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Page 63,1. 13. i
It is merely the external form. Although the changes which the external parts of insects undergo, in their different transformations, are the most remarkable, they are not consined to these p.irts alone. Very considerable changes likewise take place in their internal parts, some cf which are elongated, others contracted; some lose their sunctions) others acquire new ones, and others entirely disappear.
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Into four different classes. The explanation of the four sorts of charges mentioned in this chapter, is taken from Swammcrdam, who expresses himself on the subject, nearly in the same way with our author. Those who are not persectly versed in the different transformations of insects, will perhaps be at a loss to comprehend what is here related. I shall endeavour, in a sew words, to give as distinct an idea of them as poflible.
For this purpose, it is necessary, in the sirst place, to know, what is properly meant by tire state of nymph and chrysalis, so often mentioned. By these terms is meant, a state of impersection, attended semcti.nej with inactivity, inaction, abstinence and weakness, through which the inUct passes, after having attained a certain bulk, and in which its body receives the preparatives necessary for its passing to a state of persection. All the external parts of the insect are then found enveloped, either with their natural skin,or with'' a sine membrane, or with a hard ?.nd crufiaceous coat. In the sirst case, the limbs of the insect remain free, it preserves its power of acting, it eats, and its form is lit: le different •from what it was before. In the second case, the limbs of the insect are folded over its breast, but separate; it can neither eat, nor act, it retains hardly any traces of its former sigure, and has only a consuseJ resemblance to that which it is gning to assume. In the third case, the cover brings all these parts of the animal into one mass; it makes it equally incapable of eating and acting; it has no resemblance, either to what it formerly was, nor to what it is to be. These three sorts of change, are evidently very different, and yet, we have but two words in our language to distinguish them by. We say of the jnsects in the two sirst Rses, that they are changed into nymphs, and of those in
the last cr.se, that they have assumed the form of chrysaiidsTo these terms, it would be proper to add a third, in order to mark the disference between the sirst and second cases. It might be done, 1 think, very conveniently, by allowing the hit to retain the name of nymph, and calling those of the sirst kind lemi-nymph, or demi-nymph; a name which, perhaps, would not be inapplicable to them, considering the small degree of change they have undergone. Grasshoppers, which, instead of the long wings they acquire, have still only on their backs, the small cases, in which these wings are formed, are nymphs of this kind; they may properly be railed semi-nymphs. Those who have had an opportunity of examining a bee-hive, cannot sail to have remarked bees, st'.ll impersect in the shut cells; these are nymphs of the second order. The silk-worm surnishes a well-known example of insects under the form of a chrysalis.
Insects, which undergo no other metamorphosis, than thit which has converted them from the soft substance of an egg, to a wjl-formed and living body, are those which constitute the sirst chss of transformations spoken of in this chapter. They increase in size; the greater part cast their skin; some of their parts acquire a greater size than the rest, and sometimes take a disserent colour from what they had before. This is almost the whole change which these undergo.
The transformations of the insects of the other three classes do not terminate here: after having cast off their skins, for the most part several times, and after having acquired their destined bulk, all become either semi-nymphs, nymphs, or chrysalids. They pass a certain time under this form, and upon quitting it, assume that of a persect insect, capable of generation. It is from the diversity which takes place in these three forts of changes, that the principal characters, wjiich distinguish the insects of the second, from those of the sirst and third class are taken.
The insects of the second class, are those that pass thro' the state which I have called the state of semi-nymph. They do not undergo a transformation which is entirely complc.it, but in their last change, they have generally still all the members they had before, without having acquired any others, except jhey have got wings: and as we have already remarked, the semi-nymph differs little in form, from the animal which produced it. What always distinguishes it most, is, that there is seen upon its back, at the bale of the thorax, the cases in which the wings are formed, which before that, appeared but little, and often not at all. ]n other respects, it walks, runs, leaps and swims, as before. The difference betweeti the semi-nymph, and the winged insect which it produces, ib not always so obscure. In some species, it is even so great, that it is with difficulty we can discover a trace of irs sirst form; but ihis is not general, and the greater part, in their last state, differ in no other material part from the nymph, but in the wings.
The insects of the other two classes, do not enjoy the fame advantage with the other. They lose the Use of all their members when they enter upon their transformation, and havd rio resemblance to what they were before. An ahimal os these two classes, which before had no legs, or had sive, six, seven, eight, nine, ten, or eleven pnirs.of legs, has now no mofe nor less than three pairs, which, with the/ wings and antenna:, are,folded under its breast, and there remain immovcable.
What distinguishes these two list classes from each other, is, that the insects of the third class quit their skin, when they change into nymphs, or into chrysalids, and that those of the fourth change into nymphs under their skin, which, hardens round them, and serves them then for a case.
These are thq principal differences which Swammerdam and the author sind in these four classes. They consist, to express it in two words, in this, that the insects of the sirst class, after issuing from the e^g, undergo no other transformation: that thole of the second sufser an incdmple^t change, and become senii-nymphs, before arriving at their' ultimate form: that those of the third and fourth classes, before- arriving at their persect state, become, the sirst nymphs or chrysalids, and the others nymphs, by a total change of form, but with this difference, that thole of the third class quit their skirt at becoming nymphs or chrys.Jid'j and that those of the fourth become nymphs without quitting their skin.
M. de Reaumur, to whom Natural History is indebted for so many beautisul discoveries, found, in the transformation of insects of the fourth class, a new character, which ho one, perhaps, had observed before, and •i'hich, 1 think, distinguishes them more essentially from those of tire cher
u cUsscs, classes, than the changing into nymphs, without quitting' their skin. He discovered* that they undergo one transformation more than other insects: that before becoming nymphs, they assume under their skin, an elliptical form, or that of an elongated spheroid, in which no part of the animal is discernible; that in this state, the head, the thorax, the wings and legs of the nymph are inclosed in the interior cavity of the abdomen, from which they issue successively, by the anterior part, nearly in the same way as the extremity of the singer of a glove, which has been drawn in, is pushed out again. Thus, the insects of this class,are not solely distinguished from others, by their changing into nymphs under their skin: but principally, in that before becoming nymphs, they undi rgo a double transformation. According to this idea, the differences of the four orders of transformations may be reduced to terms simpler and more easily comprehended, by faying, that insects of the sirst order, after issuing from the egg, attain their persect state, without being previously disposed to it, by a change of formj that those of the second class are prepared for it, by an incompleat change of form; and those of the fourth, by a. double change of form.
* Lyonet here gives examples of these four classes of transformations. The sirst is exemplisied by the common earth-worm. The second class, by a dragon-fly, (Libellula puella.) The third, by insects of the three different orders: i. A pseudo-caterpillar, which seeds on the willow, with two and twenty seet, (Tenthredo marginata.) 2. A waterbeetle of the largest size, (Dytiscus piceus.) And 3. A caterpillar with sixteen teet, which lives on the trunks of willows, oaks, &c. (Phalæna Cossus.) The fourth class is illustrated by a white maggot, which proceeds from the eggs deposited by the large blue flies in flelh, when it is about to turn putrid. (Musca vomitoria.)
The celebrated Bergman, before he betook himself to the illustration of mineralogy, had been fond of the study of insects, and he has left us a classification of larvæ, a concise view of which, it is hoped, it will not be improper to give in this place.
The metamorphosis of larvæ, fays Bergman, consists in the excoriation, or deposition of the external skin of the insect, joined with a change os form. This, in general, is • twofold, to wit, from Ui: larva to the pupa, and from that,
to she perfect insect. An insect, subject to metamorphosis is called a larva, as long as it continues under the form it assumed, when it first came from the egg, though many of them, during that time, cast their (kin. It is called pupa, under the new form which it acquires, when it has thrown off the appearance of a larva.
Pupae are either chrysalids, nymphs, or semi-nymphs. A hard, motionless pupa, that does not eat and shews obscurely the members of the future insect, is called a chrysalis. The nymph is a tender pupa, lying at rest, not eating, and ■which shews clearly the separate members of the future insect. But the semi-nymph is a running pupa, that eats, and is hardly different from the larva, except in having the vagina; of the wings, which the larva wants.
The chief differences of larvae lye in the feet, and in the head. As to the feet, some larvae want them altogether, others have them, differing in number and figure. We are not accustomed to see animals with heads that undergo changes in the form; but this wonderful faculty is shewn by entomology. For many larvae have a membranaceous head, that often changes its shape.
Larvæ may be divided into eight- classes, one of these, (the Midae) have a membranaceous head, all the rest have it hard or horny. The first class is called BraSJi. The larvæ that belong to this class, have membranaceous and horny feet, of the former, always more than ten, of the latter, six. All these change into nymphs, and afterwards become Tenthredos. The second class comprehends the Cavipœ. Their character is, to have never more than ten membranaceous feet, furnished with hooks, and six horny feet. These change into chrysalids, and then become Lepidopteræ.
Simulta is the name of the third class. These larvæ have six horny feet, no membranaceous ones: the mouth furnished with teeth. These change into chrysalids, nymphs or semi-nymphs, and ac last, belong to the orders Coleoptera, Neuroptera, or Aptera.
The fourth class is called Ipedeu Their character is six horny feet, and no membranaceous ones. Mouth without teeth, furnished with a single rostrum. The Ipedes turn into nymphs or semi-nymphs, and these into insects of the Hemiptera order.
The fifth class are the Scrphi. They have fix horny feet, and no membranaceous ones. Mouth without teeth, furUu a mined