596 THE PANORPOID COMPLEX, iii.. 



Section viii. The Venation op the Mecoptera. 

 (Text-figs. 60-62.) 



Text-fig. 60 shows a diagrammatic representation of the wings 

 of the Archetype of this very ancient Order. In constructing 

 this Archetype, the following points have had to be borne in 

 mind : — 



Text-Fig-60. 

 Wings of the Archetype of the Order Mecoptera. Lettering as on p. 535. 



(1) In most of the existing genera, the cross-vein system is 

 fairly strongly developed, and usually has the effect of causing 

 a slight zig-zagging of the main veins. In the fossil genera, the 

 cross-vein system is very weakly developed, and, in the oldest 

 genera, there is practically no deviation, due to cross-vein 

 struts, in the courses of the main veins. This is well shown both 

 by the Permian genus Permochorista (6) and the Triassic Meso- 

 chorista (20), as well as by most of the Liassic forms. Conse- 

 quently the typical zig-zagging of the main veins seen in many 

 recent genera is omitted from the Archetype. The system of 

 dotted cross-veins given in Text-fig. 60 is intended to represent 



