. The biology of dragonflies (Odonata or Paraneuroptera). Dragon-flies. 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-hearing 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. Fig. 1. Exoskeleton of head, thorax, and first two abdominal segments, a. Austro- phlebia costalis Tillyard, 9>
. The biology of dragonflies (Odonata or Paraneuroptera). Dragon-flies. 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-hearing 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. Fig. 1. Exoskeleton of head, thorax, and first two abdominal segments, a. Austro- phlebia costalis Tillyard, 9> dorsal view. b. The same, ventral view. c. The same, lateral view. d. 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; awi antenna; ap costal process; /Is urosternite; .4< urotergite; axillary; C costa; Cu cubitus; ex coxa; dr dorsal carina; e eye; epic epicranium; epm epimerum; ejis episternum; fr frons; /rj its superior, fr,^ its anterior portion; Fm; fore-win^; fygena: /(S humeral suture; i/w hind-wing; ips inira- episternum; U lateral lobe of labium; Im labium; Ir labrum; Zsj first, Zsg second lateral suture; 71/media; mi membranule; mcZ mandible; me median eye-line; ml median lobe of labium; ml mentum; A'' notum; occ occiput; ocl lateral, ocm median ocellus; orb orbit; ot occipital triangle; P prothorax; pc postclypeus; PI pleurum; PN postnotuni; pol postocidar lobe; PS post- sternum ; B radius; S sternum; Sc subcosta; Sp spiracle; t temple; v vertex; vt vertical tubercle, (a-d and Gx2; e, f x 5J.) Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Tillyard, Robin John, 1881-1937. Cambridge [Eng. ] : University Press
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