The larvæ of the aquatic Neuroptera, Sisyra, Sialis, and Corydalus possess lateral pointed bristle-like tracheal gills, which in Sisyra are 2–jointed; those of Sialis are, in the living larva, curved upwards and backwards (Fig. 444). Corydalus is also provided with a ventral tuft of delicate filamentous gills, which, however, according to Riley, do not appear until after the first moult.
While the nymphs of Agrionidæ (which have rectal gills) respire chiefly by the large caudal foliaceous gills (Fig. 445), there are, according to Hagen, two genera of the Calopteryginæ (Euphæa, Fig. 445, and Anisopleura) whose nymphs possess seven pairs of external lateral tracheal gills, in shape like those of Sialis, besides three caudal and three rectal tracheal gills.[[74]]
Fig. 444.—Larva of Sialis lutarius.—After Miall.
Fig. 445.—Caudal tracheal gill of nymph of Agrion.
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 Æschna 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 Euphæa are completely evaginated.
Fig. 446.—Nymph of Euphæa, showing the lateral gills: a, one enlarged.—Folsom del.
In the Trichoptera, all of which, except Enoicyla, are apneustic, and most of which have tracheal 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 genera (Neuronia, Phryganea, etc.) the gills are represented by conical hooks on the sides of the 1st abdominal segment, which are evidently respiratory, as they contain numerous tracheæ. The tracheal gills are either single or more rarely form tufts (Figs. 447, 448).