552 DISTRIBUTION OF SPIRACLES IN INSECTS. 
ment, in the larvæ of the higher Hymenoptera, i.e., the bees and 
wasps (I have examined Bombus, Xylocopa, Halictus, Andrena, 
Vespa and Polistes), there are no spiracles on the prothorax, but 
a pair on each of the two following thoracic segments. Tn all 
these the thoracic spiracles are as well developed as those on the 
abdomen, and in Bombus larvæ the tracheæ proceeding from the 
spiracles are as well developed, being large and elongate barrel- 
shaped just after leaving the stigmata, and beyond subdividing 
into several branches. In two genera of Tenthredinidæ, and prob- 
ably in the family generally, the spiracles are arranged as in ns 
lepidopterous larvæ, there being but one pair, the prothoracie. — 
n the Uroceride, however, Tremex in its larval state has ie 
pairs, one prothoracic and one metathoracic, the anterior pair twice 
as large as the posterior pair. So it would seem that while no 
known hymenopterous larva has more than two pairs of spi pri 
on the thorax, yet three pairs may be found on different rings A l 
different groups, though not actually existing in one individual. 
The ideal number of pairs is three, or for the entire body cleven. 
In the Diptera the Cecidomyiæ have nine pairs of stigmata, 0 : 
which one is thoracic (on the prothorax), while the eight other 
pairs are abdominal. In the Muscidæ, there are two pairs only, : 
one prothoracic, the other anal, or situated on the ninth no ; 
of the abdomen. So that in this group we have ten cai meee 
which bear spiracles, though no single species is known to w 
more than nine pairs of spiracles. 7 
In the Coleoptera there are usually nine pairs of ie 
thoracic, and eight abdominal. The thoracic spiracles mee 
on the pro- or meso-thoracic segment.* In the adult Melolo a 
and other beetles Strauss shows that a spiracle exists pene ‘ : 
meso- and meta-thorax, which is not present in the larva- 
be so, then the ideal number of pairs in Coleoptera ig ton a 
In the Hemiptera and Orthopterat there are two wo - 
gments 5 oie 
thoracic spiracles present on i the two antore: ae 
the thors? 
*It is often difficult to say on which segment of the coleopterous mei or 
spiracles are placed, they are so near the suture separating preys" of Car 
segm . pium, To 
Cetonia (by some they are stated to be on the meso-thoracic ring » ee ring ( 
and Xanthochroe the spiracles are said to be place p nts, 
In Magdalinus they are situated o 
and in others on the anterior edge of the meso-thoracic 
tGryllidæ and Acrydii (Dufour). 
