214 DEVELOPMENT OF THE WING-VENATION OF ODONATA, 



tiiid hind wings, thus producing differences in the venation ? Such 

 an appUcation, though beyond the scope of the present paper, 

 would be well worth making by some student more intimate with 

 the vagaries of Protodonate wing-venation than myself. 



There remains now to be carried out a thorough study of the 

 enibryonic and early post-embryonic development of the tracheal 

 system in Odonata. Such a stud}' will almost certainly reveal 

 the true phylogenetic stages of Odonate larval history, and I 

 hope to be able to give a full account of them in a future paper. 

 If it should be proved to bear out the theory offered in this 

 Section, we shall have, in the Odonnta, a double tracheal meta- 

 morphosis — first from spiracular to anal breathing in the young- 

 larva, and secondly from anal breathing back to spiracular 

 breathing at metamorphosis — which will be more wonderful even 

 than the remarkable changes, now known to every biologist, 

 which took place in the blood-system of the Vertehrata when 

 they began to desert the sea and make their homes on dry land 

 — changes which to-day are being repeated in the ontogeny of 

 every air-breathing Vertebrate. 



REFERENCE LETTERS. 



A, anal tracliea or vein : Aj, A„, Ag, A^, its four branches— A' second- 

 ary anal vein — Ab, anal bridge — Ac, anal crossing { = " first cubito-anal 

 cross-vein " — Al, anal loop — Al', secondary anal loop (of ^Eschna) — arc, 

 arculus — At, anal triangle— AT^, ATo, alar trunks of fore and hindwings 

 — Br, bridge-vein— C, costal trachea or vein — Cu, cubital trachea or vein; 

 Cuj, Cuo, its two branches,; Cuoa, Cu^b, distal and proximal branches of 

 the latter — Cual, cubito-anal or Italian loop — Cuspl, cubital supplement 

 (-=midrib of Italian loop) — DT, dorsal longitudinal tracheal trunk — Fw, 

 forewing — Hd, head — H\v, hindwing — lb, labial trachea — M, median 

 trachea or vein; M^, Mo, Mg, M^, its four branches — m, membranule — 

 MM, combined meso- and metathorax — Mspl, median supplement — N, 

 DQflus — o, oblique vein — Pi, Po, pg, first, second and third pedal trachetB 



Plr, pleural ridge — Prt, prothorax— ps, branch-trachea to region of 



second stigma — R, radial trachea or vein; R^, Rs, its two branches [Rs = 

 ♦' radial sector "]—Rspl, radial supplement — Sc, subcostal trachea or vein 



st, subtriangle — St^, St^, anterior and posterior stigmata, or spiracles — 



t, triangle — TA, thoracic or posterior tracheal anastomosis — Vr, remnant 

 of visceral trunk — VT, visceral longitudinal tracheal trunk. 



