WINGS 



447 



below figures of two systems that have been used by eminent 

 Dipterologists for the description of the nervures and cells. The 

 comprehension of these features of the Dipterous wing will be facili- 

 tated by noticing that the wing being extended at right angles to 

 the body is divided by the longitudinal nervures into two great 

 fields, anterior and posterior, with an interval between them : 

 this interval is traversed only by a short cross-vein (marked x in 

 Fig, 215 A, and i in B). This cross- vein may be placed near the 

 base or nearer to the tip of the wing ; it is of importance because 

 no nervure in front of the median area traversed by it can corre- 



A 



FIG. 215. Nervuration of Dipterous 

 wing. A, Wing of a Tipulid, accord- 

 ing to Loew, who uses the following 

 nomenclature : a, costal nervure ; b, 

 mediastinal ; c, subcostal ; d, radial ; 

 e, cubital ; /, discoidal ; y, postical ; 

 h, anal ; i, axillar ; x, transverse, 

 ?/, posterior transverse, nervure ; 

 1, 2, mediastinal areas ; 3, sub- 

 costal ; 4, cubital ; 5, anterior basal ; 

 6, posterior basal ; 7, anal ; 8, pos- 

 terior marginal ; 9, discoidal. B, 

 Wing of an Acalypterate Muscid 

 (Ortalis), according to Schiner, who 

 uses the following nomenclature : 

 (nervures, small letters ; cells, capi- 

 tal letters) : a, transverse shoulder ; 

 b, auxiliary ; c to h, first to sixth 

 longitudinal ; i, middle transverse ; 

 k, posterior transverse ; I, m, n, o, 



costa ; p, anterior basal transverse ; q, posterior basal transverse ; r, rudiment of a fourth 



nervure ; s, axillary incision : A, B, C, first, second, and third costal cells ; D, marginal ; 



E, sub-marginal ; F, G, H, first, second, and third posterior ; I, discal ; K, L, M, first, 



second, and third basal cells ; N, anal angle ; 0, alula. 



spond with a nervure placed behind it in another wing. The 

 very different nature of the nervuration in the two wings we have 

 figured will readily be appreciated by an inspection of the parts 

 posterior to the little cross-vein. On the hind margin of the 

 wing, near the base, there is often a more or less free lobe (Fig. 

 215, B, 0) called the " alula " : still nearer to the base, or placed 011 

 the side of the body, may be seen one or two other lobes, of which 

 the one nearer the alula is called the " tegula," or (when a 

 lobe behind it is also present) the " upper tegula," (the " anti- 

 tegula " of Osten Sacken) ; the other being the " lower tegula." 

 These two terms are erroneous, the word tegula being definitely 

 applied to another part of the Insect-body. In speaking of this 

 structure in the following pages, we have preferred to call it the 



