. Agricultural news. Agriculture -- West Indies; Plant diseases -- West Indies. 39 { THE AGRICULTURAL NEWS. December 11, 1909. INSECT NOTES. NATURAL HISTORY OF INSECTS. Part IV. 1iEsi'ie.\toiiy and Nekvous or are in spots of ltESPIE.\TION. Insect;; breathe by means of air-tubes (tracheae) which begin at openings in the boily wall, and extend throughout all parts of the .structure. The openings, which are called spiracles, or stigmata, are valvular, and are capable of being opened and closed. On the outside, they are also generally protected by hairs. There are usual
. Agricultural news. Agriculture -- West Indies; Plant diseases -- West Indies. 39 { THE AGRICULTURAL NEWS. December 11, 1909. INSECT NOTES. NATURAL HISTORY OF INSECTS. Part IV. 1iEsi'ie.\toiiy and Nekvous or are in spots of ltESPIE.\TION. Insect;; breathe by means of air-tubes (tracheae) which begin at openings in the boily wall, and extend throughout all parts of the .structure. The openings, which are called spiracles, or stigmata, are valvular, and are capable of being opened and closed. On the outside, they are also generally protected by hairs. There are usually ti-n stigmata on each side of the insect body, but there are sometimes less, and they also vary in their position, according to the life- habits of the insect. They may be distinctly seen with the naked eye in many insects. In certain large caterpillars, they are surrounded by tine lines, colour, which make them prominent In the grasshopper, they may be easily seen: two on the sides of the thorax, and eight on the abdomen The tracheae are composed of chitin, and are con- tinuous with the body wall. The smaller air- tubes are simple tubular structures, but the larger are strengthened on the inside by ridge s, arranged sjrirally. The tracheae from the stigmata connect with main , which extend the length of the body, and from which the branches and smaller tubes communicate with all parts. In Fig. 46, the cross-shaded portions are the tracheae, and the very fine cross- lines represent the thickenings mention- ed above. In large insects whicli fly flies, butterflies. Fk;, -IG. TiiAi'iiKAi, System. long distances, such pond- and moths, some beetles, flies, bees, etc., there often occur large distensions of certain tracheae to form air sacs, which probably are of use to the insect in making the body more buoyant, and in increasing the rapidity of breathing. All insects are air breathers; those which live in the water must come to the surface from time to time for a sup-
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