180 INTERNAL ANATOMY OF INSECTS. 
in the Libellulina, those of the anterior wings are con- 
fined to the anterior portion, and those of the posterior 
pair to the posterior? The muscles for flight in gene- 
ral differ from others by their mass, length, and colour ; 
the bundles of fibres are very distinct, strong, and par- 
allel; their direction is uniform, according to the mo- 
tion they are to produce; their fibres are either attached 
to the solid parts to be moved, or to cupules, but they 
never terminate in a tendon; the muscles are perfectly 
independent of each other, and the wings can be moved 
by them separately’. As to their denomination and 
kind—the principal ones are the /evators and depressors, 
which with respect to the trunk, as was before observed, 
are constrictors and laxators. ‘The levator muscles form 
several distinct bundles in Coleoptera, Lepidoptera, &c.; 
in the Diptera there are three‘; in the Libellulina they 
seem to be single, are all environed with a blackish pel- 
licle, with numerous aérial vesicles, symmetrically ar- 
ranged, filling the interstices. ‘The most common num- 
ber is a levator to each wing; there are often, however, 
as in the cockchafer and the dragon-fly, two depressors °: 
but in the Hemiptera, Lepidoptera, and Tenthredo L., the 
secondary wings have distinct levators, but not depress- 
ors‘; the other Hymenoptera have only a pair of eaché. 
The other wing-muscles are of asecondary description, and 
auxiliary to the above. ‘Their office is to extend and close 
the wings: so that though the denomination of extensor 
will suit the former, that of flexor is not so proper for 
* Chabr. Sur de Vol des Ins. c. iii. 344. t. viii. f. 8, 9. 
> Ibid. c. i. 440. * Ibid, 444. d [bid. 445. c. iti, 359. 
© Ibid. c. it. 332. c¢. iii, 359.- * Ibid. cv i. 445. 
® foid. c. iv. 78. 
