Chapter L: M N is a guide for the eye, in order to direct it in the axis of the (12)

“The same observation and experience make it also familiar to us, that, besides the first way of propagating vegetables from their respective fruit and seed, they are also propagated from cuttings, and every one knows that a twig of a willow particularly, cut off and only stuck into the ground, does presently take root and grow, and become as real and perfect a tree as the original one from which it was taken. Here then we find in the vegetable kingdom quite common, the very thing of which we have an example before us in the animal kingdom, in this new-discovered insect. The best philosophers have long observed strong analogies between these two classes of beings; and the more they have penetrated into nature, the more they have extended this analogy: now in such a scale, who is the man that will be bold to say, just here animal life entirely ends, and here vegetable life begins? or, just so far, and no farther, one sort of operation goes; and just here another sort, quite different, takes its place? or again, who will venture to say, life in every animal is a thing absolutely different from that which we dignify by the same name in every vegetable?” Thus does the author endeavour to persuade the prejudiced, and lead them to pay attention to the facts which were now laid open to their view, and which were further confirmed by a letter from M. Trembley, in January 1740; which letter was strengthened by an extract from the preface to the sixth volume of Reaumur’s history of insects. In March, 1742, Mr. Folkes gave an account of them to the Royal Society, from observations made on several polypes which had been sent by M. Trembley from Holland to him. The insects now began to be known, and were soon found in England, and the experiments that had been made on them abroad were published by Mr. Folkes,[108] my father,[109] and Mr. Baker:[110] conviction now became too strong for argument, and metaphysical objections gave way to facts. The animal is described in the following manner:

HYDRA.[111]

Flos: os terminale, cinctum cirris setaceis. Stirps vaga, gelatinosa, uniflora, basi se affigens.[112]

[108] Philosophical Transactions.

[109] Micrographia Illustrata.

[110] Natural History of the Polype.

[111] The hydræ or polypes have generally been denominated Insects: is
there not a manifest impropriety in the application of this term to
them? If we admit of the systematic arrangement of LINNÆUS, we find
that he has divided the animal kingdom into six classes: 1. Mammalia.
2. Aves. 3. Amphibia. 4. Pisces. 5. _Insecta_; and 6. _Vermes_. Of the
last or _Vermes_, the Zoophytes (from ζωοφυτον, or animal plant)
constitute the fifth order. He defines it as Animalia composita,
efflorescentia more vegetabilium: amongst these he includes the
various species of Vorticellæ and Hydræ.

The term animalculæ, or small animals, is certainly not inapplicable
to them, but they differ materially in the peculiar characteristics by
which insects are distinguished, see page 179, and pages 215-220. They
do not undergo those transformations to which insects are subject, and
which have been so fully described in the preceding part of this work:
their figure, habits, and œconomy are also very different. In short,
they seem to be in every respect, except their minuteness, quite a
distinct race of animated beings, as will be more fully exemplified in
the following pages. EDIT.

[112] Lin. Syst. Nat. p. 1320.

This animal fixes itself by its base, it is gelatinous, linear, naked, can contract itself, and change its place. Its mouth, which is at one end, is surrounded by hair, like feelers. It sends forth its young ones from its sides, which drop off.

1. Hydra viridis, tentaculis subdenis brevioribus.

Green polype, generally with about ten short arms; it is represented in Plate XXI. Fig. 5.

2. Hydra fusca, tentaculis suboctonis longissimis.

This polype has very long arms, often eight in number; it is represented at Plate XXI. Fig. 7. The arms are several times longer than the body.

3. Hydra grisea, tentaculis subseptenis longioribus.

This polype has also generally long arms, in number about seven; it is of a yellowish colour, small towards the bottom; it is represented at Plate XXI. Fig. 6.

4. Hydra pallens, tentaculis subsenis mediocribus.

The arms of this polype are generally about six in number, and of a moderate length.

5. Hydra hydatula, tentaculis quaternis obsoletis corpore vesicario. Plate XXI. Fig. 1, 2, 3, 4.

This polype has a vesicular body, and four obsolete arms; is found in the abdomen of sheep, swine, &c.

6. Hydra stentorea, tentaculis ciliaribus corpore infundibuliformi.

This polype has been called tunnel-shaped; the mouth is surrounded with a row of hairs; it is represented at Plate XXII. Fig. 27 and 28.

7. Hydra socialis, mutica torosa rugosa.

Bearded, thick, and wrinkled. Plate XXI. Fig. 11.

OF THE HYDRA VIRIDIS, HYDRA FUSCA, AND HYDRA GRISEA.

Plate XXI. and XXIII.

These three species of the hydra having been those on which the greatest number of experiments have been made, and of which we have the best information, it is of these only I shall speak in the following account, unless it is particularly mentioned otherwise.

There are few animals more difficult to describe than the hydra, as it has scarce any thing constant in its form, varying continually in its figure: they are often so beset with young, as to appear ramose and divaricated, the young ones constituting as it were a part of the parent’s body.

Whoever has looked with care at the bottom of a wet shallow ditch, when the water is stagnant, and the sun has been powerful, may remember to have seen many little transparent lumps, of a jelly-like appearance, about the size of a pea, and flatted on one side; the same appearances are also often to be seen on the under side of the leaves of those weeds or plants that grow on the surface of the water; these are the hydræ gathered up into a quiescent state, and seemingly inanimate, because either undisturbed or not excited by the calls of appetite to action. They are generally fixed by one end to some solid substance, at the other end there is a large opening, round about which the arms are placed as so many rays round a center, which center is the mouth.

They are slender and pellucid, formed of a tender kind of substance, in consistence something like the horns of a snail, and can contract the body into a very small compass, or extend it to a considerable length. They can do the same with the arms; with these they seize minute worms and various kinds of aquatic insects, bring them to the mouth, and swallow them. After the food is digested, and the nutritive parts which are employed in sustaining its life are separated from the rest, they reject the remainder by the mouth.

The first polype which Trembley discovered was one of the hydra viridis, represented in Plate XXI. Fig. 5. These are generally of a fine green colour. The indications of spontaneous motion were first perceived in the arms of these little creatures; they can extend or contract, bend and wind them divers ways. Upon the slightest touch they contract themselves so much, as to appear little more than a grain of a green substance, the arms disappearing entirely. He soon after found the hydra grisea, Fig. 6, and saw it eat, swallow, and digest worms much larger than itself. This discovery was soon followed by that of the hydra fusca, Fig. 7.

The most general attitudes of these hydræ are those which are represented in Fig. 5 and 6 of the same plate. They fix the posterior extremity _b_ against a plant or other substance, as _e f_; the body _a b_; and the arms _a c_, being extended in the water. There is a small difference in the attitudes of the three kinds which we are now describing.

The bodies of the hydra viridis, Fig. 5, and of the hydra grisea, Fig. 6, diminish from the anterior to the posterior extremity by an almost insensible gradation. The hydra fusca does not diminish in the same gradual manner, but from the anterior extremity _a_, to the part _d_, which is often two-thirds of the length of their body, it is nearly of an equal size; from this part it becomes abruptly smaller, and goes on from thence of a regular size to the end. The number of arms in these three kinds are at least six, and at most twelve or thirteen, though eighteen may sometimes be found on the hydra grisea. They can contract their bodies till they are not above one-tenth of an inch in length; they can also stop at any intermediate degree, either of contraction or extension, from the greatest to the least. The species represented at Fig. 5, are generally about half an inch long when stretched out. Those exhibited at Fig. 6 and 7, are about three-fourths of an inch, or one inch in length, though some are to be found at times about an inch and half long. The arms of the hydra viridis, Fig. 5, are seldom longer than their bodies; those of Fig. 6 are commonly one inch long, while those of Fig. 7 are generally about eight inches; whence Trembley has called it the long-armed polype.

The bulk of the hydræ decreases, in proportion as they extend themselves, and vice versa. They may be made to contract themselves, either by touching them, or agitating the water in which they are contained. They all contract themselves so much when, taken out of the water, as to appear only like a little lump of jelly. They can contract or extend their arms without extending or contracting the body, or the body, without making any alteration in the arms; or they can contract or dilate only some of the arms, independent of the rest: they can also bend their body and arms in all possible directions. Those represented at Fig. 7 let their arms in general hang down, making different turns and returns, often directing some of them back again to the top of the water. They can also dilate the body at different places, sometimes at one part, and then again at another; sometimes they are thick set with folds, which, if carelessly viewed, might be taken for rings.

They have a progressive motion, which is performed by that power by which they stretch out, contract, and turn themselves every way. For suppose the hydra or polype, _a b_, Fig. 16, to be fixed by the tail _b_, having the body and the arms _a_ extended in the water; in order to advance, it draws itself together, by bending itself so as to bring the head and arms down to the substance on which it is to move; to do this, it fixes the head or the arms as in Fig. 17; when these are well fixed, it loosens the tail, and draws it towards the head, as in Fig. 18, which it again loosens, and resting on the tail, stretches it out, as in Fig. 19. It is easy to see from this account, that their manner of walking is very analogous to that of various terrestrial and aquatic animals. They walk very slow, often stopping in the middle of a step, turning and winding their body and arms every way. Their step is sometimes very singular, as in the following instance: suppose the polype _a b_, Fig. 20, to be fixed by the tail _b_, the body and arms being extended in the water, it first bends the fore-part towards the substance on which it is moving, and fixes it thereto, as at _a_, Fig. 21; it then loosens the lower end, and raises it up perpendicular, as in Fig. 22; now bending the body to the other side, it fixes the tail, as in Fig. 23; then loosening the anterior end, it rises up, as in Fig. 24.

They descend at pleasure to the bottom of the water, and ascend again, either by the sides, or upon some aquatic plants; they often hang from the surface of the water, resting as it were upon the tail; or, at other times they are suspended by one arm from it. They walk also with ease upon the surface of the water. If the extremity of the tail _b_, Fig. 7, be examined with a magnifying glass, a small part of it will be found to be dry, and 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.

Hence, when a polype 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 means to be supported, and give it time to dry, which it always does upon these occasions. They attach themselves so firmly by the tail to aquatic plants, stones, &c. as not to be easily driven from the place where they have fixed themselves; they often further strengthen these attachments by means of one or two of their arms, which they throw out and fix to adjacent substances, as so many anchors.

The mouth of the polype or hydra is situated at the fore-part of the body, in the middle between the shooting forth of the arms. The mouth assumes different appearances, according to the different purposes of the insect; sometimes it is lengthened out, and forms a little conical nipple, as in Plate XXIII. A. Fig. 13; sometimes it appears truncated, as in Plate XXI. Fig. 8; at other times the interval between the arms appears closed, as in Plate XXIII. A. Fig. 2 and 12; or hollow, as in Fig. 11 of the same plate. If it be observed with a deep magnifier in either of the two last cases, a small aperture may be discovered.

The mouth of the polype opens into the stomach, which is a kind of bag or gut that goes from head to tail; this may be perceived by the naked eye, when the animal is exposed to a strong light, or a candle placed on the opposite side to the eye; for the colour of the polype does not destroy the transparency thereof. The stomach will, however, be better seen, if the eye be assisted by a deep magnifier; one of them is represented as highly magnified in Plate XXI. Fig. 8. To be fully satisfied whether they were perforated throughout, Trembley cut one transversely into three parts; each piece immediately contracted itself, and became very short; being then placed in a shallow glass full of water, and viewed through the microscope, they were found to be visibly perforated. Their microscopic appearance is represented in Plate XXIII. A. Fig. 6, 7, 8; its mouth was at the anterior end _a_, Fig. 8, of one of these parts. The tail was at the end _b_ of the third part, Fig. 6; as this piece was also perforated, it plainly appears that the tail of the hydra is open. The perforation, which is thus continued from one end to the other, is called the stomach, because it contains and digests the aliments. The skin which incloses the bag, and forms the stomach, is the skin of the polype itself; so that the animal may be said to consist of but one skin, disposed in the form of a tube or gut open at both ends. On opening the polype, no vessels are to be distinguished; and whatever be the nature of its organization, it must reside in the skin.

The skin must be so far organized, as to perform all the operations necessary for the nutrition and growth of the animal, without considering those that are necessary for its various motions. Whatever are the means the Author of Nature has employed for these purposes, we are ignorant of them. If their skin be examined by a microscope, it appears like shagreen, or as if it were covered with little grains; these are more or less separated from each other, according to the degree in which the body is extended or contracted.

If the lips of a polype be cut transversely, and placed so that the cut part of the skin may lie directly before the microscope, the skin throughout its whole thickness will be found to consist of an infinite number of these grains. To know whether the inside of the stomach was formed of similar grains, several of them have been laid open and examined by the microscope; the interior surface was then found to consist of an immense number of them, being as it were more shagreened than the exterior one, and less transparent. The grains are not strongly united to each other, but may be separated without much trouble. Plate XXIII. A. Fig. 10, represents a piece of skin thus laid open. To examine these particulars further, a piece of skin a, Fig. 9, was laid in a few drops of water, on a piece of glass before the microscope, and some of the grains were separated from it, as at b c d, by pressing them with the point of a pin; in endeavouring to open them, they spread themselves into all parts of the water, and at last remained in heaps, as at e and f.

If a polype be carefully placed before the microscope, without wounding it, you will seldom be disappointed in seeing some of these grains detach themselves from the superficies thereof, and that even in the most healthy.

But if the grains separate themselves in large quantities, it is the symptom of a very dangerous disorder; the surface of the polype thus attacked becomes more and more irregular, and is no longer well terminated and defined as before. The grains fall off on all sides, the body and arms contract and dilate, it becomes of a white shining colour, loses its form as at a, Fig. 4, and then dissolves into a heap of grains, as at b, Fig. 5. The progress of this disorder is most easily observed in the hydra viridis.

A very attentive and accurate examination shews that the skin is formed of a kind of glareous substance, a species of gum, which fills up the intervals between the grains, in which they are lodged, and by which they are attached, though weakly, together. It has been already observed, that it is to these grains that it owes its shagreen-like appearance; it is from them also that it derives its colour; for, when they are separated from the polype, they are the same colour with it, whereas the glareous matter is without any distinguishing colour. The construction of the polype seems then to be confined to these glandular grains, to the viscous matter, and the invisible fibres which act upon the glareous substance.

The structure of the arms of the polypes is very analogous to that of their body. When they are examined by the microscope, either in a contracted or dilated state, their surface is shagreened; if the arm be much contracted, it appears more so than the body; on the contrary, it appears less so in proportion as they are more extended; almost quite smooth when at their full extension; so that in the hydra viridis the appearance of the arms is continually varying, and these variations are more sensible towards the extremity of the arm than at its origin, as, in Plate XXI. Fig. 10; but more thinly scattered, or farther asunder, in the parts further on, as at Fig. 9. The hairs which are exhibited in this figure cannot be seen without a very deep magnifier, however they indicate a further degree of organization in this little animal. The extremity is often terminated by a knob.

All animals of this kind have a remarkable attachment to turn towards the light, and this might naturally induce the inquirer to look for their eyes; but how carefully soever this search has been pursued, and however excellent the microscope with which every part has been examined, yet no appearance of this organ has been found. Notwithstanding this, they constantly turn themselves toward the light; so that if that part of the glass in which we placed them be turned from it, they will be found the next day to have removed themselves to the side that is next the light, and the dark side will be quite depopulated.

OF THE FOOD OF THE HYDRÆ, AND THEIR METHOD OF SEIZING AND SWALLOWING THEIR PREY.

As the hydra fusca, Plate XXI. Fig. 7, has the longest arms, its manner of feeding, and the different manœuvres it makes use of to seize and manage its prey, are more remarkable than those of the two other species; it will be, therefore, this kind only which will be principally spoken of under the present head. To obtain a proper view, it should be placed in a glass seven or eight inches deep. If the polype be fixed near the top of the glass, the arms for the most part hang down toward the bottom. This is a very convenient situation for feeding it, and observing its management of the food.

The polypes are in general very voracious: an hungry one extends its arms as a fisherman his nets; it spreads them every way, so that they form a circle of considerable extent, every part of which is entirely within the reach of one of them. In this expanded posture it lies in expectation of its food; whatever comes within the verge of this circle is seized by one or other of its arms: the arms are then contracted till the prey is brought to the mouth, when it is soon devoured. While the arms are contracting and exerting themselves vigorously to counteract the efforts of the animal, which it has seized, to escape, they may be observed to swell like the muscles of the human body when they are in a state of exertion.

Though in general all ideas are derived from the senses, there are certainly some that seem infused into us independently of the exertions of any sense. This may be confirmed by many instances of animal instinct; among others, it may be illustrated by the polype. Who taught it, when just separated from the parent stock, to expand its arms, that it might catch its prey? That its native element abounded with insects? or that these were its proper food? No sense that we are acquainted with could first give the information.

The polype does not always wait for its prey, it feels for it, and in a manner follows it. It may be asked how can it perform this if destitute of vision? or do the glandular grains answer the purpose of eyes? Who can answer the question? what are our own eyes but glandular grains of a larger size? If this should be the case, our hydra, like the libellulæ and other insects, would realize, nay, exceed the fables of the ancients, being an Argus entirely composed of eyes. Be this as it may, they are certainly in possession of some sensation by which they are informed of the approach of their prey, and which renders them attentive to all that may confirm or destroy this perception.

When the arms of a polype are extended within a glass, put a centipe or any kind of worm into it, see Plate XXIV. A. Fig. 1, and with the point of a pin push it towards one of the arms; as soon as it touches this it is seized; the worm or centipe endeavours by quick and strong efforts to disengage itself, often swimming and dragging the arm from one side of the glass to the other. This violent motion of the prey obliges the polype to contract strongly the arm; in doing which, it often twists it in the form of a cork-screw, as at o i, by which means it shortens it more rapidly. The struggles of the devoted animal soon bring it in contact with another arm; these contracting further, the little creature is presently engaged with all the arms, and by degrees conveyed to the mouth, against which it is held and subdued.

When a polype has nothing to eat, its mouth is generally open, but so small, that it can scarce be perceived without the assistance of a magnifying glass; but as soon as the arms have conveyed the prey to the mouth, it opens itself wider, and this in proportion to the size of the animal that is to be devoured; the lips gradually dilate, and adjust themselves accurately to the figure of the prey. The greatest part of the animals on which the polype feeds, are to its mouth, what an apple the size of our heads would be to the mouth of a man.

The worms or other minute animals which are seized by the polype, are not always brought to the mouth in the same situation; if they be presented to it by one of their extremities, it is not requisite that the polype should open its mouth considerably, and in effect it only opens it so wide, as precisely to give entrance to the worm, Fig. 5. If it be not too long for the stomach, it remains there extended; but if it be longer, the end which first enters is bent, so that when the worm is entirely swallowed, it may be seen lying folded in the stomach, Plate XXIV. B. Fig. 12.

If the middle, or any other part of the worm, be presented to the mouth of the polype, it seizes this part with the lips, extending them on both sides, and applying them against the worm, so that the mouth assumes the form of a boat, pointed at each end, Plate XXIV. A. Fig. 2; the polype gradually closes the two points of its boat-like lips, and by this motion and suction swallows the worm, Fig. 4.

The polypes kill worms so speedily, that Fontana thinks they must contain the most active and powerful venom; for the lips of a polype scarce touch the worm, but it expires, so great is the energy of the poison it conveys into it, though no wound can be observed in the dead animal.

As soon as the stomach is filled, its capacity is enlarged, the body is shortened, Plate XXIV. A. Fig. 6, the arms are for the most part contracted, the polype hangs down without motion, and appears to be in a kind of stupor, and very different from its shape when extended; but in proportion as the food is digested, and it has voided the excrementitious parts, the body lengthens, and gradually recovers its usual form.

The transparency of the polype permits us to see distinctly the worm it has swallowed, Plate XXIV. B. Fig. 12, which gradually loses its form. It is at first macerated in the stomach of the polype, and when the nutritious juices are separated from it, the remainder is discharged by the mouth, Fig. 13. It is with these, as with other voracious animals, as they devour a great quantity of food at once, so also they can fast for a long time. The history of insects furnishes many examples of this kind.

One circumstance is observable, which probably contributes much to the digestion of their food, namely, that the aliments are continually pushed backward from one extremity of the stomach to the other; this motion may be easily observed with a microscope, in a polype which is not too full, and in which the food has been already divided into little fragments. For these observations, it is best to feed the polype with such food as will give a lively-coloured juice; as for example, those worms whose intestines are filled with red substances: for by these means we shall see that the nutritious juices are conveyed not only to the extremity of the body, but also into the arms; from whence it is probable that each of the arms form also a kind of gut, which communicates with that of the body. Some bits of a small black snail that is frequently to be found in our ditches, was given to a polype. The substance of this skin was soon reduced into a pulp, consisting of little black fragments; on examining the polype with the microscope, these particles were perceived to be driven about the stomach, and to pass from head to tail, and into their arms, even where these were as fine as a thread; they were afterwards forced into the stomach, and from thence to the tail, from whence they were again driven into the arms, and so on.

The grains take their tinge from the food which nourishes the polypes; these grains become red or black, if the polype be fed with juices that are either red or black; and they are more or less tinged with these different colours, in proportion to the strength and quantity of the nutritive juices. It is also observable, that they lose their colour if fed with aliments that are not of the same colour with themselves.

The polypes feed on the greater part of those insects that are to be found in fresh water. They may be nourished with worms, the larvæ of gnats, &c. they will also eat larger animals if they are cut into small pieces, as snails, large aquatic insects, small fish, butcher’s meat, &c. Sometimes two polypes seize the same worm, and each begins to swallow its own end, continuing so to do till their mouths meet, Plate XXIV. A. Fig. 8; in this position they remain for some time, at last the worm breaks, and each has its share; sometimes the combat does not end here, for each continuing to dispute the prize, one of the polypes opens its mouth advantageously, and swallows the other with its portion of the worm, Plate XXIV. B. Fig. 14; this combat ends more fortunately for the devoured polype than might be at first expected, for the other often gets the prey out of its stomach, but lets it out again sound and safe, after having imprisoned it above an hour. From hence we learn, that the stomach of the polype, which so soon dissolves the animal substances which are conveyed into it, is not capable of digesting that of another polype.

Plate XXIV. A. Fig. 5, represents a polype with one half a centipe in its mouth, as at a; the other part without, as at m. Fig. 1 represents one suspended in water by a piece of packthread; c n, a centipe seized by it, and drawn partly towards the mouth; i o, the bendings in the arm; p, an arm in search of a small aquatic insect. Fig. 2, a polype stretching itself into a boat-like form, to take or swallow a worm lying sideways. Fig. 4, the same polype with the worm swallowed and bent within it. Fig. 6, is a polype in the situation they generally assume when they have satisfied their voracious appetite. Fig. 7, one that has swallowed a small monoculus. Fig. 9, a, one whose arms are loaded with monoculi. Fig. 10, a polype full of them from head to tail. Fig. 3, one that has only swallowed a few of them. Fig. 8, represents two polypes engaged in combat for a worm, of which both of them have swallowed a part.

Plate XXIV. B. Fig. 11, represents a polype engaged with a very large worm. Fig. 12, a worm seen within the skin of a polype. Fig. 13, a polype disgorging the excrementitious parts of a worm.

Plate XXI. Fig. 12, a polype that has swallowed a small fish, and taken the shape thereof.

OF THE GENERATION OF THE HYDRÆ.

As the hydra fusca and the hydra grisea are considerably larger than the hydra viridis, it is more easy to observe the manner of their producing their young. It is upon these, therefore, that most of the observations here recited have been made. If one of them be examined in summer, when the animals are most active, and more particularly prepared for propagation, it will be found to shoot forth from its side several little tubercles, or knobs, which grow larger and larger every day; after two or three days inspection, what at first appeared but a small excrescence, takes the figure of a small animal, entirely resembling its parent. It does not inclose a young polype, but is the real animal in miniature, united to the parent, as a sucker to the tree.

When a young polype first begins to shoot, the excrescence terminates in a point, as at e, Plate XXIV. B. Fig. 24; so that it is rather of a conical figure, and of a deeper colour than that of the body. This cone soon becomes truncated, and in a little time appears cylindrical. The arms then begin to shoot from the anterior end c i. The tail adheres to the body of the parent, but grows gradually smaller, till at last it only adheres by a point b, Fig. 23, it is then ready to be separated; for this purpose the mother and young ones fix themselves to the glass, or other substance upon which they may be situated. They have then only to give a sudden jerk, and they are divided from each other. There are some trifling differences to be observed now and then in their performing this operation, which it would be too tedious to enumerate here. A polype, a b, Fig. 20, with a young one, c d, places its body in an arch of a circle a d b, against the sides of the glass, the young one being fixed at the top d of the arch, with its head also fixed against the glass; so that the mother, by contracting the body, and thus becoming straight, loosens herself from the young one.

The young ones shoot in proportion to the warmth of the weather, and the nature of the food eaten by the mother; some have been observed to be perfectly formed in twenty-four hours, while others have required fifteen days for the same purpose; the first were produced in the midst of summer, the latter in a cold season.

The tail of the young polype communicates with, and partakes of the food from the parent in the same manner as its own arms do, and the food lies in the same manner as in the arms. When this fœtus is furnished with arms, it catches its prey, swallows, digests, and distributes the juices thereof even to the parent body; every good is common to each. Here then we have evident communication between the fœtus and the mother; this communication was further proved by the following experiment. A large polype, one of the hydra fusca, was placed on a slip of paper, in a little water; the middle of the body of the young one was cut, and the superior part of that end which remained fixed to the parent was found to be open. The parent polype was then cut on each side of the shoot. Thus a short cylinder was obtained, which was open at both ends. This being viewed through a microscope, the light was seen to come through the side slip, or young one, into the stomach of the old one. For further conviction, the cylindrical portion was cut lengthways; on observing these parts, not only the hole t of the communication, Plate XXIV. B. Fig. 17, was distinctly seen, but one might see through the end o of the young one. On changing the situation of these two pieces of prepared polypes, and looking through the opening e, Fig. 18, the day-light was seen through the hole of communication i.

This communication, between the parent polype and its young ones may be seen on feeding them; for, after the parent a b, Plate XXIV. B. Fig. 22, has eaten, the bodies of the young ones swell, being filled with the aliments as if they themselves had been eating. In the hydra fusca the young ones do not proceed from the tail part b c, Plate XXIII. B. Fig. 16, but only from the part a c, with this exception, there is no particular part of the body before the rest, on which they produce their young. Some of them have been so closely observed, and have so greatly multiplied, that there would be scarce any impropriety in saying they produced their young ones from all the exterior parts of their body. A polype puts forth frequently five or six young ones at the same time. Trembley has had some that have produced nine or ten at the same time, and when one dropped off another came in its place.

Though this gentleman had for two years thousands of them under his eye, and considered them with the most scrupulous attention, he never observed any thing like copulation. To be more certain on this head, he took two young ones the instant they came from their parent, and placed them in separate glasses; they both multiplied, not only themselves, but their offspring, which were separated and watched in the same manner to the seventh generation; nay, they have even the faculty of multiplying while they adhere to the parent. The arms of the young ones do not sprout till the body has attained some length.

Several excrescences or buds often appear at the same time on a polype, which are so many polypes growing from one trunk; whilst these are developing, they also bud, which buds again put forth little ones, the parent and the young ones forming a singular kind of animal society, in which all participate of the same life, and the same wants. In this state, the parent appears like a shrub thick set with branches. Several generations are often thus attached to one another, and all to the parent polype; after a time, this tree of polypes or hydræ is decomposed, and gives birth to new generations, or fresh genealogical trees. Here we see a surprizing chain of existence continued, and numbers of animals naturally produced, without any union of sexes; every polype raising a numerous posterity by a kind of animal vegetation.

From Fig. 16, Plate XXIII. B. the reader may form an idea of the promptitude with which these creatures increase and multiply; the whole group formed by the parent and its young was about an inch and an half long, and one inch broad, the arms of the mother and her nineteen little ones hanging down towards the bottom of the vessel; the animal would eat about twelve monoculi per day, and the little ones about twenty among them, or rather more than thirty for the group.

OF THE RE-PRODUCTION OF THE HYDRÆ.

So strange is the nature of this creature’s life, that the method by which other animals are killed and destroyed becomes a means of propagating these. When divided and cut to pieces in every direction that fancy can suggest, it not only continues to exist, but each section becomes an animal of the same kind.

A polype cut transversely or longitudinally, in two or three parts, is not destroyed; each part in a little time becomes a perfect polype. This species of fecundity is so great in these animals, that even a small portion of their skin will become a little polype, a new animal rising as it were from the ruins of the old, each small fragment yielding a polype. If the young ones be mutilated while they grow upon the parent, the mutilated parts are re-produced; the same changes succeed also in the parent. A truncated portion will put forth young before it is perfectly formed itself, or has acquired its new head and tail; sometimes the head of the young one supplies the place of that which would grow out of the anterior part of the trunk.

If a polype be slit, beginning at the head, and proceeding to the middle of the body, a polype will be formed with two heads, and will eat at the same time with both. If the polype be slit into six or seven parts, it becomes a hydra with six or seven heads. If these be again divided, we shall have one with fourteen; cut off these, and as many new ones will spring up in their place, and the heads thus cut off will become new polypes, of which so many new hydræ may again be formed; so that in every respect it exceeds the fabulous relation of the Lernean hydra.

As if the wonders already related of the polype were not sufficient to engage our attention to these singular animals, new circumstances, as surprizing as the foregoing, present themselves to convince us of the imperfection of our ideas of animality, and of the greatness of the power of our LORD and SAVIOUR, who is the source and origin of every degree of life, in all its immense gradations, as unity is the origin of number in all its varied series, multiplied proportions and combinations; and as numbers may be considered as recipient of unity, in order to make manifest the wonderful powers thereof, so the universe and its parts are adapted to receive life from the source of all life, and thus become representatives of his immensity and eternity.

The polypes may be as it were grafted together. If the truncated portions of a polype be placed end to end, and then pushed together with a gentle force, they will unite, and form a single one. The union is at first made by a fine thread, and the portions are distinguished by a narrow neck, which gradually fills up and disappears, the food passing from one portion to another. Portions not only of the same, but pieces of different polypes may be thus united together. You may fix the head of one polype to the trunk of another; and that which is thus produced, will grow, eat, and multiply like another.

There is still another method of uniting these animals together, more wonderful in its nature, and less analogous to any known principles of animation, and more difficult to perform. It is effected by introducing one within the other, forcing the body of one into the mouth of the other, and pushing it down so that their heads may be brought together: in this state it must be kept for some time; the two individuals are at last united, and grafted into each other; and the polype, which was at first double, is converted into one, with a great number of arms, and performs all its functions like another.

The hydra fusca furnishes us with another prodigy, to which we know nothing that is similar either in the animal or vegetable kingdom. They may be turned inside out like a glove, and, notwithstanding the apparent improbability of the circumstance, they live and act as before. The lining or coating of the stomach now forms the epidermis, and the former epidermis now constitutes the coating of the stomach. A polype thus turned, may often have young ones attached to its side. If this be the case, after the operation they are of course inclosed in the stomach. Those which have acquired a certain size extend themselves towards the mouth, that they may get out when separated from the body; those which are but little grown, turn themselves inside out, and by these means place themselves again on the outside of the parent polype.

The polype thus turned combines itself a thousand different ways. The fore-part often closes itself, and becomes a supernumerary tail. The polype which was at first straight, now bends itself, so that the two tails resemble the legs of a pair of compasses, which it can open and shut. The old mouth is at the joint as it were of the compasses; it cannot, however, act as one, so that a new one is formed near it, and in a little time a new species of hydra is formed with several mouths.

Plate XXIII. B. Fig. 18, represents the upper part of a polype that has been divided into two parts; a, the upper, c, the lower part, the end c being something larger than that of a common polype, and is sensibly perforated; in the summer time this part often walks and eats the same day it is cut. Fig. 17, the other part of the same polype; the anterior end is very open, and the edges of it turned a little outwards, which afterwards folding inwards, close the aperture. This end now appears swelled, as at c, Fig. 21; the arms shoot out from this end: at first three or four points only begin to shoot, as at c, Fig. 20, and while these increase in size, others appear between them; they can seize their prey and eat before their arms have done growing. In the height of summer the arms will often begin to shoot in twenty-four hours; but in cold weather it will be fifteen or twenty days before the head is formed. Fig. 22, represents a polype that was cut close under the arms; this became also a complete animal in a little time.

The sides of a polype that has been cut longitudinally, roll themselves up in different ways, generally beginning at one of the extremities, rolling itself up in a heap, as in Plate XXIII. B. Fig. 19, with the outside of the skin inwards; it soon unrolls itself, and the cut sides form themselves into a tube, whereof the edges a b and e i, Fig. 15, on both sides meet each other and unite. Sometimes they begin to join at the tail end, at other times the whole sides gradually approach each other. The sides join so close, that from the first moment of their junction no scar can be discovered. Fig. 14, represents a polype partly joined, as at i b, the part c a e not yet closed. Fig. 29, represents a polype, the heads of which have been repeatedly divided, by which means it becomes literally a hydra. Fig. 24, represents a polype that has been turned, endeavouring to turn itself back again, the skin of the anterior part lying back upon the other; the arms varying in their direction, being sometimes turned towards the head, see Fig. 24 and 26, at others, towards the tail. The anterior extremity c, formed by the edges of the reversed part a, remained open for some days, and then began to close; new arms shot out near the old ones, and several mouths were formed at those parts where the arms joined the body. Fig. 23, 25, 27, 28, represent the different changes that took place in another polype that had been turned inside out, and the different revolutions it went through before it acquired a fixed state; a c always shews the part the polype had turned back, and a b the part it could not turn back.

A polype, which has been partly turned back, remains but a little time in that situation. Fig. 28, a, the part where the portion it had turned back joined to the body a b; this became straight, and formed a right angle with a b; the same day another head appeared at e, and several arms, a o, a n, began to shoot from the mouth a; at the other side of this mouth there were the old arms a d. The next day the portion a c was drawn near the body, and formed an acute angle with it, as at Fig. 25. Fig. 27, represents the same swelled, after having swallowed a worm. Four days afterwards its form had varied considerably, as may be seen by comparing Fig. 25 and 28, having now one common mouth, and two small polypes growing on it.

We may now be permitted to make a few reflections on this singular animal. On considering the various properties that have been already described, many particulars will be found in them that are very analogous to others that are continually carrying on around us; we perceive that there is a successive unfolding of new parts. In every organized frame there is a continual effort to extend its sphere of action, and enlarge the operation of that portion of life which is communicated to it. This gradual evolution requires a secret and curious mechanism, to regulate and modify by re-action the continued conatus of the forming principle within it. The polype is an organized whole, of which each part, each molecule, each atom, tends to produce another; it is, if we may so speak, one entire ovary, a compound of germ, or seed. In cutting a polype to pieces, the nourishing juices, which would have been employed in supporting the whole, are made to act upon each portion.

When a polype is divided longitudinally, it forms two half tubes; the opposite edges of these approach, and in a very short time form a perfect tube. The sides are made to touch each other by certain motions and contractions of the piece; but as soon as the edges come in contact, a slight adhesion takes place, the corresponding vessels unite, and new ones are unfolded, as in a vegetable graft; by these means the points of connection and cohesion are multiplied, the motion of the fluids is re-established, and with them the vital œconomy. This is performed with more rapidity than in vegetables, because the polype is nearly gelatinous, and its parts are extremely ductile; this ductility is supported and preserved by the element which it inhabits. The same reasoning applies equally to explain the formation of so many heads to a polype, as constitute it a real hydra.

A new polype is formed out of small portions or fragments, in a very different manner, the operations in nature being always varied, according as the circumstances differ; each fragment is puffed up, the skin separated, and an empty space is formed within it; this part is to become the stomach of the rising polype, which soon sends forth arms, and is formed to the perfection proper to its kind. We learn from this instance that the skin of the polype is not so simple as was at first imagined; for we find it dividing itself into two membranes, and forming thereby a cavity fit to perform all the functions of a stomach; but why these membranes are separated in the small portions, and not in the larger, we cannot tell; but though we are ignorant of this, and many more circumstances relative to the re-production of these little animals, yet the foregoing facts enable us to understand better the nature of the existence of these polypes which have been turned inside out.

For as that part which formed the interior skin of the stomach in the little fragments before-mentioned, became the exterior part of the animal, the inside of the polype is consequently so similar to the exterior skin, that one may be substituted for the other, without injuring the vital functions; from hence we might, in some measure, have inferred the possibility of the polypes living, after they have been turned inside out, independent of the fact itself.

The viscera of the animal are situated in the thickness of the skin, and absorbing pores are placed both on the inside and outside, so that the animal can live whether the skin be turned one way or the other. The Author of nature did not create the polype to be turned as we turn a glove; but he formed an animal whose viscera were lodged in the thickness of the skin, and with powers to resist the various accidents to which it was unavoidably exposed by the nature of its life; and the organization necessary for this purpose was so constructed, that the skin might be turned without destroying life.

Every portion of a divided polype has, like the vegetable bud, all the viscera necessary to its existence; it can, therefore, live by itself, and push forth a head and tail, when placed end to end against another piece. The vegetation consists in uniting the portions, the vessels of each part increase in length, and a communication is soon formed between them, which unites the whole. The ease with which the parts unite, is as has been observed before, probably owing to their gelatinous nature; for we find many similar instances in tender substances. The solid parts of the embryo, as the fingers, unite in the womb; tender fruit and leaves may be also thus united.

A portion of these creatures is capable of devouring its prey almost as soon as it is divided from the rest. In the structure of those animals which are most familiar to us, a particular place is appropriated for the developement and passage of the embryo. But on the body of an animal, which, like a tree, is covered with prolific gems, it is not surprizing that the young ones should proceed from its sides, like branches from a tree. The mother and her young ones form but one whole; she nourishes them, and they contribute to her existence, as a tree supports, and is reciprocally supported by its branches and leaves.

OF THE HYDRA PALLENS.