[52] The professional swimmer avoids bobbing, and rests the side of his head on the water to diminish its weight and increase speed.
[53] The greater power possessed by the limbs during extension, and more especially towards the end of extension, is well illustrated by the kick of the horse; the hind feet dealing a terrible blow when they have reached their maximum distance from the body. Ostlers are well aware of this fact, and in grooming a horse keep always very close to his hind quarters, so that if he does throw up they are forced back but not injured.
[54] The outward direction given to the arm and hand enables them to force away the back water from the body and limbs, and so reduce the friction to forward motion.
[55] History of British Birds, vol. i. p. 48.
[56] The guillemots in diving do not use their feet; so that they literally fly under the water. Their wings for this purpose are reduced to the smallest possible dimensions consistent with flight. The loons, on the other hand, while they employ their feet, rarely, if ever, use their wings. The subaqueous progression of the grebe resembles that of the frog.—Cuvier’s Animal Kingdom, Lond. 1840, pp. 252, 253.
[57] In the swimming of the crocodile, turtle, triton, and frog, the concave surfaces of the feet of the anterior extremities are likewise turned backwards.
[58] The effective stroke is also delivered during flexion in the shrimp, prawn, and lobster.
[59] “On the Various Modes of Flight in relation to Aëronautics.” By the Author.—Proceedings of the Royal Institution of Great Britain, March 1867.
[60] Nature and Art, November 1866, p. 173.
[61] In this form of lever the power is applied between the fulcrum and the weight to be raised. The mass to be elevated is the body of the insect, bat, or bird,—the force which resides in the living pinion (aided by the inertia of the trunk) representing the power, and the air the fulcrum.