THE WINGS OF INSECTS 



393 



It should be remembered that the coalescence of two veins results in 

 the obliteration of the cell that was between them. Thus when veins R2 

 and Rz coalesce, as in Rhyphus (Fig. 410), the cell lying behind R2+3 is cell 

 i?3, and not cell Ri+.u cell Ri having been obliterated. 



When one of these principal cells is divided intcj two or more parts by 

 one or more cross-veins, the 

 parts may be numbered, 

 beginning with the proximal 

 one. Thus in Rhyphus (Fig. 

 410) cell Ml is divided by the 

 medial cross-vein into two 

 parts, which are designated as 

 cell 15/ M2 and cell 2d M-i, 

 respectively. 



There are many cases 

 where two or more adjacent 

 cells have been united by the 

 atrophy of the vein or veins 

 separating them. A com- 

 pound cell thus formed is 

 designated by a combination 

 of the terms applied to the 

 elements of the compound 

 cell. When, for example, 

 the stem of media is atro- 

 phied, the cell resulting from 

 the combination of cells R 

 and M is designated as cell 

 R -F M. 



The application of this 

 system of naming cells of 

 the wing is an easy matter 



Fig. 413. — Wings of Bombyx mori. 



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 seen later that in certain 

 Neuroptera the area R2 is divided by several longitudinal veins, which are 

 connected by many cross-veins, the area Ro (which is strictly homologous 

 with cell R2) being composed of a large number of secondary cells. 



The corrugations of the wings. —The wings of comparatively few insects 

 present a flat surface; in most cases we find that the membrane is thrown 

 into a series of folds of corrugations. This corrugating of the wing in some 

 cases adds greatly to its strength. This is well shown by the wings of 



