veins,* but, if we except the Lepidoptera, it is usually present and in- 

 distinguishable in structure from the other principal veins ; and ex- 

 cept by writers on the Lepidoptera, it has been generally recognized 

 and named as one of the principal veins of the wing. It seems de- 

 sirable, therefore, to include it in numbering the wing-veins. 



In fact, there are much stronger reasons for counting costa a vein 

 than there is for including the anal furrow in the list of veins, as is 

 done by these very writers who exclude costa. The anal furrow arose 

 iu an entirely different way than did the wing-veins,f and except in 

 the Lepidoptera it almost never resembles a vein in structure. But, 

 as the anal furrow becomes a well-developed vein in the Lepidoptera, 

 and is present, though in a different form, in nearly all winged insects, 

 it simplifies the nomenclature to include it in the list of veins. 



There is one other point which the student should clearly under- 

 stand in order to avoid confusion when he comes to use the special 

 works treating of the Lepidoptera. Although costa is present in the 

 wings of many of the more generalized moths, it is wanting, as a rule, 

 in the Lepidoptera. This fact being overlooked by the writers on this 

 order, they have applied the term costa to the vein that is called sub- 

 costa in other orders of insects, and have applied the term subcosta to 

 the vein that bears the name radius in other orders. It is to be hoped 

 that writers on the Lepidoptera will soon conform to the usage of 

 writers on all other orders of insects. The change need necessitate 

 little if any confusion, as the use of the term radius will indicate 

 that the writer using it has adopted the uniform nomenclature for all 

 orders. 



Convex veins and concave veins. — In most insects, 

 except L-epidoptera, the wings are more or less corrugated. 

 This is very well shown in the wings of dragon-flies, one of 

 which should be examined at this point in the course. Note 

 that as a result of this corrugation some of the wing-veins 

 extend along the summits of ridges ; such wing-veins 

 are termed convex veins. Other wing- veins of a corrugated 

 wing extend along the bottoms of furrows ; such veins are 

 termed concave veins. 



Note that a corrugated wing is much stiffer than it would 

 be otherwise. 



Numbering of the cells of the wings. — In numbering 



*See Evolution and Taxonomy, p. 59. 

 t Evolution and Taxonomy, p. 60. 



