. The microscope and its revelations. me kind of sieve at their entrance by v «/ which particles of dust, soot, &c., which would otherwise enter theair-passages, are filtered out; and this sieve may be formed by the interlacement of thebranches of minute growths from theborder of the spiracle, asin the common fly (). or in the ; :or it may be a membraneperforated with minuteholes, and supported upona framework of bars thatis prolonged in like mannerfrom 1 lie thickened marginof 1 he aperture (fig. 744),as in the larva- of theMelolontlta (cockchafer). Not iinfrei
. The microscope and its revelations. me kind of sieve at their entrance by v «/ which particles of dust, soot, &c., which would otherwise enter theair-passages, are filtered out; and this sieve may be formed by the interlacement of thebranches of minute growths from theborder of the spiracle, asin the common fly (). or in the ; :or it may be a membraneperforated with minuteholes, and supported upona framework of bars thatis prolonged in like mannerfrom 1 lie thickened marginof 1 he aperture (fig. 744),as in the larva- of theMelolontlta (cockchafer). Not iinfrei|iient ly the centre of t he aper-ture is occupied by an impervious disc, from which radii proceedto its margin, as is well seen in the spiracle of Ti/mln (craiie-lly).1 Ill those aquatic larva- which breathe air \\ e often find one 1 Consult Landois and Thiele, Der,Tracheenverschlusa den Insecti-n, mItrifl f. WISS. /.lint, xvii. p. 187. FIG. 742.—Portion of a large trachea of Dytiscus,with some of its principal FIG. 743.—Spiracle of common tly. RESPIRATORY APPARATUS 997 of the spiracles of the last segment of the abdomen prolonged into atube, the mouth of which remains at the surface while the body isimmersed ; the larvas of the gnat tribe may frequently be observedin this position. There are many aquatic larva3, however, which have an entirelydifferent provision for respiration, being furnished with external leaf-like or brush-like appendages into which the trachea? are prolonged, sothat by absorbing air from the water that bathes them they may con-vey this into the interior of the body. We cannot have a better exampleof this than is afforded by the larva of the common Uphemera (dayfly), the body of which is furnished with a set of branchial appendagesresembling the fin-feet of branchiopods, whilst the three-prongedtail also is fringed with clusters of delicate hairs which appear tominister to the same function. In the larva of the Lil>cUnl<i(dragon
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
