@The ancient murrelet go on by beating the wings both in the air and in the water. The thickset spindleshaped body and the slender short wings are their characteristics, though they are not so the penguins. The number of secondaries is rich to give the sufficient structural intensity for the wings. Since there exists the bouyancy comparable to the gravity in the water, they flap the wings with zero angle of attack, then the vertical force on the wings is canceled out over a cycle and the horizontal force gives the thrust. If the wings are flapped with negative (or positive) angle of attack, the vertical force on the wings are not canceled out over a cycle, but it gives negative (or positive) lift. The murrelet seems to use such thrust and negative (or positive) lift to the diving and rising. If the murrelet flaps down strongly at comparatively large angle of attack and flaps up weakly at comparatively small angle of attack, then it will be able to get large thrust and disappeared lift. Since the density of water is lager order by 1000 compared with that of air, the angle of attack and the flapping velocity may be small by that order. Then in the water the primaries are folded and only the secondaries are used to the diving and the propulsion. The virtual inertia force must be considered at the accelerative motion in the water. The webfeet located reaward are not used to the propulsion but to the steerage.