THE GENERAL FEATURES OF WINGS 



81 



Additional definitions. — In concluding this general account of the wings 

 it is necessary to define a few terms that are not included in the preceding 

 pages. 



The ciihiio-anal excision. — In many insects there is a notch in the margin 

 of the wing at the point where the preanal and anal areas join ; this mav be 

 termed the cuhito-anal excision. 



Convex and concave veins. — In many insects the wings are corrugated 

 like a partly open fan. In this case, the wing-veins that follow the crests 

 of ridges are termed convex veins; 

 and those that follow the furrows, 

 concave veins. The corrugating of the 

 wings is very marked in the Odonata, 

 the Ephemerida, and in the anal area 

 of the hind wings of the Orthoptera. 



The ambient vein. — Sometimes the 

 entire margin of the wing is stiffened 

 by a veinlike structure ; this has been 

 designated the ambient vein by writers 

 on the Diptera. 



The humeral veins. — In certain 

 Lepidoptera and especially in the 

 Lasiocampidas and the butterflies the 

 humeral area of the hind wings is 

 greatly expanded and in many cases 

 is strengthened by the development of 

 secondary veins. These are termed 

 the humeral veins (Fig. 69, h v). 



The pterostigma or stigma. — A 

 thickened opaque spot which exists 

 near the costal margin of the outer 

 part of the wing in many insects is known as the pterostigmaov stigma. The 

 pterostigma is present in the fore wings of most Hymenoptera, in both wings 

 of the Odonata, and in the fore wings of the Psocidae and Mantispida^. 



The ImllcB. — The bull<s are weakened places in veins of the wing where 

 they are crossed by furrows. The bullae are usually paler in color than the 

 other portions of the wing. They are common in wings of the Hymenoptera 

 (Fig. 70) and of some other insects. 



The bullae are teniied thyridia by some writers. 



The appendiculate cell. — In the front wings of some Hymenoptera the 

 tip of vein Ri curves away from the margin of the wing and coalesces with 

 the tip of vein R3 at some distance from it. The space thus formed 

 between the united tips of veins Ri and R3 and the costal margin of the 

 wing is teiTned the appendiculate cell (Fig. 7 1 , ap) . 



Fig. 69. 



S(/^ uiA 



Wings of Clisiocampa americana; 

 h V, humeral veins. 



