ANIMALCULE, in general, signifies a little animal; and thus the term might be applied to every animal which is considerably inferior in size to ourselves. It hath been customary, however, to distinguish by the name of animalcules only such animals as are of a size so diminutive, that their true figure cannot be discerned without the assistance of glasses; and more especially it is applied to such as are altogether invisible to the naked eye, and cannot even be perceived to exist but by the assistance of microscopes.
By the help of magnifying glasses, we are brought into a kind of new world; and numberless animals are discovered, which from their minuteness must otherwise for ever have escaped our observation; and how many kinds of these invisibles there may be, is still unknown; as they are discerned of all sizes, from those which are barely invisible to the naked eye, to such as resist the action of the microscope, as the fixed stars do that of the telescope, and with the best magnifiers hitherto invented appear only as so many moving points.
The smallest living creatures our instruments can show are those that inhabit the waters: for though possibly animalcules equally minute, or perhaps more so, may fly in the air, or creep upon the earth, it is scarce possible to bring such under our examination; but water being transparent, and confining the creatures in it, we are able, by applying a drop of it to our glasses, to discover, to a certain degree of smallness, all that it contains.—Some of the most curious of these animalcules, which have been described by microscopical observers, we shall here give an account of.
1. The Hair-like Insect. This is called by Mr Baker on account of its shape; being extremely slender, and frequently an hundred and fifty times as long as broad. The body or middle part, which is nearly straight, appears, in some, composed of such rings as the windpipe of land animals is made up of; but in others seems rather sealed, or made up of rings that obliquely cross one another. Its two ends are hooked or bent, pretty nearly in the same degree, but in a direction opposite to one another; and as no eyes can be discerned, it is difficult to judge which is the head or tail. Its progressive motion is very singular, being performed by turning upon one end as a centre, and describing almost a quarter of a circle with the other, as represented in the figure. Its motions are very slow, and require much patience and attention in the observer. These creatures are so small, that millions of millions of them might be contained in an inch square. When viewed singly, they are exceedingly transparent, and of a beautiful green colour; but when numbers of them are brought together, they become opaque, lose their green colour, and grow entirely black.
Notwithstanding the extreme minuteness of these animalcules, they seem to be fond of society; for, after viewing for some time a parcel of them taken up at random, they will be seen disengaging themselves in a kind of regular order. If a multitude of them are put into a jar of water, they will form themselves into a regular body, and ascend slowly to the top, where after they have remained for some time exposed to the air, their green colour changes to a beautiful sky blue. When
VOL. II. PART I.
they are weary of this situation, they form themselves into a kind of rope, which slowly descends as low as they intend; but if they happen to be close to the side of the jar, they will descend upon it. They are so nearly of the specific gravity of water itself, that they will either remain at the bottom, float on the surface, or be suspended in the middle, according as they are originally placed, or as they themselves have a mind.
A small quantity of the matter containing these animalcules having been put into a jar of water, it so happened, that one part went down immediately to the bottom, whilst the other continued floating on the top. When things had remained for some time in this condition, each of these swarms of animalcules began to grow weary of its situation, and had a mind to change its quarters. Both armies, therefore, set out at the same time, the one proceeding upwards, and the other downwards; so that, after some hours journey, they met in the middle. A desire of knowing how they would behave on this occasion, engaged the observer to watch them carefully; and to his surprise he saw the army consider- able degree of sagacity, that was marching upwards, open to the right and left, to make room for those that were descending. Thus, without confusion or intermixture, each held on its way: the army that was going up, marching in two columns to the top, and the other proceeding in one column to the bottom, as if each had been under the direction of wise leaders.
The hair-like insect was first discovered in a ditch at Norwich, one end of which communicates with the river there, and the other end with a second ditch, into which several kennels empty themselves. The length of this ditch, when Mr Baker wrote his account of this prodigious animalcule, was at least 100 yards, and its breadth nine. The bottom, for more than a foot thick, was covered with a blackish green substance, in appearance like mud, made up for the most part of these insects; but, supposing only a half or a quarter part of it to be composed of them, according to the dimensions we have given, their numbers must exceed all imagination.
2. Eels in paste, &c. When paste is allowed to stand till it become sour, it is then found to be the habitation of numberless animalcules, which may be discerned by the naked eye; and though their form cannot be perfectly distinguished, their motion is very perceptible, and the whole paste will seem to be animated. Fig. 4. represents one of these anguillae magnified. Eels in paste are the most remarkable property of these insects is, that they are viviparous. If one of them is cut through near the middle, several oval bodies of different sizes will be seen to issue forth. These are young anguillae, each of them coiled up and enclosed in its proper membrane, which is so exquisitely fine, as scarce to be discernible by the greatest magnifier, while it encloses the embryo animal. The largest and most forward immediately break through this covering, unfold themselves, and wriggle about in the water nimbly; others get out, uncoil, and move themselves about more slowly; and the least mature continue entirely without motion. The uterus, or vessel that contains all these oval bodies, is composed of many ringlets, not unlike the aspera arteria of land animals, and seems to be considerably elastic; for as soon as the animalcule is cut in two, the oval bodies are thrust out with some degree of violence, from the springing back or action of this bowel. An
3 A
hundred
hundred and upwards of the young ones have been seen to issue from the body of one single cell, whereby the prodigious increase of them may be accounted for; as probably several such numerous generations are produced in a short time. They seem to be all prolific; and unless trial happens to be made upon one that has brought forth all its young, or when the paste has been kept for a very long time, the experiment will always succeed.—This property of these cells being viviparous renders it highly improbable that they ever become flies.
Animalcules of a similar kind are likewise found in vinegar; and, like those already described, are found to be viviparous. But it is not only in acid matters that such appearances are observed. In some fields of wheat, many grains may be observed, that appear blackish outwardly, as if scorched; but when opened are found to contain a soft white substance, which, attentively considered, appears to be nothing else than a congeries of threads or fibres lying close to each other in a parallel direction, much resembling the unripe down of some thistles on cutting open the flower heads before they begin to blow. This fibrous matter discovers not the least sign of life or motion, unless water is applied; but immediately on wetting, provided the grains of wheat have been newly gathered, the supposed fibres separate, and appear to be living creatures. Their motions at first are very languid; but gradually become more vigorous, twirling and wriggling themselves somewhat in the manner of the cells in paste, but always slower than they, and with a great deal less regularity.
If the grains of wheat are grown dry by keeping, and in that condition are cut open, the fibrous matter is very distinguishable; and, on putting water to it, will separate with great readiness, and seem like fine tubes or threads tapering at both ends: but not the least motion will be perceived till they have been in water for several hours, and sometimes they will never move at all. But if the same grains are steeped in water for three or four hours, or buried for some days in the earth, till they are fully saturated with moisture, and then opened with a penknife; on taking out a small portion of the white matter carefully, and spreading it thin upon a slip of glass, the animalcules will be seen bunched together, and extended longitudinally, but without motion: and though, upon the application of water, they will not revive so soon as those taken from fresh grains, whole moisture has never been exhaled; yet, after remaining an hour or two in water, they are constantly found alive and vigorous, even though the grains have been kept in a dry condition for several years. It is necessary, however, to adapt, in some measure, the time of continuing the grains in water or earth to the age and dryness of them: for if they are not opened before they are too much softened, the animalcules will be dead; and unless the hulks are opened to let those creatures out after they have been steeped, they inevitably perish in them: otherwise, they will continue alive in water for many months; and, should the water dry away, may be revived again by giving them a fresh supply.
3. The Proteus. This animalcule has been dignified by Mr. Baker with the name of Proteus, on account of its assuming a great number of different shapes, so as scarce to be known as the same animal in its various
transformations; and indeed, unless it be carefully watched while passing from one shape to another, it will often become suddenly invisible, as happened more than once to Mr. Baker.
When water, wherein any sort of vegetable has been infused, or animals preserved, has stood quietly for found. some days, or weeks, in any glass or other vessel, a slimy substance will be collected about the sides: some of which being taken up with the point of a penknife, placed on a slip of glass in a drop of water, and looked at through the microscope, will be found to harbour several kinds of little animals that are seldom found swimming about at large; among which the proteus is one. Its shape is better understood from the figure, than from any description that could be given. Its substance and colour seems to resemble that of a snail; and its whole shape seems to bear a considerable resemblance to that of a swan. It swims to and fro with great vivacity: but will now and then stop for a minute or two; during which time its long neck is usually employed as far as it can reach, forwards, and on every side, with a somewhat slow, but equable motion, like that of a snake, frequently extending thrice the length of its body, and seemingly in search of food.
There are no eyes, nor any opening in the head like a mouth, to be discerned: but its actions plainly prove it to be an animal that can see; for though multitudes of different animalcules swim about in the same water, and its own progressive motion is very swift, it never strikes against any of them, but directs its course between them with a dexterity wholly unaccountable, should we suppose it destitute of sight.
When the proteus is alarmed, it suddenly draws in its long neck, represented in fig. 5. and 6. transforming itself into the shape represented in fig. 7. when it becomes more opaque, and moves about very slowly with the large end foremost. When it has continued some time in this posture, it will often, instead of the head and neck it had formerly, put forth a new one, with a kind of wheel machinery, represented fig. 8. the motions of which draw a current of water to it from a considerable distance. Having often pulled in and thrust out this short head, sometimes with and sometimes without the wheel work, the creature, as if weary, will remain motionless for a while; then its head and long neck will be very slowly protruded, as in fig. 9. and it soon resumes its former agility. Sometimes it disposes of its neck and head, as represented in fig. 10.
4. The Wheel Animal, or Vorticella. This wonder- ful animalcule is found in rain water that has stood where some days in leaden gutters, or in hollows of lead on the tops of houses; or in the slime or sediment left by such water; and perhaps may also be found in other places: but if the water standing in gutters of lead, or the sediment left behind it, has any thing of a red colour in it, one may be almost certain of finding them therein. Though it discovers no signs of life except when in the water, yet it is capable of continuing alive for many months after it is taken out of the water, and kept in a state as dry as dust. In this state it is of a globular shape, exceeds not the bigness of a grain of sand, and no signs of life appear: but being put into water, in the space of half an hour a languid motion begins, the globe turns itself about, lengthens itself by slow degrees,
Animalcule. degrees, assumes the form of a lively maggot, and most commonly in a few minutes afterwards puts out its wheels; swimming vigorously through the water, as if in search of food; or else, fixing itself by the tail, works the wheels in such a manner as to bring its food to it.
Fig. 23. and 24. show the wheel animal in its globular form; fig. 11. and 12. in its maggot state; and fig. 13, 14, 15, 16, 17, 18, 19, 20, 21, and 22. show the different appearances of its wheels, and also its various intermediate changes between the globular and maggot state.
Its wheel work described. The most remarkable part of this animalcule is its wheel work. This consists of a couple of femicircular instruments, round the edges of which many little fibrille move themselves very briskly, sometimes with a kind of rotation, and sometimes in a trembling or vibrating manner. When in this state, it sometimes unfaltness its tail, and swims along with a great deal of swiftness, seemingly in pursuit of its prey. Sometimes the wheels seem to be entire circles, armed with small teeth, like those of the balance wheel of a watch, appearing projected forwards beyond the head, and extending sideways somewhat wider than its diameter. The teeth or cogs of these wheels seem to stand very regularly at equal distances: but the figure of them varies according to their position, the degree of their protrusion, and perhaps the will of the animal itself. They appear sometimes like minute oblong squares, rising at right angles from the periphery of a circle, like ancient battlements on a round tower; at other times they terminate in sharp points, and altogether resemble a kind of Gothic crown. They are often seen in a kind of curvular direction, all bending the same way, and seeming like so many hooks; and now and then the ends of them will be perceived to be clubbed like mallets. This figure, however, as well as the first, they assume but rarely.
Shows all the marks of a real rotation. As these wheels are everywhere excessively transparent, except about their circular rim or edge, where the cogs are set, it is very difficult to determine by what contrivance they are turned about, or what their real figure is, though they seem exactly to resemble wheels moving round upon an axis. It is also hardly possible to be certain whether those circular bodies in which the teeth are set, are of a flat form, or hollow and conical; but they seem rather to be of a conical figure. The difficulty of conceiving how an articulation could be contrived so as to cause a real rotation, hath caused many people imagine that there was a deception in this case: But Mr Baker assures us, that when the wheels are fully protruded, they never fail to show all the visible marks of a regular rotation; and, in some positions, the same cogs or teeth may be traced by the eye during a complete revolution.
Shows great quickness of sensation. All the actions of this creature seem to imply sagacity and quickness of sensation. At the least touch or motion in the water, they instantly draw in their wheels; and Mr Baker conjectures, that their eyes are lodged somewhere about the wheels; because, while in the maggot state, its motions are slow and blundering; but after the wheels are protruded, they are performed with great regularity, swiftness, and steadiness.
Notwithstanding the minuteness of this animalcule, the microscope generally discovers others in the same
drop of water, compared with which the wheel animal may be said to be a whale. The transparency of its body, therefore, allows its internal parts to be seen, which cannot be perceived in the minutest animalcules, on account of the smallness of their size. a, is the appearance of the head; and though it is everywhere transparent, a ring or circle, more particularly remarkable for its clearness, is commonly perceived about the middle of the forehead, a little above the mouth. This, Mr Baker thinks, might justly be called the seat of the brain. Many vessels which seem to take their origin from thence are discernible in the head, wherein some transparent fluid appears continually agitated by a kind of fluctuating motion.
The thorax, b, is joined to the head by a very short neck, c, and appears to be about the sixth part of the whole length of the animal. In the middle of the thorax is placed the heart, d, where its systole and diastole are plainly visible. It is seen through the back of the insect, shutting and opening alternately with great regularity and exactness. Its size is proportionable to the creature's bigness; and its shape, during the systole, is nearly circular, being composed seemingly of two femilunar parts, which then approach each other laterally, and form between them a roundish or horse-shoe-like figure, whose upper side is flat, and the under one convex. The diastole is performed by a seeming separation, or opening, of these two femilunar parts, whereby the transverse diameter of the heart is very much enlarged. This separation begins exactly in the middle of the lower part next the tail; and opens to such a considerable width upwards, that the two parts, when at their utmost distention, seem only joined by an arched vessel at their anterior end. The alternate motions of contraction and dilatation are performed with great strength and vigour, in pretty much the same time as the pulsation of the arteries of a man in health. The motions of the heart are communicated to all the internal parts of the thorax, and seem to extend a great deal further; for a strict examination discovers, at the same time, throughout the whole animal, contractions and dilatations going on, that are apparently correspondent thereto. These motions of the heart, however, are sometimes suspended or imperceptible for two or three minutes: after which they are renewed, and go on again with the same regularity as before. From the under part of the thorax proceeds a small transparent horn represented at a, fig. 11. and 12. It is never visible but when the animal turns on its back or side.
The blood or circulating fluid of the wheel animal is so absolutely colourless, that the current of it through the vessel is indistinguishable by glasses. A sort of irregular agitation of some fluid is indeed perceived, which is perhaps a compound motion of currents running different ways, and forming such an appearance, though no single current is anywhere distinctly visible.
Immediately below the thorax is another annular division, e, joining upwards to the thorax and downwards to the abdomen, the entrance whereof it serves occasionally to enlarge or diminish. The abdomen, f, is by much the largest part of the animal, and contains the stomach and intestines. When the insect is full of food, these bowels appear opaque and of a blood-red colour, extending quite through the belly and great part
part of the tail, and exhibiting a variety of contractions and dilatations. The belly is capable of stretching out greatly in length, or being shortened very much, and widening its diameter. It assumes many shapes, and becomes occasionally a case for all the other parts of the body.
Besides the above mentioned one, there are found in the waters several other species of animals furnished with wheels, some of which appear to have a rotatory, and others a vibratory, motion. Fig. 25. represents a kind found in the ditch at Norwich, where the hair-like insect is produced. They differ from the foregoing only in having very long tails. Fig. 26, 27, and 28. represent a species of wheel animals, which are also covered with shells. The body of this species consists of three parts, in like manner as the other; only the thorax and abdomen, in this, are not separated by any gut, or intermediate vessel, but are joined immediately together. The heart is plainly perceived, having a regular systole and diastole, at a, as in the former species. These creatures occasionally draw themselves entirely within their shells; and the shell then appears terminated by six short spikes on one side and two on the other.
The young ones of this species are carried in oval fasciuli, or integuments, fastened externally on the lower part of their shells somewhere about the tail; these fasciuli are sometimes opaque only at one end, and seemingly empty at the other; sometimes they appear opaque in the middle, with a transparency all round, as in fig. 26. When the young one is about to burst its integuments, the parent assists it greatly, by wagging its tail, and striking the oval bag, so that the young one's head becomes as it were forced into the water, though the tail cannot be so soon disengaged. In this condition the young one sets its wheel a-going, and exerts all its endeavours to free itself from its confinement. When it has got clear, it swims away, wagging its tail as the old one does, and leaving the integument adhering to the shell of the parent. The old one then uses a number of efforts to get rid of this incumbrance, striking against it with her tail, fixing the end of her tail upon it, and then darting her body forward; with several very odd motions not easy to be described. This kind of wheel animals are great tormentors of the water flea, Pulex aquaticus arboreseens of Swammerdam; of which a figure is given from that author (Plate XXXVI.); fig. 2. shows the natural size of the flea; and fig. 1. shows it magnified, with some of the wheel animals adhering to it. These insects are often found in great numbers in the same water: and when that is the case, it is not uncommon to discover five or six of these crustaceous wheel animals fastened by their tail to the shell or horns of the flea; causing it, seemingly, a vast deal of uneasiness: nor can they be driven away, or shaken off, by all the efforts the flea can use for that purpose.
5. The Bell-flower Animal, or Plumbed Polype. These animalcules dwell in colonies together, from ten to fifteen (seldom falling short of the former number, or exceeding the latter), in a slimy kind of mucilaginous or gelatinous case; which, out of the water, has no determined form, appearing like a little lump of slime; but, when expanded therein, has some resemblance to the figure of a bell with its mouth upwards; and is
usually about half an inch long, and a quarter of an inch in diameter. These bells, or colonies, are to be found adhering to the large leaves of duckweed, and other aquatic plants. They may be most easily discovered by letting a quantity of water, with duckweed in covered. it, stand quietly for three or four hours in glass vessels in a window, or other place whence a strong light comes: for then, if any are about the duckweed, they will be found, on careful inspection, extending themselves out of their cases, and making an elegant appearance.
The bell, or case, which these animals inhabit, being very transparent, all the motions of its inhabitants may be discerned through it distinctly. It seems divided internally into several apartments, or rather to contain several smaller fasciuli, each of which encloses one of these animals. The openings at the tops of these fasciuli, are but just sufficient to admit the creature's head and a small part of its body to be thrust out beyond them, the rest remaining always in the case. It can, however, occasionally retire into its case altogether; and never fails to do so when alarmed by any sudden motion of the water, or of the vessel which contains it.
Beside the particular and separate motion which each of these creatures is able to exert within its own case and independent of the rest; the whole colony together has a power of altering the position of the bell, or even of removing it from one place to another; and hence this bell is sometimes found standing perfectly upright, as in fig. 29. and 33. and sometimes bending the upper part downwards, as in fig. 30. As these animalcules seem not to choose to stay together in societies whose number exceeds 15, when the colony happens to increase in number, the bell may be observed to split gradually, beginning from about the middle of the upper or anterior extremity, and proceeding downwards towards the bottom, as in fig. 32. till they at last separate entirely, and become two complete colonies independent of each other, one of which sometimes removes to another part of the vessel.
The arms of each individual of this colony are set round the head, to the number of 40, having each the of an individual. figure of an Italic f, one of whose hooked ends is fastened to the head; and all together, when expanded, compose a figure shaped somewhat like a horse's shoe, convex on one side next the body, but gradually opening and turning outwards, so as to leave a considerable area within the outer extremities of the arms. When the arms are thus extended, the creature, by giving them a vibrating motion, can produce a current in the water, which brings the animalcules, or whatever other minute bodies are within the sphere of its action, with great velocity to its mouth, situated between the arms; where they are taken in if liked, or driven away by a contrary motion. The food is conveyed immediately from the mouth or opening between the arms, through a narrow neck, into a passage seemingly correspondent to the oesophagus in land animals; down which it passes into the stomach, where it remains for some time, and then is voided upwards, in small round pellets, through a gut whose exit is near the neck. The body consists of three divisions; in the uppermost of which are contained all the above-mentioned intestines, which are only to be discerned when the creature is full, at which time they become opaque. The other two di-
visions, which are probably fixed to the bell, seem to be of no other use than to give the creature a power of contraction and extension. The arms are not able to contract like those of the common polype; but when the animal retires into its case, they are brought together in a close and curious order, so as to be easily drawn in. Though their general appearance, when expanded, is that of a cup whose base and top are of an horse-shoe form, they sometimes separate into four parts, and range themselves as in fig. 36. so as to resemble four separate plumes of feathers. Though their eyes cannot be discovered, yet Mr Baker thinks they have some perception of the light: for when kept in the dark, they always remain contracted; but on being exposed to the light of the sun or of a candle, they constantly extend their arms, and show evident signs of being pleased.
Fig. 29. represents one complete colony or bell standing erect, with all the animals out of their kingdom, and their arms extended, exhibiting all together a very pretty appearance. a, represents two oval bodies, supposed by Mr Baker to be eggs.
Fig. 30. shows all the creatures withdrawn into their cells, and the end of the bell hanging downwards.
Fig. 33. shows the bell erect, with only one of the animals coming out, in order to show its connexion with the bell.
Fig. 34. shows the head and arms of a single polype closing together, and disposing themselves in order to be drawn into the bell.
Fig. 35. shows one complete animal greatly magnified, to show its several parts more distinctly; viz. a, the head, resembling a horse shoe; b b, the arms seen from one side; c, the narrow neck; d, the oesophagus; e, the stomach; f, the gut or last intestine through which the food passes after being digested in the stomach; g, the anus, where the feces are discharged in little pellets; h i, that part of the bell which surrounds the body of the animal, and closes upon it when it retires down.
Fig. 37. The head and arms seen in front.
6. The Globe animal. This animalcule, represented fig. 38. seems exactly globular, having no appearance of either head, tail, or fins. It moves in all directions, forwards or backwards, up or down, either rolling over and over like a bowl, spinning horizontally like a top, or gliding along smoothly without turning itself at all. Sometimes its motions are slow, at other times very swift; and, when it pleases, it can turn round, as it were upon an axis, very nimbly, without removing out of its place. The whole body is transparent, except where the circular black spots are shown in the figure. Some of the animals have no spots, and others from one to seven. The surface of the whole body appears, in some, as if all over dotted with points; in others, as if granulated like flagreen: but their more general appearance is, as if beset thinly round with short moveable hairs or bristles, which probably are the instruments by which their motions are performed. These animalcules may be seen by the naked eye, but appear only like moving points.
7. The Pipe animal. These creatures are found on the coast of Norfolk, living in small tubes or cases of sandy matter, in such multitudes as to compose a mass sometimes of three feet in length. Fig. 39. shows a
piece of such a congeries broke off, where seas represent the mouths or openings of the pipes wherein the little animals make their abode. Fig. 40. shows one single pipe, with its inhabitant, separated from the rest, and magnified nine or ten times in diameter. The pipe or case b is made of sand, intermixed here and there with minute shells, and all cemented together by a glutinous slime, probably issuing from the animal's own body c, which is composed of muscular ringlets like those of a worm, capable of great extension or contraction. The anterior end or head, d, is exceedingly beautiful, having round it a double row of little arms disposed in a very regular order, and probably capable of extension, in order to catch its food, and bring it to its mouth. Some of these tubes are found petrified, and constitute one species of syringoides.
8. An Insect with net-like arms. The properties and shape of this little animal are very extraordinary. It is found only in cascades, where the water runs very swift. There these insects are found in clusters, standing erect on their tails; and resembling, when all together, the combs of bees at the time they are filled with their aureliae. On being taken out of the water, they spin threads, by which they hang exactly in the same manner as the garden spider. Fig. 42. shows one of these insects magnified. Its body appears curiously turned as on a lathe; and at the tail are three sharp spines, on which it raises itself, and stands upright in the water; but the most curious apparatus is about its head, where it is furnished with two instruments like fans or nets, which serve to provide its food. These it frequently spreads out and draws in again; and when drawn up, they are folded together with the utmost nicety and exactness, so as to be indiscernible when brought close to the body. At the bottom of these fans a couple of claws are fastened to the lower part of the head, which, every time the nets are drawn in, conduct to the mouth of the animal whatever is taken in them. When the creature does not employ its nets, it thrusts out a pair of sharp horns, as in fig. 41. where the insect is shown magnified about 400 times.
Some of these creatures being kept with water in a vial, most of them died in two days; and the rest, having spun themselves transparent cases (which were fastened either to the sides of the glass, or to pieces of grass put into it), seemed to be changed into a kind of chrysalis: but, before taking this form, they appeared as in fig. 43. which shape they likewise assumed when weary with catching their food, or when lying in wait for it. None of them lived above three days; and though fresh water was given them two or three times a-day, yet, in a few hours, it would stink to a degree scarce conceivable, and that too at several yards distance, though, in proportion to the water, all the property of included insects were not more than as 1 to 150,000. This makes it probable, that it is necessary for them to live in a rapid stream, lest they should be poisoned by the effluvia issuing from their own bodies, as no doubt they were in the vial.
9. A curious aquatic worm. This animalcule is shown, magnified, at fig. 31. It is found in ditch water; and is of various sizes, from to of an inch in length. About the head it is somewhat of a yellowish colour; but all the rest of the body is perfectly colourless and transparent, except the intestines, which are considerably
Animalcule. considerably opaque, and disposed as in the figure. Along its sides are several papillæ, with long hairs growing from them: it has two black eyes, and is very nimble. But the most remarkable thing in this creature is a long horn or proboscis; which, in the large ones, may be seen with the naked eye, if the water is clear, and is sometimes of an inch in length: this it waves to and fro as it moves in the water, or creeps up the side of the glass; but it is not known whether it is hollow, or of what use it is to the creature itself.
35 Its horn or proboscis.
36 Spermatie animals, when discovered.
37 General appearance the same in every animal.