In the second case, however, the body is sustained in the air by a limb in which the bones of the hand are enormously increased in length, and so sustain a great expanse of naked skin, which is the flying membrane of the bat's wing.

Certain fishes and certain reptiles can also flit and take very prolonged jumps in the air.

The flying-fish, however, takes these by means of a great elongation of the rays of the pectoral fins--parts which cannot be said to be of the same nature as the constituents of the wing of either the bat or the bird.

The little lizard, which enjoys the formidable name of "flying-dragon," flits by means of a structure altogether peculiar--namely, by the liberation and great elongation of some of the ribs which support a fold of skin.

In the extinct pterodactyles--which were _truly_ flying {65} reptiles--we meet with an approximation to the structure of the bat, but in the pterodactyle we have only one finger elongated in each hand: a striking example of how the very same function may be provided for by a modification similar in principle, yet surely manifesting the independence of its origin.