60 



AN INTRODUCTION TO ENTOMOLOGY 



The margivs 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-h)\ the outer margin (Fig. 70, 

 h-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, h)\ 



2dA*Cu, 



Fig. 71. — Wing of Conops; ac, axillary excision; /, posterior lobe. 



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

 a?gle (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 alulas are 

 termed the sgi^amcB by some writers, and the calypteres by others. 



Fig. 72. — Wings of the honeybee; 

 A, hamuli. 



