IN THE LARV^ OF ANISOPTERID DRAGONFLIES. 145 



(2) the Papillate Type. A careful study of these two types will give us a 

 much clearer idea of what the Simplex System is really like. 



1. Undulate Type. (Text-fig. 2 ; Plate 18. fig. 1 ; Plate 21. fig. 17 ; 

 Plate 22. figs. 22, 25.) 



This type has been found by me in the gills of Petaliira and Austro- 

 gomphus (text-fig. 2). Dr. Pis has also found it in Cordidegaster. It 

 therefore occurs just in those genera which are already acknowledged, from a 

 study of other characteristics, to be the most archaic of living Anisopterid 

 dragonflies. The principal characteristics of the type is that each main 



Text-fig. 2. — Austrogomphus ochraceus, Selys. 



Posterior portions of three holobranchs from the everted gill-basket of a full-o-rown larva. 



Undulate Type. Semi-diagrammatic, drawn from a whole mount. (X30.) 



longitudinal gill-fold is thrown into fairly regular folds or undulations. 

 These folds do not stand directly out into the rectal cavity, normal to the 

 circumference, but slant away posteriad, and lie so close to one another that 

 they give the appearance of a somewhat complicated frill with its folds all 

 running towards the posterior end of the rectum (text-fig. 2). 



The cross-folds are of the same folded or undulate type, but much less 

 prominent, and appear to be more crumpled and irregular. ^Their position 

 in relation to the main folds is well shown in text-fio-. 2. 



Along the free borders of the folds the cuticle carries a series of tiny 

 chitinous hooks placed at wide, intervals apart and directed backwards. 

 These are scarcely visible at all in Au&trogomplms, but can bel clearly made 

 out in Petalura under a high power. 



