24 
variable and unreliable, but the relative positions of the princi- 
pal veins and cross-veins are constant, and useful as distinguish- 
ing characters. i 
On the front margin of the wing, near its apex, is a con- 
spicuous opaque cell, the stigma. The strong vein which runs 
along its inner side, extending the whole length of the wing, 
is the radius. 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 swbcosta, extending as far as 
the nodal sector. On either side of the subcosta is a row of 
cells separated by short cross-veins, the antecubital cells and 
cross-veins. On either side of the radius, between the nodal 
sector and the apex of the wing, are similarly the posteubital 
cells and cross-veins. Behind the base of the radius is a large 
cell, the basilar 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 branch. 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 be 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, and 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 supratriangu- 
lar space. 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 
