tion is not effected by a hook and eye, but by a hook or hooks sliding on a bar. As the wings move forwards to expand, and to take their position for the proper muscles of flight to act upon them, the hooks catch of themselves, and they are not put out of gear till the wings resume the position of rest. This arrangement is constant, but which wing shall furnish the hooks, and which the slide-bar or catch, depends on the anatomy of the particular family.

One more point yet remains to be considered in the structure of the wings. Still speaking of the fore-wing, which in the wasp is essentially the stroke-oar, we find that its nervures, as they become thicker and stronger on approaching the root of the wing are gathered into three ridges, forming a narrow neck. From this neck, just as in our bones, the condyles of the joint take their origin. The form of the condyles or articulating surfaces scarcely admits of any exact measurement in such a small speck as the root of a wasp's wing presents. The necessities of the case, however, show that the form and mode of attachment must be such as to allow for a movement in a horizontal direction-as the wasp standsfrom the position of repose to that of extreme extension. A vertical, or up and down movement, and a rotatory, or feathering movement, have also to be provided for, in combination with this, in the mode of articulation of the wings. The human anatomist scarcely needs to be reminded of the resemblance of this compound movement to that which is provided for so exquisitely in our wrists and elbows, and in each case by a different mechanism. As the wasp stands, the roots of her wings are very nearly in the same

horizontal plane. But as she lies obliquely on the air in flight this plane slopes downwards and backwards, so that the down stroke of the conjoined wings must be delivered forwards.

It is quite unnecessary to say that a mere flapping of the wings, to and fro, however rapid, regular, or long-continued, could not do anything in the way of flight; it would disturb the air and nothing more. Some arrangement must be adopted to render the stroke more effective in one direction than the other. To explain how this is accomplished will require, and must excuse, a long digression on the mechanism of flight.

The problem of flight has always attracted much attention, and, from the time of Dedalus downwards, mechanical invention has been strained to contrive flying machines on the most various principles, all agreeing only in one point, that of failing to accomplish their object; all legends to the contrary notwithstanding.* The Aeronautical Society of Great Britain† has had no better success as yet than private adventurers in the same field of air, but we are much indebted to it for having elicited an essay from Mr. Wenham,‡ explaining the correct principles on

* See Browne's 'Religio Medici,' Gairdner's edition, p. 38, and Appendix C, for references on this subject to Du Bartas and others. First Annual Report,' small 8vo, London, 1866, records some very curious experiments on aërostation, and enumerates no less than forty patents which have been taken out since 1842 in connection therewith.

On Aërial Locomotion, and the Laws by which heavy bodies impelled through the air are sustained. 'Engineering.' Ap. 19, 1867, p. 360, and Annual Report,' sup. cit.

I

which a flying machine should be constructed. From this, and from a Lecture by Dr. Pettigrew,* I have endeavoured, without entering too deeply into the question, to gather as much as may be read with interest in connection with the flight of wasps. Though the flight of insects is only discussed incidentally and by way of illustration to that of Birds by the Duke of Argyll,† yet I must add his thoughtful work to the list of authorities on this subject.

The first thing to be attended to in the construction of a flying-machine is of course how it shall support itself in the air; for such a machine, to have an independent motion, must be heavier than the surrounding medium. This principle is not satisfied in the construction of balloons; these cannot be regarded in any proper sense of the word as flying machines; they simply float about in the air, while the supporting power of the gas lasts, whichever way the wind may drive them. And our power of guiding these unwieldy monsters is limited pretty much to raising and lowering them, and to taking advantage of the different direction of the currents of air to be found, if so it should happen, at different heights. A parachute perhaps is a step nearer to a real flying machine, though it can only be compared to a flying squirrel, or to a beetle deprived of its wings dropping gently down, by the aid of its elytra, to the ground. A child soon learns to turn the supporting power of the air to advantage when he plays

* On the various Modes of Flight in relation to Aeronautics. 'Journal of the Royal Institution of Great Britain,' March 22, 1867. + The Reign of Law,' small 8vo, London, 1867, particularly Chapter III, on the Machinery of Flight in Birds.

at ducks and drakes with flat bits of tile, and the Australian boomerang is essentially a flying-machine of the same humble order. So too, according to most observers, is the flying-fish. In all these, however, an initial impulse is necessary. Kites supply a nearer illustration of what the insect world displays in such infinite variety, successful flying-machines, though they have been oftener recommended than applied to practical uses. In kites the traction on the string may be taken to represent the weight of the body of the insect, which pushes it forwards and downwards, just as the string draws the kite in the same direction. In this instance the difficulty of supporting a heavy body in the air by mechanical means is fairly surmounted; but this is only half the problem of flight, for the string limits the range within which it can fly. And even this amount of success, and within these narrow limits, is dependent on the direction of the wind which supports the weight by its upward pressure.

It might seem that the proper way to investigate this question would be to study the sustaining and the propelling principles separately. This may be done to a certain extent; and the beetle, indeed, supplies a living instance where the instruments of support and propulsion are distinct, being represented by the wing-covers and the wings respectively. In wasps, however, which are the example which we have to keep constantly before us, the two functions are inseparably united; and, generally speaking, the difference between support and propulsion is a mere matter of direction. Still, we may find an available distinction accordign as the current of air, and the influence of gravity

act on the passive insect body, or as the insect itself acts on the surrounding medium. And I have arranged, as far as practicable, the successive steps of this inquiry according to this view.

As to the PASSIVE element: Mr. Wenham calculates that the area of the supporting surface bears the proportion of about one square foot to each pound weight to be supported. This would secure a descent of no more than twenty-two feet in a second of time at an uniform velocity: being the speed at which one meets the ground at the end of a drop of eight feet. This proportion is pretty generally observed in different kinds of birds, "hornets, bees, and other insects." But there are some striking exceptions, "some of the duck-tribe, classed among the strongest and swiftest of flyers" having little more than half that area of wing.

Having thus ascertained the extent of the surface which should be opposed to the air, we have next to consider the influence which the form and direction of this surface exercise. A round body heavier than the air, such as a bullet, falls straight to the ground through still air; or in a wind it falls diagonally. If this same body is flattened out to an area duly proportioned to its weight, it falls straight through still air, only more slowly. But in a wind it will fall more or less obliquely, or it may even rise, like a kite, according to the force of the wind, and the direction in which the wind meets its surface. So it is with insects or birds. A dead beetle or rook falls like a plummet: a live sea-gull, as motionless all the while as a dead rook, soars with her wings extended, driven upwards by the air through which she is