IN THE LAEV^ OF ANISOPTEEID DRAC40NFLIES. 153 



o£ the Undulate Type of o-ill. The capillaries are very numerous and vary 

 somewhat in fineness. In Austroceschna and Braclii/tron they seem to be 

 much of the same calibre as in Corduleg aster, but in Dendroceschna and 

 AustropKlebia they are o£ excessive fineness and very difficult to photograph. 

 In these genera, too, there is a more extensive branching o£ the gill-trachese, 

 so that each " frill " is supplied more or less completely with capillaries 

 thrown out from a single branch. 



Number of Capillaries in the Gill-basket. 



In Austroceschna we should assign about 200 complete capillary loops to 

 each secondary efferent trachea (inclusive of its large branches). Each 

 hemibranch receives, on an average, 12 of these sets. Hence the total 

 number of complete loops is 12 x 12 X 200, or 28,800. 



In Dendroceschna, it is almost impossible to attempt an approximation. 

 Each " frill " must carry a minimum of at least 20 loops. The edge of each 

 groove or plication carries 16 or more " frills," and there are 12 grooves to 

 a hemibranch. Thus we get a total of 12 X 12 x 20 X 16, or 46,080 complete 

 loops in the gill-basket ! The much larger larva of Austrophlehia probably 

 contains an even greater total. The very great increase in the number of 

 loops in these genera, compared with Austroceschna and Brachytron, is 

 probably correlated with their habits of hiding under rocks in fast mountain- 

 streams, where the act of inspiration is perhaps difficult and intermittent. 



2. Foliate Type. 



We now pass on to a very interesting type of gill, found only, so far as is 

 known, in the two large and widely distributed genera uEschna and Anax, 

 both belonging to the tribe ^schinni of the subfamily ^schnince. Of these 

 two genera, ^schna alone exhibits the normal or typical foliate gill-form. 

 In Anax there is an additional complication in the form of an abundant 

 development of small papillse. We must, therefore, subdivide the foliate 

 type into two sub-types — the normcd foliate type of ^Bschna, and the ptajnllo- 

 foliate type of Anax. 



2 A. Normal Foliate Sub-type. (Text-figs. 6-7 ; Plate 19. figs. 5-6 ; 

 Plate 21. fig. 15 ; Plate 22. figs. 23, 26.) 



This sub-type has been studied by me in ^d^schna brevistyla, and appears 

 to agree very closely with the form of gill found in the Palgearctic members 

 of the same genus. In it the gills of each hemibranch form a series o£ 

 leaves with narrowed stalks and broadly expanded distal ends. The 

 secondary efferent trachea forms the axis of each stalk, while the capillaries 

 are confined to the expanded leaf. On entering the base of the leaf the 



