EXTERNAL ANATOMY OF INSECTS. 585 



plified in the common cock-chafer and many others of 

 the Order. I have not, however, discovered traces of 

 it either in the Silphidce, Staphylinidce, or the vesicatory- 

 beetles (Meloe L.) ; or even in such, species of Carabus 

 L. and Cicindela L. that I have examined; while in 

 Dytiscus it is very visible. In the Orthoptera it is nearly 

 obsolete ; but in Locusta Leach, under the metapnystega, 

 one on each side, is a pair of seemingly pneumatic 

 pouches which may be mistaken for it. It is almost 

 equally inconspicuous in both sections of the Hemiptera. 

 As to the Lepidoptera, — in Pieris Brassier, it resembles 

 in some degree, though in miniature, the metaphragm of 

 the Coleoptera ; but in Sphinx 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 Libellulina it is a mere ridge. 

 In some Uymenoptera, as Cimbex sericea, the drone-bee at 

 least, &c.j 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 pneumatic 

 pouch, which might easily be mistaken for a metaphragm. 

 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 L.), and you will 

 detect in the same situation a very large convex or gib- 

 bous one notched below, which occupies almost the whole 

 orifice : this is the metaphragm. 



5. Septula a . These are the smaller ridges of the inte- 

 rior of the alitrunk, which afford a point of attachment to 

 a Ibid. Fig. 9-11./". 



