complex in insects. Lyonnet found 3,993 muscles in a caterpillar, and while a large proportion belong to the internal organs, over a thousand assist in locomotion. Hence the muscular power of insects is enormous. A flea will leap two hundred times its own height, and certain large, solid beetles will move enormous weights as compared to the bulk of their bodies.

8. Larva of a beetle (Photuris).

In walking, as seen in the accompanying figure (Fig. 8), three legs are thrown forward at a time, two on one side and one on the other.

Flies and many other insects can walk upside down, or on glass, as easily as on a level surface. A fly's foot, as in most other insects, consists of five joints (tarsal joints), to the last one of which is appended a pair of stout claws, beneath which is a flat, soft, fleshy cushion or pad, split into two (sometimes three) flaps, beset on the under surface with fine hairs. A part of these hairs are swollen at the end, which is covered with "an elastic membranous expansion, capable of close contact with a highly polished surface, from which a minute quantity of a clear, transparent fluid is emitted when the fly is actively moving." (T. West.) These hairs are hence called holding, or tenent, hairs. With the aid of these, but mainly, as Mr. West insists, by the pressure of the atmosphere, a fly is enabled to adhere to perfectly smooth surfaces. His studies show the following curious facts. "That atmospheric pressure, if the area of the flaps be alone considered, is equal to just one-half the weight of a fly. If the area covered by the tenent hairs be added, an increase of pressure is gained, equal to about one-fourth the weight of a fly. This leaves one-fourth to be accounted for by slight viscidity of the fluid, by the action I have so often alluded to, which may be called 'grasping,' by molecular attraction, and, doubtless, by other agents still more subtle, with which we have at present scarcely any acquaintance."

How Insects Fly. Who of us, as remarked by an eminent ornithologist, can even now explain the long sustained, peculiar flight of the hawk, or turkey buzzard, as it sails in the air without changing the position of its wings? and, we would add, the somewhat similar flight of a butterfly? It is the poetry of motion, and a marvellous exhibition of grace and ease, combined with a wonderful underlying strength and lightness of the parts concerned in flight.

Before we give a partial account of the results obtained by the delicate experiments of Professor Marey on the flight of birds and insects, our readers should be reminded of the great differences between an insect and a bird, remembering that the former, is, in brief, a chitinous sac, so to speak, or rather a series of three such spherical or elliptical sacs (the head, thorax and abdomen); the outer walls of the body forming a solid but light crust, to which are attached broad, membranous wings, the wing being a sort of membranous bag stretched over a framework of hollow tubes (the tracheæ), so disposed as to give the greatest lightness and strength to the wing. The wings are moved by powerful muscles of flight, filling up the cavity of the thorax, just as the muscles are the largest about the thorax of a bird. Moreover in the bodies of insects that fly (such as the bee, cockchafer, and dragon fly), as distinguished from those that creep exclusively, the air tubes (tracheæ) which ramify into every part of the body, are dilated here and there, especially in the base of the abdomen, into large sacs, which are filled with air when the insect is about to take flight, so that the specific gravity of the body is greatly diminished. Indeed, these air sacs, dilatable at will by the insect, may be compared to the swimming bladder of fishes, which enables them to rise and fall at will to different levels in the sea, thus effecting an immense saving of the labor of swimming. In the birds, as every body knows who has eaten a chicken, or attended the dissection of a Thanksgiving turkey, the soft parts are external, attached to the bony framework comprising the skeleton, the wing bones being directly connected with the central back bone; so that while these two sorts of animated flying machines are so different in structure, they yet act in much the same manner when on the wing. The difference between them is clearly stated by Marey, some of whose conclusions we now give almost word for word.

9. Figure cut by an insect's wing.

The flight of butterflies and moths differs from that of birds in the almost vertical direction of the stroke of their wings, and in their faculty of sailing in the air without making any movements; though sometimes in the course they pursue they seem to resemble birds in their flight.

9. Figure cut by an insect's wing.

The flight of insects and birds moreover differs in the form of the trajectory in space; in the inclination of the plane in which the wings beat; in the role of each of the two alternating (and in an inverse sense) movements that the wings execute; as also in the facility with which the air is decomposed during these different movements. As the wings of a fly are adorned with a brilliant array of colors, we can follow the trajectory or figure that each wing writes in the air. It is of the form of a figure of eight (Fig. 9), first discovered by Professor J. Bell Pettigrew of Edinburgh.

10. Figure cut by a bird's wing.

By an ingenious machine, specially devised for the purpose, Professor Marey found that a bird's wing moves in an ellipse, with a pointed summit (Fig. 10). The insect beats the air in a distinctly horizontal plane, but the bird in a vertical plane. The wing of an insect is impervious to the air; while the bird's wing resists the air only on its under side. Hence, there are two sorts of effects; in the insect the up and down strokes are active; in the bird, the lowering of the wing is the only active period, though the return stroke seems to sustain the bird, the air acting on the wing. The bird's body is horizontal when the wing gives a downward stroke; but when the beat is upward, the bird is placed in an inclined plane like a winged projectile, and mounts up on the air by means of the inclined surfaces that it passively offers to the resistance of this fluid.

In an insect, an energetic movement is equally necessary to strike the air at both beats up and down. In the bird, on the contrary, one active beat only is necessary, the down beat. It creates at that time all the motive force that will be dispensed during the entire revolution of the wing. This difference is due to the difference in form of the wing. The difference between the two forms of flight is shown by an inspection of the two accompanying figures (11, 12). An insect's wing is small at the base and broad at the end. This breadth would be useless near the body, because at this point the wing does not move swiftly enough to strike the air effectively. The type of the insectean wing is designed, then, simply to