NORTH AMERICAN DIPTEKA. 335 



as usual, the articulation is very closely to the fulcrum. Laterally 

 we see the palpifer, now completely without chitinous connection 

 with the rest of the maxilla, stoutly produced toward the base and 

 with but a small apical process. The palpi themselves are almost 

 completely separated from the palpifer, except by muscular attach- 

 ments, and the blunt character of the apical process itself, indicate its 

 disuse as a piercing organ, almost as well as the fact that it is not equal 

 in length to either the labium or lacinia, and so does not reach to the 

 ti|) of the central aggregation of mouth parts. In fact here, more 

 than in any other species heretofore figured, the palpifer is discon- 

 nected from the other mouth organs, and first changes its function 

 from that of a piercing organ to one offering assistance in flexing 

 and extending the proboscis as a whole. 



The peculiar extensibility of the membrane enveloj)ing the mouth 

 parts is not confined to the species figured, but is notable in all of 

 the five species of Syrphidse examined. It requires no force to ex- 

 tend it, and is not elasticity ; but neither is the extension spontaneous 

 in macerating or preservative media. In placing the prepared 

 specimen on a slide, in position pre{)arat()ry to mounting, the exten- 

 sion is readily made with a blunt needle, and its limit is easily known. 

 Whether the insect itself has the power of making the extension 

 voluntarily I do not know, and observation on living specimens 

 would be required ; it is, however, reasonable to assume that the 

 power exists. 



Eristalis is interesting in another respect, for, in the three species 

 examined, the labrum, in its proper position, and normal in shape, 

 marking the frontal margin of the oral opening, is easily distin- 

 guished ; its claim to form a part of the internal mouth is thus ab- 

 solutely negatived, for every organ represented in the mosquito is 

 also represented in Eristalis, and as the labrum exists independently 

 of all, it is of course an absolute impossibility that it can find a 

 homologue in any of these parts. 



Another of the Syrphidse, Sphcerophoria cijliudrica, may be use- 

 fully presented here, as an advance in the basal development of the 

 pal[)ifer. Only the necessary parts are figured, as the structure does 

 not in other respects differ from that of Eristalis in any important 

 features. The palpifer to the right of the figure is shown complete, 

 and without the palpus. The apical development is seen to be small, 

 merely rudimentary in fact, wliile the basal prolongation is very 

 decided, with broad, flat surfaces for muscular attachment. The 



