Points wherein the screws formed by the wings differ from those in common use, 151 The wing at all times thoroughly under control, 154 The natural wing when elevated and depressed must move forwards, 156 The wing ascends when the body descends, and _vice versâ_, 159 The wing acts upon yielding fulcra, 165 The wing acts as a true kite both during the down and up strokes, 165 Where the kite formed by the wing differs from the boy’s kite, 166 The angles formed by the wing during its vibrations, 167 The body and wings move in opposite curves, 168 THE WINGS OF INSECTS, BATS, AND BIRDS. Elytra or wing cases and membranous wings; their shape and uses, 170 THE WINGS OF BATS. The bones of the wing of the bat; the spiral configuration of their articular surfaces, 176 THE WINGS OF BIRDS. The bones of the wing of the bird; their articular surfaces, movements, etc., 178 Traces of design in the wing of the bird; the arrangement of the primary, secondary, and tertiary feathers, etc., 18O The wing of the bird not always opened up to the same extent in the up stroke, 182 Flexion of the wing necessary to the flight of birds, 183 Consideration of the forces which propel the wings of insects, 186 Speed attained by insects, 188 Consideration of the forces which propel the wings of bats and birds, 189 Lax condition of the shoulder-joint in bats and birds, 190 The wing flexed and partly elevated by the action of elastic ligaments; the nature and position of said ligaments in the Pheasant, Snipe, Crested Crane, Swan, etc., 191 The elastic ligaments more highly differentiated in wings which vibrate rapidly, 193 Power of the wing, to what owing, 194 Reasons why the effective stroke should be delivered downwards and forwards, 195 The wing acts as an elevator, propeller, and sustainer, both during extension and flexion, 197 Flight divisible into four kinds, 197 The flight of the Albatross compared to the movements of a compass set upon gimbals, 199 The regular and irregular in flight, 201