The dimensions of the scales do not bear any certain proportion to the size of the insect which is clothed with them ; those from the broad wings of the noble Satnrnia Atlas, for example, eight or nine inches in expanse, being exceeded in size by some from those of our little native Muslin Moth, an inch wide.

You will say that what I am about to show you is a lovely object ; but for its right display I must use a low magnifying power,—not higher than a hundred diameters, —with condensed light falling upon the surface. It is a small fragment cut from the wing of Papilio Paris, showing several rows of the scales in their natural arrangement. The gem-like radiance of the glittering green scales on the black ones, by which they are environed, glares out with a splendid effect ; and, what is more interesting, set,—those you can trace the manner in which they are of each row slightly overlapping the bases of another row, like slates on a roof,—and also the mode in which they are inserted. The clear horn-coloured membrane of the wing is seen raised in shallow transverse steps (if I may use such a term), so that if it were divided longitudinally, the edge would appear cut into saw-like teeth. Along the margins of these ridges are set minute sockets, which are very distinctly seen, where the scales have been displaced; in these the tiny foot-stalks of the scales are inserted.

The little Beetles with which we are familiar under the name of Weevils, characterised by their long slender snouts, at the end of which they carry curiously folding antenna?, and which constitute the family Curcidionidce, are in many cases clothed with scales, to which they owe their colours and patterns. Several of our native species display a green or silvery lustre, which under the microscope is seen to be produced by oval scales. But these are eclipsed by the splendour of many tropical species ; especially that well-known one from South America, which is called the Diamond Beetle, and scientifically Entimus imperialism from its unparalleled magnificence.

A piece of one of the wing-cases of this beetle is gummed to the slide now upon the stage. We look at it by reflected light with a magnifying power of 130 diameters. We see a black ground, on which is strewn a profusion of what look like precious stones blazing in the most gorgeous lustre. Topazes, sapphires, amethysts, rubies, emeralds, seem sown broadcast; and yet not wholly without regularity, forthere are broad bands of the deep black surface, where there are no gems ; and, though at consider- SCALES OF DIAHOXD-BEETLE. able diversity of angle, they do all point with more or less precision in one direction, viz., that of the bands. G 9

These gems are flat transparent scales, very regularly oval in form, for one end is rather more pointed than the other; there is no appearance of a foot-stalk, and by what means they adhere, I know not ; they are evidently attached in some manner by the smaller extremity to the velvety black surface of the wing-case. The gorgeous colours seem dependent in some measure on the reflection of light from their polished surface, and to vary according to the angle at which it is reflected. Green, yellow, and orange hues predominate ; crimson, violet, and blue are rare, except upon the long and narrow scales that border the junctions of the wing-cases, where these colours are the chief reflected. Yet there appears to be some positive colour in their substance ; for in these latter scales, which, projecting beyond the edge of the wing-case, can be examined as transparent objects, and that with a high power, the transmitted light is richly coloured with the same tints as the same scales displayed under the Lieberkuhn.

We may derive pleasant instruction from continuing our observations on a few other wings of insects. If you have ever thought on the subject, you have probably taken for granted that the various sounds produced by insects are voices uttered by their mouths. But it is not so. No insect has anything approaching to a voice. Vocal sounds are produced by the emission of air from the lungs, variously modified by the organs of the mouth. But no insect breathes through its mouth ; no air is expelled thence in a single species ; it is a biting, or piercing, or sucking organ; an organ for the taking of food, or an organ for olfence or defence; but never an organ of sound.

The wings are in most cases the immediate causes of insect sounds; and, in the case of the Two-winged Flies (Dipt era), Kirby seems to have shown on sufficient evidence that the humming is produced by the friction of the root or base of the wings against the sides of the cavity in which they are inserted. *

There is a pretty little beetle (Clytus), not uncommon in summer in gardens, remarkable for the brilliant gamboge-yellow lines across its dark wing-cases, which makes a curious squeaking sound when you take it in hand. You think it is crying; but if you carefully examine it with a lens while the noise is uttered, you will perceive that the cause is the grating of the thorax against the front part of the two wing-cases. Several other beetles produce similar sounds when alarmed, by rubbing the other end of the wing-sheaths with the tip of the abdomen. Many of those genera which feed on ordure and carrion do this.

But the noisiest of all insects are those of the classes Orthoptera and Ilomoptera, the Crickets and Grasshoppers, and the Treehoppers. And these shall bring us back to our microscope, to which we shall return with the more zest, after this little interval of repose for our strained eyes.

Listen ! we hear, coming up the kitchen stairs, the chirping of the House-cricket (Acheta domestica).

We will catch one for investigation.

Kow, you see, each of the upper wings (or wing-cases) has a clear space near the centre, of a triangular form, crossed by one or two slender nervures. This space has received the name of the tympanum or drum. It is bounded externally by a broad dark nervure, which with a low power we see is scored with three or four longitudinal furrows, of course separated by as many horny ridges. In front of the clear drum, and forming a curved base to the triangle, a horny ridge passes across, tapering outwards, which is roughened throughout its length by close-set teeth exactly like a file. When the insect chooses to be musical, it partially opens and then closes its wing- * " Introd. to Entom." ; Lett. xxiv. See, however, the quotation from Burmeister on p. 91, infra.

cases, causing the two files to rub across each other; and this gives rise to the peculiar ringing vibration, the intensity of which is heightened by the tense " drum " acting as a sounding-board.

So at least some say ; but M. Goureau, who has published some elaborate observations on the chirping of insects,* asserts that the sound is chiefly owing to the action of the "file" (which he calls the "bow") on the longitudinally ridged nervure, which he calls the "treblestring."

We see in this individual that is so obliging as to produce its chirping before us, that he elevates the wingsheaths so as to form an acute angle with the body, and then rubs them together with a very brisk horizontal motion ; but which of the nervures it is that actually produces the sounds, it would require a very careful and elaborate series of experimental researches to determine. It has been asserted that the legs play a part in the music by being rubbed against the bows ; this, however, seems improbable from their relative position.

In the Southern United States, I have had opportunities of seeing and of hearing a very noisy performer of the Gryllus tribe, called the Katedid (Pteropliylla concava), which sings throughout the night in the foliage of the trees. The sounds, reiterated on every side, resemble a score or two of quarrelsome people with shrill voices, divided into pairs, the individuals of each pair squabbling with each other ; " I did ! " " You didn't ! " "I did ! " " You didn't !" the objurgation maintained with the most amusing pertinacity, and without a moment's intermission. Here the wing-sheaths, which are large and as it were inflated, are certainly the organs of sound. A portion of each is turned, at right angles to the remainder, over the back, so that the one partly overlaps the other. The musical organ consists of a hard glassy ridge in front, * " Ann. Soc. Ent. de France."

oehind which is a transparent membrane, which appears tightly stretched over a semicircular rim, like the parchment of a drum, answering in structure and in function to the part so compared in the Cricket.

This Gryllus I found would chirp freely, when held in my fingers, provided I held it by the head or thorax, so as not to interfere with the freedom of the wing-cases : though these needed only to be partially opened, the bases being merely slightly separated without affecting the general contiguity. The two glassy ridges were rubbed across each other, making the sharp crick. Ordinarily this was done thrice, three distinct but rapid crossings making the sound represented by the word " Katedid ; " but occasionally the insect gave but a single impulse, uttering as it were but one syllable of the word.

The Locusts and Grasshoppers, however, do, it appears, make use of their hind legs in producing their chirp. If you look at this Grasshopper's leg, you will see that the thigh is marked with a number of transverse overlapping angular plates, and that the shank carries a series of short horny points along each side. The insect, when it chirps, brings the shank up to its thigh, and rubs both to and fro against the wing-sheaths, doing this by turns with the right and left legs, which causes the regular breaks in the sound. The drum, on which this rubbing vibrates, has been described by the anatomist, De Geer :—"On each side of the first segment of the abdomen," says he, " immediately above the origin of the posterior thighs, there is a considerable and deep aperture of rather an oval form, Avhich is partly closed by an irregular flat plate or operculum of a hard substance, but covered by a wrinkled flexible membrane. The opening left by this operculum is semilunar, and at the bottom of the cavity is a white pellicle of considerable tension, and shining like a little mirror. On that side of the aperture which is towards the head there is a little oval hole, into which the point of a pin may be introduced without resistance. When the pellicle is removed, a large cavity appears. In my opinion this aperture, cavity, and above all the membrane in tension, contribute much to produce and augment the sound emitted by the Grasshopper." *

In this case we may without hesitation conclude that the friction of the thigh-plates and shank-points on the rough-edges of the wing-cases, produces the musical vibration on the tense membrane, as rubbing a wet glass with the finger will yield a loud musical note.

The most elaborate contrivance for the production of sounds among the Insect races, however, is found among the Cicada?, celebrated in classical poetry as the very impersonations of song and eloquence. I regret I cannot show you this apparatus ; for though we have a British species,—lately discovered in the New Forest,—it is very rare. Should you travel, however, either in the old or new world, you will have abundant opportunities of using your microscope to verify the following :— description by our prince of entomologists, Mr. Kirby

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