CHAP. VI. A GENERAL VIEW OF THE INTERNAL PARTS OF INSECTS, AND MORE PARTICULARLY OF THE CATERPILLAR OF THE PHALAENA COSSUS---A DESCRIPTION OF SUNDRY MISCELLANEOUS OBJECTS.
The interior part of insects includes four principal viscera; the spinal marrow, the intestinal bag, the heart, and tracheal vessels.
The spinal marrow, or principal trunk of the nerves of insects, is a whitish thread, extended the whole length from the head to the hindermost part, furnished at intervals with small knots or ganglions. From these knots proceed the nervous threads that are supposed to be the instruments of sensation and motion.
On the medullary thread is placed the intestinal bag, which is equal to it in length; it is a long gut, in which are contained the oesophagus, the stomach, and intestines.
Along the back, and parallel to the intestinal bag, runs a long thin vessel, in which may be perceived through the skin of the insect alternate contractions and dilatations; this part is supposed to perform the functions of the heart.
The tracheal vessels of insects are very similar to those of plants; are of the same structure, colour, and elasticity, and are, like them, dispersed through the whole body.
A clearer idea of these parts will be obtained by the short extract I shall give of M. Lyonet’s work; which, at the same time that it displays the wonderful organization of insects, shews how worthy it is of the attention of a rational being; and, though this description is confined to a particular species, it will be found to accord in general with a great number.
Of all the modifications of which matter is susceptible, the most noble is undoubtedly the organization thereof. In the structure of animals, the Sovereign Wisdom is exhibited to our view in the most striking manner. The body of an animal is a little particular system more or less complicated, and which, like the system of the universe at large, is the result of the combination and connection of a multitude of different parts, which all conspire to produce one general effect, the manifestation of the principle which we term life. So wonderful are these combinations that we are incapable of comprehending, or even of admiring sufficiently the astonishing apparatus of springs, levers, counter-weights, tubes of different diameters, &c. which constitute these organical machines. The interior parts of the insect, the most despicable in appearance, would absorb all the powers of the most able anatomist. He would be lost in the labyrinth as soon as he attempted to explore all its windings. A truth that will be evident to every one who considers only the small portion here introduced of the anatomy of the caterpillar inhabiting the trunk of the willow-tree. This caterpillar produces the phalÆna cossus, or goat-moth. M. Lyonet in his admirable work entitled, “Traite Anatomique de la Chenille qui ronge le Bois de Saule,” has given an ample and minute description of this insect. In the following concise abstract enough will appear to convince the reader of the utility of microscopic glasses, in displaying the wonders of the creation, and to afford additional proof that the attention of the Almighty is not confined merely to objects of magnitude.
In a former edition of this work, I entered into a more minute detail of the several parts contained in the figures exhibited in plate XII. This account I have now omitted, as after all it could not convey a clear idea of the muscles alone, much less of the different parts of the caterpillar, without a reference to other plates of M. Lyonet’s work. I therefore concluded it would be better to let the figures speak for themselves, and then give a general description of the interior parts of the caterpillar; referring the reader for full particulars to the original.
Figures 1 and 2 represent the muscles of the caterpillar, when it is opened at the belly. Fig. 3 and 4 exhibit a view of the muscles when it is opened at the back. Fig. 5 and 6, an anatomical delineation of the head; so complex is this organ, that in order to give an adequate idea of its structure, M. Lyonet has employed no less than twenty figures. Fig. 7 is an out-line of the head more magnified than in the last figures. In order to obtain the views here exhibited, the muscles were freed as well from fat, as from the nerves and other vessels.
The BODY of the caterpillar in the Plate Fig. 2 and 3, is divided into twelve parts, corresponding to its rings marked by the numbers 1 to 12; to the first number the word RING is affixed. Each of these rings is distinguished from that which follows, and that preceding it, by a kind of neck or small hollow part. By conceiving a line to pass through these necks, and forming boundaries to the rings, we acquire twelve more divisions, Fig. 1 and 4; these are also marked with the numbers 1 to 12; to the first the word DIVISION is annexed. The several parts exhibited in the divisions, Fig. 1, are the muscles; those in Fig. 2, under the word ring, are also muscles, which appear when those in Fig. 1 are removed, lying under them.
The anatomical delineation of the muscles of the head, Fig. 5 and 6, should be considered as consisting of two figures, which join in the middle, being terminated by the superior and inferior lines. The head, as here represented, is magnified about three-hundred times. H H are the two palpi: the truncated muscles d, belong to the lower lip, and form a part of those which give it motion: K, the two ganglions of the neck united: I I, the two silk vessels: L, the oesophagus: M, the two dissolving vessels: the Hebrew letters denote the continuation of the cephalic arteries: S T U W and X are the ten abductor muscles of the jaw: under e e and f f are seen four occipital muscles: a a, a nerve of the first pair, belonging to the ganglion of the neck; b, a branch of this nerve.
Fig. 7 is an outline of the head magnified considerably more than in the last figure, exhibiting the nerves as seen from the under part. Excepting in two or three instances, only one nerve of each pair is shewn, as a greater number would have occasioned confusion. The nerves of the first ganglion of the neck are designed by capital letters; those of the ganglion a, are distinguished by Roman letters; those of the small ganglion, by Greek characters; and those of the frontal ganglion, except one, by numbers.
A GENERAL VIEW OF THE INTERIOR PARTS OF THE CATERPILLAR.
The MUSCLES have neither the exterior form, nor the colour of those of larger animals. In their natural state they are soft, and have the appearance of a jelly; they are of a greyish blue, and the silver-coloured appearance of the aerial or pulmonary vessels, which creep over and penetrate their substance, exhibits under the microscope a most beautiful spectacle. When the caterpillar has been soaked for some time in spirit of wine, they lose their elasticity and transparency, and become firm, opake, and white; the aerial vessels disappear. At first sight they might be taken for tendons, as they are of the same colour and possess almost the same lustre. They are generally flat, and of an equal size throughout; the middle seldom differs either in colour, substance, or size, from the extremities. The ends are fixed to the skin; the rest of the muscle is generally free and floating; several of them branch out considerably; the branches extend sometimes so far, that it is not always easy to discover whether they are distinct and separate muscles, or parts of another. They are of a moderate strength; those that have been soaked in spirit of wine, when examined by the microscope, will be found to be covered with a membrane which may be separated from them; they then appear to consist of several parallel bands, disposed according to the length of the muscle. These, when divided by the assistance of very fine needles, appear to be composed of still smaller bundles of fibres, in the same direction; which, when examined by a very deep magnifier, and in a favourable light, appear twisted like a small cord. The muscular fibres of the spider, which are much larger than those of the caterpillar, are found on examination to consist of two substances, one soft, and the other hard; the last is twisted round the former spirally, and thus gives to it the afore-mentioned cord-like appearance. If the muscles are separated by means of very fine needles, in a drop of some fluid, we find that they are not only composed of fibres, membranes, and aerial vessels, but also of nerves; and, from the drops of oil that may be seen floating on the fluid, that they are also furnished with many unctuous particles. The muscles in a caterpillar are very numerous, exceeding by much those of the human body; the reader may form some idea of their number by inspecting Fig. 1 2 3 and 4 of Plate XII. They occupy the greatest part of the head; there is an amazing number at the oesophagus, the intestines, &c. the skin is as it were lined by different beds of them, placed one under the other, and ranged with very great symmetry. The number of muscles that our observer has been able to distinguish is truly astonishing; he found 228 in the head, 1647 in the body, and 2066 in the intestinal tube, making in all 3941!
The SPINAL MARROW, and the brain of the caterpillar, if it can be said to have any, seem to have very little relation to those of man; in the last, the brain is inclosed in a bony cavity; it occupies the greatest part of the head, and is anfractuose, and divided into lobes. There is nothing similar to this in the caterpillar; we find indeed in the head of that which we are describing, a part which seems to answer the purpose of the brain, because the nerves that are disseminated through the head are derived from it; but then this part is unprotected, and so small, that it does not occupy one-fifth part of the head; the surface is smooth, and has neither lobes nor anfractuousness; and if we must call this a brain, the caterpillar may be said to have thirteen, as there are twelve more such parts following each other in a line; they are nearly of the same size with that in the head, and of the same substance, and it is from them that the nerves are distributed through the whole body. Lest the idea of thirteen brains might be disagreeable to his readers, Lyonet has called these parts ganglions. The spinal marrow in the human species descends down the back, inclosed in a bony case; is large with respect to its length, and not divided into branches, diminishing in thickness in proportion as it is removed further from the brain. In the caterpillar, the spinal marrow goes along the belly, is not inclosed in any tube, is very small, forks out at intervals, and is nearly of the same thickness throughout, except at the ganglions. For a description of the numerous vessels, and curious texture of these parts, reference must be had to the original work of Lyonet. The substance of the spinal marrow, and of the ganglions, is not near so tender and easily separated as in man; it has a very great degree of tenacity, and does not break without considerable tension. The substance of the ganglions differs from that of the spinal marrow, as no vessels can be discovered in the latter, whereas the former are full of very delicate ones. The patient anatomist of the caterpillar has counted forty-five pair of nerves, and two single ones; so that there are ninety-two principal nerves, whose ramifications are innumerable.
The TRACHEAL ARTERIES of the caterpillar are two large aerial elastic vessels, which with their numerous ramifications may be pressed close together, and drawn out considerably, but return immediately to their usual size when the tension ceases; they creep under the skin close to the spiracula, one at the right side of the insect, the other at the left, each of them communicating with the air, by means of nine spiracula; they are nearly as long as the body, beginning at the first spiraculum, and going a little farther than the last, terminating in some branches which extend to the extremities of the body. Round about each spiraculum the tracheal artery pushes forth a great number of branches, which are again divided into smaller ones; these further subdivide, and spread through the whole body of the caterpillar. This vessel and its principal branches are composed of three coats, which may be separated one from the other. The exterior covering is a thick membrane, furnished with a great number of fibres, which describe a vast variety of circles round it, communicating with each other by numerous shoots. The second is very thin and transparent; no particular vessel is distinguished in it. The third is composed of scaly threads, which are generally turned in a spiral form, and come so near each other, as scarce to leave any interval; these threads are curiously united with the membrane which occupies the intervals, and form a tube which is always open, notwithstanding the flexure of the vessel. There are also many other peculiarities in its structure, which cannot be well explained without more plates. The principal tracheal vessels branch out into 236 smaller ones, from which there spring 1326 different ramifications.
The part of the caterpillar which naturalists call the HEART, without being certain that it performs the functions thereof, is of a nature very different from that of larger animals. It is almost as long as the caterpillar itself, lies immediately under the skin at the top of the back, entering into the head, and terminating near the mouth. It is large and spacious towards the last rings of the body, and diminishes very much as it approaches the head, from the fourth to the twelfth division; it has on both sides, at each division, an appendage, which partly covers the muscles of the back; but, growing narrower as it approaches the lateral line, forms a number of irregular lozenge-shaped bodies. This muscular tube has been called the heart of the caterpillar; first, because it is generally filled with a kind of lymph, which has been supposed to be the blood of the caterpillar; secondly, because in all caterpillars, whose skin is in some degree transparent, continual, regular, and alternate dilatations and contractions may be perceived along the superior line, beginning at the eleventh ring, and going on from ring to ring to the fourth, whence this vessel has been considered as a file of hearts; but still this viscera seems to have very little relation to the heart of larger animals; we find no vessel opening into it, to answer to the aorta, vena cava, &c. &c. Near the eighth division are two white oblong masses, that join the tube of the heart; they have been called reniform bodies, because they are something similar to a kidney in their shape.
The CORPUS CRASSUM is, with respect to volume, the most considerable part of the whole caterpillar; it is the first and only substance that is seen on opening it, forming a kind of sheath, which envelopes and covers all the entrails, and introducing itself into the head, enters all the muscles of the body, filling the greatest part of the empty spaces in the caterpillar. It is of a milk-white colour. In its configuration it is very similar to the human brain. When the different masses of the corpus crassum which covers the entrails are removed, the largest parts are the oesophagus, the ventricle, and the large intestines.
The OESOPHAGUS descends from the bottom of the mouth to about the fourth division. The anterior part which is in the head is fleshy, narrow, and fixed by different muscles to the crustaceous parts thereof; the lower part which passes into the body is wider, and forms a kind of membranaceous bag, which is covered with very small muscles; near the stomach it is again narrower, and is as it were bridled by a strong nerve, which is fixed to it at distant intervals.
The VENTRICLE begins a little above the fourth division, where the oesophagus finishes, and terminates at the tenth division; it is about seven times longer than it is broad; the anterior part, which is the broadest, is generally folded. The folds diminish with the bulk, in proportion as it approaches the intestines. An assemblage of nerves cover the surface, it is surrounded by a number of aerial vessels, and opens into a tube, which Lyonet calls the large intestine.
There are three of these large tubes or INTESTINES, each of which differs from the other so much, both in structure and character as to require a particular name to distinguish them; though this is not the place to enumerate these characteristic differences. As most caterpillars are endued with a power or faculty of spinning, they are provided with two vessels where the substance is prepared, which, when drawn out, and extended in the air, becomes a silken thread; these two vessels are termed the silk-vessels or tubes; in the caterpillar of the cossus, they are often above three inches long, and are distinguished into three parts, the anterior, the intermediate, and posterior. It has also two other vessels, which are supposed to prepare and contain the liquor by which it dissolves the wood on which it feeds.
Thus have we endeavoured to give the reader some idea of the wonderful organization of this apparently imperfect animal. Assuredly the four-thousand[100] muscles employed in the construction of the caterpillar of the cossus cannot be considered without the deepest astonishment: their admirable co-ordination and junction with other parts equally numerous, yet all harmonizing and acting together as if they were essentially one, naturally lead the mind to consider the nature and perfection of creation, and to perceive that it is an exhibition of the highest wisdom; and that this wisdom, which in the minutest things gives evidence of such an immense attention to order and use, has, no doubt, framed the whole for some great purpose; but what that purpose is, exceeds the present limits of the human understanding to discover.
A DESCRIPTION
OF
SUNDRY MISCELLANEOUS OBJECTS,
EXHIBITED
IN SEVERAL PLATES OF THIS WORK.
OF THE LEPAS ANATIFERA OR BARNACLE.[101]
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, soft and 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.
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 the tube 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 obtained its 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]
OF THE LEUCOPSIS DORSIGERA.
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 this plate was 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.
OF THE LOBSTER INSECT.
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]
OF THE THRIPS PHYSAPUS.
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 reticular eyes. 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.
OF THE SKIN OF THE LUMP SUCKER.
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.
OF THE CIMEX STRIATUS.
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 ornamented with 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.
OF THE CHRYSOMELA ASPARAGI.
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.
OF THE MELOE MONOCEROS.
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 the animal in swimming, and form very agreeable objects for the microscope. Fig. 2 and 4 are the same objects of the natural size.
OF THE SCALES OF FISH.
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.
