10 



THE IMAGO 



[CH. 



It seems fairly certain that, originally, only the first of these 

 segments was preoral. Thus it corresponded with the prostomium 

 of Annulate Worms, and is not strictly to be considered as an 

 appendage-bearing segment. The mouth itself has moved from an 

 original ventral position, to take up a place at the extreme anterior 

 end of the head. Hence the original ventral surfaces of segments 



vt ant 



F. 



Fig. 1. Exoskeleton of head, thorax, and first two abdominal segments. A. Austro- 

 phlebia costalis Tillyard, $, dorsal view. B. The same, ventral view. c. The 

 same, lateral view. i>. Head of the same, front view. E. Head of Lestes, 

 dorsal view. F. The same, lateral view. G. Metathorax of Orthetrum, ventral 

 view. A analis; A' secondary analis; ac. anteclypeus; air ante-alar ridge; 

 ant antenna; ap costal process; As urosternite; At urotergite; ax axillary; 

 C costa; Cu cubitus; ex coxa; dr dorsal carina; e eye; epic epicranium; 

 epm epimerum; eps episternum; fr frons; fr 1 its superior, fr z its anterior 

 portion; Fw fore-wing ; </gena: hs humeral suture ; Hw hind -wing ; ips infra - 

 episternum ; II lateral lobe of labium ; Im labium ; Ir labrum ; ^ first, ls z 

 second lateral suture ; M media; mb membranule; md mandible; me median 

 eye-line; ml median lobe of labium; mt mentum; A 7 notum; occ occiput; 

 ocl lateral, ocm median ocellus ; orb orbit ; ot occipital triangle ; P prothorax ; 

 pc postclypeus ; PI pleurum ; PN postnotum ; pol postocular lobe ; PS post- 

 sternum ; R radius ; S sternum ; Sc subcosta ; Sp spiracle ; t temple ; v vertex ; 

 vt vertical tubercle. (A-D and ox 2; E, px5J.) Original. 



