INTRODUCTION. 13 



several characters adopt nearly the opposite form to that in the 

 .Nematocera. Of these perhaps the principal is the anal cell, 

 which is always wide open in the Nematocera, normally widening 

 towards its tip, whereas in the Brachycera it normally contracts 

 towards its tip, frequently very strikingly so ; and in a large 

 number of genera it is completely closed more or less near the 

 wing-margin, either by the gradual approximation of the 5th and 

 6th veins or by the lower branch of the former turning down, 

 frequently at a sharp angle or well-rounded curve, often in the 

 latter cases closing the cell some distance from the margin of the 

 wing. In the higher families of Brachycera the anal cell is very 

 elongate, extending generally to the wing-margin, but in sub- 

 sequent families, notably the Empilve, it is considerably shortened 

 through the almost or quite recurrent ending of the lower branch 

 of the 5th vein in the anal vein at or before the middle of the 

 latter, whilst in DolichopoeievE and LoNCHOPTERin^E it is shorter 

 still. It increases in length again in two out of the three first 

 families of the Cyclorrhapha, though it is short in one of them 

 (PEATYPEZiDiE), whilst in the higher Muscids it is always com- 

 paratively short, and in the lower Muscidje normally short or 

 absent, although conspicuous exceptions occur (some Ortalin^e 

 and Trypetin.e, for example). In the Conopid^e, one of the two 

 families* that may be regarded as forming the transition from the 

 BRACHYCERA-like Cyclorrhapha to the Mitscidve (s. Jatiss.) it is 

 long in the Conopinje and short in the Myopihtje, which tends to 

 prove the intermediate nature of the Conopidje. 



The auxiliary and 1st vein are generally obviously present, 

 separate and simple, but in some groups of Acaeyptrata they 

 are frequently coalescent.f The 2nd vein is nearly always verv 

 prominent and simple ; the 3rd, which is nearly always simple in 

 JSTematocera, is normally forked in the higher families of Brachy- 

 cera. The 4th and 5th veins in these latter families are generally 

 both forked, but in the highest three families of the Cyclorrhapha 

 (Platypezidje, PiPtrNCULiD.E, and Syrphie^;) there are normally 

 only three endings to the two veins, in which cases it is the 5th 

 vein that is considered forked, its upper branch forming part or 

 the whole of the hinder side of the discal cell. This cell in the 

 jNematocera is confined to the Tipulid.e and BhyphidjE- — that is 

 to say, the two families generally placed next to the Brachycera, 

 in which latter the cell is a standard feature, though exceptions 

 occur (some Eyipilve), — and it is prominently retained in the 

 calyptrate Muscids and the bulk of the Acaeyptrata. The 

 anterior cross-vein is nearly always present, though rudimentary 

 in some StratiomyievE ; but the posterior cross-vein disappears 

 after the higher families are passed, if the theory of the forked 

 5th vein be upheld. J 



* The other being the CEstridje. 



"I" They are then called the 1st vein, following Schiner. 



J It may as well be stated here that I am by no means convinced that this 

 is the correct interpretation, 



