166 MR. E. J. TILLYARD ON THE RECTAL BREATHING-APPARATUS 



This papillla also seems to me to be homologous in structure with the 

 tubercles already mentioned. The papillas in Anax arise as small tubercles 

 into which, later on, capillaries become sucked or drawn in. In the case of 

 the tubercles, the swelling up the wall only affects the local epithelium to 

 such an extent as to cause a swelling or thickening of it in the region of the 

 tubercle. By further eversion, the epithelium, and later on the capillaries 

 running in it, could be so drawn out as to bound a hollow cylindrical process 

 —that is to say, a typical respiratory papilla. 



The lamellas in Austrocordulia are delicately tinted with a pale mauve or 

 purplish pigment. 



Text-fig. 15. — Austrocordulia refracta, Till. 

 Tip of lamella, with supravortical papilla. From a photouiicrograph. (x420.) e/i, chiti- 

 nous hooks on papilla ; tl, loops of capillaries within the papilla ; v, vortex of 

 capillaries. 



(3) Hemicordulia (text-fig. 14 ; Plate 20. fig. 12). — The form of the 

 lamellae in this genus, representing the tribe JEucorduliini, is very typical of 

 that tribe. Each lamella is about twice as long as its breadth across the 

 middle ; the actual base-line, however, being much wider, owing to a long 

 slender extension of the distal edge of the lamella. The tip is almost right- 

 angled, the distal or outer edge being nearly straight in this region, while 

 the inner edge is broadly convex. The lamellar vortex is very close to the 

 tip, and only moderately well formed. The number of lamellte in a hemi- 

 branch is usually 24, sometimes 25 or 2&, The basal pads are small rounded 

 discs, of a transparent orange-colour. The v^hole of the gill-apparatus is 

 suffused with the most beautiful delicate purplish-mauve pigmeut. The 

 capillaries are numerous and of considerable fineness. 



(4) CordideiDhya (Plate 22. tigs. 24, 27).— The gill-basket of this interest- 

 ing genus very closely resembles that of Hemicordidia. The lamellse, 

 however, are slightly longer and narrower^ and more regularly rounded at 

 the tips. They resemble the lamellae of the more typical LihellulincB more 



