THE ir/A'G-S- OF HYMENOPTERA 



375 



In 2\pis (Fig. 396), the position of the medio-cubital cross-vein is nearly 

 the same as in Macroxyela; but the coalescence of the media with the 

 radius has extended much farther, with the result that the section of the 

 media that is between the radius and the medio-cubital cross-vein extends 

 backward from the point where it separates from the radius to its junction 

 with the medio-cubital cross-vein; from this point the media extends out- 

 ward as in the more generalized forms. This results in the course of the 

 main stem of media being Z-shaped. 



In the forms in which the condition just described exists, and this is true 

 of a very large portion of the members of the order, the section of the 

 media that is between the radius and the medio-cubital cross-veins forms 

 with this cross- vein what appears to be a cross-vein, extending from the 

 radius to the cubitus, from which the main stem of the media appears to 

 arise. But it is now obvious that this apparent cross-vein is a serial vein 

 consisting of a section of the media and the medio-cubital cross-vein. 



In Apis, and in many other genera of the more specialized H\TTienop- 

 tera, the shortening of the cubitus as a result of an extending of the coales- 



Fig. 396. — Wings of Apis. vSee Fig. 397, for more detailed lettering. 



cence of veins Cui and ist A has left the cubital end of the medio-cubital 

 cross-AX'in stranded upon vein iM,i. 



Modification of the course of a vein by the coalescence of its tip with an 

 adjacent vein. — Examples of this kind of modification of the courses of 

 veins have been described in the discussion of the venation of the wings of 

 the more generalized Hymenoptera. Attention was called there to the 

 changes that have taken place in the courses of the branches of the radial 

 sector, the branches of media, and the branches of cubitus. Some of the 

 modifications of the courses of veins which are evident in the more general- 

 ized H^TTienoptera are greater in the more specialized Hymenoptera. Note 



