This you may observe with the unassisted sight ; and you may mark also, how, from time to time, a portion, more or less, of the bubble of gleaming air is inhaled or expired by the animal, causing a diminution or increase of its volume ; and this of itself would convince you that it is the spiracles of the animal which are thus protected. The application of a low magnifying power, say from thirty-five to fifty diameters,—for we can hardly use a higher power than this to the animal while alive,— will reveal a few more of the details. We see, then, that the extremity of the last segment forms a circular disk, hollowed in the centre, where it is perforated with the two orifices of the air-pipes. The margin of this disk carries about thirty stiff but slender spines or bristles, some of which are branched in a forked manner. Each bristle

GBVB OF CHAMELEON-FLY. bears, on its two opposite sides—viz. , on those aspects which face the next bristle on either hand—two

insects: their breathing organs. series of not very close-set branchlets, set like the plumes of a feather, or the pinnae of a fern-leaf, which give it the elegant plumose appearance which the unassisted eye recognises. The bristles have a granulose surface near the extremity, and terminate in fine points.

The curious faculty of repelling water, which the interior surface of this plumy coronet possesses, is of the highest value in the economy of the insect ; for, on the one hand, it permits the breathing orifice to be brought into contact with the air, even when nearly a quarter of an inch below the surface ; and, on the other hand, it allows the volume of air inclosed within the funnel to be perfectly isolated, and carried securely away, as a reservoir for the wants of the animal, when engaged in its avocations of necessity or pleasure, in the recesses of its sub-aquatic groves. It is remarkable that so complete is this repellent power, that when the tail is at the surface the animal may make a very perceptible descent without breaking the continuity of the air, the surface presenting the curious phenomenon of a deep funnelshaped dimple leading down to the tail.

The chameleon-fly is not, however, so abundant and so universally distributed as that you may always calculate upon being able to repeat these observations when you will. I shall, therefore, show you an analogous example, much more easily obtained. Both are inhabitants of our fresh waters : the chameleon-grub lives in ponds, crawling among the stems of aquatic plants, and occasionally visiting the surface in the manner you have seen ; but it is uncertain^; in some seasons not uncommon, in others, scarcely to be met with by the most persevering search. For my next specimen, I have but to go with a basin to the water-butt in the yard, and take a dip of the surface-water at random : I shall be pretty sure of a score at least.

Here they are swarming, as I told yon. What, those tilings'? why, they are gnat-grubs. Well, don't despise them, you will find tliem worth looking at. I dare say you have never submitted them to half an hour's microscopical examination. I have caught one with a spoon, and put it into this narrow glass trough of water, that it may rest conveniently on the stage.

We will take a cursory glance at its entire person. Here is a flat, roundish head, a great globose, swollen thorax, and a long, slender, many-jointed :—the body, ending in a curious fork. But all is curious head, with its horny transparency ; its pair of rod-like antennae, covered with minute points ; its two black eye-patches ; and its jaws, beset with strong, curved hairs, set in radiating rows, and, ever and anon, working to and fro with the most rapid vibrations : the thorax,—so transparent, with its amber-like clearness, that you can discern the dorsal vessel, which contains the blood, ever dilating and collapsing with the most beautiful regularity ; and, beneath this, the gullet, through which, now and then, descends a dark pellet of food, to join the mass already lodged in the stomach farther down,—a result, by the way, that explains that incessant vibration and pumping motion of the mouth-organs, which thus evidently are engaged in collecting food from the water ; though, even with this power, we can see no solid matter taken in, till we discern it agglomerated in the swallowed pellets: the body, or abdomen, with its ten joints, all (with a slight exception) the counterparts of each other ; and each carrying its own dilatation of the dorsal vessel, and its own portion of the long and well-filled intestinal canal. All these, I say, are very interesting and curious to observe ; especially when we select, as I have done, a young individual for examination ; since the tissues then possess a translucency which is essential to our seeing with distinctness anything of the internal organization, but which soon gives place to opacity, as the insect advances in age.

Very curious, too, are the hairs with which the whole surface of the animal is furnished at certain definite points. But these are seen to more advantage in an older specimen; for, in this one of tender hours, they are nearly simple ; whereas, in an opaque, nearly full-grown individual, every hair is seen to be studded with secondary points, that project from its surface throughout its length. These hairs are arranged in beautiful radiating pencils or tufts, and scattered, as I have said, at definite points over the whole body :—there is a tuft on each antenna ; one on the forehead ; one in front of each eyespot ; several circles of them set round the thorax ; one circle of scanty pencils set round each segment of the body, and a few smaller tufts scattered about besides; all of them springing from minute round warts.

The extremity of the abdomen deserves, however, a separate investigation, and we will now direct our attention to the tail-end of our tiny grub. There are ten segments to the abdomen; at the eighth it seems to divide into two branches, one longer than the other. This appearance, however, is due to the circumstance that the respiratory tube is sent forth from the eighth segment, and that the ninth and tenth segments are bent away at an angle from the general line of the body.

The ninth segment is very small : the tenth is squarish, with rounded corners, and is brought to a thin edge. Around the margin there is the most exquisite array of hairs possible ; at one corner there are three pencils ; while round the opposite, and down the corresponding side run, in two rows, twelve pencils, set very close to each other, and each containing a large number of very slender hairs. The extreme end of the segment is ornamented with four diverging organs of taper conical form and crystalline clearness, through the midst of each of which passes a very fine branch of the air-tube system, which gives off still more attenuated branchlets in its course.

We have not yet, however, examined the origin of this air-breathing system. There is but one entrance to the air, or rather two placed close together, at the end of that round column, which is sent off from the eighth segment of the abdomen. This column, which is roughened all over with minute points, and fringed with rows of hairs, ends in a horny, conical point, which seems entire while under water, but no sooner does it come to the surface, than it is seen to split into five triangular pieces, which open widely, and expose a hollow, at the bottom of which are the two spiracles.

From these the two main air-pipes are seen to commence, and to proceed along the centre of the column, thence into the abdomen, which they traverse, one along each side, sending off slender branchlets all along, and becoming more and more attenuated themselves ; till, at length, we trace them into the thorax, and thence through the slender neck into the head itself, until they terminate in fine points close to the back of the mouth. It needs, it is true, a very transparent specimen to follow the tracheal tubes thus through their entire course ; but in such it can be clone without difficulty. And it is very instructive to do so ; inasmuch as one such personal examination of an insect, under a good microscope, will make you far more familiar with the peculiarities of its physiology than the clearest book- descriptions, or even the best and most elaborate plates, alone.

Perhaps you may think I have kept you too long over these gnat-grubs ; but my reason for being more minute in the examination of this creature is, that its extreme abundance in every place, and through the greatest part of the year, puts it in the power of every one to procure a specimen alive and healthy almost whenever he chooses ; and, therefore, it is peculiarly available for microscopic study : while the transparency of its tissues, and its generally simple organization, make it a more than usually suitable object for investigation : besides which, there are the beautiful and interesting points in the details of its structure, which I have been endeavouring to bring before you.

Not less interesting and remarkable is the change in the position of the spiracles, which takes place as soon as this grub arrives at the pupa or chrysalis state. The skin of the active, fish-like larva splits down the back, and out presses an equally active little monster; which, if you did not know it, you would never think of connecting with the grub from which it has proceeded; so totally different is it in form, in structure, and in motions.

We shall easily find some in our basin that have passed into this stage. Yes, here is one, which will please to take its place in the glass trough with its younger brothers. How strange the transformation ! It reminds us of a lobster, though, of course, the resemblance is only apparent. With the naked eye we see that the thorax is greatly enlarged, not only actually, but proportionally ; that it forms an oval mass, occupying some five-sixths, at least, of the entire animal ; the rest, apparently, being taken up by a slender, many-jointed abdomen, which curves round the great thorax, and, bending under it, ends in a very delicate, transparent swimming-plate. It is this curving abdomen, with its terminal swimmer, and its backward strokes in swimming, that constitute the resemblance to a prawn or lobster.

If we now bring a low power with reflected light to bear on it, we shall see the progress the animal has made in this its change of raiment. The thorax shows on its sides the future wings, crumpled and folded down, the nervures of which we can discern distinctly. The elegant little head, too, can be well made out ; its eyes now perfectly marked with the numerous six-sided facets that belong to the matured organs of vision in these creatures; its antenna?, like slender rods, folded down side by side along the inferior edge of the thorax ; the short palpi lying outside these ; and within, both the lancets and piercers that are destined to subserve the blood-sucking propensities of our sanguinary little subject, when it attains its winged condition ;—all encased in the transparent pupa-skin, that lies like a loose wrapper around everything.

The extremity of the abdomen has now nothing to do with respiration, and hence it is never brought to the surface of the water, as it was constantly before. The little animal still habitually lives in contact with the air, coming up to it with rapid, impatient jerks, whenever it has descended ; but it is invariably the summit of the thorax that is uppermost, and when the creature rests, it is this part that touches the surface.

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