THE WINGS OF PLECOPTERA 



247 



the first stages in the development of intercalary veins, in the anal area of 

 the hind wings. 



In concluding this brief summary of the special features of the wing of 

 the Plecoptera it seems desirable to define some terms freqtiently used by 

 writers on this order. 



The transverse cord. — In many genera of this order there is a nearly 

 continuous series of cross-veins extending across eacli wing just beyond the 



Sci SCi 



. Fig. 246. — Wings of Eusthenia specatbilis. 



middle of its length ; this series of cross- veins is termed the anastomosis by 

 writers on the Plecoptera. As it is not formed by an anastomosing of veins 

 the use of the term, transverse cord, defined in chapter III, is preferable. 



The pterostigma. — In most members of this order a specialized ptero- 

 stigma has not been developed ; but the term pterostigma is commonly 

 applied to the cell beyond the end of the subcosta and between the costa 

 and vein Ri, even though it is of the same color and texture as the remainder 

 of the wing. 



The basal anal cell. — A very constant feature of the anal area of the 

 wings of Plecoptera is the presence of a cross-vein near the base of the wing, 

 which extends from the first anal vein to the second. The cell that is 

 closed by this cross-vein is termed the basal anal cell (Fig. 245, ha). 



