INTERNAL ANATOMY OF INSECTS. 181 
their antagonists; their office being not so much to 
bend, as to bring back the wing to its station of repose. 
The folding of certain wings, as those of Coleoptera, 
Dermaptera, the Vespide, &c., seems more the function 
of the abdomen than of the wing-muscles: this you may 
easily see, as I have often done, if you attend to any Sta-. 
phylinus, when after alighting from flight it proceeds to 
fold up its wings under the elytra. Perhaps the term 
retractor might not be inapplicable to the muscles in 
question. Both these and the extensors are usually 
small slender muscles, but sometimes numerous?. ‘They 
are larger in Coleoptera, Lepidoptera, and Tenthredo L.°. 
The muscles that open and shut the elytra of Coleoptera, 
and probably of Heteropterous Hemiptera, and which 
also aid their movements during flight, are very slender“. 
With regard to the attachment and insertion of the wing- 
muscles, it is according to two very distinct types, one 
of which appertains to insects in general, and the other 
is peculiar to the Libellulina. In insects in general, the 
principal muscles for flight have not their insertion in 
the wings, but act upon their bases by the intervention 
of small long pieces. ‘The depressors occupy the middle 
and upper region of the alitrunk, and are inserted ante- 
riorly and posteriorly upon the concave surfaces of two 
transverse horny semi-partitions, adapted by their elas- 
ticity to dilate the trunk—and thus acting the part of 
both diaphragm and ribs? : but in the Lebellulina, as in 
birds, these muscles are placed on each side of the point 
2 Ibid. c. 1, 415, 442. ¢. iv. 80. » bid. c. i. 442. 
¢ Ibid. 439~. * Chabrier dnalyse, 28. The 
latter part of this passage is copied from a M.S. note of the author’s 
in my copy. —W. K. 
