GENERAL EXTERNAL STRUCTURE OF INSECTS. 23 



occurs between the radius and the media near the center of the wing 

 and is called the radio-medial cross-vein. Another one, the medio- 

 rahifal, is similarly located between the media and the cubitus, 

 while a fourth, called the median, occurs between the second and 

 third branches of the media. The areas of the wing surface inclosed 

 by the veins, the cross-veins, and the margins of the wing are known 

 as the cells. 



A great many ditferent names are applied by different entomolo- 

 gists to the veins of the wings, both of the same and of different 

 insects. The nomenclature here given is the one first consistently 

 applied by Comstock and Needham and now used by a large number 

 of entomologists working in different orders of insects. 



The wing is articulated at its base (except in mayflies and dragon- 

 flies) to the anterior and posterior wing pro>*esses of the notum 

 (fig. 6, AA^P and I'XF) and to the wing process of the pleurum (fig. 

 4, WP) by several small articular sclerites called axillaries. Two 

 of these, the first {lA,v) and the fourth {4Ax), form a hinge with the 

 anterior and the posterior notal wing processes, respectively, while 

 the second {^^Lr) articulates below^ with the wing process of the 

 pleurum, constituting thus a sort of pivotal element. The f/iird axil- 

 lary {3Ax) intermediates between the bases of the anal veins and the 

 fourth axillary — except when the latter is absent (as it is in nearly 

 all insects except Orthoptera and Hymenoptera), in which case it 

 articulates directly with the posterior notal process. The thin mem- 

 brane of the wing base may be called the axiUary memhrane {AxM). 

 On its anterior edge is a hairy pad, the tegnla (Tg), which is some- 

 times a large scale overlapping the humeral angle of the wing. The 

 posterior margin of the axillary membrane is thickened and may be 

 called the axillary cord {AxC) or l)as<d Ih/ament of the wing. 



The base of the costa is not directly associated with any of the 

 axillaries, but is specially connected by tough membrane below with 

 the episternal paraptera. The subcosta abuts against the end of 

 the curved neck of the first axillary. The radius is either attached 

 to or touches u})on the anterior end of the second. The media and 

 cubitus are usually associated with each other at their bases and also 

 more or less closely with one or two median plates {ni) in the wing 

 base. These plates, however, are not of constant shape and occur- 

 rence as are the articulating axillaries. The anals are generally 

 attached to the outer end of the third axillary, which acts as a lever 

 in the folding of the wing, 



A few insects have a generalized wing almost identical with the 

 diagram (fig. G), but most of them depart from it in varying degrees. 

 Few go so far, however, as the honey bee, whose venation is very 

 different, but yet the fundamental basal structure is the same even 



