From the Greek ttoXvq (polus), many, and Z,wov (animal). A name would presently die ; and though in its own substance it would not yield any nutriment to the capturer, yet by becoming the centre of a crowd of busy infusoria, multitudes of which would constantly be drawn into the tentacular vortex, and swallowed, it would be ancillary to its support ; and the organ in question would thus play no unimportant part in the economy of the animal. given to a certain group of animals which are, as it were, made up or many individuals massed together. By some naturalists they are called Bryozoa, a term derived from /3puor (bruon), sea-mos*7 and Z,Coov.

Chapter V. Insects: Wings and their Appendages

I propose now to reveal to you some of the microscopic marvels of the insect world ; a race vastly more populous than all of the other animate tribes put together ; for the most part so minute as to be peculiarly suitable subjects for our present investigations, and so furnished with elaborate contrivances and exquisite pieces of mechanism, as to elevate our thoughts at every turn to the majesty of the Divine wisdom displayed in the most minute of His creatures. Let us begin with their wings.

The most perfect fliers in existence are Insects. The swallow and the humming-bird are powerful on the wing, and rapid ; but neither these nor any other " winged fowl " can be compared with many of the filmy-winged Insects. The common House-fly, for example, will remain for hours together floating in the air beneath the ceilings of our dwelling-rooms, hovering and dancing from side to side, apparently without eflbrt and without fatigue. It has been calculated that in its ordinary flight the House-fly makes about 600 strokes with its wings every second, and that it is carried through the air a distance of five feet during that brief period. But, if alarmed, the velocity can be increased six or seven fold, as every one must have observed, so as to carry the insect thirty, or five and thirty, feet in the second. " In the same space of time," observes Mr. Kirby, "a race-horse could clear only ninety feet, which is at the rate of more than a mile in a minute. Our little fly, in her swiftest flight, will in the same space of time go more than the third of a mile. Now compare the immense difference in size of the two animals (ten millions of the fly would hardly counterpoise one racer), and how wonderful will the velocity of this minute creature appear ! Did the fly equal the race-horse in size, and retain its present powers in the ratio of its magnitude, it would traverse the globe with the rapidity of lightning." *

Bees, again, are accomplished masters of aerial motion. The Humble-bees, notwithstanding their heavy bodies, are the most powerful fliers of this class. The same excellent entomologist tells us that they " traverse the air in segments of a circle, the arc of which is alternately to right and left. The rapidity of their flight is so great that could it be calculated, it would be found, the size of the creature considered, far to exceed that of any bird, as has been proved by the observations of a traveller in a railway carriage proceeding at the rate of twenty miles an hour, which was accompanied, though the wind was against them, for a considerable distance by a Humblebee (fiombus siibinterrujrtus), not merely with the same rapidity, but even greater, as it not unfrequently flew to and fro about the carriage, or described zig-zag lines in its flight. The aerial movements of the Hive-bee are more distinct and leisurely." f

You have doubtless often admired the noble Dragonfly, with its four ample and wide-spread wings of gauze, hawking in a green lane or over a pool in the noon of summer. It sails, or rather shoots with arrowy fleetness hither and thither, now forwards, now backwards, now to the right, now to the left, without turning its body, but simply by the action of its powerful and elegant wings. Leeuwenhoek once saw an insect of this tribe chased by a swallow in a menagerie a hundred feet long. The Dragonfly shot along with such astonishing power of wing, to the * "Intr. to Entorr." ; Lett, xx f Ibid.

right, to the left, and in all directions, that this bird of rapid flight and ready evolution was unable to overtake and capture it, the insect eluding every attempt, and being in general fully six feet in advance of the bird. A Dragonfly has been known to fly on board a ship at sea, the nearest land being the coast of Africa, five hundred miles distant, a fact highly illustrative of its power of wing.

It is a point of interest to know the structure of the organs by which such results are accomplished, and therefore we will devote an hour to the microscopical examination of the wings of one or two insects. Let us begin with the common Fly, one of which, a fine blue-bottle, is somewhat noisily buzzing in the window ;— " The blue-fly sung i' the pane/'— as if to invite our attention to him. Well, we will borrow one of his wings for the lesson ; and, putting it into the stage-forceps, we shall be able to turn it in any direction for observation beneath the microscope.

At first it seems a very thin transparent membrane, of a shape between triangular and oval, with a few fine black lines running through it, and along one edge. But on bringing a greater magnifying power to bear on it, we see that the clear surface is covered with minute short stiff hairs, each of which has an expanded base. And still further, by delicate focussing, we find that there are two sets of these hairs, which come into view alternately, those of one row projecting upward towards our eye, those of the other downward. They are placed on both the upper and under surfaces, and are in fact appendages of two distinct membranes, applied to each other. There is some reason to believe that these hairs are delicate organs of touch, communicating impressions through the skin to a sensitive layer beneath ; at least such seems their function on the body, and we may judge from analogy that it is not different here.

The black lines are elastic, horny tubes, over which the membranes are spread and stretched, like the silk of an umbrella by its ribs. The upper membrane is firmly attached to the tubes (which are called nervures); the lower has but a slight adhesion, and is easily stripped from them. The nervures originate in the body, and diverge like a fan to various points of the tip, and to the upper and lower edges; some of them, however, terminate in the substance of the wing without reaching the edge, and some send off cross branches by which two are connected together. They generally maintain the same thickness throughout ; but there are enlargements, where the branches join the main trunks. These nervures are hollow ; and are during life filled with a subtle fluid, which is supplied from the vessels of the body. They contain also ramifications of the exquisite spiral airvessels, which we shall presently consider, so that both air and blood circulate in them.

But in this wing of a Bee all these structures may be seen to greater advantage. The membrane appears perfectly uniform by transmitted light, even with so high a magnifying power as 600 diameters, at least on a cursory examination ; though, by careful manipulation, we may discern faint traces of angular lines which divide the whole surface into irregular areas. But, by using reflected light at an oblique angle, this areolation, w rhich indicates the primary cells of the structure, is much plainer, and each area is perceived to carry a single hair in its centre.

The hairs themselves here take the character of curved spines, not unlike those of a rose-bush. Along the front edge of the wing they are straight, stout, densely crowded, and overlapping in an inclined position ; but the most interesting modification of these organs is seen at the front edge of the posterior pair. Unlike the Fly, wrhich has but a single pair of wings, the Bee has two pairs, of which the fore pair is the larger and more horny, the hinder pair seeming to be, as it were, cut out of the hinder and inner side of the fore ones. The two edsres—the hinder edo-e of the fore pair and the front edge of the hind pair — then correspond ; but it is necessary that, during flight, when the wings are expanded, the two wings on each side should maintain this relative position, neither overlapping the other, but

DOUBLING AND HOOKS IX A BEE S WI>"G. together presenting one broad surface, wherewith to beat the air. There must be, therefore, some contrivance for locking together the two edges in question, which yet shall be capable of being unlocked at the pleasure of the animal ; for the wings during repose slide over one another. This contrivance is furnished by a series of hairs or spines running along the front edge of the hindwing ; they are bent up into strong semicircular hooks, arching outwards, looking, under a high power, like the hooks on a butcher's stall. On the other hand, the margin of the fore-wing is strengthened, and is turned-over with a shallow doubling, so as to make a groove into which the hooks catch ; and thus, while the fore-wings are expanded, the hooks of the other pair are firmly locked in their doubled edge ; while, as soon as flight ceases, and the wings are relaxed, there is no hindrance to the sliding of the fore over the hind pair.

The wings of many insects are interesting on account of the organs with which they are clothed. A familiar example is furnished by the common Gnat, a wing of which is on the slide now before us. There is the same

general structure as before,—two clear elastic membranes stretched over slender horny tubular nervures, and studded on both surfaces with short spine-like hairs, which in this case, however, are very numerous and minute. But, along the nervures, and along other lines which run (generally) parallel with the front margin, and also along the whole margin, there are set long leaf-like scales of very curious appearance and structure.

Confining our attention to one of these lines, suppose one of the nervures, we see that its course is marked on the upper membrane by five rows of minute elevated warts, arranged obliquely with one another. Erom each of these warts springs a slender stem, which gradually dilates into a thin leaf-shaped plate of transparent substance, having from four to eight or ten longitudinal ribs. They project in a radiating manner, all inclined towards the tip of the wing. The same line on the under-surface carries the like number of leaf-like plates, corresponding in arrangement, structure, form, and direction with those on the upper side. The margins of the wing all round are furnished with similar organs, with this difference, that whereas the SCALES ON A GNAT'S WING. plates along the lines are, as it were, cut off abruptly at their greatest diameter, the marginal ones converge again with a gracefully curved outline, to a fine point : a form which is seen to the greatest advantage along the hind edge of the wing ; while those of the front margin are thicker, and more densely crowded.

There are, however, other Insects which display these or similar appendages in far greater profusion, and in much variety of form and appearance. In the fissures or

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