From the egg which the parent May-fly drops into the water, a six-legged grub is very soon hatched. This grub proceeds forthwith to excavate for himself a home in the soft bank of the river, below the surface of the water, and there remains for two long years, feeding upon the decaying matters of the mould. During this aquatic residence, the little creature finds it necessary to breathe; and that he may do so comfortably, notwithstanding his habits of seclusion, and his constant immersion in fluid, he pushes out from his shoulders and back a series of delicate little leaf-like plates. A branch of one of the air-tubes of his body enters into each of these plates, and spreads out into its substance. The plates are, in fact, gills--that is, respiratory organs, fitted for breathing beneath the water. The little fellow may be seen to wave them backwards and forwards with incessant motion, as he churns up the fluid, to get out of it the vital air which it contains. When the grub of the May-fly has completed his two years of probation, he comes out from his subterranean and subaqueous den, and rises to the surface of the stream. By means of his flapping and then somewhat enlarged gills, he half leaps and half flies to the nearest rush or sedge he can perceive, and clings fast to it by means of his legs. He then, by a clever twist of his little body, splits open his old fishy skin, and slowly draws himself out, head, and body, and legs; and, last of all, from some of those leafy gills he pulls a delicate crumpled-up membrane, which soon dries and expands, and becomes lace-netted and brown-fretted. The membrane which was shut up in the gills of the aquatic creature, was really the rudiment of its now perfected wings.