SYRPHIDAE OF MAINE. 203 



none. They also agree in lacking a specialized head, the ante- 

 rior segments being usually bluntly accuminate, and in no way 

 constricted or marked off from the rest of the body. A few 

 filth-inhabiting larvae have the anterior segments globose and 

 slightly constricted from the succeeding ones making a feebly- 

 differentiated false-head. All the larvae of Syrphidae carry on 

 aerial respiration through stigma'ta or spiracles near the ante- 

 rior and posterior ends of the body,* and lack them on the 

 intermediate segments. The posterior spiracles are ahvays situ- 

 ated on the ends of tw.o elongate or very short tubes which are 

 fused mesad throughout their length, never forked or divergent, 

 except very slightly at the tip or in very young larvae ; and 

 consist of three pairs of slit-like spiracles and a pair of circular 

 plates or "buttons." The anterior larval spiracles (Fig. 33-1-?; 

 34-2; 36-4) are small, situated dorso-lateral near the ante- 

 rior end and may be somewhat elevated on cornua or quite 

 sessile. The head-segments bear a pair of short, fleshy, sen- 

 sory structures corresponding to antennae and certain chitinized 

 external mouthparts. The oesophagus has also a chitinized 

 cephalo-pharyngeal framework or skeleton. The mouth and 

 anus are terminal or slightly ventrad at the two extremities. 



The somites are not clearly differentiated and in some genera, 

 notably Microdon, are indistinguishable. Usually they are indi- 

 cated externally by groups of transverse wrinkles between 

 which groups the body is slightly constricted. But more espe- 

 cially by the presence of a transverse row of specialized vestiture 

 consisting typically of twelve hairs or spines either with or 

 without subtending, conical, wart-like papillae, called the seg- 

 mental spines or elevations (35, p. 18). Sometimes these 

 spines are very inconspicuous, sometimes instead of the single 

 spine we have a clump of several soft hairs ; but in all the larvae 

 I have examined, except the species of Microdon, the segmental 

 vestiture is specialized or differentiated in some way from the 

 other vestiture of the body, the integumental vestiture. 



Although the segmentation is obscure in this family, for 

 convenience of description I have assumed (35, pp. 18 and 20) 

 that there are twelve somites represented in the larva. I have 



*I have so far failed to find anterior spiracles on the larvse of 

 Microdon which I have examined. 



