HEXAPODA 



33 



order of insects have used different sets of terms. This condition of 

 affairs was incident to the beginning of the science, the period before 

 the correspondence of the veins in the different orders had been worked 

 out. But now the time has come when it seems practicable to apply a 

 uniform nomenclature to the wing veins of all orders; and the following 

 set of terms is proposed for that purpose. 



The principal veins of the wing, those that arise at or near the base 

 of the wing, are termed, beginning with the one lying on the costal mar- 

 gin, the costa, the subcosta, the radius, the media, the cubitus, and the 

 anal veins. The radius, media, and cubitus are usually branched, and 

 there may be several anal veins. 



In addition to the principal or longitudinal veins, there may be a 

 greater or less number of cross-veins — veins extending transversely from 

 one longitudinal vein to another. 



The principal veins may be designated by numbers as well as by 

 names ; the following table indicates the correspondence of the names and 

 numbers : 



Costa = vein I. 

 Subcosta = vein II. 

 Radius = vein III. 

 Media = vein V. 



Cubitus = vein VII. 

 ist anal vein = vein VIII. 

 2d anal vein = vein IX. 

 3d anal vein = vein XI. 



It was formerly believed that in certain insects three other longitu- 

 dinal veins were present; these were numbered IV, VI, and X respec- 

 tively; hence these numbers are omitted in the above table. 



At the time the first edition of this book was written, it was thought 

 best to designate the veins by numbers; but owing to a lack of uniform- 

 ity in the numbering of the veins by different writers, it is now clear that 

 the names are to be preferred. In the lettering of figures, abbreviations 

 of the names can be used as is done in Figure 66. 



idA 



Fig. 66. — Wing of a fly, Antsopus. 



The divisions of a branched vein are numbered, beginning with the 

 one nearest the costal margin of the wing; and these numbers are in- 

 dicated by sub-figures. For example, the five branches of the typical 

 radius are designated thus, Ri, R 2 , R3, R4, Rs- 



When two or more branches of a branched vein coalesce, the com- 

 pound vein is designated by an expression indicating this coalescence, as 

 R2+3. In this way it is possible to indicate some of the changes that 

 have taken place in the development of the species; and to make use of 



