THE GENERAL FEATURES OF WINGS 



79 



as they traverse the costal area of the wing, that area that corresponds to 

 cell C in the few-veined wings, and it is well that it be retained; although, 

 morphologically, they are marginal accessory veins, that arise as branches 

 of the subcosta; this is the case at least in the Neuroptera, where they 

 reach their highest development. 



Other cross-veins in many-veined wings. — In other cases where it is 

 desired to refer to the number or nature of the cross-veins in a certain area 

 of the wing it can be done by reference to that area of the wing. Thus, for 

 example, the Myrmelionidas are characterized by the absence of cross-veins 

 in cell Sc while in the closely allied Nymphidas the subcostal area of the wing 

 is traversed by many cross-veins. 



The terminology of the cells of the wing. — In descriptions of wings it is 

 often desirable to refer to one or more cells. It is necessary, therefore, to 

 have a terminology of the cells of the wing, as well as of the wing-veins. 



Having named the wing-veins, the simplest possible method of desig- 

 nating the cells of the wing is to apply to each the abbreviation of the name 

 of the vein that normally 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 teiTn to homologous cells through- 

 out the insect series. Figure 6 7 represents a wing of Rhyphus with the veins 

 and cells labeled. 



The cells of the wing fall naturalh' into two groups: first, those on the 

 basal part of the wing; and second, those nearer the distal end of the wing. 



Rx Aj + 5 



zdA 



Fig. 67. — Wing of Rhyphus. 



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 Ijang behind radius- 

 one is designated as cell Ri. 



