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chevrette was indifpenfable to the exclufion of the fole from the egg? If the eggs of those that spawned in the veffel remained fterile, while the others produced young, the reafon of the difference might have been, either that the males had not fertilised the spawn of the former, and that they had rendered fertile that containing the eggs attached to the chevrette; or perhaps, that these eggs, needing a degree of agitation to make them hatch, the firft had not in the veffel, the neceffary agitation which they would have received in the fea, while the chevrettes, by their motions, would have procured a fufficient agitation to the others.

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This is fo rapid. I fhould think it useless to observe, that the proverb here mentioned, exceedingly exaggerates the matter, if I did not know, that many people believe it literally true. It is, however, true, that of infects which are not remarkably minute, the generation of fleas, aphides, and other vermin of that fort, goes on with the greatest rapidity. As to larger infects, a whole year is neceffary for their paffing from one generation to another. The fpecies which multiply twice a year, are in much fmaller numbers, as are those which need more than a year to produce their like.

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It is allowed, that infects, &c. This is not an univerfal opinion. The furest way is, not to decide on a fubject we cannot know. When we take a general view of the operations of infects, the great uniformity, which at once appears in the economy of each fpecies, would make us believe, that they act merely by instinct. But, when we examine their proceedings in detail, and when we fee, that they not only vary their operations, according to the neceffity of the cafe; but that, when they are placed in difficult circumstances, in which, according to the ordinary courfe of things, they fhould not naturally find themfelves, we obferve, they do not fail to make the most of their refources, and that they can, with much industry, remedy accidents, and extricate themselves from very embarraffing fituations, we are then tempted to allow them a portion of reafon.

PACE

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It is merely the external form. Although the changes which the external parts of infects undergo, in their different transformations, are the most remarkable, they are not confined to thefe, parts alone. Very confiderable changes likewife take place in their internal parts, fome of which are elongated, others contracted; fome lofe their functions, others acquire new ones, and others entirely difappear.

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Into four different claffes. The explanation of the four forts of changes mentioned in this chapter, is taken from Swammerdam, who expreffes himself on the fubject, nearly in the fame way with our author. Those who are not perfectly verfed in the different transformations of infects, will perhaps be at a lofs to comprehend what is here related. I fhall endeavour, in a few words, to give as distinct an idea of them as poffible.

For this purpofe, it is neceffary, in the firft place, to know, what is properly meant' by the ftate of nymph and chryfalis, fo often mentioned. By thefe terms is meant, a ftate of imperfection, attended fometimes with inactivity, inaction, abftinence and weakness, through which the infect pailes, after having attained a certain bulk, and in which its body receives the preparatives neceffary for its paffing to a ftate of perfection. All the external parts of the infect are then found enveloped, either with their natural skin, or with a fine membrane, or with a hard and cruftaceous coat. In the firft cafe, the limbs of the infect remain free, it preferves its power of acting, it eats, and its form is little different from what it was before. In the fecond cafe, the limbs of the infect are folded over its breaft, but separate; it can neither eat, nor act, it retains hardly any traces of its former figure, and has only a confufed refemblance to that which it is going to affume. In the third cafe, the cover brings all thefe parts of the animal into one mafs; it makes it equally incapable of eating and acting; it has no refemblance, either to what it formerly was, nor to what it is to be. These three forts of change, are evidently very different, and yet, we have but two words in our language to diftinguish them by. We fay of the infects in the two firft cafes, that they are changed into nymphs, and of those in

the

the last cafe, that they have affumed the form of chryfalids· To thefe terms, it would be proper to add a third, in order to mark the difference between the first and fecond cafes. It might be done, I think, very conveniently, by allowing the last to retain the name of nymph, and calling those of the firft kind femi-nymph, or demi-nymph; a name which, perhaps, would not be inapplicable to them, confidering the fmall degree of change they have undergone. Grafshoppers, which, instead of the long wings they acquire, have ftill only on their backs, the fmall cafes, in which these wings are formed, are nymphs of this kind; they may properly be called femi-nymphs. Those who have had an opportunity of examining a bee-hive, cannot fail to have remarked bees, ftill imperfect in the fhut cells; these are nymphs of the second order. The filk-worm furnishes a well-known example of infects under the form of a chryfalis.

Infects, which undergo no other metamorphofis, than that which has converted them from the foft fubftance of an egg, to a well-formed and living body, are those which conftitute the first clafs of transformations fpoken of in this chapter. They increase in fize; the greater part cast their fkin; fome of their parts acquire a greater fize than the reft, and sometimes take a different colour from what they had before, This is almost the whole change which these undergo.

The transformations of the infects of the other three claffes do not terminate here: after having caft off their fkins, for the most part feveral times, and after having ac quired their deftined bulk, all become either femi-nymphs, nymphs, or chryfalids. They pafs a certain time under this form, and upon quitting it, affume that of a perfect infect, capable of generation. It is from the diverfity which takes place in thefe three forts of changes, that the principal characters, which distinguish the infects of the fecond, from thofe of the first and third clafs are taken.

The infects of the second class, are those that pass thro' the ftate which I have called the ftate of femi-nymph. They do not undergo a transformation which is entirely compleat, but in their laft change, they have generally still all the members they had before, without having acquired any others, except they have got wings; and as we have already remarked, the femi-nymph differs little in

form

form, from the animal which produced it. What always diftinguishes it moft, is, that there is feen upon its back, at the base of the thorax, the cafes in which the wings are formed, which before that, appeared but little, and often not at all. In other refpects, it walks, runs, leaps and fwims, as before. The difference between the femi-nymph, and the winged infect which it produces, is not always fo obfcure. In fome species, it is even fo great, that it is with difficulty we can difcover a trace of its first form; but this 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 infects of the other two claffes, do not enjoy the fame advantage with the other. They lofe the use of all their members when they enter upon their transformation, and have no resemblance to what they were before. An animal of these two claffes, which before had no legs, or had five, fix, seven, eight, nine, ten, or eleven pairs of legs, has now no more nor less than three pairs, which, with the wings and antennæ, are folded under its breast, and there remain immoveable.

What distinguishes thefe two laft claffes from each other, is, that the infects of the third clafs quit their skin, when they change into nymphs, or into chryfalids, and that thofe of the fourth change into nymphs under their skin, which hardens round them, and serves them then for a cafe.

:

These are the principal differences which Swammerdam and the author find in thefe four claffes. They confift, to exprefs it in two words, in this, that the infects of the first clafs, after iffuing from the egg, undergo no other transformation that thofe of the fecond fuffer an incompleat change, and become femi-nymphs, before arriving at their ultimate form that thofe of the third and fourth claffes, before arriving at their perfect ftate, become, the first nymphs or chryfalids, and the others nymphs, by a total change of form, but with this difference, that thofe of the third clafs quit their fkin at becoming nymphs or chryfalid; and that thofe of the fourth become nymphs without quirting their fkin.

M. de Reaumur, to whom Natural History is indebted for fo many beautiful discoveries, found, in the transforma tion of infects of the fourth clafs, a new character, which no one, perhaps, had obferved before, and which, I think, diftinguishes them more effentially from thofe of the other

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claffes, than the changing into nymphs, without quitting their fkin. He difcovered, that they undergo one transformation more than other infects: that before becoming ry pbs, they affume under their skin, an elliptical form, or that of an elongated fpheroid, in which no part of the animal is difcernible; that in this ftate, the head, the thorax, the wings and legs of the nymph are inclosed in the interior cavity of the abdomen, from which they iffue fucceffively, by the anterior part, nearly in the fame way as the extremity of the finger of a glove, which has been drawn in, is pufhed out again. Thus, the infects of this clafs, are not folely diftinguished from others, by their changing into nymphs under their fkin: but principally, in that before becoming nymphs, they undergo a double transformation. According to this idea, the differences of the four orders of transformations may be reduced to terms fimpler and more eafily comprehended, by faying, that infects of the firft order, after iffuing from the egg, attain their perfect state, without being previously difpofed to it, by a change of form; that those of the fecond clafs are prepared for it, by an incompleat change of form; and thofe of the fourth, by a double change of form.

*Lyonet here gives examples of thefe four claffes of transformations. The firft is exemplified by the common. earth-worm. The fecond clafs, by a dragon-fly, (Libellula puella.) The third, by infects of the three different orders: 1. A pfeudo-caterpillar, which feeds on the willow, with two and twenty feet, (Tenthredo marginata.) 2. A waterbeetle of the largest size, (Dytifcus piceus.) And 3. A caterpillar with fixteen feet, which lives on the trunks of willows, oaks, &c. (Phalana Coffus.) The fourth clafs is illuftrated by a white maggot, which proceeds from the eggs depofited by the large blue flies in flesh, when it is about to turn putrid. (Mufca vomitoria.)

The celebrated Bergman, before he betook himself to the illustration of mineralogy, had been fond of the study of infects, and he has left us a claffification of larvæ, a concise view of which, it is hoped, it will not be improper to give. in this place.

The metamorphofis of larvæ, fays Bergman, confifts in the excoriation, or depofition of the external skin of the infect, joined with a change of form. This, in general, is twofold, to wit, from the larva to the pupa, and from that,

to