DIPT Eli A. 



61J 



behind, the space between them being very ample, and divided by a longitudinal impression 

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

 over the abdomen. 



These insects live in the larva state between the scales of the abdomen of some Andrenae 

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

 time as their wings. Although apparently far removed, in many respects, from the Hymen- 

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

 Eulophi. 



M. Peck has observed the larva- of Xenos Peckii, which is found in Wasps ; it is oval-oblong, 

 without feet, annulated, with the anterior extremity ddated into a head, and the mouth formed 

 of three tubercles. These larvae are transformed to pupae in the same situation, and beneath 



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

 amination of Xenos Russii, and without changing 

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

 insect.) Probably the two prebalancers are ser- 

 viceable in enabling the insect to disengage itseli 

 from between the scales of the abdomen of the in- 

 sects in which they have lived. 



They are a kind of (Estri of insects. We shall 

 subsequently see that a species of Conops under- 

 goes its changes in the interior of the abdomen o' 

 Bombi. 



They compose [four genera] Xmos, Rosai; 

 Slylops, Kirby [and Elenchus and Halictophagua, 

 Curtis]. They chiefly vary in the form of the 

 antenna:. The species of the first-named genus live 

 Hir. i.To.— a. styiop, u»ni, dm. «i*oi a, n»Knifiedi c. ah- in Wasps, and those of Stylopa in AndretUB. See 



circus, with the heads ol two of iti Larva? exserted betw . ,. ,. . . . , 



the abdominal rhiip a ; d, larva extracted and magnified on these insects the llK'lllO'.r ot Klinv, 111 the 



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

 which I have published in the "Entomological Transactions']. 



THE TWELFTH ORDER OF INSECTS — 



THE DIPTERA (Amtliata, I 



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



them two moveable slender bodies named haltered, or balancers, (which I.atn ille, in a note, 



endeavours to prove cannot be the representatives of bind wings, but rather of a pan- of 



Spines observed in the metathorax of some 1 1\ menoptcra. such OB Crypt OCerus). The luckei is 

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



a canal on the upper side of the proboscis, which is terminated by two flesh] Lip-like lobes, "t- 



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



The body is composed, as in other hexapod insects, of three principal pieces ; the ocelli, 

 when present, are [almost 1 always three in number, [two in some Tipulidte], The antennae 



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

 their form, composition, and appendages, with those of the Nocturnal I.epidoptna, hut hi the 



