CURIOSITIES RESPECTING INSECTS.—(Concluded.)

Animalcules—The Cheese Mite—The Hydra, or Polypes.

Animalcules.

The microscope discovers legions of animalcules in most liquors, as water, vinegar, beer, dew, &c. They are also found in rain, and several chalybeate waters, and in infusions of both animal and vegetable substances, as the seminal fluids of animals, pepper, oats, wheat, and other grain, tea, &c. &c. The contemplation of animalcules has rendered the term, infinitely small bodies, extremely familiar to us. A mite was anciently thought the limits of littleness; but we are not now surprised, to be told of animals twenty-seven millions of times smaller than a mite. Minute animals are found proportionably much stronger, more active and vivacious, than large ones. The spring of a flea in its leap, how vastly does it outskip any thing the larger animals are capable of! A mite, how vastly swifter does it run than a race-horse! M. De. L’Isle has given the computation of the velocity of a little creature, scarcely visible by its smallness; which he found to run three inches in half a second: supposing now its feet to be the fifteenth part of a line, it must make five hundred steps in the space of three inches; that is, it must shift its legs five hundred times in a second, or in the ordinary pulsation of an artery. The excessive minuteness of microscopical animalcules conceals them from the human eye. One of the wonders of modern philosophy is, to have invented means for bringing objects, to us so imperceptible, under our cognizance and inspection: creatures, a thousand times too little to be able to affect our sense, should seem to have been very safe; yet we have extended our views over animals, to whom these would be mountains. In reality, most of our microscopical animalcules are of so small a magnitude, that through a lens, whose focal distance is the tenth-part of an inch, they only appear as so many points; that is, their parts cannot be distinguished, so that they appear from the vertex of that lens under an angle not exceeding a minute.

If we investigate the magnitude of such an object, it will be found nearly equal to ³/100000 of an inch long. Supposing, therefore, these animalcules of a cubic figure, that is, of the same length, breadth, and thickness, their magnitude would be expressed by the cube of the fraction ³/100000, that is, by the number ²⁷/1000,000,000,000,000 that is, so many parts of a cubic inch, is each animalcule equal to. Leuwenhoek calculates, that a thousand millions of animalcules, which are discovered in common water, are not altogether so large as a grain of sand. In the milt of a single cod-fish, there are more animals than there are upon the whole earth; for a grain of sand is bigger than four millions of them. The white matter that sticks to the teeth also abounds with animalcules of various figures, to which vinegar is fatal; and it is known, that vinegar contains animalcules in the shape of eels. In short, according to this author, there is scarcely any thing which corrupts, without producing animalcules. Animalcules are said to be the cause of various disorders. The itch is known to be a disorder arising from the irritation of a species of animalcules found in the pustules of the body; when the communication of it by contact from one to another is easily conceived, as also the reason of the cure being effected by cutaneous applications.

In the Philosophical Transactions, vol. 89, is a curious account of animalcules produced from an infusion of potatoes, and another of hemp-seed, by the late Mr. Ellis.

“On the 25th of May, 1768,” he says, “Fahrenheit’s thermometer 70°, I boiled a potato 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 immediately covered it close with a glass cover. At the same time I sliced an unboiled potato, 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, covering it with a glass cover, placed both vessels together. On the 26th of May, twenty-four hours afterwards, I examined a small drop of each by the first magnifier of Wilson’s microscope, whose focal distance is reckoned ¹/50th part of an inch; and, to my amazement, they were both full of animalcules, 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 for two or three days, the experiment will succeed. I procured hemp-seed from different seedsmen, in different parts of the town; some of it I put into the New-River water, some into distilled water, and some into very hard pump-water: the result was, that in proportion to the heat of the weather, or warmth in which they were kept, there was an appearance of millions of minute animalcules in all the infusions; and, some time after, oval ones made their appearance, 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 they moved forwards.”

The Cheese-mite.—This minute creature is a favourite subject for microscopic observations. It is covered with hairs or bristles, which resemble in their structure the awns of barley, being barbed on each side with numerous sharp-pointed processes. The mite is oviparous: from the eggs proceed the young animals, resembling the parents in all respects, except in the number of legs, which at first amount only to six, the pair from the head not making their appearance till after casting their first skin. The eggs, in warm weather, hatch in about a week, and the young animal may be seen sometimes for a day together struggling to get rid of its egg-shell. The mite is a very voracious animal, feasting equally upon animal and vegetable substances. It is also extremely tenacious of life: for, upon the authority of Leuwenhoek, though highly discreditable to his sense of humanity, we are assured that a mite lived eleven weeks after he had glued it to a pin, in order to make his observations.

We shall close the account of the curiosities of insects with a description of The Hydra, or Polypes.—In natural history, this is a genus of the Vermes Zoophyta class and order; an animal fixing itself by the base; linear, gelatinous, naked, contractile, and furnished with setaceous tentaculÆ, or feelers; inhabiting fresh waters, and producing its deciduous offspring, or eggs, from the sides. There are five species, H. gelatinosa, minute and gelatinous, milk-white, cylindrical, with twelve tentaculÆ shorter than the body: it inhabits Denmark, in clusters on the under side of Fuci. But on the viridis, the fusca, and the grisca, the greatest number of experiments have been made by naturalists, to ascertain their true nature and very wonderful habits. They are generally found in ditches. Whoever has carefully examined these, when the sun is very powerful, will find many little transparent lumps of the appearance of jelly, the size of a pea, and flatted upon one side. The same kind of substances are likewise to be met with on the under side of the leaves of plants that grow in such places. These are the polypes in a quiescent state, and apparently inanimate. They are generally fixed by one end to some solid substance, with a large opening, which is the mouth; the other having several arms fixed round it, projecting as rays from the centre. They are slender, pellucid, and capable of contracting themselves into a very small compass, or of extending to a considerable length. The arms are capable of the same contraction and expansion as the body, and with these they lay hold of minute worms and insects, bringing them to the mouth, and swallowing them. The indigestible parts are again thrown out by the mouth.

The green polype was that first discovered by M. Trembley: and the first appearances of spontaneous motion were perceived in its arms, which it can contract, expand, and twist about in various directions. On the first appearance of danger, they contract to such a degree, that they seem little longer than a grain of sand, of a fine green colour, the arms disappearing entirely. Soon afterwards, he found the grisca, and afterwards the fusca. The bodies of the viridis and grisca diminish almost insensibly from the anterior to the posterior extremity; but the fusca is for the most part of an equal size, for two-thirds of its length, from the anterior to the posterior extremities, from which it becomes abruptly smaller, and then continues of a regular size to the end. These three kinds have at least six, and at most twelve or thirteen arms. They can contract themselves till their bodies do not exceed one-fourth of an inch in length, and they can stop at any intermediate degree of expansion or contraction. They are of various sizes, from an inch to an inch and a half long. Their arms are seldom longer than their bodies, though some have them an inch, and some even eight inches long. The thickness of their bodies decreases as they extend themselves, and vice versÂ; and they may be made to contract themselves, either by agitating the water in which they are contained, or by touching the animals themselves. When taken out of the water, they all contract so much, that they appear only like a little lump of jelly. They can contract or expand one arm, or any number of arms, independently of the rest; and they can likewise bend their bodies or arms in all possible directions. They can also dilate or contract their bodies in various places, and sometimes appear thick set with folds, which, when carelessly viewed, appear like rings. Their progressive motion is performed by that power which they have of contracting and dilating their bodies. When about to move, they bend down their heads and arms; lay hold by means of them, or some other substance to which they design to fasten themselves; then they loosen their tail, and draw it towards the head; then either fix it in that place, or stretching forward their head as before, repeat the same operation. They ascend or descend at pleasure in this manner upon aquatic plants, or upon the sides of the vessel in which they are kept; they sometimes hang by the tail from the surface of the water, or sometimes by one of their arms; and they can walk with ease upon the surface of the water. On examining the tail with a microscope, a small part of it will be found to be dry above the surface of the water, and, as it were, in a little concave space, of which the tail forms the bottom; so that it seems to be suspended on the surface of the water, on the same principle that a small pin or needle is made to swim. When a polype, therefore, means to pass from the sides of the glass to the surface of the water, it has only to put that part out of the water by which it is supported, and to give it time to dry, which it always does upon these occasions; and they attach themselves so firmly by the tail to aquatic plants, stones, &c. that they cannot be easily disengaged: they often further strengthen these attachments by means of one or two of their arms, which serve as a kind of anchors for fixing them to the adjacent substances.The fusca has the longest arms, and makes use of the most curious manoeuvres to seize its prey. They are best viewed in a glass seven or eight inches deep, when their arms commonly hang down to the bottom. When this or any other kind is hungry, it spreads its arms in a kind of circle to a considerable extent, inclosing in this, as in a net, every insect which has the misfortune to come within the circumference. While the animal is contracted by seizing its prey, the arms are observed to swell like the muscles of the human body when in action. Though no appearance of eyes can be observed in the polype, they certainly have some knowledge of the approach of their prey, and shew the greatest attention to it as soon as it comes near them. It seizes a worm the moment it is touched by one of the arms, and in conveying it to the mouth, it frequently twists the arm into a spiral line like a corkscrew, by which means the insect is brought to the mouth in a much shorter time than otherwise it would be; and so soon are the insects on which the polypes feed killed by them, that M. Fontana thinks they must contain the most powerful kind of poison; for the lips scarcely touch the animal, when it expires, though there cannot be any wound perceived on it when dead. The worm, when swallowed, appears sometimes single, sometimes double, according to circumstances. When full, the polype contracts itself, hangs down as in a kind of stupor, but extends again in proportion as the food is digested, and the excrementitious part is discharged.

The manner in which the polypes propagate, is most perceptible in the grisca and fusca, as being considerably larger than the viridis. If we examine one of them in summer, when the animals are most active, and prepared for propagation, some small tubercles will be found proceeding from its sides, which constantly increase in bulk, until at last, in two or three days, they assume the figure of small polypes. When they first begin to shoot, the excrescence becomes pointed, assuming a conical figure and deeper colour than the rest of the body. In a short time it becomes truncated, and then cylindrical, after which the arms begin to shoot from the anterior end. The tail adheres to the body of the parent animal, but gradually grows smaller, until at last it hangs only by a point, and is then ready to be separated. When this is the case, both the mother and young ones fix themselves to the sides of the glass, and are separated from each other by a sudden jerk. The time requisite for the formation of the young ones is very different, according to the warmth of the weather, and the nature of the food eaten by the mother. Sometimes they are fully formed, and ready to drop off, in twenty-four hours; in other cases, when the weather is cold, fifteen days have been requisite for bringing them to perfection. The polypes produce young ones indiscriminately from all parts of their bodies, and five or six young ones have frequently been produced at once; nay, M. Trembley has observed nine or ten produced at the same time.

When a polype is cut transversely, or longitudinally, into two or three parts, each part in a short time becomes a perfect animal; and so great is this prolific power, that a new animal will be produced, even from a small portion of the skin of the old one. If the young ones be mutilated while they grow upon the parent, the parts so cut off will be re-produced; and the same property belongs to the parent. A truncated portion will send forth young ones before it has acquired a new head and tail of its own, and sometimes the head of the young one supplies the place of that which should have grown out of the old one. If we slit a polype longitudinally through the head to the middle of the body, we shall have one formed with two heads; and by again slitting these in the same manner, we may form one with as many heads as we please. A still more surprising property of these animals is, that they may be grafted together. If the truncated portions of a polype be placed end to end, and gently pushed together, they will unite into a single one. The two portions are first joined together by a slender neck, which gradually fills up and disappears, the food passing from one part into the other; and thus we may form polypes, not only from different portions of the same animal, but from those of different animals. We may fix the head of one to the body of another, and the compound animal will grow, eat, and multiply, as if it had never been divided. By pushing the body of one into the mouth of another, so far that their heads may be brought into contact, and kept in that situation for some time, they will at last unite into one animal, only having double the usual number of arms. The hydra fusca may be turned inside out like a glove, at the same time that it continues to eat and live as before. The lining of the stomach now forms the outer skin, and the former epidermis constitutes the lining of the stomach.