EYENINGS AT THE MICROSCOPE ; OR, RESEARCHES AMONG THE MINUTER ORGANS AND FORMS OF ANIMAL LIFE, BY PHILIP HENRY GOSSE, F.R.S. A NEW EDITION, REVISED AND ANNOTATED. PUBLISHED UNDER THE DIRECTION OE THE COMMITTEE OE GENERAL LITEBATUBE AND EDUCATION, APPOINTED BY THE SOCIETY EOB PBOMOTING CHBISTIAN KNOWLEDGE. LONDON: SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE; SOLD AT THE DEPOSITORIES : 77, GREAT QUEEN STREET, LINCOLN’S INN FIELDS; 4, ROYAL EXCHANGE ; 48, PICCADILLY ; AND BY ALL BOOKSELLERS. 1877, LONDON PRINTED BY JAS, TrUSCOTT AND SON, Suffolk Lane, City. PEEFACE. To open the path to the myriad wonders of creation, which, altogether unseen by the unassisted eye, are made cognisable to sight by the aid of the micro- scope, is the aim and scope of this volume. Great and gorgeous as is the display of Divine power and wisdom in the things that are seen of all, it may safely he affirmed that a far more extensive prospect of these glories lay unheeded and unknown, till the optician’s art revealed it. Like the work of some mighty genie of Oriental fable, the brazen tube is the key which unlocks a world of wonder and beauty before invisible, which one who has once gazed upon it can never forget, and never cease to admire. This volume contains hut a gleaning : the author has swept rapidly across the vast field of marvels, snatching up a gem here and there, and culling one and another of the brilliant blossoms of this flowery region, to weave a specimen chaplet, a sample coronal, which may tell of the good things behind. Yet the selection has been so made as to leave untouched no considerable area of the great field of Zoology which is under the control of the microscope; so that the student who shall have verified for himself the obser- vations here detailed, will he no longer a tyro in IV PREFACE. microscopic science, and will be well prepared to extend bis independent researches, without any other limit than that which the finite, though vast, sphere of study itself presents to him. The staple of the work now offered to the public consists of original observation. The author is far from thinking lightly of the labours of others in this ample field ; but still, it is true, that respecting very many of the subjects that came under his notice, he found, in endeavouring to reproduce and verify pub- lished statements, so much perplexity and difficulty, that he was thrown back upon himself and nature, compelled to observe de novo, and to set down simply what he himself could see. The ever-accumulating stock of observed and recorded facts is the common property of science ; and the author has not scrupled to reproduce, to amplify, or to abridge his own obser- vations which have already appeared in his published works and scientific memoirs, as freely as he would have cited those of any other observer, in which he had confidence, and which were germane to his pur- pose. Yet, in almost all cases, the observations so used have been subjected to renewed scrutiny, and have been verified afresh, or corrected where found defective. In order to relieve as much as possible the dryness of technical description, a colloquial and familiar style has been given to the work ; which has been thrown into the form of a series of imaginary conversaziones , or microscopical soirees , in which the author is sup- posed to act as the provider of scientific entertain- ment and instruction to a circle of friends. It is proper to add, however, that the precision essential PREFACE. V to science has never been consciously sacrificed. A master may be easy and familiar without being loose or vague. A considerable amount of information will be found incidentally scattered throughout the work on microscopic manipulation, — the selecting, securing, and preparing of the objects for examination ; — an important matter, and one which presents a good deal of practical difficulty to the beginner. Not a little help will be afforded to him, also, on the power to observe and to discriminate what he has under his eye. In almost every instance, the objects selected for illustration are common things, such as any one placed in tolerably favourable circumstances, with access to sea-shore and country-side, may reasonably expect to meet with in a twelvemonth’s round of research. The pictorial illustrations are almost co-extensive with the descriptions ; they are one hundred and thirteen in number ; all, with the exception of eighteen,* productions of the author’s own pencil, the great majority having been drawn on the wood direct from the microscope, at the same time as the respective descriptions were written. He ventures to hope that they will be found accurate delineations of the objects represented. Torquay, February , 1859. * The subjects on pp. 48, 48, 98, 100, and 151, have been copied, under the courteous permission of the publisher, from Dr. Carpenter’s valuable work, “ The Microscope, and its Revelations.” (Churchill, London.) PKEFACE TO THE PKESENT EDITION. In preparing a new edition of this Work for the press, every page has passed under the Author’s eye, and has been examined with earnest care. A very large portion of it consisting of his own original re- searches, there was little room for alteration ; but new facts, interesting in themselves, and germane to the subjects herein treated, which have been recorded since, he has used to enrich the work. These have been uniformly added in the shape of marginal notes; leaving the text untouched, a reflection of Microscopical Science fifteen years ago. P. H. G. Torquay, Jan . 1874. CONTENTS PAGE CHAPTER I. Hairs, Feathers, and Scales . 1 CHAPTER II, Blood 25 CHAPTER III. MOLLUSCA : THEIR SHELLS, TONGUES, EYES, AND EARS . . 39 CHAPTER IY. Sea-mats and Shelly Corallines *59 CHAPTER Y. Insects : Wings and their Appendages . .70 CHAPTER YI. Insects : their Breathing Organs . 98 CHAPTER YII. Insects: their Feet 109 CHAPTER Yin. Insects: Stings and Ovipositors 125 CHAPTER IX. Insects : their Mouths 138 Vlll CONTENTS, PAGE CHAPTER X. Insects : their Ears and Eyes .... . . 158 CHAPTER XI. Crabs and Shrimps 171 CHAPTER XII. Barnacles 191 CHAPTER XIII. Spiders and Mites 203 CHAPTER XIY. Wheel-bearers 223 CHAPTER XY. Worms 258 CHAPTER XYI. Sea-urchins and Sea-cucumbers 276 CHAPTER XYII. Jelly-fishes 307 CHAPTER XYIII. Zoophytes 325 CHAPTER XIX. Sea- anemones : their Weapons 355 CHAPTER XX. Protozoa and Sponges .376 CHAPTER XXI. Infusoria 389 LIST OP ILLU STKATION S. PAGE Human Hair 2 Hog’s Bristle 5 Fibre of Sheep’s Wool 7 Hair of Cat 8 Hairs of Mole 9 Hair of Sable 9 Hair of Mouse 10 Tip op Small Hair of Mouse 11 Hair of Bat 11 Hair of Indian Bat 12 Tip of Hair of Dermestes 14 Barb of Clothing Feather of Fowl 15 Barb from G-oose-quill 16 Scales of Perch 17 Scales of Gold-fish 19 Scale of Flounder 21 Scales of Pike 23 Spicula of Gold-fish’s Scale 24 Blood Disks 28 Circulation in Frog’s Foot .32 Perophora 33 Cuttle- shell .41 Section of Nacre from Pearl Oyster 43 Tongue of Trochus . . . 48 Structure of Eye in Snail 54 Leafy Sea-mat 62 Doubling and Hooks in a Bee’s Wing . . . .74 Scales on a Gnat’s Wing 75 X LIST OF ILLUSTRATIONS. PAGE Bristle-tail 76 Scale op Bristle-tail 77 Battledore-scale op Polyommatus Alexis .... 80 Fringed Scale of Pieris 81 Scales of Diamond-Beetle 83 Air-pipe of Fly 95 Spiracle of Fly 98 Spiracle of Leather-coat . 99 Spiracle of Cockchafer- grub 100 Grub of Chameleon Fly 102 Foot of Fly 116 Foot of Water-Beetle 118 Sting of Bee 127 Gall-Fly, and Mechanism of Ovipositor . . . .128 Outer Saw of Saw-Fly 133 Inner Saw of Saw-Fly 134 Mouth of Beetle 140 Jaws of Bee 142 Lancets of Female Gnat 150 Tongue of Blow-Fly 151 Sucker of Butterfly 156 Antenna of Cockchafer 162 Antenna of Oak Egger Moth 164 Ear of Crab .* 172 Daphnia 179 Cypris 181 Zoea of Shore-Crab 183 Second Stage of Shore-Crab 185 Third Stage of Shore-CRab 187 Adult Shore-Crab 188 Hand of Barnacle 193 Young of Barnacle 197 Fang of Spider 206 Eyes op Spider 207 Claws op Spider 217 Head of Cheese-Mite 221 Brachionus 232 Mouth of Brachionus 235 LIST OF ILLUSTBATIONS. xi PAGE Whiptail 239 Skeleton Wheel-Bearer 243 Sword-Bearer 247 Tripod Wheel-Bearer 249 Two-Lipped Tube- Wheel 252 Wheels of Tube- Wheel 253 Foot of Nais 262 Throat of Leech Laid Open 269 Jaw of Leech 270 Pushing Poles of Serpula . . . . . . .273 Hooks of Serpula 274 Spine of Echinus 281 Head of Pedicellaria Tridens ...... 284 Sucker of Urchin 289 Pores of Urchin 289 Sucker-plate of Urchin 292 Dumb-Bells in Holothuria 298 Wheel in Chirodota 298 Anchor-plate in Synapta 299 Larva of Sea-Urchin 303 Young Sea-Urchin : Development of Disk .... 305 Cydippe . . . 310 Sarsia 316 Thaumantias 319 Otolithes of Thaumantias 320 Turris and its Young 324 Laomedea 328 Tentacle of Laomedea 329 Stauridia 342 Lares 345 Polypes of Cow’s Pap 351 Spicula of Cow’s Pap 353 Portion of Acontium 357 Cinclides 358 Cnida of Madrepore 364 Cnida of Tealia 367 Cnida of Corynactis 370 Forms of Amceba 379 Xll LIST OF ILLUSTRATIONS. PAGE Section of Sponge 886 Three-sided Euglena 391 Swan-neck and its Divisions 394 Paramcecium . 398 COLEPS AND CHILOMONAS 399 VORTICELL^E 402 Acineta 407 Yaginicola 410 Euplotes 416 EVENINGS AT THE MICROSCOPE. x ♦ CHAPTER I. HAIRS, FEATHERS, AND SCALES. Not many years ago an eminent microscopist received a communication inquiring whether, if a minute portion of dried skin were submitted to him, he could determine it to be human skin or not. He replied that he thought he could. Accordingly a very minute fragment was for- warded to him, somewhat resembling what might be torn from the surface of an old trunk, with all the hair rubbed off. The professor brought his microscope to bear upon it, and presently found some fine hairs scattered over the surface ; which, after carefully examining them, he pro- nounced with confidence to be human hairs, and such as grew on the naked parts of the body ; and declared the person who had owned them to have been of a fair com- plexion. This was a very interesting decision, because the frag- ment of skin was taken from the door of an old church in Yorkshire ; * in the vicinity of which a tradition is pre- * I am writing from memory, having no means of referring to the original record, which will he found in the first (or second) volume of the “Transactions of the Microscopical Society” of London. The general facts, however, may be depended on. B 2 EVENINGS AT THE MICEOSCOPE. served, that, about a thousand years ago, a Danish robber had violated this church, and, having been taken, had been condemned to be flayed, and his skin nailed to the church- door, as a terror to evil-doers. The action of the weather and other causes had long ago removed all traces of the stretched and dried skin, except that, from under the edges of the broad -headed nails with which the door was studded, fragments still peeped out. It was one of those atoms, obtained by drawing one of the old nails, that was now subjected to microscopical scrutiny ; and it was interest- ing to find that the wonder-showing tube could confirm the tradition with the utmost certainty ; not only in the general fact, that it was really the skin of man, but in the special fact of the race to which that man belonged, viz., one with fair complexion and light hair, such as the Danes are well known to possess. It is evident from this anecdote that the human hair presents characters which are so indelible that centuries of exposure do not avail to obliterate them, and which readily distinguish it from the hair of any other creature. Let us then begin our evening’s entertainment by an examination of a human hair, and a comparison of it with that which belongs to various animals. Here, then, is a hair from my own head. I cut off about half-an-inch of its length, and, laying it between two plates of glass, put it upon the stage of the microscope. I now apply a power of 600 diameters ; that is, the apparent increase of thickness is the same as if six hundred of these hairs were placed side by side. Now, with this eye-piece micro- meter, we will first of all measure its diameter. You see, crossing the bright circular field of human hair, view, a semi-pellucid cylindrical object ; that is the hair. You see also a number of fine HAIRS, FEATHERS, AND SCALES. 3 lines drawn parallel to each other, exactly like those on an ivory rule or scale, with every fifth line longer than the rest, and every tenth longer still. This is the micrometer, or scale by which we measure objects ; and the difference in the length of the lines, you will readily guess, is merely a device to facilitate the counting of them. By moving the stage up or down, or to either side, we easily bring the hair exactly into the centre of the field ; and now, by adjusting the eye-piece, we make the scale to lie directly across the hair, at right angles with its length. Thus we see that its diameter covers just thirty of the fine lines ; and as, with this magnifying power, each line represents 1-10, 000th of an inch, the hair is 80- lOjOOOthSjZz^-^rd of an inch, in diameter. In all branches of natural history, but perhaps pre- eminently in microscopic natural history, — owing to its greater liability to error from deceptive appearances, — we gain much information on any given structure by com- paring it with parallel or analogous structures in other forms. Thus we shall find that our understanding of the structure of this hair will be much increased when we have seen, under the same magnifying power, specimens of the hair of other animals. In order, however, to explain it, I must anticipate those observations. What we see, then, is a perfectly translucent cylinder, having a light brown tinge, and marked with a great number of delicate lines, having a general transverse direction, but very irregularly sinuous or winding in their individual courses. These lines we perceive to be on the surface ; because, if we slowly turn the adjustment- screw, the lines grow dim on the central part of the cylinder, while those parts that lie near the edges (speak- ing according to the optical appearance) come into dis- tinctness. Presently the edges of the cylinder become sharply defined, and are seen to be cut into exceedingly shallow saw-like teeth, about as far apart as the lines; b 2 4 EVENINGS AT THE MICROSCOPE. these, however, are so slight that they can be seen only hy very delicate adjustment. We go on turning the screw, and presently another series of transverse lines, having the same characters as the former, but differing from them individually, come into view, at the sides first, and presently in the middle, and then, as we still turn, become dim, and the whole is confused. In fact, our eye has travelled, in this process, from the nearer surface of the hair, right through its transparent substance, to the farther surface ; and we have seen that it is surrounded by these sinuous lines, which the edges— or those portions of the hair which would be the edges, if it were split through the middle (for, optically, this is the same thing) — show to be successive coats of the surface, suddenly terminated. If we suppose a cylinder to be formed of very thin paper, rolled up, and then, by means of a turning- lathe, this cylinder to be tapered into a very lengthened cone, the whole would be surrounded by lines marking the cut-through edges of the successive layers of paper ; and, owing to the thickness of the paper not being mathe- matically equal in every part, these edges would be sinuous ; exactly as we see in these lines upon the hair. The effect and the cause are the same in the two cases. A hair is closely analogous to the stem of a plant; inasmuch as it grows from a root, by continual additions of cells to the lower parts, which, as they lengthen, push forward the ever-extending tip. Indeed, in some of the hairs which we shall presently look at, there is the most curious resemblance to the stem of a palm, with the pro- jections produced by the successive growth and breaking away of leaf-bases around the central cylinder. Inter- nally, too, the resemblance is remarkable ; for, if we split a human hair, and especially if we macerate it, i.e. soften it by soaking it, in weak muriatic acid, we shall find it composed of (1) a thin but dense kind of bark, forming the successive overlapping scales just described ; HAIRS, FEATHERS, AND SCALES. 5 (2) a fibrous substance, extending from the bulb to the point of the hair. By soaking the hair in hot sulphuric acid, this fibrous substance resolves itself into an immense number of very long cells, pointed at each end, and squeezed by mutual pressure into various angular forms. “ A human hair, of one-tenth of a line in thickness,* has about 250 fibrils in its mere diameter, and about 50,000 in its entire calibre : so that these ultimate fibrils are finer than those of almost any other known tissue, from the great elongation and narrowing of their constituent cells as they are drawn out into the shaft of the hair during growth ; and hence the expanded bulb of the hair, where the cells are yet spherical and soft.”f (8) Running through the very centre of the fibrous portion may be sometimes discerned a dark slender line, which is a sort of pith (medulla) composed of minute roundish cells, filled with air, and arranged in two or three rows. J hog’s bristles. The bristles of the Hog bear much resemblance to the human hair. On this slide is one ( a ), which you perceive * This is nearly thrice as great as the diameter I have given above, which is the result of several careful admeasurements of different hairs, taken from childhood and adult age. f Grant, “ Outl. Comp. Anat.,” 647. X 11 The cortical (or bark-like) substance has different colour, accord- ing to the colour of the hair ; generally, the colour is diffused through its whole mass ; less frequently, the colour depends on granular pigment scattered through its substance in small masses. The cortical substance 6 EVENINGS AT THE MICKOSCOPE. is just thrice as thick as the hair that we have been examining, or -p^th of an inch in diameter. The sinuous lines across the surface are proportionally far finer and closer together, and no saw-teeth are visible at the edge, the most delicate adjustment showing only a minute undu- lation in the outline ; that is to say, the overlapping scales are far thinner, and therefore their terminations are nearer together, in the hair of the Swine than in that of Man. I will now show you a transverse section of a similar bristle, which I will obtain thus : I take this old brush, and with a razor cut off one of the bundles of bristles, close to the wood ; then I take off as thin a shaving as I can cut, wood, bristles, and all : I repeat the same opera- tion two or three times. Now, having picked out the shavings of wood, I take up with the point of my pen- knife a few of the dust-like atoms that remain, and scatter them on this plate (or slide) of glass, and these I cover with another plate of thin glass ; for this dust is composed of thin transverse slices of the bristles, and as I scatter contains a number of cavities filled with air, most evident in the hair from aged persons, or in dry hair. “ The central portion, the medulla, forms, when well developed, an axis- cylinder, one-fifth, or one-fourth, the diameter of the hair, with sharp outlines, generally central, but often a little excentric in position. It is often wanting in human hair, especially in blond hair. ... In woolly hair it is always wanting; also in the hair of the new-bom child. The medullary substance is often interrupted, and sometimes consists of only a few dark points lying in the axis of the hair . . . The medullary substance has been thought to contain the pigment : this is not so, the supposed pigment- granules being very minute air-bubbles. The cause of the colour of the hair is found in the diffuse pigmentation of the cortical substance. The cause for the hair becoming grey or white is to be found in the disappearance of the diffuse pigmentation of the cortical substance, the cause of which is not yet known. The medullary substance can be more easily seen in white hair than in coloured.” (From a valuable memoir, entitled, “ Hair in its Micro- scopical and Medico-legal Aspects,” by Dr. E. Hofman ; transferred to the “English Mechanic” for May 9, 1873, from the “New York Medical Journal.”) HAIRS, FEATHERS, AND SCALES. 7 them, some will fall upon their cut ends, so that we shall look through them endwise. Here is one, very suitable for examination ( b ), — since it is not a whole section, the razor having passed somewhat obliquely across it, coming out beyond the middle, where it thins away to an edge. The outline is not circular, but elliptical; that is, the hair is not round, but flattened. There is no separable cortex , or bark, and the whole sub- stance appears as if made up of exceedingly fine fibres, of vhich we see the ends cut across. A rough dark line occupies the middle of the slice, in the plane of the gieater diameter ; but at the edge of the slice we are able tc see that this is not a solid core, as has been sometimes sipposed, but a cavity passing up through the hair. It is surrounded by a layer of cells, called medullary, and which appear black, because they are filled with air. The finer hairs of the Horse and the Ass, such as those selected from the cheeks, have the sinuous edges of the plates about as close as in human hair. But they are distinguished at mce by the conspicuousness of the medullary portion, which is thick, and quite opaque, md is broken up (especially towards each ex- iremity of the hair) into separate longitudinal rregular masses. The fine wool of the Sheep is clothed with mbrications,* proportionally much fewer than hose of human hair, while the diameter is dso much less. Thus these examples, selected rom fine flannel and from coarse worsted, /ary in diameter from 2Woth to T^-th of an nch ; and there are, upon an average, about wo imbrications in a space equal to the dia- fibre of neter. No colour is perceptible in these spe- SHEEP’S W00L- * A structure is said to be imbricated when it is arranged like tiles «n the roof of a house. 8 EVENINGS AT THE MICROSCOPE. cimens ; they are as transparent and colourless as glass. The imbricated plates project here considerably more tl/an in either of the examples we before examined ; the “ teeth,” however, form an obtuse angle. We shall presently see the importance of this imbri- cate structure ; but we will first look at a few more ex- amples, in which we shall find it still more strongly de- veloped, in conjunction with some other peculiarities. All the hairs that we have looked at are what I have called fibrous in their interior texture, but those of many animas are more distinctly cellular. Thus, in these specimens, plucked from the fur of tie Cat that lies coiled up on the hearthrug, we see, first, tl at the imbrications are short, being about eqial to the diameter in length, but are very strongly marked; though, like those of the Sheep wool, obtuse. Hence the outline is extremely like that of the stem of an old rough palm tree. There is a distinct bark (cortex), whicl is thick, and marked with longitudinal lines which add to the resemblance just alluded to The interior is clear, marked off at prett regular intervals by the broad flattened me dullary cells, in single series, each cell occu pying, for the most part, the whole breadtl of the interior. These cells are transparent and apparently empty ; but their walls ap pear -opaque and almost black, — an optica illusion, dependent on the absorption of th light by their surfaces at certain angles witl the eye of the beholder. The fibrous portion is her almost displaced by the great development of the medul lary cells. In the larger hairs of the Mole, which we will now lool at, the bark is very thin ; and though the surface i marked with sinuous lines, these do not project into teeth HAIR OF CAT. HAIRS, FEATHERS, AND SCALES. 9 HAIRS OP MOLE. The pith here again forms the greater portion of the hair, the cells of which it is composed being placed in single series, which, for the most part, extend all across the body of the hair, though they are some- what irregular both in size and shape. They are rather flattened, and appear per- fectly black (that is, opaque) by transmitted light, their sur- faces absorbing all the rays of light. The small hairs of the same animal, however, are very different in form : they are flattened, so as to appear twice as broad in one aspect as in another at right angles to it; and, what is curious, the scales of the hark project into strongly-marked imbrica- tions on one side, and are scarcely perceptible on the other. Here, as in the larger hairs, there is a single row of oval transverse cells, perfectly opaque. The hair of many of the smaller Mammalia shows considerable diversity of form, according to the part which we select for observ- ation. Thus, if we take a long hair out of this Sable tippet, and examine it near the base, we see [a) that it is very slender, cl transparent, and colour- less, covered with strongly- marked imbrications, which are not obtuse teeth, but HAIR OP SABLE. 10 EVENINGS AT THE MICROSCOPE. long, pointed, overlapping scales, about ten of which form a complete ring, or whorl, as it is. called. The fibrous portion is moderately thick ; inclosing a wide pith of roundish cells, set in two rows, that allow the rays of light to be transmitted through their central parts. As we trace the hair upwards ( b ), by moving the stage of the microscope, by-and-by it swells and rapidly increases in thickness ; the imbrications are scarcely perceptible ; while the pith-cells have greatly augmented in number and in breadth. These are ar- ranged in confused close-set, transverse rows, and are nearly opaque. Still tracing up the same hair, as we approach the tip, the bark and fibrous part become very thin ; the cells are fewer and fewer till they cease altogether, and a long slender point, of a clear yellow tinge, without cells, pre- sents transverse wavy lines of imbrication scarcely pro- jecting. The hair of the common Mouse is a pretty and inter- esting object. In the larger speci- mens the fibrous portion is reduced almost to nothing. The imbrica- tions project very little, but care- ful observation reveals slanting lines proceeding from the “teeth;” which show that the whole surface is clothed with large pointed scales, which are very thin, and lie close. The pith consists of large flattened cells, arranged thus : one row passes up through the centre, and other similar ones are set in a circle around it, so that a longitudi- nal section would show three paral- lel rows. These cells are translucent, and some of them HAIR OF MOUSE. HAIBS, FEATHERS, AND SCALES. 11 are either wholly or partially lined with a clear yellow pigment, or colouring matter. The smaller hairs from the same little animal are scarcely distinguishable from those of the Cat, already described, except that the imbrications are proportionally larger. In all, the extremity is drawn out to a lengthened fine point, and is occupied with clear yellow cells, except the very tip, which is colourless, and imbricated with sinuous whorls, each consisting of a single scale. But it is in the Bats that the imbricated character attains its greatest development. On this slide is a number of hairs from the fur of one of our English Bats, in which it is far more conspicuous than in any example we have yet seen. In the middle portion of each hair the scales lie close, embracing their successors to the very edges, or nearly; but the lower part, which is more slender, re- sembles a multitude of trumpet-shaped flowers formed into a chain, each being inserted into the throat of another. The lip of the “ flower ” is generally oblique, and here and there we small can perceive that each is formed of two half- H0T encircling scales ; for one scale occasionally mouse. SpringS from level of its fellow, so as to ofbat. make the imbrication alternate. Even this, however, is far excelled by a species of Bat from India, of whose hair I have now specimens on the stage. The trumpet-like cups are here very thin and transparent, but very expansive ; the diameter of the lip being, in some parts of the hair, fully thrice as great as that of the stem itself. The margin of each cup appears to be undivided, but very irregularly notched and cut. In the middle portion of the hair, the cups are far more crowded than in the basal part, more brush -like, and less 12 EVENINGS AT THE MICROSCOPE. elegant ; and this structure is continued to the very extremity, which is not drawn out to so attenuated a point as the hair of the Mouse, though it is of a needle -like sharpness. The trumpet- shaped scales are, it seems, liable to be removed by accident ; for in these dozen hairs there are several in which we see one or more cups rubbed off, and in one the stem is destitute of them for a considerable space. The stem so denuded closely resembles the basal part of a Mouse’s hair in its ordinary condition. This character of being clothed with overlapping scales, each growing out of its predecessor, is common, then, to the hairs of the Mammalia, though it exists in different degrees of development. It may be readily detected by the unaided sense, even when the eye, though as- sisted by the microscope, fails to recog- nise it. Almost every schoolboy is familiar with the mode by which the tip of any hair may be distinguished from its base ; and, even of the least fragment, the terminal end from the basal end. A hair is rubbed to and fro between the finger and thumb, and it regularly travels through in the direction of its base ; thus enabling the boy after one or two rubs to pronounce a very decided opinion on the subject. Now you see the cause of this property lies in the imbricate structure ; the scales may be ever so thin and close, but still they project sufficiently in any speci- men to present a barrier to motion in the direction of the tip when pressed between two surfaces, such as the fingers, while they very readily move in the opposite. But more than the success of a schoolboy’s magic depends on the imbricate surface of hairs. England’s time-honoured manufacture, that which affords the highest HAIRS, FEATHERS, AND SCALES. 13 seat in her most august assembly, depends on it. The hat on your head, the coat on your back, the flannel waistcoat that shields your chest, the double hose that comfort your ancles, the carpet under your feet, and hundreds of other necessaries of life, are what they are, because mammalian hairs are covered with sheathing scales. It is owing to this structure that those hairs which pos- sess it in an appreciable degree are endowed with the property of felting ; that is, of being, especially under the combined action of heat, moisture, motion, and pressure, so interlaced and entangled as to become inseparable ; and of gradually forming a dense and cloth-like texture. The “body” or substance of the best sort of men’s hats is made of lamb’s wool and rabbit’s fur, not interwoven, but simply beaten, pressed, and worked together, between damp cloths. The same property enables woven woollen tissues to become close and thick ; every one knows that worsted stockings shrink in their dimensions, but become much thicker and firmer, after they have been worn and washed a little; and the “stout broad-cloth,” which has been the characteristic covering of Englishmen for ages, would be but a poor, open, flimsy texture, but for the inti- mate union of the felted wool fibres, which accrues from the various processes to which the fabric has been sub- jected. In a commercial view, the excellence of wool is tested by the closeness of its imbrications. When first the wool- fibre was submitted to microscopical examination, the ex- periment was made on a specimen of Merino ; it presented 2,400 little teeth in an inch. Then a fibre of Saxon wool, finer than the former, and known to possess a superior felting power, was tried: there were 2,720 teeth in an inch. Next a specimen of South-Down wool, acknowledged to be inferior to either of the former, was examined, and gave 2,080 teeth. Finally, the Leicester wool, whose 14 EVENINGS AT THE MICROSCOPE. felting property is feebler still, yielded only 1,850 teeth per inch. And this connexion of good felting quality with the number and sharpness of the sheathing scales, is found to be invariable. The hairs of many insects are curious and interesting. Here you may see the head of the hive bee, which is moderately clothed with hair ; each hair is slender and pointed, and is beset with a multitude of other short hairs, which project from the main stem, and stand out at an angle : these are set on in a spiral order. Here, again, is one of the hinder legs of the same bee : the yellow hair, which you can see with the naked eye, consists of strong, horny, curved spines, each of which is scored obliquely, like a butcher’s steel. These legs are used, as you are well aware, to brush off the pollen from the anthers of flowers, wherewith the substance called bee-bread, the food of the grubs, is made : and in this specimen, you may see hundreds of the beautiful oval pollen- grains entangled among these formidable- looking spines. These rusty hairs are from a large cater- pillar (that of the Oak Egger Moth, I be- lieve) ; they appear, when highly magnified, like stout horny rods drawn out to a sharp point, and sending forth alternate short pointed spines, which scarcely project from the line of the axis. But there is scarcely any hair more curious than that of a troublesome grub in museums and cabinets, the larva of Dermestes lardarius, which lives upon fur-skins, and any dried animal substances. It has a cylindrical shaft, dermestes. which is covered with whorls of large close-set spines, four or five in each whorl, closely succeeding each other; the upper part of the shaft is surrounded by a whorl of larger and more knotted spines, and the extremity HAIRS, FEATHERS, AND SCALES. 15 is furnished with six or seven large filaments or threads, which appear to have a knob-like hinge in the middle, by which they are bent up on themselves. The feathers of Birds are essentially hairs. That shrivelled membrane which we pull out of the interior of a quill when we make a pen, is the medullary portion, dried. There is a beautiful contrivance in the barbs, or beards, of most feathers, which I will illustrate by this feather from the body-plumage of the domestic fowl. Every one must have ob- served the regular arrangement of the vane of a feather, and the ex- quisite manner in which the beards of which it is composed are con- nected together. This is espe- cially observable in the wing-fea- thers— a goose-quill for example, where the vane, though very light and thin, forms an exceedingly firm resisting medium, the indi- vidual beards maintaining their union with great tenacity, and re- suming it immediately, when they have been violently separated. Now this property is of high importance in the economy of the bird. It is essential that with great lightness and buoyancy — for the bird is a flying creature — there be power to strike the air with a broad resisting surface. The wide vanes of the quill-feathers afford these two requisites, strength and lightness; the latter depending on the material employed, which is very cellular, and the former on the mode in which the indivi- dual barbs, set edgewise to the direction of the stroke, take a firm hold on each other. Now, in the body-feather, which is under the micro- BARB OP CLOTHING FEATHER OF FOWL. 16 EVENINGS AT THE MICROSCOPE. scope, we see that the central stem carries on each side a row of barbs, which interlock with each other. The mag- nifying power shows ns that these barbs are not simple filaments, but are themselves doubly bearded in the same fashion ; and further, that these little beards, called bar- bules, of the second series, ara furnished with a third series. It is in this third series of filaments, called bar- bulets, that the tenacity in question resides. If we isolate one of the primary beards, by stripping away a few on each side of it, and again put it on the stage, we see that the secondary barbules of one side are armed differently from those of the other side. Those of the lower side carry short and simple barbulets, whereas those of the side which looks towards the point of the feather bear much longer ones ; and, moreover, many of them are abruptly hooked backwards. Now, whenever the primary beards are brought into contact, some of these hooks catch on the barbule next above, and, slipping into the angles formed by the barbulets, hold there, and thus the two contiguous beards are firmly locked together. In the beard of the goose-quill, the structure is essentially the same, but the barbulets are far more numerous and more closely set; they are also proportionally much larger — both those which are hooked and those which are simple. Indeed, the latter mani- fest a tendency to the hooked form, and by all these peculiari- ties the interlocking power is aug- mented. It is interesting to ob- serve the great expansion of the beard in a direction towards the interior surface of the feather — towards the stroke, as I just now BARB FROM GOOSE-QTJILL. HAIRS, FEATHERS, AND SCALES. 17 observed. This is to increase the resisting power, as a thin board set edgewise will bear a great weight without bending or breaking, provided it can be kept from yield- ing sidewise. The barbules are arranged only on the very edge, the upper edge, of the beard. We will now examine some specimens of scales of Fishes, all of which are very interesting and beautiful ob- jects, under low powers of the microscope ; though higher powers are requisite to resolve their structure. We will use both. The scales of almost all the Fishes with which we are familiar, fall under two kinds, which have been named ctenoid (or eomb-like), and cycloid (or roundish). The SCALES OF PERCH. Pereh affords us good examples of the former kind. On this slide are three scales from the body of this fish : the one on the left side is taken from the back (&) : the middle one from the lateral line ( b ) ; and the one on the right from the belly (c). In order to understand these objects, we must remember that the scales of Fishes are horny or bony plates, developed in the substance of the proper skin, with a layer of which they are always covered. In most cases (as, for example, the Perch), the hinder end of each scale projects, carrying with it the thin layer of skin with which it is invested ; and thus the scales overlay one another, like the tiles of a house, or like the feathers of a bird, and that for a like purpose. For as the rain, c 18 EVENINGS AT THE MICROSCOPE. falling on the housetop, has a tendency to flow down- wards, from gravitation; and as the slope of the roof is in that direction, the current passing over each tile is deposited from its bottom-edge on the middle of the next, whence it still flows down to the free edge, — and so in succession. So the motion of the bird through the air, and of the fish through the water, produces the very same effect as if these fluids were in motion, and the animals were still ; and therefore the bodies of the latter are, as it were, tiled with feathers or scales, the free edges of which, looking in the opposite direction to the coming of the current (that is, the same direction as its flow), de- posit the successive particles of the moving fluid in the midst of the successive feathers or scales. Thus two results ensue, both essential to the comfort of the animal : first, the air or water does not run upward between the feathers or scales to the skin ; and secondly, the surface presents no impediment to free motion. This latter ad- vantage will be appreciated, if you take hold of a dead bird by the legs, and push it rapidly through the air tail- foremost: the feathers will instantly rise and ruffle up, presenting a powerful resistance to movement in that direction. These scales of the Perch have their hinder, or free edge, set with fine crystalline points, arranged in succes- sive rows, and overlapping. Their front side is cut with a scolloped pattern, the extremities of undulations of the surface that radiate from a common point behind the centre. These undulations are separated by narrow fur- rows, across which, contrary to the ordinary rule, the close -set lines that follow the sinuosities of the outline are not visible. Under the microscope they look as if they had been split in these radiating lines, after the whole number of layers had been completed, and the fissures had then been filled with new transparent substance. The middle scale is, as I have said, from the lateral HAIRS, FEATHERS, AND SCALES. 19 line. Along each side, in most fishes, may be observed a line, known as the lateral line, formed by scales of peculiar form. They are commonly more bony than the other scales, and are pierced by a tubular orifice for the escape (as is generally supposed, though this has been denied) of a mucous secretion, which is poured out from glands be- neath, and thus flows over the body for the double purpose of protecting the skin from the macerating influence of the surrounding water, and of diminishing friction in swimming. Let us now look at some scales of the cycloid kind. The great majority of our fishes are clothed with such as are of this description. This dead Gold-fish shall give us examples. The three scales in the upper row are from SCALES OP GOLD-FISH. the lateral line, the left-hand one ( a ) taken just behind the head, the second ( b ) near the middle of the body, and the right-hand one (c) near the tail. Of the lower row, the first ( d ) is from the back, the second ( e ) from the middle c 2 20 EVENINGS AT THE MICROSCOPE. of the belly, and the last (/) from the throat. Thus we see there is considerable variety in form presented by the scales even of the same individual fish. They all, how- ever, differ from those of the Perch, in this respect ; — that their free overlapping edges are entire, or destitute of the crystalline points which we saw in the former examples ; while they agree in having the front edges, by which they are during life imbedded in the skin, cut into waves or sinuosities. The lower part, as we now look at them, is the free portion of each, which alone is visible in the living fish, the other parts being concealed by the three neigh- bouring scales that overlap it, — above, in front, and below. In those from the lateral line, the tube already referred to is seen to pervade each, running through it longitudi- nally, so that it opens behind on the outer surface, and in front on the inner or under surface of the scale. In the scales near the front of the line, just behind the head, the tube is large and prominent (a), while in the scales at the opposite extremity it becomes slender ; diminishing, in the very last scale, viz., at the commencement of the tail-fin, to a mere groove. The whole surface of each scale, when viewed under a lens of low power, is seen to be covered with concentric lines, following the irregular sinuosities of the outline. These lines are the edges of the successive layers of which the scale is believed to be composed, each layer being added in the process of growth to the under surface, and each being a little larger every way than its predecessor ; thus the scale is a very depressed cone, of which the centre is the apex. There is a marked difference (indicated in the figures) between that part of the surface which is ex- posed, and that which is covered by the other scales ; the concentric marks in the former are much coarser and less regular, often being interrupted, and seeming to run into each other, and frequently swelling into oval scars. This may, perhaps, be owing to the surface having been par- HAIRS, FEATHERS, AND SCALES. 21 tially worn down by rubbing against the gravel of the bottom, or against other objects in the water. Besides the concentric lines, there are seen on many of the scales, especially those of the lateral line, radiating lines varying in number from one to twenty, or more, diverging from the centre towards the circumference, and frequently con- nected by cross lines forming a sort of net-work around the centre (see c). Under the microscope, these lines appear to be elevated ridges, dividing the concentric lines ; but of their use I am ignorant. What I have just stated is the ordinary explanation of these fine concentric lines ; but a careful examination of the structure with much higher powers than we have been using, induces me to doubt its correctness. Keverting to the scales of the Perch, let us notice the clear diverging bands, which look as if the whole scale had been split in several places, and the openings thus made filled with uniform clear substance. The same structure is seen in many other scales, as in this cycloid one from the Flounder, which, being coarsely lined, shows the structure well ; or in these from the Green Wrasse. I will now apply to one of these a power of 600 diameters, concentrating the light thrown through the scale from the mirror by the achromatic condenser,* and examine the scale anew. You now see two distinct layers ; the upper one which bears the con- centric lines, and a lower clear one which not only fills the * Called achromatic, from its being so constructed as not to split the light coming through it and cause colour. The term is formed from the Greek «, not, and xP«Ma (chroma), colour. SCALE OF FLOUNDER. a. Natural size. 22 EVENINGS AT THE MICROSCOPE. radiating bands, but underlies the whole of the lined parts. The concentric lines of the upper layer do not now appear to be edges of successive plates, but irregular canals run- ning through the solid substance. This, however, is decep- tive : for, by delicate focussing, we perceive that each portion marked by these lines is really in a different plane from the others, that the highest is at the centre of radia- tion of the scale, and that each is successively lower till we reach the margin. But now, if with very sharp scissors we cut one of these scales longitudinally through the centre, and examine the cut edge, we find that each of these lines forms a distinct ridge. On the other hand, the under layer of clear substance is quite smooth, and always a little exceeds the margin of the concentrically lined portion. The clear substance that fills the radiating slits agrees both in texture and level with this lower layer, and is manifestly continuous with it. Hence, I think that, in these slit scales, the upper layer is formed, as commonly believed, by successive deposits from beneath ; but that, after a few have been deposited, they begin to slit, probably by contraction in becoming solid ; that the lower layer is formed after each upper one is hardened, exceeding its length by a little, and filling up the slit ; that this lower layer becomes the upper layer of the next course, slitting, and turning up its terminal edge as it hardens ; that then the lower layer is deposited on this, filling up the slit as before ; and that this process goes on as long as the fish lives. It is curious that, in the scales of the Pike, the portions thus separated by slitting, instead of expanding and leaving spaces to be filled up, actually close over each other, the divided parts overlapping considerably, as you may see in these specimens. The left' hand scale («) is from the back ; the central one (b), which has only a deep narrow incision instead of a tube, is from the lateral line ; and the third (c) is from the belly of the fish. HAIRS, FEATHERS, AND SCALES. 23 Let us return now to the scales of our Gold-fish, and examine a highly interesting structure connected with them. The brilliant golden or silvery reflection that con- stitutes the beauty of these lovely fishes, depends not on the scales themselves, but on a soft layer of pigment spread over their inner surface, and seen through their translucent substance. On carefully detaching a scale, we see on the under side, opposite to that portion only which was ex- posed (all the concealed parts being colourless), a layer of soft gleaming substance, easily separable, either silvery or golden, according to the hue of the fish. If now we remove a small portion of this substance with a fine needle, and SCALES OF PIKE. spread it on a plate of thin glass, we shall find, by the aid of the microscope, that it consists of two distinct sub- stances ; the one giving the colour, the other the metallic lustre. With a power of 300 diameters, the former is seen to be a layer of loose membranous cells, of an orange colour in what are properly called the Gold-fishes, and whitish or pellucid in the Silver-fishes. If we now add a minute drop of water to the mass, and gently agitate it with the point of a needle, and again submit it to the microscope, we shall have a beautiful and interesting spec- tacle. The water around the mass is seen to be full of an infinite number of flat spicula or crystals, varying much in size, but of very constant form, a flat oblong prism . 24 EVENINGS AT THE MICROSCOPE. with angular ends (as represented in the accompanying engraving). By transmitted light they are so transparent and filmy as to be only just discernible ; but by reflected light, and especially under the sun’s rays, they flash like plates of polished steel. But what ap- pears most singular, is that each spicu- lum is perpetually vibrating and quiver- ing with a motion apparently quite spon- taneous, but probably to be referred to slight vibrations of the water in which spicxtla op gold-fish’s they float ; and each independently of the rest, so as to convey the impres- sion to the observer that each is animated with life, though the scale be taken from a fish some days dead. Owing to this irregular motion, and consequent change of position, each spiculum, as it assumes or leaves the reflecting angle, is momentarily brightening or waning, flashing out or retiring into darkness, producing a magic effect on the admiring observer. To this property, I suppose, is to be attributed the beautiful pearly play of light that marks these lovely fishes, as distinguished from the light reflected by an uniformly polished surface. I have found the pearly pigment of the scales to be provided with similar spicula in fishes widely differing in size, structure, and habits ; as the Gudgeon and Minnow, the Pike and the Marine Bream. The spicula of these fishes agree in general form with those of the Gold-fish ; and also in size, with the exception of trifling variations in the comparative length and breadth. The colouring matter is lodged in lengthened cylindrical cells, arranged side by side, and running across the scale ; that is, in a direction at right angles to the lateral line. BLOOD. 25 CHAPTER II. BLOOD. The microscope is daily becoming a more and more im- portant aid to legal investigation. An illustration of this occurred not long ago, in which a murder was brought home to the criminal by means of this instrument. Much circumstantial evidence had been adduced against him, among which was the fact, that a knife in his possession was smeared with blood, which had dried both on the blade and on the handle. The prisoner strove to turn aside the force of this circumstance by asserting that he had cut some raw beef with the knife, and had omitted to wipe it. The knife was submitted to an eminent professor of microscopy, who immediately discovered the following facts : — 1. The stain was certainly blood. 2. It was not the blood of a piece of dead flesh, but that of a living body; for it had coagulated where it was found. 3. It was not the blood of an ox, sheep, or hog. 4. It was human blood. Besides these facts, however, other important ones were revealed by the same mode of investigation. 5. Among the blood were found some vegetable fibres. 6. These were proved to be cotton fibres, — agreeing with those of the murdered man’s shirt and neckerchief. 7. There were present also numerous tesselated epithelial cells. In order to understand the meaning and the bear- ing of this last fact, I must explain that the whole of the internal surface of the body is lined with a delicate mem- brane (a continuation of the external skin), which dis- 26 EVENINGS AT THE MICROSCOPE. charges mucus, and is hence termed mucus membrane. Now this is composed of loose cells, which very easily separate, called epithelial cells ; they are in fact constantly in process of being detached (in which state they con- stitute the mucus), and of being replaced from the tissues beneath. Now microscopical anatomists have learned that these epithelial scales or cells, which are so minute as to be undiscernible by the unaided eye, differ in appear- ance and arrangement in different parts of the body. Thus, those which line the gullet and the lower part of the throat are tesselatcd , or resemble the stones of a pave- ment ; those that cover the root of the tongue are arranged in cylinders or tall cones, and are known as columnar; while those that line some of the entrails carry little waving hairs {cilia) at their tips, and are known as ciliated epithelium. The result of the investigation left no doubt remaining that with that knife the throat of a living human being, which throat had been protected by some cotton fabric, had been cut. The accumulation of evidence was fatal to the prisoner, who without the microscopic testimony might have escaped. But what was there in the dried brown stain that deter- mined it to be blood ? And, particularly, how was it proved to be not the blood of an ox, as the prisoner averred ? To these points we will now give a moment’s attention. With this fine needle I make a minute prick through the skin of my hand. A drop of blood oozes out, with which I smear this slip of glass. The slip is now on the stage of the instrument, under a power of 600 diameters. You see an infinite number of small roundish bodies, of a clear yellowish colour, floating in a colourless fluid, but so numerous, that it is only here and there, as near the edges of the smear, that you can detect any interval in their continuity. BLOOD. 27 These bodies are what we frequently call the blood- globules, or, more correctly, blood- disks ; since their form is not globular, but thin and flat, like that of a piece of money. The slightness of their colour is dependent on their extreme thinness : when a larger number lie over each other the aggregated colour is very manifest, as it then becomes either full dark red, or bright rich scarlet ; for to these disks blood is entirely indebted for its well- known hue. The blood of all vertebrate animals is com- posed principally of these bodies, which when once seen are easily recognised again : the microscope then readily determines whether any given red fluid or dried stain is composed of blood. The disks in the blood of Mammalia, or animals which suckle their young, are circular or nearly so, and slightly concave on both of the surfaces. On the other hand, in Birds, Fishes, and Reptiles, their form is elliptical, and the surfaces are flat, or slightly convex. This distinction, then, will at once enable us to determine Mammalian blood.* But to determine the various tribes of this great class among themselves, we must have recourse to another criterion, — that of dimensions. The blood-disks of Man nearly agree in size with those of the Monkey tribe, of the Seals and Whales, of the Elephant, and of the Kangaroo. Most other quadrupeds have them smaller than in Man ; the smallest of all being found in those animals which chew the cud. The little Musk-deer of Java has disks not more than one-fourth as large as the human, but these are remarkably minute ; no other known animal approaches it in this respect : those of the Ox are about three -fourths, and those of the Sheep little more than half the human average. Tables have been made out, showing the comparative * The Camels among Mammalia, and the Lampreys among Fishes, are exceptions to the above rule ; the former having elliptical and con- vex blood-disks, the latter circular and slightly concave. 28 EVENINGS AT THE MICROSCOPE. size of these corpuscles in various animals, and such tables are very useful; but we must bear in mind that the average dimensions only are to be looked for ; since in any given quantity of blood under examination, we shall not fail to see that some disks exceed, while others come short of, the dimensions of the majority. Generally speaking, the blood- disks in Birds and in Fishes are about equal in size : their form is, however, that of a more elongated ellipse in Birds than in Fishes. They may be set down as averaging in breadth the diameter of the human disks, while their length is about half as much again, or a little more, in most Birds. BLOOD DISKS. a Man. i Blenny. c Frog. d Newt. It is in Reptiles that we meet with the largest disks, and especially in those naked-skinned species, the Frogs and Newts. A large species inhabiting the American lakes — Siren lacertina — has disks of the extraordinary size of l-400th of an inch long by 1 -800th broad, or about eight times as large as those of Man, in linear measure. Our common Newts afford us the largest examples among British animals, but they do not reach above half the size just mentioned. Taking this drop of blood from my finger as a standard of comparison, we find, on applying the micrometer, that BLOOD. 29 the disks run from l-2500th to l-oOGOth of an inch ; but that the great majority are about l-3300fch in diameter. On these slides are samples of other kinds. This is the blood of a Fish — the common Blenny or Shanny ( Blen - nius pholis). Here we see at once the oval form of the disks ; their average is l-2800th by l-3800th of an inch. Here is the blood of a Frog ( liana temporaria) ; these are more than twice the size of the fish’s ; for they average l-1250th by 1- 1800th of an inch. And, finally, I can show you a drop of blood from this Smooth-newt ( Iasso - triton punctatus). The large size of the disks is now plainly seen, and so indeed is the elegance of their form : in this case, as in the last, we see in each disk a distinct roundish nucleus. These run from 1- 703th to l-950th in length by l-1100th to l-1600th in breadth; but the average are about 1 -800th by 1-1 300th of an inch. It may interest you to see these blood disks in their proper situation, and to observe the motion which they possess during the life of their owners. It is, indeed, one of the most instructive modes of using this wonder-work- ing instrument to look through it at living structures, and watch the different processes of life as they are carried on under our eyes. Nor is this at all difficult to accomplish ; for a large number of animals are so small that we can easily put them upon the stage of the microscope ; and are withal so transparent that their coverings and various tissues offer little or no impediment to our discerning the forms and movements of the contained viscera. And in cases where the entire animal is too large to be viewed under the microscope as a whole, it sometimes happens that, by a little contrivance, we can so secure the creature as to look without interruption on certain parts of the body which afford the requisite minuteness and transparency. I have here a living Frog. You perceive that the web which connects the toes is exceedingly tbir> and trans- lucent, yet arteries and veins meander through its delicate 30 EVENINGS AT THE MICROSCOPE. tissues, which are then clothed on both surfaces with the common skin. But you ask how we can induce the Frog to be so polite as to hold his paw up and keep it steady for our scientific investigation. We will manage that with- out difficulty. Most microscopes are furnished (among their accessory apparatus) with what is called a frog-plate, provided for this very demonstration. Here is mine. It is a thin plate of brass, two inches and a half broad and seven long, with a number of small holes pierced through it along the margins, and a large orifice near one end, which is covered with a plate of glass. This is to be Froggy’s bed during the operation, for we must make him as comfort- able as circumstances will admit. Well, then, we take this strip of linen, damp it, and proceed to wrap up our unconscious subject. When we have passed two or three folds round him, we hind a tape round the whole, with just sufficient tightness to keep him from struggling. One hind-leg must project from the linen, and we now pass a needle of thread twice or thrice through the drapery and round the small of this free leg, so as to prevent him from retracting it. Here then he lies, swathed like a mummy, with one little cold foot protruded. Lay him carefully on the brass plate, so that the webbed toes shall stretch across the glass. Now, then, we pass another tape through the mar- ginal -holes, and over the body, to bind it to the brass ; of course taking care not to cut the animal, but only using just as much force as is needful to prevent his wrigglings. Now a bit of thread round each toe, with which we tie it to as many of the holes, so as to expand the web across the glass. A drop of cold water now upon the swathes to keep him cool, and a touch of the same with a feather upon the toes to prevent them from drying (which must be repeated at intervals during the examination) — and he is ready. BLOOD. 31 What a striking spectacle is now presented to us, as with a power of 300 diameters we gaze on the web of the foot ! There is an area of clear colourless tissue filling the field, marked all over with delicate angular lines, some- thing like scales ; this is the tesselated epithelium of the surface. Our attention is caught by a number of black spots, often taking fantastic forms, but generally some- what star-like ; these are pigment cells, on which the colour of the animal's skin is dependent. But the most prominent feature is the blood. Wide rivers, with tor- tuous course roll across the area, with many smaller streams meandering among them ; some pursuing an inde- pendent course below the larger, and others branching out of them, or joining them at different angles. The larger rivers are of a deep orange-red hue, the smaller faintly tinged with reddish-yellow. In some of these channels the stream rolls with a majestic evenness ; in others it Shoots along with headlong impetuosity ; and in some it is almost, or even quite, stagnant. By looking with a steady gaze, we see that in all cases the stream is made up of a multitude of thin reddish disks, of exactly the same dimen- sions and appearance as those we saw just now in the Frog’s blood ; only that here, being in motion, we see very distinctly, as they are rolled over each other, that they are disks, and not spherules ; for they forcibly remind us of counters, such as are used for play, supposing they were made out of pale red glass. It is charming to watch one of these streams : selecting one of medium size, where the density is not too great to see the individual disks, and, fixing our eye on the point where a branch issues from one side of the channel, mark the disks shoot by one after another, some pursuing the main course, and others turning aside into the branch, perhaps so small as to allow of only a single disk to pass at once. The streams do not pursue the same uniform direction. 32 EVENINGS AT THE MICROSCOPE. The larger ones do indeed ; and their course is from the extremity of the toes towards the body : these are the veins ; but the smaller streamlets flow in any direction, and frequently send out side -branches, which presently return into the stream from which they issued, or unite with others in a very irregular net- work. These are the capillaries which feed the veins, and which are themselves fed by the arteries, whose course is in the oppo- site direction, viz., from the body. These, however, are with dif- ficulty seen : they are more deeply seated in the tissues, and are less spread over the webs, being generally placed along the bor- ders of the toes ; they are, moreover, fewer and smaller than the veins ; but the blood in them usually flows with more impetuous rapidity. The variations in the impetus of the current which we observe in the same vessel are probably owing to the men- tal emotions of the animal ; alarm at its unusual position, and at the confinement which it feels when it endeavours to move, may suspend the action of the heart, and thus cause an interruption in the flow ; or analogous emotions may quicken the pulse. We will, however, now release our little prisoner, who, though glad to be at liberty, is, as you see, none the worse for his temporary imprisonment. Let us now look at the circulation of the blood in one of the Invertebrate Animals. In this thin glass cell of sea- CIRCULATION IN FROG’S FOOT. BLOOD. 33 water is a small fragment of sea-weed, and attached to one of its slender filaments you may see three or four tiny knobs of jelly, clustered together like a bunch of grapes. These are animals ; each endowed with a distinct life, but associated together by a common stalk, which maintains the mutual vital connexion of the whole. It is one of the Social Tunicata, and is named Perophora Listen. Though each globose knob is no larger than a small pin’s head, it is full of organs which carry on the various func- tions of life ; and, because the whole tissues are as trans- parent as crystal, they allow us to watch the processes with perfect ease. Take a peep at it. It is a gelatinous sac, of a form intermediate between globular and cu- bical, flattened on two opposite sides, with a sort of wart at the summit and another at the side, each of which is pierced with a pursed orifice. The upper of these ori- fices admits water for respiration and food ; the latter passes through a digestive system, and is discharged through the side orifice. The di- gestive organs lie on that flattened side which is farthest from your eye, and are therefore dimly seen. The globose body is inclosed in a coating of loose shape- less jelly, that passes off from one of the lower corners and forms a short foot -stalk, which unites with similar D 84 EVENINGS AT THE MICKOSCOPE. foot-stalks from the sister globules, and all together are attached to the sea-weed. Each foot-stalk has an organic core, into which a vessel passes from the body. Your attention is first arrested by the breathing sac, with its rows of oblong cells, all in wheel-like motion. It is indeed a wonderful object ; but for the present neglect this, as we will return to it shortly, and direct your consi- deration to the course of the blood. It is true the fluid which I so name is not red, like that of the Frog which you have just been gazing at, nor does it carry disks of the same elegantly regular form. But you have the advantage here of tracing, at one view, the whole course of the circulation, from its first rush out of the heart, to its return into that organ again. At the bottom of the interior, below the breathing sac, there is an oblong cavity, through whose centre there runs a long transparent vessel, formed of a delicate membrane, the appearance of which resembles that of a long bag, pointed (but not closed) at either end, and then twisted in some unintelligible manner, so as to make three turns. This is the heart ; and within it are seen many minute colourless globules, floating freely in a subtle fluid : this is the nourishing juice of the body, which we may, without much violence, designate the blood. Now see the circula- tion of this fluid. The membranous bag gives a spasmodic contraction at one end, and drives forward the globules contained there ; the contraction in an instant passes on- ward along the three twists of the heart (the part behind expanding immediately as the action passes on), and the globules are forcibly expelled through the narrow but open extremity. Meanwhile, globules from around the other end have rushed in as soon as that part resumed its usual width, which in turn are driven forward by a periodic repe- tition of the contraction and expansion of the heart. The globules thus periodically driven forth from the heart, now let us watch, and see what becomes of them. BLOOD. 35 They do not appear to pass into any defined system of vessels that we may call arteries, but to find their way through the interstices of the various organs in the general cavity of the body. The greater number of globules pass immediately from the heart through a vessel into the short foot-stalk, where they accumulate in a large reservoir ; but the rest pass up along the side of the body, which (in the aspect in which we are looking at it) is the right. As they proceed (by jerks, of course, impelled by the contractions of the heart), some find their way into the space between the breathing surfaces, through narrow slits along the edges of the sac, and wind along between the oval ciliary wheels, which we will presently consider. Besides these, however, other globules wind along between the outer surfaces of the sac and the inner surface of the body-walls. But to return to the current which passes up the right side : arriving at the upper angle of the body, the stream turns off to the left abruptly, principally passing along a fold or groove in the exterior of the breathing sac until it reaches the left side, down which it passes, and along the bottom, until it arrives at the entrance of the heart, and rushes in to fill the vacuum produced by the expansion of its walls after the periodic contraction. This is the perfect circle ; but the minor streams that had forked off sideways in the course, as those within the sac for example, find their way to the entrance of the heart by shorter and more irregular courses. One or two things connected with this circulatory system are worthy of special notice. The first is, that its direc- tion is not constant, but reversible. After we have watched this course followed with regularity for perhaps a hundred pulsations or so, all of a sudden the heart ceases to beat, and all the globules rest in their circling course, that we had supposed incessant. Strange to behold, after a pause of two or three seconds, the pulsation begins again, but at d 2 36 EVENINGS AT THE MICROSCOPE. the opposite end of the heart, and proceeds with perfect regularity, just as before, but in the opposite direction. The globules, of course, obey the new impulse, enter at their former exit, and pass out at their former entrance, and perform their circulation in every respect the same as before, hut in the reverse direction. Those globules that pass through the vessel into the foot-stalk appear to accumulate there as in a reservoir, until the course is changed, wljen they crowd into the heart again, and perform their grand tour. Yet there is a measure of circulation here, for even in the connecting vessel one stream ascends from the reservoir into the body, as the other (and principal one) descends into it from the heart ; and so, vice versa. I have spoken of these motions as being performed with regularity ; but if you look closely, you will see that this must be understood with some qualification. The pulsa- tions are not quite uniform, being sometimes more languid, sometimes more vigorous ; perhaps forty beats in a minute may be the average ; but I have counted sixty, and, pre- sently after, thirty ; I have counted twenty beats in one half-minute, and only fifteen in the next. The period during which one course continues is equally uncertain ; but about two minutes may be the usual time. Sometimes the pulsation intermits for a second or so, and then goes on in the same direction ; and sometimes there is a curious variation in the heart’s action, — a faint and then a strong beat, a faint and a strong one, and so alternately for some time. The phenomena of respiration are so closely connected with those of circulation that it is not at all out of the way to turn from the latter to the former ; not to say that it would be high treason against scientific curiosity if I were to remove this object without explaining to you that mar- vellous play of wheels that occupies the largest part of the area that you behold. As you look on the globe, you ob- BLOOD. 37 serve, hanging down from the upper extremity, and reaching nearly to the bottom in one direction and almost from side to side in another, a transparent square veil, which is indeed a flat membranous bag, having its sides pretty close together, with small openings along its edges, and an orifice at the bottom leading into the stomach. The mouth of this sac is in close connexion with the upper or principal orifice, and therefore receives the water, which is constantly flowing in, while that aperture is ex- panded. This fluid then bathes the whole interior of the sac ; but a portion of it escapes by the lateral openings into the cavity of the body, between the sac and the mantle, and is discharged through the secondary, or side orifice. The inner surface of this transparent sac is studded with rings of a long oval figure, set side by side in four rows. These rings appear to consist of a slight elevation of the general membranous surface, so as to make little shallow cells, the whole edges of which are fringed with cilia, whose movements make waves, that follow each other round the course in regular succession. In truth it is a beautiful sight to see forty or more of these rings, all set round their interior with what look like the cogs on a watch wheel, dark and distinct, running round and round with an even, moderately rapid, ceaseless motion. These black running figures, so like cogs and so well defined as they are, are merely an optical delusion ; they do not represent the cilia, but merely the waves which the cilia make : the cilia themselves are exceedingly slender close- set hairs, as may be seen at the ends of the ovals, where a slight alteration of position prevents the waves from taking the tooth-like appearance. Sometimes one here and there of the ovals ceases to play, while the rest continue ; and, now and then, the whole are suddenly arrested simultane- ously, as if by magic, and presently all start together again, which has a most charming effect. A still more singular 38 EVENINGS AT THE MICROSCOPE. circumstance is, that while in general the ciliary wave runs in the same direction in the different ovals, there will be one here and there in which the course is reversed ; and I think that the animal has the power of choosing the direc- tion of the waves, of setting them going and of stopping them, individually as well as collectively. The object of these ciliary wheels is to keep up a con- stant current in the water. This fluid, as I have said, enters from without, through the upper orifice of the body, and is hurled over the whole surface of the breathing sac by means of the ciliary waves, parting with its oxygen, as it goes, to the blood, which streams, as we saw, every- where between the rows of wheels. But the water has another function : it carries particles of organic matter with it, which are suitable for the nourishment of the creature ; these atoms are carried by the currents to the bottom of the sac, and are poured into the stomach, where they are digested ; the remains, together with the waste water, being discharged through the lateral orifice. Thus we see how closely connected are the three great processes of circulation, respiration, and digestion. MOLLUSCA. 39 CHAPTEB III. MOLLUSCA: THEIR SHELLS, TONGUES, EYES, AND EARS. One of the most interesting aspects of microscopic study is that in which it reveals the intimate structure of objects, which, to the unassisted eye, appear simple or nearly so, but which prove by the aid of magnifying power to be complex. Thus we are often introduced to very curious contrivances (if I may use such a word in reference to the works of God), by which difficulties are overcome, and substances, which would seem at first wholly unfit for certain duties, are in the most admirable manner adapted to fulfil them. The combination of strength and lightness is always a difficult problem in human art ; its successful solution always excites our admiration. In the Divine mechanics, too, it is very often required, and the variety of modes in which it is accomplished are in the highest degree novel and suggestive. We lately saw one of these in the struc- ture of a feather, in the contrivance by which extreme lightness of material was made, by a most remarkable arrangement, to offer a firm resistance to opposing force. I have now another example to show you, in which a material, in itself heavy, is by its arrangement made very light, while it preserves its strength. You have seen many times, when walking along the yellow sands kissed by the rippling waves, the shell, or bone, as it is sometimes called, of the Cuttle-fish.' You know that it consists of a shallow boat-shaped shell, the hollow of which is filled with a white substance, which can 40 EVENINGS AT THE MICROSCOPE. be scraped away even with the finger-nail, and which is sometimes used as pounce, to rub on paper from which writing has been erased. It is this substance of which I mean now to speak. The possessor of this structure is a member of the numerous class Mollusca,* which are generally charac- terised by being inclosed in shells. Now shell, as we all know, is a solid, stony substance, much heavier than water ; take into your hand that large Cassis on the mantel-piece, and observe its great weight and compact- ness. It is, in fact, real limestone ; differing from that of the rocks only in this, that it has been deposited by the living organic cells of an animal, and arranged in a de- finite form. We will presently examine other examples. The “ cuttle -bone ” is a shell, not indeed inclosing the animal, but inclosed by it, being contained within a cavity in the substance of the fleshy mantle ; cut open the mantle, and the shell instantly drops out. The Cuttle is a rapid swimmer through the open sea. A shell so large as this, if solid and compact like that of the Cassis, would condemn it to grovel on the bottom, and frustrate all the instincts of its nature. On the other hand, it needs the strength and support of a solid column. Wonderful to tell, the calcareous f shell is made not only to be no hindrance to its swimming, but to contribute greatly to its buoyancy : it is what the string of corks is to the. bather who cannot swim, it is a .float. Throw this entire cuttle-shell into water ; it floats on the surface as buoy- antly as if it were actually carved out of cork. I cut with a keen knife a little cube out of the shell, and, fixing it on the end of the revolving stage -needle, apply a low power, say seventy diameters, using reflected * From the Latin mollis, soft; a name given by Cuvier to this class from their bodies being always soft, whether bearing shells or not. + From calx, Latin for lime. MOLLUSCA : THEIR SHELLS. 41 light. We are looking now at the perpendicular section ; is it not a beautiful object? you might fancy yourself looking at one of the noble icebergs that majestically navigate the polar seas, when it is rendered porous and laminated by the rains of spring. You see a number of thin horizontal tiers or stages, perfectly parallel and equi-dis- tant, about one -for- tieth of an inch apart, rising above each other like the floors of an edifice. These are connected together by an infinite multi- tude of thin pillars of crystal, or rather leaves, some of which show their edges towards us, others their broader sides, and others are broken off at various distances, the frag- ments standing up from the floor, or depending from the roof, like stalactites and stalagmites in a cavern.* This whole series of crystal floors and supporting plates is formed of calcareous matter, — limestone, in short ; but though the latter are set in such close array that the eye cannot penetrate to any appreciable distance between them, their extreme thinness renders the whole structure very light, the interstices being occupied by air. But now if I give the stage-needle half a revolution, we shall have the horizontal section presented to the eye. In this aspect we acquire much more information as to the structure. The cut has been made very close to one of * In calcareous districts the water trickling through into caverns often forms shapeless masses on the floor or hanging like icicles from the roof ; in the former case they are called stalagmites , in the latter stalactites. » CUTTLE-SHELL. a Perpendicular. b Horizontal. 42 EVENINGS AT THE MICROSCOPE. the horizontal floors, which we see marked all over with a great number of lines, each of which runs hither and thither, in a very sinuous pattern. The lines are made up of a brilliant sparkling substance ; they are, in fact, the basal portions of what we saw in the other section as thin perpendicular plates ; I have cut off the plates close to the bottom, and what we see is their insertion into the floor. Thus we perceive that what we took for a multitude of plates, were but the various doublings and infoldings of a single plate of great length, running quite across the floor : an arrangement by which the strength of the ma- terial is greatly augmented. You have often seen the mode in which light walls are made of corrugated iron, especially at railway stations ; and are doubtless aware that the corrugation, or bending in or out, imparts a strength to it which the mere sheet iron, if set up as a smooth, plane surface, would in no wise possess. The principle is exactly the same in the two cases ; but the corrugation of the limestone plates in the cuttle -shell is far more perfect than that of the iron ; added to which there is the other advantage, that the aggregate mass of material is made highly buoyant by the large bulk of empty space that intervenes between the sinuous folds of the crystal plates. It may be interesting to compare with this the structure of the more solid shells of bivalves, which have been so elaborately studied by Dr. Carpenter. In general, these consist of two very distinct layers, well seen in the valve of the Pearl Oyster and its allies. The Pinna, or Wing- shell, the largest of our native bivalves, affords us a good example, especially of the external layer, since here this layer projects beyond the inner one, in thin transparent edges, which gives us an opportunity of examining their structure without any artificial preparation. This frag- ment, taken from the edge of one of those leafy expan- sions, we will examine with a low magnifying power. Each mollusca: theik shells. 48 of its surfaces has a sort of facetted, or honeycombed appearance; and the broken edges, which even to the naked eye appear fibrous, are seen to resemble a number of basaltic columns. “ The shell is thus seen to be com- posed of a vast number of prisms, having a tolerably uniform size, and usually presenting an approach to the hexagonal shape. These are arranged perpendicularly, or nearly so, to the surface of the lamina of the shell ; so that its thickness is formed by their length, and its two surfaces by their extremities.”* SECTION OF NACRE FROM PEARL OYSTER. The inner layer of such shells is remarkable for pos- sessing in different degrees the property of reflecting rain- how-like colours, often with great delicacy and splendour ; and this is termed nacre , or familiarly “ mother-of-pearl.” This iridescent lustre depends, as Sir David Brewster has shown,f upon a multitude of grooves or fine lines, which run in a very waved pattern, but nearly parallel to each other, across the surface of the nacre. “As these lines are not obliterated by any amount of polishing, it is f “ Phil. Trans.,” 1814. * Carpenter, “ The Microscope,” 590. 44 EVENINGS AT THE MICROSCOPE. obvious that their presence depends upon something pe- culiar in the texture of this substance, and not upon any mere superficial arrangement. When a piece of nacre is carefully examined, it becomes evident that the lines are produced by the cropping out of laminse of shell, situated more or less obliquely to the plane of the surface. The greater the dip of these laminae, the closer will their edges be ; whilst the less the angle which they make with the surface, the wider will be the interval between the lines. When the section passes for any distance in the plane of a lamina, no lines will present themselves on that space. And thus the appearance of a section of nacre is such, as to have been aptly compared by Sir J. Herschel to the surface of a smoothed deal board, in which the woody layers are cut perpendicularly to their surface in one part, and nearly in their plane in another.” * Those beautiful objects,— so much prized for personal adornment, — pearls, are concretions accidentally formed within the shells of such mollusks, and are wholly com- posed of the inner layer. Drs. Kelaart and Mobius have recently published some highly interesting observations on the causes both of the iridescence and of the pearly lustre ; and these I will cite from the abstract translation of them made by Mr. Dallas. “ The surface of pearls is not perfectly smooth, but covered with very fine microscopic elevations and depres- sions. These are more or less irregular in their altitude, but approach most nearly to equality in pearls of the finest water. In pearls which exhibit a certain iridescence, and which, when turned in different directions towards the eye, present even very faint bluish, greenish, and reddish tints, the surface is found to present delicate irregular curved furrows, which either run tolerably parallel to each other, or form small irregular closed curves. This is due to the mode of growth of the pearl, in which thin layers * Carpenter, “ The Microscope.” SQ*. MOLLUSCA I THEIR SHELLS. 45 of nacre, of small dimensions, have been laid over each other. There is no continuous layer over the pearl, but a number of small portions which sometimes overlie the margins of the subjacent layers, and sometimes leave them uncovered. This structure is seen most distinctly in the pearl shell, where the conditions are rendered more simple by the layers being deposited on a flat, or but slightly curved surface. The distance of the furrows from each other is not always the same ; sometimes they may be recognised with the simple lens, while on other parts they approach within s^Vo#1 of an inch of each other. That the iridescence of nacre, or the nacreous colour, as distinguished from pearly lustre, is caused by the inter- ference of the light reflected from these furrows and the intervening edges of the strata, is proved by the circum- stance, ascertained by Brewster, that impressions of * mother-of-pearl taken in red or black sealing-wax exhibit the same phenomena of colour distinctly. In pearls, in consequence of their spherical form, the different masses of coloured light are so diffused that they unite to form white light ; and this takes place with the greater perfec- tion in proportion as the furrows are lost, and become converted into a surface of fine elevations and depres- sions. “ For their lustre, pearls are indebted to their being composed of fine layers, which allow light to pass through them ; whilst the numerous layers, lying one under the other, disperse and reflect the light in such a manner that it returns and mixes with that which is directly thrown back from the outer surface. It is the co-operation of light reflected from the surface, with light dispersed and reflected in the interior, that gives rise to lustre ; for this reason the knots of window-glass exhibit pearly lustre, and the membranes of pearls deprived of their line are almost as lustrous as solid pearls, except that their whiteness is destroyed. * The two masses of light entering the eye, act 46 EVENINGS AT THE MICROSCOPE. upon it from different distances. Now, as it adapts itself to the body seen through the transparent layer, it cannot distinctly see the light reflected from the surface, and the consciousness of this infinitely perceptible reflection produces the phenomena of lustre.’ * The thinner and the more transparent the layers of which the pearl consists, the more beautiful is its lustre ; and in this respect the sea-pearls excel those of our river-mol- lusks.” f We will pass now, by an easy transition, from the shells of the Mollusca to their tongues. Who that looks at the weather-worn cone of the Limpet, as he adheres sluggishly to the rock between tide-levels, would suspect that he carries coiled up in his throat a tongue twice as long as his shell ? And that this tongue is armed with thou- sands of crystal teeth, all arranged with the most consum- mate art in a pattern of perfect regularity ? It sounds almost like a fable to be told that the great Spotted Slug, which we sometimes find crawling in damp cellars, carries a tongue armed with 26,800 teeth ! Yet there is no doubt of the fact. You see on this slip of glass a very slender band about two inches in length. This is the tongue of the common Periwinkle. While it was in the living animal, its fore-part occupied the floor of the mouth, whence it passed down below the throat, and, turning towards the right side, formed a close spire of many whorls, exactly like a coil of rope, which rested on the gullet. Here we have it ex- tracted, uncoiled, cleansed, and affixed to a slip of glass for microscopical examination. Only a small portion of the band is visible at a time with such a power as is necessary to display the structure ; but by means of the stage-movement we can bring the whole in succession under the eye, and discover that, with some modifications of form, the same essential plan of * Dove, “ Farbenlebre,” 117. f “ Ann. veiv (temnein), to cut , are so called from the ease with which their masses may be broken or cut through; whence their popular name of brittle-worts. They are usually considered to belong to the vegetable kingdom. 382 EVENINGS AT THE MICROSCOPE. Diatom, which is thus brought into the midst of the sarcode, a vacuole being new-made for its reception. This, then, performs the part of a temporary stomach : the digestible portions of the prey are extracted, and then the insoluble shell of flint is, as it were, gradually squeezed to some part of the exterior, and gradually forced out, the vacuole disappearing with it, or perhaps retaining a minute portion of the fluid, and thus perpetuating itself for a while. This is the earliest condition in which the process of digestion can be recognised. Another genus somewhat similar is Arcella, but it differs in being furnished with a more or less rounded shell ( lorica ), like a little box. In examining the matters that adhere to the stems of duckweed, and other water plants, we frequently observe little circular bodies of a yellowish or reddish-brown colour, some much darker than others, but all having a central round spot paler than the rest. On first examination they seem inert and dead, but if we closely watch one, we perceive that it is endowed with the power of motion ; and we directly discern, thrust out from its edge, variable processes, in the form of arms, of clear, perfectly colourless, and most delicate jelly, sometimes pointed, sometimes blunt, which slowly change their form and position. By the aid of these, a feeble and irregular motion is given to the box, which is sometimes turned partly over ; when we perceive that its under side is flat or probably concave, and that its outline is cut into facets. The lorica is somewhat flexible, for the edges at two opposite points are sometimes bent down towards each other, so as to give the creature the form of a crescent. The internal viscera are dimly discernible through the coloured lorica , and resemble those of Amoeba. A dark oval ring is commonly seen at one side, which is probably the outline of the contractile bladder. It may, in fact, be considered as an Amoeba , whose external surface has the power of secreting a symmetrical shell of horny or PROTOZOA AND SPONGES. 383 chitinous substance. The lorica is about — ^-th of an inch in diameter. This species is named Arcella vulgaris. Laying aside our live-box with its contents for the present, we will have recourse to the tanks of sea-water for one or two other objects of intermediate interest. On the green and brown mossy sea-weed which covers the rocks on the bottom, you see many white specks clinging to the filaments ; and there are several adhering to the sides of the tank. These are little living shelled animals of the class Foraminifera , and these which you see include several species. By bringing your eye, assisted by the lens, to bear upon one of these latter, you perceive that it is a little discoid spiral shell, of very elegant form, marked with curved diverging grooves. This is the pretty little Polystomella crisp a, a fair sample of its class, and though not more than ^th of an inch in diameter, it is a giant compared with the Arcella. There is more, however, than the shell to be seen ; though so filmy and shadowy, that I wonder not at your overlooking it. Extending from two opposite sides of the shell to a distance each way considerably exceeding its diameter, you discern fine threads of clear jelly, running out in long points. The power you employ is not suffi- cient to enable you to resolve their detail : and for this I will try to secure a specimen for the microscope. In this other live-box, then, I inclose one of the white specks from the moss-like clothing of the stones. It is, I see, of another species, namely, polymorphina oblonga, but it will answer our purpose equally well. At present we see only the shell, the removal of the animal having induced it in alarm to withdraw the whole of its softer parts within the protection of its castle. We must have a few minutes’ patience. Now look again. From the sides of the opaque shell we see protruding tiny points of the clear sarcode ; these gradually and slowly, — so gradually and slowly that the 384 EVENINGS AT THE MICROSCOPE. eye cannot recognise the process of extension — stretch and extend their lines and films of delicate jelly, till at length they have stretched right across the field of view. The extension is principally in two opposite directions corre- sponding to the long axis of the shell ; though the branched and variously connected films often diverge considerably to either side of these lines, giving to the whole a more or less fan-shaped figure. These films are as irregular in their forms and sizes as the expansion of the sarcode of Amoeba , with which they have the closest affinity. Their only peculiarity is their tendency to run out into long ribbons or attenuated threads, which, however, coalesce and unite whenever they come into mutual contact, and thus we see the threads branching and anastomosing with the utmost irregularity, usually with broad triangular films at the points of diverg- ence and union. There can be no doubt that the object of these length- ened films, which are termed pseudopodia* is the capture of prey or food of some kind ; perhaps the more sluggish forms of minute animalcules, or the simpler plants. These the films of sarcode probably entangle, surround, and drag into the chambers of the shell, digesting their softer parts in temporary vacuoles, and then casting out the more solid remains, just as the Amoeba does. Though this beautiful array was so very deliberately put forth, it is, as you perceive, very rapidly withdrawn on any disturbance to the animal, as when we agitate the water by slightly moving or turning the cover of the live- box. Another fact, of which you may convince yourself, by watching manifest, though small, changes of position in the shell, while under observation, is, that it is by means of the adhesion and contraction of the pseudopodia, that the animal drags itself along a fixed surface. This it can * Literally, false feet , from the Greek \J/ev8os (pseudos), a falsehood , and ttous (pous), genitive ™Sos (podos), afoot. PROTOZOA AND SPONGES. 885 effect so assiduously, that I frequently find them in the morning adhering to the tank-sides three or four inches from the bottom, though, on the previous evening, none were visible on the glass. Thus they must crawl, on oc- casion, from a hundred to a hundred and fifty times their own diameter in a night. The structure of a Sponge is much the same as that of these animals, with the exception that its solid part or skeleton is not a continuous covering by which the sarcode is invested, but consists of fibres or points or rods of vary- ing form, which are clothed with the sarcode. This loose sort of skeleton may be of homy or chitinous matter, like that of Arcella, or calcareous like that of the Foraminifera ,* or it may be siliceous, — that is, composed of flint (silex). In some cases, as in the common Turkey Sponge, the horny skeleton consists of a network of solid but slender fibres, very tough and elastic, which branch and anasto- mose in every direction, at very short intervals, as you may see by looking at this atom, which I cut off from a dressing- sponge. In the lime and flint Sponges, however, the continuity and cohesion of the skeleton does not depend upon the organic union of the constituent parts, as it does in the loose and open network of the Turkey sponge. For it is made up of an immense multitude of glassy needles, all separate and independent, between themselves, yet so con- trived that they do hold together very firmly, and in a great number of cases are arranged on a prescribed plan, so as to give a certain form and outline to the aggregate. If you have ever shaken up a box of dressing-pins, and have then endeavoured to take one out, you know how by their mere interlacement they adhere together in a mass, * A group of animals with shells, resembling in appearance those of the common nautilus ; and, like them, consisting of several chambers divided from one another by walls which are pierced with numerous minute holes, in Latin called foramina ; — whence their name. 386 EVENINGS AT THE MICROSCOPE. so that by taking hold of one you may lift a bristling group of scores. Somewhat on the same principle are the cal- careous and siliceous pins (spicula) of a Sponge held to- gether by mutual interlacement. Yet their cohesion is aided by the tenacity of the living sarcode which invests them ; for I have found that specimens of Grantia (cal- careous Sponges with needles of three rays), when long macerated in water, so that the sarcode is dissolved, have very slight power of cohesion among their spicula. To understand the structure of a sponge we will shave a thin sectional slice from this Halichondria suberea . This when alive is of an orange colour ; and is always found closely investing turbinate, or top-shaped, shells which are inhabited by Hermit-crabs. We will macerate the slice in tepid water for a quarter of an hour, and then examine it in the live -box. The surface is a thin layer of greater density than any other part, and is composed of coloured fleshy granules, — SECTION OF SPONGE. omitting for the present, the skeleton. Of the same sub- stance is the whole slice composed, but looser and more open as it recedes from the surface. It is separated by PEOTOZOA AND SPONGES. 387 blank spaces which are larger towards the centre, smaller and more numerous as they approach the exterior. These openings are sections of so many canals, by which the whole substance of a sponge is permeated. The surface is perforated with minute pores, at which the surrounding water enters on all sides. These presently unite into slender pipes, which, irregularly meandering, are continually uniting into larger and yet larger canals ; of which the greater open spaces that you see are the oblique divisions. These have certain outlets, called oscula , on the surface, from which the stream is poured that has thus made the grand tour of the whole interior. Such oscula , as you perceive on the remainder of the Halichondria, are usually raised on slight eminences ; and resemble, especially when in living action, miniature vol- canoes, vomiting torrents of water and granules of effete matter, instead of fire and ashes. During life these granules were much more diffused, and formed a considerable portion of the living flesh, the re- mainder being composed of a glairy sarcode, almost fluid. The whole was maintained in position by the solid spicula of flint, which you see abundantly in this slice. These take a curious form, exactly that of the pins which we use on our dressing-tables ; each consisting of a cylindrical slender - rod, pointed at one end, and at the other sur- mounted by a globular head, the whole formed of glass, — flint glass literally. You see them bristling all round the edge of the section, being stuck into the surface of the sponge, exactly as pins are loosely stuck into a pin- cushion. The heads and points, too, project into the cavities; more, however, than they did during life, for you must make allowance for the shrinking of the soft parts ; and thus you perceive how the whole structure is permeated by these glassy pins, which seem td be entangled together quite at random without rule or arrangement. And yet there is an arrangement discernible here ; for the canals c c 2 388 EVENINGS AT THE MICROSCOPE. are formed by the manner in which these are grouped ; and this is seen much more clearly in the case of the three- rayed needles of lime in the Grantice, Mr. Bowerhank has shown that in G, compressa the substance is divided into very regular chambers in a double series, divided by a diaphragm, whose axis is at right angles to the axis of the sponge ; and that these chambers are defined by walls made up of the three-rayed needles in their mutual inter- lacement. INFUSORIA. 389 CHAPTER XXI. INFUSORIA. We will now resume our examination of the drop of pond- water, and the fragments of Myriophyllum , which have been waiting for us in the live-box. Our attention then shall first be given to some elegant creatures of a brilliant translucent green hue, which are gracefully gliding about. They are of the genus Euglena , so called because each is furnished with a very conspicuous spot of a clear red hue, situated near the head, which Ehrenberg, on account of its resemblance to the lowest forms of eyes in the Rotifer a, that are somewhat similar in colour and appearance, pronounced to be an organ of vision. More recent physiologists, however, doubt the correctness of the conclusion. The animals are of several kinds. The most numerous is an active little thing of about 2-5-oth of an inch in length when extended, though from its extreme versatility it is as difficult to assign to it a definite size as a definite shape. It seems to be the E. sanguined , so called because it is said to occur sometimes of a deep red hue, and in such vast profusion as to give the waters the appearance of blood. I have never seen it, however, other than as it now appears, rich emerald green in the body, with the two extremities perfectly clear and colourless. I might, per- haps, describe its ordinary form as spindle-shaped, with a pointed tail, and a blunt, rounded head ; but it is remark- able for the variableness of its shape. It is capable of 890 EVENINGS AT THE MICROSCOPE. assuming an appearance very diverse from what it had half a minute before, so that you would hardly identify it, if you were not watching its evolutions. Whether this ability to prove an alias be at all dependent on the remarkable clear-headedness of the subject, I leave for those who are skilled in metaphysics to determine. Away they go, tumbling over and over, revolving on the long axis as they proceed, which they do not very rapidly, with the blunt extremity forward. Here is another form, a little larger than the former, but much more slender ; yet from the slowness and steadi- ness of its movement more easy of observation. It is named E. acus , or “ the Needle Euglena.” This is an animalcule of great elegance and brilliancy ; its sparkling green hue, with colourless extremities, and its rich pale crimson eye, are very beautiful. It commonly swims ex- tended, with a slow gliding motion, turning round on its long axis as it proceeds, as may be distinctly seen by the rotation of certain clear oblong substances in its body. These, then, are seen not in the interior, but near the surface, as they would appear if imbedded in the flesh around a hollow centre. The interior is probably not hollow, but occupied with pellucid sarcode. These were assumed by Ehrenberg, but on no adequate grounds, to be organs connected with reproduction. They vary in number in different individuals, and those which contain the greatest number are thereby more swollen. They appear to be separated into two series, one anterior, the other posterior. The animal is capable of bending its head and body in various directions, but is most beautiful when straight. The front is furnished with a slender thread-like proboscis. This species affords us a good opportunity of observing the red spot, which, for con- venience sake, we may still term an eye. It seems to be an irregular oblong vacuole, or excavation in the sarcode, filled with a clear ruby-red fluid. The red spot in the INFUSORIA. 391 Uotifera is connected with a well-defined crystalline lens, whose definite form and high refractive power may in many cases be distinctly marked ; but here nothing of the kind is seen; the spot itself has no certain shape, and does not appear to be bounded by a proper wall. Some forms, which are by general consent admitted to be plants, have similar spots ; and hence it has been, rather too hastily, I venture to think, concluded that they have no connexion with vision. I think it still possible that a sen- sibility to the difference between light and darkness may be the function of the organ. I have found that this animal, when allowed to dry on a plate of glass, retains its form and colour perfectly ; but in about two days the eye-spot, which at first becomes much larger in the drying, gradually loses all traces of its brilliant colour, probably by the evaporation of the contained fluid. Another pretty species you see gliding along among the rest, called E. triquetra, or the Three-sided. It bears a resemblance to a broad rounded leaf, with the foot-stalk forming a short transparent point, and the mid-rib ele- vated into a sharp ridge. The under side seems slightly concave. This is equally attractive with the others. It is persistent in form, and appears not to be even flexible. Its motion is slow, and as it goes, it rolls irregularly over and over in all directions, not revolving on its long axis, and thus giving you very satisfactory views, though only momentary, of the keel with which the back is furnished. It is in the turnings of such minute creatures that the microscopist often gets a glimpse of peculiarities of form, which a view of the animal when in repose, however long continued, fails to reveal. Longitudinal interrupted lines THREE-SIDED EUGLENA. 392 EVENINGS AT THE MICROSCOPE. are seen running down the body of this pretty leaf, which do not appear to mark irregularities of the surface, and therefore are probably internal. Ehrenberg calls these and similar collections of granules “ ova,” or eggs ; but this is to cut the knot instead of untying it. There is no sufficient reason to believe that these animals increase by ova. About the front of all these Euglence , you may discern now and then a slight flickering or quivering in the water. The power we are using, though best for the general display of the form, is insufficient to resolve this appear- ance : I will put on a higher objective. You now see that there proceeds from the frontal part of the body a long and very slender filament, which is whisked about in the manner of a whip-lash. This is considered to be the organ of locomotion ; but I rather doubt that such is the function ; the smooth and even gliding, often rotating, action of the creature, seems more like that produced by minute and generally- distributed cilia, than that caused by the lashings of a single long thread. Yet two more species of this extensive genus we dis- cern in this well-stocked drop of water. They have received the appellations of the Pear ( E . pyrum) and the Sloth ( E . deses). The former is the most minute we have yet seen and seems to be scarce ; but it is highly curious and interesting in appearance. It much resembles in outline a fish of the genus Balistes ; the muzzle being somewhat protruded and truncate, and the form rhom- boidal ; it terminates in a slender pointed tail. The body is obliquely fluted, which gives a very singular effect ; for from the transparency of the tissues the lines of the opposite side can be discerned crossing those next the eye, and dividing the animal into lozenge-shaped areas. The colour is sparkling green, but the tail and the edges of the body are clear and colourless, and there is a bright red eye. At other times this Euglena takes the form of a INFUSORIA. 393 claret-bottle or an oil-flask ; the muzzle being broadly truncate or even indented. Its motion is rapid : a swift gliding in the direction of its long axis ; it turns continually on the same axis, which gives a waving irregularity to its course, and has a pretty effect from the continual crossing of the flutings in the revolving. This specimen is about y^th °f an inch *n length, including the tail. Euglena deses is much larger, being about y-J oth of an inch in length, though the tail is very short. It has a thick body, with a round, blunt head ; it tapers suddenly to the tail. Its colour is bright green with a red eye ; but the presence of an infinite number of irregular oblong granules and lines with several globular vesicles, gives an opacity and a blackness to its appearance. In its manners it is sluggish ; it never swims or glides gracefully and swiftly among its playful companions, but contents itself with twining slowly among the downy stems and filaments of the water-plants, or crawls upon the surface of the live- box. It does not appear to change its form, otherwise than its soft and flexible body necessitates, as it twines about. But enough of the Euglenas. For I have just caught sight of a much more curious creature, the Swan Animal- cule ( Trachelocerca olor ). It is reposing on one of the leaves of the Myriophyllum , its long and flexible neck lengthening and contracting at pleasure, the tip thrown about in quick jerks in every direction, somewhat like a caterpillar when it touches several points impatiently with its head. If we admire the graceful sailing of a swan upon a lake, the swelling of its rounded bosom, the elegant curves of its long neck, we shall be struck with the form and motion of this animal. The form has much resemblance to that of a swan, or still more to that of a snake-bird ( Plotus ) ; the body, swelling in the middle, tapers gradually into 894 EVENINGS AT THE MICROSCOPE. slender pointed tail at one extremity, and at the other into a very long and equally slender neck, which is terminated by a slight dilatation. The whole is perfectly transparent, but the body is filled with numerous minute globular vessels, or temporary stomachs. The grace of its motion, as it glides along with a free and moderately swift pro- gression through the clear water, or winds through the intricate passages of the green conferva, throwing its long neck into elegant curves, is very remarkable. There are, I see, two of them, which, however, take no notice of each other, even when passing close to each other ; the neck of SWAN-NECK AND ITS DIVISIONS. one is much longer than that of the other. Now and then, when gliding along, the neck is suddenly contracted, but not wholly, as if something had alarmed or displeased the animal ; the body also can be swollen or lengthened at pleasure ; it can move in either direction, but the neck usually goes foremost, extended in the direction of the motion, and seems to be used to explore the way. I had once an opportunity of seeing the process of increase by spontaneous self- division in this creature. It was an unusually large specimen, found in an old infusion of sage leaves. When I discovered it, it was darting about its long neck in the most beautiful contortions. As it was partly hidden by the vegetable fibre present, I INFUSORIA. 395 turned the glass cover so as to alter the position of the contents. On again looking, the Swan was in a clear part of the field, but in the form of a dark globose mass, the neck being entirely contracted. It was quite still, except a continual slight alteration of the form by the protrusion or contraction of parts of the outline. The body seemed full of minute globules, set in a granular mass of a blackish hue, and the outline was not a continuous line, but formed a multitude of rounded elevations. Presently it protruded the clear neck, but only for a short distance, and then retracted it as before ; when the only indication of the presence of this organ was a depression in one part of the surface, somewhat like the mouth of a closed Actinia, where there was a slight but incessant working, very much like the irregular motion on the surface of boiling water, in miniature ; there was also an indistinct ciliary action at this part, not of rotation, nor of vibration, but a sort of waving. At this point I had occasion to get up from the table, and though I was not away more than a minute, on my return I observed a strong constriction around the middle of the body. It was transverse, for the depressed and ciliated mouth was at a point exactly at right angles to the constriction. From the depth to which this latter extended in so few minutes, I supposed the process of separation would be very rapid ; for I could very soon see a line of light all across at intervals, and the two halves seemed to slide freely on each other. Yet they remained long without much apparent progress, or even change, except that the anterior half at one time threw forth its neck a short distance ; at this time it looked extremely like a bird, bridling up its lithe neck and swelling bosom ; while, to make the resemblance perfect, it began to imitate the action of a fowl picking up grain, bobbing its head hither and thither : so curious are the analogies of nature ! Along the dividing line there had appeared very early in the posterior half a distinct ciliary 396 EVENINGS AT THE MICROSCOPE. action ; after a while (how, I do not exactly know), with- out the general relation of position being changed, the mouth of the anterior (which must now be called the old) animal appeared on the side, and at the point corre- spondent in the other, a similar ciliary wreath appeared, while the action along the dividing line was no longer seen. So that the division which was at first transverse now appeared longitudinal. I believe, however, the ani- mals were really separated before this, though they re- mained in contact, for as they slid over each other it was manifest that each had an independent action. At length about an hour and a- half after the first appearance of the constriction, the new animal threw out its clear neck to a great length, writhing it about with rapid agility, and forming the most elegant curves, like those of a serpent, often completely encircling its own body with it. It still remained, however, in contact with its parent, which after a time also protruded its neck in the same manner. Both then retracted and remained still for a while ; and again, almost simultaneously threw out their long necks and then retired to sluggish repose. Among the sediment, the grains of which are driven hither and thither by their spasmodic, jerking movements, you see several individuals of another sort of creature, — the Chrysalis Animalcule ( Paramcecium aurelia). This is a “ Triton among minnows; ” for it is greatly larger than any of those we have yet observed, and is just visible to the naked eye, when we hold up the live -box obliquely against the light ; for then the animals appear as the smallest possible white specks. Bringing them again under the microscope, each pre- sents a pellucid appearance, and an oblong figure, of which the fore part is somewhat narrowed. The back rises in a rounded elevation, and the mouth is situated as far back as the middle of the body upon the under surface, where its position is marked by a sort of long fold, the sides of INFUSORIA. 897 which are fringed with long cilia, whose vibrations are very marked. The whole surface, on both sides, is covered with minute cilia, arranged in longitudinal rows, of which, according to the great Prussian professor, there are from thirty to sixty on each surface, each row bearing sixty or seventy cilia. This must be considered as an approxima- tion ; for we may well doubt the accuracy of the counting, when the objects are so very evanescent as these vibrating cilia. The vacuoles, and the temporary stomachs, more or less completely filled with the brown and green food, which the animals are collecting from the decayed vegetable matters, are sufficiently numerous and conspicuous ; but they may be rendered still more so by the device of mixing a little carmine with the water. The ciliary currents are thus instantaneously rendered strikingly visible. The crimson atoms are attracted from all quarters towards the tail of the animal, whence they are urged in a rapid stream along one side towards the head, around which they are hurled, and then down the other side to the tail, pouring off in a dense cloud in a direction contrary to that in which they origi- nally approached. But now the gathered currents have produced their ex- pected result ; for many of the globular vacuoles are already become of a beautiful rosy hue, from the minute particles of the pigment which have been whirled to the mouth, and swallowed. The feature of greatest interest, however, in this animal is the contractile bladder. Two of these organs are usually seen co-existent in each individual, placed, the one on the front, the other in the rear of the mouth, but near the opposite, — i.e., the dorsal , surface of the body ; for as the creature slowly revolves on its longitu- dinal axis, the line of the vesicles alternately approaches and recedes from that of the mouth. They are remarkable for their structure. Par from the simplicity in which the 398 EVENINGS AT THE MICKOSCOPE. organ is usually presented to us in the animals of this class, the contractile bladders are here very complex. Each when distended is globular ; and it is surrounded by a number of others of much smaller dimensions, and of a drop-like form, so set as to radiate around the principal vesicle as a centre, the rounded portion of each in apparent contact with the vesicle, and the slender extremity run- ning off as an attenuated point till lost to sight in the sarcode. The main vesicles alternately become distended, and suddenly contract to a point ; while the radiating cells are continually varying in size, though in a less degree. It is customary to describe the secondary vesicles as coming into view at the instant of the contraction of the primary PARAMCECIttM. one, and to suppose that the emptying of the one is the filling of the other, but I have not been able to observe this mutual relation satisfactorily made out. The smaller as well as the larger vesicles are conspicuous from their colourless transparency ; for the general sarcode of the body, though pellucid, is only so in the same degree as glass, slightly smoked ; besides that its clearness is often impaired by crowds of granules and minute globules. You ask what is that comparatively large oval body attached by its side to one of the leaves of the plant. It is the egg of some considerable Kotifer, probably Euchlanis , which is always glued to some filament or stem of a water- plant. It may interest you to watch the progress of the contained embryo, which you can readily do, since the egg- shell is as transparent as glass, and the infant animal already displays the movements of independent life. Mean- INFUSORIA. 399 while I will tell yon the tragical and lamentable history of just such an embryo as this, that was eaten up before it was born, under my own eye. One of the depredators was a very amusing animalcule, which is sufficiently scarce to make its occurrence a thing of interest, especially to a young microscopist, as I was at the time. A large egg of (as I believe) Euchlanis dilatata had been laid during the night on a leaf of Nitella, in the live-box. When I observed it, the transparency of the shell allowed the inclosed ani- mal to be seen with its viscera, which occasion- ally contracted and ex- panded ; the place of the mastax I could distinctly make out. The cilia were vibrating, not very ra- pidly, but constantly, on the front, where there was a vacant space between the animal and the shell. From seven a.m. when I first saw it, I watched it for about eight hours, without perceiving any change ; but at that hour having withdrawn for a short time, I perceived on my return that a portion of the animal was outside the shell. The appearance was that of a small colourless bladder oozing out at an imperceptible aperture ; and this oval vesicle quickly but gradually increased, until it was half as large as the egg itself. A little earlier than this point, the cilia were seen on the front or lower side of the excluded portion, and these began to wave languidly in a hooked form. They thus seemed much longer and more substantial than when rotating in the perfect animal. When excluded to the extent just named, some little crea- tures that were flitting about found it, and began to assemble round it. These were far too rapid in their COLEPS AND CHILOMONAS. 400 EVENINGS AT THE MICROSCOPE. movements to allow me to identify them before, or to per- ceive anything else than their swift motion and oval form ; but this attraction, causing them to become still, allowed me to perceive their singular and beautiful structure. Each consists of an oval vase open at the top, the margin of which is cut into a number of little points ; the sides are marked by a series of ribs, which run down longitudinally, and are crossed by other transverse ones; the rounded bottom is furnished with three short points, so that the whole reminded me of a barrel with its staves and hoops, set on a three-legged stool. Within the body, which is colourless, are seen small dark spots which are probably the stomach-vacuoles. Thus I identified these little barrels with Coleps hirtus of Ehrenberg, but I found no record of their carnivorous propensities. One after another whirled into the field, and after a few gyrations became stationary at the head of the half-born Euchlanis , just as I have seen vultures gather one by one to a carcase. "Very soon there were a dozen or fifteen of them, some of which were ever shifting their places, and some were playing around, or revolving on their longitudinal axes, I found that their object really was to prey on the soft parts of the creature just excluded from the egg ; for, by carefully watching one, I distinctly perceived particles of the flesh fly off, as it were, and disappear in the body of the Coleps. The appearance was that of steel filings drawn to a magnet, for the mouth of the Coleps was not in actual contact with the flesh ; and therefore, I suppose, the surface having been in some way ruptured (which I could see it was), the loose gelatinous atoms were sucked off by a strong ciliary cur- rent. They did not attack any other part, and after having continued their murderous occupation about ten minutes, they one by one departed. The ciliary motion of the Euchlanis ceased immediately after it was first attacked, and I suppose it was soon killed, for it did not increase in size in the least afterwards. When the Colepes left it, a INFUSORIA. 401 great portion, perhaps a third, of the excluded parts was devoured. As soon as the depredators were gone, or even before, others more diminutive, but more numerous, were ready to take their place. The drop of water under review had been found amazingly full of a small oval Monas, perfectly transparent, of an oval form, with some granules visible in the interior. They were about 2Wo^ an inc^ in length. They filled the whole field, gliding about very nimbly, but so close as but just to allow space for motion, and that in several strata. By the morning these were collected in masses, which to the naked eye looked like little undefined white clouds, but which under the microscope showed the Monads in incalculable multitudes, but for the most part in still repose. Some were seen moving to and fro, how- ever, and, in the course of the day, most of them became again active. As soon as the Colepes had forsaken their prey, the Monads began to gather round it, cleaving to the same parts, and apparently imbibing the juices, for the extruded parts still slowly decreased, until at length these were reduced to about one -third of their original di- mensions. A close examination of these latter when they had settled to rest showed me that they were of the species Chilomonas paramcecium* There is an indentation on one side of the front where the mouth is situated : here there is a ciliary action ; the projecting part, called the lip, is said to be furnished with two slender flexible proboscides, but my power was not sufficient to discern any trace of these. A sort of a ridge, or keel, runs down the length of the body, perceptible by a slight line ; numbers of stomach- cells also are perceptible. The motion of these lip-monads was not very rapid when unexcited ; it is performed by a sort of lateral half-roll, the two sides alternately being turned up, like a boat broadside to a swell, and the line of progression is undulating. D D 402 EVENINGS AT THE MICROSCOPE. And now, having pretty well exhausted the contents of this live-box, let us try a dip from this other phial from another locality, equally productive, if I am not mistaken. Yes ; for, to begin, the stalks of Nitella here are fringed with populous colonies of the most attractive of all the Infusoria, the beautiful Vorticella. The species is not the common bell-shaped one, but the smaller with pursed mouth, the little V. microstoma. Look at this active group, Consisting of a dozen or so of glassy vases, shaped something like pears, or elegant VORTICELLJE antique urns, elevated on the extremities of long and very slender stalks, as slender as threads, and about six times as long as the vases. The stalks grow from the midst of the floccose rubbish attached to the plant, and diverge as they ascend, thus carrying their lovely bells clear of one another. Each vase is elegantly ventricose, or swollen, in the INFUSORIA. 403 middle, terminating below in a kind of nipple to which the stalk is attached, and above in a short wide neck with a thickened rim. This last is highly sensitive and con- tractile ; its inner edge is set round with a circle of vibratile cilia, which, when in full play, produce a pair of small circular whirlpools over two opposite points of the brim. The cilia themselves cannot be distinguished, but their optical expression is curious. At the two opposite points of the circular margin, as seen in perspective when slightly inclined towards the observer, viz., at those points where the cilia, from their position with regard to the eye, would be crowded together, there are seen two dark dashes, representing, doubtless, two ciliary waves, but which have all the appearance of tangible objects, some- times withdrawn, sometimes protruded, and often vibrated with a rapid snatching movement. These vases are of the usual appearance in Infusoria. Their substance is the clear transparent colourless sarcode, but it contains within it more or less of the cloudy nebulous matter which we have been lately familiar with. There are several globular vesicles or vacuoles, some ready to imbibe colour from pigment, and others already occupied with brown food; while in each case we see, near the centre of the vase, a longish body of clear granular texture, which is called the nucleus, and which seems to play an essential part in the vital economy of the animal. The movements of a group such as that we are looking at are very sprightly and pleasing. The vases turned in all directions, some presenting their mouths, some their sides, some their bases, to the eye ; inclined at various angles from the perpendicular, and bending in diverse degrees upon the extremity of their stalks ; swaying slowly and gracefully to and fro, as driven hither and thither by the ciliary currents ; and, above all, ever flying up and down within the length of their radius, as a bird when confined by a string ; — all these circumstances impart a dd2 404 EVENINGS AT THE MICROSCOPE. charm to this elegant animalcule, which enables us to look long at it without weariness. This last movement is peculiar, and worthy of a moment’s closer examination. The stalk, when extended to the utmost, is an elastic glassy thread, nearly straight, like a wire, but never so absolutely straight as not to show slight undulations. The stalk, when thus drawn tight, is highly sensitive to vibrations in the surrounding medium ; and as in the circumstances in which we observe the animals, such vibrations must be every instant communi- cated to the vessel in which they are confined, the stalks are no sooner fully extended than they contract with alarm. This depends on a contractile cord which passes throughout the entire length of the stalk, and which is distinctly visible in the larger species as a narrow band. We can scarcely err in considering this ribbon as a rudimentary condition of muscle, though we do not recognise in it some of the characteristic conditions which we are accustomed to see in it in higher animals. The contraction of the muscle is very sudden, energetic, and complete. With a rapidity which the eye cannot follow, the vase is brought down almost to the very base of the stalk. Then it slowly rises again ; and now we see, what we could not discern in the act of contraction itself, that in that act the stalk was thrown into an elegant spiral of many turns, which at the utmost point of contraction were packed close on each other, but which in the extending act gradually separate, and at length straighten their curves. In any stage of the extension, the sudden contact of the vase with any floating or fixed object apparently causes alarm, and induces the vigorous contraction ; but vibra- tions, even when so violent as those produced by tapping the stage of the microscope with the finger-nail, have no effect unless the stalk be tense, its own power of vibration being then only developed, just as a cord becomes musical in proportion to its tension. INFUSORIA. 405 It is not until we view these creatures with a good microscope that we acquire an adequate idea of their beauty ; for myself, at least, it was so. I had seen en- gravings of many of the invisible animalcules, and had read technical descriptions ; but of their brilliant transpa- rency, their sudden and sprightly motions, their general elegance and delicacy, and the apparent intelligence with which they are endowed, neither books nor engravings had given me any conception. Some of the individuals under our present examination are exhibiting phenomena of no less interest than their form and motionSi Some of the stalks are terminated by two vases instead of one, which appear to spring from a common point. These, however, are the result of the spontaneous splitting of one ; and in other examples you may see the process in different stages ; or, if your patience endure a couple of hours’ watching, you may trace the whole phenomena, as I have done, from the moment when it first becomes perceptible, to its completion in the free- dom of one of the newly-formed animalcules. For instance, you perceive that one of the bells instead of being vase-shaped has assumed a globular form. By keeping your eye on this for only a few moments, you de- tect a depression forming in the midst of its front outline, which momentarily deepens, until it is manifestly a cleft. The division proceeds downwards, the two halves healing simultaneously, so that they are at all times perfectly smooth and rounded ; at length two vases appear, side by side, where a few minutes before there had been but one. One of these is destined to be ultimately thrown off, while the other retains sole possession of the stalk. You soon see which it is that is going to emigrate : for, though the two are alike in size, the roving one early closes the mouth of the vase, becoming smooth and globular there, never to open again. The cilia, now therefore become useless, disappear by absorption ; but meanwhile a new 406 EVENINGS AT THE MICROSCOPE. circle of these organs is developed around the basal ex- tremity of the vase, and these, every instant becoming more vigorous in their motions, sway the little globe about on its point of attachment. At length the connexion yields, breaks, and the animalcule shoots away, rowed by its hundred oars, to find a new abode, and to found a new colony. Here and there you see shooting through the group, with a rapid gliding movement, an oblong clear body. This is one of the vases, formed by self- division, and exer- cising its newly found power of locomotion. It is giddily roving hither and thither, until the instinct of wandering ceases, when it will soberly settle down, affix itself by the point which was formerly its mouth, whence a new stalk will gradually grow, and opening a new mouth in the midst of the new crown of cilia. I believe that the division is sometimes transverse in- stead of longitudinal, the cleft occurring by constriction across the middle of the vase ; but this I have not seen. In whatever direction it takes place, it is essential that the oblong granular body, called the nucleus, which you see in each vase, be divided, the cleft passing through the middle of this substance, a portion of which is therefore appro- priated to each new-made animal. That the essential vitality of the creature resides in this nucleus is shown by another and highly curious mode of increase, namely, that which is effected by encystion. Let us search the live-box carefully; for, amidst so great a pro- fusion of Vorticella as we have on this Nitella , it will go hard if we do not find some individuals in the encysted stage. Look at this elegant object. It resembles a trumpet of the clearest glass, with a rounded extremity, and with the base affixed to the weed, from which it stands up erect. Within the expanded part of the trumpet there is a turbid mass, with a perfectly defined outline, from several points INFUSORIA. 407 of which proceed radiating pencils or tufts of long, straight, stiff, elastic filaments, like threads of spun glass, varying greatly in length, and each terminated by a little knob of the same material. The tout ensemble of this object is very attractive and beautiful, and its history is a tale of marvels. No wonder that Ehrenberg, supposing this form to be an independent animal, gave it a generic and specific name. He called it Acineta mystacina. For who would have sus- pected that this stiff and motionless object, with its tufts of 408 EVENINGS AT THE MICROSCOPE. flexible but inanimate threads, had any connexion with the sprightly vases which we have been examining ? Yet it is the same animalcule, in what we may, with a certain liberty of phrase, call its chrysalis condition ! The history of the Vorticella , as it has been elaborately worked out by Dr. Stein, exhibits phenomena analogous to those marvellous changes which we lately considered under the appellation of the Alternation of Generations. Large individuals withdraw their circle of cilia, close up the mouth, and become globular, and then secrete from their whole surface a gummy substance, which hardens into a spherical transparent shell called a cyst, inclosing the Vorticella in its cavity. Within this cyst is seen the hand- shaped nucleus, unchanged, and what was the contractile bladder, which, however, no longer contracts. By-and-by this torpid Vorticella enlarges itself irregularly, pushing out its substance in tufts of threads, and frequently protruding from one side a larger mass, which becomes an adhering stalk. Thus it has become an Acineta , such as we now behold. From this condition two widely different results may proceed. In the one case, the encysted Vorticella sepa- rates itself from the walls of the Acineta , contracts into an oval body, furnished at one end with a circle of vibratory cilia, by whose movements it rotates vigorously in its prison, while the more obtuse end is perforated by a mouth leading into an internal cavity. In the interior of this active oval body there are seen the band-like nucleus, and a cavity which has again begun to contract and to expand at regular intervals. It is, in fact, in every respect like a Vorticella vase, which has just freed itself from its stalk. Presently, the perpetual ciliary action so far thins away the walls of the Acineta that they burst at some point or other, and the little Vorticella breaks out of prison, and com- mences life afresh. The Acineta, meanwhile, soon heals its wound, and after a while develops a new nucleus, which INFUSORIA. 409 passes through the same stages as I have described, and bursts out, a second Vorticella . But the cycle of changes may be quite different from this. For sometimes the nucleus within the Acineta , in- stead of forming a Vorticella , breaks itself up into a great number of tiny clear bodies, resembling Monads, which soon acquire independent motion, and glide rapidly about the cell formed by the inclosed Vorticella-bo&y as in a little sea. But, by-and-by, this body, together with the Acineta wall, suddenly bursts, and the whole group of Monad-like embryos are shot out, to the number of thirty or upwards. The Acineta now collapses and disappears, having done its office, while the embryos shoot hither and thither in newly acquired freedom. It is assumed, on pretty good grounds, that these embryos soon become fixed, develop stalks, which are at first not contractile, and gradually grow into perfect Vorticellce , small at the beginning, but capable of self-division, and of passing into the Acineta stage, and gradually attaining the full size of the race. Some forms of the same family, Vorticelladce , are inter- esting as dwelling in beautiful crystalline houses, of various shapes, always elegant. All these have been ascertained to pass through the same or similar Acineta stages. Co- thurnia imberbis is one of the prettiest of these. The cell is of an elegant ampulla-like form, perfectly transparent and colourless, set on a stiff foot, or short pedicle, which shows many transverse folds, like those of leather. From the mouth of the vase projects the animal, whose form may be distinctly traced through the clear walls of the cell attached to its bottom, whence it stretches upward when seeking prey, or to which it shrinks when alarmed. In the former condition the body resembles a much elongated Vorticella , with a similar circular orifice, set round with cilia. Often the animal performs its ciliary vibrations within the shelter of its house, not venturing to 410 EVENINGS AT THE MICROSCOPE. protrude beyond its rim. If carmine has been mixed with the water, the atoms are seen in the customary vortex, and some are occasionally drawn into the cell nearly half-way down its cavity, and then swiftly driven out again. On a slight tap upon the table the animal withdraws, and in the same moment the urn bends down upon its leathery pedicle, at a point where there is always an angle, until the rim of the cell is in contact with the plant to which it is attached. This action is instantaneous. Presently, however, it rises, and resumes its former position, and then the mouth of the cell slowly opens, and the animal again protrudes, the cilia appearing first, and finally the head or front part of the animal, which is then opened and begins to rotate. Very similar to this are the Vaginicolce, but the cells which they inhabit are not stalked, but are immovably affixed to plants. In V. crystallina, the cell is a tall gob- let, standing erect, perfectly colourless ; while in V. de- cumbens, it is slipper-shaped, attached along its sides, and of a golden-brown hue, but still quite transparent. Here is, fortunately, a group of the latter species, scattered about the leaves of the Nitella. Though, in general, both in form and habits, closely like the Cothui'nia, yet the Vaginicola has some peculia- INFUSORIA. 411 rities of interest. The cilia are more developed, and can be more distinctly seen than in either Cothurnia or Vorticella, forming, when in swift action, a filmy ring above the margin, along which, as if upon a wheel, one or more dark points are frequently seen to run swiftly round : the optical expression, as I presume, of a momentary slackening in the speed of the wave. The act of self-division takes place in this animal, as in the Vorticella ; and it is curious to see two Vaginicolce, exactly alike, lovingly inhabiting the same cell. One of the cells which we are now examining is in this doubly-tenanted condition. I will now exhibit to you some examples of the most highly organised forms of this class of animals, in which we discern a marked superiority over any that we have yet looked at, and a distinct approach to those animals whose more precise movements are performed by means of special limbs. These creatures are very common, both in fresh and sea-water, wherever vegetable matter is in process of decomposition ; and hence their presence can at all times be commanded by keeping infusions. In this old infusion of sage leaves, for instance, they occur in vast multitudes, past all imagination ; as you may see with a lens in this drop. This group belongs to the genus Stylonychia, and as I believe, to the species 8, pustnlata . It presents the form of an oval disk, which, when seen sidewise, is found to be flat beneath and convex above. It commonly swims with the belly upwards, and, when exhibited on the stage of the microscope, in almost every case, this surface is pre- sented to the eye. It darts about very irregularly, with a bobbing motion, rarely going far in one direction, but shooting a little distance, and then instantly receding, turning short round, and starting hither and thither, so fitfully that it is very difficult to obtain a fair sight of its structure. Its margin, however, is surrounded by short 412 EVENINGS AT THE MICROSCOPE. cilia; the mouth, which is a long opening on the front part, and at the left side (as to the animal) of the ventral surface, is fringed with long cilia, which are continually vibrating. These are the organs of the darting motion ; but the creature crawls like a mouse, along the stems of conferva , &c., which it performs by means of curved spines, called uncini, near the front part, the points of which are applied to the stem, and also by long stiff styles or bristles, which project backward and downward from the hinder part. Sometimes the animalcules crawl for a moment back-downward, on the inner surface of the glass cover, when the bases of the anterior curved spines appear dilated like large spots. The spines are not capable of much action, but they are rapidly used. The general appearance of the creature reminds us of the little Wood- louse or Armadillo of our gardens. The interior of the body is occupied with a granular substance, in which are scattered many globular vesicles of different sizes. The animal is very transparent, and almost colourless. They increase very fast by transverse division, which is per- formed under the microscope, so as greatly to increase the number under examination, even in an hour or two. A constriction forms in the middle of one, which quickly deepens, dividing the oblong creature into two of circular figure. The mouth of the new one, with its vibratile cilia, is formed long before separation is complete, and at the same end and side as in the parent. The styles and bris- tles then form, and the creatures are held together for a few seconds by these organs, even when the bodies are distinctly severed. When separated, they retain the round form for some time. When a drop of such water is examined between two plates of glass, it is amusing to observe the numbers that congregate in the little pools left by the gradual drying of the fluid. This probably becomes unfit for respiration ; for the motion of the cilia becomes more and more languid, INFUSORIA. 413 and the creatures die before the water is dry. They not only die, hut vanish , so that, — where there were scores, so close that in moving they indented each other’s sides and crawled over one another, — if we look away for a few minutes, and again look, we see nothing but a few loose granules. This puzzled me, till I watched some dying, and I found that each one burst and, as it were, dissolved. The cilia moved up to the very last moment, especially the strong ones in front, until, from some point in the outline, the edge became invisible, and immediately the animal became shapeless, and from the part which had dissolved the interior parts seemed to escape, or rather the skin, so to speak, seemed to dissolve, leaving only the loose viscera. From the midst of these then pressed, as if by the force of an elastic fluid within, several vesicles of a pearly appear- ance, varying in number and size, and then the whole be- came evanescent. You will have observed that the admixture of carmine to the water, while the animalcules were active, shows the direction of the ciliary motion with great distinctness. The particles form two eddies, one on each side of the front, which meet in the centre in a strong current, and pass off behind the mouth on each side. We do not per- ceive that any of them swallow the particles of carmine, for the internal vessels remain colourless. I have found that if a drop of water containing these animals be placed on a slip of glass exposed to the open air, they do not burst as the water dries away, but dry flat on the glass, their bodies broader but shorter than when alive, and quite entire. Their cilia are then very manifest. On being again wetted, though after only a few minutes’ desiccation, I have never been able to revive them, nor any other Infusoria in like circumstances, notwith- standing what is stated in books. Here is another species in equally amazing profusion, S. mytilus. Its form is oblong, with rounded extremities, 414 EVENINGS AT THE MICROSCOPE. the anterior obliquely dilated. This species affords a good example of the various organs of locomotion. A trans- parent oblong shield, which is quite soft and flexible, is spread over the back, which does not prevent our eyes discerning all the organs through it ; though, much more commonly, the animal, when under the microscope, crawls, belly-upward, beneath the glass cover of the live-box. Around the anterior part, which is broadened, are placed cilia, which are vibratile ; these are continued round the mouth, a sort of fold on the side. Towards the posterior extremity on each side are other rows of cilia, which being large are well displayed. On the ventral surface, chiefly towards the front part, are seen several thick pointed processes, shaped like the prickles of a rose, but flexible, and capable of being turned every way. These are the uncini, and are evidently used as feet, the tips being applied to the glass. The optical effect of the throwing about of these uncini , when the place which they touch is in focus, is very curious. They are rapidly moved, but without regularity ; the tips bend as they touch the surface of the glass ; some of them seem to have accessary hairs, equally long, but slender, proceeding from the same base. On the hinder quarter of the ventral surface are several thick pointed spines ; these are inflexible, nearly straight, placed side by side, but not in regular order, some reaching beyond others. I have not seen these used, but they commonly remain sticking out in a horizontal direction. These organs are termed styles . Besides these, there are three slender bristles, called setcet placed at the hinder extremity, the central one in the line of the body, the others radiating at an angle. These are dis- tinguished from the cilia, not only by their length, but by not being vibratile. The motions of these animals are powerful, but irregular and fitful, very much like those of the former species. They dart hither and thither, back- ward as well as forward, occasionally shooting round and INFUSORIA. 415 round in a circle, with many gyrations, much like the pretty little polished beetles ( Gyrinus ) that play in mazy dances on the surface of a pool. The two extremities seem covered with minute pits or stipplings, but colourless ; the central part is occupied with yellowish granules of different sizes. I once witnessed the dissolution of one of these animals under peculiar circumstances. Two or three stems of an aquatic plant had become crossed in the live-box so as to form an area, into which the Stylonychia had somehow introduced himself. There was just room for him to move backward and forward without turning, and the space was about three times his own length. Within this narrow limit he impatiently continued crawling to and fro, moving his uncini with great rapidity, and showing their extreme flexibility; for, as he applied them now to the stem, now to the surface of the glass, these whip -like uncini were sometimes bent double. The so-called styles at the posterior extremity, though less frequently used so, were yet occasionally bent and applied to the surface as feet, so that they are certainly not inflexible as supposed, nor do I see any essential difference between them and the uncini. The whole body was flexible, taking the form of any passage or nook into which it was thrust, yet recovering its elasticity immediately the pressure was removed. Its proper form appeared to be convex above and concave beneath, rather than flat. After having been thus employed about half-an-hour under my observation, it became still, moving only its cilia, when I left it a little while, and on my return found that it was dissolved ; the outline having entirely disappeared, and nothing being left but the granules, and globular vesicles, that had constituted its viscera, some of which still contained the carmine which had been very perceptible in the living animal. This was the more remarkable, as there was plenty of water. It looked like suicide, — a spontaneous choosing of death rather than hopeless captivity. 416 EVENINGS AT THE MICEOSCOPE. Common as these Stylonychia are, and abundant beyond all calculation, where they do occur, from their tendency to self-division, they are not so universally met with as their cousins, of the genus Euplotes. These are still more highly organised, and will please you by their ac- tivity and sprightly intelligence, I am sure. Here are several individuals in the live -box at this moment. They differ from the Stylonychice, in having the soft body covered with a plate of crystal mail, hard and in- flexible, much like the shield of a Tortoise. Several species have this glassy shield marked with delicate lines running lengthwise ; sometimes in the form of parallel ridges, as in a little species found in infusions (perhaps E. charon), at others forming rows of minute round knobs, as E. truncatus, the species now before us. The shield is ample, considerably overlapping the soft body ; it rises into an arched form in the centre ; and is more or less round or oval. The mouth is oblique, and extends a long way down the under surface ; it is set with strong and fine cilia, which also spread over the front. The organs of motion are, as before, long styles, pointed and rather stiff pro- cesses, which project from beneath the shell backwards and downwards, and soft hook-like uncini, which are set chiefly near the fore part of the inferior surface. In the species before us these are about six or seven in number, but in E. charon they are more numerous. The twinkling rapidity with which these little feet are applied to the surface in crawling affords a pleasing sight : particularly when the animal is running back- downwards on the upper glass plate of the live-box. Some species have bristles INFUSORIA. 417 (or setce) affixed to the hinder part of the shell, from which they diverge. In E. truncatus these are four, but they ^re wanting in E. char on. The body displays a mass of granules, vacuoles, and vesicles of different sizes. These are very beautiful objects ; and their sprightly motions and apparent intelligence give them an additional interest. They crawl more than they swim, running with great swiftness hither and thither, frequently taking short starts, and suddenly stopping. The specimens which we are examining are taken from water which had been kept in a jar for several weeks. The vegetable matters are decaying, and among the stems and filaments this prefty species crawls and dodges about. It seems reluctant to leave the shelter of the decaying solution ; sometimes one will creep out a little way into the open water ; but in an instant it darts back, and settles in among the stems and flocculent matter. Any attempt by turning the glass cover to bring it out into view only makes it dive deeper into the mass, as if seeking concealment. This is about g-J-^th °f an inch in length of lorica ; and the E. charon is not more than one-fourth of this size. These creatures remind one of an Oniscus, especially when in profile. There is an animal very closely allied to these, but much more beautiful, being of a clear greenish translucency, with several vesicles filled with a rose-coloured or purple fluid of much brilliancy. This creature, which bears the name of Chlamidodon, has the peculiarity of a set of wand- like teeth arranged in a hollow cylinder. And with these we dismiss the Infusoria, a class of animals which, from their minuteness, the number and variety of their species, their exceeding abundance, the readiness with which they may be procured, and, as it were, made to our hand (by simply steeping vegetable matter in water), and the uncertainty which still prevails as to many parts of their structure and economy ; and E E 418 EVENINGS AT THE MICROSCOPE. therefore, as to their true affinities in the great plan of creation, — offer one of the most promising fields of research which a young microscopist could cultivate. These are Thy glorious works, Parent of good, Almighty ; Thine this universal frame, Thus wondrous fair. Thyself how wondrous then I Unspeakable, Who sitt’st above these heav’ns, To us invisible, or dimly seen In these Thy lowest works ; yet these declare Thy goodness beyond thought, and power divine. THE END. INDEX Acineta, 407. Acontia, 356. Air-tubes of Fly, 95. Alcyonium, 349. Alternation of Generations, 324, 333. Amoeba, 378. Anchors of Synapta, 299. Animalcules, 389. Antennae of Chafer, 162. Crab, 171. Fly, 166. Gnat, 166. Insects, 158. Moths, 163. Skipjack, 163. Weevil, 160, Aphrodite, 263. Arcella, 383. Barnacles, 192. hand of, 192. Transformations of, 195. Bee, eyes of, 170. foot of, 119. mouth of, 142. sting of, 125. wing of, 73. Beetle, mouth of, 138. “ Bird’s-head,” 64. use of, 68. Blood of Beasts, 27. Birds, 28. Fishes, 28. Frog, 29. Man, 27. Reptiles, 28. Tunicate, 33. Brachionus, 225. Bristle-tail, scales of, 77. Bug, mouth of, 143. Bugula, 64. Butterfly, scales of, 79, 80. sucker of, 153. Caryophyllia, weapons of, 364. Chameleon-fly, 101. Cheese-mite, 220. Chilomonas, 401. Chirodota, 298. Cicada, drum of, 89. ovipositor of, 136. Cilia of Cydippe, 310. Infusoria, 397, 403, 409. Rotifera, 223, 252. Cinclides, 358. Cnidae, 342, 356. Cockchafer, antennae of, 162. spiracle of, 100. Coleps, 399. Contractile Bladder, 250, 380, 397. Corkscrew Coralline, 63. Corynactis, weapons of, 369. Cothumia, 409. Cows’ paps, 349. Crabs, 171. ears of, 172. eyes of, 174. stages of, 182. Crane-fly, spiracle of, 99. Craspeda, 364. Cricket, drum of, 85. Cuckoo-fly, ovipositor of, 128. Cuttle-shell, 39. Cyclops, 175. Cydippe, 308. Cypris, 180. Daphnia, 178. 420 INDEX, Dead-men’s fingers, 349. Diamond-beetle, scales of, 83. Dragon-fly, 71. eye of, 166. Dumb-bells of Holothuria, 297. Dyticus, foot of, 117. Earthworm, 259. Ecthoraeum, 366. Egger-moth, 163. Euglena, 389. Eunice, 268. Euplotes, 416. Eyes of Crab, 174. Dragon-fly, 166. Harvestman, 209. Infusoria, 389. Insects, 166. Rotifera, 236, 389. Scallop, 50. Snail, 54. Spider, 207. Eeathers, structure of, 15. Eission of Infusoria, 394, 405. Flea, mouth of, 146. Fly, antenna of, 166. flight of, 70. foot of, 115. spiracle of, 98. tongue of, 151. wing of, 72. Foot of Actinurus, 249. Bee, 119. Beetle, 117. Brachion, 227. Dinocharis,-241. Fly, 109. Silkworm, 123. Spider, 217. Whiptail, 239. Foraminrfera, 383. Frog, blood of, 31. Froghopper, ovipositor of, 135. G-alathea, 186. Gall-fly, egg-tube of, 128. Gnat, antennae of, 166. grub of, 103. mouth of, 149. wing of, 74. Grantia, 386, 388. Grasshopper, sounds of, 86. Hair of Bat, 12. Bee, 14. Beetle, 14. Hair of Cat, 8. Hog, 5. Horse, 7. Man, 2. Mole, 9 Moth, 14. Mouse, 11. Sable, 9. Sheep, 7. Halichondria, 386. Harvestman, 209. Heart-urchin, 292. Horse-fly, mouth of, 145. House-fly, 70. Humble bee, 71. Hydractinia, 334. Infusoria, 389. Insects, 70. air-tubes of, 93. antennae of, 158. eyes of, 166. feet of, 109. mouths of, 138. sounds of, 84. stings, &c., of, 125. Jelly-fish, 307. Katedid, 86. Laomedea, 326. medusoids of, 331. Lares, 345. Larva of Urchin, 301. Leech, 269. Limpet, tongue of, 46. Locomotion, variety in, 258. Lombrinereis, 268. Luminosity of Medusa, 319. Lynceus, 177. Madrepore, weapons of, 364. Mastax, 233. Medusae, 307. transformations of, 333. Medusoids, of Laomedea, 331. Stauridia, 343. Megalopa, 182. Mite, cheese, 220, water, 222. Mollusca, ears of, 55. eyes of, 51. shells of, 39. tentacles of, 50. tongues of, 46. Moths, antennae of, 163. INDEX. 421 Moths, scales of, 79, 81. Mouth of Bee, 142. Beetle, 138. Brachion, 230. Bug, 143. Flea, 146. Gnat, 148. House-fly, 151. Sea-worm, 267. Swordbearer, 246. Tube- wheel, 251. Whiptail, 238. Murder, discovery of, 25. Nacre, 43. Nais, 262. Nucleus of Infusoria, 406. Nymphon, 218. Otolithes of Medusae, 320. Slug, 56. Ovipositor of Cuckoo-fly, 128. Gall-fly, 128. Saw-fly, 131. Paramcecium, 396. Pearls, 44. Pedicellariae, 282. structure of, 282. use of, 288. Periwinkle, eating of, 49. tongue of, 50. Perophora, circulation in, 34. respiration in, 36. Phyllodoce, 265. Pleasures of Sea-shore, 325. Podura, scales of, 78. Polymorphina, 383. Polynoe, 262. Polypes of Alcyonium, 350. Hydractinia, 334. Laomedea, 326. Lar, 348. Polystomella, 383. Polyzoa, 60. Proteus, 378. Protozoa, 376. Pseudopodia, 384. Robber, story of, 2. Rotifera, 223. Sabella, 343. Sagartia, 356, 366. Sarsia, 313. Saw-fly, ovipositor of, 130. Scales of Butterflies, 79. Bristle-tail, 77. Diamond- beetle, 83. Flounder, 21. Gnat, 75. Gold-fish, 19, 24. Perch, 17. Pike, 23. Podura, 78. Sugar-louse, 77. Wrasse, 21. Scallop, eyes of, 50. Sea-anemones, weapons of, 315. Sea-cucumber, 296. dumb-bells of, 297. Sea-mat, 59. Sea-mouse, bristles of, 264. Sea-shore, pleasures of, 325. Sea-urchin, spines of, 277. larvae, 301. pedicellariae, 282. pores, 290. skeleton, 302. suckers, 305. Serpula, 271. Shell of Cuttle, 39. Pearl-oyster, 42. Pinna, 42. Shore-crab, 182. Silkworm, foot of, 123. spinner of, 157. Skeleton Wheel-bearer, 241. Slug, ears of, 55. tongue of, 46. Snail, eye of, 54. Spicula of Alcyonium, 352. Chirodota, 299. Fish-scales, 24. Holothuria, 298. Sponges, 385. Synapta, 299. Spiders, eyes of, 207. fangs of, 205. foot of, 217. habits of, 210. silk of, 211. spinner of, 213. Spines of Heart-urchin, 292. Sea-urchin, 277. Spinner of Silkworm, 157. Spider, 213. Spiracles of Insects, 97, 106. Sponges, spicula of, 386. Stauridia, 340. Sting of Bee, 125. 422 INDEX. Stylonychia, 411. Suckers of Sea-cucumber, 296. Sea-urchin, 288. Sugar-louse, 77. Swan-neck, 393. Sword-bearer, 246. Synapta, 299. Tentacle of Cydippe, 309. Hydractinia, 339. Laomedea, 329. Scallop, 50. Thaumantias, 319. Thaumantias, 319. Tongue of Butterfly, 154. My, 151. Limpet, 46. Periwinkle, 46. Slug, 46. Trochus, 47. Trachelocerca, 393. Transformations of Barnacle, 195. Crab, 182. Galathea, 188. Medusa, 323. Polype, 324. Sea-urchin, 301. Tube- wheel, 256. Vorticella, 408. Tripod Wheel-bearer, 248. Trochus, tongue of, 47. Tube- wheel, 251, Turris, 321. Urchin, Sea, 276. Vacuoles, 381. Vaginicola, 410. Vorticella, 402. Water-fleas, 175. Weapons of Anemones, 355. Corynactis, 369. Madrepore, 364. Sea-worms, 262. Weevil, 160. Scales of, 83. Wheel-bearers, 223. Wheels of Brachionus, 226. Chirodota, 298. Whiptail, 238. Wing of Bee, 73. 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