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 forever 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 reflect 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 shew 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, here give an account of.

1. The Hair-like Insect. This is so 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 sculled, 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 society viewing for some time a parcel of them taken up at random, random, they will be seen disposing 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 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 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 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 an 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 pastes, &c. When paste is allowed to stand till it becomes four, 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. The most remarkable property of these insects is, that they are viviparous. If one of them is cut thro' near the middle, several oval bodies of different sizes will be seen to issue forth. There are young anguillae, each of them coiled up and inclosed in its proper membrane, which is so exquisitely fine, as scarce to be discernible by the greatest magnifier, while it incloses 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 vesicle 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. A hundred and upwards of the young ones have been seen to issue from the body of one single eel, 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 eels 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 eels in paste, but always slower than they, and with a great deal of 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 veritable, 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 bundled 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, whose moisture has never been exhale; 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 necessity in time of continuing the grains in water or earth to the making 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 husks 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. 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 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 wonderful animalcule is found in rain-water that has stood 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 anything 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; Plate XXIV the globule turns itself about, lengthens itself by flow (A) 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. shew 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. shew the different appearances of its wheels, and also its various intermediate changes between the globular and maggot state.

The most remarkable part of this animalcule is its wheel-wheel-work. This consists of a couple of semicircular instruments, round the edges of which many little fibrillae move themselves very briskly, sometimes with a kind of rotation, and sometimes in a trembling or vibrating manner. When in this state, it sometimes unfastens its tail, and swims along with a great deal of twirliness, 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 curvilinear 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.

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 those wheels moving round upon an axis. It is 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.

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 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 is plainly visible. It is seen through the back of the insect, shutting and opening alternately with great regularity and exactness. Its size is proportionate to the creature's bigness; and its shape, during the systole, is nearly circular, being composed seemingly of two semilunar 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 semilunar 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 diffusion, 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 pulsations 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 vessels is indistinguishable by glases. 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, tho' no single current is any where 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 of the tail, and exhibiting a variety of contractions and dilatations. The belly is capable of stretching out (A) 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 abovementioned one, there are found in other kinds of 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 faculi, or integuments, fastened externally to the lower part of their shells somewhere about the tail: these faculi 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 a 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 wheels 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 aquatilis arboricola of Swammerdam, of which a figure is given from that author (Plate XXIV. B): 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 waters: 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 Plumed Polype. These animalcules dwell in colonies together, from ten to fifteen, (feldom falling short of the former number, or exceeding the latter), in a flimsy kind of mucilaginous or gelatinous case; which, out of the water, has no determined form, appearing like a little lump of slime; but, 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 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 sacculi, each of which includes one of these animals. The openings at the tops of these sacculi, 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.

Besides 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 animaleules 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 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 the 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 animaleules, 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, thro' a gut whose exit is near the neck. The body consists of three divisions; in the uppermost of which are contained all the abovementioned intestines, which are only to be discerned when the creature is full, at which time they become opaque. The other two divisions, 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 polypi; 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. Tho' 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 shew 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. shews all the creatures withdrawn into their cells, and the end of the bell hanging downwards.

Fig. 33. shews the bell erect, with only one of the animals coming out, in order to show its connection with the bell.

Fig. 34. shews the head and arms of a single polype closing together, and disposing themselves in order to be drawn into the bell.

Fig. 35. shews one complete animal greatly magnified, to show its several parts more distinctly; viz. a, the head, resembling an horse-shoe; b, the arms seen from one side; c, the narrow neck; d, the oesophagus; e, the stomach; f, the gut or last intestine thro' which the food passes after being digested in the stomach; g, the anus, where the faeces 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 animaleule, represented Globe 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 beget thinly round with short moveable hairs or brittle, which probably are the instruments by which their motions are performed. These animaleules 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. shews a piece piece of such a congeries broke off, where a a a represent the mouths or openings of the pipes wherein the little animals make their abode. Fig. 40. shews 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 *firingoides*.

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. shews 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 doth 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 glass 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 included insects were not more than as 1 to 1,150,000. 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 $\frac{1}{4}$ to $\frac{1}{2}$ an inch in length. About the head it has somewhat of a yellowish colour; but all the rest of the body is perfectly colourless and transparent, except the intestines, which are considerably opaque, and disposed as in the figure. Along its sides are several papillae, 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 $\frac{1}{10}$ of an inch in length: it sways 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.

10. Spermatic Animals, and Animalcula Infusoria. The discovery of living animalcules in the semen of spermatic animals, is claimed by Mr. Leeuwenhoek and Mr. Nicholas Hartsoeker; who both say, they published it about the end of the year 1677, or beginning of 1678: but Mr. Leeuwenhoek having given the most particular description of, and made by far the greatest number of experiments concerning them, the discovery is commonly attributed to him.

According to this naturalist, these animalcules are found in the semen masculinum of every kind of animal; but their general appearance is very much the same, nor doth their size differ in proportion to the bulk of the animal to which they belong. The bodies of all of them seem to be of an oblong oval form, with long, tapering slender tails issuing from them; and as by this shape they resemble tadpoles, they have been frequently called by that name; tho' the tails of them, in proportion to their bodies, are much longer than the tails of tadpoles are: and it is observable, that the animalcules in the semen of fishes, have tails much longer and more slender, than the tails of those in other animals; insomuch, that the extremity of them is not to be discerned without the best glasses, and the utmost attention. Fig. 21. No. 1, 2, 3, 4, represent the spermatic animalcules of the rabbit; and No. 5, 6, 7, 8, those of a dog; according to Mr. Leeuwenhoek.

The numbers of these animalcules are inconceivable. On viewing with a microscope, the milt, or semen masculinum of a living cod-fish, innumerable multitudes of animalcules were found therein, of such a diminutive size, that he supposed at least 10,000 of them capable of being contained in the bulk of a grain of sand; whence he concludes, that the milt of this single fish contained more living animalcules than there are to be found people living in the whole world. To find the comparative size of these animalcules, Mr. Leeuwenhoek placed an hair of his head near them; which hair, through his microscope, appeared an inch in breadth; and he was satisfied, that at least 60 such animalcules could easily lie within that diameter; whence, their bodies being spherical, it follows, that 216,000 of them are but equal to a globe whose diameter is the breadth of a hair. He observed, that, when the water wherewith he had diluted the semen of a cod-fish was exhaled, the little bodies of the animalcules burst in pieces; which did not happen to those in the semen of a ram; and this he imputes to the greater firmness and consistency of the latter, as the flesh of a land-animal is more compact than fish.

These animalcules appear to be very vigorous, and are continuous of life; for they may be observed to move long after the animal from which they are taken is dead. They have this peculiarity also, that they are continually in motion, without the least rest or intermission, provided: provided there is fluid sufficient for them to swim about in. These animalcules are peculiar to these men; nothing that has the least token of life being discovered, by the best glases, either in the blood, spittle, urine, gall, or chyle. Great numbers, however, are to be found in the whitish matter that sticks between the teeth; some of which are of an oval figure, and others resemble cels.

The Animalcule Infusoria, take their name from their being found in all kinds either of vegetable or animal infusions. Indeed, there is scarce any kind of water, unless impregnated with some mineral substance, but what will discover living creatures.—Mr Lewenhoeck says, that at first he could discover no living creatures in rain-water; but after standing some days, he discovered innumerable animalcules, many thousands of times less than a grain of sand, and in proportion to a mite as a bee is to a horse.—In other rain-water, which had likewise stood some time, he found the smallest sort he had ever seen; and, in a few days more, met with others eight times as big as these, and almost round.—In another quantity of rain-water, that had been exposed like the former, he discovered a kind of animalcules with two little horns in continual motion. The space between the horns was flat, though the body was roundish, but tapering a little towards the end; where a tail appeared, four times as long as the body, and the thickness of a spider's web. He observed several hundreds of these within the space a grain of sand would occupy. If they happened on the least filament or string, they were entangled in it; and then would extend their bodies into an oblong round, and struggle hard to disengage their tails. He observed a second sort of an oval figure, and imagined the head to stand at the sharpest end. The body was flat, with several small feet moving exceeding quick, but not discernible without a great deal of attention. Sometimes they changed their shape into a perfect round, especially when the water began to dry away. He met also with a third sort, twice as long as broad, and eight times smaller than the first: yet in these he discerned little feet, whereby they moved very nimbly. He perceived likewise a fourth sort, a thousand times smaller than a louse's eye, and which exceeded all the rest in briskness: he found these turning themselves round, as it were upon a point, with the celerity of a top. And he says, there were several other sorts.

The production of animalcule infusoria is very surprising. In four hours' time, an infusion of cantharides had produced animalcule less than even the tails of the spermatic animals we have already described. Neither do they seem to be subject to the fate of other animals; but, several kinds of them at least, by dividing themselves in two, to enjoy a sort of immortality. Nor do the common methods by which other animals are destroyed, seem to be effectual for destroying their vital principle. Hot mutton-gravy, secured in a vial with a cork, and afterwards set among hot ashes to destroy as effectually as possible every living creature that could be supposed to exist in it, has nevertheless been found swarming with animalcules after standing a few days.

In the Philosophical Transactions, Vol. LIX., we have the following curious account, given us by Mr Ellis, of animalcules produced from an infusion of potatoes and hempseed.

"On the 25th of May 1768, Fahrenheit's thermo-

meter 70°, I boiled a potatoe in the New-River water till it was reduced to a mealy consistence. I put part of it, with an equal proportion of the boiling liquor, into a cylindrical glass-vessel that held something less than half a wine-pint, and covered it close immediately with a glass-cover. At the same time, I sliced an unboiled potatoe; and, as near as I could judge, put the same quantity into a glass-vessel of the same kind; with the same proportion of New River water not boiled; and covered it with a glass cover; and placed both vessels close to each other.

"On the 26th of May, 24 hours afterwards, I examined a small drop of each, by the first magnifier of Wilson's microscope, whose focal distance is reckoned at \( \frac{1}{10} \) part of an inch; and, to my amazement, they were both full of animalcule of a linear shape, very distinguishable, moving to and fro with great celerity; so that there appeared to be more particles of animal than vegetable life in each drop.

"This experiment I have repeatedly tried, and always found it to succeed in proportion to the heat of the circumambient air; so that even in winter, if the liquors are kept properly warm, at least in two or three days the experiment will succeed.

"What I have observed are infinitely smaller than spermatic animals, and of a very different shape: the truth of which, every accurate observer will soon be convinced of, whose curiosity may lead him to compare them; and I am persuaded he will find they are no way akin.

"At present I shall pass over many other curious observations, which I have made on two years experiments, in order to proceed to the explaining a hint which I received last January from Mr De Saufure of Geneva, when he was here; which is, that he found one kind of these animalcule infusoria that increase by dividing across into nearly two equal parts.

"I had often seen this appearance in various species a year or two ago, as I found upon looking over the minutes I had taken when I made any new observation; but always supposed the animal, when in this state, to be in coition.

"Not hearing, till after M. De Saufure left this kingdom, from what infusion he had made his observation; his friend Dr de la Roche of Geneva informed me, the latter end of February last, that it was from hempseed.

"I immediately procured hempseed from different feeds-men in distant parts of the town. Some of it I put into New-River water, some into distilled water, and some I put into very hard pump water. The result was, that in proportion to the heat of the weather, or the warmth in which they were kept, there was an appearance of millions of minute animalcule in all the infusions; and, some time after, some oval ones made their appearance, as at fig. 3, b, c. These were much larger than the first, which still continued; these wriggled to and fro in an undulatory motion; turning themselves round very quick all the time that they moved forwards. I was very attentive to see these animals divide themselves; and at last I perceived a few of the appearance of fig. 3, d, e, as it is represented by the first magnifier of Wilson's in two microscopes; but I am so well convinced by experience, that they would separate, that I did not wait to see the operation; however, as the following sketches, which I have drawn from five other species, will very fully ex- plain this extraordinary phenomenon, there will be no difficulty in conceiving the manner of the first. See Plate XXIV figs. 4, 5, 6, 7, 8.

"The proportion of the number of these animals which I have observed to divide in this manner, to the rest, is scarce 1 to 50; so that it appears rather to arise from hurts received by some few animalcules among the many, than to be the natural manner in which these kinds of animals multiply; especially if we consider the infinite quantity of young ones which are visible to us through the transparent skins of their bodies, and even the young ones that are visible in those young ones while in the body of the old ones.

"But nothing more plainly shews them to be zoophytes, than this circumstance, That when, by accident, the extremity of their bodies has been shrivelled for want of a supply of fresh water, the applying more fresh water has given motion to the part of the animal that was still alive; by which means, this shapeless figure has continued to live and swim to and fro all the time it was supplied with fresh water.

"I cannot finish this part of my remarks on these animals, without observing, that the excellent Linnæus has joined the beroe with the volvox, one of the animalcula infusoria. The beroe is a marine animal, found on our coasts; of a gelatinous transparent nature, and of an oval or spherical form, about half an inch to an inch diameter; divided like a melon into longitudinal ribs, each of which is furnished with rows of minute fins; by means of which, this animal, like the animalcula infusoria, can swim in all directions with great swiftness. In the same manner I have seen most of those minute animals move so swift that we could not account for it, without supposing such a provision in nature, which is really true, but cannot be seen till the animals grow faint for want of water; then, if we attend, we may with good glasses plainly discover them.

"I have lately found out, by mere accident, a method to make their fins appear very distinctly, especially in the larger kind of animalcules, which are common to most vegetable infusions; such as the terebella. This has a length body, with a cavity or groove at one end, like a gimlet: by applying, then, a small stalk of the horse-hoe geranium, (or geranium zonale of Linnæus), fresh broken, to a drop of water in which these animalcules are swimming, we shall find that they will become torpid instantly; contracting themselves into an oblong oval shape, with their fins extended like so many brittle all round their bodies. The fins are in length about half the diameter of the middle of their bodies. Before I discovered this expedient, I tried to kill them by different kinds of salts and spirits; but though they were destroyed by this means, their fins were so contracted, that I could not distinguish them in the least. After lying in this state of torpidity for two or three minutes, if a drop of clean water is applied to them, they will recover their shape, and swim about immediately, rendering their fins again invisible."

Fig. 3, 4, 5, 6, 7, 8, represent different species of animalcules infusoria, mentioned by Mr Ellis as belonging to the genus of volvox of Linnæus.

Fig. 3 represents the volvox ovalis, or egg-shaped volvox; at (b) and (c) it is expressed in its natural shape; at (a) the manner in which it becomes two ani-

Vol. I. that those plants which formerly were supposed to be produced by equivocal generation arose from seeds, and the animals, in like manner, from a male and female. But as the microscope threw light upon one part of nature, it left another involved in darkness; for the origin of the animalcule infusoria, or of the spermatic animals already mentioned, remains as yet as much unknown as that of many other kinds was when the doctrine of equivocal generation reigned in full force.

The discovery of spermatic animalcules was thought to throw some light on the mysterious affair of generation itself, and these minute creatures were imagined to be each of them individuals of the same species with the parent. Here the infinite number of these animalcules was an objection, and the difficulty remained as great as before; for, as every one of these animalcules behoved to be produced from a male and female, to explain their origin by animalcular generation in the same manner, was only explaining generation by itself.

This hypothesis, therefore, having proved unsatisfactory, others have been invented. Mr. Buffon, particularly, hath invented one, by which he at once annihilates the whole animalcular world; and in this he hath been followed by several very ingenious philosophers. For a particular account of this, so far as it concerns generation, we must refer to that article; but as he gives such a particular account of his having examined the human semen, that we cannot doubt of his accuracy, we shall here contrast his account with that of Mr. Leeuwenhoek already mentioned.

Having procured the seminal vessels of a man who died a violent death, he extracted all the liquor from them while they were still warm; and having examined a drop of it with a double microscope, it had the appearance fig. 9. Large filaments appeared, which in some places spread out into branches, and in others intermingled with one another. These filaments clearly appeared to be agitated by an internal undulatory motion, like hollow tubes, which contained some moving substance. He saw distinctly this appearance changed for that fig. 10. Two of these filaments, which were joined longitudinally, gradually separated from each other in the middle, alternately approaching and receding, like two tense cords fixed by the ends, and drawn asunder in the middle. These filaments were composed of globules that touched one another, and resembled a chaplet of beads. After this, he observed the filaments swelled in several places, and perceived small globular bodies issue from the swelled parts, which had a vibratory motion like a pendulum. These small bodies were attached to the filaments by small threads, which gradually lengthened as the bodies moved. At last, the small bodies detached themselves entirely from the filaments, drawing after them the small thread, which looked like a tail. When a drop of the seminal liquor was diluted, these small bodies moved in all directions very briskly; and had he not seen them separate themselves from the filaments, he would, he says, have thought them to be animals. The seminal matter was at first too thick, but gradually became more fluid; and, in proportion as its fluidity increased, the filaments disappeared, but the small bodies became exceedingly numerous. Each of them had a long thread or tail attached to it, from which it evidently endeavoured to get free. Their progressive motion was extremely slow, during which they vibrated to the right and left, and at each vibration they had a rolling unsteady motion in a vertical direction.

At the end of two or three hours, the seminal matter becoming still more fluid, a greater number of these moving bodies appeared. They were then more free of incumbrances; their tails were shorter; their progressive motion was more direct, and their horizontal motion greatly diminished. In five or six hours, the liquor had acquired almost all the fluidity it could acquire, without being decomposed. Most of the small bodies were now disengaged from their threads; their figure was oval. They moved forward with considerable quickness, and, by their irregular motions backward and forward, they had now more than ever the appearance of animals. Those that had tails adhering to them, seemed to have less vivacity than the others; and of those that had no tails, some altered both their figure and their size. In twelve hours, the liquor had deposited at the bottom of the vial a kind of ash-coloured gelatinous substance, and the fluid at top was almost as transparent as water. The little bodies being now entirely freed from their threads, moved with great agility, and some of them turned round their centres. They also often changed their figures, from oval becoming round, and often breaking into smaller ones. Their activity always increased as their size diminished. In 24 hours, the liquor had deposited a greater quantity of gelatinous matter, which, being with some difficulty diluted in water, exhibited an appearance somewhat resembling lace. In the clear semen itself only a few small bodies were now seen moving; next day, these were still farther diminished; and after this nothing was to be seen but globules, without the least appearance of motion. Most of the above-mentioned appearances are shown fig. 10, 11, 12, 13, 14, 15, 16. Fig. 17. and 18. represent an appearance of the globules in another experiment, in which they arranged themselves in troops, and palled very quickly over the field of the microscope. In this experiment they were found to proceed from a small quantity of gelatinous mucilage.

From these experiments, Mr. Buffon concludes, that what have been called spermatic animals, are not creatures really endowed with life, but something proper to compose a living creature; and he distinguishes them by the name of organic particles. The same individual kinds of animals he declares he has found in the fluids separated from the ovaria of females; and for the truth of this appeals to the testimony of Mr Needham, who was an eye-witness of his experiments. He also brings an additional proof of his doctrine from Mr Needham's observations on the milt of the calmar, a species of cuttle-fish. Here the spermatic animals, at least what have the only appearance of life, are vastly larger than in any other creature, so as to be plainly visible to the naked eye. When magnified, they appear as at fig. 19. and 20. a. Their first appearance is at fig. 19. a and b, when they resemble springs inclosed in a transparent case. These springs were equally perfect at first as afterwards; only in time they contracted themselves, and became like a kind of screw. The head of the case is a species of valve which opens outward, and through which everything within may be forced out. It contains, besides, another valve b, a little barrel c, and a spongy... Thus the whole machine consists of an outer transparent cartilaginous case, the superior extremity of which is terminated by a round head formed by the case itself, and performs the office of a valve. This external case contains a transparent tube; which includes the spring, a piston or valve, a little barrel, and a spongy substance. The screw occupies the superior part of the tube and case, the piston and barrel are situated in the middle, and the spongy substance occupies the inferior part. These machines pump the liquor of the milk; the spongy substance is full of this liquor; and, before the animal spawns, the whole milk is only a congeries of these bodies which have sucked up all the liquor of it. Whenever these small machines are taken out of the body of the animal, and put in water, or exposed to the air, they begin to act, as represented fig. 19. and 20.; the spring mounts up, and is followed by the piston, the barrel, and the spongy substance which contains the liquor; and, as soon as the spring and the tube in which it is contained begin to issue out of the case, the spring plait, and the whole internal apparatus moves, till the spring, the piston, and the barrel, have entirely escaped from the case. When this is effected, all the rest instantly follow, and the milky liquor which had been pumped in, and confined in the spongy substance, runs out through the barrel.

According to this account, the milk of the calf contains no animalcules; and therefore we may from analogy conclude, that the small moving bodies which are to be seen in the semen of other animals, are not really creatures endowed with life. Mr Buffon extends the analogy still further; and concludes, that all the moving bodies which are to be found in the infusions either of animal or vegetable substances are of a similar nature. "To discover, says he, whether all the parts of animals, and all the seeds of plants, contained moving organic particles, I made infusions of the flesh of different animals, and of the seeds of more than 20 different species of vegetables; and after remaining some days in close glasses, I had the pleasure of seeing organic moving particles in all of them. In some they appeared sooner, in others later; some preferred their motions for months, and others soon lost it. Some at first produced large moving globules resembling animals, which changed their figure, split, and became gradually smaller. Others produced only small globules, whose motions were extremely rapid; and others produced filaments, which grew longer, seemed to vegetate, and then swelled and poured forth torrents of moving globules."

This last observation gave rise to a new system. Baron Munchausen, perceiving that the last mentioned moving globules, after moving for some time, began again to vegetate, concluded that they were first animals and then plants.—This strange hypothesis Mr Ellis has overturned in the paper already quoted; in which he asserts, that they are no other than the seeds of that genus of fungi called mucor or moulding; and that their motion is owing to numbers of minute animalcules attacking them for food. "Having (says he), at the request of Dr Linnæus, made several experiments on the infusion of mushrooms in water, in order to prove the theory of Baron Munchausen, that their seeds are first animals, and then plants, (which he takes notice of in his System of Nature, p. 1326;) under the genus of chaos, by the name of chaos fungorum seminum) it appeared evidently, that the seeds were put into motion by very minute animalcules, which proceeded from the putrefaction of the mushroom: for, by pecking at these seeds, which are reddish, light, round bodies, they moved them about with great agility in a variety of directions; while the little animals themselves were scarce visible, till the food they had eaten had discovered them. The satisfaction I received from clearing up this point, led me into many other curious and interesting experiments.

"The ingenious Mr Needham supposes these little transparent ramified filaments, and jointed or coraloid bodies, which the microscope discovers to us on the surface of most animal and vegetable infusions when they become putrid, to be zoophytes, or branched animals: but to me they appear, after a careful scrutiny with the best glasses, to be of that genus of fungi called mucor, or moulding; many of which Michelius has figured, and Linnæus has accurately described.

"Their vegetation is so amazingly quick, that they may be perceived in the microscope even to grow and feed under the eye of the observer.

"Mr Needham has pointed out to us a species that is very remarkable for its parts of fructification. (See Philosophical Transactions, vol. xlv. tab. 5. fig. 3, n. A.) This, he says, proceeded from an infusion of bruised wheat.

"I have seen the same species arise from the body of a dead fly, which was become putrid by lying floating for some time in a glass of water, where some flowers had been in the month of August, 1768. This species of mucor sends forth a mass of transparent filamentous roots; from whence arise hollow stems, that support little oblong oval seed-vessels, with a hole on the top of each. From these I could plainly see minute globular seeds issue forth in great abundance with an elastic force, and turn about in the water as if they were animated.

"Continuing to view them with some attention, I could just discover, that the putrid water which surrounded them was full of the minute animalcules; and that these little creatures began to attack the seeds of the mucor for food, as I have observed before in the experiment on the seeds of the larger kind of fungi or mushrooms. This new motion continued the appearance of their being alive for some time longer: but, soon after, many of them arose to the surface of the water, remaining there without motion; and a succession of them afterwards coming up, they united together in little thin masses, and floated to the edge of the water, remaining there quite inactive during the time of observation.

"As this discovery cleared up many doubts which I had received from reading Mr Needham's learned dissertation, I put into the glass several other dead flies, by which means this species of mucor was propagated so plentifully, as to give me an opportunity of frequently trying the same experiment to my full satisfaction.

"Lately, these jointed coraloid bodies, which Mr Needham calls chaplets and pearl necklaces, I have seen frequently very distinctly. These appear not only on an infusion of bruised wheat when it becomes putrid, but on most other bodies when they throw up a viscid scum and are in a state of putrefaction. These, then, are evidently no more than the most common mucor, the..." seeds of which are everywhere floating in the air; and bodies in this state afford them a natural proper foil to grow upon. Here they send downwards their fine transparent ramified roots into the moisture which they float upon; and from the upper part of the scum, their jointed coraloid branches rise full of seed into little grovelike figures. When a small portion of these branches and seeds are put into a drop of the same putrid water upon which the scum floats, many of these millions of little animalcules with which it abounds, immediately seize them as food, and turn them about with a variety of motions, as in the experiments on the seeds of the common mushrooms, either singly, or two or three seeds connected together; answering exactly to Mr Needham's description, but evidently without any motion of their own, and consequently not animated."

Mr Buffon, however, is not content with denying life only to those beings where the signs of it are the most equivocal; but includes in the same rank of organic particles, almost every animal too small to be discovered by the naked eye, and even some of those whose motions are evidently perceptible to the eye. "Almost all microscopic animals," says he, "are of the same nature with the moving bodies in the seminal fluids and infusions of animal and vegetable substances. The cells in paste, in vinegar, &c. are all of the same nature, and derived from the same origin. There are, perhaps, as many beings that either live or vegetate, produced by a fortuitous assemblage of organic particles, as by a constant and successive generation. Some of them, as those of the calmar, are only a kind of machines, which, though exceedingly simple, are very active. Others, as the spermatic animalcules, seem to imitate the movements of animals. Others resemble vegetables in their manner of growth and extension. There are others, as those of blighted wheat, which at pleasure can be made alternately either to live or die, and it is difficult to know what they should be compared. There are still others, and in great numbers, which are at first a kind of animals, then become a species of vegetables, and again return alternately to their vegetable state. The cells in paste have no other origin than the union of the organic particles of the most essential part of the grain. The first cells that appear are certainly not produced by other cells; but tho' they are not propagated themselves, they fail not to engender other living cells. By cutting them with the point of a lancet, we discover smaller cells issuing in great numbers out of their bodies. The body of this animal seems to be only a sheath or sac, containing a multitude of smaller animals, which perhaps are other sheaths of the same kind, in which the organic matter is assimilated into the form of cells."

Though we can by no means pretend to account for the appearance of these animalcules, yet we cannot help observing, that our ignorance of the cause of any phenomenon is no argument against its existence. Though we are not able to account in a satisfactory manner for the origin of the native Americans, we suppose Mr Buffon himself would reckon it absurd to maintain that the Spaniards on their arrival there found only organic particles moving about in disorder. The case is the very same with the cells in paste. They are exceedingly minute in comparison with us; but, with the solar microscope, Mr Baker has made them assume a more respectable appearance, so as to have a diameter of an inch and an half, or two inches, and a length proportional. They swarm up and down very briskly; the motion of their intestines was plainly visible; when the water dried up, they died with apparent agonies, and (B) their mouths gaped very wide. Were we to find a creature of the size of this magnified cell, gaffing in a place where water had lately been, we certainly would never conclude it to be an organic particle, or a fortuitous assemblage of them; but a fish. Why then should we conclude otherwise with regard to the cell while in its natural state, than that it is a little fish? In reasoning on this subject, we ought always to remember, that, however essential the distinction of bodies into great and small may appear to us, they are not so to the Deity; with whom, as Mr Baker well expresses himself, "an atom is as a world, and a world but as an atom."—Were the Deity to exert his power for a little, and give a natural philosopher a view of a quantity of paste filled with cells, from each of whose bodies the light was reflected as when it passes through a solar microscope; instead of imagining them organic particles, the paste would appear like a little mountain; he would probably look upon the whole as a monstrous assemblage of serpents; and be afraid to come near them.

Wherever, therefore, we discover beings to appearance endowed with the principle of self-preservation, or whatever else we make the characteristic of animals, neither the smallness of their size, nor the impossibility of our knowing how they come there, ought to cause us doubt of their being really animated.—At the same time, it must also be remembered, that motion is not always a characteristic of animal life, even though the moving bodies should avoid one another, or any seeming obstacle placed in their way. We know, that inanimate bodies, when electrified, will avoid others endowed with an electricity of the same kind, and adhere to those which have the opposite one. As we are by no means acquainted with the utmost powers of electricity, but on the contrary, from what we do know of it have all the reason in the world to conclude that it can produce effects utterly beyond our comprehension, it is impossible for us to know what share it may have in producing the motions observed in vegetable-infusions, or in the semen of animals.—We may also further observe, that though in Mr Ellis's experiment of the boiled potatoe he took it for granted that every seed of animal life would be destroyed by the boiling water, yet even this cannot be proved; nay, on the contrary, it hath been proved by undeniable experiments, that the human body itself hath endured a heat of 240 degrees of Fahrenheit (28 degrees above that of boiling water) without injury. The eggs of these animalcules might therefore be strong enough to resist the heat hitherto used in Mr Ellis's or any other experiment.

A considerable objection to the existence of animalcules in the semen, or any other part of animal bodies, must arise from the total exclusion of air, which is found so necessary to the life of larger animals. Some instances, however, have been observed of large animals being found in such situations as they could not possibly have enjoyed the least benefit from the air for a great number of years; and in this state they have not only lived, but lived much longer than they would otherwise have done. In Toulon harbour, and the road, are found solid hard stones, and perfectly entire; containing, in different cells, secluded from all communication with the air, several living shell-fish, of an exquisite taste, called Dae- tyli, i.e. Dates: to come at these fish, the stones are broken with mauls. Also, along the coast of Anco- nia, in the Adriatic, are stones usually weighing about 50 pounds, and sometimes even more; the outside rug- ged, and easily broken; but the inside so hard, as to require a strong arm and an iron maul to break them: within them, and in separate niches, are found small shell-fish, quite alive, and very palatable, called Solenae or Cappe lumbus. These facts are attested by Gaffendi, Blondel, Mayol, the learned bishop of Salturara, and more particularly by Aldrovandi a physician of Bo- logna. The two latter speak of it as a common fact, which they themselves saw.

In the volume for 1719, of the Academy of Sciences at Paris, is the following passage.

"In the foot of an elm, of the bigness of a pretty corpulent man, three or four feet above the root, and exactly in the centre, has been found a live toad, middle-sized, but lean, and filling up the whole vacant space: no sooner was a passage opened, by splitting the wood, than it scuttled away very hastily: a more firm and sound elm never grew; so that the toad cannot be supposed to have got into it. The egg whence it was formed, must, by some very singular accident, have been lodged in the tree at its first growth. There the crea- ture had lived without air, feeding on the substance of the tree, and growing only as the tree grew. This is attested by Mr Hubert, professor of philosophy at Caen."

The volume for the year 1731 has a similar obser- vation, expressed in these words.

"In 1719 we gave an account of a fact, which, tho' improbable, was well attested; that a toad had been found living and growing in the stem of a middling elm, with- out any way for the creature to come out or to have got in. M. Seigne, of Nantes, lays before the aca- demy a fact just of the very same nature, except that, instead of an elm, it was an oak, and larger than the elm, which still heightens the wonder. He judges, by the time requisite for the growth of the oak, that the toad must have subsisted in it, without air, or any adventi- tious aliment, during 80 or 100 years. M. Seigne seems to have known nothing of the fact in 1719."

With the two foregoing may be clasped a narrative of Ambrose Pare chief surgeon to Henry III. king of France, who, being a very sensible writer, relates the following fact, of which he was an eye-witness.

"Being (says he) at my feet, near the village of Meudon, and overlooking a quarry-man whom I had set to break some very large and hard stones; in the middle of one we found a huge toad, full of life, and without any visible aperture by which it could get there. I began to wonder how it received birth, had grown and lived; but the labourer told me, it was not the first time he had met with a toad, and the like creatures, within huge blocks of stone, and no visible opening or fissure."

Observations of living toads, found in very hard and entire stones, occur in several authors, particularly Baptist Fulgoia doge of Genoa, the famous phy- sicians Agricola and Horitius, and lord Verulam; others give very specious account of snakes, frogs, crabs, and lobsters, being found alive, inclosed within blocks of marble, rocks, and large stones.

An instance similar to these, of the truth of which we have no reason to doubt, was observed in this coun- try in the year 1773, where a large toad was found in the middle of a piece of coal having not the least visible crack or fissure.

Upon the whole, therefore, though philosophers are not yet able to discover how these minute creatures are produced; yet, that there really are animals much smaller than what we can discern with our naked eye, seems to be indisputable. The subject, however, is still evidently obscure, and will no doubt require the ut- most attention of philosophers, as well as further im- provements in the construction of microscopes, fully to investigate it.