48 I February, 



They .iro also more uniform throunjhout the whole (xroup, and much 

 less liable to vary abiiormally in individual specimens. We commence 

 with them, partly on this account, and partly because they divide 

 the wing into areas named from them, and from these areas again are 

 named most of the (transverse) "nerves" and the "cells" or divi- 

 sions of the areas bounded by them. 



Starting from near each other, and near the base of the wing, five main " veins" 

 run, all more or less in the direction of its apes, bat radiating apart, like the 

 fingers of an extended hand. 



The first pair start at a and b ; these are the casta and the subcosta. The costa 

 follows the actual margin of the wing, and the subcosta runs nearly parallel to it 

 for about half the length of the wing, when it bends upwards and unites with the 

 costa at_/, just before the stigma (the shaded area in Fig. 3). 



From (/ and e start another pair, the brachius and tlie humerus. These run 

 both somewhat parallel to the lower margin of the wing, but neither of them coin- 

 ciding with it ; again, for about half the total length of the toing. Then the humerus 

 turns upward and joins the brachius at g (just as, at /, the subcosta joins the costa). 

 The brachius is continued a little further, to x, and there disappears. 



The fifth of these " veins," starting at c, is called the medius. It runs at first 

 straight along the middle of the wing (equidistant therefore between the two pairs 

 described above) for half its length. Then it bends downwards as though to join 

 the brachius, but at t* turns suddenly off, resuming its horizontal course, then (at 

 ii) is again deflected, and reaches the margin at v. 



Besides the above ^ye main veins, we have two which may be called subsidiary 

 — they are confined to the superior (apical) quarter of the wing, and have the a,^- 

 pea.ra,nce of branching out of the subcosta. One leaves it just before its junction 

 with the costa (at a point about //-) and, bending first down and then a little up, 

 finally joins the costa (on the margin of the wing) at its apex k. This is the 

 radius. The other — called the cubitus — leaving the subcosta earlier (i. e., nearer 

 its base) at I bisects, roughly, the area between the radius and the apical portion 

 of the medius, and so proceeds not always in so straight a line as the Figure shows 

 to the point 1/ on the margin. 



Thus we liave in all five main and two subsidiary longitudinal nervures or 

 " veins," and these divide the wing into longitudinal areas or " fields" as follows. 



Between the costa and the subcosta is contained the intercostal field. Between 

 the brachius and the humerus is the humeral field, familiar to all students of Saw- 

 flies under the name of the " lanceolate cell." Then between the subcosta and the 

 medius lies the medial field, and between the medius and tlie brachius the brachial 

 field. (A certain similarity in form and size will probably have been noticed by 

 the reader between the intercostal and humeral fields and the medial and brachial 

 fields respectively. This will help him perhaps in forming a mental picture of the 

 neuration as a whole). 



Next we have the radial area lying above the radius, and the cubital area below 

 the radius and above the cubitus. Between the cubitus and the apical half of the 



i a; is not part of the medius, but is one of the transverst nervures. 



