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Show 222 INSECTA. ORDER XII. DIPTERA(I). . . · bing characters of dipterous Insec. ts consist The dJstmgUis tended wings, With, a1 m ost . ti • two membranous, ex l (2) in siX eet , vable bo dI' es ab o v e them called ha teres . ; . a always, two mo setaceous pieces, varymg m sed of squamous, . h . sucker compo . d · ther enclosed 1n t e superJOr ~ two to six, an ei l' nu. mber ,fr om robosm.f orm sh ea th terminated by tw. o Ips, or groove o a P . t'culated laminre which form a covere d by one or two 1nar 1 sheath for it(3). . t of other Hexapoda, is composed of Their. bo.dy, hke tha The number of ocelli, when any are three prmmpal parts. The antennre are usually inserted present, is always three. (1) .Bnthiata, Fab. . that these organs do not represent the second (2) In order to be convmced 1 T' ula with that of some Hymenop· wings we must compare the thorax of a tr~e lrocerus where the posterior stig· terou: Insect, and particularly of a ~em~l eth:;rymeno;tera, the segment bearing mata are very appar~nt. . Here, as m .a htl developed or incomplete, and ~erely the second pair of wmgs, IS but very slig 1' y r and extremely short piece tmme-follows a small, very narrow, trans:%;~~w~nt~e 'metathorax, which forms that semi· diately under the scutellum •. Nex h articulated appendages of Insects I h~ve segment which in my Me~mr o~ ~ e . ne with two stigmata, more exterlOr called mediate. On e~ch stde of ~:~sa ali;~~ distance from them. The thor~x ?f than the spines, and situated at. . . xce t that the semi-segment, whtch m these Tipulse exhibits the same dtspostbon, e dp . gs t's here somewhat less dis· the Hymenoptera gt.v es ·m sert io n to the secon w. 1nd a' t either of the ends. T he f · can be perceive . tinct, and that no trace o wmgs . 't t'on of the spines, and the stigmata halteres (balanc.i ers) occupy the p. reCi'sde s1 utah 1 that this posterior extremt' ty of in like manner ,.a re ext eri·O r. It 1s ev1 endst t etnh, mediate segment, that m· wb 't c h the thorax bel\ring the hal teres c~rrespon ~ ~ d which in several Acrydia the musical organs of the male Ctcadre at·~ P. ~ce ' an of the same sex presents analogou~ pecuharitles.. f the same family, in the (3) This proboscis is elongated, m several spectes o manner of a long siphon. lHPTERA. 223 on the front and approximated at base; those of the Diptera of our first family resemble those of the Nocturnal Lepidoptera iu form and composition, and frequently in their appendages, but in the following and greater number of families they consist of but two or three joints, the last of which is fusiform or shaped like a lenticular or prismatic palette, furnished either with a little styliform appendage, or a thick hair or seta, sometimes simple and sometimes hairy. Their mouth is only adapted for extracting and transmitting fluids. When these nutritive substances are contained in particular vessels with permeable parietes, the appendages of the sucker act. as lancets, pierce the envelope, and open a passage to the fluid, which, by their pressure, is forced to ascend the internal canal to the pharynx, situated at the base of the sucker. The sheath of the latter, or the external part of the proboscis, merely serves to maintain the lancets in situ, and when they are to be employed it is bent back. This sheath appears to represent the inferior lip of the triturating Insects just as the appendages of the sucker, at least in those genera where it is most complete, seem to be analogous to the other parts of the mouth, such as the labrum, mandibles, and maxiJire( l ). , The base of the proboscis frequently bears two filiform or clavate palpi, composed, in some, of five joints, but in the greater number of one or two. The wings are simply veined, and most frequently horizontal(2). The use of the halteres is not yet well known ; the Insect moves them very rapidly. In many species, those of the last families particularly, and above the halteres, are two membranous appendages resembling the valves of a shell, and connected by one of their sides, called (ailerons or cuillerons) ( 1) This anterior part of the head, called clypeus (my epistoma ), is here represented by that superior portion of the proboscis that precedes the sucker and palpi. (2) Tbese organs, like those of the Hymenoptera, furnish good, secondary, di-risional characters. 1 was the first who employed them. See the works of Fallen, Kirby, }Ieigen, Macquart, &c. |