Entomology : with special reference to its biological and economic aspects . ccording toFig. 167. ^^ , , . 1 oung and Langley, the radia-tions of an ordinary gas-flamecontain less than three per visible rays, the remainderbeing heat or chemical rays, ofno value for illuminating pur-poses ; while the light-givingefficiency of the electric arc isonly ten per cent, and that ofsunlight only thirty-five percent. The light of the fire-fly, however, may be rated at()ne hundred per cent.; thislight, then, is perfect, and asyet unapproached by artificialmeans. As to the use of this lumi-nosity,
Entomology : with special reference to its biological and economic aspects . ccording toFig. 167. ^^ , , . 1 oung and Langley, the radia-tions of an ordinary gas-flamecontain less than three per visible rays, the remainderbeing heat or chemical rays, ofno value for illuminating pur-poses ; while the light-givingefficiency of the electric arc isonly ten per cent, and that ofsunlight only thirty-five percent. The light of the fire-fly, however, may be rated at()ne hundred per cent.; thislight, then, is perfect, and asyet unapproached by artificialmeans. As to the use of this lumi-nosity, there is a generalopinion that the light existsfor the purpose of sexualattraction—a belief held bythe author in regard to PJw-timis, at least. Another viewis that the light is a warningsignal to nocturnal birds, batsor other insecti\-orous animals;this is supported by the factthat lampyrids are refused by birds in general, after ex-perience; young birds readily snap at a fire-fly for the firsttime, but at once reject it and thereafter pay no attention tothese Tracheal system of an insect, a, an-tenna; b, brain; /, leg; 11, nerve cord;p, palpus; s, spiracle; st, spiracular, orstigmatal, branch; t, main tracheal trunk;V, ventral branch; is, visceral branch.—After KoLBE. ANATOMY AND PHYSIOLOGY 133 9. Respiratory SystemIn insects, as contrasted with vertebrates, the air itself isconveyed to the remotest tissues by means of an elaborate sys-tem of branching air-tuljes, or iracJiccv, which receive airthrough paired segmentally-arranged spiracles. Each spiracleis commonly the mouth of a short tube which opens into amain tracheal trunk (Fig. 167) extending along the side of
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectentomology, bookyear1
