OP THE MOUTH PARTS OF CERTAIN INSECTS. 



193 



incomplete articulation between galea and subgalea. By separating olV the galear 

 structures, the relation of palpifer and lacinia in Simnlium is illustrated (on PI. I, 

 Fig. 1'), and the convergence of the two at tip is not distortion, though perhaps a 

 little exaggerated by pressure. The result of this change of position is that a section 

 made near the base of the proboscis would show as illustrated on PI. I, Fig. 2\ while 

 one made nearer the tip would show as in Fig. 1''. Incidentally it will pi'ove interest- 

 ing to compare these sections with that oi' Bittncs stricjosus (Pi. Ill, Fig. 4''), leaving 

 out of consideration the abnormal labium of the latter. The resemblance is ijerfect, 

 and tlu' rc'somblancc expresses fully the actual condition of the matter. A very simi- 

 lar state of affairs exists in the Asiluh' (PI. Ill, Fig. 1"). Ilei'e the palpifer is the 

 only maxillary i)iercing organ, and the figure itself shows clearly how easily it would 

 swing inside the amj^le space left in the subgalea for its entrance. The curvature of 

 the organ is such, also, that when in place it meets the central ligula so as to form a 

 solid puncturing organ. 



So in Ghrysops (PI. II, Fig. 14) the structure is seen to be similar to that in 

 Simulium ; but here, as almost everywhere else in the order, it is cylindrical or nearly 

 so, in marked contrast with the lacinia, which is always flattened. 



As we get into types that have lost the piercing habit, the function of the palpifer 

 fails or changes. If the species have a short, nonflexcd proboscis, it simply dwindles 

 from disuse. So in Stratiomyia and in LepHs (PI. II, Figs. 1 and 2) it simply forms 

 a little chitinous appendage to the palpus — a mei-e remnant without function. If on 

 the other hand, the species are al)le to flex the [)rol)Oscis, another change talces place. 

 There is needed then some lever to which muscles for flexing can be attached, and no 

 structure seems to have been so easily ada])table as the palpifer. So Ave find in the 

 Mnjmkp, where only slight flexion is rccpiired, only a small l)asal extension, shown at 

 PI. II, Figs. 4 and 3, for Empis spectahili.-< and Mdonchas tnstit<, and at 1*1. Ill, Fig. 

 2'', for Ithamphomiiia lougiccmda. 



In tbe Bomhyliiihr is a step foi'ward. The insects are not prcdaceous, have the 

 habit of hovering over flowers and using the [)roboscis in feeding in that position. 

 This requires a much better control, and as a result the basal extension is much better 

 developed, as shown in PI. II, Figs. G and 7, illustrating Bomhylius and Anthrax. 



As we get into types like Eridalis and other Syrphidw, the basal extension be- 

 comes the most prominent and the piercing portion diminishes in size (PI. II, Fig. 5), 

 and keeping step with this modification is a gradual separation of the palpus itself 

 from the jialpifer. This is well illustrated both in ErisUdis and Spha'ro2)7ioria, iiud 

 this tendency continues until in Lunllia (PI. II, Fig. 10) the separation is complete, 

 though tlu' piiueing portion of i1k- palpilrr is yet distinguishalilc. In f '(dliphard even 



