NO. 1331. 



DRAGON-FLY WING VENATION— NEEDHAM. 



727 



qoneurid they are four. Those antenodals which early chance become 

 "matchecr' across l)otli costal and subcostal spaces ])race the deepening 

 subcostal furrow lietter and are more sure to ])c preserved. 



Then there is a reduction of cross veins which seems not solely 

 directed toward strengthening those that remain, ])ut rather toward 

 clearing out of spaces between the points of ti'ansverse union of longi- 

 tudinal veins." This clearance takes place in difierent places in Libel- 

 lulida^ and in Gomphina>, correhited with the difference in shape and 

 position of the triangle in the two groups. In the former the cross 

 veins disappear (see Pachydiplax, Plate XLVIl, fig. 1) from the spaces 

 adjacent to the subnodus and the oblique vein and under the stigma. 

 In the latter (see GoiiqtJtiis diJ<(tatii-^, Plate XXXIII, fig. 1) from the 

 spaces just beyond the arculus. In the ^schnins^, with triangles 

 similarlv disposed, while the cross veins do not actually disappear just 

 beyond the arculus, we find sometimes (as in A)i<i.i\ Plate XL. tig. 3) 



Fig. 21.— Diagram showing how hexagonal cells become rectangles and how crossveins 

 become matched in transverse lines across the wing. 



all the veins on the anterior side of the base of vein J/",, between it 

 and the radius, so dwindled that little more than thin membrane 

 remains. This is much more evident in the actual wing than in the 

 figure. 



\^'e have already referred to the matching of nodal crossveins. in 

 the Agrionina? this process is carried so far that all the crossveins of 

 the body of the wing become arranged in transverse lines. A com- 

 parison of the wings of Archilcdes (Plate LI, fig. (>). Zr.s-^t.v (Plate LIII, 

 fig. 1), Argia (Plate LIII, fig. 5), and Nehallennla (Plate LIV, fig. 8) will 

 illustrate the progress of this tendency. 



"Allowing, perhaps^, for readier flexion of the portion of the wing posterior to the 

 cleared spaces, though of this I am not sure. In :\Iynneleonid;e (Plate XXXVI 

 fig. 2) subcosta and radius are strongly bound together at base and at stigma, while 

 the long narrow space between is free from cross veins. It would seem, since the 

 wing is easily flexed behind this space, the costal margin remaining rigid, that an 

 imaginary axis of flexion joins the two strong yet elastic terminal points of union. 



