106 NEW ZEALAND ENTOMOLOGY. 



feeding on various small insects, chiefly those belonging to 

 the present family, but in lack of these it will even devour 

 individuals of its own species. It is consequently a most 

 difficult insect to rear, and it was a long time before 

 I succeeded in obtaining a single imago in captivity. 

 When mature the insect leaves the water, and an apparently 

 perfect imago escapes through a rent in the thorax in the 

 usual way. In a few hours, however, a second moult occurs, 

 the wings gaining additional size and beauty, and the anal 

 setae becoming very much more elongated than before (Fig. 

 4). This second change, which has so perplexed some 

 entomologists, is merely an apparent departure from the 

 general rule, a careful examination of the exuviae of the 

 dragonflies, and pupa shells of many other insects, revealing 

 a delicate membrane within, which invests the imago, and 

 is cast off at the same time as the harder external envelope. 

 In the case of the mayflies, the retention of this internal 

 membrane some two or three hours longer than usual, will 

 fully explain its apparently unique metamorphosis. 



Family PERLID.E. 

 Stenoperla prasina (Plate XVI., fig. 3, 3a larva). 



This is the green gauzy-winged insect which we see flying 

 feebly over running water, during the twilight, throughout 

 the summer. 



Its larva (Fig. 3a) is aquatic, hiding itself under stones, 

 and devouring the unfortunate Ephemera found in similar 

 situations. Towards the end of its career the rudimentary 

 wings become very conspicuous, at which time it is a most 

 interesting object. The curious appendages on each side 

 of the abdomen are gills, which the larva is constantly 

 vibrating, in order to obtain a fresh supply of aerated 

 water. When mature, it ascends the stem of some 

 aquatic plant, the skin becomes dry and brittle, and 

 finally bursting, allows the perfect insect to escape, 



