any of thofe fragments of the veffels, which were attached to them internally; but this muft neceffarily have happened, had the communication of the external air by these tigmata in the bronchiæ remained open, or had the infect, when inclofed in its chryfalis, been able to breathe through them.

If the reader is unwilling to draw a more general conclufion from thefe laft experiments, it may at leaft, I think, be inferred from them, that the chryfalis of the sphinx liguftri lives for fome time without refpiration, and that its two anterior open ftigmata ferve only to facilitate the evaporation of the fuperabundant humours, and to permit the external air to fupply their place.

PAGE 55, 1. 15.

It is not to be doubted. It is not on the fingle experiment here related, that our knowledge of the refpiration of infects is founded. That experiment does not appear to me fo decifive, as fome may perhaps imagine. Even though an infect fhould not refpire naturally, it might happen, if its parts are tender, and not apt to stretch, that, when placed in an exhaufted receiver, it would be killed. It would be fufficient for this purpofe, that the air, which is difperfed in different parts of its body, fhould be there confined, in fuch a manner as to have no convenient iffue. Thus, as foon as the air which furrounds the animal, and preffes on it in all directions, is removed, the air within its body will not fail, in confequence of its natural elafticity, to dilate itself exceedingly, and thus to burst the membranes and veffels which keep it confined; this would certainly occafion the death of the animal, though the want of refpiration had no fhare in it. We have proofs lefs doubtful of the refpiration of infects. The fact appears to me fufficiently demonftrated, with refpect to many species of aquatic infects: I fpeak of those which are often feen thrufting the extremity of their abdomen to the furface of the water, and remaining there, as if fufpended. These extremities are with them the organs of refpiration, and they keep them thus in the air, for the purpofe of breathing. To be certain of this, we need only cover the furface of the water where they are, with fomething which may prevent them from thus bringing their tail to the furface. They will immediately be feen greatly agitated, and fecking with extreme inquietude, iome

opening

opening through which to push it. If they find no openirg, they are feen foon afterwards, to fall to the bottom and die, often in much lefs time than would be neceffary to drown the most delicate terreftrial infect: an evident proof of the refpiration of these animals, and that it is abfolutely neceffary to their exiftence. It is proper, however, to inform thofe who would make this experiment, that all aquatic inf. cts, which refpire at the pofterior part of the body, do not die equally foon when deprived of the air. The dytifci can refift this proof for a long time; but their larvæ can fupport it but for a few minutes.

As to lungs, it is eafy to aflure ourselves that infects have them, even without the trouble of diffection; we need only examine, in the water, the greater part of their exuvia, where we fall fee floating, great quantities of white veffels, which are connected, by their principal trunks, with what was the orifice of the organs of refpiration. Thefe veffels are the fragments of the lungs. Thefe lungs, in infects, divide into fuch an infinite number of bronchiæ difperfed over their whole body, that all the parts are, as it were, embarraffed with them, and it is often difficult, when we diffect an infect, to lay afide all those filaments, which confound by their number, every thing that appears. After this, would we not be furprifed to learn, that thefe pulmonary veffels are not tubes compofed of a single membrane; but veffels always open, compofed of a cord or thread, the turns of which are like thofe of a spring wound round a cylinder, and which thus form hollow cylinders, which open a paffage to the air? But this is not the only wonderful circumftanee in the mechanism of thefe lungs. M de Reaumur found, that the ftrings which form them, have, in fome infects, fix raifed fides, fo that they seem to be compofed of fix threads, nearly cylindrical, faftened to one another. Who would have imagined, that fuch fimall veffels were conftructed with so much art?

PAGE 55, 1. 24.

It is found at the mouth. It is feldom at the mouth or at the head, that the respiratory organs of infects are to be found: nay, perhaps, there is not a fingle inftance of their being fituated in that place. As it is on the authority of Frifch that the auther advances this fact, I think myself obliged to obferve, that the experiment which induced Frifch to believe, that the aquatic larvæ of the fmaller dra

gon-flies

gon-flies refpire by the under part of the mouth, is by no means decifive. Thefe animals have the mouth, and all the under part of the head covered with a mask, attach ed to a kind of arm, which, iffuing from the under fide of the thorax, and making a bend, is folded back, and touches the animal under the chin. It is by means of this arm, if I may call it fo, that the animal puts on, or takes off the mafk from its mouth at pleafure. When this larva is feized between two fingers, even when it is dead, and its abdomen a little preffed, it is furpriting to fee it often raife its muzzle, project the angle of the arm from under the thorax, lower its mafk, and, when the preffure is removed, put it on again. Frisch, who, like me, had made the experi ment, draws from it a confequence which I cannot approve. He affirms, that this mark, and the arm by which it is at tached to the chin, is the organ by which the animal refpires, and the motion made by this arm when the abdomen of the larvæ is preffed, is a proof of this; becaufe, according to him, the motion fhews, that the air is communicated from the abdomen to the arm by the chin. But I am afraid, he is deceived in the conclufion which he thus draws. It is my opinion, that thefe animals, while they continue in the state of larvæ, refpire water and not air; and that they infpire the water, not by the mafk, but by their pofterior part, through which alfo they difcharge it. The expiration is more vifible than the inspiration, but it is eafy to convince one's felf, that both are performed by the pofterior extremity. Let a filk thread, fuch as is fpun by the filk worm, be taken, and its extremity rolled up between the fingers into a little clew. This clew, when moistened, finks to the bottom, and being fufpended by fo flender a thread, it receives all the motions which the larva communicates to the water. Let it be brought near to the orifice at the posterior part of the animal, and it will be feen, that the clew is alternately repelled and attracted, fo as to fhew distinctly, that its return to the body of the animal, is the effect of an actual attraction, as it is much more quick than it would be, were it the effect, merely of its own weight. These infects, therefore, refpire by their posterior extremity, and it is water, and not air which they refpire. Thus, when their' abdomen is preffed under water, they are made to lower the mask: but no bubble of air iffues, any more than it does. from the other extremity; and we never fee that these a

nimals mount to the furface of the water to take in air; which many aquatic infects do which refpire air. Befides, the action of lowering the mafk, which they often do when their abdomen is prefled, by no means proves that they refpire by that organ. On the contrary, it fhews, that the fluid, which at that time is very vifibly accumulated in a part of the arm, towards the infide of the angle, has no exit, as the turgefcency lafts as long as the preffure is continued; and this may be reiterated at pleasure, even in a dead animal, which would not happen, did the fluid escape by that way. The mask has another ufe, much more certain; it is cleft in the fame direction with the mouth, and re-cleft by another fiffure, which falls perpendicularly on the first from the front of the muzzle. Upon the approach of an animal fuited to their tafte, thefe infects inftantaneously lower the mafk, and opening the clefts, they lay hold of their prey, and keep it inclofed and firm between thefe clefts, while they devour it at their leifure. The principal organs, which are to ferve the purposes of refpiration, when they are to breathe air, after they are changed into dragonflies, inftead of water which they breathe at this time, have their origin or openings on the thorax, where they are diftinguifhed by two ftigmata, and in thefe terminate all the pulmonary veffels which already contain air, even while the infect still lives in the water. It is difficult to say how the air gets into thefe; for, as was faid before, the animal is never seen coming to the furface of the water to receive it. But that they do contain air is a certain fact, of which it is eafy to be fatisfied. We have only to put the water, which contains a few of these animals, over a gentle fire, and when it begins to grow warm, we shall see the air within them ex pand and efcape in bubbles, fometimes with noise, by the two ftigmata of the thorax. Thefe remarks, I think, fhew fufficiently, that dragon-flies, at least thofe of the fpecies I am fpeaking of, before their transformation, refpire by the hinder part, and afterwards by the thorax, and that therefore, the organs of their refpiration, are by no means placed near the mouth in them, more than in any other infect that 1 know.

PAGE 55, 1. 25.

At the extremity of their body, towards the tail. It is not only at the extremity of the abdomen, and at the thorax,

that

that infects respire, great numbers refpire by the fides. The orifices, by which they receive the external air, vary in number, according to the different fpecies: they are generally from two to eighteen. The orifice is generally marked on the fkin of the animal, by a little fcaly plate, open in the middle, and furnished with membranes or threads, to prevent the ingrefs of improper fubftances. Thefe plates are called ftigmata, for want of a better name.

*This is what I have obferved in the long and flender water bugs. These have at the extremity, a tail as long as their whole body. This cannot be the tube by which their eggs are depofited; for the males have it, as well as the fer males. Befides, it is evidently the organ of refpiration, for after they have been fometime under water, they fuddenly rife to the furface, and thrufting out their tail, take in the air, which they repeat as often as they have occafion.

Frifch likewife obferved fomething fimilar in an aquatic larva, which changes into a fly, (the Mufca chamælion.) This animal has two apertures at the tail, which resemble two noftrils, by which it breathes.

PAGE 55, 1. 29.

*Air too thick. This is obfervable in the great water beetle, dytifcus. It lives in the water, but the air which it finds there, is not fufficient for it, but it is obliged to raife the extremity of its body out of the water, for the purpose of relpiration. The obfervation," fays Lyonet," with regard to this beetle, is common to a great number of "water beetles." We may add, probably to then all.

66

PAGE 55, 1. penult.

* Infects can live without air for four-and-twenty hours.We know, that, upon pouring water on pepper, a great number of animalcules are difcovered in the liquor. Derham relates, that he put a quantity of thefe into an exhausted receiver, for four-and twenty hours. He expofed them afterwards to the air for a day or two, when he found that fome of them were dead, and others ftill alive.

PAGE 56, 1. 7.

Or of lethargy. It is certain, that, among thofe infects which outlive the winter, there are many that pafs it withent much motion; but this reft does not become lethargic, except

Tt