THE GENERAL FEATURES OF WINGS 



In the formation of an intercalary vein there is a straightening out of 

 veins that form part of the boundaries of polygonal cells into a longitudinal 

 line. Different stages of this development can be seen in the wings of 

 dragon-flies; see figures in Chapter XL 



Intercalary veins did not exist in the wings of the Palaodictyoptera. 

 Their development is correlated with the development of corrugated wings. 

 In the preanal area of recent insects, intercalary veins are found only in the 

 Ephemerida and in the Odonata. In the anal area they are found in these 

 two orders and- in the Orthoptera, where the convex veins are accessory 

 and the concave veins intercalar>'. In paleozoic insects they were present 

 in the Protodonata and Protoephemeroidea, and judging from some 

 published figures, they were present in some of the Protoblattoidea. 



When it is desirable to refer to a particular intercalary vein it may be 

 done by combining the initial I, indicating intercalary, with the designation 

 of the area of the wing in which the intercalary vein occurs. For example, 

 in the wings of most May-flies in which the venation is not reduced, there 



<^r R' /? . 



Fig. 63. — The wings of Prionoxyshis. 



is an intercalary vein between veins Cui and Cu2, i. e. in the area Cui. 

 This intercalary vein is designated as ICui (Fig. 6i). 



When more than one intercalary vein exists in a single area of the wing, 

 as in area Mi of Epeorus (Fig. 6i), and it is desired to designate them 

 individually, it can be done by the use of appended letters. Thus, for 

 example, the three intercalary veins in area Mi of Epeorus may be desig- 



