EXTERNAL ANATOMY OF INSECTS. 583 
Coleoptera; but in Macroglossa Stellatarum and Lasio- 
campa Quercus it has a sinus on each side, but no middle 
one. In Panorpa it nearly closes the posterior orifice 
of the trunk, but in the Zidellulina it is a mere ridge. 
In some Hymenoptera, as Cimbex sericea, the drone-bee 
at least, &c., it is a large convex bifid piece. In the 
wasps, under the spiracle of the metapnystega on each 
side, as in the Locusta, is what I also take to be a pneu- 
matic pouch, which might easily be mistaken for a me- 
taphragm. They have, however, a very conspicuous 
metaphragm, as probably have most Hymenoptera, to 
which the muscles that move the wings are attached. 
In the Diptera Order this part is very conspicuous. If 
you remove the abdomen of any common Tipula, you 
will find that the posterior orifice of the trunk is closed 
above by a pair of oblong, vertical, convex, diverging 
plates;—do the same by any fly (Musca, &c.) and you 
will detect in the same situation a very large convex or 
gibbous one notched below, which occupies almost the 
whole orifice: this is the metaphragm. 
5. Septula*, These are the smaller ridges of the in- 
terior of the alitrunk, which afford a point of attachment 
to many muscles, and run in various directions both on 
the interior of the crust and of the metaphragm. These 
little seams are not to be found so generally in the other 
Orders; but very frequently, as has been before ob- 
served, where there is an exterior impression of the 
crust, or a suture, one of these forms its internal base. 
ii. Processes of the pectus*. We are next to consider 
2 Prate XXII. Fic. 9—11. 2". > Ibid. Fic. 5—7. 
