THE WINGS. 



23 



Fig. 28. 



called, beginning at the costa, or front edge, the costal, subcostal, 

 median, submedian, and internal, and sometimes the median 

 divides into two, making six 

 veins. The costal vein is un- 

 divided ; the subcostal and me- 

 dian are divided into several 

 branches, while the submedian 

 and internal are usually simple. 



The venation of the fore- 

 wings affords excellent marks 

 in separating genera, but that 

 of the hind wings varies less, 

 and is consequently of less use. 



The wings of many insects 

 are divided by the veins into 

 three well-marked areas ; the 

 costal, median, and internal. 

 The costal area (Fig. 316) forms 

 the front edge of the wing and 

 is the strongest, 

 since the veins are 

 nearer together than 

 elsewhere, and thus 

 afford the greatest 

 resistance to the air 



Fig. 28. Fore and hind wings of a Butterfly, showing the venation. I. fore wing; 

 a, costal vein; 6, subcostal vein; 61, 62, 63, 64, 65, five subcostal veinlets; c, inde- 

 pendent vein (it is sometimes a branch of the subcostal, and sometimes of the me- 

 dian vein); rf, median vein; rfi, d2, rfs, rf4, four median veinlets; e, submedian vein; 

 /, internal vein ; h, interno-median veinlet (rarely found, according to Doubleday, 

 except in Papilio and Morpho) ; 6 and d are situated in the " discal cell ; " fifi, g2, gs, 

 the upper, middle, and lower discal veinlets. In the Bombycidas and many other 

 moths g^ and g'i are thrown off from the subcostal and median veins respectively, 

 meeting in the middle of the cell at g"^. They arc sometimes wholly absent. 



II. The hind wing; the lettering and names of the veins and veinlets the same 

 as in the fore \ring. — Slightly changed from Dotibledrig. 



Fig. 29. Fore wing of a Hymenopterous insect, c, costal vein; sc, subcostal 

 vein ; m, median vein ; sm, submedian vein ; i, internal vein ; c, 1, 2, 3, the first, 

 second, and third costal cells ; the second frequently opaque and then called the 

 pterostigmn. sc, 1, 2, 3, 4, the four subcostal cells; m, 1, 2, 3, 4, the median cells; 

 am, 1, 2, 3, the three submedian cells ; t'l, the internal cell ; this is sometimes divided 

 into two cells, and the number of all but the costal cells is inconstant, the outer 

 row of cells (4, 4, 3) being the first to disappear. 



The costal edge extends from c to c ; the outer c, the apex ; the outer edge extends 

 ft-om the apex (c) to a, and the iniier edge extends from n, the inner angle, to the 

 insertion of the wing at i.— Original. Figs. 30-32 /rom Scudder. 



