. Bird lore . most in-sects have wings. A few species probably never had wings, and some othershave given up flying, so that their wings have become small and weak anduseless. If we examine any typical insect, such as a butterfly, a grasshopper • or a bee. we observe that the wings consist of two pairs of flat, thin struc- 258 Bird-Lore tures, stiffened with branching ribs that make them resemble more or lessclosely the leaves of certain plants. They are jointed at their attachment tothe body and can be moved with greater or less freedom by the insect, thetip of each wing describing a figure 8
. Bird lore . most in-sects have wings. A few species probably never had wings, and some othershave given up flying, so that their wings have become small and weak anduseless. If we examine any typical insect, such as a butterfly, a grasshopper • or a bee. we observe that the wings consist of two pairs of flat, thin struc- 258 Bird-Lore tures, stiffened with branching ribs that make them resemble more or lessclosely the leaves of certain plants. They are jointed at their attachment tothe body and can be moved with greater or less freedom by the insect, thetip of each wing describing a figure 8 in flight. A study of the develop-ment of insect wings shows that they are really nothing but great flat ex-pansions of the sides of two rings of the body, the second and third behindthe head of the animal. Their shape varies greatly in different insects, andon it depends the character of the flight in any particular instance. Insectswith both pairs of wings broad and of nearly uniform shape and size have a. PTERODACTYL Courtesy of F. A. Lutas slow, unsteady flight. This is the case with many moths and butterflies. In-sects of powerful and rapid flight, like the hawk-moths, often seen hoveringabout flowers in the twilight, have the fore-wings long, narrow and pointedand the hind-wings small. In some of these swift-flying insects, like theflies,—our common house-fly, for example,—the hind-wings are reduced tolittle rudiments, called balancers, or halteres, which no longer function aswings. Finally, insects with a gliding flight, like the grasshoppers, havesmall narrow fore-wings and broad, fan-shaped hind-legs. The wings of all back-boned animals differ from those of insects in be-ing peculiar modifications of limbs which were originally used for walking,or, in the case of the flying fish, for swimming. They are not mere expan- The Structure of Wings 259 sions of the sides of the body, as in insects, although similar expansions maybe developed in connection with the limbs
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbirds, booksubjectorn
