DIPTERA. 



615 



1ji;'!iiiu1, (lie sjiafo between tliem being very ample, and divided by a longitudinal impression 

 in the middle. The posterior extremity of the metathorax is prolonged into a large scutclhim 

 over the abdomen. 



These insects live in the larva state between the scales of the ahdomeu of some Aiidremc 

 and Wasps, belonging to the subgenus Pulistes. They move their prebalancers at the same 

 time as their wings. Although ajiparcutly far removed, in many respects, from the Ilymen- 

 optera, I nevertheless consider them nearest allied to some of these insects, such as the 

 Ei(lo/>kl. 



M. Peck lias observed the larvic of Xenos Peckii, ivliich is found iu Wasps ; it is oval-oblong, 

 without feet, annulated, v.ith the anterior extremity dilated into a head, and the mouth formed 

 of three tubercles. These larva; are transformed to pupic in the same situation, and beneath 



their own skin, as it appears to me from an ex- 

 amination of Xeiios Rossii, and without changing 

 its form. (See the memoir of M. Jurine upon this 

 insect.) Proljabiy the two prebalancers are ser- 

 viceable in enabling the insect to disengage itself 

 from between the scales of the abdomen of (he in- 

 sects in which they have lived. 



They are a kind of tEstri of insects. We shall 

 subsequently see that a species of Conops under- 

 goes its changes in the interior of the abdomen o' 

 Boiiiui 



They compose [four genera] Xmos, Rossi; 

 Stijlops, ICirby [and Elenchus and Halictophuyiis, 

 Curtis]. They chiefly vary in the form of the 

 antenmc. The species of the first-named genus live 

 in Wasps, and those of Stylops in Andrena. See 

 on these insects the memoir of Kirb}', in the 

 eleventh volume of the hinnaan Transactions ; [also the work of Curtis, and several memoirs 

 which I have published in the Entomological Transactions^. 



FiLr. ISO.— A. Stylops Dalii, nat, size; D, 

 dreiia, with tlie ht-adsot two of its Urva 

 the abiloininal riii^s a ; d, larva i-xtractt 



1 and majjaified 



THE TWELFTH ORDER OF INSECTS,- 



THE DIPTERA (Antliata, Fab.),- 



Ilas for its characters six feet, two membranous extended wings, having almost always beneath 

 tliem two moveable slender bodies named halteres, or balancers, (which Latreille, in a note, 

 endeavours to prove cannot be the representatives of hind wings, but rather of a jiair of 

 sjiines observed in the metathorax of some Ilymenoptera, such as Cryptocerus). The sucker is 

 composed of scaly, setiform pieces, of variable number (from two to six), and either inclosed in 

 a canal on the upper side of the proboscis, which is terminated by two fleshy lip-like lobes, or 

 covered by one or two inarticulated plates, which serve it for a sheath. 



The body is comjiosed, as in other hexa])od insects, of three principal pieces ; the oceUi, 

 when present, are [almost] always three in number, [two in some Tipulids]. The antennje 

 are ordinarily inserted on the forehead; those of our first family have much relation, both in 

 their form, composition, and ajipcndages, with those of the Nocturnal Lepidoptera, but m the 



