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A mammal that uses its webbed forelimbs to fly.

Bat

A mammal that uses its webbed forelimbs to fly.

An extreme form of the expanded foot, which is adapted for swimming.

Expanded Foot

An extreme form of the expanded foot, which is adapted for swimming.

The foot of a frog, which is useful in and out of water.

Frog Foot

The foot of a frog, which is useful in and out of water.

"In this foot each toe is provided with its swimming membrane; the membrane being closed when the foot is flexed, and expanded when the foot is extended."—Pettigrew, 1874

Foot of Grebe

"In this foot each toe is provided with its swimming membrane; the membrane being closed when the foot…

"Swan, in the act of swimming, the right foot being fully expanded and about to give the effective stroke, which is delivered outwards, downwards and backwards, as represented at r of fig. 50; the left foot being closed, and about to make the return stroke, as shown at s of fig. 50. In rapid swimming, the swan flexes its legs simultaneously and somewhat slowly; it then vigorously extends them."—Pettigrew, 1874

Swimming Swan

"Swan, in the act of swimming, the right foot being fully expanded and about to give the effective stroke,…