Speed attained by insects, 188 Speed of wing movements partly accounted for, 120 Spine, spiral movements of, transferred to the extremities, 33 Straus-Durckheim’s artificial wings, 233 Swimming of the fish, whale, porpoise, etc., 66 Swimming of the seal, sea-bear, and walrus, 74 Swimming of man, 78 Swimming of the turtle, triton, crocodile, etc., 89 Terrestrial animals have smaller travelling surfaces than amphibia, amphibia than fishes, and fishes than insects, bats, and birds, 8 The travelling surfaces of animals increase as the density of the media traversed decreases, 7, 8 The travelling surfaces of animals variously modified and adapted to the media on or in which they move, 34 Walking, swimming, and flying correlated, 5 Walking of the quadruped, biped, etc., 9, 10, 11 _Wave_ wing of Pettigrew, 236 Do. how to construct on insect type, 240 Do. how to construct to evade the superimposed air during the up stroke, 241 Do. can be driven at any speed, 251, 255 Do. can create currents and rise upon them, 253 Do. can make new currents and utilize existing ones, 251, 255 Do. as a propeller, 256 Do. as an aërial screw, 256 Do. forces required to apply to the air, 245, 246 Do. necessity for supplying root of, with elastic structures, 247 Wave wing, _compound_, 242 Weight necessary to flight, 110 Weight contributes to flight, 112 Weight, momentum, and power to a certain extent synonymous in flight, 114 Wing of the bird and the extremity of the biped and quadruped are screws, structurally and functionally, 12, 136 Wing in flight describes figure-of-8 curves, 12 Wing during its action reverses its planes and describes a figure-of-8 track in space, 140 Wing when advancing with the body describes looped and waved tracks, 143 Wing, margins of, thrown into opposite curves during extension and flexion, 146 Wing, tip of, describes an ellipse, 147 Wing and body reciprocate in flight, and each describes a wave track, 12 Wing moves in opposite curves to body, 168 Wing ascends when body descends, and _vice versâ_, 159 Wing during its vibrations produces a cross pulsation, 148 Wing vibrates unequally with reference to a given line, 150, 231 Wing, compound rotation of, 149 Wing a lever of the third order, 103 Wing acts on yielding fulcra, 8, 104, 165 Wings, their form, etc., all wings screws, structurally and functionally, 136 Wing capable of change of form in all its parts, 147 Wing-area variable and in excess, 124 Wing-area decreases as the size and weight of the volant animal increases, 132 Wing, natural, when elevated and depressed must move forwards, 156 Wing, angles formed by, when in action, 167 Wing acts as true kite both during down and up strokes, 165 Wing, traces of design in, 180 Wing of bird not always opened up to same extent in up stroke, 182