880 



RADIAL AND ZY(;OPTEkID SECTORS, &C., 



tion. My views, howevei-, have now undergone a change, owing 

 to the fact that I have recently seen a bridge formed in the 

 Odonata, as it were under my very eyes, and the process does 

 not agree with Needham's dictum. I refer to the aberrant con- 

 dition which I discovered in .Veosticta, and which is figured in 



Text-fig.3. — Foimation of bridge (5r) and oblique vein (0) in Anisoptera 

 (LihtlhiJid(f). a, Tracheation of wing at last larval instar. h. Cor- 

 responding imaginal venation. 



Text-fig. 4. Here is the case of a genus in which, apart from its 

 extreme reduction, the venational plan is simple and primitive. 

 Ordinarily, !io bridge is present. Owing to the extreme narrow- 

 ness of the wing, M.^ lies for most of its length very close under 

 Ms. In the aberration, Mg becomes hitched on to Ms, not 

 gradually, by progression distad along M towards Ms, but per 

 sal turn. And the imaginal wing-venation keeps its original 

 position, in the form of the bridge (br), clearly visible as a pig- 

 ment band. 



Searching through a long series of imagines of JVeosticta, I am 

 able to Hnd two wings which have clearly been derived from 

 this aberrant tracheal condition. In both, the change in the 

 position of Mj basally is betrayed by the shortening and sliglit 



