i6 



ECONOMIC ENTOMOLOGY 



cipal veins as in many Neuropteroids and Orthopteroids; second, by the 

 addition of cross veins; and third, by the reduction of the number of veins 



§£L Sc2 



3dA 2dA 



IstA 



Fig. 21. 



-The hypothetical primitive type of wing venation. 

 Needhatn.) 



{After Comslock and 



through coalescence of adjacent veins, or by the disappearance of veins, 

 as in most moths, flies and hymenopters. The chief longitudinal veins 



are the costa (C), an unbranched vein on 

 or near the front margin; the suhcosta 

 (Sc); the radius (R); the media (M); the 

 cubitus (Cu); and the anal veins (A), 

 typically three but often reduced to one 

 or two. 



A knowledge of the different types of 

 venation is very important in classifica- 

 tion. The Comstock-Needham system of 

 terminology is adopted in this Classbook, 

 and students should consult the recent 

 work of Professor Comstock — The Wings 

 of Insects — for a full discussion of the 

 general characteristics of the wings of the 

 several orders of insects. 



Clothing of the Wings. — While the wings 

 of many insects are naked, many are 

 covered with fine setae, hairs, or scales. 

 The coating of scales is the most distinc- 

 tive feature of the wings of the Lepidop- 

 tera. These scales are modified setae, 

 being evaginations of greatly enlarged 

 hypodermal cells. They are provided 

 with ridges, these serving to increase their rigidity and their protec- 



FiG. 22. — Various forms of 

 scales. A, E, Thysanuran 

 {Machilis); B, beetle {Anthre- 

 nus); C, butterfly (Pieris); D, 

 moth (Limacodes) . 



