or **AURELIA**, in natural history, a state of rest and seeming infertility, which butterflies, moths, and several other kinds of insects, must pass through before they arrive at their winged or most perfect state.

In this state, no creatures afford so beautiful a variety as the butterfly kinds, and they all pass through this middle state without one exception. The figure of the aurelia or chrysalis generally approaches to that of a cone, or at least the hinder part of it is in this shape; and the creature, while in this state, seems to have neither legs nor wings, nor has any power of walking. It seems indeed to have hardly so much as life. It takes no nourishment in this state, nor has it any organs for taking any; and indeed its posterior part is all that seems animated, this having a power of giving itself some motions. The external covering of the chrysalis is cartilaginous, and considerably large, and is usually smooth and glossy: but some few of them have a few hairs; some are also as hairy as the caterpillars from which they are produced; and others are rough, and, as it were, shagreened all over.

In all of these there may be distinguished two sides; the one of which is the back, the other the belly of the animal. On the anterior part of the latter, there may always be distinguished certain little elevations running in ridges, and resembling the fillets wound about mummies: the part whence these have their origin, is esteemed the head of the animal. The other side, or back, is smooth, and of a rounded figure in most of the chrysalises; but some have ridges on the anterior part, and sides of this part; and these usually terminate in a point, and make an angular appearance on the chrysalis.

From this difference is drawn the first general distinction of these bodies. They are by this divided into two classes; the round and the angular kinds. The first are, by the French naturalists, called *feves*; from the common custom of calling the chrysalis of the silk-worm, which is round, by this name.

There is something more regular in this distinction than might at first be conceived; for the division is continued from the fly-state: the rounded chrysalises being almost all produced by the *phalena* or moths; and the angular ones by the *lapidaria*, or day-flies. There are several subordinate distinctions of these kinds; but, in general, they are less different from one another than the caterpillars from whence they are produced.

The head of those of the first class usually terminates itself by two angular parts, which stand separate one from the other, and resemble a pair of horns. On the back, eminences and marks are discovered, which imagination may form into eyes, nose, chin, and other parts of the human face.

There is a great variety and a great deal of beauty in the figures and arrangement of the eminences and spots on the other part of the body of the chrysalises of different kinds. It is a general observation, that those chrysalises which are terminated by a single horn, afford day-butterflies of the kind of those which have buttoned buttoned antennae, and whose wings, in a state of rest, cover the under part of their body, and which use all their fix legs in walking, those of many other kinds using only four of them. Those chrysalises which are terminated by two angular bodies, and which are covered with a great number of spines, and have the figure of a human face on their back in the greatest perfection, afford butterflies of the day-kind; and of that class the characters of which are, their walking on four legs, and using the other two, that is, the anterior part, in the manner of arms or hands. The chrysalises which have two angular bodies on their heads, but shorter than those of the preceding, and whose back shows but a faint sketch of the human face, and which have fewer spines, and those less sharp, always turn to that sort of butterfly the upper wings of which are divided into segments, one of which is so long as to represent a tail, and whose under wings are folded over the upper part of the back. A careful observation will establish many more rules of this kind, which are not so perfect as to be free from all exceptions; yet are of great use, as they teach us in general what sort of fly we are to expect from the chrysalis, of which we know not the caterpillar, and therefore can only judge from appearances.

There are the principal differences of the angular chrysalises; the round ones also have their different marks not less regular than those.

The greater number of the round chrysalises have the hinder part of their body of the figure of a cone; but the upper end, which ought to be its circular plane base, is usually bent and rounded into a sort of knee; this is usually called the head of the chrysalis; but there are also some of this kind, the head of which is terminated by a nearly plane surface: some of the creeping ten-legged caterpillars give chrysalises of this kind, which have each of them two eminences that seem to bring them towards the angular kind.

Among the angular chrysalises there are some whose colours seem as worthy our observation as the shapes of the others. Many of them appear superbly clothed in gold. These elegant species have obtained the name of chrysalis and aurelia, which are derived from Greek and Latin words, signifying gold; and from these all other bodies of the same kind have been called by the same names, though less, or not at all, entitled to them. As some kinds are thus gilded all over, so others are ornamented with this gay appearance in a more sparing manner, having only a few spots of it in different places on their back and belly. These obvious marks, however, are not to be depended upon as certain characters of distinction: for accidents in the formation of the chrysalis may alter them; and those which naturally would have been gilded all over, may be sometimes only so in part; and either these or the others may, by accident, be formed, as to show nothing of this kind at all, but be only of a dusky brown. Those, however, which have neither silver nor gold to recommend them to your eyes, do not want other colours, and those beautifully variegated. Some of them are all over of an elegant green, as is the chrysalis of the fennel-caterpillar; others of an elegant yellow; and some of a bright greenish tinge, variegated with spots of a shining black: we have a very beautiful instance of this last kind in the chrysalis of the elegant cabbage-caterpillar. The general colour of the chrysalis of the common butterflies, however, is brown.

Some are also of a fine deep black; and of these many are so smooth and glossy, that they are equal to the finest Indian japan. The common caterpillar of the fig-tree gives an instance of one of these most beautiful glossy ones; the caterpillar of the vine affords another of these fine black chrysalises.

The rounded chrysalises do not afford any thing of that variety of colouring so remarkably beautiful in the angular ones; they are usually of a dusky yellow, in different shades, and are often variously spotted with black: but these, as well as all other chrysalises, before they arrive at their fixed colour, pass through several other temporary ones; some being of a different colour when first produced from the caterpillar, from what they are a few days afterwards; and some varying so greatly, though only in degree, as not to be distinguishable, even by the most convergent eye, from what they were when first produced. The green rough caterpillar of the cabbage has a chrysalis which is green at first; and from that gradually goes through all the shades of green to a faint yellow, which is its lasting colour; and one of the oak caterpillars yields a chrysalis beautifully spotted with red at its first appearance; but these spots change to brown for their fixed colour: the third day from their formation usually fixes their lasting colours; and if they are observed to turn black in any part after this time, it is a sign that they are dead or dying.

The several species of insects, as a fly, spider, and an ant, do not differ more evidently from one another in regard to appearance, than do a caterpillar, its chrysalis, and a butterfly produced from it; yet it is certain, that these are all the product of the same individual egg; and nothing is more certain, than that the creature which was for a while a caterpillar, is, after a certain time, a chrysalis, and then a butterfly. These great changes produced in so sudden a manner, seem like the metamorphosis recorded in the fables of the ancients; and indeed it is not improbable that those fables first took their origin from such changes.

The parts being distinguishable in the chrysalis, we easily find the difference of the species of the fly that is to proceed from it. The naked eye shows whether it be one of those that have, or of those that have not, a trunk; and the assistance of a microscope shows the antennae so distinctly, that we are able to discern whether it belongs to the day or night clasps; and often to what genus, if not the very species: nay, in the plume-horned kinds, we may see, by the antennae, whether a male or female phalena is to be produced from the chrysalis; the horns of the female being in this state evidently narrower, and appearing less elevated above the common surface of the body, than those of the male.

All these parts of the chrysalis, however, though seen very distinctly, are laid close to one another, and seem to form only one mass; each of them is covered with its own peculiar membrane in this state, and all are surrounded together by a common one; and it is only through these that we see them; or rather we see on these the figures of all the parts moulded within, The chrysalis is soft when first produced, and is wetted on the front with a viscous liquor; its skin, though very tender at first, dries and hardens by degrees; but this viscous liquor, which surrounds the wings, legs, &c., hardens almost immediately; and in consequence falls off all those limbs, &c., into a mass, which were before loose from one another: this liquor, as it hardens, loses its transparency, and becomes brown; so that it is only while it is yet moist that these parts are to be seen distinct.

It is evident from the whole, that the chrysalis is no other than a butterfly, the parts of which are hid under certain membranes which fasten them together; and, when the limbs are arrived at their due strength, they become able to break through these membranes, and then expand and arrange themselves in their proper order.

The first metamorphosis, therefore, differs nothing from the second, except that the butterfly comes from the body of the caterpillar in a weak state, with limbs unable to perform their offices, whereas it comes from the chrysalis perfect.

M. Reaumur has given us many curious observations on the structure and uses of the several coverings that attend the varieties of the caterpillar-kind in this state.

The creatures in general remain wholly immovable in this state, and seem to have no business in it but a patient attendance on the time when they are to become butterflies; and this is a change that can happen to them, only as their parts, before extremely soft and weak, are capable of hardening and becoming firm by degrees, by the transpiration of that abundant humidity which before kept them soft; and this is proved by an experiment of M. Reaumur, who, inclosing some chrysalises in a glass tube, found, after some time, a small quantity of water at the bottom of it; which could have come there no other way, but from the body of the inclosed animal. This transpiration depends greatly on the temperature of the air; it is increased by heat, and diminished by cold; but it has also its peculiarities in regard to the several species of butterfly to which the chrysalis belongs.

According to these observations, the time of the duration of the animal in the chrysalis state must be, in different species, very different; and there is indeed this wide difference in the extremes, that some species remain only eight days in this state, and others eight months.

We know that the caterpillar changes its skin four or five times during its living in that state; and that all these skins are at first produced with it from the egg, lying closely over one another. It parts with, or throws off all these one by one, as the butterfly, which is the real animal, all this time within, grows more and more perfect in the several first changes. When it throws off one, it appears in another skin exactly of the same form; but at its final change from this appearance, that is, when it throws off the last skin, as the creature within is now arrived at such a degree of perfection as to need no farther taking of nourishment, there is no farther need of teeth, or any of the other parts of a caterpillar. The creature, in this last change, proceeds in the very same manner as in all the former, the skin opening at the back, and the animal making its way out in this shape. If a caterpillar, when about to throw off this last skin, be thrown into spirits of wine, and left there for a few days, the membranes within will harden, and the creature may be afterwards carefully opened, and the chrysalis taken out, in which the form of the tender butterfly may be traced in all its lineaments, and its eyes, legs, &c., evidently seen. It is not necessary, however, to seize upon this exact time for proving the existence of the chrysalis or butterfly in the caterpillar: for if one of these animals be thrown into spirit of wine, or into vinegar, some days before that time, and left there for the flesh to harden, it may afterwards be dissected, and all the lineaments of the butterfly traced out in it; the wings, legs, antennae, &c., being as evident here, and as large, as in the chrysalis.

It is very plain from this, that the change of the caterpillar into chrysalis is not the work of a moment; but is carrying on for a long time before, even from the very hatching of the creature from the egg. The parts of the butterfly, however, are not disposed exactly in the same manner while in the body of the caterpillar, as when left naked in the form of the chrysalis: for the wings are proportionally longer and narrower, being wound up into the form of a cord; and the antennae are rolled up on the head; the trunk is also twisted up and laid upon the head; but this in a very different manner from what it is in the perfect animal, and very different from that in which it lies within the chrysalis; so that the first formation of the butterfly in the caterpillar, by time arrives at a proper change of the disposition of its parts, in order to its being a chrysalis. The very eggs, hereafter to be depolished by the butterfly, are also to be found not only in the chrysalis, but in the caterpillar itself, arranged in their natural, regular order. They are indeed in this state very small and transparent; but after the change into the chrysalis, they have their proper colour.

As soon as the several parts of the butterfly, therefore, are arrived at a state proper for being exposed to the more open air, they are thrown out from the body of the caterpillar surrounded only with their membranes; and as soon as they are arrived after this at a proper degree of strength and solidity, they labour to break through these thinner coverings, and to appear in their proper and natural form. The time of their duration in this state of chrysalis is very uncertain, some remaining in it only a few days, others several months, and some almost a year in appearance. But there is a fallacy in this that many are not aware of. It is natural to think, that as soon as the creature has inclosed itself in its shell, be that of what matter it will, it undergoes its change into the chrysalis state. And this is the case with the generality; yet there are some which are eight or nine months in the shell before they become chrysalises; so that their duration in the real chrysalis state is much shorter than it naturally appears to be. M. Reaumur carefully watched the auriculated caterpillar of the oak in its several changes, and particularly from its chrysalis, which is of this last kind, into the fly; and has given an account of the method of this as an instance. stance of the general course of nature in these operations.

The membranes which envelope the creature in this chrysalis state are at first tough and firm, and immediately touch the several parts of the inclosed animal; but by degrees, as these parts harden, they become covered, some with hairs, and others with scales. These, as they continue to grow, by degrees fall off the several particular membranes which cover the parts on which they are placed, to a greater distance, and by degrees loosen them from the limbs. This is one reason of those membranes drying and becoming brittle.

The middle of the upper part of the corselet is usually marked with a line which runs in a longitudinal direction; and this part is always more elevated than the rest, even in the comical kinds, which are not otherwise angular. This line is in some very bold and plain; in others, it is so faint as not to be distinguishable without glasses; but it is always in the midst of that line that the shell begins to open. The motion of the head of the butterfly backwards first occasions this crack; and a few repetitions of the same motion open it the whole length of the line.

The clearing itself, however, entirely, is a work of more time in this case, than is the passing of the chrysalis out of the body of the caterpillar. In that case there is a crack sufficiently large in the skin of the back, and the whole chrysalis being loose comes out at once. But in this case, every particular limb, and part of the body, has its separate case; and these are almost inconceivably thin and tender, yet it is necessary that every part be drawn out of them before it appear naked to the open air. As soon as all this is effected, and the animal is at full liberty, it either continues some time upon the remains of its covering, or creeps a little way distant from it, and there rests. The wings are what we principally admire in this creature. These are at this time so extremely folded up, and placed in so narrow a compass, that the creature seems to have none at all; but they by degrees expand and unfold themselves; and finally, in a quarter of an hour, or half an hour at the utmost, they appear at their full size, and in all their beauty. The manner of this sudden unfolding of the wings is this: the small figure they make when the creature first comes out of its membranes, does not prevent the observing that they are at that time considerably thick. This is owing to its being a large wing folded up in the nicest manner, and with folds so arranged as to be by no means sensible to the eye, for the wing is never seen to unfold; but, when observed in the most accurate manner, seems to grow under the eye to this extent. When the creature is first produced from the shell, it is everywhere moist and tender; even its wings have no strength or stiffness till they expand themselves; but they then dry by degrees, and, with the other parts, become rigid and firm. But if any accident prevents the wings from expanding at their proper time, that is, as soon as the creature is out of its shell, they never afterwards are able to extend themselves; but the creature continues to wear them in their contracted and wholly useless state; and very often, when the wings are in part extended before such an accident happens, it flops them in a partial extension; and the creature must be contented to pass its whole life with them in that manner.

M. Reaumur has proved, that heat and cold make great differences in the time of hatching the butterfly from its chrysalis state: and this he particularly tried with great accuracy and attention, by putting them in vessels in warm rooms, and in ice-houses; and it seemed wholly owing to the halting or retarding the evaporation of the abundant humidity of the animal in the chrysalis state, that it sooner or later appeared in the butterfly form. He varnished over some chrysalises, in order to try what would be the effect of thus wholly preventing their transpiration; and the consequence was, that the butterfly came forth from these two months later than their natural time. Thus was the duration of the animal in this state lengthened; that is, its existence was lengthened; but without any advantage to the creature, since it was in the time of its state of inaction, and probably of insensibility.

Though this was of no consequence, Mr Reaumur deduces a hint from it that seems to be of some use. He observes, that hens eggs, of which we make so many uses, and eat in so many forms, are properly a sort of chrysalis of the animal; their germ, after they are impregnated by the cock, containing the young animal alive, and waiting only a due degree of warmth to be hatched, and appear in its proper form. Eggs tranpire notwithstanding the hardness of their shells; and when they have been long kept, there is a road found near one of their ends, between the shell and the internal membrane; this is a mark of their being stale, and is the effect of an evaporation of part of their humidity: and the same varnish which had been used to the chrysalis, being tried on eggs, was found to preserve them for two years, as fresh as if laid but the same day, and such as the nicest palate could not distinguish from those that were so. See Eggs.

It is not yet known how much farther this useful speculation might be carried, and whether it might not be of great use even to human life, to invent something that should act in the manner of this varnish, by being rubbed over the body, as the athlete did of old, and the savages of the West Indies do at this time, without knowing why. But to return to the insects which are the subjects of this article; their third state, that in which they are winged, is always very short, and seems destined for no other action but the propagation of the species. See Papilio.