TRACHEAL GILLS OF LARVM 



469 



Hagen has also detected in the under side of the 5th abdominal segment of 

 Epitheca and Libellula a pair of sacs of the shape of a Phrygian bonnet, each 

 of which contains a smaller sac lined with epithelium, as in yEschna they occur 

 in the 5th and 6th, and in Gomphus in the 4th, 5th, and 6th segments. This 

 serial arrangement appears to confirm Hagen's suggestion that they are survivals 



of abdominal gills, which in 

 Euphsea are completely evag- 

 inated. 



In the Trichoptera, all 

 of which, except Enoi- 

 cyla, are apneustic, and 

 most of which have tra- 

 cheal gills, the latter are 

 filamentous, and arise 

 either from the dorsal 

 and ventral sides of the 

 abdominal segment, or 

 they grow out from the 



sides ; while in certain 



-ITU FIG. 445. Can- 

 genera (.Neuroma, 1 hiy- dal tracheal gill of 

 . , , nymph of Agrion. 



ganea, etc.) the gills are 

 represented by conical hooks on the 

 sides of the 1st abdominal segment, 

 which are evidently respiratory, as 

 they contain numerous tracheae. The 



F I(J . 444. Larva of Stalls lutariwt. FIG. 44fi. Nymph of Euphipa. showing the lateral 



After Miall. gills: </, one enlarged. Folsoni tlil. 



tracheal gills are either single or more rarely form tufts (Figs. 447, 

 448). 



In Hydropsyche (Fig. 448) the tracheal gills persist throughout 

 life, while in other genera they only last through the pupal stage. 

 When first hatched, the larva of Phryganea lacks gills. The larvae 

 of most of the Hy dropsy chidse, Rhyacophilidae, and Hydroptilidae 



