12 



OUTLINES OF ENTOMOLOGY. 



Tig 5. 



A. 



In their general structure the wings of insects show a number of 

 very distinct plans or types, which have been made the basis for the 

 system of classification commonly adopted. 



The wings are attached to the mesothorax and metathorax, and 

 where present are always four in number, except in the order of the 

 two-winged flies (Diptera), where only the upper pair are fully devel- 

 oped, the lower pair being represented by little hammer-like organs, 



called Halter es or Poisers. 



Wings are composed of membrane, more 



or less transparent, stretched over a frame- 

 work of horny tubes, termed veins or 

 nerves. The number and arrangement of 

 these tubes constitute the Venation orNeu- 

 ration of the wings, to which frequent refer- 

 ence is made in descriptions of insects^ 

 There are usually from three to five princi- 

 pal veins in each wing. These branch and 

 intersect very differently in the types of 

 different families. The spaces between the 

 veins are called cells, which are also named 

 and numbered in regular order.* 



The first or upper wings are variously 

 designated as the Anteriors, the Superiors 

 A, i and ii, upper and under wings r the Primaries, while to the lower or un- 

 oi iSJ'SKtaiSSr.ShS?" * ^ pair are applied the opposite terms of 

 Posteriors or Secondaries. Many of the best writers use the simple 

 terms of fore and hind wings. 



These organs exhibit an almost endless variety of outline, texture 

 and ornamentation. The wings of butterflies and moths, for example, 

 are broad and of rather frail texture, and are covered with minute 

 scales and hairs of rich and varied colors. The upper wings of beetles 



* The outline and veination of the wings of insects are made great use of in classi- 

 fication, and for the convenience of any that may be interested, I append the term& 

 applied to margins, veins and cells as follows : On the wing of an insect the upper 

 edge, from where it is joined to the body to the most distant point, is the costa or 

 costal edge. The extreme point is the apex. (In the figure A, just above Z> 4 .) The 

 outer edge extends from the apex to the inner angle at d 4 , and the inner edge from 

 this point to the insertion of the wing. The veins are the costal vein, just below 

 a; 6, sub-costal vein ; d, median vein; J 1 , 6 2 , b s . 6 4 and b 5 , sub-costal veinlets ; d 1 , 

 d 2 , d 3 and d 4 , median veinlets ; e, internal vein ; /, discal cell . The other cells bear 

 the names of the veins which enclose them and are numbered from the costal vein. 

 In, B a is the costal vein ; 1, 2, 3, costal cells ; 4, 5, 6, sub-costal cells ; 7, 8, 9, median 

 cells ; 10, 11, 12, sub-median cells ; 13, internal cell. The veins and cells in the under 

 wings correspond to the principal ones in the upper. 



