EVENINGS AT THE MICROSCOPE. E V E N I N G S AT THIE MICROSCOPE; ol, RESEARCHES AMONG THE MINUTER ORGANS AND FORMS OF ANIMAL LIFE. lBY PHILIP HENRY GOSSE, F.R.S. NEW YORK: D. APPLETON AND COMPANY, 443 & 445 BROADWAY. 1860. PREFA CE. 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 Microscope, 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 be 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 that 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 but 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 Vi PREFACE. 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 observations here detailed, will be no longer a tyro in microscopic science, and will be well prepared to extend his 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 caime under his notice, he found, in endeavouring to reproduce and verify published 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 observations 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 1had confidence, and which were germane to his pur PREFA:CE. Vii pose Yet in allnost 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 conveqsraziones, or microscopical soirees, in which the author is supposed to act as the provider of scientific entertainment and instruction to a circle of friends. It is proper to add, however, that the precision essential 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 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. Viii PREFACE. 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, 54, 112, 114 (the lower figures), and 175, have been copied, under the courteous permission of the publisher, from Dr. Carpenter's valuable work, " The Microscope, and its Revelations." (Churchill, London.) LIST OF ILLUSTRATIONS. HUMAN HAIR..................................................... 3 HOG'S BRISTLE.........................................,....................... 6 FIBRE OF SHEEP'S WOOL.................................................. 8 HAIR OF CAT......................................................... 9 HAIRS OF MOLE.............,............................................. 9 HAIR OF SABLE............................................................ 10 HAIR OF MOUSE...................................... 11 TIP OF SMALL HAIR OF MOUSE............................................... 11 HAIR O BAT.................................................................. 11 HAIR OF INDIAN BAT................................ 12 TIP OF HAIR OF DERMESTES............................................... 15 BARB OF CLOTHING FEATHER OF FOWL.................................... 16 BARB FROM GOOSE-QUILL....................................................... 17 SCALES OF PERCH..................................... 19 SCALES OF GOLDFISH................................................. 21 SCALE OF FLOUNDER........................................... 23 SCALES OF PIKE..................................................... 24 SPICULA OF GOLDFISH SCALE.................................................. 25 BLOOD DISKS...................................................................... 31 CIRCULATION IN FROG'S FOOT................................................. 35 PEROPHORA.............3............,.............. 36 CUTTLE-SHELL.................................................................... 45 SECTION OF TACRE FROM PEARL OYSTER................................. 48 TONGUE OF TROCHUS............................................................ 54 STRUCTURE OF EYE IN SNAIL..................6............................ 62 LEAFY SEA-MAT...........,........,...........,....... 70 DOUBLING AND HooKs IN A BEE'S WING.,,............................. 83 X LIST OF ILLUSTRATIONS. SCALES ON A GNAT'S WING................................................. 84 BRISTLE-TAIL......................................................... 85 SCALE OF BRISTLE-TAIL....................................................... 86 BATTLEDOOR-SCALE OF POLYOMMATUS ALEXIS.............................. 89 FRINGED SCALE OF PIERIS............................................... 91 SCALES OF DIAMOND-BEETLE..............93...................... 93 AIR-PIPE OF FLY........................................................ 109 SPIRACLE OF FLY......................................................, 112 SPIRACLE OF LEATHER-COAT..................................... 114 SPIRACLE OF COCKCHAFER-GRUB......................................... 114 GRUB OF CHAMELEON FLY......................................... 117 FOOT OF FLY...................................................................... 132 FOOT OF WATER-BEETLE.................................. 134: STING OF BEE.................................... 144 GALL-FLY, AND MECHANISM OF OVIPOSITOR.............................. 146 OUTER SAW OF SAW-FLY............................................... 153 INNER SAW OF SAW-FLY................................................. 154 MOUTH OF BEETLE............................................... 162 MAXILLA AND LOWER LIP OF BEE.................................. 164 LANCETS OF FEMALE GNAT.................................................. 173 TONGUE OF BLOW-FLY................................................ 175 SUCKER OF BUTTERFLY....................................... 180 ANTENNA OF COCKCIIAFER.................................... 187 PORTION OF ANTENNA OF OAK EGGER MOTH1.............................. 190 EAR OF CRAB............................................................. 199 DAPHNIA.................................................... 207 CYPRIS................:........................ 209 CYPRIS..; 209 ZOEA OF SHORE-CRAB............................................ 212 SECOND STAGE OF SHORE-CRAB.............................................. 214 THIRD STAGE OF SHORE-CRAB............................................... 216 ADULT SHORE-CRAB........................................ 217 HAND OF BARNACLE............................................................. 224 YOUNG OF BARNACLE........................................................... 228 FANG OF SPIDER................................................... 238 EYES OF SPIDER.......................................................... 239 CLAWS OF SPIDER............................................... 250 HEAD OF CHEESE-MITE.............................. 255 BRACHIONUS....................................................................... 267 MOUTH OF BRACHIONUS................................................... 270 WHIPTAIL...................2.................................,, 275 SKELETON WHEEL-BEARER...................................................... 279 LIST OF ILLUSTRATIONS. Xi PAGE SWORD-BEARER.................................................................. 285 TRIPOD WHEEL-BEARER..................................................... 286 TWO-LIPPED TUBE-WHEEL..................................................... 290 AVHIEELS OF TUBE-WHEEL.......................... 291 FOOT OF NAIS.................................... 301 THROAT OF LEECH LAID OPEN.................................... 310 JAW OF LEECH..................................................................... 311 PUSHING-POLES OF SERPULA..................................... 314 Hoois OF SERPULA....................................................... 316 SPINE OF ECHINUS................................................................ 323 HEAD OF PEDICELLARIA.................................................... 326 SUCKER OF URCHIN................................ 332 PORES OF URCHIN..................................... 332 SUCKER-PLATE OF URCHIN................................... 335 DURM-BELLS IN HOLOTHURIA................................. 342 WHEEL IN CHIRODOTA....................................... 34 ANCHOR-PLATE IN SYNAPTA................................ 344 LARVA OF SEA-URCHIN................................................... 347 DEVELOPMENT OF DISK........................................ 350 CYDIPPE.......................................... 357 SARSIA.............................................................................. 3 THAUMANTIAS.........................................................367 OTOLITHES OF THAU3IANTIAS........................... 368 TURRIS AND ITS YOUNG................................. 372 LAOEDEA.......................................................................... 377 TENTACLE OF LAOHVIEDEA...................................................... 379 STAURIDIA................. 393 LARES.......................................................................... 396 POLYPES OF COW'S PAP......................................................... 403 SPICULA OF COW's PAP....................... 406 PORTION OF ACONTIU.......................................................... 409 CINCLIDES........................................................................... 411 CNIDA OF MADREPORE.......................................................... 417 CNIDA OF TEALIA CRASSICORNIS.......................................... 420 CNIDA OF CORYNACTIS...................................... 424 FORMS OF A BA........................................................... 434 SECTION OF SPONGE....................................................... 442 THREE-SIDED EUGLENA............................................... 447 SWAN-NECK AND ITS DIVISIONS................................ 450 PARAMECIU........................................... 454 X11 LIST OF ILLUSTRATIONS. COLEPS AND CHILOMONAS............................................... 455 VORTICELL....................................................................... 459 ACINETA...................................................................... 464 VAGINICOLA....................................................................... 468 E PLOTES........................................................................... 475 EVENINGS A.T THE MICROSCOPE. CHAPTER I. HAIRS, FEATHERS, AND SOALES. NOT many years ago an eminent microscopist received a communication inquiring whether, if a minute portion of dried skin were submitted to him, hle could determine it to be Ahuman skin or not. He replied, that he thought he could. Accordingly a very minute fragment was forwarded 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; after carefully examining which, he pronounced with confidence that they were human hairs, and such as grew on the naked parts of the body; and still further, that the person who had owned them was of a fair complexion. This was a very interesting decision, because the fragment of skin was taken from the door of an old church in Yorkshire; * in the vicinity of which a tradi* I am writing from memory, having no means of referring to the original record, which will be found in the first (or second) volume of the 1 2 EVENINGS AT THE MICROSCOPE. tion is preserved, that about a thousand years ago a Danish robber had violated this church, and having been taken, was 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 these atoms, obtained by drawing one of the old nails, that was subjected to microscopical scrutiny; and it was interesting 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 one 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 so indelible that centuries of exposure have not availed 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 va. rious 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 size is the same as if six hundred of these hairs were placed side by side. Now, " Transactions of the Microscopical Society " of London. The general facts, however, may be depended on. HAIRS, FEATHIEnS, AND SCALES. 3 with this eye-piece micrometer, we will first of all measure its diameter. You see, crossing the bright circular field of view, a semi-pellucid cylindrical object; that is the hair. You see also a number of fine lines drawn parallel to each other, exactly like those on an ivory rule or scale, with every fifth line longer 1l! W41! 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 get the I hair to be exactly in the centre of the field; and now, by adjusting the eye-piece, we make the scale to lie directly across the hIair, at right angles with its length. Thus we:,P see that its diameter covers just thirty of i the fine lines; and as, with this magnifying HIUAN AIR. power, each line represents 1-10,000th of an inch, the hair is 30-10,000ths,- 3 -,rd of an inch, in diameter. In all branches of natural history, but perhaps preeminently in microscopic natural history,-owing to its greater liability to error from illusory appearances, —we gain much information on any given structure by comparing 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 wahen 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. ~4: EVENINGS AT THE MICROSCOPE. 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 in their individual courses. These lines we perceive to be on the surface; because, if we slowly turn the adjustmentscrew, the lines grow dim on the central part of the cylinder, while those parts that lie near the edges (speaking according to the optical appearance) come into distinctness. 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; these, however, are so slight that they can be seen only by 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 turu, become dim, and the whole is confused. In fact olr eye has travelled, in this process, firom 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, with 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 mathematically equal in every part, HAIRS, FEATHERS, AND SCALES. 5 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 stemn of a plant; inasmuch as it grows fromn a root, by continual additions of cells to the lower parts, which, as they lengthen, push forward the ever-lengthening 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 projections produced by the successive growth and sloughing of leaf-bases around the central cylinder. Internally, too, the resemblance is remarkable; for, if we split a htuman hair, and especially if we macerate 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; (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."t (3) X This is nearly thrice as great as the diameter I had given above, which was the result of several careful admeasurements of different hairs, taken from childhood and adult age. t Grant. Outl. Comp. Anat. 647. 6 EVENIING S AT THE MBICROSCOPE. Running throngh the Avery centre of the fibrous portion may be sometimes discerned a dark slender line, which is a sort of pith (medullac), composed of minute roundish cells, filled -wNith air, and arranged in two or three rows. b IIOG'S BnISTLE. The bristles of the Hog bear much resemblance to the humanl hair. On this slide is one, which you perceive is just thrice as thick as the hair that we have been examining, or T-T,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 undulation 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 operation two or three times. Now, picking out the shavings of wood, HAIRS, FEATHERS, AND SCALES. 7 I take up a few of the dust-like atoms with the point of my pen-knife, 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 them, some will fall upon their cut ends, so that we shall look through them endwise. HIere is one, very suitable for examination,. —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 substance appears made up of excessively fine fibres, of which we see the ends cut across. A rough dark line occupies the middle of the slice, in the plane of the greater diameter; but at the edge of the slice we are able to see that this is not a solid core, as has been sometimes supposed, but a cavity passing up through the hair. It is surrounded by a layer of medullary cells, 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. lBut they are distinguished at once by the conspicuousness of the medullary portion, which is thick, and quite opaque, and is broken up (especially towards each extremity of the hair) into separate longitudinal irregular masses. The fine wool of the Sheep is clothed with imbrications, proportionally much fewer than those of human hair, while the diameter is also much less. Thus these examples, selected from fine flannel and from coarse 8 EVENINGS AT THE MICROSCOPE. worsted, vary in diameter from',,th to 7- tll of an inch; and there are, upon an average, about two imbrications in a space equal to the diameter. No colour is perceptible in these specimens; they are as tlransparent and colourless as glass. Tile imbricated plates project here considerably more than in either of the examples we befoire examined; the "teeth," however, form an obtuse We shall presently see the importance of this imbricate structure; but we will first look at a 1" few more examples, in which we shall find it still more strongly developed, in conjunction \ with some other peculiarities. All tile hairs that we have looked at are what I have called fibrous in their interior texture, but those of mzanv animals are more distinctly cellular. FIE OF Thus, in these specimens, plucked from the SIIEEPS W'Lfur of the Cat that lies coiled up on the hearthrug, we see, first, that the imbrications are short, being about equal to the diameter in length, but are very strongly marked; though, like those of the Sheep's wool, obtuse. IHence, the contour is extremely like that of the stipe of an old rough palmhn-tree. There is a distinct bark (cortex), which is thick, and marked with longitudinal lines, which add to the resemblance just alluded to. The interior is clear, marked off at pretty regular intervals by the broad flattened medullary cells, in single series, each cell occupying, for the most part, thle whole breadth of the interior. These cells are transparent and apparently empty; but their walls appear opaque and almost black,-an optical illusion, dependent on the absorption of the light by their surfaces at IAIRS,'EATHERS, AND SCALES. 9 certain angles with the eye of the beholder. The fibrous portion is here almost displaced by the great development of the medullary cells. In the larger hairs of the Mole, which we will now look at, the bark is very thin; and though the surface is marked with silluous lines, these do not project into teeth. 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 i lb most part, extend all across the body of tle hair, though they are somewhat irregular both in size and shape. They are rather fiattened, and appear perfectly black (that is, opaque) by transmitted light, their surfaces I absorbing all the rays of light. The small HAIR OF CAT. 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 I l curious, the scales of the bark I project into strongly-marked imbrications on one side, and aire scarcely perceptible on thle \ ]ii other. Here, as in the lal gei rl' oval transverse cells, perfectly'{,. opaque. The hair of man. of the smaller Mammalia shows con.,-,,~ siderable diversity of form, according to the part which we select for observation. Thus, if we take a long hair out of this Sable tippet, 1v* 10 EVENINGS AT THE MICROSCOPE. and examine it near the base, we see that it is very slender, transparent, and colourless, covered with strongly-marked imbrications, whichl are not obtuse teeth, but long, pointed, overlapping scales, about ten of which complete a whorl. The fibrous portion is moderately thicek; inclosing a wide pith of roundish cells, set in two rowTs, that allow the rays of light to be transmitted through their central parts. As we trace the hair upwards, by moving the stage of the mlicroscope, by and by it swells and rapidly increases in thickness; the imibrications are scarcely perceptible; while the pithI' 1 cells have greatly augmented in number and in breadth. til These are arranged in confused, close-set, transverse rows, and are nearly opacque. Still tracing up the same hair, as we approach the The lai l tip, the bark and fibrous t part become very thin; the cells are fewer and fewer till they cease altogether, HI.IR OF SABLE. and a long slender point, of a clear yellow tinge, without cells, presents transverse wavy lines of imbrication scarcely projecting. The hair of the common Mouse is a pretty and interesting object. In the larger specimens the fibrous portion is reduced almost to nothing. The imbrications project very little, but careful observation reveals slanting lines proceeding from the "teeth;" which show that the whole surface is clothed with long pointed IAIRS, FEATHERS, AND SCALES. 11 scales, which are excessively thin, and lie close. The pith consists of large flattened cells, arranged thus one row passes up through the cell-!.. tle, and other similar ones are set in a circle around it, so that a longitu-, dinal section would show three par-:"7 x/ "/ allel rows. These cells are tlranslu- \+ i|1 cent, and somle of them are either Wholly or partially lined with a clear jK/" yellow pigment. The slnaller hairs from the /ii'''. " same little animal are scarcely, distinguishable from those of. tile Cat, already described, ex- IIxR OF MOUsE. cept that the imbrications are proportionally larger. In all, the extremity is drawn out to a lengthened fine point, and is occupied withll clear yellow cells, except the very tip, which is colourless, and imnbricated with sinuous whorls, each consisting of a single scale. But it is in the Bats that the imbricatecl character attains its greatest development. On this slide is a number of hairs from the fiur 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 suecessors to the very edges, or nearly; but the lower part, which is more slender, resembles TIP OF a multitude of trumpet-shaped flowers forimecld"i1 or I[o:,into a chain, each being inserted into the MOUSE. tllroat of another. The lip of the "flower" is generally oblique, and here and there we can perceive 12 EVENINGS AT TIHE MICOSCOPE. that each is formed of two half-encircling scales; for one scale occasionally springs from the level of its fellow, so as to make the imbrication alternate. Even tlhis, however, is far excelled by a species of Bat firom India, of wlhose hair I have now specimrens 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 cpll appears to be undivided, but very irregularly notched and cut. In the middle portion of the hair, the cu)ps are far morle crowded than in the basal part, more bruslllike, and less elegant; and this structure is continued to the very extremity, whllich is not driawn out to so attenuated a point as the hair of the Mouse, though it is of a needle-like sharpness. Tlle t~rumpet-slhaped scales (:,,1\ /i are, it seems, liable to be removed. by laccient; for in these dozen hairs tlere are several, in which we see one or more cups rubbed off, and in one the / stem is destitute of themn for a consid-,I bhl' "~I erable space. Tlle stem so denuded, ~i, V', fclosely resembles the basal part of a IMouse's hair in its normal condition. xj ~?t'i'.<4 This character of being clothed witl overlapping scales, eacll girowing out of }' [iIli~ its predecessor, is common, then, to thle hairs of the Mammalia, thouglh it exists in different degrees of development. It Ilk P OF INDIAN BAT. may be readily detected by the unaided sense, even when the eye, though assisted by the emicroscope, fails to recognise it. Almost every schoolboy is familiar with the mode HAIRS, FEATHERS, AND SCALES. 13 by which the tip of any hair may he distinguished from its base; and even of the least firagment, the terminal end from the basal end. The initiated lad assembles a few younger ones, and says, "Now you may make a mark with ink on one end of a white horse-hair, and I'll tell you, by feeling it, which end you have marked." HIe does, infallibly. HIe rubs it to and fro between his thumb and finger, and the hair regularly travels through in the direction of its base: one or two rubs of course determine this, and the verdict is given oracularly. Now you see the cause of this property lies in the imbricate structure; the scales may be excessively thin and close, but still they project sufficiently in any specimen to present a barrier to motion in the terminal direction when pressed between two surfaces, such as the fingers, while they very readily move in tile 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 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 ankles, 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 possess 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 14 EVENINGS AT THE MICROSCOPE. like texture. Tile "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 intimate union of the felted wool-fibres, which accrues from the various processes to which the fabric has been subjected. in a commercial view, the excellence of wool is tested by the closeness of its imbrications. WVhen first the wool-fibre was submitted to microscopical examination, the experiment was made on a specimen of Merino; it presented 2,400 serratures 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 serratures in an inch. Next a specimen of South-Down w.ool, acknowledged to be inferior to either of the former, was examined, and gave 2,080 serratures. Finally, the Leicester wool, whose felting property is feebler still, yielded only 1850 serratures per inch. And this connection 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 subordinate short hairs, which project from the main stem, and IIAIRS, FEATHERS, AND SCALES. 15 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, curvecl 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 grnbs, 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 caterpillar (that of the Oak Egger MIoth, I believe); they appear, when highly magnified, like stout horny rods drawn out to an acute point, and sending forth alternate short pointed spines, which scarcely projct from the line of the axis. But there is scarcely any hair more curious than that of a troublesome grub in mnuseums and cabinets, the larva of Dermnestes8 lardarius, which lives upon fur-skins, and any dried animal substances. It has a cylindrical shaft, 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 is furnished with six or seven large filaments, which appear to have aTIP OF HAIl OF knob-like hinge in the middle, by which they are bent up on themselves. The feathers of 13irds are essentially hairs. That shrivelled membrane which we pull out of the interior 16 EVElNINGS AT THII MICROSCOPE. of a quill when we make a pen, is the medullary portion, dried. There is a beautiful contrivance in the barbs of most feathers, which I will illustrate by this feather from the body-plumage of the domestic fowl. Every one must have observed the regul ar arrangement of the vane of a feather, and the exquisite manner in which, the beards of which it is composed are connected together. This is specially observable in the wing-feathers, —a goose-quill, for example; where the vane, though very light and thin, forms? an exceedingly firm resisting medium, the individual beards inaintaining their union with great tenacity, and resuming 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,ARB OF CLOTHIN G-FEATHER with great lightness and buoyOF OW. ancy-for the bird is a fyinyg 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 individual 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 microscope, we see that the central stem carries on each side a row of barbs, which interlock with each other. The IIAIRS, FElATIIERS, AND SCALES. 1[ magnifying power shows us that these barbs are not simple filaments, but are themselves doubly bearded in the same fashion; and further, that these barbules of the second series are furnished with a third series. It is in this third series of filaments that the tenacity in qulestion 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 abrnptly 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, /I there, and thus the two contiguous I beards are firmly locked together. In the beard of the goose-quill, 4 the structure is essentially the, same, but the barbulets are far more numerous and more closely set; they are also proportionally bAB FOGOOSE-UILL. much larger, —both those which are hooked and those which are simple. Indeed, the latter manifest a tendency to the hooked form, and by all these peculiarities the interlocking power is augmented. It is interesting to observe the great dilatation of the beard in a direction towards the inferior surface of the feather,-towards the stroke, as I just now ob 18 EVENINGS AT THE MICROSCOPE. served. 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 yielding laterally. 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 objects 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 comb-like), and cycloid (or roundish). The Perch 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 (fig. a); 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, falling on the house-top, has a tendency to flow downwards, 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 one, whence it still flows down to the free edge of this one, and so in succession. So the motion of the bird through the air, and of the fish IIAIRS, FEATHEiRSY AND SCALES. 19 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), deposit the successive particles of the moving fluid inlthe 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 hmotion. This latter advantage 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 successive rows, and overlapping. Their front side is cut a b c SCALES OF PERCII. with a scolloped pattern, the extremities of undulations of the surface that radiate fiom a common point behind the centre. These undulations are separated by narrow 20 EVENINGS AT THE MICROSCOPE. furrows, across which, contrary to the ordinary rule, the close-set concentric 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 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 beneath, and thus flows over the body for the double purpose of protecting the skin from the mascerating 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 the lateral line, the left-hand one (c) 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 of the belly, and the last (f) from the throat. Thus we see there is considerable variety in form presented by the scales even of the same individual fish. They all, however, 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 IIA NIRS) FlEATERS, A-ND SCALES. 21 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 a b c e f SCALES OF GOLDFISH, other parts being concealed by the three neighbouring 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 longitudinally, so that it opens posteriorly on the outer surface, and anteriorly 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 concen 22 E]VENINGS AT THE MICROSCOPE. tric lines, following the irregular sinuosities of the out line. 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 exposed, and that which is covered by the other scales; the concentric marks in the former are much coarser and less regular, often being interruptedcl, and seeming to run into each other, and frequently swelling into oval scars. This may, perhaps, be owing to the surface having been partially 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 connected 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. Reverting 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 IIAIRS, FEATHEES, AND SCALES. 23 fiiom the Flounder, which, being coarsely lined, shows the structure wrell; or in these from the Green WTrasse. I will now apply to one of these a power of 600 diameters, concentrating the light thrown through the scale from the mirror by thef acheromatic condenser, / and examine the scale anew. You - now. see'two __,. distinct layers; the upper one which bears the concentric lines, and a lower clear one which not only SCALE OF FLOUNDER. fills the radiating bands, a. Natral nze. 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 running through the solid substance. This, however, is illusory: for, by delicate focussing, we perceive that each portion imarked by these lines is really in a different plane from the others, that the highest is at the centre of radiation of the scale, and that each is successively lower till we reach the margin. lBut 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 tliese liies forms a distinct ridge. On the other hand, the under layer of clear substance is quite smooth, and always a little exceeds the nmargin 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. HIence, I think that, in these slit scales, the upper layer is formed, as commonly believed, by successive 24I EVE NINGS AT TIHE MICROSCOPE. 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 (ca) is from the back; the central one (b), which has only a b SCALES OF PIKE, a deep narrow incision instead of a tube, is from the lateral line; and the third (c) is from the belly of the fish. 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 constitutes the beauty of these lovely fishes, depends not on the scales themselves, but on a soft layer HAIRS) FEATHElSn AND SCALES. 25 of pigpment spread over their inner surface, and seen through their translucent substance. On carefully detadhing a scale, we see on the under side, opposite to that portion only which was exposed (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 spread it on a plate of thin glass, we shall find, by the aid of the microscope, that it consists of two distinct substances; the one giving the colour, the other the metallic lustre. WVith 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 mlicroscope, we shall have a beautiful and interesting spectacle. The water around the mass is seen to be full of an infinite number of flat spicula or crystals, varying mnuch in size, but of very constant form, a flat oblong prism 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 y flash like plates of polished steel. lBut SPICL OR GOLDFISHES SCALE. what appears most singulalr, is that each spiculum is perpetually vibrating and quivering with a motion apparently quite spontaneous, but probably to be referred to slight vibrations of thile water in 2 26 EVENINGS AT THE MICROSCOPE. which they float; and each independently of the rest, so as to convey the impression 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 s-urface. 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 mat ter 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. 27 CHAPTER II. BLOOD. TEiE microscope is daily becoming a more and more important 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 neck-kerchief. 7. There were present also numerous tessellated epithelial cells. In order to understand the meaning and the bearing of this last fact, I 28 EVENINGS AT TIH-E MICROSCOPE. must explain that the whole of the internal surface of the body is lined with a delicate membrane (a continnation of the external skin), which discharges mucus, and is hence termed mlucous 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 constitute the mucus), and of being replaced from the tissues beneath. Now microscopial anatomists ]have learned that these epithelial scales or cells, which are so minute as to be nndiscernible by the unaided eye, differ in appearance and arrangement in different parts of the body. Thus, those which line the gullet and the lower part of the throat are tesselatecl, or resemble the stones of a pavement; 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 viscera of the abdomen 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 hu2gna 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 imight have escaped. [But what was there in the dried brown stain that determined it to be blood? And, particularly, how was it proved not to be 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 BLOOD. 29 the stage of the instrument, with 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. These bodies are what we frequently call the bloodglobules, or, more correctly, blood-dsk8cs; since their form is not globular, but thin and flat, like a piece of money. The slightness of their colour is dependent on their extreme tenuity: when a larger number lie over each other the aggregated colour is very manifest, as it then becomes either a full dark red, or bright rich scarlet; for to these disks blood is entirely indebted for its well-known hue. All vertebrate blood is composed 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 are circular, or nearly so, and slightly concave on both of the surfaces. On the other hand, in tBirds, 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 Mlan nearly agree in size with those of the Monkey tribe, of the Seals and Whales, of * The Camels among Mammalia, and the Lampreys among Fishes, are exceptions to the above rule; the former having elliptical and convex blood-disks, and the latter circular, and slightly concave. 30 EVENINGS AT THE MICROSCOPE. the Elephant, and of the Kangaroo.: Most other quadrupeds have them smaller than in Man; the smallest of all being found in the ruminating animals. The little MAusk-deer of Java has disks not more than onefourth 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 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 mnore, in most Birds. 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 1-400th of an inch long by 1-800th broad, or about eight times as large as those of Man. Our common Newts afford us the largest examples among 13ritish animals, but they do not reach above half the size just mentioned. BLOOD. 31 Taking this drop of blood from my finger as a standard of comparison, we find, on applying the micrometer, that the disks rumn from 1-2500th to 1-5000th of an inch; but that the great majority are about 1-3300th in diameter. On these slides are samples of other kinds. This is the blood of a Fish, —the common Blenny or Shanny (Blenzznis pholis). Here we see at once the oval form of the disks; their average is 1-2800th by 1-3300th of an inch. Here is the blood of a Frog (Rana ternporarica); these are more than twice the size of the fish's; for they average 1-1250th by 1-1800th of an inch. And, finally, I can show you a drop of blood from this Smooth-newt (Ii;ssotriton punctatus). The large size of the disks is now conspicuous, 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-OOth to 1-950th in length, by 1-1100th to 1-1600th in breadth; but the average are about 1-800th by 1-1300th of an inch. t ~d, BLOOD-DISKS. a Man. b Blenny. c Frog. d Newt. It may interest you to see these blood-disks in their proper situation, and to observe the motion which 32 EVENINGS AT THE'MICROSCOPE. they possess during the life of their owners. It is, indeed, one of the most instructive modes of using this wonder-working 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 withal so transparent that their integuments 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 microscopically 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 thin and translucent, yet arteries and veins meander through its delicate 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 without 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 BLOOD. 33 must make him as comfortable 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 pass 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 retracing it. Hiere 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 marginal 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. 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, something like scales; this is the tessellated epithelium of the surface. Our attention is caught by a number of black spots, often taking fantastic forms, but 2* 34 EVENINGS AT THE MICROSCOPE. generally somewhat star-like: these are pigment cells, on which the color of the animal's skin is dependent. But the most prominent feature is the blood. Wide rivers, with tortuous course, roll across the area, with many smaller streams meandering among them; some pursuing an independent 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. B13y 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 dimensions 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 their 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. 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 BLOOD. 35 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 network. These are the capillaries, which feed the veins, and which are themselves fed by the. arteries, whose course is in the opposite direction, viz., fiom the body. These, however, are with difficulty seen: they are more deeply seated inl the tissues, and are less spread over the webs, being generally placed along the borders of the / toes; they are, more- s a over, fewer and smaller than the veins; but thea ioto~ Fo s nnoo 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 mental 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 36 EVENINGS AT TIHE -ICROSCOPE. of sea-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 Perophorca listeri. Though each globose knob is no larger than a small pin's head, it is full of organs which carry on the various functions of life; and, because the whole tissues are as transparent 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 cubical, flattened on two opposite sides,,I,= m:\ with a sort of wart at the surnmit and another at the side, / >\f~tt00~0 each of whlich is NI, pierced wNith a pirs~ i~,/;~'j~[,f ti',, ~ ed orifice. The.p~'~~7 per of these orifices admits wvater for re_S \ m spiration and food; '~ the ranmi of the incus with the ) maxillin; while the walls of the mastax with the two edges MOUTH OF oRACIIIONUS. of its orifice correspond with the mouth, with its labrum and labium. It is true we are somewhat startled to find a mouth placed far down within the cavity of the breast; but there are other forms in this class, some of which I may be able to show you, where the mastax has essentially the same structure, in which it is placed at the front WHEEL-BEAREIRS. 271 margin of the body, from which the jaws can be freely protruded. The difficulty will seem less if you weigh the following considerations:The integument in the Rotifera is very flexible and, especially in the frontal regions, is extremely invertible. In those genera in which the mouth apparatus can be brought into contact with the external water, it is ordinarily, to a greater or less degree, retracted within the body, by the inversion of the surrounding parts of the exterior, while, in those genera in which it is permanently inclosed, analogy requires us to consider the condition as induced by a similar inversion, but of permanent duration..If we imagine the head of a softbodied Insect-larva retracted to a great degree (as is done partially by many Dipterous larvqe), the skin of the thoracic segments would meet together in front, around a purse-like opening, which would be the orifice of such a buccal funnel as exists in most Rotffera. In the latter, it is the normal condition; in the former, it is merely accidental and temporary. We need not devote any more minute consideration to the digestive apparatus in our little ]Brachion, but there are some other points in its structure which are worth noticing. In the central line of the body, just above the mouth, as you see the animal in a dorsal view, there is a square speck of a rich crimson hue, the edges of which, when we view it under reflected light, glitter and sparkle like a precious stone. But when we obtain a perfectly lateral view, we perceive that the situation of this gem-like speck is considerably nearer the dorsal side of the shell than the mouth, and that it forms a wart-shaped prominence on a large turbid mass which occupies the whole front portion of the animal. 272 EVENINGS AT THE MICROSCOPE. By comparison of this organ with the corresponding parts in other genera, there is every reason to infer that this turbid mass is an enormous brain, the nervous matter being in a very diffuse condition; and that the ruby seated on it is an eye, consisting of a crystallille lens, and a layer of crimson pigment beneath it. The oval bodies that you see attached to the hinder part of the shell are eggs. MIost of the females that we meet with carry one or more, sometimes to the number of six or seven. The specimen we are examining had two at first, one on each side the foot-orifice; but just now a third was excluded-an operation which occupied but an instant —and this took its place besides the former two, so that we now see three. These eggs are generally carried by the parent until the young are hatched. The oldest of these three is nearly ready for hatching, and if you watch awhile you will see the birth of the young. At first exclusion, the egg which was seen some time before in the ovary, as a semi-opaque mass, of well-defined but irregular shape, immediately ass-umes a form perfectly elliptical, and its coat hardens into a brittle shell. This is so transparent that the whole process of maturation can be watched within the shell. The yelk is at first a turbid mass, in which are many minute oil-globules. Soon it divides into two nmasses, then into four, then into eight, sixteen, and so on, by the successive cleavage of each division, as fast is it is made, till these divisions are very numerous. Then we begin to see spontaneous movements; the outline of the young separates in parts from the wall of its prison, folds are seen here and there, and fitful contractions and turnings take place. Soon an undefined spot of red appears, which gradually WHEEL-BEARERS. 273 acquires depth of tint and a definite form, and we recognise the eye. Slight waves are seen crossing one end of the egg; these become more and more vigorous and rapid, and at length we see that here is the situation of the frontal cilia. -The mastax appears, and the jaws, and soon the latter begin to work; though it must be only by way of practice, for it is hard to im agine what they can yet find to masticate. All these phenomena have successively appeared in the egg we are now watching; and at this moment you see the crystalline little prisoner, writhing, and turning impatiently within its prison, striving to burst folth into liberty. Now a crack, like a line of light, shoots round one end of the egg, and in an instant the anterior third of the shell is forced off, and the wheels of the infant Brachion are seen rotating as perfectly as if the little creature had had a year's practice. Away it glides, the very image of its mother, and swims to some distance before it casts anchor, beginning an independent life. At the moment of the escape of the young, the pushed-off lid of the egg resumes its place, and the egg appears nearly whole again, but empty and perfectly hyaline, with no evidence of its fracture, except a slight interruption of its outline, and a very faint line running across. This is a female young: the male is totally iunlike the female, and is very much smaller. We can always tell whether an egg is going to produce male or female young, by the great difference in its size, the female being more than twice the bulk of the male egg. All of one brood are of the same sex; we never see a Brachionrus with male and female eggs at -the same time. 12 274 EVENINGS AT THE MICROSCOPE. What is very strange, is, that the male has no shell, no spines, no mouth, no jaws, no stomach, no intestines; no ciliary wheels; its cilia, which are very long and powerful, being arranged in one circle round the whole front. Its movements are exceedingly fleet. Perlhaps you are tired of Braccionus, and are ready to cry out'" Ohe! jam satis! " * Well, then, I will turn him off and show you another elegant little creature the Whiptail (lctstigocerca carinatci). I have here in a bottle some stalks of the Water-tHorsetail (CGhara vulgaris), which I obtained in a pond a few weeks ago. These I examine in this wv ay. Taking hold of the COaracc with a pair of pliers, I pull it partially out of water, and, allowing it to rest on the neck of the bottle, I cut off with a pair of scissors, or with a penknife on my nail, about one-fourth of an inch of the tips of three of four leaves, which adhere together by their wetness. These tips I place in the live-box with a drop of water, and having separated them with a needle, I put on the cover, and examine them with a triple pocket lens; holding up the box perpendicularly, not opposite the light, but obliquely, so that the field is dark; but the light reflected and refracted by the animalcules shows them out beautifully white and distinct even the luinute.:ones. The forms and some characters of the middling and larger can be quite discerned thus; for example, the slender tail of the one I am now going to show you, I can thus see. The position of any particular individual to be examined being thus marked, it is readily put under the object-glass of the microscope. I have found these leaves very pro. * "0 dear! quite enough of this " W-IIEEL-BE AnEIRS. 2 7 5 ductive of the more stationary animalcules, the Rotifera especially. It was in this way I this morning found the pretty and delicate little Whiptail, which I am going to make the subject of our evening's study. It is inclosed in a glassy shell (lorica) of a long oval form, from which rises on the front half of the back a thin ridge which in the middle has a height nearly equal to half the diameter of the body, but tapers off at each end. Its base is corrugated with wrinkles. This is not set on symmetrically, but leans over considerably to the right side. Its basal portion is hollow, and is continuous with the general cavity of the shell, for we sometimes see portions of the viscera in its interior. WHIPTAIL. The head of the animal is rounded, and divided into several blunt eminences or lobes, which are set with cilia; these rotate constantly, but irregularly and feebly, and do not make manifest wheels, as Brachionus does. A small antenna projects from the back of the head, capable of being erected or inclined. A long brain descends along the base of the ridge, carrying a bright and rather large crimson eye set like a wart on its interior angle. Instead of the flexible and contractile foot )f Brackiioyntus, the Whiptail has a single horny spine of great slenderness, and exceeding in length the whole body. 276 EVENINGS AT THE MICROSCOPE. This spine probably represents not the foot, but one of the toes at the end of the foot. For it is attached to a very short foot, in the midst of two or three bract-like spines, one of which, longer than the rest, and distinctly movable, probably represents the other toe undeveloped. The long spine is set on by a proper joint, a globose bulb being inserted into a socket, which allows it free motion, in all directions except backward. The socket itself is contained in a second joint, the basal part of which is inserted at some distance within the aperture of the lorica. This articulation is formed by an infolding of the skin, but is permanent in its position. The most remarkable circumstance connected with this elegant little animnal is the unusual form of the dental apparatus, which differs so immensely from that of Brc/ehionots, that we should never recognise them as being the same organs, if we had not numerous intermediate links, which by insensible gradations connect the two remote forms. The mcastax is a somewhat slender sac, much produced in length, and with the component lobes greatly and irregularly developed. The dincus has a fulcrmum of great length and slenderness, a straight rod with a dilated foot. The rateri are small, and pincer-shaped, but with the angles greatly produced. The mzalles have long, slender, incurved czatnubria, and simple unc'i. But the remarkable circumstance is the non-symmetrical character of the apparatus. The left side is much more developed than the right. The left angle of the incuts descends to a greater distance than the right; and its extremity is dilated into an expansion, with several irregular points, to which muscular threads wIEEL-BEARERS. 277 are attached. The ramsns also of the same side is larger than its fellow; so with the mnallei. The mnaubriumn of the right is comparatively short, very slender. and of uniform thickness; with a long, slender, rodlike ttncus, doubly bent in the middle. The left is much longer, irregularly swollen, clubbed at the articulation, and bearing a thick, curved, knotted uncus, which terminates at a point not precisely opposite the tip of its fellow. These circumstances, combined with the unsymmetrical character of the dorsal ridge, of the foot-spine, and of some other organs, render this genus a highly curious one to the naturalist. The little Whiptail is as lively in its motions as it is elegant in its form. When swimming, it glides with considerable swiftness through the water, turning frequently on its course, and often partially revolving on its long axis. When inclosed, as is often the case, by two fragments of the filamentous Chara, it travels along the sides of its inclosure, nibbling, as it goes, the floccose and sedimentary deposits on the surfaces of the leaves. The long spine-foot is conlmonly carried inertly after it; when the animal suddenly turns, of course the tail is bent at the basal joint, but it is not habitually whisked about, as is the tail of Brachionu8s, nor is it so much used as a support or turning point. The animal has the power of so using it, however, and of adhering with considerable force to the glass of the box or the side of a phial, by its point. We have hitherto looked at our Rotifera by transmitted liglht, and their crystalline transparency renders them beautiful objects when thus exhibited. But we will now look at the Whiptail by the direct. light of the sun upon it, condensed, but not to a burning point, by the bull's-eye lens. 278 EVENINGS AT THIE MICROSCOPE. It now possesses a peculiar beauty of another character. The body generally is colourless as a vase of glass, but reflects the rays brightly from its polished surface. An advancing egg in the ovary is opaque white, as is the front part of the mastax; the stomach and intestine filled with vegetable matter are of a yellow-green; the rotating head appears of a pale blue, and the eye shines out as a speck of opaque vermilion. WVith the dipping-tube I will now take up a drop of water from the bottom of the Charac-jar, allowing a little of the loose sediment to flow in also. This is a random cast; we know not what we may get, though we are pretty sure to catch something. Now then for the examination. I-a! here is the curious Skeleton Wheel-bearer Dinocharis )OGicUmm; -nay, several of them. This genus is remarkable for possessing true joints in the foot; not merely telescopic inversions of the skil, but permanent articulations with swollen condyles, resembling those of the antennme of a beetle. Hence the Skeleton has great freedom and precision of motion; using the tips of the long toes as a fixed point, it throws its body hither and thither to a great distance, with remarkable agility. These joints admit of forward and lateral flexure, but you never see the body brought backward beyond a perpendicular position, the swelling of the terminal portion of each articulation precluding further motion in that direction; just as the joints of our knees and elbows permit bending in one direction but not in the other. This is another indication that these divisions are true joints; and I direct your attention to the point, WHEEL-BEARERS. 279 because the fact helps to indicate that this class of animals has its proper affinities with the AnTICULATA, which has been denied by most naturalists. SKELETON WVHEEL-BEARER. The form is curious. Elevated at the summit of a long foot, consisting of three joints, which surmount two unusually lengthened and slender toes, is a vaseshaped lorica, which is three-sided. Its surface is covered all over with minute points, very closely set, so that it resembles shagreen; besides which it forms numerous sharp ridges, which run across transversely. The two sides run off into thin lateral wings, which 280 EVENINGS AT THE MICROSCOPE. comle to a sharp edge; the back angle also forms a ridge, but less sharp and thin. In front, the shell, or lorica, is as it were cut off abruptly, like the rim of a goblet, but out of this rises a second column, connected with the rim by an elastic membrane, which allows some freedom of motion. This column is widely divided in front and behind, and rises to a point on each side. When the rotatory front is withdrawn, these points approach and meet, closing the orifice; but when the head is protruded they are widely separated. Internally, we see the usual viscera contained in so narrow a cavity that we are ready to suppose the walls of the lorica unusually thick; this is, however, an optical illusion, dependent on its dilatation into those angular wings already noticed. The cavity penetrates into them; for in one of these specimens I see those curious convoluted threads that are believed to be connected with respiration, within the lateral wings. The stomachs are generally full of green and brown food, but they will not imbibe carmine. Let us look, however, a Imoment longer at the'singular foot. Between the first and second joints there are two projecting spines; these differ much in different individuals as to their length, slenderness, and direction; sometimes being quite short, at others as long as the toes; generally, they arch downwards, but occasionally they stand out straight, or even curve upwards. In some specimens these spines appear to be processes of the first joint, but in others we can see distinctly that they belong to a little intermediate piece between the'first and second apparent joints. Between the two toes, on the hinder aspect, projects from the last joint a small spine, which is perhaps the rudiment WEEL-BEARERS. 281 of a third toe, since we find that number in some genera of this class. The whole foot, including the toes, is rough with the shag'reen-lilhe points that cover the lorica. You have already noticed the rapidity and fitfill irregularity which the long and many-jointed foot confers upon the movements of this curious little form. From the toe-tips, as a point of adhesion, it throws its body to and fro, or from side to side, in a peculiar manner. The toes are sometimes sprawled out, like the legs of an expanded pair of compasses, and sometimes the joints of the foot are suddenly bent in zig-zag fashion, and then as abruptly straightened. Thile animal swims gracefully, but only with moderate swiftness, the rotatory crown of cilia being small though forming the usual vortices when the animal is moored; while thus swimming, the toes are gracefully stretched behind, nearly in contact with each other. It is lively in its motions, but these seem performed without any ostensible object; we do not often see it attempt to eat, or nibble at any substance. I think we never find the Skeleton except among the sediment at the bottom of the water in which it is kept; among which also we frequently see the remains of defunct specimens-the skeleton of the Skeleton; this itself makes a pretty object: the lorica, with its points and ridges, the thoracic column, the foot with its joints and spines, and the toes, being perfectly preserved, and rendered even more clear than during life, because of the removal of all the soft internal parts by decay, and by the efforts of those little scavengers, the smaller species of inftsorial animalcules. These quickly find their way into the interior of any dead animal with a 282 EVENINGS AT THIE MICROSCOPE. shelly case, as a Wheel-bearer, a Water-flea, or an Insect, and soon devour every particle of soft flesh, cleaning out the case in the most tidy manner. Here is a tiny subject which will test your powers of observation, and possibly your patience, in satisfactorily defining its structure, partly on account of its swift motion and irregular leaps, and partly on account of its extreme transparency. It is a crystalline cup, somewhat like the body of a wine-glass, without any foot, but bearing many flat sword-shaped processes, which, proceeding from the breast, commonly lie fiat on each side, down the body, the points projecting below. These are evidently stiff and highly elastic, and their use is manifest to any one who sees the creature in active motion. It swims with a rapid gliding progress, head foremost, but at almost every moment it makes a sudden forcible jerk or leap backwards or to one side, and that so quickly that the eye often cannot follow it in the transition. The organs by which these jumps are effected are the long breast-spines, which are suddenly thrown out in various directions, and they may frequently be seen extended the instant after a leap. lWhen we consider that the creature is jerked often four or five times its own length, through so dense a fluid, we shall perceive how strong the muscular action must be which moves the lever-like spines. The creature is thrown irregularly, often with the side foremost, or the back, or made to perform a somersault in the act. It is probably a sensitiveness to danger or annoyance that prompts these violent leaps; at least, it frequently performs them, after a momentary examination of any floating matter with which its course brings it into contact. WHEEL-3BEAERS. 283 The rotatory organs, the source of the common gliding motion, are not very large or conspicuous; the cilia appear to be set all along the brow. The eye is very noticeable: it is placed near the front and seems to be of a deep bluish-black hue. I have not, however, as yet introduced the nimble little stranger by name. We may call it familiarly the Sword-bearer, but Professor Ehrenberg has named it Polyarthra platyptera. This eminent authority on all that concerns these minute forms has placed the species among those which are destitute of a horny lorica or shell. But he is certainly in error here, for, as you may see, there is manifestly a stiff lorica, which covers the back and sides, but which gapes widely in the middle of the under side, throughout its length. From the lateral points, however, a membrane may be seen for a short distance, which doubtless protects the viscera from actual exposure. The sword-like fins appear to be twelve in number, arranged in groups, or bundles, of three each; one bundle being set on each side of the dorsal, and one on each side of the ventral aspect, at about one fifth of the entire length from the frontal points. These are all that we can ordinarily count; but I have seen more: one day, while examining a specimen that presented a vertical aspect to me-end-on, to speak familiarly-the fins being all expanded, I saw with perfect distinctness a seventh pair, proceeding from the middle of the breast. They are fiat, thin, narrow blades, of exceeding delicacy; all distinctly serrated on both edges, the teeth pointing from the base outward; each is strengthened by a central rib. They 284 EVENINGS ATr THE MICROSCOPE. are jointed independently, on rounded shelly knobs, and are doubtless moved by strong muscles. Under pressure, the knobs and the fins are brought out with beautiful distinctness. Here again we have true jointed limbs. On the front you may discern a pair of tiny antenne, each bearing a pencil of very fine bristles. And just below the level of their base, in the centre of the dorsal region, you see the large eye, of a deep red hue, so deep that it firecuently looks as if it were actually and intensely black. Just below- the eye apparently, but considerably more towards the ventral aspect, there is a huge mastax, occupying almost half the length of the whole body. The jaws are very simple in their construction, and therefore very instructive, for they contain the same elements as in TBrachlor tots; but from their excessive tenuity, and for other reasons connected with the form of the animal, they are calculated to tax to the utmost your perseverance and skill in manipldation to resolve them. They were an enigma to me for years. The great macstax is pear-shaped, pointing obliquely towards the middle of the belly. This form is owing to the great length of the f/dcreumn, and the wide curvature of the mallei. The rami are very broad, somewhat square at their base, flat, but much arched longitudinally. They open and shut vigorously, with a snapping action, but are not protruded fiom the front; their whole interior edges come into contact. The mallei are simple slender bent rods, apparently without distinct articulation. During life they are thick and irregular in outline, owing to their being invested with dense muscles; as is the whole upper portion of the WHEEL-BEAnERS. 285 mazstcax. These muscles conceal or disguise the form and action of the parts during life, but the introduction of a drop of solution of potash into the water instantly dissolves away the fleshy parts, leaving the solid organs, or those composed of chitine, beautifully clear, SWORD-BEARER. and fit for observation. Without this aid it would be impossible to resolve the structure of these minute animals. The little Sword-bearer, like the Brachionus, carries its eggs attached to the hinder part of its body, for some time after they are discharged; the minute green oval bodies that you see sticking to the side of this specimen, are not, however, eggs, but parasitic animalcules (olaciuem vesioculosum), which very frequently infest this species, adhering to various points of the shell, and even to the sword-fins. 2S6 EVENINGS AT THE MICROSCOPE. What I have now to submit for your examination is one of the rarest species of the class, and certainly not the least singular in its form. It is the Tripod Wheel-bearer (Actinr.r8 Nw eptluniz8). When fully extended, its length exceeds that of almost every other species, for it reaches about one-twentieth of an inch, but its extreme thread-like slenderness precludes the unassisted eye from taking cognizance of it, as its thickness, even when greatest, is not more than one sixhundredth of an inch. From this excessive length and tenuity, the appearance of the creature is very remarkable. It may be likened to a cylindrical tube, out of which protrude a great number of draw-tubes from -' a both extremities, principally the ~" posterior one. Those in front ter-~ aminate in an oval proboscis, which having a sort of finger at its extremity, and two eyes, with an antennal tube projecting obliquely backwards, presents, when viewed laterally, a strong resemblance to the head of a rabbit, the antenna representing the ears. In front, and just below this headlike proboscis, is a double swelling, containing the rotatory orTRIPOD WtlEEL-BEARER. z Y gans, which are small and seldom unfolded. The eyes are deep black; probably, as in the last example, a red of great intensity. Whlen the head is withdrawn, the integument is very clearly seen to be introverted. The body consists of one long cylindrical tube, which receives three or four short joints to WHEEL-BEARERS. 287 complete the abdomen; at the dorsal aspect of the extremrity of the last of these is the cloaca; at this point the diameter is already very much attenuated; but, there are eight or nine more joints which constitute the foot, and these are of extreme slenderness. Towards the extremity, two processes are given off behind, each consisting of a club-shaped piece, with a slender bristle at the tip. The foot terminates in three long, slender, cylindrical divergent toes, which are flexible, and commonly bent outward; they are equal in thickness, and truncate. These are often retracted in various degrees, even when the foot is otherwise extended. Owing to the slenderness of the body, the viscera are greatly elongated. The mastax, as usual in this family, consists of two hemispheres (each bearing two teeth, set transversely, but converging to the centre); it is situated at a considerable distance from the wheels, and is reached by a long buceal funnel. The digestive canal is a long sac, apparently undivided; it originates directly from the mastax, with, I think, two small basal glands; its posterior extremity becomes gradually tapered to the cloaca. In the specimen we are examining, a small quantity of ftecal matter of a yellowish-brown colour is collected in two small masses, near the extremity. Along the ventral aspect runs the ovary, which in this specimen contains two long oval eggs in advanced development; from their transparent brightness, I suspect the young are produced before birth. I think I can detect a contractile bladder, but am not certain. The dorsal region of the trunk is marked with strong rugged lines running longitudinally; these loolk like corrugations of the integument, but I incline to 288 EVENINGS AT THE MICROSCOPE. think them the strongly developed muscles for the retractation of the foot. Muscles are seen running through the joints of the foot, until they can no longer be traced, from their tenuity. The viscera can be demonstrated with difficulty, partly owing to the longitudinal muscles, which are so strong and close, and partly from the incessant contraction and elongation of the parts, which drive the internal organs hither and thither. It refuses, you see, to swallow carmine, which might have assisted us. This singular animal is lively in its motions, especially in the protrusion and retractation of the extremities. These are constantly alternating, and a very curious sight it is to see the immense length of foot suddenly thrust forth from the body, in which it had been completely hidden, the starting out of the horizontal processes, and the diverging of the long toes as these are successively uncovered. The latter do not seem to be often used as instruments of prehension or adhesion. Indeed the animal does not appear very much given to change of place, but lies in the water, alternately contracting and elongating. Frequently, as the foot is thrust out, the body is made to bend forward so as to form a right angle (see the engraving, in which the animal is thus represented at a; b represents it when the head is rotating, but the foot is almost wholly withdrawn within the body; in which state the resemblance to a telescope, or to a nest of glass-tubes, is striking). The last specimen of this class of tiny favourites that I shall show you, is one of more than ordinary beauty. It is the Two-lipped Tube-wheel of the Hornwort (Iimniacs ceratophylli). Hitherto we have seen WHEE-BEL- ARERS. 289 such examples as have the power of freely swimming fiom place to place at pleasure; but there is a considerable group, of which this is a member, which are permanently stationary, being fixed for life to the leaves or stems of the vegetation that grows under water. The stiff and spinous whorls of the Hornwort (CeratopAyZlumn demnersum), that grows commonly in sluggish streams and pasture-pools, is a favourite resort of the species, but it is not confined to any one plant. IHere, for instance, it has chosen as the site of its residence the much-cleft leaves of the Water Crowfoot (Ran2uncul~us aquatilis); those leaves, I mean, which, growing wholly under the water, are divided into a multitude of slender finger-like filaments, so different from those which float on the surface, and which are merely notched. You can readily find the Tube-wheels by the aid of a pocket lens, and even with the naked eye when you have seen one or two. By holding up this phial, in which a little plant of the Crowfoot is growing, and searching, with the lens, the window being in front of you, the filaments one by one, you will readily perceive, here and there, little shining objects standing up, or projecting in various directions from the surface of the leaves. The colony is rather numerous in this case, and we shall have no difficulty in selecting our specimens. On this filament, which I have seized with the joints of a pair of pliers, I can see at least half a dozen of the little parasites. This, then, I will nip off firom the plant, and put it with its tiny population into the live-box. Here it is, ready for examination. Several of the animals are in the field of view; but 13 290 EVENINGS AT THE BIICROSCOPE. we will look at one at a time. A long narrow tube, slightly widening at the mouth, is affixed by the lower extremity to the slender filaments of water-g'rass, cro-wfoot, &c. It is about one-fifty-fifth of an inch in length, pellucid but tinged with brownish yellow. It appears to be of a gelatinous texture, and is covered with extraneous substances, such as decaying animal or vegetable latters, which adhere to its surface. Froml the mouth of the tube protrudes a transparent colourless animal, the head of which is rounded, with the extremity pursed up. Suddenly it unfolds its flower-like wheel, which consists of two broad nearly circular lobes united, the T magin of which is set with strong cilia,. nl.uch resembling those of the Iast species. Each cilionm appears to be curved, and to be thickened at the middle-the opTUBl5~I:LE. tical expression of the ciliary wave; and the effect of the rotation, as each seems to pursue its fellows around the circular course down the dividing sinuosity, on the opposite sides, and around the margin again, is very striking. The cilia at the front are interrupted between the lobes. In the centre of each lobe is a broad plate, surrounded by a bright ring, and crossed by radiating lines which also extend towards the ciliated margin; probably these are muscular filaments. The funnel is between the lobes, and leads by a short cesophagus to a bulbous transparent mastax, in which are seen jaws that work on each other. Below this is a long capacious sac, without con VI-IEEL-BEARERS. 291 volutions or constrictions) but apparently granular in its texture. The alimentary canal is bent upwards through the whole length, terminating in an orifice behind the rotatory organ; for though I have not traced it when empty, I have seen the f~ecal matter driven rapidly upward as through a canal, until the mass was discharged just behind the sinuous cleft. On our mixing carmine with the water the effect is very striking; the particles, whirled round in two circular vortices, are poured in an accumulated torrent through the sinuosity, and over the elevation at the front of the head. We presently perceive a slender line of crimson passing down below the mastax, which indicates a slender stomach-tube there; and, after a while, a little ball of the same pigment accumulates and is seen resting a little lower down. This then indicates the forin and position of the stomach; it must be a very slender canal, terminating in a small rounded bag, at about one-third of the distance from the mastax to the base of the tube. WHIEELS OF TUBE-WHIEEL. The lengthened sac which you see is the ovary, from which the eggs are discharged into the lower part of the case. The mouth needs a little explanation in detail. As 292 EVENINGS AT THE MICROSCOPE. you see it, you probably discern little resemblance in its parts to the same organ in Brac/ionts8, and -yet essentially it is formed of the very same constituents; and as it is very instructive to observe the modifications, in different animals, of a common model of any particular organ, it will be worth while to devote a few minutes' careful observation to this structure. before us, especially as it is here seen with more than usual brilliancy and clearness. The mastax, then, which you see in the centre of the animal, just below the level of the beautiful flower-like wheels, consists as usual of three subglobose lobes; one on each side appropriated to each malleus, and the third descending towards the ventral aspect, which envelops the incus. The mallei are.more intimately united to the rami of the incus than in the former type, each uncus forming, with its ramus, a well-defined mass of muscle, enclosing the solid parts, and in form approaching the quadrature of a globe; two flat faces opposing and working on each other. Across the upper surface of the mass the uncus is stretched, as three long parallel fingers arched in their common direction, and imbedded in the muscular substance; their points just reaching the opposing face of the ramus, and meeting the points of the opposite uncus, when closed. The manubriumn is much disguised, by being greatly dilated transversely, forming three bowlike loops of little solidity, to the chord of which the fingers are soldered, not articulated. The surface of the dense muscular mass displays striae parallel to the fingers, and, as it were, continuing their number towards their dorsal extremity, becoming fainter till they are imperceptible. These striae do not disappear WHEEL-BEARERS. 293 when the muscular parts are dissolved by potash; and hence I infer the existence of a delicate investiture of solid substance similar to that of the teeth, &c., enclosinlg the muscular mass. The incus, which cannot be separated from the mallei, thus consists of two portions, corresponding to the rami in Brachionus, &c., each of which forms the lower part of the quadrantic nmass just described. At the ventral extremity they are articulated to a slender fulcrum,' which is a little bent downward. The solid fiamework of each ranmus sends off, from its inferior surface, a slender curved process, which is connected with the extremity of the fulcrum. The action of this apparatus is as follows: —The ciliary vortices produced by the waves of the coronal disk, pass together through the upper sinus, and are hurled in one streami along the centre of the face, nearly to the projecting chin. HIere is placed the orifice of the buccal funnel, a perpendicularly descending tube of considerable width, slightly fninel-shaped at the top, the interior surface of which is strongly ciliated. It descends straight upon the mastax, over the part where the unci unite. B3ut just above this point there are two valves projecting from the walls of the tube, also well ciliated. These can be brought into contact, or separated in various degrees, at will, and being very sensitive, they regulate the force of the inflowing current, and doubtless exclude hurtful or useless substances. The current now flows along the two ramii of the incus, as I have already described; and, passing between their separated points, descends into the cesophagus, a slender ducet opening beneath them, and leading to the digesting stomach. 294 EVENINGS AT THE MICROSCOPE. As this current, passes, the manducatory apparatus acts upon the particles of food which it brings in its course. The quadrantic masses approach each other and recede, with a rapid rolling movement, in the direction of the curvature of the mallei; while, at the same time, the rami of the incus open and close their points, rise and sink, and occasionally perform a kind of shoveling action. The points of the fingers of the unci, meeting each other, doubtless pierce and tear the Infusoria swallowed, and the striated faces of the quadrantic masses bruise, squeeze, and grind them down. When the muscular investiture is dissolved away by potash, the essential identity of the whole structure with that of the type already described, becomes abundantly evident. Even the mallei, which in some aspects present difficulty, when viewed vertically, are but little changed; the fingers are parallel instead of divergent, and the handle-like character of the manubrium is lost; but three areas, enclosed by loops or carinm of solid substance, reveal their true nature. We will now see if we canll separate the animal fiom its tube, so as to examine its lower parts. By a gentle pressure upon the bottom of the tube with the edge of a penknife, which I bring to bear upon it by the aid of this simple microscope, the creature is induced to wriggle out of his case. Replacing now the cover of the live-box, and placing it again on the stage of the compound microscope, we see that the lower part of the body forms a foot analogous to that of a Brachionuls, covered with ring-like wrinkles, and separated from the body by an abrupt constriction and WHEEL-BEARERS. 295 diminution of the diameter. At the very extremity there is a sort of sucking-disk, by which we may presulme the hold of the animal upon the plant is maintained. No organic connexion subsists between the foot and the tube; for the latter is not anl essential part of the animal, though absuidly called a lorica by Ehrenberg, but only an accumulation of mucus successively exuded from the body, and thrown off in the form which it possesses by the contractions and other movements of the body. But see! the poor naked creature is writhing in contortions, which become more and more convulsive and spasmodic: and now it evinces great rigidity in these, till the body has become almost shapeless, portions of the surface being here and there violently forced out into projections, and the foot strongly curled up. The only signs of life that now remain are the occasional fitful workings of the jaws. Are we then to suppose that the shelter of the gelatinous case is needful to its continued existence, or did I inflict a mortal injuLy upon it when I laid the edge of lny penknife upon its lower part to drive it forth? Most probably the latter is the true solution. Out of the colony that remains, we will now select another specimen, with ripening eggs, in order to watch the development of the young. Here is one with three eggs lying obliquely in the tube, one of which is already showing the impatient movements of the embryo within. Ha! now the egg-shell has burst, and the little creature escapes from its prison, and quickly malkes its way to the mouth of the parenttube. Now it is fiee, and swims away rapidly, in a giddy headlong manner. It is quite unlike its mother; 296 EVENINGS AT THE MICROSCOPE. for its form is trumpet-shaped, resembling that of a Stentor with a wreath of cilia around the head, interrupted at two opposite points: the central portion of the head rises into a low cone. There is as yet no trace of the beautiful double-petalled flower. It has been whirling giddily about the live-box for about a quarter of an hour, but now it begins to manifest tokens of weariness; or rather the time is approaching for it to select a place of permanent sedentary abode. Its motion is sensibly retarded; it now and then adheres to the glass momentarily, by its foot, and moves forward by successive jerks, not proceeding more than its own length at a time, and this apparently with effort. The periods of its remaining stationary become longer, so that you may suppose it finally settled two or three times, before its wanderings are quite over, some shock or alarm sending it off to a little distance again. At length it wanders no more; its foot holds fast to the glass, and its movements are confined to whirlings round and round on this as a pivot, and to sudden contractions of length. Presently we see a very delicate film surrounding the point of attachment;-the first rudiment of the tube, a ring of mucus thrown off from the skin, and pressed down to the foot by the contractions of the body. Meanwhile, the ciliary crown is dividing itself into two, and now we see already the essential form and appearance of the mature animal, every moment developing its perfection. wORMS. 297 CHIAPTER XV. WORMS. AN examination of the diverse modes in which locomotion is performed among animals, and the various organs and modifications of organs that subserve this important purpose, would form no uninteresting chapter in natural history. You have two feet, your dog has four; in the bird, two of these are converted into wings, with which it rises into the air; in the fish all of them are become fins, with which it strikes the water. But it is in the invertebrate classes that we discover the strongest variations. The Poulpe " flops" awkwardly but vigorously along, by the alternate contractions and expansions of the web that unites its arms; the Snail glides evenly over the herbage by means of its muscular disk; the Scallop leaps about by puffs of water driven from its appressed lips; the Lobster shoots several yards in a second by the blow of its tail upon the water; the Gossamer Spider floats among the clouds upon a balloon that it has spun fromrn its own body; the Centipede winds slowly along upon a hundred pairs of feet; the Beetle darts like an arrow upon three; and the Butterfly sails on the atmosphere with those painted fans which are properly " a6rial gills." How elegantly does the Planaria swim by the undulation of its thin body, and the Miledusa by the pumping forth of the water held within its umbrella! How wondrously does 13* 298 EVENINGS AT THE MICROSCOPE. the Ecldnu8s glide along the side of the tank on its hun-. dreds of sucking-disks! How beautiful, and at the same time how effective, are the ciliary wheels of the Brachionus. I am now going to show you some other examples of travelling machinery in an humble and despised, but fair from uninteresting class 6f animals, —-tle Worms. Here is an Earth-worm upon the garden-border. With what rapidity it winds along, and now it pokes its sharp nose into the ground, and now it has disappeared! If your eye could follow it, you would see that it makes its way through the compact earth not less easily nor less rapily than it wound along the surface. If you take it into your hand, you perceive no feet, wings, fins, or limbs of any kind; only this long cylinder of soft flesh, divided into numerous successive rings, and tapering to each extremity. The very snout which you saw enter so easily into the substance of the soil, is no hard bony point, but formed of the same soft yielding flesh as the other parts. And yet with no other implement does the little worm penetrate whitllersoever it will through the ground. How does it effect this. The fineness of the point to which the muzzle can. be drawn is the first essential. This can be so attenuated that the grains of adherent soil can readily be separated by it, when its action is that of the wedge. The body being drawn into the crevice thus imade, the particles are separated still farther. Now another provision comes in; the whole surface of the skin secretes and throws off a quantity of tenacious imucus or slime, as you will immediately perceive if you handle the Worm; this has the double effect of causing the pressed WORMS. 299 particles of soil to adhere together, and then to form a cylindrical wall, of which they are the bricks, and the slime the mortar; and also of greasing, as it were, the whole interior of the burrow or passage thus made, so that the Worm can travel to and fro in it without impediment; while the fact that the slime is continually poured forth afresh prevents the least atom of earth from adhering to its body. This you have doubtless observed, or may observe in a moment, if you will take the trouble to thrust a spade into the ground and give it two or three shakes. You will presently see on all sides the alarmed Earth-worms coming swiftly to the surface, and will notice how perfectly sleek and clean they are. But these contrivances are only accessories: we have not yet discovered the secret of the easy movement. The mere elongation of the snont is no explanation of the disappearance of the Worm in the burrow; for you will naturally and reasonably say that this elongation cannot extend beyond a certain limit; and what then? No further progress can be made unless the hinder parts of the body are, by contraction, drawn up towards the elongated front; —but what holds the front in place meanwhile? Why, when the muscles contract, does not the taper, wedge-like muzzle slip back and lose the ground it had gained? This we will now look at. I take up this Worm and put it in a narrow glass cell, where we may watch its movements. It presently begins to elongate and contract its body vigorously, apparently alarmed at its unwonted position; and the mucus is thrown off in copious abundance. We apply a low microscopic power to it, and catch glimpses, now and again, as it writhes 300 EVENINGS AT THE MICROSCOPE. about, of a number of tiny points protruded and retracted with lrlythmical syimmretry througll the skin. Its mobility precludes our discerning much nmore than that these points are very numerous, that they are arranged in four longitudinal lines, running along the ventral side of the animral-two lines on each sideand that in each line there is a point protruded from each of the many rings of which the Worm's body is made up. In order to see a little more of these organs we must sacrifice a Worm; having killed it, and divided the body in the middle, I cut off, with sharp scissors, a small transverse portion, say two or three rings, and press the ifragment between plates of glass. Now, with a higher magnifying power, we dliscern in the midst of the translucent flesh the points in question. They are not, however, single; but each protrusile organ consists of a pair of transparent, brittle, glassy rods, shaped like an italic f, of which the recurved points are directed backwards when thrust out from the skin. The mode in which these assist the progression of the Worm is well described by Professor Rymler Jones. "s The attenuated rings in the neighbourhood of the mouth are first insinuated between the particles of the earth, which, from their conical shape, they penetrate like a sharp wedge; in this position they are firmly retained by the numerous recurved spines appended to the different segments; the hinder parts of the body are then drawn forward by a longitudinal contraction of the whole animal-a movement which not only prepares the creature for advancing further into the soil, but by swelling out the anterior segments forcibly dilates the passage into which the head had been already thrust: WORMS. 301 the spines upon the hinder rings then take a firm hold upon the sides of the hole thus formed; and, preventing any retrograde m.ovement, the head is again forced flrward through the yielding mould; so tllhat, by a repetition of the process, the animal is able to advance with the greatest apparent ease through substances wlicll it would at first seem utterly impossible for so helpless a being to penetrate." * Implements analogous to these are found in most of the animals of the class Annrelida, to which the Earth-worm belongs. But in this creature you see them in their simplest form: it is to the aquatic'Worms that you must look if you wish to see the amazing diversity, complexity, and delicacy of these organs. In these there are one or two pairs of " feet" on each ring, consisting of wart-like prominences, which are perforate and protrusile, and through the middle of which work a number of bristles (setce), arranged in a radiating pencil, something like the hairs of a paintbrush. In this transparent and colo-urless little KNais from fresh water, you may see their form and arrangement; in complexity they present an advance upon the Earth-worm, for here there are some seven or eight bristiles in each pencil, which radiate in the same plane, and are graduated in length; they are very slender, bent at the tip, and as transparent as if drawn out of spun glass. It is inter- FOOT OF NAIS. esting to observe with what lightning-like rapidity they * Gen. Outline, p. 202. 302 EVENINGS AT THE MICROSCOPE. are thrust out and withdrawn in constant succession, as the body is ever lengthening and shortening. Let us exchange this little freshwater Worm for a marine one. IH-ere is a Polynde, a curious genus, very common under stones at low water on our rocky shores. It is remarkable on several accounts. All down the back we discover a set of oval or kidney-shaped plates, which are called the back-shields (dorsal elytra); these are flat, and are planted upon the back by little footstalks, set on near the margin of the under surface: they are arranged in two rows, overlapping each other at the edge. These kidney-shaped shields, which can be detached with slight violence, are studded over with little transparent oval bodies, set on short footstalks, which are perhaps delicate organs of touch. The inter"mediate antenna, the tentacles, and the cirri, or fila-'ments of the feet, are similarly fringed with these little appendages, which resemble the glands of certain plants, and have a most singular appearance. If we remove the shields, we discover, on each side of the body, a row of wart-like feet, from each of which project two bundles of spines of exquisite structure. The bundles, expanding on all sides, resemble so many sheaves of wheat, or you may more appropriately fancy you behold the armoury of some belligerent sea-fairy, with stacks of arms enough to accoutre a numerous host. But if you look closely at the weapons themselves, they rather resemble those which we are accustomed to wonder at in missionary museums-the arms of some ingenious but barbarous people from the South Sea Islands-than such as are used in civilised warfare. Here are long lances, made like scythe-blades, set on a staff with a hook at the tip, as if to capture the fleeing WORMS. 303 foe and bring him within reach of the blade. Among them are others of similar shape, but with the edge cut into delicate slanting notches, which run along the sides of the blade like those on the edge of our reapinghooks. These are chiefly the weapons of the lower bundle; those of the upper are still more imposing. The outmost are short curved clubs, armed with a row of shark's teeth to make them more fatal; these surround a cluster of spears, the long heads of which are furnished with a double row of the same appendages, and lengthened scymitars, the curved edges of which are cut into teeth like a saw. Though a stranger might think I had drawn copiously on my fancy for this description, I am sure, with your eye upon what is on the stage of the microscope at this moment, you will acknowledge that the resemblances are not at all forced or unnatural. To add to the effect, imagine that all these weapons are forged out of the clearest glass instead of steel; that the larger bundles may contain about fifty, and the smaller half as many, each; that there are four bundles on every segment, and that the body is composed of twenty-five such segments, and you will have a tolerable idea of the garniture and armature of this little Worm, that grubs about in the mud at low-water mark. Should it ever be your fortune to fall in with a species of Sea-mouse (Aphrodite hystrix) which inhabits our southern coast a little way from the shore, you may be delighted and surprised with a modification of these organs, which exhibits a more than ordinarily obvious amount of creative forethought and skill. I will describe them in the words of the learned historians of these animlals, MM. Audouin and Milne-Edwards: 304 EVENINGS AT TIE MICROSCOPE. "The feet are divided into two very distinct branches, the lower of which is large, conical, of a yellowish-brown hue, and much shagreened on the surface. The upper branch is much less salient than the lower. We observe at the foot of the dorsal shields two bundles of rigid bristles: the one, expanded like a fan and applied upon the shields, is fixed immediately outside the insertion of those organs; the bristles which compose it are awl-shaped, without teeth, slightly curved, and directed inwards and backwards; their colour is a clear brown, with golden reflections. Tle second bundle is inserted more externally, on a tuberculous footstalk, and points horizontally backwards and outwards. The bristles which enter into its composition are very long, very strong, and terminated by a lance-shaped point, of which the edges are garnished with teeth curved backwards towards the base. These are veritable barbed arrows, having the extremities sometimes exposed, but often concealed in a sheath which is formed of two horny pieces, capable of opening and of closing again upon them. "The use of these two valves it is not difficult to detect. They protect the points of the arrow, and permit the Aphrodite to receive them again into its body unharmed; whereas, without this precaution, the tissues which they traverse would be cut and mangled. But when these weapons are deeply plunged into a foreign body, as into the soft flesh of those animals which annoy the Worm, since the sheath does not penetrate with them but folds back, it follows that their teeth are inserted without any protection, and that on account of their backward direction they can be withdrawn only with great difficulty; thus, in most cases, WORMS. 305 the dart becomes broken; but the animal is furnished with so great a number, that these losses are scarcely felt, and there remain to it amply sufficient for its defence in all contingences." * You will have noticed that the learned French zoologists seriously countenance the notion that these exquisitely elaborated organs are weapons of offence. But in this I think they are in error, misled by the resemblance, already alluded to, which they bear to weapons of human construction. The manner in which they act as implements of locomotion has been beautifully demonstrated by Dr. Williams in the Nereidous Worms, of which he observes that in nearly all species the feet are constructed with express reference to progression on solid surfaces. In many instances, the bristle is compound, consisting of a staff with a variously armed point or blade jointed to its extremity. " Viewed by the light of mechanical principles, nothing can be so obvious as the reason why the setac in these, as in nearly all other Annelida, are jointed. If they consisted of rigid, unbending levers, it is manifest that they would prove most awkward additions to the sides of the animals; if fixed too deeply in the surrounding soil, they would not act at all as levers; if too superficially, the Worm would be compressed in its tube at the moment when the setce of the opposite feet would meet in a straight line. These difficulties are effectually and skilfully obviated by the introduction of a joint or a point of motion on each seta. This is one instance among many which the eye of the mechanician would detect on the organization of the Annelida in which * Litt. de la France, ii.'71. 306 EV.1 NINGS Ar THE MICROSCOPE. Nature takes adroit advantage of mechanical principles in the attainment of her ends." * Look now, in illustration of these principles, at the bristle-feet of this beautiful green PAyllodoce. No doubt you have often seen it in the little hollows of our rocky ledges, and especially on beds of young mussels, and probably you have admired the elegant ease with which its lithe and tortuous body writhes and winds, like a bit of green silken cord, in and out among the compactly crowded shells. You have wondered, too, at the difficulty which attends the attempt to take it up, not on account of the rapidity of its motions, but because of the extreme slenderness and slipperiness of the subject, and of the power which it possesses of insinuatig itself into the smallest crevice. The foot in this genus has but a single branch, and a single pencil of bristles, which is placed between the flat swimmilg leaf that ornaments each segment and the lower cirrus. The bristles are of the compound jointed form, but the joint is fixed in a peculiar manner. The basal portion is drawn out into a very slender long straight shaft, terminating in a knob somewhat resembling the end of a limb-bone. This is slit in one direction to receive the terminal piece, which is shaped somewhat like a lance-head, and is inserted into the slit exactly as a knife-blade is fixed into the haft. The head is in fact a knife-blade, with a thickened back and a very thin edge, which is notched into teeth of the most exquisite delicacy. The blade is slightly curved, and drawn out into a long acute point; and the whole bristle is formed out of an elastic horny substance (prob* Rep. on Brit. Annelidvs, 211. wTORMS. 307 ably chitine) that rivals in transparency and brilliancy the purest flint-glass. I might adduce a vast variety of examples of these organs in the Marine Worms, all of which would clharm you by their elegance and by their extreme diversity; but I have other things to show you in this interesting class of animals, which fortunately are so common on all our shores, that you will have no difficulty in procuring plenty of specimens for your private observation and study. And if you need intelligent guidance, you cannot have a better mentor than Dr. Williams, whose admirable " Report on the British Annelide" I have just cited. Before we dismiss our little Phyllodcoce to its home in the aquarium, we must try to get a sight of its pretty mouth. The Worms are somewhat wayward in displaying this part of their charms, sometimes exposing it at intervals of a second or two for very many times in succession, at others sullenly keeping it closed; and no efforts that I am aware of on our part will induce the display: we must await their pleasure. It is, in fact, a turning of the throat inside out. In most of the Worms the head is minute, and what seems to be the mouth is but the orifice from which the throat or proboscis is everted. In the Phtyllodoces this- organ is a great muscular sac, in some species equalling in length one-fourth of the whole body. IHa! there it appears! What a chasm yawns in the under side of the head, as the interior begins rapidly to protrude, turning inside out as it comes forth, like a living stocking, until it assumes the form of an enormous (comparatively enormous, of course) pearshaped bag, the surface of which is beset with a multi 308 EVENINGS AT THE MICROSCOPE. tude of secreting warts or glands, somewhat like the papillae which stud the tongue in higher animals! The extremity, which is perforated, is surrounded by a muscle, by means of which it contracts forcibly on whatever it is applied to, and thus holds it firmly, while the re-inversion of the sac drags it into the body to be digested. But this huge proboscis disappears as rapidly and as wonderfully as it was revealed. Commencing at what is now the outer extremity, which is quickly turned in, the whole swiftly returns to its cavity in the inverse order to that in which it was extended; and now that it is all engulphed, we marvel that. so vast a sac can be packed away in so slender a case. In this intsance the armature of the proboscis is feeble; but we have species which are very elaborately armed. There is a minute species of Lomn?,brinereis, which commonly appears in our aquaria after they have been some time established, and breeds in vast numbers on the floccose matter that clogs the bottom and sides. In this tiny Wormn there is a formidable array of jaws, resembling black hooks, which we may discern through their pellucid tissues, snapping and cutting viciously like so many pairs of hooked scissors. Though I have often had this little species in my tanks in copious abundance, I regret to say I cannot find any at this moment for our examination, and shall therefore content myself with translating for you MMA. Audouin and Mlilne-Edwards' description of the jaws as they appear in a closely-allied form, but of far greater dimensions, Ean~ice. "The proboscis is not very protrusile; when it is withdrawn its external orifice is longitudinal, and the WORMS. 309 jaws are fixed on each side, all facing the medial line. When it is projected, however, the two margins of the longitudinal cleft become transverse in separating, and the jaws follow the same movement, and diverge in the ratio of their forwardness. A kind of lower lip which is affixed to the under side of the proboscis, is composed of two horny blades united towards their front extremity, and prolonged behind into points. The jaws are to the number of seven; three on the right and four on the left; the two upper ones are perfectly alike, and mutually opposed; they are large, narrow, pointed recurved hook-wise at the tip, and jointed at their hinder ends on a double horny stem shorter than themselves. The second pair of jaws are large, broad and fiat, mutually alike, and jointed on the lower side of the first pair;... their internal edge is straight and cut into deep teeth. The third pair are small, thin, concave, and notched; they are affixed by their inferior edge outside and in front of the second pair, which they conceal during repose. Finally, the supernumerary jaw, which is found on the left side only, is small, semi-circular, toothed, and placed between the second and third pairs. All these pieces are surpassed by the margin of the proboscis, which is often hard and black." * From this complex and formidable mouth we will pass to one of quite another form, not less effective, perhaps more formidable, but ordained by the goodness of God to be a most valuable agent in the relief of humnan suffering. I mean the Medicinal Leech, of which we can readily procure a specimen from our friend the apothecary. * Litt. de la France, ii. 138. 310 EVENING S AT THE MIICROSCOPE. Here it is. There is no protrusile proboscis, but the throat is spacious, and capable of being everted to a slight degree. The front border of the mouth is enlarged so as to form a sort of upper lip, and this combines with the wrinkled muscular margin of the lower and lateral portions to form the sucker. With the dissecting scissors I slit down the ventral margin of the sucker, exposing the whllole throat. Then, the edges being folded back, we see md eimplanted in the walls on the dorsal region of the cavity three white eminences of a cartillaginous texture, which rise to a THROAT OF LEECH IAID OPEN. sharp crescentic edge; they form a triangular, or rather a triradiate figure. Now, if you recollect, this is the figure of the cut made in the flesh wherever a Leech has sucked, as it is of the scar which remains after the wound has healed. For these three little eminences are the implements with which the animal, impelled by its blood-sucking instincts, effects its purpose. But to understand the action more perfectly, we must use higher powers. I dissect out of the flesh, then, one of the white points, say the middle one, and laying it in water in the compressorium, flatten the drop, but use no more pressure than just enough for that.'Now I apply a power of 150 diameters, and we will look at it in succession. You have under your eye a sub-pellucid mass, of an irregular oval figure, and of fibrous texture, one side of which is thinned away apparently to a keen edge of a somewhat sermi-circular outline. But along wORMS. 311 this edge, and as it were imbedded into it for about one-third of their length, are set between seventy and eighty crystalline points, of highly refractive substance, resembling glass. These points gradually decrease in size towards one end of the series, and at length cease, leaving a portion of the cutting edge toothless. At the end where they are largest, they are nearly close together, but at length are separated by spaces equal to their own thickness. The manner in which they are inserted closely resembles, in this aspect, the implantation of the teeth in the jaw of a dolphin or crocodile. But this appearance is illusory. By affixing the little jaw to the revolving needle, we bring the edge to face our eye. It is not an edge at all; but a narrow parallel-sided margin of considerable breadth. And the teeth are not conical points, as they seemed when we viewed them sidewise, but flat triangular plates, with a deep notch in their lower edge. Thus they partly embrace, and are partly inserted in, the margin of the jaw. Observe now how beautifully. this apparatus subserves the purpose for which it is intended. By means of its sucker, the Leech creates a vacuum upon a certain part of the skin, exactly like that produced by a cupping-glass. The skin covered is drawn into the hollow so far as to render it quite tense, by the JAw oF LEEC, (in part). pressure of the surrounding air. Thus it is brought into contact with the edges of the three jaws, to which, 312 EVENINGS AT THE MIICROSCOPE. by means of powerful muscles attached to them, a seesaw motion is communicated, which causes the little teeth soon to cut through the skin and superficial vessels, from which the blood begins to flow. The issue of the vital fluid is then promoted by the pressure around, and so goes on until the enormous stomach of the Leech is distended to repletion. It has been suggested that this whole contrivance, with the instinct by which it is accompanied, is intended for the benefit of Man, and not of the Leech. Blood seems to be by no means the natural food of the Leech; it has been ascertained to remain in the stomach for a whole twelvemonth without being digested, yet remaining fluid and sound during the entire period: while, ordinarily, such a substance cannot in one instance out of a thousand be swallowed by the animal in a state of nature. Whether this be so or notwhether man's relief under suffering were the sole object designed, or not, it was certainly one object; and we may well be thankful to the mercy of God, who has ordained comfort through so strange an instrumentality. The progress of marine natural history, as studied in the aquarium, has made our drawing-rooms and halls familiar with a multitude of curious and beautiful creatures which a few years ago were known only, and that very imperfectly, to the learned professors of technical science. Among the forms which embellish our tanks are several species of Serpzulc, and Worms allied to it. The shelly contorted tube which this painted Seaworm inhabits, and which it has built up itself around its own body, with stone and cement which that body supplied, is well known to you; as is also the curious wORMS. 313 conical stopper with which it closes up its bottle as with cork, when safe at home, and the lovely crown of gorgeously coloured fans which it expands when it takes ("' the air," I was about to say, but rather) the water. You are familiar, too, with the lightning-like rapidity with which, while in health and vigour, the Serpula, on the slightest alarm, retreats into his fortress, taking care to clap the door to after him. But perhaps you have never had an opportunity of examining the mechanism by which this rapid flight is effected. As there are two distinct movements performed by the Worm-the slow and cautious and gradual protrusion, and the sudden and swift retreat-so there are two distinct sets of organs by which they are performed. Shall I sacrifice one from this fine group to demonstrate the mechanismn? Well, then, I carefully break the shelly tube, and extract the WVorm uninjured. Its form is, you perceive, much shorter and more dumpy than you would have supposed from looking at the tube; and it is somewhat flattened, having a back- and a belly-side. On the former there is a sort of shield, the sides of which bear wart-like feet, -about seven pairs in all-which are perforated for the working of protrusile pencils of bristles, similar in structure and in function to those which we lately examined. Here is one of the pencils extracted. To the naked eye it is a yellowish body with a satiny lustre; and this effect depends upon the light being reflected from a number of nearly parallel lines-the staves of the spear-like bristles, which the eye cannot resolve in detail. A drop of the caustic solution of potash 14 314- EVENINGS AT' T'IIE IICROSCOPE. cleanses the bundle from the fleshy matter which would otherwise obscure the vision, and now I place it on the stage. With this power of 400 diameters you see a multitude-some twenty or thirty, or more-of very long, slender, straight rods, of a clear yellowish horny substance, set side by side, like a sheaf of spears in an armory. Each one merges, at its upper end, into a sort of blade, which is slightly bent, and which tapers PUSHING-POLES OF SERPULA. to an exceedingly fine point. But its chief peculiarity is that the blade has a double edge, not like a twoedged sword, the edges set on opposite faces, but on the same face, set side by side, with a groove between them; and each edge is cut with the most delicate and close-set teeth, the lines of which pass back upon the blade, as in our reaping-hooks. These pencils of spear-like bristles are the organs by which the protrusion of the animal is performed. Their action is manifestly that of pushing against the walls of the interior, which on close examination are seen to be lined with a delicate membrane, exuded from the animal's skin. The opposite feet of one segment protrude the pencils of bristles, one on each side, the acute points and teeth of which penetrate and catch in the'lining membrane; the segments behind WORMS. 315 this are now drawn up close, and extend their bristles; these catch in like manner; then an elongating movement takes place; the pencils of the anterior segments being now retracted, they yield to the movement and are pushed forward, while the others are held firm by the resistance of their holding bristles; thus gradually the foreparts of the animal are exposed. But this gradual process would ill suit the necessity of a creature so sensitive to alarm, when it wishes to retreat. We have already seen how, with the fleetness of a thought, its beautiful crown of scarlet plumes disappears within its stony fastness: let us now look at the apparatus which effects this movement. If you look again at this Serpula recently extracted, you will find, with a lens, a pale yellow line running along the upper surface of each foot, transversely to the length of the body. This is the border of an excessively delicate membrane; and on placing it under a higher power (say 600 diameters), you will be astonished at the elaborate provision here made for prehension. This yellow line, which cannot be appreciated by the unassisted eye, is a muscular ribbon over which stand up edgewise a multitude of what I will call combs, or rather sub-triangular plates. These have a wide base; and the apex of the triangle is curved over into an abrupt hook, and then this is cut into a number (from four to six) of sharp and long teeth. The plates stand side by side parallel to each other, along the whole length of the ribbon, and there are muscular fibres seen affixed to the basal side of each plate, which doubtless give it independent motion. I have counted 136 plates on one ribbon; there are two ribbons on each thoracic segment, and there are seven such seg 316 EVENINGS AT THE MIICROSCOPE. ments:- hence we may compute the total number of prehensile comb-like plates on this portion of the body to be about one thousand nine hundred, each of which is wielded by muscles at the will of the animal; while, as each plate carries on an average five teeth, there are nearly ten thousand teeth hooked into the lining nlembrane of the cell, when the animal chooses to descend. Even this, however, is very far short of the total number, because long ribbons of hooks of a similar structure, but of smaller dimensions run across the abdominal segments, which are much more numerous than the thoracic. No wonder, with so many muscles wielding so many grappling hooks, that the retreat is so rapidly effected! 11i0K OF ERULA rll/! HOOK5 OF SE'PULA. SEA-URCHINS AND SEA-CUCUMBERS. 317 CHAPTER XYI. SEA-URCHINS ANI) SEA-CUCUIMBERS. PEERING about among the rocks to-day at low-tide, I found, on turning over a large stone, an object which, though familiar enough to those who are conversant with the sea and its treasures, would surprise a curious observer fresh from the fields of Warwickshire. It is a ball, perfectly circular, and nearly globular-only that its under part is a little flattened-hard and shelly in its exterior, which is however densely clothed with a forest of shelly spines, each-one of which has a limited amount of mobility on its base. On attempting to remove it, I find that it adheres to the stone with some firmness, and that on the exercise of sufficient force, it comes away with a feeling as if something were torn, and I find that a multitude of little fleshy points are left on the stone. Having dropped mny prize into a glass collecting-jar of sea-water, I presently see that it is slowly marching up the side, sprawling out on every side a multitude of transparent hands, with which it seems to feel its way, and -which are evidently feet also, for on these it crawls along at its own tortoisepace. And I now see that it is the knobbed ends of some of these feet which were torn away by my forcible act of ejectment, and left clinging to the stone. It was not the first time that I had seen the Sea 318 EVENINGS AT THE MICROSCOPE. urchin (Echinvus miliaris); and I might have passed it by with a feeling of satiated curiosity, had I not recollected our evening's amusement. Oh, ho! said I, what a fund of microscopic entertainment is inclosed in this stone box! So I brought it home, and now produce it as the text of our conversazione. Every part is a wonder; but we must examine each in order. Take the spines first. As we examine these organs on the animal crawling at ease over the bottom of a saucer of sea-water, using this triple lense, we see that each is a taper pillar, rounded at the summit, and swelling at the base, where it seems to be inserted into a fleshy pedestal, on which it fireely moves, bending down in all directions, and describing a circle with its point, of which the base is the centre. Each. spine is for the greater portion of its length of a delicate pea-green hue, but the terminal part is of a fine lilac or pale purple. The whole surface appears to be fluted, like an Ionic column, but this is an illusion, as you will see presently. 1 now detach one of the spines, cutting it off with fine-pointed scissors as near the base as I can reach. I put it, with as little delay as possible, into the live-box, and examine it with a high power, say 600 diameters. Look at it. You see the ciliary currents very distinctly; and if you move the stage so as to bring the basal portion into view, you may discern even the cilia themselves, very numerous and short, quivering with a rapid movement. The currents are not longitudinal, but transverse, and somewhat peculiar. The floating atoms which come within their vortex are drawn in at right angles to the axis of the spine, and SEA-URCHINS AND SEA-CUCUIMBERS. 319 are presently hurled away in the same plane; forming a circle, whose plane is perpendicular to the direction of the spine. - The surface upon which these cilia are set is a transparent gelatinous skin, of extreme tenuity, stretched tightly over the solid portion, which it completely covers, and studded with minute oval orangecoloured grains. The substance of which the spines are composed is best seen by crushing a few of these organs into fiagments. We now see a texture beautifully delicate; they are formed of calcareous substance as transparent as glass, and reflecting the light like that material; hard but very brittle; clear and solid, with a fibrous appearance in some parts, but in others excavated into innumerable smooth rounded cavities which join each other in all possible ways. It is to this structure that the spine owes its strength, its lightness, and its brittleness. This arrangement of the calcareous deposit in a sort of glass full of minute inter-communicating hollows, is very peculiar, but it is invariably found in the solid parts of this class of animals; so that the experienced naturalist, on being presented with the minutest fiagment of solid substance, would, by testing it with his microscope, be able at once to affirm with certainty, whether it had belonged to an Echinoderrm or not. And this uniformity obtains in all the divers forms which the animals assume, and in all the various organs which are strengthened by calcareous deposits -Crinoid, Brittle-star, Five-finger, Urchin, Sea-gherkin, or Synapta;-ray, plate, spine, sucker-disk, lantern, pedicellaria, dumb-bell, wheel, or skin-anchorwhenever we find calcareous matter, we invariably 320 EVENINGS AT THE MICROSCOPE. find it honey-combed, and eroded, as it were, in this reiarkable fashion. Dr. Carpenter has described this texture so well, that I shall not apologise for quoting his words to you, especially as you will have an opportunity here of testing their correctness, by personal observation.' It is," he remarks, "in the structure of that calcareous skeleton, which probably exists, under some form or other, in every member of this class, that the microscopist finds most to interest him. This attains its highest development in the Echiinida, in which it forms a box-like sliell, or' test,' composed of numerous polygonal plates jointed to each other with great exactness, and beset on its external surface with'spines,' which may have the form of prickles of no great length, or mrlay be stout, club-shaped bodies, or, again, may be very long and slender rods. The intimate structure of the shell is everywhere the same: for it is composed of a network, which consists of carbonate of lime, with a very small quantity of animal matter as a basis, and which extends in every direction (i. e. in thickness, as well as in length and breadth), its areolme or interspaces fireely communicating with each other. These' areole,' and the solid structure which surrounds them, may bear an extremely variable proportion one to the other; so that, in two masses of equal size, the one or the other may greatly predominate; and the texture may have either a remarkable lightness and porosity, if the network be a very open one, or may possess a considerable degree of compactness if the solid portion be strengthened. Generally speaking, the different layers of this network, which are connected together by pillars that pass from one SEA-URCHINS AND SEA-CUCUMBERS. 321 to the other in a direction perpendicular to their plane, are so arranged that the perforations in one shall correspond to the intermediate solid structure in the next, and their transparency is such, that when we are examining a section thin enough to contain two or three such layers, it is easy, by properly'focussing' the microscope, to bring either one of them into distinct view. From this very simple but very beautiful arrangement, it comes to pass that the plates of which the entire'test' is made up, possess a very consideraable degree of strength, notwithstanding that their porousness is such, that if a portion of a fractured edge, or any other part from which the investing membrane has been removed, be laid upon fluid of almost any description, this will be rapidly sucked up into its substance." e To return, however, to our spine. When we look at it laterally, the appearance is such that we cannot but firmly believe, that it is grooved throughout with straight and deep longitudinal furrows. ZBut if we break off the same spine transversely, and so exhibit it that the broken end shall be presented to the eye, we perceive that there are no grooves; but that the points in the circumference, which seemed to be-the summits of the ridges, which are very narrow, are really lower than the intermediate spaces, which we supposed to be the grooves, and that the surface of these spaces is really convex in a slight degree. The explanation of these contradictory appearances is easily given. Meanwhile, however, they read an important lesson to the inexperienced microscopist, not to decide too hastily on the character of a surface * The Microscope, p. 553. 14* 322 EVENINGS AT THE MICROSCOPE. or a structure, friom one aspect merely. So many are the chances of illusion, that the student should always seek to view his subject in different aspects, and under varying conditions of light, position, &c. It is by making a thin transverse section of a spine — cutting off a slice of it, to speak in homely phrase — that we shall demonstrate the structure, which is very beautiful. This is an operation requiring much delicacy and practice, and implements for the special purpose; and hence it is best performed by professional persons, who prepare microscopic objects for sale. You may see such a section, however, on this slide; but I do not know whether the spine belongs to the species we are examining. The whole central portion is formed of the spongelike calcareous matter, which, from the variously reflected and refracted rays of light, appears nearly opaque, and of a bluish colour by transmitted light. This structure sends forth radiating points (mlaking longitudinal ridges, of course, in the perfect spine;) and it is the opacity of these points (or ridges) which reach the circumference, that gives to the spine the appearance of being fluted. Indeed it would be fluted if this were the entire structure; but the open space left between these projecting radii is filled with the solid glassy matter, having, as we see, a convex surface. This; however, from its perfect transparency, is not seen when we look at the side of the spine, the eye going down to the bottom of the interspace. The spine is, in fact, a fluted column of spongy glass, with the grooves filled with solid glass. We have not yet seen, however, the beautiful SEA-URCHINS AND SEA-CUCUMBERS. 323 mechanism appropriated to the movement of these spines. You can hardly see thisI to advantage in the living ani- AV tl fli mal, but here is the entire shelly' box of a dead Echinus, on which, while for the most part the surface is denuded of spines, a few dozen remain sufficiently attached to show what I wish to demonstrate, viz., the mode of articulation. You observe that the whole globose shell is covered with tiny knobs, differing in size, and not set in very regular, or at least not SPINE OF ECIIINUS. very obvious order, but showing Secmnent of Section. a tendency to run in lines from pole to pole of the globe. Giving attention to one of the larger of these knobs, under a lens it is seen to be a hemispherical eminence on the shell, the very summit of which is crowned by a tiny nipple of polished whiteness, resembling ivory. Now if we carefully lift one of the still remaining spines fiom its attachment, which in its present dried state is so fragile that the slightest touch is sufficient for the purpose, we shall note that its base rests on this tiny nipple; and on turning it up, and bringing the magnifying power to bear upon its base, we see that this is excavated with a hollow, whose dinmensions exactly correspond with those of the nipple. It is indeed a true " ball and socket " joint, like that of the human hip or shoulder, and is surrounded by a capsular ligament to keep it in place, the muscles which sway the spine from side to side and cause it to rotate, being inserted outside the capsule. Professor 324 EVENINGS AT THE MICROSCOPE. Edward Forbes calculates that upon a large Echinus, such as this dried specimen of E. splicera, there are more than four thousand spines, every one of wlhich has the structure, the mechanism, and the mnovements that we have been examining. Well may he say, that' truly the skill of the Great Architect of Nature is not less displayecl in the construction of a Sea-urcllin than in the building up of a world! " To return now to our little E. nziliaris, which has been all this time coursing round and round his saucer, wondering, perchance, at the narrowness and shallowness of the White Sea in which he finds himself. Again we peer, lens to eye, over the bristling surface, and discern, shooting up amidst tlhe spines, and almost as thickly crowded as they, multitudes of the tiny organs which have caused so much doubt and discussion among naturalists. Miller, the great marine zoologist of Denmark, who first discovered them, thought them parasitic animals, living piratically upon the unwilling Urchin, and accordingly gave them generic and specific names. The term Pedicellaria, which he assigned to his supposed genus, is that by which modern naturalists have agreed to call thein still, though the word is not now used in a generic sense, since it is indubitably established that they are not independent animals, but essential parts of the Urchin itself:. Mliller described three distinct sorts, and I have added a fourth to tlhe number; they are named P. triphylla, th.idens, globifera, and stereophylla. They all agree in thlese particiulars:-that each has a' long, slender, cylindrical, fleshy stem, through the centre of which runs an axis or rod of calcareous substance; that the base of the stem rests on the skin of the Urchin; that on the-s:um SEA-URCHINS AND SEA-CUCUMBERS. 325 mit is placed a head consisting of three pieces, which are capable of being widely opened and of being closed together, at least at their tips; that the edges of these pieces, which come into mutual contact, are furnished with teeth, which lock into each other; that the headpieces (like the stem) consist of calcareous centres, clothed with flesh; that, besides the opening and shutting of the head, the stem can be swayed from side to side; and that all these movements are spontaneous, and apparently voluntary. It appears that the headpieces close on any object presented to them, such as the point of a needle, and hold with considerable force and tenacity, so that the Pedicellaria may be drawn out of the water without relaxing its grasp. Looking at one of the first-named kind, the PCdicelacria trzlphylla, of this Echlinuzs miliaris, we see that it consists of three broad and thick sub-triangular pieces, jointed into a head, set on a thickish stein of transparent gelatinous fibrous substance, through which a slender core of calcareous matter runs that looks fibrous and blue. The three movable pieces or blades are convex externally, concave internally; thin in substance, firnished along their Opposing or concave sides with two longitudinal ridges or keels, each of which is cut into the most beautifuilly fine teeth, so that the edge of each ridge looks like a shark's tooth; the, edges of the pieces are also similarly toothed: these shut precisely into each other. In the larger E. sphcera, the head-blades of this kind have one stout central ridge, which is rounded and not toothed. It forms the front of a great interior cavity, which opens by two orifices on each side of the column. 326 EVENINGS AT THE MICROSCOPE. The movable pieces inclose a skeleton of calcareous substance, glassy, colourless, and brittle, in which, according to the plan I have already described, are excavated a multitude of oval cavities which form irregular rows; a central line runs down each piece, that is solid and free from cavities. This calcareous skeleton is encased in a gelatinous flesh, similar to and continuous with that of the stalk. This is the smallest kind, the head being about W'tlh of an inch in height. Considerable mlodifications are found to exist in the details of each form, in the relative proportions which the parts bear to each other, and so forth;' so that two forms, which in t their extreme conditions widely dif-' fer, mutually approach, and appear to run into each other. This is the case with the present, and with the form which I will now show you. P. tridens is much larger than any of the other forms, the movable head being about h-lth of an inch in length, and the whole organ about'th of an inch. This may be considered as essentially P. tripliylla, modified by the blades being greatly drawn out in length, and at the same time rendered quite slender, so that they may be called pins; they meet I''! only at the points, where they often HEAD OF PEDICELLAIRIA TRID ENS. cross, the interspaces of the basal parts being open. The inner edges of these are notched with teeth as in P. triphylla, Of which those near the SEA-UTRCIINS AND SEA-CUCUMBERS. 327 tips are larger and cut into subordinate teeth of exquisite minuteness. We have here an opportunity of seeing that the oval or square markings, which are thickly placed throughout the calcareous substance of the blades, are certainly cavities in it; for in those examples in which the pins, which are very brittle, are broken, the edge of the fracture is not even, but jagged with holes exactly corresponding with the marks in question; so that the structure is the same as that of the spines and of all the other solid parts of the Urchin. We will now examine some specimens of P. tridens, treated with potash, which will enable us to see the calcareous support better. The head-blades expand at the base into three-sided prisms or pyramids, each of the two interior sides of which is indented with a large cavity, leaving a projecting dividing ridge, armed with teeth somewhat remote from each other. The one exterior angle is toothed in a corresponding manner, but the opposite angle appears plain. The angle of one blade-base fits into the cavity of its neighbour; and, so far as I have observed, when the two edges thus overlap, it is the toothed one that is on the outside. Looking from the circumference towards the centre of the head, it is the left angle that is toothed and external, the right being plain and sheathed. This observation, however, applies only to E. nilictris; for, in the corresponding organs of E. spheerc, both sides of the trigonal base appear fintoothed, except close to the bottom, where a deep notch indents each margin. Viewed from beneath, the head assumes an outline which is rondo-triangular;: but yet such that each side of the triangle- has a veryobtuse projecting. angle in 328 EVENINGS AT THE MICROSCOPE. the middle, where the blade-bases meet each other. They fit accurately, and each has a deep oblong cavity in its bottom, which does not, as I conceive, communicate with the interior. By selecting one of these heads, which has been divested of its fleshy parts by immersion in caustic potash, and then well cleansed by soaking in clean water, and placing it under a low power of the microscope-100 diameters, for example-with a dark ground, and the light of the lamp cast strongly upon it by means of the Lieberkuhn, or the side-condenser, we shall have an object of most exquisite beauty. The material has all the transparency and sparkling brilliance of flint-glass, while the elegantly-shaped pins, the perfect symmetry of the prismatic bases, the arch which is lightly thrown across their cavity, the minute teeth of the tips locking accurately into each other, and the oval cavities in the whole structure set in regular rows, and reflecting the light from thousands of points, constitute a spectacle which cannot fail to elicit your admiration. P. globifera is formed on the same model as P. tri/phylla,but is more globose, and each piece appears to have a deep cleft at the point, which does not extend to the interior side, where a thick ridge runs down from the point to the base. At the summit of this ridge, in each of the three divisions, there is set a strong acute spine, directly horizontally inwards, so that the three cross each other when the blades close, which they do energetically-a formidable apparatus of prehension! The stem is much more slender than in P. triphylla, and the height of the head of one of average size is only - d of an inch. It is peculiar also SEA-URCHINS AND SEA-CUCUMBERS. 329 in being slender throughout, and in having the. knobbed calcareous stalk extending up to the head, which appears to work on it. In each of the other sorts the stalk extends only through a part of the distance, above which the investing fleshy neck becomes wider and empty. But the internal structure is not quite the same as in the others. The main portion of the head is composed of gelatinous flesh; the calcareous support being reduced to that ridge which runs up the interior side of the blade. This is somewhat bottle-shaped, with a bulbous base, and a long slender neck, with two edges on the inner face, which are armed with horizontal hooked spines, some of which are double, and the whole terminates in a sort of ring, formed by tle last pair of spines, which unite into the acute horizontal point that I have already mentioned. The skeleton is filled with oval cavities like that of the others. The fourth kind of Ped'icellaria, which I call P. stereophylla, is quite distinct from either of the others. It is very minute, the head being only,- th of an inch in llheight. The head is a prolate solid spheroid, cut into three segmennts, exactly as if an orange were divided by three perpendicular incisions meeting at the centre. Thus the blades meet accurately in every part when closed, but expand to a horizontal condition. These are almost entirely calcareous, being invested but thinly with the gelatinous flesh. They are filled with the usual oval cavities, set in sub-parallel arched series. The head is set on a hollow gelatinous neck nearly as wide as itself, and thrown into numerous annular wrinkles- its walls are comparatively thin, disclosing a 330 EVENINGS AT THE MICROSCOPE. wide cavity apparently quite empty, as the blue calcareous stem extends only half-way from the base to the head. At this point the neck contracts rather abruptly, and continues to the base, but just wide enough to invest the stem. This sort is confined, so far as I have seen, to the ovarian plates and their vicinity, where they are numnerous. Thus these tiny organs, so totally unlike anything with which we may parallel them in other classes of animals, do not merely afford us amusement, and delight us by their elegance of shape and sparkling beauty, the variety and singularity of their forms, the elaborateness of their structure and the prefection of their mechanism, but excite our marvel as to'what can be the object Wihich they subserve in the economy of the creature —what purpose can be fulfilled by so many hundreds of organs so singular, and scattered over the whole surface of the shelly body. It is very difficult to answer this question. The only organs with which they can be compared are the singular "birds' heads" in so many of the Polyzoca, which we looked at some time ago. But, unfortunately, a like mystery enshrouds the use of those processes, and the only light that we have as yet upon either form is that of dim conjecture. It has been supposed that, in both cases, the function of the prehensile forceps is to seize minute animalcules or floating atoms of food, and pass them to the mouth: but the supposition is involved in great difficulties; as the organs, however fitted for prehension, seem peculiarly unsuited for transmitting objects; besides that the great majority Lof them are placed very remote from the mouth. I can SEA-URCHINS AND SEA-CUCUMBERS. 331 only repeat the conjecture which I have hazarded in the ease of the Polyzoan " birds' heads," viz., that the Pecliceicaricu are intended to seize minute animals, and to hold them till they die and decompose, as baits to attract clouds of Inf8tsorica, which, multiplying in the vicintiy of the Urchin, may afford it an abundant supply of food There is yet another series of organs which stretch out fiom every part of the periphery of this living box; scarcely less numerous than either the spines or Pedicellariwce, but very different from both. They are what I alluded to just now as the feet. Let us pay a moment's attention to their appearance and action, before we examine their structure. WVe see, then, extending from various points of the shelly case of tire Urchin, and reaching to twice or thrice the length of the longest spines, slender pellucid tubes, slightly tapering towards their fiee extremity, which then abruptly dilates into a hemispherical knob, with a fiat end. These very delicate organs are extended or contracted at the will of the animal, turned in every direction, waved hither and thither and evidently have the faculty of adhering very firmly by their dilated tips to any object to which they are applied. So much we can discern as we watch the creature disporting in this vessel of water; but we will now endeavour to learn a little more about its structure and economy. Selecting for this purpose a sucker which is extended to great length, I snip it across with a pair of sharp scissors, as near the base as I can. Mark the result. The terminal knob which was attached to the bottom of the saucer maintains its hold; but the tube 332 EVENINGS AT THE MIICROSCOPE. has suddenly shrunk up to a sixth part of its former length, exchanging at the same time its smooth slender-,,.,ness and translucency for / ~ a corrugated semi-opacity. I push the knob aside wvith a needle's point and thus destroy its adhesion; which done, I take up the severed and /t~P shrunken sucker, and lay it in a little sea-water in the live-box. SUCKER OF URCMIN. Under a power of 180 diameters we see that the tunbe is composed of two series of muscular fibres, the one set running lengthwise, the other transversely or annularly; the former bytlleir contraction diminishing the length of the tube, the latter diminishing its calibre. The muscular walls are covered with a transparent skin, studded with round orange-coloured spots, perhaps glandular, exactly similar to those we saw on the exK'~'. terior of the spines and PedicelNoa, to illustrate the action I_,? — %'$ i of these tubular feet, I must again have recourse to the denuded shell of a preserved V lt1x EchintwS. Taking this globose empty ox into your hand, hold:-. it up against the light, looking PORES OF URCHIN. in at the large orifice, which was once occupied by the mouth; — you see that the Whole shell is pierced with minute holes-pores, which SEA-IITROIINS ANnD SEA-CUCUMBERS. 333 are arranged in ten longitudinal or meridional lines, associated so as to make five pairs of lines. Now, with a lens, scrutinize more minutely a portion of any one of these lines, and you discern that it is composed of a multitude of pores, which have a peculiar order of arrangement among themselves; that is to say, they form minor rows which cross, obliquely or diagonally, the course of the meridional line. These rows are tllemselves double, the pores running in pairs, not however with mathematical symmetry. In this species, there are three pairs of pores in each row, and so there are in the one which I have here alive, but in other of our native species the rows consist of five pairs. These pores are intimately connected with the tubular feet, each of which springs from a portion of the shell that is perforated with a pair of pores; so that the cavity of every tube communicates with the interior of the shelly box by two orifices. Now on the interior side of these two pores-that is, within the cavity of the shell-there is placed a little membranous, or rather muscular, bladder, filled with a fluid which is not materially different from seawater. There is a free communication between the bladder within and the tube without the shell, by means of the pair of pores through which the fluid passes. By means of the muscular fibres, which are under the control of the Urchin's will, any portion of this double vessel can be contracted to a certain extent. Suppose it is the interior bladder; the effect of the contraction of its walls is to diminish its capacity, and the contained fluid is forced through the pores into the tube without. The longitudinal fibres of this part being at the same moment relaxed, the tube is lengthened be 334 EVENINGS AT THE MICROSCOPE. cause of the injected water. Suppose, now, ill turn, the fibres of the tube contract, while those of the bladder relax; the fluid is driven back, the bladder dilates, and the tube shortens, until, if the animal so please, its swollen tip is brought close up to the pores. By mechanism so beautiful and simple is the prolongation or abbreviation of these organs effected. WVe noticed, however, that the extremities of the tubes had an adhesive power, which faculty it is that constitutes them feet. They are prehensile, and thus they afford, as we observed in the living Urchin, the means by which it takes hold of even a smooth and vertical surface, as the side of a glass tank, and drags up its body thereby. Putting, now, the extremity of this cut-off tube under graduated pressure, having first applied to it a drop of caustic potash, we see that it carries a beautiful glassy plate of extreme thinness, which lies free in the swollen cavity of the termination of tile tube. This plate is circular in form, apparently notched at the margin, and cut with four or five (for the number varies) incisions, which reach almost to the centre. The substance is formed of the common clear brittle calcareous matter of the skeleton, hollowed into numberless cavities, according to the general plan. The centre is perforated with a larger round orifice. The appearance of marginal notching is deceptive; and indicates a structure analogous to what we see in the spine. The notched line indicates the extent of the spongy structure; but beyond this the plate extends into a perfectly circular smooth edge, but is constituted of a layer of calcareous substance so thin that there is no room for the ordinary cavities within it. SEA-URCHINS AND SEA-CUCUMBERS. 335 The round aperture in the centre plays an important part in the function of the organ. The foot adheres on the same principle as that by which children take up large flat stones with a piece of wetted leather, to the middle of which a string is attached. The boy drops his sucker on the stone, and treads firmly on it, to bring it into close contact with the surface; then he pulls at the string perpendicularly, by which the central part of the leather is SUCKER-PLATE OF URCIIIN. lifted a little way from the stone, leaving a vacuum there; since the contact of the edges with the stone is so perfect that no air can find entrance between them. Now the pressure of the atmosphere upon the leather is so great that a considerable weight, perhaps half-a-dozen pounds, may be lifted by the string before the union yields. Well, the very counterpart of this amusing operation is repeated by the clever " Urchin" whose performances we are considering. The tube is his string; the dilated end with the plate in it, his leather; his muscular power acts like the other urchin's tread, to press the bottom of the sucker against the surface of the rock. Then he pulls the string; in other words, he drags inwards the centre of the muscular bottom of the sucker, which is, as it were, sucked up into the central orifice of the plate. Thus a vacuum is formed beneath the middle of the sucker, on which the weight of the incumbent water and atmosphere united presses with a force far more than sufficient to resist the weight of his body, when he drags upon it, andl, as it were, warps htimself up to the adhering point. 336 EVENINGS AT THE MICROSCOPE. Here is in my cabinet a specimen of a Sea-urchin of a less regular form: it is the IHeart-Urclin (Amph/idotus cordctus). Essentially, its structure agrees with that of the more globular forms, but it is heartshaped, and the two orifices, instead of being at opposite poles, are separated only by about one third of the circumference. It shows also singular impressed marks on its shell, as if made by a seal on a plastic sub. stance. But what I chiefly wish to direct your attention to are the spines. These differ much from the kindred organs in Echinuzs, being far more numerous, very slender, curved, thickening towards the tip, and lying down upon the shell in the manner of hair, whence the species is sometimes called the Hairy Sea-egg. The array of spines has a glittering silky appearance in this dried state. WVe will now put a few of them under a low power of the microscope, using reflected light and a dark background. They thus present a very beautiful appearance; elegantly-formed curved clubs, made of a substance which seems to be between glass and ivory, having the whiteness of the latter and the glittering brilliance of the former. The entire surface appears to be exquisitely carved with excessively minute oval pits, arranged in close-set lines, with the most charming regularity. It is the light reflected from the polished bottoms of these pits that imparts to the surface its sparkling brilliancy. At the bottom of the spine there is a little depression, which fits a tiny nipple on a wartlike prominence of the shell, as we saw in Echinus; but a little way above this point there is a singular projection or shoulder of the calcareous substance, SEA-URCHINS AND SEA-CUCTUMBERS. 337 which is set on at a very oblique angle with the axis of tile spine, reminding one, as we look at the spine laterally, of the budding tines on the horn of a young deer. At first, perhaps, you are at a loss to know what purpose this shoulder can serve;' but by turning to the shell and carefully observing the spines in their natural connexion with it, you will observe that the obliquity of its position accurately corresponds with the angle which the individual spines form with the surface of the shell from which they spring; and that the shoulder has its plane exactly parallel with the latter, but raised a little way above it. Now the entire shell, during life, was clothed with a living vascular flesh, having a thickness exactly corresponding to the distance of the shoulder from the shell., This shoulder, then, was an attachment for the muscular bands, whose office it was to move the spine to and fro; the projection affording the muscles a much better purchase, or power, than they could have had if they had been inserted into the slender stem itself. The tubercles on the shell show a structure which corresponds with this. They are very minute; but each of them is regularly formed, and is crowned with its little polished nipple, on which, as I have said, the spine works, as by a ball-and-socket joint. These are arranged with perfect regularity in quincunx, and by close examination you will see that each is inclosed in a little area formed by a very low and narrow ridge of the shell, which makes a network. On the lateral portions of the under surface the meshes of this net are particularly conspicuous, and we see that they constitute shallow hexagonal cells, in the midst of which 15 338 EVENINGS AT THE MICROSCOPE. is seated the tubercle; yet not in the exact centre either, but nearer the front than the back of the area inclosed. Now this elevated ridge affords, doubtless, the insertion of the other end of the muscles that move the spine; the ridge giving a better purchase than a flat surface, as the keel on the breastbone of birds is deep in proportion to the vigour of the muscles used for flight. And, surely, the apparently trivial fact that the space behind the tubercle is greater than that in front, is not without significance, since it implies a thicker muscle at that part, which accords with the circumstance that such would be the insertion of the muscle-band whose contraction produces the outward stroke by which the sand is forced away from the bed. But what is the need of so much care being bestowed upon the separate motion of these thousands of hair-like spines, that each individual one should have a special structure with special muscles, for its individual movement? The hairs of our head we cannot move individually: why should the Hleart-Urchin move his? Truly, these hairs are the feet with which he moves. The animal inhabits the sand at the bottom of the sea in our shallow bays, and burrows in it. By going carefully, with the lens at your eye, over the shell, you perceive that tile spines, though all formed on a common model, differ considerably in the detail of their form. I have shown you what may be considered the average shape; but in some, especially the finer ones that clothe the sides, the club is slender and pointed; in others, as in those behind the mouth, which are the largest and coarsest of all, the club is dilated into a long SEA-URCHINS AND SEA-CUCUMBERS. 339 flat spoon; while in the long, much-bowed spines which densely crowd upon the back, the form is almost uniformly taper throughout and pointed. The animal sinks into the sand mouth downwards. The broad spoons behind the mouth come first into requisition, and scoop away the sand, each acting individually and throwing it outwards. Observe how beautifully they are arranged for this purpose! diverging from the median line with the curve backwards and outwards. Similar is the arrangement of the slender side-spines; their curve is still more backwards, the tips arching uniformly outwards. They take, indeed, exactly the curve which the fore-paws of a mole pos sess-only in a, retrograde direction, since the Urchin sinks backwards-which has been shown to be so effective for the excavating of the soil and the throwing of it outwards. Finally, the long spines on the back are suited to reach the sand on each side, when the creature has descended to its depth, and by their motions work it inward again, covering and concealing the industrious and effective miner. Thus we have another instance added to the ten thousand times ten thousand, of the wondrous wisdom of God displayed in the least and most obscure things. " All thy works shall praise thee, 0 Lord! " (Ps. cxlv. 10.) There is an order of animals which naturalists put in the same category as the Sea-urchins, but which an unscientific observer would regard as possessing little or no affinity with them. Some are like long, soft, and fleshy worms, and others, which come the nearest to the creatures we have been looking at, have still the lengthened form, which, however, So closely resembles 340 EVENINGS AT THE MICROSCOPE. that of a warty angled cucumber that the animals 1 allude to are familiarly called Sea-cucumbers (Holothquriadce). The marine zoologist frequently finds them beneath stones at extreme low water, and larger forms —as big in every direction as a marketable cucumber-are occasionally scraped from the bottom of the deep sea by means of that useful instrument, the dredge. If you drop one of them into sea-water you will presently see from one extremity an exquisite array unfold like a beautifully cut flower of many petals, or, rather, a star of ramifying plumes. Soon it begins to climb the walls of your aquarium, and then you catch the first glimpse of its affinity to the Urchins; for tile short warts which run in longitudinal lines down the body, corresponding to the angles, gradually lengthen themselves, and are soon perceived to be sucking-feet, analogous in structure and in function to those with which the Star-fish and Sea-urchin creep along. But the relationship becomes more apparent still when we find that the Cucumber has a skeleton of calcareous substance deposited on exactly the same plan as in the Urchin, viz., around insulated rounded cavities. It is true you may cut open the animal and find nothing at all more solid than the somewhat tough and leathery skin; but a calcareous skeleton is there notwithstanding, though in truth only a rudimentary one. If we were to cut off a considerable fragment of the skin, and spread it out to dry upon a plate of glass, and then cover it with Canada balsam, we should find-assisted by the translucency which is communicated to the tissues by the balsam —that the skin is filled with scattered atoms of the calcareous structure, perfectly agreeing with that with which the solid frame-work of SEA-URCHIIINS AND SEA-CUCUBERS. 341 the Urchin is built up, but minute and isolated in the flesh instead of being united into ofne or more masses of definite organic form. But the atoms I speak of are still more perfectly seen by dissolving the piece of skin in boiling potash, and washing the sediment twice or thrice in pure water; this may then be spread upon a glass slide, and covered with a plate of thin glass, when it forms an interesting and permanent object for study. I have here a slide which is the result of such treatment; to the naked eye it appears sprinkled with the finest dust, but under magnifying power it is seen to consist of numberless calcareous bodies, of great beauty, and very free from extraneous matter. The elegance of the forms is remarkable, and also their uniformity; for though there do occur here and there among them plates of no regular shape, perforated with large or small roundish orifices, yet the overwhelming majority are of one form, subject to slight modifications, in shape and size. Neglecting, then, the irregular pieces, we perceive that the normal form is an oval of open work, built up by the repetition of a single element. That element is' a piece of clear glassy material, highly refractive, of the shape of a dumb-bell-two globes united by a thick, short column. The oval is constructed thus:suppose two dumb-bells to be placed in contact, side by side, and soldered together, there would be of course an oval aperture between their columns. Then two others dumb-bells are united to these in a similar manner, but one on each side, so that the globes of each shall rest in the valley between the former globes now united. These then are soldered fast in like manner; 342 EVENINGS AT THE MICROSCOPE. and the result is that there are three oval apertures. The next step is that on the top of the four united globes two other dumb-bells stand erect, and lean over towards each other till their upper globes come into contact, their lower ones remaining remote; these are soldered to the mass and to each other, at the points of contact, leaving a fourth aperture. The same is repeated at the opposite end by two other dumb-bells;and the structure is complete as you see it. In almost all cases the two united globes of these terminal elements are fused into one globe, and in not a few instances the appearance is as if these two dumbbells were but one, bent over in a semi-circular form; but still a good many specimens occur in DUIJB-BELLB IN IIOLOTlHUrIA. which the two dumnb-bells can be quite distinguished from each other. The calcareous matter that solders the elements together seems abundant, and has the appearance that would be presented if they had been made of solid glass, and united by glass in a state of fusion; the latter having apparently run together, so as to smooth and round angles and fill up chinks, even where, as is often the case, the globes themselves have only mutually approximated, and not come into actual contact. The average dimensions of these oval aggregations may be'004 inch in length, and a little more than'002 in width; but some specimens occur which are a little larger, and others a little smaller than this; while the irregular plates are sometimes three tines thre length. SEA-URCHINS AND SEA-CUCUMBERS. 343 Some of tihe more worm-like members of this class have, however, a skeleton composed of pieces imbedded in their skin, of even more remarkable shapes than these. One of these is the Cldrodotc 1. violacea — a native of the southern coasts' of Europe. We have indeed a British species of the same genus, a specimen of which is in my possession, but I have vainly examined the skin for any structure analogoous to this.' In the Medi- WHEEL IN CIIRODOTA. terranean species the skin, especially of the belly-side, is described as filled with plates exactly resembling broad and thin wheels of glass, supported by four, five, or six radiating spokes, and having the inner edge of the hoop cut into teeth of excessive delicacy. Another animal remarkable for its cuticular furniture is the genus Synaptca, which is very similar in form, and closely allied to the Ch4irodota. It is very common in the Adriatic and Mediterranean seas, but has not yet been taken on the British coasts. I would counsel you, however, to have your eyes open if you have the opportunity of searching our coasts; for, as Miiller found one species, the Synapta inlcerens, on the shores of Denmark, it is not at all unlikely that we may possess either it or some other. Should it ever come into your hands, slit open the skin of the belly, where you will * The most careful and repeated search has not availed me to find in the skin the least trace of calcareous atoms; but this may possibly be because I had unfortunately preserved my specimen in acetate of alumina and the acetic acid has perhaps dissolved the lime. 344 EVENINGS AT THE MIICROSCOPE. find, embedded -in little papill] or warts, some highly curious spicula or calcareous forms. Each, consists of an oblong plate, perforated with large holes in a regcular manner, and having a projection on its sur'face near one extremity, to which is jointed a second piece, lhaving thle most singularly true resemblance to an anN -LATE IN chor. The flukes of this anchor project SYNAPTA. from the skin, the shank standing obliqluely upward firom the plate, to which it is articulated by a dilatation, where the ring would be, which is cut into teeth. Among the multitude of transparent creatures that swim in the open sea, few are more interesting than -those which constitute the infant state of the very animals that we have lately been examining —the Seaurchins and their allies. It is a productive way of obtaining subjects for microscopic research, to go out in a boat on a quiet summer's day, especially in the afternoon, when the sun has been shining, or when evening is waning into night, and with a fine muslin net stretched over a brass ring at the end of a pole, skim the surface of the smooth sea. At intervals you take in your net, and having a wide-mouthed glass jar ready, nearly filled with sea-water, invert the muslin in it, when your captives, small and great, float off into the receiver. After a few such essays, unless yon have very bad success indeed, you will see even with the naked eye, but much more with a lens, that the water in your jar is teeming with microscopic life; and though many of your captives will not long survive the loss of their freedom, still meanwhile you may secure many an interesting object, and examine it, SEA-URCHINS AND SEA-CUCUMIBERS. 345 while yet the beauty and freshness of life remain. And moreover, with care and prudence, some selected subjects may be maintained in vigour, at least long enough to afford you valuable information on the habits, economy, metamorphosis, and development of animals, of which even the scientific world knows next to nothing. I have just been so fortunate as to obtain in this way the larval stage of one of our Sea-urchins, and have it now in the thin glass trough which is on the stage of the microscope. It is just visible to the unassisted sight as a slowly moving point in the clear water, when the vessel is held up to the light; but with the low power which I am now using, it is distinctly made out in all its parts, and is an object of singular elegance and beauty. It is, as you see, somewhat of the figure of a helmet; the crest rising to a perpendicular point, which is rounded, the vizor or mask descending far down and ending in two points, and a long ear hanging down on each side, so as to reach the shoulders of the wearer. Of course such comparisons are fanciful, but they assist one in intelligible description. Now, the entire helmet is composed of a gelatinous flesh of the most perfect transparency, so that we can see with absolute clearness everything that is within it. And the first thing that strikes us is, that a frame-work or skeleton of extreme delicacy, composed of glassy rods, supports the whole structure. Look carefully at this, and mark its symmetry and elegance. There is, then, first, a rod which passes through the crest perpendicularly, and' carries at its lower extremity a horizontal ring. To the opposite sides of this ring are 156 346 EVENINGS AT THE MICROSCOPE. soldered two other very slender'rods, passing down nearly in a perpendicular direction, but a little diverging; and two other shorter rods pass down from the front of the ring, parallel to these. After a while each lateral pair of rods is united by a short cross-piece, and the result is four lengthened rods, two of which go down through the vizor into the chin-points, and two larger and stouter ones through the ears into the shoulder-points. This, then, is the solid skeleton, the interest of which is much enhanced, when we observe that it is formed, on the common plan, out of perforated lime-glass, the two ear-rods and the crest-rod being pierced with a regular series of oval holes, and bearing on their edges corresponding projecting points. Now, to turn again to the gelatinous flesh. The inner surface of the vizor, or that which would be in contact with the.face of the wearer, supposing it to be a real helmet, has a great squarish orifice with a thickened margin, which we see by its movements to be highly sensitive and contractile. This square orifice is the mouth of the larva, and it leads into a cavity in the upper part of the vizor, which is the gullet; and this in its turn terminates in a narrowed extremity, which passes into the orifice of a greater and higher cavity, the lip of which embraces it just as the bung-hole of a barrel receives and embraces the tube of a funnel. The latter cavity occupies the chief part of the volume of the helmet, the four rods diverging to inclose it. It is the stomach. It adds to the beauty of the little helmet-shaped creature, that while the greater portion of the substance is of the most colourless transparency, the summit of the crest and the tips of the shoulder-points are tinged with a lovely rose-red. The whole exterior surface is, SEA-URCHINS AND SEA-CUCUMBERS. 347 moreover, studded with those minute and glandular specks, with which every part of the adult Urchin is covered; and the light is reflected from the various prominences with sparkling brilliancy. The little creature moves through the water with much grace, and with a dignified deliberation; the crest being always uppermost, and the perpendicular position invariably maintained. It does not appear capable of resting, its movements depending on incessantly vibrating cilia. These organs we perceive densely clothing the long ear-pieces, but more especially accumulated and more vigorous in a thickened, fleshy band, which passes partly round the whole helmet, at the origin of these pieces. You do not discern the slightest resemblance of form between this little slowly-swimming dome and the spined and boxed Urchin which crawls over the rocks; and you wonder by what steps the tiny atom of one-fortieth of an inch in length is led to its adult stage. Fortunately I can satisfy your curiosity on this point, not indeed from my own observations, but by those of Professor Johann Miiller, whose discoveries of the developments of these and kindred animals are among the most interesting, because the most startling, of the marvels which modern zoology has revealed to us. The whole process is full of surprising details, to which the change of the caterpillar to a chrysalis, and that. of the chrysalis to a butterfly,- LLVA OF SBA-UCOHIN. present no parallel, wonderful as those changes of form 348 EVENINGS AT THE MICROSCOPE. appear and are. There we have but modifications of outward form, produced by the successive mioults or castings of the external skin, and the gradual growth of the animal, which -has from the first been present, though veiled. But the construction of the Seaurchin is by no means a process of skin-casting, nor has it any recognised parallel in the whole economy of natural history. It is a development perfectly unique. I will endeavour to malke you acquainted with the results arrived at from the researches of the eminent German zoologist to whom we are indebted for almost all we know on the matter. Let me first premise that this beautiful helmetshaped creature is not the future Urchin; and, strange to say, that only a very small portion of the present structure, namely, the stomach and gullet, will enter into its composition. The helmet is a kind of temporary nurse, within which the future Urchin is to be formed, and by which it is to be carried from place to place by its ciliary action, while the young animal is gradually acquiring the power of independent life, when the whole constitution of the nurse wastes away and vanishes! The first trace of the young Urchin is a filmy circular plate, which is not symmetrical with the helmet, nor formed even on the same plane, but appears obiiquely fixed on the exterior of the stomach, on one side, close to the arch of transparent flesh which stretches from one of the points of the vizor to one of the earpoints. Hlerr Miiller compares the larva (which is not helmet-shaped in every species) to a clock-case, of which the vizor, with its hanging gullet and mouth, form- the pendulum, and then the newly-formed disk SEA-URCHINS AND SEA-CUCUTMBERS. 349 represents the face of the clock, only it is put on the side instead of thle front. Now this tiny disk gradually grows into the form and assumes all the organs of the Urchin, while the enveloping nurse, flesh, rods, and all, waste away to nothing. The disk, soon after its appearance, is seen to bear prominences on its surface, in which is traced the figure of a cinque-foil, the elements being five warts set symmetrically. These lengthen and grow into suckers, essentially identical with those of the adult, but most disproportionately large. In the five triangular interspaces between these, little points and needles of solid calcareous glass begin to form, very much like the crystals that shoot across a drying drop of a soluton of some salt; these catch and unite, first into -T, and then into H-forms, and then into irregular networks. Meanwhile, fleshy cylindrical columns spring up from the surface, one in each of these interspaces, and presently develop, within their substance, a similar framework of porous glass; these soon manifest themselves to be the spines, and each is seated on a little nucleus of network, on which it possesses the power of rotating. At the same time pedicellarim begin to be formed; and, what is specially marvellous, they are first seen, not on the disk, which alone is to be the future Urchin, but on the interior wall of the helmet, which is even now in process of being dissipated, and even on the opposite side to that which carries the disk. They commonly appear four in number, arranged in two pairs; and one can see in them-they being, like the suckers, large out of all proportion to the disk — the stem, and the.: three-leaved heads, which already exercise their characteristic snapping movements, 350 EVENINGS AT THE MICROSCOPE. The disk is meanwhile enlarging its area; and the spines and suckers, gradually lengthening, at length push themselves through the walls of the helmet; the hanging points and crest of which are fast diminishing by a kind of insensible absorption; the ciliary movements become less vigorous, and the mouth closes up. But, correspondently, the Urchin is beginning to acquire its own independent power of locomotion; for the ef-z suckers, now, ever sprawling about, are capable of adhering o oto any foreign body with w? hich they come into contact, and of dragging the whole o structnre about, by their proper contractions. The cilia that cover the thickened fringing band still exercise their Developmemt of Disk. powers, and are the last to disappear. When the disk has grown to such an extent as to spread over about half of the larval stomach, very little remains of the helmet, except the middle portions of the glassy rods and the ciliary bands; all the rest of this exquisitely modelled framework having vanished by insensible degrees, no one knows how or where. The stomach and gullet indeed are gradually sucked into the ever-growing disk; but all the rest, flesh and rods, fringes, bands, and cilia, waste away to nothing. The mouth of the larva has no connexion with the mouth of the Urchin. The little isolated patches of glassy network continue to spread through the flesh SEA-URCHINS AND SEA-CUCUMBERS. 351 of the disk, until the whole forms one uniform structure, and constitutes a series of plates. The mouth is that spot in the centre, over which the calcareous frame is last extended; and it is first distinguishable by the appearance of five glassy points, which soon develop themselves into the five converging jaws, which we see forming such a curious apparatus on the inferior side of the Sea-Urchin. Actual observation has not traced the infant animal beyond the stage of the development; but specimens have been taken by Professor Miiller swimming in the sea, in which scarcely a rudiment of the larva remained. They had the form of round flattened disks, which freely moved their spines and crawled about the sides of the vessel in which they were kept, by means of their suckers, exactly in the manner of the adult Urchin. Thus'" ends this strange, eventful history; " and in reviewing it, one can scarcely avoid being impressed with a sense of the majesty of God in these His humble works. By what wonderful, what unexpected roads does He arrive at the completion of His designs! and if such things as these are only now bursting upon our knowledge, after six thousand years of man's familiar contact with the inferior creatures, how many more wonders may yet remain to be unfolded, as science pursues herinvestigations into the Divine handiwork! And yet, how do this and all similar manifestations of power and wisdom, sink into insignificance before the grand marvel, the wonder of wonders, the great mystery of godliness-that GOD WAS MANIFEST IN THE FLESH! We are surprised and delighted when we see one creature change, as it were, into another, but too often the 352 EVENINGS AT THE MICROSCOPEo story of that greater wonder, that God should have become man, falls upon listless ears and cold hearts: and yet the former, which we scarcely weary of tracing, concerns only the well-being of a poor dull creature scarcely raised above the life of a plant, whereas the latter had for its object the lifting of cre.atures from a state of ruin and wrath to immortal life and everlasting glory; and the creatures are —ourselves! JELLY-FISHES. 353 CHAPTER XVII. JELLY-FISHES. As this afternoon was delightfully calm and warm -the very model of an autumnal day-I took my muslin ring-net and walked down to the rocks at the margin of the quiet sea. Nor was I disappointed; for the still water, scarcely disturbed by an undulation, and clear as crystal, was alive with those brilliant little globes of animated jelly, the Ciliograde and Nakedeyed Miedusse, apparently little more substantial than the clear water itself. MI-ultitudes of them were floating on the surface, and others were discerned by the practised eye, at various depths, shooting hither and thither, now ascending, now descending, now hanging lightly on their oars, and now, as if to make up for sloth, darting along obliquely with quickly-repeated vigorous strokes, or rolling and revolving along, in the very wantonness of humble happiness. After gazing awhile with admiration at the undisturbed jollity of the hosts, I made a dip with my net, the interior of which, on lifting it from the water, was lined with sparkling balls of translucent jelly. They were far too numerous to allow nme to transfer them all to captivity; they would soon have choked up land destroyed one another; I therefore selected the finest 354 EVENINGS AT THE MICROSCOPE. and most interesting, shaking an example or two of each kind into my glass jar of sea-water, where they immediately began to frolic and revel as if still in the enjoyment of unrestricted liberty. And here they are. Among these bright and agile beings which are shooting their wayward traverses across each other, and intertwining their long thread-like tentacles, we will select one or two for examination, as samples of their kindred. And first let me isolate this active little Bero6 (Cydippe pornmformi8~), which I dip out with a tea-spoon and transfer to this other glass jar, that we may watch its form and movements unaffected by the presence of its companions. We see, then, a little ball, almost perfectly globular, except that a tiny wart marks one pole, of the size of a small marble, and apparently turned out of pure glass, or ice, or jelly-according to your fancy —perfect transparency and colourlessness being its characteristics, so much that it is not always easy to catch sight of the little creature, except we allow the light to fall on the jar ill a particular direction. From two opposite sides of the globe proceed two threads of great length and extreme tenuity, which display the most lively and varied movements. These filaments shall occupy us for a few moments. aWe trace them to their origin, and find that they proceed each from the interior of a lengthened chamber, on each of two opposite sides of the animal. Suddenly, on the slightest touch of some foreign object, one of the threads is contracted to a point and concealed within its chamber,' but is presently darted forth again. When the lovely globe chooses to remain still, the JELLY-FISHES. 355 threads hang downward, gradually lengthening more and more, till their extremities lie along the bottom of the jar, extended to a length of six inches from the chamber. Then we see that this delicate thread is not simple, but is furnished along one side, throughout its length, at regular distances, with a row of secondary filaments, which project at right angles from the main thread. These secondary filaments constitute an important element in the charm which invests this brilliant little creature. They are about fifty in number on each thread, and some of them are half an inch long, when fully extended, but it is seldom that we see them thus straightened; for they are ever assuming the most elegant spiral coils, which open and close, extend and contract, with an ever-changing vivacity. The animal has a very perfect control over the threads, as well as over the secondary filaments in their individuality. One, or both, are frequently projected from their chambers to their full extent by one impulse; sometimes the extension is arrested at any stage, and then proceeded with, or the thread is partially or entirely retracted. Sometimes the secondary filaments are coiled up into minute balls scarcely perceptible, or only so as to give to the main thread the appearance of small beads remotely strung on a fine hair; then a few nncoil and spread divergently; contract again, and again unfold; or many, or all, interchange these actions together, with beautiful regularity and rhythmical uniformity, repeating the alternation for many times in rapid succession. The beauty and diversity of the forms assumed by these elegant organs beguile us to watch them with 356 EVENINGS AT TIIE MICROSCOPE. unwearied interest, and we wonder what is their function. For, with all our watching, this is by no means clear. They are certainly not organs of motion. At times it seems as if they were cables intended to moor the animal, while it floats, at a given depth; or we see them with their extremities spread upon the bottom, to which they appear to have a power of adhering, thus forming fixed points, from which the little globe rises and falls at pleasure, shortening or lengthening its delicate and novel cables, maintaining all the while its erect position. WVhen the Oydcippe swims, however, which it does with great energy, the threads seem unemployed, streaming loosely behind, and evidently taking no part in the progression, though still adding beauty and grace to the tout enseinble. The organs by which the sprightly motions of the whole animal are affected are of quite another character, and shall now engage our attention. You have doubtless observed, while gazing on the animal, a peculiar glittering appearance along its sides, mingled in certain lights with brilliant rainbow-reflections. Now let us take an opportunity, when it apploaches the side of the glass, to examine this appearance with a lens. The globe, you see, is marked by longitudinal bands, eight in number, set at equal distances, and ranging like meridians, except that they do not quite reach to either pole. These bands are the seats of the motile organs, which are highly curious, and in some sort peculiar. Each band is of considerable width in the middle, but becomes narrower towards the extremities. It carries a number-usually from twenty to thirty-of flat JELLY-FISHES. 35'7 thin membranous fins, set at regular distances, one above the other, which may be considered as single horizontal rows of cilia, agglutinated together into flat plates. Each plate has a rapid movement up and down, from the line of its insertion into the band, as from a hinge, and thus striking the water downwards, like a paddle. The whole band may be likened to the paddle-wheel of a steamer, except that the paddles are set in a fixed line of curvature instead of a revolving circle. OYDIPPE. The effect, howevers is exactly the same: that of paddling the beautiful little globe vigorously through the water. The prismatic colours are produced by the play of light on their glittering surfaces, which are ever presented to the eye of the beholder at changing angles. We rarely see these rows of paddle-fins wholly at rest, but occasionally one or two bands will be alone in a state of vibration; or one or more will suspend their action while the rest are paddling. Sometimes in a band 358 EVENINGS AT THE MICROSCOPE. that is at rest, a minute and momentary wave will be seen to run rapidly along its length. All these circumstances show that the ciliary motion is perfectly under the control of the anilnal's will, not only in the aggregate, but in every part. In an excellent memoir on this animal by Mr. R. Patterson of BelIfst,* there are some interesting observations on the power of its tissues to become tinged with extraneous colours, a fact which may be useful to you in your researches, as enabling you with more ease and precision to demonstrate the internal structure. "' From the inconsiderable quantity of solid material," remarks this observer, " which enters into the body of the Beroes, and the rapid circulation of water, which is apparent throughout their frame, we would naturally suppose that any tinge which the body might accidentally acquire would be extremely fugitive. It was found, however, to be much less so than d priori would have been expected. Mly attention was drawn to this peculiarity by the circumstance of all my glass vessels being one evening occupied by Beroes and Crusacea, so as to compel me to place a small Medusa in a tin vessel, which chanced to be rusted at the seams. Next morning the colourless appearance of the animal was changed into a bright yellow, which appeared to pervade every part, and doubtless arose firom the oxide of iron, diffused through the sea-water. This tint remained during the entire day, although the animal was transferred to pure sea-water. Wislling to try if the vessels of the Bero6 would become distinct, if filled with some coloured fluid from which the animal could suddenly be withdrawn, and viewed through the usual * Trans. Roy. Irish Academy, vol. xix. pt. 1. JELLY-FISHES. 359 transparent medium of sea water, I placed a Bero6 in a weak infusion of saffron. At the end of twenty minutes its colour had undergone a perceptible change. I allowed it, however, to remain immersed for about six or seven hours, when it had assumed a bright yellow hue. It was then placed in pure sea-water, but retained its yellow colour for twenty-four hours afterwards; and though it gradually became fainter, it was very perceptible even at the expiration of forty-eight hours." I am sure you will pardon my interrupting your microscopic gazings for a moment by quoting the following charming lines by the Rev. Dr. Drummond, which were elicited by his having watched with pleasure the elegant form and motions of this little creature. " Now o'er the stern the fine-meshed net-bag fling, And from the deep the -little Beroi bring: Beneath the sun-lit wave she swims concealed By her own brightness;-only now revealed To sage's eye, that gazes with delight On things invisible to vulgar sight. When first extracted from her native brine, Behold a small round mass of gelatine, Or frozen dew-drop, void of life or limb: But round the crystal goblet let her swim'Midst her own element-and lo! a sphere Banded from pole to pole-a diamond clear, Shaped as bard's fancy shapes the small balloon To bear some sylph or fay beyond the moon. From all her bands see lucid fringes play, That glance and sparkle in the solar ray With iridescent hues. Now round and round She wheels and twirls-now mounts-then sinks profound. Now see her, like the belted star of Jove, Spin on her axis smooth-as if she strove To win applause-a thing of conscious sense, Quivering and thrilling with delight intense. Long silvery cords she treasures in her sides, 360 EVENINGS AT THE MICROSCOPE. By which, uncoiled at times, she moors and rides; From these, as hook-hairs on a fisher's line, See feathery fibrils hang, in graceful twine, Graceful as tendrils of the mantling vine, These, swift as angler, by the fishy lake, Projects his fly, the keen-eyed trout to take, She shoots with rapid jerk to seize her food, The small green creatures of crustaceous brood; Soon doomed herself a ruthless foe to find, When in th' Actinia's arms she lies entwin'd. Here prison'd by the vase's crystal bound, Impassable as Styx's nine-fold round, Quick she projects, as quick retracts again, Her flexile toils, and tries her arts in vain: Till languid grown, her fine machinery worn By rapid friction, and her fringes torn, Her full round orb wanes lank, and swift decay Pervades her frame till all dissolves away. So wanes the dew, conglobed on rose's bud, So melts the ice-drop in the tepid flood: Thus too shall many a shining orb on high That studs the broad pavilion of the sky, Suns and their systems fade, dissolve, and die." While we have been admiring our lovely little iydcippee, and comparing notes with other observers and admiirers, other species as small, as transparent, as sprightly, and scarcely less elegant, have been ilpatiently waiting for their share of admiration; shooting to and fro, tossing their little bells of ductile glass about, and alternately lengthening and snatching-in theil sensitive tentacles, in astonishment at our stoical indifference to their charms, and saying, szmo more, with the little urchin whose feelings were hurt by the neglect of his papa's visitor —'" You don't notice how beautiful I be?" A thousand pardons, sweet little Sctrsia! We will now give you ou r -unndivided: attention and for this JELLY-FISHES. 361 end we must take the liberty of catching you and of transferring your translucency to isolated gran deur in this other glass. HIa! but you don't want to be caught, eh? And so you pump and shoot round and round the jar as the spoon approaches! Truly you are a supple little subject, difficult to catch as a flea,; and difficult to hold (in a spoon) as an eel. But here you are at last, lyinog as motionless and as helpless in the silver as a half-imelted atom of calf's-foot jelly, to which, indeed, you possess no small resemblance. Look at the pretty little Medusa in his new abode, at once recovering all his jelly-hood as he feels the water laving him, and dashing about his new domain with a vigour which makles up for lost time. It is a tall bell of glass, a little contracted at the molth —its outline forming an ellipse, from which about a third has been cut off. Thle margin of this bell calrries four tiny knobs, set at equal distances, and thus quartering the peripheryy; and these are the more conspicuous because each one is marked witl a bright orange-coloured speck. Physiologists are pretty well agreed to consider such specks as these, on the margins of the smaller AJedusce, as eyes, —rudilnentary organs of vision, capable, probably, of appreciating the presence and the stimulus of light, without the power of forming any visual image of external objects. You will not gain much information about their function firom microscopic examination; for all you can discern is an aggregation of coloured specks (pigment-granules) in the midst of the common jelly. Tle knobs, however, are connected with other organs; for from each of theim depends a highly sensitive and very contractile tentacle. Sometimes one, or 16 362 EVENINGS AT THIE MICROSCOPE. more, or all, of these organs hang down in the water motionless, lengthening more and more, especially when the bell is still, until they reach a length some twelve or fifteen times that of the bell, or umbrella. Then suddenly one will be contracted, and, as it were, shrivelled, to mere fragments of a quarter of an inch long; then lengthened again to an inch or two; then shortened again. Now the little bell resumes its energetic pumping, and shoots round and round in an oblique direction, the summit always going foremost, and the tentacles streaming behind in long trailing lines. Now it is again arrested; the bell turns over on one side and remains motionless, and the tentacles, as " fine as silkworms' threads," float loosely in the water, become mutually inter-tangled, instantly free themselves, pucker and shrivel up, slowly lengthen, and hang motionless again, or, as the bell allows itself to sink slowly, are thrown into the most elegant curves and arches. Though these tentacles look at first like simple threads of extreme tenuity, yet when viewed closely they are seen to be composed of a succession of minute knobs separated by intervals-like white beads strung on a thread; the beads being more remote fiom each other in proportion as the tentacle is lengthened. This structure is worthy of a more mninute investigation. We will, therefore, confine our little Sarsia in this narrow glass trough, which is sufficiently deep to allow its whole form to be immersed, though somewhat flattened; which is an advantage, as its movemuents are thereby impeded. Now, with a power of 300 diameters you see that each of the knobs of the tentacle is a thickening or swelling of the common JELLY-FISHES. 363 gelatinous flesh, in which are imbedded a score or two of tiny oval vesicles, without any very obvious arrangement; but for the most part so placed that the more pointed end of each is directed toward the circumference of the thickening. The intermediate slender portions of the tentacle-the thread on which the beads are strung-is quite cestitute of thlese vesicles. These little bodies are called cnidce, and, in the whole of this class of animals, and also in that of Zoophytes, they play an important part in the economy of the creature. I shall probably take occasion to exhibit them to you under conditions more fi'avourable than are presented here, viz. in the Sea-Anemones, where they attain far greater dimensions; and therefore I will merely say here that each one of these tiny vesicles carries a barbed and poisoned arrow, which can be shot forth at the pleasure of the animal with great force, and to an amazing length-that hundreds are usually shot together-and that this is the provision which the All-wise God has given to these apparently helpless animals for securing and subduing their prey. Thlere is, however, another organ still more conspicuous in our little Sarsica, of which I have not yet spoken. As the whole animal has the most absolute transparency, we see that the roof of the bell is much thicker than the sides, and that it gradually thins off to the edge. The interior surface is called thle sub-umbrella, and it carries within its substance four slender tubes, which, radiating fiom. the centre of the roof, proceed to the margin, where they communicate with another similar canal which runs round the circumference, sending off branches into the tentacles, This is the circulatory system; and you may see, with the magni 364 EVENINGS AT TIIE MICROSCOPE. fying power which you are at present using, that a clear fluid is moving rapidly within all these canals, carrying minute granules; not with an even forward current, but with an irregular jerking vacillating movemnent, as if several conflicting eddies were in the stream. Yet we discern that, on tle whole, the grannles are. moved forward; passing from the centre of radiation towards the margin, when we see them slip into the marginal canal from tlie several mnoutlhs of the radiating canals. This is a very simple and rudimIentatry blood-system. There is here no heart with its pulsations, no proper arteries or veins, no lungs for oxygenation; but the products of digestion are tllemselves thus circulated through the system. And this brings me back to the central point, whence you see depending the curious organ I spoke of. A long cylinder of highly moveable and evidently sensitive flesh hangs down from the middle of the roof exactly like ~SASTA. the clapper of a bell; and, as if to add to the resemblance, this same clapper is suspended by a narrow cord, and is terminated by a knob. Sometimes this whole organ is allowed to hlang about as low as the edge of the bell; then it gradually lengthens to twice, thrice, nay to five times that JELLY-FISHES. 365 length; the tongue lolling out of the mouth to a most uncouth distance, and even the suspending cord (as I presume t term the attennated basal portion) reaching far beyond the margin; then, on a sudden, like the tentacles, the tongue is contracted, thrown into wrinkles, curled into curves, and the whole is sheltered within the concavity; presently, however, to loll out again. This proboscis-like organ is called the pedunele, and its office is that of a stomach, of which the knob at the end is the month, having a terminal orifice with four minute lips. The flexible substance and rapid motions of this pedluncle are suited to enable it to seize small passing animals that constitute its prey; and I have seen the Sarscia in confinement seize with the mouth, and swallow, a newly-hatched fish, notwithstanding the activity of the latter. For holurs afterwards, the little green-eyed fry was visible, the engulfment being a very slow process; but the Medusa never let go its hold; and gradually the tiny fish was sucked into the interior, and passed up the cavity of the peduncle, becoming more and more cloudy and indistinct as digestion in the stomach dissolved its tissues. The greater portion of the food is by-and-by disclarged fi'om the mouth, the fluids which have been extracted fronm it being on the other hand carried up thronghl the base of the peduncle, and distributed along the four radiating vessels, conveying nutrition, supply of waste, and growth to all parts of the system. We may now liberate our little Sarsia, with thlaniks for the gratification he has afforded us, to resume his active play among his many companions. Meanwhile 366 EVENINGS AT THE MiICROSCOPE. we will look for one of another kind along the group. Iterve is a pretty and interesting species. Active it is, but less vigorously rapid in its movements, than either the Bero' or the Sarscia. It is, as you see, something less than a hemisphere, or resembling a watch-glass in shape, about three-fourths of an inch in diameter. In general character it resembles the Sctrsia, but the peduncle is small, never reaching to the level of the margin, and its mouth is teraminated by four expanding fleshy lips, which are extremely flexible and versatile. The four radiating vessels here carry, just before they merge into the marginal canal, a dilatation of the commnon flesh, which, as you see, bulges out the surface of the umbrella. We will examine one of these dilatations with the microscope. It is, as you perceive, occupied by a number of clear globes, each of which has another minute globose body in its interior. They are very diverse in size, some being very small, others comparatively large, and it is to the dimensions of these latter that the swelling of the surface of the umbrella is due. These vesicles are the eggs of the animal considerably advanced towards maturity; and the dilatations around the radiating vessels are the ovaries. The margin, however, presents us with the most obvious, and perhaps the most interesting, points of diversity from the little &Sctrsia. In the little beauty before us-whose name, by the way, Tkaumanticts pilosella, I have not yet told you-the outline is friinged with about fifty short and slender tentacles, each of which springs from a fleshy bulb, in which is set a speck JELLY-FISHES. 36T of deep purple. Tlhese collections of coloured granules, which I have already explained to be rudimentary eyes, have a very charming effect, and give a beautiful appearance to the little creature, as if its translucent crystalline head were encircled with a coronet of gems. You shall see them, however, un- der circumstances which will make TIIAUMANTIAS. them appear more lustrously gemmeous still. Come with me, and I will carry the glass containing our little,Thaumnantias into the next room. You need not bring the candle, or what I am going to show you will be quite invisible. Take hold of this pencil, and having felt for the glass, disturb the water with it. Ha! what a circle of tiny lamps flashes out! You struck the body of the Tcarumcntidas with the pencil, and instantly, under the stimulus of alarm, every purple eye became a phosphoric flame, Touch it again; again the crown of light flashes out, but less brilliantly; and each tiny lamp after sparkling tremlulously for a moment, wanes, and the whole gradually, but quickly, go out, and all is dark again. [But it is tired of lighting up for nothing-or its gas is exhausted-or it is become used to the pencil and is not alarmed-or, at all events, you may knock it, and push it, but it refuses to shine any mlore. Back with it then to the microscope, and let us see if it possesses any other points of interest for us there. Yes: we have not exhausted the organs of the margin yet. Between the tentacles which springll from bulbs there are a good many more, far more 368 EVENINGS AT THE MI[ICROSCOPE. minute, without any bulbs;-from four to seven between every two of tile primary ones. WVe won't mind these, but bringing the margin itself illto focus, and moving it along the stage horizontally, we presently see one and another singular organs. They are eight in all, two being placed, but irregularly, in each of the four qluadratures of the circle formed by tile radiating canals. There are auditory vesicles, or organs of hearing, very closely similar to those which we see imbedded in the bosom of the Snail and other Mlolluisca. Here they are comparatively large, and unusually well OTOLITIIES OF THAUMAN'TIAS. furnished. Each is a semi-oval enlargement of the flesh of the margin, in close connexion withl the walls of the marginal canal, hollowed so as to inclose a capacious cavity, in which are placed a considerable number-from. thirty to fifty in this individual-of otolithes, or spheres of solid, transparent, higllly refractive substance. They are arranged in a double line, forming a crescent, and those whllich are nearest thle centre are longer than those towards the extremities of the line. I believe some observers have seen oscil JELLY-FISHES. 369 latory and rotatory movements among these spherules, as ill tile Jfollusca; but I have invariably found them motionless in all the species of Medusa that I have examined, as you see them here. One more little beauty fiom our stock, and we have done with these. There is one that mnoves among the rest like a bead of coral, the smallest of all, yet the most brilliant. eere is another, and here another of the same sort; which has been named by Professor Edward Forbes, Turris neglecta, because naturalists before him had neglected to notice it, just as we have been doing, engrossed by its larger confreres. Beautiful as is this little gem, it is not so large as a dried pea, scarcely larger than a grain of hemp-seed. It is described as "6 mitre shaped; 9 in other words it is a tall bell, with the margin slightly bent inwards, and the sides a little constricted. The umnbrella is thick, and being very muscular is not so translucent as those we have been examining; hence it has a pellucid white appearance. B3ut through this shines its chlief beauty; the peduncle is veryv large, and globose at the upper or basal part, which is usually, as here, of a pale scarlet or rich orange hue. Imbedded in this orange-coloured flesh are seen many points of a lovely rose-purple, which two colours blending together, and softened by their transmission though the sub-pellucid umbrella, have a peculiar brilliancy. But stay! here I have one more advanced in age, which will exhibit some peculiarities of interest in the economy of these frail but charm-ing creatures. In this specimen, which is somewhat lalger than the former, the margin of the umbrella is a little 370 EVENI:NGS AT THE MICROSCOPE, turned back, displaying mlore clearly the peduncle with its brilliant ovaries. These, too, are more turgid, and the rosy points are seen projecting from their interior, and some of them even ready to fall. And look! here on the bottom of the glass are lying half-adozen or more of similar purple points, whose rich hue lenders them plainly discernible, after a slight searching, to the unassisted eye. I will collect one or two with a capillary tube of glass, and submit them to your examination under the microscope. You now discern that these bodies are perfectly oval in form. One might, indeed, call them eggs, for they perform the part of such organisms; but that these have soft walls, covered on their whole external surface with fine vibratile cilia, by the action of which they are endowed with the power of fiee locomotion. We see them, in fact, gliding about the water of the live-box under view, with an even and somewhat rapid motion, which aj)pearcs to be guided by a veritable will. Under this power they are seen to be of a soft rich lake-crimson hule, all over. These little gemmllules have a somewhat romantic history of their own. I am afraid that these we see are too recent to afford us any help in tracing it, and therefore I must be satisfied with telling you what I have observed of it on former occasions. After the beautiful little Coral Jelly has swum about a few days, the mnbrella begins to turn outward and backward, and to contract more and more, until at length, it lies in shrivelled folds around the top, leaving the whole peduncle exposed. Long before this, it has lost its power of swimming, and lies helpless on its side upon the bottom. Meanwhile the JELLY-FISHES. 371 orange ovaries have swollen; the purple gemmules have become developed, and have gradually worked their way through the ovaries, and fallen one by one upon the bottom. There then they glide about for a little time, perhaps for a day or so, by means of their vibrating cilia. At length each little gemmule loses its power of wandering, its motion becomes feebler, and more intermitted, and finally ceases altogether. The little being now rests on some solid body-a stone or a shell-to which it firmly adheres. Its two extremities grow out, adhering as they extend, and sometimes branching, but still in close and entire contact with the support. At length, after a day or two, from some point of the upper surface of this creeping root, a kind of wart buds forth, and soon grows into an erect slender stem, which presently divides into four straight, slender, slightly divergent tentacles, which grow straight upward to a considerable length. The whole structure retains the rich purple hue of the original gemmule. Beyond this point I have not pursued the history of the little ]Turris from personal observation; nor am I aware that any naturalist besides has studied the development of this particular genus. But the history of other genera is known; and as the phenomena they exhibit are quite parallel to those which I have been describing, so far as these have been traced, we may fairly conclude that there is the same parallelism in the subsequent stages. Assuming this, then, the little crimson stem with four rays-a veritable polype-buds forth four more tentacles in the interspaces, making the total number 372 EVENINGS AT THE MIICROSCOPE. eight; these in like manner increase progressively to sixteen, tllirty-two, and sixty-four. It now possesses a close resemblance to tile HIy-dra of our ditches, only having more tentacles; and, like it, tile MIedusa-larva buds forth fiom its sides young Hydra-like polypes, which take the form of tllheir imecliate parent, fall off, attach themselves, bud forth more, and so on. All these catclh living prey with their tentacles, swallow them with their mouths, and digest them nwith their stomachs, exactly like real polypes, and thus produce generation after generation of similar beings: Years may pass in this stage, during which numberless polypes are formed. At length the original stock, or any one of its descendants, takes on an important change. Its body lengthens, and becomes cut as it were into a number of rings, as if tied tightly round with thread, or like the body of an Annelid. TURRIS AND ITS YOUNG. These segments become increasingly distinct, until at length each is seen to be a shallow cup, notched at its margin, and sitting in the concavity of the one next JELLY-FISHES. 373 below it. This structulre is developed first in those at the free extremity of the polype, and progressively downwards; and the terminal cups are nearly fr'ee, rocking in their successors'with every wave, while the lowest segments are scarcely visible as such. At length the extreme cup rocks and oscillates until the slender thread of connexion is snapped, and it is free. It at once turns itself over, so as to present its concavity downwards, and contracting its margin with the well-known pulmonic spasm, shoots away with the movement as well as the form of a veritable Medusa. The little progeny has, at length, after passing through so many changes, returned to the image of its parent. Such are, in brief, the phenomena of one of the most remarkable series of facts that modern zoology has discovered, and which have been propounded under the title of the Law of Alternation of Generations. 3f74: EVENINGS AT T-THE MICROSCOPE. CHAPTER XVIII. ZOOPHYTES. IT is pleasant to go down to the shore on a bright autumnal morning at low water, when the tide has receded far, exposing great areas of wet sand and wildernesses of rugged rocks draped with black and red weed. It is pleasant to make our way on cautious foot round some fiowning point whose base is ulsually beaten by the billows; to travel among the slippery boulders, now leaping from one to another, now winding between them, now creeping under their beetling roofs: to penetrate where we have never ventured before, and to explore with a feeling of undefined awe the wild solitudes where the hollow sea growls, and the grey gull wails. It is pleasant to get under the shatlow of the tall cliffs of limestone, to creep into low archling caves, and there to stoop and peer into the dark pools, which lie filled to the brim with water as clear as crystal, and as unruffled as a well. VWhat microcosms are these rugged basins! How full of life all unsuspected by the rude stone-cutter that daily trudges by them to and from his work in the marble quarry of the cliff above! What arts, and wiles, and stratagems are being practised there! what struggles for mastery, for food, for life! what pursuits and flights! what pleasant gambols! what conjugal and parental affections! what varied enjoyments! what ZOOPHYTES. 375 births! what deaths! are every hour going on in these unruffled wells, beneath the brown shadow of the ulmbrageous oarweed, or over the waving slopes of the bright green Ulvca, or among the feathery branches of the crimson Ceracmiun! I have just been examining some of these rockwells, and have rifled them of not a few of their living treasures, bringing home the opimcn s8polia,* that you may share with me in the enjoyment of examining them. The Zoophytes are here in their glory. Such places as those I speak of are the very metropolis of the zoophytic nation. Look at this great leaf of the fingered Tangle: see how its broad olive-brown expanse is covered with tiny forests of white braliching threads, which spread and spread till they run off into the fingets of the much split leaf; and not only on one side, for the under surface is as densely clad with the shaggy burden as the upper; the smooth leathery tissue being covered with a network of creeping roots, branching and anastomosing everywhere, like the railways on Bradshaw's map. This double forest is wholly composed of a single species, called Ictornedea geniculata; nay, I believe it is but one single individual. That is to say, the whole of these multitudinous ralified threads and stems, with their innumerable polypes, have all extended by gradual though rapid growth friom a single germ, and all are connected even now, so that a common life pervades the whole. - But we will look awhile at it in detail till we have mastered its external features, and then I will tell you something of its history and economy. * Rich spoils. 376 EVENINGS AT THE AITCROSCOPE. With the unassisted eye we can discern plainly enou'gh the outline and plan of this compound organism. Along the smooth and lubricous surface of the olive weed runs a fine thread of a pellucid white appearance, so firmly adherent that if you attempt to remove it with a needle's point, you find that you only tear either the leaf or the thread. The course is generally in a straight line, but does not ordinarily pursue the same direction far, commonly turning off with an abrupt angle at intervals of about an inch, and thus meandering in a zig-zag fashion, very irregularly, branching fi'equently, and uniting with a thread already formed, when the creeping one has to cross it. Thus the basal network is formed; but meanwhile, from every angle, and often fromn intermediate points, a free erect thread has shot up-like the stem of a tiny plant-to the height of an inch, rarely more; not, however, straight, but with frequent zig-zag angles, whence the name geniczulata, or "6 kneed." At every angle a slender branch is sent forth, pursuing the same direction as that of the joint from the summit of which it issued, and terminating in a tiny knob. In the angles of some of these branchlets are seated oblong vesicles, twice or thrice as large as the terminal knobs. And this is pretty well all that we can make ouit with the naked eye. Cutting carefully off with scissors a narrow strip of the leaf, I drop it into the parallel-sided cell of glass half-filled with sea-water, and examining it first with a low power, and afterwards with a highler. We now see that the creeping thread is a tube of horny substance, flatttened on its under side, and that the erect stems and their branches are similar tubes, whose cavities are in ZOOPHYTES. 377 firee communication with that of the creeping root. The wall is thin, and perfectly transparent and cololurless; tlhe whiteness of the whole being dependent on a soft medullary core of living jelly, which, permeates tle whole structure, on which the horny sheath is as it were almouldecd. This medulla is pierced with a canal, through which a fluid circulates, carrying along numerous mninute granules with a quivering, jerking Inotion; this is doubtless the nutrient fluid conveying the products of digestion to every part of the common structure. Where the branches issue from tlle angles of the stem, the medulla, and consequently the horny sheath, is dilated into a knob; immediately above this there is a jointlike constriction in the tube, and the branch itself is in sected by four or five sucl; constrictions, so as to form as many rings. Its extremity LAOMEDEA. then expands into an elegant cup, or vase, of extreme tenuity and transparency, shaped like a wine-glass, with the rinm undivided, but so thin and subtle as to be seen with the greatest difficulty. These cups, or cells, are each the proper habitation of a p)olype, wlhich is nothing else but the termination (ini tllis direction) of the living, growing, vascular pith. The latter becomes exceedingly attenuated to pass 378 EVENINGS AT TIlE MICROSCOPE. through a very narrow orifice in the centre of a horny diaphragm, or sort of false bottom, which passes across the bottom of each cell. It then dilates into a soft contractile animal, whose body-but look for yourself; for here, full in the field of the microscope, is one expanding in the highest vigour and beauty. It is a long trumpet-shaped body of granular flesh, the mouth of which just reaches the brim of the cup, over which it spreads on all sides. From its margin spring some eighteen or twenty tentacles-the exact number varying in different individuals-arranged in one or two close-set circles, like a crown. These organs, which, as you see, fall into elegant double curves, like the branches of a chandelier, are roughened with knobbed rings, something like the horns of a goat; this structure we will presently submit to more close exanmination. In the midst of the space surrounded by the tentacular crown there is protruded, at the pleasure of the animal, a large, fleshy, funnel-shaped mouth, the lips of which are highly sensitive and versatile, continually changing their forml-protruding, contracting, bending in upon themselves, now closing, now opening the mouth, and, as it were, testing the immediate vicinity, like a very delicate organ of some unknown sense. The whole polype is much too minute for us to attempt, with any probability of success, the amputation of one of the tentacles with scissors. But by cutting off a polype, cell and all, and putting it into the compressorium, we may be able, by means of the graduated pressure, to flatten the whole, and thus discern the gnarled structure of the tentacles. A very high magnifying power is needed for this. ZOOPHYTrES. 379 ITere, then, we have one of the tentacles flattened between the glass plates, but still retaining its integrity. We find that the thickenings are similar in character to those of the tentacles of Scs8ica, which we lately observed. They are, in fact, accunmulations of cnidce-those peculiar weapons of power, which I shall presently describe in full —but here e \J ) they are symmetrically arranged in single rows, each pointing upward and outward. To return to the living specimen on the leaf: you see seated in the angles of the branches here and there elegant urn-shaped cells, j laroer than. the polype-cells, each with a sort of' shoulder and a narrow neck. The common pith passes TENTACL. OF LAOEDIA; firom the joint into the bottom of fattemed. these, and then extends through the centre till it reaches the mouth. In somne of the urns this forms merely a slender columnn, expanding at the mouth, but in others it enlarges at irregular intel'vals into large knobs or masses of granular flesh, which are confusedly grouped together, eight or ten in one capsule. This latter is the most interesting condition; let us watch it. While doing so, let me inform you that these urns are the reproductive organs, and tile fleshly masses are embryos of peculiar character, which are developed out of the nutrient medulla. The largest of those now under observation is, as you see, moving, and slowly working its way out of its glassy prison. Two or three flexible finger-like bodies are protruding from the 380 EVENINGS AT THE MICROSCOPE. orifice of the urn, and more are joining them; we see they are tentacles, protruded in a loose bundle, just as the polype emerges from the cell. It is a somewhat slow process; but at lengthl the fleshy mass squeezes itself forth, as if pushed out by some contractile force behind; while we see the fluids, carrying granules, run into the parts of the tentacles which are already free. The embryo is liberated. For a few seconds it appears helpless, and falls through the water in a collapsed state, so that we cannot discern its proper form. It gives a spasmodic contraction or two, feeble at first, then more vigorous; the tentacles lengthen, the body expands, and —lo! it is not a polype, but a MIedusa! And now take your eye for a moment from the microscope, and glance at this glass jar, in which the oarweed with its colony of Zoophytes has been standing for a few hours. Hold it between yoU1' eye and the light; do you not see that the water is alive with tiny dancing atomns? Hundreds are there, playing and pumping throughl the fluid with a sort of flapping motion, which, when you get on sidewise in clear view, will not fail to remind you of the flagging flight of some heavy-bodied, long-winged bird.'These are the Medusa-shaped progeny of the Laomedeca. But let us return to the one of which we have just witnessed the birth, and which is still flapping to and f'ro in the narrow glass trough. You see a pellucid colourless disk or umbrella of considerable thickness, about one-sixtiethl of an inch in' diameter in its average state of expansion. Its substance has a reticular appearance, probably indicating its cellular texture. Internally, the disk rises to a blunt point in the centre. ZOOPHYTES. 381 whence four vessels diverge to opposite points of the margin. These form elevated ribs, the surface being gradually depressed from each to the centre of the interspace. Externally, the centre of the disk is produced into a fieshy peduncle, having a narrow neck, and then expanding into a.sort of secondary disk, of a square formn, with the angles rounded. This organ, which is capable of varied, precise, and energetic motions, corresponds to the peduncle of a true Medusa, the angles being the lips. These lips, which correspond in their direction to the four internal ridges, are very protrusile, and when the little animal is active are continually being thrust out in various directions, sometimes everted, but more commonly made to approach each other in different degrees; sometimes one being bent-in towards the centre, sometimes all closing-up around a hollow interior. These four lobes, thus perpetually in motion, and changing within certain limits their form and their relation to each other, remind one of the lips or the tongues of more highly organized animals. The substance of this peduncle appears to be delicately granular; but there is a very manifest tendency to a fibrous character in its texture, the fibres being directed from the exterior towards the interior, supposing the lobes to have their points in contact. Let us now look at the margin of the disk. IHere are attached twenty-four slender tentacles, six in eachl quadrant formed by the divergent ribs, or radilating canals. Each tentacle springs from a thickened bulb, which is imbedded in the margin of the disk; it is evidently tubular, but the tube is not wider in the bulb than in the filament. The general surface is rough with projecting points, which in some assume a very regular 382 EVENINGS AT THE MIICROSCOPE. nmuricate appearance, and the tentacle terminates in a blunt point. The discal part of the bulb is fringed with a row of minute bead-like spherules. Around the edge of the circumference of the disk, on the exterior, are arranged eight beautiful and conspicuous auditory vesicles. They are placed in pairs, each pair being approximate, and appropriated to each of the quadratures of the circle. Each of these organs consists of a transparent globe, not enveloped in the substance of the disk, but so free as to appear barely in contact with it: it contains a single otolithe, of high refriactive power, placed not ill the centre, but towards the outer side. The inexperienced naturalist, on first seeing these organs, would unhlesitatingly pronounce them eyes, and the otolithe the crystalline lens. They are, however, pretty certainly, rudimentary organs of hearing; the crystalline globule or otolithe being capable of vibration within its vesicle. Their exact counterparts are found in many of the smaller Iedusoe, as we lately saw in the T/Aumcaneias. The disk is endowed with an energetic power of contraction, by which the margin is diminished, exactly like that of a MIedusa swimming; and the tentacles have also the power of individual motion, though in general this is languid, their rapid flapping being the effect of the contraction and expansion of the disk, producing a quick involution and evolution of the margin, and carrying the tentacles with it. Occasionally, however, all the tentacles are strongly brought together at their tips, with a twitching grasping action, like that of fingers, which is certainly independent of the disk, and mnay be connected with the capture of the prey. Now every detail of the structure here, as well as ZOOPHYTES. 383 the general form, appearance, and habits, agrees with the small naked-eyed Meduste, so closely, that if we had not witnessed the birth of the little creature fiom the reproductive cell of a LZaomcclde, we should have pronounced it with unhesitating confidence a true Acaleph. The peduncle, it is true, seems out of place being on tile outside of the dome, instead of hanging suspended friom its interior; but this difference is only apparent, and arises fiom the circumstance that the disk is reverted. If you suppose the edge of the disk to be turned in the opposite direction, you will have the peduncle in its normal place: the umbrella in these specimens is carried within, and the sub-umbrella without; an inversion which is probably accidental. Comparing now this strange production of a Miledusa by a Polype, with what I lately told you of the production of Polypes by a Medusa (as in the case of the lovely little T2rri,), you will have some acquaintance with the wondrous phenomena which have of late years been surprising and interesting naturalists-viz., those of the Alternation of Generations; in which as Chamisso, the first discoverer of the strange facts, observed-" a mother is not like its daughter, or its own mother, but resembles its sister, its grand-daughter, and its grandmother." The Polype gives birth to a generation of Medusm which lay eggs, which develop into Polypes. The Medusa on the other hand lays eggs (gemmules), which develop into Polypes, which at length divide themselves into colonies of Medusoe. At first you will perhaps see nothing remarkable in another object which I collected in my rock-ramble today. A Hermit-crab in an old Ncdica shell; both common things enough. Yet look more narrowly. 384 EVENINGS AT THE MICROSCOPE. The greater portion of the shell is not smooth, has no such porcelain-like polish as the Ncatica usually has, but is clothed with a sort of downy nap, a coarse sponginess of a greyish hue, splashed with yellowish and pink tints. The shell is invested with Hydrcactinia. We restore the strange partnership —shell, fleece, and crab-to the glass of sea-water; where we soon see the whole tumbling about the bottom in uncouth agility. Assist your eye with this pocket-lens, and look again. The shaggy nap upon the shell now bristles with tall slender polypes, crowded and erect, like ears of corn in a field. -No high power of magnification is necessary to furnish us with considerable entertainment fiom this populous colony. The polypes stand individually nearly half an inch in height; each consists of a straight slender column, surmounted by eight straight rod-like tentacles, four of which stand erect, slightly diverging, and the other four, alternating with these at their origin, extend horizontally like the arms of a turnstile. The rough jolting of the crab over the stones the expanded polypes bear with equanimity; they are used to it; and though their tentacles wave and stream hither and thither, they are not retracted on this account. But just touch with the point of the pencil in your hand any part of the shaggy fleece, and instantly the whole colony retire together, as if by a common impulse, apparently shrinking into the substance of the shell. Yet they soon re-appearl one after another quickly protruding its closed tentacles, which are presently expanded as before. ZOOPHYTES. 385 The explanation of this phenomenon is, that the whole colony of polypes are but the free points, or feeding mouths of a common living film, which invests the shell; just as in Laomedea, the polypes that inhabit the vase-like cells are the off-shoots or free points of the common medulla. The ilnvesting film will sometimes in captivity spread upon the glass side of a tank, and then develop all the polypes and organs proper to the complete organism. When this is the case, an admirable opportunity is presented for studying with ease and precision the economy of the creature; and it is to the skill with which Dr. T. Strethill Wright has availed himself of such an opportunity* that I am indebted for the chief part of the facts that I am going to tell you, connected with the form and appearance, of which you can here judge for yourself. The spreading filmn or polypary is a thin coat of transparent jelly, slightly coloured with various tints, which secretes and deposits within its substance a still thinner horny layer of chitine. This rises here and there into numerous spines and points, which are curiously ridged with toothed keels; and these ridges run in various directions over the horny layer also, making a fine network over it. The investing flesh, however, fills up all the cavities and areas so inclosed. The mode in which the polypary increases is by throwing out from its edge a creeping band, exactly analogous to the root-thread of the l~aomedea. This "' propagative stolon, after leaving the point of its origin, increases rapidly in diameter, and sends out' See Edin. New Philosophical Journal, for April, 1857. 17 386 EVENINGS AT THE ~MICROSCOPE. irregular branches. The tips of these branches are covered with a glutinous cement, by which they attach themselves tenaciously to glass, or other surface near them. Flaving attached themselves, they expand laterally, at the same time throwing out finger-like prolongations, which, as they come in contact with each other, coalesce, until a fleshy plate is found adherent to the glass. Polypes are developed both from the loose branches and the attached polypary; and the latter is clearly seen to be permeated by a beautiful system of anastomosing canals, connected with the hollow bodies of the polypes. Within these canals may be detected an intermittent flow of fluid, containing particles, the dancing motion of which indicates the presence of ciliary action, and which, having passed in one direction for a short time, are arrested, and after a slight period of oscillation, commence to flow in an opposite direction." The polypes which are developed from this living carpet are not all of the same form. No fewer than five distinct sorts exist, at one and the same time, and I doubt not we shall be able to find and to identify them all, on this well-grown specimen. First, there are the alimentary polypes, which we have already cursorily glanced at. Within the space inclosed by the two circles of tentacles, there is a mouth with soft protrusile lips, which can be pushed out and folded back so as to hide tentacles, column, and all. Scattered amongst these we see numerous polypes, which agree in general form with these, but with some remarkable abstractions and additions. They have no mouth nor stomach, and the tentacles are reduced to ZOOPHYTES. 387 the smallest possible warts or protuberances denticulating the dilated tip. But the additions are still more peculiar. From the middle part of the column a number, from four to nine, of great oval sacs project, each attached by one end, while the other stretches out horizontally, thus surrounding the slender column. Each of these sacs is an ovarian capsule, and contains several ova of a brilliant yellow or crimson hue. Thus we have the second form, —that of the reproductive polypes. In some places single ovarian capsules stand up alone from the fleshy carpet, agreeing in every respect with those which we have just examined, except that they are sessile, instead of being carried by a polype. The fourth form is that of the tentacular polype. Here and there, from amidst the forest of shorter polypes,-alimentary and reproductive,-white threads are seen protruding, which extend to a length four or five times as great as theirs, and hang down or loosely float in the water. They are found on the outskirts of the whole compound structure, and at each extremity of the long diameter of the mouth of the supporting shell, so that they must, in their natural condition, reach to the ground, along which the crab-tenanted shell is carried, enabling the Zoophyte to seize and appropl-iate the atoms scattered by the crab whenever he takes his meals. The tips of these organs are covered with a dense pavement of large thread-cells; and they must doubtless perform the office of general purveyors to the composite animal. But still more remarkable, more extraordinary than all we have been considering, are the objects which 388 EVENINGS AT THE MICROSCOPE. are now in view in the field of the microscope. You see a number of bodies, which Dr. Wright calls ophidian or spiral polypes, and which, as he truly observes, are "like small white snakes, closely coiled in one, two, or three spirals, and grouped immediately round thie nmouth of the shell." The habits of these polypes are still stranger than their forms. "' When touched, they only draw their folds more closely together. But if any part of the polypary, however distant from them, be irritated, the spiral polypes uncoil, extend, and lash themselves violently backwards and forwards, and then quickly roll themselves up again; and that not irregularly or independently of each other, but all together, and in the same direction, as if moved by a single spring. A violent laceration of the polypary causes these polypes to remain extended and stretched like a waving and tremulous fringe across the mouth of the shell, for several minutes. The ophidian polypes (evidently a barren modification of the reproductive polype) are never found in any other situation on the polypary than in that before described, or round the margins of accidental holes in the shell. They have no mouth, and the tentacles are rudimentary. The walls of the body are very transparent, from the extreme vacuolation of the inner tissue. The muscular coat, as might be expected fiom the active movements of the polypes, is highly developed, and forms a beautiful object on the dark polarized field of the microscope, each spiral coil shining out as a bright double ring, divided by four dark sectors. The outer tissue of the whole body and tentacles is crowded with the larger thread-cells. The ophidian polypes are, doubtless, organs of defence or ZOOPHYTES. 389 offence, like the motile spines and bird's head processes of the Polyzoa, or the pedicellarie of the Echinodermatac; but it is difficult to assign a reason for their peculiar situation. They vary much in number and size in different specimens of IHydractinia, but are rarely altogether absent." * The reflections of the able zoologist who first called attention to these varied developments, and his comparisons of them with those of another polype-form which we have lately been observing, are so interesting and instructive that you will not deem it needful that I should apologize for citing them. "In our consideration of the HEydractinia," he observes,' our attention is arrested by the multitude of objects grouped together to constitute a single animal, their variety in form, and the sympathy which subsists between the different parts. The singular spinous skeleton; the expanded membrane of the polypary, with its beautiful internal network of tubes and delicate peripheric prolongations; the alimentary polyps, some white and filiform, others thick, fleshy, crimson, or yellow sacs, obligingly everted, to expose their interior to our microscopic eye; the reproductive polyps, with their richlycoloured generative sacs; the sessile generative organs of the polypary; the ophidian polyps, coiled in neat spirals when at rest, but starting into furious action, like a row of well-drilled soldiers, when injury is inflicted on the body to which they are attached; and, lastly, the tentacle polyps, floating in the water like long and slender threads of gossamer, or dragging up heavy loads of food for the common good;-these, together with the intimate relation and sympathy sub* Dr. Wright, op. cit. 390 EVENINGS AT THE MICROSCOPEo sisting between the polypary and its associated organs, all combine to form an object of the highest interest, and indicate that, in this fixed yet travelling zoophyte, we have a type of structure transitional between the dendritic 2~Hydroidce and the more highly organized Acaleph. In the simplest acalephoid form, such as the mnedusoid of Companularia [or Iaomedea,] (which is nothing mnore than an extension of the polypary specially organized for independent and motile life,) we have (as in I]ydractJnica) an expanded polypary, represented by the umbrella, and permeated by vascular tubes firom the confluence of which last spring, at the centre, the tentacular polyps, various in number; and between them the reproductive polyps, represented by the sessile generative sacs." * You see here a jar, on the glass side of which are traced a number of very fine white lines, barely discernible by the unassisted eye. But by the aid of the lens you see that each line is a. long and slender thread, which creeps along the glass, and at length starts out from it free for a short distance, and is then terminated by a long club-shaped body, which carries at its extremity four horizontally divergent organs, like the arnms of a turnstile. Tracing down the threads to their lower extremlities, you, see that they are branches of one thread, which creeps irregularly over a filamentous sea-weed growing from a stone in the jar. The sea-weed had been in the vessel for several weeks, and the water having been undisturbed, the knobbed thread, which was originally confined to the plant, continued to grow, -and coming into contact with the glass spread upon it. Many other threads have ex* Ibid., op. cit. ZOOPHYTES. 391 tended from the creeping root, some of which stand up freely in the water, with their knobbed extremities floating in the wave. This is one of the Polype tribe, named Stcauridiac producta, and as its form and structure are interesting, we will devote a few moments to its examination. We can easily sever one or two of the freely floating threads, and transfer the amputated portions to one of the live-boxes of the microscope. The motions and appearance of the club with its organs will be, for a while, little affected by the violence. The long cylindrical thread is enveloped in a transparent horny tube, which, however, so closely invests it, that it is with difficulty distinguished. The clubshaped head, or individual polype, is an enlargement of the thread, which protrudes from the investing tube. It is swollen in the middle and rounded at the end, and many of the heads, which are more ventricose than the rest, contain a bubble of air in the centre. This air is doubtless taken in at the mouth, which is situated at the extremity; for, though you can discern no perforation, yet there is an aperture capable of being opened widely at the pleasure of the animal, and surrounded by protrusile, contractile, and expansile fleshy lips. I have several times seen this mouth opened, and partly everted, in kindred species; and once I had an opportunity of witnessing a quite unexpected use to which it was applied, viz. that of a great sucking disk. I had put the animal in such a live-box as this-the two glass surfaces being just sufficiently wide apart to allow it free liberty to turn about in all directions as far as it wished. On my looking at it after a momentary interval, I saw that the extremity had suddenly be 392 EVENINGS AT THIE MICROSCOPE. come a large circular disk of thrice the diameter of the body: its substance was gelatinous, full of oblong granules, arranged concentrically. I neither saw this disk evolved nor retracted; but after some time, on looking at it, the same phenomenon was repeated. In order to obtain a better sight of it, but without suspicion of what I was about to effect, I slightly tnrned the tube of the box, carrying with it the alga to which the polype was attached, my eye upon it attentively observing all the time. The base of the polype moved away fiom its position, but the broad disk was immovable. I continued to turn the upper glass, until at length the body was dragged out so as to be considerably attenuated; still the disk maintained its hold on the lower glass, with no other change than that of being elongated in the direction in which it was dragged. At length it slowly gave way, and resumed its original shape by gradual and almost imperceptible diminution of the circumference. Around this expansile, but now fast-closed mouth, you observe four tentacles, radiating in a plane at right angles to the axis of the thread, towards the four cardinal points; they are long, slender, straight, and each is terminated by a globose head of considerable size, resembling the arms of certain screw-presses, which are loaded with terminal globes of metal to increase their impetus when turned. The structure of these tentacles is very interesting. The stem contains a core or central chain of large cells, which take a somewhat square outline fromn mutual pressure. The surface is roughened with small swellings, from each of which projects a long and excessively attenuated hair (palpocil), which is probably a very del ZOOPHYTES. 393 icate organ of touch. The terminal globe is filled with proportionally large oval vesicles, each with a central cavity, which are arranged in a divergent manner around the centre, so that their tips shall reach the surface of the globe; these are those potent weapons of offence called thread-cells (cnidce). The surface of the globe is covered with short thick palpocils, which Dr. T. S. Wright considers as prehensile organs. "These palpocils arise, each as a somewhat rigid process, from the side of one of the large thread-cells, buried in the head of the tentacle; and they probably convey an impression from bodies coming into contact with them, to the thread-cell, causing the extrusion of its duct." Besides these globeheaded tentacles, there are, on the lower part of the club-foot, four other organs similar in every respect, except that they BSLVIDIA. are not furnished with heads, nor any terminal dilatation whatever. They project horizontally as the knobbed ones, but their origin, and the respective lines of'their radiation, are intermediate or alternate; in other words, if we consider the globe-heads as pointing N.-E. S. and W., the siun ple ones point N.-E., S.-E., S.-W., and N.-W. From the carefully made observations of several 17* 394 EVENINGS AT THE IBhGCROSCOPE. excellent naturalists-as Duj ardin, Steenstrup, Dalyell, Lov6n, and others-it appears that this beautiful and elegant little Polype gives birth to medusa-shaped young. Contrary, however, to the rule in lcaormedea, the Medusa is in this case pushed forth as a bud from the side of the club, without any protecting capsule. The process is exceedingly like a plant developing a,, flower; for the bud grows until it at length expands blossom-like, and a beautiful little umbrellaform Medusa is seen adhering to the Polype. At length the brilliant little living flower becomes detached; and, after swimming freely for a time, discharges ova or gemmules from its ovaries, which develop into a creeping-root-thread, and finally into the club-headed threads of the Stauridia. Some objects which I have to exhibit to you are altogether unique as to their appearance; and, if you are not as imperturbable as a philosopher of the:roa, or a Mohawk Indian, will certainly excite both your risibility and your wonder. For some little time I have been keeping in this tank a specimen of that rather rare and very interesting Sabella, the AmnpItrite vesiceulosa of AMontagu.* You see it is a worm, inhabiting a sort of skinny tube, much begrimed with mud, about two inches of its length being exposed; the remainder, or about as much more, being concealed among the sand and sediment of the bottom. A beautiful object is presented by the gill-fans of this worm. These organs are always elegant, whatever species of the genus is before us; but here, in addition to the charm of the slender filaments, so delicately fringed with their double comb-like rows of cirri, the *Linn. Trans. xi. 19. ZOOPHYTES. 395 tip of each bears a dark purple spherule. That of the anterior filament on each side is much larger than the rest, and forms a stout, globose, nearly black ball; the others diminish to about the twelfth on each side, where they disappear. These balls are placed on the inner or upper face of the filament-stem, at the point where the pectination ceases, the stem itself being continued to a slender point beyond it, and constituting the "short hyaline appendage" of Montagu. From their great resemblance to the tentacle-eyes of the Gasteropod Mollusca, I have little doubt that these are organs of vision. If so, the profusion with which the SabellC is furnished in this respect may account for its excessive vigilance; which is so great, that not only will the intervention of any substance between it and the light cause it to retire, but very frequently it will dart back into its tube almost as soon as I enter the room, even while I am ten feet distant. It is not, however, to the tube, nor to the worm, that I wish specially to direct your attention: yet it is necessary that I say a preliminary word about the former. Ordinarily the tubes of these worms are formed of the fine impalpable earthy matters (clay, mud, &c.) held in suspension in the sea, incorporated with a chitinous secretion fiom the body of the animal; and therefore the surface of the tube is always rough and opaque. [But in this individual case, probably owing to the habitual stillness of the water in the vessel not holding in suspension the particles of mud that ordinarily enter into the composition of the tube, the latest-formed portion is composed of pure transparent chitine, without any perceptible earthy element. This clear terminal portion of the tube you may perceive to be occupied 396 EVENINGS AT THE MIICROSCOP:E. by a curious pfarasite. About twenty bodies, having a most ludicrously close resemblance to the bhuman figure, and as closely imitating certain hiumnan motions, are seen standing erect around the mouthl of tle tube, now that the Sabella has retired into the interior, and are incessantly bowing and tossing about their arms in the most energetic manner. LAZES. As soon as you have recovered from your surprise at this strange display, we will begin to examine the performers more in detail. A slender creeping tllhread, irregularly crossing and anastomosing, so as to form a loose network of about three meshes in width, surrounds the margin of the Sabella's tube, adhering firmly to its exterior surface, in the clitinouns substance of which it seems imbedded. Here and there free buds are given ofif especially from the lower edge; while from the upper threads spring the strange forms that have attracted our notice. These are spindle-shaped bodies, about -elth of an inch in height, whose lower extremitities are of no greater thickness than the thread from ZOOPrrTES. 39t which they spring; with a head-like lobe at the summit, separated from the body by a constriction, immediately below which two lengthened arms project in a direction towards the axis of the tube. Such is the external form of these animrals, and their movements are still more extraordinary. The head lobe of each one moves to and fro freely on the neck, the body sways from side to side, but still more vigorously backward and forward, frequently bending into an arch in either direction; while the long arms are widely expanded, tossed wildly upward, and then waved downward, as if to mimic the actions of the most tumultuous human passion. Whenever the Sabella protrudes from its tube, these guardian forms are pushed out, and remain nearly in contact with the Annelid's body, moving but slightly; but no sooner does it retire than they begin instantly to bow forward and gesticulate as before. These movemelrts are continued, so far as I have observed, all the time that the Scbella is retracted, and are not in any degree dependent on currents in the surrounding water, whether those currents be produced by the action of the Annelid or by other causes. They are not rhythmical; each individual appears to be animated by a distinct volition. Applying a higher magnifying power than we have yet used to the animals, we find that the head-lobe encloses a central cavity; that the arms are also hollow, with thick walls, marked with transverse lines, indicating flattened cells, and muricated on the exterior; and that the body contains an undefined, sub-opaque nucleus, doubtless a stomachal cavity. I cut out, with fine scissors, a segment of the tube, 398 EVENINGS AT THIE MICROSCOPE. including two of the parasites, with the portion of the network of threads that carried them. They have become imimediately paralysed by the division of the threads, but those that remain on the tube are unaffected by the violence. Subjecting one of the animals so cut out to the action of the compressorium, with a power of 560 diameters, the arms are seen to be formed of globose cells, made slightly polyhedral by mutual pressure, set in single series. The interior of these organs is divided by partitions, placed at intervals of about the diameter. Some at least of the cells contain a small bright excentric nucleus. When the tissues were quite crushed down by the pressure of the compressorium, a quivering motion was visible among the disjointed granules, but it was very slight. No trace of Cilia, nor any appearance of ciliary motion, was perceptible during life. When I first discovered these strange beings, I was as much astonished by what I saw as you are; nor could I imagine to what class of animals they were to be referred. Neither did I know whether their presence on the tube of the worm was a mere accident, or whether it indicated a predominal instinct. On, both these points, however, light has been shed. This larger Sabella tube was not the only one infested with the parasites. I observed them on at least two smaller specimens of the same species, in the same situation, and with precisely the same movements. The extremity of one of these smaller tubes I cut wholly off, and placed in the live-box of the microscope. Two of the parasites only were on it, which were active at first, but in about an hour-probably from the exhaustion of the oxygen in the small quantity of water in ZOOPHYTTES. 399 closed-the decomposed, or rather disintegrated, the outline dissolving, and the external cells becoming loose and ragged, and the whole animal losing its definite form. One of these specimens, however, while yet alive and active, afforded me an observation of value. I had already associated the form conjecturally with the Hydroid Polypes, and was inclined to place it in the family Coryziclct, considering the arms to be tentacles, and the head-lobe to be homologous with themn in character, but abnormal in form. It appeared to be a three-tentacled Coryne, with the tentacles simple instead. of capitate. But while I was observing the individual in question, I saw it suddenly open the head-lobe, and unfold it into the form of a broad shovel-shaped expanded disk, not however flat, but with the two halves inclining towards each other, like two leaves of a halfopened book. This immediately reminded me of the great sucking-disk which, as I lately told you, I had seen evolved from the obtuse summit of Stauridia producta, and confirmed my suggestion of the natural affinities of the form. Altogether unlike, in their shape, and in the unwonted vivacity and peculiarly human character of their movements, all the other members of their natural family that I had ever seen or heard of, these curious creatures have afforded much entertainment, not only to myself, but to those scientific friends to whom I have had opportunities of exhibiting them. When I see them surrounding the mansion of the Sabella, gazing, as it were, after him as he retreats into his castle, flinging their wild arms over its entrance, and keeping watch with untiring vigilance until he reappears, it 400 EVENINGS AT THE MICROSCOPE. seems to require no very vivid fancy to imagine them so many guardian demons; and the Lares of the old Roman mythology occurring to memory, I described the form under the scientific appellation of clar Sabellarunm. You may, however, if it pleases you better, call them "witches dancing round the charnled pot." The Polypes that we have as yet been looking at are all of simple structure individually, though some of them we have seen united into a very populous community of compound life. We will now look at some whose organization is of a higher, that is, more complex character. On this old worm-eaten oyster shell which has been dredged up from the bottom of the sea, you observe several rounded lumps. They are of a cream-white hue, of somewhat solid texture, tough and hard to the touch, and studded all over with shallow depressions or pittings. The largest of these is not more than an inch and a half in height, by two-thirds of an inch in thickness; but specimens often occur of twice or thrice these dimensions, and much more divided than this; sometimes forming a rude resemblance to a hand of stumpy round fingers of sodden flesh —whence the fishermen call the object, "Dead men's fingers," or, sometimes, by a comparison equally apt, " Cows' paps." To zoologists it is known as Alcyoniuzn digitatunm. Certainly there is nothing very attractive in these white lumps, as they now appear; but then they are now in undress; they do not expect to see company out of water. Their drawing-room is beneath the waves, in some submerged cave of ocean, where the sun's ray never penetrated, and where the only light is that dim green haze reflected from the sand and oo;00PrTE. 401 shingle of tile sea-floor, save when, on gala occasions perchance, the LZaonedece that fringe the walls light up their myriads of fairy lamps, and the tiny _Meclesce crowd in to the watery festivities with their elfish circlets and spangles of living flame. It is then that the Cows' paps " take their hair out of papel," and display their loveliness to advantage. Unfortunately, we have no card of invitation to these submarine routs, but perhaps we may induce one of the more juvenile of these beauties to indulge us, as a special favour, with a sample of the effect; particularly if we can improvise a ball-room suited to the occasion. Let us try. Selecting the very smallest specimen-a tiny thing no larger than a pea-I try to detach it without inj ur'y, by inserting the tip of my pocket-knife under the fiilled lamina of oyster-shell on which it rests, and working off the friagment. I have succeeded: here it is; its attachment unbroken; it is still firmly adherent to the severed slice of shell, which is so small that I can drop it with its burden into this narrow trough of glass. The whole concern-trough, shell, and polype -is now to be dropped into this capacious jar of freshly dipped sea-water, and put away for an hour into a dark closet. Now let us see the result. Yes, it is as I expected. The united stimulus of the darkness and the sea-water has acted on the Cow's pap, just as would the rising and covering tide in its native cavern, after it had been left exposed for some hours by the recess of the 402 EVENINGS AT THE MICROSCOPE. sea. It is fully expanded, and is now as lovely as just now it was unpleasing. In the first place it is swollen to twice its former dimensions, and has acquired at the same time a semipellucidity, and a more delicate hue. iBut in place of the pits on the surface (there were not more than half a dozen in this little specimen, which makes it more suitable for examination), it is coveied with tall polypes, standing out on all sides, of crystalline clearness and starry forms, each eminently beautiful in itself, and surrounding the whole mass with a sort of atmosphere of almost invisible and impalpable lustre peculiarly charming. Coy as these deep-water strangers are of displaying their beauties in our glaring aquariums, they will bear, when once they are expanded, a good deal of shaking with equanimity. Hence I may be able to transfer the trough with its contents from the jar to the stage of the microscope, and thus enable you to gaze on its details for a little while, before the dull sensorium of the creature is sufficiently warned of its ungenial position to cause it to shut itself up and resume its ugliness. As the protruded polypes are exactly alike, it will be enough to confine our attention to one. It is an elevated tubular column of translucent substance, terminating in an expanded flower of eight slender pointed petals, which spring outward with a graceful swell, so as to give the form of a shallow bell to the general outline. The base springs, like the foot of a tree, from the margin of a cell, which penetrates the substance of the mass, into which we can see far down, and into which the whole of the now extended and expanded ZOOPHYTES. 403 blossom was withdrawn when we first saw it, leaving only the shallow depression to mark its situation. The form of the column is in general that of the trunk of a tree, or that of a long cone; but there is a sudden constriction just above the base, and another below the point, where what may be called the flower expands. It is the petals of this latter which constitute the principal charm of this creature. They are, properly speaking, the tentacles of the Polype, answering in function and position to those on the ILaornedea, but differing considerably from them in form. Each of the eight is thick and broad at its origin, and quickly tapers to a point: on each of two opposite sides-viz. those which look towards the two adj oining tentacles, runs a row of delicately slender filaments, which at the POLYPES OF COW'S PAP. middle part of the tentacle are moderately long, but diminish regularly as they approach either end. Starting from the side of the tentacle, in the plane of its 404 EVENINGS AT THE MICROSCOPE. transverse diameter, these elegant pinnoa presently arch downwards, but with perfect uniformity and symmetry. By means of the high magnifying power which I have now applied, each of these pinnoe is seen to be roughened with whorls of knobs, which are accumulations of cnidre, analogous to those which we lately demonstrated in the tentacle of Laomedlea. In the midst of the area surrounded by the petallike tentacles, a narrow slit opens into the stomach. This organ is a flat sac, resembling an empty pillowcase hanging down in the centre of the column, and open at the lower end. From this end, which does not extend to more than one-sixth of the depth of the cavity, three threads, much convoluted and irregularly thickened, spring off at each side and arch downwards, for a short distance. These are the reproductive organs, which firinge the free edges of as many delicate membranes which run up as perpendicular partitions between the stomach and outer wall, uniting with both, and thus dividing the space surrounding the stomach into chambers open at the bottom. There are eight of these septa, but one on each side is destitute of the fringing convoluted thread. The whole surface of the interior-the walls, the stomach, and the septa-is clothed with fine vibratile cilia, by the action of which constant currents are maintained in the water, which bathes every part of the cavity, freely entering at the mouth. We can distinctly trace these ciliary currents hurling along with irregular energy the products of digestion, in the form of translucent granules, especially along the edges of the septa. Though the substance of the polype be soft and ZOOPHYTES. 405 flexible, it contains solid elements. Just below the expansion of the tentacular blossom, we see imbedded in the skin a vast aggregation of calcareous spicula. Individually, these are very minute, and their form is swollen in the middle, and taper at each extremity, the whole roughened with projecting knots. Collectively, they are grouped in regular forms, crowded into dense masses at the foot of each tentacle; the mass having a three-pointed outline, of which the central and largest point runs up into the tentacle. Towards the lower region of the column, spicula again occur, scattered throughout the skin, and crowded into groups, one on each interseptal space. These spicula are of a very different shape from the upper ones; for they form short thick cylinders, with each end dilated into a star of five or six short branches, which are again starred at their truncate ends. If we now sacrifice our little Cow's pap to our scientific curiosity, we shall see something of its internal structure. When removed fiom the water, the blower-like polypes soon retract. I now cut open the mass lengthwise with a keen knife, and you see that it is permeated by canals running from the base towards every part of the circumference, dilating here and there to form the cells which protrude and retract the polypes. This is a complete system of watersupply: the surrounding sea-water entering at the mioniths of the several polypes, bathes the whole interior, and conveys oxygen and the products of digestion together to every part of the compound organism. The fleshy substance which surrounds these canals is of a loose spongy character, and grates beneath the 406 EVENINGS AT THE MICROSCOPE. knife; a circumstance which is owing to the predominance of the calcareous element here, as you will see when I extract a small portion of it, and, laying it on a slip of glass, treat it with caustic potass. The microscope now reveals a large number of spicula, far larger than those we have hitherto observed, and different from either sort in form. These resemble very gnarled branches of oak, with the branchlets broken off close to their origin, leaving ragged and starred ends. SPICULA OF COWLs PAP. BEA-ANEM[ONES: THEIR WEAPONS. 407 CHAPTER XIX. SEB-AoNEXMONES: THEIR WEAPONS. A VERY vast amount of the energy of animal life is spent either in making war, or in resisting or evading it. Offence and defence are sciences which the inferior creatures can in nowise neglect, since all are interested in one or other, and many in both; and various are the arts and devices, the tricks and stratagelns, the instincts and faculties, employed in that earnest strife which never knows a suspension of hostilities. All classes of animals, invertebrate as well as vertebrate, are warriors by profession: the Spider is as carnivorous as the Lion, and more strategic; and the invisible Brachion is as ruthless and insatiable as either. An enumeration and description of the diverse Wea.pons, by means of which this truceless warfare is carried on, would male a volume: nor would the subject be then exhausted; for since it enters so largely into the very existence of animal life, the discoveries of advancing science are ever bringing to light new forms and modifications, strange and unexpected contrivances, all calculated to enhance our view of the inexhaustible resources of the Lord God Omnipotent, "6 who is wonderful in counsel, and excellent in working." 408 EVENINGS AT THIE MICROSCOPE. I am going to bring under your notice this evening some highly curious examples of animal weapons, of which the very existence was until lately altogether unsuspected; yet so profuisely distributed that they are eminently characteristic of the two great classes of animals we have been recently considering-viz., the Medusoe and the Zoophytes. They have repeatedly fallen under our observation in examining the specimens of these creatures which we hlad selected, but I had reserved the fuller elucidation of them for an occasion in which they should come before us under circumstances of such unusual development as greatly to facilitate our researches. The weapons I speak of are the cnidce or nettling-cells. Look at this beautiful Scarlet-fiinged Anemone (Sagarta miniata), expanding to the utmost its disk and tentacles in the clear water of the tank. I touch its body; instantly the blossom-like display is withdrawn; the column closing over it in the form of a hemispherical button, which goes onr contracting spasmodically. At the same time see these white threads which shoot out from various points of the surface; new ones appearing at every fresh contraction, and streaming out to a length of several inchesresembling in appearance fine sewing cotton, twisted and tangled irregularly. Now the animal has attained its utmost contraction, and the threads lengthen no mnore. But already they are disappearing; each is returning into the body by the orifice at which it issued. It is, as you may see by examining it carefully with a lens, gradually contracting into small irregular coils, at that end which is attached to the animal; and these little coils are, one SExA1-ANFMONE]S: TIFEIR Wj1EAT ONS. 409 after another, suckedl in, as it were, through an imperceptil)le orifice.'Before thle w]lole have disappeared, we will secure a portion for examination. For this end I cut off witlh a sharp scissors about one-sixth of an incli of tlhe extremity of one of the threads, which now I transfer to a drop of sea-water in the comlpressorium. These threads are called acontia. Examiining this fiagment under a low power of the microscope, we readily see that, thougllh at first it seems a solid cylinder, it is really a flat narrow ribbon PORTION OF ACONTIUM (flatte,,ea). with the edges curved in, which can at pleasure be brought into contact, and thuls constitute a tube. Like all other internal organs in these animals, its surface is riclhly ciliated, and the ciliary currents not only hurl along whatever floating atoms chance to approach the 410 EVENINGS AT TIHE MICROSCOPE. surface, but cause the detached fragments themselves to wheel round and round, and to swim away through the water. Though there is not the slightest trace of fibre in the structure of the acontium, when scrutinized even with a power of eight hundred diameters, the clear jelly, or sarcode, of which its basis is composed, is endowed with a very evident contractility; the filament can contract or elongate; can extend itself in a straight line, or throw its length into spiral curves and contorted coils; can bring its margins together, or separate them in various degrees; can perform the one operation in one part, and the other at another, and thus can enlarge or attenuate the general diameter of the cord, apparently at will; and some of these changes can be effected even in the fragment detached from the animal, thus proving that the motile power, whatever it is, is localized inl the constituent tissue itself. Under pressure the edges of the flattened acontium appear to be thronged with clear viscous globules, overlapping one another, and protruding; indicating one or more layers of superficial cells, doubtless forming the epithelium. As the pressure is increased, these ooze out as long pear-shaped drops, and immle. diately assume a perfectly globular form, with a high refriactive power, Below these are packed a dense crowd of cnidw, arranged transversely. Before we proceed to the examination of these curious organs in detail, it may be well to devote a moment's attention to the mechanism by which the acontia themselves are projected from the body. As this was first described (so far as I am aware) by SIEA-ANlEAONES:'1THEIR WEY IAPONS. 411 myself,t* I will take the liberty of citing some of my observations on the matter. " The emission of the acontica is provided for by the existence of special orifices, which I term Cinclides. The integurment of tile body, in the Sacyartice, is perforated by minute foramina, having a resemblance in appearance to the spiracula of Insects. They occur in the interseptal spaces; opening a comn-. munication between these (and. therefore the general visceral cavity) and the external water. It follows that they are placed in perpendicular rows, but I have not been able to trace any CINCLIDES. other regularity in their arrangement. So far as I have seen, they are so scattered, tlhat one, two, or even more contiguous intersepts may be quite destitute of a cinelis. I would not, however, attach too much weight to this negative evidence, since the animal has the power of closing them individually at will, and that so completely that the most careful scrutiny does not detect their presence. Perhaps the best mode of examining them is' to put a small specimen of S~. diaCthus or S. bellis into a narrow parallel-sided glass-cell, filled with sea-water. After a while the animal will be much distended; the exhaustion of the oxygen impelling the Anemone * In a memoir entitled, " Researches on the Poison Apparatus in the *Actiniada," read before the Royal Society, Feb, 4th, 1858, 412 EVENINGS AT THE MICROSCOPE. to bathe its organs with as large a quantity of the fluid as it can inllale. The pellucidity of all the integuments will be thus greatly increased. A strong lamplight being now reflected, by means of the mirror thronlgh the animal on the stage of the microscople, an illch or a half-inch object-glass will probably reveal the orifices in question with much distinctness. " The appearance of the cinclides may be compared to that which would be presented by the lids of tle human eye, supposing these to be reversed; the convexity being inwards. Each is an oval depression, with a transverse slit across the middle. When closed, this slit may sometimes be discerned merely as a dark line-the optical expression of the contact of the two edgces; but, when slightly opened, a brilliant line of light allows the passage of the rays fr'om the lamp to the beholder. From this condition the lids mlay separate in various degrees, until they are retracted to the margin of the oval pit, and the whole orifice is open. The dimensions of the cinclides vary not only with the species, and probably also with the size of the individual, but with the state of the muscular contraction of the integument, as, also, I think, with the pleasure of the animal. In a small specimen of S. dicantAhus, I found the width of a cinzclis measured transversely, 2 7th of an inch; but that of another, in the samle animal, was more than twice as great, viz., 3 o-th of an inch. This was on the thiclkened marginal ring, or parapet, which in this species surrounds the tentacles, where the cinclides are larger than elsewhere. Watching a specimen of S. nivea under the microscope, I saw a cinclis begin to open, and gradually expand till it was almost cirecular in outline, and SEA-ANEMIONES: THEIR WEAPONS. 413.45th of an inch in diameter. I slightly touched the animal, and it in an instant enlarged the aperture to r-, th of an inch. In a specimen of S. bellisH, less than lhalf-grown, I found the cinceicles numerous, and sufficiently easy of detection, but rather less defined than in diamnths or nivea. They occurred at about every fourth intersept, three intersepts being blind for each perforate one, and about three or four in linear series, but not quite regularlI in either of these respects. In this case they were about,; tlh of an inch in transverse diameter-a large size; and I measured one which Wvas even l'jth of an inch. By bringing the animal before the window, I could discern the light through the tiny orifices with my naked eye. From several good observations, and especially fiom one on a cinclis, widely opened, that happened to be close to the edge of the parapet of a dianl/tus, I perceived that the passage is not absolutely open, at least in ordinary, but that an excessively thin film lies across it. By delicate focussing, I have detected repeatedly, in different degrees of expansion, and even at the widest, the granulations of a membrane of excessive tenuity, and one or two scattered cnldce, across the bright interval. On another occasion, in the case of a cinclis at the edge of the parapet, a position singularly favourable for observation, I saw that this subtle filmn was gradually pushed out until it assumed the foiin of a hemispherical bladder, in which state it remained as long as I looked at it. At the same time the onutline of the cinclis itself was sharp and clear, when brought into focus further in. The film, whatever it be, is superficial, and does not appear to be a 414 EVENINGS AT THE MICROSCOPE. portion of the integument proper. I take it to be a film of mucus (composed of deorganized epithelial cells), wllich is constantly in process of being sloughed from all the superficial tissues in this tribe of animals, and which continues tenaciously to invest their bodies, until, corrugated by the successive contractions of the animal, it is washed away by the motions of the waves. As, however, one film is no' sooner removed than another commences to form, one would always expect external pores so minute as these to be veiled by a mucus-film in seasons of rest. The pressure of this film is sufficient evidence that the cinclides are not excretory orifices for the outflow of the respired water, in the manner of the discharging siphon in the Bivalve MOLLUSCA: — at least that no current constantly, or even ordinarily, passes through them. I have watched them continuously for periods sufficient to detect such discharge if it were periodic. On one occasion (viz., that in which the film was protruded like a blown bladder) a minute Infusorial aninalcule chanced to pass across, close to the surface of the film; this would have been a decisive test of the existence of a ciliary current; but not the slightest deviation in the little atom's course could be detected. That the cinlclidcs are the special orifices through which those missile weapons —the aconltia —are shot and recovered, rests not merely on the probability that arises froln the co-existence of the two series of facts I have above recorded, but upon actual observation. In a rather large S. dianthzus, somewhat distended, placed in a glass vessel between my eye and the sun, I saw, with great distinctness, by the aid of a pocket SEA-ANEMlONES: THEIR WEAPONS. 415 lens, many acontia protruded from the cinclides, and many more of the latter widely open. Tile acontia, in some cases, did not so accurately fill the orifice but that a line of bright light (or of darkness, according as the sun was exactly opposite or not) was seen partially i)ordering the issue of the thread, while the thickened rim of the cizclis surrounded all. The appearance of the orifices whence the acontia issued was that of a tubercle or wart, and the same appearance I have repeatedly marked in examples observed on the stage of the microscope; namely, that of a perforate pimple, or short columnar tube. This was clearly manifest when the animal, slowly swaying to and fro, brought the sides of the cinclis into partial perspective. On another occasion I witnessed the actual issue of the aeontia from the ciezclicles. I was watching, under a low power of the microscope, a specimen of a S. nivea, while, by touching its body rudely, I provoked it to emit its missile filaments. Presently they burst out with f'orce not all at once, but some here and there, then more, and yet more, on the repeated contractions of the corrugating walls of the body. Occasionally, the fiee extremity of a filament would appear, but more fiequently the bigyht of cc bent one, and very often I saw two, and even three, issue from the same cinclis. The successive contractions of the animal under irritation, caused the acontia already protruded to lengthen with each fresh impetus, the bights still streaming out in long loops, till perhaps the free end'would be liberated, and it would be a loop no longer; and sometimes a new thread would shoot from a cinclis, whence one or two long ones were 416 EVENINGS AT THE 5MICROSCOPE. stretching already; while, as often, the new-comers would force open new cinclicles for themselves. The suddenness and explosive force with which they burst out, appeared to indicate a resistance which was at length overcome: —perhaps (in part at least) due to the epithelial film above mentioned, or to an actual epiderin, which, though often ruptured, has ever, with the aptitude to heal common to these lowly structures, the power of quickly uniting again. It appeared to me manifest from this and other similar observations, that no such arrangement exists as that which I had fancied:-tlhat a definite cizclis is assigned to a definite acontium, or pair of acontia; and that the extremity of the latter is guided to the former, with unerring accuracy, by sbome internal mechanisnm, whenever the exercise of the defensive faculty is desired. What I judge to be the true state of the case is as follows: The acontia, fastened by one end to the septa or their mesenteries, lie, while at rest, irregularly coiled up along the narrow interseptal fossoe. The outer walls of these fossue are pierced with the cinclides. When the animal is irritated, it iinmediately contracts: the water contained in the visceral cavity finds vent at these natural orifices, and the forcible currents carry with them the acontia, each through that cinclis which happens to lie nearest to it. The frequency with which a loop is forced out shows that the issue is the result of a merely mechanical action; which is, howeverl, not the less worthy of admiration because of the simplicity of the contrivance, nor the less manifestly the result of Divine wisdoml working to a given end by perfectly adequate means. The ejected acontia, loaded with their deadly cnidce in SEA-ANEMONES THEIR WEAPONS. 417 every part of their length, carry abroad their f-ltal powers not the less suiely than if each hlad been provided with a proper tnbe leading fiom its free extrelmity to tile nearest cinclis." Curious as these contrivances are, there is -yet much more to be told: these are preparatory and ancillary, as it were, to the elaborate mechanism by which the ultimate object of the whole provision is to be attained. The acontinm is but a reservior for the weapons -a kind of quiver for the arrows; and the cilnclis is a provision for getting them ready for action: we have not yet looked at the arrows themselves. They occur under three principal forms; and for the investigation of these we shall find it convenient to have recourse to different species. The first and most generally distributed form is the Chambered Cnida, as it is also the most elaborately organized. I know of no species in which it can be examined under so favourable circumstances as the pretty Mladrepore (Cyathina Smithii) of our south-western CNIDA OFI,-ADREFORE. coasts; and as I have several specimens of that species in my aquarium, subjects are at hand for our investigation. The clear tentacles are, as you perceive, crowned with opaque globular heads; if I should nip off one of these heads and flatten it by means of the compressorirum, you would see it ]iterally composed of 18* 418 EVENINGS AT THE MICROSCOPE. cnidce, the ends of which project side by side, as close as they can be packed one against another. But still larger examples mnay be obtained from the craskpeda. With a smart sudden blow I break the stony skeleton of the Madrepore in sunder-the flesh tearing apart also; and thus I expose the interior of the living animal. A great number of pellucid ribbons are now seen, very much convoluted, which are named craspedar. These are almost composed of large renidce. I remove with fine pliers a small fragment of one of these ribbons, and placing it between the plates of the compressorium, flatten it gradually till the plates are brought into as close contact as they can be. A high power now being put on, examine the organ in question. You see a multitude of perfectly transparent, colourless vesicles, of a lengthened ovate figure, considerably larger at one end than at the other; one of average dimensions measures in length' 0th of an inch, and in greatest diameter 0,,1-th. "In the larger (the anterior) moiety, passing longitudinally through its centre, is seen a slender chamber, fusiform or lozenge-folrm, about w~th of an inch in its greatest transverse diameter, and tapering to a point at each extremity. The anterior point merges into the walls of the cnidce at its extremity, while the posterior end, after having become attenuated like the anterior, dilates with a funnel-shaped mouth, in which the eye can clearly see a double infolding of the chamberwall. After this dcouble fold the structure proceeds as a very slender cord, which passing back towards the anterior end of the capsule, winds loosely round and round the chamber, with some regularity at first, but SEA-ANEMONES: THEIR WEAPONS. 419 becolning involved in contortions more and more intricate, as it fills up the posterior moiety of the cavity. The fusiform chamber appears to be marked on its inner surface with regularly recurring serrations, which are the optical expression of that peculiar arma ture to be described presently. " Under the stimulus of pressure when subjected to microscopical examination, and doubtless under nervous stimulus, subject to the control of the will, during the natural exercise of the animal's functions-the czidce suddenly emit their contents with great force, in a regular and prescribed manner. It must not be supposed, however, that the pressure spoken of is the immediate mechanical cause of the emission; the contact of the glass-plates of the compressoriumn is never so absolute as to exert the least direct force upon the walls of the capsule itself; but the disturbance produced by the compression of the surrounding tissues excites an irritability, which evidently resides in a very high degree in the interior of the enidCe; and the projection of the contents is the result of a vital force. "In general, the eye can scarcely, or not at all, follow the lightning-like rapidity with which the chamber and its twining thread are shot forth from the larger end of the cnidwe. But sometimes impediments delay the emission, or allow it to proceed only in a fitful manner-a minute portion at a time; and sometimes, from the resistance of friction (as against the glass-plate of the compressorium), the elongation of the thread proceeds evenly, but so slowly as to be watched with the utmost ease; and sometimes the process which has reached a certain point normally, 420 EVENINGS AT TIlE MIICROSCOPE. becomes from some cause arrested, and the contents of the cell remain permanently fixed in a transition state. Thus, a long continued course of patient observation is pretty sure to present some fortuitous combinations, and abnormal conditions, whicll greatly elucidate phenomena, that normally seemed to defy investigation. "In watching any particular enidclr, the moment of its emission mlay be predicted with tolerable accuracy, by the protrusion of a nipple-slhaped wart friom the anterior extremity. Tllis is the \ "~ base of the thread. The process of its protrusion is often slow and gradual, until it has attained a length abont equal to twice its own diameter, when it suddenly yields, rand the contents of \' / < the cnicldc dart forth. At this instant I llave, in many instances, leard a distinct crack or crepitatioi, )both in the examination of this species and of Sagartica paracitica. "When fully expelled, the thread or wire, which is distinguished by the term ectorceutm, is often twenty, thirty, or even forty times the length of the cnticlt; though in some species, as in most of the Sagcrtlice, it fiequently will not exceed one-and-a-half, or two times CNIDA OF B. CRASSI- the length of thle cnicda. coxnIs, dizscharged.;, dirged. The ecthorcea which are discllarged by elanzbered cnidce, are invariably firnished with a peculiar armature. The basal portion, for a length SEA-ANEMONES: THEIR WEAPONS. 421 equal to that of the cmida, or a little more, is distinctly swollen, but at the point indicated it becomes (often. abruptly) attenuated, and runs on for the remaillder of its length as an excessively slender wire of equal diameter throughout. In the short ecthorcea of Sagartia, the attenuated portion is obsolete.'It is chiefly upon this ventricose basal portion that the elaborate armature is seen, which is so characteristic of these remarkable organs. For around its exterior wind one or more spiral thickened bands, varying in different species as to their number, the number of volutions made by each, and the angle which the spiral forms with the axis of the ecthorceuvm. The whole spiral formed of these thickened bands, is termed the screw, or strebla. -" In the ecthorceca emitted by chambered cmzidce from the crapeda of Tealir crassicornis, the screw is formed of a single band, having an inclination of 45~ to the axis, and becoming invisible when it has made seven volutions. In those from the same organ in S. _parasitica, we find a screw of two equidistant bands, each of which makes about six turins-twelve in all-having an inclination of 70~ from the common axis. In those similarly placed in Cyactt/ina Smithii, [now under your observation,] the strebla is composed, as you may perceive, of three equidistant bands, each of which makes about ten volutions-thirty in all-with an inclination of about 40~ from the axis. In every case the spiral runs from the east towards the north, supposing the axis to point perpendicularly upwards. " Sometimes, especially after having been expelled for some time, the wall of the ecthorcurn becomes so attenuated as to be evanescent, while the strebla is still 422 EVENINGS AT T HE MICROSCOPE. distinctly visible. An inexperienced observer would be liable, under such circumstances, to suppose that the screw, when formed of a single band, as in T. crassicornzs, is itself the wire; an error into which I had myself formerly fallen. An error of another kind I fell into, in supposing that the triple screw of the wire in C. Smitlii was a series of overlapping plates: the structure of the armature is the same in all cases (with the variations in detail that I have just indicated); and the structure is, I am now well assured, a spiral thickened band running round the wall of the eethorcuwun on its exterior surface. I have been able when examininog such large forms as those of Corynacctis ciridis and C(yatlinac Smnithli, with a power of 750 diameters, to follow the course of the screw, as it alternately approached and receded from the eye, by altering the focus of the object-glass, so as to bring each part successively into the sphere of vision. " These thickened spiral bands afford an insertion for a series of firm bristles, which appeal to have a broad base and to taper to a point. Their length I cannot determinately indicate, but I have traced it to an extent which considerably exceeds the diameter of the ecthorccum. These barbed bristles are denominated Jterygia. "The number of pterygica appears to vary within slight limits. As well as I have been able to make out, there are but eight in a single volution of the onebanded strebla in T. crassicornis; while in the more complex screws of S. parasitica, Cor. viridis, and Ciy. Szmithii, there appeared to be twelve in each volution. " The barbs, when they first appear, invariably project in a diagonal direction from the ectlorcetun; and SEA-ANEMIONES: THEIR WEAPONS. 423 sometimes they maintain this posture. But more conmonly, either in an instant, or slowly and gradually, they assume a reverted direction. "' From some delicate observations made with a very good light, I have reason to conclude that the strebla, and even the pterygia, are continued on the attenuated portion of the ecthorceum, perhaps throughout its length. In Coti. viridis and Cyathina Smithii, I have suc. ceeded in tracing them up a considerable distance. In the latter I saw the continuation of all these bands, with their bristles, but what was strange, the angle of inclination had become nearly twice as acute as before, being only 22~ from the axis. The appearance of the attenuate portion, as also of the base of the ventricose part, is exactly that of a three-sided wire, twisted on itself; the barbs projecting from the angles. "The next form of these organs is the Tangled Cnida. This form is very generally distributed, and is mingled with the former in the various tissues. In the genus Sctgartia, however, it is by far the rarer form, while in Actinia and Ant/wea it seems to be the only one. " The pretty little (Corynzactis viridis is the best species that I am acquainted with for studying this kind of cnidce. [A fragment of its craspeda I have here ready for your observation, prepared exactly like that of C. SXmithii.] Their figure is near that of a perfect oval, but a little flattened in one aspect, about 5uth of an inch in the longer, and Tth in the shorter diameter. Their size, therefore, makes them peculiarly suitable for observations on the structure and functions of these curious organs. Within the cavity lies a thread (ecthiorum) of great length and tenuity, coiled 424 EVENINGS AT THE 3MICROSCOPE. up in some instances with an approach to regularity, but much more commonly in loose contortions, like an end of thread rudely rolled into a bundle with the fingers. "TLThe armature of this kind does not differ essentially from that already described. It is true, I have detected it only in Coryncactis, where the short ecttorceaum of the Tangled Cnida is surlrounded throlughout its length by a barbed strebla of three bands. The barbs are visible, under very favourable conditions for observation, even while the tangled wire rermains enclosed in the cnida, but their optical expression is that of serratures of the walls, without the least appearance of a screw. This, I say, is the only species in which I have actually seen tle armature of the ectlorcewmn in this kind of cd"IC, but I infer its existence from analogy in other species, where the conditions that can be recognised agree with those in this, though the excessive attenuation of the parts precludes actual observation of the structure in question.' Spiral Cnidm constitute the third form. In a few species, as Sagartia parasitica, Tealia crassicornis, and Ceriantrhus nemnbranaceus, I have'ound very elongated fusiform ctidw,, which seem composed of a slender cylindrical thread, coiled into a very close and regular spiral. In some cases the extrem- CNIDA OF CORYCTIS ities are obtuse, but in others, as in T. crassico'rnis [an example of which I now show you] the posterior ex SEA-ANEMONES: THEIR WEAPONS. 425 tremity runs off to a finely attenuated point, the whole of the spire visible even to the last, the whole bearing no small resemblance to a multispiral shell; as one of the Cerit/iadce or Ta.rritelladce. The ecthorceumm is discharged reluctantly firom this form, and I have never seen an example in which the whole had been run off. So excessively subtile are the walls of the cnidec, that it was not until after many observations that I detected them; in an example from T. crassicornis, which had discharged about half of the wire, I have not seen the slightest sign of armature on the ecthorcuun. So far us my investigations go, these Spiral Cnide are confined to the walls of the tentacles, in which, however, they are the dominant form." Such, then, is the form and armature of these organs. 1But I have not yet done with them. The emission of the wire, strange to say, is a process of distinct eversion from beginning to end. The ectlo/rcezam is not a solid, but a tubular, prolongation of the walls of the cnida, turned-in, during its prinal condition, like tihe finger of a glove drawn into the cavity. Of' this fai'ct you may convince yourself by a carefull watching of the phenomena before you. Maainy of the ectlorcea from the tangled enidce now under your eye run out, not in a direct line, but in a spiral direction. Select one of these, and you will perceive that each bend of the spire is made, and stereotyped, so to speak, in succession, while the tips go on lengthening; the tip only progresses, the whole of the portion actually disclharged remaining perfectly fixed; which could not be on any other supposition than that of evolution. In the discharge of the chambered kind-to revert to those which we were just now examining-we saw 426 EVENINGS AT THE MICEOSCQPE. the ventricose basal part first appear; the lower barbs flew out before the upper ones, and all were fully expanded before tile attenuated portion began to lengthen. "This, again, is consistent only with the fact of the evolution of the whole. On several occasions of observation on the chambered cmvidce of Cyathdna co izthii, I have actually seen the unevolved portion of the ecthorweum running out through the centre of the evolved ventricose plortion. But perhaps the most instructive and convincing example of all was the following. One of the large tangled enidee of ceorynactis virdis had shot about half of its wire with rapidity, when a kind of twist, or' kink,' occurred against the nipple of the cnidca, whereby the process was suddenly arrested. The projectile force, however, continuing, caused the impediment to yield, and minute portions of the thread flew out piecemeal, by fits and starts. By turning the stage-screw I brought the extremity of the discharged portion into view, and saw it. slowly evolving, a little at a time. Turning back to the enida, I saw the kink gradually give way, and the whole of the tangled wire quickly flew out through the nipple. I once more moved the stage, following up the ecthorceugnm, and presently found the true extremity, and a large portion of the wire still inverted; slowly evolving, indeed, but very distinct throughout its whole course, within the walls of the evolved portion. "' From all these observations there cannot remain a doubt of the successive eversion of the entire ectlwrYou ask, What is the nature of the force by which the contained thread is expelled? "That it is a potent force is obvious to any one who makes the sudden SEA-ANEMONES: THEIR WEAPONS. 427 explosive violence with which the nipple-like end of the cicdla gives way, and the contents burst forth; as also the extreme rapidity with which, ordinarily, the whole length is evolved. A curious example of this force once excited my admiration. The ecthorceum from a cnidca of Corynactis virdis was in coulse of rapid evolution, when the tip came full against the side of another cnida already emptied. The evolution was momnentarily arrested, but the wall of the empty capsule presently was seen to bend inward, and suddenly to give way, the eethorcaumn forcing itself in, and shooting round and round the interior of the enida. "' The most careful observations have failed to reveal a lining membrane to the cnida. I have repeatedly discerned a double outline to the walls themselves, the optical expression of their diameter; but have never detected any, even the least, appearance of any tissue starting from the walls, as the ecthorce7in bursts out. My first supposition, reluctantly resigned, was, that some such lining membrane, of high contractile power, lessened, on irrita-tion, the volume of the cavity, and forced out the wire. " The cnida is filled, however, with a fluid. This is very distinctly seen occupying the cavity when, from any impediment, such as above described, the wire flies out fitfully; waves, and similar motions, passing from wall to wall. Sometimes, even before any portion of the wire has escaped, the whole mass of tangled coils is seen to move irregularly firom side to side, within the capsule, from the operation of some intestine cause. lThe emission, itself is a process of injection; for I have many times seen floating atoms driven forcibly along the interior of the ecthorceum, sometimes 428 EVENINGS AT THE MIICROSCOPE. swiftly, and sometinles more deliberately. Nothing that I lhave seen would lead me to conclude that the wall of tlle cnidca is ciliated. "I consider, then, that this fluid, holding organic corpuscles in suspension, is endowed with a high degree of expansibility; that, in the state of repose, it is in a condition of compression, by the inversion of the ectAorceum; and that, on the excitement of a suitable stimulus, it forcibly exerts its expansile powel, distending and, conseqttently, projecting, the tubular ccthorceutn -the only part of the wall that will yield without actual rupture." It has been proved that the execution of these weapons is as effectual as tlleir 1mechanism. is elaborate. The wire shot with such force penetrates to its base the tissues of the living animals which the Anemone attacks, when its barbs preclude the withdrawal of the dart. But the entrance of bodies so excessively slender would. of itself inflict little injury y; there is evidently the infusion at the same time of a highly subtile poison into the wound; some venomous fluid escaping with the discharge of the ecthorce3uan, which has the powver, at least when augmented by the simultaneous intromission of scores, or hundreds, of the weapons, of suddenly arresting animal vigour and speedily destroying life, even in creatures-fishes for example-far higher than the zoophyte in the scale of organization. I have seen a little fish in perfect health come in accidental contact with one' of the acontia of an irritated Sagartica, when all the evidences of distress and agony were instantly manifested; the little creature darted wildly to and fro, turned over, sank upon the bottom, struggled, flurried, and was dead. SEA-ANEAMONES: THEIR WEAPONS. 429 " Admitting the existence of a venomous fluid, it is difficult to imagine where it is lodged, and how it is injected. The filrst thought that occurs to one's mind is, that it is the organic fluid which we have seen to fill the interior of the cnida, and to be forced through the everting tubular ecthorcezan. But if so, it cannot be ejected through the extremity of the ect/horeetun, because if this were an open tube, I do not see how the contraction of the fluid in the cnitda could force it to evolve; the fluid would escape through the still inverted tube. It is just possible that the barbs may be tubes open at the tips, and that the poison-fluid may be ejected through these. But I rather incline to the hypothesis, that the cavity of the ecthorceutm, in its primnal inverted condition, while it yet remains coiled,tp in the cbida, is occupied with the potent fluid in question, and that it is poured out gradually within the tissues of the victim, as the evolving tip of the wire penetrates fkrther and farther into the woulnd." I do not think that the whole range of organic existence affords a more wonderful example than this of the minute workmanship and elaboration of the parts; the extraordinary modes in which certain prescribed ends are attained, and the perfect adaptation of the contrivance to the work which it has to do. We must remember that all this complexity is found in an animal which it is customary to consider as of excessively simple structure. But the ways of God are past finding out. These are but parts of His ways. 430 EVENINGS AT THE MICROSCOPE. CHAPTER XX. PROTOZOA AND SPONGES. WE are so accustomed to see certain of the vital functions of animals performed by special organs or tissues, that we wonder when we find creatures which move without limbs, contract without muscles, respire without lungs or gills, and digest without a stomach or intestines. But thus we are taught that the function is independent of the organ, and, as it were, prior to it; though in nine hundred and ninety-nine cases out of a thousand it be associated with it. In truth, the simplest forms of animal life display very little of that division of labour, the minuteness of which increases as we ascend the organic scale; the common tissue is not yet differentiated (to use the awkward term which is becoming fashionable, among physiologists) into organs, but is endowed with the power of fulfilling various offices, and performing many functions. In all probability, the function is but imperfectly performed; the specialization of certain tissues, and their union into organs, and the complexity of such combinations, no doubt, perform the given function in a far more complete degree; and it is the number and elaborateness of these that constitute one animal higher in the scale than another. The human lung is no doubt a more complete breathing apparatus than the entire PROTOZOA AND SPONGES. 431 ciliated surface of an Infusory, and the human eye sees more perfectly than the loose aggregation of pigment granules on the edge of a Medusa. But this diversity is essential to creation, as the great and wondrous plan which we see it to be; and, meanwhile, we may rest satisfied that the humble requirements of the lowest organism are met adequately by its humble endowments. This evening I propose to show you some of these humble conditions of animal life-the lowest of the lowly. I have here two or three phials of very rich water dipped from the fresh-water ponds in the neighbourhood. All collections of water are not equally productive; and very far indeed is the popular notion from correctness, that every drop of water which we drink contains millions of animalcules. You may find many collections of clear water, springs, streaims, and pools, fiom. which you may examine drop after drop in succession, with the highest powers of the microscope, and scarcely discover a solitary animalcule. Again, it is not stagnant and fetid pools that are the richest in vitality; though no doubt you will always obtain some forms abundantly enough in such conditions. According to my own experience-an experience of many years-the paucity or profusion of animal life in any given collection of water can never be determined beforehand; the season, the situation, the aspect, the character of the country, and inany other unsuspected conditions, may influence the result; which yet one may often give a shrewd guess at. Generally speaking, small ponds, in which a good deal of sub-aquatic vegetation grows-and particularly if this be of a minutely-divided character, such as XAfyrioAphyiluqm, 432 EVENINGS AT THE MICROSCOPE. Chara, &c., and whose surface is well covered with duckweecl (Iemnzaq), yields well; and, in collecting, it is desirable so to dip as that some of the fine loose sedinent of the bottom may flow into your phial, and then to pluck up one or more of the filamentous water-plants, and introduce these into your vessel. Now, to examine such a collection, proceed as I am about to show you. I hastily glance with the pocketlens over the foliage, and selecting such filaments as seem the most loaded with dirty floccose matter, I pluck off with pliers one or two, together with one or two of tile cleaner ones that are higher up on the plant, nearer the growing point. H4aving laid these on the lower glass of the live-box, I take up with the tip of a fine capillary tube, or a pipette, a minute quantity of the water at the bottom, which flows in as you see, carrying a few granules of the sediment. This drop I discharge upon the glass of the live-box, put on the cover, and place the whole on the stage of the microscope. First let us use a low power-one hundred diameters or so —in order to take a general glance at what we have got. Hlere is an array of life, indeed! Motion arrests the eye everywhere. "The glittering swift and the flabby slow" are alike here; clear crystal globules revolve giddily on their axes; tiny points leap hither and thither like nimble fleas; long forms are twisting to andt firo; busy little creatures are regularly quartering the hunting-ground, grubbing with an earnest devotedness among the sediment, as they march up the stems; here are vases with translucent bodies protruding from the mouths; here are beauteous bells, set at the end of tall threads, ever lengthening and short PROTOZOA AND SPONGES. 433 cuning; lere are mlaelstrlrns in miniature, and tempests in far less than a teapot; rival and interfering currents are whirling round and round, and making series of concentric circles among the granules. Surely here is material for our study. I see an object slowly creeping along the glass, w]hich will be just the thing for our pur'pose. It is the Pr'oteus (Amnbba dbfuens). Let me put on a hligher power, and sublnit it to your observation. You see a flat area of clear jelly, of very irregnular form, with sinnosities and jutting points, like the outline of some island in a map. A great number of minute blackish granules and vesicles occupy the central part, but tile edges are clear and colourless. A large bladder is seen near one side, which appears filled \with a subtile fluid. But while you gaze on it, you perceive that its form is changing; that it is not at two successive moments of exactly the same shape. This individual, whlich, when you first looked at it, was not unlike England in outline, is now, though only a few minutes have passed, something totally different; the projecting angle that represented Cornwall is become rounded and more perpendicular; the broken corner that we might have called Kent has formed two little points, up in the position of Lincolnshire; the large bladder which was in the place of the Eastern counties is lnoved up to the Durham coast, and is, moreover, greatly diminished; and other like changes have taken place in other parts. Lo! even while speaking of these alterations, they ha.ve been proceeding, so that another and a totally diverse outline is now presented. A great excava19 434 EVISENINGS ATr THE MICROSCOPE. tion takes the place of Dorset; Kent is immensely prolonged; the bladder has quite disappeared, &c.; but it is impossible to follow these changes, which are ever going on without a moment's intermission, and without the slightest recognisable rule or order. FORMS OF AMmBQA. Successively drawno from one individual. The projections are obliterated or exaggerated; the sinuosities are smoothed, or deepened into gulfs, or protruded into promontories; firths form here, capes there; not by starts, but evenly, and with sufficient rapidity to be appreciable to the eye while under actual observation; though the alterations are more striking if you take your eye off the object for a few seconds, and then look again; and still more so, if you try to sketch the outline. Individuals vary greatly in dimensions; this specimen is about one hundred and twentieth of an inch in long diameter, but others I have seen not more than one-tenth as large as this, and some. twice as large. Disregarding now this peculiarity of change of form, which has procured for it the name of the old versatile sea-god that was so difficult to bind, we will concentrate our attention on some other points not less PROTOZOA AND SPONGES. 435 interesting. That great bladder undergoes changes besides those gradual alterations of place which are dependent on the general form. It slowly but manifestly increases in size up to a certain extent, when it rather suddenly diminishes to a point, and immediately begins to fill again, as slowly as before. These alterations go on with some regularity, and we cannot observe them without becoming convinced that it is a process of filling and emptying; that the bladder gradually fills with a fluid which is either secreted by its walls or percolates into it fiom the surrounding tissue; which fluid, when full, the bladder discharges by a sudden contraction of its outline. But whither the fluid goes it is difficult to determine; I have never been able, in this or in any other instance of its occurrence-though this contractile bladder is characteristic of the extensive classes Infatsoria and Rotifera-to see any issue of fluid firom the body at the moment of contraction, and therefore conclude that it is discharged into the body, perhaps back again into the tissues whence it was taken up, and whence it is about to be collected again. HIence, it is probably the first obscure rudiment of a circulation; the fluids impregnated with the products of digestion being thus collected and then diffused throughout the soft and yielding tissues. The smaller' bladder-like spaces that you see in considerable numbers in the substance of the animal, are collections of fluid contained in excavations of that substance, which are called vacuoles, differing from vesicles, inasmuch as they seem to have no proper wall or inclosing membrane, but to be merely casual separations of the common substance, such as 436 EVENINGS AT THE MICROSCOPE. would be made by drops of water in oil. These vacuoles appear to be connected with the digestive functionl; for very many of them are not clear, but are occupied with granules more or less opaque, and of exceedingly various dimensions. That these collections of granules are food, you will see by this experiment. I mingle a little carmine with the water, just enough to impart a visible tinge to it, and close the live-box again. Already you perceive that some of the tiny globules are become turbid and red, and that their opacity and colour are deepening perceptibly. We see by this that the particles of carmine have been taken into the jelly-like sarcode, and are accumulating in little pellets surrounded by fluid, in these casual hollows of its substance. The process is rendered still more obvious when, as is often the case, some Dicatomccea, with a hard siliceous shell, becomes the food of the Amonba. The apparently helpless jelly spreads itself over the organism, so as soon to envelope it; the flesh, which having no skin can unite with itself wherever the parts come into contact, closes over the Diatom, whicl 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 perllaps 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. PROTOZOA AND SPONGES. 4337 Another genus somewhat similar is Arcelct, but it differs in being furnishedcl with a more or less rounded shell (loricac), 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 thle 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, solnetimes 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 sometirnes turned partly over; when we perceive that its under-side is fiat 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 Amwba. 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 Amcnba, whose external surface has the power of secreting a symmetrical shell of horny, or chitinous substance. The lorica is about -,tlh of an inch in diameter. This species is named Arcellct vulgctris. Laying aside our live-box with its contents for the present, we will have recourse to the tank of sea-water for one or two other objects of interme 438 EVENINGS ATr THE MICROSCOPE. diate 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 Foramninferca, 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 crispa, a fair sample of its class, and though not more than Ath 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 sufficient 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, Polymo]phine oblong, 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 PROTOZOA AND SPONGES. 439 that the eye cannot recognise the process of extension -stretch and extend their lines and filns of delicate jelly, till at length they have stretched right across the field of view. The extension is principally in two opposite directions corresponding 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 filns are as irregular in their forms and sizes as the expansion of the sarcode of Amcoaob, 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 divergence and union. There can be no doubt that the object of these lengthened 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 Amceba 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 440 EVENINGS AT THE MICROSCOPE. changes of position in the shell while under observation, is, that it is by Ineans of the adhesion and contraction of tle pseudopocdia that the animal drags itself along a fixed surface. This it can effect so assidnously, that I fiequently find them in the morning adhering to the tank-sides three or four inches fiom the bottorm, though on the previous evening none were visible on the glass. Thus they must crawl, on occasion, fromn a hundred to a hundred and fifty times their own diameter in a night. The structure of a Sponge is mluch the same as that of these animals, with the exception that its solid part or skeleton is not a continuous covering by which the sarcole is invested, but consists of fibres or points or rods of varying form, which are clothed with the sarcode. This loose sort of skeleton mnay be of horny or chitinous matter, like that of Arcella, or calcareous, like that of the Foramnin'fera, or it may be siliceous —that is, composed of flint (silei). 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 anastomose in every direction, at very short intervals, as you may see by looking at this atom, which I cut off firom 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 Tu'l'rkey sponge. For it is made up of an immense multitude of glassy needles, all separate and independent, between themselves, yet so contrived that they do hold together very firmly, and in a great number of cases are arranged PROTOZOA AND SPONGES. 441 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, so that by taking hold of one you may lift a bristling group of scores. Somewhat on the same principle are the calcareous and siliceous pins (spitcula) of a Sponge held together 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 Grantica (calcareous 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 Hffalichondrica szberea. This when alive is of an orange colour; and is always found closely investing turbinate 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-oinitting for the present, the skeleton. Of the same substance is the whole slice composed, but looser and more open as it recedes from the surface. It is separated by 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 19* 442 EVENINGS AT THE MICROSCOPE. the surrounding water enters on all sides. These presently unite into slender pipes, which, irregularlymneandering, 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 out that has thus made the grand tour of the SECTION OF SPONGE. whole interior. Such osculc, as you perceive on the remainder of the fIaliclwondria, are usually raised -on slight eminences; and resemble, especially when in living action, miniature volcanoes, 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 remainder 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 PROTOZOA AND SPONGES. 443 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 surmounted 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 to be entangled together quite at random without rule or arrangement. And yet there is an arrangement discernible here; for the canals 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. Bowerbank has shown that in G. compressct the substance is divided into very regular chambers in a double series, separated 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 interlacement. 444 EVENINGS AT THE MICROSCOPE. CHAPTER XXI. INFUSORIA. REPVENONSa d nos rmouZtons. We will resume our examination of the drop of pond-water, and the fragments of Jyriophyllumv, 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 genuls Eugleca, 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 Rotife'ra, 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 imost numerous is an active little thing of about w-5-thl of an inch in length when extended, though fomin its extreme versatility it is as difficult to assign to it a definite size, as a definite shape. It seems to be the E. scanguinea, so called because it is said to occur sometimes of a deep red lhue, 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 enlerald green in the body, with the two extremities perfectly NvUSoRA. 445 clear and colourless. I might perhaps dcscribe its ordinary form as spindle-shaped, with a pointed tail, and a blunt, rounded head; but it is remarkable for the variableness of its shape. It is capable of 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 you who are skilled in metaphysics to determine. Away they go tumblinga over and overl revolving on the long axis as they ploceed, 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 steadiness of its movement more easy of observation. It is named E. acus, or " the Needle Euglena." This is an animalcule of great elegance and brilliance; its sparkling green hue, with colourless extremities, and its rich pale crimson eye, are very beautiful. It commonly swims extended, 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 reprloduction. 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 446 EVENINGS AT THE MICROSCOPE. capable of bending its head and body in various directions, but is most beautiful when straight. The front is flrnished with a slender thread-like proboscis. This species affords us a good opportunity of observing the red spot which, for convenience 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 Rotiferrc 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 can have no connexion with vision. I think it still possible, that a sensibility 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 amongst the rest, called E. triquetra, or the Three-sided. It bears a resemblance to a broad rounded leaf, with the footstalk forming a short transparent point, and the mid-rib elevated 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, INFUSORIA. 44T 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 4?/~. which the back is furnished. It is in the turnings of such minute creatures that the microscopist often gets a glimpse of peculiariTHRIEE-SIDED EGLENA. ties of form, which a view of the animal when in repose, however long continued, fails to reveal. Longitudinal interrupted lines are seen running down the body of this pretty leaf, which do not appear to mnark 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 untyiing 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 appearance: I will put on a higher objective. You now see that there proceeds from thefirontal 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, of the creature, seems more like that produced by minute and generally distributed ciliae, than that caused by the lashings of a single long thread. Yet two more species of this extensive genus we 448 EVENINGS AT THE MICROSCOPE. discern in this well-stocked drop of water. They have received the appellations of the Pear (E. pyrum), and the Sloth (F. deses). The former is the most minute we have yet seen, and seems to be scarce; but it is highly curious and interestinog in appearance. It much resembles, in outline, a fish of the genus Balistes; the muzzle being somewhat protruded and truncate, and the form rhomboidal; 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 lozengeshaped 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 Egylena takes the form of a 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 v-}Ith of an inch in length, including the tail. Euqglenazc deses is much larger, being about,I th 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 dblong 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 congeners, but contents itself with twining slowly among the flocose INFUSORIA. 449 stems and filaments of the water-plants, or crawls upor the surface of the live-box. It does not appear to change its form, otlerwise than its soft and flexible body necessitates, as it twines about. But enough of the Eyglenas. For I have just caught sight of a still more curious creature, the Swan Animalcule (Trackelocercat olor). It is reposing on one of thle leaves of the lyriophyllhm, 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 inore to that of a snake-bird (Plotus); the body, swelling in the middle, tapers gradually into a slender pointed tail, at one extremity, and at the other, into a very long ancd equally slender neck, which is terminated by a slilght dilitation. The whole is perfectly transparent, but the body is filled with numerous minute globular vessels, or teinporalry stomachs. The grace of its motion as it glides along with' a free and moderately swift progression through the clear water, or winds throngh the intricate passages of the green conferva, thrlowing 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 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 450 EVENINGS AT THE MICROSCOPE. or displeased the animal: the body also can be swollen or lengthened at pleasure; it call 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 infuision 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 fibres present, I partly turned the glass cover 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. I't 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 SWAN-NECK AIND ITS DIVISIONS. 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 INFUSORIA. 451 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 bnt incessant working, very amuch 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 nmuch apparent pirogress, 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 action; after a while (how, I do not exactly know) without 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 correspondent 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 452 EVENINGS AT THE MICROSCOPE. now appeared longitudinal. I believe, however, the animals were really separated before this, thllough they remained in contact, for as they slid over each otlier, 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, aluiost simultaneously, threw out their long necks, and again retired to sluggish repose. Among the sedimrent, the grains of which are driven hither and thither by their spasmodic jerking movements, you see several individuals of another sort of creatures —the Chrysalis Animalcule (Pcaramcecium? aaerelia.) This is a "whale 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 presents a pellucid appearance, and an oblong figure, of which the fore part is somewhat narrowed. Tile 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 malrked by a sort of long fold, the sides of which are fiinged with long cilia, whose vibrations are very marked. The INFUSORIA. 453 whole surface, on both sides, is coveled 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 approximation; 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 stomaachs, more or less completely filled with the brown and green food, which. the animals are collecting fiom tlhe 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 tle water. The ciliary currents are thus instantaneously rendered strikingly visible. The crimson atoms are attracted fiom 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 originally approached. But now the gathered currents have produced their expected result; for many of the globular vacuoles are already become of a beautiful rosy lnhue, fiom 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 longi 454 EVENINGS A' THE MICROSCOPE. tudinal axis, the line of the vesicles alternately approaches and recedes from that of the mouth. They are remarkable for their structure. Far from the sim-r plicity in which the organ is usually presented to us in the animals of this class, the contractile bladders are here very complex. Each when distended is globular; PABiAMC&OIUM. and it is surrounded by a number of others of much smaller dimensions, and of a drop-like form, so set as to radiate round the principal vesicle as a centre, the rounded portion of each in apparent contact with the vesicle; and the slender extremity running 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 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. INFUSOiIA. 455 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 Rotifer, probably Echlanis, which is always glued to some filament or stem of a water-plant. It may interest you to watchl the progress of the contained embryo, which you call readily do, since the egg-shell is as transparent as glass, and the infant animal already displays the movements of independent life. Meanwhile I will tell you 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) Euchtanis dilatatac had been laid during the night on a leaf of NVitella, in the live-box. When I observed it, the transpa- % A GO v F'y rency of the shell allow- 0 <. ed the enclosed animal to be seen with its vis- cera; which occasionally contracted and expand- ed; the place of the nas-' i A tax I could distinctly make out. The cilia were vibrating, not very COLEPS AND CHILOMONAS. rapidly, but constantly, on the front, where there was g vacant space between the animal and the shell. From T7. R., 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 per 456 EVENINGS AT THE [MICROSCOPE. ceived on my return tllat a portion of the animal was outside the shell. The appearance was thllat 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 whllen rotating in the perfect animal. When excluded to the extent just named, some little creatures that were flitting about found it, and began to assemble round it. These were far too rapid in their movements to allow me to identify them before, or to perceive any thing else than their swift motion and oval folrm; but this attraction causing themn to become still, allowed ine 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 malked by a series of ribs, wlhich run down longitudinally, and are crossed by other transverse ones; the rounded bottom iS furnislhed with three short points; so that the whole reminded me of a barrel with its staves and hoops, set on a threelegged stool. Within the body, which is colourless, are seen small dark spots, which are probably thle stoinach-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 vultumes gather one by one to a carcase. Very soon there were a dozen or INFUSORIA. 457 fifteen of them, some of which were ever shifting their places, and some were playing around, or revolving on their longitudinal axis. I found that their object really was to prey on the soft parts of the creature just excluded froll 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 current. 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 Euchldanis 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 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 1Monas, perfectly transparent, of an oval form, with some granules visible in the interior. They were about,-oo,th of an inch 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, whicb, to the naked eye, looked like little undefined white clouds, but which under the microscope showed 20 458 EVENINGS AT THE MICROSCOPE. the Monads in incalculable multitudes, but for the most part in still repose. Some were still moving to and fro, however, and, in the course of the day, most of them became again active. As soon as the C'oepes had forsaken their prey, the Monads began to gather around 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 dimensions. A close examination of these latter, when they had settled to rest, showed me that they were of the species COhilomnonas paranceciumn. 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. 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 nmost attractive of all the Infusoria, the beautiful Forticellce. The species is not the common bell-shaped one, but the smaller with pursed month, the little V. microstoma. INFUSORIA. 459 Look at this active group, consisting of a dozen or so of glassy vases, shaped something like pears, or elegant 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 fioccose rubbish attached to the plant, and diverge as they ascend, thus carrying their lovely bells clear of one another. Each vase is elegantly ventricose in the middle, terminating below in a kind of nipple to which the stalk is attached, and above in a short wide neck with VORTICELLZE. a thickened rim. This last is highly sensitive and contractile; its inner edge is set round with a circle of vibratile cilia, which, when in full play, produce a pair of small circular vortices over two opposite points 460 EVENINGS AT TIlE MICROSCOPE. 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, fiom 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, sometimes withdrawn, sometimes protruded, and often vibrating 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 charm to this elegant animal INFUSORIA. 461 cule, 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 rendered tense by extension, is highly sensitive to vibrations in the surrounding medium; and as in the circumstances in which we observe the animals, suclh vibrations niust be every instant communicated to the vessel in which they are confined, the stalks are no sooner tense than they contract with alarm. This depends on a contractile cord which passes throughout t the entire length of the stalk, and which is distinctly visible in the lalger 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 in which we are accustomed to see it in higher animals. The contraction of the lmuscle 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; 462 EVENINGS AT THE MICROSCOPE. but vibrations, even when so violent as those produced by tapping the stage of the microscope with the fingernail, have no effect unless the stalk be tense, its own power of vibration being then only developed, just as a cord becomes musical in the ratio of its tension. 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 engravings of many of the invisible animalcules, and had read technical descriptions; but of their brilliant transparency, 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 examrnination are exhibiting phenomena of no less interest than their form and motions. 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 lhave done, from the moment when it first becomes recognisable, to its completion in the frieedom of one of the newly formed animnalcules. 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 detect 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 INFUSORIx. 463 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 circle of these organs are developed around the basal extremity 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. HIere 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 exercising its newly found power of locopmotion. 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 instead 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 464 EVENINGS AT THE MICROSCOPE. of which is therefore appropriated 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, fbr amidst so great a profusion of lVorticella as we have ACINETA. 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 trumn INFUSORIA. 465 pet of the clearest glass, with a rounded extremity, and with the bese 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 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 suspected that this stiff and motionless object, with its tufts of 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, inclosing the Vorticella in its- cavity, in the form of a simple vesicle. Within this vesicle is seen the band-shaped nucleus, unchanged, and what was the contractile bladder, which, however, no longer contracts. By and by this torpid Vorticella enlarges itself il20* 466 EVENINGS AT THE MICROSCOPE. regularly, 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 Iorticella separates 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 all 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 commences life afresh. The Acineta, meanwhile, soon heals its wound, and after a while develops a new nucleus, which 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, instead of forming a Vorticella, breaks itself up into a great number of tiny clear bodies, reserrbling Monads, which soon acquire independent motion, and glide rapidly about the cell formed by the inclosed Vorticella-body 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 nnmber of thirty or up INFUSORIA. 467 wards. The Acinetac 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 Acinetac stage, and gradually attaining the full size of the race. Some forms of the same family, Vorticelladce, are interesting 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. Cothkurnia imberbis is one of the prettiest of these. The cell is of an elegant ampullalike 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 protrude beyond its rim. If carmine be 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 the-re 468 EVENINGS AT THE MICROSCOPE. 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 ar e t Vaginicolce, but the cells which they inhabit are not stalked, but are immovably affixed to plants. In V. crystallina, the cell is a tall goblet, standing erect, perfectly colourless; while in V. clecumbens, it is slipper-shaped, attached along its side, and of a golden-brown hue, but still quite transparent. Itere is, fortunately, a group of the latter species, scattered about the leaves of the lVitella. Though, in general, both in form and habits, closely like the Cothurnia, yet the V7qginicola has VAGINICOLA. some peculiarities of interest. The cilia are more developed, and can be more distinctly seen than in either Cothurnia or Vorticella, formnig, when in swift action, INTFUSORIA. 469 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 Vorticellce; and it is curious to see two Vaginicocla, 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 organized 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 excessively common. both in fresh and sea water, wherever vegetable matter is in process of decomposition; and hence their presence can at all times be comnmanded 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 Stylonychca, and I believe to the species S. pustulata. It presents the form of an oval disk, which, when seen sideways, is found to be flat beneath and convex above. It cornmonly swims with the belly upwards, and when exhibited on the stage of the microscope, in almost every case, this surface is presented 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 470 EVENINGS AT THE MICROSCOPE. difficult to obtain a fair sight of its structure. Its margin, however, is surrounded by short cilia; the mouth, which is a long opening on the fi'ont part, and at the left side (as to the animal) of the ventral surface, is fiinged 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 urincini, 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 performed 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 bristles then form, and the creatures are held together for a few seconds by these organs, even when the rNFUSORIA. 47t bodies are distinctly severed. When separated, they retain the round form for some time. When a drop of water is examined between two plates of glass, it is amusing to observe the numbers that congregate in the sinuosities 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, and the creatures die before the water is dry. They not only die but 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 appearance, varying in number and size, and then the whole became 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 vortices, 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 perceive that any of them swallow 472 EVENINGS AT THE MICROSCOPE. 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, hor any other Infptsoria in like circumstances, notwithstanding what is stated in books. HIere is another species in equally amazing profusion, S. mytil1us. Its form is oblong, with rounded extremities, the anterior obliquely dilated. This species affords a good example of the various organs of locomotion. A transparent oblong shield, which is quite soft and flexible, is spread over the back, which does not prevent the eye 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 unzcini, and are evidently used as feet, the tips being applied to the glass. The optical effect of the throwing about of these uncdni, when the place INFUSORIA. 473 which they touch is in focus, is very curious. They are rapidly moved, but without regularity; the tips biend as they touch the surface of the glass; some of thllem seem to have accessary hairs, equally long, but slender, proceeding fiom 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 setce, placed at the hinder extremity, the central one in the line of the body, the others radiating at an angle. These are distinguished fiom 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, backward as well as forward, occasionally shooting round and round in a circle, with many gyrations, much like the pretty little polished beetles (Gyrinu8s) 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 9f 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 Stylonychda had somehow introduced himself. There was just room for himn to move backward and forward without turning, and the space was about three times his own 474: EVENINGS AT THE MICROSCOPE. 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 thenl 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 imy 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. Common as these Stylonyclicea are, and abundant beyond all calculation, where they do occur, from their tendency to self-division, thev are not so universally met with as their cousins, of the genus Eauplotes. These are still more highly organized, and will please you by their activity and sprightly intelligence, I am sure. Here are several individuals in the live-box at this moment. INFUSORIA. 475 They differ from the Slylonychice, in having the soft body covered with a plate of crystal mail, hard and inflexible, much like the shield of a Tortoise. Several species have this glassy shield marked with delicate lines running lengthwise; somnetimes in the form of parallel ridges, as in a little species found in infusions (perhaps E. chacron;) 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 ob\ lique, and extends a long way down the under surEUPLOTES. face; 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 processes, which project from beneath the shell backwards and downwards, and soft hook-like uncini which are set chiefly near the forepart 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 (or seta) affixed to the hinder part of the shell, from which they diverge. In E. truncatus these are four, but they are wanting in E. charon. The body displays a mass of granules, vacuoles, and vesicles of different sizes. 476 EVENINGS AT THE MICROSCOPE. 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 sterns and filaments this pretty 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 floccu lent 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 2ith of 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 rosecoloured or purple fluid of much brilliancy. This creature, which bears the name of Chlarnidodon, has the peculiarity of a set of wand-like teeth arranged in a hollow cylinder. And with these we dismiss the InAfusoria, 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 pre INFUSORrA. 477 vails as to many parts of their structure and economy; and 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! 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. INDEX. Acineta, 464. Cinclides, 411. Acontia, 410. Cnidce, 379. Air-tubes of Fly, 107. Cockchafer, antennae of, 187. Alcyonium, 399. spiracle of, 114. Alternation of Generations, 374, $84. Coleps, 456. Anreba, 433. Contractile Bladder, 435, 453. Anchors of Synapta, 345. Corkscrew Coralline, 71. Animalcules, 444. Corynactis, weapons of, 423. Antennae of Chafer, 187. Cothurnia, 467. Crab, 197. Cows' paps, 400. Fly, 191. Crabs, 197. Gnat, 192. ears of. 197. Insects, 184. eyes of, 201. Moths, 188. stages of, 210. Skipjack, 188 Cranefly, spiracle of, 113. Weevil, 185. Craspeda, 418. Aphrodite, 303. Cricket, drum of, 97. Arcella, 437. Cuckoo-fly, ovipositor of, 145. Cuttleshell, 44. Barnacles, 221. Cyathina, weapons of, 417. hand of, 223. Cyclops, 203. transformations of, 226. Cydippe, 356. Bee, eyes of, 196. Cypris, 208. foot of, 136. mouth of, 163. Daphnia, 207. sting of, 142. Dead men's fingers, 400. wing of, 82. Diamond beetle, scales of, 92. Beetle, mouth of, 160. Dragon-fly, 80. " Bird's-head," 72. eye of, 193. use of, 77. Dumb-bells of Holothuria, 342. Blood of Beasts, 29. Dyticus, foot of, 134. Birds, 30. Fishes, 30. Earthworm, 298. Frog, 31. Ecthormeum, 421. Man, 29. Egger-moth, 188. Rleptiles, 30. Euglena, 444. Tunicate, 36. Eunice, 308. Brachionus, 260. Euplotes, 475. Bristletail, scales of, 85. Eyes of Crabs, 201. Bug, mouth of, 166. Dragon-fly, 193. Bugula, 71. Harvestman, 241. Butterfly, scales of, 90, 91. Infusoria, 444. sucker of, 177. Insects, 193. IRotifera, 272, 446. Chameleon-fly, 115. Scallop, 60. Cheese-mite, 253. Snail, 61. Chilomonas, 457. Spider, 238. Chirodota, 343. Cicada, drum of, 102. Feathers, structure of, 16. ovipositor of, 157. Fission of Infusoria, 450, 462. Cilia of Cydippe, 357. Flea, mouth of, 170. Infusoria, 452, 459. Fly, antenna of, 192. Rotifera, 257, 290. flight of, 78. INDEX. 4179 Fly, foot of, 124. Luminosity of Medusa, 367. spiracle of, 112. Lynceus, 205. tongue of, 175. wing of, 80. Madrepore, weapons of, 417. Foot of Actinurus, 287. ] Medusue, 354. Bee, 136. transformations of, 372. Beetle, 134. Medusoids of Laomedea, 380. Brachi.on, 262. Stauridia, 394. Dinocharis, 280. Megalopa, 210. Fly, 132. Mite, cheese, 253. Silkworm, 140. water, 255. Spider, 251. Mollusca, ears of, 62. Whiptail, 275. eyes of, 58. Foraminifera, 438. shells of, 43. Frog, blood of, 33. tentacles of, 57. Froghopper, ovipositor of, 156. tongues of, 52. Moths, antennae of, 188. Galathea, 216. scales of, 89, 90. Gall-fly, egg-tube of, 146, Mouth of bee, 163. Gnat, antennue of, 192. Beetle, 160. grub of, 118. Brachion, 266. Gnat, mouth of, 171. Bug, 166. wing of, 84. Flea, 169. Grantia, 441, 443. Gnat, 171. Grasshopper, sounds of, 99. House-fly, 167. Sea-worm, 307. Hair of Bat, 11. Sword-bearer, 284. Bee, 14. Tube-wheel, 291. Beetle, 15. Whiptail, 276. Cat, 9. Murder, discovery of, 27. Hog, 6. Horse, 7. Nacre, 48. Man, 3. Nais, 301. Mole, 9. Nucleus of Infusoria; 463. Moth, 15. Nymphon, 251. Mouse, 11. Sable, 10. Otolithes of Meduse, 368. Sheep, 8. Slug, 62. Halichondria, 441. Ovipositor of cuckoo-fly, 145. Harvestman, 241. Gall-fly, 146. Heart-urchin, 336. Saw-fly, 148. Horse-fly, mouth of, 168. House-fly, 78. Paramcecium, 452. Humble bee, 79. Pearls, 50. Hydractinia, 384. Pedicellarime, 324. structure of, 325. Infusoria, 444. use of, 330. Insects, 78. Periwinkle, eating of, 55. air-tubes of, 108. tongue of, 52. antennae of, 184. Perophora, eyes of, 193. circulation in, 36. feet of, 124. respiration in, 40. mouths of, 160. Phyllodoce, 306. sounds of, 97. Pleasures of Sea-shore, 374. stings, &c., of, 142. Pudora, scales of, 87. Polymorphina, 438. Jelly-fish, 355. Polynoe, 302 Polypes of Alcyonium, 403. Katedid, 98. Hydractinia, 389. Laomedea, 385. Laomedea, 37o. Lar. 396. medusoids of, 380. Polystomella, 438. Lares, 396. Polyzoa, 67. Larva of Urchin, 347. Proteus, 433. Leech, 309. Protozoa, 430. Limpet, tongue of, 52. Pseudopodia, 439. Locomotion, variety in, 298 Lombrinereis, 308. Robber, story of, 1. 480 INDEX. Rotifera, 257. Stylonychia, 473. Suckers of Sea-cucumber, 340, Sabella, 394. Sea-urchin, 332. Sagartia, 421. Sugar-louse, 86. Sarsia, 360. Swan-neck, 449. Saw-fly, ovipositor of, 151. Sword-bearer, 282. Scales of Butterflies, 91. Synapta, 345. Bristle-tail, 86. Diamond-beetle, 93. Tentacle of Cydippe, 356. Flounder, 23. Hydractinia, 388. Gnat, 84. Laomedea, 385. Goldfish, 20. Scallop, 57. Perch, 19. Thaumantias, 368. Pike, 24. Thaumantias, 367. Podura, 87. Thread-cells, 417. Sugar-louse, 86. Tongue of Butterfly, 177. Wrasse, 23. Fly 175. Scallop, eyes of, 57. Limpet, 52. Sea-anemones, weapons of, 407. Tongue of Periwinkle, 52. Sea-cucumber, 340. Slug, 52. dumb-bells of, 341. Trochus, 53. Sea-mat, 70. Trachelocerca, 449. Sea-mouse, bristles of, 303. Transformations of Sea-shore, pleasures of, 374. Barnacle, 229. Sea-urchin, spines of, 318. Crab, 215. larvae of, 347. Galathea, 216. pedicellarise of, 324. Medusa, 372. pores of, 333. Polype, 381. skeleton of, 319. Sea-urchin, 345. suckers of, 332. Tube-wheel, 296. Serpula, 313. Vorticella, 467. Shell of Cuttle, 44. Tripod Wheel-bearer, 286. HIaliotis, 49. Trochus, tongue of, 55. Pearl-oyster, 47 Tube-wheel, 291. Pinna, 47. Turris, 370. Shore-crab, 210. Silkworm, foot of, 140. Urchin, Sea, 318. spinner of, 181. Skeleton Wheel-bearer, 278. Vacuoles, 436. Slug, ears of, 64. Vaginicola, 469 tongue of, 52. Vorticella, 466. Snail, eye of, 61. Spicula of Alcyonium, 404. Water-fleas 207, 208. Chirodota, 343. Weapons of Anemones, 407. Fish-scales, 25. Corynactis, 423. Holothuria, 340. Mladrepore, 418. Sponges, 441. Sea-worms, 302. Synapta, 343. Weevil, 185. Spiders, eyes of, 238. scales of, 92. fangs of, 236. Wheel-bearers, 257. foot of, 250. Wheels of Brachionus, 260. habits of, 234. Chirodota, 343. silk of, 242. Whiptail, 247. spinner of, 244. Wing of Bee, 82. Spines of Heart-urchin, 336. Fly, 80. Sea-urchin, 318. Gnat, 83. Spinner of Silkworm, 180. Wool, 14. Spider, 244. aWorms, 297. Spiracles of Insects, 112, 114. Sponges, spicula of, 441. Zoea of Crab, 209. Stauridia, 391. Zoophytes, 376. Sting of Bee, 142. THE END.