46 INTERNAL ANATOMY OF INSECTS. 
spiracle over each of the four last legs of the Libellulina a , 
but in the remainder of the Neuroptera Order they have 
eluded my search. In the Hymenoptcra and Diptera 
they are nearly in the same situation, being placed be- 
hind the wings on each side of the mctathorax ; in the 
latter Order with the poiser near them on the inner side 5 : 
in this also, the spiracles of the trunk are without lips, 
except in the larvae, but are often merely an orifice, 
sometimes fringed with hairs ; this is particularly con- 
spicuous in Syrphus, in which these orifices are very 
large, and in some species closed by an elegant double 
fringe of white hairs. This is doubtless to prevent the 
entrance of any particles of dust or the like. 
We are next to consider the situation of the spiracles 
of the abdomen : these which are supposed to be appro- 
priated exclusively to inspiration, are usually more nu- 
merous than those of the trunk, by which it is probable 
that expiration is performed, and have principally at- 
tracted the notice of Entomologists : they are either dor- 
sal, lateral, or ventral. In Dytiscus, Copris, &c. amongst 
the beetles, all the spiracles are dorsal; in the larvae of 
Coleoptera and Lcpidoptera they are lateral ; and in the 
Heteropterous Hemiptera they are usually ventral : in 
Dynastes they are commonly found of all three descrip- 
tions; — the three first being dorsal, the two next lateral, 
and the last pair ventral c . In some instances, as in 
Perga Kirbii, and probably other Hymenoptera, these 
organs are planted in that portion of the dorsal segment 
which turns under, as was observed in a former letter d , 
3 Chabrier sur le Vol des Ins. c. iii. t. vi./. 4. Sa, Sp. 
» Plate IX. Fig. 21. wi". 
e Plate VIII. Fig. 9. d Vol.. III. p. 705—. 
