i034Left: Vorticella, with posterior circlet of cilia in process of separation—Stein.Right: Vorticella in process of self-division. A new frontal wreath in formation in each of the semi-lunar spaces.Different specimens and species ofVorticellævary in the length of their bells from one three or four thousandth to one hundred and twentieth of an inch, and when they are tolerably large, the dark ground illumination produces a beautiful effect. The bells shine with a pearly iridescent lustre, and their cilia flash with brilliant prismatic colours.i035Left: Vorticella microstoma, showing alimentary tube, ciliated mouth, and formation of a gemma at the base, 300 linear.—Stein.Right: Vorticella microstoma, the encysted animal protruding through a supposed rupture of the tunic.TheVorticellinabelong to the upper division of theProtozoa—theciliata, or ciliated animalcules, and they have a mouth, an œsophagus, and an orifice for the exit of their food.Many observers used to ascribe to those creatures acomplete intestinal canal, but such an apparatus is now believed not to exist in any of the Infusoria. Food particles, after leaving the œsophagus, are thrust forward into the sarcode, or soft flesh, and any cavity thus formed acts as a stomach.The bells or cups are not, as might be fancied from a casual inspection, open like wineglasses at the top, but furnished with a retractile disk or cover, on which the cilia are arranged. Their stalks are not simple stems, but are hollow tubes, which in the genus Vorticella are furnished with a muscular band, by whose agency the movements are principally made.Some of the Vorticellids will be observed to leave their stalks, having developed cilia round their base, and may be seen to swim about in the enjoyment of individual life. They are also capable of becomingencysted, that is, of secreting a gelatinous cover.i036Encysted Vorticella, showing the obliteration of special organs by the advancement of the process.—Pritchard.These changes are exhibited in the annexed cuts, which are copied from known authorities. By careful observation of the bodies of Vorticellids, a contractile vesicle may be observed, which appears to cause a movement of fluids, that is probably connected either with respiration or secretion.Another piece of apparatus in this family, but not confined to it, is the so-callednucleus, which in this case is of a horseshoe shape and granular texture, and greater solidity than the surrounding parts. The functions of this organ formed the subject of various conjectures, but it is now generally held to be an ovary.i037Vorticella microstoma, in process of encystment, 300 linear; in the last the inclosing tunic is plainly developed.—Stein.In common with many of the lower animals, the Vorticellids have three ways of multiplying their race. One byfission, or division of their bodies: another bybuds, somewhat analogous to those of plants; and another by reproductive germs. These processes will come again under our notice, and we shall leave the Vorticellids for the present by observing that if they are fed with a very small quantity of indigo or carmine, the vacuoles or spaces, into which their nutriment passes, will be clearly observed. Ehrenberg thought in these and similar creatures that every vacuole was a distinct stomach, and that all the stomachs were connected by an intestinal canal; hence his namePolygastrica, or many stomached. In these views he has not been followed by later observers, and it is probable he was misled, partly by pushing the process of reasoning from the analogies of higher animals much too far, and partly by the imperfection of the glasses he employed.i038Rotifer vulgaris.—A, mouth, or gizzard; B, contractile vesicle.—Micrographic Dictionary.N.B.—When the cilia and tail part are retracted, and the body shortened, the creature assumes an obtuse oval form.Having thus briefly considered the Vorticellids we must turn to the wheel-bearer, who belongs to a higher race than even the ciliatedProtozoa. We left her crawling about with her snout or proboscis protruded, but now she has moored herself by her tail-foot, pulled in her nose, and put out two groups of cilia,which look like revolving wheels, and a little below them is seen a gizzard in a state of active work. After a little while she swims away with her wheels going, and her tail, forked at the end, is found to be telescopic, or capable of being pulled in and out. As the cilia play, the neighbouring water is agitated, and the multitudes of small objects are brought by the whirlpools within her ravenous maw. But the strangest thing of all is that inside her body is seen a young one; in this case a large and fine infant, which, like "a chip of the old block," imitates the parental motions, thrusts forth its cilia and works its gizzard.[3]In other genera the eggs are hatched externally, but this one is ovoviparous, and carries its nursery inside.[3]This was met with in the summer, but is described here to avoid repetition. I do not know whether the eggs are hatched in very cold weather.A very slight investigation is sufficient to show that in the wheel-bearer we have made a great advance towards a higher organization than we discovered in the preceding creatures. We witness what the learned call a "differentiation" of parts and tissues, and a "specialization" of organs. The head is plainly distinguishable from the body, the skin or integument is distinctly different from the internal tissues, behind the eyes we can detect a nervous ganglion or miniature brain, the gizzard is a complicated piece of vital mechanism, such as we have not met with before, and in various parts of the transparent inside we see organs to which particular functions are assigned.It was at one time thought that Rotifers were hermaphrodite—uniting both sexes in one body—but that idea is now generally abandoned, for in many species the males have been discovered, and the fair sex may be gratified to hear that they are without doubt the "inferior animals." Their function is simply to assist the female in producing young, and as this can be quickly accomplished, their lives are short, and they are not supplied with the gizzard and digestive apparatus, which their lady-loves possess. Much discussion has taken place as to the rank which the Rotifers hold in the animal kingdom, some naturalists thinking them relations of the crabs, and others believing them to belong to the family of the worms. Professor Huxley, who adopts the latter view, which has the most friends, groups the lowerAnnulosatogether under the name ofAnnuloida, in which he includesAnnelides, or worms of various kinds, theEchinodermata(or "spine skins," among which are the star-fish and sea hedgehogs), and some other families. He considers the Rotifers to be "the permanent forms of Echinoderm larvæ." This does not mean that they were ever produced by Echinoderms, and had their development checked, but that they resemble them in organization, and illustrate a general law, observable in animated beings, namely, that the lower creatures are like the imperfect stages of higher animals, and that all things are formed according to general principles, and exhibit a uniformity of plan.Mr. Gosse adopts a different view, and while admitting a connection between the Rotifers and the worms,adduces important reasons for associating them with the insects.Leaving zoologists to settle their position, we may remark that the Rotifers form a very numerous family, presenting very great diversities of structure, some of the most interesting of which we shall meet with in the course of our rambles; but they all possess a gizzard, which, though differing in complexity, is throughout formed upon the same principle, and that we must now explain.We have called the masticatory apparatus of the Rotifers agizzard; but Mr. Gosse, who has done most to elucidate its structure, contends that it is amouth; and in some species it is frequently protruded, and used like the mouth of higher animals. Taking one of the most typical forms of this organ, and drawing our illustrations from Mr. Gosse's admirable paper in the "Transactions of the Royal Society," we may describe it, when completely developed, as consisting of three lobes, having a more or less rounded form. The eminent naturalist we have named calls the whole organ themastax, and states that it is composed of dense muscular fibre. The tube which leads down to it he designates the "buccal (mouth) funnel," and the tube that issues from it, and conveys the food to the digestive sac or stomach, he calls theœsophagus, in conformity with the nomenclature applied to creatures whose mouths are in the usual place. Inside the mouth-gizzard are placed two organs, which work like hammers, and which Mr. Gosse therefore namesmallei. The hammers work against a sort of anvil, which iscalledincus, the Latin for that implement. Each hammer consists of two portions articulated by a hinge joint. The lower portion, themanubrium, or handle, gives motion to the upper portion, which from its shape is named theuncus, or hook. Theunciare furnished with finger-like processes of teeth, which vary in number. There are five or six in the best developed specimens. These hooks or teeth work against each other, and against theincus, or anvil, which consists of distinct articulated portions, of which the principal are tworami, or branches, jointed so that they can open and close like a pair of shears. These two rest upon the third portion, which is called thefulcrum. Some faint idea of the working of the toothed hammers may be obtained by rubbing the knuckles of both hands together, but the motion is more complicated, and theramiplay their part in the trituration of the food. Mr. Gosse states that when an objectionable morsel has got as far as this mouth-gizzard,"it is thrown back by a peculiar scoop-like action of theunci, very curious to witness." The foregoing diagram will help the reader to comprehend this description, but no opportunity should be lost for viewing this remarkable organ busy at work in the living animals.i042Gizzard of Notomata.The respiration of the Rotifers is supposed to be effected by the passage of water through vessels running round them, and called the "water vascular system," and in addition to their eyes, which often disappear in adult specimens, the organ we described as standing out like a pig-tail, as our acquaintance crawled along, is thought to act as anantenna, or feeler, and brings its possessor in further relation to the external world. It is also called thecalcar, or spur, and is furnished with cilia or bristles at its extremity.Sometimes the particles swallowed by the Common Rotifer are large enough for their course to be traced, but there is frequently a great commotion and grinding of the gizzard, without any appreciable cause, although doubtless something is taken in, and when the creature is tired, or has had enough, we see both head and tail retracted, and the body assumes a globular form. In another chapter, when viewing a Philodine, we shall see how in the family to which the Common Rotifer belongs, the gizzard departs from the perfect type.CHAPTER III.FEBRUARY.Visit to Hampstead—Small ponds—Water-fleas—Water-beetle—Snails—Polyps—Hydra viridis—The dipping-tube—A glass cell—The Hydra and its prey—Chydorus sphæricus and Canthocamptus, or friends and their escapes—Cothurnia—Polyp buds—Catching Polyps—Mode of viewing them—Structure of Polyps—Sarcode—Polyps stimulated by light—Are they conscious?—Tentacles and poison threads—Paramecium—Trachelius—Motions of Animalcules, whether automatic or directed by a will—Their restless character.i044Thas been a bitterly cold night, and as the sun shines on a clear keen morning, and glistens in the hoar-frost which covers the trees, it might seem an unpropitious time for visiting the ponds, in search of microscopic prey. We will, however, try our luck, and take a brisk trot to the top of Hampstead Heath, where the air is still keener, and the ice more thick. Arriving at the highest point, London appears on one side enveloped in its usual great coat of smoke, through which St. Paul's big dome, with a score or two of towers and steeples, can be dimly made out; while looking towards Harrow-on-the-Hill, or Barnet, we see the advantage of country air in the sharpness with which distant objects cut the blue sky. We leave the large ponds for another time,and hunt out the little hollows among the furze and fern. One looks promising from the bright green vegetation to be discovered under the sheet of ice, which is almost firm enough to bear human weight.Breaking a convenient hole we hook up some of the water-plants, and place them in a wide-mouthed vial, which we fill with water, and cursorily examine with a pocket-lens. Some water-fleas briskly skipping about, and a beautiful little beetle, with an elegant dotted pattern on his brown back, and a glistening film of air covering his belly, show that we have not been unsuccessful, although we must wait till we get home to know the extent of our findings, among which, however, we can only discern the graceful spiral shell of a small water-snail, thePlanorbis.Arriving at home the bottle was left undisturbed for some hours in a warm light place, and then on being examined several specimens of that beautiful polyp, theHydra viridis, were seen attached to the glass, and spreading their delicate tentacles in search of prey. One of the polyps is carefully removed by thedipping-tube, a small glass tube, open at both ends. The forefinger is placed upon the top, and when the other end is brought over the object the finger is raised for an instant, and as the water rushes in the little hydra comes too, and is placed in a glass cell, about half an inch wide, and one tenth of an inch deep. These cells are obtained from the opticians, and cemented with varnish or marine glue to an ordinary glass slide. After an object has been placed in one of them, a little water is taken up in the dipping-tube, and the cellfilled until the fluid stands in a convex heap above its brim. We then select around glass cover, and pressit gently on the walls of our cell. A few drops of superfluous water escape, and we have the cell quite full, and the cover held tight by force of the capillary attraction between the water and the glass.i046Hydra viridis with developed young one, and bud beginning to sprout.The polyp deposited in one of these water cages is then transferred to the stage of the microscope, and its proceedings watched. At first it looks like a shapeless mass of apple-green jelly. Soon, however, the tail end of the creature is fixed to the glass, the body elongates, and the tentacles (in this case eight) expand something after the manner of the leaves of a graceful palm.By accident two small Water Fleas were imprisoned with the polyp, and one (a shrimp-like looking creature, carrying behind her a great bag of eggs) came into contact with the tentacles, and seemed paralysed for a time. The hydra made no attempt to convey the captive to its mouth, but held it tight until another Water Flea, a round merry little fellow (Chydorus sphæricus), came to the rescue, and assistedCanthocamptusto escape by tugging at her tail. This friendly action may not have been prompted by the intelligence which seemed to suggest it, but those who have kept tame soldier-crabs and prawns in an aquarium, will not be indisposed to attribute to the crustaceans more brains than they have usually credit for. It must, however, be confessed that the subsequent conduct of Mrs. Canthocamptus did not indicate the possession of much prudence, for she learnt no lesson from experience, but repeatedly swam against her enemy's tentacles, suffered many captures, and only escaped beingdevoured through the indifference, or want of appetite, which the polyp evinced.i048A, Canthocamptus minutus; B, Chydorus sphæricus; C and D, Capsules and poison-thread of polyp; E, Tricodina pediculus, side view and under view; F, Kerona polyporum.—Microg. Dict.On the body of theCanthocamptuswere some small transparent vases or bottles, containing living objects, which sprang up and down. These weremembers of theVorticellafamily, calledCothurnia, and will be hereafter described.i049Hydra viridis, in various shapes.Watching the hydra it was curious to note the changes of form which these creatures are able to assume. Now the tentacles were short and thick, and the body squat; now the body was elongated, like the stem of a palm tree, and the tentacles hung gracefully from the top. From some of the polyps little round buds were growing, while other buds were already developed into miniature copies of the parent, and only attached by a slender stalk. In a few days many of these left the maternal side, fixed their own little tails to the glass, and commenced housekeeping on their own account.Polyps may be obtained at all times of the year by bringing home duckweed, conferva, and other water-plants from the ponds. Some hauls may be unsuccessful, but if one pond is not propitious others should be tried. The plants should be put in a capaciousvessel of water, and placed in the light, where, if polyps be present, they will show themselves within twenty-four hours, either attached to the sides of the glass, or hanging from the plants, or suspended head downwards from the upper film of the water. They are elegant objects, and may be kept without difficulty for some weeks. After being confined in a small quantity of water for purposes of examination, they should be carefully replaced in the larger vessel, and may thus be used again and again without suffering any injury. A low power—a three or two-inch glass—or a one-inch, reduced by employing the erector—is the most convenient for examining the whole creature, but higher powers are necessary to make out its minute structure. They should be viewed with direct and oblique light, as transparent and also as opaque objects. In the latter case the "Lieberkuhn," or polished silver speculum, is convenient, and if the microscope is not furnished with Lister's dark wells, a small piece of black paper may be stuck behind the object, by simply wetting it with the tongue.[4][4]The side silver reflector is useful for illuminating such objects.Although the polyps are remarkable for the simplicity of their organization, they do not the less exhibit the wonderful nature of animal life. Their bodies are composed of the substance, calledsarcode, in which is imbedded a colouring matter resembling that in the leaves of plants; every part possesses irritability and contractility, and they are very sensitive to the stimulus of light. The outer layer of their bodies isharder than the inner layer. These layers are severally calledectodermandendoderm. They may be cut and grafted like trees, and if turned inside out, the new inside digests and assimilates as well as the old. Whether any form of consciousness can belong to creatures which have no distinct nervous system is open to doubt, but it would seem probable from their movements that food and light afford them something like a pleasurable sensation in a very humble degree. If we were sufficiently acquainted with the secrets of molecular combination we might discover that the various functions of these simple organisms were discharged by differentparticles, although it is only in higher creatures that muscular particles are aggregated into muscles, or nerve particles into nerves.Having examined the general appearance and proceedings of the hydra, let us cut off a tentacle, or take a small specimen and gently crush it by pressing down the cover of the live box, and place the object so prepared under a power of about three hundred linear. If we then illuminate it with a moderate quantity of oblique light, we shall discover round the edge of the tentacle a number of small cells or capsules, from some of which a very slender wire or thread will be emitted.[5]These are the stinging organs of the polyp, and resemble those which Mr. Gosse has so ably elucidated in the sea anemones. Some writers have endeavoured to show that they are not stinging organs at all, but so large an amount of evidence to the contrary is accumulated in Mr. Gosse's 'Actinologia Britannica,'that no reasonable doubt remains. The stinging capsules of the polyp are shown in the annexed sketch, and also the way in which they are employed, for itfortunately happened that on exposing one of the hydras to pressure in the live box, a small worm (Anguillula) escaped, which had been pierced with the minute weapons which are supposed to convey a poison into the wound. The authors of the 'Micrographic Dictionary' think that the prongs of the forks, which will be seen to point upwards in the sketch,[6]are springs, and occupy a reversed position in the capsule cells, and that their function is to throw out the threads. However this may be, the polyps, and similarly endowed creatures, have the power of darting out their poison threads with considerable force, and Mr. Gosse found that the anemone was able to pierce a thick piece of human skin.[5]See illustrationabove.[6]See illustrationbelow.i052Anguillula pierced by stinging organs of the Hydra viridis.The same excellent observer attributes the emission of the anemone poison threads, which he considers hollow, to the injection of a fluid. In their quiescent state, he thinks they are drawn in, like the finger of a glove, and are forced out as the liquid enters their slender tubes. Possibly the polyp stinging organs may have the same structure.Notwithstanding their dangerous weapons, polyps are often infested with a parasite, theTrichodina pediculus, as shown in Fig.E, page 49, and it must happen that either this visitation is not disagreeable, or that the Trichodina is not influenced by the poison.As the plants in the bottles decayed, some of the animalcules died off and others appeared. In one bottle, containing decaying chara,Parameciaabounded. TheParamecia, of which there are various species,have always been favourite objects with microscopists. The Germans call them "slipper animalcules," and they vary in size from 1—96"[7]to 1—1150". They are flat rounded-oblong creatures, with a distinct integument or skin, "through which numerous vibratile cilia pass in regular rows."[8]They are furnished with a distinct mouth, and adult specimens exhibit star-shaped contractile vesicles in great perfection.[7]The usual mode of giving dimensions is by fractions thus expressed: 1—96" means one ninety-sixth of an inch.[8]'Micrographic Dictionary.'The swarm of specimens before us belong to one species,Paramecium aurelia, theChrysalis animalcule, and they crowd every portion of the little water-drop we have taken up, and examined with a power of about one hundred linear. When they are sufficiently quiet a power of about four hundred may be used with advantage, and Pritchard recommends adding a little indigo and carmine to the water, in order to see the cilia more clearly, or rather to render their action more plain. The cilia are disposed lengthwise, and Ehrenberg counted in some rows sixty or seventy of them, making an aggregate of three thousand six hundred and forty organs of motion in one small animated speck. This number seems large, but although we have never performed the feat of counting them, we should have expected it to prove much greater. Unlike most animalcules they are susceptible of being preserved by drying upon glass, and we subjoin a figure from Pritchard, of one thus treated, in which the star-shaped vesicles are clearly seen. These curious organs communicate with other vessels, and, as we have previously stated, are probably connected with respiration and excretion.i055Paramecium aurelia. A dried specimen showing the vesicles.—Pritchard.The genusParameciumis now confined to those creatures which exhibit rows of longitudinal cilia of uniform length, which are destitute of hooks, styles, or other organs of motion than the cilia, which have a lateral mouth, and no eye-spots. One mode of increase is by division, which may be easily observed; another is through the formation of true eggs as traced by Balbiani.Another of the treasures from the pond was a species ofTrachelius, or long-necked ciliated animalcule, which kept darting in and out of a slimy den, attached to the leaf of a water-plant. The body was stout and fish-shaped, the tail blunt, and the neck furnished with long conspicuous cilia, which enabled the advancing and retreating movements to be made with great rapidity. The motions of this creature exhibit more appearance of purpose and design than is common with animalcules,but in proportion as these observations are prolonged, the student will be impressed with the difficulty of assuming that anything like a reasoning faculty and volition, is proved by movements that bear some resemblance to those of higher animals, whose cerebral capacities are beyond a doubt. It is, however, almost impossible to witness motions which are neither constant nor periodic, without fancying them to be dictated by some sort of intelligence. We must, nevertheless, be cautious, lest we allow ourselves to be deceived by reasoning so seductive, as the vital operations of the lowest organisms may be merely illustrations of blind obedience to stimuli, in which category we must reckon food, and until we arrive at forms of being which clearly possess a ganglionic system, we have no certainty that a real will exists, even of the simplest kind; and perhaps we must go still higher before we ought to believe in its presence.Ehrenberg was much struck with the restless character of many infusoria—whether he looked at them by day or by night, they were never still. In fact their motions are like the involuntary actions which take place in the human frame; and if attached to their bodies we observe cilia that never sleep, the living membrane of some of our own organs, the nose, for example, is similarly ciliated, and keeps up a perpetual though unconscious work.CHAPTER IV.MARCH.Paramecia—Effects of Sunlight—Pterodina patina—Curious tail—Use of a Compressorium—Internal structure of Pterodina—Metopidia—Trichodina pediculus—Cothurnia—Salpina—Its three-sided box—Protrusion of its gizzard mouth.i057HEParamecia, noticed in the last chapter, have increased and multiplied their kind without any fear lest the due adjustment between population and food should fail to be preserved. A small drop of the scum from the surface of the water in their bottle is an astounding sight. They move hither and thither in countless numbers, seldom jostling, although thick as herrings in a tub, and in many portions of the field the process of self-fissure, or multiplication by division, is going on without any symptoms of discomfort on the part of the parent creature. This is an interesting sight, but we will not linger over it, for the sun is shining, and there is enough warmth in the air to make it probable that the ponds will be more prolific than in the cold winter months. Sunshine is a great thing for the microscopic hunter; it brings swarms of creatures to the surface, and the Rotifers are especially fond of its genial beams. Evenif we imitate it by a bright lamp, we shall attract crowds of live dancing specks to the illuminated side of a bottle, and may thus easily effect their capture by the dipping-tube.i058Pterodina patina.This year the March sunshine was not lost, for on the third of that month I obtained a bottleful of conferva from a pond about a mile from my house, and lying at the foot of the Highgate hills. Water-fleas were immediately discovered in abundance, together with some minute worms, and a ferocious-looking larva covered with scales; but what attracted most attention was a Rotifer, like a transparent animated soup-plate, from near the middle of which depended a tail, which swayed from side to side, as the creature swam along. The head exhibited two little red eyes; two tufts of cilia rowed the living disk through the water, and the gizzard worked with a rapid snapping motion, that left no doubt the ciliary whirlpools had brought home no slender stores of invisible food. Sometimes the end of the tail acted as a sucker, and fixed the animal tightlyto the glass, when the wheels were protruded, and the body swayed to and fro. Then the sucker action ceased, and as the creature swam away, a tuft of cilia was thrust out from the extremity of the tail. A power of one hundred linear was sufficient to enable the general nature of this beautiful object to be observed, but to bring out the details, much greater amplification was required, and this would be useless if the little fidget could not be kept still.i059450 Pterodina patina—gizzard.The size of the creature, whose name we may as well mention wasPterodina patina, rendered this practicable, but required some care. The longest diameter of the body, which was not quite round, was about 1—120", so that it was visible to the naked eye, and as a good many were swimming together, one could be captured without much difficulty, and transferred with a very small drop of water to the live-box. Then the coverhad to be put on so as to squeeze the animal just enough to keep it still without doing it any damage, or completely stopping its motions. This was a troublesome task, and often a little overpressure prevented its success.Some observers always use in these cases an instrument called acompressorium, by which the amount of pressure is regulated by a lever or a fine screw; but whether the student possess one or not, he should learn to accomplish the same result by dexterously manipulating a well-made live-box. We will suppose thePterodinasuccessfully caged, and a power of about one hundred and fifty linear brought to bear upon her, for our specimen is of the "female persuasion." This will suffice to demonstrate the disposition and relation of the several parts, after which one of from four hundred to five hundred linear may be used with great advantage, though in this case the illumination must be carefully adjusted, and its intensity and obliquity frequently changed, until the best effect is obtained.We find, on thus viewing the Pterodina, that it is a complex, highly organized creature, having its body protected by acarapace, like the shell of a tortoise, but as flexible as a sheet of white gelatine paper, which it resembles in appearance. Round the margin of this carapace are a number of little bosses or dots, which vary in different individuals. The cilia are not disposed, as at first appeared, in two separate and distinct disks, but are continuous, as in the annexed sketch. Down each side are two long muscular bands, distinctlystriated, and when they contract, the ciliary apparatusis drawn in. As this contraction takes place, two apparently elastic bands, to which the ciliary lobes are attached, are bent downwards, till they look like the C springs behind a gentleman's carriage; and they regain their former position of slight curvature, when the cilia are again thrust out.i061Pterodina patina—tail-foot.The gizzard is three-lobed, and curiously grasped by forked expansions of the handles of the hammers. The tail, or tail-foot, can be withdrawn or thrust out at the will of the creature; and when in a good position for observation, a slight additional pressure will keep it so for examination. Delicate muscular longitudinal bands, forked towards the end of their course, supply the means of performing some of its motions, and one, or perhaps two, spiral threads extend through the upper half of its length, and either act as muscles, or as elastic springs for its extension. The intestines and other viscera are clearly exhibited, and a strong ciliary action conducts the food to the gizzard-mouth.To return to the tail. One spiral fibre is easily discovered;but I have often, and at an interval of months, seen the appearance of two, and am in some doubt whether this was a deception, arising from the compression employed, or was a genuine indication.i062A. Metopidia acuminata, as drawn by Mr. Gosse. B. Specimen as seen and described in text. c. Mouth or gizzard.Where this Rotifer occurs I have usually found it plentiful, but unfortunately could obtain no constant supplies after I had determined to make a special study of the remarkable tail, which is much more complicated than I have described. ThePterodinalived for some time in captivity, and for a week or two I could obtain them from my glass tank. They were likewise to be found for some weeks in the same part of the pond, but not all over it, until one day not a single specimen could be discovered, notwithstanding a persevering searchnor was I afterwards able to get any from that pond during the remainder of the year.i063Trichodina pediculus.Several other Rotifers, with and without carapaces, were among the same mass of confervæ, among them aMetopidia, with a firm shell, a forked jointed tail, and a projection in front which worked like a pickaxe among the decaying weed. There were likewise specimens of the long-necked animalcules (Trachelii), groups of Vorticella, some specimens of Volvox, and a smallTrichodina pediculus, which, when magnified two hundred and sixty linear, was about the size of a sixpence and equally round. The edge was beautifully fringed with a circle of cilia; in an inner circle was a row of locomotive organs, and the centre exhibited vacuoles constantly opening and shutting. This creature, as before explained, is often found as a parasite upon the polyps. On one occasion a glimpse was caught of a Rotifer similar in shape to the common wheel animalcule, but with a yellow inside. Possibly it was the object so beautifully delineated by Mr. Gosse, in his "Tenby," and described as the "Yellow Philodine," but this must remain in doubt, as it managed to escape before it could be secured.i064A. Cothurnia imberbis—('Micrograph. Dict.') B and C. The specimens described in text. The figures give the linear magnification.By the 18th of the month the Vorticellids were much more plentiful, and their changes easily watched; many left their stalks while under the microscope, after which some rushed about like animated and demented hats, others twirled round like tee-to-tums, while others took a rest before commencing their wild career. But the common Vorticellæ were not the only or the most interesting representations of their charming order, for upon some threads of conferva were descried several elegant crystal vases standing upon short foot-stalks, and containing little creatures that jumped up and down like "Jack in the box." These were so minute, that a power of four hundred and thirty linear was advantageously brought to bear upon them. When elongated their bodies were somewhat pear-shaped, but more slender, and variegated with vacuoles and particles of food. The mouths resembled those of Vorticellæ, and put forth circles of vibrating cilia. They were easily alarmed, when the cilia were retracted, and down they sank to the bottom of their vases, quickly to rise again. In one bottle there were two living in friendly juxtaposition. This was not a case of matrimonial felicity, nor of Siamese twins, but offission, or reproduction by division. The original inhabitant of the tube finding himself too fat, or impelled by causes we do not understand, quietly divided himself in two, and as the house was big enough, no enlargement was required. How many stout puffy gentlemen must envy this process; how convenient to have two thin lively specimens of humanity made out of one too obese for locomotion. Man is, however, sometimes the victim of his superiororganization, and no process of "fission" can make the lusty lean.[9][9]Balbiani in his 'Recherches sur les Phénomènes Sexuels des Infusoires,' speaks of the Vorticellids as the only Infusoria dividing longitudinally. In other species such appearances arise from conjunction.The bottles in which these creatures live, in happy ignorance that they are called by so crackjaw a name asCothurnia imberbis, were described asCarapacesby Ehrenberg, but they bear no resemblance to the shell of a turtle or crab. They are thrown off by the animals who preserve no other connection with them than the attachment at the bottom.The Micrographic Dictionary describes the family Ophrydina as corresponding to Vorticellina with a carapace. Stein places them with Vorticellids, &c., amongst his Peritricha, which are characterised by a spiral wreath of cilia round the mouth.Towards the end of the month a great number of black pear-shaped bodies (Stentor niger), visible to the naked eye, were conspicuous in some water from the Kentish Town ponds. Upon examination they were found to be filled with granules that were red by reflected, and purple by transmitted light. Each one had a spiral wreath of cilia, with a mouth situated like those of the stentors, hereafter to be described, but none of them became stationary, and in a few days they all disappeared. Stein divides Ehrenberg's Stentor igneus from S. niger; the creature described seems to have agreed with Stein'signeus, which he describes as having blood-red lilac, cinnabar, or brown-red pigment particles, and as much smaller than his S. niger. In the samewater were specimens of that singular Rotifer, theSalpina, about 1—150" long, and furnished with alorica, or carapace, resembling a three-sided glass box, closed below, and slightly open along the back. At the top of this box were four, and at the bottom three, points or horns, and the creature had one eye and a forked tail. Keeping him company was another little Rotifer, named after its appearance,Monocerca rattus, the 'One-tailed Rat.' This little animal had green matter in its stomach, which was in constant commotion. I ought to have observed that the Salpina repeatedly thrust out its gizzard, and used it as an external mouth. In the annexed sketch the Salpina is seen in a position that displays the dorsal opening of the carapace. Its three-cornered shape is only shown by a side view.Here we close a brief account of what March winds brought in their train. The next chapter will show the good fortune that attended April showers.i067Salpina redunca.CHAPTER V.APRIL.The beautiful Floscule—Mode of seeking for Tubicolor Rotifers—Mode of illuminating the Floscule—Difficulty of seeing the transparent tube—Protrusion of long hairs—Lobes—Gizzard—Hairy lobes of Floscule not rotatory organs—Glass troughs—Their construction and use—Movement of globules in lobes of Floscule—Chætonotus larus—Its mode of swimming—Coleps hirtus—Devourer of dead Entomostraca—Dead Rotifer and Vibriones—Theories of fermentation and putrefaction—Euplotes and Stylonichia—Fecundity of Stylonichia.i068EWliving creatures deserve so well the appellation of "beautiful" as theFloscularia ornata, or Beautiful Floscule, although to contemplate a motionless and uncoloured portrait, one would imagine that it exhibited no graces of either colour or form. Mr. Gosse has, however, done it justice, and the drawing in his "Tenby" is executed with that rare combination of scientific accuracy and artistic skill, for which the productions of his pencil are renowned.
i034Left: Vorticella, with posterior circlet of cilia in process of separation—Stein.Right: Vorticella in process of self-division. A new frontal wreath in formation in each of the semi-lunar spaces.
Different specimens and species ofVorticellævary in the length of their bells from one three or four thousandth to one hundred and twentieth of an inch, and when they are tolerably large, the dark ground illumination produces a beautiful effect. The bells shine with a pearly iridescent lustre, and their cilia flash with brilliant prismatic colours.
i035Left: Vorticella microstoma, showing alimentary tube, ciliated mouth, and formation of a gemma at the base, 300 linear.—Stein.Right: Vorticella microstoma, the encysted animal protruding through a supposed rupture of the tunic.
TheVorticellinabelong to the upper division of theProtozoa—theciliata, or ciliated animalcules, and they have a mouth, an œsophagus, and an orifice for the exit of their food.
Many observers used to ascribe to those creatures acomplete intestinal canal, but such an apparatus is now believed not to exist in any of the Infusoria. Food particles, after leaving the œsophagus, are thrust forward into the sarcode, or soft flesh, and any cavity thus formed acts as a stomach.
The bells or cups are not, as might be fancied from a casual inspection, open like wineglasses at the top, but furnished with a retractile disk or cover, on which the cilia are arranged. Their stalks are not simple stems, but are hollow tubes, which in the genus Vorticella are furnished with a muscular band, by whose agency the movements are principally made.
Some of the Vorticellids will be observed to leave their stalks, having developed cilia round their base, and may be seen to swim about in the enjoyment of individual life. They are also capable of becomingencysted, that is, of secreting a gelatinous cover.
i036Encysted Vorticella, showing the obliteration of special organs by the advancement of the process.—Pritchard.
These changes are exhibited in the annexed cuts, which are copied from known authorities. By careful observation of the bodies of Vorticellids, a contractile vesicle may be observed, which appears to cause a movement of fluids, that is probably connected either with respiration or secretion.
Another piece of apparatus in this family, but not confined to it, is the so-callednucleus, which in this case is of a horseshoe shape and granular texture, and greater solidity than the surrounding parts. The functions of this organ formed the subject of various conjectures, but it is now generally held to be an ovary.
i037Vorticella microstoma, in process of encystment, 300 linear; in the last the inclosing tunic is plainly developed.—Stein.
In common with many of the lower animals, the Vorticellids have three ways of multiplying their race. One byfission, or division of their bodies: another bybuds, somewhat analogous to those of plants; and another by reproductive germs. These processes will come again under our notice, and we shall leave the Vorticellids for the present by observing that if they are fed with a very small quantity of indigo or carmine, the vacuoles or spaces, into which their nutriment passes, will be clearly observed. Ehrenberg thought in these and similar creatures that every vacuole was a distinct stomach, and that all the stomachs were connected by an intestinal canal; hence his namePolygastrica, or many stomached. In these views he has not been followed by later observers, and it is probable he was misled, partly by pushing the process of reasoning from the analogies of higher animals much too far, and partly by the imperfection of the glasses he employed.
i038Rotifer vulgaris.—A, mouth, or gizzard; B, contractile vesicle.—Micrographic Dictionary.N.B.—When the cilia and tail part are retracted, and the body shortened, the creature assumes an obtuse oval form.
Having thus briefly considered the Vorticellids we must turn to the wheel-bearer, who belongs to a higher race than even the ciliatedProtozoa. We left her crawling about with her snout or proboscis protruded, but now she has moored herself by her tail-foot, pulled in her nose, and put out two groups of cilia,which look like revolving wheels, and a little below them is seen a gizzard in a state of active work. After a little while she swims away with her wheels going, and her tail, forked at the end, is found to be telescopic, or capable of being pulled in and out. As the cilia play, the neighbouring water is agitated, and the multitudes of small objects are brought by the whirlpools within her ravenous maw. But the strangest thing of all is that inside her body is seen a young one; in this case a large and fine infant, which, like "a chip of the old block," imitates the parental motions, thrusts forth its cilia and works its gizzard.[3]In other genera the eggs are hatched externally, but this one is ovoviparous, and carries its nursery inside.
[3]This was met with in the summer, but is described here to avoid repetition. I do not know whether the eggs are hatched in very cold weather.
[3]This was met with in the summer, but is described here to avoid repetition. I do not know whether the eggs are hatched in very cold weather.
A very slight investigation is sufficient to show that in the wheel-bearer we have made a great advance towards a higher organization than we discovered in the preceding creatures. We witness what the learned call a "differentiation" of parts and tissues, and a "specialization" of organs. The head is plainly distinguishable from the body, the skin or integument is distinctly different from the internal tissues, behind the eyes we can detect a nervous ganglion or miniature brain, the gizzard is a complicated piece of vital mechanism, such as we have not met with before, and in various parts of the transparent inside we see organs to which particular functions are assigned.
It was at one time thought that Rotifers were hermaphrodite—uniting both sexes in one body—but that idea is now generally abandoned, for in many species the males have been discovered, and the fair sex may be gratified to hear that they are without doubt the "inferior animals." Their function is simply to assist the female in producing young, and as this can be quickly accomplished, their lives are short, and they are not supplied with the gizzard and digestive apparatus, which their lady-loves possess. Much discussion has taken place as to the rank which the Rotifers hold in the animal kingdom, some naturalists thinking them relations of the crabs, and others believing them to belong to the family of the worms. Professor Huxley, who adopts the latter view, which has the most friends, groups the lowerAnnulosatogether under the name ofAnnuloida, in which he includesAnnelides, or worms of various kinds, theEchinodermata(or "spine skins," among which are the star-fish and sea hedgehogs), and some other families. He considers the Rotifers to be "the permanent forms of Echinoderm larvæ." This does not mean that they were ever produced by Echinoderms, and had their development checked, but that they resemble them in organization, and illustrate a general law, observable in animated beings, namely, that the lower creatures are like the imperfect stages of higher animals, and that all things are formed according to general principles, and exhibit a uniformity of plan.
Mr. Gosse adopts a different view, and while admitting a connection between the Rotifers and the worms,adduces important reasons for associating them with the insects.
Leaving zoologists to settle their position, we may remark that the Rotifers form a very numerous family, presenting very great diversities of structure, some of the most interesting of which we shall meet with in the course of our rambles; but they all possess a gizzard, which, though differing in complexity, is throughout formed upon the same principle, and that we must now explain.
We have called the masticatory apparatus of the Rotifers agizzard; but Mr. Gosse, who has done most to elucidate its structure, contends that it is amouth; and in some species it is frequently protruded, and used like the mouth of higher animals. Taking one of the most typical forms of this organ, and drawing our illustrations from Mr. Gosse's admirable paper in the "Transactions of the Royal Society," we may describe it, when completely developed, as consisting of three lobes, having a more or less rounded form. The eminent naturalist we have named calls the whole organ themastax, and states that it is composed of dense muscular fibre. The tube which leads down to it he designates the "buccal (mouth) funnel," and the tube that issues from it, and conveys the food to the digestive sac or stomach, he calls theœsophagus, in conformity with the nomenclature applied to creatures whose mouths are in the usual place. Inside the mouth-gizzard are placed two organs, which work like hammers, and which Mr. Gosse therefore namesmallei. The hammers work against a sort of anvil, which iscalledincus, the Latin for that implement. Each hammer consists of two portions articulated by a hinge joint. The lower portion, themanubrium, or handle, gives motion to the upper portion, which from its shape is named theuncus, or hook. Theunciare furnished with finger-like processes of teeth, which vary in number. There are five or six in the best developed specimens. These hooks or teeth work against each other, and against theincus, or anvil, which consists of distinct articulated portions, of which the principal are tworami, or branches, jointed so that they can open and close like a pair of shears. These two rest upon the third portion, which is called thefulcrum. Some faint idea of the working of the toothed hammers may be obtained by rubbing the knuckles of both hands together, but the motion is more complicated, and theramiplay their part in the trituration of the food. Mr. Gosse states that when an objectionable morsel has got as far as this mouth-gizzard,"it is thrown back by a peculiar scoop-like action of theunci, very curious to witness." The foregoing diagram will help the reader to comprehend this description, but no opportunity should be lost for viewing this remarkable organ busy at work in the living animals.
i042Gizzard of Notomata.
The respiration of the Rotifers is supposed to be effected by the passage of water through vessels running round them, and called the "water vascular system," and in addition to their eyes, which often disappear in adult specimens, the organ we described as standing out like a pig-tail, as our acquaintance crawled along, is thought to act as anantenna, or feeler, and brings its possessor in further relation to the external world. It is also called thecalcar, or spur, and is furnished with cilia or bristles at its extremity.
Sometimes the particles swallowed by the Common Rotifer are large enough for their course to be traced, but there is frequently a great commotion and grinding of the gizzard, without any appreciable cause, although doubtless something is taken in, and when the creature is tired, or has had enough, we see both head and tail retracted, and the body assumes a globular form. In another chapter, when viewing a Philodine, we shall see how in the family to which the Common Rotifer belongs, the gizzard departs from the perfect type.
FEBRUARY.
Visit to Hampstead—Small ponds—Water-fleas—Water-beetle—Snails—Polyps—Hydra viridis—The dipping-tube—A glass cell—The Hydra and its prey—Chydorus sphæricus and Canthocamptus, or friends and their escapes—Cothurnia—Polyp buds—Catching Polyps—Mode of viewing them—Structure of Polyps—Sarcode—Polyps stimulated by light—Are they conscious?—Tentacles and poison threads—Paramecium—Trachelius—Motions of Animalcules, whether automatic or directed by a will—Their restless character.
Thas been a bitterly cold night, and as the sun shines on a clear keen morning, and glistens in the hoar-frost which covers the trees, it might seem an unpropitious time for visiting the ponds, in search of microscopic prey. We will, however, try our luck, and take a brisk trot to the top of Hampstead Heath, where the air is still keener, and the ice more thick. Arriving at the highest point, London appears on one side enveloped in its usual great coat of smoke, through which St. Paul's big dome, with a score or two of towers and steeples, can be dimly made out; while looking towards Harrow-on-the-Hill, or Barnet, we see the advantage of country air in the sharpness with which distant objects cut the blue sky. We leave the large ponds for another time,and hunt out the little hollows among the furze and fern. One looks promising from the bright green vegetation to be discovered under the sheet of ice, which is almost firm enough to bear human weight.
Breaking a convenient hole we hook up some of the water-plants, and place them in a wide-mouthed vial, which we fill with water, and cursorily examine with a pocket-lens. Some water-fleas briskly skipping about, and a beautiful little beetle, with an elegant dotted pattern on his brown back, and a glistening film of air covering his belly, show that we have not been unsuccessful, although we must wait till we get home to know the extent of our findings, among which, however, we can only discern the graceful spiral shell of a small water-snail, thePlanorbis.
Arriving at home the bottle was left undisturbed for some hours in a warm light place, and then on being examined several specimens of that beautiful polyp, theHydra viridis, were seen attached to the glass, and spreading their delicate tentacles in search of prey. One of the polyps is carefully removed by thedipping-tube, a small glass tube, open at both ends. The forefinger is placed upon the top, and when the other end is brought over the object the finger is raised for an instant, and as the water rushes in the little hydra comes too, and is placed in a glass cell, about half an inch wide, and one tenth of an inch deep. These cells are obtained from the opticians, and cemented with varnish or marine glue to an ordinary glass slide. After an object has been placed in one of them, a little water is taken up in the dipping-tube, and the cellfilled until the fluid stands in a convex heap above its brim. We then select around glass cover, and pressit gently on the walls of our cell. A few drops of superfluous water escape, and we have the cell quite full, and the cover held tight by force of the capillary attraction between the water and the glass.
i046Hydra viridis with developed young one, and bud beginning to sprout.
The polyp deposited in one of these water cages is then transferred to the stage of the microscope, and its proceedings watched. At first it looks like a shapeless mass of apple-green jelly. Soon, however, the tail end of the creature is fixed to the glass, the body elongates, and the tentacles (in this case eight) expand something after the manner of the leaves of a graceful palm.
By accident two small Water Fleas were imprisoned with the polyp, and one (a shrimp-like looking creature, carrying behind her a great bag of eggs) came into contact with the tentacles, and seemed paralysed for a time. The hydra made no attempt to convey the captive to its mouth, but held it tight until another Water Flea, a round merry little fellow (Chydorus sphæricus), came to the rescue, and assistedCanthocamptusto escape by tugging at her tail. This friendly action may not have been prompted by the intelligence which seemed to suggest it, but those who have kept tame soldier-crabs and prawns in an aquarium, will not be indisposed to attribute to the crustaceans more brains than they have usually credit for. It must, however, be confessed that the subsequent conduct of Mrs. Canthocamptus did not indicate the possession of much prudence, for she learnt no lesson from experience, but repeatedly swam against her enemy's tentacles, suffered many captures, and only escaped beingdevoured through the indifference, or want of appetite, which the polyp evinced.
i048A, Canthocamptus minutus; B, Chydorus sphæricus; C and D, Capsules and poison-thread of polyp; E, Tricodina pediculus, side view and under view; F, Kerona polyporum.—Microg. Dict.
On the body of theCanthocamptuswere some small transparent vases or bottles, containing living objects, which sprang up and down. These weremembers of theVorticellafamily, calledCothurnia, and will be hereafter described.
i049Hydra viridis, in various shapes.
Watching the hydra it was curious to note the changes of form which these creatures are able to assume. Now the tentacles were short and thick, and the body squat; now the body was elongated, like the stem of a palm tree, and the tentacles hung gracefully from the top. From some of the polyps little round buds were growing, while other buds were already developed into miniature copies of the parent, and only attached by a slender stalk. In a few days many of these left the maternal side, fixed their own little tails to the glass, and commenced housekeeping on their own account.
Polyps may be obtained at all times of the year by bringing home duckweed, conferva, and other water-plants from the ponds. Some hauls may be unsuccessful, but if one pond is not propitious others should be tried. The plants should be put in a capaciousvessel of water, and placed in the light, where, if polyps be present, they will show themselves within twenty-four hours, either attached to the sides of the glass, or hanging from the plants, or suspended head downwards from the upper film of the water. They are elegant objects, and may be kept without difficulty for some weeks. After being confined in a small quantity of water for purposes of examination, they should be carefully replaced in the larger vessel, and may thus be used again and again without suffering any injury. A low power—a three or two-inch glass—or a one-inch, reduced by employing the erector—is the most convenient for examining the whole creature, but higher powers are necessary to make out its minute structure. They should be viewed with direct and oblique light, as transparent and also as opaque objects. In the latter case the "Lieberkuhn," or polished silver speculum, is convenient, and if the microscope is not furnished with Lister's dark wells, a small piece of black paper may be stuck behind the object, by simply wetting it with the tongue.[4]
[4]The side silver reflector is useful for illuminating such objects.
[4]The side silver reflector is useful for illuminating such objects.
Although the polyps are remarkable for the simplicity of their organization, they do not the less exhibit the wonderful nature of animal life. Their bodies are composed of the substance, calledsarcode, in which is imbedded a colouring matter resembling that in the leaves of plants; every part possesses irritability and contractility, and they are very sensitive to the stimulus of light. The outer layer of their bodies isharder than the inner layer. These layers are severally calledectodermandendoderm. They may be cut and grafted like trees, and if turned inside out, the new inside digests and assimilates as well as the old. Whether any form of consciousness can belong to creatures which have no distinct nervous system is open to doubt, but it would seem probable from their movements that food and light afford them something like a pleasurable sensation in a very humble degree. If we were sufficiently acquainted with the secrets of molecular combination we might discover that the various functions of these simple organisms were discharged by differentparticles, although it is only in higher creatures that muscular particles are aggregated into muscles, or nerve particles into nerves.
Having examined the general appearance and proceedings of the hydra, let us cut off a tentacle, or take a small specimen and gently crush it by pressing down the cover of the live box, and place the object so prepared under a power of about three hundred linear. If we then illuminate it with a moderate quantity of oblique light, we shall discover round the edge of the tentacle a number of small cells or capsules, from some of which a very slender wire or thread will be emitted.[5]These are the stinging organs of the polyp, and resemble those which Mr. Gosse has so ably elucidated in the sea anemones. Some writers have endeavoured to show that they are not stinging organs at all, but so large an amount of evidence to the contrary is accumulated in Mr. Gosse's 'Actinologia Britannica,'that no reasonable doubt remains. The stinging capsules of the polyp are shown in the annexed sketch, and also the way in which they are employed, for itfortunately happened that on exposing one of the hydras to pressure in the live box, a small worm (Anguillula) escaped, which had been pierced with the minute weapons which are supposed to convey a poison into the wound. The authors of the 'Micrographic Dictionary' think that the prongs of the forks, which will be seen to point upwards in the sketch,[6]are springs, and occupy a reversed position in the capsule cells, and that their function is to throw out the threads. However this may be, the polyps, and similarly endowed creatures, have the power of darting out their poison threads with considerable force, and Mr. Gosse found that the anemone was able to pierce a thick piece of human skin.
[5]See illustrationabove.
[5]See illustrationabove.
[6]See illustrationbelow.
[6]See illustrationbelow.
i052Anguillula pierced by stinging organs of the Hydra viridis.
The same excellent observer attributes the emission of the anemone poison threads, which he considers hollow, to the injection of a fluid. In their quiescent state, he thinks they are drawn in, like the finger of a glove, and are forced out as the liquid enters their slender tubes. Possibly the polyp stinging organs may have the same structure.
Notwithstanding their dangerous weapons, polyps are often infested with a parasite, theTrichodina pediculus, as shown in Fig.E, page 49, and it must happen that either this visitation is not disagreeable, or that the Trichodina is not influenced by the poison.
As the plants in the bottles decayed, some of the animalcules died off and others appeared. In one bottle, containing decaying chara,Parameciaabounded. TheParamecia, of which there are various species,have always been favourite objects with microscopists. The Germans call them "slipper animalcules," and they vary in size from 1—96"[7]to 1—1150". They are flat rounded-oblong creatures, with a distinct integument or skin, "through which numerous vibratile cilia pass in regular rows."[8]They are furnished with a distinct mouth, and adult specimens exhibit star-shaped contractile vesicles in great perfection.
[7]The usual mode of giving dimensions is by fractions thus expressed: 1—96" means one ninety-sixth of an inch.
[7]The usual mode of giving dimensions is by fractions thus expressed: 1—96" means one ninety-sixth of an inch.
[8]'Micrographic Dictionary.'
[8]'Micrographic Dictionary.'
The swarm of specimens before us belong to one species,Paramecium aurelia, theChrysalis animalcule, and they crowd every portion of the little water-drop we have taken up, and examined with a power of about one hundred linear. When they are sufficiently quiet a power of about four hundred may be used with advantage, and Pritchard recommends adding a little indigo and carmine to the water, in order to see the cilia more clearly, or rather to render their action more plain. The cilia are disposed lengthwise, and Ehrenberg counted in some rows sixty or seventy of them, making an aggregate of three thousand six hundred and forty organs of motion in one small animated speck. This number seems large, but although we have never performed the feat of counting them, we should have expected it to prove much greater. Unlike most animalcules they are susceptible of being preserved by drying upon glass, and we subjoin a figure from Pritchard, of one thus treated, in which the star-shaped vesicles are clearly seen. These curious organs communicate with other vessels, and, as we have previously stated, are probably connected with respiration and excretion.
i055Paramecium aurelia. A dried specimen showing the vesicles.—Pritchard.
The genusParameciumis now confined to those creatures which exhibit rows of longitudinal cilia of uniform length, which are destitute of hooks, styles, or other organs of motion than the cilia, which have a lateral mouth, and no eye-spots. One mode of increase is by division, which may be easily observed; another is through the formation of true eggs as traced by Balbiani.
Another of the treasures from the pond was a species ofTrachelius, or long-necked ciliated animalcule, which kept darting in and out of a slimy den, attached to the leaf of a water-plant. The body was stout and fish-shaped, the tail blunt, and the neck furnished with long conspicuous cilia, which enabled the advancing and retreating movements to be made with great rapidity. The motions of this creature exhibit more appearance of purpose and design than is common with animalcules,but in proportion as these observations are prolonged, the student will be impressed with the difficulty of assuming that anything like a reasoning faculty and volition, is proved by movements that bear some resemblance to those of higher animals, whose cerebral capacities are beyond a doubt. It is, however, almost impossible to witness motions which are neither constant nor periodic, without fancying them to be dictated by some sort of intelligence. We must, nevertheless, be cautious, lest we allow ourselves to be deceived by reasoning so seductive, as the vital operations of the lowest organisms may be merely illustrations of blind obedience to stimuli, in which category we must reckon food, and until we arrive at forms of being which clearly possess a ganglionic system, we have no certainty that a real will exists, even of the simplest kind; and perhaps we must go still higher before we ought to believe in its presence.
Ehrenberg was much struck with the restless character of many infusoria—whether he looked at them by day or by night, they were never still. In fact their motions are like the involuntary actions which take place in the human frame; and if attached to their bodies we observe cilia that never sleep, the living membrane of some of our own organs, the nose, for example, is similarly ciliated, and keeps up a perpetual though unconscious work.
MARCH.
Paramecia—Effects of Sunlight—Pterodina patina—Curious tail—Use of a Compressorium—Internal structure of Pterodina—Metopidia—Trichodina pediculus—Cothurnia—Salpina—Its three-sided box—Protrusion of its gizzard mouth.
HEParamecia, noticed in the last chapter, have increased and multiplied their kind without any fear lest the due adjustment between population and food should fail to be preserved. A small drop of the scum from the surface of the water in their bottle is an astounding sight. They move hither and thither in countless numbers, seldom jostling, although thick as herrings in a tub, and in many portions of the field the process of self-fissure, or multiplication by division, is going on without any symptoms of discomfort on the part of the parent creature. This is an interesting sight, but we will not linger over it, for the sun is shining, and there is enough warmth in the air to make it probable that the ponds will be more prolific than in the cold winter months. Sunshine is a great thing for the microscopic hunter; it brings swarms of creatures to the surface, and the Rotifers are especially fond of its genial beams. Evenif we imitate it by a bright lamp, we shall attract crowds of live dancing specks to the illuminated side of a bottle, and may thus easily effect their capture by the dipping-tube.
i058Pterodina patina.
This year the March sunshine was not lost, for on the third of that month I obtained a bottleful of conferva from a pond about a mile from my house, and lying at the foot of the Highgate hills. Water-fleas were immediately discovered in abundance, together with some minute worms, and a ferocious-looking larva covered with scales; but what attracted most attention was a Rotifer, like a transparent animated soup-plate, from near the middle of which depended a tail, which swayed from side to side, as the creature swam along. The head exhibited two little red eyes; two tufts of cilia rowed the living disk through the water, and the gizzard worked with a rapid snapping motion, that left no doubt the ciliary whirlpools had brought home no slender stores of invisible food. Sometimes the end of the tail acted as a sucker, and fixed the animal tightlyto the glass, when the wheels were protruded, and the body swayed to and fro. Then the sucker action ceased, and as the creature swam away, a tuft of cilia was thrust out from the extremity of the tail. A power of one hundred linear was sufficient to enable the general nature of this beautiful object to be observed, but to bring out the details, much greater amplification was required, and this would be useless if the little fidget could not be kept still.
i059450 Pterodina patina—gizzard.
The size of the creature, whose name we may as well mention wasPterodina patina, rendered this practicable, but required some care. The longest diameter of the body, which was not quite round, was about 1—120", so that it was visible to the naked eye, and as a good many were swimming together, one could be captured without much difficulty, and transferred with a very small drop of water to the live-box. Then the coverhad to be put on so as to squeeze the animal just enough to keep it still without doing it any damage, or completely stopping its motions. This was a troublesome task, and often a little overpressure prevented its success.
Some observers always use in these cases an instrument called acompressorium, by which the amount of pressure is regulated by a lever or a fine screw; but whether the student possess one or not, he should learn to accomplish the same result by dexterously manipulating a well-made live-box. We will suppose thePterodinasuccessfully caged, and a power of about one hundred and fifty linear brought to bear upon her, for our specimen is of the "female persuasion." This will suffice to demonstrate the disposition and relation of the several parts, after which one of from four hundred to five hundred linear may be used with great advantage, though in this case the illumination must be carefully adjusted, and its intensity and obliquity frequently changed, until the best effect is obtained.
We find, on thus viewing the Pterodina, that it is a complex, highly organized creature, having its body protected by acarapace, like the shell of a tortoise, but as flexible as a sheet of white gelatine paper, which it resembles in appearance. Round the margin of this carapace are a number of little bosses or dots, which vary in different individuals. The cilia are not disposed, as at first appeared, in two separate and distinct disks, but are continuous, as in the annexed sketch. Down each side are two long muscular bands, distinctlystriated, and when they contract, the ciliary apparatusis drawn in. As this contraction takes place, two apparently elastic bands, to which the ciliary lobes are attached, are bent downwards, till they look like the C springs behind a gentleman's carriage; and they regain their former position of slight curvature, when the cilia are again thrust out.
i061Pterodina patina—tail-foot.
The gizzard is three-lobed, and curiously grasped by forked expansions of the handles of the hammers. The tail, or tail-foot, can be withdrawn or thrust out at the will of the creature; and when in a good position for observation, a slight additional pressure will keep it so for examination. Delicate muscular longitudinal bands, forked towards the end of their course, supply the means of performing some of its motions, and one, or perhaps two, spiral threads extend through the upper half of its length, and either act as muscles, or as elastic springs for its extension. The intestines and other viscera are clearly exhibited, and a strong ciliary action conducts the food to the gizzard-mouth.
To return to the tail. One spiral fibre is easily discovered;but I have often, and at an interval of months, seen the appearance of two, and am in some doubt whether this was a deception, arising from the compression employed, or was a genuine indication.
i062A. Metopidia acuminata, as drawn by Mr. Gosse. B. Specimen as seen and described in text. c. Mouth or gizzard.
Where this Rotifer occurs I have usually found it plentiful, but unfortunately could obtain no constant supplies after I had determined to make a special study of the remarkable tail, which is much more complicated than I have described. ThePterodinalived for some time in captivity, and for a week or two I could obtain them from my glass tank. They were likewise to be found for some weeks in the same part of the pond, but not all over it, until one day not a single specimen could be discovered, notwithstanding a persevering searchnor was I afterwards able to get any from that pond during the remainder of the year.
i063Trichodina pediculus.
Several other Rotifers, with and without carapaces, were among the same mass of confervæ, among them aMetopidia, with a firm shell, a forked jointed tail, and a projection in front which worked like a pickaxe among the decaying weed. There were likewise specimens of the long-necked animalcules (Trachelii), groups of Vorticella, some specimens of Volvox, and a smallTrichodina pediculus, which, when magnified two hundred and sixty linear, was about the size of a sixpence and equally round. The edge was beautifully fringed with a circle of cilia; in an inner circle was a row of locomotive organs, and the centre exhibited vacuoles constantly opening and shutting. This creature, as before explained, is often found as a parasite upon the polyps. On one occasion a glimpse was caught of a Rotifer similar in shape to the common wheel animalcule, but with a yellow inside. Possibly it was the object so beautifully delineated by Mr. Gosse, in his "Tenby," and described as the "Yellow Philodine," but this must remain in doubt, as it managed to escape before it could be secured.
i064A. Cothurnia imberbis—('Micrograph. Dict.') B and C. The specimens described in text. The figures give the linear magnification.
By the 18th of the month the Vorticellids were much more plentiful, and their changes easily watched; many left their stalks while under the microscope, after which some rushed about like animated and demented hats, others twirled round like tee-to-tums, while others took a rest before commencing their wild career. But the common Vorticellæ were not the only or the most interesting representations of their charming order, for upon some threads of conferva were descried several elegant crystal vases standing upon short foot-stalks, and containing little creatures that jumped up and down like "Jack in the box." These were so minute, that a power of four hundred and thirty linear was advantageously brought to bear upon them. When elongated their bodies were somewhat pear-shaped, but more slender, and variegated with vacuoles and particles of food. The mouths resembled those of Vorticellæ, and put forth circles of vibrating cilia. They were easily alarmed, when the cilia were retracted, and down they sank to the bottom of their vases, quickly to rise again. In one bottle there were two living in friendly juxtaposition. This was not a case of matrimonial felicity, nor of Siamese twins, but offission, or reproduction by division. The original inhabitant of the tube finding himself too fat, or impelled by causes we do not understand, quietly divided himself in two, and as the house was big enough, no enlargement was required. How many stout puffy gentlemen must envy this process; how convenient to have two thin lively specimens of humanity made out of one too obese for locomotion. Man is, however, sometimes the victim of his superiororganization, and no process of "fission" can make the lusty lean.[9]
[9]Balbiani in his 'Recherches sur les Phénomènes Sexuels des Infusoires,' speaks of the Vorticellids as the only Infusoria dividing longitudinally. In other species such appearances arise from conjunction.
[9]Balbiani in his 'Recherches sur les Phénomènes Sexuels des Infusoires,' speaks of the Vorticellids as the only Infusoria dividing longitudinally. In other species such appearances arise from conjunction.
The bottles in which these creatures live, in happy ignorance that they are called by so crackjaw a name asCothurnia imberbis, were described asCarapacesby Ehrenberg, but they bear no resemblance to the shell of a turtle or crab. They are thrown off by the animals who preserve no other connection with them than the attachment at the bottom.
The Micrographic Dictionary describes the family Ophrydina as corresponding to Vorticellina with a carapace. Stein places them with Vorticellids, &c., amongst his Peritricha, which are characterised by a spiral wreath of cilia round the mouth.
Towards the end of the month a great number of black pear-shaped bodies (Stentor niger), visible to the naked eye, were conspicuous in some water from the Kentish Town ponds. Upon examination they were found to be filled with granules that were red by reflected, and purple by transmitted light. Each one had a spiral wreath of cilia, with a mouth situated like those of the stentors, hereafter to be described, but none of them became stationary, and in a few days they all disappeared. Stein divides Ehrenberg's Stentor igneus from S. niger; the creature described seems to have agreed with Stein'signeus, which he describes as having blood-red lilac, cinnabar, or brown-red pigment particles, and as much smaller than his S. niger. In the samewater were specimens of that singular Rotifer, theSalpina, about 1—150" long, and furnished with alorica, or carapace, resembling a three-sided glass box, closed below, and slightly open along the back. At the top of this box were four, and at the bottom three, points or horns, and the creature had one eye and a forked tail. Keeping him company was another little Rotifer, named after its appearance,Monocerca rattus, the 'One-tailed Rat.' This little animal had green matter in its stomach, which was in constant commotion. I ought to have observed that the Salpina repeatedly thrust out its gizzard, and used it as an external mouth. In the annexed sketch the Salpina is seen in a position that displays the dorsal opening of the carapace. Its three-cornered shape is only shown by a side view.
Here we close a brief account of what March winds brought in their train. The next chapter will show the good fortune that attended April showers.
i067Salpina redunca.
APRIL.
The beautiful Floscule—Mode of seeking for Tubicolor Rotifers—Mode of illuminating the Floscule—Difficulty of seeing the transparent tube—Protrusion of long hairs—Lobes—Gizzard—Hairy lobes of Floscule not rotatory organs—Glass troughs—Their construction and use—Movement of globules in lobes of Floscule—Chætonotus larus—Its mode of swimming—Coleps hirtus—Devourer of dead Entomostraca—Dead Rotifer and Vibriones—Theories of fermentation and putrefaction—Euplotes and Stylonichia—Fecundity of Stylonichia.
EWliving creatures deserve so well the appellation of "beautiful" as theFloscularia ornata, or Beautiful Floscule, although to contemplate a motionless and uncoloured portrait, one would imagine that it exhibited no graces of either colour or form. Mr. Gosse has, however, done it justice, and the drawing in his "Tenby" is executed with that rare combination of scientific accuracy and artistic skill, for which the productions of his pencil are renowned.