[100]Lyonet sur la Chenille de Saule, p. 584.
[100]Lyonet sur la Chenille de Saule, p. 584.
Plate XIII.Fig. 1 and 2.
This is a tender and brittle shell-fish of a very peculiar species; its length is about an inch, and its diameter about three quarters of an inch. The shell is not composed of two pieces or valves, as in others, but of five; two of these are larger than the rest, to which are affixed two smaller ones; the fifth piece is long, slender, and crooked, running down length-ways, and covering the joinings of the other pieces. The shell part is of a pale red, variegated with white; it adheres to a neck or pedicle of an inch long, and about a fifth of an inch in diameter; by which means it affixes itself to old wood, to stones, to sea-plants, or any other solid substance that lies under water. It can shorten or extend this neck at pleasure, which resembles a small gut, and is usually full of a glareous liquor; it is composed of two membranes, an external one, hard and brown, an internal one, softand of an orange colour. The large portions of the shell open and shut in the manner of the bivalves; the others, being moveable by means of their membranaceous attachments, give way to the opening of these, and to the motions of the body of the fish in any direction. It is furnished with a cluster of filaments or tentacida, placed in a row on each side, usually twelve, sometimes fourteen in number. They are a kind of arms appropriated for catching its prey, and therefore placed so as to surround the mouth of the animal, which is situated between them, and consequently easily receives what they thrust towards it. By the motion of these arms, which may be exerted in such a manner as to play either within or without the cavity of the shell, it forms a current of water, which brings with it the prey it feeds upon. Fig. 1 represents two of these arms as magnified by the microscope; Fig. 2, the natural size of those from which these drawings were made. Each arm consists of several joints, and each joint is furnished on the concave side of the arm with a brush of fibrillæ or long hairs. The arms, when viewed in the microscope, seem rather opake; but they maybe rendered transparent, and form a most beautiful object, by extracting out of the interior cavity a bundle of longitudinal fibres, which runs the whole length of the arm. Mr. Needham[102]thinks the motion and use of these arms illustrates the nature of that rotatory motion which some writers have thought they discovered in the wheel animal.
[101]This animal is classed by Linnæus among the Vermes Testaceæ. Its generic character is: Animal, resembling a triton; Shell, consisting of several unequal valves; affixed by its base. Specific character: Pedunculated Barnacle, with compressed shell consisting of five valves. Syst. Nat. p. 1107, 1109.Edit.[102]Needham’s Microscopical Observations.
[101]This animal is classed by Linnæus among the Vermes Testaceæ. Its generic character is: Animal, resembling a triton; Shell, consisting of several unequal valves; affixed by its base. Specific character: Pedunculated Barnacle, with compressed shell consisting of five valves. Syst. Nat. p. 1107, 1109.Edit.
[102]Needham’s Microscopical Observations.
In the midst of the arms is a hollow trunk, consisting of a jointed fibrous or hairy tube, which incloses a long round tongue or proboscis, that the animal can push occasionally out of thetube or sheath, and retract at pleasure. The mouth of this animal is singular in its kind, consisting of six laminæ, which go off with a bend, indented like a saw on the convex edge, and by their circular disposition are so ranged, that the teeth in the alternate elevation and depression of each plate, act against whatever intervenes between them. The plates are placed together in such a manner, that to the naked eye they form an aperture not much unlike the mouth of a contracted purse.
The western isles of Scotland, and some other parts of the British dominions, are abundantly stored, at certain times of the year, with a bird of the goose kind, commonly known in those places by the name of the brent goose or barnacle. These birds rarely breed with us, but seek, for their sitting season, islands less frequented than those where we find them in common. The seeing the birds so frequent, and yet never finding any of their nests, induced ignorant people to believe they never had any, and that they were not bred like other birds.
About the very shores where these birds are most common, the lepas anatifera is also found in great abundance. The fishermen, who observed vast quantities of these shells affixed to rotten wood, or dead trees that were floating in the water, or lodged by it on the shore, were soon led to imagine that the fibrous substances that hung out of them resembled feathers, and persuaded themselves that the geese, whose origin they could before by no means make out, were bred from them, instead of being hatched, like other birds, from eggs.[103]It was afterwards affirmed, that the shells themselves originally grew on the trees, in the manner of their fruit; and that the young bird, having in the shell obtainedits plumage, dropt from thence into the water. From this arose the opinion that the barnacle or brent goose was the produce of a tree.[104]
[103]Hill’s Natural History of Animals.[104]The absurd idea, that the brent goose or barnacle derived its origin from this shell, was not confined to the illiterate; men of science, incautiously confiding in the bold assertions of the ignorant, appear to have given full credit to this truly curious hypothesis, and disseminated the knowledge of it in their writings. Even Gerard, the author of the Herbal, caught the infection: so confident was he of the fact, that he invited the credulous to apply to him for full satisfaction; his words are, “For the truth hereof, if any do doubt, may it please them to repaire unto me, and I shall satisfie them by the testimonie of good witnesses.” See his Herbal, page 1587.Barbut says, “This fabulous account originated from the sea-fowls, when ready to lay their eggs, depositing them on the marine plants; and, pecking sometimes these anatiferous shells, oblige the fish to come out, which having devoured, they lay eggs in their place. The young when hatched break through their prison, and fly away.” Genera Vermium, Pars ii. page 13.Edit.
[103]Hill’s Natural History of Animals.
[104]The absurd idea, that the brent goose or barnacle derived its origin from this shell, was not confined to the illiterate; men of science, incautiously confiding in the bold assertions of the ignorant, appear to have given full credit to this truly curious hypothesis, and disseminated the knowledge of it in their writings. Even Gerard, the author of the Herbal, caught the infection: so confident was he of the fact, that he invited the credulous to apply to him for full satisfaction; his words are, “For the truth hereof, if any do doubt, may it please them to repaire unto me, and I shall satisfie them by the testimonie of good witnesses.” See his Herbal, page 1587.
Barbut says, “This fabulous account originated from the sea-fowls, when ready to lay their eggs, depositing them on the marine plants; and, pecking sometimes these anatiferous shells, oblige the fish to come out, which having devoured, they lay eggs in their place. The young when hatched break through their prison, and fly away.” Genera Vermium, Pars ii. page 13.Edit.
Plate XVII.Fig. 1, 2, and 3.
This very beautiful and singular insect was first pointed out to me by T. Marsham, Esq. Sec. L. S. who had seen it in the cabinet of insects belonging to the Queen, in the royal observatory at Richmond. Her Majesty was pleased to permit me to have the drawing taken from it, from which thisplatewas engraved. When Mr. Marsham first saw it at Richmond, he considered it as a non-descript insect, and an unique in this country. But he has since found that it is mentioned by Fabricius, in his Systema Entomologiæ, as a new genus under the name of leucospis dorsigera. There is one of the insects in the cabinet of the celebrated Linnæus, now in the possession of J. E. Smith, M. D. F. R. S. & Pr. L. S. Sulz, and other writers, have also described it.
It appears at first sight like a wasp, to which genus the folded wings would have given it a place, had not the remarkable sting or tube on the back removed it from thence. It is probably a species between, and uniting the sphex and wasp, in some degree partaking of the characters of both. The antennæ are black and cylindrical, increasing in thickness towards the extremity; the joint nearest the head is yellow, the head is black, the thorax is also black, encompassed round with a yellow line, and furnished with a cross one of the same colour near the head. The scutellum is yellow, the abdomen black, with two yellow bands, and a spot of the same colour on each side between the bands. A deep black polished groove extends down the back, from the thorax to the anus, into which the sting turns and is deposited, leaving the anus very circular; a yellow line runs on each side the sting. The anus and the whole body, when viewed with a shallow magnifier, appear punctuated; these points, when examined in the microscope, appear hexagonal, as in the plate; and in the center of each hexagon a small hair is to be seen; the feet are yellow, the hinder thighs very thick and dentated, forming also a groove for the next joint; they are yellow with black spots. This insect is found in Italy, Switzerland, France, and Germany. Fig. 1 shews it very much magnified; Fig. 2 is a side view of it less magnified; Fig. 3 is the object of its real size.
Plate XVIII.Fig. 1 and 6.
This extraordinary little creature was found by my ingenious friend, Mr. John Adams, of Edmonton; he was at the New Inn, Waltham Abbey, where it was spied by some labouring men who were drinking their porter. The man who first perceived it,thought it was of an uncommon form; on a more minute inspection, it was supposed to be a louse with unusual long horns; others thought it was a mite. This produced a debate, which attracted the attention of my friend, who obtained the insect from them for further observation. Mr. Martin has given some account of it in the third volume of “The Young Gentleman and Lady’s Philosophy.” Mr. Adams favoured me with the insect, that an accurate drawing might be taken from it, which I thought would be highly pleasing not only to the lovers of microscopic observations, but also to the entomologist. It appears to be quite a distinct species from the phalangium cancroides of Linnæus, of which a good drawing has been given by Hooke, Rösel, Schæffer, &c.; it has also been described by Scopoli, Geoffroy, and other naturalists; not one, however, of these descriptions agrees with the animal under consideration. The abdomen of this is more extended, the claws are larger and much more obtuse; the body of the other being nearly orbicular, the claws slender, and finishing almost in a point, more transparent, and of a paler colour. It is very probable, that there are several species nearly similar. Mr. Marsham has two in his possession, one like the drawings of Reaumur, the other not to be distinguished from that which is represented in the plate, except that it wants the break or dent in the claws, so conspicuous in this. The latter he caught on a flower in Essex, the first week in August, firmly affixed by its claws to the thigh of a large fly, and could not disengage it from thence without considerable difficulty; to accomplish which, he was obliged to tear off the fly’s leg, and was much surprized to see the bold little creature spring forward full a quarter of an inch, and once more seize its prey, from which he again found it very difficult to disengage it. Fig. 1 represents the insect considerably magnified, Fig. 6 the natural size.[105]
[105]According to Aldrovandus, this insect was not unknown to Aristotle, who mentions it as being found in books and paper. Wolphius, on the authority of Gesner, says that a few are to be met with in some parts of Switzerland. Scaliger also notices it, having found two of them in his books. It has been by various systematic writers referred to different genera; De Geer has instituted a new genus for it under the name of chelifer; Fabricius has remanded it to that of scorpio, to which perhaps it is more nearly allied than any other.Amongst the number of naturalists who have observed and described the insect, it appears rather extraordinary that none have met with one similar to that in the plate, in respect to the break in the claws. In a cabinet of curious microscopic objects which I purchased several years since, and which originally came from Holland, there were four of them in the most perfect condition. A botanical friend, Mr. Young, also favoured me with a living one which he found among some plants collected by him in one of his excursions; but, as his box contained a variety of plants, and he did not discover the insect till his return, it was impossible to ascertain the particular one on which it was taken. All these resembled the one here exhibited, excepting the claws being longer and more slender, and being deficient in the distinguishing characteristic; I have lately seen another, in which the two fangs that are shewn highly magnified in Plate 85 of the Naturalist’s Miscellany, are very apparent, being so large, as to exceed in diameter the thickest part of the claws.My respectable friend, Matthew Yatman, Esq. informs me, that some years since one was found on a bottle of wine packed in saw-dust, at the house in which he then resided in Percy street; on putting the point of a pin towards it to remove it from the bottle, it ran backward, put itself into an attitude of defence, and opened its claws as meditating vengeance. In the same cellar one had many years previous been discovered, sufficiently large to admit its being fastened to a card with thread by a young gentleman, being at least four times the usual size.Rösel says it dwells among paper, in old books and their bindings, in chests of drawers, and in the crevices of old buildings. In order to discover whether the insect possessed a sting, he often by various means endeavoured to irritate it; but it never shewed the smallest inclination to defend itself, on the contrary, it always endeavoured to avoid a contest; if so, it evidently appears that those few met with in this country are of a more bold and warlike disposition.Seba asserts that these insects resemble the large scorpions, the tail excepted, which is small, and usually concealed by being drawn close to the under part of the abdomen; but in this respect he must probably have been mistaken, as it does not appear that this circumstance has been noticed by any other person.Edit.
[105]According to Aldrovandus, this insect was not unknown to Aristotle, who mentions it as being found in books and paper. Wolphius, on the authority of Gesner, says that a few are to be met with in some parts of Switzerland. Scaliger also notices it, having found two of them in his books. It has been by various systematic writers referred to different genera; De Geer has instituted a new genus for it under the name of chelifer; Fabricius has remanded it to that of scorpio, to which perhaps it is more nearly allied than any other.
Amongst the number of naturalists who have observed and described the insect, it appears rather extraordinary that none have met with one similar to that in the plate, in respect to the break in the claws. In a cabinet of curious microscopic objects which I purchased several years since, and which originally came from Holland, there were four of them in the most perfect condition. A botanical friend, Mr. Young, also favoured me with a living one which he found among some plants collected by him in one of his excursions; but, as his box contained a variety of plants, and he did not discover the insect till his return, it was impossible to ascertain the particular one on which it was taken. All these resembled the one here exhibited, excepting the claws being longer and more slender, and being deficient in the distinguishing characteristic; I have lately seen another, in which the two fangs that are shewn highly magnified in Plate 85 of the Naturalist’s Miscellany, are very apparent, being so large, as to exceed in diameter the thickest part of the claws.
My respectable friend, Matthew Yatman, Esq. informs me, that some years since one was found on a bottle of wine packed in saw-dust, at the house in which he then resided in Percy street; on putting the point of a pin towards it to remove it from the bottle, it ran backward, put itself into an attitude of defence, and opened its claws as meditating vengeance. In the same cellar one had many years previous been discovered, sufficiently large to admit its being fastened to a card with thread by a young gentleman, being at least four times the usual size.
Rösel says it dwells among paper, in old books and their bindings, in chests of drawers, and in the crevices of old buildings. In order to discover whether the insect possessed a sting, he often by various means endeavoured to irritate it; but it never shewed the smallest inclination to defend itself, on the contrary, it always endeavoured to avoid a contest; if so, it evidently appears that those few met with in this country are of a more bold and warlike disposition.
Seba asserts that these insects resemble the large scorpions, the tail excepted, which is small, and usually concealed by being drawn close to the under part of the abdomen; but in this respect he must probably have been mistaken, as it does not appear that this circumstance has been noticed by any other person.Edit.
Plate XVIII.Fig. 3, 4, and 5.
The insect, which is represented very considerably magnified at Fig. 3, is of the hemiptera class. It was first described and figured by De Geer in the Swedish Transactions for 1744, under the name of physapus ater, alis albis; Linnæus afterwards introduced it in a subsequent edition of the Systema Naturæ distinguished by the name thrips physapus.
These insects live upon plants, and particularly in flowers. The one figured here is the black thrips, with white wings; the antennæ have six articulations; the body is black; the wings whitish, long, and hairy; the head small, with two large reticulareyes. The antennæ are of an equal size throughout, and divided into six oval pieces which are articulated together. The extremities of the feet are furnished with a membranaceous and flexible bladder, which it can throw out and draw in at pleasure. It places and presses this bladder against the substances on which it is walking, and seems to fix itself thereby to them; the bladder sometimes appears concave towards the bottom, the concavity increasing or diminishing in proportion to the degree of pressure.
They have four wings, two upper and two under ones; these last are with great difficulty perceived, they are fixed to the upper part of the breast, lying horizontally; both of them are rather pointed towards the edges, and have a strong nerve running round them, which is set with a fringe of fibrillæ, tufted at the extremity. The wings are represented by themselves at Fig. 4; the insect of the real size at Fig. 5. They are to be found in great plenty in the spring and summer, in the flowers of the dandelion, and various other plants.
Plate XVIII.Fig. 2 and 7.
For a full description of this singular fish, I must refer the reader to Pennant’s British Zoology, vol. iii. p. 117. The Linnean name is cyclopterus lumpus. Fig. 2 is a piece of the skin highly magnified: there are no scales on the body, but a great number of tubercles, which are here exhibited. Fig. 7 is the natural size of the object.
These fishes being extremely fat, renders them an agreeable diet to the natives of Greenland, in which seas they abound in the months of April and May; they also resort in multitudes during spring to the coast of Sutherland, near the Ord of Caithness in North Britain, where the seals prey greatly upon them, leaving the skins; numbers of which thus emptied float at that season ashore. When a good specimen is procured, it forms a most beautiful object for the opake microscope.
Plate XX.Fig. 1 and A.
This is a beautiful insect of the hemiptera class, or that kind where the elytra are only in part crustaceous, and which do not form a longitudinal suture down the back, but fold over about one-third of their length toward the bottom, where it is also partly transparent. It is of the genus cimex, and called striatus by Linnæus. Its colours are bright and elegantly disposed: the head, proboscis, and thorax are black. The thorax is ornamentedwith yellow spots, the middle one large, and occupying almost one-third of the posterior part; the other two are on each side, and triangular. The scutellum has two yellow oblong spots, pointed at each end; the ground of the elytra is a bright yellow, spotted and striped with black. The nerves are yellow, and there is a brilliant triangular spot of orange, which unites the crustaceous and membranaceous parts; the latter is brown and clouded. The feet are of a fine red, and the rings of the abdomen are black, edged with white. This pretty insect is to be found in June, upon the elm-tree. It is represented at A of the natural size.
Plate XX.Fig. 2 and B.
A very common, though elegant insect of the coleoptera class, is represented at Fig. 2, as seen in the lucernal microscope, and of its natural size at B; it is called by Linnæus chrysomela asparagi, from the larva feeding on the leaves of that plant. Its shape is oblong, the antennæ black, composed of many joints nearly oval. The head is of a bright, but deep blue; the thorax red and cylindrical; the elytra blue, with a yellow margin, and three spots of the same colour on each, one at the base of an oblong form, and two united with the margin; the legs are black, but the under side of the belly is of the same blue colour with the elytra and head. This little animal, when viewed by the naked eye, scarcely appears to deserve any notice; but when examined by the microscope, is one of the most pleasing opake objects we have. It is found in June, on the asparagus after it has run to seed. De Geer says, that it is very scarce in Sweden.
Plate XX.Fig. 3 and C.
The insect which comes at present under our inspection is particularly adapted to shew the advantages of the microscope, which alone will discover the peculiarities of its figure; this is so remarkable, that entomologists appear undetermined as to its genus. Geoffroy formed a new one for it, under the title of notoxus, in which he has been followed by Fabricius; even Linnæus himself could not determine at first where to place it, for in the Fauna Suecica he makes it an attelabus, but in the last edition of the Systema Naturæ he has fixed it as a meloe, calling it the meloe monoceros; but still he adds, “genus difficile terminatur forte huic proximum.” Both Geoffroy and Schæffer have given figures of it, but as they had not that kind of microscope which would assist them, their figures are imperfect.
The head is black, and appears to be hid or buried under the thorax, which projects forwards like a horn; the antennæ are composed of many articulations, and with the feet are of a dingy yellow. The hinder part of the thorax is reddish, the fore part black. The elytra are yellow, with a black longitudinal line down the suture; there is a band of the same colour near the apex, and also a black point near the base; the whole animal is curiously covered with hair. Geoffroy says it is found on umbelliferous plants: the one here described was found in May; the natural size is seen at C.
Plate XIX.Fig. 1 and 3,
Represent two magnified views of the feet of the monoculus apus of Linnæus. They are curiously contrived to assist theanimal in swimming, and form very agreeable objects for the microscope. Fig. 2 and 4 are the same objects of the natural size.
The outside covering or scales of fish afford an immense variety of beautiful objects for the microscope. They are formed in the most admirable manner, and arranged with inconceivable regularity and symmetry: some are long, others nearly round, others again square; varying in shape, not only in different species, but even considerably on the same fish; those which are taken from one part not being entirely similar to those which are taken from another.
Leeuwenhoeck supposed each scale to consist of an infinity of scales laid one over the other; or, more simply, of an infinity of strata, of which those next to the body of the fish are the largest.
These strata, when viewed with the microscope, exhibit specimens of wonderful mechanism and exquisite workmanship. In some scales we discover a prodigious number of concentric flutings, too fine, as well as too near each other, to be easily enumerated; they are probably formed by the edges of each stratum, denoting the limits thereof, and the different stages of the growth of the scale. These flutings are often traversed by others diverging from the center of the scale, and generally proceeding from thence in a straight line to the circumference.
Plate X.Fig. 7, exhibits a scale from a species of the parrot fish of the West-Indies, considerably magnified. Fig. 8, the real size of the scale.
Plate X.Fig. 9, is a magnified scale of the sea-perch, which is found on the English coast. Fig. 10, the same scale of the natural size.
Plate XIX.Fig. 7, a scale from the haddock, as seen in the microscope. Fig. 8, the same of the natural size.
Plate XIX.Fig. 9, a scale from a species of perch from the West-Indies, magnified. Fig. 10, the scale of its real size.
Plate XIX.Fig. 11, a scale from the sole-fish, delineated as it appears in the microscope; the pointed part is that which stands without the skin, as may be seen in Fig. 5, which represents a piece of the skin of a sole, as viewed by the opake microscope. Fig. 6 and 12, the same objects of their real size.
Having in the two preceding chapters given the reader such a general idea of the history and œconomy of a great variety of those minute animated bodies, called insects, as I am inclined to hope has not only afforded him entertainment and instruction, but tended to excite an emulation for further researches; I shall endeavour to gratify so laudable a disposition, by introducing him to a class of beings whose œconomy and singular properties equally engage the attention of the philosopher and the natural historian; a scene which opposes our general system of vitality, and which presents to the eye of the mind, as well as that of the body, a series of astonishing wonders. It is among the minutiæ of nature that we find her models most diversified, and displaying the marvellous fecundity of its powers.
The polypes described in this chapter are fresh-water insects, of the genus of hydra, of the order of zoophytes, and class of vermes. The body consists of a single tube, furnished at one end with long arms, by these it seizes small worms, and conveys them to its mouth. It has, according to our general notions, neither head, heart, stomach, nor intestines of any kind; and iswithout the distinction of sexes, yet extremely prolific. From the simplicity of its structure those of its œconomy and functions are probably derived. When they are cut or divided into a number of pieces, the separated parts in a very little time become so many perfect and distinct animals; each piece having a power of producing a head, a tail, and the other organs necessary for its existence.
They are generally known by the name of polype; but as this was thought by many to be improper, because that, strictly speaking, they have no feet, Linnæus called the genus hydra, probably from their property of re-producing the parts which are cut off, a circumstance that naturally brings to mind the fabulous story of the Lernean hydra. Dr. Hill called them biota, on account of the strong principle of life with which every part is endued.
Leeuwenhoeck, whose indefatigable industry in his researches after small insects permitted very few things to escape his notice, discovered these animals, and gave some account of them in the Philosophical Transactions for the year 1703. There is also in the same volume a letter from an anonymous hand on this subject. We had, however, no regular account of them, their various habits, their different species, or of their wonderful properties, till the year 1740, when they first engaged the attention of M. Trembley, to whose assiduity and observations we are indebted for the display of their nature and œconomy.
Previous to the successful experiments of this gentleman, Leibnitz and Boerhaave, as well as some of the ancient philosophers, reflecting on the various gradations in the scale of animated nature, had endeavoured to prove that there might be degrees of life between the animal and the plant, and that animals might befound which would propagate by slips, like plants. These conjectures were verified by Trembley, but not in consequence of any pre-conceived ideas in favour of such a supposition; on the contrary, it was only by repeated observations that he could destroy his own prejudices, and join these wonderful beings to the animal kingdom.[106]
[106]A great part of the knowledge of the ancients consisted in an extensive variety of ingenious hypotheses, the result of intense study and application; and it need not excite surprize, if, amongst a number of suppositions, some of them have since been found conformable to truth.The moderns, animated by the example of the great Bacon, by an abundance of experiments frequently repeated, and the assistance of good instruments, have introduced unquestionable demonstration in the place of speculation; this renders the present philosophy very far superior to that of the ancients.Thus it is with respect to the subject now under consideration; many of the ancients conjectured that animated beings might exist possessed of the wonderful properties of the hydra; that some of them, however, were even witnesses of the fact, cannot well be disputed; though it may be fairly presumed, that their knowledge of this animal, comparatively with that we are now in possession of, was very circumscribed and imperfect.St. Augustine relates that one of his friends performed the experiment before him, of cutting a polype in two, and that immediately the two parts thus separated betook themselves to flight, moving with precipitation different ways. The original passage is too long to be here inserted, but may be found in his work “De Quantitate Animæ,” c. 62, p. 431, col. 1.Aristotle, speaking of insects with many feet, expresses himself nearly in the same manner; without naming the particular creatures to which he alludes, he observes, that there are of these animals or insects, as well as of plants and trees, some that propagate themselves by shoots; and, as what were but the parts of a tree before, become thus distinct and separate trees; so, in cutting one of these animals, the pieces which before composed altogether but one animal, become suddenly so many distinct individuals. And he adds, that the soul in these insects is in effect but one, though multiplied in its powers, as it is in plants. Aristot. de Histor. Animal. tom. 1, lib. 4, cap. 7, pag. 824, & de Part. Animal. lib. 4, tom. 1, cap. 6, pag. 1029. &c. This will suffice to shew that the ancients were not entirely unacquainted with the subject before us; though it does not derogate from the merit of Leeuwenhoeck, Trembley, and other ingenious naturalists, by whose assiduous and patient investigations we have obtained a more perfect knowledge of this astonishing class of animated beings.Edit.
[106]A great part of the knowledge of the ancients consisted in an extensive variety of ingenious hypotheses, the result of intense study and application; and it need not excite surprize, if, amongst a number of suppositions, some of them have since been found conformable to truth.
The moderns, animated by the example of the great Bacon, by an abundance of experiments frequently repeated, and the assistance of good instruments, have introduced unquestionable demonstration in the place of speculation; this renders the present philosophy very far superior to that of the ancients.
Thus it is with respect to the subject now under consideration; many of the ancients conjectured that animated beings might exist possessed of the wonderful properties of the hydra; that some of them, however, were even witnesses of the fact, cannot well be disputed; though it may be fairly presumed, that their knowledge of this animal, comparatively with that we are now in possession of, was very circumscribed and imperfect.
St. Augustine relates that one of his friends performed the experiment before him, of cutting a polype in two, and that immediately the two parts thus separated betook themselves to flight, moving with precipitation different ways. The original passage is too long to be here inserted, but may be found in his work “De Quantitate Animæ,” c. 62, p. 431, col. 1.
Aristotle, speaking of insects with many feet, expresses himself nearly in the same manner; without naming the particular creatures to which he alludes, he observes, that there are of these animals or insects, as well as of plants and trees, some that propagate themselves by shoots; and, as what were but the parts of a tree before, become thus distinct and separate trees; so, in cutting one of these animals, the pieces which before composed altogether but one animal, become suddenly so many distinct individuals. And he adds, that the soul in these insects is in effect but one, though multiplied in its powers, as it is in plants. Aristot. de Histor. Animal. tom. 1, lib. 4, cap. 7, pag. 824, & de Part. Animal. lib. 4, tom. 1, cap. 6, pag. 1029. &c. This will suffice to shew that the ancients were not entirely unacquainted with the subject before us; though it does not derogate from the merit of Leeuwenhoeck, Trembley, and other ingenious naturalists, by whose assiduous and patient investigations we have obtained a more perfect knowledge of this astonishing class of animated beings.Edit.
Though natural history is so fruitful in extraordinary facts, it has hitherto produced none so singular as the various properties of the different species of the hydra.
I shall endeavour, first, to trace the progress of this discovery, in which we shall see with what sage caution and accuracy Trembley, and other naturalists examined this wonderful phænomenon, and what accumulated evidence was judged necessary to establish the fact.
We find M. Trembley writing in January, 1741, to M. Bonnet, that he did not know whether he should call the object which then engaged his attention, a plant or an animal. “I havestudied it,” says he, “ever since June last, and have found in it striking characteristics of both plant and animal. It is a little aquatic being. At first sight, every one imagines it to be a plant; but if it be a plant, it is sensitive and ambulant; if it be an animal, it may be propagated by slips or cuttings, like many plants.” It was not till the month of March, in the same year, that he could satisfy himself as to their nature.
When Reaumur saw, for the first time, two polypes formed from one that he had divided into two parts, he could hardly believe his eyes; and even after having repeated the operation an hundred times, and again examined it an hundred more, he says that the sight was not become familiar to him.
The first account the Royal Society received of the surprizing properties of the hydra, was in a letter from M. Buffon, dated the 18th of July, 1741, to Martin Folkes, Esq. their president, acquainting them with the discovery of a small insect called a polypus, which is found sticking about the common duck weed, and which, being cut in two, puts forth from the upper part a tail, and from the lower end a head, so as to become two animalsinstead of one. If it be cut into three parts, the middlemost puts out from one end a head, and from the other a tail, so as to become three distinct animals, all living like the first, and performing the various offices of their species: which observations are, adds Buffon, well averred.
There is no phænomenon in all natural history more astonishing than this, that man, at pleasure, should have a kind of creative power, and out of one life make two, each completely formed with all its apparatus and functions, its perceptions and powers of motion and self-preservation; and as complete in all respects as that from which they derived their existence, and equally enjoying the humble gratifications of their nature.[107]
[107]Goldsmith’s History of the Earth and Animated Nature.
[107]Goldsmith’s History of the Earth and Animated Nature.
Mr. Folkes, in confirmation of the foregoing article, communicated to the Society a letter from the Hon. W. Bentinck, Esq. at the Hague, dated September, describing the insects discovered by Trembley, adding, that he himself had seen them. In November, a letter was read from Dr. Gronovius, of Leyden, giving an account of a water insect not yet known to, or described by any author; after describing it, he adds, “but what is more surprizing, if this animal is cut into five or six pieces, in a few hours there will be as many animals, exactly similar to their parent.” The accounts of this animal were so extraordinary, that they were not credited until Professors Albinus and Musschenbroeck were provided with some specimens, and found all that had been related thereof to be exactly true.
November 25, a letter from Cambridge was read to the Royal Society, in which the author endeavours to lessen, by reason, the prejudices which then combated the belief of these facts. “Someof our friends,” says the author, “who are firmly attached to the general metaphysical notions they have formerly learned, reason strongly against the possibility of such a fact: but I have myself owned on other occasions, my distrust of the truth, or certainty at least, of some of those principles, and I shall make no scruple of acknowledging, that I have already seen so many strange things in nature, that I am become very diffident of all general assertions, and very cautious in affirming what may or may not possibly be. The most common operations both of the animal and vegetable world, are all in themselves astonishing, and nothing but daily experience and constant observation can make us see without amazement an animal bring forth another of the same kind, or a tree blossom and bear leaves and fruit.
“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 topersuade 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:
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 ofLinnæus, 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 orVermes, 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, seepage 179, andpages 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.
[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 ofLinnæus, 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 orVermes, 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, seepage 179, andpages 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 inPlate XXI.Fig. 5.
2. Hydra fusca, tentaculis suboctonis longissimis.
This polype has very long arms, often eight in number; it is represented atPlate 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 atPlate 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 atPlate XXII.Fig. 27 and 28.
7. Hydra socialis, mutica torosa rugosa.
Bearded, thick, and wrinkled.Plate XXI.Fig. 11.
Plate XXI.andXXIII.
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 oneside; 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 inPlate 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 posteriorextremitybagainst a plant or other substance, ase f; the bodya b; and the armsa 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 extremitya, to the partd, 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 extendingor 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 tailb, having the body and the armsaextended 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 polypea b, Fig. 20, to be fixed by the tailb, 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 ata, 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 tailb, 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 inPlate XXIII. A.Fig. 13; sometimes it appears truncated, as inPlate XXI.Fig. 8; at other times the interval between the arms appears closed, as inPlate 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 inPlate 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 inPlate XXIII. A.Fig. 6, 7, 8; its mouth was at the anterior enda, Fig. 8, of one of these parts. The tail was at the endbof 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 itwere 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 thendissolves 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, inPlate 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 tolook 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.
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 beobserved 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, seePlate 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 formof 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 twopoints 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, foreach 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.
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 contractingthe body, and thus becoming straight, loosens herself from the young one.