THE WINGS 



61 



transverse portion has been frequently called the " supernumerary cross-vein." 

 The fourth, fifth and sixth veins arise at the base of the wing. A small cross- 

 vein, which joins the basal part of the third vein with the fourth vein, is 

 called the anterior cross-vein. Another cross-vein joins the fourth vein and 

 the upper branch of the fifth vein and is called the posterior cross-vein. The 

 posterior cross-vein is usually a short distance behind the anterior cross-vein, it 

 may, however, be in line with it or even beyond it. There is also a humeral 

 cross-vein, close to the base of the wing between the costa and the auxiliary vein. 

 Between the first and auxiliary veins and behind the origin of the second vein 

 is the subcostal cross-vein. Besides these veins there are chitinizations resem- 

 bling veins and sometimes in continuation of them. These are variously de- 

 veloped in the different forms. The second and third veins are usually thus con- 

 tinued longitudinally backward from the point of angulation. A particularly 

 heavy chitinization follows the fifth vein on the anal side, and in Megarhinvs, 





Fig. 3. — Venation of wing of Culex. 



where the chitinizations are particularly marked, there is also a chitinization in 

 front of the lower branch of this vein. In some forms there is a chitinization, 

 usually poorly defined, which traverses the hindmost area of the wing (the 

 axillary cell) longitudinally and forms a more or less well-marked fold. In 

 MegarUnus it is particularly distinct. In the case of certain African mosqui- 

 toes this fold bears a few scales. It has been incorrectly looked upon by Theobald 

 as a seventh vein and upon this character he founded a subfamily, the Hepta- 

 phlebomyinae. 



The relative length of the fork and the stem, particularly in the second vein, 

 is in some cases of diagnostic value, not only specifically but generically. Thus 

 the genera Megarhinus and Uranotcenia are remarkable for the very short 

 branches of the second vein. The part of the wing enclosed by the two branches 

 of the second vein is the second marginal cell ; it is often incorrectly called the 

 first submarginal cell. The position of the posterior cross-vein in relation to 

 the anterior cross-vein is also of significance in classificaton, although there is 

 naturally some individual variation. 



The wings are clothed with scales along the veins and along their margins. 

 These scales show great diversity in shape and characters in different species and 



