610 



CAUDAL GILLS OF ZYOOPTKHID LAKV^, 



Text -tig. 8.").' 



cult to make it out 

 completely collapsed. 



Striirt'iire of the GUIs in f./ie Third Instar. 

 (Text-fig.35). 

 The gills are still filiform, and resemble those 

 of the second instar very closely; the principal 

 difference being that, in each lateral gill, a branch- 

 trachea of small calibre is 

 developed from the base 

 of the main trunk, and 

 runs for some distance up 

 the gill. This branch lies 

 on the outer side of the 

 gill, a little more dorsally 

 placed than the larger 

 trachea from which it is 

 derived. It is very diffi- 

 in sections, as it is usually 

 The main trunk now lies 

 very little below mid-laterally on the inner side 

 of the gill, and projects very definitely into the 

 hsemocoele. It also reaches nearly to the gill-tip. 

 Striicture of the Gills in the Fourth Instar. 

 (Text-figs.36, 37). 

 In this instar, we notice the first external sign ^ 

 of a change from the filiform to the lamellar type 

 of gill, slight though it be. For at least half of 

 its length, the gill remains filiform. But the distal 

 half shows a distinct, though very slight, attempt 

 at flattening and widening out, so that the gill 

 becomes shaped as shown in Text-tig. 36. In the t 

 lateral gills, the branch-trachea is now very dis- 

 tinct, being at least lialf the calibre of its parent- Text-tig. 86. t 

 trunk, and running along more than three-fourths of the length 



* T.S. through caudal gills of Aiistroayrion cyane Selys, third instar, at 

 about one-third from base. Lettering as in Text-fig. 34; tr', branch-trachea 

 fi'om near base of main trachea {tr) in lateral gills; ( x 370). 



t Lateral caudal gill of An.stroagrion cyane Self's, fourth instar; side- 

 view; ( X 90). 



