorless curtain; this it pushes aside and passes oninto the trap. The curtain-like valve is at- tached by its upper and lateral margins, therefore hanging before the opening in the utricle, and swing- ing inward, but so arranged that it cannot be forced outward by any creature small enough to pass within. Indeed the power that the valve seems to exert is as- tonishing. Small fish have been found with the tail or even with the head inside the utricle, and firmly: held by the pressure of the valve. In these cases, however, it seems probable that the struggles of the dying fish may have wedged it fast, rather than that the valve has held it. Small worms and worm-like larve have been found half in and half out of these fatal traps, for once past the curtain-like valve the little animal never escapes. And no sooner has it entered than it begins to show ‘signs of discomfort; if it has a shell it- withdraws its legs and head and. closes the shell; if a worm or AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 53 infusorian it speedily becomes languid, its movements cease, and it finally dies, as does every creature that ventures into Utriculdria’s utricles, which evidently contain something more than simple water. If these bladders are torn to pieces under the micro- scope with the needles, the remains of many kinds of minute creatures will be seen, the soft - parts of the captives having been dis- solved, absorbed, and gone to nourish the plant. The whole inner surface of the utricles is lined by innumerable color- ‘less four-parted bodies, one of which is : shown much magnifiedin Fig. 10, They: ore are distinctly visible only when the utri- Inner Surface of . cle is torn to pieces. They are said to fea ge vie be the glands which absorb the fluid in which the entrapped animals have been dissolved. CERATOPHYLLUM DEMERSUM (Fig. 11). This is commoner and more abundant than Myrio- phyllum, for which it is often mistaken, although the. two have only a remote general likeness. The leaves of Myriophyllum are fine and soft, those of the Cerato- phyllum rather coarse and stiff. In the latter they are whorled with six to eight in each circle, but instead of being divided on each side down to the mid- dle line-(the midrib), as in Myriophyllum, they appear to separate into two narrow parts near the main stem, while each division then often divides into two other parts. Both these arrangements are represented in Fig. 11, where the whorl is shown’ separated, as was donein Myriophyllum. The leaves always bear several very small but visible spines on their sides, as in the 54 AQUATIC MICROSCOPY FOR BEGINNERS. figure, and when taken from the water they usually do not fall against the stem, but remain stiffly extended. The plant is found in still, shallow places, growing in thick masses with the stem often considerably branched. It makes an excellent retreat for certain Rotifers and worms, but the leaves are so heavy and rigid that they are not as easily prepared for microscopical examination as Fig. 11.—Whorl of Leaves of e Ceratophyllum. are those of Myriophyllum; they often refuse to lie flat, and thus tilt the cover-glass and allow the water to run away. But with neither of these plants will the student try to place an entire whorl of leaves in the cell. It is always best to clip off with scissors a part of a single leaf, and to examine it for whatever may be attached. Work with the microscope is delicate work, and the smaller the object, within certain limits, the better. Many novices make the mistake of trying to examine too large a specimen or too much of a mass at once. LEMNA +POLYRRHIZA (Fig. 12) AND LEMNA MINOR (Fig. 13). DUCKMEAT. FF These are small plants, very common and often so abundant that the entire surface of large ponds is cov- ered by them as by a green carpet. The water in such cases is so completely covered and concealed that the observer is tempted for a moment to step on it. The two species resemble each other, yet they differ so widely that a glance will distinguish them. AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 55 Each consists of a small green, more or less oval leaf or frond floating on the water, with one or more rootlets hanging from beneath, but never taking root in the mud. Usually two, three or four fronds are attached together, so as to form an irregular star.. Lemna polyrrhiza, the ‘‘many-rooted Lemna” (fig. 12), has the largest fronds, is a deeper green, and, as itS specific name signifies, has many rootlets, often a dozen, hanging in a clus- ter from each. It can always be recog- nized by this root-cluster and by the dull purple color of the lower surface. It seems to like the sun better than Lemna minor, and is oftener found abundantly on open ponds, while the latter appears to prefer ditches with high banks and shade. Lémna minor (77g. 13) has smaller, more oval and thinner fronds. It is lighter green in color, the lower surface is never purplish, and it has but one rootlet to each frond. Both species have a peculiar little cap on the free end of, each rootlet, where it is more easily seen with the naked eye on Lémna polyrrhiza, as it is there usually darker than the rest of the Fig. 12.—Lémna polyrrhiza. rootlet. There are several other species, but Fig. 13.— they are’ so seldom found that they need Lémna caione not be included in this list. They all multiply by the growth of young fronds from the edges of the old and mature, this accounting for the clusters so commonly seen. They also bloom, but the flowers are extremely small and are rarely ob- served. The student will be fortunate to find speci- 56 AQUATIC MICROSCOPY FOR BEGINNERS, mens in blossom. The flowers burst out of the mar- gin of the frond, and consist of only those parts needed to fertilize and to mature’ the few small seeds. The rootlets are valuable to the microscopist, as - they are favorite places for many just such creatures that he most wants. The lower surface of the fronds, especially of Lémna polyrrhiza, should be gently scraped ina drop of water for certain Rotifers not often found elsewhere. It is also much visited by small worms, but not so frequently as the leaves of the white water-lily. ANACHARIS CANADENSIS (Fig. 14.) This plant is readily recognized by the arrangement of the leaves in circles, or whorls, of three each, two of which are shown in Fig. 14. The stem is brittle, and fragments -easily take root, so that the plant spreads rapidly. Having been accidentally introduced into England, it is said to have grown so fast that it has choked up some of the shallower streams and to have become a nuisance. It is abun- dant in this its native country, but it never acts so badly here. The whole plant is semitransparent, with leaves = Ftg. 14.—Ané- about half an inch long springing directly pa ree from the stem, and tapering to the point. These leaves, under the microscope, exhibit a remark- able phenomenon. All plants are formed of cells, or cavities of various sizes and shapes, surrounded on all sides by a delicate, membrane called the cell-wall. The cells are seldom empty during life. Their contents are chiefly the AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 57 soft, colorless, jelly-like substance called vegetable protoplasm, and the small-green grains (the chlorophyl) which give the green color to the plant. In Anacharis the walls of the leaf cells are transparent, so that the microscope shows a part of what is taking place within thecell; andit is a wonderful sight, for the protoplasm is slowly moving around the walls, carrying the chlorophyl grains with it. Up one side of that micro-. scopic cell travels the strange procession; across, down, and up, slowly and steadily the stream and the grains. move round and round. Sometimes a little thread of colorless protoplasm leaves the main cur- rent and starts across by a shorter road, and some- times the current pauses, stops, and refuses to move again. The streams in two cells lying side by side -may flow in the same or in opposite directions, with. only the thin wall between them. What causes these remarkable movements is not known. Cold seems to retard, and warmth to hasten the flow, and often, when the chlorophyl has increased so that the green grains crowd the cells, the circulation ceases appar- ently because the chlorophyl has not left enough’ space for free movement. .The botanists call this cir- culation of the protoplasm cycldésis. It is also finely seen in the long, narrow. ribbon-like leaves of Vallisneria, an abundant and common plant in slowly flowing streams. ; To show the cyclésis, the Anacharis leaf needs only to be cut close to the stem, placed in the cell in water, covered by athin glass, and examined by a high-power objective. The one-inch lens will not. show it dis- tinctly. The plant is a fruitful source of supply for our two 58 AQUATIC MICROSCOPY FOR BEGINNERS, - common species of Hydra (Chapter VI.), which often occur there so plentifully that two or three hang from almost every leaf. SPHAGNUM MOSS (Fig. 15). On the wet shores of shady bogs this pale-green moss grows in great patches, thick, soft, and elastic. It is a beautiful plant anywhere, but it is especially so when it appears greenly glimmering beneath ‘the shallow water, while the shadows of elder and azalea, and the broad leaves of the tangled smilax vines, make the neighboring thicket dim and cool, even when the hot sun smites the bordering fields. In such pleasant surroundings Rhizopods ne IV.) and Infusoria (Chapter V.) ‘“are found in abundance. For the former, Sphagnum is an unfailing source of ‘supply. The water pressed out of a little pinch of the moss will be sure to contain many indi- viduals and species. From a singlesmall bunvh, Dr. Joseph Leidy, when studying the. Rhizopods, obtained thirty- eight species and many indi- viduals of those animals, be- Fig. 15. — Portion of Leaf of sides numerous active diatoms ad (Chapter III.) and desmids (Chapter III). The leaves make exquisite microscopic objects, ou account of their peculiar and beautiful structure. Each leaf is formed of two kinds of cells, a and 4, (Fig. 15). The large ones, a, will, when magnified, AQUATIC PLANTS USEFUL TO THE MICROSCOPIST. 59 immediately attract the attention. They are hollow, and usually empty, and have. a spiral thread running around the walls. At certain stages of growth the cell-wall also has one or more small openings, c, so that the water is able to pass in and fill the cell. This may explain why the plant retains its moisture for so long, and why it is so easily wetted, having become for these reasons, a favorite substance with the florist for packing his bulbs and other small plants when these are to be carried to a distance. The second kind of cells, 4, is found between the large ones. They are much smaller, narrower, and commonly contain chlorophyl grains, which, while usu- ally not abundant enough to tinge the whole moss a bright green, yet give it that beautiful pale hue almost characteristic of it. These cells will probably need to be searched for the first time the beginner studies a sphagnum leaf, as they are not apt to catch the eye, but the difference in structure, especially the absence of the spiral fibre, should serve to distinguish them from the large, empty cells, which form the chief part of the leaf. The moss seems to have no roots. The lowest parts of the thick mass which it makes are usually dark and partly decayed, and it is there that the Rhizopods are most abundantly found, although many sun-loving forms are equally numerous in the brighter, better lighted upper region. On no account should the student pass a sphagnum swamp, nor even a little patch in those places where it grows more rarely, without taking some to be examined at home. Such a gathering will always repay the slight trouble needed ‘to make it. 60 AQUATIC MICROSCOPY FOR BEGINNERS, RICCIA FLUITANS (Fig. 16). Near the writer’s home this little floating plant (pro- nounced vicksia) is so abundant that it often covers small pools with a layer two inches deep. Elsewhere, on larger ponds, itisnotuncommon. It often comes to the collecting-bottle tangled in the leaves of Utricularia, Myrio- -phyllum, or Ceratophylium, or it floats on still waters in little island- Fig. 16.—Riccia flditans. like patches. Its form is seen in Fig. 16. It has no leaves; indeed it is all leaf; the botanist calls it a radiately expanding frond, with narrow di- visions, whose ends are notched. The plant is green, and may be an inch or more wide when spread out, and is often larger and more branched than shown in the figure. It has no roots, but floats freely wherever the currents or the winds send it. Shady places seem to be its favorite haunts. ' Asa microscopic object it is rather large and thick, ‘but it forms a good place to examine for certain Algz (Chapter IIJ.) which tangle themselves about it in fine green threads, appear to favor it, and may often be seen with the naked eye if the single frond is placed in water above a white surface. DESMIDS, DIATOMS, AND FRESH-WATER ALG. 61 CHAPTER III. DESMIDS, DIATOMS, AND FRESH-WATER ‘ALG&. Tuer desmids and diatoms are two closely related groups of minute aquatic plants which the beginner will at first probably have some trouble to distinguish from each other; yet after a very little experience he will be able to recognize them at a glance. Both are plants formed of only a single cell, but their beauty and variety of form, their peculiar movements and wonderful structure, place them amongst the most at- tractive of living microscopic objects. And they are among the most frequent. Scarcely a drop of water from a pool in spring or summer can be examined with- out showing a desmid or a diatom. The desmids are usually found in the freshest and sweetest water. In salt or brackish marshes, where diatoms flourish as well as in a mill-pond, desmids never occur. ‘They also seem to prefer open pools on which the sun shines brightest and the shadows are fewest, where they probably seek warmth rather than the strong light, for they seldom form patches on the mud as the diatoms do, but adhere to the stems of other plants as a green film; or conceal themselves. among the dissected leaves of the aquatic vegetation, oramong tangled masses of Alge. 4 62 AQUATIC MICROSCOPY FOR BEGINNERS. A living desmid is always green; a living diatom is always brown. This difference in color makes it easy to distinguish the two groups of plants, although there are other points that can be used by even acolor-blind student. The cell wall of the desmid—that is, the thin sack which surrounds the soft green contents—is soft and flexible. Ifthe cover-glass is pressed down firmly with a needle the desmid can be flattened or squeezed out of shape, and the cell-wall can often be ruptured, so that the green and colorless mixture of jelly-like matter filling the plant is forced out. The cell-wall of a diatom is hard and brittle. The cover-glass may be pressed upon until the glass breaks, yet the diatom will not be flattened nor its shape changed. It may roll over and look quite different in form when viewed in another position, but it will prob- ably roll back and appear as at first. It can be fractured, however; and it breaks as if made of glass or of some other hard and brittle material, and the yellowish-brown contents may flow out, but the broken place will not be an aperture torn with irregular, more or less rounded margins, as it was in the crushed des- mid; the edges will be sharp and angular, and ‘the diatom ‘will probably break into several fragments. Vet with the most skilful manipulation it is rather difficult purposely to break any but the largest of the diatoms, few of which are visible to the unaided sight of the. acutest eye. The brittle, hard-coated little plants are often found in fragments, but according to the writer's experience they are broken accidentally, either by being piled on top of each other and so crushed by the cover-glass, or by the rough contact with one another when gathered. DESMIDS, DIATOMS, AND FRESH-WATER ALG#. 63 The desmids float freely in the water; many diatoms do the same. Several species of desmids are attached to one another side by side to form long bands; many diatoms are arranged in a similar way. Some des- mids are surrounded by a colorless jelly-like envelope; so are some diatoms. The desmids never grow on the ends of stems secreted by themselves, and at- tached to other plants or to submerged objects; many diatoms are found growing on the extremities of long colorless and: branching stalks like microscopic trees, these stems being supported by other objects in the water. Some of the commonest diatoms will be found in great abundance growing in this way on the leaves of Myriophyllum. Any object that may apparently be either a desmid or a diatom is not a desmid if it is on the end of a stem of its own formation. Most desmids have the ability voluntarily to change their position. They can move from place to place, as they frequently do when under the microscope, slowly travelling across the field of view in an exceedingly in- teresting way. When mixed with mud or with other extraneous matters, as they often are when gathered and carried home ina bottle, they will gradually work themselves to the surface and. collect in a green film or line on the side of the vessel next the window, whence they can be easily taken by the dipping-tube. Diatoms have a similar power of movement; but they are usually much more active, and their motions more rapid than those of desmids. And while the desmids move stately and slowly in one direction, a diatom may travel quickly half-way across the field of view, _and without amoment’s hesitation, and without turning around, may at once return by its former path or dart 64 AQUATIC MICROSCOPY FOR BEGINNERS. off obliquely on a new one. -Amoving diatom always seems to have important business on hand, and to be anxious to accomplish it. An object, therefore, that may be either a desmid or a diatom is not a desmid if, it moves rapidly and changes its course suddenly and quickly. ees a The cause of this motion is in each case a mystery. Many theories havé been proposed to explain it, but none is satisfactory. If the reader can discover how the desmids and the diatoms move themselves his name will be rernembered among naturalists to the end of time. The surface of a desmid may be smooth, finely stri- ated lengthwise, roughened by minute dots or points, or it may bear several wart-like elevations or even spines of different shapes; its edges may be even or notched, prolonged into teeth, or variously cut and divided. It is these ornaments, in connection with the graceful form and the pure usually homogeneous green color, that make the desmids so attractive to every student of microscopic aquatic life. Fresh- water diatoms occasionally have tooth-like processes, but they are never spine-bearing; yet’ the markings of their surfaces are among the most exquisite of Na- ture’s handiwork, and among the most varied. Dots, hemispherical bosses, hexagons, transverse and longi- tudinal lines of astonishing number- and fineness, are among their many surface sculpturings, the delicacy and the closeness of which defy description by any but the mathematician. So numerous and close to- gether are the surface lines of some that they are used to test the good qualities of the best and highest- power objectives. There are no perfectly smooth dia- DESMIDS, DIATOMS, AND FRESH-WATER ALGA, 65 toms, although many may appear to be so with a low- power lens; but the splendid glasses of the best Amer- ican makers will compel any diatom to show how it is marked and roughened. In each extremity of many desmids, especially in the crescent-shaped ones, is a small colorless, appa- rently circular space containing numerous minute black particles in incessant motion. These little granules, which are said to be crystals, are sometimes so few that they can be counted if sufficiently magni- fied, while in other individuals they appear to be innu- merable. Their motion resembles the swarming of microscopic bees. It can scarcely be described, but once seen it can never be forgotten. The spaces con- taining them are called vacuoles, and are never pres- ent in diatoms. It is true that in some of the latter, when dying or dead, many minute black particles are visible, dancing and swarming in clusters within the cells, but this ‘‘Brownian movement” is common to many microscopic creatures after death. In the desmids there is also often seen a circulation of the protoplasm similar to the cycldsis in the leaf- cells of Andcharis, a movement of the cell contents never observed, so far as I am aware, in any diatom. Between the cell-wall and the green coloring matter, the chlorophyl, there seems to be a narrow space filled with colorless protoplasm, and it is here that the cir- culation takes place. It is a steady, rather rapid flow, several currents streaming lengthwise up and down the cell, carrying the minute starch grains and other enclosed particles in their course. It has been said that these currents sometimes enter the vacuoles, and that the latter obtain their supply of swarming gran- 6 66 AQUATIC MICROSCOPY FOR BEGINNERS. ules from the particles in the streams; it has also been stated that occasionally one or more of the swarming granules leaves the vacuole, enters the current, and journeys round the cell. These statements are cor- rect. Although the occurrence seems rather uncom- mon it may be the reader’s good fortune, as it has been the writer’s, to see one or more of these intra-vacuolar crystals leave their spherical dwelling place, and pass into the protoplasmic stream, to be carried up and . down with the currents that flow beneath the cell-wall. I have seen several crystals thus escape to liberty from the same vacuole, in the extremity of a Closter- zum. But witha high-power objective (the one-fifth, for instance) it is not difficult to select a granule in the general stream, and follow it as the current car- ries it down one side to the vacuole and again upward with an ascending current to continue the round. The vacuoles themselves are visible with a good low- power objective, but to see distinctly the swarming granules and the general cycldésis a one-fourth or one- fifth is needed. In addition to the desmids and the diatoms, almost every pond and stream contains other minute plants of interest to the microscopist, called the fresh-water Algze, which he probably already knows, if not by this name, at least by their general appearance, for they form those green masses floating like a scum on the surface, or those soft green clouds attached to sticks and stones and dead leaves. The Alge often havea repulsive appearance as they collectin thick and heavy patches, but under the microscope they reveal beauty undreamed of. All those slimy, slippery green streamers usually so abundant in still water during the DESMIDS, DIATOMS, AND FRESH-WATER ALG, 67 summer are Alge. The reader need have no trouble to recognize them as Alge after a little experience, but since he at first may be somewhat uncertain as to which of the three classes of plants his specimen may belong, the following Key has been constructed to aid him. To use it, compare the plant with it in the fol- lowing way: Suppose the specimen is a single cell, shaped like a crescent, as described in the first sentence of the Key. The reader will notice (a) at the end of the line, mean- ing that he shall now seek a description somewhere in the table below with a at the beginning of the line. Finding three such lines, he reads the first, ‘‘Color green,” which is the color of the specimen under the microscope; ‘‘the plant a floating hollow sphere,” which does not describe it, since it is crescent-shaped. He then reads the second ‘‘a” line: ‘‘Color green, the plant not a hollow sphere,” which is of course correct, as his plant isnot a sphere. The (é) at the end refers to another line below headed by 4. There being but one such, the plant must be a desmid; but to learn which of the numerous desmids it is, he turns to Sec- tion J. -of this chapter, where is another Key to help him find the name of the genus. Again, suppose he obtains a floating mass which, when lifted on the hand or in a dipper, he sees to be a fine, delicate green net. To find the section to which this belongs, read each numbered sentence at the be- ginning of the Key: 1 will not do, since the specimen _is not spherical, crescentic, nor circular; 2 will not do, because the plant is not in-long threads; 3 and 4 do not describe it, because it is neither star-shaped nor formed of oval cells with two bristles on each end; but 68 AQUATIC MICROSCOPY FOR BEGINNERS, 5 calls for a green net often visible to the naked eye, which describes the specimen, giving the name of its genus, Hydrodictyon, and referring the student to the Alge, Section III. of this chapter. After using this preliminary Key for a few times, he will be able to de- cide at a glance through the microscope to which sec- tion his specimer belongs. Key to the Desmids, Diatoms, and Fresh-water Alge. 1. Plants formed of a single, crescent-shaped, spher- ical, barrel-shaped, oblong and constricted, or circular and flattened, cell, sometimes arranged side by side in long ribbons, but seldom end to end; color green or brown (a). 2, Plants formed of many cells arranged end to end in long threads; coloring matter usually green, often in spiral bands or other patterns on the cell-wall (2). 3. Plants formed of several green cells grouped in the shape of a flat disk with from six to many short blunt star-like points; floating free. Pedtdstrum (Alga, LIL.). 4. Plants formed of from two to eight narrowly-oval green cells placed side by side, each terminal cell with two curved colorless bristles; floating free. Scenedésmus (Alga, L11.). 5. Plants forming a green net visible to the naked eye. Hydrodictyon (Alge, IfL.). a. Color green, the plant a floating hollow sphere. Volvox (Alga, IITL.). a. Color green, the plant not a hollow sphere (4). a. Color golden-brown (c). DESMIDS, DIATOMS, AND FRESH-WATER ALG. 69 b. Cell-wall smooth, rough, warty, or spine-bearing, also soft and flexible; always floating freely, never growing on stems permanently adherent to other objects, but sometimes attached side by _ side to form long bands or ribbons; a vacuole with swarming granules often present in each end. (Désmids,; L.) c. Cell-wall marked transversely, often-also longi- tudinally, by lines, smooth bands, or dots; never spine-bearing; cell-wall hard and brittle; floating freely, or growing on colorless stems permanently attached to other objects. (Diza- toms, II.) @. Plants forming cloud-like clusters, long stream- ers, or scum-like floating masses visible to the naked eye; color bright green or olive, some- times almost black; the cells under the micro- scope united end to end to form long, sometimes branching filaments. (die, //L.) 1. DESMIDS. * As the desmids are singly invisible to the naked eye, the student can know what he has gathered only after reaching home, except in those rare instances where the little plants have become congregated together in such quantities that a good pocket-lens will show their forms. I have more than once found Closterium in this profusion, but never any other. The early spring, as early as the last of March or the first of April, in the writer’s locality (central New Jersey), is perhaps the best time of the year to gather them, or indeed any of the Alge. At that time all these plants seem more vigorous, their vital functions are performed more as + 7O AQUATIC MICROSCOPY FOR BEGINNERS. actively, and the observer is then almost sure to see some of them in conjugation, or union of two separate cells, and, it may be, the formation of the spores. This spore-formation, however, is more frequently seen in the thread-like Algz than in the single-celled desmids. , There are more than four hundred known species of desmids in.this country. Perhaps an undue proportion has been included in the following list, but Nature of- fers them so freely and abundantly, and they are so attractive, that they must be their own excuse. The following Key to the genera is to be used as di- rected for the ‘‘Key to the Desmids, Diatoms and Fresh-water Alge,’’ except that when the name of the genus has been found, the reader should then refer to the paragraph on a subsequent page headed by that name, where he will find one or more species described and figured. Thus, if he has a green, half-moon- ‘shaped plant under the microscope, to learn its name let him turn to this Key, the second line of which de- scribes it, since .it is not in ribbons nor bands; he then should refer to the lines headed by d, the first one of which describes the plant as a ‘‘cell more or less crescent-shaped,” and giving the generic name CiZos- terium, 6 being the number of the paragraph further on in this section of the chapter, where several species are noticed, Key to Genera of Desmids. 1. In ribbons or narrow bands (a). 2. Not in ribbons nor bands (2). a, In a transparent, jelly-like sheath (4). a. Not a jelly-like sheath (c). d, * & mR 8 DESMIDS, DIATOMS, AND FRESH-WATER ALG. 71 Each cell with two teeth on each narrow end. Didyméprium,. i. Each cell deeply divided almost into two parts. Spherozésma, 2. Each cell without teeth and not divided. Ayalo- théca, 3. Cells barrel-shaped, the band not twisted. Bam- busina, 4. Cells not barrel-shaped, the band twisted. Des- midium, 5. Cells more or less crescent-shaped. Clostérium, 6. Cell cylindrical, spindle-shaped, hour-glass, or dumb-bell shaped (/). . Cell flattened, oblong, circular, or often divided into arms (e). Mostly circular or broadly elliptical, often cut and divided by slits and depressions; marginal teeth usually sharp. Aficrastérias, 7. Mostly oblong or elliptical, the margin wavy, the depressions rounded. wdstrum, 8. Cell constricted in the middle; no arms nor sharp spines (g). Cell constricted in the middle, with arms or sharp spines (A). Cell not constricted in the middle; no arms nor sharp.spines. (2). Ends notched, cell cylindrical. TZetmémorus, 9. Ends not notched, cell cylindrical. Doctdium, 10. Ends not notched; cell more or less dumb-bell or hour-glass shaped (/). Arms, three or more, radiating, tipped with one or more points. Staurdstrum, 12. 72 AQUATIC MICROSCOPY FOR BEGINNERS. © A. Arms none; spines four, two on eachend. Ar- throdésmus, 14. A. Arms none; spines several, on the edges; a round- ed, truncate, or denticulate tubercle in the center of each semi-cell. Xanthidium, 13. z. Chlorophyl in a spiral band, cell cylindrical. Spz- rotenia, 15. 7. Chlorophyl not ina spiral band, cell cylindrical (2). 2. Surface roughened by oblong often tooth-like elevations. TZriplocéras, 16. k. Surface smooth, ends rounded, neither divided nor notched. Pénium, 17. /. End view with from three to six or more angles (m). 7. End view not angular, margins smooth, dentate, or crenate, without spines; ends always entire. Cosmdrium, 11. m. Angles obtuse, acute, or with horn-like prolonga- tions. Staurdstrum, 12. Tt. DIDYM6PRIUM, Each cell in the band longer than broad; two round- ed or angular teeth on each narrow end; case or sheath distinct, colorless. D. Grevillid, Fig. 17. edi eater a Fig. 17.—Didyméprium Grevillii: Fig. 18.—Sphzrozésma pulchrum. 2. SPHAROZOSMA. Each ‘cell in the band about twice as long as broad, DESMIDS, DIATOMS, AND FRESH-WATER ALGH. 73 divided on both ends almost to the middle; sheath large, colorless. Five cells are shown in the figure. S.. pilchrum, Fig, 18. 3. HYALoTHECA. The ribbons are often very long, and the narrow ends of each cell are sometimes slightly constricted, as shown in the lower part of the figure, but the depres- sion is never deep enough to form teeth; sheath color- less. A. dissdliens, Fig. 19. rc for Fig. 19.—Hyalothéca dissf{liens. Fig: 20.—Bambusina Brebissénii. 4. BamBusfna. The cells in form somewhat resemble barrels or casks joined together end to end, with two narrow hoop-like elevations around the middle of each. J. Brebissénit, Fig. 20. 5. Desmfpium. The twisted appearance of the band is due to the fact that the cells are triangular, as may sometimes be seen when they break apart and turn over on end, but the i iy three angles are not all in the nll same line, each cell being slightly rotated laterally.. When the side of the band is looked at, it is these angles that are seen like a dark oblique or zigzag line traversing the ribbon. Each cell is slightly toothed on both the narrow ends. Common. D. Swartazit, Fig. 21. Fig. 21.—Desmidium Swartzii. 74 AQUATIC MICROSCOPY FOR BEGINNERS. 6. CLosTERIUM (Figs. 22 to 31). All the species of this genus are more or less cres- cent-shaped, some being more curved than others, but none having exactly straight sides. Near each end of almost every one will be seen a clear circular vacuole containing many small, dark, swarming granules. These have already been referred to, as has the move- ment of the protoplasm between the cell-wall and the layer of green coloring-matter, Closterium being the only desmidin which this cycldsis can be seen easily, if it ever occurs in others. There are thirty-five species of the genus, the following being some of the com- monest. The convex margin is called the ‘‘back,” the concave border the ‘‘ventrum.” Some Species of Clostérium. 1. Ends not lengthened into a colorless beak (a). 2. Ends lengthened into a colorless beak (/). a. Back slightly convex, the whole cell but slightly curved (8). a. Back strongly convex, ventrum nearly straight (c). a. Back strongly convex, ventrum strongly concave with a central enlargement (2). a. Back strongly convex, ventrum without a central enlargement. (e). é. Ventrum nearly straight; vacuoles close to the rounded ends; fifteen or twenty chlorophyl globules in a central longitudinal row in each semi-cell. C. “in-, edtum, Fig. 22. 0900000909999, 99090000005, ; Soe ° Fig. 22.—Clostérium lineatum. DESMIDS, DIATOMS, AND FRESH-WATER ALGH. 75 6. Ventrum nearly straight; body tapering toward the rounded, sometimes curved, ends; vacuoles small, often scarcely visible. C. junctdum, Fig. 23. Fig. 23.—Clostérium juncidum. 4. Ventrum and back equally curved; ends tapering; from ten to fourteen chlorophyl globules in a central, longitudinal row in each semi-cell; vacuoles very small. C. acérdsum, Fig. 24. ¢. Ends rounded; chlorophyl often arranged in nar- oeert e@o000g5H ooe? : Pe0e ooo pe Poa dD Fig. 24.—Clostérium acerésum row, longitudinal bands; chlorophyl globules numerous; vacuoles near the ends; cell very large. C. Liinula, Fig. 25. Fig. 25.—Clostérium Linula. @. Ends rounded; chlorophyl often arranged in nar- row, longitudinal bands; chlorophyl globules of- ten numerous; vacuoles close to the ends. C. Ehrenbérgit, Fig. 26. Fig. 26.—Clostérium Ehrenbergii. Fig. 27.—Clostérium acumindtum. 76 AQUATIC MICROSCOPY FOR BEGINNERS. e. Large, crescent-shaped; center broad, ends acute, vacuoles small. C. acumindtum, Fig. 27. e. Small, crescent-shaped, distance between the ends about ten times the central diameter; center narrow, vacuoles indistinct. C. Didne, Fig. 28. Fig. 28,—Clostérium Diane. Fig 29.—Clostérium Vénus e. Very small, crescent-shaped, from eight to twelve times as long as broad; center narrow, ends sharp, vacuoles distinct. C. Véwus, Fig. 29. f/f. Each beak about as long as the green body, sometimes shorter; whole cell slightly curved; vacuoles usually indistinct. C. rostrdtum, Fig. 30. Fiz. 3o.—Clostérium rostratum. ; f. Each beak exceedingly fine, longer than the ‘spindle-shaped green body, the tips alone curved. .C. setdceum, Fig. 31. oo Fig. 31.—Clostérium setaceum. 7. MICRASTERIAS (Figs. 32 to 39). Each Micrastérias is incompletely divided across the middle into two equal and similar halves, or semi- cells, by a deep slit, the sides of which may be either close together or somewhat separated. The margins of both semi-cells are also much incised and notched, but both in the same way, the description of one-half, DESMIDS, DIATOMS, AND FRESH-WATER ALG#, 77 therefore, applying equally well to the other. There are more than forty species of the genus. The reader must expect to find many forms not included in this list, which contains only some of the most common in the writer’s vicinity. Some Species of Micrastérias, 1. More or less circular in outline (a). 2. Not circular; divided into radiating arms (4). 3. Not circular; not divided into arms; central slit gaping (c). a. Each semi-cell divided by four deep cuts into one terminal and four s side-lobes, each side- 2 lobe divided by a | a shorter incision into_ ot, : two sections, each sec- FA se = tion by a still shorter cut divided into two Yj XN SS divisions, each division Uf) Ws Y j AN by a yet shorter cut ale divided into two parts, Fig 32.—Micrastérias radiésa. and each part with two teeth. Desmid very large. M. radidsa, Fig. 32. a. Each semi-cell divided by four incisions into one end-lobe and four side-lobes; each side-lobe divided by a shorter cut into two parts and each part with two teeth. End-lobes often dentate. M. rotata, Fig. 33. 78 AQUATIC MICROSCOPY FOR BEGINNERS. Fig. 34.—Micrastérias truncata. oe a. Each semi-cell divid- > ed by two incisions into one end-lobe Fig. 33.—Micrastérias rotata, shorter cut divided and two side-lobes, each side-lobe by a into two parts, and each part with two teeth. End-lobes broad, often with two teeth on each end. M&M. trun- cdta, Fig. 34. Ne, b. Each semi-cell divided by deep Fig. 35.—Micrastérias arcuata. Ae S Fig. 36.—Micrastérias dichétoma, rounded depressions into four tapering, slightly curved arms, the whole desmid having eight undivided arms. M. arcudta, Fig. 35. Fig. 37.—Micrastérias Kitchéllii. DESMIDS, DIATOMS, AND FRESH-WATER ALGE, 79 6. Each semi-cell divided by two acute depressions into one end-lobe and two side-lobes, each side- lobe divided by an acute depression into two short parts, each part divided by an acute depres- sion into two short arms, and each arm with two teeth; arms of the end-lobes each with two teeth; the whole desmid with twenty short arms. JZ. dichétoma, Fig. 36. ‘ s 2 3 Fig. 38.—Micrastérias éscitans. Fig. 39.—Micrastérias ldticeps. c. Divided into one end-lobe and two side-lobes (¢). @d. Side-lobes divided by a shallow notch into two parts extending beyond the end-lobes, each part with two teethon bothends. M&M. Kitchéliz, Fig. 37. @d. Side-lobes not divided into two parts, but extend- ing beyond the end-lobes; terminal lobes some- times notched laterally, as shown in the figure, sometimes not. WM. dscitans, Fig. 38. d, Side-lobes not divided into two parts, not extend- ing beyond the end-lobes. MW. ddticeps, Fig. 39. 8. EUASTRUM (FIGS. 40, 41, 42). Eudstrum is almost divided into two halves by a central slit across the middle, but the cell outline is 80 AQUATIC MICROSCOPY FOR BEGINNERS. never circular as in Micrastérias, and the margins are wavy, never sharply toothed. The ends are usually notched. There are about forty species. 1. Each half-cell oblong; an end-lobe present in both halves, and formed by a short rounded incision on each side. £. crdssum, Fig. 40. Fig. 40.—Euastrum Fig. 41.—Eudstrum Fig. 42, —Eudstrum. crassum. didélta. ansdtum, 2. Each half-cell somewhat triangular, without distinct end-lobes (a). a. Sides wavy, gradually expanding towards the cen- tral incision. ££. ddélta, Fig. 41. a. Sides hardly wavy, suddenly expanding towards the central incision. Small. £. ansdtum, Fig. 42. g. TETMEMORUS (FIGS. 43, 44). 1. Widest in the middle, the ends tapering. T7. granuldtus, Fig. 43. Fig, 43.—Tetmémorus granulatus. Fig. 44,—Tetmémorus Brebissén DESMIDS, DIATOMS, AND FRESH-WATER ALG, 81 2. Not widest in the middle, the ends not tapering. Le Brebissénii, Fig. 44. 10. Docipium (Fics. 45, 46). 1. A slight, rounded enlargement on each side of the central constriction; smooth; no terminal vacuoles. D. Badculum, Fig. 45. Ce)! Se Fig. 45.—Docidium Baculum. Fig. 46 —Docidium crenuldtum. 2. Two or several small enlargements on each side of the central constriction, giving the margins a wavy outline; coarsely punctate; from 8 to 16 times longer than broad. WD. crenuldtum, Fig. 46. 11. CosMARIuM (Fics. 47, 48, 49, 50). The ends of Cosmdrium aré never notched nor incised. They may be, and often are, rough or warty, but the ends are always entire. There are about one hundred species. ‘The following are common: 1. Surface smooth; cell less than twice -as long as ‘broad, two sémi-cells evenly rounded. C. Rdéfsii, Fig. 47. 2. Surface smooth; cell about twice as long as broad, the margins of each semi-cell slightly sloping tow- ard the flattened ends. C. pyramiddtum, Fig. 48. —Cosma- Fig. 48. —Cosma- Fig. 49. —Cosma- Fig. 50- —Cosma- Fig. Raa ig. pyrami- - rium margari- rium Brebiss6- datum. tiferum. nii. 82 AQUATIC MICROSCOPY FOR BEGINNERS, 3. Surface roughened by rounded, pearly elevations. C. margaritiférum, Fig. 49. 4. Surface roughened by small, sharp-pointed conical elevations. C. Brebissénit, Fig. 50. 12, STAURASTRUM (Figs. 51, 52, 53, 54). .In front view, or in the position in which the desmids usually lie when undisturbed, Staurdstrum resembles Cosmarium, but in end-view it is always angular. It is sometimes rather‘troublesome to get Staurastrum, or indeed any other desmid, tilted up on end so that it can be examined in that position, but ina moderately deep cell, with considerable water, and under a low- power objective, it can usually be turned over by gently tapping and pressing the cover-glass with a needle. Staurdstrum is a large genus, containing about one hundred and twenty species. 7 In each of the succeeding figures 4 represents the end-view of the desmid. 1. Cell dumb-bell shaped; without arms; surface roughened by small elevations. St, punctuldtum, Fig. 51. Are, Fig. 51.—Staurdstrum punctuldtum, Fig. 52.—Staurdstrum furcigerum, 2. Cell not dumb-bell shaped; with arms (a). a. Cell triangular in end-view, the angles toothed; arms in a cluster of about three on the end of the cell, their ends toothed. St. furcigerum, Fig. 52. DESMIDS, DIATOMS, AND FRESH-WATER ALGE. 83 a, Cell triangular in end- view, the angles _pro- longed as narrow arms, the ends of which are three-toothed ; surface roughened. St. gracile, Fig. 53. a. Cell with six or seven 26 2 ° Fig. 53.—Staurdstrum gracile. Fig. 54.—Staurdstrum macrécerum. radiating arms, their ends three-toothed. Sv. macrécerum, Fig. 54. 13. XANTH{DIUM (Figs. 55, 56). The cells bear near both ends a prominence or tu- bercle which may be rounded and smooth, truncate, or apparently encircled by small beads. 1. Cell about twice as long as broad; spines short, their ends irregularly toothed; tubercles circular, beaded. This is the only species with toothed spines. X. armdtum, Fig. 55. Fig. 55.—Xanthidium Fig, 56.—Xanthidium Fig. 57.—Arthrodes- armatum. antilopeum. mus incus, 2. Cell not twice as long as wide, each half-cell some- what kidney-shaped; spines in four or six pairs 84 AQUATIC MICROSCOPY FOR BEGINNERS. on each semi-cell, not divided ‘nor toothed, but often curved; tubercle a curved row of bead-like elevations. X. antilopeum, Fig. 56. 14. ARTHRODESMUS (Figs. 57, 58). -1. Spines on the same side curving or spreading from. each other; surface smooth. A. ducus, Fig. 57. 2. Spines on the same side curving toward each other; surface smooth. A. convergens, Fig. 58. Fig. 58.—Arthrodésmus convérgens. Fig. 59.—Spirotenia condensita. 15. SPIROTANIA, Ends rounded; spiral band closely wound. SS. con- densdta, Fig. 59. 16. TRIPLOCERAS. Surface roughened by small projections arranged in rows around the cell, their tips notched or finely toothed; cell from twelve to twenty times as long as broad. TZ. verticilldtum, Fig. 60. This is classed by the authorities on the subject, in thegen us Docidium, and is therefore called Docidium verticillatum. Fig. 60,—Triplocéras verticillatum. 17. PE&NIUM. Cylindrical; ends rounded, surface smooth. P. Brebissénii, Fig. 61. If it is desired to preserve any of the desmids or DESMIDS, DIATOMS, AND FRESH-WATER ALGA, 85 the Algz, the following solution will be found to be an excellent medium. In it the plants retain their green color for along time, and the cell-contents have less tendency to shrink from the cell- wall than with any other of the many media often recommended. Any Me hee druggist can make the solution. It is composed as follows: Camphorated water and distilled water, of each, 50 grammes; glacial acetic acid, o.5 gramme; crystallized chloride of copper, and crystallized nitrate of copper, of each, 2 grammes; dissolve and filter: The solution was origi- nally devised by M. Petit, a French microscopist. The plants should be placed in a cell made of shel- lac, a few drops of this preservative copper-soiution added, and the cover fastened down with shellac. If any other cement, except perhaps Brown’s rubber-ce- ment, is used with this solution it will inevitably run under and ruin the preparation. If the reader should find the desmids so pleasing that he desires to study them rather than to learn the names and appearance of a few of the commonest as here given, he should refer to the Rev. Francis Wolle’s monograph, entitled ‘‘The Desmids of the United States,’ and to Stokes’s ‘‘Fresh-water Algez and the Desmidiee of the United States,” the latter being an extended, mostly artificial, key to the genera and the species of these attractive plants, founded on Wolle’s classification. II. DIATOMS. For along time there was much discussion as to the animal or vegetable nature of the diatoms, but that they are plants is now the general belief. Their 86 AQUATIC MICROSCOPY FOR BEGINNERS. peculiar motion was one great reason for classing them among the animals, although some undoubted plants have even a more rapid movement. No class of microscopic objects, except, perhaps, the Infusoria, is so abundant. No ditch or pond is without them. No pool is too small to harbor them; even a depression made by a cow’s hoof in a wet meadow soon becomes a home for them. They will probably form some of the first things to attract the attention of the novice in the use of the microscope. Their shape is as varied as their number is great, and their hard and glass-like surface is most beauti- fully lined and dotted, and sculptured in delicate tracery. Most plants are comparatively soft, but the diatoms are noteworthy for the hard case enclosing the semi-fluid, yellowish-brown contents, a case that is indestructible. It may be heated to redness, it may be boiled in strong acids and in alkalies, and at the end be as it was before, as gracefully formed and as beautifully marked. Indeed, properly to study the surface markings, the diatoms should be treated by some method to destroy the coloring matter often obscuring these geometrical designs, which, for many purposes, make them so highly valued. For the be- ginner, however, who desires only to recognize a dia- tom when he meets with: one in the field of his micro- scope, and to learn its name, if possible, such prepa- ration is unnecessary. These plants are also peculiar in their structure. In this they have often been compared to a pill-box. The diatom is formed of two parts called valves, one of which may be likened to the pill-box proper, and the other to the lid, since it slips over the upright DESMIDS, DIATOMS, AND FRESH-WATER ALG. 87 edge of the lower and usually younger valve. The entire box-like diatom is called the frustule; the sur- faces of the upper and lower valves are usually marked, and usually but not always shaped, alike, and are called the sides. But when the frustule happens to be turned so that the narrowest part, or that part corre- sponding to the thickness of the pill-box, and called the front, is towards the observer, then the shape is so different from that of the valves as often to puzzle the beginner. If in doubt about the position, gently tap the cover-glass with a needle, when the frustule will generally roll over on its broad side. All this seems somewhat bewildering at first, but there will be no difficulty if it is borne in mind that the thickness of the pill-box corresponds to the front of the frustule, and the broad surfaces of the lid and bottom to the sides of the valves. In addition to the valves which together form the frustule, there is another part, of which less is heard among diatomists, although it is important and is it- self sometimes striated or sculptured. This corre- sponds to that portion of the pill-box remaining after the top and the bottom have been removed. The part of the box therefore corresponding to the height or thickness of the diatom frustule, is called, in the dia- tom, the hoop, and after the frustule has been cleaned and the valves separated, the hoop may often be seen lying in the mounting medium, frequently set up on its edge, and still retaining somewhat of the contour of the original frustule. These hoops are sometimes rather puzzling when first found in a mounted prepa- ration of diatoms, as they generally resemble very narrow, curved or rounded filaments which may lead 88 AQUATIC MICROSCOPY FOR BEGINNERS. ~ the observer to suppose that some extraneous and foreign object has been accidentally included in the mount. - ; Besides the ordinary markings on the valves—that is, the transverse lines which are sometimes so coarse that they are called ribs—each valve frequently bears a line or,a marrow smooth. band down the middle, named the raphé, while at each end and at the center there is often a small rounded spot resembling a circu- lar space, but being in reality a thickening, and called a nodule. Immense beds of fossil frustules are found in many parts of the world, especially in Our own country. In Maryland and in New Jersey diatomaceous earth is obtained containing exquisite forms. In Virginia a certain deposit is especially renowned, since it is eighteen feet thick and underlies the city of Rich- mond. This has afforded the student some of the rarest and most valued frustules, or valves, for the frustule, before its sculpturing can be properly studied, must be separated into its two valves. To have produced such a mass they must have existed in incalculable numbers in a great body of water where, undisturbed for a long time, they died and sank to the bottom year after year, their skeletons accumulating as others continued to fall. To appreciate the prob. able length of time during which they existed with nothing to interrupt their .peaceful life, as well as the number of diatoms needed to make such a deposit, it is only necessary to know that a sin- gle frustule is seldom thicker than the one ten-thous- andth of an inch. At the present day living diatoms are >sften found DESMIDS, DIATOMS, AND FRESH-WATER ALG. 8&9 in large numbers forming a yellowish-brown film on the mud in shallow water. In such cases it is no trouble toskim them up and so to gatherthem. Usually however, the reader will first see them floating freely about his slide, or attached to various plants. But few are visible to the naked eye except when collected in great masses, and only. then as brownish patches; the individual valves are seldom seen without the microscope, and then only by the most acute and best educated eye. They are difficult to study and ‘to identify. To examine them properly demands the highest-power objectives of the best construction, anda skill in the use of the microscope and accessary optical apparatus not often at the beginner’s command. Much has been written about them, but the literature of the subject is so widely scattered through the scientific magazines that only those who make a special study of the subject can hope to ‘have it in their libraries. But the beginner need not despair. With ease he can learn to recognize a diatom whenever seen, and to know the names of the commonest forms, and this is all he will care to learn at first. Yet he will find it a satisfaction to be able to say to a friend, ‘‘That is a diatom,” and to explain its box-like structure.’ The following Key has been made to assist the reader in ascertaining the names of a few of the. com- monest fresh-water forms, It is impossible to include even a tithe of the plants, and the microscopist will surely find many not mentioned in the succeeding list, but from the brownish color, the movements common to so many, and the hard, dotted, lined, or otherwise sculptured valves, he can readily know them to be go AQUATIC MICROSCOPY FOR BEGINNERS. members of the Déatomacee after he has observed and recognized one. More than this he can scarcely hope to do. The golden brown coloring matter will often be seen contracted to a narrow strip, or to a spot at each end, while frequently the frustule will be entirely colorless. Diatoms are the favorite food of many microscopic animals, which absorb the cell-contents, often leaving the hard and indigestible valves color- less, but otherwise unchanged. Key to Genera of Diatoms. 1. Growing in bands or ribbons (a). 2. Growing on colorless stems or in a jelly-tube (c). 3. Growing with their concave sides attached to other plants (e). 4. Free-swimming (/). a. Band curved or coiled. Merddion, 1. a. Band zigzag; frustules attached together iby the corners, Didtoma, 2. a.Band uneven, frustules long, narrow, rapidly sliding on one another. Sacilldria, 3. a. Band straight, or nearly so, edges even, frustules motionless (6). 6. Each frustule six times as long as broad. Fragi- ldria, 4. 6. Each frustule twice as long as broad. Aimantt- dium, 5. c. In a narrow jelly-tube; valves boat-shaped. Zn- cyonéma, 6. On the ends of-colorless stems (¢). . Walves boat-shaped. Cocconéma, 7.- . Valves wedge-shaped. Gomphonéma, 8: VAD DESMIDS, DIATOMS, AND FRESH-WATER ALG, QI e. Valve six to seven times as long as broad; ribs conspicuous, oblique. LZpithémia, 9. é. Valve oval, nearly'as long as broad. Cuocconéis, 10, Valve not curved nor S-shaped (g). Valve in side view arched, the convex margins scalloped. undétia, 11. Valve long S-sbaped. Pleurosigma, 12. Valve boat-shaped or obovate, the ribs sub-pir- allel, conspicuous. Suriré/la, 13. Valve boat-shaped, ribs none. Mavicula, 14. Valve strongly ribbed transversely; a nodule at each end and in the center. Pinauldria, 15. Valve not ribbed; with a central longitudinal, and a transverse smooth band, together form- ing across. Stauronéis, 16. oS Se segs = 1, MER{DION CIRCULARE (Fig. 62). Fig. 62.—Merfdion circuldre .Fig. 63.—Didtoma vulgare. Valves wedge-shaped, transverse lines indistinct; bands spiral, often broken into small curved sections (Fig. 62). Common. 2. DIATOMA VULGARE (Fig. 63). Frustules oblong, their four angles being right- angles; the band often attached to aquatic plants; easily separable into its component frustules (Fig. 63). Common. Q2 AQUATIC MICROSCOPY FOR BEGINNERS. 3. BACILLARIA, (Fig, 64). Frustules long and narrow, united laterally, freely and rapidly sliding backward and forward over one another; colony free-swimming (Fig. 64). This is probably one of the most interesting of the common fresh-water diatoms, on account of its strange movements. When quiet, as it prob- ably will be immediatly after being placed on the slide, the band will some- what resemble a row of Fig. 64.—Bacilldria. fence-pickets lying in contact side by side. Suddenly each picket shoots forward until they all are nearly end to end, the band becoming a long irregular line, when they quite as suddenly close together again. This alternate back- ward and forward gliding is continued until the diatoms become apparently exhausted, or the oxygen in the water is consumed. What prevents one frustule from slipping off the end of the other is not known; indeed the cause of the entire frantic perform- ance can only be guessed at. All the species-of the genus Bacilldria are said to live in salt or in brackish water, but the form which I have ventured to identify as a sweet- | water variety of B. paraddxa is if not uncommon in fresh-water ponds. _ : : bp bi! as 2 1 Fig. 65 and 65a.—Fiag- in my vicinity.in New Jersey. ilatia capucina, 4. FRaciLArta capucfna (Figs. 65 and 652). Frustules very narrow, never wedge-shaped, band long Fig. 65 shows the ribbon of united frustules; DESMIDS, DIATOMS, AND FRESH-WATER ALGA. 93 Fig. 65a the appearance of a single valve more highly: magnified. ‘The ends of the valves are somewhat wedge-shaped. 5 HIMANT{DIUM PECTINALE (Fig. 66). Frustules much wider than the preceding; transverse lines distinct on both sides of a narrow central smooth space (Fig. 66). A is the side view of a single frus- tule. ; Fig. 66.—Himantidium pectindle. 6 ENCYONEMA PARADOXUM (Fig. 67). The jelly-tubes are usually very slightly. if at all, branched, the frustules commonly arranged in a longi- tudinal series with- in the tubes, which are attached to qther plants (Fig. 67). 7 COCCONEMA LANCEOLATUM (Figs. 68 and 682). Fig. 67.—Encyonéma paradéxum. Stems often much branched; at- tached to aquatic plants and to other submerged objects; frustules on the ends of the branches, in side view (valves) slightly curved, with a median longitudinal line having a nodule at each end and one in the center (Fig. 68). The frustules are. often found floating freely, when they are usually seen in side view. Fig. 68¢ shows a single valve highly magnified. Figs. 68 and 68a.— ‘occonéma. lan- ceolatum. 94 AQUATIC MICROSCOPY FOR BEGINNERS. 8 GOMPHUNEMA ACUMINATUM (Fig. 69.) _ Stems often much branched, but frequently found unbranched; at- tached to other plants; frustules slightly swollen in the center, the narrow end of the wedge being at- tached to the stem (Fig. 69). g EPITHEMIA TURGIDA (Fig. 70). Valves curved or bent, transverse lines coarse and conspicuous (Fig. : 70). Often found separated from OP ae aes supporting plant, and floating freely. 1o Cocconfils PEDfcuLus (Fig. 71). Valves oval, with a line (raphé) down the center and a small nodule in the middle; attached by one valve to aquatic plants, especially to the leaves of Andcharts (Fig. 71). , Fig. 70.—Epithémia Fig. 71.—Cocconé{s Fig. 72.—Eunétia ~turgida. pediculus. tetraodon, tr EUNOTIA TETRAODON (Fig. 72.) Valves curved, a small nodule at each end of the concave margin; the convex border apparently scal- loped, but in reality bearing four or more rounded ridges (Fig.°72). DESMIDS, DIATOMS, AND FRESH-WATER ALG. 95 12 PLeuRosicMaA (Fig. 73.) Valves long S-shaped, widest in the middle and ta- pering to each end, one of which curves towards the right-hand side, the other towards the left-hand (Fig. 73). A narrow S-shaped line, the raphé, extends down the center of the valve with a nodule conspicuous in the middle only. There are nearly two- hundred known species and varieties of this genus, most of which may be recog- nized by this peculiar and beautiful curva- ture of the sides, the word Pleurosigma meaning S-shaped sides. The valves are ‘ Fig. 73.—Pleuro- sigma, very finely striated in three directions, transverse and decussately oblique, the lines being remarkably close together, and demanding a comparatively high-power objective of excellent construction to see them. The valves are therefore often used to test the good quali- ties of certain objectives. To the beginner, however, all the Pleurosigmas will probably appear to be smooth. The species most frequently used as a test is P. anguldtum, a salt-water form. , 13 SURIRELLA SPLENDIDA (Fig. 74). The valves are obovate in form, with transverse ribs large and conspicuous, the spaces between them seeming to be lower than the edges of the valves, thus giving the latter the appearance of having a narrow wing around the margin (Fig. 74). The members of this genus are also used as test-objects, the one most commonly employed, Surirella gemma, beinga marine species. - Fig. ie eieeilas spléndida. 96 AQUATIC MICROSCOPY FOR BEGINNERS, 14 NAvVfcULA CUSPIDATA (Fig. 75). Valves somewhat diamond-shaped, or rhombic, widest in the center, tapering with straight margins to each <—_- > end; a straight line (raphé) Fig. 75-—Navicula cuspidéta. Gown the middle ‘with a cen- tral nodule (Fig. 75). 15 PINNULARIA (Figs. 76 and 77). 1. Margins of the valves parallel, their ends and center somewhat inflated; transverse ribs large and con- spicuous; a line (the raphé) down the middle, with a nodule at each end and at.the center; frustule’ large. Common. VP. major, Fig. 76. MMMM TOSS Fig. 76.—Pionuldria major. Fig. 77.—Pinnularia viridis. 2. Margins of the valves slightly convex, the ends.and the center not inflated; ribs large and conspicu- ous; a line (the raphé) down the middle, with a nodule at each end and one in the center; frustule smaller than the preceding. ' It is named green (viridis), as some one has said, probably. because it is always brown. P. wiridis, Fig. 77. This is one of the commonest of our fresh-water diatoms. Diatomists now class Pinnularia with Navicula, and call these forms Navicula major and Navicula viridis. ee + 16 STAURONEIS PHONOCENTERON (Fig. 78). Valves widest in the middle, tapering with convexly curved margins to both ends; central and transverse DESMIDS, DIATOMS, AND FRESH-WATER ALG. 97 bands smovth and conspicuous. Common (Fig. 78). The cruciform smooth band is the characteristic by which it may be at once recognized. For a collection of illus- trations of the diatoms of ee this country the reader LSS should refer to Wolle’s “Diatomacee of North America, illustrated with twenty-three hundred figures.” Fig. 78.—Stauronéis phoenocénteron. III. FRESH-WATER ALG. The Alge often collect together and form green clouds in the water or a scum-like growth on the. sur- face. Frequently, however, the student will find iso- lated filaments under his microscope, and not know how they were placed there, or he will find single threads adherent to other aquatic objects which he may be examining. The color of the visible masses is usually bright green; it may be brownish if the plants are in fruit, or the natural tint of the individual alga may be brownish or purplish, or, when massed to- gether, almost black. Many species are coated witha mucous or slimy material that makes them slippery, and difficult to handle or to remove from the water unless a dipper or a spoon be used, sometimes not even then. They. are seldom found in any abundance in deep water, appearing to prefer shallow ponds and slowly flowing streams, where they may have plenty of warmth and light. Few of the species are free-swim- ming. Most kinds are adherent to submerged leaves, stones, or sticks; some form feathery Clusters of branching filaments; others surround themselves by 8 798 > * AQUATIC MICROSCOPY FOR BEGINNERS. little balls of translucent jelly often found studding leaves of grass or other objects in the water. The following have been partly described in the Key on a preceding page. 1. ScENEDfsMuUS (Fig. 79). . The cells are usually four, attached together by their long sides. The spines on the narrow ends of the two terminal cells are curved towards each other, and a spine sometimes grows from the middle of one of the central cells. The plant is common. S. cauddtus, Fig. 79." Fig. 79.—Scenedésmus caudatus. Fig. 80.—Pedidstrum Boryanum. 2, PrpIASTRUM (Fig. 80). The green cells are usually so arranged as to leave narrow colorless bands between them, and occasion- ally, in those species formed of a great number of ad- herent cells, several apparently empty colorless spaces are scattered about the disk. In the latter cases the marginal teeth, which are always colorless, are often numerous but they are usually more or less conspicu- ously arranged in groups of two each. In the species here figured the marginal teeth are generally twelve in number. FP. Soryanum, Fig. 80. There are about a dozen known species in this country. ‘Most of them are not rare. DESMIDS, DIATOMS, AND FRESH-WATER ALGE. 99 3. VG6LVoOX. A small sphere continually in movement, rolling through the water in a graceful manner, its surface studded with green points. Undera low power itseems like a hollow globe, and the cause of the motion “is a mystery; but the 41-inch objective, when the Vol- vox moves slowly or rests, shows that each of the green points that together stud the surface, bears two. fine cilia or little hairs continually vibrating and lash- ing the water. It is from their vibrations that the. Volvox receives its rolling motion. The deep-green balls often seen within the larger globe are young plants in different stages of development. When ma- tured the mother-globe ‘is ruptured, and the young plants then float out and roll away through the water, revolving there as they are often seen to do even be- fore leaving the parent, and there leading an independ- ent existence. The water in some localities is, in June, so filled with these rolling globes that it is colored green by them, and when the collecting-bottle is held against. the light they become visible to a sharp eye as small pale-green spheres. The diameter of a full grown plant is about one-fiftieth of an inch. V. globdtor. They occur everywhere but are not common any- where. In thosé localities where they usually exist, they seem to have periods of profusion and of de- ficiency. Ina small and shallow but permanent pond where several years ago I found them literally and actually by the million, I have never since been able to discover a single specimen. Thisis not an instance of periodic deficiency, but of complete absence. Still, ‘the rule seems to hold good for this country. In Eng- 100 AQUATIC MICROSCOPY FOR BEGINNERS. land the beautiful creatures appear to be more perma- nent denizens of shallow pools, and more frequently collected, They have had a varied experience with the sys- tematists, or those scientific men who appear to be happy only when they are arranging the objects of Nature in classes and groups, for these pretty globes have been classified among the plants, then among the animals, and back and forth in a way that. would have bewildered them perhaps, if they had been conscious of it, but certainly in a way to bewilder a reader who has tried to follow the changes to and fro, and tried to get the unfortunate things safely lodged in the one:group orthe other. At present, they are said tobe animals. That is, their latest investigator has so de- cided. By the time this book is out of the printer’s hands Vélvox may again be a plant. It has been here referred to asa plant and included among the plants for convenience, the writer trusting to the explanation of its vicissitudes to impress the reader with the fact that, just now, Vélvox is not a -plant. 4. Hypropictyon (Fig. 81). A yellowish-green scum is sometimes seen on the wa- ter, which, when spread out over the figures, proves to be a net of delicate hexagonal meshes. It may grow to ten or twelve inches in length, and form floating masses several inches in thickness. The nets are composed ofnarrow, short, cylindrical cells, and are, under a low power, remarkably beautiful. The figure shows a part of anet, H. utriculdtum, Fig. 8. In my locality in New Jersey, Hydrodictyon oc- DESMIDS, DIATOMS, AND FRESH-WATER ALG#,. I0I1 curs so profusely at times that it might be collected by the wheel-barrow load. It is not uncommon else- where. The masses which the Algee in general form are usually composed of great numbers of long. threads, commonly called filaments, and matted together, prob- ably by their rapid growth, among other causes. Each filament is built up of many cells attached to each other by their narrow ends, the single filament being for convenience, considered a single and entire plant. The Algz have no roots, al- though they may fasten themselves by one end to sub- merged objects, while a few single-celled terrestrial forms have minute branching filaments which may be called rootlets, growing from them and penetrating the ground (Botrydium). Some are simple, straight, or curved cellular threads; some give off branches which generally resemble the main plant or stem. Their color is usually some shade of- green, although a few purplish and brownish ones are known. ‘The fol- lowing is a key to those genera referred to in this book. Fig. 81.—Hydrodictyon utriculatum. Key to Genera of Fresh-water Alga. 1. Color brownish-green, bluish, or olive (a). 2. Color pure green (d). a. Filaments branched (4). a. Filaments not branched (c). 102 AQUATIC MICROSCOPY FOR BEGINNERS. é. Branches with many, whorled, moniliform threads; plant slippery. Batrachospérmum, t. c. Cells moniliform; plant with larger scattered spherical cells. Anabaena, 2. ec. Cells not moniliform; plant bluish green; twist- ing, bending, gliding. Oscil/dria, 3. @. Green color in one or more spiral bands in each cell. Spirogyra, 4. d. Green color in two star-shaped masses in each cell. Zygnéma, 5. d. Green color not in patterns (e). é. Terminal cells with a colorless, hair-like bristle (Ff): Terminal cells without a bristle. Vauchéria, 6. . Forming small green, visible, jelly-lixe masses. Chetéphora, 7. . Not forming jelly-like masses (g). . Cells of the branches green, those of the stem larger, colorless, but with a transverse green band. Draparndlda, 8. Cells of branches and stem green; bristles with a swollen base. Aulbochete, 9. wy SWS 9 I. BATRACHOSPERMUM (Fig. .82). The plant often grows abundantly, attached to sub- merged objects, in springs, ditches; and ponds. It varies in length from an inch or less to one or two feet, and in color it may be bluish-green, brownish, or pur- plish. It is covered with a mucous substance that makes it an exasperating thing to take out of the water as itis so slippery and so difficult to handle. It is much branched, the branches being formed of many short threads in whorls, each thread conspicuously DESMIDS, DIATOMS, AND FRESH-WATER ALGA, 103 beaded. The whorls of branches are often so close to- gether that the entire plant, as it floats beneath the water, seems to be a string of little balls. Under the microscope each moniliform thread is usu- ally seen to be terminated by a colorless hair-like bristle. This, however, it not always present. With a high power the ends of the beaded fila- ; ments may De séen to run Me: 8 —Beuachosptecum down the main stem in long, narrow, almost colorless cells. B. moniliférme, Fig. 82. 2. ANABANA (Fig. 83). Filaments moniliform, freely floating, the cells spherical, the larger scattered ones globular, yellowish. The filaments are often curved, and sometimes surrounded by a delicate gelatinous material, in which the filaments are often collected together in a mass. There are Fig. 83.—Anabena. several species, all of which closely resemble each other (Fig. 83). ‘They are supposed to be a stage in the development of some other alge. Similar filaments, but with a gela- tinous sheath, belong to the genus Nostoc. 3. OSCILLARIA (Fig. 84). .These plants are found almost everywhere in stand- ing water. They often form thick floating mats of a 104 AQUATIC MICROSCOPY FOR BEGINNERS. dark purplish or almost blackish color, or they are found entangled among other plants in a dark green film. Under the microscope they consist of filaments com- posed of very many short cells that vary a good deal in width according to the species, of which there are several. They can usually be recognized by Fig. 84.—Oscillaria. the bluish-green color and by their characteristic motions. Some are like straight rods of cells bending slowly from side to side; others twist and writhe, and coil themselves into circles, only to uncoil slowly and re- peat the movements. Some deliberately glide for- ward, the tip gradually and gracefully bending and curving. The movements, when the plants are in a healthy condition, are incessant. The beginner need never be ata loss to recognize one of the several species of Oscilldria. ‘Three forms are shown in the figure. (Fig. 84.) Oscillaria is not in a sheath. A similar alga is not uncommon whose filaments are singly enclosed within a colorless sheath plainly visible at the extremities of the plant, where it projects as an empty, membrarous tube. ‘This is Zyngsya and may be readily mistaken for Oscillaria unless the sheath is determined to be present or not. 4. SPIROGYRA (Figs. 85, 86). The Spirogyre are easily recognizable by the beauti- ful spiral bands of green within each cell, as shown.in Fig. 85. There may be one, two, or several of these DESMIDS, DIATOMS, AND FRESH-WATER ALG#&, 105 spirals winding within the cell-wall, the number help- ing to determine the species, of which there are many. The plants usually grow in masses, and especially form. Fig. 85.—Spirogyra. those soft green clouds apparently floating just under the surface of the water. They are often’ entangled among submerged objects, but almost as often free. Their manner of producing spores is remarkable, but not confined to them, as other Algz have a simi- lar method. Each of the cells of two filaments lying side by side begin, usually atthe same time, to protrude from those sides nearest each other a narrow tube. ‘These tubes meet and grow together, so that the two plants soon resemble a ladder, the original filaments forming the sides, the tubes being the rounds. The coloring matter then falls away from the cell-walls, and the entire contents of the cells of one filament pass through the rungs of this living ladder into the opposite cells, where the contents of both mingle. From this commingling the spore is formed, one in each cell, and is, when ripe, ovoid and dark brown. This conju- gation, as it is called, and the result- ing spores are shown in Fig. 86. The ; plants are often found in this condition Fig. 36.—spirogyra in in June and July, sometimes even con earlier than June. 106 AQUATIC MICROSCOPY FOR BEGINNERS. 5. ZYGNEMA (Fig. 87). This usually floatsunattached. The cells are rather wide and short, the internal stellate masses, by which it may always be recognized, being dark green in color. - The formation of the spores resembles that of Spirogyra. It is found in conjugation in Fig. 87.—Zygnéma insigne. April. Z. insigne, Fig. 87. 6. VAuCHERIA (Fig. 88). A damp green mat growing on the mud in shallow water, not rarely exposed to the air, and resembling felt both to touch and sight, will usually prove to be Vauchéria. The filaments are very long, with few widely separated branches. The green matter is dif- fused over the cell-wall, and when the latter is broken, flows out and often forms. green globules and irregular masses. The spores are produced in two ways, both of which the beginner will see, as they are not rare early in the year. In one method the end of a filament enlarges and becomes club- shaped, while a partition grows across it near the handle of the club. The contents of this new cell be- come dark, opaque, and hardened. The’ free end uf the cell Fig. 88,—Vauchéria, “ nowbreaks, and the DESMIDS, DIATOMS, AND FRESH-WATER ALG&, Io7 spore slowly passes out, being squeezed into an hour- glass shape as it does so. No sooner is it free than it is off like a flash, being covered by rapidly vibrating cilia. But it soon settles down, and finally develops into a filament like the parent. In the other method the filament produces from the side, as shown in Fig. 88, a small ovoid cell, and near it a narrow curved or coiled tube. Presently the free ends of each of these cells open, and the contents of the tube pass into the ovoid cell, in which a spore without cilia is finally formed. This spore is said to fallin the mud and to remain unchanged for many ‘months, sometimes all winter, but finally developing into a Vauchéria like the one from which it sprung. In some of the species the ovoid cells are grouped in a cluster of several, and the whole, with the coiled. tube, is raised above the filament on the end of a short stem. 7. CH&TOPHORA (Fig. 89). The light-green jelly-like masses into which this Alga grows are found attached to submerged leaves of Fig. 89.—Chzet6phora élegans. 108 AQUATIC MICROSCOPY FOR BEGINNERS. grass, to twigs, or other small objects of the kind. They are often almost spherical, varying in size from that of a pin-head to that of a marble. The surface is smooth, and so slippery that to pick up one of these Chetéphora jellies with the fingers is next to impossible. The plant within the jelly is formed of fine branching filaments usually radiating in all direc- tions from a common center, the branches being shorter and most numerous near the surface of the gelatinous mass, their ends bearing a fine, colorless hair or bristle. Under a low-power objective the plant, if carefully flattened out, is beautiful, and is justly named ‘‘elegant.” Ch. elegans, Fig.-89. It is common. Only a small portion of the growth is shown in the figure. 8. DRAPARNALDIA (Fig. 90). There need be no trouble in recognizing this Alga. It grows attached to many submerged objects, the fine branches giving it a deli- cate, feathery appearance to the naked eye. Under the mi- croscope it is seen to be much branched, the branches being arranged in clus- ters, each branch being formed of cells smaller than those of the main stem, and filled with chlorophyl, while each terminal cell is ended by a long, colorless’ hair. The cells of the stem are but little longer Fig. 90.—Draparndldia glomerdta. DESMIDS, DIATOMS, AND FRESH-WATER ALG&, than wide, and are usually colorless except for a narrow, light green chlorophyl band surrounding the center. WD. glomerdta, Fig. 90. It is common. a small part of a plant is shown in the figure. g. BuLBOCHATE (Fig. gt): This genus can always be recog- nized by the swollen or bulbous bases of the long hairs that tip many of the cells. It grows asa guest on larger Alge, or on the leaflets of Ceratophyllum or of other aquatic plants (Fig. 91). The Rev. Francis Wolle has com- pleted his monographs on our fresh-. water microscopic flora by the addition of his work on ‘‘The Fresh- water Algxz of the United States,” to which the student is referred. Fig. g1.—Bulbocheete. 109 Only 110 AQUATIC MICROSCOPY FOR BEGINNERS, CHAPTER IV. RHfzoPoDs, THe Rhizopods are the lowest animals in the scale of life. Scarcely more than a drop of jelly-like proto- plasm, the lowest of these lowly creatures live, move, eat, and multiply. Some are so far down in the scale that they are actually only a particle of soft and unprotected protoplasm, moving, like the common Ameba, which is one of the Rhizopods, by protruding long, thread-like projections of its own substance from any part of its body, and withdrawing them again into its substance, where they entirely dis- appear. These protruded parts, by means of which the creatures move and capture their food, are called pseudopodia, from two Greek words, meaning false feet. And since they often extend to long distances from the body of the animal, dividing and branching somewhat after the manner of roots, the group of lowly animals producing these pseudopodia is named the Rhizopods, or root-footed, a word also from the Greek. The Ameeba, and those Rhizopods nearest to it in structure, are formed of naked protoplasm; they are simply a drop of colorless, living jelly. But some higher in the same group secrete or build around RH{ZOPODS. I1l their soft bodies a protective shell, often of exquisite form and remarkable construction. Thus the mem- bers of one genus, Difftigia, build themselves shells of sand grains cemented together with the most perfect regularity, every grain exactly fitting to its place. Yet, when the young Difflugia happens to be where suitable sand is scarce, it will build its shell of diatoms,~ often using those that are longer than the completed covering, attaching them lengthwise, side by side, and parallel to each other. Another genus, Arcélla, secretes from its body a brown shell of delicate membrane which, with a high power, is seen to be formed in minute hexagons. And still another, Clathrulina, the most beautiful of all the fresh-water Rhizopods, lifts itself on a long stem, and there surrounds its body by a hollow latticed sphere, and through the large and rounded openings in the walls extends its pseudopodal rays in search of food. In the unprotected forms—those without a shell— the pseudopodia are protruded from any part of the body; in those furnished with a shell they are pro- truded from that portion of the ‘body immediately in . contact with the mouth of the shell, through which they often extend for along distance as exceedingly fine; branching threads. With a few exceptions the bodies of the Rhizopods are colorless; in those excep- tions the coloration is usually due to the presence of colored food, and so is diffused throughout, the entire protoplasm, or it is confined to the: parts near the surface, the central portion being nearly colorless. The pseudopodia are always colorless. Not only do the Rhizopods move by means of these ‘false feet,” but they capture food with them, consum- I12 AQUATIC MICROSCOPY FOR BEGINNERS, ing both plantsand animals. Diatoms, Desmids, Infu- soria (Chapter V.), Rotifers (Chapter VIII.), almost any living things small enough to be seized, are accepta- ble. When a desirable morsel is found, the end of the pseudopodium touching it usually expands, and a wave of the body substance flows along it until the object is surrounded, like an island of food in a sea of proto- plasm. The whole broadened pseudopodium is then withdrawn into the body, carrying the food with it; or if the captured object is unusually large, or if it strug- gles a good deal, several pseudopodia may come to the -assistance of the first, or a great wave-like out-flow from the body may envelop both pseudopodia and food. Vhese peculiar animals have no distinct mouth and no distinct stomach. The mouth in the shelless ones is formed at any point on the surface wherever the creature chooses to open itself and take in the food- particle; and the stomach is in any part of the internal substance; the food is digested wherever it may happen to enter and remain. They have no eyes, yet they seem to direct their course and avoid unpleasant or in- jurious obstacles. They haveno nerves, yet when dis- turbed they contract into a small ball-like mass, or withdraw themselves into their shell. They also ap- pear to feel some sort of sensation of hunger, for they are often seen to take food, and they select what they like. They are numerous and common. They are to be found in any shallow pond, or pool, or body of still water. They glide among aquatic plants and Algae, especially on the lower surface of water-lily leaves, and among Myriophyllum and Ceratophyllum. Sphagnum moss is sure to contain them in abundance, as has al- x . RH{ZOPODS. 113 ready been stated. But the mud is an accessible and fruitful source of suppiy. To obtain them, gently scrape with a big iron spoon or with the edge ofa tin dipper, the surface of the ooze from the mud in shallow ponds, and transfer it to the collecting-bottle. Let the muddy mixture stand fora few minutes until the Rhizopods settle towards the bottom, and carefully pour of some off the water, adding more ooze if desired. Pour the mud and water into saucers, and set these near the window, when the Rhizopods will make their way to the surface, and may be removed by the dipping-tube. Do not place the saucer in the sunlight; Rhizopods prefer a little shade. They are invisible, consequently the collector must collect on faith, as he must usually do when out ona microscopical fishing tour. But he will seldom be dis- appointed if he gathers the surface ooze from the edges of somewhat shady ponds, and avoids those places long exposed to thé sun, and never sinks the scraper into the thick black mud, which contains no animal life of any kind. They are small and easily overlooked in the field of the microscope, but when one of the unprotected forms and a single shell-bearing Rhizopod are recognized, the observer will never again overlook any of them in the material on his slide. The Amceba will probably be the first seen, as a colorless, jelly-like body, very soft, and changeable in shape, slowly moving forward and suddenly altering its course and extending itself in numerous long, blunt, finger-like pseudopodia, which are lengthened or shortened at the creature’s will. Or he may see a small pear-shaped collection of sand- grains slowly moving about the slide, apparently with- 9 114 AQUATIC MICROSCOPY FOR BEGINNERS. out a cause, although in such cases a careful examina- tion of the narrow or stem end of the pear will show long, fine, and colorless pseudopodia issuing from the mouth, and he will know it to be a Rhizopod. After he has recognized a living shell he will have no trouble thereafter in knowing a dead one, and by referring to the following Key he will be able to learn its name, unless it is a member of a very uncommon genus. Key to Genera of Rhizopods. 1. Body without a shell (a). 2. Body with a shell (e). a. a. d. ~~ Wares Without fine, hair-like rays; pseudopodia thick and blunt (4). With fine, hair-like rays (in the addition to pseu- dopodia) on all parts of the body (c). Body colorless, very changeable in shape; often large. Ameba, 1. Body orange in color or brick-red, with short pin- like rays. Vampyrélla; 2. Body colorless or greenish (d). Rays, not the pseudopodia, rigid, forked at the ends; body often green. Acanthocystis, 3. Rays flexible, not forked. Actindphrys, ‘4, or Actinospherium, 5. Shell a latticed globe on a long stem. Clathru- lina, 12. Shell formed apparently of sand-grains (/). Shell not formed of sand-grains (g). . Not inclined; pear-shaped; or globular with spines at the summit. Dzifftigia, 6. Inclined; circular or oblong, thicker and with spines at the rear. Centropyxts, 7. RH{ZOPODS. 1I5 Shell usually brown, sometimes colorless (2). Shell colorless, ovoid, not curved (7). . Shell often yellowish, retort-shaped, neck curved, mouth downward, circular. Cyphodéria, 11. A. Circular, depressed, with or without marginal teeth. INFUSORIA. 149 k. Cilia large, few, scattered (/). &. Cilia fine, numerous (m). 7, Body more or less circular in outline. Euplotes, 18. 2. Body more or less oblong in outline. Stylonychia, 19. m. Mouth followed by a conical tube of rods. Ch#- lodon, 20. m. Mouth followed by a brown, sickle-shaped mem- brane. Loxddes, 21. 1. DENDROMONAS (Fig. 106). The stem is many times divided into numerous branches, and the branches themselves are also much divided, with one small Infusorium, of- ten two, at the end ‘of each. The whole has a_ beautiful, but colorless tree-like ap- pearance, the stem being often found attached to Cerato- phyllum. The ani- mals have each two flagella, but they are visible only to a high- power objective. There is no special mouth. A particle of Fig. 106.—Dendrémonas. food dashed down by the flagella against any part of the body sinks into its soft side and is thus swallowed without a throat. The whole colony is often more branched than is shown in the figure. It can be recog- nized with a good one-inch objective. 150 AQUATIC MICROSCOPY FOR BEGINNERS. a 2. CarcHfsium (Fig. 107). The stem, attached to. plants or to other submerged objects, is divided at the summit into many branches, with one Infusorium at the end of each, and many others scattered along them with shorter branches of their own. Through the main stem and through all the branches extends a cord-like muscular thread that suddenly contracts when the animals are frightened or disturbed, and pulls the entire colony down toward the point of attachment to the plant. But each Fig. 107,—Carchésium. branch may contract one at a time and draw its burden of infusorial fruit down to the main stem without disturbing any other portion of the col- ony; or all the.branches may contract at the same time. Therefore, while the individual animals are connected together, they are still somewhat independent. The front border of each body is surrounded by a circle of cilia visible under a high power. They are the only cilia on the creatures. When the animal is contracted these cilia are folded together, each body then resembling a little ball. They vibrate rapidly, producing circular currents that bring to the mouth any food particles which may be in the vicinity. The entire colony is colorless, and may include as many as a hundred Infusoria on the branches. It can be seen with a low power objective. The independent INFUSORIA. I51 contraction of the branches and of the stem will dis- tinguish it from all other tree-like Infusoria. 3. Epistyiis (Fig. 108). As in the two preceding, the stem of Zprstylis is often much branched. The Infusoria at the ends of the branches can alone contract, which they often do with. a jerk, settling back on their stalk as if they meant to impale themselves, or dropping and nodding like flowers fading on their stems. The bodies of the expanded animals are somewhat bell-shaped, their widest part being the free end which closes when the body.contracts. The front border is encircled by a row of cilia, to be properly discerned only with a high-power objective. The one-inch lens, however, will show the rapid currents produced, because all small particles in their neighborhood are caught up and dashed around in the mimic whirl- pools. The animals select from these streams anything which they may want and let the rest sweep by; they have a distinct mouth near the center of the frontal region. The entire colony is usually colorless. It is often found attached to Cerato- phyllum. Fig. 108.—Epistylis. 4. VORTICELLA (Fig. 109). The unbranched stem of Vorticél/a contains a spiral muscular thread like a thin cord, which with surprising suddenness contracts into close.coils, and draws the Infusorium down with it, the bell-shaped body con- tracting at the same time into a spherical mass. 152 AQUATIC MICROSCOPY FOR BEGINNERS. The Vorticelle are common, scarcely a leaflet of any aquatic plant being without them, They are usu- ally colorless, although green ones do occur. The body is bell-shaped, the narrow part of the bell being fastened to the top of the contractile stem. The front border is surrounded by a circle of fine cilia which need a high power to show them. These produce currents in the water similar to those of Epistylis, and for the same food-collecting purposes. The contractions of the stem are surprising in their sudden- ness. While the observer is quietly gazing at the graceful creature whirling its cilia and making tremendous whirlpools on a small scale, it disappears like a flash, and the student feels like looking for it on the table. But presently it begins to rise slowly from .the plant against Fig. 109.—Vorticélla. which it was crouching, and the spirally coiled stem lengthens as it straightens. Frequently it is hardly extended be- fore it again leaps out of sight, or close to the object that supports the stem. This. will probably be one of the first Infusoria to attract the beginner’s attention, and he will think it a wonderful thing, as it is. The figure (109) shows some extended and some contracted. They are often found in clusters, sometimes of a hundred or more, all bobbing and swaying ina laughable way, for when one contracts it usually sets them all off. INFUSORIA,. 153 5. DINnOpRYON (Fig. 110). In the early spring, as early as March, among the Algz then found go abundantly in the shallow pools, colonies of very small, vase-shaped lorice are often obtained. - They are sometimes attached to a plant or filament of Alga, or as often they float. freely through the water, as they are fastened to the plant by a very slight tenure, and are easily detached, then floating © freely. The lorice are transparent and colorless, and may be overlooked, but the Infusorium within each one is rather conspicuous to even a low- power objective, for it hasa narrow green band on each side of the . body, and often a minute red eye- like spot in the center of the front order. The lorice are united to- ther into colonies by the attach- ment of one or two sheaths to the fat edge of the one behind, until branching clusters. of some size are formed. The front border of each enclosed Infusorium bears two flagella, one long and one short, but they are seen with difficulty even with a moderately high-power objective. The lashing of all the flagella ina large colony urges it rapidly through the water. Ac- cording to my experience Dindbryon is seldom found in the summer. Fig, 110.—Dinébryog 154 AQUATIC MICROSCOPY FOR BEGINNERS. 6. VacinfcoLa (Fig. 111). The lorica is colorless, transparent, and about three times as long as broad. In form it is long vase- shaped, or nearly cylindrical, the base, or the part fastened to the plant or other object, being usually rounded. The animal, when it projects, extends for a considerable distance beyond the opening at the front of the lorica. When fright- ened, or disturbed in any way, it quickly closes up its broader front part, and retreats as far into the sheath as possible. When recov- ered from its fright it slowly ascends to the opening, expands itself and resumes its fishing operations. It is fastened to the extreme end of the lorica by the tip of the body; from the sides it is entirely free. On its front border it has a wreath of fine cilia in continuous motion when the animal is extended. The Fig. 111.—Vaginicola. body is soft and flexible, and is sometimes of a pale greenish tint, but the lorica, I think, seldom changes color even with age. It is not uncommon to find two bodies in one sheath, where they seem to live together in peace and harmony. This may be an advantage to both, for two wreaths of cilia can, of course, produce stronger currents, and so bring more food to the mouths of the always hungry creatures. Vagindcola is common on Lemna and on Myriophyllum. 7. PLATYCOLA (Fig. 112). - The lorica is flattened, and is in outline almost cir- INFUSORIA. 155 cular. It is always adherent to some submerged ob- ject by the broad flat side, the opposite or upper sur- face being convex. The opening, through which the animal extends itself, as in Vaginicola, is at one end, and is often prolonged into a short neck. The fein shows a side view with the animal extended. When young the lorica is color- less, but it soon changes. to a deep brown, often becoming so opaque that the body of the Infu- sorium cannot be seen through its walls. The body itself is usually color- less; it is attached by its tip to the side opposite the mouth of the lorica. When frightened it darts back into the sheath as Vaginicola does. Two animals are not seldom found in one lorica. It is not uncommon on Ceratophyllum and on other aquatic plants. Fig. 112,—Platycola. “e 8. CoTHURNIA (Fig. 113). The observer may at first mistake this for a small Vaginicola, as the lorice somewhat resemble each other in shape; but Cothirnia can always be distin- guished by the little stem or foot-stalk that lifts it a short distance from the plant to which it is attached. This foot-stalk in some species is very short, and must be especially looked for; in others it is some- what conspicuous. The lorica is vase- shaped, often with the sides variously curved. It changes to a brown color as it grows old. The body of the enclosed Infusorium is _€%),235,¢ 156 AQUATIC MICROSCOPY FOR BEGINNERS. not colored. In its action it resembles Vaginicola and Platycola, being similarly attached to the posterior end of the lorica, and having a similar circle or wreath of cilia around the front border. ‘Iwo animals are some- times found in one lorica. g. STENTOR (Figs. 114, 115, 116). The Sténtors vary a good deal in shape in the same species, the bodies of all being at will somewhat changeable in form. ‘The largest are trumpet-shaped, and are, asarule, permanently attached to some ob- ject by the narrow end of the body. They also com- monly form a soft, brownish, granular sheath or lorica, to the bottom of which they retreat when disturbed, folding together the wide trumpet-shaped frontal bor- der. ‘heentire surface of the body in all the species is cili- ated, but the cilia are small and fine. Around the edge of the anterior border is a circle of longer and larger vibratile hairs, visible with a moder- ately low power. The Sten- torsareallcommon. The fol- lowing Key may help the be- ginner to recognize some of those most frequently seen. Key to some species of Sténtor. 1. Attached, trumpet-shaped, and often forming a short, soft granular sheath (a). 2, Free-swimming, more or: AN less ovoid; green, red, Fig. 114.—Sténtor polymérphus. blue or-almost black (4). INFUSORIA, 157 a. Body large, trumpet-shaped, greenish; often without a visible sheath, and when one is formed it is sometimes soon abandoned, the Stentor swimming about freely. The body is slightly changeable in shape. Several Stentors of this species are often found close together, having formed in common a soft sheath divided ~ into irregular compartments, one. for each In- fusorium. SS. polymérphus, Fig. 114. a. Body long, and narrowly trumpet-shaped, the frontal region divided into two lobes, one of which is almost at right angles to the other. The body has many long, fine, stiff hairs (setee) pro- jecting from it, and visible under a high-power (4-inch) objective. The sheath is always present. It is narrow, cylindrical, brown, and about one-half as long as the ex- tended body. This Stentor is never free-swimming, and is never found in company with others of the same species. It is not un- common on Ceratophyllum and on other aquatic plants. S$. Bar- rétii, Fig, 115. 4. Body green or red, the red color often limited to the part just be- “® 76h" neath the wide frontal border where the circle of large cilia is. Sometimes the red color is diffused over the whole body, but usually the green matter so obscures it that it remains invisible unless specially looked for, 158 AQUATIC MICROSCOPY FOR BEGINNERS, This species is often extremely abundant at the bottom of shallow ponds in early spring. The green color then always entirely conceals the red. SS. ¢gveus, Fig. 116. 6. Body large, indigo-blue. This in shape when extended, resembles Fig. 114; when contracted it is not unlike Fig. 116. Very com- moninsomelocalities. S. cerdleus. S 6. Body dark brown, almost black. Fig. ni Sletion This in form likewise resembles Fig. 116. Common. S. n@er. to. ASTASIA (Fig. 117). Body long, narrow, and'colorless; exceedingly soft, and Changeable in shape, altering its form as it glides Fig. 117.—Astasia. over the slide, which it does rapidly. It has one long straight flagellum at the front. It is common, but may be overlooked by reason of the absence of color. 11, Euciéna (Fig. 118). Body long and rather narrow, being widest in the middle and tapering to both ends. It is exceedingly changeable in form, and bright green or red in color. The front end may be seen with a high power to be notched as if the Infusorian had two lips, the long, vi- brating, and colorless flagellum appearing to issue from the notch. There is sometimes a small red spot near the front end, supposed to be an imperfect eye. ‘ INFUSORIA, 159 It is often absent inan old Zugléna. At the posterior end is a short, pointed, stiff, and sometimes curved tail- like prolongation which is usually colorless. The Infu- sorium is common, occasionally occurring in such numbers that it ai tinges the water green. There ~=ihiky is another species, or another variety of this species, whose body is bright crimson. It also is so abundant at times that it colors the water blood-red. The flagel- lum is often lost, a fact which may at first give trouble in the identification of the animal. Fig. 118.—Eugléna. 12. CHILOMONAS (Fig. 119). This colorless little creature is very common in vegetable infusions. It may be recognized by the Sere? Loo8 2290c9e9008 Fig. 119.—Chilémonas. Fig. 120.—Phacus Fig. 121.—Phdcus pleuronéctes. longicatidus. notch at the widest or front end, and the curve of the back which makes it look almost hunch-backed. Un- der a high power it shows two flagella, one of them throwing itself into a coil or loop when the Infusorium settles down to rest, which, by-the-way, it frequently does. The body is filled with small colorless disks which the iodine solution turns blue, showing that they are probably starchy. 160 AQUATIC MICROSCOPY FOR BEGINNERS. 13. PHAcus (Figs. 120, 121). “The body of Phacus is flattened, thin, and rather like a small leaf. It is widestin front, usually rounded, and tapering from the center to the short, pointed, colorless tail-like prolongation; at the broad end it has one long flagellum, often difficult to see. There are in our ponds, several species, all of which are green. 1. Body not twisted at the rear, tail short, curved. PA. pleuronéctes, Fig. 120. 2. Body twisted or not at the rear, tail long, straight. Ph. longicatidus, Fig. 121. 14. UV&LLA (Fig. 122). The little animals forming these rapidly swimming and revolving colonies are united by their narrow ends . - into almost spherical microscopic masses, varying in number from two or three up to forty or fifty, or even more. Each Infusorium has a narrow, yellowish-green band down each side of the somewhat egg-shaped Fig. 122.—Uvélla. Fig. 123—Trachelocérca, body, and two long, fine flagella at the broader front end. The colonies are common in early spring in shallow pools with Algz. INFUSORIA. 161 15. TRACHELOCERCA (Fig. 123). This will probably be a greater surprise to the ob- server the first time he sees it than any other common Infusorium, on account of the remarkable neck, which can be stretched out to five or six times the length of the body, and drawn back until it almost entirely disap- pears Thebody, without the neck, issomewhat spindle- shaped, and occasionally ends ina short, tail-like re- gion. The Infusorium is often concealed in a mass of fragments or under a heap of dirt, with only that wonderful neck visible, stretching and bending and writhing like a colorless snake, as its searches the slide for food. The end of the neck is rather pointed and bears the mouth at the tip. The whole Infusuriom is covered with fine cilia. It is common. 16. AMPHILEPTUS (Fig. 124). This is one of the largest of the free-swimming In- fusoria, sometimes measuring ;; inch in length. The neck is not extensile as in Trachelocerca, although it Fig. 124.—Amphiléptus. is the longest part of the whole animal. The body, exclusive of theneck, is somewhat spindle-shaped, taper- ing more rapidly toward the rear than toward the front. The latter or neck-like region is flexible and is capable of being turned and twisted about in a way that often suggests the movements of an elephant’ strunk. The whole body is covered with fine cilia. The mouth is at the base of the neck, on the lower or ventral surface. 12 162 AQUATIC MICROSCOPY FOR BEGINNERS. 17. PARAMA:CIUM (Fig. 125). This is often called the ‘‘slipper animalcule’” from its shape. It is frequently found in the ponds, but is especially abundant in vegetable infusions. The hollow place resembling the opening in the slipper for the foot, is the part leading to the mouth near the’ center of the lower surface. The whole body is cov- ered with fine cilia, and sometimes a cluster of longer, coarser Cilia is noticeable on the posterior extremity of the body. In the writer’s locality this cluster of cilia is present on all the specimens; I have never seen a Paramecium without it. This Infusorium increases rapidly by dividing into two parts across the middle. Its movements are rapid. Fig. 125.—Paramecium. Fig. 126.—Euplotes. 18. EupLéotxs (Fig. 126). This is one of the walking Infusoria, the cilia on the flat lower surface being very large and strong, the animal using them for swimming, or it walks about the. slide or climbs among aquatic plants by resting part of its weight on their tips as if they were legs. When the creature happens to be turned on its back, these large cilia may often be seen pattering irregularly against the cover-glass. They vary in number from ten to twelve. The front border has a row of finer INFUSORIA. 163 but still large cilia extending down the side of the flat surface to the mouth near the center of that part of the body. Four straight, stiff hairs project from the posterior margin, two or them often being divided into fine branches. The back of the Infusorium has no cilia, but is a hard surface, almost like a shell. The animal is very active. There are several species com- mon among Ceratophyllum and Myriophyllum. Fig. 127.—Stylonychia. Fig. 128.—Chilodon. Fig. 129.—Loxddes. 1g. STYLONYCHIA (Fig. 127). To the beginner the members of this genus will closely resemble Euplotes, as all the cilia are confined to the frontal border, to the part about the mouth, and irregularly distributed over one side of the flat lower surface as walking organs. It can, however, easily be distinguished from Euplotes by its shape, being much more oblong. Sometimes it is long and narrow, while Euplotes is always more or less circular. It has no cilia on the back, which is usually hard and shell-like. 164 AQUATIC MICROSCOPY FOR BEGINNERS. The species are several, being especially common in vegetable infusions. 20. CHiLopon (Fig. 128). The body is oval and flattened, the lower or flat ventral surface alone being ciliated. ‘The front border is convex, and rather sharply pointed at one corner, the side of the body extending from this corner to the round- ed posterior margin being nearly straight, while the opposite side is strongly convex. The back is smooth and naked. From the pointed corner a curved line of cilia extends back over the flat surface to the mouth, which opens into a cone-shaped bundle of fine rods visible under a high power. The ends of these rods can be seen with a moderately low power, encircling the mouth like beads. The Infusorium lives upon smaller Infusoria and diatoms, which it seizes by pro- truding this peculiar throat, the rods separating as the food is slowly swallowed. Chz/odon is common in still waters. 21. Loxdépes (Fig. 129). The body is long and narrow, the frontal border be- ing convex, with one corner rather acute; but on one side, just below the pointed corner; is a concave space containing a brown, sickle-shaped body lining the hollow which is part of the Infusorium’s throat, The upper portion, or blade of the sickle, seems only to stiffen that part of the cavity, the true mouth being at the beginning of the short handle. The cilia are fine, and are on the lower flat surface only. The body is flexible, often bending on itself. The Infusorium is common in some localities. HYDRAS. 165 CHAPTER VI. HYpRAS, When Hercules was going about doing those wonder- ful things of which we have all heard, it was suggested that he should turn his attention in the direction of Lake Lerna, near Argos, where a monster with a hun- dred heads was making itself unpleasantly active. He visited the place and interviewed the creature, but when he had cut off one of the heads, he must have been surprised to see two new ones sprout out of the bleeding surface. It was discouraging, but the hero began to have the best of the contest when he began to burn the fresh cuts with a hot iron. The monster was the Hydra of mythology. Science has preserved its memory by giving the name to a common and pe- culiar creature inhabiting all our ponds and ditches. The fresh-water Hydra (there are no salt-water Hydras) has a soft and elastic body, elongate cylindrical in form, attached by the tip of one end to an aquatic plant or other submerged object, and from eight to ten long fine arms arranged around a mouth at the op- posite end. There are two species, the green (#. v¢rédis) and the brown (A. vulgaris), both being very common, The whole animal is elastic, and when extended may 166 AQUATIC MICROSCOPY FOR BEGINNERS. be an inch long and easily visible to the naked eye; _ when contracted it resembles: a minute globule of green or of brown jelly, with the shortened arms at the summit like small rounded knobs or projections. It is exceedingly active so far as the arms are con- cerned, for the body is always adherent to some sub- merged object. The arms or tentacles are usually stretched out to their fullest extent, then often ex- ceeding the body in length, and waving and twisting about in search of prey. The figure (Fig. 130) shows several Hydras nearly the natural size adherent to Lemna rootlets. Fig. 130.—Hydras adherent to Lemna rootlets. The body is like a narrow cylindrical bag, the hollow part of the little sack being the stomach, and commun- icating directly with the external water, in which the Hydra lives, by means of the mouth, around which are HYDRAS. 167 arranged the arms or tentacles. These tentacles are themselves hollow, and communicate with the cavity of the stomach. The food consists of small worms, water-fleas or other Entomostraca (Chapter X.),- or even of little pieces of raw beef, if the observer chooses to feed them. They seize the living victim as it is swimming past, by twining a tentacle around it and drawing the struggling creature down to the mouth, through which it is thrust into the stomach: The act of seizure takes place so rapidly that the eye canseldom follow it. The observer can usually only know that the prey is caught and is slowly approaching the oral aperture. Often when the captured object is too large or strong for one arm to hold, several tentacles bend over and twine around it. A creature once caught rarely escapes. When a gathering of aquatic plants is brought home, the Hydras soon make their way to the lightest side of the aquarium or bottle and attach themselves to the glass. At such times I have often amused myself, and doubtless pleased the Hydras, by feeding them with small larve or with aquatic worms. Take in the for- ceps a small aquatic worm by one end, and present the wriggling thing to a Hydra’sarm. No second invita- tion is needed. The worm is embraced as quick as a flash, and, if too long to be swallowed all at once, part of it will hang out of the mouth until the other end is partly digested, but the tentacles in the meanwhile, will not cease to fish for more. Itis said that if the Hydra and the worm.are placed together in a deep cell under the microscope, the performance can be watched through’ a low-power objective. JI have never suc- ceeded in doing this, but there is no trouble in feed- 168 AQUATIC MICROSCOPY FOR BEGINNERS. ing the creatures in an aquarium. They never eat any but animal food, and they are always hungry. The body and tentacles of Hydra viridis are rough- ened by little elevations or warty prominences. ‘The brown species (4. vulgaris) is not so much roughened. These warts contain what are called the stings. These are small oval or vase-shaped hollow bodies, with a fine thread coiled in the interior, and four minute spines. near the summit. When the Hydra is irritated by the pressure of the cover-glass these stings are thrown out : violently, and the long stiff thread can be well seen. When in the animal’s body they cannot be easily examined. One is shown much magnified in Fig. 131. They are often found on the slide when no Hydra is to be seen, and they are sometimes notice- able sticking in the body of some worm or Fig.131.— larva that has escaped a fatal embrace. I Hydra sting : have more than once found a Chirénomus larva (Chapter VII.) in a dying condition and ornamen- ted by a spiral band of these stings in its skin, it hav- ing evidently had a tussle with a Hydra and escaped. The Hydra increases in numbers rapidly by a process of budding. A little protuberance appears on one side of the body, enlarging and growing, and finally, while still attached to the parent, developing tentacles, then resembling the-mature animal in everything except in size. And it is not unusual to see one or more still younger Hydras sprouting from these before they are free from the parent. The body of the young Hydra is hollow, and communicates with the body-cavity of the parent. It captures food like the parent, andit is said to be no uncommon sight to see the old and the young HYDRAS. 169 both seize the same worm. In such cases the strong- est wins, unless the worm breaks in the unfilial strug- gle, when the parts go into the one common stomach, through two separate mouths. Often two young Hydras may be noticed growing from the sides of a single older one, instances of which are shown in Fig. 130. The budded young finally separate from the pa- rent, then leading an independent life, and soon pro- ducing young Hydras from their own sides, if they have not already done so. 5 ‘The creatures are very hardy. They will endure much harsh treatment, and seem to thrive under it. They have been made the victims of many apparently cruel experiments,’ but they are probably not very sensitive to a feeling of pain. The sensation of hunger, and a sense of touch delicate enough to know when a desirable morsel or an obnoxious object comes in con- tact with the tentacles, are probably the extent of their feelings. Trembley, a Dutch naturalist who studied the Hydra as long ago as 1739, first called at- tention to the harsh treatment they would endure and live. Inarather quaint, old-fashioned translation it is said that, ‘‘If one of them be cut in two, the fore part, which contains the head and mouth and arms, lengthens itself, creeps, and eats on the same day. The tail part forms a head and mouth at the wounded end, and shoots forth arms more or less speedily as the heat is favorable. If the polype be cut the long way through the head, stomach, and body, each part is half a pipe, with half a head, half a mouth, and some of the arms at one of its ends. The edges of these half-pipes gradually round themselves and unite, beginning at the tail end; the half-mouth and _half- 170 AQUATIC MICROSCOPY FOR BEGINNERS. stomach of each becomes complete. A polype has been cut lengthwise at seven in the morning, and in eight hours afterwards each part has devoured a worm as long as itself.””. Trembley also sliced them across, and found that each piece developed a cluster of ten- tacles; and he finally turned them inside out, and in a few days the maltreated creature swallowed food, al- though its old skin was now lining. its stomach, and its old stomach-membrane had now become its skin. This, at least, is Trembley’s account. More recent experimenters, however, have doubted the correctness of this explanation, preferring to believe that while Trembley was absent or a little absent-minded the everted Hydra quietly turned itself right side out, and so deceived its tormentor. There is a peculiar parasitic Infusorium (Fig. 132) often seen in considerable numbers gliding rapidly over the body and arms of the Hydra, especially of Hf, viridis, They do not seem to be objec- tionable guests, as the Hydra never appears to notice them. It is said that they infest sick or weakly victims only, but that is not according to the writer’s experience, if the condition of the Hydra may be judged by appearance, activity, and appetite. Several Fig. 132.— Of these parasites are shown on a portion of pedeuts a tentacle in Fig. 132. Each is shaped like te” ashort dice-box, with a circle of fine cilia at each end, but none on the rest of the body. It glides along rapidly on the ends of the dice-box, running out to the tips of the tentacles and skirting fearlessly around the edges of the mouth. It is the Trichodina pediculus. HYDRAS, 171 The Hydra also occasionally has another form of In- fusorial parasite running over its skin. This is de- pressed and somewhat kidney-shaped in contour, and has cilia only on one surface, the lower or ventral surface. It is called-Keréna polypérum, It is not so common as Trichodina. If the observer desires to preserve the Hydra asa permanently mounted object for the microscope, he may be easily gratified, thanks to the late Mr. A. H. Breckenfeld, of San Francisco, who has devised an admirable method which the writer has tried and recommends. Transfer the Hydras to a slip in a large drop of water, where they can be seen if the slideis held above white paper. When their tentacles are fully extended, ‘‘quickly move the lamp directly under the drop, with the top of the chimney about an inch beneath the slide, and hold it in that position for from three to five seconds, the exact time depending principally upon the intensity of the heat. Then quickly remove the slide and place it upon a slab of marble or of metal. When cool, pour the drop contain- ing the zoophytes into the prepared cell on the slide which has been held in readiness; add a drop or two of a suitable preservative fluid, arrange the little ani- mals, if necessary, by means of a needle or a camel’s- hair brush (using very great care, however, as the ten- tacles will be destroyed by the least rough handling), cover with thin glass, and finish as in the case of any fluid mount.” I have not found it necessary to use two slips of glass. If a deep shellac-cell that has been made for some time and is perfectly dry and hard is used, the Hydras may be placed in it and there cooked and allowed to remain, as a high degree of heat is not 172 AQUATIC. MICROSCOPY FOR BEGINNERS. needed. When cold, arrange the arms if necessary, add a drop of weak glycerine and water, and cement the cover-glass with shellac. The Hydras thus pre- pared can be kept indefinitely, and at any time shown to admiring friends. . I have at this wricing a prepara- tion thus made, and in perfect condition although it is ten years old. Both the green and the brown species are abundant during the summer among Anacharis and Lemna, SOME AQUATIC WORMS, ETC. 173 CHAPTER VII. é SOME AQUATIC WORMS, CHZATONOTUS, AND CHIRONO- MUS LARVA, The collector of microscopical objects from the ponds and slow streams is doubtless familiar with the appearance of the bristle-bearing worms (Fig. 153), on account of their general resemblance to those long-suffering creatures which he in his youth impaled ona hook and with them sought the nearest water. The extensive bristles of the aquatic worms are an addition which greatly lessen their resemblance-to the common earth-worm, and their transparency is another characteristic.that may temporarily mislead the ob- server, but their elongated bodies and general worm- like aspect tell the story. In addition to the bristles which most members of this class possess, there are usually two or more rows of long, curved spines (Fig. 154), on the ventral or lower surface. These can be protruded or withdrawn into the body at the possessor’s will, and when pro- truded are used to assist the worm tocrawl. They are therefore called the podal spines or foot-spines. | They may not be noticed when retracted unless spec- ially searched for, but having observed them and the bristles in a row on each side above them, the student 174 AQUATIC MICROSCOPY FOR BEGINNERS. need have no trouble in knowing where to class the worms; yet with another division of the group the ob- server may not fare so well. These worms have flattened, usually almost opaque bodies, with the entire surface densely clothed by fine cilia, and, probably on account of the stir and disturb- ance which the cilia make in the water, naturalists have classed the worms together under the name of the Zurbelléria, from a Latin word meaning a stir or bustle. Their motions are rapid and apparently with- out effort. They glide smoothly and swiftly over sub- merged objects, or not rarely swim back downward on the surface of the water. Some of these Turbelldrians are shown in Fig. 145. There is still another group of common aquatic worms, but to recognize them will give even the beginner very little trouble. They are often rather sluggish in their movements; they have a perfectly transparent, usually smooth, thread-like body, which is apparently truncate in front, and prolonged posteri- orly in a sharpened, point-like tail. They have no bristles nor cilia, and they rather closely resemble a microscopic eel; indeed the scientific name, Angutllula means a little eel. These are closely allied to the well-known vinegar eels and to the equally common paste-worms. Many members of all these classes are found in the superficial sediment of shallow ponds, in the crevices of wet and water-soaked logs, under submerged stones, among the leaflets of Myriophyllum, Sphagnum and other water-plants. Sphagnum seems a favorite place for several kinds. I have obtained members of five genera, Wats, Pristina, Déro, Chetogdster, and olo- SOME AQUATIC WORMS, ETC. 175 séma, by placing a little piece of the moss in a watch- glass with a small quantity of water, and gently tear- ing away the leaves with needles, when the concealed worms hurried out and were readily -captured with the dipping-tube. If the watch-crystal stands on black paper this work is facilitated, as the translucent worms then appear to the naked eye as minute, writhing, silvery threads. In this chapter the reader will also find descriptions of two very Common microscopic aquatic animals, one of which is certainly not a worm, the proper position of the other being rather doubtful. They are Che- ténotus and the Chirénomus larva (Figs. 133, 134), both having somewhat worm-like bodies. They are here referred to for the convenience of both reader and writer. The beginner will be sure at first to mistake Chironomus larva for a worm. The bodies of all the aquatic worms are soft and easily injured. It is best, therefore, in studying them to use a cell shallow énough somewhat to restrain their move-- ments when the cover-class is added, but deep enough to avoid undue pressure or they will rapidly go to pieces. The following Key will assist the beginner in deter- mining to which class his worm or worm-like creature may belong, leading to the hames of the groups under which some of their generic titles may be found: 1. Body with four leg-like appendages bearing hooked bristles; eyes distinct; head large, brown- ish-red. ‘Chirdénomus larva, J. 2. Body without leg-like appendages (a). a. Tail forked; mouth small, circular, on the front part of the lower or ventral flat surface; back 176 AQUATIC MICROSCOPY FOR BEGINNERS. convex, usually bearing spines, prickles, or scales. Cheténotus. LI, a. Tail not forked (4). 6. Posterior extremity often bearing finger-like ap- pendages, never long, coarse bristles (c). 4. Posterior extremity rounded, often bearing long bristles; animal free-swimming, movements swift. Dasydytes, III. ¢. Body entirely and finely ciliated, usually flattened, not divided into distinct segments or rings. Turbelidria, 1V. c. Body smooth, without cilia, bristles or spines, worm-like; posterior extremity pointed. Auguzl- lula, V. c. Body elongated, divided into segments or rings, with ‘bristles, podal spines or both. Olgo- cheta, VI. 1. CHIRONOMUS LaRVA (Fig: 133). Chirénomus larva has a worm-like, more or less seg- mented, colorless body, eight or nine times as long as wide, a large head, the mouth parts usually being dis- tinctly apparent. The four short rudimentary leg-like appendages are in pairs on each end of the long body, the brownish hooks, or strong curved bristles on their extremities being more or less retractile, while in some forms two clusters of long bristles spring from the upper surface near the posterior border of the ani- mal. ‘The perfect insect into which this larva will de- velop is a two-winged fly resembling the mosquito. These are often seen in great numbers above the ponds and marshes. The species are numerous, but have never been studied by American entomologists. SOME AQUATIC WORMS, ETC. 177 The eggs are common on sticks, floating chips, or other objects in the water, or even in freely floating masses. ‘They are deposited in an immense amount of jelly, huge in bulk when compared with the size of the insect, the eggs appearing to the naked eye as dis- tinct but minute, often brownish, specks, arranged in beautifully regular rows. Fig. 133.—Chirénomus larva. It is always interesting aswell as important for the collector to take home all the little jelly-like egg masses which he may find attached to submerged ob- jects. If placed in a watch-glass or in an: ‘‘individ- 13 178 AQUATIC ‘MICROSCOPY FOR BEGINNERS. ual” butter-dish, and the’water kept fresh and pure, they will usually hatch, and thus give the observer valuable information often not otherwise obtainable. Chironomus eggs can hardly be described so that the reader shall recognize them at first glance, but if once hatched at home they will afterwards always be recog- nizable. The first little mass of jelly experimented with may prove to be snails’ eggs, but they will be none the less interesting. They may also prove to be the eggs of water-mites (Chapter XI.). The beginner will, of course, not mistake the green jelly-globules of Chetophora for insect eggs. 2. CH£TONOTUS (Fig. 134). There are several species of these lithe and grace- ful little creatures in our fresh waters, and they so closely resemble one another in external form that they can be distinguished only by the cuticular ap- pendages, or the coat-of-mail by which most of them are protected. They are readily to be found by fish- ing for them with a dipper, as recommended for Fig. 134.—Chzetdnotus larus. Fig. 135. Rhizopods, since they are fond of gliding over the soft ooze at the bottom of shallow ponds. If the collector will also sweep his dipper under the lily leaves and among the submerged stems of Nuphar, or of other aquatic plants, he will not be disappointed. The animal consists of a free-swimming, flexible, and elongated body, the anterior extremity usually enlarged SOME AQUATIC WORMS, ETC. 179 to form what may be called the head, aslight constriction behind this part constituting the neck; the broadened central portion ofthe body is formed with convex lateral borders and a more or less strongly arched back or dorsum, this region being variously appendaged with spines or with scales, and suddenly narrowed to produce the posterior extremity, which is forked, and bears two conspicuous but short tail-like prolongations. The lower or ventral surface is a flat and nearly level plane extending the entire length of the body. It bears one longitudinal band of cilia near each ‘lateral border, seldom more. The head is usually somewhat triangular, and formed of three or of five rounded lobes, and has two tufts of vibratile hairs on each side. The mouth its on the ventral surface of the head, and under a moderate amplification seems to be a circular opening, but with an objective of high power it will be found to be beaded and somewhat complicated in structure, as shown in Fig. 135. The whole upper surface of the body is, in the dif- ferent species, covered with rounded papille, scales, spines, or prickles, or with both scales and spines at the-same time. Inthe latter kinds the scales cover the back. and sides, and the spines spring from these appendages, arching back towards the forked tail. And in all cases these little scales are imbricated, like the shingles on a roof, only they have the peculiar habit of overlapping in what seems to be the wrong way, because their free margin, or that region which represents their free margin, points toward the animal's head, or in a direction exactly opposite to that of the scales of a fish. They are usually minute, and require high powers to show them properly. 180 AQUATIC MICROSCOPY FOR BEGINNERS. ‘The two caudal prolongations are movable and flexi- ble. Their chief use seems to be to anchor the animal to the glass slide or cover, or to some object in the water, clinging with their tips, and apparently assisted by a secretion that is supposed to exude from them, this sticky fluid passing from two ovate glands usually visible in the upper or anterior part of each. The mouth opens into a strongly muscular cesopha- gus, which itself opens into the intestine, a tapering, tubular passage lined with nucleated cells and passing in almost a straight course along the median line to terminate between the two caudel prolongations. If the observer can get the animal in such a position that he can focus down on the front of the head, he will see that the cavity of the cesophagus is triangular. It is not very diffcult to do this, since the little creat- ures are exceedingly restless; they are continually turning and writhing about, and lifting the head in various directions. This feature in its structure can often be seen in the animal while still in the egg, for even there, when almost ready to escape, it is exceed- ingly restless. The eggs are not rarely found on the slide, with the young Chztdnotus doubled up and squirming within. ‘ The eggs by which Chetonotus is reproduced are formed in an ovary difficult to see unless occupied by an egg, ‘but placed in the median line of the body im- mediately above the intestine. Usually only one egg is formed at atime, but it is not rare to see two or more in various stages of ovarian development. Upon the absence or presence of an egg in the ovary de- pends, to a great extent, the degree of convexity of the back. The eggs are dropped anywhere in the water, and left to the care of Nature. SOME ‘AQUATIC WORMS, ETC. 181 The. food consists of the minute particles of decayed animal and vegetable matter so abundant in the soft -surface of the mud at the bottom of our shallow ponds. These particles are taken in with a peculiar and a sud- den snapping movement of the cavity of the cesopha- gus, easily to be seen but difficult to describe. Dia- toms are rarely swallowed. So far as their classification is concerned, these at- tractive little animals have given naturalists a good deal of trouble. Some have said that they belong with the Rotifers; others have placed them among the Infusoria; others have called them low worms, putting them among the Turbellaria; and still others think, and they are doubtless correct,’ that Chatonotus should stand in a group by itself, among the worms, and not-very far from the Rotifers, the group to be named the Gastrotricha. They are all rapid swimmers, and on that account are rather difficult to study, but by following one for a little while, it will usually be seen to settle down and begin to seek food, and that is the observer’s oppor- tunity, unless he desires to kill the specimen, and study it after death, a procedure that is seldom satisfactory. The following Key leads to some. of our common forms: Key to Species of Chatonotus and to its Allies. § Posterior extremity forked (A). § Posterior extremity not forked but bearing several long, coarse bristles, Dasydytes. r. A. Upper surface without spines, prickles or scales, (2). A. Upper surface having scales, spines, spinous scales or prickles, (4). 132 AQUATIC MICROSCOPY FOR BEGINNERS. a. Back smooth and naked, or transversely furrowed or bearing small, hemispherical elevations, Lethydium. 2. 6. Caudal prolongations much shorter than the. body, not segmented nor ringed; dorsal scales, when present, rounded, Cheténotus. 3. é. Caudal prolongations long, ringed or segmented, often curved; scales rhomboid or diamond- shaped, Lepidodérma. 4. “IIT. (1). DASYDYTES SALTITANS (Fig. 136). In contour this lively creature remotely resembles Chetonotus (Fig. 134), but differs in a shorter, more chubby body, in ‘the presence of a more distinctly formed neck, but especially in the absence of a furcate caudal extremity. The body is colorless and trans- parent. Its internal structure is not very widely dif- ferent from that of Chetonotus, but in general ap- pearance the animal lacks the graceful form and the attractive movements of the Chetonotus. ‘The pos- terior extremity is simply rounded or truncately con- vex. Its movements are much less smoothly gliding and facile. The habitat of both genera is the same, being chiefly near the bottom of shallow ponds. The head is distinctly three-lobed, the frontal lobe being the smallest and bearing on its anterior bordera colorless, apparently chitinous plate or cephalic shield. Both surfaces of the head are ciliated, the cilia being very long and fine, and arranged in two distinct, transversely encircling series, the posterior row pro- jecting and vibrating anteriorly, while the anterior series projects and vibrates posteriorly. The neck is about as long as the head, sometimes SOME AQUATIC WORMS, ETC. 183 rather longer. It is movable and exceedingly flexible, the Dasydytes continually bending from side to side in search of food, orupward and downward. The ani-- mal occasionally has the habit of turn- ing somersaults, accomplishing this feat by flexing the neck under the ven- tral surface and throwing the body over forward. From each side of what may perhaps be called the shoul- ders, arise from four to six large, coarse bristles, each as long as the en- tirebody. These sets of bristles cross each other obliquely above the back, and project beyond the rounded pos- terior extremity. Without these the dorsal surface would be naked, ex- cept for the presence of two, fine, almost vertical tactile hairs, each of which arises from a small papilla near "® "365703870" each postero-lateral border. The ventral surface is not easily seen, as the animal usually keeps obstinately directed downward. But the ventral cilia are essentially similar to those of Cheto- notus and arranged in two lateral, longitudinal bands. But near the center of this aspect originate four strong coarse bristles, or sete, two long and much exceeding in length that of the whole body, and two shorter, the four projecting beyond the posterior border. These are springing sete by whichthe Dasydytes makes those surprising leaps which suggested its specific name of saltitans, or leaping, often jumping, and always unex- pectedly, to a distance sometimes exceeding twice its own length. This seems to be great but in reality it 184 AQUATIC MICROSCOPY FOR BEGINNERS. is small, as the length of the body is only about 4> inch. When swimming its movements are more rapid than those of Chzetonotus. . The mouth is nearly apical. The cesophagus has a snapping movement similar to that visible in Cheto- notus, although the food is usually engulfed by suction, living and comparatively large Infusoria being taken as well as organic particles. Dasydytes saititans does not seem to be common. It was originally discovered near Trenton, N. J., where it is not rare, and it has been found near West Point, N. Y. It has not been reported elsewhere. 2. IcTHYDIUM. 1. This resembles a Chetonotus with a smooth, naked back, all scales, spines and prickles being absent.. The spines and other dorsal appendages are rep- resented by two hairs standing almost vertically on the neck, and two on the rear part of the back. These are usually seen with difficulty, but they are present on all the species, even the scaly and the spinous ones of Chetonotus: The egg of this species is also smooth. In other particulars it re- sembles Chetonotus. This is lethydium podura: 2, The characteristic of this form is in the deep trans- verse furrows conspicuously developed on the back and sides. ‘The body is transparent, and un- usually soft and flexible. The posterior region be- tween the arch of the back and the caudal furca- tion is narrowed, and much longer .than in other species. The esophagus is short, being not more than one-sixth the length of the body. Jethydium sulcatus. SOME AQUATIC WORMS, ETC. 185 3. Asimilar animal, but with the dorsal and lateral surfaces closely covered with small hemispherical ' elevations arranged in oblique lines, and giving the creature a peculiarly neat and attractive ap- pearance. Jcthydium concinnus. 3. CH-ET6NoTUuS (Figs. 134, 135.) “‘Bristle-back,” the literal meaning of the word, seems to be a misnomer when those forms are con- cerned in which the bristles are replaced by scales, but the structure is such that the only resting place for these creatures is in the genus Chetonotus. The following key leads to a few of the common species. A, RN Upper surface bearing scales only; scales rounded, /oricatus, 1. . Upper surface bearing spines or prickles only (a). Upper surface bearing both spines and scales (4). Upper surface bearing posterior spines and an- terior prickles (c). Spines long, covering the entire upper surface; mouth beaded, maximus, 2. : Spines short, covering the entire upper surface; mouth not beaded, /arus, 3. Spines not covering the entire upper surface (¢). Back with a subcentral, transverse hedge of large spines; scales double, acanthddes, 4. Back without distinct spinous hedge; scales not double, spénifer, 5. ; Spines in four transverse rows, five spines in each, acanthdphorus, 6. Spines in transverse rows, less than five spines in each, endrmis, 7. 186 AQUATIC MICROSCOPY FOR BEGINNERS. d. Spines eight; in two longitudinal rows of three each, with one anterior and one posterior cen- tral spine, octondrius, 8. d. Spines in two transverse rows, not projecting be- yond the ends of the central prolongations, Spindsulus, 9. @. Spines in two transverse, highly-arching rows, the posterior longest and projecting beyond the ends of the caudal prolongations, longispindsus, 10, 1. CHA&TONOTUS LORICATUS (Fig. 137). The scales on the back and sides are aranged in ims bri¢ated rows, the convex free margins being directed forward. Although so completely covered, the body is very flexible, the scales freely sliding over each other when the animal curves to one side. The mouth is obliquely placed, as may be seen when the Che- tonotus is viewed in profile, and its internal margin is strongly bedded. The eggs are armed by hollow pap- ill, or by short hollow spines whose summits are bifid or emarginate. Fig. 137.—Chzténotus loricdtus. 2. CHATONOTUS MAXIMUS. The back and sides are covered with spines which ’-are often rather longer on the posterior. region than elsewhere. They are arranged in longitudinal parallel rows, yet they often seem to be irregularly scattered, so that the animal presents an untidy, disheveled, and disreputable appearance. The spines are min- SOME AQUATIC WORMS, ETC. 187 utely forked near the free ends. The branching is very uneven and is easily overlooked, one branch be- ing very small, often scarcely more than a minute linear projection. The ventral cilia are in two longitudinal lateral bands, and the space between is clothed with short, hispid, recurved hairs, two or more long fine bristles projecting from the same part beyond the posterior border, between the two caudal branches. 3. CuHTONOTUS LARUS (Fig. 134). The whole upper surface is clothed with short, conical spines in longitudinal rows, these appendages being recurved and not branched. They are often largest posteriorly. The mouth is not beaded. The ventral cilia are in two broad longitudinal bands near the lateral margins, and the intervening space often bears two additional parallel lines of cilia, which may be absent from some specimens. These cilia, as in all the species, subserve locomotion. The egg is smooth, or hispid with short hairs. 4. CHETONOTUS ACANTHODES (Fig. 138). The upper surface of this form is. wondrously well protected. It possesses both spines and scales, the latter imbricated, and their somewhat pointed free margins directed forward, each one bearing a small supplementary scale or scale-like thickening on its posterior part, from which springs a recurved, un- equally furcate spine. Near the body-center the dorsal surface is traversed by a series of large, stout spines rising obliquely upward and backward, and forming a kind of spinous hedge, the surface behind 188 AQUATIC MICROSCOPY FOR BEGINNERS. these appendages bearing few small conical thorns or none. The body-margins are fringed by short spines. The central space on the ventral aspect between the two longitudinal, lateral bands of cilia, is beset with short, fine, recurved prickles, and five or more long bristles project from the same surface beyond 138—Chatonotus the border of the posterior bifurca- ecanthodes tion, while on each side of the body near the posterior extremity there are two large re- curved spines. The animal is usually found among Sphagnum. 5. CH&HTONOTUS SP{NIFER (Fig. 139). Among Riccia and Lemna in shallow ponds this well-armored form is not rare. The upper surface is covered by rounded imbricated scales, the free margins directed forward. From each scale arises a stout, recurved, unequally and minutely furcate spine, whose base is enlarged and thickened. ‘These spines do not. commonly originate from the center of the scales, but near the posterior part, and between the margins of those: 1aterally contiguous. The spines are largest and stoutest on the back proper, decreasing gradually over the neck and head, and rapidly over the posterior parts, while across the dorsal surface immediately in front of the caudal bifurcation extends a supple- mentary series of four thorns, longer and stouter than those on any other part of the body. The posterior region of the space between the longitudinal ventral bands of cilia bears five bristles, arranged to form a long triangle, the apex pointing forward. SOME AQUATIC WORMS, ETC, 189 The eggs vary considerably in external ornamenta- tion, showing three paterns. In one, the ends and one side bear low, stout, hollow processes, whose apices are truncate, and four- or five-parted when viewed from above. In another, the appendages are long, hollow, conical spines, whose distal ends are trifid or quadrifid, the branches in profile appearing very fine and delicate, but when viewed from above are seen to taper to the ends, where each terminates in a widely spreading furcation. In the third form, one side and both ends are covered by an irregular network of raised lines, the meshes being four- or five- angled, while the opposite side is rugose with fine, minutely sinuous lines. Fig. 139.—Cheeténotus spinifer. Fig. 140.—Chzeténotus acanthdéphorus. 6. CHATONOTUS ACANTHOPHORUS (Fig. 140). The superior surface of the head and neck and the lateral body-margins are clothed with recurved prickles or short spines, while the dorsal region proper bears four rows of long thorns, each row arched towards the head, and each formed of five unequally furcate spines, with an additional one on both sides near the pos- terior extremity. The spines rise from an enlarged Igo AQUATIC MICROSCOPY FOR BEGINNERS. base, so that the animal is almost completely clothed in an armor composed of these basal enlargements. 7. CHATONOTUS ENORMIS (Fig. 141). The upper and lateral surfaces of the head and neck are clothed with short, recurved prickles, which also extend along the ventro-lateral margins, The central and posterior parts of the back bear thirteen posteri- orly directed, but only slightly curved, spines arranged in transverse rows, with three in the first row, four in the next following, two widely separated in the third, three in the fourth, while the fifth series consists of a single centrally located one. On each side near the posterior margin are two long, conspicu- ous, and recurved thorns, apparently belonging to the series of small spines fringing the lateral body- margins. Fig. 141:—Chzeténotus Fig. 142.—Chaetdnotus Fig. 143.—Chaeténotus enérmis. spinésulus, longispinésus. 8. CHATONOTUS OCTONARIUS. This isa small, active form, readily recognizable by the arrangement of the recurved dorsal spines. These SOME AQUATIC WORMS, ETC. Ig! are unequally branched, and placed in two lateral lon- gitudinal rows of three spines each, with one anterior and one posterior central thorn. It seems to be the least common of the species. g. CHATONOTUS sPIN6sULUS (Fig. 142). The back usually bears seven unequally furcate spines in two transverse rows—four spines in the an- terior series, three in the posterior. Occasionally the lateral thorns in the posterior row are suppressed, and in some individuals the front series contains but three. The lateral body-margins are bordered by short, con- ical setee, which are constant in all the specimens thus far observed. The rest of the upper surface is with- out appendages of any kind, except the four tactile vertical bristles present in all species. The egg is his- pid. with short hairs. 1o, CHATONOTUS LONGISPINOsUS (Fig. 143). The spines vary from four to eight, the latter being the usual complement. They are nearly one-half the length of the body, and curve upward and backward in a wide arch from the center of the back. In front of the anterior row the surface is setose with stiff, re- curved bristles, and the body-margins are fringed by coarse, rigid sete. The dorsal spines are always in two transverse rows, but the number varies from four in each to three in one and five in the other. They are unequally furcate. 4. LEPIDODERMA RHOMBOIDEs (Fig. 144). This is easily -recognizable by the peculiar head, the minute rhombic scales* covering the back and sides, 1g2 AQUATIC MICROSCOPY FOR BEGINNERS. and by the remarkably long and jointed caudal branches, each of the latter forming from. one-third to one-fourth of the entire length of the body. The animal is the largest of the group, yet discovered, measuring ;, inch long. Pa The caudal branches are rit composed of about twenty /] Z sections or joints, each of which is slightly constric- Fig. ar —Lepidodérma rhomboides. ted. The head is broadly rounded, and formed of three lobes, one frontal and two lateral, the former terminating on each side in a single, acuminate, hook- like process, habitually in close apposition with the anterior region of the lateral lobes, of which the pos- terior extremities also terminate each in a single hook-like continuation, rather more conspicuous than those at the front. The mouth is beaded, and has im- mediately behind it on the ventral surface a deep, narrow, transverse, and slit-like depression, rather less than one-half as long as the diameter of that part of the head. This is a problematical feature. The back and sides are completely clothed by mi- nute, imbricated, rhombic scales, their front pointed. margins being directed towards the head. They are not more than 3,45, inch in length, and when examined with a high power (oné thousand diameters) they present a beautiful appearance. The lateral margins then seem to be thickened, and the posterior border of each scale appears to bear a minute supplementary scale in the shape of a triangle. The margins are sometimes convex. SOME AQUATIC WORMS, ELC. 193 Although the observer may not be able distinctly to see these scales, the very long, characteristic caudal branches, with their joints, and the sulcation behind the mouth, will be sufficient to identify the specimen. IV. TURBELLARIA. The ciliated or Zurbelldrian worms seem to prefer the bottom of shallow ponds, probably because the food supply there is better and more easily obtained. They are soft and flexible, and some are slightly changeable in shape, having the power to lengthen themselves, to extend the posterior border into a short projection, ur to narrow the front into an apology for a head. Some, however, have the anterior region naturally prolonged into a short snout. They are usually brownish and almost opaque, the opacity being increased by the large amount of food commonly pres- ent in the stomach. ‘Three forms are shown in Fig. 145. Fig. 145.—Three Turbelldrian worms. The cilia clothing the entire surface are visible only under a high power. The result of their motion, how- 14 194 AQUATIC MICROSCOPY FOR BEGINNERS. ever, can be seen with the one-inch objective, as they produce currents in the water that sweep away small objects with some rapidity. Two or more small black or reddish eye-spots are often present near the front border, and, in some of these worms,. may be rather complicated in structure, having a covering that may not inappropriately be called a cornea, a refracting body corresponding to a crystalline lens, pigmentary or coloring matter, and a nerve. The location of the mouth varies widely in-the differ- ent families. It may be at or near the front border, at some point nearer the center of the ventral surface of the body, or even close to the posterior margin. It is usually large and expansile, and is often followed by a large and very muscular organ called the pharynx, which some of the worms can protrude, and with it snap up their living prey. The lining of the pharynx may be finely ciliated. The stomach occupies the largest portion of the body, usually extending from the pharynx to the pos- terior border-of the animal. In some it is simply a great sack, receiving all that the mouth and pharynx turn into it; in others it divides into many branches whose terminations may be seen near both sides of the body. The stomach seldom has a posterior opening, for as a rule, there is no intestine.. After the nutriment has been digested and absorbed from the food, the insoluble remains must be ejected through the mouth. It isno unusual sight, therefore, to see one of these ciliated worms vomit up a mass of indigestible and empty Rhizopod shells, Rotifer cara- paces, together with many unrecognizable particles SOME AQUATIC WORMS, ETE, 195 and fragments. The Turbellarians seem to prefer ani- mal food, usually selecting Rhizopods and Rotifers, but they are as fond of Infusoria, which must be as nourishing and much more easily digestible. I have more than once lost an interesting specimen of Infu- sorium because one of these-Turbellarian worms had been included under the cover-glass: there were a worm and an Infusorium; a pause; a single snap, and only the worm remained. Propagation takes place in two ways—by eggs and by transverse fission; that is, one worm divides across the middle and so makes two, each of these again di- viding. And often before the division has been en- tirely accomplished, both halves are also partly di- vided, so that the single body seems to be formed of several incomplet2 worms. The eggs of the common- est species are brownish egg-shaped bodies, dropped anywhere in the mud or the water, or they may have a stem which attaches them to submerged objects, from which they are easily broken. The last men- tioned kinds of eggs may be readily recognized, be- ing formed of a yellowish-brown, transparent chitinous membrane, egg-shaped, and with the stem almost equalling their own length. If the observer be for- tunate he may see the worm escape by pushing off the top of the egg, which falls away like a round cover, leaving an empty case shaped like a deep cup. These empty vases are often found at the bottom of long- standing collections of plants in the microscopical aquarium. The Turbellarian worms are common, but the ob- server can scarcely hope to learn even the generic name of those that he may find. He will be safe, 196 AQUATIC MICROSCOPY FOR BEGINNERS, however, if he refers to them all as Turbellarians, or Turbellarian worms. The subject has not been stud-* ied extensively by American naturalists, and there is, consequently, nothing in the language to which the be- ginner can be referred for help. The worms are often visible to the naked eye as minute whitish or flesh-colored floating bodies, or like small bits of white thread in appearance. There are two forms frequently met with which are huge when compared with most of these ciliated creatures, need- ing no microscope to identify them. Both are found on the lower surfaces of submerged stones or sticks, or gliding over the sides of the collecting-bottle. The body of one of these common Turbellarians may be about half an inchin length and nearly five times aslongas broad. Itis opaqueandalmostblack. Near the anterior border are two black eyes, which are made conspicuous by the presence of an oblong white space in front of each. The mouth is near the center of the body, and opens on the lower or ventral surface. The worm glides smoothly and rather rapidly over a submerged surface. Naturalists have named it Plandria torva. The second one referred to somewhat resembles Plandria térva, but is usually smaller, and has the an- terior or the head end more nearly triangular. It is similar in its movements and in the presence of two black eyes near the front border, each at the inner margin of a white space, thus giving the worm a cross- eyed appearance. The body is nearly white, and has a dark line passing lengthwise through the center and giving off on both sides many short branches which are themselves often branched, these dark lines on the e SOME AQUATIC WORMS, E'C. IQ7 white body giving the creature arather pleasing ap- pearance. They are not for ornament, however, but are the branches of the stomach indistinctly seen through the walls of the body. The mouth is near the center of the lower surface. The worm may measure half aninchin length. It has been named- Drendocelum ldcteum. The entire surface of both these common Turbellar- ians is finely and closely ciliated. The color of the body will at once inform the observer which one he has captured, as they are not microscopic in size. V. ANGUILLULA (Fig. 146). The body is thread-like, perfectly transparent and colorless, about fifteen times as long as broad, rather widest in the middle, whence it slightly tapers towards both.ends. The frontal border is rounded, but with a low power appears as if truncated. The round mouth is at the center of this end, and leads into an oblong pharynx or throat. The tail is usually long and sharply pointed. The .worm’s move- ments are generally slow and deliber- ate, but occasionally it has a lively spell, thrashing about greatly to the detriment of other objects on the pig, 146.—Anguillula. slide, and often becoming a nuisance. It is reproduced by eggs, one or more often being visible within the transparent body. Anguillule are common in wet moss, among the leaflets of aquatic plants, and in the ooze of the ponds. The well-known ‘‘vinegar-eel” is an Anguillula (4z- 198 AQUATIC MICROSCOPY FOR BEGINNERS. guillula acéti); and the paste-worm (A. giitinis) belongs to the same genus. Some naturalists regard these as the same species. VI. OLIGOCHATA. The fresh-water, bristle-bearing worms whose bodies are never ciliated, show more or less distinctly that they are formed of segments or rings. Each segment usually has on'both sides near the back'one or more long, fine, hair-like bristles extend- ‘ing outward into the water, and together forming a series along each side of the body. On the lower surface are two or more rows of stouter, inflexible, gracefully curved spines, the rows being formed of clusters of two or more, the free end of each spine be- ing usually divided by a deep notch, so that it appears like a double hook, the parts being unequal in size and in degree of curvature. These spines are used to assist in the worm’s movements and are therefore called podal spines or foot-spines. They can be protruded from the body, or partly withdrawn into it, at the ani- mal’s will. ‘The long bristles are used as an assistance in swimming. On some of these worms both bristles and podal spines are present; in others one or the other set of organs may be absent. The podal spines, which with but few exceptions are present, are each gracefully curved like a longitalic S, their shape resembling the line which artists have called the ‘line of beauty.’ The free end, or the one projecting into the water, is forked in a way already ‘described, and shown in Fig. 154. The body or shaft has, at some point ofits length, aglobular enlargement or ashoulder, below which the spine is often much narrowed. SOME AQUATIC WORMS, ETC. 199 These organs are used by being protruded and forced against the surface over which the worm is traveling. They are arranged in a row on each side of the vent- ral surface, each'row being composed of many clusters, and each cluster of from two to ten spines. The worm Can protrude several clusters at once, or two on the opposite sides of the same segment or body-ring, but it seems unable to extend them any more irregu- larly. The bristles are exceedingly flexible, and are ar- ranged in two rows on the sides near the upper surface, one series on each side. They are usually much longer than the width of the body, and may be so ar- ranged with several or with only one on each lateral margin of thesegment. ‘They are sometimes accompa- nied by a straight spine much shorter than the bristle, and projecting beside it. The free ends of these rudi- mentary spines are occasionally finely forked. The bristles are absent in some genera. The aquatic worms are usually visible to the naked eye as fine whitish or yellowish threads, sometimes an inch or more in length when extended. They are found abundantly among aquatic plants, and in the mud of shallow ponds. When allowed to remain in the collecting-bottle they will often make their way to the lighted side, where some will form sheaths or pro- tective cases from bits of Lemna or various floating fragments or particles. The mouth may be close to the front end, or at some distance back, since in a few worms the front border is extended ina long flexible snout. The posterior border of the body is rounded in many forms, while in others it is expanded into a broad, funnel-like region, 200 AQUATIC MICROSCOPY FOR BEGINNERS, with several finger-like prominences surroundingit. In such worms these parts are ciliated on the inner side, the currents thus produced being supposed to bring at least a portion of the oxygen needed for respiration. The alimentary canal extends through the center of the entire body, and i» usually crowded with the brownish remains of-undigested food. The whole cavity of the body outside of the aliment- ary canal is filled with a colorless fluid visible only by means of the movements of the corpuscles often to be seen floating to and fro as the worm moves under the cover-glass. The beginner must not mistake this fluid for the blood, which in many of the bristle-bearing forms is red and contained in two distinct longitudinal vessels, one extending lengthwise above, the other lengthwise below the intestine. These vessels unite at both ends of the body, so as to form a long, closed tube, with branches springing from the front part, or from the upper or dorsal tube as it passes through each seg- ment, where they then appear as pulsating loops. Usually the blood is impelled by the regular pulsa- tions of the dorsal vessel, a wave-like contraction pas- sing along and driving the fluid before it. In two genera (Zudifex and Ocnerdédrilus) there are little pul- sating hearts attached to the dorsal vessel in the neighborhood of the frontal border. Reproduction is by eggs or by tranverse fission, the latter being most frequently observed. Most of these worms live upon animal food, seem- ing to prefer Rhizopods and Rotifers to almost any- thing else; only a few are vegetarians. SOME AQUATIC WORMS, ETC. 201 Key to Genera of Microscopic, chiefly Fresh-water, Worms. (Oligocheta). t. Body with both bristles and podal spines (a). 2. Body with podal spines only (4). 3. Body with bristles only (/). a. Anterior extremity without a finger-like prolon- gation (d). Anterior extremity with a flexible, finger-like prolongation. Préstina, 1.. Podal spines forked; worms aquatic (c). Podal spines not forked; worms aquatic (g). Podal spines not forked; worms living beneath decaying bark of dead trees. nchytreus, 2. Podal spines, from six to ten in each cluster, the clusters in two rows. Chetogadster, 3. Podal spines, two only in each cluster, the clus- ters in four rows. Lumbriculus, 4. Posterior extremity without finger-like append- ages (¢). _ Posterior extremity widened, ciliated, with sev- ‘eral retractile, finger-like appendages. Devo, 5. Posterior extremity ciliated, with two long, non- retractile, finger-like appendages. Awldpho- rus, 6. é. Bristles and podal spines in separate rows (4). e. Bristles and podal spines alternate in the same row. Stréphuris, 7. Body variegated with brick-red or orange colored spots; blood colorless. -oloséma, 8. Podal spines in clusters of four each; body the color of raw meat. Ocnerddrilus, 9. Podal spines in clusters of two each. Lumdbrtcu- lus, 4. 202 -AQUATIC MICROSCOPY FOR BEGINNERS. A. Worm with two small anterior pulsating hearts; blood bright red. TZzbifex, 10. A. Worm without distinct hearts; dorsal vessel pul- sating; blood red. Ndis, 11. 1. Pristina (Figs. 147, 148, 149). Body nearly cylindrical, transparent, frequently : very long, and often showing that it is preparing to divide across the middle to produce two worms. In these cases the proboscis of the new worm becomes conspicuous at the center of the long body. The mouth is near the base of the snout like prolongation, this narrow extension of the upper lip varying much in length in the various species. The one represented in Fig. 147 belongs to a common form in the writer’s locality, and is unusually long. Ch. Fig. 147.—Snout of Fig. 148.—Posterior extrem- Fig. 149.—Posterior ex- a Pristina, ity of a Pristina. tremity of a Pristina. i The posterior extremity is commonly nearly as shown in Fig. 148, and surrounded by many short stiff hairs, it being the tail-end of the Pristéna whose proboscis is shown in Fig. 147. Occasionally this part has three long trailing appendages, as in Fig. 149. The blood is usually red. The bristles are long and fine, and are often accom- panied by one or more short, nearly straight, rudimen- tary spines. The podal spines are in two rows on the SOME AQUATIC WORMS, ETC. 203 ventral surface, each cluster frequently containing as .Many as eight. The posterior part of the intestine is ciliated. The worms are found among aquatic plants, seeming es- pecially fond of Sphagnum and of Lemna as a home. They are not rare. 2, ENCHYTRAUS. The body is white or yellowish white, thread-like, and from about one-half to nearly one inch long. : The worms are found under damp logs or beneath de- caying bark, often in considerable numbers. The podal spines are usually short, nearly straight, and not forked. The blood is pale or colorless. There are two species, which are not difficult to distinguish from each other. -In one (Zuchytreus vermiculdris) the body is yellow- ish white, and varies in length from five-twelfths to eight-twelfths of an inch. The podal spines are in clusters of from three to five spines each. This species is usually found under damp and decaying logs, and is less:common than the following. In the second (£. socidlis) the body is opalescent- white and translucent, varying from five-twelfths to ten-twelfths of an inch in length. The podal spines are from five to seven in each cluster, the anterior fascicles generally containing seven, the posterior five. The mouth is triangular. This species is most fre- quently found in more or less social groups beneath the moist bark of old stumps or in the decaying parts of trees, and usually near the ground. 3. CHAETOGASTER. Body transparent, often showing evidences of trans- 204 AQUATIC MICROSCOPY FOR BEGINNERS. verse fission. The podal spines are in two rows, the. clasters containing four to eight spines each, being . usually most numerous toward the posterior extremity. The mouth is large, oblique, and surrounded. by many very short stiff hairs. It is often used, when the worm is on the slide, as a sucker, clinging to the glass and drawing the body towards it. The intes- tine, in the species common in-the writer’s vicinity, is much and irregularly constricted, a feature which gives it the appearance of a series of various-sized pouches. The blood is pale or colorless. The blood-vessels are distinct as narrow, pulsating, longitudinal tubes. Chetogdster is one of the most interesting forms on account of its perfect transparency and the absence of bristles, which allows an uninterrupted view of the whole surface, as well as of the internal organs, 4. Lumsricu us. The body is translucent, but often brightly colored at the sides or in the central parts. The blood is bright red, and the dorsal vessel gives off several short, lateral, pulsating branches in each segment of the body. These short branches fre- quently approach the surface, and give it a mottled ap- pearance, the spots fading and beappedrins i as the branchescontract and expand. There are four rows of podal spines, with but two in each cluster, each being curved, forked at the end,* and with an.enlargement or shoulder near the center *Since this was written a species has been observed with undivided podal spines. It has been included in the Key. SOME AQUATIC WORMS, ETC. 205 At a short distance from the attached end ofeach pairis often to be found another pair which aresmall and may be overlooked on the front of the body when the worm is not dividing transversely. When it is undergoing transverse fission the posterior part may be so well supplied with these small secondary podal spines that their number and arrangement may confuse the be- ginner, the rows then appearing to be eight, with two -spines in each cluster, or four rows with clusters of four spines each. However, if the observer will ex- amine the front half of the dividing worm, and be guided by the podal spines there, he will have little trouble in recognizing Lumbriculus. 5. Déro (Fig. 150). The posterior extremity is broad and funnel-like, its upper plane often being oblique. Its inner surface is finely ciliated, as are the finger-like projections and theinternal surface of the posterior part of the intestine, which is connected with it and forms a portion of it. The cilia produce cur- \ rents over these parts which are sup- posed to absorb the oxygen for pur- MZ 1e-Josthion poses of respiration. The finger-like processes vary in number from two to eight. They can be elongated or drawn back into the funnel, which can also be retracted and almost closed. When extended they may be much longer than the funnel-like termination of the body, or they may not reach to its margins. The blood is red. The podal spines vary from three to five in each cluster. These worms are often found on the sides of the 206 AQUATIC MICROSCOPY FOR BEGINNERS, collecting-bottle after it has been standing for some time. Usually they bury themselves in the mud, with the posterior part of the body and the expanded fun- nel-like region protruded from small mud-chimneys of ° their own formation. The body may measure half an inch or more in length. 6. AULOPHORUS (Fig. 151). The posterior extremity is not wider than the width- of the body, andthe two finger-like appendages may. be straight or slightly curved. They are blunt, and covered with short stiff hairs. The worm usually builds a tubular sheath of various fragments and floating particles, in which it lives, but to the walls of which it is not adherent, as it Fig- 51. Pos’ frequently doubles on itself, glides iv ofan Aule- through the tube, and thus reverses its position. It moves by jerks, ‘‘alter- nately extending the fore part of the body and pro- jecting the podal fascicles forward, and hooking into the surface on which it is creeping, and then contract- ing the fore part of the body and dragging along the back part enclosed within the tube.’”* It often helps itself along by clinging to the slide by its protruded throat or pharynx. The podal spines vary from five to nine in each cluster. The fascicles of bristles are each accom- panied by from one to three rudimentary spines, which are nearly straight, and end in a broadened, spade- like expansion. The blood is'red. *Dr, Joseph Leidy, in the American Naturalist, June, 1880. SOME AQUATIC WORMS, ETC. 207 7. Srrépuuris (Fig. 152), The podal spines and bristles are arranged alter- nately with each other, as in Fig. 152, and together form a single row of clusters on each side of the lower surface of the body. The spines are slightly curved, long and forked, the 1 bristles being three times their length. i The mouth is triangular. The blood is bright red and the vessels large. The body is thread-like, transparent, and may be from one to two inches in Te abe. length. The front end is whitish, the Yosef Stréehu tail end yellowish. It lives in the mud beneath shallow water, and buries itself with about two-thirds of the tail end protruding and constantly vibrating. When disturbed in disappears into its bur- row with astonishing rapidity. Dr. Joseph Leidy, who discovered this peculiar creature, says: ‘‘While walking in the outskirts of the city [Philadelphia] I noticed in a shallow ditch numerous reddish patches of from one to six inches square, which, supposing to be a species of Alga, I stooped to procure some, when to my surprise I found them to consist of millions of the tails of Stréphuris dgilis, all in rapid movement. The least disturbance would cause a patch of six inches square so suddenly to disappear that it resembled the movement of a single body.” ¢ 8. /EOLOSOMA. The bristles are of unequal length, and are arranged, in clusters of four each, the clusters themselves form- ing a single row on each side of the body. There are 208 AQUATIC MICROSCOPY FOR BEGINNERS. none in advance of the mouth, which is large U-shaped, the arms of the U pointing forward, the whole being surrounded with a thick border. The pharynx is broad and ciliated within. ; The body is colorless, the brick-red or orange- colored spots scattered over the internal surface giv- ing the worm a beautiful appearance. _£oloséma is found in ditches among Algz, on which it feeds. It is not very active in its movements. The’blood is colorless. It increases rapidly by trans- verse fission. Among the Sphagnum in the writer’s locality there ‘not uncommonly occurs a worm which I have ventured to identify as a member of this genus. It externally differs from the species referred to above in having fewer and larger red spots, which seem to be on the outer surface of the skin, where they are most abun- dantly collected near the two extremities, being few- est on the central region of the, body. The bristles are so arranged that they appear to form two rows of clusters on each side, being separated into two groups in each cluster. The worm‘thus seems to have four rows, instead of two as in the preceding species. Its movements are also much more active. It is likewise a vegetarian. 9. OCNERGODRILUS. This remarkable worm has thus far been found, by Dr. Gustav Eisen who discovered it, only in Fresno County, California, where it was obtained among fine Alge growing to the sides of a submerged wooden box, and also occasionally in the mud with a part of the tail end protruding and motionless. The body is SOME AQUATIC WORMS, ETC. 209 rather less than an inch long, one-twelfth of an inch wide, and presenting the peculiar color mentioned in the Key. Its movements are very slow. The podal spines are slightly curved, but not forked at the ends. They are arranged in clusters of four spines each, the clusters forming two rows, one on each side of the body. The cesophagus is long and remarkably muscular. It is surrounded and somewhat obscured by a pair of large glands, and has near its posterior extremity two large appendages similar in structure to the cesophagus itself. The blood is yellowish-red. The dorsal vessel, at some distance behind the front end of the body, divides into three branches, which pass forward, and near the anterior border unite by means of a network of fine tubules. The worm has four hearts, two on each side of the dorsal vessel, one pair being near the eighth, and one pair near the ninth cluster of podal spines. The dorsal vessel divides in front of the first pair of hearts. The ventral blood-vessel is forked, but with only two branches. 10. - TUBIFEX. A common and, in some places, very abundant little worm, measuring from one-half to one and one-half inches in length. The body is thread-like in its narrowness, transparent and colorless, although the bright crimson blood gives it a hue so vivid to the naked eye that, where the worms are numerous, it often seems to tinge the mud in which they live. They. are seldom found free-swimming, but live a comparatively sedentary life, with about one-half of 15 @ 210 AQUATIC MICROSCOPY FOR BEGINNERS. the body concealed in their burrow, the remaining parts protruding into the water, and constantly wav- ing to and fro beyond the edge of the little tubular chimneys which they erect. These little towers are often conspicuous objects on the surface of the mud in shallow still water, the worms instantly disappearing into them at the slightest disturbance. Among certain French and German writers on the subject, there is a difference of opinion as to which end of the worm is buried and which end protrudes into the water. As the protruding parts are continually moving, and as the worms also dart into the mud with such astonishing swiftness, to decide the matter is rather difficult. It is, however, probably the tail end. The bristles are comparatively short and appear to be arranged in a single row on each side of the body, whereas there is really an additional row of podal spines on both sides of the worm. These podal spines are entirely retractile, and are therefore. often over- _looked unless specially searched for. Even then it will perhaps be necessary to compress the worm rather forcibly between the slide and the cover-glass before, they will become conspicuous. They are but slightly curved, and seem to be forked. With very high magnifying power (about eight-hun- dred diameters ) some of the bristles present a curious aspect. The free extremity is widened and forked, the.two prongs of the fork being apparently connected by a thin membrane which is longitudinally striated. Sometimes this membrane splits into fine hairs. These widened bristles are most common on the young worms. The bright red blood is contained in two principal SOME AQUATIC WORMS, ETC. 2I1 tubular vessels, one above, the other below the tortu- ous intestine. The upper, or dorsal one, has con- nected with it near the anterior end of the body two little contractile hearts, one on each side, which can be seen through the hyaline animal throwing out the blood with considerable force. The two vessels are connected with each other by smaller branches, a pair in each segment or body-ring, one being on each side. There is also on each side of the body—two in each segment—a narrow colorless tube, ciliated within, and resembling those found in Nais and in other aquatic worms. They are most conspicuous in the posterior rings, and are supposed to represent kidneys in func- tion. Tubifex is reproduced by eggs, which probably make their escape after the parents’ death, and after. the body has fallen to pieces, as the living creature has no natural passage for their exit. Huxley, how- ever, says that they pass out through the segmental organs—the ciliated tubes referred to in the preceding paragraph. ur. NAts (Figs. 153, 154). The body of Nais is whitish or yellowish and usually very active. The podal spines and bristles are each arranged ina row on both sides of the worm, the bristles near the front end usually being longest. Each cluster of podal spines contains four or more. - The mouth is round. The front border ue the body bears numerous fine, short hairs. Two dark or black eye-spots are generally present, one on each side in advance of the mouth. The blood is red. 212 AQUATIC MICROSCOPY FOR BEGINNERS. Many narrow, colorless tubes, with a ciliated lining, are to be noticed on both sides of the intestine. They are much looped and twisted, and are supposed to Fig. 153.—Nais. play some part in respiration, or to represent the kid- neys of animals higher in the scale. They are bathed inthe colorless fluid filling the cavity of the body, and float out of position rapidly as this fluid flows to and fro, following the movements of the worm. dis is one of the commonest of our aquatic worms being very frequently found (Poe among Algz in shallow Fig. 154.—Podal Spine of Nai, | Water, or on the leaflets of various plants, especially, according to the writer’s experience, in Sphagnum, in company with Pristina and Cheetogaster. To those that desire to make a profound study of the aquatic worms, F. E. Beddard’s ‘‘Monograph on the Order of Oligochzta’’ may be commended. It is published in London. There is no American book on the subject. ROTIFERS. 213 CHAPTER VIII. ROTIFERS. When these transparent microscopic animals are swimming or taking food, there is usually an appear- ance of two, small, rapidly rotating wheels on the front border of the body, an appearance that sug- gested the name of Rotifera, or Wheel-bearers, for the group. The two organs certainly do seem like rapidly revolving wheels when viewed under a low pow- er, but they are in reality two disks or lobes bearing - marginal wreaths of fine cilia, which vibrate so quickly that the eye can usually perceive the effect only. It is by the action of these cilia that the Rotifer swims and captures food, the currents produced by them, when the animal is at rest, setting in towards the mouth, which is often situated between the ciliary (or cilia-bearing) disks, and carrying particles of food which the Rotifer accepts or rejects. Asa rule the ciliary disks are two separate organs, but they may be united into one, or the Rotifer may have the front margin of the body bordered by a single series of cilia, or the disks may be entirely absent and replaced by long, ciliated arms, as in Stephandceros, or by clusters of long, fine hairs as in Flosculdria, both of which are Rotifers. 214 AQUATIC MICROSCOPY FOR BEGINNERS. Most of these animals have eyes at some period of their life, or little red or black specks supposed ta be imperfect eyes. They are often to be noticed near the front of the body in young individuals, but in the old they are as often absent. Their number and posi- tion have sometimes been used as characters by which the genera and species were classified, but, since they often disappear with age, they can be of little value for this purpose, certainly of none to the beginner. The eyes, when present, are-almost without excep- tion, attached to the brain, which in some Rotifera, is an enormous organ, often filling most of the front re- gion in advance of the eye. Such Rotifers should be among the most intelligent of animals, if intelligence is ever commensurate with mere mass and not with quality, and fineness of structure. The body is inclined to be cylindrical, yet there are some that resemble flat disks and oblong figures. Neither are they all free-swimming. Some are per- manently adherent to the leaflets of aquatic plants or to other submerged objects, but these generally form a protective sheath about themselves, into which they retire when frightened or disturbed, in a manner simi- lar to that of some Infusoria; and, as in the Infusorial loricee, the sheaths may be formed of a stiff membrane or of the softest and most gelatinous material, or they may be built of particles of flocculent rubbish, or of rejected food-fragments. In all instances the sheaths are the work of the Rotifers inhabiting them, and none of the sheath-building Rotifers are free-swim- mers.* Most of the free-swimmers, however, may - - *Since the foregoing was written three have been discovered in England. But this need not trouble the beginner. ROTIFERS. 215 become temporarily adherent by means of their foot and toes. The. body of these free-swimming forms may be soft and flexible, and without any greater pro- tection than is afforded by the skin, or it may be en- closed within a hard, shell-like coating.called a lorica. The bodies of all sheath-building Rotifers are without a lorica, the sheath or tube being a sufficient protec- tion. In the other kinds the lorica is as colorless and transparent as a glass box, all the creature’s organs being plainly visible through its walls. The front part of the body, which bears the cilia or the ciliary disks, and often the long tail-like prolongation of the poste- rior part can be drawn within it, and the Rotifer thus be shut inand protected from harm. The soft-bodied forms have a similar habit of drawing in the two ex- tremities, taking advantage of the hardened skin. This is one of the Rotifers’ characteristics. The long tail-like part at the posterior end of the body is called the foot, and the one or two short divis- ions at the free end of the foot are, of course, the toes. The true tail of the Rotifer is usually a small affair, which the observer must not mistake for the more im- portant foot, although it is placed on the foot, and sometimes near to the body. It may be represented by a single short point; it may be in two parts and rather conspicuous; or it may be entirely absent. The uses of the foot seem to be to act as a rudder to guide the Rotifers when swimming, as they do ina hurried, headlong way, and to anchor them when they desire to fish for food, the toes then adhering to the surface of the slide or other object, thus holding the animal against the propelling power of the ciliary disks. In some of the group, especially in the com- 216 AQUATIC MICROSCOPY FOR BEGINNERS. monest of all—Rdtifer vulgdris—the whole foot is ar- ranged with joints that slide on each other like the joints of a spy-glass. In this and in similar forms the Rotifer can not only swim, but it can crawl or creep like a leach, by fixing the front of the body against the slide, drawing in the telescopic joints of the foot and clinging with the toes; the front is then loosened, the foot extends and carries the whole body forward for a short distance, when the action is repeated. A Rotifer can do this with surprising rapidity, and so travel over considerable microscopic distances in a short time. The mouth is usually placed between the two ciliary disks, when they are present, near the center of the frontal portion of the body, or, in many forms near the front, but on the lower surface of the animal. Those Rotifera with the mouth in the last mentioned position usually feed by gliding along with the front of the body in contact with the plant, tearing and biting off small particles as they go. These may be called the nibbling Rotifers, and form by far the greater number of known species. Following the mouth is usually a tubular passage: leading to a pair of wonderful jaws inside of the body, which, with a low-power objective, can be seen in action through the transparent tissues of the animal. These jaws are always present in the creatures, and are a-great help to the beginner, for as soon as he ob- serves them pounding and crunching away inside of a transparent, legless, microscopic animal, he may be sure that his specimen is a female Rotifer. The ciliary disk: may be absent, or replaced by arms or hairs or by some other. substitute, but if thése internal jaws ROTIFERS. 217 are present the specimen is-a Rotifer, and can be noth- ing else. By some observers these remarkable organs are called the gizzard, which they are not. The best word to apply to them in mastax. It is really the ani- mal’s true mouth, the passage leading to it from the frontal region being only a part of the preoral tract. ‘The mastax is the most hard-working part of the creature’s anatomy, except, perhaps, the cilia. When the currents produced by the latter bring an acceptable morsel of food to the preoral aperture, it is passed down to the mastax, where it is crushed and allowed to goon to the stomach. In some Rotifers the part is very complicated. In the simpler forms it consists of two apparently semicircular plates surrounded by a thick envelope of powerful muscle, the flattened sides acting against each other and crushing the food be- tween them. The surface of each plate usually bears several transverse parallel ridges, to be seen with a high power, each ridge projecting a short distance be- yond the straight internal edge, and forming low teeth. These ridges, when the mastax is closed, are received in the depressions or furrows between those on the opposite plate, thus making an effectual crushing instrument. In other forms the mastax consists of three parts, one being immovable, and used as an anvil on which the other two pound the food as it passes by. In.the nibbling Rotifers the entire mastax is protruded through the preoral aperture, and bites, tears, and nibbles at acceptable food-masses. If the observer finds it difficult to make out the form and structure of the mastax, as he probably will when it is examined in action within the body, he may suc- ceeded in isolating the organ by killing the Rotifer 218 AQUATIC MICROSCOPY FOR BEGINNERS, with a strong solution of caustic potassa allowed to run under the cover-glass—a small drop at a time. This will dissolve the soft parts, and permit the hard, insoluble mastax to float out, when it can be examined with a high-power objective. Seven kinds or types of these organs are described by microscopical anatomists. The Rotifers are reproduced by eggs, which are sometimes hatched within the parent’s body, when the animals are said to be ovo-viviparous. This, how- ever, isnot common. The eggs are usually semitrans- parent, ovoid bodies, often to be seen on the slide among other matters, with the enclosed Rotifer im- perfectly developed, and the mastax grinding away in- side of the unhatched body, where it cannot possibly have anything to crush. The only parallel to this of which I know is Professor Agassiz’s statement that the jaws of the young snapping-turtle snap while the crea- ture is still within the egg. The Rotifers may drop their eggs anywhere and leave them to the care of Nature, or they may pru- dently attach them to a leaf or to some other aquatic object. Very often they are adherent to the posterior part of the parent, and are carried about until the young are hatched. In those permanently attached Rotifers that form a soft sheath this is a common oc- currence, and several eggs may at almost any time be seen in the lower part of the lorica, or adherent to the animal’s foot. In such instances, when the young are hatched, they creep up between the parent’s body and the side of the sheath, and escape at the front. They swim about fora short time, and then secrete or build a sheath of their own, which they never volun- tarily leave. ROTIFERS, 219 The eggs are usually smooth; sometimes, however, they are covered with short spines or hairs. It isa peculiar and interesting fact that although there are male and female Rotifers, the males are sel- dom seen. In some species they have never been found, and are therefore entirely unknown. Those that have been discovered are much smaller than the females of the same species; they are always free- swimming, and are without a mastax and alimentary canal, or with the latter so imperfectly developed that it is useless. Male Rotifers, therefore, never take food. It is not probable that the beginner will meet with them, or at least that he will recognize them as the males, or indeed as Rotifers. This group of microscopic animals is almost as com- mon and abundant as are the Infusoria, and they are found in similar places. They are specially fond of hiding in masses of Ceratophyllum, or among the leaflets of any aquatic plant. Indeed, almost any pond or shallow body of still water may be examined with a certainty of finding them. They have even been spar- ingly obtained from the moss that grows between the bricks in damp pavements. Some species develop in vegetable infusions, but as a rule they prefer fresh water. A good method by which to capture them for the microscope after a pond-hunting expedition, when we may be sure we have the creatures somewhere in the vessel, is to take a portion of a plant carefully out of the gathering, and rinse it in a watch-glass full of water, preferably in the water which will drip from the - plant, or which may be dipped from the collecting- bottle itself. The Rotifera will be sure to be washed 220 AQUATIC MICROSCOPY FOR BEGINNERS. from among the leaflets, and may be captured by the dipping-tube. If left on the table near a window they will, like most microscopic creatures, both plants and animals, in a short time, collect on the lighted side. / The reader will, of course, not expect that all the genera and species are included in this little book. He will obtain many whose names he cannot hope to learn in this short account. He can, however, know them to be Rotifers by the presence of the mastax, which makes them one of the most easily recognizable groups of microscopic animals, and they form one of the most interesting classes of creatures for micro- scopical study. Few of our American forms have been carefully investigated, and there is no American treatise on the subject to which the reader can be re- ferred. The only work on the Rotifera in the English language is Hudson & Gosse’s ‘‘The Rotifera; or Wheel-Animalcules,”’ published in London, a valuable monograph and one which every student of micro- scopic pond-life should possess, although it does not deal extensively with American species. The ‘‘Wheel- Animalcules” of this country form an extensive field for scientific research and one that should be culti- vated. There is room here for many discoveries, and likewise an opportunity to ‘add greatly to the world’s store of scientific information. In using the following Key, the reader should bear in mind that the mucilaginous sheath of some of the Rotifers is usually colorless, and rather difficult to see distinctly unless it have particles of dirt, or of other extraneous matters, adherent to it. At times, how- ever, it may be almost as conspicuous as the animal foo ROTIFERS. 221 which it encloses. The Key refers only to those ‘forms included in this book. Key to Some Genera of Rotifera. 1. In an attached, gelatinous or other kind of sheath (2). 2. Not in a sheath, but in attached clusters (@). 3. Free-swimming singly or ina clustered group (e). a. Clustered; sheaths soft, gelatinous, colorless; ciliary disk single, heart-shaped, Lacinuldria, 1. . Not clustered, but sometimes in family groups; sheath gelatinous (4). Not clustertd; sheath not gelatinous (c). With five long, erect, ciliated arms on the front border, Stephandéceros, 2. With several (from 2 to 7) groups of many long, fine, radiating hairs (seta) on the front border. Flosculéria, 3. With a broadly oval or circular ciliary disk; sheath gelatinous, semi-opaque, or with pellets, Gicistes, 4. Sheath formed of rounded, brownish pellets, Melicérta, 5. Sheath not formed of pellets, but membranous; brownish or colorless, Zimnias, 6. Ciliary disk horseshoe-shaped, Megaldtrocha, 7. In acluster of coherent, gelatinous tubes; ciliary disk horseshoe-shaped, Conochilus, 8. e. Not clustered; with lorica (g). e. Not clustered; without lorica; ciliary disks two (f). Eyes two, cervical, Prilodina, 9. 222 AQUATIC MICROSCOPY FOR BEGINNERS. J. Eyes two, on the frontal column (proboscis); toes three, the middle one small and-not easily seen, Rdtifer, 10. 3 g. Lorica with a visor-like projection in front, Stephanops, 11. g. Lorica circular, flattened; foot long, cylindrical, * retractile, Pterodina, 12. g. Lorica vase-shaped; foot long, with two exceed- ingly long toes, Scarédium, 13. g. Lorica with 6, long, narrow, movable, oar-like appendages on each side, Polydrthra, 14. g. Lorica with several tooth-like spines on the front border, Brachiénus, 15. 1. LACINULARIA. The clusters contain numerous individual members which secrete a common, soft, colorless, or pale yel- lowish, and short sheath with no special shape, this formless jelly-like enclosure surrounding only the posterior portion of the colony, where it must serve as an exceedingly inefficacious protection, if it serve any. The Rotifers themselves are somewhat trumpet- shaped when extended, and toa certain extent resemble Megaldtrocha (Fig. 160). The ciliary disk is single and horseshoe shaped. It is closed and drawn partly into the body when the Rotifers retire intq their apology for a sheath, as they often do, the whole colony continually waving and bobbing and bowing as the members retire, or ascend to expand themselves, the sheaths usually forming a little mass of jelly-like substance, from all parts of which the Rotifers project. The colonies are commonly adherent to Ceratophyllum ROTIFERS, 223 or to Myriophyllum, and are often visible to the un- aided eye as grayish little balls. 2. STEPHANGcEROS (Fig. 155). The body of this, the most beautiful of all the Rotifera is somewhat spindle-shaped, and ends in a long, flexi- ble, tail-like foot which is attached to some submerged object. It has its characteristic fea- ture in the five long, slightly curved arms arranged in a row about the edge of the front border, these arms being ‘held aloft, and forming a beautiful object for the microscopist, but an effectual trap for wandering Infusoria, which are attracted or drawn into it by some means not easy to make out, but probably by ciliary action difficult to observe. The front of the body is like a deep open funnel leading down to the pre- oral aperture, to the mastax, and to the stomach. The ordinary ciliary disk is absent, being replaced by the beautiful arms, but around the lower inside border of the funnel-like front there are many fine cilia that produce the currents in the water by which the living food is drawn to the trap. These cilia are exceedingly fine and difficult to see even with a high-power objective. The sheath is usually colorless and transparent but with considerable firmness. It often surrounds the body up to the origin of the arms. When a small animal once enters the cage formed by these arms, beautiful objects as they are, it seldom Fig. 155. Stephanéceros. 224 AQUATIC MICROSCOPY FOR BEGINNERS. escapes, but is gradually driven down into the funnel, when the Rotifer partly closes the front opening, and with a perceptible gulp swallows the captive and passes it on to the mastax. Stephanéceros does not seem to be. common. The writer has found it sparingly on Myriophyllum as late as the middle of November, but never at any time in any numbers. 3. FLoscurAria (Fig. 156). The front of the body or the preoral passage is here also like an open funnel, the narrow part leading to the mastax. The ciliary disk is, in the species here re- ferred to (/. ornata), replaced by five little rounded elevations on the front margin, each bearing a thick cluster of long, fine, radiating sete, which are flexible, and movable at the animal’s will, but which never vibrate like cilia. Thelong foot is attached to a sub- merged object, and is surrounded by a soft, transparent sheath. When the Rotifer retires into this protective covering, it folds the wide front part of the body together, the clusters of long setze seem to become _, ; : ? < Fig. 156.—Floscularia much tangled into a single bunch, and ornéta. the creature slips back into the sheath. When she comes out, the bunch of sete trembles in a charming way, reminding the observer of that quivering of hot air often seen above a warm surface on a summer day. The front border opens, the clusters of stiff hairs are spread apart, and the Rotifer is ready for something to eat. Any little ani- . ROTIFERS. 225 mal slipping in between the seta seldom comes out again. The Floscularia gently contracts the frontal opening and directs the victim towards the preoral aperture where it is gulped down as in Stephanocerus, and the mastax finishes it. Several eggs are often to be seen attached to the foot. This splendid Rotifer is common, and where one is found others will usually be near by. 4. (CEcisres (Fig. 157). When a bottle of pond water containing various plants is allowed to stand for a while undisturbed, there will often form on the sides very delicate, thread- like objects, frequently branching and otherwise resembling brownish Algez, waving and trembling as the 4 bottle is stirred. They are so soft that they can hardly be removed with the dipping-tube without break- ing them. They are the sheaths of a Rotifer, which she makes froma sticky secretion exuded by her body, and from small particles of any kinds that may be floating in the vicinity. The inner surface seems to be smooth, but the outside is rough, irregular, and flocculent. Fig. 157.—(Ecistes. The Rotifer projects from the open end, clinging to the supporting object by means of an expanded, sucker-like foot. As the tube lengthens by the deposit of new material at the summit, she takes a step forward so as to keep her expanded ciliary disk in the open water. If the student will allow a mixture of 16 226 AQUATIC MICROSCOPY FOR BEGINNERS. pulverized indigo and water to run under the cover- glass, he may witness the formation of the sheath. A blue ring of indigo will speedily appear at the top of the soft tube. 5. ME ticérta (Fig. 158). The sheath of Melicérta resembles that of no other common Rotifer. It is built of pellets, which she makes and places in rows around her body, thus erect- ing a reddish or yellowish-brown lorica that cannot be mistaken. The body itself is colorless, and is always attached to an aquatic support by the tip of the long foot. The ciliary disk consists of four parts or lobes of different shapes and sizes, and the little creature has in addition to these, a peculiar and rather complicated organ for making the pellets. The whole front part of the body can be folded together into a rounded mass when Melicerta is frightened and retires to her sheath. When her fright is over, she slowly protrudes this rounded mass from the aperture, gradually spreads it open, sets the cilia at work, and proceeds to eat and to build. The last she seems to do almost continuously, up to a certain point, Fig. 158.—Meli- for as her body grows, her house must be cérta ringens. ee i ; enlarged to receive it. ; The ciliary disk of Melicerta will repay the most careful study. And careful observation will be needed to learn just how the three distinct currents that she makes in the wate1 are produced. One current brings food-particles to the mouth, where she selects ROTIFERS. 227 the acceptable morsels and passes them on to the mas- tax; a second current carries away the fragments for which she has no use; and the third sets in towards the little organ that makes the pellets. This is a small cavity into which the building material is poured, and where it is turned about rapidly by the fine cilia which line it. An adhesive secretion is exuded that causes the particles to adhere to one an- other, and the revolving motion gives the pellet the shape of a Minié-bullet, or, in another species, makes them -spherical. When the pellet is formed to the Rotifer’s liking and all is ready for the final act, Meli- certa rotates or twists herself in the tube bends her body forward, and deposits the pellet on the top row exactly in the right place, and there she cements it fast with an invisible, insoluble cement. The entire act is performed so quickly, that the first time the ob- server sees it he is so surprised that he sees nothing. It is remarkable that, as a rule, Melicerta forms a pellet while standing at that side of the sheath oppo- site to the point where she intends finally to place it. There are two somewhat’ common species in our waters, one making almost spherical pellets ( Aeticerta ringens), the other forming her ‘‘bricks” in the shape of the Minié rifle-bullet ( AZe/icerta contfera), with the conical extremities pointing outward. 6. Limntas (Fig. 159). The attached sheath formed by this Rotifer is a rather rigid, always membranous, and nearly cylindri- cal tube, yet somewhat widest in the upper region. When young it is usually colorless and ‘smooth, but it changes with age, becoming brown or blackish, and 228 AQUATIC MICROSCOPY FOR BEGINNERS. floating particles roughen it by adhering to the outersurface. The animal living within it is colorless. The ciliary disk is divided into two lobes, which she folds together when frightened and forced to retire to the lower regions of her domicile for protection. The sheath is secreted from the body of the occupant. It is not built up of par- ticles picked out of the currents that flow from the ciliary discs; neither is it, as with some forms, composed of faecal matter. Limnias is not rarely found attached to the leaflets of Ceratophyllum, and is proba- Fig. s59-Lim- bly named Limnias ceratophylli for that rea- phylli. son, although it is almost as often to be obtained from Myriophyllum. There is another species of Limnias also rather common in the writer’s locality, but which differs from Limnias ceratophylli in having the sheath apparently formed of narrow rings, so that the edges, as seen un- der the microscope, seem finely waved or scalloped. By this character it may be easily distinguished from L. ceratophylli. Itis named Limnias annuldta. 7. MEGALOTROCHA (Fig. 160). The clusters formed by Megalétrocha are not rarely so large that they become visible to thé naked eye as little whitish masses clinging to the leaflets of Myrio- phyllum, which it seems to prefer. With the pocket- lens the indiv'dual Rotifers may be seen rising and bobbing about as they expand or contract, but a low power of the compound microscope is needed to ap- preciate their beauty. The expanded body is some- ROTIFERS. what trumpet-shaped, very soft and flexible, and when young is colorless, becoming slightly yellowish as it in- creases in age. The eggs are often to be noticed adhering to the lower part of the parent. When the young one is hatched, it either remains in the old colony to increase the size of the cluster, or it leaves and founds a new group, so that in favorite localities colonies of almost any number of members may be obtained. _ The Rotifers of old colonial clust- ers are often infested by an Infusorial 229 \ 1 \ \ ) Fig. 160.—Mega- létrocha. parasite, which runs over the surface and apparently feeds on the mucous matters secreted by the Rotifers’ skin. It is called Chilodon megalétroche, and resembles, in a general way, the Chilodon shown by Fig. 128. 8. ConocuiLus (Fig. 161). e In the writer’s locality free-swimming colonies of Conochtlus volvox are among the Rotifers most frequently met with, . especially in the spring of the year when they seem most numerous and, like many other denizens of the ponds, have all their functions exceedingly active. The rounded, freely floating colonies are visible to the naked eye as they roll Fig. 161, — Cono- through the water, especially if the ves- chilus. sel containing them be held against the 230 AQUATIC MICROSCOPY FOR BEGINNERS, light. Each Rotifer inhabits a gelatinous tube of its own secretion, but these sheaths are soclosely pressed together that they soon become confluent, or coher- ent, and the jelly-mass seems to be common property. This is especially true with the older and larger colo- nies, which are formed by the pretty constant addition to them of young Conochili, the whole cluster thus varying in age with the age of its members, and gradually but surely increasing in size, until the mass becomes so large that it breaks apart, the separated groups sailing off as if nothing unusual had occurred. These Rotifers have their feet directed toward a .common center, the bodies radiating outward, and the ciliary disk of each projecting, with a portion of the body beyond the mucusand into the water. The ciliary disk is horseshoe-shaped. As many as a -hundred members have been seen in a‘single colony. Repro- duction is by means of eggs. g. PHILODiNA (Fig. 162). This particular species is readily distinguishable from the common Rotifer (Rotifer vulgdris) by the spinesscattered over the back and sides of the hardened and minutely roughened body, and by the fact that the two eyes are placed, not on the proboscis, but at some distance behind the front border, while in Rotifer vulgdris they are close together on the proboscis. This position of the eyes, or what is called the cervical position, is an infallible point by which all members of this genus may be Fig. x62.-Phil- distinguished from all the members of the odina acu- 7 leata. genus Rotifer. ROTIFERS. 231 The body is flexible, yet the skin is hardened and bears several conspicuous curved spines, two of which are on the sides—one on each—and pointing forward. The foot bears two tail-like spurs, which are shown in the figure projecting beyond the body. The Rotifer is peculiar, and not uncommon. I have found it in summer, and have taken it from under the ice in Feb- ruary. Its color is usually some shade of brown. 10. RoTIFER VULGARIS (Fig. 163). This is the commonest of all the Rotifers. Hardlya drop of water from the proper localities comes to the microscope-stage without bringing with it one or more of this abundant and cosmopolitan species. It is usually one of the first animals to at- tract the attention of the microscopist at his earliest attempt to investigate the life within the nearest pond or ditch, and to the: end remains almost a constant companion. The white body is long, spindle-shaped, and tapers from near the middle to both extremities where the two anterior ciliary - - disks are unfolded. Ever since the anitnal was described by Ehrenberg in 1838, until | within a few years past, it has been des: | ~ cribed as having only two toes, whereas it has three; they are small but ‘distinctly beens three in number. This is one of the " ‘tifer. many statements of microscopical observations which have been accepted as correct on the dictum of some’ acknowledged authority, who worked many years ago 232 AQUATIC MICROSCOPY FOR BEGINNERS. and with objectives immensely inferior to even the cheapest and lowest grade lenses now at our dis- posal. However, futifer wulgdris has three toes at the extremity. of a long foot, which is jointed and which, by means of these telescopic joints, can be entirely re- tracted into the body. : Between the two ciliary lobes is a narrow cylindrical projection ciliated at the truncaté tip, and nearly al- ‘ways bearing two little red eye-spots close together. This is called the proboscis. When hungry, the Rotifer clings to the slide by her three toes, expands the ciliary disks, and sends a food- bearing current through the. preoral passage to the true mouth, the mastax. When desirous of changing her localitv, she may either loosen her hold by the tips of her toes and be carried through the water by the action of the frontal cilia, or she may fold the ciliary. lobes together, and go looping about by cling- ing with the tip of the proboscis while she draws up the foot, when, fastening it to a new place, she lets go with the proboscis, extendsthe body, takes a new hold with the foot, and thus moves forward rapidly, some- what with the movements of the ‘‘measuring-worms.” otifer vulgaris produces her young alive, and in that connection is a problem which the reader has an op- portunity to solve, or at least, to try to solve. It is that although the living young has been seen to leave the parent’s body through the posterior intestimal re- gion, the cloaca, it is not known how those young pass from their free position in the mother’s body-cavity, to the cloaca whence they have been seen to issue into the surrounding water. Another interesting fact is, that although Rotifer vulgaris is so common everywhere ROTIFERS. 233 and, as Dr. C. T. Hudson remarks, has been studied in thousands of specimens by many practiced observers during the century and a half which has elapsed since the animals were discovered, the male Rotifer vulgaris is not known. 11. STEPHANOPS (Fig. 164). There are several species of these pretty little Roti- fera, all of which may be known as members of this genus by the extension of the front of the lorica over the ciliary disk, like the visor of a boy’s cap. A not uncommon species is shown by Fig. 164, in side view, so asto exhibit the long bristle springing from the back, and the curved visor which, in the figure, looks like a hook above the front- al cilia, yet is, in front view, a circular shield. This Rotifer is one of the Fig. 164.—Stéphanops. nibblers. The mastax is protruded from the preoral aperture, which is near the front of the lower flattened surface, and bites and tears the food it meets with. The animal is often to be seen gliding over aquatic plants nibbling as it goes. The lorica is thin and somewhat flexible, and it ex- tends over the sides of the body, so as to give the Roti- fer an ovate outline when seen from above or from be- low. The bristle on the back is very movable and flexible. In another species (S¢. Zame/laris), the lorica is pro- longed at the posterior border into two lateral teeth. In another (S¢. muticus), this part is without teeth, and the dorsal bristle (seta or slender spine) is also ab- 234 AQUATIC MICROSCOPY FOR BEGINNERS. sent, as it is in all the known American species, ex- cept the one shown in Fig. 164. St. muticus is not un- common. tz, Preropina (Fig. 165). The lorica is almost circular, much flattened, and perfectly transparent. The an- terior border has a broad notch with rounded margins, over which extends a lip with a central round- ed projection. The ciliary disks are two, and rather widely separ- ated. There are usually two eye- spots. The foot is long, tail- like, ‘exceedingly flexible, and so wrinkled transversely that it appears to be formed Fig. 165.—Pterodina of narrow rings. It -” fer can be withdrawn en- tirely into the lorica, and the Rotifer | seems to take pleasure in doing so. It. | has no tail, but is terminated by a small sucker bordered by a ring of fine cilia: The Rotifer is often seen among the leaf- lets of Ceratophyllum and other aquatic plants. Pe 13. SCARIDIUM (Fig. 166). The transparent, glassy lorica is. rather squarely vase-shaped, somewhat flattened, Fig. 166-Scar- and generally has a tooth-like projection — idium. on each side of the posterior border. The Rotifer can always be recognized by its two exceedingly long ROTIFERS. 235 toes. The foot is formed of two joints slightly enlarged at the ends. The Rotifer is not very common. 14. Poty4rTura (Fig. 167). The contour of the lorica is somewhat like that of an egg, with both ends cut squarely off. The char- acter, however, by which the Rotifer may always be known is the presence of the twelve long, serrated oar- like appendages which project backward from the front part of the upper. and lower surfaces, from near what may perhaps be called the shoulders. They are arranged in clusters of three each, one group being on each side below, and one on each side above, only six being shown inthe figure. By them the Rotifer _ Fig. 167.—Pols arthra. makes long, quick, sudden leaps, often jumping so rap- idly that it can hardly be seen; it appears to spread the appendages andtovanish. Occasionally it turns a com- plete somersault. The cilia are arranged in a row along the front border. There is no foot. The mas- tax is pear-shaped and large, but its structure is diffi- cult to make out. The Rotifer has only one eye, which appears to be near the center of the upper front surface. The little creature has been called by some writers the ‘‘sword-bearer,” and is said to be quite common in some localities, but I have never been fortunate enough to find it in the waters near my home. It is not rare in New York. 236 AQUATIU MICROSCOPY FOR BEGINNERS. 15. BRAcHIONUS (Fig. 168). There are numerous species of this genus; all of which may be known by the presence of a lorica with several tooth-like projections or long spines on the front margin, and often likewise at the rear; by the two ciliary disks and, when present, the single eye- spot. The species whose empty lorica is shown in Fig. 168, is very — attractive in its glass-like transpar- ency, active movements, and beauti- ful lorica. It is not uncommon, and ; may be easily recognized by the ten O long teeth or spines on the front border—the central one on the upper Fig. 168.—Brachiénus, Side or back being largest, and bent usually at a right angle—and by the four posterior spines. The foot is long, narrow, and has two toes. Eggs are occasionally to be noticed attached to the posterior margin of the lorica. Itis Brachionus milt- tarts. The surfaces of the lorica are tessellated, or marked in polygonal areas, and covered by small raised points, all of which add much to its beauty and its -in- terest. FRESH-WATER POLYZOA. 237 CHAPTER IX. FRESH-WATER POLYZOA. The reader now approaches a group of microscopic animals whose beauty is so exquisite, so delicate, so refined in its comeliness and grace, that no description could be too extravagant, no rhetoric too fervid when applied to the charming little creatures. Yet most of this fairness seems wasted so far as human apprecia- tion is concerned, for how few among the millions of human beings in all the land know, or care to know, what the Polyzoa are, or how they look, or where they live, or whether they live at all? Nature was never in better mood than when she began the development of the Polyzoa, so she fashioned them with care, and placed them most abundantly in all our slow streams and shallow ponds, where they live and die and melt away in the shade of the lily-leaves, where no human eye sees their loveliness until a wandering lover of Nature spies them and is happy. The word Polyzoa is formed of two Greek words meaning ‘‘many animals,” referring to their habit of living in colonies, which sometimes reach an immense size. These clusters are, with but one exception, always attached to some submerged object, except im- mediately after leaving the egg, when the young ani- 238 AQUATIC MICROSCOPY FOR BEGINNERS. mals lead a short, free-swimming life. When once at- tached they are adherent till death. The animals themselves are small, but often appar- ent toa trained eye; they are always visible under a good pocket-lens. The colonies, however, of all the “fresh-water forms need no magnifying; some of them are even conspicuous. These communities are formed of the protective coverings or sheaths.secreted by the animals. Some take the form of marrow, brownish tubes, adherent to the lower surface of floating chips, boards, waterlogged sticks, or even occasionally of lily-leaves or to the submerged stems of grasses. The little tubes branch like miniature trees, and spread over the surface to which they adhere as if the delicate tree had been flattened down and pressed so hard that it could never again rise up; or they may. be attached by the base only, the trunk and the branches then floating- and waving in the water. The animals secreting these tubes live in them,: projecting a part of the body beyond the orifice, and quickly retreating when frightened. And they are usually exceedingly ‘timid, retiring into the tubular home at a slight dis- turbance of ‘the water, needing.a long time in which to recover and again to look out .at the entrance, there to spread their beautiful tentacles. In other forms the colony is surrounded by a thick, rather firm, jelly-like material, from which the ani- mals protrude themselves, and into which they retreat. These jelly masses are usually colorless and semi-trans- parent, or they may be tinged a pale red. They are to be found in the purest of still water, adherent to sticks, capping a submerged stump with a cushion of living jelly, clinging like crystalline globules to any FRESH-WATER POLYZOA. 239 projecting rootlet or water-soaked object beneath the surface, even to smooth stones. In bulk they may be like a boy’s marble, or a cart-wheel, with every inter- mediate:size. They vary so much that to find a good comparison is not easy, and it is only right to say, lest some lover of these lovely creatures should be envious, that a colony the size of a cart-wheel has, in the writer’s locality, been found but once, the foundation of this remarkable growth ey being the rim of an old wheel. When the tubular or the jelly-like colonies are removed to the collecting-bottle, they appear lifeless and unat- tractive. The jelly may excite wonder by its size, or curiosity to know what it can be, yet otherwise it will not be noticeable. But wait a while. Place the bottle in the shade and wait a few minutes; then with a pocket-lens look at the surface of the jelly or at the tips of the branching tubes. Treat them with care; move them gently. The little creatures are easily frightened, and like a flash leap back into their pro- tective case. Perhaps while you gaze at the reddish jelly a pink little projection appears within the field of your lens, and slowly lengthens and broadens, retreat- ing and reappearing it may be many times, but finally, after much hesitation, it suddenly seems to burst into bloom. A narrow body, so deeply red that it is often almost crimson, lifts above the jelly a crescentic disk ornamented with two rows of long tentacles that seem as fine as hairs, and they glisten and sparkle like lines of crystal as they wave and float and twist the delicate threads beneath your wondering gaze. Then, while you scarcely breathe, for fear the lovely vision will fade, another and another spreads its disk and 240 AQUATIC MICROSCOPY FOR BEGINNERS. waves its silvery tentacles, until the wh»le surface of that ugly jelly-mass blooms like a garden in Paradise— blooms not with motionless perianths, but with living animals, the most exquisite that God has allowed to- develop in our sweet waters. Perhaps you make an in- articulate cry to your companion, who is probably won- dering why you are so stilland what you are doing on the ground with the lens so close to the bottle, and as he too gets down and brings his lens to bear, maybe he jars the water, and the lovely Polyzoa flash their tentacles together and dart backward into the mass, leaving it as indescribably ugly as before. If he takes you to task, tell him to wait and look. And while he looks the little bodies again slip outward, the crescen- tic disks again spread wide open, the shining tentacles unfold and curl and lash the water until once more the ugly jelly-mass becomes a thing of indescribable beauty. This is Pectinaté/a, well named the magnifi- cent. The jelly'is formed by the animals, and is in reality a collection of protective lorice, the huge masses often found being the result of the increase in the numbers of the Polyzoa inhabiting them; or, as must frequently occur where they are abundant, of the union of many contiguous growing colonies. A single animal begins the cluster; it becomes two by a process of budding, the bud finally becoming another. Polyzoén, secreting more jelly, budding in its turn, so that the community may in the end contain number- less members, and the mass may measure several feet in diameter. The color of the animals is usually a pale red or flesh tint, deepening to crimson about the mouth, which is placed near the center of the crescen- FRESH-WATER POLYZOA,. 241 tic or horseshoe-shaped disk of tentacles. In the largest, and therefore the oldest, colonies the jelly may exhibit many scattered white spots composed of carbonate of lime. There is another jelly-forming colony called Crista- téla, which the beginner may mistake for young Pecti- natella. It is to be distinguished by the absence of those great masses which characterize Pectinatella, by the general appearance of thecolony, and by its motion. A community of Cristatella is usually long and narrow, often measuring several inches inlength. Onespecies is about eight inches long, one-fourth of an inch wide, and one-eighth thick. Young colonies are, of course, smaller, and are rounded. It has the power which no other fresh-water Polyzoén possesses—to travel from place to place, yet moves slowly, a colony about an inch in length moving an inch in twenty-four hours. All the fresh-water Polyzoa, of which there are sev- eral genera and species, have on the front part of the body a disk which bears the tentacles. Itis named the lophophore, and.is, in some forms, horseshoe-shaped, in others nearly circular. The tentacles are arranged on it as on a base, usuallyin a double row. The word is Greek, and means ‘‘wearing a crest.” - In those Polyzoa which secrete hardened, tubular, tree-like sheaths on the surface of submerged objects, the lophophore is protruded from the orifice in the end of the branch much as in Pectinatella, and there is only one animal to each limb or hollow twig. The protrusion and expansion of the lophophore can be seen with a pocket-lens, as in Fig. 169 (from Professor Alpheus Hyatt’s work on the Polyzoa), when it resem- ‘bles in form that of Pectinatella. Those’ inhabiting 17 242 AQUATIC MICROSCOPY FOR BEGINNERS, the tubular sheaths seem much more timid than those in the gelatinous forms, retreating on slighter provo- cation, and remaining longer before they reappear and again spread the lophophore and the tentacles. They are as graceful and as attractive—perhaps they are more so, since they seem more delicate and less able to protect themselves. The tentacles are finely ciliated, as the microscope will show. Thecurrents produced bythe active vibra- tions of the cilia on the sixty to eighty tentacles of Pectinatella, or the eighteen to twenty in other mem- bers of the group, are powerful, and setting in towards the center of the lophophore, they sweep the entrapped food to the mouth. The body of the Polyzoén is a transparent, mem- branous sack, with the lophophore and the mouth at the free end, most of the rest being immersed in the jelly, or concealed in the brown opaque sheath. The mouth has on one border a short tongue-like organ, which can close the opening and prevent the escape of the food, and extending from the mouth to the stom- ach, is the food-passage or cesophagus. The stomach itself is a widened tube, usually conspicuous on ac- count of its contents and thealternate narrow, reddish- brown and yellow bands traversing it lengthwise. It is suspended in the hollow body, and is bathed by a colorless fluid which fills the body-cavity and extends also into the hollow tentacles. The stomach is fol- lowed by the tubular intestine, which curves forward, and generally opens below and on the outside of the lophophore. The animals have no heart and no blood, unless the liquid in the space between the outer walls of the stomach and the inner walls of the body can be said to be blood. FRESH-WATER POLYZOA. 243 When the animal is frightened, the sides of the lo- phophore close together, the tentacles collect them- selves into a bundle, and the front of the Polyzoén is drawn back into the body, a muscle around the border closing that opening. The jelly of Pectinatella and the hardened tubes of the other forms are, therefore, the protectors of the body, while the body receives and encloses the lophophore and tentacles, which are thus doubly protected. When the danger is past, the tips of the bundle of tentacles are cautiously pushed out into the water, the lophophore follows, and if the creature’s confidence is restored, the crowns are spread open in all their indescribable grace and beauty. The favorite food consists of small Algz and Infuso- ria, which the ciliary currents sweep toward the mouth, the tentacles forming a cage from which the most act- ive little animals seldom escape unless the captor is willing. And not only are the tentacles used to cap- ture the food, but ‘‘for a multitude of other offices. They are each capable of independent motion, and may be twisted or turned in any direction; bending in- ward, they take up and discard objectionable matter, or push down into the stomach and clear the cesopha- gus of food too small to be acted on by the parietal muscles.” To examine the Polyzoa under the microscope de- mands adeep cell to hold a large quantity of water and to prevent the cover-glass from pressing on the bodies. It is often better to place the microscope in an up- right position and to omit the thin cover. In this ar- rangement the water trembles easily, and not only in- terferes with the distinctness of the image, but terri- 244 AQUATIC MICROSCOPY FOR BEGINNERS. fies the timid creatures on the slide. The observer must, therefore, be careful not to touch the table, and to make his examination in a quiet room. The charming creatures will ask a little attention and some gentle treatment, but what they will show with the help of a one-inch objective will amply repay for all the outlay of time and of patience. The following Key to the genera will help the stu- dent to name the forms he may find. Key to Genera of Fresh-water Polyzoa, In a jelly-mass (a). In adherent, branching cylindrical tubes (4). In adherent, branching colonies formed of tubular, club-shaped cells (c). 4. In attached, pendent stems formed of urn-shaped cells (d). a. Jelly-mass rounded, adherent, often very large. Pectinatélla, 1. a. Jelly-mass long, narrow, slowly traveling. Cras- tatélla, 2. a. Jelly-mass small, sacciform, finally lobed or branched. (Very rare). Lédphopus, 3. 4. Lophophore horseshoe-shaped. Plumatélla, 4. 6. Lophophore circular. Fredericélla, 5. c. Lophophore circular, tentacles in a single row. Paludicélla, 6. @. Lophophore circular or oval, tentacles in a single row. Ornatélla, 7. DW iow I, PECTINATELLA MAGN{FICA (Fig. 169). The appearance to the naked eye of the colorless jelly-like substance surrounding the bodies, and of the animals themselves, has already been referred to. FRESH-WATER POLYZOA, 245 Pectinatélla is not sensitive to sound, but a jar or a shock to the water sends the animals into their con- tracted state with surprising suddenness. The col-: onies are numerous throughout the summer and until October, being most frequently found in the shade, although they may live.in the sun if below the water. Exposure to air and sunlight together is speedily fatal. Therefore transfer the jelly to the collecting- bottle as soon as possible, otherwise you will have, on your return home, nothing but a softening, slimy mass that ous " i My will soon force you to throw ~ it away. If suspended in a aA large vessel of water kept fresh by frequent change, Pectinatella will live for some time in captivity. In Fig. 169 Ais KS (after Hyatt) is shown a small pig. 160,—Pectinatélla mag- colony with the lophophores -nifica. and tentacles expanded and enlarged, as they appear with a good pocket-lens. The absence of color and motion, however, makes a great difference in their beauty. In old colonies, especially late in the season, there are often to be seen many small, rounded, brown bodies, which as the animals die, float to the surface of the water. These are the winter eggs or statoblasts. They are formed within the body, and escape only after the Polyzoén dies and melts. away, when they float out and remain unchanged until the warmth of spring develops them. Under the microscope the statoblasts of Pectinatella are seen to be encircled by a row of double hooks, as 246 AQUATIC MICROSCOPY FOR BEGINNERS. shown in Fig. 176. I have collected them late in the fall, and, keeping them in a small aquarium in a warm room, have had them hatch out in November. The young fastened themselves to the sides of the glass bowl, where they appeared like delicate grains of translucent pearl. “There was no jelly at this early stage, and each little Pectinatella stood alone, conse- quently all the internal organs were even more dis- -tinctly visible than usual through their hyaline bodies. I hoped to see them develop into colonies, but the sur- roundings were not entirely favorable, perhaps the proper food was not attainable, so they died. Each mature polyzoan has from fifty to eighty ten- tacles. 2. CRISTATELLA. The form and mowements of Cristatella have already been referred to on a preceding page. The young colonies are rounded, and are found in the same local- ities with Pectinatella, The statoblasts are circular and have two rows of double hooks, one row around the border, the other nearer the center (Fig. 177). The hooks are not simple as in those of Pectinatella, but have several branches at the top of the stem, and the tips are forked. According to the writer’s experience, Cristatella is not common. fs 3. Lépuorus. A species of Lophopus has been found in California and the same form has been obtained by the writer in a small pond on the Pennsylvania side of the Delaware River opposite Trenton, N. J. It has not been re- FRESH-WATER POLYZOA. 247 ported elsewhere, and therefore seems to be exceed- ingly rare in this country. In Europe it was the first member of the Polyzoa to be discovered, as it was by Trembley, the famous experimenter with Hydra, one hundred and fifty years ago. The only known species has been named Lophopus Trembley: in his honor. The colonies form small jelly-masses attached to the rootlets of Lemna, to floating sticks or to other sub- merged objects, these little masses being slightly motile, after the manner of Cristatella, as affirmed by some observers and denied by others. The masses are transparent, the attached base in the old colonies be- coming opaque while in the young it is as hyaline as the rest of the mass. The jeily-masses are at first sac- like, finally becoming lobed or even branched. The polyzoa are irregularly scattered throughout the colony, extruding the horseshoe-shaped lophophore as do the other and commoner forms. Lophopus as a colony varies from one-tenth to one- half inch in diameter, each mature member of the cluster bearing from fifty to sixty tentacles on its lophophore. The statoblasts are produced in two forms, both of which are shown in Fig. 175. 4. PLUMATELLA (Fig. 170). The tubes containing the animals may be attached only at the base, or the whole colony may be adherent to the submerged surface on which it grows. It is to be found in shallow water, usually near the shore. To see the lophophore and expanded tentacles, if the colony is small, it may be removed by slicing the wood to which it is attached, the slice to be placed in a watch-glass of water on the microscope stage, which 248 AQUATIC MICROSCOPY FOR BEGINNERS. must, of course, be in a horizontal position. The mirror may then be swung above the stage, and Plumatéla viewed by reflected light as an opaque ob- ject It is exquisitely beautiful in this position, as is Pectinatella or any of the Polyzoa; but the animals are very timid. To see the expanded ten- tacles will therefore de- mand much time and patience. Plumatella is almost as common as Pectina- tella. A board or a log that has been floating Fig. 170,—Plumatélla; colony and : . expanded lophophore. undisturbed in the pond will, during the summer, be almost sure to afford a rich harvest of Plumatella if its under surface be examined. The statoblast of Plumatella is shown in Fig. 174. 5. FREDERICELLA.., The colonies of this Polyzoén are found in the shadiest places and near the shores of shallow ponds, growing like Plumatella, and often in company with it, on the lower surfaces of floating or submerged objects. The whole colony may be adherent, or only the base, the stem and branches then floating. A single animal inhabits eachhollow branch, and resembles Plumatella in appearance and in structure. It may be distin- guished from Plumatella, however, by the oval or nearly circular lophophore, that of Plumatella being FRESH-WATER POLYZOA. 249 -horseshoe-shaped. The colonies are usually small, covering a small space. The tentacles are never more than twenty-four in number. The statoblasts are more or less ovate or reniform, and are without spines or hooks (Fig. 173). 6, PALUDICELLA (Fig. 171). These colonies may always be distinguished from all other tube-making Polyzoa by their jointed appear- ance, each joint or cell being club-shaped. The colonies are ir- regularly branched, and are built up of a single row of cells placed end to end, the narrow end, or the handle of the club, be- ing attached to the broad end of the cell immediately behind it. The opening through which the animal protrudes its circular lophophore is at one side of the broad end of each celland near the top. The base alone may be attached, or the stem may be adherent and some of the branches free, as in the figure. * Fig. 171.—Paludicélla. 7. URNATELLA (Fig. 172). ‘The form and appearance of this Polyzoén are so characteristic that it need never be mistaken; but while the other members of the group are usually rather conspicuous to the eye of a microscopist, Urnatélla gracilis must beespecially searched for. The 250 AQUATIC MICROSCOPY FOR BEGINNERS. colonies, or stem-like growths which it forms, are composed of urn-shaped cells or segments united end to end, and attached by a single disk-like enlargement to the supporting object from which they hang sus- pended. The lower surface of stones, beneath which the water constantly flows, seems to be Urnatella’s favorite haunt. The stem-like colonies of urns are usually found two together pendent from thesame disk of attachment, and appearing somewhat like a string of beads—this being due chiefly to the alternate bands of brownish-white and black surroundingeachurn, In length the stems vary from one-eighth to one-sixth of an inch, rarely reaching one-fourth. To be seen ona wet stone with the unaided vision, therefore, demands a trained eye. The cells or urns are joined end to end, the en- larged central portion of each being light-colored, while both the narrowed ends are dark or black. A single colony is seldom formed of more than a dozen urns, the stems thus built up being straight or somewhat curved, or even, on occasion, loosely coiled. At times the stem is branched, the secondary limb originating near the point of attachment of one cell with the pre- ceding, but soon falling off or voluntarily breaking away. On each side of every segment of the mature stems is a small, cup-shaped projection, the two appearing almost like handles to the urns. These are supposed to be the remains of branches, or of those segments which have fallen away and gone to begin new colonies in another place. Each urn, therefore, has at some time two urns attached to it, one on each side, and occasionally a specimen will be found with one or more branches still adherent. FRESH-WATER POLYZOA. 251 The central enlarged portion of the urns is translu- cent, light-colored, and often with many transverse wrinkles and transverse brownlines, It is also brown spotted, and has many little tubercles of the same color. The necks of the urns where they are joined together to form the stems, are opaque and black. The first or foundation segment of the growth is larger than the other members of the group, and its base expands into a broad disk, which adheres to the Fig. 172.—Urnatélla. stone and supports the entire stem. Through the center of the whole collection of urns passes acylindrical cord whose purpose would seem to be to strengthen the fragile pile, and to give it the great flex- ibility which it possesses. The two segments near the free end of the stem are small- er than the others and rather different in shape. They are also nearly transparent and colorless. They seem to be urns in the process of growth, while those below are matured and hardened. It is only the terminal segments that con- tain the living animal, the urns which form the stem be- low them being filled with a soft, translucent, granular substance packed into the cavity around the central cord. The animal that produces this beautiful series of 252 AQUATIC MICROSCOPY FOR BEGINNERS. brown urns lives at the free end of the filament, soli- tary and alone, with the exception of the temporary companionship of those short branches which sprout out near it, as shown in Fig. 172. It is these short growths which are supposed to drop off and to leave the cup-shaped scars on each side. Rarely are there -more than two of these projecting scars on each urn. The animal itself, which terminates the main stem and its branches, when in active condition, appears, Dr. Joseph Leidy, its discoverer, says, as a bell-shaped body with a widely expanded oval or nearly circular mouth, directed obliquely to one side or ventrally. The mouth of the bell is bordered by a broad waving band or collar, from the inside of which springs a cir- cle of tentacles. Of these there are usually sixteen, though sometimes from twelve to fourteen, They are invested with an epithelium furnished with moderately long, active cilia.* Like most of these beautiful creatures, Urnatella is exceedingly timid and sensitive. At the slightest dis- turbance the tentacles are folded together and drawn into the mouth of the bell, which closes around them, and the entire stem suddenly bows itself down to the ground, or, when long, rolls itself into a loose coil. No eggs nor statoblasts have been observed. Dur- ing the winter the urns do not seem to become sepa- rated from one another. ‘‘Perhaps, as reproductive bodies, after the polyp-bells perish, they remain in conjunction securely anchored through the first of the *“Urnatella gracilis: A Fresh-water Polyzoén.” By Professor Joseph Leidy. Journal of the Academy of Natural Sciences os Phil- adelphia, vol. ix. FRESH-WATER POLYZOA. . 253 series, and are preserved during the cold of winter until under the favorable condition of spring, they put forth buds and branches, which, by separation and settle- ment elsewhere, become the foundation of new col- onies.” I have known the statoblasts of Pectinatella to be formed in so great profusion in the autumn, that the surface of a pond perhaps half an acre in extent, was as densely covered with them as the surface of the lit- tle pools along the railroad is sometimes covered with cinder-scales. It is these statoblasts which are so often seen as dark-brown little bodies thickly stud- ding the surface of the half-dead masses of Pectinatella jelly in September or later, and floating on the water, or entangled among Algz or other aquatic plants, whence they are not rarely collected by the microsco- pist and come to the microscope-stage to make the observer wonder. ‘ Although small, the largest nreasuring perhaps +), inch in diameter, their rich, dark-brown color makes them easily visible even to the naked eye, especially when in any abundance. Fig. 173.—Statoblast Fig. 174.—Statoblast Fig. 175.—Two forms of Stato- of Fredericella. of Plumatella. A, blast of Lophopus. A, anriulus, annulus. They are all oval -or subcircular in outline, and much flattened, while some are bordered by one or two 254 AQUATIC MICROSCOPY FOR BEGINNERS, rows of doubly barbed hooks, whose purpose, I imag- ine, may be to prevent the statoblast from being swept away by the currents, since the hooks form most effectual anchors. These marginal spines’ or Fig. 176.—Statoblast of Pec- Fig. 177.—Front and side views of Stato- tinatella, A, annulus. blast of Cristatella. A, annulus. double hooks are visible with a good pocket-lens, but on the majority there is a structure demanding the compound instrument forits elucidation. This is the annulus, a brown ring encircling the body of the stato- blast and composed of innumerable hexagonal cells. It occurs on all known forms except on those of a single genus, Fredericella (Fig. 173), where the winter egys are entirely smooth. Within the body of each Polyzoan is a cord-like structure extending from the lower end of the stomach to the base of the cell-like posterior part of the ani- mal. This is named the funiculus, and from it the statoblasts are formed by a process of budding. ‘‘They arise,” says Professor Alpheus Hyatt, ‘within bud-like swellings of the funiculus, and, enlarging, slowly push out to the surface of the cord, and up- wards toward the stomach, until finally they hang upon FRESH-WATER POLYZOA. 255 the exterior, arranged alternately on either side, the youngest being at the lower end.” Each Polyzoan seems capable of producing only a limited number, yet the Polyzoa forming even a single colony are so numerous that the number produced is in the aggregate something astonishing. Their mode of escape by the death of the parent has already been mentioned. The winter eggs of each Polyzoan genus are charac- teristic, and from the appearance of even a single one, if mature, its generic origin may be ascertained. It is always a satisfaction to know a thing when it is seen, and to be able to give a positive answer to the oft-re- peated question, ‘‘What is it?’ And these little brown specks are sooner or later sure to bring out that question, either from the observer himself or from his friends. By means of the subjoined Key and the fig- ures of the statoblasts in the text, the origin of these winter eggs may be determined. In the figures 4 points out the annulus. Key to the Statoblasts of the Fresh-water Polyzoa. A. Reproduction probably by the urn-shaped seg- ments of the stem, Urnatella, Fig. 172. A, Reproduction by-statoblasts (a). Statoblasts without spines (0). . Statoblasts with spinous margins (2). Without a cellular annulus, Fredericella, Fig. 173. With a cellular, dark-brown annulus (c). With a cellular, purplish-blue, iridescent annulus, Paludicella. c. Extremities rounded, Plumatella, Fig. 174. “SSR - 256 AQUATIC MICROSCOPY FOR BEGINNERS. ss Extremities acute,sometimes prolonged, Lophopus, Fig. 175.* ‘ d. Spines in a single, marginal series, double-hooked, Pectinatella, Fig. 176. d. Spines in tworows, variously hooked, Crzstatella, Fig. 177. Those who desire to be fully informed as to the anatomy of the charming creatures which form the group of the fresh-water Polyzoa, and to distinguish the several species, are referred to Professor Alpheus Hyatt’s work on ‘‘The Polyzoa,’’ published by the Es- sex Institute, Salem, Mass., and to Professor Joseph Leidy’s papers on the subject in the Journal of the Academy of Natural Sciences of Philadelphia, *The statoblasts of Lophopus are here keyed and figured, as the reader may at some time find them before he isso fortunate as to dis- cover the Polyzoan itself, and thus be led to search for the animals, the winter eggs having put him on their track. ENTOMOSTRACA AND PHYLLOPODA. 257 CHAPTER X. ENTOMOSTRACA AND PHYLLOPODA. The reader is familiar with the crayfish, lobster, and crab as members of that great group of animals called the Crustacea, because they are covered by a hard, shelly coating; but, with the exception of the crayfish, he may associate them all with salt water, while in reality our fresh-water ponds are densely peopled with minute crustacean creatures. The little fresh-water animals are often enclosed in a bivalve shell, which some of them have the power to open and to shut; or the back of the body may be sim- ply hardened, but without a distinct shell. The feet, or legs, are usually numerous, and very hairy or bristly; in one section of those referred to in this chap- ter they are flattened, and each one bears near the body a flattened plate; consequently, since these parts are somewhat leaf-like, these animals have, as a class, been called the leaf-footed or the Phyldpoda, which is putting the words into Greek. Many others, to be found much more abundantly and frequently than the Phyllépoda, are without these plates, although the feet are as numerous and, in some, almost as flat, and the shells or shelly back as well marked. These have been, by naturalists, grouped together under the name 18 258 AQUATIC MICROSCOPY FOR BEGINNERS. of the ELxtomdstraca, meaning little animals in a shell, but the translation of the word has no distinctive sig- nification, since members of both groups are little ani- mals and both have shells. The Entomostraca are more abundant in fresh water than the Phyllopoda, and are remarkably active. They are usually visible to the unaided eye as little whitish specks, skipping, flirting, or jerking them- selves through the water, although probably few. will measure more than one-twelfth of an inch in length. Under the microscope some are, as already stated, seen to be enclosed in a bivalve shell, while others are entirely free from so distinct a covering. The feet are arranged in pairs, and may be numer- ous. They serve in the-shell-bearing forms, not only as swimming organs, but as gills or similar contri- vances for the absorption of air.from the water for the aeration of the little animals’ blood. This is probably one reason why they are. kept in such incessant motion. Even when the shell-bearing Entomostraca come to rest, to feed, or for some other purpose, certain of the feet keep up a ceaseless beating of. the water, as can be readily seen through their transparent case. The mouth-parts are complicated, much patience and microscopical skill being needed to investigate and understand them. On each side of the head, however, ard usually near the mouth, are two thread- like’but jointed organs called the antenne, and these the beginner must recognize, as they often become important aids in learning the animal’s place and name. They vary in length, one on each side often being short and difficult to see distinctly, while the other two are usually long and conspicuous. They are ENTOMOSTRACA AND PHYLLOPODA. 259 all formed of short and well-marked joints, the num- ber varying greatly in the different genera, sometimes in different species of the same genus. , One or more black or dark-red eye-spots are com- monly present. In some the eye is single, and in the center of the forehead. It may also be slightly mov- able at the will of its possessor. The young animal, as not rarely happens, may have two distinct eyes, which, as it grows older, become joined into one and covered by the shell. In many forms there is in addi- tion to the true eye, a collection of opaque matter usually situated betow the eye but which may be mis- taken for it. This is the so-called ‘‘pigment fleck,” which, in some Entomostraca, is supposed to act toa certain degree as an eye: It is never movable, as the true eye often is, and by this immobility may be recognized. A careful examination of the true eye with a comparatively high-power objective, will reveal still further differences between it and the pigment fleck. The reader should, however, be on his guard, and not too hastily decide that the specimen has more than a single eye. The heart is frequently visible, especially in the shell-bearing forms, being there placed at the back of the body near the head. It beats rapidly, and appar- ently sends the colorless blood quickly through the system. All these animals increase and multiply through the formation of eggs, which may remain within the shell and there be hatched, or they may be attached to the parent’s body in external clusters. In the shell-bear- ing forms they are passed into a brood cavity at the back between the body and the shell, where 260 AQUATIC MICROSCOPY FOR BEGINNERS they are kept until the young are hatched, when the latter make their escape into the water, to care for themselves. In those forms without shells the eggs are passed out of the body into one or two small, pear-shaped sacks called external ovaries, where they remain until hatched. In these cases, however, the egg masses are carried about by the parent and become conspicuous objects. Itis a common occurance to find the little animals apparently loaded with the burden of eggs, and not uncommon to see the young escape. The “common Cyclops” is an instance. No member of the Entomostraca is so frequently seen nor so abundant as the Cyclops, and hardly any other affords so good an example of this method of depositing and caring for the eggs in external overies, Cyclops having two of the latter, while some other almost equally common forms have but one. The external ovaries are usually long, pear-shaped bodies attached one on each side near the posterior extremity of the animal, where it narrows to form its tail-like region. The eggs are round, unless they are made polygonal by pressure, almost black, and entirely opaque. In Canthocamptus there is but one external ovary. Both kinds are shown in Figs. 185 and 186, In many instances the young, when first hatched, bear so slight a resemblance to the parent that some of them have been described and named as entirely different animals; and it was not until they were seen leaving the egg while still attached, or in the external ovary, that their true character was discovered. This is especially true of Cyclops, the young of which is shown in Figure 186. It changes its skin several ENTOMOSTRACA AND PHYLLOPODA. 261 times before it begins to resemble its mother, a simi- lar peculiarity being noticeable in many of the Ento- mostraca. These little crustaceans are found in almost every body of still water. Some.prefer the surface, where, on asunshiny day, they are occasionally seen in im- mense numbers, sinking when a cloud shades them, and rising again to the sunlight. Others are to be taken only in deep water, while still others can be uob- tained only at night. Many however, are collected in every gathering of aquatic plants. ‘They abound at all seasons of the year, even in midwinter. Their movements are rapid and characteristic. An ‘Ento- mostracan may be readily recognized as such by the unaided sight, on account of the peculiar leaping, or short, jerking motions with which it travels through the water. They are not only interesting little creatures to the: microscopist, but they are exceedingly useful as well. ‘They play an important part in the food-supply of fishes, forming the chief article of diet for some of our best fresh-water fishes. And they are almost as im- portant as scavengers. Their favorite food is dead and decaying Algz and animal matter, which, if allowed to remain in the great abundance in which it often exists, our ponds and slow streams would before long become putrid and unbearable. “But these nu- merous little creatures, by eating this refuse matter, transform it into an innocent and innocuous material, and confer a benefit both on themselves and on us. Prof. C. L. Herrick, writing on this subject, says, ‘‘Their importance depends largely on their minute size and unparalleled numbers. The majority of non- 262 AQUATIC MICROSCOPY FOR BEGINNERS. carnivorous crustaceans are so constituted that their diet is nearly confined to such floating particles of matter as are present in the water in a state of more or less fine comminution; for, nearly without prehensile organs, these animals, by means of a valvular or, at most, ladle-like labrum, dip from the current of water kept flowing by the constant motion of the branchial feet, such fragments as the snail.and scavenger-fish -have disdained; bits of decaying Algze, or the broken fragments of a disintegrated mosquito, all alike accept- able and unhesitatingly assimilated. The amount of such material that they will dispose of in a short period of time is truly astonishing.” When the shallow ponds are dried by the summer heat, the Entomostracans bury themselvesin the mud, and there remain quiescent, but alive, so long as any moisture is present. When the mud is completely. dried they die, but the eggs have the ability to endure heat and dryness without injury, and to develop and mature as the pools aga'n become filled by the rain, or by the melting snow of.early spring. The Phyll6poda may likewise often be recognized -without a microscopical examination, in this case by their large size and’ their almost universal habit of. swimming on the back. Sranchipus, sometimes called the fairy shrimp, and Artemia, or the brine shrimp, are nearly an inch in length. As in the Entomostraca, the bodies of the. Phyllo- poda may be incased in a bivalve shell or not. The broad, flattened feet are numerous, but the branchial or breathing-plates already referred to may be small and inconspicuous, and therefore difficult to be ob- served by the beginner. They are especially well- ENTOMOSTRACA AND PHYLLOPODA. 263 marked in Artemia (Fig. 188), and in. Branchipus (Fig. 189). Eyes are usually present, and large. In some forms they are elevated on stalks, thus reminding the observer of the stalked eyes of the lobsters. The eggs of the bivalve Phyllopoda are kept within a brood cavity, somewhat as in smiliarly incased Ento- mostraca, while in the shell-less forms they are car- ried about in a bottle-shaped sack at the end of the body, near the origin of the long, narrow, tail-like portion. In both kinds the young bear scarcely the remotest resemblance to the adults. ; In the fresh and brackish waters of the eastern part of the country there are but few genera of the Phylld- poda represented, and none have yet been found in the ocean; while on the western plains and among the Rocky Mountains they abound. These latter forms are, however, not included in those referred to in the following list. All these little crustaceans should be examined ina deep cell, to prevent the weight of the cover-glass from crushing their bodies. The shells and the shelly coating give them the appearance of firmness or of hardness, but they are delicate and easily injured. The large Phyllépoda will need an especially deep and extensive cell. : The following Key will lead to the common genera of both divisions of these attractive animals. The only trouble the observer may meet with in using it will probably be in determining whether the specimen is a Phyllopod or an Entomostracan; but as the former are large. and swim on the back, they may usually be determined by these appearances alone, and the name learned by the Key, in connection with a pocket-lens. 264 AQUATIC MICROSCOPY FOR BEGINNERS. The two Entomostracans, Didptomus, and Canthocdmp- tus, are separated in the Key by the number of the joints in their long antenne. This.seems to be a very minute character to use in so artificial a table, but it need not be an annoyance to the reader, since the antennez of these two common little crustaceans differ so conspicuously in size and length that the joints need not be actually counted; a glance will show which is Canthocamptus, with its short, rather incon- spicuous antenne, and the single egg-sack, and which is Cyclops, with the long antenne and two external egg-sacks. The beak referred to is the front part of the shell extended in a long, usually curved and pointed pro- longation, containing the eye and portions of the ani- mal’s head. Key to Genera of Entoméstraca and Phylldépoda. 1. Legs with flat plates near the body; animal swim-. ming on the back (4). 2. ‘Legs without flat plates (a). a. Body enclosed in a bivalve shell (4). a. Body not enclosed in a shell (g). 6. Shell with a sharp posterior spine, or a tooth on or near the upper posterior angle (c). b. Shell without a posterior spine, or with from one to four small teeth on the lower posterior angle (2). ¢. Smooth; spine on the upper angle, or near the middle of the border.. Daphnia, 1. * c. Smooth, brown; spine on the lowerangle. Sca- pholéberis, 2. c. Reticulated; spine on the lower angle; antenne large, cylindrical. Bdsmina, 3. ENTOMOSTRACA AND PHYLLOPODA. 265 Reticulated; spine or tooth on the upper angle; antenne long, with two branches. Ceriodaph- nia, 4. . Beaked in front (e). Not beaked; oval, both ends rounded; smooth or hairy. Cypris, 5. Posterior border with from one to four small teeth. Camptocércus, 6. Posterior border without teeth (/). Shell nearly spherical; posterior border truncate. Chydorus, 7. Shell not spherical; posterior border convex; an- tenne small. Alonépsis, 8. Shell not spherical; posterior border truncate; antenne large, long, and branched. Sida, 9. . Body long and narrow; antennz long, twenty- five jointed. Dzdptomus, to. . Body long and narrow; antenne short, from four toten jointed. Canthocdmptus, 11. . Body racket (battledore) shaped, with two exter- nal ovaries. Cyclops, 12. . Body enclosed in a bivalve shell (7). . Body not enclosed in a shell (/). Shell nearly spherical, smooth. Lémneétis, 13. Shell oval or oblong, flattened, amber-colored, with longitudinal lines. sthéria, 14. In brine pools and salt lakes; eyes black, on stalks. Artémia, 15. In fresh water; males with large frontal append- ages; females without frontal appendages, but with an external and posterior, broad, short, bottle-shaped egg-sack (4). Frontal appendages much twisted and coiled; body slender. Chtrocéphalus, 16. 266 AQUATIC MICROSCOPY FOR BEGINNERS. &. Frontal appendages not twisted nor coiled; body stout. Branchipus, 17. ENTOMOSTRACA i. DApHNtA (Fig. 178). There are several species of Daphnia, all of which may be known by the presence, on the posterior border, of a sharp spine, which is never onthe lower angle. It varies in length in the different species, sometimes being nearly as long as the shell, and extending obliquely upward. It also varies in length and in position on the same individual, being longest in the young, and becoming short with age. In the species figured (Daphnia pilex) it is usually on the upper angle, but not rarely as shown in the cut. In very old specimens it may be entirely absent, but it is always present at some time in the animal’s life. The shell is oval and slightly flattened. The an- tenne are prominent, and are usually divided into two parts at the free end, each division bearing several feathery bristles. The feet are flattened, and: gener- ally in rapid motion, so as to bring food to the mouth, and ogygen to the blood. The heart is noticeable as a small colorless organ under the shell of the back near the head. It pulsates rapidly. The eye is large Fig. 178.—D4 phnia. ENTOMOSTRACA AND PHYLLOPODA. 267 and conspicuous. The eggs are placed in a brood cavity, as shown in the figure, and there hatched, the young being very different in appearance from the. parent. Daphnia is common in the spring. 2. SCAPHOLEBERIS. The shell is somewhat beaked and usually dark brown. The surface may be indistinctly reticulated or entirely smooth. From @ésmina, for which the be- ginner may be inclined to mistake it, the absence of the curved, cylindrical antennze common to that species will distinguish it. The posterior spines are short. The eye is large and conspicuous. The egg is carried in the brood-cavity, and it is said that but one egg is present atatime. This Entomostracan is com- mon. 3. Bésmina (Fig. 179). The-student will have no trouble in recognizing Boésmina, on account of the long, large, cylindrical an- tenne, each one curving downward from the side of the head like the trunk of a microscopic elephant. The shell is oval, colorless, and the posterior border bears a spine at its lower angle, never at any other point. The net- work of lines on the surface may” extend over the entire shell or / be restricted to some one part. Fig. 179.—Bésmina. The eye is large. The eggs are hatched in.a brood-cavity on the back beneath the shell. The heart is visible near the center of the back. Bosminais not so common as Daphnia. 268 AQUATIC MICROSCOPY FOR BEGINNERS. 4. CERIODAPHNIA, The ‘shell is oval, oblong, or somewhat four-sided, and always beautifully, if coarsely and conspicuously, reticulated, the meshes being hexagonal and compara- tively large. The head is separated from the body by a depression in the shell, and just behind the rather small eye-like spot it has a slight elevation. The eye is usually near the rounded lower margin or tip of the beak-like head. The antenne resemble those of Daphnia, being long, and divided into two three- jointed branches of equal length. The angle or tooth on the upper corner of the posterior border is usually sharp and conspicuous. This Entomostracan is abundant in the writer’s lo- cality. It is visible to the nakedeye, being about one- twenty-fifth of an inch long. In the aquarium its movements are almost distinctive. It seems to prefer the center of the vessel, where it darts upward fora short distance with a jerk, only to allow itself to sink back to the starting-point. A glass jar well stocked with these pretty creatures leaping up and down ir- regularly and incessantly is an interesting sight. Un- der the one-inch objective the little animal ismore than interesting. 5. Cypris (Fig. 180)). The shell entirely surrounds the animal, so that the little creature, when danger threatens, shuts itself in as com- pletely as a clam or a mussel, and allows itself to fall to the is bottom. The form varies from Fig. 180.—Cypris. an oval to a kidney shape, ac- ENTOMOSTRACA AND PHYLLOPODA. 269 cording to the species, and the color may be green or brown, or whitish and marked with several dusky bands, the latter being our common and abundant species. It may be smooth or entirely covered with fine hairs, or only the free borders may be fringed. The shell is never opened wide, but the legs and feathery antenne project from a narrow cleft between the valves, the little animal swimming rapidly by their aid, or creeping about the slide or over the aquatic vegetation. Cypris is reproduced by eggs, but ‘‘the mass of eggs, including about twenty-four, is attached by the female to water-plants with the aid of a glutinous secretion, an operation which lasts about twelve hours.” 6. Camproceércus (Fig. 181). The shell is elongated, somewhat quadrangular, transparent, and marked by lines traversing the sur- face lengthwise. The beak is blunt, and usually curved downward, or it may extend slightly away from the body, the head being strongly arched. The teeth on the posterior border (not shown in the figure) are small, and vary from one to four. The eye is small. The eggs are carried in a brood-cavity. The animal occurs chiefly in lakes and in large ponds. Fig. 181.—Camptocércus. Fig. 182.—Chydorus. 270 AQUATIC MICROSCOPY FOR BEGINNERS. 7. CHyborus (Fig. 182). The surface of this nearly spherical shell is usually reticulated. The beak is long, curved, and pointed, being sharp in the female. The posterior border is truncate in young specimens, becoming more rounded in the old. The eye is present and single. The eggs are hatched in the brood-cavity, as usual. The ani- mal occurs abundantly early in the spring, usually near the bottom where it lives chiefly on vegetable matters. The motion is rolling, and somewhat un- steady and uncertain in appearance, 8, ALONOPsIS (Fig. 183). The lower or free edge of the shell is fringed with bristles, which are longestin front. The beak is long, pointed, and separated : by some distance from the body of the shell. Eye large. One of the feet (the third) has a long _ spine. fringed with short “hairs on the edges, and often reaching to the posterior margin Fig. 183.—Alondpsis. of the shell. The sur- face is usually marked by a few conspicuous diagonal lines. The animal’s movements are slow. go. Sfpa. The shell is long and narrow, with the head sepa- rated from the body by a slight depression. The pos- ENTOMOSTRACA AND PHYLLOPODA. 271 terior margin is nearly straight, and has no spine nor tooth. The antenne are large and somewhat resem- ble those of Daphnia, although in Sida they are rather stouter, and are divided into two wnegual branches. There is but one species, Svda crystdllina. It is com- mon in some localities. to, Diarromus (Fig. 184). Diaptomus may be recognized by the very long an- tenne, which are often equal to the body in length. The stout body, including the.head, is composed of six joints or segments, while the posterior, narrowed or tapering region, the abdomen, of five, although in the female, two of the latter may be united, thus giv- ing it a three-jointed appearance. ' The animal is among the largest of the Entomos- traca, frequently measuring one-tenth of an inch in length. The color is often brilliant, varying in the different species, and even in the different parts of the body of the same specimen. It may be deep red, brilliant purple, bluish with purple-tipped antenne, whitish or colorless. The animals may found in shallow pools in the fall and early spring, and occa- sionally in-slowly flowing streams. The external ovary is single. Fig. 184.—Diaptomus. . Fig. 185.—-Canthocdmptus with a young form. 272 AQUATIC MICROSCOPY FOR BEGINNERS. 11, CANTHOCAMPTUS (Fig. 185). After Cyclops and Daphnia this is the commonest fresh-water Entomostracan in the writer’s vicinity.