100 



CAUDAL GILLS OF ZYGOPTERID LARV.E, 



strong ehitinous bases, indicating the original set of spines end- 

 ing at the node: on the inner edge, there is a set of strong 

 ehitinous bases carrying small bristles along the basal fourth of 

 the gill, corresponding with the series of spines in the same posi- 

 tion in Isclunira. {Cf. Plate ii., ligs.16, 17). 



This gill-fonn is obviously a simple reduction 

 from the subnodate form seen in Ischinira, and 

 is very closely allied to it. 



3. Xanthoenemis zdandica 8elys. Length of 

 gill, when full-grown, about 4 mm. Gills lan- 

 ceolate, broadest near tips, then suddenly nar- 

 rowing to form the sharply-pointed tips. Colour 

 pale brownish, yellowish or greenish, a band of 

 medium brownish pigment across the broad 

 part near the tip. Tracheal system much as in 

 Ischniira, but with fewer branches, more regu- 

 larly placed. Outer edge of gill furnished from 

 base to near tip with short bristles, set in a 

 regular series of strongly-projecting ehitinous 

 bases. A few irregularly placed bristles along 

 basal portion of inner edge. Towards tip, both 

 edges carry some long, delicate hairs (Text-fig. 27). 



(/)) Thp Horizontal Lamellar Sub-type. 

 (Text-figs. 28-29; Plate i., figs.8-11; Plate vi., figs.40-45). 



This extraordinary form of gill is only found, as far as I am 

 aware, in the Australian genus Argiolestes, belonging to the sub- 

 family Megapodagrionime. I do not think that it will prove to 

 be typical of that ancient subfamily, in which we might reason- 

 ably expect to find a more generalised form of gill dominant, 

 when the larvj>» of many genera become known. 



The gills are broad, leaf-like structures spread out in the hori- 

 zontal plane, so as to resemble closely in form the "tail-fan" of 

 Decapod Crustacea. In life, they are held out extended at an 

 angle of from 10° to 20° to the plane of rest. When walking, 



* Benodate median gill of Xanthoenemis zeJandica (Selys). From a 

 cleared whole mount; ( x \7)\, 



Text-fig. 2' 



1 



