576 THE PANORPOID COMPLEX, iii., 



50 shows the base of the pupal wing in a species of the Bomby- 

 liid genus Comptosia. Only the median and anal tracheas are 

 missing. The cubital trachea is complete, and shows the cubital 

 fork situated at the extreme base of the wing, with Cu 2 ap- 

 parently fused with 1A almost for its entire length. Thus not 

 only is the above interpretation of the limits of Cu x correct, 

 but we see also that the vein called 2 A by Comstock (15, fig. 

 368) is in reality Cu 2 -f-l^- m this genus. 



Section v. The Anal Veins. 



(Plate xxxiii., figs. 19-20, Plate xxxiv., fig. 22, and Text- 

 figs. 51-54 . ) 



Throughout the Panorpoid Complex, the anal veins are norm- 

 ally three in number, viz. lA, 2A and 3A. These three veins 

 are all normally convex, the membrane between them being 

 usually more or less concave, and sometimes carrying definite 

 grooves or furrows, which do not, however, carry true veins in 

 them . 



The anal tracheae in the freshly-turned pupa stand in a group 

 by themselves, and are easily recognised by their comparatively 

 small calibre, and by the fact that they usually lie well apart 

 from the cubitus. Corresponding with the sizes of the areas 

 which they serve, the first analis is normally the largest of the 

 three, the second of intermediate size, and the third the smallest. 

 Exceptions to this rule occur when the first or second analis 

 becomes shortened in the formation of a basal Y-vein; or when, 

 owing to expansion of the anal area of the hindwing, both 2A 

 and 3A may become very much lengthened, so as to be of ap- 

 proximately the same length as 1A. 



Reductions in the number of anal veins from the normal three 

 are . only found in specialised types within the vai'ious Orders . 

 In many cases in which an examination of the imaginal vena- 

 tion fails to disclose a definite 3A, the corresponding trachea 

 may still be found in the pupal wing, thus proving that the re- 

 duction is a specialisation from a more archaic condition in 

 which 3 A occurred. In some of the higher Planipennia, both 

 the anal tracheae and veins are much reduced; and it is neces- 

 sary to make a very carefvd examination of the freshly-turned 

 pupal wings in situ, in order to determine the limits of the three 

 anal veins. 



