388 



D I P T E R A. 



<legrees of development, from the exceeding length 

 in the MacrocereB and Megistocerte to the scarcely 

 visible size in the Hippoboscce. In the TipididcK we 

 find these organs composed of numerous articulations. 



A, Antennae of Tipula , B, of Tabanns ; c, of Musca. 



In the Tabanulee and Berida: they are very short, and 

 the terminal articulations become almost indistinct, 

 so that in the Mu&cidce, &c., where they are very 

 short, and appear to be composed only of three joints, 

 having a terminal bristle, it is impossible not at once 

 to perceive that the terminal joints are, with the 

 exception of those composing the seta, so entirely 

 soldered together that their union is not visible. The 

 eyes are lateral, and in many instances those of the 

 males are much larger than in the females, uniting 

 upon the crown of the head. In others they are so 

 large as to occupy nearly the entire head, leaving but 

 a small space only for the mouth. 



In those species which have the mouth more per- 

 fectly developed than the rest, and which consist of 

 the blood-thirsty gnat and gadfly, we find a series of 

 organs, greatly modified of course as to their form, 

 in order to fit them for their functions, but which, as 

 to their number, correspond with those of the mouth 

 of the true mandibulated insects, so that it is equally 

 impossible for us to arrive at any other conclusion 

 than that the parts of the mouth of the fly represent, 

 in an altered state of development, the parts of the 

 mouth of the beetle. We accordingly find that the 

 mouth iu Tabanus consists of a large fleshy organ, 

 having a fleshy pair of lobes at its extremity, and 

 >which, being the lowest part of the mouth, corresponds 

 with the lower lip of the beetle. At the sides of this, 

 and rather higher in the mouth, is attached a pair of 

 lancet-like organs, having a pair of large biarticuiate 

 palpi arising from the base, these constitute the 

 maxillae and the maxillary palpi. Still higher in the 

 mouth another pair of lancets appears, which repre- 

 sent the mandibles, whilst a larger horny piece, chan- 

 nelled beneath for the reception of the others, and 

 which forms the upper lip (labrum). Within the 

 mouth another very fine lancet appears, analogous to 

 the tongue of the grasshoppers, an organ seldom de- 

 veloped to any extent in the coleoptera. When we 

 consider the habits of these insects, it is evident how 

 necessary it is that the organisation of the mouth 

 should be fitted for a different employment from that 

 of masticating. These habits are essentially suctorial, 

 and the food of the insects is essentially fluid ; broad 

 horny organs would therefore be useless, whereas a 

 series of acute instruments for puncturing and pene- 

 trating deeper and deeper into the food, and a fleshy 

 canal, up which, by suction, fluids easily pass, is what 

 would exactly be looked for in the workmanship of 

 an omniscient and all providing Artificer. 



In other groups of dipterous insects, and more 

 especially in those which prey upon their companions 

 (Atiltda-, JEmpid<e, &c.), we find diminished forces 



in the organisation of the mouth, the lancet-like man- 

 dibles have vanished, but all the remaining organs 

 appear in full development. In the Syrphidce the 

 maxillae become smaller, and in Musca they are 



A, Mouth of Tabanus ; B, of Musca. 



completely lost. In the (Edridtc the entire mouth is 

 sometimes completely obliterated. The legs are ge- 

 nerally long and slender : some instances occur when 

 then are disproportionately long, whilst in others they 

 are more or less thickened and spined. The wings 

 agree in their veining with the anterior pair of the 

 Hymenoptera rather than with those of the Neuroptera, 

 only there are fewer transverse nerves. In one group 

 however, Neinestrina, the wing is reticulated nearly as 

 much as in the Neuroptcra. In comparing the upper 

 wing of a bee with the wing of a fly, no particular 

 resemblance is to be traced betsveen the direction 

 and position of the veins, but if both the front and 

 hind wings of the bee be compared together with the 

 wing of some flies, as the Syrphidce t and particularly 

 Aphrites, we are enabled to trace a very great resem- 

 blance between them in this respect. M. Macquart 

 employs this circumstance as a forcible argument in 

 support of the opinion that the balancers of the Dipteru 

 do not represent the lower wings of the bee. Tho 

 uses to which these balancers are applied are not yet 

 decidedly ascertained ; the insect moves them with 

 extreme rapidity, especially when a buzzing- noise is 

 produced, and it U important to observe that they 

 are placed close to the mouth of a pair of tin 1 lin-uthiny 

 pores. Many species are moreover provided at the 

 base of the wings behind with a pair of membranous 

 doubled organs, somewhat like the valves of a shell, 

 which are termed alvlets; one of these is attached to 

 the wing, and the other to the sides of the thorax. 

 The size of these alulets is in inverse proportion to 

 that of the halteres. The abdomen is generally 

 attached to the thorax by a portion only of its basal 

 diameter, it is composed of from five to nine visible 

 articulations, and is generally pointed at the extremity 

 of the females, enabling them the more readily to 

 introduce their eggs into the situations in which they 

 are deposited. In those species which have the ab- 

 domen composed of the fewest segments, those which 

 appear to be wanting are transformed into a kind of 

 ovipositor, consisting of a series of little tubes sliding 

 one into another like a telescope. The sexual organs 

 of the males are external in many species, and folded 

 beneath the abdomen. The legs are terminated by 

 a tarsus consisting of five joints, the lust of which is 

 armed with two small claws, and very often with two 

 or three membranous lobes or pulvilli. It is by the 

 assistance of these terminal organs of the foot that 

 the fly is enabled to perform the curious mechanical 

 feat of walking with the back downwards, against 

 gravity, upon the ceilings of rooms, highly polished 

 ss, &c. From the experiments of Sir Everard 

 Home, it has been generally considered that this was 

 effected by the formation of a vacuum, by means of 



