The larva of the present species (Fig. 4a) occurs abundantly under stones in rapid streams. It may be immediately distinguished from its numerous congeners by its large head and conspicuous black eyes. It is carnivorous, {106}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 setæ 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 exuviæ 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 PERLIDÆ. _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 _Ephemeræ_ 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 aërated 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, {107}and in a few hours its wings are sufficiently hardened for flight. Several other species occur in New Zealand, one of the commonest being _Perla cyrene_, a black insect much resembling _S. prasina_, but considerably smaller; its larva may be occasionally found, and is at once known by its dark colour. TERRESTRIAL Group. Family PSOCIDÆ. _Psocus zealandicus_, n.s. (Plate XVI., fig. 2, 2a larva).