INTRODUCTION. 31 



latent. But this study is difficult, because it can give positive 

 results only when pursued upon fresh specimens. 



The female ovipositor consists of two pairs of horny valves, 

 usually attenuated and pointed at the tip. Their length and 

 shape afford occasionally useful characters. 



The most important and at the same time the most tangible 

 of all the characters used for the classification of the Tipididse 

 are afforded by the vrings and their venation.' The shape of the 

 wings, their breadth in comparison to their length, the shape of 

 their anal angle, etc., deserve to be noted. Their membrane, when 

 examined under a strong magnifying power, will always appear 

 pubescent (the wing of Antoclia appeared pubescent under a 

 power of 150) ; nevertheless in describing a wing, we call it 

 glabrous, when the pubescence is not discernible to the naked 

 eye nor to a lens of low power, and however indefinite the limit 

 between a pubescent and a glabrous wing, in our sense, may seem, 

 the practical application of these terms is hardly ever doubtful. 

 In the same way, the wing-veins are always pubescent ; but we 

 call them so only when the pubescence is long enough to be 

 striking under an ordinary entomological lens ; otherwise we 

 consider them as glabrous. 



The terminology of the venation used by me is, in the main, that 

 of Mr. Loew, as explained in the first volume of these Ponographs 

 (pp. xv-xxiv). In some respects, however, it had to be modified, in 

 order to be rendered applicable to the Tipididse. The principal 

 difficulty lies in the name to be given to what I will call below the 

 great cross-vein and to the portion of the fifth longitudinal vein, 

 beyond this cross-vein. If the diagram below is compared to 

 the three diagrams given on page xxiv of the first volume of 

 the Monographs, it will be easily perceived that the portion of the 

 fifth vein, lying beyond the cross-vein in the Tipididse, corres-. 

 ponds to the posterior basal transverse vein of the wing of Ortalis 

 {Monogr. I, p. xxiv, fig. 1, q). The great cross-vein of the Tipu- 

 lidse, if traced back to the wing of Ortalis, would be found to 

 form a part of the fifth longitudinal vein (1. c. fig. 1, ggg). The 

 course of the fifth longitudinal vein of Ortalis, if traced out upon 

 the wing of a Tipulid, would be found to run along the great 



' The term venation, used by English authors, is certainly preferable to 

 neuration, which has been used in the first volumes of these Monographs. 



