THE WINGS OF INSECTS 413 



Note the total atrophy of certain veins and the partial atrophy of others. 

 Where veins have become very weak but are still visible this fact can be 

 indicated by the use of dotted lines. 



Determine the homologies of the veins and of the cells of the wing by an 

 application of the knowledge gained by the study of the typical hymenop- 

 terous wing. 



A fore wing of a siricid. — A printed figure of a fore wing of a horn-tail 

 of the genus Sirex will be furnished for study. 



Note that near the apex of the wing there is a short, compound vein 

 formed by the coalescence of the tips of two veins, one of which extends 

 back from the costal margin of the wing. The space between this com- 

 pound vein and the costal margin of the wing is termed the appendicidate 

 cell. It may be lettered ap in your figure. 



Letter each of the veins indicated by arrows in your figure and the tips 

 of the anal veins. 



Letter the cells of the wing. 



An example of a change in the course of a vein by the coalescence of its 

 base with an adjacent vein. — Note the course of media in the fore wing of 

 Sirex. The coalescence of the base of this vein with radius has been carried 

 so far that now media follows a Z-shaped course. 



Examples of the specialization of wings by the atrophy of veins. — Even 

 in the most generalized liATnenopterous wings known one or two of the 

 wing-veins have been lost. We will now study wings in which the atrophy 

 of veins has proceeded farther than in those already studied. 



A jore wing of Janus ahhreviatus. — Letter the veins in your figure of the 

 fore wing of this species. 



A jore wing of Odontatdacus editus. — In this wing the anal furrow and the 

 axillary furrows are distinct, the position of each of these furrows is indi- 

 cated by a dotted line. 



Compare j^our figure of this wing with that of Janus ahhreviatus and 

 indicate by penciled, dotted lines the probable former position of each of 

 the veins that are wanting. 



What is the probable composition of the single vein that is preser\^ed in 

 the anal area ? 



Letter this anal vein with the term indicating its most obvious element. 



The switching of the base of the radial sector. — Compare the figures of 

 the wings of Jauns and Odontaidaciis with that of the typical h}Tnenop- 

 terous wing and describe the change that has taken place in the support of 

 the base of the radial sector of Odontaulaciis . 



This change is known as the switching of the base of the radial sector; 

 it has taken place in all of the Clistogastra, the more specialized of the two 

 suborders of the H}Tnenoptera. 



The formation of serial veins. — In the wings of many Hymenoptera 

 there exist what appear to be simple veins that are really compound veins 



