BY FREDERICK A. A. SKUSE. 31 



space, called the lateral callosity of the metanotum (callus 

 metanoti lateralis). The poisers or balancers (halteres) have their 

 origin beneath this callosity, and in front of each of them we see 

 the spiracle of the metatborax (stigma metathoracis). The mem- 

 branous covers sometimes found above this spiracle have the 

 name of covering scales (tegulce or squamce). 



III. The ahdomeyi. 

 The upper side is genei'ally so called, the name of belly (venter) 

 being applied to the under side. The terminal joint is furnished 

 in the male with appendages destined to take hold of the female 

 in cajyuld, and if they partake of the form of pincers and are 

 not bent under the body these are called forceps ; in the female 

 with the organ for laying eggs (ovipositor^, which may either be 

 called the borer (terebra) or the style (stylus), depending on its 

 shape. 



IV. The vnngs. 



A precise nomenclature of the veins and cells of the wings is 

 of the utmost importance ; their existence and mutual arrangement 

 afford tlie most valuable criteria in the systematic distribution of 

 the order, and in the definition of the species. Dr. Schiner ( Verh. z-b. 

 Gesellsch. in Wien, Band XIV.) has proposed a new, and, in many 

 respects, excellent nomenclature for the veins and cells of the 

 wings in the Diptera ; but 1 prefer to fall back upon that of Prof. 

 Loew, which preceded the other by two years, and at the same 

 time adequately fulfils its purpose. 



As pointed out by Prof. Loew, the venation of the wings 

 throughout all the Diptera occurs merely as modifications of a 

 common type, and that type is to be found amongst the Muscidse. 

 For illustration, however, he selects three wings, one from the 

 Ortalidto (Ortalis\ the second from the Empidso (EmpisJ, and the 

 last from the A.%\\'\(iiVii( Dasypogo^i), from which three he can deduce 

 the whoh; plan of venation, and consoquontly tlie cellular .sy«tem. 

 As an endeavour to simplify matters 1 will combine in a single 

 diagram the wings referred to, and form an ideal typical wing, 

 thus enabling me to tabulate six or seven pages of Prof. Loow's 



