Chambers's Edinburgh Journal, No. 437, page 19 by Various Authors
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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.
The wings of the insect are then a sort of external lungs, articulated with the body by means of a movable joint, and made to subserve the purposes of flight. Each wing is formed of a flattened bladder, extended from the general skin of the body. The sides of this bladder are pressed closely together, and would be in absolute contact but for a series of branching rigid tubes that are spread out in the intervening cavity. These tubes are air-vessels; their interiors are lined with elastic, spirally-rolled threads, that serve to keep the channels constantly open; and through these open channels the vital atmosphere rushes with every movement of the membraneous organ. The wing of the May-fly flapping in the air is a respiratory organ, of as much importance to the wellbeing of the creature in its way, as the gill-plate of its grub prototype is when vibrating under the water. But the wing of the insect is not the only respiratory organ: its entire body is one vast respiratory system, of which the wings are offsets. The spirally-lined air-vessels run everywhere, and branch out everywhere. The