14 BRACHYCERA. 



The brachycerous venation attains its most perfect form perhaps 

 in the TABANID.E, and it is elaborated most in the ASILIDJE, 

 NEMESTRINID.E, MiDAio., and CYRTiD*! (despite the latter 

 family also exhibiting some very simple venational types), being 

 quite eccentric in the last three families, many of the longi- 

 tudinal veins in the hinder part of the wing running more or 

 less pai-allel to the hind margin; whilst in certain genera of 

 NEMESTRINID^ an additional character is the net-like system of 

 very numerous small cross-veins. An isolated instance of a cell 

 being subdivided hy numerous cross-veins occurs in Lycastris 

 (SYRPHID^), in which the subcostal cell is so divided. 



After the BRACHYCERA the venation becomes more simplified, 

 and is, speaking broadly, remarkably uniform in type throughout 

 the MUSCID.S, in the higher groups of which (Tachinicls, Dexiids, 

 Sarcophagids, and Muscinids) the 1st posterior cell is quite or 

 nearly closed by the upturned apical section of the 4th vein, 

 whilst in the ANTHOMYINJE and the various subfamilies forming 

 the ACALYPTRATA that cell is broadly open. Numerous minor 

 differences occur in these groups, but the type of venation 

 remains the same. Passing on to the PUPIPARA, some genera 

 may be observed to possess peculiar venation, but they need not 

 be discussed here. 



The general form of the body exhibits the widest diversity. 

 The head may be variously proportioned to the body, perhaps 

 attaining its minimum of size in the CYRTIDYE and its maximum 

 in PIPUXCULID.E, but normally it is approximately of the same 

 width as the thorax and usually more or less semicircular. The 

 thorax and abdomen both vary greatly in length and breadth in 

 relation to one another, and range from the flattened form in some 

 STRATIOMYIDJE to the humped thorax in many EMPID.T; and to the 

 globular or balloon-like abdomen in most CYRTID.I, the whole 

 body in many species of the latter family being practically 

 spherical. As regards vestiture, a short pubescence over the 

 greater part of the thorax and abdomen is common to the vast 

 majority of genera in BRACKYCERA, a few restricted groups being 

 for all practical purposes absolutely bare (Scenophins). The earlier 

 families are erernochsetous that is, possess no distinct bristles of 

 a chaetotactic nature on the head or thorax ; but such bristles 

 gradually appear in successive families, as witnessed by the apical 

 spurs on the tibiae in LEPTID.E, spicules or stick-like spines on the 

 legs in some BOMBYLIIDJE, and real bristles and spines in that family, 

 in DOLICHOPODID^, EMPID.E, and THERETID;E, culminating in the 

 powerful chsetotactic system in most ASILIDJE ; after which these 

 characters gradually diminish or practically disappear (as in 

 PIPIINCULIDJE and SYRPHIDJS), reappearing and attaining probably 

 their greatest development in the order in the TACHININ.E, the 

 highest group of the MTTSCID^E (. latiss.). The pubescence, 

 always soft in STRATIOMYIDJE, attains its greatest development 

 perhaps in BOMBYLIID^:, THEREYID.E, and ASILIDJE ; and true 



