IN THE LARV^ OF ANISOPTERID DRAGONFLIES. 



151 



.liolobranch in position 1 is supplied by the more dorsal or left-hand series of 

 secondary efferents arising from the upper set of primary efferents given off 

 by the right dorsal longitudinal tracheal trunk. 



The diagrams in Plate 22. figs. 23, 24, show the method of tracheal supply, 

 and should be carefully compared with that for the Simplex System 

 (Plate 22. fig. 22). 



We shall now turn to the study of the three main types of gill into which 

 the Duplex System may be divided, viz. (1) the Implicate, (2) the Foliate, 

 and (3) the Lamellate. 



1. Implicate Type. (Text-fig. 5 ; Plate 18. figs. 3, 4 ; Plate 21. fig. 18.) 



This type of gill has been found by me in larvee of the genera Dendro- 



ceschna, Austroplilehia, and Aitstroceschna. 

 Dr. E,is has also found it in the Palaearctic 

 genus JBrachi/tron. All these genera belong 

 to the tribe JBracht/tronini of the subfamily 

 yFJschnini. Hence we may fairly claim the 

 Implicate Type as characteristic of, and peculiar 

 to, this tribe of dragonflies. 



The Implicate Type may be said to corres- 

 pond, in the Duplex System, to the Undulate 

 Type in the Simplex System. That is to 

 say, the two types show, in the method of 

 distribution of the capillaries and finer tra- 

 cheal branches^ a very close similarity. This 

 may be seen by comparing Plate 18. figs. 1 

 and 3, in both of which portions of the gills 

 have been smoothed out by means of acameFs- 

 hair brush before being photographed. How- 

 ever, in the broader aspects of structure and 

 development, the two systems are very dis- 

 tinct. The Implicate Type may be easily un- 

 derstood as a derivative of the Undulate Type 

 by the suppression of the main longitudinal 

 gill-folds in the latter, and the upgrowth of 

 the small cross-folds to project far into the 

 rectum, so as to form the six pairs of hemi- 

 branchs of the Implicate System — these cross- 



Text-fig. 5. — Austroceschna 

 multipunctata, Mtartin. 

 Posterior two-thirds of three 

 hemibranchs from the everted 

 gill-basket of a full-g-rown 

 larva. Ivijjlicate Type. Semi- 

 diagrammatic, drawn from a 

 -whole mount, (x 30.) 



folds still retaining their undulate charac- 



teristics, but taking on a special shape and arrangement of their own. The 

 complicated formation resulting from this may be well studied in text-fig. 5. 

 From this figure it will be seen that each separate gill projects from its base- 



11* 



