fiY R. J. TILLYARD. 



larvjfi are rock-dwellers in fast mountain-streams, being only found 

 in the shallow rapids, and never in the deep still pools. Tliey cling 

 to the under-surface of Hat rocks lying in the main current^ in 

 company with large (undescribed) Ferlid larvae, which they some- 

 what resemble, except for their gills. They are, however, unlike 

 the Ferlid larvae, very sluggish, and are only capable of rapid 

 movements when in the water. When a rock is lifted up with 

 a Diphlebia-l'dirvai beneath it, the dragging of the huge gills upon 

 the wet rock-surface eft'ectuall}^ prevents any speedy movement. 



The gills can be fixed and kept in 70 

 per cent, alcohol, without collapsing; but, 

 when dehydrated and cleared, they almost 

 invariably collapse. They are, therefore, 

 exceedingly diflticult to section satisfac- 

 torily. They are very opaque, dull grey, 

 brownish, or blackish, according to the 

 locality and the colour of the rocks in- 

 habited. In sandstone or ironstone 

 creeks, a brownish colour prevails; in 

 granitic or basaltic creeks, grey or black- 

 ish. Their shape varies somewhat in 

 different individuals. Sometimes the 

 gills are so tense as to be definitely 

 sausage-shaped; in other cases, the gills are not so tense, and 

 there is just a suspicion of the formation of longitudinal edges 

 or midribs. In the latter case, the lateral gills may be described 

 as triquetral, but with extremely convex faces. 



The whole cuticle of the gill is covered by irregularly placed 

 hairs, most of which are long and slender. They are especially 

 long and numerous upon the posterior pointed portion of the 

 gill, giving it a somewhat shaggy appearance. 



The cuticle itself is quite clear and unpigmented. It is com- 

 posed of numerous exceedingly thin parallel strata, the outermost 

 of which differs from the rest in staining deeply and easily with 

 eosin. The total thickness of the cuticle only averages about 8/x. 



The hypodermis is a very thin epithelial layer, only about 



Gills of Diphlehia lesto'ides Selys, in natural position, dorsal view; ( x 4). 



Text-fig. 1; 



