m] 



THE WINGS 



65 



Sectors, Supplements, Bridges, Transverse Veins. 



The term sector in Odonata is usually restricted to extra veins 

 developed along definite trachea! branches; while intercalated 

 veins formed in any position without the aid of a definite tracheal 

 branch are called supplements. The distinction is somewhat 

 arbitrary, since two or three very distinct tracheae may aid in 



D. 



Fig. 23. Comparison of venation of the Synlestinae and the Megapodagrioninae. 

 A. Synlestes weyersi Selys, venation (wing 31 mm.). B. The same, more 

 enlarged tracheation of the larval wing in the region of the long bridge, 

 c. Enlarged tracheation of larval wing of Argiolestes icteromdas Selys. 

 D. The same species, imaginal wing-venation (wing 28 mm.); notice absence 

 of bridge. Br bridge; Ms Zygopterid sector; oblique vein. Original. 



the formation of a strong supplement (e.g. Mspl in Aeschna). 

 A bridge is a supplement formed backwards towards the base of 

 the wing in such a way as to continue the line of an important 

 vein, so that this latter may appear much longer in the imaginal 

 venation than it really is when the tracheation is examined. 

 T. D.-F. 5 



