CIG 



INSECTS 



fullowmg families tlicy aru only enmiioseil of two or three joints, tlie last of Hliicli is genenilly 

 fusiform or lentieular, ivith a small stylii'orm appendage, or hair, either simple or bearded. 



The mouth is only fit for extracting and draiving 

 forth fluid matters, and when these ,iri; im'losed 

 in pro|M.'r vessels, with an envelope easily jjicreed, 

 the jiieees of the sueker aet as lancets, piercing 

 this I'nvelope, and forming a passage for the 

 NJ%___ liipiiil, ivliieli ascends by the pressure of these 

 V.^ X lancets together, to the pharynx, situated at the 

 ^^-r^ base of the sucker, the sheath of which serves 

 Fig i:ii,^>, i„„.i -.fT.ll,.l.,u^■, n, ii.n.i ..r Mii't.-,. only as a defence to these hiuccts, and is gene- 



rall)' folded upon itself in theii' action. This sheath appears to represent the lo\^er lip of mas- 

 ticator)- nisects, and the setie, at least lu those with the most conijdicatcd mouth, rc]iresent 

 tlie other parts, such as the laljruin, mandibles, and maxdhe. The clypeus, or epistonie as J call 

 it, is represented by the Ijasal part of the proboscis preceding the sucker and palpi; the base 

 of the proboscis mostly Ircars t\\o filiform or clavate pal]ii, comjiosed in some of five joints, 

 but in most of only two. The wings are simply veined, and generally horizontal. As in the 

 Ilymenoiitera, their veins furnish good secondary characters of groujis. 



The use of the balancers is not kno\^ii ; the insect moves them \\\[h great rapidity. i^Ianv 

 species, es])ecially tliose of the terminal faaiilies, have above the lialancers two niembranous 

 pieces, like the two valves of a shell, attached together at one side, and which are termed 

 alidets. One of these pieces is iiniteij to the wing, and ]iartakes of its movements, at which 

 tunc the two valves ai'e upon the same ]>lane. The size oi' these \^inglets is in inverse pro])or- 

 tiou to that of the halteres ; the prothorax is always very short, and often its lateral portions 

 are alone visible. In some species of Scenopinus, Culkidix, and PsycJiodo, thev are very 

 prominent, like tubercles. The mesothorax alone occupies the greatest ])art of the thorax ; 

 in front of whieti, on each side, and behind the )n-otliorax, are two spiracles, and two others 

 are observed near the base of the bahmeers. As in the Ilymenoiitera, those of the meso- 

 thorax are hidden or obliterated. 



The alidomen is attached to the thorax only by h portion of its transverse diameter; it con- 

 sists of from five to nine segments, and is generally terminated by a point in the females : in 

 those \\hich have it composed of the smallest number of joints the terminal ones often form 

 a kind of ovipositor, composed of tubular pieces, entering into each other like those of a 

 telescope. The male sexual organs are external in many species, and curved beneath the 

 abd(mien. The legs, which are long and narrow in the majority, are terminated by a .5-joiiited 

 tarsus with two ungues, and often ^\ith two w threi.' vesicular puh'iUi. JMaiiv of these insects 

 do us much damage, either in sucking our o\mi Idood or that of our domestic .animals, by 

 depositing their eggs upon their bodies, so that their larva; may there obtain nourishment ; 

 or by infecting our viands and cereal plants with the same intention. Others, in return, are 

 useful, Ijy devouring obnoxious insects, consuming dead carcases, or other deca\ iin.^ animal 

 matter, wdnch would otherwise render the air we breathe impure, as v.ell as bv hastening the 

 decomposition of putrid i\ liter. 



The duration of the life of dipterous insects arrived at the final state is very short. They 

 all undergo a com|ilete metamorphosis, but modified in two material \va\s. The larvrc of 

 many change their skin in order to undergo their transformation to pupic, and some spin a 

 cocoon; but the others do not moult ; their skin hardens, contracts, and generally shortens, 

 becoming a strong cocoon, of an egg-like form, for the inclosed pupa. The bodv of the larva 

 is detached, leaving its own proper lu-gans attached to the skin within, snch as the parts of the 

 mouth, &e. : shortly afterwards the inclosed insect assumes the form of a soft and o'elatinous 

 mass, without any of the jiarts of the future insect being visible; smne da\s afterwards, how- 



