24 



variable and unreliable, but the relative positions of the princi- 

 pal veins and cross-veins are constant, and useful as distinguish- 

 ing characters. 



On the front margin of the wing, near its apex, is a con- 

 spicuous opaque cell, the st'ujiHd. The strong vein which runs 

 along its inner side, extending the whole length of the wing, 

 is the radin.s. This is intersected about midway of the wing by 

 a vein (the nodal sector) which starts at the margin in a notch 

 of the costa called the nodus. Between the costal margin and 

 the basal half of the radius is the SHhcosfa, extending as far as 

 the nodal sector. On either side of the subcosta is a row of 

 cells separated by short cross-veins, the antecuhital cells and 

 cross-veins. On either side of the radius, between the nodal 

 sector and the apex of the wing, are similarly the posfcnhital 

 cells and cross-veins. Behind the base of the radius is a large 

 cell, the Ixisilof space, bounded posteriorly by the cubitus and 

 outwardly by a conspicuous cross-vein, the arculus. Near the 

 middle of the arculus arise, jointly or separately, two longitudi- 

 nal veins, the upper and lower sectors of the arculus. The up- 

 per sector is the main stem of the median vein, the lower is its 

 posterior lu-anch. The bases of the media and the radius form 

 one vein as far as the arculus. The anterior branch of the up- 

 per sector is the principal sector. It also is intersected by the 

 nodal sector. The next apparent branch of the upper sector, 

 running parallel to and just behind the nodal sector, is really 

 a branch of the radius, and should he called the radial sector. 

 Two adventitious longitudinal veins, formed by the stringing 

 together of cross-veins, are the apical sector, just behind the 

 tip of the radius, aiid the supplementary sector, behind the radial 

 sector. A little beyond the arculus, the cubitus leads to the in- 

 ner angle of a conspicuous triangular cell, or group of cells, 

 known as the triangle. The elongate cell (sometimes subdivided 

 by minor cross-veins) above the triangle is the supndrianjju- 

 lar sp<(ce. The next and last principal longitudinal vein, behind 

 the cubitus, is the anal vein. Of the numerous apparent branches 

 that it sends back toward the hind margin of the wing, three 



