590 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxix. 



(fig. 60), it is attached as far distant from media as its own length, 

 standing ahnost perpendicular between radius and cubitus. 



In the wings just described the modifications of the origin of media 

 and the changes in the position of the medio-cubital cross-vein marks 

 out a distinct line of development, the changes proceeding from a 

 generalized to a very specialized condition. 



The families Megalodontid* (fig. !>2) and Siricidje (figs. 86-91) illus- 

 trate a very diflerent line of specialization. In those groups, when 

 the cross-vein reaches a position similar to that found in Xiphydria 

 (fig. 8.5), it becomes fixed in its location and all further modifications 

 are due to the migration of the base of media. With the genus Xei'is 

 (fig. 89), there is a perpendicular transverse vein forming the apex of 

 the cell M. The anterior half of this vein represents the transverse 

 part of M and the posterior half the medio-cubital cross-vein. The 

 peculiar condition found here has been brought about by the coales- 

 cence of the base of media with radius to a point opposite the anterior 

 end of the medio-cubital cross- vein. This coalescence has been carried 

 farther and farther until in the genera Tremex (fig. 91) and Megalo- 

 dontes (fig. 92) the medial vein separates from radius distinctly beyond 

 the apex of the anterior end of the medio-cubital cross-vein, while the 

 vein forming the apex of the cell M is a fairly straight but very 

 oblique vein with M apparently arising from its middle, as has been 

 described. 



All the branches of media are fairly constant in position and depart 

 but little from the condition found in the typical hymenopterous 

 wing. Only the more marked of these secondary ijiodifications will 

 be discussed here. 



The transverse part of Mg in many of the highl}^ specialized genera 

 of the Tenthredinidffi, as Lohoceras (fig. 82), Acordulecera (fig. 88), 

 Perrei/la (fig. 80), and Dlelocerus (fig. 79), has migrated toward the 

 base of the wing so that the length of the medial cross-vein is greatly 

 reduced. In Ory^sm (fig. 97) the transverse part of Mg is entirely 

 wanting, and if it were not for the presence of the first anal cell and 

 the interrelation of the transverse pai't of M and the medio-cubital 

 cross-vein, it might be easily mistaken for the wing of a Braconid. 



M3+^ has undergone a slight modification in direction in many gen- 

 era. This will be best understood if we look first at some of the 

 genera of the Xyelidse (figs. 31-35) and Lydidie (figs. 36-43). In these 

 genera it will be noted that if this vein were continued at the same 

 angle to the margin of the wing that it would reach the margin at a 

 point at or beyond the apex of the cell 1st A, while if the medio- 

 cubital cross-vein be continued it would end near the free part of 2d 

 A. If now we examine such genera as Pteronm (fig. 68), lloplocampa 

 (fig. 61), Mrmoctenus (fig. 67), and Clad his (fig. 66), we find that with 

 the marked migration of the cubital end of the medio-cubital cross- 



