" If you look at the under side of the body of a male, the first thing that will strike you is a pair of large plates of an irregular form—in some semi-oval, in others triangular, in others again a segment of a circle of greater or less diameter, covering part of the belly, and fixed to the trunk between the abdomen and the hind legs. These are the drum-covers or opercula, from beneath which the sound issues. At the base of the posterior legs, just above each operculum, there is a small pointed triangular process, the object of which, as Reaumur supposes, is to prevent them from being too much elevated. When an operculum is removed, beneath it you will find on the exterior side a hollow cavity, with a mouth somewhat linear, which seems to open into the interior of the abdomen : next to this, on the inner side, is another large cavity * De Geer, ii. 471.

of an irregular shape, the bottom of which is divided into three portions; of these the posterior is lined obliquely with a beautiful membrane, which is very tense—in somespecies semi-opaque, and in others transparent—and reflects all the colours of the rainbow. This mirror is not the real organ of sound, but is supposed to modulate it. The middle portion is occupied by a plate of a horny substance, placed horizontally, and forming the bottom of the cavity. On its inner side this plate terminates in a carina or elevated ridge, common to both drums. Between the plate and the after-breast (post- ])ectus) another membrane, folded transversely, fills an oblique, oblong, or semilunar cavity. In some species I have seen this membrane in tension; probably the insect can stretch or relax it at its pleasure. But even all this apparatus is insufficient to produce the sound of these animals; one still more important and curious yet remains to be described. This organ can only be discovered by dissection. A portion of the first and second segments being removed from the side of the back of the abdomen which answers to the drums, two bundles of muscles meeting each other in an acute angle, attached to a place opposite to the point of the macro of the first ventral segment of the abdomen will appear. In Reaumur's specimens, these bundles of muscles seem to have been cylindrical ; but in one I dissected {Cicada Capensis) they were tubiform, the end to which the true drum is attached being dilated. These bundles consist of a prodigious number of muscular fibres applied to each other, but easily separable. Whilst Reaumur was examining one of these, pulling it from its place with a pin, he let it go again, and immediately, though the animal had been long dead, the usual sound was emitted. On each side of the drum-cavities, when the opercula are removed, another cavity of a lunulate shape, opening into the interior of the abdomen, is observable. In this is the true drum, the principal organ of sound, and its aperture is to the Cicada what our larynx is to us. If these creatures are unable themselves to modulate their sounds, here are parts enough to do it for them : for the mirrors, the membranes, and the central portions, with their cavities, all assist in it. In the cavity last described, if you remove the lateral part of the first dorsal segment of the abdomen, you will discover a semi-opaque and nearly semicircular concavo-convex membrane with transverse folds; this is the drum. Each bundle of muscles, before mentioned, is terminated by a tendinous plate, nearly circular, from which issue several little tendons that, forming a thread, pass through an aperture in the horny piece that supports the drum, and are attached to its under or concave surface. Thus the bundle of muscles, being alternately and briskly relaxed and contracted, will by its play draw in and let out the drum: so that its convex surface being thus rendered concave when pulled in, when let out a sound will be produced by the effort to recover its convexity; which, striking upon the mirror and other membranes before it escapes from under the operculum, will be modulated and augmented by them. Probably the muscular bundles are extended and contracted by the alternate approach and recession of the trunk and abdomen.

" And now, my friend," adds the excellent author, " what adorable wisdom, what consummate art and skill are displayed in the admirable contrivance and complex structure of this wonderful, this unparalleled apparatus ! The great Creator has placed in these insects an organ for producing and emitting sounds, which in the intricacy of its construction seems to resemble that which He has given to man and the larger animals for receiving them. Here is a cochlea, a meatus, and, as it should seem, more than one tympanum ! " * * " Intr. to Ent." ; Lett. xxiv.

insects: wings and their appendages.

In some instances the sounds of insects more nearly approach the character of true voices ; at least so far as they are produced by the emission of air from the breathing organs, yet not by means of the mouth. One of the most eminent of living entomologists, Dr. Burmeister, tells us so. Finding that the buzz of a large fly (Eristalis tenax) still continued after the winglets, the poisers, and even the wings, had been quite cut off except their stumps (only in this last case the sound was somewhat weaker and higher), he conceived that the spiracles, or breathing holes, lying between the meso- and meta-thorax must be the instruments of the sound; which, accordingly, he found to cease entirely when they were stopped with gum, though while the wings were in vibration. Pursuing his researches, he extracted one of these spiracles, and opening it carefully, found its posterior and inner lip, which is directed towards the commencement of the trachea, to be expanded into a small, flat, crescent-shaped plate, upon which are nine parallel, very delicate, horny lamina3 , the central one being the largest, while those on each side become gradually smaller and lower; so it is, he is persuaded, in consequence of the air being forcibly driven out of the trachea and touching these lamince, that they are made to vibrate and sound, precisely in the same way as with the glottis of the larynx. Dr. Burmeister (who remarks that Chabrier, in his Essai sur le Vol cles Insectes, p. 45, etc., has also explained the hum of insects as produced by the air streaming from the thorax during flight, and also speaks of lamina;, which lie at the aperture of the spiracles), in order to be certain that the lamina? in question in the posterior spiracles of the thorax are alone concerned in producing sound, also inspected the anterior ones, but without finding in them any trace of these lamime. He explains the weaker and sharper tones produced when the wings, all but the very roots, are cut off, as resulting from the weaker vibrations of the contracting muscles, and consequently less forcible expulsion of the air when the vibratory organs are removed ; and he thinks, with Chabrier, that some air may escape through the open trachece of the wings which are cut off. Though he regards these lamina? as the cause of humming in bees and flies, he does not decide that other causes may not produce the buzz of cockchafers, etc., in the thoracic spiracles of which he could not discern them.* * a Man. of Entom.,"46S.

Chapter VI. Insects: their Breathing Organs

In order to understand the passage last quoted from Burmeister, you ought to know something of the manner in which breathing is performed among insects. Essentially, breathing is the same function, wherever it occurs ; and it does occur, doubtless, in all animals under some form or other. It is the absorption of oxygen from without to the fluids within, to repair the waste constantly produced by vital energy. But it may be obtained from different sources, and imbibed in various modes.

All insects in the perfect state are air-breathers; that is, they procure their oxygen from the air as we do ; and most of them are such in their earlier stages. Even in exceptional cases, viz., those larvaa or pupae which are provided with what represent gills, and appear to be dependent on the water for their respiration, the exception is rather apparent than real, for the function is still performed in air-vessels. Now these air-vessels shall afford us some interesting microscopical observations.

This brown fly, which is buzzing and hovering on invisible wings over the flowers in the garden, you perhaps take for a bee. No; it has but two wings; for I have caught it, and you may ascertain the fact for yourself; it belongs to the genus Syrphus. Having caught it, I deprive it of life by means of the very organs I am going to examine, for I turn a tumbler over it and insert under the ed^e a lighted lucifer-match. In a few seconds it is dead— suffocated; for phosphoric and sulphuric acids introduced into the breathing tubes quickly destroy life. I presently take it out, and, putting it into a dissectingtrough under a lens, cut up the abdomen with a pair of fine-pointed scissors. Then I pin open the divided abdomen to the bottom of the trough, which is coated with wax for the purpose; and, looking at it with the lens—but you shall look for yourself.

Well, you see little else but the polished brown walls of the body and a number of fine white threads. It is those threads that we want. With a small camel's-hair pencil I move them to and fro in the water, and soon perceive that they are like little trees with comparatively thick trunks, sending off many branches, which gradually become exceedingly slender. Here and there short thick branches break out on two opposite sides, and on each side are connected with the wall of the abdomen. Here then with the fine scissors I snip them across, and lift up a portion with the hair pencil into a drop of water which J have already put into the live box. The cover now flattens the drop, spreads the white threads,—and the object is ready for our eye.

We have before us a considerable portion of the tracheal system of the fly. And though, owing to the complication of the parts, and the injury our rude anatomy has done, we cannot trace the beautiful regularity which exists in life, we may see the principle on which they are arranged, and much of the perfection with which they are constructed.

Here then is a system of pipes, some large, some small ; the smaller branching forth from the large, and themselves sending off yet smaller branches, which in their turn divide and subdivide until the final ramifications are excessively attenuated. Besides these, we see here and there ovate or barrel-shaped reservoirs, having the same appearance and intimate structure as the pipes, but of much larger calibre and connected with them by a branch.

This, I say, is the breathing system, or a large portion of it. These pipes receive the air from without through trap-doors which we will examine presently, and convey it to the most distant parts of the body. In ourselves the air is inhaled into a great central reservoir—the lungs ; and the blood dispersed through every part is brought to this reservoir to be oxygenated. In insects it is the blood that is collected into a great central reservoir, and the air is distributed by a minutely divided system of vessels over the blood-reservoir.

The trachece or air-pipes have a silvery white appear-

AIE-PIPE OF FLY.

ance by reflected light ; but if we use transmitted light and put on a high power, we discern a wonderful structure, which I will describe in the eloquent language of Professor Rymer Jones, and you shall estimate its truth as you examine the object :—

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