THE GENERAL FEATURES OF WINGS 



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from the posterior lateral an^^le of the notum, and thus serves as a mark for 

 determining^ the ijosterior limits of the notum. 



The axillary membrane.— The membrane of the wing base is termed by 

 Snodgrass the axillary membrane; it extends from the tegula at the base of 

 the costal margin of the wing to the axillary cord at the base of the anal 

 area of the wing ; in it are found the axillary sclerites ; it is most prominent 

 at the base of the anal area of the wing, where it is margined by the axillary 

 cord. 



anr r pnr 



The alula. — In certain families of the Dip- 

 tera and of the Coleoptera the axillary mem- 

 brane 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 squamce by some writers, and the 

 calypteres by others. 



The articulation of the wings. — The wings 

 are articulated to the lateral margins of the 

 notum of the two wing bearing segments. In 

 the membrane at the base of each wing, the 

 axillary membrane, there are several axillary 

 sclerites, which are relatively constant in posi- 

 tion but which vary in form in different 

 insects. 



These axillary sclerites have been much 

 studied for nearly one hundred years. They 

 were described in the early part of the last ^rnc 



centurv bv Jurine (1S20), Chabrier (1820), Fig. 37. — Lateral view of a wing- 



and Straus-Durckheim (1828); the more * bearing segment" (From 



^ ' ' Snodgrass). 



important of the later papers on this subject 



are those of Amans (1885), Lowne (1892), Voss (1905), Berlese (1909), 



and Snodgrass (1909, 1910 a, 1910 b.). 



The accounts by Snodgrass are the most complete and logical, and as his 

 terminology of the parts of the thorax to which the wings are attached and 

 of the axillary sclerites is the simplest I have adopted it here. The follow- 

 ing statement is compiled from these accounts. 



The thoracic supports of the wings. — Figure 37 is a diagram, given by 

 Snodgrass, of a lateral view of a generalized, wing bearing segment, left 

 side. The chief supports of the wing are two processes of the notum and one 

 of the pleurum; these are the anterior notal ifing process (ANP). the 

 posterior notal wing process (PNP), and the wing process of the pleurum 

 (WP). Behind the posterior notal wing process is the attachment of the 

 axillary cord (AxC). 



