No. 376.] THE WINGS OF INSECTS. 235 
discal cell used in descriptions of Lepidoptera, Diptera, Tri- 
choptera, and Corrodentia (Psocide), but in no two of these 
orders is it applied to the same cell. 
Having named the wing-veins, the simplest possible method 
of designating the cells of the wing is to apply to each the 
abbreviation of the name of the vein that forms its cephalic 
(front) margin. It should be borne in mind, however, that by 
modifications of the typical arrangement of the wing-veins, a 
vein that normally forms the cephalic margin of a cell may 
apparently bear a very different relation to it; and this must be 
taken into account if we are to apply the same term to homolo- 
gous cells throughout the insect series. 
The cells of the wing fall naturally into two groups: first, 
those on the basal part of the wing; and second, those nearer 
the distal end of the wing. The former are bounded by the 
principal veins; the latter, by the branches of the forked veins; 
a corresponding distinction is made in designating the cells. © 
Thus the cell lying behind the main stem of radius and on the 
basal part of the wing is designated as cell R; while the cell 
lying behind radius-one is designated as cell Rr. 
It should be remembered that the coalescence of two veins 
results in the obliteration of the cell that was between them. 
Thus when veins 22 and R, coalesce, as in Leptis (Fig. 6), the 
cell lying behind vein R2+;3 is cell R} and not cell R2+3, cell 
R2 having been obliterated. 
When one of these principal cells is divided into two or more 
parts by one or more cross-veins, the parts may be numbered, 
beginning with the proximal one. Thus in Leptis (Fig. 6), cell 
Mz is divided by the medial cross-vein into two parts, which are 
designated as 1st M2 and 2d M2, respectively. 
The application of this system of naming the cells of the 
wing is an easy matter in those orders where the wings have 
few veins; but in those orders where many secondary veins are 
developed it is more difficult of application. In the latter case 
we have to do with areas of the wing rather than with separate 
cells. Thus, for example, it will be shown later that in certain 
Neuroptera the area R2 is divided by several longitudinal veins, 
which are connected by many cross-veins, the area R2 (which 
