60 



AN INTRODUCTION TO ENTOMOLOGY 



The margins of wings. Most insect wings- are more or less 

 triangular in outline; they, therefore, present three margins: the 

 costal margin or costa (Fig. 70, a-6); the outer margin (Fig. 70, 

 b-c)\ and the inner margin (Fig. 70, c-d). 



The angles of wings. The angle at the base of the costal margin 

 of a wing is the humeral angle (Fig. 70, a); that between the costal 

 margin and the outer margin is the apex of the wing (Fig. 70, 6); 



Fig. 71. Wing of Conopx; as, axillary excision; /, posterior lobe. 



and that between the outer margin and the inner margin is the anal 

 angle (Fig. 70, c). 



The axillary cord. The posterior margin of the membrane at the 

 base of the wing is usually thickened and corrugated; this cord-like 

 structure is termed the axillary cord. The axillary cord normally 

 arises, on each side, from the posterior lateral angle of the notum, and 

 thus serves as a mark for determining the posterior limits of the 



notum. 



The axillary membrane. The 

 membrane of the wing base is 

 termed the axillary membrane; 

 it extends from the tegula at the 

 base of the costal margin to the 

 axillary cord ; in it are found the 

 axillary sclerites. 



The alula. In certain families 

 of the Diptera and of the Coleop- 

 tera the axillary membrane is 

 expanded so as to form a lobe or 

 lobes which fold beneath the base of the wing when the wings are 

 closed; this part of the wing is the alula or alulet. The alulae are 

 termed the squama by some writers, and the calypteres by others. 



Fig. 72. Wings of the honeybee; 

 h, hamuli. 



