778 



AN INTRODUCTION TO ENTOMOLOGY 



In many families there is a notch in the inner margin of the wing 

 near its base (Fig. 995, a. e) ; this is the axillary excision; that part of 

 the wing lying between the axillary excision when it exists, and the 

 axillary membrane is the ;/?05^m or io6^ (Fig. 995, /). In certain fami- 

 lies the axillary membrane, the membrane of the wing base, is ex- 

 panded so as to form a lobe or lobes which fold beneath the base of 

 the wing when the wings are closed; this part of the wing is the alula 

 or alulet. The alulaj are termed the squamcs by some writers and the 

 calypteres by others. The alulse are well developed in the common 



/?, /?,+j 



2d A+Cu2 



Fig. 995. — Wing of Conops. 



House-fly. Each alula, in those species where the alulae are well de- 

 veloped, consists of two lobes which fold over each other when the 

 wings are closed. These two lobes are designated as the upper squama 

 or squamula alaris and the lower squama or squamula thoracalis re- 

 spectively. The alulae are called the tegulas by many writers on Dip- 

 tera ; but the term tegula was first used in insect anatomy for the cup- 

 like scale which covers the base of the wing in certain insects, as most 

 Hymenoptera, and should be restricted to that use. The terms alula 

 and alulet are also often misapplied, being used to designate the pos- 

 terior lobe of the wing. 



The legs vary greatly in length and in stoutness. The coxse are 

 usually long, and in most of the fungus-gnats (Mycetophilidas) they 

 are very long. When pulvilli are developed they are membranous 

 pads, one beneath each tarsal claw. A third 

 appendage, the empodium, often exists be- 

 tween the two pulvilli of each tarsus. The 

 empodia may be bristle-like or tapering (Fig. 

 996) or membranous, resembling the pulvilli 

 in form (Fig. 997) in the last case they are 

 described as pulvilliform. 



In descriptions of flies the number of 

 tibial spurs borne by the different pairs of 

 legs is often indicated by a brief formula, as, 

 for example; "Tibial spurs i :2:2" indicates that the fore tibiae bear 

 each one spur; the middle tibiae, two; and the hind tibas two. 



Fig. 996. 



Fig. 997. 



