Animal life in the sea and on the land . filled with air, thetracheae supply the blood abundantlywith oxygen, and at the same time di-minish the weight of the body. Thesetubes are composed of elastic threadswound in a close spiral (Fig. 69),giving them great strength and light-ness, and preventing the possibility of their being pressed together and closed. The tracheae open on the surface of the body in small holes, called stigmata, which are arranged on the sides of the thorax and abdomen, and are so contrived as to admit air freely, while they exclude water or dust. A drop of oil on the abdo
Animal life in the sea and on the land . filled with air, thetracheae supply the blood abundantlywith oxygen, and at the same time di-minish the weight of the body. Thesetubes are composed of elastic threadswound in a close spiral (Fig. 69),giving them great strength and light-ness, and preventing the possibility of their being pressed together and closed. The tracheae open on the surface of the body in small holes, called stigmata, which are arranged on the sides of the thorax and abdomen, and are so contrived as to admit air freely, while they exclude water or dust. A drop of oil on the abdomen of an insect will kill it by closing the stigmata and causing suffocation. 9. Insects have no Voices.—No insect isknown to have a voice. The various noisesof insects, so commonly heard, are causedby the rapid vibration of their wings, orby rubbing together some hard parts oftheir bodies. 10. Metamorphosis.—Most young insects Fig. 68.—AlimentaryCanal of a Beetle. b, oesophagus ; c, crop;d, gizzard; e, stom-ach ; g, iu(; Fig. 69. —Tra-cheae of an In-sect, showingElastic SpiralThread. INSECTS. 113 are very different from their parents, and before reachingtheir perfect state they pass through a succession ofchanges called metamorphosis. As butterflies are fa-miliar insects, let us take them for an example, and studythe changes through which they pass.
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1887
