170 



MR. R. J. TILLYARD ON THE RECTAL BREATHING-APPARATUS 



Duplex System which we find in the subfamily ^scJmince. The point cannot 

 be definitely settled, of course, without a careful study of the gill-basket of 

 some newly-hatched Libellulid larva. This I hope to carry out shortly. 

 Meanwhile, we must be content to regard the Lamellate Type as arising from 

 a very simple and early form of the Simplex System by the complete supres- 

 sion of the main folds, and the development of the cross-folds into lamellse. 



The Basal Pads. (Text-fig. 16 ; Plate 22. figs. 25-27.) 



We owe to Sadones a very excellent and careful study of these interesting 

 organs in Libellula dep)ressa. In this species — and, in fact, in all the Libellulidse 

 — the formation of the basal pads is very highly specialized. Clearly, then, it 

 would be both unwise and unprofitable to speculate on the origin of such a 

 highly developed structure without at first studying its formation in the less 



Text-fig. 16. — Dendroceschna cojispersa, Till. 



Transverse section through base of gill from a full-grown larva, (x 440.) 



6/:>, basal pad ; hy, hypobranchial tissue ; tr, trachea. 



highly specialized form of gill-basket. In attempting to indicate the 

 boundaries of each cell-territory of this peculiar structure, it is probable 

 that Sadones was somewhat misled by his lack of knowledge of the structure 



