580 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



pletely closing the base of the cell R. This coalescence continues 

 until the stem of media and the stem of radius are combined for 

 almost their entire length, while the cell R is crowded toward the 

 middle of the wing and is found as a small trapezoidal-shaped area 

 near the base of the stigma (figs. 7-8). 



The radius, R, lies just in front of media (tig. 1). Near the middle 

 of the wing it breaks up into five branches. In its primitive condi- 

 tion radius divides by a series of characteristic dichotomies, separating 

 first into two unequal parts, Rj, and a large part which, together with 

 all its branches, is known as the radial sector. The radial sector 

 divides into two equal branches, each of which in turn divide into two 

 more branches. This characteristic dichotomy is entirely lost in the 

 Hymenoptera. The suppression of the dichotomy of the radius has 

 been brought about by the coalescence of the stems R^+g and R^+j. 

 This coalescence has proceeded so far that the branches of the sector 

 now arise from a common stem (tigs. 2-3). With the coalescence of 



%*R..> 



1st A+2d A+Sd A-^Cu^+2^31^ 



Fig. 5. — Modified hypothetical type. 



the stems of Rg+g and R^+g, Rj and R^ begin to migrate toward the 

 apex of the wing, to stifl'en the area vacated by R^ and R., which have 

 migrated toward the tip of Mj (tigs. 2-4). R^ and R^ each in turn 

 coalesces with M^ and closes the cells Rg and R^ at the margin of the 

 wing. The coalescence proceeds farther and farther until the free 

 parts of Rr, and R^ appear like cross-veins extending between Rj and 

 Ml, and the cells Rg and R^ as quadrangular areas within the disk of 

 the wing (tigs. 5-7). The primitive condition maintained b}^ M^ near 

 the middle of the wing is undoubtedly due to the early coalescence of 

 Rr, and R^ with it and holding it in place. 



The subcosta, Sc, lies just in front of the radius and parallel with it. 

 It breaks up into two branches, Scj and Scg, near the margin of the wing 

 (tig. 1). The anterior branch is preserved in practicall}^ its primitive 

 condition throughout the series. The posterior branch bends down 

 and touches Rj (tig. 2), with which it anastomoses more and more 

 {^gf^. 4-6), until there is only a small portion of the distal end free 

 i^tig. 7). This anastomosing of Sc.^ and Rj divides the cell Sc into 



