NO. 1438. WIXGS (} F THE TENTHREDINO IDEA —Ma cGILLIVRA Y. 577 



III.— THE ORIGIN OF THE HYMENOPTEROUS TYPE. 



In order that the reader can follow more intelligentl_y the later 

 discussions, the following- general description of the origin of the 

 wing of the Hynienoptera is introduced at this point. Use has been 

 made of the following series of hypothetical figures to show how the 

 existing arrangement of wing-veins was in all probability developed 

 from a wing similar to that of the Comstock and Needham hypotheti- 

 cal type. This series begins, therefore, with this hypothetical type 

 and concludes with a typical generalized hymenopterous wing, which 

 is the wing of Mac/t'oxyela ferrughiea to which has been added the 

 free part of Cu.,. To the hypothetical type I have added the cross- 

 veins which are present in hymenopterous wings. These cross-veins 

 are as follows: 



The radial cross-vein /% situated between Kj and K.,; this is wanting 

 in the Hymenoptera only in certain genera of the Tenthredinoidea. 





Fi<;. 1. — Hypothetical wim:; tyhe. 



The radio-medial cross-vein r-m., situated between radius and 

 media. 



The medial cross-vein w, situated between M^ and M.,. 



The medio-cubital cross- vein m-cu^ situated between media and 

 cubitus. 



Beginning with the anal veins, the veins will l)e taken up in order, 

 proceeding from the hind to the front margin of the wing. 



The anal veins are three in number, simple, till the anal portion of 

 the wing, and are known as 1st A, 2d A, and 3d A. The first modifi- 

 cation of the anal veins to be noted is the coalescence of the tips of 2d 

 A and 3d A, resulting in the closing of the second anal cell at the 

 margin of the wing (fig. 2). This coalescence proceeds farther and 

 farther and the 1st A migrates toward the combined tip of 2d A and 

 3d A and combines with it, shoving the second anal cell toward the 

 base of the wing and closing the first anal cell at the margin (figs. 3-1). 

 Coincident with this apical coalescence, the base of 2d A migrates 



