136 ENTOMOLOGY 
Spiracles.—The paired external openings of the trachez 
occur on the sides of the thorax and abdomen, there being 
never more than one pair to a segment. Though the thysa- 
nuran Japyx has 11 pairs, no winged insect has more than 10; 
although there are in all 12 segments which may bear spiracles 
—the three thoracic and the first nine abdominal segments. 
( Additional details are given on page 66. ) 
The spiracles, or stigmata, are usually provided with bris- 
tles, hairs or other processes to exclude dust; or the hairs of 
the body may serve the same purpose, as in Lepidoptera and 
Diptera; in many beetles the spiracles are protected by the 
elytra; in other beetles, however, and in many Hemiptera and 
Diptera the spiracles are unprotected externally. Larve that 
live in water or mud may have spiracles at the end of a long 
FIG: 1173. 
Apparatus for closing the spiracular trachea in a beetle, Lucanus. A, trachea 
opened; B, closed; b, bow; bd, band; c, external cuticula; /, lever; m, muscle; s, 
spiracle; t, trachea.—After JupEIcH and NITSCHE. 
tube, which can be thrust up into the pure air; this is true of 
the dipterous larve of Eristalis, Bittacomorpha (Fig. 172) 
and Culex (Fig. 229). 
Closure of Spiracles.—As a rule, a spiracle is opened and 
closed periodically by means of a valve, operated by a special 
occlusor muscle. In dipterous larve the closure is effected by 
the contraction of a circular muscle, but Coleoptera and Lepi- 
doptera, among other insects, have a somewhat complex. appa- 
ratus for closing the trachea immediately behind the spiracle. 
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