POLYPE, or POLYUS, in zoology, a small freshwater insect, belonging to the genus of hydra, in the class of worms, and order of zoophytes, in the Linnaean system; which, when cut into a number of separate pieces, becomes in a day or two so many distinct and separate animals; each piece having the surprising property of producing a head and tail, and the other organs necessary for life, and all the animal-functions.
The first discovery of this animal was owing to M. LeuwenHOCK, who, in the year 1703, presented to the Royal Society of London a description of it, and an account of its uncommon way of producing its young: but the discovery of its amazing property of reproducing the several organs from its various pieces was not made till the year 1740, by M. TREMBLEY, at the Hague.
The production of its young is indeed different from the common course of nature in other animals: for the young one issues from the sides of its parent in form of a small pimple or protuberance, which, lengthening and enlarging every hour, becomes in about two days a perfect animal, and drops from off its parent to shift for itself: but before it does this, it has often another growing from its side; and sometimes a third from it, even before the first is separated from its parent.
M. TREMBLEY observes, that there is no distinguished place in the body of the polypus by which the young are brought forth. He has seen some of them that have produced young ones from all the exterior parts of their bodies.
They breed quicker in hot than in cold weather; and what is very extraordinary is, that there never has yet been discovered among them any distinction of sex or appearance of copulation; every individual of the whole species being prolific, and that as much if kept separate, as if suffered to live among others.
If the method of this little animal's producing its young be very amazing, its reproduction of the several parts, when cut off, is much more so. The discovery of this was perfectly accidental; for M. TREMBLEY, who had often met with the creature in the water, and from its fixed residence in one place, and some other observations, not being able to determine whether it was an animal or a vegetable, made the trial by cutting it asunder; when, to his amazement, he found, that in a few days each of those pieces was become a perfect animal, the head part having shot forth a tail, and the tail a head.
A thousand other trials, by cutting the animal in different manners, first by M. TREMBLEY, and afterwards, at his request, by Monf. REAUMUR and BERNARD de
de Jussieu at Paris, and Mr Folkes, Mr Baker, and the other naturalists in England, were the result of this; and all succeeded in the same manner by those who repeated them.
It is not easy to say what is the size of this creature; for it can contract or extend its body at pleasure from the length of an inch or more, and the thickness of a hog's bristle, to the shortness of a single line, with a proportionable increase of thickness. Its body is round and tubular; at one end of which is the head, surrounded with six, eight, ten, or more arms, with which it catches its prey; and at the other, the anus and tail, by which it fixes itself to any thing it pleases.
There have been many different species of it discovered; the most elegant of which, the polype a panache, or plumed polype of M. Trembley, seems much to resemble the wheel-animal † (so called from having the appearance of two wheels in its head) which Mr LeuwenHOCK discovered, living in a sheath or case, and affixed to the roots of duckweed.
All the species are found in clear and slowly-running waters, adhering by the tail to sticks, stones, and water plants; and live on small insects. They are easily kept alive a long time in glasses, often changing the water, keeping the glasses clean, and feeding them with a small red worm common in the mud of the Thames, or with other small insects.
The creature has its name from the Greek πολυς "many," and πυς a "foot," signifying an animal with many feet; but a more apposite one might easily have been invented, since it has in reality no feet at all. What were originally taken for feet, are what have since been called its horns, and of late, more properly, its arms, their office being to catch its prey.
This animal is first of a worm-shaped figure, and of the same kind of tender substance with the horns of a common snail: it adheres by one end, like a sucker, to water-plants and other substances; the other end, which is the head, is surrounded by many arms or feeders, placed like rays round a centre: this centre is its mouth; and with these tender arms, which are capable of great extension, it seizes minute worms, and various kinds of water-insects, and brings them to its mouth; and often swallows bodies larger than itself, having a surprising property of extending its mouth wider in proportion than any other animal. After its food is digested in its stomach, it returns the remains of the animals upon which it feeds through its mouth again, having no other observable emunctory. In a few days there appear small knobs or papillæ on its sides: as these increase in length, little fibres are seen rising out of the circumference of their heads, as in the parent animal; which fibres they soon begin to use for the purpose of procuring nourishment, &c. When these are arrived at mature size, they send out other young ones on their sides in the same manner; so that the animal branches out into a numerous offspring, united together, and growing out of one common parent. Each of these provides nourishment not only for itself, but for the whole society; an increase of the bulk of one polype, by its feeding, tending to an increase in the rest. Thus a polype of the fresh-water kind becomes like a plant branched out, or composed of many bodies; each of which has this singular cha-
racteristic, that if one of them be cut in two in the middle, the separated part becomes a complete animal, and soon adhering to some fixed base, like the parent from which it was separated, produces a circle of arms: a mouth is formed in the centre; it increases in bulk, emits a numerous progeny, and is in every respect as perfect an animal as that from which it was severed.
The several strange properties recorded of this animal, though very surprising, are, however, none of them peculiar to it alone. The Surinam toad is well known to produce its young, not in the ordinary way, but in cells upon its back. Mr Sherwood has very lately discovered the small eels in four palls to be without exception full of living young ones. And as to the most amazing of all its properties, the reproduction of its parts, we know the crab and lobster, if a leg be broken off, always produce a new one: and M. Bonet, M. Lyonet, Monf. de Reaumur, and Mr Folkes, have all found, on experiment, that several earth and water worms have the same property, some of them even when cut into thirty pieces. The urtica marina, or sea-nettle, has been also found to have the same; and the sea-star-fish, of which the polype is truly a species, though it had long escaped the searches of the naturalists, was always well known by the fishermen to have it also.