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 FORM AND HABIT: THE FEET. 29 Sparrows use both feet in searching for food, jumping quickly backward and throwing the leaves behind them. Parrots use their foot as a hand. Some Hawks carry nesting material in it, and all birds of prey strike their quarry with their strongly curved claws, which are then used to carry, or hold it while it is being torn by the bill. The foot of the Fish Hawk is a magnificent organ. The nails are strong and well curved ; the inner surface of the toes is set with sharp, horny spikes, and the outer toe is partly reversible, so that the bird grasps its slippery prey from four dif- ferent points. As a weapon the foot is especially effective, the use of spurs being too well known to require comment. Os- triches kick with their feet, and can, it is said, deliver a blow powerful enough to fell a man. But by far the best instance of modification in the structure of the feet is furnished by Grouse. It is an Fig. 15.— Foot of Fish Ilawk, showing large claws, and spicules on under surface of toes. (Vs natural size.) Fig. 1G. — Naked toes of Kuffed Grouse in suduner ; fringed toeis of Ruffed Grouse in winter, (^a natural size.) unusual case of seasonal adaptation in form. During the summer the toes of Grouse are bare and slender, but as